ASSESSMENT OF THE PERFORMANCE OF HYDROGEL VALVES FOR USE IN INGESTIBLE SENSOR DEVICES: APPROACHES FOR STABILIZING THE pH IN MICROFLUIDIC RESERVOIRS

摘要

Recently, biocompatible batteries that use gastric fl uid as electrolyte have been proposed as possible power sources for ingestible sensor devices, which can measure and transmit vital body functions such as body core temperature, pH, pressure, etc. Biocompatible batteries can overcome the limitations of conventional batteries, namely the need for encapsulation, which leads to bulky and difficult–to-swallow devices. However, to ensure a more stable cell voltage and to enable the use of the sensor during its passage through the entire gastrointestinal tract, it is preferrable that the electrolyte can be contained inside a microreservoir to keep it in stable conditions. To extend the potential operating time of biocompatible, gastric-fl uid-powered microbatteries, we have investigated the possibility of using microfl uidic reservoirs realized in Si and glass that comprise pH-sensitive, microstructured hydrogel valves, to store the gastric acid and to stabilize the pH even when exposed to a medium of different pH. The shape evolution of the hydrogel valves inside the microfl uidic reservoirs that contained simulated gastric fl uid (pH 1.21) and after being exposed to simulated intestinal fl uid (pH 6.8) was observed by time lapse optical microscopy, and the change of the pH over time was estimated from micro-Raman spectroscopy using methyl orange as a molecular probe. For the microfl uidic reservoirs containing hydrogel valves, time-resolved imaging showed that the hydrogel valves appeared to close after about 15 min. The variation of the pH values over time in the microfl uidic reservoirs without hydrogel valves showed an almost linear increase, reaching a pH value of approximately 4.8 ± 0.3 after about 26 min, whereas in the case with integrated hydrogel valves, the same value was reached after about 85 min. It is expected that the integration of hydrogel valves in microfl uidic reseroirs can enable more stable operation of gastric fl uid-powered batteries and extend their operating time.