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Gamma irradiation, which is one of the more conventional sterilization methods, was used to induce the hydrogelation of silk fibroin in this study. The physical and chemical characteristics of the irradiation-induced silk fibroin hydrogels were investigated. Silk fibroin solution with a concentration greater than 1 wt% formed hydrogel when irradiated by gamma rays at a dose of 25 or 50 kGy. The hydrogel induced by 50 kGy of radiation was more thermally stable at 80 °C than those induced by 25 kGy of radiation. When compared to the spontaneously formed hydrogels, the irradiated hydrogels contained a greater fraction of random coils and a lower fraction of β-sheets. This finding implies that gelation via gamma irradiation occurs via other processes, in addition to crystalline β–sheet formation, which is a well-established mechanism. Our observation suggests that crosslinking and chain scission via gamma irradiation could occur in parallel with the β–sheet formation. The irradiation-induced hydrogels were obtained when the solution concentration was adequate to support the radiation crosslinking of the silk fibroin chains. This work has, therefore, demonstrated that gamma irradiation can be employed as an alternative method to produce chemical-free, random coil-rich, and sterilized silk fibroin hydrogels for biomedical applications. [ABSTRACT FROM AUTHOR]

Hydrogels are soft materials that contain high water content within their 3-dimensional structure. Such extremely hydrated environment allows hydrogels to recapitulate the structure of many native tissues inside the body. In biomedical application, hydrogels have been extensively used as biocompatible materials, drug delivery systems, and tissue-engineered scaffolds that can be designed to possess either permanent or slow-degradation properties. In this research, we applied gamma irradiation to develop transparent and conformal hydrogel sheets with sufficient mechanical strength from poly(vinyl alcohol) (PVA) and further modified the based PVA matrix with naturally-derived silk fibroin (SF) protein and silver nitrate (AgNO3) for wound healing purpose. The physical and mechanical properties of based PVA hydrogels formed at varied irradiation doses from 10 - 80 kGy were first characterized. The dose of 60 kGy was found to be optimal to process flexible and elastic PVA sheets with equilibrium degree of swelling of 1000%, gel fraction of 90%, and tensile strength of 19 kPa. To further enhance water absorption capacity, 10 - 40% (w/w) silk fibroin was added to the based PVA matrix. Based on water absorption and gel fraction data, hydrogel sheets with 8PVA:2SF formulation was selected for antibacterial test. Disc diffusion assay showed that the incorporation of 0.4 mM AgNO3 in 8PVA:2SF hydrogel sheets could inhibit the growth of Staphyllococcus aureus and Pseudomonas aeruginosa. These results demonstrated that a prototypic, antibacterial hydrogel sheet dressing composed of both synthetic and natural polymers could be developed within a single-step by gamma irradiation technique. [ABSTRACT FROM AUTHOR]

Radiolytic synthesis provides a convenient and environmentally-friendly approach to prepare metallic nanoparticles in large scale with narrow size distribution. In this report, colloidal silver nanoparticles (AgNPs) were synthesized by gamma radiation using poly(vinyl alcohol) (PVA) or silk fibroin (SF) as stabilizers and were evaluated for their antibacterial properties. The conversion of metallic silver ions to silver atoms depended on irradiation dose and stabilizer concentration as determined by UV-Vis spectrophotometry and transmission electron microscopy. The uniformly dispersed AgNPs with diameter 32.3 ± 4.40 nm were evaluated as antiseptic agents in films composed of chitosan, SF, and PVA that were processed by irradiation-induced crosslinking. Using disc diffusion assay, the films containing 432 ppm AgNPs could effectively inhibit the growth of both Staphylococcus aureus and Pseudomonas aeruginosa. Therefore, we have demonstrated in our present study that gamma radiation technique can potentially be applied in the mass production of antibacterial wound dressings. [ABSTRACT FROM AUTHOR]