Research ArticleBIOMIMETICS

Autonomic perspiration in 3D-printed hydrogel actuators

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Science Robotics  29 Jan 2020:
Vol. 5, Issue 38, eaaz3918
DOI: 10.1126/scirobotics.aaz3918
  • Fig. 1 Material design and SLA 3D-printed actuator.

    (A) Chemistry of ionic composite hydrogels via photopolymerization of AAm and NIPAm in the presence of sulfonate-modified SiO2 and Fe3O4 using riboflavin photoinitiator, triethanolamine co-initiator, and MBA as a cross-linker. (B) Simplified architecture of the SLA 3D printer with resin replacement mechanism and exploded view of the actuator, which constitutes multimaterial layers; pink color represents the PAAm, brown color constitutes PNIPAm, and h represents the height of PAAm and PNIPAm body. (C) 3D-printed actuator with high surface area and multimaterial design. (C1) Actuator with pore design, texture, and strain-limiting layer. (C2) Animated model showing perspiration. (C3) 3D-printed actuator that resembles the animated model.

  • Fig. 2 Material characterization.

    (A) Apparent viscosity ηapp of AAm and NIPAm solution (plotted data are the average of N = 3 trials). (B) Tangent modulus, i.e., the calculated slope in the stress-strain curve at 15% compressive strain, for PNIPAm and PAAm at different temperatures (shaded regions represent SE in the line of best fit; error bars are SD; N = 7). (C) Gravimetric swelling ratio of 3D-printed PAAm sample versus temperature and time (plotted data are the average of N = 7 concurrent samples). (D) Gravimetric swelling ratio of 3D-printed PNIPAm sample versus temperature and time (plotted data are the average of N = 7 concurrent samples).

  • Fig. 3 Pore size, volume change, and bending characterization.

    (A) Pore size variation of PAAm/PNIPAm samples with different diameters and temperatures (shaded regions are SDs; N = 7). (B) Volumetric change in actuator at different temperatures and time. (C) Pneumatically actuated hydrogel actuator to attain maximum bending angle. (D) Bending angle versus input volume, actuator tested by water and air with different actuator designs (error bars mark the SD; N = 3; shaded regions represent SE in line of best fit).

  • Fig. 4 Sweating experiments.

    (A) 3D-printed hand: hydraulically controlled fingers assembled in a palm chassis. (B) Temperature variation in hydraulically actuated hand and actuators using thermal camera. (B1) Temperature recorded during the perspiration of a hand under forced convection. (B2) Temperature recorded during the perspiration of a single actuator under forced convection. (B3) Temperature recorded during the perspiration of an actuator under free convection. (C) Sweating test comparison with and without pores in different convection modes (shaded regions are SD; N = 3).

  • Fig. 5 Grasping and object cooling test with different heat capacity objects.

    (A) Grasping of metallic object in hot water in vertical state. (B) Grasping of an irregular soft foam. (C) Grasping of a cylindrical metallic object using three-point gripper. (In the reported thermal images, temperature scale bar is changing with time. Moreover, we measured the surface temperature only on the object using customized polygons according to the object shape.)

  • Fig. 6 Comparative physiology of the evaporative cooling capacity in animals and our finger actuator normalized to body weight.

Supplementary Materials

  • robotics.sciencemag.org/cgi/content/full/5/38/eaaz3918/DC1

    Section S1. Temperature dependence of mechanical properties

    Section S2. Gel fraction analysis

    Section S3. UV-visible spectroscopy

    Section S4. Photo-differential scanning calorimetry (photo-DSC)

    Section S5. Differential scanning calorimetry (DSC)

    Section S6. Physical property measurement system (PPMS)

    Section S7. Heat transfer test in high and low surface area

    Section S8. Modeling of heat capacity in finger-like actuators

    Section S9. Thermal manipulation of hot objects

    Fig. S1. 3D-printed actuator.

    Fig. S2. Hydrogel ink characterization.

    Fig. S3. 3D-printed material characterization.

    Fig. S4. Thermal property characterization.

    Fig. S5. Swelling and bending tests.

    Fig. S6. Experimental setup for testing bending, sweating, and grasping.

    Fig. S7. Effect of heat transfer rate with high and low surface area hydrogel actuator.

    Fig. S8. Sweating and grasping tests with different types of hot objects.

    Movie S1. Printing.

    Movie S2. Color change.

    Movie S3. Bending.

    Movie S4. Sweating.

    Movie S5. Grasping.

  • Supplementary Materials

    The PDF file includes:

    • Section S1. Temperature dependence of mechanical properties
    • Section S2. Gel fraction analysis
    • Section S3. UV-visible spectroscopy
    • Section S4. Photo-differential scanning calorimetry (photo-DSC)
    • Section S5. Differential scanning calorimetry (DSC)
    • Section S6. Physical property measurement system (PPMS)
    • Section S7. Heat transfer test in high and low surface area
    • Section S8. Modeling of heat capacity in finger-like actuators
    • Section S9. Thermal manipulation of hot objects
    • Fig. S1. 3D-printed actuator.
    • Fig. S2. Hydrogel ink characterization.
    • Fig. S3. 3D-printed material characterization.
    • Fig. S4. Thermal property characterization.
    • Fig. S5. Swelling and bending tests.
    • Fig. S6. Experimental setup for testing bending, sweating, and grasping.
    • Fig. S7. Effect of heat transfer rate with high and low surface area hydrogel actuator.
    • Fig. S8. Sweating and grasping tests with different types of hot objects.
    • Legends for movies S1 to S5

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    Other Supplementary Material for this manuscript includes the following:

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