Microfluidic fibers for water collection and smartphone-integrated wearable sensors

Abstract

The present work includes two main aspects: microfluidic fibers for water collection and smartphone-integrated wearable sensors. Exploring water resources is a significant challenge to human livelihood, industry manufacturing, and agricultural irrigation for the relief of freshwater scarcity in arid, semiarid, and rural regions. Inspired by spider silk, combing heterogeneous structures and specific surface chemical compositions is of increasing interest to prepare wetting-controlled fibers, fibrous surfaces, and 3D materials. Many fabrication methods have recently been developed for bioinspired artificial fibers, such as coating, electrospinning, and microfluidic technologies. However, the morphologies of generated fibers are usually fixed, and restricted to the material properties and the device configurations. Controllable manipulation of the macroscale topographies and the microscale morphologies of the as-prepared microfibers is crucial. The first part of the present work contains the fabrication of heterotypic microfibers in applications of water collection and dehumidification. We developed a bioinspired microfiber with hourglass-shaped knots (named hourglass-shaped microfibers) via integration of microfluidic technologies and non-solvent-induced phase separation (NIPS) post-treatment. By regulating the oil core spillage process and the spindle fiber templates, these hourglass-shaped microfibers were endowed with tunable morphologies, adjustive densities, high specific surface areas, enhanced surface roughness, enhanced dehumidification, and water collection abilities. In addition, the work also built up a 3D printed template method to fabricate well-controlled microfibers with tunable dimensions. The resultant fibers demonstrated various morphologies, unique mechanical properties, excellent fog collection abilities. Our heterotypic microfibers could serve as the promising candidates for dehumidifying, fluid control, directional transportation of droplets, and large-scale water harvesting. Recently, wearable electronics have been widely studied in the field of monitoring an individual’s dynamic physiological status, such as real-time tracking of human signs (such as blood pressure, heart rate, and body temperature), and continuous analysis of biological metabolites in body fluids. Especially, flexible wearable electrochemical biosensors have been developed for providing the epidermal perspiration information including glucose, lactate, urea, Na+, and K+. PH and temperature are significant critical indicators of potential diseases and influencing factors of enzyme activities. Therefore, developing a wearable device for pH and temperature monitoring is of great importance for personalized health monitoring. The second part of the present work centers on a smartphone-integrated wearable pH monitoring system, featuring a disposable multifunctional sensing patch and reusable wireless communication circuitry. The sensing patch exhibited a reliable performance with a near-Nernstian response of 60.8 mV/pH in the physiological pH range between 4.5 and 8.5, and a negative temperature coefficient (NTC) of resistance in sensitivity of 1.58%/ºC in the temperature range between 25 °C and 45 °C. Mergence between the sensing patch and the personalized miniaturized printed circuit board (PCB) implemented the data acquisition, signal processing, and wireless transmission to a smartphone. Our sensor was demonstrated to not only function the ex-situ measurements in multiple biofluids (salvia and urine) but also realize the on-site sensing of human perspirations during fitness. This wearable platform could advance the development of a low-cost, high-performance method for non-invasive analysis in applications of personalized medicine, disease diagnosis, and environmental analysis.