Many biological tissues and even single cells show a strain-stiffening behaviour, i.e. they stiffen upon extension. If a surface beneath a cell is strained, the cell forms focal adhesions and subsequently, actin filaments arrange as stress-fibres, which crosslink via proteins, within the cell. Hence, these bundled stress-fibres increase the overall stiffness of the cell in response to stretch. Taking the cell’s strain-stiffening behaviour as an inspiration, a synthetic, mechanical metamaterial design has been achieved. The intracellular effect is mimicked by the structural features of the complex three-dimensional material: Parallel elastic slats between several backbones form the elements that induce the strain-stiffening effect. During elongation of this cell-inspired material, the flexible slats touch each other causing a change in the mechanical properties of the structure, which leads to stiffening. The strain-stiffening effect that we investigate is highly non-linear, tuneable, rate and material independent and reversible.

By variations in the geometry of the material’s structure, the mechanical properties can be finely tuned, allowing our metamaterial to provide optimal function and optimal mechanical properties for usage in biomedical applications. Since mimicking the mechanical properties of tissue with synthetic materials is a highly important aspect in implant design, the tunability of our material was investigated with finite element analysis, tensile tests and adaptation of three-dimensional geometry and variation in total scale, thus promoting the integration of this strain-stiffening structure in future applications.