Polystyrene microdispenser for blood tests using hydrophobic passive valve

This paper proposes a polystyrene microdispenser to meter and discharge 200 nl of plasma solution with high reproducibility. To produce at low cost, hydrophobic passive valves with a simple structured fabricated by injection molding were used for the metering principle. After evaluation using a plasma solution, the microdispensers coated with fluoric resin showed reproducibility of discharged fluid volume with a coefficient of variance of 1.25%. On the other hand, those coated with dimethyl silicone caused a backflow of the discharged fluid to the metering channel, resulting in the degradation of reproducibility. To evaluate the dynamic behavior of the fluid in the channels, we measured not only the static contact angle, but also repeatedly measured the contact angles and various kinds of dynamic contact angle, e.g. the extension advancing angle and the sliding angle. We show the possibility that repeatedly measuring the contact angle can be used for selection of a surface treatment which does not cause backflow. In addition, we propose a method of estimating the discharge pressure, using an extension of the advancing angle and the sliding angle. This method enables closer estimation to the actual measurements than the conventional method based on the static contact angle.