Fingertip-Sized Pressure Sensor for Luer Taper of Three-Way Stopcock in Liquid Channel

We developed an easily attachable fingertip-sized pressure sensor (FSPS) for a three-way stopcock in a liquid channel of a heart–lung machine. The FSPS has a double-pipe structure with a semispherical soft film cap on the pointed end and a diaphragm semiconductor strain sensor on the other end. An enclosed space of variable volume covered with the soft film cap prevents the semiconductor strain sensor from coming into direct contact with blood, and the double-pipe structure decreases the strain on the strain sensor when inserting the FSPS into the female-fitting part of the luer taper. It is difficult to fabricate a very fine double-pipe structure by cutting or injection molding. Instead, we fabricated it by using a three-dimensional (3D) printer. Moreover, it is difficult to fabricate a semispherical soft film cap with a 3D printer, so we fabricated it with a resin casting method using silicone resin. Experiments on the FSPS using a variable pressure liquid channel showed that it is not affected by inserting it into the female-fitting part of the luer taper and that it can accurately measure pressure in a liquid channel within a pressure range from 0 to 100 kPa.