Development of a Flow-free Gradient Generator Using a Self-Adhesive Thiol-acrylate Microfluidic Resin/Hydrogel (TAMR/H) Hybrid System

Abstract

Microfluidic gradient generators have been used to study cellular migration, growth, and drug response in numerous biological systems. One type of device combines a hydrogel and polydimethylsiloxane (PDMS) to generate “flow-free” gradients; however, their requirements for either negative flow or external clamps to maintain fluid-tight seals between the two layers have restricted their utility among broader applications. In this work, a two-layer, flow-free microfluidic gradient generator was developed using thiol-ene chemistry. Both rigid thiol-acrylate microfluidic resin (TAMR) and diffusive thiol-acrylate hydrogel (H) layers were synthesized from commercially available monomers at room temperature and pressure using a base-catalyzed Michael addition. The device consisted of three parallel microfluidic channels negatively imprinted in TAMR layered on top of the thiol-acrylate hydrogel to facilitate orthogonal diffusion of chemicals to the direction of flow. Upon contact, these two layers formed fluid-tight channels without any external pressure due to a strong adhesive interaction between the two layers. The diffusion of molecules through the TAMR/H system was confirmed both experimentally (using fluorescent microscopy) and computationally (using COMSOL). The performance of the TAMR/H system was compared to a conventional PDMS/agarose device with a similar geometry by studying the chemorepulsive response of a motile strain of GFP-expressing Escherichia coli . Population-based analysis confirmed a similar migratory response of both wild-type and mutant E. coli in both of the microfluidic devices. This confirmed that the TAMR/H hybrid system is a viable alternative to traditional PDMS-based microfluidic gradient generators and can be used for several different applications.

Cells collectively migrate during ammonium chemotaxis in Chlamydomonas reinhardtii

“…A custom Python code was used to fit the experimental line scan data (Figure S2A) to Equation S2; however, since the collected data is measurements of the dye absorbance intensity, concentrations (C and C0) in Equation S2 were replaced with intensity (I and I0). This is a common approach used to model mass transfer of dyes in water 47 . I0 was assumed equal to the highest measured intensity in the dish which corresponds to position immediately outside of the agarose block at the 1 h time point.…”

Rapid synthesis of biocompatible bilayer hydrogels via frontal polymerization

“…Frontal polymerization (FP) is a fast and self‐sustained polymerization mode, in which only initiation energy is required to form a stable front for the reaction system, and then the propagating front rapidly converts monomers into polymers upon the intrinsic exothermic nature 23–25 …”

Bacterial chemotaxis in static gradients quantified in a biopolymer membrane-integrated microfluidic platform

“…14,[24][25][26] While hydrogelbased devices are often comprised of biocompatible materials such as agarose, 22,27 collagen, 28,29 or polyethylene glycol (PEG), 30 gradients over a large concentration range are challenging to produce due to the relatively large lateral dimensions of hydrogels (often in the range of a few hundreds of μm), 24 or take hours to establish. 31 On the other hand, membrane-based devices offer an enhanced range of chemical gradients because the diffusion of biomolecules through semipermeable membranes can be accommodated from a few to tens of μm. 24,32 This is an important aspect of our in situ membrane assembly process.…”