Wei-Hua Yao

A novel method was used to synthesize a nanosilver-doped multiwall carbon nanotube (MWCNT-Ag), and subsequently, the novel poly(lactic acid) (PLA)- and MWCNT-Ag-based biocompatible and antimicrobial nanocomposites were prepared by melt blending. Based on energy dispersive X-ray spectrometry images, an MWCNT-Ag was successfully synthesized. The effect of the MWCNT-Ag on the PLA bionanocomposites was investigated by evaluating their thermal and mechanical properties, antifungal activity, and cytotoxicity. The nanocomposites exhibited a high degree of biocompatibility with the MWCNT-Ag content, which was less than 0.3 phr. Furthermore, tensile strength testing, thermogravimetric analysis, differential scanning calorimetry, and antibacterial evaluation revealed that the tensile strength, thermostability, glass transition temperature, and antibacterial properties were enhanced by increasing the MWCNT-Ag content. Finally, hydrolysis analysis indicated that the low MWCNT-Ag content could increase the packing density of PLA.

Granular tapioca was thermally blended with poly(lactic acid) (PLA). All blends were prepared using a plasti-corder and characterized for tensile properties, thermal properties and morphology. Scanning electron micrographs showed that phase separation occurred, leading to poor tensile properties. Therefore, methylenediphenyl diisocyanate (MDI) was used as an interfacial compatibilizer to improve the mechanical properties of PLA/tapioca blends. The addition of MDI could improve the tensile strength of the blend with 60 wt% tapioca, from 19.8 to 42.6 MPa. In addition, because PLA lacked toughness, acetyl tributyl citrate (ATBC) was added as a plasticizer to improve the ductility of PLA. A significant decrease in the melting point and glass-transition temperature was observed on the basis of differential scanning calorimetry, which indicated that the PLA structure was not dense after ATBC was added. As such, the brittleness was improved, and the elongation at break was extended to several hundred percent. Therefore, mixing ATBC with PLA/tapioca/MDI blends did exhibit the effect of plasticization and biodegradation. The results also revealed that excessive plasticizer would cause the migration of ATBC and decrease the tensile properties.

Porcine dermal collagen is successfully digested by clostridium histolyticun collagenases (CHC) at varying compositions and conditions. Collagen fragments thus prepared, with significantly low molecular weight but visible denaturation temperatures and/or triple helix structures, may be useful for clinical applications. As evidenced by Sodium dodecyl sulfate - polyacrylamide gel electrophoresis (SDS-PAGE) and gel permeation chromatography (GPC) analyses, relatively high molecular weights of α ₁ , α ₂ subunit, β ₁ , β ₂ dimmers and γ trimmers of the collagen fragments gradually disappear as their incubation temperature and/or time values increase. The time values corresponding to the disappearance of sigmoid plots in the denaturation curves, denaturation endotherm in DSC thermograms and γ bands in SDS-PAGE patterns of digested collagen specimens are the same and reduce significantly as their incubation temperatures increase. Fourier transform infra-red analyses results suggest that the percentages of preserved triple helix structures present in collagen molecules of digested collagen specimens also reduce significantly with increasing the incubation temperature and time values. Possible reasons accounting for the degradation, denaturation and physicochemical properties of digested porcine dermal collagens are explored in this study.