Development of micromachined flow sensor for drip infusion system

In this work, we developed a MEMS flow sensor for application to a drip infusion system. The MEMS sensor is composed of a silicone rubber layer, a film sensor with a flow rate measurement element consisting of a metal heater and thermistors formed on a thin polyimide film, and a PDMS layer with a flow channel that utilizes a plastic plate as a substrate. In the drip infusion system, the flow sensor needs to have high sensitivity in a low flow rate range under a low driving temperature condition in order to achieve high-precision drug delivery. Therefore, we utilized the calorimetric method as a flow rate measurement principle to improve the sensor sensitivity and set the driving condition of the sensor to 40 °C or less to prevent deterioration of the infusion drug. Experiments under these conditions showed that our flow sensor had high sensitivity in the low flow rate range of 5.0 g/min or less. We also evaluated the flow rate detection function using various liquids having the same properties as the drip infusion solution in the driving temperature of 40 °C or less and found that the flow sensor could sufficiently measure each solution within the set flow rate range.