Dongliang Chen

Poly(para-Dioxanone)/Inorganic Particle Composites as a Novel Biomaterial

In this work, poly(para-dioxanone) (PPDO) was mixed with 1% (by weight) calcium carbonate (CaCO(3)), beta-tricalcium phosphate (beta-TCP), or calcium sulphate dihydrate (CSD) by solution co-precipitation. Samples were compression molded into bars using a platen-vulcanizing press. The morphology, thermal and mechanical properties, and crystalline structure of the composites were investigated using differential scanning calorimetry, polarized optical microscopy, scanning electron microscopy, and X-ray diffraction. All results suggest that three types of inorganic particle in this system promote the crystallinity of PPDO and act as an effective nucleating agent: the relative degree of crystallinity of PPDO increased from 30.74% to 100%, and the crystallization temperature of PPDO was increased by 18 degrees C. On the other hand, the mechanical properties of PPDO were changed by the presence of inorganic particles: the tensile strength of PPDO/CSD increased by 11.46%.

Microwave-assisted ring-opening polymerization of poly (glycolic acid-co-lactic acid) copolymers

Abstract The microwave-assisted synthesis of poly(glycolic acid-co-lactic acid) (PGLA) copolymers by ring-opening polymerization of glycolide (GA) and L-lactide (L-LA) was studied. The microwave irradiation time and feed ratios on the molecular weights, as well as the thermal properties of the copolymers were discussed. These copolymers were characterized by 1H-NMR, GPC and DSC. It was found that the largest molecular weight ([η]: 0.8745 dL/g) of PGLA5050 was obtained at the irradiation time of 5 min. The color of the copolymers changed from white to light brown, and the yield was higher with the extension of the irradiation time. The molar component ratio of GA in PGLA (FG) was higher than the initial GA feed ratio (nGA) in the raw materials. As the nGA content increased, the glass transition temperature (Tg) of the copolymers decreased and the melting temperature (Tm) of the copolymers increased.

Nonisothermal crystallization behaviour of poly( ρ -dioxanone) and poly(L-lactic acid) blends

Blends of poly(ρ-dioxanone) (PPDO) and poly(L-lactic acid) (PLLA) in different proportions were prepared by solution co-precipitation. The nonisothermal crystallization behaviour of pure PPDO and PPDO/PLLA blends was investigated by differential scanning calorimetry. The Avrami, Ozawa and Mo models were used to analyse the nonisothermal kinetics. The addition of PLLA significantly increases the crystallization peak temperature and crystallinity of PPDO, but has little effect on crystallization half-time. The activation energies of crystallization were calculated using the Kissinger equation. The results suggest that PLLA plays two roles in the nonisothermal crystallization of PPDO; PLLA both promotes the crystallization of PPDO as a nucleating agent and meanwhile restricts the motion of PPDO chains.

In vitro and in vivo degradation of potential anti-adhesion materials: Electrospun membranes of poly(ester-amide) based on l-phenylalanine and p-(dioxanone)

Electrospun membranes of poly(p-dioxanone-co-l-phenylalanine) (PDPA) hold potential as an anti-adhesion material. Since adjustable degradation properties are important for anti-adhesion materials, in this study, the in vitro and in vivo degradation processes of PDPA electrospun membranes were investigated in detail. The morphological analysis of these membranes revealed the main degradation conditions of PDPA membranes. The weight remaining and molecular weight variation showed that the overall degradation rate of the membranes could be adjusted by modulating the molecular structure of the PDPAs. Especially, α-chymotrypsin could catalyze the degradation process of PDPAs. Based on these results, the in vitro degradation mechanism was demonstrated, and confirmed by 1 H NMR of the hydrolysis products. Finally, the in vivo degradation and biocompatibility of different PDPAs were investigated. The kinetic study showed that the in vitro and in vivo molecular weight loss of PDPAs have the first-order characteristics. The in vivo degradation rate of the most Phe-containing PDPA-3 is the slowest, and this result relates to the biocompatibilities of PDPAs.

Isothermal Crystallization and Melting Behavior of Composites Composed of Poly(L-lactic Acid) and Poly(glycolic Acid) Fibers

Several composites of poly (L-lactic acid) (PLLA) with poly (glycolic acid) (PGA) fibers were prepared. The isothermal crystallization kinetics and melting behavior of PLLA and all of the composites were characterized by using differential scanning calorimetry. The experimental data were processed by using the Avrami equation. The relative parameters, such as the Avrami exponent and half-time crystallization, revealed that PGA fibers had positive effects on the crystallization of PLLA, but these effects had only a minimal dependence on the PGA fiber content. Moreover, at low isothermal crystallization temperatures (85°C∼110°C), recrystallization during the heating scan was observed, which could lower the melting point of the samples to a certain extent.