We uncover anisotropic permeability in microfluidic deterministic lateral displacement (DLD) arrays. A DLD array can achieve high-resolution bimodal size-based separation of microparticles, including bioparticles, such as cells. For an application with a given separation size, correct device operation requires that the flow remains at a fixed angle to the obstacle array. We demonstrate via experiments and lattice-Boltzmann simulations that subtle array design features cause anisotropic permeability. Anisotropic permeability indicates the microfluidic array's intrinsic tendency to induce an undesired lateral pressure gradient. This can cause an inclined flow and therefore local changes in the critical separation size. Thus, particle trajectories can become unpredictable and the device useless for the desired separation task. Anisotropy becomes severe for arrays with unequal axial and lateral gaps between obstacle posts and highly asymmetric post shapes. Furthermore, of the two equivalent array layouts employed with the DLD, the rotated-square layout does not display intrinsic anisotropy. We therefore recommend this layout over the easier-to-implement parallelogram layout. We provide additional guidelines for avoiding adverse effects of anisotropy on the DLD.

中文翻译：

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确定性横向位移阵列中的各向异性渗透率

我们发现微流体确定性侧向位移（DLD）阵列中的各向异性渗透率。DLD阵列可以实现基于高分辨率双峰大小的微粒分离，包括生物微粒（例如细胞）。对于具有给定分隔尺寸的应用，正确的设备操作要求流量与障碍物阵列保持固定角度。我们通过展示微妙的阵列设计特征的实验和晶格-玻尔兹曼模拟会导致各向异性渗透。各向异性渗透率表明微流体阵列引起不希望的横向压力梯度的内在趋势。这会导致倾斜的流动，并因此导致临界分离尺寸的局部变化。因此，颗粒轨迹可能变得不可预测，并且该设备对所需的分离任务毫无用处。对于在障碍柱和高度不对称柱形状之间具有不相等的轴向和横向间隙的阵列，各向异性会变得很严重。此外，在DLD所采用的两个等效阵列布局中，旋转正方形布局不显示固有各向异性。因此，我们建议此布局优于易于实现的平行四边形布局。