Surface Modification Of Hydroxyapatite(HA) Nanoparticles And The Preparation Of Its Nanocomposites

Hydroxyapatite(HA), Ca10(PO4)6(OH)2, an important component of mammalian bone and teeth, has good oste-conductivity and oste-inductivity. Polyactide(PLLA), have proven to be the most attractive biodegradable polyesters, has excellent biodegradability,biocompatibility and mechanical properties, it can be broken down into non-toxic Kreb's Cycle by bio-organisms. In this thesis, research was focused on two methods in modified the surface of and HA, preparating HA/PLLA composites. HA/PLLA composites combine both the advantages of HA and PLLA, possessing biodegradability and bone conductivity, can be used for bone tissue engineering scaffolds.1. The surface of hydroxyapatite nanoparticles was modified by poly(L-phenylalanine)(PPha). Firstly, hydroxyapatite nanoparticles (n-HA) were treated by y-aminopropylthriethoxysilane (APS) and amino functionalized hydroxyapatite nanoparticles (HAAPS) were obtained. Then HAAPS was used to initiate the ring opening polymerization (ROP) of L-phenylalanine N-carboxyan hydride (Pha-NCA) to obtain poly(L-phenylalanine) grafted hydroxyapatite nanoparticles (PPha-g-HA). The synthesis route was monitored by Fourier transform infrared spectroscopy(FTIR),thermal gravimetric analysis (TGA),the power X-ray diffraction (XRD). By controlling different conditions,the surface grafting amounts of PPha on HA range from20.26%to38.92%. The power X-ray diffraction (XRD) analysis confirmed that the ROP only underwent on the surface of HA nanoparticles without changing its bulk properties. The MTT assay prove that the biocompatibility of modified HA was very good, which showed the potential application of modified HA in bone tissue engineering.2. The surface of hydroxyapatite nanoparticles was modified by Poly(N-s-z-L-Lysine)(PLys(z)). PLys(z) brushes which grafted on HA nanoparticles (PLys(z)-g-HA) was prepared via the ring opening polymerization (ROP) of N-carbobenzoyloxy-L-Lysine-N-carboxyanhydride (PLys(z)-NCA) by HAAPS initiated. The synthesis route was monitored by FTIR, TGA, XRD. The FTIR of PLys(z)-g-HA compared with HA and HAAPS, there are two stronge peak appeared in1649cm-1and1709cm-1, which are characteristics of peaks of carbonyl (amide I) and estergroup, respectively. On the one hand, it proved PLys(z) take on the surface of HA. On the other hand, by controlling different conditions, the surface grafting amounts of PLys(z) on HA range from5.9%to28.99%, further demonstrates our conclusion. The XRD and MTT can tell us PLys(z)-g-HA nanoparticles without changing HA bulk properties and the biocompatibility of modified HA was very good, even in low concentration of PLys(z)-g-HA can promote the cell viability.3. The preparation of PLys(z)-g-HA/PLLA composites. Different concentration of PLys(z)-g-HA composites were perpared by thermal induced phase separation method with PLys(z)-g-HA and PLLA as the materials. DSC was used to characterize the effect of PLys(z)-g-HA on the crystallizaton of PLLA. The thermal of PLLA and PLys(z)-g-HA/PLLA composites demonstrated that the PLys(z)-g-HA could enhance the thermal stability of PLLA. The results showed that the PLys(z)-g-HA worked as a nucleating agent and enhanced the crystallization speed of PLLA.