Dual-Crystallizable Silk Fibroin/Poly(L-lactic Acid) Biocomposite Films: Effect of Polymer Phases on Protein Structures in Protein-Polymer Blends.

Fang Wang,Yingying Li,Christopher R Gough,Qichun Liu,Xiao Hu

doi:10.3390/ijms22041871

Fang Wang, Yingying Li + Show 3 more

Open Access

https://doi.org/10.3390/ijms22041871

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Abstract

Biopolymer composites based on silk fibroin have shown widespread potential due to their brilliant applications in tissue engineering, medicine and bioelectronics. In our present work, biocomposite nanofilms with different special topologies were obtained through blending silk fibroin with crystallizable poly(L-lactic acid) (PLLA) at various mixture rates using a stirring-reflux condensation blending method. The microstructure, phase components, and miscibility of the blended films were studied through thermal analysis in combination with Fourier-transform infrared spectroscopy and Raman analysis. X-ray diffraction and scanning electron microscope were also used for advanced structural analysis. Furthermore, their conformation transition, interaction mechanism, and thermal stability were also discussed. The results showed that the hydrogen bonds and hydrophobic interactions existed between silk fibroin (SF) and PLLA polymer chains in the blended films. The secondary structures of silk fibroin and phase components of PLLA in composites vary at different ratios of silk to PLLA. The β-sheet content increased with the increase of the silk fibroin content, while the glass transition temperature was raised mainly due to the rigid amorphous phase presence in the blended system. This results in an increase in thermal stability in blended films compared to the pure silk fibroin films. This study provided detailed insights into the influence of synthetic polymer phases (crystalline, rigid amorphous, and mobile amorphous) on protein secondary structures through blending, which has direct applications on the design and fabrication of novel protein–synthetic polymer composites for the biomedical and green chemistry fields.

Highlights

In recent years, silk fibroin (SF) extracted from the natural silkworm cocoon has attracted attention as one of the most promising bioengineering materials due to its unique molecular structure, excellent biocompatibility, morphologic flexibility, ability to promote cell adhesion and growth, and lower inflammatory response [1,2,3,4,5,6]
SF/poly(L-lactic acid) (PLLA) composite membranes with different mass ratios were prepared by reflux condensation and stirring blending
As the silk fibroin content in the composite membrane gradually increased, a regular circular convex–concave structure was shown on the porous junctions of the material surface

Summary

Introduction

Silk fibroin (SF) extracted from the natural silkworm cocoon has attracted attention as one of the most promising bioengineering materials due to its unique molecular structure, excellent biocompatibility, morphologic flexibility, ability to promote cell adhesion and growth, and lower inflammatory response [1,2,3,4,5,6]. SF is transformed into various tunable morphologies such as nanofibers, thin films, and particles by controlling the secondary structure of SF proteins It is difficult for a single material to fit all the requirements of a specific biological function or a desired application because of defects in individual material properties. A novel nonwoven sheet of SF/polyurethane blending for cardiovascular tissue engineering exhibited good miscibility and feasible mechanical properties [8,10]. These changes in the material properties are closely related to their structure and morphology. Our previous study [12] illustrated that a nanocomposite structure transition to a micro-composite structure in the silk and non-crystallizable polylactic acid composites occurred when the silk content comprised at least 30% of the material, which affected their mechanical properties and cell adhesion

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