Cardiomyopathy, long associated with adults following injury or aging, has recently moved to the forefront of the pediatric population. Improved repair of cardiac birth defects, as well as enhanced treatment of acute cardiac injury in the pediatric population has led to increases in the incidence of cardiomyopathy in the young. Cardiomyopathy is the leading reason for transplantation in the young, and the mortality and transplant rate after 2-years is 40% [1, 2, 3].

As the damage is quite localized, therapeutics that can deliver local factors and/or cells are needed. Cell based therapies have been met with enthusiasm, however much debate still lingers on the optimal delivery method. Indeed, many cells are damaged during injection or migrate away from the site of injection, making biomaterial-based grafts more necessary [4]. These grafts, while promising, have many shortcomings when combined with cell therapy including poor cell engraftment, survival and differentiation. Biomaterials derived and/or inspired from the natural provisional ECM, i.e. fibrin clots, hold great promise in this regard since these materials display endogenous ligands for the support of cell adhesion, invasion and homing to the site of injury. Unfortunately, clinically useful formations of fibrin-based materials generate polymers with nanoscale porosities, which greatly limit cell invasion and remodeling rates, linking them to ECM degradation mechanisms.

We have recently discovered an enabling technology based on the incorporation of ultralow crosslinked (ULC) microgels within dense fibrin polymers that permit the maintenance of clinically relevant properties (e.g. mechanically robust clots) while simultaneously imparting permissive cell invasion. Our technology, which mimics the native structural functions of glycosaminoglycans within blood clots and effectively decouples cell invasion from ECM degradation by allowing cells to simply mechanically displace very soft (deformable), but not hard, particle assemblies. These modified fibrin polymers can be used for either the delivery of exogenous growth factors or cells, or both.

In this seed grant application, we propose to explore both acellular and cellular constructs in the augmentation of vascular reperfusion and tissue repair in a model of cardiomyopathy. Specifically we will test the efficacy of 1) the delivery of VEGF and 2) the delivery of cardiac progenitor cells (CPCs) within microgel-fibrin hybrid matrices for the repair of cardiac defects and improved cardiac function following injury. Our central hypothesis is that soft microgel assemblies, known to maintain fibrin mechanical properties, will enable enhanced cell invasion within dense fibrin polymers resulting in improved angiogenesis, tissue repair and cardiac function following injury. This hypothesis is based on our significant preliminary data demonstrating the effects of incorporation of ultrasoft microgel assemblies within fibrin on cell invasion and angiogenesis (Barker) and the potential of CPCs and biomaterials in the enhanced repair of cardiac defects. [9-14].