U.S. patent application number 15/804856 was filed with the patent office on 2022-01-06 for porous photonic crystals for drug delivery to the eye.
This patent application is currently assigned to The Regents of the University of California. The applicant listed for this patent is The Regents of the University of California. Invention is credited to Emily Anglin, Lingyun Cheng, Frederique Cunin, William Freeman, Yang Yang Li, Michael J. Sailor.
Application Number | 20220000768 15/804856 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-06 |
United States Patent
Application |
20220000768 |
Kind Code |
A9 |
Freeman; William ; et
al. |
January 6, 2022 |
POROUS PHOTONIC CRYSTALS FOR DRUG DELIVERY TO THE EYE
Abstract
A minimally invasive controlled drug delivery system for
delivering a particular drug or drugs to a particular location of
the eye, the system including a porous film template having pores
configured and dimensioned to at least partially receive at least
one drug therein, and wherein the template is dimensioned to be
delivered into or onto the eye.
Inventors: |
Freeman; William; (Del Mar,
CA) ; Sailor; Michael J.; (La Jolla, CA) ;
Cheng; Lingyun; (San Diego, CA) ; Cunin;
Frederique; (Montpellier, FR) ; Anglin; Emily;
(San Diego, CA) ; Li; Yang Yang; (Hong Kong,
HK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of California |
Oakland |
CA |
US |
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Assignee: |
The Regents of the University of
California
|
Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20180055765 A1 |
March 1, 2018 |
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Appl. No.: |
15/804856 |
Filed: |
November 6, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11665557 |
Feb 17, 2009 |
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15804856 |
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13854039 |
Mar 29, 2013 |
8945602 |
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11665557 |
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60623409 |
Oct 29, 2004 |
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International
Class: |
A61K 9/00 20060101
A61K009/00; A61F 9/00 20060101 A61F009/00; A61K 47/24 20060101
A61K047/24 |
Goverment Interests
STATEMENT OF GOVERNMENT SPONSORED RESEARCH
[0002] This invention was made with Government support under grant
no. F49620-02-1-0288 awarded by the Air Force Office of Scientific
Research (AFOSR), under grant no. EY07366 awarded by the National
Institutes of Health, and grant no. DMR-0503006 awarded by the
National Science Foundation. The U.S. Government has certain rights
in the invention.
Claims
1. A drug delivery device for use in the controlled delivery of a
particular drug or drugs to a particular location of the eye, the
device comprising: micron sized porous silicon or silicon dioxide
particles having pores configured and dimensioned to at least
partially receive at least one drug therein; and wherein the
particles are suitable to be delivered into or onto the eye.
2. The device of claim 1, wherein the inner walls of the pores are
covalently modified so that the binding efficacy of the at least
one drug is enhanced and/or drug release profiles of said pores has
been tuned.
3. The device of claim 2 wherein the covalent modification of the
inner walls is selected from the group comprising functional
alkenes, silicon oxide, functional organohalides, and metals.
4. The device of claim 1 wherein the particles are oxidized so as
to trap the drug or drugs in the pores.
5. The device of claim 1 wherein the particles are suitable for
intraocular injection.
6. The device of claim 1, wherein said particles have a monitorable
optical code.
7. The device of claim 1 wherein said drug or drugs comprises one
of the group consisting of angiostatic steroids, metalloproteinase
inhibitors, a VEGF binding drug, pigment epithelium derived factor,
an 8-mer peptide fragment of urokinase, and dexamethasone.
8. 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, fracturing the template into micron sized
particles, said particles being sized and configured to be
delivered into or upon a surface of the eye; and loading either the
template or the micron sized particles with the drug.
9. The method of claim 8 wherein the particles are suitable for
injecting intraocularly.
10. The method of claim 9 wherein the particles have a monitorable
optical response depending on the quantity of drug disposed in the
pores.
11. The method of claim 9 wherein the particles have a monitorable
optical response depending on the amount of porous material
present.
12. The method of claim 8 further comprising trapping the drug or
drugs in the pores by oxidizing the porous template around the drug
or drugs.
13. The method of claim 8 further comprising covalently modifying
the inner walls of the pores to enhance binding efficacy of the at
least one drug and to tune release profiles of said pores.
14. A micron sized porous silicon or silicon dioxide particle
having pores configured and dimensioned to at least partially
receive at least one drug therein; and wherein the particle is
suitable to be delivered into or onto the eye.
15. The particle of claim 14, wherein the inner walls of the pores
are covalently modified so that the binding efficacy of the at
least one drug is enhanced and/or drug release profiles of said
pores has been tuned.
16. The particle of claim 14, wherein said drug is selected from
the group consisting of angiostatic steroids, metalloproteinase
inhibitors, a VEGF binding drug, pigment epithelium derived factor,
an 8-mer peptide fragment of urokinase, and dexamethasone.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/665,557, having a filing date of Feb. 17,
2009, which is a U.S. National Stage Application of International
Application No. PCT/US2005/039177, filed Oct. 31, 2005, which
application claims priority to U.S. Provisional Application No.
60/623,409, filed Oct. 29, 2004, the disclosures of which are
incorporated herein by reference.
FIELD OF THE INVENTION
[0003] A field of the invention is nanostructure synthesis. Other
fields of the invention include drug delivery, bioimplant materials
and self-reporting bioresorbable materials.
BACKGROUND OF THE INVENTION
[0004] Diseases of the eye are numerous and frequently difficult to
treat effectively. For example, some areas of the eye are difficult
to reach with systemic medications, while medications applied
topically tend to be transient and require numerous and repeated
applications. Surgical treatment of still other diseases is
invasive and often problematic as well, with many patients
ineligible for surgical treatment.
[0005] For example, intraocular diseases, such as age-related
macular degeneration (ARMD) and choroidal neovascularization (CNV),
are the leading cause of irreversible vision loss in the United
States, and yet currently available treatments for subfoveal CNV,
which comprise the majority of CNV cases, are associated with only
marginal visual improvement and outcomes. As few as one quarter of
patients with CNV associated with ARMD are laser eligible, and at
least half of those treated experience recurrence of the disease
with poor visual outcomes. Similarly, photodynamic therapy using
verteporfin is only useful for the small minority of patients with
vessels that are angiographically classified as "predominantly
classic," and even then the visual outcomes of such treatments are
disappointing.
[0006] Pharmacologic therapy using local drug delivery or systemic
drug delivery is also being investigated using drugs that are
antiangiogenic. Such drugs include angiostatic steroids,
metalloproteinase inhibitors and VEGF binding drugs. However, the
problem common to all of these promising drugs is the transient
nature of the therapeutic level requires frequent intravitreal
injection.
[0007] Nonspecific uveitis is another devastating eye disease that
affects millions of people in the world. Uveitis produces a wide
spectrum of inflammation of most parts of the eye and chronic
uveitis can be devastating in adults and children. Surgically
implanted steroids have shown that high intraocular doses for
sustained times are extremely beneficial to choronic uveitis
patients, but this implant has surgically related side effects.
[0008] Intravitreal injection is being used in clinical trials of
therapeutic agents, but pose a risk of infection that is estimated
to be 0.5% per injection. Due to the short vitreous half-life of
most small molecules after intravitreal injection, frequent
injection is needed, which significantly increases the chance of
intraocular infection.
[0009] 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, can not be easily
customized to release drugs with different physicochemical
properties, and do not "report" drug release information.
[0010] Extraocular diseases are also difficult to treat because,
for example, eye drops applied topically require repeated and
frequent doses.
SUMMARY OF THE INVENTION
[0011] The invention provides 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 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 represents a chemical reaction for the oxidation of
the porous Si around a candidate molecule according to one
embodiment of the invention;
[0013] FIG. 2 illustrates a chemical modification reaction whereby
a candidate molecule is attached to an inner pore wall according to
another embodiment of the invention;
[0014] FIG. 3 is a schematic diagram illustrating a templated
synthesis of polymer photonic crystals using porous Si masters
according to a first embodiment of the invention; and
[0015] 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;
DETAILED DESCRIPTION OF THE INVENTION
[0016] The invention 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.
[0017] For intraocular diseases, such as glaucoma, age-related
macular degeneration (ARMD), choroidal neovascularization (CNV),
uveitis and others, 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.
[0018] For extraocular diseases, such as viral keratitis, chronic
allergic conjunctivitis, 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. Separately, 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. 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.
[0019] Advantageously, the invention 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,
Si/polymer or SiO.sub.2/polymer composite.
[0020] Preferred devices and methods are also self-reporting such
that drug release and quantity remaining are susceptible of
monitoring. Embodiments of the invention 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.
[0021] A first preferred embodiment includes injection of porous
microscopic nanostructured silicon particles impregnated with a
particular drug or drugs. While the invention contemplates use of
numerous porous microscopic particles, preferred particles include
porous silicon or silicon dioxide particles (so called, "smart
dust"), which are prepared with a designed 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 invention 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.
[0022] Porous silicon is especially advantageous in that porous
silicon films have a large free volume (typically 50-80%), and thus
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 with multiple drugs, and the photonic properties of a
nanostructured material as a means to non-invasively determine the
rate and amount of drug delivered has never been tested in the eye.
The porous silicon photonic crystal particles are impregnated with
a particular drug, 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 same, see published U.S. application Ser.
Nos.: 20050101026 entitled, "Photoluminescent polymetalloles as
chemical sensors," 20050042764 entitled, "Optically encoded
particles," 20050009374 entitled, "Direct patterning of silicon by
photoelectrochemical etching," 20040244889, entitled, "Porous
silicon-based explosive," and 20030146109 entitled, "Porous thin
film time-varying reflectivity analysis of samples." The "smart
dust" photonic crystal particles may be optimized for intravitreal
delivery of one or more of a vast array of drugs such as, for
example, pigment epithelium derived factor (PEDF), an 8-mer peptide
fragment of urokinase (uPA), dexamethasone, and a host of other
drugs, small molecules, proteins, peptides and nucleic acids. 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 second, the pores themselves may be chemically modified to bind
the candidate drug.
[0023] 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.
[0024] The porous film is lifted off the silicon substrate, and it
is then broken into micron-sized particles having a size conducive
to intraocular injection. For example, in one preferred 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 invention, 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.
In this manner, the amount of drug may be quantified to determine
how much remains within the particles, and whether administration
of additional doses are necessary.
[0025] 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 is predicted to
result 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. 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.
[0026] 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.
[0027] By way of example only, binding and release of a DNA 16-mer,
IgG (using a Protein A receptor) and 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.
[0028] 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. Both
the porous silicon film and/or its imprint possess a sinusoidally
varying porosity gradient, providing sharp features in the optical
reflectivity spectrum that have been 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. Previous studies have demonstrated the biocompatibility of
porous Si in vitro and in animal models.
[0029] Other preferred embodiment 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.
[0030] A second preferred embodiment of the invention 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 invention. While the second 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.
[0031] Accordingly, the second embodiment of the invention 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.
[0032] 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. 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.
[0033] Thus, for example, the invention contemplates 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.
[0034] Another preferred embodiment includes the use of episcleral
plaques. An episcleral plaque is an extraocular way to deliver
drugs and the intraocular dust Injection promotes monitoring of
drug levels non-invasively. The invention contemplates 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.
[0035] While the invention is contemplated for use with a virtually
unlimited number of pharmaceutical candidates, several exemplary
drugs will be discussed herein.
[0036] 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. In particular, PEDF, the 8-mer peptide
fragment of uPA and dexamethasone all have short intravitreal
half-lives.
[0037] 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.
[0038] Impregnation of the porous material may proceed in several
ways. First, the candidate drug may be "physically" trapped within
the pores, or second, the pores themselves may be chemically
modified to bind the candidate drug.
[0039] 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 above equation is a
molecular oxidant such as O.sub.2, 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.
[0040] 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 only 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.
[0041] During chemical modification, a molecule is attached to the
inner pore walls via covalent bonds. The inner pore walls can be
configured to be chemically modified by one of the group consisting
of functional alkenes, silicone oxide, functional organohalides,
and metals. In the porous Si system, proteins, DNA, and various
small molecules can be attached following several different
procedures. The preferred 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.
[0042] The surface amine can then be functionalized with the 8-mer
peptide fragment of uPA using standard peptide coupling
methods.
[0043] The 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 PSi),
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.
[0044] 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.
[0045] 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, we previously studied
PL imprints impregnated with caffeine. We found that 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.
[0046] Embodiments of the invention 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 preferentially leach drug out one side of the film,
allowing greater control of the drug delivery parameters.
Manufacturing variables are channel sizes and packing.
[0047] Insofar as the invention 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.
[0048] 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.
[0049] 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 and the drug
level will sustain above the EC for months.
[0050] A preferred 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.
[0051] More particularly, one preferred method of the invention
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.
[0052] The photonic crystals are then loaded with a drug or drugs.
The pores of the photonic crystals are large enough to allow
infiltration of small drugs such as dexamethasone. Drug can be
loaded into the film or particles by infiltration from solution. In
a typical preparation, the drug loading solution consisted of
6.times.10-2 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.
[0053] Once the drug is loaded into the pores of the photonic
crystals, the photonic crystals are then injected into the patient.
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
ophthalmoscopically 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.
[0054] 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.
[0055] Experimental Data and Results:
[0056] 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 ophthalmoscopically
clear view of the fundus without any observed toxicity. The
particles lasted in the vitreous for one week without any
noticeable abnormalities.
[0057] 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.
[0058] 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.
[0059] 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
ophthalmoscopy. 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.
[0060] 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.
[0061] 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 burns. 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). [55] Administration of the drug intravitreally
using a proposed porous silicon smart dust should maintain the
desired intraocular drug level.
[0062] Thermal Oxidation of Porous Si Particles
[0063] 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 tile
chemical modification conditions such as thermal oxidation time,
temperature, and ambient atmosphere.
[0064] Electrochemical Grafting of Organic Reagents
[0065] The hydride-terminated surface of p-type or p.sup.++-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.
[0066] Thermal Hydrosilylation of Organoalkenes
[0067] 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.
[0068] 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 ophthalmoscope, 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 ophthalmoscope.
[0069] 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 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] In Vivo Studies
[0074] 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
ophthalmoscopic 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.
[0075] 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.
[0076] 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).
[0077] 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.
[0078] While various embodiments of the present invention have been
shown and described, it should be understood that modifications,
substitutions, and alternatives are apparent to one of ordinary
skill in the art. Such modifications, substitutions, and
alternatives can be made without departing from the spirit and
scope of the invention, which should be determined from the
appended claims.
[0079] Various features of the invention are set forth in the
appended claims.
* * * * *