Titanium Surface Electrochemical Deposition Of Nano-hydroxyapatite Coating

This article made a systematic research on the HAp coatings deposited on titanium surface with electrochemical method. By controlling different experimental parameters, the nanometer HAp coatings of different crystal morphologies were successfully prepared on the titanium surface. The structure, the micro-morphology, ingredients and orientation of the HAp crystals were characterized with the analytic testing methods such as XRD, SEM, TEM and FTIR. Furthermore, the growing rules of the HAp nano-rod were obtained through observing the growing process of the nano HAp crystals by means of SEM. Using HRTEM, the lattice of nano ribbon-like HAp crystal was observed. The mechanism of nano ribbon-like and rod-like HAp crystals' formation was studied, which provided the theoretical basis and technical support for the clinic application.Homogeneous coatings were attained by electrochemical method in electrolytes containing Ca²⁺ and PO₄^3- ions with Ca/P ratio being 1.67. SEM observation showed that the HAp crystals prepared with higher concentration electrolyte (4x10^-2M Ca²⁺) are ribbon-like with thickness of nanometer size, a morphology seldom reported previously. In an electrolyte of lower concentration (6x10^-4M Ca²⁺), the HAp crystals formed are rod-like with a hexagonal cross section and diameter of about 70-80nm. XRD patterns and IR spectra confirmed that the coatings consist of HAp crystals. TEM micrograph s and SAD indicated that the longitude direction for both ribbon-like and rod-like crystal is <002>, and the flat surface of the ribbon is (110). HRTEM showed that the ribbon-like crystal is a mixture of HAp and OCP.A series of hydroxyapatite coatings under different deposition durations (2, 5, 10, 30 and 60 min) were prepared and characterized to investigate the coating's growth behavior. Following laws of coating growth were observed: (1) Preferential growth with the c-axis of the HAp crystal perpendicular to working surface is detected in the XRD measurements with the peak of (002) crystal face being greatly intensified; (2) After formation of the interior needle-like crystal, several tiny HAp platelets could beadsorbed on its surface and result in forming a piece of crystal layer out of the interior one. According to this kind of growth mode, the innermost HAp crystal will be enwrapped by several crystal layers so as to form the final morphology of the HAp crystal. (3) With subsequent growth, the HAp crystals lose their needle-like character and become more rod-shaped. The final morphology of HAp is a rod-like crystal with a regular hexagonal cross section, of which the diameter is about 80nm of the inner layer and 110nm of the outer layer.Besides, the experiment also researched on the influences of different ions (cation: Na+, anion: Cl^-, CH₃COOH, C₃H₅O₃^-) on the morphology of HAp crystals. SEM observation shows that when NH₄H₂PO₄ was substituted by NaH₂PO₄, it didn't have great influence on the ribbon-like HAp while was obviously influential to the morphology of the rod-like HAp. The diameter of the rod-like HAp crystal increased obviously (around 180nm) and the length of that decreased. When NO₃^2- was replaced by Cl^-, the influence became little. When NO₃^- was substituted by CH3COOH", the nano rod-like HAp coatings got more coherent and denser. When using C₃H₅CaO₃ to replace Ca(NO₃)₂, the morphology of HAp crystals prepared with the fresh electrolyte retained rod-shaped. However, after a week's placed of the former electrolyte, great changes took place in the morphology of the deposited crystals, with the rod-like crystals turning into the granule-like ones.