Guided Design of Strain-Adaptive Polymer Networks*

Mimicking the mechanical behavior of biological tissues is crucial for medical implants and wearable electronic devices. Many biological tissues are supersoft at small deformations (Young’s Modulus E₀<10 kPa) and stiffens as deformation increases. This combination of softness and nonlinear elasticity cannot be duplicated by synthetic elastomers composed of linear polymers. Graft polymers (combs or bottlebrushes), consisting of linear backbones with grafted side chains, endow polymeric materials with diluted backbone entanglements and backbones pre-stretching due to steric repulsions between side chains. These distinct features pave the way for the design of supersoft materials with controllable nonlinear elasticity. Such materials can be prepared by chemical crosslinking of graft polymers or by self-assembly of linear-bottlebrush-linear triblock copolymers. We have developed a design strategy to encode the nonlinear mechanical response of soft materials through the architecture of graft polymer networks by changing the strand length, side chain length, side chains grafting density and block lengths. Materials replicas of jellyfish, artery and skin tissues based on poly(dimethylsiloxane) bottlebrushes were synthesized to verify the design approach.