PEG-l-PAF and PEG-d-PAF: Comparative Study on Thermogellation and Biodegradation

l -Polypeptides and d -polypeptides can be prepared from natural l -amino acids and non-natural d -amino acids, respectively. In this study, poly(ethylene glycol)–poly( l -alanine- co - l -phenyl alanine) (PEG- l -PAF) and poly(ethylene glycol)–poly( d -alanine- co - d -phenyl alanine) (PEG- d -PAF) with similar molecular weight and composition, but different stereochemistry were investigated, focusing on thermogelling behavior and biodegradation. The sol-to-gel transition temperature of both PEG- l -PAF and PEG- d -PAF aqueous solutions decreased from 26 to 7 °C as the concentration increased from 4.0 wt % to 9.0 wt %. Dynamic light scattering, transmission electron microscopy, circular dichroism spectra, and 13 C NMR spectra suggested that the sol-to-gel transition involved changes in molecular assemblies resulting from dehydration of PEG for both PEG- l -PAF and PEG- d -PAF. In particular, the significant differences between PEG- l -PAF and PEG- d -PAF were observed for histocompatibility as well as in vitro/in vivo degradation. Only PEG- l -PAF was significantly degraded by cathepsin B and elastase, as well as under in vivo conditions. The histocompatibility assayed by the H&E staining method showed that formation of the collagen capsule around the PEG- d -PAF gel was thicker than the PEG- l -PAF gel, indicating that acute inflammation was milder with PEG- l -PAF gel than with PEG- d -PAF gel. Current study emphasizes the significance of stereochemistry in biomaterial development.