ARTICLES EXHIBITING A BIOCOMPATIBLE SURFACE LAYER AND PROCESS FOR PROVIDING ARTICLES WITH SUCH A SURFACE LAYER

Abstract: A process for providing a surface of glass, silicon, aluminium or silicone rubber of an article useful within medicine with a biocompatible surface layer. Said surface is reacted (after oxidation when required) with a silane containing at least one epoxy group and the surface thus treated is then reacted with a polysaccharide containing at least one hydroxyl group. The invention also relates to an article exhibiting a biocompatible surface layer of a polysaccharide containing at least one hydroxyl group, which polysaccharide is covalently bound to a surface of glass, silicon, aluminium or silicone rubber of the article by means of a silane.

Description: ARTICLES EXHIBITING A BIOCOMPATIBLE SURFACE LAYER AND PROCESS FOR PROVIDING ARTICLES WITH SUCH A SURFACE LAYER : .- : The present -invention relates to articles exhibiting a biocompatible surface -layer and a * process for providing articles with such a surface layer. More particularly, the invention relates to articles exhibiting at least one surface of glass, silicon, aluminium or silicone rubber coated with a biocompatible surface layer and a process for providing articles exhibiting at least ' one surface of glass, silicon, aluminium or silicone rubber with a biocompatible surface layer. The object of the present invention is to provide articles. useful within medicine with a biocompatible surface layer. This means, for instance for articles intended for use in contact with blood, that the article which is alien to the blood is treated in such a way that it does not induce coagulation or formation of thromboses. Prior art technique to provide articles useful in medicine with a biocompatible surface layer often compris¬ es an alteration in the surface energy of the material. An improvement in the properties of various materials has been obtained by modifying the surface layers either to a more hydrophobic character or to a more hydrophilic character. Hydrophobization of the surface layer, for instance by the methylization of a glass surface, results in a decrease in the effectiveness of the surface activat- ed coagulation system of the blood. However, proteins such as fibrinogen are bound comparatively firmly to such surfaces and to this protein layer certain cells, the thrombocytes, can be bound and activated whereafter coagulation is started even though it proceeds 'slowly. Hydrophilic surfaces, e.g. hydrolysed nylon or oxidized aluminium, have presented reduced binding of cells but the surface activated .coagulation system s not prevent- 5 ed at these surfaces.. The use of these surfaces in contact with blood thus implies the addition of anti¬ coagulants, for instance heparin, to the blood. -Another prior art surface treatment technique for ..preventing coagulation comprises binding of anticoagu- -10...lants " -into the..sur ace layer. Heparin has primarily been used with this technique. Heparin is a hexoseamine- hexuronic acid polysaccharide which is sulphatize -and ha-s acid properties, i.e. heparin is an organic acid. According to DE-A-21 54 542 articles of an organic 15 thermoplastic resin is first impregnated with an amino- silane coupling agent and the article thus treated is then reacted with an acid solution of a heparin salt to the binding of heparin in the surface layer by means of ionic bonds. Surfaces thus treated with heparin have 20 proved to reduce the coagulation reaction. A consider¬ able disadvantage of these surfaces, however, is that - the.heparin treatment does not prevent the adherence - : -. .. .of.ifchrombocytes, which, is a great problem in, for • - - -instance, heart-lung machines. 25 It is also known that water—binding gels, for instance polyhydroxyalkyl methacrylate, reduce the adsorption of proteins and present a low adhesiveness to cells (Hoffman et al. Ann. New York Acad ' . Sci., Vol. 283 (1977) 372). These properties are considered to be 30 due to the fact that gels containing water give a low surface energy in the interface to the blood. The prior art technique for manufacturing of water-binding gels, however, is impaired by disadvantages such as complicat¬ ed preparation technique and incomplete polymerisation, 35 which results in leakage of to_xic monomers. A gel-like mixture of saccharose and glycose included in" a matrix iREACT O Pl of the polysaccharide dextran or dextrin is used in accordance with previously known technique as a tube .....- for-.the connection of blood-vessels. -This mixture should have the effect that no toxicity to the patient •5 occurs and.that the implantate is dissolved in the blood after some time. . It is known that the neutral polysaccharide dextran is miscible with blood without provoking any coagulation reaction. -•The-.present -.invention combines the property of 10 water-binding -gels .w th the low- toxicity of polysaccha- rides at the same 'time -as it af ords technique for the surface treatment of material important for medical technology, such as glass, silicon, aluminium and silicon rubber. (The term "glass" as used here and in 15 the claims is intended to include also quartz.) The article according to the invention which ex¬ hibits at least one surface of glass, silicon, aluminium or silicone rubber coated with a biocompatible surface layer, is characterized in that the biocompatible 20 surface layer consists of a polysaccharide. containing :... at least one hydroxyl group, which polysaccharide is • ;-._.. ' .-covalently bound to.said surface of- glass, silicon, .. ._,.. . aluminiu -;o.r silicone rubber of the- article by means of a silane. 25 The process according to the invention for provid- . ing articles exhibiting at least one surface of glass, silicon, aluminium or silicone rubber with a bio¬ compatible surface layer is characterized in that said surface of the article, after oxidation thereof when 30 required, is reacted with a silane containing at least one epoxy group and that the surface thus treated is reacted with a polysaccharide containing at least one hydroxyl group. The silane can be an alkoxy silane (R-Si (OCH. _} 35 or a chlorosilane (R-SiCl_) , in which formulas R- represents an epoxy group which is coupled to lΥE yt OMP- . ∞ the silicone atom via a hydrocarbon chain (in most cases propyl) . The hydrolysed silane forms an active silane i (R-Si . (OH) 3 )-,-. hich.reacts with -inorganic -compounds, which exhibit.hydroxyl ..groups at their-surface. • - " Examp¬ les of such materials, are glass, silicon, " oxidized alu¬ minium and oxidized silicone rubber, which materials after hydration obtain hydroxyl groups in the surface layer. The reaqtion .between the inorganic substance of_the. ' .surface .layer and the silanol- s-prior- rt tech- .nique ..(Dow .Corning- : P.roduct Bulletin ' 23-181 ' C 1980) and this reaction proceeds in the following way: whereafter the silanol is polymerized laterally The final -result is a surface which is coated with • the functional group of the silanol. The polysaccharide can then in a second step be coupled to the " surface. In the following example the reaction between the poly- . saccharide P and a silanised surface is described, the functional group of R being an epoxy group as stated above. The polysaccharide P is bound to the epoxy group via the hydroxyl groups of the polysaccharide according to the reaction •- * ■ ~ P-OH + P-0-CH 2 -CH (OH)-CH 2 -- ^ Optimum conditions for this reaction has been investigat¬ ed previously (vide Sundberg and Porath, J. Chromatogr. 90 (1974) 87). •According to one ι aspect of the invention the poly- 5 saccharide P may be.neutral. According to another aspect of the invention the -polysaccharide can be a polysaccha¬ ride occurring in nature, s.uch as dextran, or a synthetic • po.lysaccharid'e .prepared,: .for instance by polymerization . - of mono- or disaccharides -by means of chemical reactants 10 such as epichlorohydrin. -- -..-.. . The dextran can .be ethyl-, hydroxyethyl- or 2- hydroxypropylether of dextran or dextran glycerol glycoside or hydrodextran (i.e. dextran, the reducing end groups of which are reduced to alcohol groups1 or 15 hydroxyl group-containing hydrophilic derivatives of dextran or partially degraded dextran. After the binding to the surface layer the poly¬ saccharide can be polymerized further so that a thicker * layer is obtained. This polymerization has been 20 described in SE-A-169.293. . The treated surface..proves biologically inert and - • surfaces treated .in this . ay give reduced absorption of ; ' proteins-,;._adherence.of cells and " coagulation. The ■ - • process .. ccording, to-, the present invention can be 25. applied within many different fields. Thus in heart- lung machines there are used many details which are made of aluminium. The surfaces coming into contact with blood are easily oxidized to aluminium oxide in order to be subsequently treated according to the process 30 according to the invention. This process can be applied to other mechanical details which are intended to be in contact with blood, e.g. in apparatuses for dialysis. Catheters of silicone rubber can also be treated by means of the process according to the invention. In 5 that case the silicone rubber must first be made react¬ ive by oxidizing a thin surface layer. This is effected by means of an etching process which implies that the surface layer is oxidized in an oxygen plasma at a low pressure.. This process does not result in any impair- ;.- . ment--of the properties of. ; the material. After the etch- : * 5 - ng the. surface proves hydrophilic and reactive against silanes and it can be treated by means of the process according to the invention. . •.: v.. The.invention may. also be applied in ' other connect- - ions,.:fo instance. or th -treatment of " articles of alu- - 10 .minium,.- glass..or silicone ' rubber .for sampling and/or storage of blood. - "- " ~ • - * - ' - The . invention will-in the following be illustrated by a number of working Examples but is not limited there- • to and hence modifications are of course conceivable 15 within the limits of the claims. Example 1 . a) A piece of silicone rubber having the size 4x4 centimetres and a thickness of 2 millimetres was treated ' with a 10% (v/v) solution of conventional detergents _ 20 for manual dishwashing and was subsequently rinsed -. ' ;thoroughly .with running-..distilled water. ' -The piece was . . then .etched :in - ; an oxygen plasma ' / ' 300 millibar 0 2 , 300 W, ;- ...for._3 minutes ;and then ..immediately -immersed in water. bl The piece of silicone rubber was picked up 25 from the water and the surfaces thereof were blown so that visible water disappeared whereafter it was imme¬ diately immersed in a 5% (w/v) solution of 3-σlycidoxy- propyl tri ethoxysilane (Epoxysilane) in propanol for 10 minutes. The piece of silicone rubber was completely 30 covered by the solution. Then the piece was dried in an oven at 60°C to apparent dryness, washed in distilled water and blown dry. The surface was how hydrophobic. ...cl -The piece .treated according to bl was immersed 35 into a -20%..(w/v). -solution of dextran having an average . O PI _ molecular weight ( w ) of 2,000,000 in distilled water and was allowed to react for 20 h at room temperature. The surface was now hydrophilic. Example 2 .5 * • .a) . A cove.r-glass was treated with dichromate- *.. : sulphuric acid .and thoroughly rinsed with running di¬ stilled water. . :. ■ ■ .! -■ :. - zz .-.b). -;-The .cover- glass treated according to a) was • • reacted,-.-with-'-.3_-glycidoxypropyl trimethoxysilane ' ■ ' ' . ' 10 according to Example 1 b)- above. ~ ) . The .cover glass treated according to b) was immersed into a 40% (w/v) solution of dextran having .an average molecular weight (M l of 200,000 in distill- ed water and was allowed to react for 20 h at room 15 temperature. The obtained surface was hydrophilic. The thickness of the applied layer was 4 nanometres • as determined by ellipsometry. Example 3 .a.) -A piece, of aluminium having the size 2x4 20 centimetres .and.. -thickness of about → millimetre was * . treated with ^ a..1.0%. (v/vl;.solution of conventional deter- - • .- gents -for manual -dishwashing and was subsequently rinsed with distilled water over night. b) The piece of aluminium treated according to a) 25 was reacted .with..3-glycidoxypropyl trimethoxysilane using the procedure described in Example 1 b) above. * c) The piece of aluminium treated according to b) was immersed into a 20% (w/v) solution of dextran having an average molecular weight (M w) of 200,000 in distilled 30 water and was allowed to react for 20 h at room tempera¬ ture. The obtained surface was hydrophilic. Example A Biocompatibility test Cover glasses treated analogously to Example 2 but a 201 (w/v) solution of a dextran having an- average molecular weight (M ) ^ of 2,000,000 was used in step c) were used as an article according to the invention in this experiment. The thickness of the dextran layer was 5 nanometres. The dextran-coated cover glasses were wetted and preincubated in a humidified chamber at 37 C followed by the experimental incubation with blood. Incubation was performed for 10 min at 37 C with, un-- treated rat blood obtained by cutting off ether anesthes- ized rats. Untreated cover glasses and methylized glass¬ es (Elwing, H. and Stenberg, M; J. Immunol. Meth. 44 (1981) 343-345) were used as positive controls of clot formation and platelet adhesion. After incubation, the clots were cut in two halves with a razor blade. One half was gently removed and the glasses were rinsed in phosphate-buffered saline (0.05M phosphate buffer pH 7.4) for 5-1Q sec with a flow of 1.5-2 lit/ in. Fixation was performed in 0.15M cacodylate buffer pH 7.4 with 3% glu araldehyde for 2 h, followed by dehydration in ethanol and. drying in air or in a critical point drier. Specimen were coated with gold and examined in a JEOL 100 ex Scanning Electron microscope at an accelerat- ing voltage of 20kV. Results At the end of incubation time, the blood samples had clotted against untreated glass and against methyl¬ ized glass. Blood incubated on dextran-coated glass according to the invention showed clumps of clots where¬ as the bulk stayed fluid. The clumps did not adhere to the surface, and seemed to be induced in the blood/air interface. When examined in the scanning electron micro¬ scope, the interface between untreated glass and the thrombus was found to consist of fibrin-anchored erythro- OMPI cytes and platelets. Hydrophobic, methylized glass on the other hand, induced an initial layer of adhering, activated platelets onto which other blood cells adhered. Fibrin threads were sparcely found close to the surface, but could be seen within the thrombus. Dextran-coated glass surfaces according to the invention ' failed to induce thrombus formation. When examined in the SEM, more than 90% of the surface area was free of cells and fibrin. Scattered solitary erythrocytes and -platelets could be seen. The round appearance of the platelets on the dextran-coated surface was in sharp contrast to the more extended and flat shape of the platelets seen on the hydrophobic surface, indicating that the round cells were adhering to but not activated by the dextran- coated surface. O PI

Claims: C L A I S 1. Article exhibiting at least one surf ce of glass, silicon, aluminium or silicone rubber coated with a biocompatible surface layer, characterized in that the biocompatible surface layer consists -of a polysaccha- ride containing at least one hydroxyl group, which poly¬ saccharide is covalently bound to said surface of glass, silicon, aluminium or silicone rubber of the/article by means ' of a silane. 2. Article according to claim 1, characterized in that it is a catheter or a device for sampling and/or storage of blood. 3. Article according to claim 1, characterized in that it is a heart-lung machine, in which machine aluminium surfaces of the machine coming into contact with blood are coated with the biocompatible surface layer. 4. Process for providing articles exhibiting at least one surface of glass, silicon, aluminium or silicone rubber with a biocompatible surface layer, characterized in that said surface of. the article, after oxidation thereof when required, is reacted with a silane containing at least one epoxy group and that the surface thus treated is reacted with a polysaccha¬ ride containing at least one hydroxyl group. 5. A process according to claim 4, characteriz¬ ed in that a neutral polysaccharide is used as said saccharide. 6. A process according to claim 5, characteriz¬ ed in that dextran is used as said neutral polysaccha- ride.

Inventors: NYGREN BO HAOKAN, STENBERG JOHAN EMANUEL, NYGREN, BO, HAOKAN, STENBERG, JOHAN, EMANUEL
Applicants: ASTRA MEDITEC AB
Application year: 1983
Main classification: A61M25
IPC codes: A61L26, A61L29, A61L33, A61M1, C03C17, C08J7