ROLE OF SURFACE CHARGE, WETTABILITY AND DOPANTS ON EARLY STAGE MINERALIZATION AND BONE CELL-MATERIALS INTERACTIONS OF POLARIZED HYDROXYAPATITE CERAMICS
Subhadip Bodhak, Susmita Bose, and Amit Bandyopadhyay
The objective of this research is to investigate the role of surface charge, wettability, and dopants on physical, mechanical and in vitro biological properties of bulk and coated electro-thermally polarized hydroxyapatite (HAp) ceramics. For this purpose, bulk pure HAp compacts were prepared by sintering at 1200oC for 2h and HAp coating was fabricated on Ti substrate. After electro-thermal polarization at optimized poling conditions, thermally stimulated depolarization current (TSDC) analysis revealed that less dense HAp coating samples stored lower surface charge (1.69 µC/cm2) than bulk sintered HAp compacts (4.28µC/cm2). It has been observed that increasing the surface potential led to decreasing of hydrophobicity of HAp surface without introducing any other volumetric effects in the material. In vitro bioactivity and bone cell materials-interaction results revealed that increasing surface energy and wettability on negatively charged HAp surface significantly accelerated the apatite mineralization process by selectively adsorbing Ca2+ ions which promoted better hFOB cell attachment, proliferation and faster cells differentiation, especially at early time points, over unpoled HAp surface. While electrostatic adsorption of antiadhesive molecules inhibited hFOB cell proliferation and growth on positively poled surface. Furthermore, dopants (Mg2+, Sr2+, and Zn2+) were also incorporated into pure HAp in different single, binary and ternary composition to achieve combined benefits of matching bone chemistry and polarization effect. It has been observed that small addition of Mg2+ and combined addition of Mg2+-Sr2+ are the most beneficial in enhancing density, mechanical properties as well as polarizability and charge storage ability of pure HAp. In vitro cell materials interaction study showed that presence of Mg2+ and Sr2+ can significantly improve osteoblast response and activities on negatively charged surface. Finally, the interaction specific cell adhesive fibronectin protein on different polarized surfaces of doped HAp samples has been investigated to get more comprehensive understanding on bone cell-materials interactions. Protein study results confirms that higher adsorption and better structural stability of fibronectin on negatively charged surfaces leads to superior cell-materials interactions on binary doped HAp samples over undoped HAp. Overall, research findings demonstrated the potency of developing electro-thermally polarized HAp ceramics which can provide a new basis for the development of a new generation of HAp based implants that can promote faster healing.