Mechanochemically Active Soft Robots

Abstract

The functions of soft robotics are intimately tied to their form-channels and voids defined by an elastomeric superstructure that reversibly stores and releases mechanical energy to change shape, grip objects, and achieve complex motions. Here, we demonstrate that covalent polymer mechanochemistry provides a viable mechanism to convert the same mechanical potential energy used for actuation in soft robots into a mechanochromic, covalent chemical response. A bis-alkene functionalized spiropyran (SP) mechanophore is cured into a molded poly(dimethylsiloxane) (PDMS) soft robot walker and gripper. The stresses and strains necessary for SP activation are compatible with soft robot function. The color change associated with actuation suggests opportunities for not only new color changing or camouflaging strategies, but also the possibility for simultaneous activation of latent chemistry (e.g., release of small molecules, change in mechanical properties, activation of catalysts, etc.) in soft robots. In addition, mechanochromic stress mapping in a functional robotic device might provide a useful design and optimization tool, revealing spatial and temporal force evolution within the robot in a way that might be coupled to autonomous feedback loops that allow the robot to regulate its own activity. The demonstration motivates the simultaneous development of new combinations of mechanophores, materials, and soft, active devices for enhanced functionality.

Keywords: PDMS; mechanochemistry; mechanochromic; soft robot; spiropyran; stimuli-responsive.