Electrochemical Construction Of Ordered Nano HA Coating And In Situ EIS Study On Titanium/Cell Interface

The surface modification for bioproperties and biological response of titaniumare among the most focal studies in biomaterials field.The emphases of this thesisresearch are put on some scientific and technical key problems,such as the novelcoating techniques of hydroxyapatite (HA),the control of composition and structureof HA coating,the mechanism and main influence factors of HA coating formationand the interaction of biomaterials and cells in biological environment.The aims ofthis work are to develop novel HA electrochemical deposition methods,from theaspect of bionics,to construct ordered nano structrured HA coating and its hybridcoating with both excellent biological and good mechanical properties on titaniumsubstrate,to further study the mechanism of HA formation on the Ti surface and todevelop electrochemical impedance spectroscopy (EIS) to in situ elucidate theinterfacial structure and the interactions of biomaterials and cells.The main work includes:a) construction of nano HA coating byelectrochemical deposition technique in low concentration system,b) design andcontrol of structure and composition of HA coating for fabrication of bionic artificialbone coating,c) systematical investigation of the effects of main depositionparameters on coating properties,d) further understanding of the mechanism ofelectrochemical deposition of calcium phosphates on Ti in low concentration system,and e) establishment of an in situ electrochemical cell for studying the interaction oftitanium/MG63 cell by EIS measurement.The following conclusions can be drawn:1.A pure HA coating with high crystallinity has been prepared byelectrochemical deposition method in low concentration system.The HAcoating exhibits three kinds of typical topographies,i.e.flower type,standing-up type and porous type topographies.The nano-micro structuredordered pure HA coating has been firstly constructed on titanium substrate.Preliminary in vitro test indicates that the HA coating with such specialnano-micro two level structure is of more excellent bioactivity comparedwith other kinds of HA coatings.2.The HA/Collagen hybrid coating with nano-micro ordered structure has beenfabricated as well by using electrochemical co-deposition method.The FTIR spectra demonstrates the existence of collagen in the composite coating,andthe SEM and XRD results shows that the crystal size of HA in the compositecoating is significantly decreased with the addition of collagen component,and the structure of the composite coating is more mimetic to the naturalbone when compared with the pure HA coating.3.The effect of the main preparing parameters on the HA electrochemicaldeposition in low concentration system has been systematically investigated.It is indicated that in a very wide range of preparing parameter,highlycrystallized and pure HA coating can be obtained,while the distribution ofthe crystal size,the arrangement of the crystal grains and the depositionvelocity of the HA coating are intimately related to the depositionparameters.4.The chemical composition and structure of the electrochemically depositedcalcium phosphate coating are determined by both thermodynamic andkinetic conditions.The nucleation process is mainly influenced by thethermodynamic factors,such asΔG,and the growth behavior is mainlycontrolled by the dynamic environments.The thermodynamic analysisdemonstrates that both the lower concentration of calcium and phosphorusspecies and the higher temperature in the system facilitate the pure HAformation,comparing with the traditional high concentration system.According to kinetic calculation,the apparent activity energy of the HAformation in a specific low concentration system is estimated to be 174.9kJ·mol¹.An electrochemical deposition model of HA coating in lowconcentration system has been proposed to further clarify the behaviors ofthe HA coating formation.5.An in situ electrochemical cell has been designed for the ac impedancemeasurements at biomaterial/cell interface.A home-made Ag/AgCl electrodeis introduced to the in situ cell as a reference electrode to eliminate thedistortion phenomena during the ac impedance measurement in highfrequency range.6.It is demonstrated,from the EIS analysis of titanium/cell interface,that theadhesion of cells onto the biomaterial surface may alter the surface states andstructure of double layer at the interface.The ac impedance information in the higher frequency range is mainly from the cell adsortion process ontitanium surface,which is helpful to understand the interaction betweenbiomaterials and living cells.