Fabrication, characterization and wound healing effect of silk fibroin-graphene nanoplatelets composite films

Abstract

Silk fibroin (SF) obtained from Bombyx mori silkworm cocoon is an insoluble protein-based polymer that widely used in biomaterial applications, including wound healing. A pristine SF film can be prepared via a solution casting method, but the film has poor strength (i.e. brittle). The main drawbacks of SF film are the brittleness of the films that can be overcame via post-treatment (ethanol immersion, methanol immersion and water annealing). Attenuated total reflectance- Fourier transformed infrared spectroscopy (ATR-FTIR) showed that SF films were presented in a more stable form after ethanol (80% v/v) post treatment. The peaks of silk II structure from amide I and II of the ethanol treated films were shifted to 1620 cm-1 and 1510 cm-1 and the crystallinity results is supporting by X-ray diffraction (XRD) analysis. The introduction of nano-sized graphene platelets (GNP) into the SF systems to form SF-GNP composite films could enhance the physical, mechanical and thermal properties of the film. Drawbacks, due to brittleness and less flexibility, the GNP fillers were poorly dispersed throughout the SF matrix. Hence, glycerol (20 wt.%) as a plasticizer was introduced into the SF-GNP system in order to increase the flexibility, thus assisting the dispersibility of the GNP fillers. In this study, the effects of SF-GNP and post-treated SF-GNP composite films at various GNP loadings (0.1 wt.%-1.0 wt.%) were investigated. Results from ATR-FTIR revealed a high absorption intensity at the peak position 1620 cm-1 which correspond to the ??- sheet conformation of amide I (C=O stretching) for SF-GNP composite films and the post-treated composite films. The addition of GNP had increased the crystallinities of the SF-GNP composite films obtained from the plot of XRD. Comparing the results between the FTIR and the XRD findings, the relation between SF molecular chains and graphene can be connected. Thermal stabilities of the composite films were also increased with increasing GNP and the degradation rate, as measured by thermogravimetric analysis and biodegradation test. The addition of GNP and glycerol has also improved the flexibility (strain), the SF-0.7G has shown tremendously good flexibility of the composite which an increases up to 1180 % compare to pristine SF as demonstrated by tensile and the fracture surface of the films were examined using field emission scanning electron microscopy. Images from the transmission electron microscopy also shown GNP filler had been dispersed uniformly throughout the matrix. The results of in vitro cell culture displayed that the SF-GNP composite films had supported the cell survival and exhibited the optimal biocompatibility. The SF-GNP composite films showed several potentially wound healing properties where the composites have the ability to recover from wound scratching assay test. From all of the results obtained, the SF-GNP better results in mechanical and thermal properties compared to the post-treated SF-GNP. Thus, SF- 0.7G revealed the best results compared to other formulation which shows good flexibility and wound healing properties compared to others. In conclusion, SF-GNP composite films offer a new option in biomaterial choice for the development of wound healing.