Effect of molecular weight on the structure and mechanical properties of silk sericin gel, film, and sponge.

In this study, the effect of the MW on the structure and properties of sericin film, sponge, and gel was examined. As the MW of sericin increased, the gelation of the sericin aqueous solution was found to be accelerated, and the gel strength, and the gel-sol transition temperature increased. Irrespective of the casting solvent (water and formic acid) and form of sericin (gel, film, or sponge), the crystallization of the sericins was accelerated. The mechanical properties of the sericin sponge were remarkably improved upon increasing the MW of sericin. The MW of sericin almost did not have an effect on the cell toxicity. As the MW of sericin is increased, the sericin sponge becomes denser and its porosity is reduced, leading to a decrease in the swelling ratio. These results indicate that various characteristics of the sericin forms can be modulated by controlling the MW of sericin, with enhanced potential for biomedical and cosmetic applications.

Preparation of new natural silk non-woven fabrics by using adhesion characteristics of sericin and their characterization.

Electro-spun regenerated silk webs have been extensively studied for biomedical applications because of the simplicity of their fabrication methods However, the productivity of the electro-spinning process is low for web fabrication and the mechanical properties of the electro-spun silk web are not satisfactory, which restricts its commercialization. In this study, a new silk non-woven fabric was successfully fabricated by wetting and hot press treatments using the excellent binding characteristic of sericin. The effects of the press temperature and residual sericin content on the preparation, structure, and properties of the silk non-woven fabric were examined. A press temperature of 200°C was optimum for obtaining non-woven fabrics with best mechanical properties, without yellowing. The silk non-woven fabric could not be fabricated without sericin, and a minimum of 8% sericin was required to fabricate it. As the sericin content was increased, the strength and Young's modulus of the silk non-woven fabric increased, while the tensile elongation remained constant. Regardless of the press temperature and sericin content, all the silk non-woven fabrics showed good cell viability, comparable to that of the tissue culture plate (TCP) used as a control until 4days, which however decreased compared to that of TCP after 7days.

Effect of degumming condition on the solution properties and electrospinnablity of regenerated silk solution.

The application of silk on tissue engineering scaffolds has been studied intensively because silk has an electrospinning technique using a good blood compatibility, excellent cytocompatibility and biodegradability. Silk consists of two polymers, fibroin and sericin. In spite of importance of sericin, most studies were focused on the fibroin only and the effect of residual sericin on the electrospinning performance of silk has not been considered. In this study, regenerated silk with different residual sericin contents was prepared by controlling the degumming conditions. The effects of the degumming conditions on the solution properties and electrospinning performance of silk were examined. The fast protein liquid chromatography (FPLC) measurements confirmed that the molecular weight of the regenerated silk decreased slightly with increasing residual sericin content. More molecular aggregation of silk occurred with increasing sericin content, resulting in an increase in the solution turbidity of formic acid. All silk formic acid solutions exhibited almost Newtonian fluid behavior and the viscosity increased with increasing sericin content. Interestingly, the dope solution viscosity of silk increased remarkably at sericin contents <1% (or degumming ratio >25%) leading to significant improvements in electrospinnability and an increase in the fiber diameter of the silk web.