Seeding bioreactor-produced embryonic stem cell-derived cardiomyocytes on different porous, degradable, polyurethane scaffolds reveals the effect of scaffold architecture on cell morphology.

A successful regenerative therapy to treat damage incurred after an ischemic event in the heart will require an integrated approach including methods for appropriate revascularization of the infarct site, mechanical recovery of damaged tissue, and electrophysiological coupling with native cells. Cardiomyocytes are the ideal cell type for heart regeneration because of their inherent electrical and physiological properties, and cardiomyocytes derived from embryonic stem cells (ESCs) represent an attractive option for tissue-engineering therapies. An important step in developing tissue engineering-based approaches to cardiac cell therapy is understanding how scaffold architecture affects cell behavior. In this work, we generated large numbers of ESC-derived cardiomyocytes in bioreactors and seeded them on porous, 3-dimensional scaffolds prepared using 2 different techniques: electrospinning and thermally induced phase separation (TIPS). The effect of material macro-architecture on the adhesion, viability, and morphology of the seeded cells was determined. On the electrospun scaffolds, cells were elongated in shape, a morphology typical of cultured ESC-derived cardiomyocytes, whereas on scaffolds fabricated using TIPS, the cells retained a rounded morphology. Despite these gross phenotypic and physiological differences, sarcomeric myosin and connexin 43 expression was evident, and contracting cells were observed on both scaffold types, suggesting that morphological changes induced by material macrostructure do not directly correlate to functional differences.

Characterization of biodegradable polyurethane microfibers for tissue engineering.

A polyurethane designed to be biodegradable via hydrolysis and enzyme-mediated chain cleavage, has been investigated for its use as a temporary scaffold in tissue-engineering applications. The phase-segregated nature of the polyurethane imparts elastomeric properties that are attractive for soft tissue engineering. This polyurethane has been electrospun in order to create scaffolds that incorporate several biomimetic features including small fiber diameter, large void volume, and an interconnected porous network. Material properties were evaluated via gel-permeation chromatography, differential scanning calorimetry and Raman spectroscopy before and after processing. Analysis by gel-permeation chromatography showed that the molecular weights were similar, indicating that the bulk of the polymer chains were not degraded during processing. Thermal analysis revealed that the glass transition temperature did not shift and Raman spectra of the bulk polyurethane film compared to the electrospun mat were identical, confirming that the conformation of the polymer was unaffected by the shear and electric field used in the electrospinning process. In addition, field emission scanning electron microscopy revealed that the morphology of the electrospun mats had a broad fiber diameter distribution, and mechanical analysis showed that the mats had an ultimate tensile stress of 1.33 MPa and ultimate tensile strain of 78.6%. The degradation profile was investigated in the presence of chymotrypsin. These results were compared to a previous study of thin films of this polyurethane, and it was found that the increase of surface area aided the surface-mediated erosion of the material. It is believed that an electrospun matrix of this biodegradable polyurethane shows promise for use in soft tissue engineering and regenerative medicine applications.

Investigation of recombinant human elastin polypeptides as non-thrombogenic coatings.

We investigated the use of a recombinant human elastin polypeptide as a coating on synthetic materials with a view to determining if these polypeptides could improve the blood compatibility of cardiovascular devices such as vascular conduits and arterial/venous catheters. Platelet adhesion and activation were studied in vitro using three commercially available synthetic materials: polyethylene terephthalate (Mylar), a poly(tetrafluoroethylene/ethylene) copolymer (Tefzel) and a polycarbonate polyurethane (Corethane). Coated with adsorbed polypeptide, all three synthetic materials demonstrated reduced platelet activation and adhesion in platelet rich plasma in vitro. Compared to non-coated controls, there was a significant decrease (p=0.05) in both platelet microparticle release and P-selectin expression for the polypeptide-coated surfaces. Scanning electron microscopy indicated fewer adhering platelets on coated surfaces compared to non-coated controls. In vivo, in a rabbit model, evaluations of polyurethane catheters coated with the polypeptide showed a marked increase in catheter patency and a significant decrease in fibrin accretion and embolism when compared to uncoated controls. This polypeptide shows a strong potential for use as a non-thrombogenic coating for small diameter vascular grafts. In addition, the results of this study indicate that the elastin polypeptide would be a valuable component of a tissue engineered vascular conduit.