Freeze-thaw valves as a flow control mechanism in spatially complex 3D-printed fluidic devices

In this paper, we demonstrate a proof-of-principle of a freeze-thaw valve (FTV) created in a 3D-printed fluidic device. Portions of channels are enveloped by cooling and heating jackets, and a heat transfer liquid is recirculated through the two jackets. A frozen plug is created in selected portions of the target-channel and the heating jacket ensures that a selected temperature is maintained in the rest of the channel. An FTV can be 3D-printed in a wide variety of materials as single piece devices with no moving parts without high resolution requirements of the printing process. Such valves can therefore be incorporated in devices for liquid chromatography or multi-step synthesis process.

Computational fluid dynamic simulations of a prototype T-junction piece show the two zones to be well defined at coolant and heating jacket flow-rates greater than 1 mL/min, with power consumptions of 1–3 W. The prototype was printed in Titanium 6Al-4V using selective laser melting and the frozen plug was shown to withstand 20 MPa of pressure. Switching times between states 1 (with a frozen section) and 2 (with both sections thawed) were 0.2–3 min in computational and experimental tests. The scalability of the freeze-thaw system was demonstrated using a multi-gate valve containing 33 junctions without a proportionate increase in operational complexity or switching times.