Abstract
Sericin, a natural protein from silk cocoon, has been reported for various biological properties in the biomaterials field. Modified forms of sericin have been studied for bone tissue engineering, while its unmodified form has been scarcely reported. Therefore, the purpose of this study was to evaluate physical and biological properties of unmodified sericin for potential use in bone surgery. Sericin was extracted from silk cocoons using a chemical-free boiling method. Sericin extract showed distinct bands with molecular weight ranging from 25 to 42 kDa including smear bands. Fourier transform infrared spectra presented characteristic peaks of amide I, II, and III, confirming the chemical composition of sericin. Based on biological activity, sericin extract at a concentration of 40 μg/mL increased the proliferation of osteoblast cells up to 135%, compared with the untreated control. Moreover, increase in antibacterial activity against Staphylococcus aureus, both clinical isolates and the reference strain ATCC 29213, was demonstrated for sericin extract with normal saline, while no antibacterial activity was observed for sericin with broth. It was found that sericin with normal saline showed higher zeta potential than sericin without normal saline, indicating higher system stability. This was confirmed by the average particle size of sericin extract with NaCl (3,249.3±226.1 nm) showing approximately 10 times smaller than sericin solution (29,015.9 ± 8,085.6 nm). Furthermore, sericin extract at the minimal inhibitory concentration significantly reduced the biofilm formation of S. aureus up to 95%. The study indicates biological activities of sericin, which could be applied as a dual-functional bioactive material to support bone regeneration and treat bone infections.
Highlights
The main proteins from Bombyx mori’s silk cocoon threads of raw silk are fibroin and sericin
Sericin is presently studied for biomedical applications, especially for promoting collagen production, which is important in wound healing in the skin and accelerating osteogenesis in the bone healing process [8]
Fourier transform infrared spectroscopy (FT-IR) spectroscopic characteristics of the extract were very closely similar to the commercial sericin, exhibiting amide I peak at 1655 cm-1, amide II peak at 1541 cm-1, and amide III peak at 1244 cm-1
Summary
The main proteins from Bombyx mori’s silk cocoon threads of raw silk are fibroin and sericin. In the silk textile industry, sericin is removed from fibroin in wastewater during the processing. The global silk production statistics show that approximately 50,000 tons per year of sericin is discarded [1]. Recovery and recycling of sericin from the silk process waste could provide high scientific and economic values. Sericin has interesting physical attributes of elasticity and tensile strength, and exhibits various biological activities, including antioxidant, moisturizing, antitumor, cell proliferation promoting, and collagen production supporting activities [3–7]. Sericin is presently studied for biomedical applications, especially for promoting collagen production, which is important in wound healing in the skin and accelerating osteogenesis in the bone healing process [8]. Several studies have investigated the use of sericin in wound healing applications, while bone healing has been scarcely studied. The potential of biofilm inhibition and disruption activities against Streptococcus mutans has been demonstrated for sericin extracted using urea and autoclaving [10]
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