Truly 3D microfluidic heating system with iterative structure of coil heaters and fluidic channels

A microfluidic chip, in which both the coil heater and the fluidic channel are designed in a 3D iterative structure, is developed and experimentally demonstrated. Using the empty surrounding 3D space, the microfluidic chip increases the heat transfer area, thereby increasing the fluid temperature by 51.3%, with the same power consumption, compared to heaters and channels typically designed on a 2D plane. After casting polydimethylsiloxane (PDMS) into a sacrificial mold printed using a 3D printer and dissolving the mold, the 3D coil Joule heater is fabricated by filling the interior part of the coil with liquid gallium by vacuuming. By adding an insulation wall filled with air having low thermal conductivity, an additional heating of 8.7% is achieved; this demonstrates the advantage of the 3D-printed soluble-mold technique, which can allow faster prototyping than the typical microfabrication based on soft lithography. Thus, this technique enables convenient design modifications with high priority for performance improvement. As all the components are manufactured simultaneously within a biocompatible, single PDMS body (because of the absence of bonding process between the devices), the risk of leakage in the device is inherently avoided, and the device can be bent without causing any fracture. Therefore, the reported fabrication process and devices are expected to contribute to miniaturization and performance enhancement of microfluidics; this will lead to the development of wearable 3D lab-on-a-chip devices in future.