Mavrogiannis Nicholas, Desmond Mitchell, Ling Kenny, Fu Xiaotong, Gagnon Zachary
Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Maryland Hall 220A, Baltimore, MD 21218, USA.
Micromachines (Basel). 2016 Nov 23;7(11):214. doi: 10.3390/mi7110214.
Microfluidic platforms capable of complex on-chip processing and liquid handling enable a wide variety of sensing, cellular, and material-related applications across a spectrum of disciplines in engineering and biology. However, there is a general lack of available active microscale mixing methods capable of dynamically controlling on-chip solute concentrations in real-time. Hence, multiple microfluidic fluid handling steps are often needed for applications that require buffers at varying on-chip concentrations. Here, we present a novel electrokinetic method for actively mixing laminar fluids and controlling on-chip concentrations in microfluidic channels using fluidic dielectrophoresis. Using a microfluidic channel junction, we co-flow three electrolyte streams side-by-side so that two outer conductive streams enclose a low conductive central stream. The tri-laminar flow is driven through an array of electrodes where the outer streams are electrokinetically deflected and forced to mix with the central flow field. This newly mixed central flow is then sent continuously downstream to serve as a concentration boundary condition for a microfluidic gradient chamber. We demonstrate that by actively mixing the upstream fluids, a variable concentration gradient can be formed dynamically downstream with single a fixed inlet concentration. This novel mixing approach offers a useful method for producing variable on-chip concentrations from a single inlet source.
能够进行复杂片上处理和液体操控的微流控平台，在工程学和生物学等一系列学科中实现了广泛的传感、细胞及材料相关应用。然而，目前普遍缺乏能够实时动态控制片上溶质浓度的有效微尺度混合方法。因此，对于需要不同片上浓度缓冲液的应用，通常需要多个微流控液体操控步骤。在此，我们提出一种新颖的电动方法，利用流体介电泳在微流控通道中主动混合层流流体并控制片上浓度。通过一个微流控通道结，我们使三股电解质流并排共流，使得两股外侧的传导性流包围一股低传导性的中心流。这种三层层流通过一系列电极驱动，在此过程中外侧流通过电动方式发生偏转并被迫与中心流场混合。然后，这种新混合的中心流持续向下游输送，作为微流控梯度室的浓度边界条件。我们证明，通过主动混合上游流体，在单一固定入口浓度下，下游可动态形成可变浓度梯度。这种新颖的混合方法为从单一入口源产生可变片上浓度提供了一种有用的方法。
