Description
The elasticity of PDMS has been instrumental in advancing important microfluidic technologies, ranging from early valves [1] to sophisticated organ-on-a-chip systems [2]. However, the complex multilayer fabrication often required for these devices restricts their broader applicability. To address this, Jain and Belkadi [3] recently introduced a single-layer geometry consisting of a wide and thin microfluidic channel, running parallel to two large air chambers. Controlling the pressure in the air chambers was shown to control the position of the ceiling in the microfluidic channel, with negative pressures lowering the ceiling and positive pressures raising it. While promising for biological applications, the operational range of this device has lacked rigorous characterisation, forcing reliance on trial-and-error design.
Here, we combine finite element method (FEM) simulations with experimental validation to investigate the actuation mechanism and optimise ceiling displacement. Using a Neo-Hookean model parametrised by six geometric variables, we performed a global sensitivity analysis (Sobol’s method) on 14,336 simulations. This revealed the geometric features driving deformation magnitude and allowed us to identify the configuration for maximal displacement through a targeted sweep of the three most critical parameters: PDMS layer height, channel width, and air chamber width.
Beyond displacement amplitude of the ceiling, the simulations also provide insights about the mechanisms governing the shape of the displaced ceiling. Depending on the interplay of localised compression and extension, the ceiling adopts either a U-shaped profile with a minimum at the symmetry plane, or a W-shaped profile where the center bulges upwards between two minima.The transition shape in between those two profiles is of particular interest, as it is characterised by a homogenous, flat downward deflection of the ceiling. A second sensitivity analysis identifies the parameters governing these contributions, enabling the prediction of the transition between deformation regimes. Experimental measurements of ceiling displacement validated the FEM model for three chip geometries, confirming all the predicted deformation shapes. Finally, by applying the maximised deformation geometry and modifying the channel cross-section, we demonstrate the fabrication of a fully closing microfluidic valve within a single-layer PDMS chip.
By eliminating complex multilayer fabrication, this approach renders reconfigurable technology widely accessible, facilitating its application in mechanobiology and the development of dynamic, easily manufacturable organ-on-chip systems.
[1] Unger, M. A., Chou, H. P., Thorsen, T., Scherer, A., & Quake, S. R. (2000). Monolithic microfabricated valves and pumps by multilayer soft lithography. science, 288(5463), 113-116.
[2] Huh, D., Matthews, B. D., Mammoto, A., Montoya-Zavala, M., Hsin, H. Y., & Ingber, D. E. (2010). Reconstituting organ-level lung functions on a chip. Science, 328(5986), 1662-1668.
[3] S. Jain, H. Belkadi, A. Michaut, S. Sart, J. Gros, M. Genet and C. N. Baroud (2024), Using a micro-device with a deformable ceiling to probe stiffness heterogeneities within 3D cell aggregates, Biofabrication 16 035010.