Electromechanics of lipid-modulated gating of potassium channels

Experimental studies reveal that the anionic lipid phosphatidic acid (POPA), non-phospholipid cholesterol, and cationic lipid DOTAP inhibit the gating of voltage-sensitive potassium (Kv) channels. Here, we develop a continuum electromechanical model to investigate the interaction of these lipids with the ion channel. Our model suggests that: (i) POPA lipids may restrict the vertical motion of the voltage-sensor domain through direct electrostatic interactions; (ii) cholesterol may oppose the radial motion of the pore domain of the channel by increasing the mechanical rigidity of the membrane; and (iii) DOTAP can reduce the effect of electrostatic forces by regulating the dielectric constant at the channel–lipid interface. The electromechanical model predictions for the three lipid types match well with the experimental observations and provide mechanistic insights into lipid-dependent gating of Kv channels.

Role of Electromechanical Coupling, Locomotion Type and Damping on the Effectiveness of Fish-Like Robot Energy Harvesters

In this work, an investigation into the influence of prescribed motion on a body caudal fin aquatic unmanned vehicle (AUV) energy harvester is carried out. The undulatory–oscillation locomotion inspired by fishes actuates a composite beam representative of a spinal column with a piezoelectric patch. Two patch configurations—one at the head and tail—are considered for the AUV energy harvester, with a length that would not activate a harmonic in the system. An electromechanical model which accounts for the strain of the prescribed motion and the induced relative strain is developed. Discretizing the relative strain using Galerkin’s method requires a convergence study in which the impacts of the prescribed motion, dependent on the undulation and envelope of the motion, are investigated. The combination of prescribed motion and structural terms leads to a coupling that requires multiple investigations. The removal of the undulation of the system produces a more consistent response. The performances of the two different patch configurations undergoing different prescribed motions are studied in terms of coupled damping and frequency effects. An uncoupled Gauss law-based model is adopted to compare the performance of our approach and that of the coupled electromechanical model harvester. It is demonstrated that there is a complex interaction of the phases of the prescribed and relative motions of the structure which can lead to the development or destruction of the response of the total motion or voltage for the system. The results show that the structural damping and type of locomotion are the most influential parameters on the validity of the uncoupled approach. It is also found that the optimal resistances for the coupled and uncoupled representations are the same for the two motions and patch configurations considered.

Controlling a Variable-Length Exoskeleton Link

The aim of the study is to develop a spatial electromechanical model of a variable-length link for use in telescopic manipulators, anthropomorphic robots, exoskeletons, and in studying the human musculoskeletal system. The proposed link model has two massive absolutely solid sections at the ends and a weightless section of variable length located between them. The study was carried out using the methods of theoretical mechanics, electromechanics, mathematical modeling, engineering design, numerical methods for solving systems of ordinary differential equations, control theory, nonlinear dynamics, experimental methods, and empirical data on the biomechanical properties of the human musculoskeletal system. The reliability of the obtained results is substantiated by a rigorous use of the above-mentioned methods. As a result of the study, a system of Lagrange-Maxwell differential equations was written, and an electromechanical model of an anthropomorphic system was developed in the Matlab Simulink software package. With the specified geometric and inertial parameters of a variable-length link corresponding to an average person's leg lower part and the time corresponding to the single-support motion phase, the electric motors and reducing gears implementing the human musculoskeletal system link's biomechanical motion fragment are selected. All of the selected motors have a sufficient operating parameters margin. The trajectories of all generalized coordinates along which the anthropomorphic system performs its necessary motion are determined. The mechanism load diagrams are obtained. The control system for the motors is synthesized, and the positioning error is evaluated. The novelty of the approach is that the newly developed electromechanical models of controlled variable-length links have a wide range of applying the obtained results and can be used in designing anthropomorphic robots and comfortable new-generation exoskeletons. Thus, the electromechanical model of a variable-length link with the parameters corresponding to the average person's leg lower part has been developed. The electric drives and transmissions able to implement a motion close to the anthropomorphic one have been selected; its implementation has been demonstrated, and the numerical calculation results are given.