Surface Modification Of Hydroxyapatite Nanoparticles And Research On Their Composites

Hydroxyapatite (HAP or HA) nanoparticles, which have excellent biocompatibility, osteoconductivity and strong interaction with bone tissue, are recognized as one of the bone repairing materials. However, the poor mechanical properties and biodegradability limited their applications. Thus, the composites combining the bioactivity of HAP fillers and mechanical property of polymer matrix are extensively studied.During this process, there are also some difficulties to solve. HAP has a strong tendency to agglomerate due to the inter-particle van der Waals interaction and hydrogen bonding. The interfacial adhesion between HAP filler and polymer matrix is very weak, which will induce the early failure at the interface and make the composites useless.The most commonly used method is surface modification of HAP. Surface modification of hydroxyapatite not only prevents the HAP particles from aggregating but also enhances the compatibility with polymer matrix. In the present paper, HAP nanoparticles are surface modified with four different methods.The main contents and conclusions in the dissertation are divided into the following parts.(1) Synthesis HAP nanoparticles:HAP nanoparticles were prepared by the chemical precipitation and charactered by FTIR, XRD, BET and TEM.(2) Ring opening polymerization:HAP was surface grafted with poly(?-caprolactone) (PCL) through directly ring opening polymerization. The obtained PCL-g-HAP (g-HAP) was compared with HAP. With g-HAP and HAP addition, the mechanical properties, thermal properties and porosities of composite scaffolds were also discussed.(3) Atom transfer radical polymerization (ATRP) and ring opening polymerization:HAP was surface firstly grafted with poly(2-hydroxyethyl methacrylate) (PHEMA) through ATRP method. Then the comb PCL was grafted onto HAP surface through ring opening polymerization. The additional hydroxyl groups could be effective and convenient for the high grafting amount. The dispersibility of surface-grafted HAP was significantly improved as the amount of grafted PCL increased. At the same time, the improvement on the mechanical properties of composite scaffold was more obviously.(4) Reverse atom transfer radical polymerization (Reverse ATRP):HAP nanoparticles were firstly surface-grafted with PMMA via reverse atom transfer radical polymerization (reverse ATRP), and the surface-grafted HAP was used for subsequent atom transfer radical polymerization (ATRP) of additional methyl methacrylate (MMA). The kinetic studies of reverse ATRP revealed that this was a linear increase in ln([M]o/[M]) with polymerization time. Transmission electron microscopy (TEM) indicated that the surface-grafted HAP could be dispersed in chloroform more uniformLy than HAP nanoparticles, and the dispersibility of surface-grafted HAP was significantly improved as the amount of grafted PMMA increased. Since the PMMA grafted on the HAP surface enhanced the interfacial adhesion between HAP and matrix, the compressive strength of HAP/PMMA composites were improved at the same time.(5) ATRP:The hydroxyl groups of HAP were firstly modified to bromine groups. Then through these groups, ATRP was utilized to graft poly(methyl methacrylate) on the HAP. The structure and properties of the PMMA-g-HAP particles (M-HAP) were investigated by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), differential scanning calorimeter measurements (DSC), and contact angle analyses. The contact angle analyses indicated that grafting PMMA onto the HAP surface dramatically increased the hydrophobicity of the surface. Moreover, M-HAP showed excellent dispersibility in both aqueous solution and organic solvent. Through the study of protein adsorption and release, the excellent dispersibility of HAP particles had good effects on the protein adsorption.