Bioinspired Multi-legged Soft Millirobots towards Biomedical Applications


Student thesis: Doctoral Thesis

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Award date29 Aug 2019


Nature provides precious inspiration resources for scientists to design, manufacture and optimize robots. “Softness” is one salient feature exploited by most biological systems. The fusion of soft materials with conventional robotics where rigid structures are dominantly implemented has sparked a wave of vigor and excitement in robotics science and engineering. Indeed, owing to their adaptability to sophisticated terrain and safety for human interaction, the introduction of soft materials offers promise to overcome many obstacles inherent in conventional robots. Recently, developing untethered soft millirobots is of interest for emerging applications in various industrial and biomedical settings. Despite recent success in its design and actuation, it remains challenging to achieve superior performances in harsh conditions, and self-powered wireless sensing capability.

Legs and/or feet are commonly found in many living animals, including both land animals (e.g., ant, dog, cheetah, etc.) and ocean animals (e.g., starfish, octopus, etc.), after billions of years' evolution. The legs could lift the animal's body from ground in demand manner, leading to smaller body friction to ground, higher degrees of freedom in locomotion, less energy cost, and enhanced obstacle crossing ability. Thus, legged animals usually demonstrate great adaptability to complex terrain, and can probably access virtually 100% of earth's land surface. Inspired by the flexible, soft, and elastic leg/foot structures of many living organisms, here this thesis addresses these limitations by developing an untethered soft millirobot decorated with multiple tapered soft feet architecture. In this thesis, we innovate in the design, fabrication, modeling, locomotion, functions, and sensing ability of the multi-legged soft millirobot.

Firstly, this thesis describes design and fabrication of the new untethered milli-scale (height ~ 1 mm) soft robot decorated with tapered feet structures to overcome existing challenges inherent in conventional soft robots. The fabricated legs are totally soft, constructed from mixture containing polydimethylsiloxane (PDMS) pre-polymer and iron microparticles, and can be manufactured tautologically through one-step mould-free process.

Secondly, under the trigger of external magnetic field, the proposed robot can achieve a combined discontinuous and continuous locomotion, and the soft leg's motion is reminiscent of human's walking. In addition, the theoretical static deformation and dynamic locomotion models are also built to elucidate how the tapered feet regulate robot's locomotion.

Thirdly, the multi-legged soft millirobot developed in this thesis yields superior adaptivity to various harsh environments with ultrafast locomotion speed (> 40 limb length/s), ultra-strong carrying capacity (> 100 own weight), and excellent obstacle crossing ability (stand up 90° and across obstacle > 10 body height). Moreover, the in-vitro drug delivery demonstration has been also revealed.}

Lastly, this thesis also reports a self-powered soft millirobot that can move, sense, and communicate remotely by the coupling the magnetic and piezoelectric effects. Our design integrates the robot actuation and power generation units within a thin multi-layer film (< 0.5 mm), i.e., a lower magnetic composite limb decorated with multiple feet imparts locomotion and a flexible piezoceramic composite film recoveries energy simultaneously. Under the magnetic actuation, the millirobot can achieve remote locomotion, environment monitoring, and wireless communication with no requirement of any on-board battery or external power supply. Furthermore, our robot demonstrates the sensing capability in measuring environment temperature and contact interface by carried-on and build-in sensing mode, respectively.

In conclusion, the new bioinspired multi-legged soft millirobot can achieve superior performances in both wet and dry conditions, and self-powered wireless sensing. These works revealed in this thesis represents a remarkable advance in the emerging area of untethered soft robotics, benefiting a broad spectrum of promising applications, such as in-body monitoring, diagnosis, target therapy, and drug delivery.