Surface modification of a porous hydroxyapatite to promote bonded polymer coatings

Porous hydroxyapatite (Hap) blocks were sintered at several temperatures and methyl methacrylate (MMA) grafted onto the surface in a 2-step heterogeneous system as a model example for surface modification. First, sintered porous Hap was modified with 2-methacryloyloxyethylene isocyanate (MOI) monomer in anhydrous dimethyl sulfoxide using di-n-butyltin (IV) dilaurate as a catalyst and hydroquinone as an inhibitor. Amount of the introduction of MOI monomer on porous Hap was 1.62 wt % at sintered temperature 800 degrees C, 0.68 wt % at it of 1000 degrees C, and 0.59 wt % at it of 1200 degrees C. Scanning electron microscopy (SEM) showed that porous Hap pore size and shape before and after MOI treatment were unchanged. Second, graft polymerization with MMA through the vinyl bond on porous Hap was conducted using alpha,alpha'-azobis isobutyronitrile (AIBN) as an initiator. Amount of Grafted PMMA on the MOI modified porous Hap was 2.84 wt % at sintered temperature of 800 degrees C, 6.97 wt % at it of 1000 degrees C, and 6.27 wt % at it of 1200 degrees C. MOI-modified and PMMA-grafted porous Hap were characterized using Fourier transform infrared (FT-IR) spectroscopy. The compressive strength of sintered porous Hap with grafted PMMA increased about 2.7-6.7 times compared to intact porous Hap. This 2-step surface modification on porous Hap is widely applicable to graft polymerization with vinyl polymer and conjugation with a protein or an oligopeptide, such as growth factor or an adhesion molecule, to improve Hap mechanical properties and functionality.