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. Author manuscript; available in PMC: 2019 Aug 8.
Published in final edited form as: Anal Chem. 2018 Dec 11;91(1):330–351. doi: 10.1021/acs.analchem.8b05293

Figure 3.

Figure 3.

New strategies towards unidirectional perfusion on a pumpless platform. A) A pumpless platform provides unidirectional tissue perfusion for most of the time with transient backflow.36 Reproduced from A microfluidic chip with gravity-induced unidirectional flow for perfusion cell culture, Lee, D. W.; Choi, N.; Sung, J. H. Biotechnol Prog (ref 36). Copyright 2018 Wiley. B) A pumpless platform provides unidirectional tissue perfusion for a fraction of the cycle and stalled flow for the rest of it.27 Fluid travels between a pair of reservoirs alternately through the tissue perfusion channel and the bypass channel. Reproduced from Esch, M. B.; Ueno, H.; Applegate, D. R.; Shuler, M. L. Lab Chip 2016, 16, 2719–2729 (ref 27) by permission of The Royal Society of Chemistry. C) UniChip achieves continuous unidirectional perfusion with recirculation in a gravity driven flow system 37. i) An assembled UniChip device is placed on a rocker platform that flips between +18° and −18° periodically. ii) Top view of the device shows fluidic connections. Cu, perfusion channel; a1, a2, b1, and b2, Supporting channels; v1, v2, passive valves. iii) Schematic of UniChip operation. When tilted at +18°, flow in b1 is halted by the capillary force at the air–liquid interface in the passive valve v1. Flow travels from reservoir I to reservoir II through a1, a2, Cu and b2. When tilted at −18°, flow in b2 is halted by valve v2, and flow is directed from reservoir II to reservoir I through a2, a1, Cu and b1. Under either condition, the flow direction in the perfusion channel, Cu, is kept the same, shown by the green arrows. Adapted from Wang, Y. I.; Shuler, M. L. Lab Chip 2018, 18, 2563–2574 (ref 37) with permission of The Royal Society of Chemistry.