Micro/Nanoporous Modification On Medical Titanium Surface And Biological Propertiess

Titanium implants can not satisfy the activity requirements of biomaterials. Surface modification for materials was often used to improve their biocompatibility. In this study, a microporous layer on titanium surface was gained by acid etching. Then, highly-ordered nanotube arrays on microporous surface were obtained by anodization. After further heat treatment, a layer with bioactive micro/nanopores was formed on titanium surface. Biomineralization and albumin adsorption tests were conducted to investigate bioactivity of samples with different surface structures. Polypeptide was grafted on the surfaces of nanotube and micro/nanoporous samples, and then biomineralization test was used to compare these 4 samples bioactivity. Finally, behaviors of osteoblast cell on surfaces with different morphology and component were evaluated in vitro.The effect of etching depended on acid concentration and reaction time. The size of micropores ranged from 1 to 60μm. Many small pores distributed on interior walls of large pores, forming a multiscale structure. The result of thin film X-ray diffraction (XRD) showed that besides Ti, TiH₂ existed on titanium surface after acid etching. The morphology of micropores remained and nanotube arrays were aligned on titanium surface after acid etching and anodization. The diameter of nanotubes was about 100 nm. So a structure of micro/nanoporous layer on titanium surface was gained. Besides Ti and TiH₂, monoclinic TiO₂ crystal was found on the micro/nanoporous surface by analysis of XRD. After heat treatment at 450℃for 6 hours, monoclinic TiO₂ crystal transformed into nanometer anatase crystal with a grain size of about 20nm.The four samples including smooth pure titanium, microporous, nanotube and micro/nanoporou structural samples were respectively examined in simulated body fluid (SBF) and albumin solution in phosphate buffer solution at physiological temperature and pH. The micro/nanoporous structural sample was the easiest to form HA and adsorbed the most albumins than other samples; the adsorption rate of albumin was also the fastest. The nanotube sample had better abilities of biomineralization and albumin adsorption than the other samples. The surfaces of pure titanium and micropore samples had little HA formation and albumin adsorption. The micro/nanoporous sample had the highest bioactivity was due to higher specific surface area with more anatase nanometer crystals and nanotubes than other samples. The hydroxylation of anatase can provide a layer hydration titanium dioxide with negative charge on sample surface in pH 7.40 solution. Electrostatic force provides the major driving force for HA formation and albumin adsorption.The surfaces with nanotubes were grafted Arg-Gly-Asp-Cys (RGDC) by silane coupling. The content of RGDC was more on micro/nanoporous sample than that on nanotube sample. The grafted RGDC onto the samples can accelerate biomineralization in SBF solution. The formed HA crystals were nanometer-sized, low crystallinity, calcium deficiency and preferred growth in (002) crystal plane, which was accord with the trend of apatite growth in bone.The test of osteoblast culture showed that cell adhesion, proliferation and differentiation abilities on micropore sample surface were the worst in all samples. The cell growth on nanotube surface was better than that on HA coating surface. Micro/nanoporous surface had better induction ability of cell adhesion, proliferation and differentiation than other samples without RGDC. The surfaces with grated RGDC could accelerate cell growth and cells could entirely spread in shorter time than other samples. Micro/nanoporous sample surface with RGDC could supply morphology and some factors which were required to cell adhesion, so abilities of cells proliferation and differentiation were strongest in all samples.A layer of micro/nanopores and grated polypeptide on titanium surface can enhance bioactivity of materials. The micro/nanoporous structuralization and polypeptid-grating on biomaterial surfaces was an affective surface modification method.