Development of a wearable ultrasonic sensor and method for continuous monitoring of mechanical properties of plantar soft tissue for diabetic patients

One of the long-term complications of diabetes is peripheral neuropathy, where insensitive nerves can lead to serious foot ulceration. Studies have shown that the mechanical properties of plantar soft tissues change with diabetes. Ultrasound methods could be used to measure plantar tissue thickness and mechanical properties, as a quantitative assessment tool. Diabetic shoes or orthoses are often custom-designed for each person to prevent foot injury during daily activities. This study developed an ultrasonic method and sensors that can be use between the foot and a custom insole to continuously monitor the mechanical properties of plantar soft tissue during physical activities. In the proposed sensor design, the protection layer on the sensing side (bottom electrode) was eliminated and the top side was electrically shielded to reduce environmental noises. A developed wearable ultrasonic sensor was used in a preliminary experiment to measure plantar tissue thickness. Plantar heel tissue thickness was successfully measured, decreasing from 16.2 mm to 10.1 mm with pressure changes from 0 to 190 kPa. Stress-strain pressure application and release curves and the heel tissue hysteresis parameter were also successfully calculated.