Interactions between endothelial cells and electrospun methacrylic terpolymer fibers for engineered vascular replacements.

A compliant terpolymer made of hexylmethacrylate (HMA), methylmethacrylate (MMA), and methacrylic acid (MAA) intended for use in small diameter vascular graft applications has been developed. The mechanical properties and in vitro biostability of this terpolymer have been previously characterized. The goal of this investigation was to examine the interactions between endothelial cells and the new terpolymer and to evaluate endothelial cell function. Electrospinning was used to produce both oriented and random terpolymer fiber scaffolds. Smooth solution cast films and tissue culture polystyrene were used as negative and positive controls, respectively. Human blood outgrowth endothelial cells and human umbilical vein endothelial cells were incubated with the test and control samples and characterized with respect to initial cell attachment, proliferation, viability, and maintenance of the endothelial cell phenotype. It was found that the terpolymer is cytocompatible allowing endothelial cell growth, with random fibers being more effective in promoting enhanced cellular activities than oriented fibers. In addition, endothelial cells cultured on these substrates appeared to maintain their phenotype. The results from this study demonstrate that electrospun HMA:MMA:MAA terpolymer has the potential to be used successfully in fabricating small diameter blood vessel replacements.

Characterization of model bile using fluorescence energy transfer from dehydroergosterol to dansylated lecithin.

Fluorescence energy transfer from dehydroergosterol (DHE) to dansylated lecithin (DL) was used to characterize lecithin-cholesterol vesicles in the presence of the bile salt, sodium taurocholate. At lipid concentrations approximating physiological levels, exposure of fluorescently labeled vesicles to the bile salt led to a dose-dependent increase in the DHE-to-DL fluorescence ratio during the first 24 h after mixing. The initial changes in the fluorescence ratio correlated well with conventional turbidity measurements that quantify partial micellization of vesicles as a function of bile salt loading. In addition, fluorescence energy transfer from DHE to DL revealed cholesterol enrichment of vesicles and re-vesiculation of micelles at bile salt loadings for which vesicles and micelles coexisted. Samples containing the cholesterol-enriched vesicle fraction exhibited further increases in the DHE-to-DL fluorescence ratio during a 4-week observation period but only after a significant lag period of several days. The lag period decreased with cholesterol loading, and the increase in the fluorescence ratio always preceded the appearance of microscopic, birefringent, either needlelike or platelike, cholesterol crystals, in samples that were initially supersaturated with cholesterol. Cholesterol crystals were not observed, and the fluorescence ratio did not increase, for any sample that was undersaturated with cholesterol.Taken together, these results suggest that the latter changes in fluorescence are the result of cholesterol nucleation. Fluorescence energy transfer from DHE to DL is therefore a promising technique for the characterization of model bile and, possibly, provides a direct measurement of cholesterol nucleation.