(365n) Synthetic Hydrogels with Non-Linear Chemical Gradients to Guide Encapsulated Human Mesenchymal Stem Cells from a Hydrogel to a Wound

Implantable and degradable hydrogel scaffolds are being designed to deliver human mesenchymal stem cell to treat wounds. The current delivery systems are focused on mimicking the properties of the native extra cellular matrix and assume that cells will migrate from the hydrogel to the wound where they will begin healing it. One problem with this approach is cell migration is hard to predict and consistently modeled mathematically as random. Cell migration can be increased or directed using physical or chemical cues. We have taken inspiration from the native wound healing process. When a wound occurs it releases cytokines, forming a gradient, which cause directed stem cell migration from their surrounding niches. Our work focuses on directing cell migration from the hydrogel to the wound site by creating scaffolds with chemical gradients. We use a combination of multiple particle tracking microrheology (MPT) and live cell imaging to measure pericellular cell-mediated degradation, cell persistence, and changes in cell morphology. The goal of the work is to inform and improve the design of new scaffolds for cell delivery that use a the microenvironment to instruct basic cellular functions. The scaffold is composed of 4-arm poly (ethylene glycol)-norbornene (PEG-N), a matrix metalloproteinase (MMP)-degradable peptide cross-linker, a photoinitiator and a cellular adhesion ligand. The scaffold is photopolymerized using thiol: ene chemistry. To make a gradient, we have built a custom microfluidic device and allow -thiol functionalized cytokines to diffuse through the network. The cytokine gradient is tethered to the hydrogel, allowing the encapsulated cells to interact with multiple cytokines in their microenvironment. The results showed an increase in encapsulated cell motility, elongation, and cell-mediated degradation when cytokines are uniformly tethered into the scaffold. By presenting cytokines in a gradient, cells can be guided out of a hydrogel. At this point, we hypothesize this scaffold will be effective in controlling cell motility for cell delivery and offer a solution to hindered cell migration out of a hydrogel.