During the last decade, magnesium and its alloys have been extensively studied to develop a new generation of biodegradable medical implants. The fast degradation rate of pure magnesium and related alloys in the physiological environment poses significant challenges to devices made of these materials for biomedical applications. In this study, we have designed and fabricated biodegradable helical stents made of AZ31 magnesium alloy, and have explored theirs in vitro corrosion behavior in Dulbecco's Modified Eagle's Medium (DMEM). The corrosion rate was significantly reduced by surface modifications of the helical stent, achieved through applying a biocompatible Parylene C polymer coating, or via chemical etching of the devices in inorganic solutions. The corrosion rates of the coated AZ31 Mg helical stents were compared, with uncoated samples used as a control. The results achieved indicated that all tested surface modifications successfully inhibited metal corrosion rates in vitro. Materials coated with Parylene C coating revealed a maximum corrosion rate reduction of 70% to 85% in DMEM solution.

Objective: To investigate the microstructures and mechanical characteristics of enamel and dentin of primary and permanent teeth by AFM, analyze their relationships and provide information for bionics and designs of dental materials. Methods: After embedding, cutting and grinding, 10 primary teeth and 10 permanent teeth were randomly divided into four groups. The morphology of samples was obtained by AFM and the roughness and Young’s modulus were calculated by JPK DP Data processing version 4.0 software. Results: In permanent teeth groups, the enamel rods arrange more tightly than those in primary teeth groups. The roughness of primary enamel （1203±39.5nm）was higher than permanent teeth（954.6±30.5nm）.The Young′s modulus of enamel in primary teeth（80.4±7.7GPa）was lower than permanent teeth（90.8±2.2GPa）. The roughness of dentin in primary teeth （1695±67.6nm）is higher than permanent teeth （1210±45.3nm）and the Young′s modulus of dentin in primary teeth（19.8±1.9 GPa）was lower than the permanent teeth （23.1±1.0 GPa）. Conclusions: The mechanical characteristics of primary and permanent teeth are closely related to their microstructures.

In order to prepare bioactive hydroxyapatite (Ca10 (PO4)6(OH) 2, HA) coating with ideal biocompatibility, the surface of titanium alloy was treated with the two kinds of chemical methods, which are the acid-alkali-combination method and Self-polymerization-adhesion of dopamine. After pretreatment, the treated titanium alloy plates were immersed in simulated body fluid (SBF) to form HA coating on their surface. The chemical composition of the coating was analyzed by an X-ray diffraction (XRD) and the morphology was observed by a scanning electron microscope (SEM). After that, the plates were training in vitro cytotoxicity test with MC3T3-E1 osteoblasts. Compared with the results of cell culture, the method of Self- polymerization -adhesion of dopamine showed better cell adhesion and proliferation..