Abstract: Electronic single-fibre tensile instron and amino acid auto-analyser were used to test the amino acid compositions and mechanical properties of two types of egg case silk of spider with distinct functions, i.e. , inner cover and scaffolding egg case silks in order to investigate the relationship between the structure, mechanical properties and bio-function of these unique materials. The results demonstrate that when compared with scaffolding egg case silk, the egg case inner silk has less Gly and Proline but higher Ser and polar amino acid. Its initial modulus is smaller and the value of LC: SC is higher. Its tensile curve displays an increase in the elastic region, small extent in the yield region, and buffering state in the reinforcing region, indicating very good tenacity and reproducibility of tensile behavior.

Key words: spider, egg case silk, structure, mechanical property