Preparation Of Apatite Coating On The Surface Of Silicone Rubber By Biomimetic Synthesizing

Percutaneous device is a chronically implanted mechanism through the skin for the transmission of substance and information (combined with biosensors). Except for the treatment of dialysis, it can also be used for auxiliary voice and the treatment of catheterization. Silicon rubber has been frequently used as percutaneous material, due to its excellent mechanical properties and good stabilization when implanted in vivo. While the high hydrophobicity of silicone rubber molecules would result in a poor bond with the skin, which may cause some problems, such as: the down growth of the epidermis and the infection caused by the bacterium hidden in the joint of the device and skin. Hydroxyapatite has a good biocompatibility and can bond with the tissue tightly when implanted, but it is difficult to machining hydroxyapatite ceramic into a certain shape. Besides, the Young's module of the ceramic is not consistent with the skin tissue.Biomimetic synthesizing is a newly developed route to prepare bone-like apatite layer, the coating process is carried out under a moderate condition and it is available for various kinds of substrates with a complex shape.Attempts to prepare a bone-like apatite-polymer composite have been made using a biomimetic process in which the polymer surface is modified with functional groups effective in inducing apatite nucleation. Si-OH, Ti-OH, and carboxyl or carboxylate groups have been used as the functional group. Once the apatite nuclei are formed, they grow spontaneously into a dense and uniform layer of bone-like apatite by consuming calcium ions and phosphate ions from the simulated body fluid (SBF), since SBF is supersaturated with respect to apatite. Therefore, the inducing of apatite nuclei is a crucial factor in the preparation of an apatite coating on the surface of a polymer. If apatite nuclei could be previously introduced onto a polymer surface, the resultant surface- modified polymer would form a bone-like apatite layer on its surface within a short period.In the present study, Ca²⁺ was induced onto the surface of silicone rubber by immersing it into the CaCl₂ ethanol solution which has a good compatibility with silicone rubber; the specimen was subsequently dipped in phosphate ion solution to deposit apatite nuclei onto its surface. Then the specimens were immersed in SBF and metastable calcium phosphate solution (CP solution) respectively to form a layer on its surface.The coating formed on the substrate was characterized by thin film X-ray diffraction (TF-XRD), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The results indicate that: when soaked in SBF for 7d, the layer formed on the substrate was net-like and many spheriform crystals were found; when soaked in CP solution for 1d, amorphous apatite was formed on the surface; when soaked in CP solution for 3d, the layer on the substrate was composed of well grown flake-like crystals, the growth of the layer was (001) oriented according to the analyze of TF-XRD. During the formation of the layer, CO₃^2- was involved into the structure of apatite and replaced the position of OH^-.Bovine Serum Albumin (BSA) was added into the CP solution to better simulate the condition of the body plasma. The formation of apatite in the composite solution of CP-BSA was analyzed using XRD, FT-IR and SEM. The results indicated that: the introduction of protein had a remarkable influence on the size and morphosis of the crystal grains on the surface of layer, the edges of the crystals became rough and frizzy and the crystallization became ununiform.The vitro cytotoxicity test and hemolysis test indicated that: neither the raw material nor the surface modified specimen had cytotoxicity and hemolysis effect. The specimen modified in the composite solution of CP-BSA had the most notable effect on cell proliferation.This work was supported by the National Natural Science Foundation of China (Grant No. 50472041).