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Creators/Authors contains: "Wallin, Thomas J."

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  1. In both biological and engineered systems, functioning at peak power output for prolonged periods of time requires thermoregulation. Here, we report a soft hydrogel-based actuator that can maintain stable body temperatures via autonomic perspiration. Using multimaterial stereolithography, we three-dimensionally print finger-like fluidic elastomer actuators having a poly- N -isopropylacrylamide (PNIPAm) body capped with a microporous (~200 micrometers) polyacrylamide (PAAm) dorsal layer. The chemomechanical response of these hydrogel materials is such that, at low temperatures (<30°C), the pores are sufficiently closed to allow for pressurization and actuation, whereas at elevated temperatures (>30°C), the pores dilate to enable localized perspiration in the hydraulic actuator. Such sweating actuators exhibit a 600% enhancement in cooling rate (i.e., 39.1°C minute −1 ) over similar non-sweating devices. Combining multiple finger actuators into a single device yields soft robotic grippers capable of both mechanically and thermally manipulating various heated objects. The measured thermoregulatory performance of these sweating actuators (~107 watts kilogram −1 ) greatly exceeds the evaporative cooling capacity found in the best animal systems (~35 watts kilogram −1 ) at the cost of a temporary decrease in actuation efficiency.
  2. Inspired by nature, we herein demonstrate a family of multi-responsive hydrogel-based actuators that are encoded with anisotropic swelling behavior to provide rapid and controllable motion. Fabrication of the proposed anisotropy-encoded hydrogel actuators relies on the high resolution stereolithography 3D printing of functionally graded structures made of discrete layers having different volume expansion properties. Three separate synthetic strategies based on (i) asymmetrical distribution of a layer's surface area to volume ratio via mechanical design, (ii) crosslinking density via UV photo-exposure, or (iii) chemical composition via resin vat exchange have been accordingly demonstrated for developing very smooth gradients within the printed hydrogel-based actuator. Our chemomechanical programming enables fast, reversible, repeatable and multimodal bending actuation in response to any immediate environmental change ( i.e. based on osmotic pressure, temperature and pH) from a single printed structure.