Evaluation of fibrin-based engineered heart tissue (FBEHT) as potential future strategy towards cardiac regeneration

Objectives: We have previously shown that force-generating collagen-based EHTs can be constructed in-vitro. Recently, the manufacturing process has been adapted to replace collagen I with fibrin resulting in more homogenous distribution of myocytes and standardization of the system. We sought to evaluate the potential of FBEHTs as future regenerative treatment option for diseased myocardium.

Methods: EHTs were generated from neonatal rat cardiomyocytes in a fibrin-based matrix and cast between 2 flexible silicone posts fitting 6- or 24-well-format. For implantation purposes, the geometry of EHTs was altered to obtain larger constructs. After 14–20 days in culture, EHTs were implanted onto the left-ventricular myocardium of Wistar rats. Hearts were harvested 3–28 days later for further analyses.

Results: Spontaneous contractions of the EHTs were observed after 3–5 days in culture. Contractile forces increased over the next 10–15 days resulting in coherently beating constructs. Histologically, EHTs displayed a differentiated cardiac phenotype exhibiting cross-striated α-sarcomeric-actinin and lectin-positive capillary-like structures. EHTs proved to be robust enough to be sutured onto rat hearts, covering approximately 2/3 of the anterolateral wall of the left ventricle. Upon explantation, EHTs were clearly distinguishable on the epicardial surface. Histological analyses revealed strong vascularization. Cells of a cardiac phenotype survived inside implanted EHTs for up to 4 weeks, but exhibited a lower degree of cardiac differentiation than native myocardium.

Conclusions: Preliminary data show that FBEHTs can be generated in size suitable for engraftment onto rat hearts. Further investigations are currently under way, addressing issues like cell-survival and maturation or electromechanical integration.