Collagen fixation in microfluidics: optimizing uniform flow using PDMS posts and contact line pinning

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Microfluidic devices have been emphasized as a tool for effective preclinical models. Devices integrating biomodels (here, type I collagen) afford replication of cell or tissue physiology and have been particularly impactful when studying interstitial flow and chemo invasion. The current work uses computational models and simulation to optimize microfluidic device experimental efficacy and functional use, focusing on two particular platforms proposed by Li et al. (2018) and Tung et al. (2013). Both of these designs use collagen as a model tissue, and we aim to optimize collagen fixation in the experimental channel of these microfluidic devices. Specifically, we aim to analyze flow velocity profiles in a porous media for different methods of porous media fixation. The device is a 10 mm long channel with an inlet and outlet for pressure driven flow with a 1.2 mm experimental channel in the center perpendicular to the long channel. This experimental channel is filled with type I collagen, which is used to replicate human tissue. The porous media is fixed in this center channel, with an inlet fully developed flow boundary condition of 1 μm/s average velocity, outlet boundary condition of 0 Pa, no-slip boundary conditions along all channel walls, fluid dynamic viscosity of 0.731 mPa-s, and porous media permeability and porosity of 10-11 m2 and 0.9789, respectively. Flow velocity, spatial non-uniformity, and the total cross-sectional area accounted for by the fixation method were computed. Upon initial validation of our model, we found uniform flow is able to be maintained in the contact-line pinning design, allowing for fluid flow representative of physiological flow. We then optimized the geometry by introducing Polydimethylsiloxane (PDMS) posts to improve use, reduce the amount of collagen leaking out from the experimental channel, and prevent air bubble entrapment. We found that combining the contact-line pinning method with 2-3 PDMS posts of varying surface area from 10-30% of total cross sectional area produced the most optimal results. We provide a design that reduces the cross-sectional area of the PDMS post fixation method and maintains similar flow uniformity to the contact-line pinning method.

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microfluidic; optimization; porous media flow; contact-line pinning method; PDMS posts; interstitial flow


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