Getting under your skin. Development of wearable devices for improved non-invasive diagnostics
Wearable devices offer platforms through which to interact with the information about human health that skin has to offer. From sweat analysis to electrophysiology recordings, capturing the information present on the skin can widely enhance the diagnosis of multiple diseases in an entirely non-invasive approach. However the complexity of the skin impedes easy interaction with it, requiring complicated engineering devices to obtain the information. Extensive research and material development has been done to reach more mechanically and electrically compliant ways to interface with the skin; covering all the spectra from substrates with improved conformability that make intimate contact with it, to mixed conductive polymers that reduce the electrical impedance in between the body and the electronics. The aim of this project is to create wearable devices for improved diagnostics of certain pathologies that can be addressed entirely non-invasively from the skin. Along this work, I have explored different manufacturing techniques, aiming for processes that could potentially be extended for commercial scale fabrication. First, I developed a high spatial resolution electromyography electrode array consisting on 16 electrodes minimally separated that can record muscle activity with sufficient accuracy to observe the electrical activation of the muscle travelling across it. For this device, the applicability of PEDOT:PSS:IL composites into wearable devices have been explored. Then, based on the existing work in literature, I developed a device capable of selectively stimulating the outermost part of the skin, where pain receptor fibres are located. By creating more intimate contact between the skin and the electrode, major improvement in the device performance was observed while maintaining the spatial selectivity. Finally, by aiming for a large scale fabrication of these devices, I have developed and characterized a manufacturing method for rapid prototyping of new wearable devices in lab environments. Due to lack of accuracy in the process, it was not sufficient to produce the aforementioned device. Therefore, I redesigned the cleanroom fabrication methods used so far into fabrication for large scale manufacturing processes, ensuring that the benefitial effects previously mentioned are still maintained. Development of novel wearable devices will hopefully pave the way into new diagnostic methods that are more comfortable for the patient, enhancing, simplifying and reducing the costs of the diagnosis both for the patient and the clinician without hindering the results obtained.