Microfluidic Microdialysis: Spatiotemporal Control over Solution Microenvironments Using Integrated Hydrogel Membrane Microwindows

Abstract

We present a powerful and versatile technique that enables exquisite spatial and temporal control over local solution chemistry in microfluidic devices. Using a microscope and a UV lamp, we use projection lithography to photopolymerize thin (10-25 m) hydrogel membrane ''microwindows'' (HMMs) into standard microfluidic devices. These microwindows are permeable to solute and solvent diffusion and to electric fields, yet act as rigid walls from the standpoint of fluid flow. Reservoirs of solution may thus be rapidly imposed, switched, and maintained on one side of a HMM using standard microfluidic techniques, provoking changes in solution conditions on the other side without active mixing, stirring, or diluting. We highlight three paradigmatic experimental capabilities enabled by HMMs: (1) rapid dialysis and swapping of solute and/or solvent, (2) stable and convection-free localized concentration gradients, and (3) local electric permeability. The functional versatility of hydrogel microwindow membranes, coupled with the ease and speed of their fabrication and integration into simple microchannels or multilayer devices, will open a variety of novel applications and studies in a broad range of fields.

Diffusiophoretic Focusing of Suspended Colloids

“…We have recently developed a microfluidic system that allows systematic and quantitative measurement of DP mobilities [13]. Integrated hydrogel microwindow membranes [21] enable a wide range of solute gradients to be imposed without generating convective flows, and particle DP to be visualized directly and measured quantitatively.…”

Soluto-inertial phenomena: Designing long-range, long-lasting, surface-specific interactions in suspensions

“…Such theories have been developed for gradients of electrolytes (35,37) and nonelectrolytes (51), yet difficulties in establishing sufficiently strong, stable gradients have prevented systematic experimental measurements (as is routine for electrophoresis). Recent developments in microfluidics, however, have enabled more direct studies of DP (40,(52)(53)(54)(55)(56). In particular, we have recently developed a microfluidic device (56) that enables gradients to be directly imposed, and diffusiophoretic migration to be visualized and measured under various solute and solvent gradients (40).…”

Direct Measurements of Colloidal Solvophoresis under Imposed Solvent and Solute Gradients

“…27 This method allows strong gradients to be established perpendicular to and entirely within the imaging plane, and the small channel dimensions suppress the hydrodynamic flows and instabilities often associated with strong concentration gradients. Although the transmembrane flow velocities arising with HMMs prepared in that work were already quite small small (u P ≲1 μm/s), the diffusiophoretic migration measured in the present work (u DP ∼ 1 μm/s) can be slow enough that even smaller transmembrane flows are required.…”

“…26 We have recently developed a method to impose local solute and solvent gradients within microchannels, which enabled the first direct microscopic visualization of solvophoretic migration. 27 To set up strong gradients within channels, we photopolymerize thin hydrogel membranes into so-called "microfluidic stickers" devices 28 made from the UV-curable optical adhesive NOA-81 (Norland), based on their superior solvent-compatibility compared with standard PDMS devices. Our method allows high-resolution velocity measurements of diffusiophoresis under diverse chemical gradients.…”