Microfluidics-Generated Immobilized Biomolecule Gradients on Hydrogels

Extracellular matrix (ECM)-tethered morphogen gradients play an important role in tissue development and regeneration. There is currently a limited set of model systems that can mimic these gradients in an artificial ECM-like environment. Microfluidics offers several possibilities to create soluble or substrate-adsorbed protein gradients, which does not exactly represent the in vivo conditions where many proteins are immobilized in a three-dimensional environment. For this reason, the aim of this project has been to develop a model system that immobilizes a microfluidics-generated protein gradient on a poly (ethylene) glycol (PEG) hydrogel. To achieve this, thin films of a PEG hydrogel with incorporated neutravidin were cast on a glass slide and pressure sealed with a polydimethylsyloxane piece containing the microfluidic gradient generator. A stable gradient of biotinylated proteins was then applied and monitored under the microscope. The biotinylated proteins were captured by the neutravidin within the hydrogel thereby immobilizing the gradient. After disassembling the microfluidic device, the hydrogels could directly be used for cell-based assays. As a proof of principle, hydro gels were patterned with biotinylated fibronectin gradients and seeded with primary human dermal fibroblasts. Preliminary time-lapse microscopy experiments demonstrated a fibronectin concentration-dependent behavior of the fibroblasts. This novel model system enhances microfluidically generated protein gradients in several ways, because the patterned hydrogel mimics much better the in vivo situation than adsorped protein gradients on hard substrates. This platform can serve for cell migration and differentiation studies that more closely reproduce the in-vivo microenvironment.