No abstract

Poly(ethylene glycol)-b-poly(L-alanine) (PEG-L-PA)s with L-PA molecular weights of 620, 1100, and 2480 Da and a fixed molecular weight of PEG at 5000 Da were synthesized to compare the thermosensitive behavior, and to investigate their potential as a three-dimensional (3D) culture matrix of adipose-tissue-derived stem cells (ADSCs). The sol-to-gel transition temperature and the concentration ranges where the transition was observed decreased as the L-PA molecular weight increased. ADSCs were cultured in the 3D matrixes of in situ formed PEG-L-PA hydrogels, which were produced by increasing the temperature of cell-suspended PEG-L-PA aqueous solutions. The spherical morphology was maintained in the PEG-L-PA hydrogel, while the cells underwent fibroblastic morphological changes in the Matrigel over 14 days of incubation. ADSCs exhibited high expression of type II collagen in the PEG-L-PA thermogel. In addition, they also moderately expressed the biomarker of myogenic differentiation factor 1 as the same mesodermal lineages, as well as the type III β-tubulin as a cross-differentiation biomarker. Similar to the in vitro study, the ADSCs predominantly exhibited chondrogenic biomarkers in the in vivo study. The study demonstrates that the polypeptide thermogel of PEG-L-PA is promising as a 3D culture matrix of ADSCs and as an injectable tissue engineering biomaterial.

L-Polypeptides and D-polypeptides can be prepared from natural L-amino acids and non-natural Damino 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.