In recent years, femtosecond laser two-photon polymerization technology has been widely used as a true three-dimensional machining method with nanometer precision to fabricate a variety of functional microstructures, which show broad application prospects in the fields of micro- and nano-optics, micro-sensors and micro-machine systems. However, it is still challenging to utilize femtosecond lasers to realize composite multi-material processing and further construct micro-nano-machines with multi-modalities. In view of this, Prof. Wu Dong's team at the Micro and Nano Engineering Laboratory of the University of Science and Technology of China (USTC) proposed a femtosecond laser two-in-one writing multi-material processing strategy to fabricate micromachined joints composed of temperature-sensitive hydrogels and metal nanoparticles, and subsequently developed multi-jointed humanoid micromachines with multiple deformation modes (>10). The work was published on July 17 under the title "Light-triggered multi-joint microactuator fabricated by two-in-one femtosecond laser writing" in Nature Communications.
The femtosecond laser two-in-one processing strategy includes the use of asymmetric two-photon polymerization to construct hydrogel joints and laser reduction deposition of silver nanoparticles (Ag NPs) in localized regions of the joints. In this case, asymmetric photopolymerization creates anisotropy in the crosslink density in the local region of the hydrogel micro-joint, which ultimately allows for directionally and angularly controllable bending deformations. In situ laser reduction deposition allows precise processing of silver nanoparticles on hydrogel joints, which have a strong photothermal conversion effect, enabling the mode switching of multi-joint micromachines to exhibit excellent characteristics of ultra-short response time (30 ms) and ultra-low driving power (<10 mW).
As a typical example, eight micro-joints were integrated on a humanoid micromachine. Subsequently, a spatial light modulation technique is utilized to achieve a multifocal beam in 3D space, which in turn precisely stimulates each microjoint. The synergistic deformation between multiple joints drives the humanoid micromachine to accomplish multiple reconfigurable deformation modes. Ultimately, a "dancing microrobot" is realized at the micrometer scale.
Finally, as a proof-of-concept, by designing the distribution and deformation direction of the micro-joints, the two-jointed micromanipulator can collect multiple micro-particles in both isotropic and anisotropic directions. In conclusion, the femtosecond laser two-in-one processing strategy can construct deformable micro-joints in the local regions of various 3D microstructures and realize multiple reconfigurable deformation modes. In the future, micromanipulators with multiple deformation modes will show broad application prospects in microgoods collection, microfluidic manipulation, and cell manipulation.
