An Osmotic Pressure Sensor for Monitoring the Level of Hydration in Biological Fluids

PROJECT TITLE :

An Osmotic Pressure Sensor for Monitoring the Level of Hydration in Biological Fluids

ABSTRACT:

A miniaturized hydration sensor that records the electrolyte balance in biological fluids and that translates this amount into an osmotic pressure signal has been developed. The sensor measures sixteen mm $times ,, eight$ mm and integrates a semi-permeable membrane, a piezoresistive pressure transducer, and an electronic readout platform. The dynamic measurement range of 220–340 mOsm $textL^-1$ (280 ± sixty mOsm $textL^-1)$ covers a serious state of dehydration to a heavy state of overhydration (represented by a $Delta text hydration = pm 20$ %). Ion exchange membranes were found to be the best candidates for integration with the hydration sensor. Reverse osmosis membranes with physical pores (zero Da molecular cutoff) had high ionic leakage rates, in distinction to gas permeable membranes, which proved to be nearly impermeable to water vapor. Consequently, the employment of a Nafion NR21one membrane facilitated a sensor response with a time constant of 2.5 h, that conforms to the slow change in osmotic pressure related to hydration. The low-power front-finish circuit architecture relies on an analog pressure-to-frequency converter, consuming solely thirty-nine.four $mu textW$ , and capable of recording changes in hydration with a resolution of five.71 bits (ENOB $_mathrm SNR)$ . The small size of the sensor elements, combined with the interface low-power design, renders it appropriate for more miniaturization required for implantation into the human body.

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