COATING PROCESS

Abstract: A process for the coating of an intraocular lens to impart tissue compatibility thereto, comprising the steps: a) priming said lens using a solution of a polyamine; b) coating the lens treated in step a) above with a solution of a periodate-oxidized polysaccharide selected from heparin, heparan sulphate, and chondroitin sulphate to stabilize said polyamine by covalent and/or ionical cross-linking; c) coating the lens treated in step b) above with a solution of a polyamine; and d) coating the lens treated according to step c) above with a solution of a periodate-oxidized polysaccharide selected from heparin, heparan sulphate, and chondroitin sulphate in the presence of a cyanoborohydride to convert formed labile Schiff's bases to stable secondary amines.

Description: COATING PROCESS The present invention relates to a process for the coating of intraocular lenses for the purpose of impar¬ ting tissue compatibility to said lenses. Background of the invention Any surface of a r-αn-biological origin initiates a sequence of unwanted reactions when brought into contact with living tissue or blood. The most well known reac¬ tions are those generated by the blood-contacting mate- rials that activate the platelets and the plasma coagu¬ lation system leading to the formation of a thrombus. Foreign surfaces in living tissue activate the complement and the mononuclear cellsystems, thereby creating inflam¬ matory reactions. Although the present invention is based en the use of polysaccharides selected from heparin, heparan sul¬ phate and chondroitin sulphate for the purpose of provi¬ ding stable, biocompatible coatings on intraocular eye lenses, the following discussion and disclosure will be mainly directed to heparin or heparan sulphate. However, it is important to note that the invention is not re¬ stricted to these two polysaccharides. Immobilisation of the blood-anticoagulant, heparin, to artificial, blood-contacting materials has proven to be a successful approach for achieving a thromboresistant surface suitable for short term use (days and weeks) . In this procedure, the structure characteristics of the endothelial lining of the vascular wall are mimiced by end-point attachment of heparin to the surface. The surface, prepared by end-point attachment of heparin to a polyamine has the following properties: 1) it is nonthrombogenic, 2) it does not activate the com¬ plement system, 3) it dees not activate the mononuclear cell system, 4) it adheres and stabilizes growth factors and 5) in general it adheres cells to a much lower extent than other surfaces. Examples on other products where biocompatible coa¬ tings are desired are eye lenses, breast implants, vas- cular grafts, hip joints etc. The surface in question is excellent also for blood contacting materials. There are several publications that have described the antiproliferative effect of heparin and heparan sul¬ phate on a number of different cells (smooth muscle cells, epithelial cells) . In other publications the growth factor stabilizing and activating effect of hepa¬ rin has been described. It is now generally agreed that low molecular weight heparin (less than about 2500 D) inhibits cell growth, whereas high molecular weight heparin (higher than about 6000 D) stimulates cell growth. Summary of the invention The main object of the present invention is to pro- vide a new process for the coating of intraocular lenses to impart tissue compatibility to such lenses. Another object of the invention is to provide a pro¬ cess for forming a stable coating on intraocular lenses. A further object of the invention is to provide a process for the attachment of biologically active poly¬ saccharides to the surface of intraocular lenses in such a manner as to inhibit substantial cell growth. For these and other purposes that will be clear from the following disclosure the invention provides for a process for the coating of an intraocular lens for the purpose of imparting tissue compatibility thereto. Said process involves the following steps: a) priming said lens using a solution of a poly¬ amine; b) coating the lens treated in step a) above with a solution of a periodate-oxidized polysaccharide selected from heparin, heparan sulphate, and chondroitin sulphate to stabilize said polyamine by covalent and/or ionical crosslinking; c) coating the le s treated in step b) above with a solution of a polyamine; and d) coating the lens treated according to step c) above with a solution of a periodate-oxidized polysaccha¬ ride selected from heparin, heparan sulphate, and chon¬ droitin sulphate in the presence of a cyanoborohydride to convert formed labile Schiff's bases to stable secondary amines. In the instant disclosure the expression "polyamine" is intended to cover any polyamines, including amine- containing polysaccharides, such as chitosan. Chitosan is a linear, 1,4-linked polysaccharide composed of β-D- glucoseamine units of which some are N-acetylated. Chitosan is made by N-ceacetylation of chitin, a polymer present in the shell of inter alia insects and crayfish. The degree of N-deacetylation can be controlled by hydrolysis with the use of alkali. In the present case chitosan is used in the form of commercially available hydrochloride salts having a degree of deacetylation of from about 20 to about 85%. The preferred periodate-oxidized polysaccharide is heparin or heparan sulphate, said polysaccharides being proteoglycans. Preferred polyamines are polyethyleneimines or chi¬ tosan of varying degrees of N-deacetylation. Said poly¬ amine is suitably present in an aqueous solution in a concentration of from about 0.01 to about 0.1% by weight. The periodate-oxidized polysaccharide is preferably present in an aqueous solution, for example in a concen¬ tration of about 0.01 to about 0.1% by weight, it being preferred that the pH of said solution is from about 3 to about 5. The cyanoborohydride used in combination with the periodate-oxidized polysaccharide is preferably an alka- limetal cyanoborohydride, such as sodium cyanoborohyd¬ ride. Step d) of the process defined above is preferably performed at an increased temperature, such as from about room temperature up to boiling, preferably from about 40°C to about 75°C, such as from about 50°C to about 70°C. In the process defined above it is preferred that step b) is repeated between steps c) and d) , and step a) is suitably repeated after step b) thus repeated. In the process according to the present invention the solution used in step a) above may also contain cro- tonaldehyde at a basic pH, such as between about 8 to about 10. Said pH can be maintained using a buffer or a base, such as borate buffer or an alkali metalhydroxide, for example sodiumhydroxide. According to a preferred embodiment of the process of the present invention the coating of an intraocular lens involves the following steps: a) priming said lens using a solution of a polyamine and croton aldehyde; b) coating the lens treated according to step a) above with periodate-oxidized heparin or heparan sulphate to stabilize said polyamine; c) repeating step a) above on the lens treated according to step b) above; d) repeating step b) above on the lens treated in accordance with step c) above; e) treating the lens resulting from step d) above using a solution of a polyamine; and f) coating the lens treated in accordance with step e) above with a solution of periodate-oxidized heparin or heparan sulphate in the presence of a cyanoborohydride to convert formed labile Schiff ' s bases to stable secondary amines. In order to facilitate priming of the intraocular lens it is preferred to etch the lens before starting the priming thereof, such etching suitably being performed with an oxidizing agent, for example ammoniumperoxidi- sulphate in aqueous solution, or any other oxidizing agent suitable for the intended purpose. Since the sur¬ face of intraocular lenses to be treated in accordance with the present invention usually are of a hydrophobic nature, such etching step in advance of the priming pro¬ cedure is preferred to improve adherence of the priming agent to the surface of the lens. Specific embodiments of the process To improve the understanding of the present inven¬ tion it will now be further illustrated below by non- limiting examples, wherein percentages are by weight unless otherwise defined. Preparation of solutions EXAMPLE 1 Preparation of polymine solution 500 mL of borate buffer in aqueous solution, pH 9.0, are prepared by dissolving boric acid, sodiumhydroxide pellets and sodiumchloride in water. To said buffer solu¬ tion there is added 0.5 mL of polymine, 5% in water, and 170 μL of crotonaldehyde. The solution thus prepared is designated Ll. EXAMPLE 2 An aqueous polymine solution is prepared by adding 5 L of a 5% polymine solution to 500 mL of distilled water. The pH of the resulting solution is adjusted to 9.0 using 0.5 M sodiumhydroxide. The solution thus pre¬ pared is designated L3. EXAMPLE 3 A solution of sodiumperiodate-oxidized sodiumheparin is prepared in the following manner. 1.0 g of sodiu periodate, NalO^j, is dissolved in 200 mL of distilled water. 10 g of sodiumheparin is added to the solution of sodiumperiodate and is set aside over night in the dark with stirring. The resulting solution, after adding 10 mL of glycerol thereto and stirring for 2 h, is dialyzed against water, the water being exchanged every other hour. This reults in a solution containing periodate-oxidized heparin in a concentration of about 19 mg/mL. This solution is designated L2. EXAMPLE 4 To 500 mL of distilled water there is added 4.4 g sodiumchloride and 7 mL of solution L2 prepared in Example 3. The pH of the solution is adjusted to 3.9 using 0.5 M hydrochloric acid. The resulting solution is designated L4:l. EXAMPLE 5 To 500 mL distilled water there is added 4.4 g sodiumchloride, 7 L of solution L2 from Example 3, and the pH of the solution is adjusted to 3.9 using 0.5 M hydrochloric acid. The temperature of the solution is then raised to 55°C and 15 mg sodiumcyanoborohydride is added thereto. The resulting solution is designated L :2. Coating of intraocular lenses The intraocular lenses used in the following examp¬ les are based on polymethylmethacrylate (PMMA), but the invention is equally applicable to other materials, such as polysiloxane, for example poly (dimethylsiloxane) (PDMS), poly (dimethyldiphenylsiloxane) (PDMDPS) , or hydro- philic acrylics, such as polyhydroxiethylmethacrylate. Another type of useful material is constituted by hydro¬ phobic acrylics with a low glass transition temperature, such as a mixture of acrylate and methacrylate. An examp¬ le of such material is copolymers of ethylphenylacrylates and ethylphenylmethacrylate. Such polymers have a glass transition temperature at about room temperature. EXAMPLE 6 Using the solutions prepared in Examples 1-5 intra¬ ocular lenses based on polymethylmethacrylate are treated in the following manner. Initially, the lenses are etched using a 5% ammonium peroxidisulphate aqueous solution at 60°C for 30 minutes. After rinsing with distilled water the etched lenses are then treated by immersion in solution Ll from Example 1 for 10 minutes at room temperature to provide priming of the lens. After rinsing with distilled water the lens is then immersed in solution L4 : 1 of Example 4 for 10 mi- nutes at room temperature, and after rinsing with dis¬ tilled water treatment of the lens with solution Ll from Example 1 is repeated in the same manner as above. Again, after rinsing the lens with distilled water it is finally treated by immersion into solution L4 : 2 from Example 5, said solution being heated to a temperature of 55°C and the lens is kept in the solution for 2 h. After a final rinsing of the lens with distilled water it is now provi¬ ded with a stable coating imparting tissue compatibility of the lens, and by multipoint attachment of the heparin molecules to the surface of the lens, cell growth is in¬ hibited corresponding to the use of a low molecular weight heparin having a molecular weight of less than about 2500 D. EXAMPLE 7 Example 6 is repeated but in this case the steps of treatment for 10 minutes at room temperature with solu¬ tion L4 : 1 and then a treatment for 10 minutes at room temperature using solution L3 are introduced. The lens is then treated with solution L : 2 and the procedure is concluded as in Example 6. After every treatment step the lens is rinsed with distilled water. EXAMPLE 8 Example 6 is repeated but using instead of solutions Ll and L3 as per Example 6, an alternative solution L5 containing chitosan as a primer. Said solution L5 is pre¬ pared in the following manner. An aqueous solution of the hydrochlcride salt of chitosan is prepared by dissolving chitosan having a de¬ gree of N-deacetylation of about 85% in water to a con- centration of 0.25% w/v, the solution being adjusted to pH 5.0 using hydrochloric acid. The presence of amino groups on the intraocular lens primed with solution L5 is verified with an indicator (ponceau S, Sigma) . Using a chitosan solution for priming of the lens results in similar advantageous properties of the coated lens as those obtained in Example 6. EXA.MPLE 9 Example 7 is repeated but using solution L5 of Example 8 instead of solutions Ll and L3 used in Example 6. Similar results are obtained.

Claims: CLAIMS 1. A process for the coating of an intraocular lens to impart tissue compatibility thereto, comprising the steps: a) priming said lens using a solution of a poly¬ amine; b) coating the lens treated in step a) above with a solution of a periodate-oxidized polysaccharide selected from heparin, heparan sulphate, and chondroitin sulphate to stabilize said polyamine by covalent and/or ionical crosslinking; c) coating the lens treated in step b) above with a solution of a polyamine; and d) coating the lens treated according to step c) above with a solution of a periodate-oxidized polysaccha¬ ride selected from heparin, heparan sulphate, and chon¬ droitin sulphate in the presence of a cyanoborohydride to convert formed labile Schiff's bases to stable secondary amines. 2. A process according to claim 1, wherein said polyamine is a polyethyleneimine or chitosan. 3. A process according to claim 1 or 2, wherein said polyamine is present in an aqueous solution in a concen¬ tration of from about 0.01 to about 0.1% by weight. 4. A process according to any preceding claim, wherein said periodate oxidized polysaccharide is present in an aqueous solution in a concentration of about 0.01 to about 0.1% by weight, the pH of said solution being from about 3 to about 5. 5. A process according to any preceding claim, wherein said cyanoborohydride is sodium cyanoborohydride. 6. A process according to any preceding claim, wherein step d) above is performed at an increased tempe¬ rature, from about room temperature up to boiling, pre- ferably from about 40°C to about 75°C. 7. A process according to any preceding claim, wherein step b) is repeated between steps c) and d) . 8. A process according to claim 7, wherein step a) is repeated after repeated step b) . 9. A process according to any preceding claim, wherein the solution used in step a) also contains croton aldehyde at a basic pH, such as between about 8 and about 10. 10. A process according to claim 9, wherein the pH is maintained using a buffer or a base. 11. A process for the coating of an intraocular lens to impart tissue compatibility to said lens, comprising the steps: a) priming said lens using a solution of a polyamine and croton aldehyde; b) coating the lens treated according to step a) above with periodate-oxidized heparin or heparan sulphate to stabilize said polyamine; c) repeating step a) above on the lens treated according to step b) above; d) repeating step b) above on the lens treated in accordance with step c) above; e) treating the lens resulting from step d) above using a solution of a polyamine; and f) coating the lens treated in accordance -with step e) above with a solution of periodate-oxidized heparin or heparan sulphate in the presence of a cyanoborohydride to convert formed labile Schiff ' s bases to stable secondary amines. 12. A process according to any preceding claim, wherein said intraocular lens, before priming in step a) , is etched, such as with an oxidizing agent, for example ammonium peroxidisulphate in aqueous solution

Inventors: GOUDA IBRAHIM, LARM OLLE, GOUDA, IBRAHIM, LARM, OLLE
Applicants: GOUDA IBRAHIM, LARM OLLE, MEDICARB AB, GOUDA, IBRAHIM, LARM, OLLE
Application year: 1995
Main classification: A61L27
IPC codes: A61L27, A61L33