Johnston CM, Han JC, Ruddy BP, Nielsen PM, Taberner AJ. A high-resolution thermoelectric module-based calorimeter for measuring the energetics of isolated ventricular trabeculae at body temperature. Am J Physiol Heart Circ Physiol 309: H318 -H324, 2015. First published May 22, 2015; doi:10.1152/ajpheart.00194.2015.-Isolated ventricular trabeculae are the most common experimental preparations used in the study of cardiac energetics. However, the experiments have been conducted at subphysiological temperatures. We have overcome this limitation by designing and constructing a novel calorimeter with sufficiently high thermal resolution for simultaneously measuring the heat output and force production of isolated, contracting, ventricular trabeculae at body temperature. This development was largely motivated by the need to better understand cardiac energetics by performing such measurements at body temperature to relate tissue performance to whole heart behavior in vivo. Our approach uses solid-state thermoelectric modules, tailored for both temperature sensing and temperature control. The thermoelectric modules have high sensitivity and low noise, which, when coupled with a multilevel temperature control system, enable an exceptionally high temperature resolution with a noise-equivalent power an order of magnitude greater than those of other existing muscle calorimeters. Our system allows us to rapidly and easily change the experimental temperature without disturbing the state of the muscle. Our calorimeter is useful in many experiments that explore the energetics of normal physiology as well as pathophysiology of cardiac muscle. muscle energetics; microcalorimetry; heat production NEW & NOTEWORTHY We have developed a new muscle calorimeter, which has enabled the first simultaneous measurements of the force and heat output of isolated, actively contracting, cardiac trabeculae at body temperature. This was achieved by the use of thermoelectric modules for high-resolution temperature sensing and precise temperature control.MEASUREMENTS OF THE ENERGETICS of cardiac muscle under controlled experimental conditions, and in particular at body temperature, enable better understanding of cardiac muscle function in health and disease. Studies of force production simultaneous with heat output of cardiac muscle require the use of isolated tissue preparations such as small papillary muscles (2-4, 12, 26, 34) or trabeculae carneae (17-21) as they are sufficiently small to avoid muscle anoxia (14). The use of these tissue preparations, which have approximately one-dimensional arrangements of myocytes, simplifies the interpretation of measurements. Although these tissue studies have improved our understanding of myocardial energetics, previous experiments have been performed only at subphysiological temperatures, typically 10°C below that of body temperature (3,5,10,11,13,23,25,26,28,30,31). One exception is the study by Widén (39), who made simultaneous force and heat measurements in mouse papillary muscles at body temperature. H...

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Electromagnetic actuators provide fast speeds, large forces, high strokes, and wide bandwidths. Most designs, however, are constructed from rigid components, making these benefits inaccessible for many soft robotics applications. In this work, we develop a new soft electromagnetic linear actuator using liquid gallium-indium for the conductor and neodymium-iron-boron and polymer composites for the permanent magnet. When combined in a solenoid configuration, high strokes can be generated using entirely soft components. To emulate the pulsing motion of Xenia coral arms, we develop an additional soft flexure system that converts the linear translation to rotary motion. The design and fabrication of the electromagnetic actuator and compliant flexure are first described. Models for the magnetic forces and the joint kinematics are then developed and compared with experimental results. Finally, the robot dynamics are analyzed using stochastic system identification techniques. Results show that the compliant actuator is able to achieve an 18 mm stroke, allowing the soft arms to bend up to 120 degrees. This further enables the tips of the arms to traverse an arc length of 42 mm. Bandwidths up to 30 Hz were also observed. While this paper focuses on emulating a biological system, this highly deformable actuator design can also be utilized for fully-soft grasping or wearables applications.

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We have developed a new `work-loop calorimeter' that is capable of measuring, simultaneously, the work-done and heat production of isolated cardiac muscle samples at body temperature. Through the innovative use of thermoelectric modules as temperature sensors, the development of a low-noise fluid-flow system, and implementation of precise temperature control, the heat resolution of this device is 10 nW, an improvement by a factor of ten over previous designs. These advances have allowed us to conduct the first flow-through measurements of work output and heat dissipation from cardiac tissue at body temperature. The mechanical efficiency is found to vary with peak stress, and reaches a peak value of approximately 15 %, a figure similar to that observed in cardiac muscle at lower temperatures.

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Abstract-We report a new approach to the design of directdrive linear permanent magnet motors for use in general-purpose robotic actuation, with particular attention to applications in bird-scale flapping-wing robots. We show a simple, quantitative analytical modeling framework for this class of actuators, and demonstrate inherent scaling properties that allow the production of motors with force densities and efficiencies comparable to those of biological muscles. We will show how this model leads to a set of practical design specifications for muscle-like motors, and examine the resulting trade-off between thermal management and motor fabrication complexity.