Study On The Bioactive Coating Of Zirconia Ceramics And The Enhancement Of PVA Materials

Zirconia ceramic and poly?vinyl alcohol?materials have a great potential in knee repairmen.They can be used in knee replacement and cartilage restoration respectively.However,as bio-inert ceramic,zirconia has little bioactivity and it is usually fixed through mechanical method or by bone cement.PVA hydrogel also suffers from the same problem,since it only shows biocompatibility,and has no bioactivity.What's more,PVA hydrogel prepared via physical crosslinking?freeze-thawing procedure?is also faced with the problems of relatively low mechanical strength and the solubility in water.The work of this paper consists of two parts.The first part is the preparation of bioactive coating on the zirconia ceramics used in knee replacement.The ?-Ca₂SiO₄??-C2S?coating was simply produced by slurry method,which gave the zirconia substrate bioactivity,and enable it to bond with the host bone through the hydroxyapatite layer formed by the mineralization of ?-C2 S.To eliminate defects such as bending and exfoliation of the coating,the presintering process was adopted.Different presintering temperatures were tested,and the corresponding results were analyzed.It was found that,when the zirconia was presintered at 1150?,the shrinkage of the substrate decreased to 14.7%,which was close to 12.6% of the ?-C2 S.Therefore,a shrinkage-matched coating could be obtained.The in vitro test showed that the coating had a great bioactivity after the cosintering,and it could converted into HAp when it was soaked in the 0.25 M K2HPO4 solution for 1 day.The second part of this paper is the reinforcement and bioactivation of PVA hydrogel.In this section,we combined the physical crosslinking?freeze-thawing?with the chemical crosslinking?boric acid?to prepare PVA hydrogel with higher mechanical strength.Moreover,the graphene oxide?GO?sheets,which had remarkable strength and bioactivity as well as high specific surface area,were added into the hydrogel matrix to further improve the strength and bioactivity.The XRD,FT-IR,TG,DSC and compression test were applied to study the effect of the GO on the composition,morphology,thermal stability and mechanical properties of the PVA hydrogel.At last,we added the ?-C2 S to the PVA hydrogel to improve the bioactivity.The work disclosed that both boric acid and GO had a great influence on the thermal properties: with the increase of boric acid or GO,the thermal stability increased,but the melting temperature decreased.The compression test showed that the PVA hydrogel with boric acid or GO exhibited improvement in the early stage,but when the strain increased to certain extent,the strength reduced.As for the bioactivity,it was found that when ?-C2 S powders were employed,the composite showed excellent bioactivity in the mineralization test.The XRD and FT-IR results identified the existence of HAp after the composite was soaked in the 0.25 M K2HPO4 solution for 3 day.To further investigate the influence of the boric acid and GO on the mechanical property of PVA materials,and to eliminate the interference of the freeze-thawing process,we prepared PVA films through aqueous solution method and the analysis of structure,morphology as well as mechanical property was also conducted.At the end of this part,the boric acid combined with GO was applied to the PVA film,the enhancement of which was studied.A competitive phenomenon that the addition of boric acid would influence the reinforcement effect of GO sheets was found,since both the boric acid and GO shared a similar reinforcement mechanism,i.e.through the combination with the –OH on the PVA chain to increase the links between different PVA molecules.