Fibrin and extracellular matrix as in vivo self-assembling scaffold for direct delivery of cardiac primitive cells

Cardiac tissue engineering aims at restoring cell compartment along with myocardial extracellular microenvironment. Even though countless combinations of synthetic or biological scaffolds and stem/progenitor cells of various origin have been tested so far, the most suitable candidate is yet to be found.With the aim to develop a natural injectable self-assembling scaffold able to serve as both threedimensional platform and stem/progenitor cell delivery method, we assembled fibrin gels incorporating cells and cardiac decellularized extracellular matrix (d-ECM). Cryosections of cardiac ECM were decellularized according to previously published protocol, and dECM was lyophilized and solubilized. dECM solution was mixed with the fibrin solution carrying Cardiac Primitive Cells (CPC) isolated from adult human heart and allowed to gel at 37C. Fibrin to dECM ratio (F:M) of 1:1, 1:2, 1:3 and 1:4 were tested to determine the ideal composition in terms of time of gelling and three-dimensional architecture. Gelling time varied fromone minute to twenty-four hours. Gels were cultured for three days, then fixed and processed as tissues for histological study. Histochemistry revealed the presence of viable CPC in the gelswhose architecture varied fromdensely packed to very loose. Due to time of gelling and to concentration of fibrin, the distribution of CPC in the scaffold was even only in the gel with F:M of 1:2. According to our results, the combination of CPC with fibrin and dECM at F:M of 1:2, being injectable and self-assembling at body temperature, provides an attracting alternate to bioconstructs.