Synthesis, Characterization and Evaluation of Hydroxyapatite Doped with Zinc for Several Applications

Abstract

Low bio-affinity of medical catheters often causes bacterial infection through the permeation interspaces between catheters and skin tissues. Thus, the surface modification of the biomedical polymer (e.g., silicone resin) used as catheters is desired for improving the biocompatible and antibacterial properties. As the modification materials, hydroxyapatite (Ca10(PO4)3(OH)2) (HAp), which is crystallographically and chemically similar to the components of human’s hard tissues, is a good candidate. Importantly, naturally-formed HAp is not absolutely pure and has some impurities of ions (Zn2+, Mg2+, K+, etc.), which provides biocompatibility as well as antibacterial properties. Thus, the substituted ions not only alter the space group of crystal structure, thermal stability and mechanical properties of HAp but also play an important role in the biological behaviors. In this study, the synthesis of zinc-substituted HAp (Zn:HAp) nanocrystals and subsequent formation of the nanocrystalline film on the biomedical polymer without using chemical reagents for investigating their biocompatibility as well as antibacterial properties (“Chapter 1”). In “Chapter 2”, Zn:HAp nanocrystals were synthesized by a wet chemical method. In the method, the initial (Ca+Zn)/P ratio of 1.67 and 2.00 were adjusted from the reagents (CaCl2, ZnCl2, and K2HPO4) to resultantly form the stoichiometric and carbonate HAp nanocrystals, respectively. The initial ZnCl2 was changed as the dopant concentration of Zn/(Ca+Zn) = 0.0, 2.5, 5.0 and 10 mol%. The zinc-substitution significantly suppressed the crystal growth to obtain the optimized crystalline nano-sizes for the modification. In “Chapter 3”, an electrophoretic deposition at the optimized voltage of 100 V was used for the surface modification of biomedical polymers. As a result, the nanocrystalline Zn:HAp film formation on the surfaces was successfully achieved. Furthermore, the fibroblast compatibility as well as antibacterial activity was confirmed on the film surfaces. In particular, the films made from the Zn:HAp nanocrystals with (Ca+Zn)/P =2.00 and Zn/(Ca+Zn) =5 mol% is the best possibility for the surface modification. In “Chapter 4”, the nanocrystalline Zn:HAp films were summarized to provide good biocompatibility as well as antibacterial properties on biomedical polymer surfaces, suggesting useful catheter surface modification technique.The percutaneous devices applications are shown in Table 1.1 which has been grouped as blood and body cavity access devices, then concludes for power or signal transmission and internal prosthetic devices.