Molecular weight and concentration of heparin in hyaluronic acid-based matrices modulates growth factor retention kinetics and stem cell fate.

Growth factors are critical for regulating and inducing various stem cell functions. To study the effects of growth factor delivery kinetics and presentation on stem cell fate, we developed a series of heparin-containing hyaluronic acid (HyA)-based hydrogels with various degrees of growth factor affinity and retention. To characterize this system, we investigated the effect of heparin molecular weight, fractionation, and relative concentration on the loading efficiency and retention kinetics of TGFβ1 as a model growth factor. At equal concentrations, high MW heparin both loaded and retained the greatest amount of TGFβ1, and had the slowest release kinetics, primarily due to the higher affinity with TGFβ1 compared to low MW or unfractionated heparin. Subsequently, we tested the effect of TGFβ1, presented from various heparin-containing matrices, to differentiate a versatile population of Sca-1(+)/CD45(-) cardiac progenitor cells (CPCs) into endothelial cells and form vascular-like networks in vitro. High MW heparin HyA hydrogels stimulated more robust differentiation of CPCs into endothelial cells, which formed vascular-like networks within the hydrogel. This observation was attributed to the ability of high MW heparin HyA hydrogels to sequester endogenously synthesized angiogenic factors within the matrix. These results demonstrate the importance of molecular weight, fractionation, and concentration of heparin on presentation of heparin-binding growth factors and their effect on stem cell differentiation and lineage specification.