Polypeptide-based vapor-responsive porous poly(ionic liquid) actuators: From reversible to unexpectedly irreversible actuation

Soft actuators capable of large and swift locomotion in combination with biocompatibility hold great potential in medicine and healthcare applications. In this contribution, a polypeptide-type poly(ionic liquid) (termed “PLL-PMIM-Tf 2 N”) was designed and synthesized by post-polymerization modification of poly- L -lysine; Next, via controlled electrostatic complexation with poly(acrylic acid) (PAA) or poly( L -glutamic acid) (PLG), porous membrane actuators termed PLL-PMIM-Tf 2 N/PAA or PLL-PMIM-Tf 2 N/PLG, respectively, were tailor-made. Hemolytic tests support excellent blood cell compatibility of the fully polypeptide-based PLL-PMIM-Tf 2 N/PLG actuator. The as-made soft actuators could bend significantly up to 500°with a maximum curvature of 7 cm −1 in response to solvent vapor in a fast actuation process within 2 s. Their high sensitivity towards solvent molecules equips them with skills to distinguish solvent isomers, as exemplified by butanol isomers, in terms of bending curvature due to varied molecular interactions between the actuator and the isomer. To be highlighted is an unusual irreversible actuated tubular state of the fully polypeptide-based PLL-PMIM-Tf 2 N/PLG actuator that is stable in shape and resembles bionic blood vessels. Such polypeptide-type poly(ionic liquid) actuators are of significant value in future development of biocompatible devices for medical and healthcare applications.