U.S. patent application number 09/782346 was filed with the patent office on 2001-11-29 for corneal onlay.
Invention is credited to Dalton, Beatrice Ann, Fitton, Janet Helen, Gipson, Ilene Kay, Johnson, Graham, Macrea Evans, Margaret Diana, Steele, John Gerard.
Application Number | 20010047203 09/782346 |
Document ID | / |
Family ID | 8232450 |
Filed Date | 2001-11-29 |
United States Patent
Application |
20010047203 |
Kind Code |
A1 |
Dalton, Beatrice Ann ; et
al. |
November 29, 2001 |
Corneal onlay
Abstract
A corneal onlay or corneal implant is disclosed which is to be
placed within or onto the surface of the cornea, being a
biocompatible, optically transparent, synthetic and biostable
polymeric material, said material comprising a surface that
supports the attachment and growth of tissue cells, and where the
exterior surface of the implant onto which epithelial tissue is to
be attracted and to become attached, or in the case of a corneal
onlay the anterior surface of the onlay, has a topography
comprising a plurality of surface indentations.
Inventors: |
Dalton, Beatrice Ann;
(Narrabeen, AU) ; Steele, John Gerard; (North
Rocks, AU) ; Macrea Evans, Margaret Diana;
(Chatswood, AU) ; Fitton, Janet Helen; (Tasmania,
AU) ; Johnson, Graham; (Peakhurst, AU) ;
Gipson, Ilene Kay; (Concord, MA) |
Correspondence
Address: |
THOMAS HOXIE
NOVARTIS CORPORATION
PATENT AND TRADEMARK DEPT
564 MORRIS AVENUE
SUMMIT
NJ
079011027
|
Family ID: |
8232450 |
Appl. No.: |
09/782346 |
Filed: |
February 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09782346 |
Feb 12, 2001 |
|
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PCT/EP99/05836 |
Aug 10, 1999 |
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Current U.S.
Class: |
623/5.13 ;
623/5.16; 623/6.62 |
Current CPC
Class: |
A61F 2/142 20130101;
A61F 2/145 20130101 |
Class at
Publication: |
623/5.13 ;
623/5.16; 623/6.62 |
International
Class: |
A61F 002/14 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 12, 1998 |
EP |
98115161.6 |
Claims
1. A corneal onlay or corneal implant to be placed within or onto
the surface of the cornea, being a biocompatible, optically
transparent, synthetic and biostable polymeric material, said
material comprising a surface that supports the attachment and
growth of tissue cells, and where the exterior surface of the
implant onto which epithelial tissue is to be attracted and to
become attached, or in the case of a corneal onlay the anterior
surface of the onlay, has a topography comprising a plurality of
surface indentations.
2. An onlay or implant according to claim 1 characterized in that
the plurality of indentations are equal or greater than 500 square
nanometers in surface area and equal or less than 0.7 square
microns in surface area in the plane of the surface.
3. An onlay or implant according to claim 1 characterized in that
the plurality of indentations are generally curvilinear or circular
in shape at-the plane of the surface and have minimum diameter(s)
that is/are equal or greater than 0.025 microns in diameter and
have maximum diameter(s) that is/are equal or less than 0.95
microns in diameter.
4. An onlay or implant according to claim 1 characterized in that
the plurality of indentations comprise the equivalent area in the
plane of the surface as to be equal or greater than 0.10% of the
surface area in the plane of the surface and equal or less than 20%
of the surface area.
5. An onlay or implant according to claim 1 characterized in that
the mean depth of surface indentations below the plane of the
surface is equal or greater than 0.1 microns.
6. An onlay or implant according to claim 1 characterized in that
the plurality of indentations do not provide for the ingrowth of
corneal epithelial tissue or cells or cellular processes to a depth
of further than 20 microns from the plane of the surface of the
implant.
7. An onlay or implant according to claim 1 characterized in that
the plurality of indentations have a coating or gel formed of
biological molecules or synthetic analogues thereof placed upon or
within said plurality of surface indentations.
8. An onlay or implant according to claim 1 characterized in that
it comprises pores through the implant or onlay.
9. An onlay or implant according to claim 8 characterized in that
the pores are curvilinear or circular and the diameter of the pores
is in the range of equal or greater than 0.025 microns in diameter
and equal or less than 0.95 microns in diameter.
10. An onlay or implant according to claim 8 characterized in that
the plurality of indentations are equal or less than 10.000 square
nanometers in surface area.
11. An onlay or implant according to claim 8 characterized in that
the plurality of indentations have a maximum diameter that is equal
or less than 0.4 microns in diameter.
Description
[0001] This invention is directed to an improved corneal onlay.
More specifically the corneal onlay of the invention has a surface
topography and a structure of the anterior surface which promote
overgrowth with corneal epithelium and formation of a stratified
epithelium following overgrowth, including the development of
hemidesmosomes in basal cell layer of the epithelium.
[0002] The invention is particularly directed towards an implant
for use for synthetic epikeratoplasty or as an implanted contact
lens, where placed at an subepithelial site.
[0003] The objective of the invention is to provide a polymer
surface that inherently supports tissue overgrowth without the need
for an additional surface modification or biological coating. A
further objective is to provide a polymer that combines this
property with good biostability, optical properties, and mechanical
properties that make the material suitable for the fabrication of
epikeratoprostheses. Corneal onlays as such are known. One of the
more recent findings, as disclosed in EP-A-729323, suggests that a
corneal onlay needs to be porous to allow for through passage
between anterior and posterior sides of the device of trophic
factors and nutrients. Said EP-A-729323 is illustrative for a
number of reasons, it is explaining the background state of the
art, and definitions used therein do apply also to this invention,
unless terms are expressly otherwise defined. A number of synthetic
polymers have been proposed for a corneal onlay, or other corneal
implant where epithelialisation is desired, such as hydrophobic
materials, for example perfluoropolyether based materials, or
collagen-hydrogel copolymeric materials.
[0004] However, the prior art examples do not teach, nor make
predictable, the requirements as to the topography of the surface
of a synthetic polymer for
[0005] (i) the processes of the migration of corneal epithelial
tissue across the surface of an implant;
[0006] (ii) the processes of the assembly of a stratified corneal
epithelium following movement of the tissue across the surface of
the material. In considering this migration process, it needs to be
recognized that there is a difference between the ocular
epitzhelium and other epithelia for cellular migratory processes.
In the case of the corneal epithelium, the epithelial cells that
are found in the central region of the cornea arise initially from
stem cells that lie in the limbal region (the zone that is the
transition between the conjunctiva and the cornea). That is, there
is a movement of epithelial cells from the limbal region to the
central cornea. This compares with the situation of other
epithelia, where the stem cells lie in the lower levels of the
epidermis and cellular movement preceding, during, or to permit,
stratification is towards the anterior surface;
[0007] (iii) the processes of the formation of hemidesmosomes (at
the basal epithelial cells) at and into the near surface of the
synthetic material;
[0008] other than to show that a topography that is supportive is
possible.
[0009] The disadvantages of the prior art corneal onlays are
overcome by the corneal onlay of this invention based on the
surprising finding that for migration of the corneal epithelium to
cover the onlay, it is not the pores which are relevant but a
topography comprising a plurality of indentations.
[0010] The corneal onlay or corneal implant to be placed within or
onto the surface of the cornea according to the disclosure herein
has a surface topography in order to permit the overgrowth of a
surface of the implant with corneal epithelium. The corneal
epithelium tissue overlying the corneal onlay device shows
characteristics of being a stratified corneal epithelium, including
the presence in the basal epithelial cell layer of proteinaceous
components of hemidesmosome structures.
[0011] The present invention is distinct from the prior art in that
it arises from the recognition that the topography of the surface,
independent of the porosity of the material, can promote the
overgrowth of a corneal onlay with corneal epithelial tissue.
[0012] The invention provides a polymer surface for use in a
corneal onlay, which surface has a topography that supports the
overgrowth and migration of corneal epithelial tissue at a level
that is superior to that seen for a smooth and non-porous form of
the same synthetic polymer.
[0013] A further distinguishing feature from the prior art is that
the surface according to the current invention combines this
topography, with porosity.
[0014] The invention is therefore directed to a corneal onlay or
corneal implant to be placed within or onto the surface of the
cornea, being a biocompatible, optically transparent, synthetic and
biostable polymeric material, said material comprising a surface
that supports the attachment and growth of tissue cells, and where
the exterior surface of the implant onto which epithelial tissue is
to be attracted and to become attached, or in the case of a corneal
onlay the anterior surface of the onlay, has a topography
comprising a plurality of surface indentations.
[0015] A surface that supports the attachment and growth of tissue
cells either provides said support directly, or said surface
additionally has a surface coating that supports the attachment and
growth of tissue cells.
[0016] It is important to note that the surface indentations may
comprise pores, but pores alone are not within the meaning of
surface indentation. In other words, the wording "topography
comprising a plurality of surface indentations" includes surfaces
having pores plus indentations, but excludes surfaces having pores
without additional indentations. Apart from the fact that corneal
onlays having pores, and no indentations, as disclosed in
EP-A-729323, are not within the scope of the present invention, the
indentations may have any suitable form and geometry.
[0017] Preferred characteristics of the plurality of indentations
are that they are equal or greater than 500 square nanometers in
surface area and equal or less than 0.7 square microns in surface
area in the plane of the surface, or that they are generally
curvilinear or circular in shape at the plane of the surface and
have minimum diameter(s) that is/are equal or greater than 0.025
microns in diameter and have maximum diameter(s) that is/are equal
or less than 0.95 microns in diameter.
[0018] More preferred minimum diameters are equal or greater than
0.05 microns in diameter.
[0019] More preferred maximum diameters are equal or less than 0.80
microns in diameter, even more preferred equal or less than 0.50
microns in diameter and most preferred equal or less than 0.35
microns in diameter.
[0020] Another set of preferred features of the plurality of
surface indentations is that they comprise the equivalent area in
the plane of the surface as to be equal or greater than 0.10 % of
the surface area in the plane of the surface and equal or less than
20% of the surface area. More preferred values in this context are
that the surface indentations comprise the equivalent area in the
plane of the surface as to be equal or greater than 2% of the
surface area in the plane of the surface and equal or less than 15%
of the surface area in the plane of the surface, and most preferred
is a range from equal or greater than 3% of the surface area in the
plane of the surface and equal or less than 10% of the surface area
in the plane of the surface.
[0021] It may be appropriate to make a comment on terminology used
herein: Some of the sizes of the indentations mentioned
hereinbefore refer to the size of individual indentations, and
there are a plurality of indentations of these sizes. Such
indentations may not all be identical in size but would generally
fit these size ranges. Sizes of this type are for example those
referred to in claims 2 and 3. In contrast thereto, some of the
sizes specified hereinbefore are for the totality of the
indentations in aggregate. Sizes of this type are for example those
referred to in claim 4. It is believed that the person skilled in
the art will understand this differentiation taking into account
the absolute magnitude disclosed.
[0022] It is also preferred that the mean depth of surface
indentations below the plane of the surface is equal or greater
than 0.1 microns.
[0023] It is further preferred that the surface indentations do not
provide for the ingrowth of corneal epithelial tissue or cells or
cellular processes to a depth of further than 20 microns from the
plane of the surface of the implant, or more preferred the surface
indentations do not provide for the ingrowth of corneal epithelial
tissue or cells or cellular processes to a depth of further than 20
microns from the plane of the surface of the implant in the optical
region of the implant.
[0024] The surface indentations as described hereinbefore may or
may not have a coating or gel formed of biological molecules or
synthetic analogues thereof placed upon or within said plurality of
surface indentations.
[0025] A gel as mentioned hereinbefore may be made, for example,
from collagen which is or is not chemically crosslinked to the
surface and wherein the collagen molecules within the gel are
crosslinked or uncrosslinked.
[0026] Furthermore, some or aH of the plurality of surface
indentations as disclosed hereinbefore may have continuity with
other indentations within the bulk of the material below the plane
of the surface.
[0027] Also, the existence of pores, in addition to surface
indentations, through the implant or onlay is possible. In such a
case the pores are preferably curvilinear or circular and the
diameter of the pores is in the range of equal or greater than
0.025 microns in diameter and equal or less than 0.95 microns in
diameter. More preferred values in this context are 0.05 microns in
diameter and equal or less than 0.35 microns in diameter.
[0028] A preferred corneal onlay has the following characteristics:
It combines the elements of claims 1 to 3, 1 to 4, 1 to 5, 1 to 6,
or 8 and 10 and 11. Other combinations of preferred features of the
invention are also possible and within the scope of this invention.
This statement includes aspects of the invention disclosed
hereinbefore and such aspects following hereinafter.
[0029] Further preferred aspects of the invention are in that the
topography of the anterior surface of the onlay comprises
indentations as defined hereinbefore and pores as defined
hereinbefore and that said topography consists of a plurality of
surface indentations that are equal or less than 10.000 square
nanometers in surface area.
[0030] Another preferred aspect of the invention is in that the
topography of the anterior surface of the onlay comprises
indentations as defined hereinbefore and pores as defined
hereinbefore and that said topography consists of a plurality of
surface indentations which have a maximum diameter that is equal or
less than 0.4 microns in diameter. More preferably said maximum
diameter ie equal or less than 0.2 microns in diameter.
[0031] The disclosure of the invention hereinbefore has been made
particularly with reference to intraepithelial corneal onlays and
other corneal implant materials. However, this fact should not be
understood as being limiting in any substantial way. A material
that supports the overgrowth of epithelial tissue may also have
applications as a component of other intra-epithelial implants,
such as percutaneous access devices.
[0032] The following examples are for illustration purposes only
and are by no means intended to restrict the scope of the
claims.
EXAMPLE 1
[0033] This example demonstrates that a material with a surface
that contains a plurality of surface indentations provides for
enhanced outgrowth of corneal epithelium, as compared to the same
composition of material but a form which does not contain surface
indentations. The demonstration was conducted in a cell culture
assay where the ability of the material surface to support the
overgrowth of corneal epithelial tissue is measured. This assay
format therefore duplicates the situation of a corneal onlay
device, in terms of the requirement that the surface of a corneal
onlay promote the ability of the corneal epithelium to migrate over
and cover the surface of the material.
[0034] Methods: Assembly of the materials for use in the assay
using the Boyden chamber: The materials to be tested were assembled
in modified "Boyden" chambers which have a structure such that the
upper and lower chambers are separated by 25 mm diameter discs of
the materials to be tested. These modified Boyden chambers consist
of a base and upper section, which screw together above and below
the material to be used in the culture assay. The polycarbonate
base (5 cm square and 3.8 cm high) contains an inner semi-spherical
lower chamber of 2 ml capacity. This lower chamber is connected to
the exterior by 2 channels set on opposite sides of the chamber,
which permit the diffusion of air such that the medium in the lower
well can be buffered by the 5% CO.sub.2 in air atmosphere within a
cell culture incubator. At the top of the lower section and
extending into the lower chamber, there is a 2 mm wide flat
circular ledge that supports the peripheral 2 mms of the 25 mm
diameter sample of material to be tested. The base contains a
thread, onto which screws the upper section, manufactured from
polytetrafluoroethylene. Between the lower and upper sections and
supported by the ledge, are placed the material sample to be tested
which can be either a single sheet, or alternatively two sheets of
material. If there are two sheets of materials, these sheets will
be held in very tight apposition by the pressure exerted by the
thread mechanism. A silicone gasket with an internal diameter of 23
mm and an external diameter of 25 mm is placed between the material
sample and the upper section, to enable a fluid-tight seal to be
formed and culture medium is introduced into both the lower and
upper chambers. The lower sections of the Boyden chamber were
completely filled with medium (approx. 2 ml) and 1.5 ml of medium
was added to the upper sections.
[0035] Description of materials tested: Track-etched polycarbonate
membranes (free from wetting agents, from Poretics Corporation,
USA; 0.4 microns nominal pore diameter). These membrane materials
contained columnar pores with measured diameters of 0.35 microns.
Control materials (that is, Sample A) used in the assays were
non-porous polycarbonate.
[0036] Corneal epithelial tissue overgrowth assay: Corneas were
excised from freshly enucleated bovine eyes and the bulk of the
stromal tissue and the endothelial layer were removed. A skin
biopsy punch was used to collect six mm diameter buttons of corneal
tissue from the periphery of the tissue. Explants so collected
comprised an intact epithelium with a small amount of stromal
tissue attached but greater than 90% of the stromal tissue had been
removed. The explants were placed (stromal side down) on the
material surfaces and were covered with Dulbecco's modified Eagle's
medium/Ham's F12 (ICN Flow) supplemented with 5 microgram/ml
insulin, 5 microgram/ml transferrin, 5 nanogram/ml selenious acid
(from Collaborative Research) 60 microgram/ml penicillin and 100
microgram/ml streptomycin (ICN Flow). The cultures were maintained
at 37.degree. C. in an humidified atmosphere containing 5 %
CO.sub.2 in air (v/v) for a period of nine days, with changes of
medium at day three and day six. After this period, the explants
were washed with phosphate buffered saline (PBS) and fixed in 10%
(v/v) formalin in PBS for 30 min at room temperature, washed with
distilled water and air dried for 5 minutes. The explants were
stained with 0.1% (w/v) Crystal violet (Edward Gurr Ltd) in 0.02 M
phosphate buffer (pH 7) for 30 minutes at room temperature then
washed 3 times with distilled water to remove any unbound stain.
The total area of the tissue (epithelial outgrowth+original area of
explant button) was measured by image analysis (Quantimet 570,
Leica Cambridge). An index of epithelial tissue outgrowth (Tissue
Outgrowth Index) was calculated by dividing the final surface area
of the outgrowth from each explant by the initial area of the
tissue explant. Therefore, a Tissue Outgrowth Index value of 1.0
represents a situation where there was no outgrowth of corneal
epithelial tissue onto the surface. Each experiment was repeated
twice and four replicates were set up for each treatment.
[0037] Results: The extent of corneal epithelial tissue overgrowth
was compared for three different polycarbonate materials:
[0038] Sample A: a smooth, nonporous polycarbonate surface.
[0039] Sample B: a surface made from the same material but with a
plurality of surface indentations of 0.35 micron measured diameter
on the material; the plurality of surface indentations comprise the
equivalent area in the plane of the surface as to be 9% of the
surface area in the plane of the surface. This sample was provided
by a 0.4 micron nominal diameter track-etched pore polycarbonate
membrane. In Sample B this material was assembled in tight
apposition to a non-porous material on the underside and therefore
no flux of proteins or fluids was permitted through the upper
membrane material.
[0040] Sample C: a surface with a plurality of surface indentations
on the material, and having in addition pores that enabled a flux
of fluids and proteins and nutrients through the membrane
material.
[0041] The extent of corneal epithelial tissue overgrowth onto
these samples during a nine day culture period was measured as:
1 Sample A B C Tissue Outgrowth Index value 4.9 +/- 0.6 10.1 +/-
0.8 9.0 +/- 0.8
[0042] When subjected to the Student-Newman-Keuls Multiple
Comparisons statistical test, the following conclusion was made:
Samples B and C showed a statistically significantly higher value
for the Tissue Outgrowth Index than Sample A (both at the level of
P<0.05) but there was no statistically significant difference
between Sample B and Sample C (P>0.05).
[0043] This experiment shows that for a material that supported the
overgrowth of corneal epithelial tissue onto a generally smooth
surface (Tissue Outgrowth Index greater than 1 for Sample A), this
material when in the form of a surface with a plurality of
indentations of 0.4 microns nominal diameter and 0.12 square
microns in surface area in the plane of the surface supported a
significantly superior extent of outgrowth of corneal epithelial
tissue (Samples B and C). This superior level of corneal epithelial
tissue outgrowth was also seen for the case of when the material
enabled the flux of fluid and proteins and nutrients through the
pores of the material but was not dependent upon this fluid or
molecular movement, as it was also seen for the case where the
pores at the surface of the material could not support such a flux
of fluid and proteins and nutrients.
EXAMPLE 2
[0044] This experiment showed that for a series of materials with
the same surface chemistries as to the chemical composition of the
synthetic polymer surface, the material that has a plurality of
indentations supported a significantly superior extent of outgrowth
of corneal epithelial tissue than the equivalent smooth surface.
This was seen for both a synthetic polymer surface and also for
materials which had covalently attached collagen on the surface. In
these materials the plurality of indentations in the surface were
of 0.075 microns nominal diameter and 7850 square nanometers in
surface area in the plane of the surface. The plurality of surface
indentations and pores comprised the equivalent area in the plane
of the surface as to be 2.5% of the surface area in the plane of
the surface.
EXAMPLE 3
[0045] in this example, the role of polymer surface topography in
the assembly of basement membrane and hemidesmosomes (which
together are known to be responsible for the persistent adhesion of
the stratified epithelium to its underlying stroma in intact
cornea) by epithelial cells at the tissue-material interface was
tested. Each hemidesmosome is comprised by keratin intermediate
filaments and hemidesmosomal plaque on the posterior aspect of the
basal epithelial cells, which link through the basement membrane to
anchoring fibrils that penetrate the anterior stroma, thereby
securing the epithelium to its connective tissue.
[0046] Methods and Materials:
[0047] Sample A: as described in Example 1 above.
[0048] Sample C: a surface made from the same polycarbonate
material but with a plurality of surface indentations of 0.35
micron measured diameter on the material ("value A" in following
table), and having in addition pores that enabled a flux of fluids
and proteins and nutrients through the membrane material. This
sample was provided by a 0.4 micron nominal diameter track-etched
pore polycarbonate membrane ("value B" in following table). The
plurality of surface indentations and pores comprise the equivalent
area in the plane of the surface as to be 9% of the surface area in
the plane of the surface ("value C" in following table).
[0049] Samples D, E and F are the same as Sample C, with the
exception that the Values A, B and C are modified as evident from
the following Table
2 Sample Value A Value B Value C C 0.35 micron 0.4 micron 9% D
0.075 micron 0.1 micron 2.5% E 0.72 micron 0.8 micron 10.7% F 0.9
micron 1 micron 10%
[0050] Buttons of explanted corneal tissue were placed on
triplicate samples of each surface and maintained in culture for 21
days, during which time epithelial tissue outgrew in direct contact
with the underlying polymer. Ultrathin sections of the epithelial
tissue-polymer interface were examined using transmission electron
microscopy and the formation along the interface of basement
membrane and hemidesmosomal plaque (identified from
ultramicroscopic features) was recorded.
[0051] Results: Cells constituting the basal layer of epithelial
cells on the Sample A material (a smooth and non-porous
polycarbonate surface) lay in close apposition to the polymer
surface and there was little or no evidence of basement membrane
along this tissue-polymer interface, and no evidence of
hemidesmosomal plaque components.
[0052] Cells in contact with the surface containing a plurality of
indentations of 0.075 microns diameter (Sample D) consistently
bridged these pore openings. With the surface indentations of this
size, there was a continuous basement membrane formation and a
regular pattern of hemidesmosomal plaque assembly even across the
indentation. Cells in contact with the surfaces containing a
plurality of indentations of 0.4, 0.8 or 1 microns nominal
diameters (Samples C, E and F) effectively bridged the pores,
although cell cytoplasm was observed to protrude slightly into the
mouth of some surface indentations. In contrast to the membranes
with the surface containing a plurality of indentations of 0.075
microns diameter, however, the formation of basement membrane and
hemidesmosomal plaque on each of these surfaces lacked continuity
and was restricted to those regions where the solid portion of the
polymer (between the pores) was immediately subjacent to the cells.
That is, the surface indentations interrupted the continuity of the
basement membrane and assembly of hemidesmosomal plaque, when the
surface indentations were of a size of 0.4 microns and greater in
diameter.
[0053] This work shows that the assembly of structures responsible
for persistent epithelial adhesion (including a continuous basement
membrane and hemidesmosomal plaque, as is seen at the
epithelial-stromal interface in intact corneal tissue) are
supported on a surface that contains indentations of no greater
than 0.4 microns diameter for a material that contains porosity
towards tissue factors and nutrients.
* * * * *