Responsive-Hydrogel Aquabots

Abstract

It remains a challenge to produce soft robots that can mimic the responsive adaptability of living organisms. Rather than fabricating soft robots from bulk hydrogels,hydrogels are integrated into the interfacial assembly of aqueous two-phase systems to generate ultra-soft and elastic all-aqueous aquabots that exhibit responsive adaptability, that can shrink on demand and have electrically conductive functions. The adaptive functions of the aquabots provide a new platform to develop minimally invasive surgical devices, targeted drug delivery systems, and flexible electronic sensors and actuators.

Keywords: adaptive materials; all‐liquid robots; aqueous two‐phase systems; flexible electronics; responsive hydrogels.

Figure 1

Building the thermal responsive membrane of aquabots. A) Schematic of hierarchical structures of a printed aquabot. B) Printed aquabot with hierarchical structures. The scale bar is 100 µm.

Figure 2

On‐demand shrink ability of aquabots. A) Aquabot shrinks upon heating and expands to its original size upon cooling. B,C) Enhancing the shrinkage of aquabots by decreasing the degree of photo‐cross–linking. C) Reversible photothermal shrinkage of AuNR‐ or GNP‐modified aquabots triggered by illumination of visible light at room temperature. All scale bars are 100 µm.

Figure 3

Shrink‐on‐demand aquabot passing through narrow spaces. A) Schematic and B) experimental scenarios of an aquabot navigating through the 2D channel narrower than its original size. Scale bars are 100 µm. C) Aquabot navigating through the 3D confined narrow space upon shrinking. Scale bars are 1 mm.

Figure 4

A) Stretched PNIPAM hydrogel‐membrane‐based all‐water robot under the force loading of two tweezers. The stretching ratio $\lambda =\frac{12.88}{8.04}=1.6.$ B) Measured stress‐strain curve of PNIPAM hydrogel‐membrane‐based all‐water robot. Scale bars are 1 mm.

Figure 5

Resistance measurements for conductive PANI‐PNIPAM double‐network hydrogel‐membrane‐based aquabots. A) Schematic of 4‐probe resistance measurement. B) 4‐probe resistance measurement. The neighboring probe distance is 0.5 cm. C) I–V curve of 2‐probe resistance measurement. D) Comparison of resistances measured by 2‐probe and 4‐probe methods. Scale bar is 5 mm.