Models of metabolic utilization predict limiting conditions for sustained power from conditioned skeletal muscle

Development of a resonance generator utilizing incomplete tetanus of skeletal muscle. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021;2021:7248-7251. [PMID: 34892771 DOI: 10.1109/embc46164.2021.9630681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Implantable energy harvesting system utilizing contraction of an electrically-stimulated skeletal muscle is proposed for alternative batteries of implantable medical devices. In order to realize high conversion efficiency, we propose a resonance generator utilizing vibration of the skeletal muscle, which is called as incomplete tetanus. Experimental results showed the incomplete tetanus was a suitable form for the energy harvesting and the stimulation at the frequency of 10 Hz was maximized the work of the muscle. Dimensions of the springs of the generator were designed so that its natural frequency was 10 Hz. On the simulation, the maximum generated power was achieved 122.5 μW, which is enough to power the IMDs.Clinical Relevance-The proposed system has a potential to eliminate conventional batteries in the implantable medical devices. It will be beneficial for patients since the periodical surgery for the battery replacement will be avoided.

Design optimization of contactless generator for implantable energy harvesting system utilizing electrically-stimulated muscle

We propose an energy harvesting device driven by a contraction of an electrically-stimulated skeletal muscle for an alternative battery of implantable medical devices. In order to realize a durable generator, we proposed a contactless plucking mechanism utilizing parallel leaf springs and magnets, with which the generator can be driven without friction. By utilizing this mechanism, the generator can be driven not only in a contraction phase, but also a relaxant phase. We optimized the stiffness of the parallel leaf springs, air gap between the magnets, and magnetic circuit in order to maximize generated power of the generator. The generated power of the prototype in nonliving environment was evaluated. The result showed the protype could achieve 35.8 μW, the value of which is enough to drive the implantable medical devices. Finally, the generated power was evaluated in the ex-vivo experiment using a gastrocnemius muscle of a toad with a weight of 193.4 g. In this experiment, the generator achieved 18.1 μW from only 3.5 g of the skeletal muscle. Also, we confirmed that the generated power exceeded the power consumption of the electrical stimulation on the skeletal muscle. Hence, we concluded the results showed the feasibility of the energy harvesting system with proposed mechanism.

Development of a contactless energy harvesting system driven by contraction of skeletal muscle for implantable medical devices

We propose a contactless energy harvesting system driven by the contraction of an electrically-stimulated skeletal muscle to be used to supply electrical energy to implantable medical devices. In order to realize a durable generator, the one proposed here has a contactless clutch mechanism with parallel leaf springs, with which the generator can be driven without friction. In this system, the muscle connected to the parallel leaf spring is intentionally contracted by electrical stimulation. The generator can be driven not only in the contraction phase of the muscle, but also relaxation phase. The result an evaluation showed that the prototype could generate 26.1 $\mu \mathrm{W}$ with an efficiency of 13.7%. Finally, we conducted an animal experiment using the gastrocnemius muscle of a toad with a weighing of200 g The generator was driven in the contraction phase generating 1.37 $\mu \mathrm{W}$ of power from the energy supplied by the muscle.

Implantable power generation system utilizing muscle contractions excited by electrical stimulation

An implantable power generation system driven by muscle contractions for supplying power to active implantable medical devices, such as pacemakers and neurostimulators, is proposed. In this system, a muscle is intentionally contracted by an electrical stimulation in accordance with the demands of the active implantable medical device for electrical power. The proposed system, which comprises a small electromagnetic induction generator, electrodes with an electrical circuit for stimulation and a transmission device to convert the linear motion of the muscle contractions into rotational motion for the magneto rotor, generates electrical energy. In an ex vivo demonstration using the gastrocnemius muscle of a toad, which was 28 mm in length and weighed 1.3 g, the electrical energy generated by the prototype exceeded the energy consumed for electrical stimulation, with the net power being 111 µW. It was demonstrated that the proposed implantable power generation system has the potential to replace implantable batteries for active implantable medical devices.

In vivo demonstration of a self-sustaining, implantable, stimulated-muscle-powered piezoelectric generator prototype

An implantable, stimulated-muscle-powered piezoelectric active energy harvesting generator was previously designed to exploit the fact that the mechanical output power of muscle is substantially greater than the electrical power necessary to stimulate the muscle's motor nerve. We reduced to practice the concept by building a prototype generator and stimulator. We demonstrated its feasibility in vivo, using rabbit quadriceps to drive the generator. The generated power was sufficient for self-sustaining operation of the stimulator and additional harnessed power was dissipated through a load resistor. The prototype generator was developed and the power generating capabilities were tested with a mechanical muscle analog. In vivo generated power matched the mechanical muscle analog, verifying its usefulness as a test-bed for generator development. Generator output power was dependent on the muscle stimulation parameters. Simulations and in vivo testing demonstrated that for a fixed number of stimuli/minute, two stimuli applied at a high frequency generated greater power than single stimuli or tetanic contractions. Larger muscles and circuitry improvements are expected to increase available power. An implanted, self-replenishing power source has the potential to augment implanted battery or transcutaneously powered electronic medical devices.

Design Considerations for an Implantable, Muscle Powered Piezoelectric System for Generating Electrical Power

A totally implantable piezoelectric generator system able to harness power from electrically activated muscle would augment the power systems of implanted functional electrical stimulation devices by reducing the number of battery replacement surgeries or by allowing periods of untethered functionality. The generator design contains no moving parts and uses a portion of the generated power for system operation. A software model of the system was developed and simulations performed to predict the output power as the system parameters were varied within their constraints. Mechanical forces that mimic muscle forces were experimentally applied to a piezoelectric generator to verify the accuracy of the simulations and to explore losses due to mechanical coupling. Depending on the selection of system parameters, software simulations predict that this generator concept can generate up to 690 microW of power, which is greater than the power necessary to drive the generator, conservatively estimated to be 46 microW. These results suggest that this concept has the potential to be an implantable, self-replenishing power source and warrants further investigation.

Performance of Dynamic and Isovolumetric Trained Skeletal Muscle Ventricles

BACKGROUND

Dynamic training and maintaining muscle tension are important factors during skeletal muscle ventricle (SMV) conditioning that may improve SMV performance. This study sought to determine the effects of dynamic muscle training and progressive SMV resting pressure expansion on SMV pumping capability.

MATERIALS AND METHODS

SMVs were constructed in 14 goats using the left latissimus dorsi muscle. SMVs were conditioned with a 40 ml constant-volume isovolumetric implant (n = 5, IsoVol group) or a compliant, pneumatic system that allowed dynamic shortening and direct exposure to resting pressures. Dynamic SMV resting pressure was either progressively increased from 40 to 100 to 120 mmHg (n = 5, HiP group) or maintained at 40 mmHg (n = 4, LowP group) during conditioning. After 8 to 10 weeks of electrical stimulation conditioning, SMVs were connected to a counterpulsation mock circulation system and SMV pumping performance evaluated across a range of pressures and stimulation parameters.

RESULTS

SMV pumping performance was similar in each group. Stroke works generally increased with pressure and reached a plateau in all groups above 80 mmHg (120 msec contraction approximately 80 mJ/stroke; 480 msec contraction approximately 180 mJ/stroke). Stroke volumes decreased with pressure except at high stimulation levels where loading effects were observed. Chronic changes in SMV volume significantly effected pumping performance.

CONCLUSIONS

These data suggest that acute pumping performance is not different between 8 to 10 weeks of dynamic or isovolumetric training if SMV volume is not constrained. A potentially improved SMV conditioning protocol is proposed that determines, positions, and maintains SMV volume near the initial volume for maximal isovolumetric pressure during conditioning.