U.S. patent application number 14/043787 was filed with the patent office on 2014-04-03 for compliant biocompatible device and method of manufacture.
This patent application is currently assigned to Brigham Young University. The applicant listed for this patent is Brigham Young University. Invention is credited to Anton Bowden, Brian Jensen, Kristopher Jones, Darrell Skousen.
Application Number | 20140094900 14/043787 |
Document ID | / |
Family ID | 50385908 |
Filed Date | 2014-04-03 |
United States Patent
Application |
20140094900 |
Kind Code |
A1 |
Bowden; Anton ; et
al. |
April 3, 2014 |
COMPLIANT BIOCOMPATIBLE DEVICE AND METHOD OF MANUFACTURE
Abstract
As detailed herein, a biocompatible apparatus comprises a porous
material comprising ceramic nanotubes bound together with a filler
material. The proportion of the filler material may be selected to
provide porosity for the porous material that is biocompatible, and
the porous material may be shaped to provide a compliant biomedical
device. In one embodiment, the compliant biomedical device is a
stent such as intravascular stent. A method for fabricating a
biocompatible device is also described herein. The method may
include growing ceramic nanotubes on a substrate, infiltrating the
ceramic nanotubes with a filler material to provide a porous
material having a porosity that is biocompatible, and removing the
porous material from the substrate to provide a biocompatible
ceramic device. The method may also include coating the
biocompatible ceramic device with a drug-eluting material.
Inventors: |
Bowden; Anton; (Lindon,
UT) ; Jensen; Brian; (Orem, UT) ; Jones;
Kristopher; (Provo, UT) ; Skousen; Darrell;
(Provo, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brigham Young University |
Provo |
UT |
US |
|
|
Assignee: |
Brigham Young University
Provo
UT
|
Family ID: |
50385908 |
Appl. No.: |
14/043787 |
Filed: |
October 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61708616 |
Oct 1, 2012 |
|
|
|
Current U.S.
Class: |
623/1.16 ;
264/48; 427/2.14 |
Current CPC
Class: |
A61L 2400/12 20130101;
A61F 2210/0014 20130101; A61F 2/844 20130101; B29C 59/007 20130101;
A61F 2/82 20130101; A61F 2/86 20130101; A61F 2250/0036 20130101;
A61F 2002/91558 20130101; A61L 31/122 20130101; A61F 2002/91575
20130101; A61F 2002/91583 20130101; B82Y 40/00 20130101; A61F 2/915
20130101; A61L 31/146 20130101 |
Class at
Publication: |
623/1.16 ;
427/2.14; 264/48 |
International
Class: |
A61F 2/82 20060101
A61F002/82; B29C 59/00 20060101 B29C059/00 |
Claims
1. A biocompatible apparatus comprising: a porous material
comprising a plurality of ceramic nanotubes bound together with a
filler material; wherein a proportion for the filler material is
selected to provide a porosity for the porous material that is
biocompatible; and wherein the porous material is shaped to provide
a compliant biomedical device.
2. The apparatus of claim 1, wherein the compliant biomedical
device is a stent.
3. The apparatus of claim 2, wherein the stent is an intravascular
stent
4. The apparatus of claim 3, wherein the stent is compressible for
vascular insertion.
5. The apparatus of claim 4, wherein a compressed diameter for the
stent is less than half of an uncompressed diameter for the
stent.
6. The apparatus of claim 2, wherein the stent is coated with a
drug-eluting material.
7. The apparatus of claim 1, wherein the ceramic nanotubes and the
filler material are biocompatible.
8. The apparatus of claim 1, wherein the ceramic nanotubes and the
filler material are carbon.
9. The apparatus of claim 1, wherein the porosity for the porous
material is biocompatible with vascular tissue.
10. A method for fabricating a biocompatible device, the
comprising: growing a plurality of ceramic nanotubes on a
substrate; infiltrating the plurality of ceramic nanotubes with a
filler material until a selected porosity is achieved to provide a
porous material having a porosity that is biocompatible; removing
the porous material from the substrate to provide a biocompatible
ceramic device;
11. The method of claim 10, wherein the substrate is a patterned
substrate.
12. The method of claim 11, wherein a pattern for the patterned
substrate is selected to provide a compliant device.
13. The method of claim 10, wherein the substrate comprises a
patterned layer of receptor material for growing the plurality of
ceramic nanotubes.
14. The method of claim 10, wherein the plurality of ceramic
nanotubes are grown substantially perpendicular to the
substrate.
15. The method of claim 10, wherein the biocompatible ceramic
device is a stent.
16. The method of claim 15, wherein the stent is a compressible
intravascular stent.
17. The method of claim 10, further comprising coating the
biocompatible ceramic device with a drug-eluting material.
18. The method of claim 10, wherein the ceramic nanotubes and the
filler material are biocompatible.
19. The method of claim 10, wherein the ceramic nanotubes and the
filler material comprise carbon.
20. The apparatus of claim 10, wherein the porosity is
biocompatible with vascular tissue.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application 61/708,616 entitled "Infiltrated porous carbon-nanotube
materials for micro-featured medical implants" and filed on 1 Oct.
2012 for Anton Bowden, Brian Jensen, Kristopher Jones, and Darrell
Skousen. The foregoing application is incorporated herein by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The subject matter disclosed herein relates to biocompatible
devices in general and to compliant biocompatible devices in
particular.
[0004] 2. Description of the Related Art
[0005] Ceramic materials have proven to be biocompatible for a
variety of applications. For example, pyrolytic carbon is a ceramic
material that is currently used in several specific biomedical
implant applications (including artificial heart valves), and is
especially valued for its biocompatibility and resistance to blood
clotting. Like most ceramics, its current indications for use are
limited due to its relatively brittle nature, as well as the
difficulty in producing complex geometries using traditional
ceramic forming techniques. Therefore, providing a compliant
ceramic device and a method of manufacture that is able to produce
complex geometries would be a significant advancement in the
art.
[0006] For example, stents are used for a variety of biomedical
applications including coronary artery stents, peripheral artery
stents, uterine stents, urethral stents, biliary stents, and stent
grafts (for example as used to treat abdominal aortic aneurysm). In
angioplasty applications, intravascular stents are synthetic tubes
that are implanted into the vascular system to reduce the risk of
restenosis (re-closing of the blood vessel) subsequent to
angioplasty. As shown in FIG. 1, a balloon 110 may be inserted into
an intravenous stent 120 that is in a relaxed state 120a. The
balloon 110 with the stent 120 may in turn be inserted into a
vessel 130 at a point of restricted flow 140. The stent 120 may be
expanded to an expanded state 120b by inflating the balloon 110. In
response to inflating the balloon 110 and expanding the stent 120,
the point of restricted 140 may become less restricted.
Subsequently, the balloon may be deflated and removed leaving the
stent 120 within the vessel 130 in an expanded state 120b.
[0007] Typically, the stents 120 are made of metal and coated with
a drug-eluting film that elutes tissue growth inhibition drugs for
approximately 2 weeks following implantation. Such stents have been
shown to reduce restenosis rates from approximately 30% to less
than 15%. While the reduced rates of restenosis are encouraging,
even a 10% restenosis rate represents 60,000 additional surgeries
in the US each year, with costs ranging from $30,000 to $100,000
each. Additionally, drug-eluting stents have also been associated
with higher rates of potentially deadly thrombus formation after
the drug eluting film dissipates. Thrombotic events remain the
primary cause of death after angioplasty. Consequently, a stent
that is more biocompatible than a metal stent would be a
significant advancement in the art.
SUMMARY OF THE INVENTION
[0008] As detailed herein, a biocompatible apparatus comprises a
porous material comprising a plurality of ceramic nanotubes bound
together with a filler material. The proportion of the filler
material may be selected to provide a porosity for the porous
material that is biocompatible, and the porous material may be
shaped to provide a compliant biomedical device. In one embodiment,
the compliant biomedical device is a stent such as intravascular
stent.
[0009] The porosity for the porous material may be selected to be
biocompatible with one or more types of human tissue. In addition
to having a porosity that is biocompatible, the porous material may
comprise ceramic nanotubes and a filler material that are
biocompatible. For example, the ceramic nanotubes may be formed of
carbon and the filler material may be carbon.
[0010] A method for fabricating a biocompatible device, such as the
biocompatible apparatus introduced above, is also described herein.
The method may include growing a plurality of ceramic nanotubes on
a substrate, infiltrating the plurality of ceramic nanotubes with a
filler material to provide a porous material having a porosity that
is biocompatible, and removing the porous material from the
substrate to provide a biocompatible ceramic device. The method may
also include coating the biocompatible ceramic device with a
drug-eluting material.
[0011] The substrate may be a patterned substrate. The pattern used
for the patterned substrate may be selected to provide a compliant
device with a desired flexibility. In one embodiment, the substrate
comprises a patterned layer of receptor material for growing the
plurality of ceramic nanotubes substantially perpendicular to the
substrate.
[0012] The embodiments described herein provide a variety of
advantages. It should be noted that references to features,
advantages, or similar language within this specification does not
imply that all of the features and advantages that may be realized
with the present invention should be, or are in, any single
embodiment of the invention. Rather, language referring to the
features and advantages is understood to mean that a specific
feature, advantage, or characteristic described in connection with
an embodiment is included in at least one embodiment of the present
invention. Thus, discussion of the features and advantages, and
similar language, throughout this specification may, but do not
necessarily, refer to the same embodiment.
[0013] Furthermore, the described features, advantages, and
characteristics of the invention may be combined in any suitable
manner in one or more embodiments. One skilled in the relevant art
will recognize that the invention may be practiced without one or
more of the specific features or advantages of a particular
embodiment. In other instances, additional features and advantages
may be recognized in certain embodiments that may not be present in
all embodiments of the invention.
[0014] The aforementioned features and advantages of the present
invention will become more fully apparent from the following
description and appended claims, or may be learned by the practice
of the invention as set forth hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] To enable the advantages of the invention to be readily
understood, a more particular description of the invention briefly
described above will be rendered by reference to specific
embodiments that are illustrated in the appended drawings.
Understanding that these drawings depict only typical embodiments
of the invention and are not therefore to be considered to be
limiting of its scope, the invention will be described and
explained with additional specificity and detail through the use of
the accompanying drawings, in which:
[0016] FIG. 1 is an illustration of a prior art intravenous stent
insertion process;
[0017] FIG. 2 is a flowchart diagram of a compliant biocompatible
device fabrication method;
[0018] FIGS. 3a-3f are cross sectional illustrations depicting one
embodiment of a compliant ceramic device at specific stages of one
particular embodiment of the compliant ceramic device fabrication
method of FIG. 2;
[0019] FIG. 4 is a top view illustration of one section of a
compliant stent and various parameters associated therewith;
and
[0020] FIGS. 5a and 5b are perspective view drawings depicting one
embodiment of a compliant ceramic stent.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Reference throughout this specification to "one embodiment,"
"an embodiment," or similar language means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
present invention. Thus, appearances of the phrases "in one
embodiment," "in an embodiment," and similar language throughout
this specification may, but do not necessarily, all refer to the
same embodiment.
[0022] FIG. 2 is a flowchart diagram of a fabrication method 200
for a compliant biocompatible device. As depicted, the method 200
includes providing 210 a patterned substrate, growing 220 ceramic
nanotubes thereon, infiltrating 230 the ceramic nanotubes with a
filler material, removing 240 the porous material from the
patterned substrate, and coating 250 the resulting biocompatible
device with a drug-eluting material. The fabrication method 200
facilitates fabricating a ceramic device that is both compliant
(i.e. flexible) and biocompatible.
[0023] Providing 210 a patterned substrate may include providing a
substrate made of glass, silicon, metal, or some other appropriate
material, and depositing a receptor layer thereon that facilitates
growing ceramic nanotubes. Alternately, the substrate may be made
of a receptor material facilitates growing ceramic nanotubes. In
some embodiments, a liftoff layer is deposited between the
substrate and the receptor layer to facilitate subsequent removal
of the ceramic nanotubes from the substrate.
[0024] The substrate and/or layers deposited thereon may be
patterned by machining, photolithography, cutting, stamping, or any
other method capable of producing a pattern. Patterning the
substrate may include forming one or more features on the
substrate, such as apertures, that improve the flexibility of the
device formed thereon. Alternately, the substrate itself may remain
in a substantially planar form and the patterned substrate may be
provided by patterning one of more of the layers deposited on the
substrate.
[0025] In one particular embodiment, the patterned substrate is
provided by depositing a liftoff layer of alumina and a receptor
layer of iron on a substrate of silicon, and using photolithography
to etch away regions of the receptor layer where ceramic nanotube
growth is not wanted.
[0026] Growing 220 ceramic nanotubes thereon may include chemical
vapor deposition, arc discharge, laser ablation, or any process
that facilitates ceramic nanotube growth. One of skill in the art
will appreciate that the height of the nanotubes may be much
greater than the pattern limits--particularly when photolithography
is used to provide a patterned substrate. For example, nanotubes of
greater than 500 microns in height may be grown, and pattern
dimension limits of 2-3 microns may be achieved, resulting in a
maximum aspect ratio of more than 200 to 1.
[0027] Infiltrating 230 the ceramic nanotubes with a filler
material may include chemical vapor deposition, electroplating of
metals, atomic layer deposition, dip coating with a polymer
precursor or any process that deposits a filler material between
the ceramic nanotubes. Infiltrating the ceramic nanotubes with a
filler material may bind the ceramic nanotubes together and result
in a porous material. The resulting porous material may be
substantially rigid. The resulting porous material may be a ceramic
or a ceramic nano-composite.
[0028] The infiltration time may control the proportion of the
filler material within the porous material and the porosity of the
porous material. The infiltration time and/or the proportion of the
filler material may be selected to result in a porosity that is
biocompatible. The ceramic nanotubes and the filler material may be
made of biocompatible materials. In some embodiments, the filler
material and the ceramic nanotubes are made of the same
material.
[0029] Removing 240 the porous material from the patterned
substrate may include conducting a liftoff process that etches away
the receptor layer and/or the liftoff layer disposed between the
receptor layer and the substrate. Coating 250 the resulting
biocompatible device with a drug-eluting material may include
depositing a drug-eluting material on the biocompatible device. In
one embodiment, the drug-eluting material may be a drug-eluting
polymer. One of skill in the art will appreciate that the
drug-eluting material may be application dependent and may be
omitted in certain applications.
[0030] FIG. 3 is a cross sectional illustration of the stages a
compliant device may undergo during one embodiment of the compliant
ceramic device fabrication method 200 shown in FIG. 2. Initially,
at stage 300a a substrate such as a wafer is coated with
sacrificial photoresist at locations where ceramic nanotube growth
is to be inhibited. At stage 300b, a liftoff material such as
alumina is deposited on the substrate followed by a receptor
material such as iron at stage 300c. For example, a 30-nm layer of
alumina (Al2O3) could be deposited using an e-beam evaporator and a
4-10 nm layer of iron may be deposited via a thermal
evaporator.
[0031] At stage 300d, the sacrificial photoresist is etched away
resulting in a patterned receptor layer on a planar substrate
(referred to herein as a patterned substrate). At stage 300e,
ceramic nanotubes such as carbon nanotubes are grown on the
receptor layer. The grown ceramic nanotubes may from a "forest" of
nanotubes that are substantially perpendicular to the substrate.
The spacing of the nanotubes may be determined by the spacing of
atoms or molecules on the receptor layer. Subsequently, at stage
300f the ceramic nanotubes are infiltrated with a filler material
until a selected porosity is achieved.
[0032] For specific details of one example of the above stages and
properties of compliant ceramic devices that may result therefrom,
see "Material Properties of Carbon-Infiltrated Carbon
Nanotube-Templated Structures for Microfabrication of Compliant
Mechanisms" within Proceedings of the ASME 2011 International
Mechanical Engineering Congress & Exposition, IMECE2011-64168.
The authors of the aforementioned reference include at least one
inventor of the present invention.
[0033] The proportion for the filler material relative to the
ceramic nanotubes may be selected to provide a selected porosity
for the porous material that is biocompatible. For example, the
porosity of the porous material may be selected to be biocompatible
with one or more types of human tissue such as vascular tissue,
muscle tissue, nerve tissue, epithelial tissue, connective tissue,
adenoid tissue, adipose tissue, areolar tissue, bony tissue,
cancellous tissue, cartilaginous tissue, chromaffin tissue,
cicatricial tissue, elastic tissue, endothelial tissue, epithelial
tissue, erectile tissue, extracellular tissue, fatty tissue,
fibrous tissue, gelatinous tissue, glandular tissue, granulation
tissue, indifferent tissue, interstitial tissue, lymphadenoid
tissue, lymphoid tissue, mesenchymal tissue, mucous tissue, myeloid
tissue, osseous tissue, reticular tissue, reticulated tissue, scar
tissue, sclerous tissue, skeletal tissue, subcutaneous tissue, and
tissue from various organs.
[0034] One of skill in the art will appreciate that the thickness
of atoms or molecules on the receptor layer as well as the
infiltration time may influence the maximum strain achievable by
the bulk porous material. In one embodiment, iron thicknesses of
7-10 nm and an infiltration time of approximately 30 minutes for
carbon infiltrated carbon nanotubes resulted in a maximum material
strain of approximately 2.3% for the bulk porous material. However,
by controlling the shape of the porous material compliant devices
having maximum strains of greater than 140 percent have been
demonstrated for carbon infiltrated carbon nanotubes. Furthermore,
controlling the shape of the porous material may result in a
compliant device that performs a specific biomedical function in
addition to having a desired flexibility (i.e., maximum strain).
For example, compliant fluid transport devices such as stents,
needles, and catheters and compliant fluid filtering devices such
as artificial nephrons, blood filtration screens, or as a
replacement trabecular mesh network following glaucoma surgery, may
be provided. Compliant drug delivery and dispensing devices
(consumable, implantable and skin attachable) and compliant meshes
such as hernia meshes and bandaging meshes may also be
provided.
[0035] FIG. 4 is a top view illustration of one section of a
compliant stent 400 and various design parameters associated
therewith. As depicted, the parameters include a strut thickness
410, a strut angle 420, a strut length 430, an end radius 440, and
an end radius angle 450. The geometry of the stent 400 and the
parameters associated therewith may be optimized using compliant
mechanism design principles. Furthermore, computational tools such
as stress analysis tools may be used to simulate the effects of
changing the various parameters on the properties of the compliant
stent 400. The computational tools may be provided with
measurements taken on the bulk porous material provided by the
method 200 or a portion thereof. The computational tools may be
leveraged to optimize the compliant stent 400 or the like.
[0036] FIGS. 5a and 5b are tracings of a perspective view photo of
a prototype compliant ceramic stent 500 optimized via compliant
mechanism design principles and computational tools (similar to the
process described above) and fabricated by the method of FIG. 2.
Specifically, the depicted compliant ceramic stent 500 was formed
by carbon infiltration of carbon nanotubes grown on a silicon
substrate with a liftoff layer of alumina and a receptor layer of
iron deposited thereon. The depicted compliant ceramic stent 500
was found to have a maximum strain of approximately 80 percent.
[0037] When rolled as suggested in FIG. 5b, the stent 500 or the
like, with the testing tabs 510 removed therefrom, could be used as
intravascular stent that is compressible for vascular insertion.
The compressed diameter for the stent (e.g., .about.1 mm) may be
less than half of an uncompressed diameter (e.g., .about.3 mm) for
the stent. In one embodiment, a compressed stent 500 (or the like)
is held in a compressed state via one or removable clips (not
shown). The stent 500 may be coated with a drug-eluting
material.
[0038] It should be noted that compliant biocompatible devices such
as the stent 500 may be fabricated in a final deployed (i.e.,
unstressed) geometry using the methods disclosed herein. For
example, while the examples depicted in the attached figures
leverage planar substrates, a non-planar substrate such as a
cylindrical mandrel may be used to fabricate the device stent 500
or the like.
[0039] The present invention provides compliant biocompatible
devices and enables the manufacture thereof. The present invention
may be embodied in other specific forms without departing from its
spirit or essential characteristics. The described embodiments are
to be considered in all respects only as illustrative and not
restrictive. The scope of the invention is, therefore, indicated by
the appended claims rather than by the foregoing description. All
changes which come within the meaning and range of equivalency of
the claims are to be embraced within their scope.
* * * * *