Convection-driven generation of long-range material gradients

Abstract

Natural materials exhibit anisotropy with variations in soluble factors, cell distribution, and matrix properties. The ability to recreate the heterogeneity of the natural materials is a major challenge for investigating cell-material interactions and for developing biomimetic materials. Here we present a generic fluidic approach using convection and alternating flow to rapidly generate multi-centimeter gradients of biomolecules, polymers, beads and cells and cross-gradients of two species in a microchannel. Accompanying theoretical estimates and simulations of gradient growth provide design criteria over a range of material properties. A poly(ethyleneglycol) hydrogel gradient, a porous collagen gradient and a composite material with a hyaluronic acid/gelatin cross-gradient were generated with continuous variations in material properties and in their ability to regulate cellular response. This simple yet generic fluidic platform should prove useful for creating anisotropic biomimetic materials and high-throughput platforms for investigating cell-microenvironment interaction.

Creating stiffness gradient polyvinyl alcohol hydrogel using a simple gradual freezing–thawing method to investigate stem cell differentiation behaviors

“…Recently, diverse techniques have been utilized for the systematic study of the effects of a substrate's stiffness gradient on cell behaviors. They include diffusion [21], controlled dipping into crosslinking solution [22], microfluidics/photopolymerization [23], gradient mask/photopolymerization [24], convection-alternating flow/photopolymerization [25], photopolymerization using a gradually darkening mask [26], photopolymerization using a sliding mask [16,27], temperature gradients during crosslinking [28], and controlling the height of the substrate [29]. However, the toxicity from residual monomers, precursors, photoinitiators, and crosslinkers [30e33]; different surface chemistry from different densities of crosslinkers along the gradient [22]; relatively narrow ranges of stiffness gradient [29]; and the complexity of fabrication processes are also considered as potential limitations of conventional systems.…”

Generating long material gradients by convection and alternating flow in a microchannel

“…A single flow segment required only seconds to create 2-3cm gradients of 2, 5, and 10μm microbeads (Fig. 1a) and HUVEC cells [5].…”

“…The flow was halted once solution B reached the opposite end of the channel. For diffusible species, subsequent backward and forward flow segments lengthened the gradient [5]. For example, a 3cm gradient of the biomolecule fluorescein isothiocyanate-dextran (FITCdextran) in phosphate buffer solution (PBS) was created with solution A as PBS, solution B as FITC-dextran in PBS, and with four cycles of alternating flow [5].…”

“…Various mechanisms can generate molecular gradients including diffusion [3], convection [4][5][6], differential mixing [1,7], and dip coating with electrostatics [8]. Convectionbased approaches are relatively simple, rapid, and allow the gradients to be produced in situ without additional mixing devices.…”

Microfluidic gradient platforms for controlling cellular behavior

“…It was revealed that the endothelial cells exposed to higher concentration of RGDS were highly attached in a microfluidic channel. Furthermore, a convection flow-based microfluidic device has been used to generate long-range material gradient and endothelial cell gradient [89]. To investigate cell-biomaterial interaction, the PEG hydrogel gradient and cross-gradient of composite materials (i.e.…”