A breakthrough in multi-material microfabrication

Design and Fabrication of light-triggered multi-joint microactuators (MJMAs) by two-in-one laser printing. a The human arm relies on joint bending to achieve hand raising. b The schematic diagram of a light-triggered humanoid MJMA showing multiple modalities. c Laser printing responsive hydrogel to construct the MJMA skeleton. The joint is composed of two parts with different cross-link densities, where orange and blue represent low and high cross-link densities, respectively. ST1 = 1 ms and ST2 = 3 ms are single-point scanning time during processing. d Laser reduction of Ag NPs for photothermal conversion, in which silver ammonium ions absorb photons and are reduced to Ag NPs. SEM images show the corresponding materials of hydrogel MJMAs (blue) and Ag NPs (yellow), respectively. e Two foci and four foci are modulated by the Gerchberg-Saxton algorithm to control the deformation of two and four joints, where the spatial position and intensity of the focal spot can be flexibly adjusted. When Ag NPs are irradiated by NIR light, a large amount of heat transfer from Ag NPs to hydrogel will be generated. The parts of the hydrogel with low cross-link density contract more than the part of the hydrogel with high cross-link density, thus causing directional bending of the hydrogel joint. All scale bars are 20 μm. Credit: Nature Communications (2023). DOI: 10.1038/s41467-023-40038-x

A research team, led by Prof. Wu Dong from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS), has proposed an innovative femtosecond laser 2-in-1 writing multi-material processing strategy for fabricating micromachined joints. These joints are composed of temperature-sensitive hydrogels and metal nanoparticles, and the team has successfully developed multi-jointed humanoid micromachines capable of multiple deformation modes. The research results have been published in the prestigious journal Nature Communications.

Over the years, femtosecond laser two-photon polymerization has emerged as a revolutionary three-dimensional fabrication technique with nanoscale precision. It has found applications in various domains such as micro-nano optics, microsensors, and microelectromechanical systems. However, the challenge has been to effectively utilize femtosecond lasers for multi-material processing and construct micro-nano mechanics with multiple modalities.

In this study, the researchers have employed a femtosecond laser dual-function fabrication strategy. This strategy involves using asymmetrical two-photon polymerization to create hydrogel joints and locally depositing silver nanoparticles (Ag NPs) within the joints through laser reduction. By inducing anisotropy in the cross-linking density of the hydrogel micro-joints using this asymmetric light-polymerization technique, the researchers have achieved directional and angular-controllable bending deformations.

The in-situ laser reduction deposition method allows for precise fabrication of silver nanoparticles on the hydrogel joints, which exhibit strong photothermal conversion effects. This enables the multi-joint micromachinery to exhibit ultra-fast response times (30 ms) and extremely low driving power. The researchers have successfully integrated eight micro-joints into a humanoid micro-mechanism and utilized spatial light modulation technology to achieve multi-focal beams in 3D space for precise stimulation of each micro-joint.

Collaborative deformation between multiple joints enables the humanoid micromachine to achieve various reconfigurable deformation modes, giving rise to what can be described as “dancing microrobots” at the micrometer scale. As a proof of concept, the researchers have designed a dual-joint miniature mechanical arm that can collect micro-particles in both parallel and divergent directions by controlling the distribution and deformation direction of the micro-joints.

This femtosecond laser dual-function fabrication strategy holds great promise for constructing deformable micro-joints in various 3D micro-structured areas and realizing multiple re

 

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