Ultra-soft cellular solids inspired by marine mussel plaques: scaling of the mechanical properties

The porous core of the marine mussel provides mechanical advantages of achieving substantial deformation and high toughness. Inspired by the unique mechanical behaviours of mussel plaque cores, the present study develops ultra-soft, stretchable and tough cellular solids by bio-mimicking their porosity and properties. Although scaling laws to correlate the mechanical properties of cellular solids with bulk materials have been established, they are primarily based on experimental data from stiff cellular solids. In this article, the scaling law for soft cellular solids is studied to relate tensile properties and toughness with volume fractions. Unlike conventional stiff cellular solids, the scaling law shows that soft lattices experience bending-dominated deformation at the elastic state and fail under stretching-dominated deformation. Uniaxial and planar tensile tests demonstrate that the proposed soft lattices achieved Young’s modulus of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>0.04</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>0.17</mml:mn> </mml:mrow> </mml:math> MPa, failure strain of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>135.5</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>213.9</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> and toughness of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>582</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>941</mml:mn> </mml:mrow> </mml:math> J m −2 by manipulating the volume fraction ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>0.2</mml:mn> <mml:mo>∼</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:math> ), positioning them as softer, more stretchable and tougher than the majority of engineering foams in the Ashby diagram. In addition, the toughness of soft lattices is found to be sensitive to volume fraction but insensitive to initial crack length, thickness and height ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mstyle displaystyle="true" scriptlevel="0"> <mml:mrow> <mml:mo>≥</mml:mo> <mml:mn>20</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mi mathvariant="normal">m</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> </mml:mstyle> </mml:math> ). Two distinct failure modes, truss failure and joint failure, are correlated with volume fraction. The soft lattice with a volume fraction (around 0.4) similar to mussel plaque fails at the transition of these two failure modes and achieves the highest toughness. This study contributes new insights to the materials science community and lays the foundation for the development of lightweight, damage-tolerant and high-performance metamaterials.