A Minimalistic, Synthetic Cell‐Inspired Metamaterial for Enabling Reversible Strain‐Stiffening

Abstract

Strain‐stiffening, i.e. the nonlinear stiffening of a material in response to a strain, is an intrinsic feature of many biological systems, including skin, blood vessels, and single cells. To avoid a mismatch in mechanical properties, synthetic materials in contact with such biological systems should also be strain‐stiffening. Conventional strain‐stiffening materials are either highly dependent on the applied strain‐rate, or only available for a limited stiffness regime. Both aspects limit the applicability of these materials. In contrast, living cells employ a dynamic strain‐stiffening mechanism that is based on the cross‐linking of cytoskeletal fibers in response to external stress. This strain‐stiffening of the cytoskeleton is mimicked in a mechanical metamaterial by a minimalistic structure consisting of parallel slats connected to backbones. Herein, it is demonstrated experimentally that the structures can be adapted such that the strain required for stiffening, the final stiffness, as well as the degree of stiffening can be tuned, particularly by combining several strain‐stiffening elements. These properties make the structure promising for the development of devices that should resemble the mechanical properties of human soft tissues, e.g., skin‐integrated flexible electronics and blood vessel grafts.

Hard- and Soft-Coded Strain Stiffening in Metamaterials via Out-of-Plane Buckling Using Highly Entangled Active Hydrogel Elements

“…Many polymer networks possess a similar stiffening behavior, where polymer chain coils initially uncoil under applied strain until reaching a critical value. Thereafter, the initial compliant chain bending transitions into chain stretching with a resulting stiffening. , Generally, the network structure predefines the resulting J-shaped stress–strain curves. − Strain stiffening is an important biological mechanism for self protection and gives inspiration for synthetic materials to improve reliability and durability, and avoid material failure.…”