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

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 C-13 solid-state NMR, i.e., C-13 CP/MAS, C-13 DD/MAS and C-13 r-INEPT NMR methods. In C-13 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 C-13 solid-state NMR spectra of [[3-C-13] Ser, [3-C-13] Tyr and [3-C-13] 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. (C) 2021 Elsevier Ltd. All rights reserved.