(540c) Using Rheology to Determine the Strategies hMSCs Use to Remodel the Pericellular Region in Polymer-Peptide Hydrogel Scaffolds

Hydrogel scaffolds are being explored as implantable materials to enhance wound healing and tissue regeneration. These scaffolds are designed to mimic aspects of the native extracellular matrix (ECM). In order to effectively design these scaffolds, we must determine how to leverage the material microenvironment to encourage and potentially direct cell migration for delivery. These materials mimic both physical and chemical aspects of the native ECM and enable precise engineering of the cues initially presented in the microenvironment to 3D encapsulated cells. Although these scaffolds are initially well-defined, they are designed to allow cellular remodeling and degradation. This results in a material which constantly presents new environmental cues to the cell. In our work, we encapsulate human mesenchymal stem cells (hMSCs) into a synthetic poly(ethylene glycol (PEG)-peptide hydrogel scaffold. This scaffold consists of a 4-arm star PEG backbone end-functionalized with norbornene which is cross-linked with a matrix metalloproteinase (MMP) degradable peptide sequence. Encapsulated hMSCs secrete MMPs, enabling them to degrade the hydrogel scaffold prior to and during motility. To characterize cellular re-engineering of the pericellular region we use multiple particle tracking microrheology (MPT). MPT measures dynamic temporal-spatial changes in the material properties. In MPT, 1 micron fluorescently labeled probe particles are embedded in the material and the Brownian motion of these particles is measured and used to determine material properties. Previous work determined that hMSCs degrade the pericellular region creating a microenvironment where the cross-link density decreases as distance from the cell increases. The hMSC is keeping the scaffold stiff directly around it to spread and attach prior to motility. To do this, the cell simultaneously secretes tissue inhibitors of metalloproteinases (TIMPs), which bind to the catalytic portion of the MMP making it inactive and unable to degrade the scaffold. In this work, we inhibit TIMPs to determine how this changes the rheological properties in the pericellular region and hMSC motility. After TIMP inhibition, we measure a reaction-diffusion degradation profile, which is the opposite of the degradation profile created by untreated hMSCs. Additionally, cell motility significantly increases in the scaffold. This could be due to durotaxis, the migration along a stiffness gradient to a higher moduli material, or due to a decreased material barrier in migration. This simple chemical treatment has the potential to enhance hMSC delivery to wounds from this hydrogel scaffold but it is unclear if the change in the bulk properties of the scaffold could destabilize the scaffold and the wounded tissue if used for implantation.