The Preparation And Properties Of HA/PMMA Bio-composite Materials

One of the most common bone substitutes used in clinic is polymethylmethy aery late (PMMA). PMMA can be described as an alloplastic, synthetic, nonbiodegradable polymer which has considerable versatility. However, a common problem associated with the application of PMMA is the loosening. The attachment strength of PMMA to the host bone is low, as there is not a chemical bonding between them. By mixing with bioactive fillers, such as hydroxyapatite(HA), a bony bond can be established on the interface between the composite material and the host bone. It is considered that a higher interfacial strength resulted from the chemical bonding can prevent the aseptic loosening. However, in order to meet the mechanical and bioactive requirements, the challenging tasks for preparing the composites are how to prevent HA derived from aqueous environment from agglomeration, and how to disperse the HA particles in the polymer well.In this work, we made an attempt to prepare HA particles directly in organic environment and dispersed the particles in it, in contrast of the traditional way mentioned above. HA ultrafine particles are prepared in the emulsion of chloroform and water with lecithin as the emulsifier, and the effect of lecithin on the dispersion of HA particles in chloroform has been explored. FTIR and TEM analysis show that lecithin can attach on the surface of HA particles to improve greatly their dispersion in chloroform after demulsification. Therefore, a suspension of nano-sized hydroxyapatite particles with excellent dispersion in organic media can be obtained. When mixed with PMMA, the HA fillers are dispersed homogeneously in the matrix. The results suggest that the suspension is significant to achieve a desirable interfacial condition between the inorganic fillers and the polymer during the preparation of HA-reinforced composites.With the suspension obtained, the PMMA is added into the suspension to prepare the HA/PMMA composite with different HA contents and different surface morphology. The mechanical test demonstrates that the HA component contributes greatly to the improvement of the composites' the elasticity modulus, while the compressive strength decreases slightly after it reached the maximum value.The composites are soaked in simulated body fluid (SBF) to evaluate their biologicalbehaviors. The results suggest that all the composites show bioactive as there are nano apatite/' crystallites formed on the surface of the composites. In addition, the bioactivity of thecomposites greatly depends on their morphology, the composite with surface open pores demonstrats excellent bioactivity, and the composite with interconnected pores shows potentially good bioactivity, while the dense composite shows ordinary bioactivity.This work provides an effective way to prepare high quality HA/PMMA composites, and enriches the understanding of bioactive behavior of the composites.