Shape memory alloys (SMAs) are popular as actuators for soft bioinspired robots because they are naturally compliant, have high work density, and can be operated using miniaturized on‐board electronics for power and control. However, SMA actuators typically exhibit limited bandwidth due to the long duration of time required for the alloy to cool down and return to its natural shape and compliance following electrical actuation. This challenge is addressed by constructing SMA‐based actuators out of thermally conductive elastomers and examining the influence of electrical current and actuation frequency on blocking force, bending amplitude, and operating temperature. The actuator is composed of a U‐shape SMA wire that is sandwiched between layers of stretched and unstretched thermal elastomer. Based on the studies, the ability is demonstrated to create a highly dynamic soft actuator that weighs 3.7 g, generates a force of ≈0.2 N, bends with curvature change of ≈60 m−1 in 0.15 s, and can be activated with a frequency above 0.3 Hz with a pair of miniature 3.7 V lithium–polymer batteries. Together, these properties allow the actuator to be used as an “artificial muscle” for a variety of tethered and untethered soft robotic systems capable of fast dynamic locomotion.
By using compliant lightweight actuators with shape memory alloy, we created untethered soft robots that are capable of dynamic locomotion at biologically relevant speeds.
We investigate the deployment of a thin elastic rod onto a rigid substrate and study the resulting coiling patterns. In our approach, we combine precision model experiments, scaling analyses, and computer simulations toward developing predictive understanding of the coiling process. Both cases of deposition onto static and moving substrates are considered. We construct phase diagrams for the possible coiling patterns and characterize them as a function of the geometric and material properties of the rod, as well as the height and relative speeds of deployment. The modes selected and their characteristic length scales are found to arise from a complex interplay between gravitational, bending, and twisting energies of the rod, coupled to the geometric nonlinearities intrinsic to the large deformations. We give particular emphasis to the first sinusoidal mode of instability, which we find to be consistent with a Hopf bifurcation, and analyze the meandering wavelength and amplitude. Throughout, we systematically vary natural curvature of the rod as a control parameter, which has a qualitative and quantitative effect on the pattern formation, above a critical value that we determine. The universality conferred by the prominent role of geometry in the deformation modes of the rod suggests using the gained understanding as design guidelines, in the original applications that motivated the study.thin rods | elasticity T he laying of the first transatlantic telegraph cable (1) opened the path for fast long-distance communication. Nowadays, submarine fiber-optic cables, a crucial backbone of the international communications (e.g., the Internet) infrastructure, are typically installed from a cable-laying vessel that, as it sails, pays out the cable from a spool downward onto the seabed. The portion of suspended cable between the vessel and the contact point with the seabed takes the form of a catenary (2). Similar procedures can also be used to deploy pipelines (3), an historical example of which is the then highly classified Operation PLUTO (Pipe-Lines Under the Ocean) (4), which provided fuel supplies across the English Channel at the end of World War II. One of the major challenges in the laying process of these cables and pipelines is the accurate control between the translation speed of the ship, v b , and the pay-out rate of the cable, v. A mismatch between the two may lead to mechanical failure due to excessive tension (if v b > v) or buckling (if v b < v), which for the case of communication cables can cause the formation of loops and tangles, resulting in undesirable signal attenuation (5, 6). At the microscale, deployment of nanowires onto a substrate has been used to print stretchable electronic components (7), and both periodic serpentines and coils have been fabricated by the flow-directed deposition of carbon nanotubes onto a patterned substrate (8).The common thread between these engineering systems is the geometry of deployment of the filamentary structure with a kinematic mismatch between the deposition ra...
The cellulase activity of Bacillus subtilis AS3 was enhanced by optimizing the medium composition by statistical methods. The enzyme activity with unoptimised medium with carboxymethylcellulose (CMC) was 0.07 U/mL and that was significantly enhanced by CMC, peptone, and yeast extract using Placket-Burman design. The combined effects of these nutrients on cellulase activity were studied using 22 full factorial central composite design. The optimal levels of medium components determined were CMC (1.8%), peptone (0.8%), and yeast extract (0.479%). The maximum enzyme activity predicted by the model was 0.49 U/mL which was in good agreement with the experimental value 0.43 U/mL showing 6-fold increase as compared to unoptimised medium. The enzyme showed multisubstrate specificity, showing significantly higher activity with lichenan and β-glucan and lower activity with laminarin, hydroxyethylcellulose, and steam exploded bagasse. The optimised medium with lichenan or β-glucan showed 2.5- or 2.8-fold higher activity, respectively, at same concentration as of CMC.
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