| In this paper, poly(D,L-lactide) (PDLLA) was synthesized firstly by ring opening polymerization of D,L-lactide in supercritical carbon dioxide using tin(II) 2-ethylhexanoate as catalyst. And the effects of temperature, reaction time, monomer feeding and catalyst concentration on the molecular weight and yield of PDLLA were studied. Results showed that the best reaction condition was as follows:the temperature of 100℃, reaction time of 48h, monomer concentration of 4g and catalyst concentration of 0.1%.Then, poly(D,L-lactide) (PDLLA) and chitosan-graft-poly(D,L-lactide) (CS-g-PDLLA) copolymer were synthesized in supercritical carbon dioxide using D,L-lactide and chitosan powder as raw materials and tin(II) 2-ethylhexanoate as catalyst. Then, CS-g-PDLLA/PDLLA porous scaffolds were prepared in situ by supercritical carbon dioxide extraction/pore forming technologies. The structure and properties of the graft copolymers and the molecular weight of PDLLA were characterized by FT IR,1H NMR, TG, XRD and GPC respectively. The porous structure morphology of the prepared scaffolds was observed by SEM and the porosity of the scaffolds was also measured. Results showed that PDLLA and CS-g-PDLLA were synthesised successfully in supercritical carbon dioxide fluid, and the structure of the graft copolymer, the molecular weight and yield of PDLLA can be adjusted by controlling the feeding ratio of n(D,L-LA):n(aminoglucoside), reaction temperature and time. In the best reaction condition, which n(D,L-LA):N(aminoglucoside) was 10:1, temperature of 100℃and reaction time of 48h, the grafting percentage of CS-g-PDLLA copolymer and yield of PDLLA were 117.02% and 68.75% respectively. SEM results revealed that uniformly distributed and highly interconnected pore structures with a unique long gully type microstructure were formed in the CS-g-PDLLA/PDLLA scaffolds, and the compatibility of CS-g-PDLLA with PDLLA was very good. Moreover, the depressurization rate and temperature have effects on the structure mophology of the porous scaffolds.In order to increase the grafting percentage of CS-g-PDLLA copolymer, chitosan microspheres with partical diameter of 2-10μm were firstly prepared by spray drying method, Then, CS-g-PDLLA/PDLLA porous scaffolds were prepared in situ by supercritical carbon dioxide copolymerization/extraction/pore forming technologies. In contrast with the chitosan powder prepared by freeze-drying/crushing/sieve technologies, the chitosan microspheres prepared by spray drying have less partical diameter, larger specific surface area and more uniform particle size distribution. So the grafting percentage of CS-g-PDLLA copolymer increased obviously. Moreover, the pore structure of the porous scaffolds has a better uniformly distribution and higher porosity. Meanwhile, the pore has both unique long gully and bump type microstructure, which increase it's roughness. The biocompatibility of the scaffolds were evaluated by MTT method and cell culture experiments in vitro. Results showed that scaffolds prepared by supercritical carbon dioxide copolymerization/extraction/pore forming technologies were no cell toxicity and cells compatibility were better than copolymers that were prepared by bulk ring-opening polymerization. The cells growth well on the surface of porous scaffolds and the wall of the holes.At last, in order to reduce the high hydrogen bonding and strong resistance between the molecules of CS and increase the reaction activity of CS, hydroxyethyl chitosan (HECS) was prepared firstly by the reaction of chitosan and 2-chloroethanol. HECS-g-PDLLA were prepared by bulk ring-opening polymerization and copolymertization in supercritical carbon dioxide respectively. Results showed that the reaction activity of CS obviously increased after the hydroxyethyl modification. The grafting percentages of HECS-g-PDLLA which prepared by bulk ring-opening polymerization and copolymertization in supercritical carbon dioxide were higher than that of CS-g-PDLLA corresponding prepared by the two methods mentioned above. |
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