Moisture Characteristic and Structure of High Molecular Weight Sericin Film

Abstract

Sericin, a silk protein, shows a high moistureretaining property and an ultraviolet ray absorbability, and has been applied for a textile processing of medicines and a cosmetic additives.1 It is clarified by recent studies that sericin has many physiological effects, such as an anti-oxidative effect, a cancer prevention and a dermatitis improvement, etc.2–6 Furthermore, the practical physical properties of the sericin make it a promising material for the field of medical supplies. Sericin adheres firmly with fibroin protein. Since it has high molecular weight, most of sericin is insoluble in water at room temperature.7 Industrially, sericin can be extracted by the scouring of silk fabric and silk yarn in an alkaline solution under high temperature and pressure. The molecular weight of the sericin obtained is greatly lowered by the hydrolysis, and then the water solubility increases. Therefore, the material, such as a film or membrane, composed only the low molecular weight sericin is lacking in the practicability, because of the material simply dissolves in the water. One of the authors examined the chemical cross-linking using dimethylolurea (DMU), and membranes obtained showed water resistance.8 However, to utilize for medical supplies, it is desirable to unused the other substance, such as cross-linking agent because of toxicity. In addition, Katoh suggested that the physiological effects of sericin depend on the molecular weight.9 Recently, we developed a new process to efficiently obtain the sericin, which maintain high molecular weight.10, 11 Furthermore, we found that the film prepared by this sericin showed water resistance and large mechanical properties. In order to apply this material to the medical field, it is necessary to evaluate the moisture characteristic or the structure. In this paper, it is reported that the high molecular weight sericin film compared with the cross-linking sericin film on moisture characteristic and structure. EXPERIMENTAL