Preparation And Characterization Of Surface Modified Hydroxyapatite Nanohyrids And Composites

The artificial synthesized nanohydroxyapatite (nHA) filled biodegradable polymer composite is widely used in the area of bone tissue engineering due to its very similariry on the chemical composition and structure to the natural hydroxyapatite (HA) in the bones. However, because of the easily aggregation of the nHA in the polymer matrix, it is important to improve the compatibility of HA nanoparticles in biodegradable polymers to obtain desirable nanocomposites for bone tissue engineering applications.In order to improve the dispersion of nHA in Poly (L-Lactide)(PLLA) matrix, in this paper, HA with the derived ATRP initiators was obtained by preparation of HA from precursors in the presence of3-aminopropyl-triethoxysilane (APTS) to produce the HA surface with terminal-NH2groups (HA-NH2) and reaction of the-NH2groups of the HA-NH2nanoparticles with2-bromoisobutyryl bromide (BIBB) to produce the2-bromoisobutyryl-immobilized nanoparticles (HA-Br). The HA@PGMA and HA@PHEMA nanohybrids were synthesized that the poly (glycidyl methacrylate)(PGMA) and the poly (2-hydroxyethyl methacrylate)(PHEMA) were grafted from the surface of nHA via atoms transfer radical polymerization (ATRP), respectively. The HA@PGMA-g-PLLA nanohybrids were gained through "Graft to" method that the carboxyl-terminated Poly (L-Lide)(PLLA-COOH) was attached onto HA@PGMA onto the surface of HA via reaction between end-groups. While, the hydroxyls on the HA@PHEMA surface were used to initiate the ring opening polymerization of L-lactide to form the HA@PHEMA-g-PLLA nanohybrids by "Graft from" method. Analysis including FTIR, XRD, TGA, DSC, SEM and TEM are used to prove the successful synthesis of different nanohybrids. Unexpectedly, there were some disadvantages in these two ways to obtain PLLA grafted HA. In the former, although it was good at control of attached PLLA chain length, some of final HA@PGMA-g-PLLA demonstrated inferior solubility in chloroform. The reason was that it was hard to prevent the cross-linking side reaction completely, which was aroused by minor PLLA oligomers with two end-COOH groups. On the other hand, the latter was found a little low initiation efficiency of L-lactide and poor controlled length of the PLLA oliomgers, due to limited dispersion of HA@PHEMA in molten L-lactide and relatively low activation of hydroxyl on the surface.In order to resolve the problems above, a new strategy to prepare HA-poly (L-lactide)(HA-PLLA) nanohybrids was developed where PLLA oligomers were grafted from HA nanoparticle surfaces via surface-initiated ATRP of methylacrylate group terminated PLLA macromonomers (PLLA-MA). FTIR, XRD, TGA, DSC, SEM and TEM were introduced to prove the synthesis of HA-PLLA nanohybirds and the obtained HA-PLLA nanohybrids demonstrated good dispersibility in chloroform and good dispersion of HA-PLLA nanohybrids in PLLA matrix if the length of PLLA grafted on HA surface and improved with the increasing molecular weight of PLLA grafted on HA surface. At last, the electrospun PLLA nanofibers with sooth surface were prepared in which the HA-PLLA nanohybrids were dispersed homogeneously.From the destination of mimic the structure of the natural bones, it is essential to introduce the protein composition into the HA/biodegradable polymer composite. To improve dispersion of HA in Gelatin (Gel) matrix, HA@Gel nanohybrids were also synthesized by the gelatin template method and were proved by the analysis of FTIR, XRD, TGA, DSC, SEM and TEM. Then HA@Gel nanohybrids were added into the gelatin solution to prerare Gel/HA@Gel nanofibers and Gel/PLLA/HA@Gel nanofibers via the adjustment of process parameters. It is observed that the dispersion of the HA@Gel nanohybrids had been improved obviously compared to that of unmodified HA nanoparticles in the nanofibers.This research provided a new method based on ATRP surface grafting modification on nHA. It was confirmed the possibility of polymer-grafting modification of nano-inorganic particles for improving the dispersion in a polymer matrix. The attempts on preparation of PLLA/HA@PLLA, Gel/HA@Gel, and PLLA/Gel/HA@Gel composite nanofibrous matrixes would result in materials with desirable performance for bone regeneration and repair.