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.

Diversely halogenated spiropyrans - Useful synthetic building blocks for a versatile class of molecular switches

“…[1][2][3] Molecular switches are therefore instrumental for the development of new "intelligent" materials, [4] or molecular machines. [5] Spiropyrans belong to the most important molecular switches, because of the exceptionally large variety of diverse stimuli that can be used for switching: Their isomerization between a closed spiropyran form and an open merocyanine form can be induced by light, [6] pH, [7][8][9][10] the presence of ions, [11][12][13] pressure, [14] mechanical force [1,2,[14][15][16][17][18][19][20][21] as well as electric fields. [19,22] Of those stimuli, the light induced switching provides to be easily accessible and nondestructive.…”

Mechanical gating of a mechanochemical reaction cascade

“…Covalent polymer mechanochemistry12345 has been extensively explored in recent years for a variety of purposes, including biasing reaction pathways6789, trapping transition states and intermediates1011, catalysis12131415, release of small molecules and protons161718, stress reporting19202122, stress strengthening222324 and soft devices2526. These efforts are largely facilitated by the fact that, unlike other energy sources, mechanical force is directional and regulated by local molecular structure.…”

Mechanically‐Driven Vase–Kite Conformational Switch in Cavitand Cross‐Linked Polyurethanes

“…In conclusion, two different polymeric matrices were investigated for promoting the vase‐kite interconversion of tetraquinoxaline cavitands via mechanochemical stimulus. Elastomeric PDMS, despite being known for the successful activation of spiropyran mechanophores, failed to evidence any maxima variation via UV‐Vis spectroscopy for both di‐ and tetrafunctionalized cavitands. The use of a more rigid PU matrix, together with the incorporation of tetrafunctionalized QxCav units as unique cross‐linkers into the polymeric network, resulted in the expected responsiveness upon tensile elongation, detected both via UV‐Vis and fluorescence spectroscopy.…”