Mechanotransduction and interfacial properties in unsupported liquid biomimetic membranes are explored using the droplet-interface bilayer technique. The fluidic monolayer-membrane system afforded by this technique allows for dynamic control over the membrane dimensions and curvature, which under periodic deformations generates capacitive currents (akin to a Kelvin probe), and permits a detailed electrostatic characterization of the boundary layers as well as observation of flexoelectric effects. Both high and low displacement frequency regimes are examined, and the results show that the mechanoelectric signals generated by the membranes may be linked to the membrane electrostatic structure. In addition, we show that periodic membrane bending in a high-frequency regime generates tension sufficient to activate reconstituted mechanosensitive channels.

The caudal fin is a major source of thrust generation in fish locomotion. Along with the fin stiffness, the stiffness of the joint connecting the fish body to the tail plays a major role in the generation of thrust. This paper investigates the combined effect of fin and joint flexibility on propulsive performance using theoretical and experimental studies. For this study, fluid-structure interaction of the fin has been modeled using the 2D unsteady panel method coupled with nonlinear Euler-Bernoulli beam theory. The compliant joint has been modeled as a torsional spring at the leading edge of the fin. A comparison of self-propelled speed and efficiency with parameters such as heaving and pitching amplitude, oscillation frequency, flexibility of the fin and the compliant joint is reported. The model also predicts the optimized stiffnesses of the compliant joint and the fin for maximum efficiency. Experiments have been carried out to determine the effect of fin and joint stiffness on propulsive performance. Digital image correlation has been used to measure the deformation of the fins and the measured deformation is coupled with the hydrodynamic model to predict the performance. The predicted theoretical performance behavior closely matches the experimental values.

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Pressurized artificial muscles are reviewed. These actuators consist of stiff reinforcing fibers surrounding an elastomeric bladder and operate using a pressurized internal fluid. The pressurized artificial muscles, known as McKibben actuators or flexible matrix composite actuators, can be applied to a wide array of applications, including prosthetics/orthotics, robots, morphing wing technologies, and variable stiffness structures. Analytical models for predicting the response behavior have used both virtual work methods and continuum mechanics. Various nonlinear control algorithms have been developed, including sliding mode control (SMC), adaptive control, neural networks, etc. In addition to traditional fluid-driving methods, innovative techniques such as chemical and electrical driving techniques are reviewed. With improved manufacturing techniques, the operational life of pressurized artificial muscles has been significantly extended, thus making them suitable for a vast range of potential applications.