Recent wearable devices offer portable monitoring of biopotentials, heart rate, or physical activity, allowing for active management of human health and wellness. Such systems can be inserted in the oral cavity for measuring food intake in regard to controlling eating behavior, directly related to diseases such as hypertension, diabetes, and obesity. However, existing devices using plastic circuit boards and rigid sensors are not ideal for oral insertion. A user-comfortable system for the oral cavity requires an ultrathin, low-profile, and soft electronic platform along with miniaturized sensors. Here, we introduce a stretchable hybrid electronic system that has an exceptionally small form factor, enabling a long-range wireless monitoring of sodium intake. Computational study of flexible mechanics and soft materials provides fundamental aspects of key design factors for a tissue-friendly configuration, incorporating a stretchable circuit and sensor. Analytical calculation and experimental study enables reliable wireless circuitry that accommodates dynamic mechanical stress. Systematic in vitro modeling characterizes the functionality of a sodium sensor in the electronics. In vivo demonstration with human subjects captures the device feasibility for real-time quantification of sodium intake, which can be used to manage hypertension.

High-pressure cloud-point data are presented for poly(tetrafluoroethylene-co-19.3 mol % hexafluoropropylene) (FEP19) in CF4, C2F6, C3F8, C3F6, CClF3, CO2, and SF6 at 118-250 °C and pressures as high as 2700 bar. Cloud-point curves for a given solvent virtually superpose for FEP19 concentrations between 2 and 10 wt %. It is not possible to dissolve FEP19 in CO2 at temperatures less than 185 °C due to strong quadrupolar self-interactions relative to cross-interactions between FEP19 and CO2. The location of the cloud-point curves in pressure-temperature space are directly related to the product of the polarizability and molar density, FiRi, of the solvent as determined at the cloud-point pressure at a given temperature. The average of FiRi is 5.14 × 10 -24 mol (7% for the SCF solvents considered in this study calculated at 200 °C and it is 5.41 × 10 -24 mol (7% for all of the solvents except CF4 and CO2 at 170 °C. This simple correlation provides a means for estimating cloud-point pressures for nonpolar polymers with nonpolar solvents, or for polar solvents at very high temperatures where polar interactions are diminished. Using this correlation, it is not possible to predict when crystallization may occur or when polar interactions will dictate the phase behavior as observed for CO2 at temperatures below 185 °C. With one temperature-independent and one temperature-dependent mixture parameter the Sanchez-Lacombe equation of state (SLEOS) is capable of modeling the phase behavior of FEP19 in the solvents considered in this study except for CO2 which required two temperature-dependent parameters. It is not possible to even qualitatively model the cloud-point behavior if the two mixture parameters are set to zero. Hence, the utility of the SLEOS is limited since cloud-point data are needed to fix the values and the temperature dependence of the mixture parameters.