Coupled Mechanical-Electric Characteristics of Dehydrated Skeletal Muscles by Experimentation

Abstract

One of the important characteristics of biological soft tissues is they can convert their mechanical deformations into electrical signals and vice versa. That means the endogenous electric fields in soft tissues can be altered by external forces. This paper reports the results of our recent research on the mechanical-electric properties of frog Sartorius and Gastrocnemius muscles by oscillatory tensile tests. The muscle samples were obtained from living bull frogs. A modified Ringer’s solution with high concentration of potassium was used for depolarizing frog muscles to avoid the bioelectric affect. Both dried and fresh muscles were tested to investigate water involvement on piezoelectricity behaviour of the samples. Oscillatory tensile tests were conducted on the muscles by a force-controlled mechanical device. Different loading forces and rates were ranged in order to monitor the electric signal generated in the muscle sample by the deformation alternation. Meanwhile, the loading forces and the generated electric signals were recorded with the same time scale. The experimental results demonstrated that skeletal muscles have good mechanical-electric behaviour. When the muscle is deformed, it gives off small but measurable electrical voltages. The electric voltage in the muscle can be varied, depending on the external forces under sinusoidal or square waveform loading path. For frog Sartorius and Gastrocnemius muscles, those electric signals varied within 0.15V to 0.8V under loading forces ranged from 10N to 18N. The mechanical-electric behaviour of dried samples was more stable and reliable than fresh samples. It is because the mechanical-electric behaviour of fresh sample varies with percentage of their water content sensitively. This investigation is an essential step for understanding the mechanical-electric behaviour of biological soft tissues.