Soft robots at microscale are promising for cutting-edge applications in single cell manipulation, targeted cargo/drug delivery, and minimally invasive surgery. Especially, triggered by the innovation of material science and advanced micro/nanofabrication technologies, microbots have emerged as an appealing frontier in modern science, and thus great efforts have been devoted to this field. Nevertheless, current strategies for developing soft microbots are mostly based on a solo smart material. Consequently, concerns with respect to the isotropic response, weak mechanical strength for self-supporting, poor durability and robustness constitute the main barrier for their practical applications.
Natural musculoskeletal systems provide the inspiration for developing robust yet flexible microbots that can combine the advantages of hard-bodied and soft microbots together. However, the fabrication of artificial musculoskeletal systems generally requires programmable assembly of two or more materials of distinct properties into complex 3D micro/nanostructures at sub-micron scale, which remains a big challenge.
In this study, we report femtosecond laser programmed artificial musculoskeletal systems for prototyping 3D microbots, using relatively stiff SU-8 as the skeleton and pH-responsive protein (bovine serum albumin, BSA) as the smart muscle. To realize the programmable integration of the two materials into a 3D configuration, a successive on-chip two-photon polymerization (TPP) strategy was proposed, which enables polymerizing two or more photosensitive materials sequentially according a predesigned microstructure. Additionally, by tailoring the internal network of the musculoskeletal structure at nanoscale, both the elasticity with respect to the BSA muscle and the stiffness of the SU-8 skeleton can be tuned. As a proof-of-concept, we demonstrate a pH-responsive spider microbot and a 3D smart micro-gripper that enables controllable grabbing and releasing. Our strategy may serve as a versatile enabler for directly printing 3D microbots composed of multiple materials.
All the details of this study can be read in our article: Nature Communications .
 Ma, Z.-C. et al., Femtosecond laser programmed artificial musculoskeletal systems. Nat. Commun. 11, 4536 (2020).