Tuning Stiffness with Granular Chain Structures for Versatile Soft Robots.

Stiffness variation can greatly enhance soft robots' load capacity and compliance. Jamming methods are widely used where stiffness variation is realized by jamming of particles, layers, or fibers. It is still challenging to make the variable stiffness components lightweight and adaptive. Besides, the existing jamming mechanisms generally encounter deformation-induced softening, restricting their applications in cases where large deformation and high stiffness are both needed. Herein, a multifunctional granular chain assemblage is proposed, where particles are formed into chains with threads. The chain jamming can be classified into two types. Granular chain jamming (GCJ) utilizes typical particles such as spherical particles, which can achieve both high stiffness and great adaptability while keeping jamming components relatively lightweight, while by using cubic particles, a peculiar deformation-induced stiffening mechanism is found, which is termed as stretch-enhanced particle jamming (SPJ). The versatility of GCJ and SPJ mechanisms in soft robots is demonstrated through soft grippers, soft crawlers, or soft bending actuators, where great passive adaptability, high load capacity, joint-like bending, friction enhancement, or postponing buckling can be realized, respectively. This work thus offers a facile and low-cost strategy to fabricate versatile soft robots.

Stretch-Enhanced Anisotropic Wetting on Transparent Elastomer Film for Controlled Liquid Transport.

Direction-controlled wetting surfaces, special for lubricating oil infused anisotropic surfaces, have attracted great research interest in directional liquid collection, expelling, transfer, and separation. Nonetheless, there are still existing difficulties in achieving directional and continuous liquid transport. Herein, we present a strategy to achieve directional liquid transport on transparent lubricating oil infused elastomer film with V-shaped prisms microarray (VPM). The results reveal that the water wetting direction in the parallel and staggered arrangement of the VPM structure surface with lubricating oil infusion is the opposite, which is completely different from the wetting direction on the usual VPM surface in air. Moreover, asymmetric stretching can enhance or weaken the directional water wetting tendency on the lubricating oil infused VPM elastomer film and even can reverse the droplet wetting direction. In a closed moist environment, tiny droplets gradually coalesce and then slip away from the lubricating oil infused VPM surface to keep the surface transparent, due to the cooperation of imbalanced Laplace pressure, resulting from the anisotropic geometric structures, varying VPMs spacing, and gravity. Thus, this work provides a paradigm to design and fabricate a type of surface engineering material in the application fields of directional expelling, liquid collection, anti-biofouling, anti-icing, drag reduction, anticorrosion, etc.