Embroidered 3D capacitive sensor integrated with bandage for monitoring of volume and type of biofluids

Textile based sensors have gained tremendous attention in moisture sensing. Moisture monitoring is crucial in wound healing. To promote the healing process, it is essential to maintain an optimal level of moisture while limiting unnecessary dressing changes. The objective of this research was to test how well a textile moisture sensor can detect moisture from the body and wound fluid when attached to the dressing. To this end, a 3D interdigitated capacitive structure was embroidered with silver conductive threads on the textile substrate, and a bandage was placed in the centre of the multilayer structure. When compared to traditional planar interdigitated structures, the main innovation of the proposed 3D capacitive structure lies in a larger surface area for interaction with the surrounding environment, leading to enhanced sensitivity to changes in capacitance with the respect to the moisture. The 3D structure of the bandage increased the ratio between electrodes and surface area to impact the surface charge sensitivity towards the adsorbed charges of the wound and body fluid. To observe the performance of the sensor, the bandage was exposed to simulated body fluid and wound fluid. Between dry and wet conditions, the sensor can detect capacitance differences of several orders of magnitude. The threshold volume for the 3D bandage was 30 μL to 50 μL, depending on the type of biofluids. The capacitive bandage integration with the inductor was tested at high frequencies (1–400 MHz). The shift in impedance was observed for the tested fluids. Finally, to compare sensing properties of the proposed structure against the previously reported designs, a bandage sensitivity was checked for three different configurations: (a) the proposed 3D bandage, (b) a 2D bandage, composed of textile substrate with both electrodes embroidered on top of bandage, and (c) classical interdigital structure without bandage composed of textile with embroidered electrodes on the top of it. The sensitivity of the 3D bandage for simulated body fluid and wound fluid is >6.6% and 7.4%, respectively, higher than the other two structures. The integration of the proposed textile-based sensor into a bandage could facilitate wound care and have a significant impact on efficacy for patients.