Constant-Flow Liquid Transfer System for Skin Microperfusion Biosensing Using a Passive Flow Regulator and a Vacuum Chamber

We have developed a powerless constant-flow liquid transfer system for wearable skin microperfusion. Previously, we introduced a minimally invasive microperfusion needle capable of collecting and measuring the concentration of biological substances from subepidermal tissue. A liquid transfer system for skin microperfusion must meet several requirements, including a low and stable flow rate, low power consumption, disposability, and compact size. The new system we report here operates without electrical power by utilizing a passive constant-flow regulator in combination with a vacuum chamber. The flow regulator has a simple structure, comprising a polymethyl methacrylate plate with a microchannel, bonded to a silicone rubber film. This regulator successfully maintained a flow rate with fluctuations within ±0.5 μL/min under low suction pressures ranging from 10 to 30 kPa. To evaluate its performance, the liquid transfer system was connected to a sensor-integrated microperfusion needle inserted into porcine skin. Results from continuous liquid transfer experiments demonstrated that the system was capable of maintaining a stable, low flow rate for more than 90 min.