Spider silk with weaker bonding resulting in higher strength and toughness through progressive unfolding and load transfer

The superior mechanical properties of silk is known to come partly from its hydrogen bonds, which is determined by its amino acid sequences. Hydrogen bonds are one of the main sources of strength of silk fiber, yet the toughest silk fibers have amino acids sequences that results in lesser number of hydrogen bonds than other silk fibers. In this work, we show how such silk fiber with lower number of hydrogen bonds may result in fiber with higher toughness by investigating the process of how hydrogen bond characteristics of silk are translated into its mechanical properties. From the tensile pulling tests via molecular dynamics simulations on silk fiber with varying number of hydrogen bonds, the mechanism of how weaker bonded silk results in higher strength and toughness by synergic effect with the characteristic progressive unfolding and load transfer of silk fiber is explained. The results provide new perspectives on how silk and other fibers should be designed to achieve higher toughness.