Physico-chemical Studies of Spider's Silks Resistant to Ultra-violet Rays

紫外线通常照射在室外的圆网上，因此研究紫外线对蜘蛛丝物理性质的影响是一个有趣的课题。特别是，在紫外光照射前后，对拉绳的力学性能进行测试，对研究紫外光照射的效果具有重要意义。由拉铲的应力-应变曲线确定了拉铲的断裂强度和弹性极限强度。用电子显微镜观察了拉丝的微观结构，确定了拉丝的横截面直径，并测量了在不受紫外线照射前，蜘蛛生长不同阶段拉丝的力学性能。安全系数（弹性极限强度与蜘蛛体重的比值）测定结果表明，成熟蜘蛛的安全系数约为2，未成熟蜘蛛的安全系数约为3，紫外线照射降低了蜘蛛的断裂强度，但长时间紫外线照射后，蜘蛛的弹性极限强度基本不变。紫外线照射使构成拖丝的蛋白质分子发生分解，使拖丝的分子量降低，蜘蛛丝对紫外线的耐受性强于桑蚕丝，幼蜘蛛丝的耐受性强于成熟蜘蛛丝。

It is interesting to study the effects of ultraviolet rays upon the physical properties of spider silks because the ultraviolet (UV) rays are usually irradiated to the orb-web outdoors. Especially, it is important to measure the mechanical properties of dragline before and after the UV-irradiation to study the effects of the irradiation.The samples used here were the draglines from Nephila clavata at different stages of growth. The breaking strength and the elastic limit strength were determined from the stress-strain curve of dragline. The fine structures were also observed by electron microscope to determine the diameter of cross section of dragline.The author measured the mechanical properties of dragline at different stages of spider's growth before the UV were not incident. The safety coefficient, which is defined as the ratio of the elastic limit strength to the spider's weight, was determined to be about 2 for mature spiders and to be about 3 for immature spiders.UV-irradiation decreased the breaking strength while it did not change the elastic limit strength even after the UV-irradiation of a long time. It was made clear that the UV-irradiation decomposed the protein molecules constituting dragline and might decrease the molecular weight.The present study shows that the spider silks are stronger to the UV-rays than the silks from silkworm and that they are stronger for juvenile spiders than form mature ones.