CA1340913C

CA1340913C - Uncrosslinked (co)polyacrylonitrile hydrogels for medical and surgical uses

Info

Publication number: CA1340913C
Application number: CA000598274A
Authority: CA
Inventors: Jiri Honiger; Laurent Laroche
Original assignee: Institut National de la Sante et de la Recherche Medicale INSERM
Current assignee: Institut National de la Sante et de la Recherche Medicale INSERM
Priority date: 1988-05-02
Filing date: 1989-04-28
Publication date: 2000-02-29
Anticipated expiration: 2017-02-28
Also published as: FR2630638B1; DK212789A; FR2630638A1; DK212789D0; CN1037830A; EP0347267A1; PT90429B; JPH0271751A; IE63102B1; DE68913822T2; AU623137B2; EP0347267B1; DE68913822D1; PT90429A; AU3382089A; IE891416L; ES2062058T3

Abstract

An uncrosslinked hydrogel, its process of preparation as well as its uses as an article for medical and/or surgical purposes, e.g., tubes, filaments, films, joints, implants and the like, especially in ophthalmology are provided herein. The uncrosslinked hydrogel has a relatively high water content and is prepared from a liquid starting composition which comprises 2 to 50% by weight of a copolymer of acrylonitrile and an elefinically-unsaturated comonomer bearing anionic groups, which is either salified or unsalified. The molar ratio of acrylonitrile to comonomer is between 90:10 and 100:0. The liquid starting composition includes a suitable solvent and a suitable non-solvent for the copolymer, the non-solvent being an aqueous solution of a salt. The ratio of solvent to aqueous salt solution non-solvent is between 500:1 and 0.5:1 by weight. The hydrogel has a microporous structure, an ionic capacity between 0 and 500 mEq/kg of gel, a hydric content between 50 and 90% and has an aptitude for permanent deformation under stress, even at a temperature below 40°C.

Description

The preser..t invention relates to an uncrosslinked hydrogel, to its process of preparation as well as to its applications as an article for medical and/or surgical purposes, e.g., tubes, filaments, films, joints, implants and the like, particularly in ophthalmology.
It has already been proposed to employ polymers in hydrogel form which have relatively high water content whilst having improved mechanical and optical properties for ophthalmic purposes. (See European Patent No. 188 110 and U.S. Patent: Nos. 4,379,864 and 4,543,371).
However, the product described in U.S. Patents Nos.
4,379,864 and 4,.543,3'71 do not have a high water content;
in fact, these polymers lose the required mechanical properties, particularly for their use as an implant, when the water content is high.
The hydrogels described in European patent application No. 198 110 do not have properties of good tolerance, particularly required for an implant, to the extent that the ionic characteristics. In particularly, the electronegativity of the polymer does not permit good tolerance of the: latter to be envisaged.
French Pat~=nt FH 2,529,464 describes biocompatible materials in the form of hollow fibres or membranes. These biomaterials are: treated by a plurality of drawing stages to produce a suitable permeability. These show, for this reason, a different :structure, namely, the structure of membranes or hollow fibres for haemodialysis and/or hemofiltration.

2 13409 13 German Patent DE-A-2028956 describes a hydrogel which comprises many ionic groups, the hydrogel not possessing suitable biocompatibilty.
This is why Applicant has sought for a solution to the above problem in another direction, namely, that of providing hydroc~els having high biocompatibility for their use in the pre~parat~~_on of articles for medical and/or surgical purposes which are highly reliable. In particular, an .aim of this invention is the provision of ocular implants enabling a suitable permeability to be obtained to dif:Eerent biological molecules, the implants, not showing, consequently, the drawbacks of known implants.
Applicant unexpectedly has found that certain biomaterials, under' particular conditions, have considerable advantages, especially in the field of ocular implants.
Therefore, objects of aspects of this invention are to provide an uncrosslinl~:ed hydrogel with improved mechanical properties and with a high water content, as well as to provide a process for its preparation, such hydrogel responding bettE:r to 'the necessities of practice than the hydrogels of the prior art, particularly in that they have the advantage of conferring on the hydrogels a character of inertia with re~.pect t:o biological cells.
An obj ect of another aspect of this invention is to provide articles con;~tituted at least in part by such hydrogel.

An object of yet another aspect of this invention is to provide for the use of such articles in surgery and in medicine.
It is also an object of an aspect of the present invention to provide am article for medical and/or surgical use, e.g. , in th.e form of a tube, film, filament, joint, or implant, or the like.
According t=o one aspect of the present invention, an uncrosslinked h~~droge7_ is provided having a relatively high water content, the h~~drogel being prepared from a liquid starting composition which comprises from 2 to 50o by weight of a copolymer of acrylonitrile and an olefinically-unsaturated comonomer bearing anionic groups, which are either unsalifi~=d or are salified, in a molar ratio of acrylonitrile to comonomer of between 90:10 and 100:0, a suitable solvent and a suitable non-solvent of the copolymer comprising a.n aqueous solution of a salt, wherein the solvent and the non-solvent are present in a ratio of 500:1 and 0.5:1 by weight, the hydrogel having a microporous structure, an ionic capacity between 0 and 500 mEg of gel, a hydric content comprised between 50 and 980 and having an aptitude for permanent deformation under stress, even at a temperature below 40°C.
According t.o one variant of such hydrogel, the molar ratio of acrylo:nitrile to comonomer is between 95:5 and 99:1.
According t=o another variant of such hydrogel, the solvent is selected from the group consisting of aprotic 13409 ~3 polar organic solvents and inorganic solvents. Such solvents are known solvents of such copolymers, and are preferably water-miscible. More specifically, examples of such solvents inc:Lude N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), N-methylpyrrolidone (2NMP), and concentrated solutions of zinc chloride or of calcium chloride.
The hydroge~ls according to aspects of this invention have a residual content of solvent which is generally less than 1 o and pref=erabl~~r is less than 0 . 1 0 .
According t.o yet another variant of the invention, the non-solvent is selected from the group consisting of an aqueous solution of a suitable inorganic salt and an aqueous solution of a suitable organic salt. By a variation thereof, the non-solvent aqueous solution of a salt is at a concentration of between 0.5 and 5o by weight, so as to obtain in the composition, a salt concentration of between 0.03 and 1%, preferably between 0.05 and 1%.
Examples of suitable mineral and organic salts include sodium or potas:~ium chloride, sodium or potassium iodate, sodium or potassium bicarbonate, sodium or potassium chlorate, sodium or potassium periodate, sodium or potassium nitrate, sodium or potassium citrate, sodium or potassium tartrate, sodium or potassium ascorbate, sodium or potassium acetate, and sodium or potassium lactate. The preferred aqueous salt. solution is an aqueous solution of sodium chloride.

According to another preferred embodiment of the invention, the .anionic groups are selected from the group consisting of sulfonate, carboxyl, phosphate, phosphonate and sulfate groups.
5 The comonome:r is advantageously sodium methallylsulfonate.
Such hydrogels, of various aspects of the present invention, having a low electronegative charge, do not show interaction with the cells and hence have a distinctly improved tolerance.
Such solvents enable the production of hydrogels whose structure is particularly suitable for ophthalmological use and especially f:or keratophakia and epikeratophakia.
The introduction of the suitable aqueous salt solution as a non-solvent int=o the starting liquid composition enables the production of a hydrogel whose structure and properties are entirely adapted to articles for surgical or medical use.
By another aspect: of the present invention, a process is provided for the preparation of the uncrosslinked hydrogel the proces~> comprising the following steps:
lowering the temperature of a liquid starting composition comprising from 2 to 50% by weight of a copolymer of acrylonitrile and an olefinically-unsaturated comonomer bearing anionic group~~, which are either unsalified or are salified, in a molar ratio of acrylonitrile to comonomer of between 90:10 and 100:0, a suitable solvent and a suitable non-solvent for the copolymer, such suitable non-solvent being an aqueou:~ salt solution, wherein the solvent and the non-solvent are present in a ratio of between 500:1 and 0.5:1 by weight; immE=_rsing the product in the course of gelification in a fir~~t suitable bath to obtain a hydrogel;
and then immersing the hydrogel so obtained in at least one suitable second bath, for a sufficient time to enable the stabilization of= the lzydrogel.
According t:o one variant of the process aspect of the invention, the molar ratio of acrylonitrile to comonomer is between 95:5 and 99:1.
According t:o anot:her variant of the process according to this aspect of the invention, the solvent is selected from the group consisting of aprotic polar organic solvents and inorganic solvent;, as described above.
According to yet another variant of the process aspect of this invention, the non-solvent is selected from the group consistin<~ of an aqueous solution of an inorganic salt and an aqueous solution of an organic salt, as described above.
By one variation thereof, the non-solvent aqueous salt solution is at a concentration between 0.5 and 5% by weight so as to have, in the composition, a salt concentration between 0.03 anc. lo, preferably between 0.05 and lo/.
According to yet another variant of the process aspect of the invention, the first bath advantageously comprises at least water and/or an aqueous salt solution identical to, or different from, the non-solvent aqueous salt solution. The immersion in the first bath is preferably performed in two steps, the first step being an immersion in a cold water bath for a suitable time, the second step being an immers=Lon in a water bath at room temperature for a suitable time.
This immer;~ion in a cold water bath, in the course of the gelification, has the advantage of preventing the crumpling of the surface of the hydrogel during its formation, which would render the latter particularly useless in ophthalmology. In addition, the immersion of the gel in a water bath at room temperature, enables the substantially-complete removal of the solvent.
According to yet another variant of the process aspect of the invention, the: hydrogel is formed into a suitable article prior to the .Last step.
According to another variant of the process aspect of the invention, t:he se,~ond bath is selected from the group consisting of water and an aqueous salt solution at a temperature comb>rised between 0.5 and 5%, the aqueous salt solution being identical to, or different from, the non-solvent aqueous salt solution. By a variation of this variant, the immersion in the second bath is preferably performed at a temper=ature between room temperature and 70°C.
According to yet another variant of the process aspect of this invent=ion, the composition is prepared by dissolving the copolymer in the solvent and the non-solvent, at a solution temperature comprised between 40°
and 70°C, prior to the gelification step.

According t=o another variant of the process aspect of the invention, the temperature of cooling depends on the solvent and is advantageously between -20°C and +20°C.
The final step of the process of preparation of the hydrogel, namely the stabilization by immersion in a suitable solution (sa.lt or water), enables a dimensional stabilization o:= the hydrogel (accelerated contraction or shrinkage proce:~s) .
By another aspect of this invention, an article is provided for medical a.nd/or surgical use comprising a tube, a film, a filament, a joint, or an implant, the article being constituted at .Least in part by a hydrogel.
According ~~o anc>ther variant of this aspect of the invention, the article is in the form of an ocular implant.
Such ocular implants according to aspects of the invention find application as intraocular, epicorneal, and corneal implants, as well as in orbito-palpebral and lachrymal plastics.
According to a variant of this aspect of the invention, the shaped article may then be sterilized by any suitable means, e.g., by ultra-violet rays, or by ethylene oxide or by ionizing radiations.
By yet another aspect of the present invention, a process is provided for the manufacture of an article for medical and/or :~urgic.al use comprising a tube, a film, a filament, a joint, or an implant, the article of the desired shape arid size being formed at least in part from the hydrogel according to aspects and variants of this invention.
According t=o one variant of this process, the article is formed prior to the step of the process of preparing the hydrogel according to aspects and variants of the invention. According to another variant of this process, the hydrogel is heated to a temperature of between 50 and 90°C and is cast, in a suitable mold in two parts.
By another variant of this process, the article is formed by molding, the mold is being composed of two parts defining concave and convex surfaces of the article, and wherein the mold parts are composed of a synthetic plastics material which is compatible with the solvent. According to yet another variant of this process, the article is shaped by machining. By machining is meant, both mechanical machining and physical machining (U. V. laser).
By another aspect of this invention, a process is provided for the manufacture of an article for medical and/or surgical use comprising a tube, a film, a filament, a joint, or an implant, the article of the desired shape and size being formed of a hydrogel but being formed prior to, the process of preparing the hydrogel.
By a variant thereof, the hydrogel is prepared and shaped simultaneously in a suitable mold.
Among plastic materials which may be used in various aspects of this invention are polyoxymethylene, polyolefines, polyamides, silicones and polytetrafluoro-ethylene (PTFE).

Among the articles of variants of this invention, ocular implants are especially useful since they possess, besides the character of inertial with respect tc biological cell~~, the following optical properties : namely, 5 perfect transparency in visible light, absorption of ultra-violet rays at 280 nm, and refractive index close to that of the cornea.
They posse~~s the following physio-chemical properties, namely: high permeability to water, to physiological serum, 10 to small and medium-sized molecules, assuring the migration of nutrient substance~~ for the cornea as well as all of the metabolites; permeability to dissolved gases (O2, COZ), highly hydrophillic; a chemical nature devoid of toxic groups, of heavy metals, of remaining catalysts and of free monomers and of solvent; are easy to use; and dimensional stability, especially in a 0.9o chloride solution.
Particular biological properties provided include:
non-bioresorbabl.e in the physiological medium; good resistance to aging =Ln this medium, that is to say not showing opacif_~catio:n, coloration or degradation of physical properties; good tissue tolerance of the sites of implantations in the corneal stroma, without causing alteration of the epithelium and of the corneal endothelium; if possible, a low affinity for proteins; and can be steriliza.ble and/or re-sterilizable.
In the accompanying drawings, Figure 1 is a graph showing the absorption of light by the implant, wherein the ordinate axis represents the absorbence, and the abscissa axis represents the wavelength in nm;
Figure 2 is a graph showing the tensile strength, wherein the abscissa <~xis represents the o elongation and the ordinate axis represents the load in kg/cmz; and Figure 3 i:~ a graph showing o of cells detached as a function of time, in which the abscissa axis represents time in min and the ordinate axis represents the percentage of cells detached.
Besides thf=_ preceding embodiments and variants, the invention also includes other embodiments and variants, which will emerge from the description which follows, which refers to examples of practising the process of aspects of this invention and the processes for producing implants, as well as a descr__ption of experiments both in vitro and in vivo.
It must be understood, however, that these examples of practice, of production and of reports, are given purely by way of illustration of. the invention.
Example 1: Preparation of a hydrogel according to the invention containing 78% of water:
1. Starting liquid composition (D): 9.6 % of a 90:10 copolymer, of acrylon:itrile and sodium methallylsulfonate (dry extract), t36.6o of dimethylformamide (DMF), 3.8% of 0.9 % of NaCl, in water.
2. Preparation. of tree starting solution:
The copolymer is dissc>lved in the form of a dry extract in DMF at a temperature of 70°C, by means of a ministirrer, for a suitable length of time (5 minutes for 2 grams of solution, for example); then 0.9 % NaCl is introduced. It is homogenized by means of an ultrasonic sonotrode, for several seconds.

3. Casting:
The starting so7_ution, formed as specified at 2 is cast on a suitable support particularly a plate, at a temperature of 50°C.

4. Gelling:
The whole is cooled t.o a temperature of -15°C, and it is immediately dipped in a bath composed of 30 o CZHSOH, 0.5 0 NaCl, and 69.5 °-<s H20, at a temperature comprised between -10°C and -5°C for 5 minutes.
After dimensional stabilization, a hydrogel is obtained which contains ~Oo of H20.
Example 2: Preparation of a hydrogel according to the invention containing 800 of water:
1. Starting composition: 9% of 90:10 copolymer of acrylonitrile and of sodium methallylsulfonate (dry extract), 81 0 «f dim.ethylformamide (DMF), 10 % of 0.9 NaCl, in water.
2. Preparation. of the starting solution:
The procedure i:~ the same as that of Example 1, with the exception of the dissc>lving temperature which in this case is 40°C.
The procedure of: step 3 is identical with that of Example 1.
4. Gelling:

a) The whole i:~ cool,?d to a temperature below or equal to 4°C for 20 minul~es.
b) Immersion:
First step: the' whole is dipped in water at 0°C - 4°C for

5 minutes.
Second step: thf=_n the whole is dipped for some minutes in water at room temperature, then the membrane obtained is separated and irnmersed for some hours in the same water.
5. Stabilizat__on: The membrane is dipped for three hours in a 0.9 o NaCl solution.
Example 3: Hydrogel according to the invention containing 90 % of water:
1 . Starting composition: 5 0 of copolymer of acrylonitrile and sodium met~hallylsulfonate (dry extract), 80% of dimethylformamide (DMF) 15 % of 0.9 a NaCl, in water.

2. Prepartion of starting solution .
Procedure is the same as that of Example 1.
Steps 3, 4 amd 5 . the procedure is identical with that of Example 1.
Example 4 . HydrogE~l containing 86,6$ of water .
- Starting composition 9 ~ homopolymer (polyacrylonitrile) 81 , 1 ~ of DMI?
9,9 $ c>f 0,9 $ NaCl in water.
- The otrier steps are identical with those of example 1.
Example5 : Ocular implant .
The starting composition of Example 1 is cast directly on a suitable mold having the following characteristics .
The mo~_d used in the present embodiment is~ a combination of polyamide - silicone. The mold is composed of a 6.6 polyamide support containing the concave part: of unfilled silicone elastomer . The second part of the mold, convex, is a bead produced in elastomer-silicone of Shore A hardness 80, surface treated with an unfilled silicone, to improve the surface properties of said bead.
The concavity of the first portion of the mold was produced by the "spin-casting" method, by means of a rotating tray, ,specially designed and formed. The speed of rotation of the tray, variable and displayed, enables a desired height of a liquid meniscus to be obtained wit'~in a cylinder positioned on this plate.
Step 4 is identical with that of Example 1.
5. Stabilization . The formed article is dipped for 3 hours in a 0.9 ~ 'VaCl solution.

-,5- 1340913

6. Sterilization . Seven minutes by means of ultra-violet rays.
The implants must be checked both from the point of view of their optical qualities and their size and their tolerance both in in vitro and in vivo.
Example A . Macroscopic control of the intra-ocular implant .
After having been dipped in physiological serum, the implant is checked under a binocular lens (dimensions, relief, optical homogeneity) on a black background, in incident light. The thickness of the implant was measured by a microfeeler. The radii of curvature wE~re mE~asured by means of a microslide reader, modified, so as to enable placing under the objective lens of a cup containing the immersion liquid and the lens. The projection of the profile of the lens, focused on the median section, was traced and the rays measured with a compass.
The imp'Lants formed and tested had the following characteristics - diameter . b mm.
- central thickness of the order of 0.2 mm.
Example B . Phys:icochemical properties of the implant .
a) linear shrinkage The measuremE~nts were performed on specimens having as initial sizes . 75 x 25 x 0.8 mm.
The shrinkage of the hydrogel according to the invention, is distinctly greater in the presence of a saline solution (t).9 ~ VaC1), as shown by Table 1 below TABLE

INITIAL SHRINKAGE .

(o) COMPOSITION

in the mixture : ITi o IN o H O
Hz0 HZO SERUM z P/S/NS

5.3/83.5/11/2 3.9 94 27.6 86

7.0/82.5/10.5 5.2 91 27.6 82 9.0/81.0/10.0 6.6 88 24.3 81 11.0/80.0/9.0 7.9 86 21.7 80 13.0/79.0/8.0 9.2 85 18.4 79 19.0/75.0/6.0 1.5.7 78 17.0 72 rapid gelling 5.1/80.0/14.8 4.8 95 19.7 90 P . ;3 Solvent; NS:
Polymer; . non-solvent.

This phenomenon has its limits and the shrinkage is only manifested up tc> a certain concentration of solute.
For example, t:he gel dipped in 0.9o NaCl solution (physiological ~;erum) shows a shrinkage of 21.70. The same gel dipped in a 5o NaCl solution has almost the same shrinkage of 23°..
b) Water permeaioility, to physiological serum, to small and mediur~i molecules This is one of th~~ fundamental properties of materials for use in corneal refractive surgery and particularly for intracorneal implants. This permeability is an essential result for the maintenance of the corneal physiology on which the transparency of the cornea depends. Nutrient and metabolic flows, the transport of dissolved gases (oxygen and carbon dio~:ide), and water migration, must not be hindered by the presence of the lens.
The implants according to aspects of the present invention possess, through their particular structure, very 17 '13409 13 good permeability. The permeability to water, to physiological s~srum and to various dissolved substances, was measured by means of a test bench constituted by a tank provided with a stirrE~r. The membrane tested was placed in sealed manner in contact with a 6.6 polyamide support.
Hence it separates the tank into compartments: that of the solution, and that of the filtrate.
All the measurements were carried out on samples of hydrogel of copolymer, according to aspects of the invention, containing 800 of HZO, in the form of membranes of a thickness of 0.:35 - 0.40 mm and of 18 cm2 surface.
They were packaged in. physiological serum. The pressure gradient was maintained at 20 cm HZO.
The permeability to small and medium molecules was evaluated by the transmittance coefficient (K) expressing the ratio of th.e concentrations of the substance in the filtrate and in the solution for a stable flow rate and at room temperature.
C filtrate K -C solution Subs. C:onc.
FLOW RATE
TRANSMITTANCE
c~/1 10-5 ml . mn/cm' .
mmHg COEFFICIENT

water 4.5 -NaCl(serum) 0.09 3.5 -urea 0.7 4.0 1 creatinine 0.05 2.7 0.98 glucose 1.1 2.7 1 vitamin B12 2.10-2 3.2 1 albumine H 40.0 1.9-1.6 0.4 c) permeability to oxygen:
Tests were carried out on specimens of membrane of hydrogel:
- containing 80% of water (hydrogel according to the invention), - and 70% of water, having a thickness of 0.1!5 - 0.25 and 0.37 mm.
The permeability to oxygen was:
35 - 36.10 -" ml/cmz,icm.s.~:nm Hg, for 80% water hydrogel, whilst it is only 29.10-"/cm2/cm.:~.mm Hg, for a 70% ware hydrogel.
d) Refractive index:
It was measured by means of a refractometer known by the generic name ABBE (CARL ZE7CSS COMPANY, GERMANY) . The results are shown in Table 2 below and relate to membranes of hydrogel.
TABLE II
SPECIMEN REFRACTIVE INDEX
Hydrogel 85% HZO 1.347 Hydrogel 83% HZO 1.350 Hydrogel 78 % HZO 1. 368 e) absorption of light (visible light and ultra-violet light):
This measurement was carried our on specimens of the hydrogel according to the invention, containing 80% of water, by a spectrophotometric method.

Figure 1 shows the absorption of light by the implant.
The ordinate axis represents the absorbence:
A = - log (If/Ii), wherein If is the intensity of the light which has passed through and Ii is the intensity of the initial light.
The abscissae a:~is represents the wavelength in mm.
It is seen that there is total absorption of 280 nm whilst there is no absorption for visible light (400 - 700 nm).
f) Mechanical tests:
Figure 2 shows 'that in spite of a high water content, the tensile strength is i'airly high.
The abscissae axis represents the % elongation and the ordinates axis the load in kg/cm2.
Curve A corresponds to a hydrogel with 80% water.
Curve B corresponds to a hydrogel with 85% water.
Example C: "In 'vitro" evaluation of a hydrogel utilizable as an intra-corneal _Lmplant:
- Tissue used:
Chicken embryo c:ornea:l endothelium of 14 days incubation.
Materials:
Positive control (toxic): a filtering disk (known by the trade-mark MILLIPORE.~M AP2!5 1300) soaked in a phenol solution with 64 mg/1 in culture medium (pH 1/100);

Negative control (non toxic): Plastic treated for cell cultures (known by the trade-mark THERMANOSETM THX of Lux Corporation).
A hydrogel according to the invention (80% to 90% HZO) sterilized with W and tyndalised at the time of use (H1).
A membrane of 22 ~cm thick polyacrylonitrile for hemofiltration (known by t:he trade-mark HOSPALTM H2).
Culture Technique:
The culture medium 'was DMEM mixed V/V with gelose and supplemented with 10% of foetal calf serum. Whole corneal fragments were cultivated on the endothelial surface in contact with different materials a.nd controls.
Evaluation Criteria:
All the measurements were carried out on the same batch of 24 explants for each type of tissue and each material, after 7 days of culture. The fol_Lowing three properties were measured quantitatively: multiplication, migration and cellular adhesion by measurement of the surf<~ce area of migration of the cells and counting of cells of this migration web.
Cellular multiplication and migration:
The results are expre;ased by the cell density as a function of the migration surface area.
Cell Adhesion:
The technique of sensitivity of the cells to trypsin was used, which permitted calculation of the percentage of the cells detached as a function of time and the establishment of the corresponding curve.

- 20a -From the curve, a static <~dhesion index (SAI) was defined which is the product of the area (A) comprised between the curve and the x axis and the total number of cells. The results are expressed by the area of the curve a~ a f»nr-tine of t~ho caT

-zl- 1340913 Results and Interpretation The results are summarized in Table III below .
TABLE III - __ ._ __ _ NUMBER
OF CELL, 1 dC A SAI X 106 THX 81503000 4,91,8 18001000 4600600 0 .
.

PH1/100 8100!3!i00 2.60, 3000350 49001100 0. 410.

8 1 H1 16603:?45 6. 6~0, 2500118 25001315 0. 420.

H2 397007000 239 1730100 51701300 205_0.9 The toxic control (ph 1/100) occurs in the limiting area of the diagram of multiplication and of migration.
It show: a slight toxicity with respect to corneal endot.heliurn and permits very average cell attachment.
The non-toxic control permits very slight multiplication of the endothelial cells of the cornea which adhere t.o a very moderate degree to its surface.
H2 facilitates a high migration of the endothelium ar.~d consequently low adhesion.
H1 enables multiplication of the endothelial cells superio:c to that of the negative control and shows a distinctly superior cell attachment to that of all the other materials which is very well demonstrated by Figure 3 (X of cells detached as a function of time), in which the abscissas axis represents tj.me in min and the ordinates axis 22 1 3 4 0 9 ~ 3 represents the percentage of cells detached. In this figure, curve (1) corresponds to H2, curve (2) to the toxic control, curve (3) to the product according to the invention, curves (4) to the non-toxic control and curve (5) to PVC.
Example D: In yivo corneal tolerance test:
Implants of copolymers according to aspects of the invention, were implanted unilaterally in the corneae of six cats and nine monkeys.
These implantations permitted the evaluation of bio-compatibility of the _Lmplants and their transparency.
The operational technique calls upon either an intra stromal lamella:r dis:~ection, or, so far as possible, a lamellar dissection vaith a micro-keratome, known by the trade-mark BARRF,QUERTM
The BARRAQUERTM micro-keratome, to be realisable, necessitates the fixing of the eyeball by a pneumatic ring.
This dissection. has the advantage of sectioning, in totality, the Bowman membrane and of permitting the deformation of the front layers of the cornea on the implant.
1: Implantation in the cat:
Lamellar dissections were carried out with the manual disciser.
Operational Procedure:
General anaesthesia is performed by sub-cutaneous injection of ket:amine (30 mg/kg weight) and oxybuprocaine is instilled systematically into the eye.

A slightly arc-shaped incision with internal concavity is made at 0.25 mm depth and to 2 mm into the limb, over 8 mm length. Tlzis incision necessitates the use of a micrometric knife with a diamond blade. The lamellar dissection is continued with a dissector, known by the trade-mark BEAVERTM and with a dissector known by the PACIFIQUETM over 9 to 10 mm.
The intraocular implants were placed in position by means of a metal spatula. The sutures were done with 10/0 monofilament of polyarnide and left in place for 10 days.
After placing the implants in position, a collyrium containing dexarnethso:ne and neomycin was instilled daily into the operated eye for a month. The cats were examined daily throughout. the duration of the experiment.
Technical characteristics of the implants:
The water content: of the implants was 80% water; and the implants had a diameter of 5.5 to 6.3 mm, their thickness rangir..g from 0.20 to 0.2 mm.
The results observed in the cat were good tolerance of the keratoprothesis, without necrosis of the receptor cornea.
2. Implantation in the primate:
Operational procedure:
Nine female papio cynocephalus monkeys (baboons) were operated on..
In three cases, a, lamellar dissection as performed by a technique identical with that used in the cat; they were in fact small si:aed monkeys, not permitting the fixation of the eyeball by ~~ pneumatic ring. In the six other cases, lamellar dissection with the micro-keratome was possible.
Technical C:haraci=eristics of the Implants:
The water content of the implants was 60, 70 and 80%
water; the diameter of the implants range from 4.8 to 7 mm;
and the thickne:~s of t:he implants ranged from 0.16 to 0.27 mm.
Results:
The transparency of the cornea and the transparency of the implant werE~ remarkable .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Uncrosslinked hydrogel with a relatively high water content, prepared from a liquid starting composition which comprises: from 2 to 50% by weight of a copolymer of acrylonitrile and an olefinically-unsaturated comonomer bearing anionic groups, which are either unsalified or salified, in a molar ratio of acrylonitrile to comonomer of between 90:10 anal 100:0, a suitable solvent and a suitable non-solvent for said copolymer, said non-solvent comprising an aqueous solution of a salt, wherein said solvent and non-solvent are present in a ratio of between 500:1 and 0.5:1 by weight; said hydrogel having a microporous structure, an ionic capacity between 0 and 500 mEq/kg of gel, a hydric content between 50 and 90% and having an aptitude for permanent deformation under stress, even at a temperature below 40°C'.

2. Hydrogel according to claim 1, wherein the molar ratio of acrylonitrile to comonomer is between 95:5 and 99:1.

3. Hydrogel according to claim 1, wherein said solvent is selected from the group consisting of aprotic polar organic solvents and inorganic solvents.

4. Hydrogel according to claim 1, wherein said non-solvent is selected from the group consisting of an aqueous solution of a suitable inorganic salt and an aqueous solution of a suitable organic salt.

5. Hydrogel according to claim 4, wherein said non-solvent aqueous salt solution is at a concentration of between 0.5 and 5% by weight, so as to obtain, in said composition, a salt concentration of between 0.03 and 1% by weight.

6. Hydrogel according to claim 5, wherein said salt concentration is between 0.05 and 1% by weight.

7. Hydrogel according to claim 4, wherein said non-solvent is an aqueous sodium chloride solution.

8. Hydrogel according to claim 1, wherein said anionic groups are selected from the group consisting of sulfonate, carboxyl, phosphate, phosphonate and sulfate groups.

9. Process for the preparation of an uncrosslinked hydrogel according to claim 1, said process comprising:
a) lowering the temperature of a liquid starting composition comprising 2 to 50% by weight of a copolymer of acrylonitrile and an olefinically-unsaturated comonomer bearing anionic groups, which are either unsalified or salified, in a molar ratio of acrylonitrile to comonomer of between 90:10 anal 100:0, a suitable solvent and a suitable non-solvent for said copolymer, said suitable non-solvent comprising an aqueous solution of a salt, wherein said solvent and said non-solvent are present in a ratio between 500:1 and 0.:5 by weight;
b) immersing said product in the course of gelification in a suitable first bath, thereby to obtain a hydrogel;

and c) immersing said hydrogel so-obtained in at least one suitable second bath, for a sufficient time to permit the stabilization of said hydrogel.

10. Process according to claim 9, wherein the molar ratio of acrylonitrile to comonomer is between 95:5 and 99:1.

11. Process according to claim 9, wherein said solvent is selected from the group consisting of aprotic polar organic solvents and inorganic solvents.

12. Process according to claim 9, wherein said non-solvent is selected from the group consisting of an aqueous inorganic salt solution and an aqueous organic salt solution.

13. Process according to claim 12, wherein said non-solvent aqueous salt solution is at a concentration of between 0.5 and 5% by weight, so as to have, in said composition, a salt concentration between 0.03 and 1%.

14. The process of claim 13 wherein said salt concentration is between 0.5 and 10.

15. Process according to claim 9, wherein said bath of step (b) comprises at least one of water and an aqueous salt solution which is identical to, or different from, said non-solvent aqueous salt solution.

16. Process according to claim 15, wherein the immersion of step (b) is performed in two stages, the first stage being an immersion in cold water bath for a suitable time, and the second stage being an immersion in a water bath at room temperature for a suitable time.

17. Process according to claim 9 wherein, prior to step (c), said hydrogel is formed into a shaped article.

18. Process according to claim 9 wherein the bath of step (c) is at least. one of water and an aqueous salt solution at a concentration of between 0.5 and 5%, which is identical to, or different from, said non-solvent aqueous salt solution.

19. Process according to claim 18, wherein the immersion of step (c) is performed at a temperature between room temperature and 70°C.

20 Process according to claim 9, wherein, prior to the gelification step, said composition is prepared by dissolving said copolymer in said solvent and said non-solvent, at dissolution temperature of between 40°C and 70°C.

21. Process according to claim 9, wherein the cooling temperature depends on.the solvent and is between -20°C and 20°C.

22. Article for medical and/or surgical use comprising a tube, a film, a filament, a joint, or an implant, said article being constituted at least in part by a hydrogel according to claim 1.

23. Article according to claim 22, which is in the form of an ocular implant.

24. Article according to claim 22, which can be sterilized by a suitable means.

25. Article according to claim 22, which can be sterilized by ultra-violet rays, or by ethylene oxide, or by ionizing radiations.

26. Process for the manufacture of an article for medical and/or surgical use comprising a tube, a film, a filament, a joint, or an implant, said article of the desired shape and size being formed at least in part from the hydrogel according to claim 1.

27. Process according to claim 26, wherein said article is formed by molding, said mold is being composed of two parts defining concave and convex surfaces of said article, and wherein said mold parts are composed of a synthetic plastics material which is compatible with the solvent.

28. Process for the manufacture of an article for medical and/or surgical use comprising a tube, a film, a filament, a joint, or an implant, said article of the desired shape anal size, and wherein said article is formed subsequent to step (c) of the process for preparing said hydrogel according to claim 9.

29. Process according to claim 28, wherein said hydrogel is heated to a temperature of between 50 and 90°C
and is cast in a suitable mold in two parts.

30. Process according to claim 28, wherein said article is shaped by machining.

31. Process for the manufacture of an article for medical and/or surgical use comprising a tube, a film, a filament, a joint, or an implant, said article of the desired shape and size being formed of a hydrogel but being formed prior to step (c) of the process of preparing the hydrogel according to claim 9.

32. Process according to claim 31, wherein said hydrogel is prepared and shaped simultaneously in a suitable mold.