Light-driven soft microrobots based on hydrogels and LCEs: development and prospects

Abstract

In the daily life of mankind, microrobots can respond to stimulations received and perform different functions, which can be used to complete repetitive or dangerous tasks. Magnetic driving works well in robots that are tens or hundreds of microns in size, but there are big challenges in driving microrobots that are just a few microns in size. Therefore, it is impossible to guarantee the precise drive of microrobots to perform tasks. Acoustic driven micro-nano robot can achieve non-invasive and on-demand movement, and the drive has good biological compatibility, but the drive mode has low resolution and requires expensive experimental equipment. Light-driven robots move by converting light energy into other forms of energy. Light is a renewable, powerful energy source that can be used to transmit energy. Due to the gradual maturity of beam modulation and optical microscope technology, the application of light-driven microrobots has gradually become widespread. Light as a kind of electromagnetic wave, we can change the energy of light by controlling the wavelength and intensity of light. Therefore, the light-driven robot has the advantages of programmable, wireless, high resolution and accurate spatio-temporal control. According to the types of robots, light-driven robots are subdivided into three categories, namely light-driven soft microrobots, photochemical microrobots and 3D printed hard polymer microrobots. In this paper, the driving materials, driving mechanisms and application scenarios of light-driven soft microrobots are reviewed, and their advantages and limitations are discussed. Finally, we prospected the field, pointed out the challenges faced by light-driven soft micro robots and proposed corresponding solutions.

Fig. 1. (A) Opto-mechanical drive. (B) Photothermal drive.

Fig. 2. (A) The shape of the double-layer hydrogel bands varies with different sections and lengths, and the unwinding and reversal of the helix can be completed within 90 milliseconds (this figure has been reproduced from ref. with permission from ACS Publications, copyright 2024). (B) Various states of L-type microgels in a modulation cycle (this figure has been reproduced from ref. with permission from Wiley-VCH, copyright 2024). (C) Preparation of bilayer spiral microhydrogels (this figure has been reproduced from ref. with permission from John Wiley and Sons, copyright 2024). (D) Grasping objects using soft micro-robots made with a PVA passivation layer (this figure has been reproduced from ref. with permission from Science Robotics, copyright 2024).

Fig. 3. (A) The crawling of bionic snails (this figure has been reproduced from ref. with permission from Macromolecular Rapid communications, copyright 2024). (B) The crawling of bionic caterpillars (this figure has been reproduced from ref. with permission from American Chemical Society, copyright 2024). (C) Swimming of a bionic fish (this figure has been reproduced from ref. with permission from American Chemical Society, copyright 2024). (D) The Red Sea bass swims with the curvature and undation of its central torso (this figure has been reproduced from ref. with permission from PANS, copyright 2024).

Fig. 4. (A) (a) Reversible changes in the shape of liquid crystal polymer chairs. (b) Liquid crystal Hercules can lift up to four balls under light (this figure has been reproduced from ref. with permission from American Chemical Society, copyright 2024). (B) The polymer “crane” performs a series of motion tasks of a combined light-driven robot, including grasping, lifting, lowering, and releasing a tubular object (this figure has been reproduced from ref. with permission from Advanced Materials, copyright 2024). (C) Light-driven movements on paper surfaces and human fingernails (this figure has been reproduced from ref. with permission from Macromolecular Rapid Communications, copyright 2024).

Fig. 5. (A) Iris production process. This iris opens in the dark and closes in light (this figure has been reproduced from ref. with permission from Advanced Materials, copyright 2024). (B) (a) The LCE band is soaked in an alkaline solution to make it sensitive to humidity. (b) The treated LCE strip has less curvature at low humidity (this figure has been reproduced from ref. with permission from Advanced Materials, copyright 2024). (C) (a and b) a picture of the fly trap and the principles for capturing the object. (c) Leaves a hole in the center of the LCEs through which light is emitted (this figure has been reproduced from ref. with permission from nature communications, copyright 2024). (D) Schematic diagram of heat-induced deformation of LCE films. When the heat-induced curvature reaches the slip Angle, the glycerol droplets slide off the film along the shortest path (this figure has been reproduced from ref. with permission from Europe PMC, copyright 2024).

Fig. 6. (A) The shape change of two microhands under laser irradiation (this figure has been reproduced from ref. with permission from Advanced Materials, copyright 2024). (B) Robots use grippers to grab, transport and transport goods (this figure has been reproduced from ref. with permission from Advanced Optical Materials, copyright 2024). (C) The light-driven gripper holds the object to realize intelligent transportation (this figure has been reproduced from ref. with permission from Advanced Optical Materials, copyright 2024). (D) The four-claw microgripper moves to the target position and realizes the pick-up and placement of the object under the drive of the light (this figure has been reproduced from ref. with permission from Advanced Science, copyright 2024).