Flexible and Wearable Ultrasonic Sensor for Assessment of Skeletal Muscle Contractile Properties

Skeletal muscle is considered as a near-constant volume system and the contractions of muscle are linked to the changes in tissue thickness. Assessment of muscle contractile properties provides valuable information for various medical applications. The Ultrasound method provides a high spatial and temporal resolution measurement of the architectural changes of skeletal muscle during contractions. However, one of the challenges in ultrasound methods is motion artifacts due to the weight, size, and attachment instability of the conventional ultrasonic probe employed. A flexible, lightweight, thin, and small size ultrasonic sensor would provide a secure attachment to the skin surface without affecting the muscle contractions dynamics. Thus, in this study, a wearable ultrasonic sensor (WUS) made of a polyvinylidene fluoride (PVDF) film was employed to measure skeletal muscle contractile properties as a quantitative assessment tool. The isometric contractions of gastrocnemius (GC) muscles at a lower leg were electrically stimulated. The tissue thickness changes were measured by means of an ultrasound time-of-flight method in the through-transmission mode. Maximum contraction thickness, contraction time, contraction velocity, sustain time, and half-relaxation time were successfully extracted from the monitored thickness changes. The results demonstrated the potential of the developed WUS in measuring skeletal muscle contractile parameters.