CA1209413A

CA1209413A - Articles exhibiting a biocompatible surface layer and process articles with such a surface layer

Info

Publication number: CA1209413A
Application number: CA000428106A
Authority: CA
Inventors: Bo H. Nygren; Johan E. Stenberg
Original assignee: Astra Meditec AB
Current assignee: Astra Meditec AB
Priority date: 1982-05-14
Filing date: 1983-05-13
Publication date: 1986-08-12
Also published as: ES522361A0; ES8405624A1; US4588624A; EP0094924A3; US4673584A; FI842403A0; JPH0361B2; DK5684A; FI79027C; FI842403A; EP0094924A2; WO1983003977A1; DK5684D0; DE3370138D1; DK153922B; AU554156B2; EP0123678B1; IE831118L; EP0123678A1; FI79027B

Abstract

ABSTRACT OF THE DISCLOSURE

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 polysaccha-ride containing at least one hydroxyl group. The inven-tion also relates to an article exhibiting a biocompat-ible surface layer of a polysaccharide containing at least one hydroxyl group, which polysaccharide is co-valently bound to a surface of glass, silicon, aluminium or silicone rubber of the article by means of a silane.

Description

M 72~-1 ~ 4 ~ ~

ARTICLES EXHIBITING A BIOCOMPATIBLE SURFACE
LAYER AND PROCESS FOR PROVIDING ARTICL~S WITH
SUCH A SURFACE LAYE~

The present invention relates to articles exhibiting a biocompatible sur~ace layer and a process for proviaing articles with such a surface layer. More particularly, the invention relates to articles e~hibitin~ at least one surface of glass, silicon, aluminium or silicone rubber coated with a biocompatible surface layer and a process for providing articles exhibitin~ at least one surface of glass, silicon, aluminium or silicone rubber with a biocompatible surface layer~
The ob~ect 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 ener~y of the material.
An improvement in the properties of various materials has been obtained by modifyin~ the surface layers either to a moxe hydrophobic character or to a more hydrophilic charaeter. Hydrophobization of the surface layer, for instance by the methylization of a ~lass surface, results in a deerease in the effeetiveness of the surfaee aetivat-ed coagulation system of the blood. However, proteinssuch as fibrinogen are bound comparatively firmly to such surfaces and to this protein layer certain eells, the thrombocytes, can be bound and activated whereafter - . - -coagulation is started even though it proceeds slowly.Hydrophilic sur~aces, e.g. hydrolysed nylon or oxidized aluminium, have presented reduced binding of cells but the surface activated coagulation system is not prevent-ed at these surfaces. The use of these surfaces incontact 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-lants into the surface layer. Heparin has primarilybeen used with this technique. Heparin is a hexoseamine-hexuronic acid polysaccharide which is sulphatized and has acid properties, i.e. heparin is an organic acid.
According to DE-A~21 54 542 articles of an organic 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 proved to reduce the coagulation reaction. A consider-able disadvantage of these surfaces, howe~er, is that the heparin treatment does not prevent the adherence of thEombacytes, which is a great probl~m in, for instance, heart-lung machines.
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. ~nn. New York Acad. Sci., ~ol.
233 (1977) 372). These properties are considered to be due to the fact that gels containing water give a low surface ener~y 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, which results in leakage of toxic monomers A gel-like mixture of saccharose and glycose included in a matrix ~l2U~ 3 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 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 water-bindinq gels with the low toxicity of polysaccha-rides at the same time as it affords technique for the surface treatment of material irnportant for medical technology, such as glass, silicon, aluminium and silicon rubber. (The term "glass" as used here and in 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 surface layer consis-ts of a polysaccharide containing at least one hydroxyl group, which polysaccharide is covalently bound to said surface of glass, silicon, aluminium-o~r siliconr~ r~bber of the article by means of a silane.
The process according to the in~ention Eor 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 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 (~Si(OCH313) or a chlorosilane (R-$iCl3~, in which formulas R-represents an epoxy group CH2-CH` which is coupled to o . 4~3 the silicone atom via a h~drocarbon chain (in most cases propyl).
The hydrolysed silane forms an active silane (R--Si(OH)3), which 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 reaction between the inorganic substance of the surface layer and the silanol is prior art tech-nique (Dow Corning Product Bulletin 23-181 C 1980) and this reaction proceeds in the following way:
/ -OH / -OH
/ -OH + (OH)3Si-R--~ / -OSi(OH)2-R + H20 / -OH / -OH
whereafter the silanol is polymerized laterally -OSiOH-R
/ O
-O-i-R
O
/ I
-OSi-R
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 + CH2-CH-CH2~ P--O--CH2-CH(OH)--CH2--Optimum conditions for this reaction has been investigated previously (vide Sundberg and Porath, J. Chromatogr.90 (1974) 87).
According to one aspect of the invention the poly-saccharide P may be neutral. According to another aspect of -the invention the polysaccharide can be a polysaccharide occurring in nature, such as dextran r or a synthetic polysaccharide pre- -pared, for instance, by polymerization of mono- or disaccharides by means of chemical reactants such as epichlorohydrin.
The dextran can be ethyl-, hydroxye-thyl- or 2-h~dro-xypropylether of dextran or dextran glycerol glycoside or hydro-dextran (i.e. dextran, the reducing end groups of which are reduced to alcohol groups) or hydroxyl group containing hydro-philic derivatives of dexkran or partially degraded dextran.
After the binding to the surface layer the polysac-charide can be polymerized further so that a thicker layer is obtained. This polymerization has been described in Swedish Patent No. 169,293, granted August 27, 1959 to AB Pharmacia (invenkors - B.G.~. Ingelman and P.G,M. Flodin).
The treated surface proves biologically inert and surfaces treated in this way give reduced absorption of proteins, adherence of cells and coagulation. The process according to the present invention can be 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 subsequent-ly treated according to the process 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 that case the silicone rubber must first be made reactive by oxidizing a thin surface layer. This is effecked ~2~ 3 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-ing the surface proves hydrophilic and reactive againstsilanes and it can be treated by means of the process according to the invention.
The invention may also be applied in other connect-ions, for instance for the treatment of articles of alu-minium, glass or silicone rubber for sampling and/orstorage 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 within the limits of the claims.
Example 1 a2 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 for manual dishwashing and was subsequently rinsed thorou~hly with running distilled water. I'he piece was then etc~ed in,an oxy~en plasma, 300 millibar 2' 100 W, for 3 minutes and then immediately immers~d in water.
b) The piece of silicone rubber was picked up from the water and the surfaces thereof were blown so that visible water disappeared whereafter it was imme-diately immersed in a 5% (w/V2 solution of 3-qlycidoxy-propyl trimethoxysilane (Epoxysilane~ in propanol for 10 minutes. The piece of silicone rubber was completely covered by the solution.
Then the piece was dried in an oven at 60C to apparent dryness, washed in distilled water and blown dry. The surface was now hydrophobic.
c~ The piece treated according to b2 was immersed into a 20% ~w~y2 solution of dextran ha~ing an average ~l2~ 3 _~ 7 molecular weight (M ) 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 a~ A cover glass was treated with dichromate-sulphuric acid and thoroughly rinsed with running di-stilled water.
b) The cover glass treated according to a) was reacted with 3-glycidoxypropyl trimethoxysilane according to Examp~e 1 b) above.
c) The cover glass treated according to b) was immersed into a 40~ (w/v) solution of dextran having an average molecular weight (Mw~ of 200,000 in distill-ed water and was allowed to react for 20 h at room 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 centimetres and a thickness of about 1 millimetre was treated with a 10~ (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) was reacted with 3-glycidoxypropyl trimethoxysilane using the procedure described in E~ample ~ 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 (Mw) of 200,000 in distilled 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 ~ut a 20~ (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 dextxan-coated cover glasses were wetted and preincubated in a humidified chamber at 37C
followed by the experimental incubation with blood.
~Q Incubation ~as performed for 10 min at 37C 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 5-10 sec with a flow of 1.5-2 lit~min.
Fixation was performed in 0O~5M cacodylate buffer pH 7.4 , w,ith 3% glutaraldehyde for 2 h, followed by dehydration in ethanQl and dryin~ in air or in a critical point dr;er. Spe~imen-were coa,ted with gold an~ m;ned in a JEOL 100 cx 5canning Electron microscope at an accelerat-ing voltage of 20k~.
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 ~x~m;ned in the scanning electron micro-scope,,the interface between untreated ~lass a'na the throm,,bus was found to consist of fibrin-anchored erythro-~A, ~2~4:~3 cytes and platelets. Hydrophobic, methylized glass onthe 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 lnduce 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.

Claims

C L A I M S

1. Article exhibiting at least one surface 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 siilane 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.