U.S. patent application number 12/668349 was filed with the patent office on 2010-08-05 for materials and methods for delivering compositions to selected tissues.
This patent application is currently assigned to THE REGENTS OF THE UNIVERSITY OF CALIFORNIA. Invention is credited to Lignyun Cheng, William R. Freeman, Michael J. Sailor.
Application Number | 20100196435 12/668349 |
Document ID | / |
Family ID | 40229452 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100196435 |
Kind Code |
A1 |
Freeman; William R. ; et
al. |
August 5, 2010 |
MATERIALS AND METHODS FOR DELIVERING COMPOSITIONS TO SELECTED
TISSUES
Abstract
This invention relates to devices, systems and methods for
delivering preprogrammed quantities of an active ingredient to a
biological system over time without the need for external power or
electronics.
Inventors: |
Freeman; William R.; (Del
Mar, CA) ; Sailor; Michael J.; (La Jolla, CA)
; Cheng; Lignyun; (San Diego, CA) |
Correspondence
Address: |
Joseph R. Baker, APC;Gavrilovich, Dodd & Lindsey LLP
4660 La Jolla Village Drive, Suite 750
San Diego
CA
92122
US
|
Assignee: |
THE REGENTS OF THE UNIVERSITY OF
CALIFORNIA
Oakland
CA
|
Family ID: |
40229452 |
Appl. No.: |
12/668349 |
Filed: |
July 9, 2008 |
PCT Filed: |
July 9, 2008 |
PCT NO: |
PCT/US2008/069474 |
371 Date: |
April 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60948816 |
Jul 10, 2007 |
|
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Current U.S.
Class: |
424/423 ;
424/130.1; 424/133.1; 424/400; 424/489; 424/94.64; 514/1.1;
514/169; 514/178; 514/44R; 514/770 |
Current CPC
Class: |
A61K 9/0019 20130101;
A61P 7/10 20180101; C12Y 304/21073 20130101; A61P 1/10 20180101;
A61P 25/20 20180101; A61P 7/02 20180101; A61K 9/7007 20130101; A61P
3/04 20180101; A61P 31/00 20180101; A61P 1/04 20180101; A61P 19/00
20180101; A61P 25/24 20180101; A61P 9/00 20180101; A61P 11/00
20180101; A61P 9/12 20180101; A61P 11/06 20180101; A61P 29/00
20180101; A61P 7/00 20180101; A61K 31/7088 20130101; A61P 25/26
20180101; A61K 39/395 20130101; A61K 2039/54 20130101; A61P 19/06
20180101; A61K 38/482 20130101; A61P 9/06 20180101; A61P 9/10
20180101; A61K 39/44 20130101; A61P 3/00 20180101; A61K 9/0051
20130101; A61P 1/08 20180101; A61P 25/00 20180101; A61K 2039/505
20130101; A61P 3/10 20180101; A61P 1/12 20180101; A61P 3/02
20180101; A61K 9/14 20130101; A61P 15/00 20180101; A61P 19/02
20180101; A61P 25/06 20180101; C25F 3/12 20130101; A61K 9/143
20130101; A61P 5/14 20180101; A61P 25/18 20180101; A61P 27/02
20180101; A61K 31/573 20130101; A61K 9/5115 20130101 |
Class at
Publication: |
424/423 ;
514/770; 424/489; 514/169; 514/12; 424/94.64; 514/44.R; 424/130.1;
514/178; 424/400; 424/133.1 |
International
Class: |
A61F 2/00 20060101
A61F002/00; A61K 47/02 20060101 A61K047/02; A61K 9/14 20060101
A61K009/14; A61K 31/56 20060101 A61K031/56; A61K 38/18 20060101
A61K038/18; A61K 38/48 20060101 A61K038/48; A61K 31/7052 20060101
A61K031/7052; A61K 39/395 20060101 A61K039/395; A61K 9/00 20060101
A61K009/00; A61P 27/02 20060101 A61P027/02; A61P 31/00 20060101
A61P031/00 |
Goverment Interests
STATEMENTS REGARDING FEDERALLY SPONSORED RESEARCH
[0002] The invention was made with government support under Grant
No. DMR 0503006 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A composition comprising: a silicon-containing material
comprising a plurality of pores selectively dimensioned to obtain a
desired reflective wavelength; and a drug or biologically active
material within the pores.
2. The composition of claim 1, wherein the silicon material
comprises a silicon dioxide material.
3. The composition of claim 1, comprising a particulate size of
between about 0.1 .mu.m and 100 .mu.m.
4. The composition of claim 1, further comprising a polymeric
material capping the pores.
5. A multilayer silicon composition comprising: a silicon material;
a first surface and a second surface on the silicon material; a
plurality of pores of a first tunable size on the first surface; a
plurality of pores of a second tunable size on the second surface;
and a drug or biological agent disposed within the pores on the
first and/or second surface; wherein the silicon composition
comprises a particle size between 0.1 .mu.m and 100 .mu.m.
6. The multilayer silicon composition of claim 5, wherein the
silicon material is a silicon dioxide.
7. The multilayer silicon composition of claim 5, further
comprising a polymer capping the pores on the first side, second
side, or surrounding the material.
8. A pharmaceutical composition comprising a pharmaceutically
acceptable carrier and a composition of claim 1 or 5.
9. A method for treating a disease or disorder of the eye
comprising injecting a composition of claim 1 or 5 into the
eye.
10. The method of claim 8, wherein the release of a drug from the
composition is monitored by a change in reflective wavelength.
11. A method of preparing a device for controlled drug delivery to
a location of the eye comprising: providing a porous nanostructured
silicon-containing template having pores configured to receive a
particular drug, said template being sized and configured to be
delivered into or upon a surface of the eye; and loading the
template with the drug.
12. The method of claim 11 further comprising providing one of a
silicon template, a SiO.sub.2 template, and a SiO.sub.2/polymer
composite template.
13. The method of claim 11 further comprising disposing one of an
organic polymer, an inorganic polymer, and a bio polymer in the
template.
14. The method of claim 13 further comprising removing the
silicon-containing template from the polymer by one of chemical
corrosion and dissolution.
15. The method of claim 11 further comprising sizing and
configuring the template to be a carrier configured to be included
in a contact lens.
16. The method of claim 15 further comprising placing the contact
lens in abutment with a front extraocular surface.
17. The method of claim 11 further comprising sizing and
configuring the template to be a scleral plaque for the retrobulbar
surface of the eye.
18. The method of 17 further comprising suturing the scleral plaque
to the retrobulbar surface.
19. The method of claim 11 further comprising fracturing the
template into particles of size less than or equal to 100
micrometers in any dimension.
20. The method of claim 19 further comprising injecting the
particles intraocularly.
21. The method of claim 10 further comprising configuring the
particles to have a monitorable optical response depending on a
quantity of drug disposed in the pores.
22. The method of claim 10 further comprising configuring the
particles to have a monitorable optical response depending on the
amount of porous material present.
23. The method of claim 11 further comprising trapping the drug or
drugs in the pores by oxidizing the porous template around the drug
or drugs.
24. The method of claim 11 further comprising configuring inner
walls of the pores to enhance binding efficacy of the at least one
drug and to tune release profiles of said pores.
25-36. (canceled)
37. The composition of claim 1 wherein said drug or drugs comprises
one of the group consisting of angiostatic steroids,
metalloproteinase inhibitors, VEGF, pigment epithelium derived
factor, an 8-mer peptide fragment of urokinase, modified RNA,
modified DNA, fragments derived from immunoglobulins, and
dexamethasone.
38-41. (canceled)
42. A device for the controlled release of an active ingredient
comprising: a) a polymer layer comprising a plurality of
nano-apertures; b) a base comprising a non-porous substrate layer;
and c) at least one reservoir juxtaposed between the polymer layer
and the base, wherein the reservoir is in fluid communication with
the nano-apertures of the polymer layer and is configured to
contain an active ingredient.
43. The device of claim 42, wherein the polymer layer is produced
by: a) applying a biocompatible polymer to a porous silicon
template thereby forming a polymer-silicon composite; b) removing
the porous silicon template; and c) obtaining the polymer layer
comprising a plurality of nano-apertures.
44. The device of claim 42, wherein the device is suitable for
implantation or explantation in a biological system.
45. The device of claim 44, wherein the biocompatible polymer
comprises poly(lactide), chitosan, silicone, or poly(norborene), or
any combination thereof.
46. The device of claim 43, wherein the porous silicon template is
a thermally oxidized porous silicon template.
47. The device of claim 42, wherein the active ingredient is
suitable for inhibiting neovascularization.
48. The device of claim 42, wherein the active ingredient comprises
one of the group consisting of angiostatic steroids,
metalloproteinase inhibitors, VEGF, pigment epithelium derived
factor, an 8-mer peptide fragment of urokinase, modified RNA,
modified DNA, fragments derived from immunoglobulins, and
dexamethasone
49. The device of claim 47, wherein the active ingredient is
avastin.
50. A method of producing a hydrophilic, porous silicon substrate
comprising heating a porous silicon substrate to a temperature
above 80.degree. C. in the presence of an agent suitable for
oxidizing or hydrosilylating the silicon substrate thereby
producing a hydrophilic, porous silicon oxide substrate.
51. The method of claim 50, further comprising contacting the
hydrophilic, porous silicon substrate with a hydrophilic active
ingredient under conditions suitable for associating the substrate
with the active ingredient.
52. The method of claim 50, further comprising treating the
substrate in a manner that produces biocompatible particles for the
controlled delivery of the active ingredient to a biological
system.
53. The method of claim 50, wherein the porous silicon substrate is
heated to a temperature above 400.degree. C. to 800.degree. C. in
an oxidizing environment.
54-55. (canceled)
56. A hydrophilic, porous silicon substrate produced by the method
of claim 50.
57-58. (canceled)
59. A pulse therapy method for treating a subject, the method
comprising: a) identifying a subject having a condition and
selecting one or more active ingredients suitable for treating the
condition; b) correlating the quantity and type of active
ingredients with a pulse therapy dosing profile suitable for
treating the condition; c) configuring a device of claim 42 to
obtain a device suitable for delivering the dosing profile of b) to
the subject; and e) implanting or explanting the device in or on a
target tissue associated with the subject.
60. The method of claim 59, wherein the target tissue is ocular
tissue.
61. The method of claim 59, wherein the target tissue is associated
with joint tissue.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Application Ser. No. 60/948,816, filed Jul. 10, 2008. The
application is related to U.S. patent application Ser. No.
11/665,557 filed on Apr. 16, 2007, which is a national stage
application of International Patent Application No.
PCT/US05/039177, filed Oct. 31, 2005, the contents of which are
incorporated herein by reference in their entirety.
TECHNICAL FIELD
[0003] The invention relates to delivery systems and, more
particularly, to a device that can deliver preprogrammed quantities
of a composition over time without the need for external power or
electronics.
BACKGROUND
[0004] Drug delivery to a location of infection, disease or a
disorder to ameliorate symptoms or cure the disease and disorder
are important.
SUMMARY
[0005] Provided herein are minimally invasive controlled drug
delivery systems and methods for use in delivery of a particular
drug or drugs to the eye that include porous film or porous film
particles having pores configured and dimensioned to at least
partially receive at least one drug therein. Embodiments include
devices and methods for treating intraocular diseases where porous
film particles impregnated with a particular drug are sized and
configured to permit intraocular injection of the loaded porous
film particles. Other embodiments include devices and methods for
treating extraocular diseases, where one of a porous film,
biodegradable polymer replica, porous SiO.sub.2-polymer composite,
or porous Si-polymer composite impregnated with a particular drug
is configured to contact a portion of the eye, such as the ocular
surface or retrobulbar surface, and controllably release the drug
for surface delivery of the drug. Advantageously, release of the
drug is also monitorable such that the amount of drug remaining in
the porous substrate can be accurately quantified.
[0006] The disclosure provides a composition comprising: a silicon
material comprising a plurality of pores selectively dimensioned to
obtain a desired reflective wavelength and/or rate of drug
delivery; and a drug or biologically active material within the
pores. In one embodiment, the silicon material comprises a silicon
dioxide material. In another embodiment, the material comprises a
particulate size of between about 1 .mu.m and 100 .mu.m. The
composition can further comprises a polymeric material capping the
pores.
[0007] The disclosure also provides a multilayer silicon
composition comprising a silicon material; a first surface and a
second surface on the silicon material; a plurality of pores of a
first tunable size on the first surface; a plurality of pores of a
second tunable size on the second surface; and a drug or biological
agent disposed within the pores on the first and/or second surface.
In one embodiment, the silicon composition comprises a particle
size between 1 .mu.m and 100 .mu.m. In one embodiment, the silicon
material is a silicon dioxide. In yet another embodiment, the
composition further comprises a polymer capping the pores on the
first side and/or second side.
[0008] The disclosure further provides a method of preparing a
device for controlled drug delivery to a location of the eye
comprising: providing a porous nanostructured silicon-containing
template having pores configured to receive a particular drug, said
template being sized and configured to be delivered into or upon a
surface of the eye; and loading the template with the drug. The
method can further comprise providing one of a silicon template, a
SiO.sub.2 template, and a SiO.sub.2/polymer composite template. In
yet another embodiment, the method can further comprise disposing
one of an organic polymer, an inorganic polymer, and a bio polymer
in the template. In yet a further embodiment, the method can
comprise removing the silicon-containing template from the polymer
by one of chemical corrosion and dissolution. The method can
further comprise sizing and configuring the template to be a
carrier configured to be included in a contact lens. The method can
comprise placing the contact lens in abutment with a front
extraocular surface. In one embodiment, the method comprises
[0009] sizing and configuring the template to be a scleral plaque
for the retrobulbar surface of the eye. The method can comprise
suturing the scleral plaque to the retrobulbar surface. The method
can comprise injecting the particles intraocularly. The method can
comprise configuring the particles to have a monitorable optical
response depending on a quantity of drug disposed in the pores. In
yet another embodiment, the method can further comprise trapping
the drug or drugs in the pores by oxidizing the porous template
around the drug or drugs. The oxidizing can be performed at
repeated intervals by performing layered oxidation. For example, a
biological agent or drug can be trapped in the pores by controlled
addition of oxidants. Oxidation of the freshly prepared
(hydride-terminated) porous Si material results in an effective
shrinking of the pores. This occurs because the silicon oxide
formed has a larger volume than the Si starting material. If a drug
is also present in the solution that contains the oxidant, the drug
becomes trapped in the pores.
[0010] The disclosure also provides a minimally invasive controlled
drug delivery device for delivering a particular drug or drugs to a
particular location of the eye, said device comprising: a porous
film template having pores configured and dimensioned to at least
partially receive at least one drug therein; and wherein said
template is dimensioned to be delivered into or onto the eye.
[0011] The disclosure provides a device for the controlled release
of an active ingredient comprising: a) a polymer layer comprising a
plurality of nano-apertures; b) a base comprising a non-porous
substrate layer; and c) at least one reservoir juxtaposed between
the polymer layer and the base, wherein the reservoir is in fluid
communication with the nano-apertures of the polymer layer and is
configured to contain an active ingredient.
[0012] The disclosure further provides a method of producing a
hydrophilic, porous silicon oxide substrate comprising heating a
porous silicon substrate to a temperature above 80.degree. C. in
the presence of an agent suitable for oxidizing the silicon
substrate thereby producing a hydrophilic, porous silicon oxide
substrate.
[0013] The disclosure also provides a method of producing a
hydrophobic, porous silicon substrate comprising heating a porous
silicon substrate to a temperature above 80.degree. C. in the
presence of an agent suitable for hydrosilylating the silicon
substrate thereby producing a hydrophobic, porous silicon
substrate.
[0014] The disclosure provides a pulse therapy method for treating
a subject, the method comprising: a) identifying a subject having a
condition and selecting one or more active ingredients suitable for
treating the condition; b) correlating the quantity and type of
active ingredients with a pulse therapy dosing profile suitable for
treating the condition; c) configuring a device of the disclosure
to obtain a device suitable for delivering the dosing profile of b)
to the subject; and e) implanting or explanting the device in or on
a target tissue associated with the subject.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1A-B show methods and reactions for generating porous
Si. (A) Shows a schematic of the etch cell used to prepare porous
Si. The electrochemical half reactions are shown, and the
equivalent circuit for etching of a p-type Si wafer is shown at
right. (B) represents a chemical reaction for the oxidation of the
porous Si around a candidate molecule according to one embodiment
of the disclosure.
[0016] FIG. 2 illustrates a chemical modification reaction whereby
a candidate molecule is attached to an inner pole wall according to
another embodiment of the invention
[0017] FIG. 3A-B shows representations of photo-measurements and
polymer composites. (a) shows a schematic demonstrating the change
in a reflectance spectrum from a single layer of porous Si upon
introduction of a molecular species into the porous matrix. The
change in refractive index of the composite film results in a red
shift of the Fabry-Perot interference fringes. The reverse process
can also be monitored, yielding a blue shift in the spectrum. (B)
is a schematic diagram illustrating a templated synthesis of
polymer photonic crystals using porous Si masters according to an
embodiment of the disclosure.
[0018] FIG. 4 is a graph illustrating a correlation between the
optical thickness of an alkylated porous silicon film to the
concentration of drug appearing in phosphate buffered saline
solution over 2 hours.
[0019] FIG. 5 shows a cross-sectional scanning electron micrograph
image of an intact porous Si film prior to removal from the bulk
silicon substrate and fracture into microparticles. The pores are
aligned along the <100> direction of the original silicon
crystal.
[0020] FIG. 6A-B depicts unoxidized and oxidized porous Si
particles. (A) shows fresh porous Si particles in a droplet of 5%
dextrose solution. Particle clumping is observed due to the
hydrophobic nature of the unmodified porous Si particles. (B) shows
oxidized porous Si particles in a droplet of 5% dextrose solution.
These particles were observed to be more dispersed in solution,
presumably because of the hydrophilic nature of the SiO.sub.2
surface.
[0021] FIG. 7A-D depicts intravitreal injections of porous Si
particles. (A) is a photograph taken under a surgical microscope
immediately after intravitreal injection of fresh porous Si
particles. Particles can be observed suspended in the center of the
vitreous. A few small air bubbles mixed with the porous Si
particles are present at the top of the vitreous cavity. (B) is a
fundus photograph taken one week after the injection, showing
porous Si particles dispersed in the vitreous. (C) is a fundus
photograph taken 2 weeks after injection, indicating that most of
the particles have disappeared and those remaining were barely
observable. (D) depicts a light microscopic graph showed normal
retina detached from the retinal pigment epithelium during the
histology processing. (25.times., H&E staining).
[0022] FIG. 8A-B provides images of intravitreal hydrosilylated Si
particles. (A) is a photograph taken under a surgical microscope
immediately after intravitreal injection of hydrosilylated porous
Si particles. Particles can be observed suspended in the center of
the vitreous. (B) is a fundus photograph obtained 3 months after
injection. The particles are dispersed in the vitreous and many
demonstrated a distinctive blue color indicative of partial
degradation and dissolution.
[0023] FIG. 9A-C provides images of ocular tissue following Si
particle injection. (A) shows a surgical microscope image of a
dissected rabbit eye cup, with hydrosilylated porous Si particles
distributed on a normal looking retina. Photograph was obtained 4
months after injection. Two retina folds are present, caused during
dissection. (B) shows a scanning electron microscope image of the
hydrosilylated porous Si particles sampled from a rabbit eye 4
months after intravitreal injection. The sharp edges and pitted
surface of the particles indicate a very slow erosion process. (C)
shows a light microscopic photograph of the retina and choroid from
a rabbit eye harvested 9 months after intravitreal injection of
hydrosilylated porous Si particles. Normal chorioretinal morphology
and structures are observed. (62.5.times., H&E staining).
[0024] FIG. 10A-D provides images of oxidized porous Si particles
following injection. (A) is a photograph taken under a surgical
microscope immediately after intravitreal injection of oxidized
porous Si particles. Particles can be observed suspended in the
center of the vitreous above the optic nerve. (B) is a fundus
photograph of a rabbit eye at 2 weeks after intravitreal injection
of oxidized porous Si particles. Many violet particles and a normal
fundus can be seen. The particles were initially green upon
injection. The violet color indicates that significant oxidation
and dissolution of the particles has occurred. Some of the
particles have lost their vivid reflectance completely and appear
brown in color. (C) is a fundus photograph of the same rabbit eye,
9 weeks after intravitreal injection of oxidized porous Si
particles. Many of the particles have degraded and are no longer
observed. The fundus appears normal. (D) is a light microscopic
photograph of the retina and choroid from a rabbit eye harvested 4
months after intravitreal injection of oxidized porous Si
particles. Normal chorioretinal morphology and structures are
observed with a slight artificial retinal detachment. (25.times.,
H&E staining).
[0025] FIG. 11 provides data related to the release of bevacizumab
(Avastin) from SiO.sub.2 particles.
[0026] FIG. 12 provides data related to the unique features of the
porous Si microparticles provided herein. Such features include
spectral encoding for self-reporting capability and tunable
nanostructures for controlling release rate and for accommodating
various payloads.
[0027] FIG. 13 provides data for the release profile of Avastin
from a Si microparticle provided herein.
DETAILED DESCRIPTION
[0028] As used herein and in the appended claims, the singular
forms "a," "and," and "the" include plural referents unless the
context clearly dictates otherwise. Thus, for example, reference to
"a pore" includes a plurality of such pores and reference to "the
drug" includes reference to one or more drugs known to those
skilled in the art, and so forth.
[0029] Also, the use of "or" means "and/or" unless stated
otherwise. Similarly, "comprise," "comprises," "comprising"
"include," "includes," and "including" are interchangeable and not
intended to be limiting.
[0030] It is to be further understood that where descriptions of
various embodiments use the term "comprising," those skilled in the
art would understand that in some specific instances, an embodiment
can be alternatively described using language "consisting
essentially of" or "consisting of."
[0031] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill in the art to which this disclosure belongs.
Although methods and materials similar or equivalent to those
described herein can be used in the practice of the disclosed
methods and compositions, the exemplary methods, devices and
materials are described herein.
[0032] The publications discussed above and throughout the text are
provided solely for their disclosure prior to the filing date of
the present application. Nothing herein is to be construed as an
admission that the inventors are not entitled to antedate such
disclosure by virtue of prior disclosure.
[0033] The ability to deliver drugs locally to the site of need and
over a prolonged period of time is important as a therapeutic
method for many ailments and diseases. Many drugs are more
effective if delivered at a specific site since they can be
delivered in concentrated dosages at the point of interest, while
maintaining an overall low dosage within the total body.
Additionally, many drugs cannot be delivered by oral means because
the molecules are too fragile to survive the digestive process, or
because the molecules do not pass efficiently through the walls of
the digestive organs. Some drug therapies require long term dosing
over the course of many months or years requiring frequent visits
to a clinician for treatment. Furthermore, some drugs require
delivery in places that are inconvenient for injection, such as in
the eye or in internal organs. In all these cases, sustained drug
delivery through an implant or attached device would be of great
benefit to patients undergoing treatment.
[0034] An important application of drug delivery implant is age
related macular degeneration (AMD). Age related macular
degeneration is the leading cause of blindness in people over age
65. The National Eye Institute estimates that there are 1.6 million
individuals with AMD in the United States alone. Macular
degeneration is the physical disturbance of the center of the
retina called the macula, the part of the retina which is capable
of the most acute and detailed vision. Currently, there is no known
cure for AMD. However, new therapies are being developed which show
promise in controlling the progression of the disease. Some of
these treatments include frequent administration of protein-based
drug formulations such as Lucentis (ranibizumab) and Avastin
(bevacizumab) directly into the eye. Since these drugs consist of
large protein molecules which cannot be administered through oral
formulations, patients suffering from AMD have to receive
injections directly into their eyes once every month. The highly
invasive nature of the treatment and limitations in controlling an
effective drug concentration in the eye over a prolonged period of
time still leave these delivery methods far from ideal.
[0035] In addition to AMD, diabetic retinopathy, retinovasclar
disease, and other types of retinal degenerations are amenable to
treatment by drug delivery implant. This is because many of those
diseases also need local therapy with the same types of compounds
that are used for AMD. Treating diseases associated with
intraocular scarring such as retinal detachment (PVR) and glaucoma
can also be accomplished through sustained release of drug within
the eye to prevent unwanted proliferation.
[0036] Delivery of drugs into vitreous via liposomes or slow
release crystalline lipid prodrugs extend the drug vitreous
half-life, but traditional liposomes or self-assembling liposomes
often decrease vitreous clarity when used, cannot be easily
customized to release drugs with different physicochemical
properties, and do not "report" drug release information.
Accordingly, the current state of art does not provide a
satisfactory way to construct a small device and implement methods
for the delivery of a drug in a predetermined time dependent
manner.
[0037] Each of the features and teachings disclosed below can be
utilized separately or in conjunction with other features and
teachings to provide a drug delivery device for delivering time
dependent dosing. Representative examples of the disclosure, which
examples utilize many of these additional features and teachings
both separately and in combination, will now be described in
further detail with reference to the attached drawings. This
detailed description is merely intended to teach a person of skill
in the art further details for practicing aspects of the present
teachings and is not intended to limit the scope of the invention.
Therefore, combinations of features and steps disclosed in the
following detail description may not be necessary to practice the
invention in the broadest sense, and are instead taught merely to
particularly describe representative examples of the present
teachings.
[0038] Moreover, the various features of the representative
examples and the dependent claims may be combined in ways that are
not specifically and explicitly enumerated in order to provide
additional useful embodiments of the present teachings. In
addition, it is expressly noted that all features disclosed in the
description and/or the claims are intended to be disclosed
separately and independently from each other for the purpose of
original disclosure, as well as for the purpose of restricting the
claimed subject matter independent of the compositions of the
features in the embodiments and/or the claims. It is also expressly
noted that all value ranges or indications of groups of entities
disclose every possible intermediate value or intermediate entity
for the purpose of original disclosure, as well as for the purpose
of restricting the claimed subject matter.
[0039] As an initial starting point it is important to understand
the difference between silicon, silicon oxide and silica (i.e.,
silicon dioxide). This is mentioned because there is a fundamental
difference in the compositions, uses and biological activity of
these materials.
[0040] Silicon is the chemical element that has the symbol Si and
atomic number 14. Silicon occasionally occurs as the pure free
element in nature, but is more widely distributed as various forms
of silicon dioxide (silica) or silicates. Silicon is used in the
electronics industry where substantially pure and highly pure
silicon are used for the formation of wafers. Pure silicon is used
to produce ultra-pure silicon wafers used in the semiconductor
industry, in electronics and in photovoltaic applications.
Ultra-pure silicon can be doped with other elements to adjust its
electrical response by controlling the number and charge (positive
or negative) of current carriers. Such control is desirable for
transistors, solar cells, integrated circuits, microprocessors,
semiconductor detectors and other semiconductor devices which are
used in electronics and other high-tech applications. In photonics,
silicon can be used as a continuous wave Raman laser medium to
produce coherent light. Hydrogenated amorphous silicon is used in
the production of low-cost, large-area electronics in applications
such as LCDs, and of large-area, low-cost thin-film solar cells.
Accordingly, most commonly purchased silicon is in the form of
silicon wafers. Silicon when metabolized by the body is converted
to silane, a compound that when accumulated has toxic effects.
[0041] Silicon oxide typically refers to a silicon element linked
to a single reactive oxygen species (e.g., a radical). Such silicon
oxide compounds are useful for the additional of carbon or other
desirable elements wherein a bond is formed between the reactive
oxygen and the desired element or chemical side chain. Silicon
oxides are useful for the formation of hydrogenated silicon
oxycarbide (H:SiOC) films having low dielectric constant and a
light transmittance. Such Si--O--X (wherein X is any suitable
element other than oxygen) compounds are formed using complex
reactions including reacting a methyl-containing silane in a
controlled oxygen environment using plasma enhanced or ozone
assisted chemical vapor deposition to produce the films. In
contrast, a dioxide (further described below) comprises two (2)
oxygens linked to a silicon atom.
[0042] Silicon dioxide refers to the compound SiO.sub.2 (sometime
referred to as silica). Silicon dioxide is formed when silicon is
exposed to oxygen (or air). A thin layer (approximately 1 nm or 10
.ANG.) of so-called `native oxide` is formed on the surface when
silicon is exposed to air under ambient conditions. Higher
temperatures and alternate environments are used to grow layers of
silicon dioxide on silicon. Silicon dioxide is inert and harmless.
When silica is ingested orally, it passes unchanged through the
gastrointestinal tract, exiting in the feces, leaving no trace
behind. Small pieces of silicon dioxide are equally harmless, so
long as they are not large enough to mechanically obstruct the GI
tract or fluid flow, or jagged enough to lacerate the GI lining,
vessel or other tissue. Silicon dioxide produces no fumes and is
insoluble in vivo. It is indigestible, with zero nutritional value
and zero toxicity. Silicon dioxide has covalent bonding and forms a
network structure. Hydrofluoric acid (HF) is used to remove or
pattern silicon dioxide in the semiconductor industry.
[0043] Silicon is an essential trace element that is linked to the
health of bone and connective tissues. The chemical species of
relevance to the toxicity of porous Si are silane (SiH.sub.4) and
dissolved oxides of silicon; three important chemical reactions of
these species are given in Eq. (1)-(3). The surface of porous Si
contains Si--H, SiH.sub.2, and SiH.sub.3 species that can readily
convert to silane. Silane is chemically reactive (Eq. (1)) and
toxic, especially upon inhalation. Like silane, the native
SiH.sub.x species on the porous Si surface readily oxidize in
aqueous media. Silicon itself is thermodynamically unstable towards
oxidation, and even water has sufficient oxidizing potential to
make this reaction spontaneous Eq. (2). The passivating action of
SiO.sub.2 and Si--H (for samples immersed in HF solutions) make the
spontaneous aqueous dissolution of Si kinetically slow. Because of
its highly porous nanostructure, oxidized porous Si can release
relatively large amounts of silicon-containing species into
solution in a short time. The soluble forms of SiO.sub.2 exist as
various silicic acid compounds with the orthosilicate
(SiO.sub.4.sup.4-) ion as the basic building block (Eq. (3)), and
these oxides can be toxic in high doses. Because the body can
handle and eliminate silicic acid, the important issue with porous
Si-based drug delivery systems is the rate at which they degrade
and resorb.
SiH.sub.4+2H.sub.2O.fwdarw.SiO.sub.2+4H.sub.2 (1)
Si+O.sub.2.fwdarw.SiO.sub.2 (2)
SiO.sub.2+2H.sub.2O.fwdarw.Si(OH).sub.4 (3)
[0044] Surface chemistry plays a large role in controlling the
degradation properties of porous Si in vivo. After Si is
electrochemically etched, the surface is covered with reactive
hydride species. These chemical functionalities provide a versatile
starting point for various reactions that determine the dissolution
rates in aqueous media, allow the attachment of homing species, and
control the release rates of drugs. The two most important
modification reactions are chemical oxidation (Eq. (2)) and
grafting of Si--C species.
[0045] The various embodiments provided herein are generally
directed to systems and methods for producing a drug delivery
device that can deliver time dependent dosing without the need for
electronics or power. Accordingly, the disclosure recognizes and
addresses an important and unmet medical need for a minimally
invasive, controllable and monitorable drug delivery system and
methods of using the system that would enable long acting local
treatment of both extraocular and intraocular diseases.
[0046] Traditional methods of intraocular drug delivery include the
use of liposomes or self-assembling liposomes, which often decrease
vitreous clarity when used, cannot be easily customized to release
drugs with different physicochemical properties, and do not
"report" drug release information.
[0047] Advantageously, the disclosure provides devices and methods
for treating both intraocular and extraocular diseases that promote
sustained release of a pharmacological candidate, or drug, that is
impregnated on nanostructured silicon, such as Si, SiO.sub.2,
polymer-templated, Si/polymer, or SiO.sub.2/polymer composites.
[0048] In one aspect, the devices and methods are also
self-reporting such that drug release and quantity remaining can be
monitored. Embodiments include minimally invasive, self-reporting,
controlled delivery systems for delivering a drug or drugs to
surfaces of the eyes, both the ocular surface (cornea and
conjunctiva) and the scleral surface, as well as intraocular
portions of the eye, including the retina, choroids, lens, ciliary
body, anterior chamber, and vitreous. Such devices include not only
Si photonic crystals that include an active ingredient, but also
biodegradable polymer imprints made from porous silicon
templates.
[0049] For intraocular diseases, such as glaucoma, age-related
macular degeneration (ARMD), choroidal neovascularization (CNV),
uveitis, diabetic retinopathy, retinovasclar disease, and other
types of retinal degenerations, drug delivery to the vitreous,
retina, and choroid is a challenging task due to the formidable
obstacles posed by the blood-retinal barrier and the tight
junctions of the retinal pigment epithelium. Only small fractions
of drug administered systemically reach the target, requiring large
and potentially toxic doses when delivered systemically. Another
challenge to retinal drug delivery is the fact that drug levels
should be sustained for prolonged periods at the target site. This
is difficult using intravitreal injections because the short
half-life of most intravitreal injectable drugs. Intraocular
implants have provided sustained vitreoretinal drug levels for
treating certain retinal diseases. However, this route demands
intraocular surgery that is known to cause intraocular
complications when placing and replacing the implant.
[0050] For ocular surface diseases, such as viral keratitis,
chronic allergic conjunctivitis, glaucoma, and scleritis, some of
the same problems persist. Systemic administration of drug requires
potentially toxic doses, and topical treatments have a short
half-life, requiring numerous and frequent doses. For treating
ocular surface diseases biodegradable polymer imprints may be made
from porous silicon templates. The silicon-free polymer may be used
in drug delivery contact lenses or implants at an appropriate
location on or associated with the eye, including the ocular
surface and retrobulbar surface.
[0051] Photonic crystals have widespread application in
optoelectronics, chemical and biological sensors, high-throughput
screening, and drug delivery applications. These photonic crystals
are especially advantageous because of the relative ease with which
the optical properties, pore size, and surface chemistry can be
manipulated. Moreover, position, width, and intensity of spectral
reflectivity peaks may be controlled by the current density
waveform and solution composition used in the electrochemical etch,
thus rendering possible the preparation of films of porous Si
photonic crystals that display any color within the visible light
band with high color saturation, which is a desirable feature for
information displays.
[0052] The term photonic crystal refers to a material in which a
spatially repeating pattern produces a distinctive spectral
pattern. A photonic crystal comprises small porous silicon
particles that have been machined and sized to small crystals for
intraocular injection.
[0053] The disclosure provides compositions and methods for
injection of porous microscopic nanostructured silicon particles
impregnated with a particular drug or drugs. While the disclosure
contemplates use of numerous porous microscopic particles, typical
particles include porous silicon or silicon dioxide particles
(referred to as "smart dust"), which are nanostructure that allows
maintenance of sustained intraocular therapeutic drug levels with
minimal invasiveness and elimination of systemic side effects. In
addition to configuring the nanostructure to suit individual
applications, the disclosure also contemplates chemically modifying
the particles and the particular drug or drugs to tune and control
release profiles of the particles. Intraocular injection allows
monitoring of drug levels non-invasively.
[0054] Porous silicon is advantageous in that porous silicon films
have a large free volume (typically 50-80%). Thus having a high
capacity for a drug can be custom designed at the nanoscale to
deliver one or more drugs at a variety of customizable release
rates and the photonic properties of a nanostructured material as a
means to non-invasively determine the rate and amount of drug
delivered. The porous silicon photonic crystal particles of the
disclosure can be impregnated with a drug or plurality of drugs,
and subsequently introduced into the retina, choroids, lens ciliary
body, anterior chamber, and vitreous of the eye via injection. For
details of coded photonic particles and methods of preparing the
same, see published U.S. application serial numbers: 20050042764
entitled, "Optically encoded particles," 20050009374 entitled,
"Direct patterning of silicon by photoelectrochemical etching,"
20070148695 entitled "Optically encoded particles, system and
high-throughput screening," and 20070051815 entitled "Optically
encoded particles with grey scale spectra," which are incorporated
herein by reference.
[0055] The "smart dust" photonic crystal particles can be optimized
for intravitreal delivery of one or more of a vast array of drugs
including anti-cancer drugs and other small molecule drugs,
inhibitory nucleic acids, peptides and polypeptides. For example,
the disclosure demonstrates pigment epithelium derived factor
(PEDF), an 8-mer peptide fragment of urokinase (uPA),
dexamethasone, and a host of other drugs, small molecules, proteins
(e.g., antibodies such as bevacizumab and Fab fragments of
antibodies such as ranibizumab), peptides, and nucleic acids can be
used. These smart dust photonic crystals may be impregnated with
drugs by either trapping one or more of the drugs in porous Si
smart dust, or the pores themselves may be chemically modified to
bind the candidate drug.
[0056] Photonic crystals are produced from porous silicon and
porous silicon/polymer composites, or porous Si film or polymer
replica or Si-polymer composite may be generated as a sheet for an
exoplant. Pulsed electrochemical etching of a silicon chip produces
a multilayered porous nanostructure. A convenient feature of porous
Si is that the average pore size can be controlled over a wide
range by appropriate choice of current, HF concentration, wafer
resistivity, and electrode configuration used in the
electrochemical etch. This tunability of the pore dimensions,
porosity, and surface area is especially advantageous.
[0057] The thickness, pore size, and porosity of a given film is
controlled by the current density, duration of the etch cycle, and
etchant solution composition. In addition, a porous silicon film
can be used as a template to generate an imprint of biologically
compatible or bioresorbable materials. The porous silicon film or
its imprint possess a sinusoidally varying porosity gradient,
providing sharp features in the optical reflectivity spectrum that
can be used to monitor the presence or absence of chemicals trapped
in the pores. It has been shown that the particles (smart dust)
made from the porous silicon films by mechanical grinding or by
ultrasonic fracture still carry the optical reflectivity
spectrum.
[0058] Porous Si is a product of an electrochemical anodization of
single crystalline Si wafers in a hydrofluoric acid electrolyte
solution. Pore morphology and pore size can be varied by
controlling the current density, the type and concentration of
dopant, the crystalline orientation of the wafer, and the
electrolyte concentration in order to form macro-, meso-, and
micropores. Pore sizes ranging from 1 nm to a few microns can be
prepared. The type of dopant in the original silicon wafer is
important because it determines the availability of valence band
holes that are the key oxidizing equivalents in the reaction shown
in FIG. 1. In general the relationships of dopant to morphology can
be segregated into four groups based on the type and concentration
of the dopant: n-type, p-type, highly doped n-type, and highly
doped p-type. By "highly doped," is meant dopant levels at which
the conductivity behavior of the material is more metallic than
semiconducting. For n-type silicon wafers with a relatively
moderate doping level, exclusion of valence band holes from the
space charge region determines the pore diameter. Quantum
confinement effects are thought to limit pore size in moderately
p-doped material. For both dopant types the reaction is crystal
face selective, with the pores propagating primarily in the
<100> direction of the single crystal. For example,
electrochemically driven reactions use an electrolyte containing
hydrofluoric acid. Application of anodic current oxidizes a surface
silicon atom, which is then attacked by fluoride. The net process
is a 4 electron oxidation, but only two equivalents are supplied by
the current source. The other two equivalents come from reduction
of protons in the solution by surface SiF.sub.2 species. Pore
formation occurs as Si atoms are removed in the form of SiF.sub.4,
which reacts with two equivalents of F-- in solution to form
SiF.sub.6.sup.2-.
[0059] The porosity of a growing porous Si layer is proportional to
the current density being applied, and it typically ranges between
40 and 80%. Pores form at the Si/porous Si interface, and once
formed, the morphology of the pores does not change significantly
for the remainder of the etching process. However, the porosity of
a growing layer can be altered by changing the applied current. The
film will continue to grow with this new porosity until the current
changes.
[0060] This feature allows the construction of layered
nanostructures simply by modulating the applied current during an
etch. For example, one dimensional photonic crystals consisting of
a stack of layers with alternating refractive index can be prepared
by periodically modulating the current during an etch.
[0061] Stain etching is an alternative to the electrochemical
method for fabrication of porous Si powders. The term stain etching
refers to the brownish or reddish color of the film of porous Si
that is generated on a crystalline silicon material subjected to
the process. In the stain etching procedure, a chemical oxidant
(typically nitric acid) replaces the power supply used in the
electrochemically driven reaction. HF is typically used as an
ingredient, and various other additives are used to control the
reaction. Stain etching generally is less reproducible than the
electrochemical process, although recent advances have improved the
reliability of the process substantially. Porous Si powders
prepared by stain etch are commercially available
(http:.about..about.vestaceramics.net).
[0062] For in vivo applications, it is often desirable to prepare
porous Si in the form of particles. The porous layer can be removed
from the Si substrate with a procedure commonly referred to as
"electropolishing" or "lift-off." The etching electrolyte is
replaced with one containing a lower concentration of HF and a
current pulse is applied for several seconds. The lower
concentration of HF results in a diffusion limited situation that
removes silicon from the crystalline Si/porous Si interface faster
than pores can propagate. The result is an undercutting of the
porous layer, releasing it from the Si substrate. The freestanding
porous Si film can then be removed with tweezers or a vigorous
rinse. The film can then be converted into microparticles by
ultrasonic fracture. Conventional lithography or microdroplet
patterning methods can also be used if particles with more uniform
shapes are desired.
[0063] The ability to easily tune the pore sizes and volumes during
the electrochemical etch is a unique property of porous Si that is
very useful for drug delivery applications. Other porous materials
generally require a more complicated design protocol to control
pore size, and even then, the available pore sizes tend to span a
limited range. With electrochemically prepared porous Si, control
over porosity and pore size is obtained by adjusting the current
settings during the etch. Typically, larger current density
produces larger pores. Large pores are desirable when incorporating
sizable molecules or drugs within the pores. Pore size and porosity
is important not only for drug loading; it also determines
degradation rates of the porous Si host matrix.
[0064] Smaller pores provide more surface area and expose more
sites for attack of aqueous media. The smaller porous filaments
within the film yield greater dissolution rates, providing a
convenient means to control degradation rates of the porous Si
host.
[0065] Surface chemistry plays a large role in controlling the
degradation properties of porous Si in vivo. Immediately after Si
is electrochemically etched, the surface is covered with reactive
hydride species. These chemical functionalities provide a versatile
starting point for various reactions that determine the dissolution
rates in aqueous media, allow the attachment of homing species, and
control the release rates of drugs. The two most important
modification reactions are chemical oxidation (Eq. (2)) and
grafting of Si--C species.
[0066] With its high surface area, porous Si is particularly
susceptible to air or water oxidation. Once oxidized, nanophase
SiO.sub.2 readily dissolves in aqueous media, and surfactants or
nucleophiles accelerate the process. Si--O bonds are easy to
prepare on porous Si by oxidation, and a variety of chemical or
electrochemical oxidants can be used. Thermal oxidation in air
tends to produce a relatively stable oxide, in particular if the
reaction is performed at >600.degree. C. Ozone oxidation,
usually performed at room temperature, forms a more hydrated oxide
that dissolves quickly in aqueous media.
[0067] Milder chemical oxidants, such as dimethyl sulfoxide (DMSO,
Eq. (4)), benzoquenone, or pyridine, can also be used for this
reaction. Mild oxidants are sometimes preferred because they can
improve the mechanical stability of highly porous Si films, which
are typically quite fragile.
##STR00001##
[0068] The mechanical instability of porous Si is directly related
to the strain that is induced in the film as it is produced in the
electrochemical etching process, and the volume expansion that
accompanies thermal oxidation can also introduce strain. Mild
chemical oxidants presumably attack porous Si preferentially at
Si--Si bonds that are the most strained, and hence most reactive.
As an alternative, nitrate is a stronger oxidant, and nitric acid
solutions are used extensively in the preparation of porous Si
particles from silicon powders by chemical stain etching.
[0069] Slow oxidation of the porous Si surface by dimethyl
sulfoxide (DMSO), when coupled with dissolution of the newly formed
oxide by HF, is a mild means to enlarge the pores in porous Si
films. Aqueous solutions of bases such as KOH can also be used to
enlarge the pores after etching. Electrochemical oxidation, in
which a porous Si sample is anodized in the presence of a mineral
acid such as H.sub.2SO.sub.4, yields a fairly stable oxide.
Oxidation imparts hydrophilicity to the porous structure, enabling
the incorporation and adsorption of hydrophilic drugs or
biomolecules within the pores. Aqueous oxidation in the presence of
various ions including Ca.sup.2+ generates a calcified form of
porous Si that has been shown to be bioactive and is of particular
interest for in vivo applications. Calcification can be enhanced by
application of a DC electric current.
[0070] The porous smart silicon dust can be oxidized to increase
stability and injected into animal eyes. The smart silicon dust can
be variously modified to be a long-lasting intraocular drug
delivery vehicle to carry various therapeutic compounds. In
addition, biodegradable porous polymer imprints made from porous
silicon templates can be used as a drug delivery implant to be
placed at an appropriate location in the eye. The drug can be added
into the imprint solution before casting or engineered into the
pores after casting.
[0071] Carbon grafting stabilizes porous Si against dissolution in
aqueous media, but the surface must still avoid the non-specific
binding of proteins and other species that can lead to opsonization
or encapsulation. Reactions that place a polyethylene glycol (PEG)
linker on a porous Si surface have been employed to this end. A
short-chain PEG linker yields a hydrophilic surface that is capable
of passing biomolecules into or out of the pores without binding
them strongly. The distal end of the PEG linker can be modified to
allow coupling of other species, such as drugs, cleavable linkers,
or targeting moieties, to the material.
[0072] The oxides of porous Si are easy to functionalize using
conventional silanol chemistries. When small pores are present (as
with p-type samples), monoalkoxydimethylsilanes
(RO--Si(Me).sub.2-R') can be more effective than trialkoxysilanes
((RO).sub.2Si--R') as surface linkers. This is because
trialkoxysilanes oligomerize and clog smaller pore openings,
especially when the reagent is used at higher concentrations.
[0073] Whereas Si--C chemistries are robust and versatile,
chemistries involving Si--O bonds represent an attractive
alternative two reasons. First, the timescale in which highly
porous SiO.sub.2 is stable in aqueous media is consistent with many
short-term drug delivery applications-typically 20 min to a few
hours. Second, a porous SiO.sub.2 sample that contains no
additional stabilizing chemistries is less likely to produce toxic
or antigenic side effects. If it is desired that the porous Si
material be stable in vivo for long periods (for example, an
extended release formulation or an in vivo biosensor), Si--C
chemistries such as hydrosilylation with endcapping or thermal
carbonization with acetylene is useful. If a longer-lived oxide
matrix is desired, silicon oxides formed at higher temperatures
(>700.degree. C.) are significantly more stable in aqueous media
than those formed at lower temperatures or by ozone oxidation.
[0074] Either silicon smart dust or the episcleral one-way
releasing plaque of biodegradable polymer imprint of silicon smart
dust provide a device and method for intravitreal drug delivery
that promotes sustained intraocular therapeutic drug levels with
minimal invasiveness and elimination of systemic side effects.
Impregnation of the porous material may proceed in several
ways.
[0075] The candidate drug may be "physically" trapped within the
pores, or, the pores themselves may be chemically modified to bind
the candidate drug.
[0076] More specifically, "physical trapping" is similar to
building a ship in a bottle, where the "ship" is the candidate drug
and the "bottle" is the nanometer-scale pores in the porous Si
matrix. Small molecules can be trapped in the porous matrix by
oxidizing the porous Si around the molecule. The relevant reaction
is illustrated in FIG. 1, where "O" in the equation is a molecular
oxidant such as O2, dimethyl sulfoxide, hydrogen peroxide, or
water. Since oxidation of silicon adds two atoms of oxygen per atom
of Si to the material, there is a significant increase in volume of
the matrix upon oxidation. This has the effect of swelling the pore
walls and shrinking the free volume inside the pores, and under the
appropriate conditions, molecules present in the pores during
oxidation become trapped in the oxide matrix. One aspect of the
trapping process is the increased concentration of the active
ingredient which occurs during the trapping process. The crystals
may present a negatively charged environment and an active
ingredient, such as proteins and other drugs, may be concentrated
in the crystals to levels much higher than the free concentration
of the active ingredient in solution. This can result in 10 to 100
fold or more increase in active ingredient concentration when
associated with a crystal. For example, Avastin which has a
commercial concentration of 2.5 mg per 0.1 cc can be concentrated
by association with the crystal structures described herein. The
oxidizing can be performed at repeated intervals by performing
layered oxidation. For example, a biological agent or drug can be
trapped in the pores by controlled addition of oxidants. Oxidation
of the freshly prepared (hydride-terminated) porous Si material
results in an effective shrinking of the pores. This occurs because
the silicon oxide formed has a larger volume than the Si starting
material. If a drug is also present in the solution that contains
the oxidant, the drug becomes trapped in the pores.
[0077] Furthermore the porous silicon oxide can comprise a higher
concentration of a biological agent or drug (e.g., Avastin) than a
non-oxidized Si hydride material. For example, the oxide treatment
causes the oxidized porous Si material to absorb larger quantities
of the drug Avastin than are absorbed by the freshly prepared
(hydride-terminated) porous Si material.
[0078] The free volume in a porous Si film is typically between 50
and 80%. Oxidation should reduce this value somewhat, but the free
volume is expected to remain quite high. Most of the current drug
delivery materials are dense solids and can deliver a small
percentage of drug by weight. The amount of drug that can be loaded
into the porous Si material is expected to be much larger than, for
example, surface-modified nanoparticles or polylactide (PLA)
polymers. Experiments can quantify the amount of each of the drugs
that can be loaded into the smart dust delivery vehicle.
[0079] During chemical modification, a molecule is attached to the
inner pore walls via covalent bonds. In the porous Si system,
proteins, DNA, and various small molecules can be attached
following several different procedures. One embodiment uses
electrochemical modification. For example, reduction of
1-iodo-6-(trifluoroacetylamino) hexane at a p-type porous silicon
cathode leads to attachment of the trifluoroacetamidohexyl group.
Subsequent acid-catalyzed hydrolysis should lead directly to the
surface-bound amine species. The reactions are represented by the
equation illustrated in FIG. 2.
[0080] The surface amine can then be functionalized with a drug,
polypeptide or peptide. As demonstrated in the specific
non-limiting examples, below, the surface amine is functionalized
with an 8-mer peptide fragment of uPA using standard peptide
coupling methods.
[0081] Various approaches to load a molecular payload into a porous
Si host have been explored, and they can be grouped into the
following general categories: covalent attachment, physical
trapping, and adsorption.
[0082] Covalent attachment provides a convenient means to link a
biomolecular capture probe to the inner pore walls of porous Si for
biosensor applications, and this approach can also be used to
attach drug molecules. As described elsewhere herein, linking a
biomolecule via Si--C bonds tends to be a more stable route than
using Si--O bonds due to the susceptibility of the Si--O species to
nucleophilic attack.
[0083] The versatility of the hydrosilylation reaction for
preparing functional porous Si surfaces was recognized early in the
history of porous Si surface chemistry. One of the more common
approaches is to graft an organic molecule that contains a carboxyl
species on the distal end of a terminal alkene. The alkene end
participates in the hydrosilylation reaction, bonding to the Si
surface and leaving the carboxy-terminus free for further chemical
modification. A favorite linker molecule is undecylenic acid, which
provides a hydrophobic 10 carbon aliphatic chain to insulate the
linker from the porous Si surface. The drug payload can be attached
directly to the carboxy group of the alkene, or it can be further
separated from the surface with a PEG linker. Due to the stability
of the Si--C bond, hydrosilylation is good way of attaching a
payload to porous Si. The payload is only released when the
covalent bonds are broken or the supporting porous Si matrix is
degraded. For drug delivery this introduces a complication in that
the drug may not release from the linker, resulting in a modified
version of the drug being introduced into the body. In addition, a
drug may be susceptible to attack by silane generated during the
degradation of the porous Si scaffolding or by residual reactive
species on the porous Si material itself.
[0084] If the drug to be trapped is relatively robust, it can be
locked into place by oxidation of the porous Si host matrix. The
locking procedure takes advantage of the fact that when porous Si
is oxidized to SiO.sub.2 there is a volume expansion to accommodate
the extra oxygen atoms. This volume expansion serves to shrink the
pores, trapping anything that happens to be in them at the time.
High pH and nucleophilic nature of ammonia enhance oxidation of
freshly etched porous Si in aqueous solutions. Similar oxidation
can be induced by vapor phase pyridine. Nucleophilic groups present
on drug payloads may also participate in this reaction, as can
oxidizing species such as quinones. The silicic acid generated
during dissolution Eq. (3) can participate in sol-gel type
reactions-essentially reprecipitation of the silicic acid, but in
the form of various inorganic silicates. Common ions such as
Ca.sup.2+ and Mg.sup.2+ in solution can participate in silicate
precipitation reactions Eq. (5), and these types of precipitates
are known to be bioactive.
Si(OH).sub.4+2Ca.sup.2+.fwdarw.Ca.sub.2SiO.sub.4+4H.sup.+ (5)
[0085] Once formed, mild thermal treatments can be used to
dehydrate the oxide or silicate matrix. Heating tends to densify
and rigidify the structure by forming strong Si--O--Si linkages
(Eq. (6)).
##STR00002##
[0086] As-formed porous Si has a hydride-terminated surface that is
very hydrophobic. Oxidized porous Si is hydrophilic, and chemically
modified porous Si surfaces can be hydrophobic, hydrophilic, or
both (amphiphilic), depending on the specific functional group(s)
attached. The nature of the surface plays a critical role in
determining the amount of drug that can be loaded and the rate at
which it is released. Silicon oxide surfaces tend to present a
negative surface charge to an aqueous solution due to the low pKa
of SiO.sub.2. Often referred to as "electrostatic adsorption,"
attractive coulombic forces from this negative surface provide a
means to extract positively charged ions from solution and
concentrate them at the interface.
[0087] Whereas covalent attachment and oxidative trapping
approaches described above tend to trap their payloads fairly
irreversibly, electrostatic adsorption represents essentially an
ion exchange mechanism that holds molecules more weakly.
Electrostatics is a useful means to affect more rapid drug
delivery, as opposed to covalent or physical trapping approaches
that release drug over a period of days, weeks, or months.
[0088] The affinity of a porous Si particle for a particular
molecule can be controlled with surface chemistry. The surface of
oxidized porous Si has a point of zero charge at a pH of around 2,
and so it presents a negatively charged surface to most aqueous
solutions of interest. At the appropriate pH, porous SiO.sub.2
spontaneously adsorbs positively charged proteins such as serum
albumin, fibrinogen, protein A, immunoglobulin G (IgG), or
horseradish peroxidase, concentrating them in the process. For
example, a 0.125 mg/mL solution of the monoclonal antibody
bevacizumab (trade name Avastin, an anti-cancer drug) spontaneously
concentrates in suitably prepared porous SiO.sub.2 by a factor of
>100.
[0089] Porous Si can also be made hydrophobic, and hydrophobic
molecules such as the steroid dexamethasone or serum albumin can be
loaded into these nanostructures. Hydrophilic molecules can also be
loaded into such materials with the aid of the appropriate
surfactant. The native hydride surface of porous Si is hydrophobic.
Such techniques have been used for short-term loading and release.
Because water is excluded from these hydrophobic surfaces, aqueous
degradation and leaching reactions tend to be slow. The grafting of
alkanes to the surface by hydrosilylation is commonly used to
prepare materials that are stable in biological media; this
stability derives in large part from the ability of the hydrophobic
moieties to locally exclude water or dissolved nucleophiles.
[0090] By way of example only, binding and release of: 1) Avastin
(bevacizumab); 2) a DNA 16-mer; 3) IgG (using a Protein A
receptor); and 4) biotinylated bovine serum albumin (using a
streptavidin receptor) have been demonstrated using this
methodology. The high surface area and optical interferometric
means of detection lead to very high sensitivity for many of these
systems, and the fact that the materials are constructed from
single crystal Si substrates means they can be readily prepared
using Si microfabrication technologies.
[0091] In addition to having pore characteristics (thickness, pore
size, and porosity) that may be controlled by the current density,
duration of the etch cycle, and etchant solution composition, the
porous silicon film may also be used as a template to generate an
imprint of biologically compatible or bioresorbable materials (see
e.g., Li et al., Nanostructured casting of organic and bio-polymers
in porous silicon templates; U.S. Patent Application Publication
No. 20060236436; and Li, et al., Polymer Replicas of Photonic
Porous Silicon For Sensing and Drug Delivery Applications. Science
2003, (299), 2045-2047). Both the porous silicon film and/or its
imprint possess a sinusoidally varying porosity gradient, providing
sharp features in the optical reflectivity spectrum that can be
used to monitor the presence or absence of chemicals trapped in the
pores. It has been shown that the particles (smart dust) made from
the porous silicon films by mechanical grinding or by ultrasonic
fracture still carry the optical reflectivity spectrum. These
porous silicon particles can be oxidized to increase stability and
injected into animal eyes without toxicity to the intraocular
tissues since silica is a mineral needed by the body for building
bones and connective tissue.
[0092] A porous film can be lifted off the silicon substrate, and
can then be broken into micron-sized particles having a size
conducive to intraocular injection. For example, in one embodiment,
the micron-sized particles are sized and configured such that they
may be injected into the eye with a 25 or 27-gauge needle. The
particles act as one-dimensional photonic crystals, displaying an
optical reflectivity spectrum that is determined by the waveform
used in the electrochemical etch. This spectrum acts as an optical
barcode that can be observed through human tissue using, for
example, an inexpensive CCD spectrometer and a white light source.
For the drug delivery methods and systems of the disclosure, a drug
is impregnated and trapped in the pores, and the optical code may
be used to report on the release rate of the drug in the vitreous.
For details of sensing molecular transport in or out of the
particles, or for sensing degradation of the particles, see
published U.S. Pat. Nos. 6,248,539, 6,897,965, and 6,720,177,
"Porous semiconductor-based optical interferometric sensor," which
are incorporated herein by reference. In this manner, the amount of
drug may be quantified to determine how much remains within the
particles, and whether administration of additional doses is
necessary.
[0093] Advantageously, the optical interference spectrum used in
particle identification can be measured with inexpensive and
portable instrumentation (a CCD spectrometer or a diode laser
interferometer). Removal of the drug from the pores results in a
change in the refractive index of the porous film and will be
observed as a wavelength shift in the spectral code of the dust
particle (see, e.g., FIG. 3A). Characteristic color changes are
thus indicative of drug quantity remaining in the pores. Thus, the
term photonic crystal is used for the-film that has been machined
and sized to small crystals for intraocular injection.
[0094] A spectrometric method of detection of the oxidized "smart
dust" injected into the rabbit eyes was also investigated. One
eyepiece of the surgical microscope was connected to the input of a
fiber-optic based spectrophotometer and this allows us to
accurately focus the detecting light on the intraocular "smart
dust" particles. The disclosure also provides a camera for
monitoring the color change of the crystal outfitted with a
spectrometer to quantitate the drug release. In yet another
embodiment, a scanning laser opthalmoscope which scans the retina
and inner eye with a monochromatic light is outfitted with the
appropriate wavelength to scan and detect reflectance spectrum
changes allowing quantification of drug release.
[0095] In addition, to the use of porous silicon as a drug delivery
composition, porous Si is an attractive candidate for use as a
template because of the tunability of the porosity and average pore
size. Additionally, elaborate 1, 2, and 2.5-dimensional photonic
crystals are readily prepared in porous Si. Porous Si composites
(e.g., porous Si and a polymer) show great promise for improving
the mechanical stability and control over release rates of a
delivery system. Either the composite itself or a nanostructure
derived from the composite by removal of the porous Si template can
be used. Porous Si combined with a biocompatible polymer can yield
improved control over drug release kinetics and improved stability
in aqueous media, and the use of biopolymers that are selectively
cleaved by specific proteases provides the possibility of
tissue-specific action.
[0096] Removal of the porous Si or porous SiO.sub.2 template from a
polymer or biopolymer imprint can be achieved (depending upon the
polymer used) by chemical dissolution using aqueous KOH or HF,
respectively, providing a free-standing porous polymer film with
the optical characteristics of the master. Whether or not the
process replicates the nanostructure of the master is highly
dependent on the processing conditions and the type of polymer
used. Also, the ability of the polymer to release from the master
is dependent on the interfacial chemistry and tortuosity of the
pore network.
[0097] Two synthetic approaches can be used to generate a template
polymeric delivery composition or a porous Si polymer composite. In
one aspect, the polymer is synthesized within the porous matrix. In
another aspect, a pre-formed polymer is infused into the matrix by
melt- or solution-casting. For drug delivery applications, it is
important to use a biocompatible polymer. Any number of
biocompatible polymers can be used in the methods and compositions
of the disclosure as described herein. For example, hydrogels can
be used. Hydrogels are commonly used in opthalmologic devices,
biosensors, biomembranes, and controlled drug delivery.
Water-swollen, crosslinked polymeric networks can undergo volume
phase transitions in response to environmental changes such as pH,
ionic strength, temperature, or electric fields.
[0098] Polymer replicas can be implanted on the sclera for
trans-scleral drug release. It has been shown in rabbit eyes that
polymer replicas are biocompatible and may safely and effectively
remain in the eye for multiple months, if not years. Measurement of
the decay in intensity of the peaks in the photonic crystal
spectrum should provide a monitor of the rate of drug release from
an implanted biocompatible polymer. In order to test the above
hypothesis, drug-impregnated poly(L-lactide) (PL) films, cast from
thermally oxidized porous silicon templates, can be prepared
following a scheme, designated generally at 10, illustrated in FIG.
3. Specifically, a template (such as electropolished porous
silicon), generally at 12, is provided, having pores 14 dimensioned
to suit a particular application. A polymer, generally at 16, is
loaded into the pores 14 to form a polymer-template composite. The
template 12 is subsequently removed, leaving a polymer-based
photonic film 16. Replication of the optical spectrum in the
biocompatible polymer upon removal of the porous silicon template
can be used to confirm the replication process. The release
characteristics of the polymers can be studied.
[0099] Any number of polymeric materials can be used in the
generation of a polymeric porous structure of the disclosure.
Including, for example, nylon (polyamides), dacron (polyesters),
polystyrene, polypropylene, polycaprolactone, polyacrylates,
polyvinyl compounds (e.g., polyvinylchloride), polycarbonate (PVC),
polytetrafluorethylene (PTFE, teflon), thermanox (TPX),
poly(N-isopropylacrylamide), nitrocellulose, cotton, polyglycolic
acid (PGA), zein, collagen (in the form of sponges, braids, or
woven threads, etc.), cellulose, gelatin, poly lactic acid, poly
glycolic acid, copolymers of poly lactic or poly glycolic acid, or
other naturally occurring biodegradable materials or synthetic
materials, including, for example, a variety of
polyhydroxyalkanoates. Again, any number of polymers can work
provided the polymer is transparent at the wavelengths of interest
for the photonic application. If the template is to be removed, the
polymer should be a solid and not a liquid. Typical polymers can
include, for example, Poly dimethyl siloxane (PDMS), poly lactic
acid (PLA), PLGA, polypropylene, polyethylene, polystyrene, and
clear epoxy.
[0100] The degradation of the photonic structure in these films can
be characterized in pH 7.4 aqueous buffer solutions, in vitro and
in vivo. In accelerated degradation studies, polymer imprints
impregnated with caffeine were studied. The intensity of the rugate
peak displays an approximately exponential decay when the polymer
is dissolved in pH 10 buffer. Simultaneous measurement of the decay
of the spectral peak and the appearance of caffeine in the solution
(caffeine absorption feature at 274 nm) confirmed that the drug was
released on a time scale comparable to polymer degradation.
[0101] Embodiments of the disclosure also contemplate vectorial
drug delivery. The polymer-based photonic film shown in FIG. 3
contains a polymer "cap" 18 on one side of the film. Films prepared
in this manner will leach drug out one side of the film, allowing
greater control of the drug delivery parameters. Manufacturing
variables are channel sizes and packing.
[0102] For intraocular delivery of drugs, a doctor or clinician may
look through the iris of the eye and into the clear part of the eye
to observe the colors of the injected particles. In this manner,
the amount of drug remaining or the degree to which the particles
have dissolved may be monitored, which in turns permits the doctor
or clinician to forecast the length of time before the particles
completely dissolve, and to predict when the patient may need
subsequent injections.
[0103] Other embodiments include use of a porous silicon or
silicon/polymer composite at a particular location of the eye, or
using the porous silicon or silicon/polymer composite as a template
to generate other biologically compatible or biologically
resorbable materials for similar use. Biodegradable polymer
imprints may be made from porous silicon templates, which may be
used as drug delivery contact lenses or implants at an appropriate
location of the eye, including the ocular surface and retrobulbar
surface.
[0104] Another embodiment of the disclosure include drug(s)
impregnated in porous films configured to be worn or attached on
the front of the eye. A contact lens formed of impregnated porous
thin film material, for example, comprises and embodiment of the
disclosure. While another embodiment encompasses a contact lens, it
also contemplates other similarly curved solid template
correspondingly shaped with a front surface of the eye, as well as
being configured to join the eye at the sclera as an episcleral
plaque. The particular drug or drugs to be used with the polymer
imprint may be added to the imprint solution prior to casting or
engineered into the pores of the imprint after casting.
Accordingly, the embodiment of the disclosure provides a system and
method of drug delivery wherein porous silicon films can be
variously modified to be a long-lasting intraocular drug delivery
vehicle to carry various therapeutic compounds. In addition,
biodegradable porous polymer imprints made from porous silicon
templates can be used as a drug delivery implant to be placed at an
appropriate location in the eye. The drug can be added into the
imprint solution before casting or engineered into the pores after
casting.
[0105] For the extraocular drug delivery, the emphasis on optical
reporting declines. With the episcleral plaque, for example,
delivery is retrobulbar, and it is not as easy to use an optical
instrument to "read" these films. In this retrobulbar embodiment,
the ability of the nanostructure to set the rate of dissolution or
drug release is a property. Because the electrochemical process
used to construct porous Si can control the nanostructure to such a
precise degree, precise control of the dissolution and/or drug
release profile of the particles or of the composites is conferred.
Thus, for example, the disclosure provides a contact lens
configured and arranged to cover a front extraocular surface, where
a rim, or "carrier," of the contact lens would be either a silicon
or silicon/polymer composite film impregnated with drug(s). The
wearer would receive a sustained and monitorable release of drug
through the contact lens. Another embodiment includes the use of
episcleral plaques.
[0106] An episcleral plaque is an extraocular way to deliver drugs
and the intraocular dust injection promotes monitoring of drug
levels non-invasively. The disclosure provides use of a silicon or
silicon/polymer composite film impregnated with drugs to be affixed
or adhered to a retrobulbar surface of the eye. The patient would
thereby receive a sustained and monitorable release of drug through
the episcleral plaque.
[0107] While the disclosure provides for use with a virtually
unlimited number of pharmaceutical candidates, several exemplary
drugs will be discussed herein. For example, drug delivery for
drugs used in treating ARMD and uveitis will be shown for purposes
of illustration. These diseases require prolonged intraocular
therapeutic drug levels to halt the progress of the disease and the
deterioration of eyesight. However, the promising drugs for
treating these diseases all share a common problem, which is the
transient intraocular therapeutic level requires frequent
intravitreal injections. These promising drugs include angiostatic
steroids, metalloproteinase inhibitors, VEGF binding drugs, PEDF,
an 8-mer peptide fragment of urokinase (uPA) and dexamethasone.
These drugs may also be used to treat, for example, diabetic
retinopathy. In particular, PEDF, the 8-mer peptide fragment of uPA
and dexamethasone all have short intravitreal half lives.
[0108] Other drugs or "active ingredient" that can be used with the
smart dust of the disclosure include any one or any combination of
the following, but are not limited to, anti-angiogenic compounds
such as bevacizumab, ranibizumab, pegaptanib, and other compounds
in the angiogenic cascade. Also included are glucocorticosteroids
such as dexamethasone, triamcinolone acetonide, fluocinolone
acetonide and other comparable compounds in the corticosteroid and
cortisene families. Also included are compounds such as antacids,
anti-inflammatory substances, coronary dilators, cerebral dilators,
peripheral vasodilators, anti-infectives, psychotropics,
anti-manics, stimulants, anti-histamines, laxatives, decongestants,
vitamins, gastrointestinal sedatives, anti-diarrheal preparations,
anti-anginal drugs, vasodilators, anti-arrhythmics,
anti-hypertensive drugs, vasoconstrictors and migraine treatments,
anti-coagulants and anti-thrombotic drugs, analgesics,
anti-pyretics, hypnotics, sedatives, anti-emetics, anti-nauseants,
anti-convulsants, neuromuscular drugs, hyper- and hypoglycemic
agents, thyroid and anti-thyroid preparations, diuretics,
anti-spasmodics, uterine relaxants, mineral and nutritional
additives, anti-obesity drugs, anabolic drugs, erythropoietic
drugs, anti-asthmatics, bronchodilators, expectorants, cough
suppressants, mucolytics, drugs affecting calcification and bone
turnover and anti-uricemic drugs. Specific drugs include
gastro-intestinal sedatives such as metoclopramide and
propantheline bromide; antacids such as aluminum trisilicate,
aluminum hydroxide, ranitidine and cimetidine; anti-inflammatory
drugs such as phenylbutazone, indomethacin, naproxen, ibuprofen,
flurbiprofen, diclofenac, dexamethasone, prednisone and
prednisolone; coronary vasodilator drugs such as glyceryl
trinitrate, isosorbide dinitrate and pentaerythritol tetranitrate;
peripheral and cerebral vasodilators such as soloctidilum,
vincamine, naftidrofuryl oxalate, co-dergocrine mesylate,
cyclandelate, papaverine and nicotinic acid; anti-infective
substances such as erythromycin stearate, cephalexin, nalidixic
acid, tetracycline hydrochloride, ampicillin, flucloxacillin
sodium, hexamine mandelate and hexamine hippurate; neuroleptic
drugs such as flurazepam, diazepam, temazepam, amitryptyline,
doxepin, lithium carbonate, lithium sulfate, chlorpromazine,
thioridazine, trifluperazine, fluphenazine, piperothiazine,
haloperidol, maprotiline hydrochloride, imipramine and
desmethylimipramine; central nervous stimulants such as
methylphenidate, ephedrine, epinephrine, isoproterenol, amphetamine
sulfate and amphetamine hydrochloride; antihistamic drugs such as
diphenhydramine, diphenylpyraline, chlorpheniramine and
brompheniramine; anti-diarrheal drugs such as bisacodyl and
magnesium hydroxide; the laxative drug, dioctyl sodium
sulfosuccinate; nutritional supplements such as ascorbic acid,
alpha tocopherol, thiamine and pyridoxine; anti-spasmodic drugs
such as dicyclomine and diphenoxylate; drugs affecting the rhythm
of the heart such as verapamil, nifedipine, diltiazem,
procainamide, disopyramide, bretylium tosylate, quinidine sulfate
and quinidine gluconate; drugs used in the treatment of
hypertension such as propranolol hydrochloride, guanethidine
monosulphate, methyldopa, oxprenolol hydrochloride, captopril and
hydralazine; drugs used in the treatment of migraine such as
ergotamine; drugs affecting coagulability of blood such as epsilon
aminocaproic acid and protamine sulfate; analgesic drugs such as
acetylsalicylic acid, acetaminophen, codeine phosphate, codeine
sulfate, oxycodone, dihydrocodeine tartrate, oxycodeinone,
morphine, heroin, nalbuphine, butorphanol tartrate, pentazocine
hydrochloride, cyclazacine, pethidine, buprenorphine, scopolamine
and mefenamic acid; anti-epileptic drugs such as phenyloin sodium
and sodium valproate; neuromuscular drugs such as dantrolene
sodium; substances used in the treatment of diabetes such as
tolbutamide, disbenase glucagon and insulin; drugs used in the
treatment of thyroid gland dysfunction such as triiodothyronine,
thyroxine and propylthiouracil, diuretic drugs such as furosemide,
chlorthalidone, hydrochlorthiazide, spironolactone and triamterene;
the uterine relaxant drug ritodrine; appetite suppressants such as
fenfluramine hydrochloride, phentermine and diethylproprion
hydrochloride; anti-asthmatic and bronchodilator drugs such as
aminophylline, theophylline, salbutamol, orciprenaline sulphate and
terbutaline sulphate; expectorant drugs such as guaiphenesin; cough
suppressants such as dextromethorphan and noscapine; mucolytic
drugs such as carbocisteine; anti-septics such as cetylpyridinium
chloride, tyrothricin and chlorhexidine; decongestant drugs such as
phenylpropanolamine and pseudoephedrine; hypnotic drugs such as
dichloralphenazone and nitrazepam; anti-nauseant drugs such as
promethazine theoclate; haemopoietic drugs such as ferrous
sulphate, folic acid and calcium gluconate; uricosuric drugs such
as sulphinpyrazone, allopurinol and probenecid; and calcification
affecting agents such as biphosphonates, e.g., etidronate,
pamidronate, alendronate, residronate, teludronate, clodronate and
alondronate.
[0109] Insofar as the disclosure contemplates including a virtually
unlimited number of drugs, in vitro pharmacokinetic studies can be
used to determine the appropriate configuration of the porous
silicon film and its dust for each drug. The drug conjugated porous
silicon film and its dust can be aliquoted into vitreous samples in
cell culture dishes. Intensity of reflected light from the porous
silicon film or its dust can be measured using a low power
spectrophotometer, at the same time free drug in the vitreous
sample can be measured, as a function of time for the porous film
or dust immersed in the vitreous sample. Correlation between
spectrophotometer change and drug concentration in vitreous can be
determined and used for in vivo PK studies.
[0110] For biocompatible polymer imprints of the porous silicon
film, drug can be impregnated in the polymer casting solution. Then
the free standing polymer porous film can further conjugate with
drug molecules to fill the pores. In vitro PK studies can be
performed in a similar way as with the porous silicon film or its
dust.
[0111] Optimized porous silicon smart dust adapted to the drug
candidate will not be toxic after intravitreal injection and the
vitreous drug half-life will be in the range of weeks to months and
the drug level will sustain above the EC for months. A method
includes preparing porous Si photonic crystal particles, loading
the pores of those crystal particles with one or more drugs, and
injecting the particles into the vitreous via syringe. The amount
of drug loaded in the particles may then be monitored via one or
more of a plurality of methods, such as by visual inspection,
digital imaging, laser eye scan, or spectroscopic observation. Any
of these four methods are non-invasive, allowing the practitioner
or clinician to observe the particles through the pupil of the
eye.
[0112] More particularly, one method of the disclosure proceeds as
follows. Porous Si photonic crystals are formed from a porous
silicon film that is electrochemically etched in a single crystal
Si substrate by application of a sinusoidal current density-time
waveform. The waveform varies between 15 and 45 mA/cm.sup.2, with
70 repeats and a periodicity of 12.5 s. The one-dimensional
photonic crystal that results has a color that depends on the
waveform parameters. The conditions described above produce a film
that has a strong reflectivity maximum in the green region of the
spectrum. This is a convenient color for visual observation in the
eye, though any color or pattern of colors (multiple spectral
peaks) can be incorporated into the films. The spectral features
can range in wavelength from 300 nm to 10,000 nm. The film is
removed from the Si substrate using a pulse of current. Particles
with dimensions in the range 1 .mu.m to 270 .mu.m are generated by
ultrasonication.
[0113] The photonic crystals are then loaded with a drug or drugs.
The pores of the photonic crystals are large enough to allow
infiltration of drugs such as, for example, dexamethasone. Drug can
be loaded into the film or particles by infiltration from solution.
In a typical preparation, the drug loading solution comprised
6.times.10.sup.-2 M dexamethasone in methanol. 25 .mu.L of the
solution was pipetted onto the porous Si film and the solvent was
allowed to evaporate in air. The film was briefly rinsed with
deionized water to remove any excess drug remaining on the surface
that had not infiltrated the pores.
[0114] Once the drug is loaded into the pores of the photonic
crystals, the photonic crystals are then injected into the patient.
In another aspect, the loaded photonic crystals are oxidized to
entrap the drug. The drug-loaded crystals are placed in an
appropriate excipient and injected into the vitreous. After
intravitreal injection, the porous silicon particles floated in the
vitreous affording an opthalmoscopically clear view of the fundus
without any observed toxicity. The particles may last in the
vitreous for up to four months without any noticeable
abnormalities.
[0115] The optical interference spectrum used in particle
identification can readily be measured with inexpensive and
portable instrumentation such as a CCD spectrometer or a diode
laser interferometer. Removal of the drug from the porous
nanostructure results in a change in-the refractive index of the
porous film and is observed as a wavelength shift in the spectrum,
or a shift in the code, of the dust particle. The high surface area
and optical interferometric means of detection lead to very high
sensitivity for this system. Furthermore, particles can be encoded
to reflect infrared light that can penetrate living tissues and
enable noninvasive sensing through opaque tissue.
[0116] The described devices, systems and methods also encompass
the pulsatile delivery of active ingredients, such as
pharmaceutical compounds. By "pulsatile" is meant that a plurality
of drug doses are released at spaced apart intervals of time.
Accordingly, the devices and systems are designed, configured and
manufactured to possess release profiles (e.g., release kinetics)
suitable for treating specific conditions or multiple conditions.
It is understood that such devices and systems can include a
plurality of active ingredients each possessing a specific release
profile suitable for treating multiple conditions. A pulsatile
delivery system is capable of providing, for example, one or more
immediate release pulses at predetermined time points after a
controlled lag time or at specific sites. The system or device
allows for pulsatile drug delivery, and the administration of
differing sized dosages of active ingredients at different times
automatically, pursuant to a pre-programmed dosage profile utilized
to design, configure and manufacture a device or system provided
herein. Exemplary release profiles include those that correspond to
desired peaks and troughs related to disease symptoms.
[0117] Accordingly, provided herein are devices, systems and
methods designed to facilitate the controlled release of an active
ingredient in a biological system. In some aspects, the active
ingredient is a pharmaceutical compound. The compound can be
included in a suitable matrix or carrier. The matrix or carrier can
further include hydrophilic binders, water-soluble diluents,
surfactants, lubricants, disintegrants, antioxidants, or non
water-soluble diluents, or any combination thereof.
[0118] The term "active ingredient" is intended to mean any
compound having a therapeutic effect, and which is suitable for
administration in a device provided herein. Active ingredients
include non-peptide organic molecules, small peptides and peptide
mimetics, and the like, as well as their pharmaceutically
acceptable salts. The active ingredient itself may be stable upon
storage or under stress conditions, but when formulated with one or
more carriers it shows stability problems, e.g., it starts to
degrade.
[0119] The term "carrier" is intended to mean such carriers which
are commonly used in the pharmaceutical chemistry for preparing
pharmaceutical formulations, see, e.g., Remington: The Science and
Practice of Pharmacy, 19th Edition (1995); "Drugs and the
pharmaceutical sciences", vol. 81, 1997. In particular such one or
more carriers are selected from, but not limited to, hydrophilic
binders, water-soluble diluents, surfactants, lubricants,
disintegrants, antioxidants, non water-soluble diluents and/or
other fillers known to the skilled person.
[0120] The term "pharmaceutically acceptable salt" represents salt
forms of an active ingredient that are physiologically suitable for
pharmaceutical use. The pharmaceutically acceptable salts can exist
in conjunction with an active ingredient as acid addition primary,
secondary, tertiary, or quaternary ammonium, alkali metal, or
alkaline earth metal salts. Within the disclosure, the active
ingredient may be prepared in the form of a salt such as
pharmaceutically acceptable salts, especially acid-addition salts,
including salts of organic acids and mineral acids. Examples of
such salts include salts of organic acids such as formic acid,
fumaric acid, acetic acid, propionic acid, glycolic acid, lactic
acid, pyruvic acid, oxalic acid, succinic acid, malic acid, maleic
acid, tartaric acid, citric acid, benzoic acid, salicylic acid and
the like. Suitable inorganic acid-addition salts include salts of
hydrochloric, hydrobromic, sulphuric and phosphoric acids and the
like. The acid addition salts may be obtained as the direct
products of compound synthesis. In the alternative, the free base
may be dissolved in a suitable solvent containing the appropriate
acid, and the salt isolated by evaporating the solvent or otherwise
separating the salt and solvent.
[0121] The term "hydrophilic binder" represents binders commonly
used in the formulation of pharmaceuticals, such as
polyvinylpyrrolidone, copolyvidone (cross-linked
polyvinylpyrrolidone), polyethylene glycol, sucrose, dextrose, corn
syrup, polysaccharides (including acacia, tragacanth, guar, and
alginates), gelatin, and cellulose derivatives (including
hydroxypropyl methylcellulose, hydroxypropyl cellulose, and sodium
carboxymethylcellulose).
[0122] The term "water-soluble diluent" represents compounds
typically used in the formulation of pharmaceuticals, such as
sugars (including lactose, sucrose, and dextrose), polysaccharides
(including dextrates and maltodextrin), polyols (including
mannitol, xylitol, and sorbitol), and cyclodextrins.
[0123] The term "non water-soluble diluent" represents compounds
typically used in the formulation of pharmaceuticals, such as
calcium phosphate, calcium sulfate, starches, modified starches and
microcrystalline cellulose.
[0124] The term "non water-soluble diluent with non-swelling
properties" represents the non water-soluble diluents as indicated
above, but excluding starches and modified starches and the
like.
[0125] The term "surfactant", as used herein, represents ionic and
nonionic surfactants or wetting agents commonly used in the
formulation of pharmaceuticals, such as ethoxylated castor oil,
polyglycolyzed glycerides, acetylated monoglycerides, sorbitan
fatty acid esters, poloxamers, polyoxyethylene sorbitan fatty acid
esters, polyoxyethylene derivatives, monoglycerides or ethoxylated
derivatives thereof, diglycerides or polyoxyethylene derivatives
thereof, sodium docusate, sodium laurylsulfate, cholic acid or
derivatives thereof, lecithins, alcohols and phospholipids.
[0126] The term "antioxidant" represents the three groups of
antioxidants, true antioxidants, reducing agents and antioxidant
synergists, such as tocopherols, tocopherolesters, alkyl gallates,
butylated hydroxyanisole, butylated hydroxytoluene, ascorbic acid,
citric acid, edetic acid and its salts, lecithin and tartaric
acid.
[0127] The term "disintegrant" represents compounds such as
starches, clays, celluloses, alginates, gums, cross-linked polymers
(such as cross-linked polyvinylpyrrolidone and cross-linked sodium
carboxymethylcellulose), sodium starch glycolate, low-substituted
hydroxypropyl cellulose, and soy polysaccharides. Preferably, the
disintegrant is a modified cellulose gum such as e.g. cross-linked
sodium carboxymethylcellulose.
[0128] The drug or photonic nanocrystal of the disclosure can be
formulated for in vivo delivery using the compositions and methods
described above.
[0129] Although certain embodiments of the invention have been
described, additional embodiments and examples are provided below.
Such specific examples are not intended to limit the invention.
EXAMPLES
[0130] Porous silicon dust was injected into rabbit vitreous and no
toxicity was found compared with the fellow eyes that received the
same volume of phosphate-buffered saline (PBS) injection. The
porous silicon film was etched using a sinusoidal current varying
between 15 and 45 mA/cm.sup.2, with 70 repeats and a periodicity of
12.5 s. The film was sonicated into a dust that ranged from 1 .mu.m
to 270 .mu.m. After intravitreal injection, the porous silicon
particles floated in the vitreous affording an opthalmoscopically
clear view of the fundus without any observed toxicity. The
particles lasted in the vitreous for one week without any
noticeable abnormalities.
[0131] Thermally oxidized silicon dust was also injected into the
vitreous of four rabbits. This chemical modification of the porous
silicon film was proposed as one of the alternative methods to
increase the residence time of the porous silicon dust in vitreous.
This approach demonstrated a great increase of the residence time
of the particles in the rabbit eye compared to the previous
incompletely hydrosilylated smart dust (from less than 7 days to
longer than 3 weeks). In addition, by increasing the sonication
time during preparation, smaller and more uniform smart dust
particles were produced, which can be delivered into vitreous by
the 25 or 27-gauge needle that is commonly used for intravitreal
injection in the clinic.
[0132] Additional data supports use of completely hydrosilated
porous Si photonic crystals that have no toxicity by clinical
examination or electroretinograms or histology at 31/2 months post
injection, inclusive of shorter times. For example, 100 microliters
of the material were injected, and the characteristic color of the
crystals is seen making it clear that one can use this
characteristic for monitoring drug release in the eye.
[0133] Intravitreal injection of 100 .mu.l of oxidized porous Si
photonic crystal particles in 5% dextrose was performed. The
measured size of the smart dust ranged from 10 to 45 .mu.m with an
average of 30 .mu.m; approximately 30,000 particles were injected
into each rabbit eye. The injected particles appeared purplish
green floating in the vitreous. From the second day some of the
particles aggregated and sank onto the inferior retina. No toxicity
was seen and the smart dust particles were still visible at the
last examination 34 weeks later with at least half of the
originally injected material remaining, as assessed by
opthalmoscopy. It is therefore anticipated that the particles would
be safe and effective for at least a year if not two years. Thus,
this preliminary thermal oxidation modification has greatly
extended the time of intravitreal residence compared to the
previous incompletely hydrosilylated smart dust. The data
demonstrated that the porous silicon particle was safe as an
intravitreal drug delivery vehicle. Modifications such as oxidation
and silicon-carbon chain conjugation can be used to further
increase the stability of the silicon dust and can make it a
long-lasting slow release intravitreal drug delivery system.
[0134] A preliminary study was performed on a rat CNV model using
systemic administration of an 8-mer peptide derived from urokinase
plasminogen activator (uPA) to block the uPA-urokinase plasminogen
activator receptor (uPAR) interaction. This 8-mer peptide was
administrated subcutaneously twice daily at 200 mg/kg/d beginning
at the time of induction of CNV (with laser) to introduce CNV in
Brown Norway rats. Two weeks after laser treatment, simultaneous FA
and ICG using scanning laser angiography was performed to identify
the leaking laser bums. The results showed that this 8-mer peptide
reduced the laser induced CNV by 70% compared to the control group
(44.7% of laser burns leak in control group versus 13.4% in treated
group, p<0.001). Administration of the drug intravitreally using
a proposed porous silicon smart dust should maintain the desired
intraocular drug level.
[0135] Thermal Oxidation of Porous Si Particles: Preliminary
studies of porous Si particles oxidized and annealed at 300.degree.
C. for 2 hours in air show that the material is stable in aqueous
pH 11 buffer for several days, and recent results indicate that
this approach can dramatically increase the residence time of the
particles in the rabbit eye. In addition, by increasing the
sonication time during preparation, smaller and more uniform smart
dust particles were produced which can be delivered into vitreous
by the 28.5 gauge needle that is commonly used for intravitreal
injection in the clinic. Intravitreal injection of 100 .mu.l of
oxidized porous Si photonic crystal particles in 5% dextrose was
performed. The measured size of the smart dust ranged from 10 to 45
.mu.m with a average of 30 .mu.m; approximately 30,000 particles
were injected into each rabbit eye. The color of the injected
particles floating in the vitreous was clearly visible, which is
indicative of drug release and degradation by hydrolysis.
Degradation by hydrolysis is especially advantageous in that no
enzymes are necessary to degrade the particles. From the second day
some of the particles aggregated and sank onto the inferior retina.
No toxicity was noticed and the smart dust particles were still
visible until the last examination, which indicates that this
preliminary thermal oxidation has more than tripled the time of
intravitreal residence compared to the previous incompletely
hydrosilylated smart dust. Experiments can be performed to quantify
the residence time and correlate it with the chemical modification
conditions such as thermal oxidation time, temperature, and ambient
atmosphere.
[0136] Electrochemical Grafting of Organic Reagents: The
hydride-terminated surface of p-type or p++-type porous silicon can
be stabilized by electrochemical reduction of acetonitrile
solutions of various organo halides. Reduction of
6-iodo-ethylhexanoate, 1-iodo-6-(trifluoroacetylamino) hexane,
iodomethane, 1-bromohexane, or ethyl 4-bromobutyrate at a porous Si
cathode results in removal of the halogen and attachment of the
organic fragment to the porous Si surface via a Si--C bond. A
two-step procedure was devised involving attachment of the
functional group of interest followed by attachment of methyl
groups (by reduction of iodomethane) to residual, more sterically
inaccessible sites on the porous Si surface and found that
electrochemical alkylation greatly improves the stability of porous
Si against oxidation and corrosion in various corrosive aqueous
media, and that the methyl capping procedure provides the most
stable porous Si material yet reported. This chemistry also allows
covalent attachment of the candidate drugs for the release
studies.
[0137] Thermal Hydrosilylation of Organoalkenes: This approach
provides a porous Si material that is stable even in boiling
aqueous pH 10 solutions. This chemistry was extended to the dust
particles and find similar levels of stability. Parameters of the
reaction may be adjusted in order to identify the key parameters
leading to this instability. In particular, the surface coverage
(essentially the efficiency of the chemical reaction), the type of
organic species grafted to the surface (alkyl carboxylates, alkyl
esters, and alkyl halides), and the chain length of the alkyl
species can be investigated. Reaction conditions such as the
presence of added radical initiators, transition metal catalysts,
and photoassisted hydrosilylation can be explored.
[0138] For each modified porous silicon film, its sonicated dust
can be intravitreally injected into 3 rabbit eyes with the fellow
eyes used for control. After injection, the toxicity can be
monitored by slit lamp, indirect opthalmoscope, ERG, and pathology.
In addition, a remote spectrometer probe can be used to determine
the clearance rate of the silica dust in vitreous on living animals
through the dilated pupil. The spectrometer probe is believed to
render more accurate information since the small particles may not
be seen using indirect opthalmoscope.
[0139] A spectrometric method of detection of the oxidized "smart
dust" injected into the rabbit eyes was also investigated. One
eyepiece of the surgical microscope was connected to the input of a
fiber-optic based spectrophotometer and this allows us to
accurately focus the detecting light on the intraocular "smart
dust" particles. The disclosure also provides a camera for
monitoring the color change of the crystal outfitted with a
spectrometer to quantitate the drug release. In yet another
embodiment, a scanning laser opthalmoscope which scans the retina
and inner eye with a monochromatic light is outfitted with the
appropriate wavelength to scan and detect reflectance spectrum
changes allowing quantification of drug release. The preliminary
data showed a feasibility of this approach and the specific
wavelength of a porous Si photonic film was detected with a 1 nm
spectral resolution. This resolution is sufficient to determine
concentration of a species such as a large protein in the porous Si
film to micromolar concentration levels. As an alternative, the
probe can be adapted to a fundus camera which is used for clinical
retinal imaging. For the rabbit or rodent eyes, the fundus can be
photographed using a fundus camera without anesthesia.
[0140] In in vitro experiments, the optical codes of the porous Si
photonic crystal particles can be read using digital imaging
cameras. Since the color of the particles provides an indirect
measure of the amount of drug loaded, the most accurate measure is
obtained using a spectrometer. However, the color resolution in a
digital camera is sufficient to measure the loading to an accuracy
of 10%, which is sufficient for the present application. In order
to measure the degree of loading in porous Si "smart dust," the
color of the particles can be recorded using a color digital camera
connected to the fundus camera. Software to process the digital
images and extract concentration information can be obtained with
minor modifications to commercially available software. The
advantage of this approach is that it requires only minor
modification to existing readily available medical equipment, and
it allows acquisition of data from a large number of particles
simultaneously. If higher resolution concentration information is
needed, the illumination light can be filtered using a
monochromator or bandpass filters, providing spectral resolution
equivalent to that which can be obtained with a spectrometer.
[0141] The long-lasting porous silicon film and its imprint can be
further optimized for delivery of three candidate drugs (PEDF, an
8-mer peptide fragment of uPA, and dexamethsasone) by controlling
the pore size and morphology. These parameters are easily
controlled using the appropriate anodic electrochemical etching
current density, duration of the etch cycle, and etchant solution
composition. Since the imprint and its porous silicon template
share the similar nanostructures, it is assumed that imprints from
optimized porous silicon can also be appropriate for delivering
those drug candidates.
[0142] Additional in vivo data regarding the "smart dust" material
after intraocular injection and new in vitro data concerning the
release of dexamethasone from "smart dust" formulations is as
follows. In vivo studies The new formulation of "smart dust"
particles containing a silicon dioxide shell have been observed in
the vitreous of living rabbits for 16 weeks and they are showing
evidence of dissolution without any evidence of toxicity by slit
lamp, indirect opthalmoscopic examinations or by light or electron
microscopy. More than half of the particles appear to be present at
this time point indicating excellent potential as a long acting
drug delivery system. Injection of "smart dust" particles
containing a hydrosilylated alkyl shell into the living rabbit eye
has shown no evidence of toxicity for up to five weeks of ongoing
examination.
[0143] Additional in vivo studies demonstrated the increased
stability of "smart dust" particles containing a hydrosilylated
alkyl shell. These chemically modified particles also exhibit
slower release rates for a drug. Release of dexamethasone from the
modified porous silicon matrix is slowed by a factor of 20 compared
to unmodified porous silicon.
[0144] Chemistries have also been developed to expand the pores in
order to accommodate larger molecules within the pores, such as a
modified Fab fragment of human IgG. The pore expansion procedure
involves the enlargement of pores by treatment with
dimethylsulfoxide (DMSO) containing hydrofluoric acid (HF). The
porosity increases approximately 10% after the expansion treatment,
and it was found that this chemistry allows admission of large
molecules such as human IgG (150 kDa) and bovine serum albumin (67
kDa). As will be clear to artisans, the invention makes use the
optical properties of porous silicon photonic crystals to monitor
drug delivery rates. The shift in the reflectivity spectrum of the
film coincides with release of a drug. Optical measurements were
carried out while concurrent absorbance measurements were obtained
as the drug-infused porous silicon films were introduced in
buffered aqueous solutions. There is a linear correlation between
the increase of drug concentration in solution (i.e. drug diffusing
from the pores) and a change in the optical thickness of the porous
silicon film.
[0145] The optical properties of porous Si have been investigated
for numerous applications including chemical and biological
sensors. Porous Si is a biocompatible and bioresorbable material
that has also been investigated for in-vivo drug delivery and
biomedical device applications. Recently, a technique to produce
micro particulate photonic crystals from porous Si was developed.
The distinctive particle spectrum can be observed through human
tissue, (Li, Cunin et al., Science 299(5615):2045-7 (2003)) and it
can be used to monitor the loading and release of various organic
or biomolecules including dexamethasone, IgG and bovine serum
albumin. This optical method of monitoring molecular loading and
release is well suited for ophthalmic applications. The drug can be
housed in the porous matrix while the optical spectrum allows
non-invasive measurement of the release rate. This is the first
study to characterize the intraocular properties of porous silicon
particles that are capable of acting as a self-reporting drug
delivery system in living animal eyes.
[0146] Fabrication of Porous Silicon Particles: Porous silicon
particles were fabricated by an electrochemical etch of
single-crystalline, degenerately B-doped p-type silicon (Siltronix
Inc., <100> orientation, .about.1 m.OMEGA.cm resistivity) in
a 48% aqueous HF:ethanol (3:1 by volume) electrolyte solution. An
optical rugate structure was electrochemically etched into the Si
wafer using a sinusoidal current modulation of 15-45 mA/cm.sup.2,
with 70 repeats and a periodicity of 12.5 seconds. The films were
removed from the bulk silicon substrate by electropolishing in a
3.3% HF in ethanol solution using a current density of 200
mA/cm.sup.2 for 2 min. The manufactured porous Si film was
generally 20 microns thick (see FIG. 5) with a porosity of 67% as
determined by gravimetric analysis. The freestanding films were
then ultrasonically fractured using an ultrasonic cleaner (5 min.)
to produce particles ranging in size from 1-270 microns with over
70% particles falling in the range of 15-30 microns (estimated by
optical microscopy). For a 20 micron particle, there is an
estimated free volume of 4.times.10.sup.-9 cm.sup.3 available for
drug loading per particle, with a total free volume of
1.2.times.10.sup.-4 cm.sup.3 per particle injection in the rabbit
vitreous.
[0147] Chemical Modification of Porous Si Particles: Unmodified
porous silicon is known to be unstable in aqueous media because of
rapid oxidation of the reactive hydride species present on the
surface. In this work, two different chemical modification
reactions were performed in order to stabilize the particles. The
first method involves surface alkylation by means of thermal
hydrosilylation with 1-dodecene, and the second method is thermal
oxidation.
[0148] Surface Alkylation of Porous Si Particles: Thermal
hydrosilylation was carried out on porous Si particles immediately
after their preparation, following the method of Buriak (Buriak,
Adv. Mater. 11(3):265-267 (2002)). The particles were placed in a
Schlenk flask containing 1-dodecene and freeze-pump-thaw cycles
were performed to remove oxygen. The reaction flask was filled with
nitrogen and the mixture was heated at 120.degree. C. for 2 hours.
The particles were rinsed thoroughly with dichloromethane and
ethanol and then dried in air. The product was characterized by
FTIR, confirming the presence of alkyl species on the surface of
the particles.
[0149] Thermal Oxidation of PSi Particles: Oxidation was carried
out on porous Si particles immediately after their preparation.
Oxidation was accomplished by heating at 80.degree. C. in an oven
in ambient air for 24 hours.
[0150] Animal studies: Eleven New Zealand Red rabbits were used to
study the safety and stability of the porous silicon particles in
the rabbit vitreous. All of the animal handlings were carried out
in adherence to the ARVO Statement for the Use of Animals in
Ophthalmic and Vision Research. Using injection methods previously
published, one eye of each animal was injected with the porous Si
particles, and the fellow eye was injected with the same volume of
5% dextrose to serve as the control. Three rabbits were injected
with fresh (not chemically modified) porous Si particles, five
rabbits were injected with hydrosilylated porous Si particles, and
three were used to evaluate the oxidized porous Si particles. All
of the particles were suspended in ethanol for sterilization. Prior
to injection, the ethanol was evaporated and 1 mL of 5% dextrose
was added to .about.120 mg of the particles. One drop (.about.6
.mu.L) of sample was taken for particle sizing and counting by
light microscopy (FIG. 6, Panel A and Panel B). A 25 gauge needle
was used to deliver 100 .mu.L of the suspension (roughly 12 mg
particles) into the rabbit vitreous through the pars plana under
direct view of a surgical microscope. After intravitreal injection,
the eyes were monitored with indirect opthalmoscope, tonometer, and
biomicroscopic slitlamp on day 3 and once each subsequent week
thereafter. Fundus photography was carried out in the selected
rabbit eyes at different intervals after injection to assess
degradation of the porous Si particles. The electroretinogram (ERG)
was recorded from all eyes of the animals prior to animal
sacrifice. After animal sacrifice, the eye globes were enucleated
for histology evaluation. The vitreous containing the
hydrosilylated porous Si particles was excised from selected eyes,
and the particles were examined by scanning electron
microscopy.
[0151] Observation of unmodified porous Si particles in the rabbit
eye: A 100 .mu.L aliquot of porous Si particles in 5% dextrose
solution was injected into the vitreous of three eyes of three
rabbits using a 25 gauge needle. The particles ranged in size from
1 to 270 .mu.m and the estimated number of particles per injection
was approximately 12,000. The particles were suspended in the
vitreous at the injection site (FIG. 7, Panel A) and observed to
disperse into the surrounding vitreous during the following 2 to 3
days (FIG. 7, Panel B). No toxic effects were observed, and the
particles degraded completely in 3 to 4 weeks (FIG. 7, Panel C).
Pathologic examination by light microscopy revealed no indications
of toxicity (FIG. 7, Panel D).
[0152] Observation of hydrosilylated porous Si particles in the
rabbit eye: A 100 .mu.L aliquot of hydrosilylated porous Si
particles in 5% dextrose solution was injected into the vitreous of
five eyes of five rabbits using a 25 gauge needle. The particles
ranged in size from 1 to 300 .mu.m (longest dimension) with an
estimated 1900 particles per injection. The hydrosilylated
particles became distributed throughout the vitreous within 2 to 3
days while displaying a vivid green color. Degradation was observed
to be much slower than for the unmodified porous Si particles (FIG.
8). Four months after injection the animals were sacrificed, and
the particles were analyzed by optical and by scanning electron
microscopy. Approximately 50% of the viewable particles appeared
blue-green in color (FIG. 9, Panel A). The scanning electron
microscope images revealed sharp edges on the particles but a
pitted surface, indicating some degree of erosion (FIG. 9, Panel
B). The other three rabbits were sacrificed for histopathology. ERG
examination, tonometry, and histology did not show any indications
of toxicity (FIG. 9, Panel C) (see Table 1 below).
[0153] Observation of oxidized porous silicon particles in the
rabbit eye: A 100 .mu.L aliquot of oxidized porous Si particles in
5% dextrose solution was injected into the vitreous of three eyes
of three rabbits using a 25 gauge needle. The particles ranged from
10 to 40 .mu.m and an estimated 30,000 particles were injected. The
oxidized particles showed similar dispersion in the vitreous as the
unmodified and the hydrosilylated particles. Faster degradation
rates were observed for the oxidized particles than for the
hydrosilylated particles (see Table 1 below). Two weeks after
injection, 20% of the particles showed evidence of degradation and
roughly 80% of them were reflecting purple light (FIG. 10, Panel
B). Nine weeks after injection, over 80% of the observable
particles lost their vivid reflective property and appeared
degraded and brown. The particles had settled into the inferior
vitreous or retina (FIG. 10, Panel C). The ERG, tonometry, and
histology did not reveal any indications of toxicity (FIG. 10,
Panel D) (see Table 1 below):
TABLE-US-00001 TABLE 1 Characterization of the different porous Si
particle types used in intravitreal injection Bio- Number Maximum
Estimated microscopy of vitreous vitreous half- & Indirect
Particle eyes residence life by Intraocular ophthalmol type tested
time ophthalmoscopy pressure scopy ERG Pathology Unmodified 3 4
weeks 1 week 18.7 .+-. 4 (at week 4) Normal Normal Normal (Fresh)
5% 3 NA NA 15.7 .+-. 2 (at week 4) Normal Normal Normal dextrose
Hydrosilylated 5 >17 weeks 16 weeks 18.2 .+-. 2 (at 17 weeks)
Normal Normal Normal 5% 5 NA NA 19 .+-. 2 (at 17 weeks) Normal
Normal Normal dextrose Oxidized 3 12 to 16 weeks 5 weeks 16.7 .+-.
5 (at week 4) Normal Normal Normal 5% 3 NA NA 20 .+-. 4 (at week 4)
Normal Normal Normal dextrose
[0154] The present studies demonstrate that porous Si particles can
be safely injected into rabbit vitreous, and the unmodified
particles degrade in three to four weeks without evidence of
toxicity. Chemical modification of the particle and pore surface,
either by grafting of dodecyl species (hydrosilylation) or by
conversion to SiO.sub.2 (thermal oxidation) dramatically increases
the stability and vitreous residence time of the particles. This
indicates that hydrosilylated or oxidized porous Si particles may
be used as a long-lasting intravitreal drug delivery vehicle.
Furthermore, by controlling the extent of oxidation or
hydrosilylation, the vitreous residence time of the particles may
be manipulated to fit the specific treatment modality.
[0155] Porous Si has been studied previously in physiological
aqueous solutions and was found to dissolve into the form of
orthosilicic acid, which is vital for normal bone and connective
tissue homeostasis. (Anderson, Elliott et al. 2003) However, porous
Si dissolution has never been studied in vitreous, which is a
complex biological solution with constant fluid turn over. This
type of condition is not easily duplicated in an in vitro setting.
Therefore, the dissolution and the associated potential toxicity
must be studied directly in the living eyes.
[0156] The unique photonic properties of porous Si make this
material ideal for drug delivery by imparting a potential
self-reporting feature within the delivery system. The wavelength
of the spectral peak reflected from porous Si photonic crystals is
dependent on the refractive index (n) of the porous Si matrix (Link
and Sailor 2003). Changes in refractive index of the porous Si
layer occurs as aqueous solution (n=1.34) replaces organic
molecules or proteins (n.about.1.4) in the pores results in a blue
shift of the reflectivity peak, producing an observable color
change. A spectral blue shift is also expected as the Si matrix
(n.about.3.5) is oxidized to SiO.sub.2 (n.about.1.7) or as the
SiO.sub.2 matrix dissolves. In the present case, the initial green
color of the photonic crystals is observed to turn blue or violet
after several days to weeks in vitreous (depending on the surface
chemistry) indicating dissolution of the porous matrix. After
extended periods in vitreous, some of the particles lose their
vivid reflectance and appear brown in color. The brown color is
attributed to light absorption by residual Si in a particle whose
photonic signature has shifted into the ultraviolet range. It is
also possible that the signature spectrum of the photonic crystal
no longer exists due to extensive degradation of the periodic
nanostructure. This unique signature spectrum of the photonic
crystal could be utilized to monitor drug release through the
transparent optical medium of the eye using a simple CCD
spectrometer device that would provide a non-invasive method to
monitor drug release. This would be an advantage over other drug
delivery materials such as biodegradable and bioerodible polymeric
microparticles.
[0157] The fact that certain preparations of the porous Si
particles have long vitreous lifetimes and display no apparent
toxicity indicates that porous Si may be used as an intravitreal
delivery material. With the advent of many intravitreal injectable
therapeutics, such as dexamethasone, pegaptnib (Macugen),
bevacizumab (Avastin), and the recently FDA-approved ranibizumab
(Lucentis), repeated intravitreal injections can potentially
generate serious problems. These procedures impose life quality
issues with patients and raise the risk of intraocular infections.
Trapping such compositions in porous Si microparticles by an
encapsulant or by covalent or electrostatic interactions between
the drug and the porous Si particles, allows for the composition to
be slowly released as the particles degrade. This would eliminate
the necessity of frequent injections.
[0158] A 100 .mu.l intravitreal injection as used in the present
rabbit studies typically contains .about.30,000 porous Si
particles, each approximately 50 microns square and 20 microns
thick. It was calculated that at least .about.50 mg of
deximethasone per gram of porous Si material can be loaded.
Assuming that the porous Si particles display first order
dissolution kinetics and that drug release occurs concomitant with
particle dissolution, then the steady-state concentration of drug
in the eye can be approximated using the dissolution mechanisms of
Dove and Crerar (Geochimica Et Cosmochimica Acta 69(21):4963-4970
(2005)). With this model, the dissolution of the porous Si
particles can be approximated by this overall reaction:
SiO.sub.2+2H.sub.2O=H.sub.4SiO.sub.4
Where the species H.sub.4SiO.sub.4 represents the water-soluble
form of silicic acid. The rate expression for this reaction is
dependent on the total surface area of the particles exposed to
solution and the mass flow rate of silicic acid out of the system.
For the particulate system, the appearance of silicic acid in
solution was assumed to correlate with the appearance of drug in
solution, and that the total surface area of particles exposed to
solution is proportional to the number of particles, N. As the
particles dissolve, the drug would be released, and the
steady-state concentration of drug in the eye can be calculated
based on the following relationship that has been adapted from
Dove's model:
M.sub.d=[t.sub.1/2(drug)/t.sub.1/2(particle)].times.N.times.L
Where M.sub.d is the mass of free drug in the vitreous, N is the
number of particles injected per eye, L is the mass of drug loaded
per particle, and t.sub.1/2(drug) is the half-life of free drug in
vitreous, and t.sub.1/2(particle) is the half-life of the particles
in vitreous.
[0159] In general the longer the particle half-life, as
demonstrated for the hydrosilylated particles and oxidized
particles, the lower the steady-state concentration of drug. For
particles with a 60-day half-life and an initial loaded drug mass
of 600 .mu.g in 12 mg of PSi particles (.about.30,000 particles),
the steady-state concentration of dexamethasone with a vitreous
half-life of 3.48 h would be 1 .mu.g/mL in rabbit vitreous (1.4
ml), which is above the therapeutically relevant dose of >5
ng/mL. The particles may deliver a drug at therapeutically relevant
quantities for at least 3 half-lives of the particles (180
days).
[0160] Drugs with a longer vitreous half-life such as Avastin (5
days) should be able to further extend the period between
injections. For Avastin, a loading capacity of about 1-10, 10-20,
20-50, 50-100, or 100-500 mg of drug per gram of particles may be
suitable for treating conditions responsive to the drug. In one
example, the initial amount of drug in a 0.1 cc injection of porous
Si loaded with Avastin may be approximately 100 .mu.g of drug. If
the half-life of the particles is 60 days, then the steady-state
concentration of drug in vitreous would be .about.8 .mu.g/mL. The
therapeutically relevant dose of Avastin as an intraocular
treatment is generally considered >22 ng/mL. It is understood
that the skilled artisan can readily determine the loading capacity
of the particles provided herein based upon various factors,
including the type of active ingredient to be associated with the
particles. It is also understood that the dosage of an active
ingredient associated with treating a particular disorder can be
modified according to various methods known to the skilled
artisan.
[0161] The disclosure demonstrates the intravitreal
biocompatibility of porous Si microparticles and the feasibility of
porous Si as a platform for an intraocular drug delivery system. As
noted herein, fresh porous Si particles (3 eyes), oxidized porous
Si (porous SiO.sub.2) particles (3 eyes), and hydrosilylated porous
Si particles (5 eyes) were tested in rabbit eyes. No toxicity was
found by using slitlamp to monitor the anterior segment, or by
using indirect opthalmoscope to monitor posterior segment. The lack
of toxicity was also confirmed by eletroretinography and histology
by light microscopy. The hydrosilylated and oxidized particles were
observable in the vitreous until the end of the 4 month study.
[0162] The current study also demonstrates that the Si materials
are typically converted into particulate form by ultrasonication.
By extending the sonication time, a more evenly distributed and
smaller particles (mean size of 20 .mu.m) can be produced and they
are more compatible with the intravitreal injection method.
Further, the two chemical modifications made to the porous Si
materials (oxidation and hydrosilylation) led to dramatically
increased intravitreal stability and slower degradation. The
estimated vitreous half-life increased from one week (fresh
particles) to five weeks (oxidized particles) and to 16 weeks
(hydrosilylated particles).
[0163] Also provided herein are novel methods for producing porous
SiO.sub.2 particles by oxidation of porous Si at 800.degree. C.
Particles manufactured in this manner are more hydrophilic than the
previous oxidized ones which were processed at 220.degree. C. This
new type of porous SiO.sub.2 was injected into 6 rabbit eyes and no
toxicity (including ERG) was observed during the 5 month ongoing
study. This new type of porous SiO.sub.2 allowed more efficient
loading of the IgG-based drug Avastin, a candidate drug for
treatment of macular degeneration.
[0164] The porous SiO.sub.2 particles oxidized at 800.degree. C.
were loaded with Avastin and 100 .mu.l of particles (containing 225
.mu.g avastin) were injected into 3 rabbit eyes. 20 weeks after
injection, the vitreous Avastin level was still 50 ng/ml which is
higher than the IC.sub.50 of Avastin (22 ng/ml).
[0165] A porous Si-polymer composite plaque was prepared and
surgically implanted on the rabbit eye globe under conjunctiva and
Tenon. These plaques have the same optical feature and nano pore
structure as their porous Si film templates and the nano pores open
to only one side of the plaque, allowing unidirectional drug
release. These plaques are well tolerated by the rabbit eyes.
Accordingly, the compositions and methods provided herein achieve
slow release and long lasting drug delivery to treat macular
degeneration, diabetic macular edema, choroidal neovascularization
and retinal vein occlusion and uveitis etc vitreoretinal
diseases.
[0166] These embodiments are meant to be illustrative examples and
not exhaustive of the types of useful drug delivery structures that
can be manufactured using the materials and methods described
herein. The structures and methods discussed above will have great
utility for a variety of applications including, but not limited
to, controlled, sustained and programmable drug delivery.
[0167] While the invention is susceptible to various modifications,
and alternative forms, specific examples thereof have been shown in
the drawings and are herein described in detail. It should be
understood, however, that the invention is not to be limited to the
particular forms or methods disclosed, but to the contrary, the
invention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the appended
claims.
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