There has been a rising demand for more complex chips and multi-chips integration in microfluidics. However, chip-to-chip and chip-to-world interconnections remain simple, i.e. plastic tubing, due to its very different melting processing techniques, materials properties and insufficient knowledge of fiber electronics. These challenges can be addressed by applying new device structures and new sensing materials made available by multimaterial fiber processes, which have recently emerged as a material platform for a variety of sensing modalities. In this work, we present a new strategy that integrates different functional units, such as pumping or sensing units, into the multimaterial fibers as microfluidics interconnections.
Hundreds of meters of uniform fibers with cross-sections of 2x1 mm were produced through a thermal drawing processing. The basic structure of fiber consists a 1x0.5 mm hollow core as a fluid channel inside of polycarbonate (PC) cladding. Two conductive polymer films made of carbon black doped polyethylene (CPE, 25 um) are placed adjacent to the hollow core. CPE films are electrically insulated from the fluid channel by a thin dielectric film of polycarbonate (5 um), and can be electrically connected on the fiber surfaces with silver paint.
Multiple microfluidics-related functions, such as flowrate sensor and fluid pump, have been demonstrated with this specific fiber design. Here we specifically focus on demonstrating a hybrid in-fiber multi-segment thermal flow sensor design that enables extended measurement range at high flow-rate sensitivity and low flow resistance. We start with a first-order heat-transfer analysis to establish the analytical temperature response of a long hot film in a fiber microfluidic channel. This model predicts a limited range of linear flow-rate response for a single-segment sensor, which is confirmed by measurement. We then explore multi-segment structure sensors with a significantly extended operational range in both numerical simulations and experiments.
We report integrated multi-segment fiber flow rate sensors that combines high sensitivity (0.38 V/(uLmin-1)), large dynamic range (0-200 uL/min) and small pressure drop (8 Pa at 100 uL/min), in a 1mm x 0.5mm fluidic channel embedded in a multi-material fiber. Depends on the flow rate region of interest, one or multiple appreciate segments can be measured for the best performance, which enables us to extend measurement range within a single device. Comparing to widely used metal films, new sensing materials CPE provides 20 times higher TCR (0.09 K-1) and 107 times higher resistivity (0.2 Ωm), allowing us to obtain low pressure drop while maintaining high sensitivity. High sensitivity, low pressure drop and wide measurement range together qualify our fiber sensors as very promising functional microfluidics interconnections. Our work opens up many new opportunities for microfluidics research and is extremely suitable for biomedical applications.