In Vivo Application of Dynamic Hyaluronic Acid Material for Myocardial Infarction Therapy

Tissue-specific elasticity arises from developmental changes that occur in the environment over time, e.g. ∼10-fold myocardial stiffening from E3 to E10 in the chick embryo. Recently, we have shown that pre-cardiac mesodermal cells plated on top of a thiolated hyaluronic acid (HA) matrix engineered to mimic this time-dependent stiffening improves cardiomyocyte maturation compared to cells on static compliant matrices. Here we determined cell-matrix interactions using in vitro encapsulation assays and in vivo injections. Improved pre-cardiac and embryonic stem cell (ESC) distribution and viability was observed when cells were encapsulated and bound to immobilized, thiolated fibronectin conjugated to the HA matrix. Though not toxic to cells, we also assessed HA's local and systemic biocompatibility. Prior to assembly, HA was injected subcutaneously into Sprague-Dawley (SD) rats and samples were removed over a post-injection time course and subject to histological, immunological, and mechanical analysis. Histological analysis showed minimal infiltration of host cells and capsule formation around the matrix. Hematological analysis showed no significant systemic immune response was elicited in pre- vs. post-injection animals for all time points. Most importantly, atomic force microscopy (AFM) analysis showed dynamically increasing hydrogel stiffness over time similar to that previously found in vitro. HA was also injected into the hearts of healthy SD rats and subject to histological analysis over a post-injection time course. Though injection volume prevented mechanical measurement in the myocardium, hydrogel porosity increased, which we previously correlated with increased stiffness over time for subcutaneous injections. These in vitro data indicate that the combination of cells and developmentally appropriate matrix stiffness may significantly improve cell differentiation while in vivo data indicate the injectable feasibility of the HA matrix into the myocardium in future regenerative studies for treating heart failure post-myocardial infarction.