Preparation and Characterization of Novel Biodegradable Blend from Silk Fibroin and Rice Starch

Abstract

In this research, silk fibroin (SF) and rice starch (RS) which are natural polymers and environmentally non-toxic. In addition, they are also biocompatible and biodegradable. Both of them were blended for preparing dense and porous films which can be utilized for medical use. Starting with preliminary study on the preparation of SF and RS films, then the physical properties and structural conformation of the blended films after treating with ethanol for 30 min were studied. The physical appearance of the SF–RS blended films obtained was slightly curled up in water, in contrast with the complete curled up of the RS film due to the influence of water insolubility of -sheet SF. Moreover, the structural conformation of the SF–RS blended films analyzed by Fourier transform infrared spectrometry (FTIR) revealed the occurrence of the H-bonding between the N–H groups of SF and the O–H groups of RS. Then the SF–RS dense films were prepared by solution casting and also the optimum weight ratio of SF:RS for preparing the blended films was investigated. The solutions of SF and RS were mixed at various weight ratios and then evaporated at room temperature for 72 h. The appearing character of the films was found to be cracked when more SF was added, while the dense film at 5:95 weight ratio of SF:RS exhibited slightly more elastic. Thus this ratio was selected as optimum weigh ratio for blended film preparation. The SF–RS porous films were also prepared by freeze drying using the same 5:95 weight ratio. The mixed solution was poured into a mold, frozen at -10 to -20 C for 18 h and then sublimed in a freeze dryer for 48 h. The study of the physical properties from appearing character found that both dense and porous SF–RS films at 5:95 weight ratio were yellowish white, slightly elastic, water swelling and could dissolve slightly in water. Next step, in order to improve some properties of the dense and porous films, the modification of the films was done through the addition of STMP. The solutions of SF and RS were mixed, adjusted to pH 12, added various STMP contents and stirred about 30 min before being neutralized to pH 7, followed by film forming using solution casting. The cross-sectional morphology and mechanical properties of the films were then examined by scanning electron microscopy (SEM) and universal mechanical testing, respectively. The structural conformation of the films was investigated by FTIR and 1H NMR. The crosslinking density value of the films was determined by UV/Vis spectrophotometry via the measurement of the relative amount of methylene blue (RMB) bound to the films. Furthermore, percentages of porosity, degree of swelling, solubility, and oxygen permeability were calculated. Result from the SEM images revealed that the pore size of the dense film could not be detected, while the pores size of the modified porous films increased from 17 m to 126 m after 0.0–5.0 %w/w STMP was added. The STMP modified dense and porous films showed the decrease of tensile strength and compressive strength with the increase of STMP contents. The FTIR and 1H NMR spectra displayed the linkages within the films that occurred mainly between the O–H groups of RS and the triphosphate groups of STMP. From the MB adsorption study, the saturation time of the dense and porous films of SF–RS–1%STMP at 30 C was about 60 min. Moreover, cross-linking density of the dense and porous films increased with the increasing content of STMP, evidenced from the increase of relative amount of methylene blue adsorption. The addition of STMP also affected the physical properties of the modified dense and porous films such as porosity, degree of swelling and oxygen permeability but not the water solubility. The final study was the standard test to meet the requirements for being absorbable film considering from the residual ash and degradation of both films. The residual ashes of the modified dense and porous films after incinerating at 850 C for 3 h were found to be lower than 2 % by weight of the films, except the SF–RS–1%STMP dense film that had 2.7 % of the residual ash remained . As for the degradation of both films being immersed in 0.01 M PBS at pH 7.4 and 37 C for 1 to 56 days, Results showed that the degradation of both films ceased after soaking in 0.01 M PBS solution for about 14 days which could be regarded as passing the standard test for being absorbable films.