Surface Modification Of Nano-hydroxyapatite And The Biomimetic Synthesis Of Its Composites

As the main inorganic phase of human bone and teeth, hydroxyapatite is an excellent kind of bone implant materials due to its good biocompatibility and strong bond with bone tissue. In recent decades, the synthesis method and the medical applications of hydroxyapatite have attracted more attention, especially in the field of mechanical properties, structure of interface, biocompatibility etc. Pure hydroxyapatite has weak bond with the interface of the polymer matrix. When implanted into animal body, hydroxyapatites soon broke away from the polymer matrix, thus leading to rapid decrease of mechanical properties. How to improve the interface of the hydroxyapatites and the polymer matrix was the most important technique to prepare the composites with high properties.In order to improve the interface strength and the dispersion of filler in PLA/inorganic particles composites, and reduce the size of bioactive inorganic particles, the preparation of hydroxyapatite nano-particles, modification of surface were studied in details, thus enhancing the strength and modulus of the composites, which will be used in clinical repair of bone injury as the bone tissue engineering materials.Meanwhile, hydroxyapatite/poly(glutamic acid) composites were prepared via biomimetic process and the biomineralization of hydroxyapatite nanoparticles were studied as well. The formation and crystallization of bone, the special mineralization, and pure minerals were fully compared, on the basis of which, molecule recognition of organic-inorganic interface, nucleation and growth of crystals and microstructural ordered assembly were recognized, hence preparing composites with excellentproperties.TGA, XRD, NMR, FTIR, TEM as well as SEM were employed to characterize hydroxyapatite and its composites. The results show:(1) HAP particles were prepared using Ca(NO3)2·4H2O and (NH4)2HPO4. These powders were characterized with TEM,SEM,WAXD,FTIR. The results showed that increasing reaction temperature could advantage the producing of highly crystallized claviform HAP particles. In addition, the form and crystallinity of HAP were greatly influenced by the calcinated temperature, the higher calcinated temperature the higher crystallinity.(2) PLLA was directly grafted onto the surface of HAP particles through the ring-opening polymerization of L-lactide (LLA) in the high pure argon atmosphere, thus increasing the hydrophobicity of HAP powders. The obtained PLLA-graft-HAP(g-HAP) was characterized with 31P MAS-NMR, FTIR, TGA, TEM, SEM and GPC. The results show that about 6%PLLA can be grafted on the surface of HAP particles through chemical linkage. The PLLA/g-HAP composite was prepared through the solution method and the results of POM showed that the g-HAP particles can play the role of nucleating agent in the PLLA matrix.(3) Hydroxyapatite/poly(glutamic acid) composites were prepared via biomimetic process. TGA, XRD, FTIR and TEM were employed to characterize hydroxyapatite and its composites. Composite HAP/PBG nanocrystals were studies using Scherrer equation at different poly(glutamic acid) concentration. The results showed that poly(glutamic acid) displayed a minor inhibitory effect towards the growth of HAP crystals. The length/width ratio of the composite crystallites increased with the increasing of the poly(glutamic acid) concentration.