Femtosecond laser programmed artificial musculoskeletal systems

Abstract

Natural musculoskeletal systems have been widely recognized as an advanced robotic model for designing robust yet flexible microbots. However, the development of artificial musculoskeletal systems at micro-nanoscale currently remains a big challenge, since it requires precise assembly of two or more materials of distinct properties into complex 3D micro/nanostructures. 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 that enables structuring two photosensitive materials sequentially within a predesigned configuration was proposed. 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 provides a universal protocol for directly printing 3D microbots composed of multiple materials.

Tethered and Untethered 3D Microactuators Fabricated by Two-Photon Polymerization: A Review

“…pH-responsive materials have drawn researchers’ attention because of their easy integration with microfluidics or liquid environments. For example, a pH-sensitive hydrogel composite could be regarded as an artificial musculoskeletal system for TPP printed microgrippers [ 50 ].…”

Fabrication of Functional Microdevices in SU-8 by Multi-Photon Lithography

“…The devices were composed of the relatively stiff SU-8 and the soft pH-sensitive BSA muscle. The investigators reported that by changing the step length in fabrication of both the SU-8 skeleton and BSA muscle, the dynamic response of the dynamic spider and the folding angle of micro-gripper could be controllably varied [ 88 ]. These smart devices were realized by engineering the swelling degree of BSA on a non-swelling rigid SU-8 platform and are promising candidates for nano-scale biological applications like targeted drug-delivery.…”

Intelligent Shape-Morphing Micromachines

“…Another shape-morphing mode of rigid-flexible hybrid structures is the mechanical driving. Ma et al [ 56 ] developed a programmable artificial musculoskeletal system by combing a stiff SU-8 “skeleton” and a pH-responsive smart “muscle” into 3D micromachines and demonstrated that the mechanical “skeleton” could be driven by the “muscle” under specific pH stimuli ( Figure 2(d) ). The shape-morphing analysis of the mechanical driving is similar to the rigid-structure cases.…”

“…Here, we list eight types of applications of intelligent micromachines which are divided into motion- and target-based micromachines, as shown in Figure 4 . The motion-based micromachines include microswimmers for swimming in the liquid [ 23 , 30 , 41 – 44 ], microcrawlers for substrate locomotion [ 57 , 64 ], microjumpers for jumping [ 64 , 86 ], and micromotors for marching [ 52 , 53 , 58 , 87 ], while the target-based micromachines include microvalves for valve control of microchannels [ 35 , 36 ], microstents for extending vessels [ 54 , 88 ], microgrippers for drugs catching [ 26 , 47 , 49 , 56 , 66 ], and microcarriers for drug carrying and delivery [ 29 , 89 , 90 ]. Each application is summarized and marked with its common strategies according to the shape-morphing dimension, shape-morphing modes, and realization methods discussed above, together with their advantages and limitations (see Table 1 for details).…”

“…Reproduced with permission. Copyright 2015, American Chemical Society; (d) mechanical driving [ 56 ]. Reproduced with permission.…”