Application Of PDLLA In HA Composite And Drug Controlled Release

In the past decades, polylactide has attracted more and more attentions owing to its superior biocompatibility and biodegradability in the biomedical field. In the present work, high molecular weight poly(DL-lactide) (PDLLA) was synthesized with industrial lactic acid via ring opening polymerization. The synthesis of PDLLA, preparation and mechanical behaviors of PDLLA/hydroxyapatite (HA) composites, and releasing performance of PDLLA sustained release implants were systematically investigated.Firstly, DL-lactide was synthesized by catalysized polymerization and pyrolysis, and the related synthesis and purification processes were optimized. Then, PDLLA was synthesized by ring opening polymerization of DLLA, the effects of reactive conditions on the molecular weight and the molecular weight distribution of PDLLA were discussed. FT IR spectra and gel permeation chromatography (GPC) were employed to characterize the structure and the molecular weight of PDLLA, respectively. The results indicated that the DL-lactide with a yield ratio of 45% and PDLLA with the 184,000g.mol-1 average weight molecular could be obtained under the optimum conditions.PDLLA/HA composites with 30 wt.%HA were prepared by ultrasonic-aided solution compounding (USC) and in situ polymerization (ISP). Their mechanical, dynamic mechanical properties and morphologies were also investigated. The results showed that HA has a little prohibition on the polymerization of lactide due to the presence of water and hydroxyl groups on the surface of HA. As compared with the PDLLA/HA composite prepared by ultrasonic-aided solution compounding, the in situ polymerization of DLLA improves the dispersion of HA in PDLLA matrix and enhances the interfacial adhesion between PDLLA and HA. Thereby the glass transition temperature of PDLLA increases, and the mechanical properties of the PDLLA/HA composite are improved remarkably. Based on polylactide with the average molecular weight of 50,000g.mol-1 as the carrier, three kinds of polylactide-levofloxacin hydrochloride sustained release implants containing 5, 10 and 20 wt.% levofloxacin hydrochloride were fabricated by solvent evaporation. The effects of the levofloxacin hydrochloride content on the in-vitro drug releasing performance of sustained release implants were investigated. The results showed that the drug releasing process could be divided into two stages. In the first stage (1-7 days), drug releases quickly. The higher the content of levofloxacin hydrochloride is, the more quickly the drug releases. In the second stage (8-30 days), all of the implants exhibit the stable and slow releasing behaviors. The kinetics of the drug releasing behavior obeys the Higuchi Model, and the sustained release implants exhibit an obvious sustained release characteristic.