Biomimetic matrices for myocardial stabilization and stem cell transplantation.

Although natural biological matrices have demonstrated modest improvement in the survival of cells transplanted into the infarcted myocardium, these materials have not been amenable to systematic optimization and therefore have limited potential to treat postinfarct cardiac injuries. Here we have developed tunable bioactive semi-interpenetrating polymer network (sIPN) hydrogels with matrix metalloproteinase (MMP) labile crosslinkers to be used as an assistive microenvironment for transplantation of bone marrow-derived mesenchymal stem cells (BMSCs) into the infarcted myocardium. Injectable sIPN hydrogels were designed with a range of mechanical and biological properties that yielded material-dependent BMSC proliferation in vitro. Five groups were evaluated to treat myocardial infarction (MI) in adult mice: saline injection; green fluorescent protein (GFP)(+)-BMSCs delivered in saline; a sIPN matrix; a sIPN + GFP(+)-BMSCs; and Matrigel™ + GFP(+)-BMSCs. Injection of cells alone created a transient improvement in LV function that declined over time, and the synthetic hydrogel without cells resulted in the highest LV function at 6 weeks. Donor GFP-positive cells were detected after matrix-enhanced transplantation, but not without matrix support. Biomimetic sIPN hydrogel matrices succeeded both in mechanically supporting the injured myocardium and modestly enhancing donor cell survival. These matrices provide a foundation for systematic development of "pro-survival" microenvironments, and improvement in the long-term results of cardiac stem cell transplantation therapies.