Highly permeable silicon membranes for shear free chemotaxis and rapid cell labeling

Abstract

Microfluidic systems are powerful tools for cell biology studies because they enable the precise addition and removal of solutes in small volumes. However, the fluid forces inherent in the use of microfluidics for cell cultures are sometimes undesirable. An important example is chemotaxis systems where fluid flow creates well-defined and steady chemotactic gradients but also pushes cells downstream. Here we demonstrate a chemotaxis system in which two chambers are separated by a molecularly thin (15 nm), transparent, and nanoporous silicon membrane. One chamber is a microfluidic channel that carries a flow-generated gradient while the other chamber is a shear-free environment for cell observation. The molecularly thin membranes provide effectively no resistance to molecular diffusion between the two chambers, making them ideal elements for creating flow-free chambers in microfluidic systems. Analytical and computational flow models that account for membrane and chamber geometry, predict shear reduction of more than five orders of magnitude. This prediction is confirmed by observing the pure diffusion of nanoparticles in the cell-hosting chamber despite high input flow (Q = 10 µL min−1; vavg ~45 mm min−1) in the flow chamber only 15 nm away. Using total internal reflection fluorescence (TIRF) microscopy, we show that a flow-generated molecular gradient will pass through the membrane into the quiescent cell chamber. Finally we demonstrate that our device allows us to expose migrating neutrophils to a chemotactic gradient or fluorescent label without any influence from flow.

WAT-on-a-chip: a physiologically relevant microfluidic system incorporating white adipose tissue

“…Independent of the numerical finite element model, we employed an analytical model which we developed based on a concept recently introduced by Chung et al 42 : Application of the theoretical equations for our system results in a distribution of the flow rate in the cell chamber as shown in Fig. 3F and a maximum flow rate of less than 1/100 of the input flow rate in the media channel.…”

“…To overcome this barrier, we employed a finite element model treating the membrane as a porous media as described previously. 42 Briefly, the flow through the membrane was solved using the time-dependent solver with a finer physics controlled mesh. The iterative solver was employed using multigrid methods to further overcome computational limitations.…”

“…3E). 42 Applying this analogy to unit segments of length L P , a generalized recurrence relation can be obtained whereby the flow rate in the n th segment of the tissue chamber (with a total of N segments) is…”

“…Adapted from Ref. 42. E) Input flow rate fraction in the tissue chamber along the flow axis calculated by the analytical model.…”

Computational study of cell adhesion and rolling in flow channel by meshfree method

“…To describe the physical force from fluid flow in the rectangular micro-channel, the maximum shear stress is defined as (Chung et al 2014): $$\overline{T}=\frac{6\mu Q}{H^{2}W}$$where μ is dynamic viscosity; Q is the volumetric flow rate; L is the length of channel; H is the height of the micro-channel; W is the width of the micro-channel.…”