The Exploration Of The Mechanism Of The Electrodeposition Of Chitosan, Hydroxyapatite And The Binary Mixture

The surface morphologies of bone implant materials composed of mainlyhydroxyapatite (HA) and chitosan (CS) affect the cell adhesion and growth，and the newtissue formation and replacement.Electrodepositon techniques, which are adopted to build functional surfaces ofbiomaterials constituted of biological macromolecules and mineral membranes, arereceiving a great deal of attention. In this paper, highly oriented pyrolytic graphite withan atomically smooth surface was employed as the cathode substrate in theelectrophoretic deposition of CS, eliminating the side effect of the traditional metalliccathode to the revealing of the deposition characteristics of CS itself. SEM, TEM, AFMand XRD were applied to characterize and analyze the deposited CS coating surface.The results showed that, owing to the electric field force, the crystalline peak of its (110)plane was promoted and the orientation arrangement of the CS micro-structure existedin three levels, including the parallel arrangement of nano-scaled CS molecularaggregates in thin layers, the parallel arrangement of CS long strips with a bridge-likedstructure joined each other in micron-level composed of those aggregates, and theflower-liked CS in micron-level when the deposit was relatively thick. It has been thefirst time to explore the parallel arrangement of CS molecular aggregates in the initialstage of electrophoretic deposition and to analyze the growth mode and the surfacefeatures of the flower-liked structure.In order to explore the mechanism of the electrochemical deposition of HA, highlyoriented pyrolytic graphite, which possesses a nano-scaled smooth surface, was alsoused as the cathode substrate in the electrochemical deposition. TEM, SEM, AFM and EDS were applied to characterize the coating composition and topography to study theinfluences of deposition time, appliede voltage, applied current and the solution pH onthe HA coating. EDS shows the coating is made up with Ca-deficient HA. Moreover,with the increase of the deposition and aging time, the HA coating is more inclined togrow perpendicularly on the substrate with a higher calcium-phosphorus ratio. Thisresearch will provide necessary theoretical and experimental support for theelectrochemical deposition of HA.To explore the mechanism of the co-deposition of the binary mixture, HOPG isalso employed as the cathode plate. The mixed solution, composed of calciumphosphate solution and little amount of PC solution added by CS, is used as theelectrolyte to explore the characteristics of the co-electro-deposition such as thedeposition patterns, and the interrelationship of CS and HA, which are highlyinfluenced by the deposition time, applied voltage and the applied current. SEM, TEM,AFM and EDS are used to analyze the surface morphology of the deposited substrate.The results showed that, due to the co-electro-deposition, the two main componentscould affect each other during the deposition, which can be reflected by thedisappearance of the rod-liked CS, leaving the little spherical CS and the flake-liked HA.The existence of CS contributed to the reduced sorts of the flake-liked HA and theincreased Ca/P ratio, and the existence of HA lead to the vanish of the rod-liked CS.Electro-deposition time, applied voltage and applied current have a similar positiveimpact for the growth of the flake-liked HA pile structure interspersed by litter sphericalCS.