Design of a wireless smart insole using stretchable microfluidic sensor for gait monitoring
Jen-Hahn Low, Pei Song Chee, Eng-Hock Lim, Vinod Ganesan
Abstract
Wearable sensor enables continuous and ubiquitous real-time monitoring of the gait pattern of a patient and it eliminates the need of frequent visit to the clinics and the use of costly medical facilities. Attaching gait sensors on body, however, may not be easy as most of the reported gait sensors are made of non-stretchable materials and they are non-conformal to human skin. In this paper, we have presented an in-shoe pressure measurement system that is developed using multiple stretchable microfluidic sensors for monitoring gait parameters ergonomically. The sensor here has employed Eutectic Gallium-Indium (EGaIn) as the conductive liquid to fill up a spiral-patterned microchannel which is encapsulated inside an Ecoflex 00–50 elastomer. Fundamental studies have been performed to investigate the sensor’s behaviours when it is exposed to normal and axial applied forces. As proof-of-concept demonstration of the applicability of the proposed sensor for gait monitoring application, we have measured the localised foot pressure and dynamically by attaching two sensors on a shoe insole for detecting pressure changes around the heel and metatarsal regions. The experiment was then extended to evaluate the strain sensing by measuring the ankle angle. It has been shown that data can be captured wirelessly and displayed on a smartphone using the Bluetooth communication protocol. Owing to its unique and stretchable structure, the sensor is able to distinguish walking and running motions by analysing their stance and swing phases. This work has explored the possibility of applying a microfluidic-based structure for designing a wearable gait sensor that has good flexibility.