Structure and dynamics of biodegradable polyurethane-silk fibroin composite materials in the dry and hydrated states studied using 13C solid-state NMR spectroscopy

Abstract

In order to develop biodegradable silk fibroin (SF) –polyurethane (PU) composite materials, the biodegradable PU based on polycaprolactone (PCL) was synthesized. The structure and dynamics of the crystalline and non-crystalline regions of biodegradable PU and SF – PU composite fiber were studied in the dry and hydrated states using three kinds of 13C solid-state NMR, i.e.,13C CP/MAS, 13C DD/MAS and 13C r-INEPT NMR methods. In 13C r-INEPT NMR spectra which can observe only highly mobile hydrated components, only small peaks from non-crystalline region of PCL components in PU could be observed, but higher intensity peaks from the non-crystalline region could be observed for PU in the regenerated SF-PU composite fiber. On the other hand, the structure and dynamics of SF in SF-PU fiber was investigated by observing three kinds of 13C solid-state NMR spectra of [3-13C] Ser, [3-13C] Tyr and [3-13C] Ala-labeled SF. The fraction of random coil of SF, especially the fraction of hydrated random coil, increased for hydrated SF-PU composite fiber compared with random coil fraction of hydrated pure SF fiber. Thus, the interaction between SF and PU caused increase fraction of non-crystalline region of PCL in the PU and slightly amorphous SF region in the hydrated state.