Study on mechanism for mechanical strengthening of spider silks by ultraviolet rays as a new material.

点击翻译按钮获取中文摘要

Recently, many researchers have focused on spider silks as a new material. However, there are no reports on effects of ultraviolet(UV) rays upon the mechanical properties of spider silks. I found that UV rays mechanically strengthened the draglines secreted from Nephila clavata spiders which were active in daytime. That is, the mechanical strength increased shortly after the UV-irradiation, reached a maximum and decreased gradually.Actually, the mechanical strength of draglines increased by ca.50 % for the irradiation of UV-A, by ca.40 % for the irradiation of UV-B and ca.7 % for the irradiation of UV-C, compared with the value before the UV-irradiation. The mechanical strength strongly depends on the molecular weight. It was found by ESR method that UV-irradiation induced radicals. The radicals lead to a decrease in the molecular weight ascribed to the chemical cleavage in protein and also to an increase in the molecular weight ascribed to the cross links between protein molecules. Thus, the maximum in the mechanical strength may come from the two factors of a decrease of mechanical strength ascribed to the chemical cleavage in protein molecules and of an increase of mechanical strength ascribed to the creation of cross links. Finally, the results suggest that UV-irradiation mechanically strengthens the orb-web and lengthens the period of rebuilding the orb-web. As a result, the spider utilizes UV rays effectively as an environmental factor.