Tissue-transplant fusion and vascularization of myocardial microtissues and macrotissues implanted into chicken embryos and rats.

Cell-based therapies and tissue engineering initiatives are gathering clinical momentum for next-generation treatment of tissue deficiencies. By using gravity-enforced self-assembly of monodispersed primary cells, we have produced adult and neonatal rat cardiomyocyte-based myocardial microtissues that could optionally be vascularized following coating with human umbilical vein endothelial cells (HUVECs). Within myocardial microtissues, individual cardiomyocytes showed native-like cell shape and structure, and established electrochemical coupling via intercalated disks. This resulted in the coordinated beating of microtissues, which was recorded by means of a multi-electrode complementary metal-oxide-semiconductor microchip. Myocardial microtissues (microm3 scale), coated with HUVECs and cast in a custom-shaped agarose mold, assembled to coherent macrotissues (mm3 scale), characterized by an extensive capillary network with typical vessel ultrastructures. Following implantation into chicken embryos, myocardial microtissues recruited the embryo's capillaries to functionally vascularize the rat-derived tissue implant. Similarly, transplantation of rat myocardial microtissues into the pericardium of adult rats resulted in time-dependent integration of myocardial microtissues and co-alignment of implanted and host cardiomyocytes within 7 days. Myocardial microtissues and custom-shaped macrotissues produced by cellular self-assembly exemplify the potential of artificial tissue implants for regenerative medicine.

Living, autologous pulmonary artery conduits tissue engineered from human umbilical cord cells.

BACKGROUND: Tissue engineering represents a promising approach to in vitro creation of living, autologous replacements with the potential to grow, repair, and remodel. Particularly in a congenital operation, there is a substantial need for such implantation materials. We previously demonstrated fabrication of completely autologous, functional heart valves on the basis of peripheral vascular cells. Presently the feasibility of creating pulmonary artery conduits from human umbilical cord cells was investigated. METHODS: Human umbilical cord cells were harvested and expanded in culture. Pulmonary conduits fabricated from rapidly bioabsorbable polymers were seeded with human umbilical cord cells and grown in vitro in a pulse duplicator bioreactor. Morphologic characterization of the generated neo-tissues included histology, transmission, and scanning electron microscopy. Characterization of extracellular matrix was comprised of immunohistochemistry. Extracellular matrix protein content and cell proliferation were quantified by biochemical assays. Biomechanical testing was performed using stress-strain and burst-stress tests. RESULTS: Histology of the conduits revealed viable, layered tissue and extracellular matrix formation with glycosaminoglycans and collagens I and III. Cells stained positive for vimentin and alpha-smooth muscle actin. Scanning electron microscopy showed confluent, homogenous tissue surfaces. Transmission electron microscopy demonstrated elements typical of viable myofibroblasts, such as collagen, fibrils, and elastin. Extracellular matrix proteins were significantly lower compared with native tissue; the cell content was increased. The mechanical strength of the pulsed constructs was comparable with native tissue; the static controls were significantly weaker. CONCLUSIONS: In vitro fabrication of tissue-engineered human pulmonary conduits was feasible utilizing human umbilical cord cells and a biomimetic culture environment. Morphologic and mechanical features approximated human pulmonary artery. Human umbilical cord cells demonstrated excellent growth properties representing a new, readily available cell source for tissue engineering without necessitating the sacrifice of intact vascular donor structures.

Umbilical cord blood derived endothelial progenitor cells for tissue engineering of vascular grafts.

BACKGROUND: A substantial limitation regarding present pediatric cardiac surgery is the lack of appropriate materials for the repair of congenital defects. To address this shortcoming, tissue engineering is a scientific field that aims at in vitro fabrication of living autologous grafts with the capacity of growth, repair, and regeneration. Here we focused on tissue engineered vascular grafts using human umbilical cord blood derived endothelial progenitor cells (EPCs), as a noninvasive cell source for pediatric applications. METHODS: EPCs were isolated from 20 ml fresh human umbilical cord blood by Ficoll gradient centrifugation and cultured in endothelial basal medium containing growth factors. After proliferation and differentiation cells were analyzed by immunohistochemistry and seeded onto three-dimensional (3D) biodegradable vascular scaffolds (porosity > 95%, n = 22). Twenty-four hours after seeding the vascular grafts were positioned into a pulse-duplicator-in vitro system and grown for 48 hours under biomimetic conditions. A second group was grown 6 days statically and an additional 6 days biomimetically. Controls were cultured statically. Analysis of the grafts included immunohistochemistry, histology, and scanning electron microscopy. RESULTS: Preseeding differentiated EPCs indicated constant endothelial phenotypes including acetylated low-density lipoprotein, cluster of differentiation 31, von Willebrand factor, and endothelial nitric oxide synthetase. Seeded EPCs established favorable cell-to-polymer attachment and proliferation into the 3D tubular scaffolds. Both conditioned and static cellular constructs demonstrated positive staining for cluster of differentiation 31, von Willebrand factor, and expression of endothelial nitric oxide synthase. CONCLUSIONS: Human umbilical cord derived EPCs indicated exceptional growth characteristics used for tissue engineering of vascular grafts. These cells demonstrated a constant endothelial phenotype and related functional features. Based on these results EPCs seem to be a promising autologous cell source with regard to cardiovascular tissue engineering, particularly for the repair of congenital defects.