Study On Anti-fouling Modification Of Polyvinyl Alcohol Surface By Heparin And Its Properties

Biomedical materials are manufactured or processed materials used in medical devices or in prostheses,including synthetic polymers,metals,ceramics,inorganics,and natural macromolecules(biopolymers),etc.These materials are mainly in contact with cells,proteins,tissues,organs and organ systems.Proteins and cells would adhere to the surface of implanted biomaterials such as artificial cornea and artificial blood vessel,which will reduce the service life of the material.Therefore,it is of great significance to improve the anti-bioadhesive properties of the material.PVA hydrogel is a good biomedical material which has good biocompatibility,mechanical properties,hydrophilic properties and optical properties.In our previous study,we found cell adhesion and growth on PVA hydrogel surface when it was used as the optical center of the artificial corneal,which would affect the optical properties of the artificial corneal and increase the failure rate of implantation.In this study,we will modify PVA hydrogel by conventional chemical methods,with heparin sodium to improve its anti-adhesion ability and enhance its application performance.In this thesis,three different methods were used to graft heparin sodium onto the surface of PVA hydrogel.The physical/chemical properties and biological properties of modified materials were tested.The main results were described as follows:1.The active amino groups were introduced by the reaction between the hydroxyl groups formed by hydrolysis condensation of kh550 in the system of ethanol/water and the hydroxyl groups on the surface of PVA hydrogel,then the heparin was chemically grafted to the surface of PVA hydrogel through an amidation reaction.The optimal hydrolysis conditions of kh550were discussed by on-line test conductivity method.The effects of different concentrations of heparin sodium on the visible light transmittance of PVA hydrogels were determined and then the optimum modification concentration of heparin sodium was determined.The surface composition of the material was characterized by ATR-FTIR and XPS.The thermal stability,visible light transmittance,hydrophilicity,mechanical properties,moisture content and swelling properties of the modified and unmodified materials were also investigated.Toluidine blue method was used to determine the amount of fixed heparin sodium.The BCA method was used to determine the anti-protein adhesion ability of the samples,and the cck-8method was used to investigate the cytotoxicity and anti-cell adhesion of the materials.The results showed that the visible light transmittance of the PVA hydrogel modified by heparin sodium was nearly the same as that of the blank PVA hydrogel,the moisture content was about 75%,the contact angle of the material decreased from 38°to 33°,the swelling ratio of about 3.5,the tensile strength of about 2.5 MPa,the amount of fixed heparin grafted on the surface of PVA hydrogel was 0.6007μg/cm~2,the anti-protein adhesion ability increased by42.37%,the material cytotoxicity was 0,anti-cell adhesion of the PVA hydrogel was improved.2.The activated carboxyl groups were introduced through the acylation reaction between succinic anhydride and the hydroxyl groups on the surface of PVA.The heparin was chemically grafted to the surface of the PVA through the esterification reaction.The optimal conditions for the acylation reaction between succinic anhydride and hydroxyl groups on the surface of PVA were studied.The optimal conditions were as follows:the reaction temperature was 40℃and the reaction time was 3 h.Under these conditions,the best modification concentration of heparin sodium was 0.6 mg/mL determined by visible light transmittance and hydrophilicity.The surface composition of PVA-COOH-Hep hydrogel was characterized by ATR-FTIR and XPS.At the same time,the changes of thermal stability,mechanical properties,visible light transmittance,moisture content,swelling balance and the amount of fixed heparin of were discussed.The results showed that the tensile strength of PVA-COOH-Hep hydrogel was 1.75 MPa,the visible light transmittance was about 85%,the moisture content was 75%and the swelling ratio at swelling equilibrium was about 3.5.The amount of fixed heparin grafted on the surface of PVA hydrogel was 1.7141μg/cm~2.The anti-protein adhesion of the material was increased by 64.66%,the anti-cell adhesion ability was significantly improved,and the cytotoxicity of the material was 0.3.The active bromine groups were introduced through the acylation reaction between2-bromoisobutyryl bromide(BIBB)and the hydroxyl groups on the surface of PVA.The alkylation reaction occured through the secondary amino groups on the heparin sodium and the bromine groups on the surface of the PVA-Br hydrogel,then the heparin was chemically grafted to the surface of the PVA hydrogel.The optimum conditions for the acylation reaction were determined by surface elemental content,hydrophilicity and ATR-FTIR.The optimum reaction conditions were as follows:the optimum concentration of BIBB was 0.067 m L/m L and the reaction time was 12 h.Under these conditions,the concentration of heparin sodium was fixed at 0.01 mg/mL,and the heparin was chemically grafted to the surface of the PVA hydrogel.The properties of modified and unmodified hydrogel such as water content,swelling ratio,hydrophilicity,visible light transmittance,mechanical properties,thermal stability and the amount of fixed heparin were characterized respectively.The results showed that the water content the modified PVA-Br-Hep hydrogel was 70%,the swelling ratio at swelling equilibrium was 3.5,the watert contact angle was 58°,the visible light transmittance was more than 90%and the tensile strength was 2.0 MPa,the amount of fixed heparin on the surface of PVA hydrogel was 0.8506μg/cm~2.Compared with the blank PVA hydrogel,the anti-adhesion property of PVA-Br-Hep hydrogel was improved by 33.89%,the anti-cell adhesion ability was significantly improved,and the cytotoxicity grade was 0.Heparin sodium was grafted to the surface of PVA hydrogel through three different ways.All the modified materials had good biocompatibility and anti-cell adhesion ability.The grafted kh550 on the surface of PVA hydrogel will hydrolyze into the solution slowly,which would indirectly reduce the grafting rate of heparin.The color of the PVA hydrogel in the acylation reaction was difficult to control,so the experimental reproducibility was poor.The acylation reaction between succinic anhydride and PVA hydrogel showed good reproducibility and the highest heparin grafting rate.