Development and Characterization of Zinc-Doped Hydroxyapatite Coating on Pure Magnesium for Improvement in Biocorrosion and Cytocompatibility

Abstract

As a biodegradable implant magnesium faces an obstacle that is the corrosion rate too fast As a result magnesium implant disintegrates earlier than wound healing of the tissue around implantation site high corrosion product altered osseointegration which lost its restoration function especially in orthopedic application before the tissue completely healing and get the tissue’s original function restored and high concentration of magnesium ions released from the implant inhibited the crystalline bone growth around the implant However offers some advantages that are not available from other metals such as light in weight resemble to natural bone and Young’s modulus closer to natural bone reducing the stress shielding Hydroxyapatite which mimics the composition of the natural bone can be fabricated by chemical formula Zinc as a trace element in human bone reported plays role in biological function that induce osteoblast growth during wound healing in the bone formation process This study is to investigate the corrosion and compatibility of pure magnesium coated with zinc-doped hydroxyapatite In this experimentthe pure magnesium specimens were either inflat surface or sandblast surface Then both types of specimens were applied surface conversion coating using hydrofluoric acid)as treated specimens) and then coated with zinc (5 wt%)-doped calcium phosphate and pure calcium phosphate prepared based on sol-gel method All specimens were analyzed using electrochemical tests immersion tests and cytotoxicity assay Calcium phosphate was transformed to hydroxyapatite started from 400oC of calcination and the crystallinity of hydroxyapatite was higher in 500oC Zinc-doped calcium phosphate could successfully disappeared degradable tricalcium phosphate phase producing zinc substitute hydroxyapatite (Ca10Zn0 12 (PO4)6(O0 24(OH)1 76) phase calcium zinc phosphate phase and also fluoroapatite formation during calcination by diffusion from interface layer (MgF2) The hydrofluoric acid treated specimen groups improved the corrosion rate of magnesium compared to untreated groups which treated groups preferred pitting corrosion attack while untreated groups occurred corrosion on the whole surface Meanwhile zinc-doped calcium phosphate showed better performance as a coating layer on magnesium compared with pure calcium phosphate coating Zinc caused loss agglomeration of calcium phosphate powder and was able to coat on magnesium specimen denser than pure calcium phosphate coating Therefore magnesium substrates coated with zinc-doped calcium phosphate resulted in increasing corrosion protection according electrochemical and immersion tests Moreover the cytocompatibility tests viability and hemolysis assay showed that surface conversion the zinc-doped and pure calcium phosphate coating on substrate increased cell viability of MG63 cells and reduced hemolysis in rabbit blood In conclusion fluoride conversion and zinc (5 wt%) -doped calcium phosphate on both pure magnesium and alumina sandblast magnesium can improve their corrosion properties and enhance cytocompatibility especially for zinc-doped hydroxyapatite

Date of Award	2014 Jul 26
Original language	English
Supervisor	Ming-Long Yeh (Supervisor)