Development of a Body-Worn Textile-Based Strain Sensor: Application to Diabetic Foot Assessment

Using body-worn sensors in healthcare can bring yield clinically valuable information but risks affecting the interface under investigation. Diabetic foot ulcers (DFUs) are a significant health and economic burden, frequently leading to limb amputation with a severe impact on patient quality of life. Clinicians and patients urgently require information about foot condition to inform DFU prevention strategies, but the addition of sensors at the foot interface risks causing inappropriate loads and adverse clinical outcomes. This work proposes a novel strain-sensing technology that can be integrated unobtrusively within sock textiles at the foot interface. Context-specific set of requirements were established to evaluate potential sensing modalities. A total of 12 load-sensing methods were identified, not limited to DFU sensing to investigate possible solutions. Candidate technologies we evaluated against the specification and selected a silver-based adhesive exhibiting strain-sensitive resistance. Sensor development was undertaken through parametric experimental testing using a stretchable textile substrate. A characterisation process determined the sensor has a resolution of 0.013 $\Omega$ in a range of 0 - 430 $\Omega$ and a range of interest of 0 - 20 $\Omega$. The sensors demonstrated the capacity to cover an appropriate measurement range (0 - 12\% strain). Composite reinforcement increased strain capacity to 20\% during quasi-static testing. After development, the final sensor design performance was asessed, integrating the sensing unit within a knitted structure produced using an industrial sock-knitting machine. The system was evaluated through a cyclic loading regime. A strain threshold of 6\% was determined with a peak sensitivity gradient of 0.3 \textpm 0.02. A dynamic drift of 0.039 to 0.045\% (total range) was identified over usage, with micro-tearing identified as the mechanism of action. In conclusion, this study demonstrates a viable textile-based strain sensor capable of integration within knitted structures. It provides a promising first step towards developing a sock-based strain sensor to aid the prevention of DFU formation.