# A Light-Driven Microgel Rotor

## TL;DR

This paper presents a light-driven microgel spiral that achieves rotation through non-reciprocal shape deformations, demonstrating a new approach for microscopic locomotion with potential applications in microfluidics and soft robotics.

## Contribution

It introduces a thermo-responsive hydrogel bilayer spiral capable of controlled rotation via photothermal heating, advancing micro-robotic design with shape-changing actuation.

## Key findings

- The spiral can rotate by non-reciprocal bending deformations.
- Rotation efficiency is estimated using resistive force theory.
- The system's deformation is tunable by temperature and swelling degree.

## Abstract

The current understanding of motility through body shape deformation of microorganisms and the knowledge of fluid flows at the microscale provides ample examples for mimicry and design of soft microrobots. In this work, a two-dimensional spiral is presented that is capable of rotating by non-reciprocal curling deformations. The body of the microswimmer is a ribbon consisting of a thermo-responsive hydrogel bilayer with embedded plasmonic gold nanorods. Such a system allows fast local photothermal heating and non-reciprocal bending deformation of the hydrogel bilayer under non-equilibrium conditions. We show that the spiral acts as a spring capable of large deformations thanks to its low stiffness, which is tunable by the swelling degree of the hydrogel and the temperature. Tethering the ribbon to a freely rotating microsphere enables rotational motion of the spiral by stroboscopic irradiation. The efficiency of the rotor is estimated using resistive force theory for Stokes flow. The present research demonstrates microscopic locomotion by the shape change of a spiral and may find applications in the field of microfluidics, or soft micro-robotics.

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Source: https://tomesphere.com/paper/1907.00764