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Silk sericin is a degumming product used by the silk industry. The degumming process can affect the protein structure and molecular weight of silk sericin. The present study examined how pretreatment with 4-hexylresorcinol (4HR) affects the biomedical properties of silk sericin. Before the degumming process, silkworm cocoons were treated with 4HR solution. The protein structure of the final degumming product was evaluated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy. Untreated silk sericin (S) and silk sericin pretreated with 4HR (S+4HR) were added to RAW264.7 cells, and the expression of BMP-2 was determined. The bone-regenerating capacity of S+4HR was evaluated using the critical-sized rat calvarial defect model. Compared with S, S+4HR showed an increase in β-sheet structures. Administration of S+4HR to RAW264.7 cells increased expression of BMP-2, mainly via the TLR-mediated signaling pathway. Bone volume, as measured by micro-computerized tomography, was significantly greater in the S+4HR group than in the S, gelatin alone, and unfilled control groups (p < 0.05 each). Expression of BMP-2 and runx2 in tissue specimens was significantly higher following treatment with S+4HR than with S (p < 0.05). Taken together, these findings show that 4HR pretreatment before the degumming process increased the β-sheet structure of silk sericin, as well as inducing BMP-2 expression and bone regeneration ability.

Bone morphogenic protein-2/4 (BMP-2/4) is an osteoinductive protein that accelerates osteogenesis when administered to bony defects. Sericin is produced by silkworms, and has a biological activity that differs depending on the degumming method used. Our results indicated that the high molecular weight fraction of silk sericin (MW > 30 kDa) obtained via sonication had a more abundant β-sheet structure than the low molecular weight fraction. Administration of the β-sheet structure silk sericin increased BMP-2/4 expression in a dose-dependent manner in RAW264.7 cells and human monocytes. This sericin increased the expression levels of toll-like receptor (TLR)-2, TLR-3, and TLR-4 in RAW264.7 cells. Application of a TLR-2 antibody or TLR pathway blocker decreased BMP-2/4 expression following sericin administration. In the animal model, the bone volume and BMP-2/4 expression were higher in rats treated with a sericin-incorporated gelatin sponge than in rats treated with a gelatin sponge alone or a sponge-incorporated with denatured sericin. In conclusion, sericin with a more abundant β-sheet structure increased BMP-2/4 expression and bone formation better than sericin with a less abundant β-sheet structure.

The main flaw of silkworm cocoon originated membranes for guided bone regeneration (GBR) techniques is that the maximum size of the membrane is determined by the size of the cocoon. Flatwise-spun silk does not have any limitation to its production size. The objective of this study was to compare flatwise-spun silk mats with cocoon-derived silk mats for a GBR technique. Tensile strength, scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy and sericin contents analysis were done for in vitro test. Bone regeneration ability was tested in the critical sized defect of the animal model. In this study, flatwise-spun silk mats showed lower tensile strength and similar tensile strain to a cocoon-derived commercialized silk mat (TDI). Compared to TDIs, the flatwise-spun silk mats showed a similar second derivative spectrum, but they showed an increased abundance of the random coil and helix structures in the FT-IR spectra because of a higher content of sericin. In animal model experiments, the bone volume (BV) after the application of a flatwise-spun silk mat was similar to the volume observed after the application of a TDI. Both groups showed a significantly higher BV compared to an unfilled control group (P

There is an association between diabetes and impaired bone healing. The purpose of this study was to determine whether sericin had a positive effect on bone regeneration with streptozotocin-induced diabetes in a rat model. Sprague Dawley rats (n = 21) were assigned to one of three groups. A critical-sized bone defect was created on the calvaria. In the sericin group (S group, n = 7), the bone defect was filled with a sericin–gelatin combination, whereas in the gelatin group (G group, n = 7), only gelatin sponge was used. The control group (N group, n = 7) did not receive any graft. New bone formation was evaluated by micro-computerized tomogram and histological analysis. The regenerated bone volume in group S was the highest among the three groups (3.87 ± 2.51 mm3), followed by group N (1.71 ± 1.65 mm3) and group G (1.24 ± 1.05 mm3). The application of sericin in combination with a gelatin sponge enhanced the process of bone regeneration in streptozotocin-induced type I diabetes animal model.