Qing Cai

Enzymatic degradation behavior and mechanism of poly(lactide-co-glycolide) foams by trypsin.

The purpose of this study is to investigate the enzymatic degradation behaviors of porous poly(lactide-co-glycolide) (PLGA) foams in the presence of trypsin, in comparison with their hydrolytic degradation. To inspect the effect of trypsin on the degradation of PLGA, both the hydrolytic and enzymatic degradation of non-porous PLGA samples were also performed. The changes of molecular weight and molecular weight distribution (polydispersity) during the degradation were determined by gel permeation chromatograph. And the changes of weight, thickness and morphology with the degradation were also measured. The degradation of PLGA displayed as two stages. In the first stage, the molecular weight of PLGA decreased continuously with degradation time, whereas little weight loss occurred. But in the second stage, the molecular weight of PLGA had decreased to a low value and was almost unchanged with time, while the sample experienced significant weight loss. And it was found that the presence of trypsin could significantly accelerate the weight loss rates of all the PLGA samples, but it caused little difference in the decrease of molecular weight and the change of PLGA composition between the enzymatic and hydrolytic degradation. Therefore, the enzymatic degradation of PLGA was still primarily a hydrolysis process. A mechanism of enzymatic degradation was proposed that the trypsin could enhance the weight loss of PLGA by acting as surfactant to push the dispersion of degradation products into water even though they could not dissolve in water.

Synthesis and thermal properties of novel star-shaped poly(l-lactide)s with starburst PAMAM–OH dendrimer macroinitiator

Abstract The starburst PAMAM–OH dendrimer (generation 3) as macroinitiator for the synthesis of star-shaped polylactides in the presence of stannous octoate was investigated. Effects of molar ratios of monomer to initiator, monomer to catalyst, monomer conversion, and reaction temperature on polymerization were studied. It is found that 16–21 polylactide arms can be attached to the surface of dendrimer initiator, and the molecular weight of polylactides can be controlled by variation of molar ratios of monomer to initiator and polymerization time. Thermal analysis indicates that the star-shaped polylactides possess lower glass transition temperature, melting point, crystallinity, and maximum decomposition temperature than those of linear polylactide.

Synthesis and characterization of biodegradable polylactide-grafted dextran and its application as compatilizer.

Brush-like biodegradable polylactide-grafted dextran copolymer (PLA-g-dextran) was by a bulk polymerization reaction using a trimethylsilyl-protected (TMS) dextran as macroinitiator and stannous octoate as catalyst. After the polymerization, the TMS groups could be easily removed by immersing the copolymer in methanol for 48 h. The PLA-g-dextran copolymers were characterized by (1)H NMR, GPC and intrinsic viscosity measurements. Besides, mouse 3T3 fibroblasts were cultured on these copolymeric substrates together with pure polylactide (PLA). Although the copolymers exhibited better hydrophilicity and cell affinity compared to pure PLA because of the incorporation of glucose units and the brush-like architecture, it was found that the cells still could not migrate into the center part of scaffold made of PLA-g-dextran copolymer. In result, PLA-g-dextran copolymers themselves were not an appropriate choice for the cell scaffold material, however, it could be used as compatilizer to ameliorate the compatibility between hydrophilic dextran and hydrophobic PLA due to its amphiphilic structure, which could improve the mechanical properties of PLA/dextran blends by reducing the phase separation between PLA and dextran. Therefore, the PLA/dextran blends, which had good cell affinity and moderate mechanical strength, might be prospect cell scaffold materials.

Synthesis and properties of ABA-type triblock copolymers of poly(glycolide-co-caprolactone) (A) and poly(ethylene glycol) (B)

Abstract Poly(glycolide-co-caprolactone) (A)–poly(ethylene glycol) (B) ABA-type triblock copolymers (PGCE) were synthesized by bulk ring opening polymerization, using the hydroxyl endgroups of poly(ethylene glycol) (PEG) as initiator and stannous octoate as catalyst. The resulting copolymers were characterized by various analytical techniques. Gel permeation chromatographic analysis indicated that the polymerization product was free of residual monomers, PEG and oligomers. 1H NMR and differential scanning calorimeter results demonstrated that the copolymers had a structure of poly(glycolide-co-caprolactone) (PGC) chains chemically attached to PEG segments. All the PGCE copolymers showed improved hydrophilicity in comparison with the corresponding PGC copolymers with the same molar ratio of glycolidyl and caproyl units. The microspheres of PGCE copolymer exhibited rough surfaces quite different from the smooth surface of PGC microspheres. This phenomenon was attentively ascribed to the highly swollen ability of PGCE copolymers and the freeze-drying process in the microspheres fabrication.