Surface Modification Of Biodegradable Biomaterials And Biocompatibility Studies For Biomedical Applications

The surface modification of biodegradable biomaterials are among the most focal studiesin biomaterials field. Magnesium and its alloys have excellent biocompatiblity and similarmechnical properties to bone. Moreover,magnesium-based materials have a broad clinicalapplication prospect in the field of medical implant materials making use of its corrodibility.The reduction in their rapid corrosion rates becomes the key to implant material forload-bearing. Poly-（lactic acid）（PLA）,commonly have been used as the biodegradablemedical material, have excellent biocompatibility, nontoxicity and their biocompatibledegradation products. Therefore, PLA has gained the approval of US Food and DrugAdministration （FDA） for clinical application. However,because of its bad surfacehydrophilicity and acid degradation productions, its application as biomaterials was limited.In this paper,MgO coating、 MgO/HA coating and MgO/HA/PLA coating wererespectively prepared on the surfaces of AZ31Mg-based materials in order to better controlthe degradation of the alloy and further improve its biocompatibility.The coatingmorphology、thickness、phase composition and elemental composition were charaterized bySEM、XRD and EDS.The corrosion resistance of the different coating was evaluated byimmersion in simulation body fluid （SBF），Their biocompatibility was also investigated byhuman osteoblast cell experiments.the optimal protective coating for AZ31Mg alloy wasselected. Results show that The corrosion resistance properties of AZ31Mg alloy in SBF canbe remarkably improved by the coatings of MgO/HA/PLA at the preliminary stage of soaking.cell experiments proved that the coated Mg alloy show better cell response than the naked Mgalloy due to the fact that the cells on the surface of the coated Mg alloy have been spread andconnected with each other.MgO/HA/PLA coating is more suitable as protective coatingmaterial for AZ31Mg alloy.The hydroxyapatite （HA） coating formation on the PLA was carried out by an improvedbiomimetic mineralization. Firstly，maino groups were covalently introduced onto PLAsurface by the aminolyzing reaction between ethylenediamine and the ester gorups of PLA.Secondly，mineralization of n-HA was achieved by subjecting the membrane in a series ofcalcium and phosphate treatments, deemed as the an alternate soaking process（ASP）. Finally， SEM and AFM images of the surface modified PLA films display very high levels of surfaceroughness.Contact angle measurement indicates that it is sharp changes in topology that havethe most effect on contact angles.After further immobilization of HA on the aminolyzedsubstrata，the biocompatibility is improved greatly regardless of the bulk attributes by themeasurements of human osteoblast cell culture.In addition，a brushite （DCPD，CaHPO₄·2H2O）coating was prepared on the surface ofAZ31magnesium alloy by electrodeposition method. then，uniform Ag nanoparticles coatingswas prepared via electroless metallization method. The coating morphology、thickness、phasecomposition and elemental composition were charaterized by SEM、XRD and EDS. Theresults of the hydrogen evolution tests indicated a better protection effect of DCPD coating onthe corrosion of AZ31in SBF. osteoblast The cell culture results demonstrateted that DCPDcoating is beneficial to the proliferation of osteoblasts,which also has the betterbiocompatibility to osteoblasts than that of Mg alloy. Ag-bearing DCPD coating havedemonstrated a significant inhibitory effect to the adhesion of Staphylococcus aureus andEscherichia coli, without showing significant cytotoxicity to human osteoblast cells.