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1. Bending behavior of biomimetic scale covered beam with tunable stiffness scales

   https://doi.org/10.1038/s41598-020-74147-0  

   Tatari, Milad ; Kamrava, Soroush ; Ghosh, Ranajay ; Nayeb-Hashemi, Hamid ; Vaziri, Ashkan ( December 2020 , Scientific Reports)

   null (Ed.)

   Abstract Biomimetic scales provide a convenient template to tailor the bending stiffness of the underlying slender substrate due to their mutual sliding after engagement. Scale stiffness can therefore directly impact the substrate behavior, opening a potential avenue for substrate stiffness tunability. Here, we have developed a biomimetic beam, which is covered by tunable stiffness scales. Scale tunability is achieved by specially designed plate like scales consisting of layers of low melting point alloy (LMPA) phase change materials fully enclosed inside a soft polymer. These composite scales can transition between stiff and soft states by straddling the temperatures across LMPA melting points thereby drastically altering stiffness. We experimentally analyze the bending behavior of biomimetic beams covered with tunable stiffness scales of two architectures—one with single enclosure of LMPA and one with two enclosures of different melting point LMPAs. These architectures provide a continuous stiffness change of the underlying substrate post engagement, controlled by the operating temperature. We characterize this response using three-point bending experiments at various temperature profiles. Our results demonstrate for the first time, the pronounced and reversible tunability in the bending behavior of biomimetic scale covered beam, which are strongly dependent on the scale material and architecture. Particularly, it is shown that the bending stiffness of the biomimetic scale covered beam can be actively and reversibly tuned by a factor of up to 7. The developed biomimetic beam has applications in soft robotic grippers, smart segmented armors, deployable structures and soft swimming robots. 

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2. Inherent Photodegradability of Polymethacrylate Hydrogels: Straightforward Access to Biocompatible Soft Microstructures

   https://doi.org/10.1002/adfm.201902906  

   Li, Lei ; Scheiger, Johannes M. ; Tronser, Tina ; Long, Connor ; Demir, Konstantin ; Wilson, Christina L. ; Kuzina, Mariia A. ; Levkin, Pavel A. ( June 2019 , Advanced Functional Materials)

   Hydrogels are important functional materials useful for 3D cell culture, tissue engineering, 3D printing, drug delivery, sensors, or soft robotics. The ability to shape hydrogels into defined 3D structures, patterns, or particles is crucial for biomedical applications. Here, the rapid photodegradability of commonly used polymethacrylate hydrogels is demonstrated without the need to incorporate additional photolabile functionalities. Hydrogel degradation depths are quantified with respect to the irradiation time, light intensity, and chemical composition. It can be shown that these parameters can be utilized to control the photodegradation behavior of polymethacrylate hydrogels. The photodegradation kinetics, the change in mechanical properties of polymethacrylate hydrogels upon UV irradiation, as well as the photodegradation products are investigated. This approach is then exploited for microstructuring and patterning of hydrogels including hydrogel gradients as well as for the formation of hydrogel particles and hydrogel arrays of well‐defined shapes. Cell repellent but biocompatible hydrogel microwells are fabricated using this method and used to form arrays of cell spheroids. As this method is based on readily available and commonly used methacrylates and can be conducted using cheap UV light sources, it has vast potential to be applied by laboratories with various backgrounds and for diverse applications.

    

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3. Learning to Locomote with Artificial Neural-Network and CPG-based Control in a Soft Snake Robot

   https://doi.org/10.1109/IROS45743.2020.9340763  

   Liu, Xuan ; Gasoto, Renato ; Jiang, Ziyi ; Onal, Cagdas ; Fu, Jie ( October 2020 , 2020 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS))

   null (Ed.)

   In this paper, we present a new locomotion control method for soft robot snakes. Inspired by biological snakes, our control architecture is composed of two key modules: A reinforcement learning (RL) module for achieving adaptive goal-tracking behaviors with changing goals, and a central pattern generator (CPG) system with Matsuoka oscillators for generating stable and diverse locomotion patterns. The two modules are interconnected into a closed-loop system: The RL module, analogizing the locomotion region located in the midbrain of vertebrate animals, regulates the input to the CPG system given state feedback from the robot. The output of the CPG system is then translated into pressure inputs to the pneumatic actuators of the soft snake robot. Based on the fact that the oscillation frequency and wave amplitude of the Matsuoka oscillator can be independently controlled under different time scales, we further adapt the option-critic framework to improve the learning performance measured by optimality and data efficiency. The performance of the proposed controller is experimentally validated with both simulated and real soft snake robots. 

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4. Bioinspired Design of Light‐Powered Crawling, Squeezing, and Jumping Untethered Soft Robot

   https://doi.org/10.1002/admt.201900185  

   Ahn, Chihyung ; Liang, Xudong ; Cai, Shengqiang ( June 2019 , Advanced Materials Technologies)

   Light has been recently intensively explored to power robots. However, most existing light‐driven robots have limited locomotion modalities, with constrained locomotion capabilities. A light‐powered soft robot with a bioinspired design is demonstrated, which can crawl on ground, squeeze its way through a small channel, and jump over a barrier. The arch‐shaped robot is made up of liquid crystal elastomer–carbon nanotube composite. When a light source with a power intensity of around 1.57 W cm⁻²is scanned over the surface of the robot, it deforms and crawls forward. With an increase in the light scanning speed, it can deform sufficiently to pass through a channel 25% lower than its body height. Subjected to light irradiation, it can also deform to a closed loop, gradually store elastic energy, and suddenly release it to jump over a wall or onto a step quickly, with a jumping distance around eight times its body length and jumping height around five times its body height. Mathematical models for quantitatively understanding the multimodal locomotion of this light‐powered soft robot are also presented.

    

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5. Single-vat single-cure grayscale digital light processing 3D printing of materials with large property difference and high stretchability

   https://doi.org/10.1038/s41467-023-36909-y  

   Yue, Liang ; Macrae Montgomery, S. ; Sun, Xiaohao ; Yu, Luxia ; Song, Yuyang ; Nomura, Tsuyoshi ; Tanaka, Masato ; Jerry Qi, H. ( March 2023 , Nature Communications)

   Multimaterial additive manufacturing has important applications in various emerging fields. However, it is very challenging due to material and printing technology limitations. Here, we present a resin design strategy that can be used for single-vat single-cure grayscale digital light processing (g-DLP) 3D printing where light intensity can locally control the conversion of monomers to form from a highly stretchable soft organogel to a stiff thermoset within in a single layer of printing. The high modulus contrast and high stretchability can be realized simultaneously in a monolithic structure at a high printing speed (z-direction height 1 mm/min). We further demonstrate that the capability can enable previously unachievable or hard-to-achieve 3D printed structures for biomimetic designs, inflatable soft robots and actuators, and soft stretchable electronics. This resin design strategy thus provides a material solution in multimaterial additive manufacture for a variety of emerging applications.

    

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