EFFECTS OF PLASMA TREATMENT OF THAI SILK FIBROIN ON CELLULAR RESPONSES

Abstract

This research aimed to study the effects of plasma tretment on the physical and biological properties of Thai silk fibroin (SF). A preliminary study was conducted to evaluate whether plasma treatment could improve the biocomatibility of silk fibroin surface. Nitrogen glow discharge plasma generated by AC 50Hz power supply was employed to treat the SF film. The results showed that N2 plasma improved surface wettability and early adhesion of L929 mouse fibroblast. The XPS surface chemistry results showed that hydrophilic functional groups were induced on plasma-treated SF. The bulk chemistry of SF was unchanged after plasm treatment as confirmed by FTIR-ATR. The AFM surface topographical results indicated no significant change after plasm treatment. The encouraging results that N2 plasma could improe the biocompatibility of SF led into an in-depth investigation of plasma treatment on SF. This started with the comprehensive characterization of well-defined planar SF, which was prepared as a thin film, allowing a complete assessment of all analytical techniques. XPS results showed that well-defined SF and a surface chemistry which was similar to the theoretical molecular structrue of SF. Streaming potential indicate that SF was a negatively charged surface. The spectroscopic ellipsometry results revealed that SF thicknees was increased in a liquid environment compared to a dry state. This observation suggested that SF was a swollen material. Moreover, SF swelling degree in liquid depended on liquid ionic concentration but not on liquid temperature. Plasma experiments were conducted to find out treatment conditions for desirable surface functionalization. The results showed that the desirable surface functional groups were successfully induced on the surface. However, the induced functional groups from plasma-treated SF could be removed by rinsing with DI. The thickness loss was also observed after plasma treatment. These findings suggeted that plasma etching of SF was more prominent than plasma functionlization. The most significant plasma-treated effect was the increased elastic modulus of O2 plasma-treated SF, as revealed by AFM based nano-indentation (from 62 to 500 kPa). The characterization of other related properties (e.g. XPS spectra, degree of crystallinity,surface charge, swelling degree, surface wettability, and FN adsorption) revealed that these properties were minimally affected from plasma treatment. These findings inspired the use of plasma etching of SF to alter suface stiffness for cell-substrate interaction study. L929 and hMSC were chosen for the study based on their different ECM stiffness. In vitro results showed that the increased stiffness of plasma-treated SF enhanced L929 adhesion and spreading, not hMSC. L929 attachment and spreading were better on stiffer O2 plasma-treated SF, while hMSC spread well on all SF surfaces.