A. Wang, D. Koh, P. Schneider, K.W. Oh
University at Buffalo,
Keywords: micropumps, lab-on-a-chip
Summary:Abstract In this paper, a simple syringe-assisted pumping method was introduced. Compared with previous study , the proposed design does not require pre-designed vacuum chambers, the multiple pumps can be integrated into one device and a constant flow rate can be achieved. This method enables a point-of-care pumping with more flexibility in hand-held PDMS microfluidics devices. A constant flow with a rate ranging from 0.8 nl/s to 1.8 nl/s was achieved by adjusting PDMS wall thickness. Details One of the widely studied units in point-of-care testing is controllable, hand-held pumping [1, 2]. In our previous study , syringe-assisted pumping utilizing the gas permeability of polydimethylsiloxane was introduced. The pumping can drive the liquid without external pumps, however, there were inherent drawbacks. First, the flow rate significantly decreased after the flow entered the part of channel surrounded by a micro-chamber. This is because the air diffusion area decreased while the flow reached the dead-end channel surrounded by vacuum-chamber, resulting in a non-constant flow rate. Second, previous pumps cannot be used in the microfluidics system with integrated functions. Since the vacuum chamber is pre-integrated in the device, all of the channels will be suspect to air diffusion, which is not use with devices with integrated microfluidic components. In order to integrate multiple pumps, air diffusion from unwanted channel should be isolated. Third, a vacuum chamber was designed in-plane, which has limitation in terms of design flexibility. In this paper, we propose a compact syringe-assisted pumping, which can achieve a constant flow rate. Multiple pumps can be integrated in one device, and no pre-determined vacuum chamber is needed. As described in the paper , the flow rate Q utilizing gas-permeability of PDMS can be written as Q(t)≈k FS/C_ATM =kD (C_PDMS-C_Chamber)/C_ATM * S/t_wall →Q(t)∝S/t_wall , where k is empirical factor related to viscous effect of the pumped liquid flow. F is steady state air flux diffusing into micro-chamber through PDMS wall. S is the total surface area that allows air to diffuse into the PDMS bulk, which is equivalent to overlap area. C_PDMS, C_Chamberand C_ATM is air concentration in PDMS, micro-chamber and atmosphere respectively. t_wall is PDMS wall thickness, where we designed to be 200 um, 300 um and 400 um. Fig.1 shows a device configuration. A traditional microfluidic channel is designed as a bottom layer, while proposed pump is designed as a top layer to drive the liquid in the bottom layer. Fig. 2 shows the flow rate testing results. The thickness of the PDMS walls were designed to be 200 um, 300 um and 400 um resulting in a flow rate of 0.8 nl /s to 1.8 nl/s. In conclusion, we proposed a syringe assisted, vacuum driven micropumping providing a constant flow rate, which has the potential to be integrated into a variety of microfluidics system.