Co-expression of elastin and collagen leads to highly compliant engineered blood vessels

Elastin synthesis and physiologic compliance are significant challenges in blood vessel tissue engineering. Here, we report that a biocompatible elastomeric scaffold can support the co-expression of elastin and collagen, which likely yielded the physiologic compliance in the constructs. A biodegradable elastomer, poly(glycerol sebacate), was fabricated into highly porous tubular scaffolds. Primary baboon arterial smooth muscle cells (SMCs) were seeded in the lumen of the scaffolds followed by a 1-week culture under gentle perfusion. Circulating endothelial progenitor cells (EPCs) isolated from baboon peripheral blood was seeded directly on the smooth muscle layer in the lumen on day 8. The constructs were perfused using a pulsatile flow system for another 2 weeks before characterization. In another set of experiments, the SMCs were cultured for 7 weeks and were co-cultured for 1 week with the EPCs. Constructs obtained using either set of culture conditions contained elastin and collagen: Masson's trichrome stain showed a circumferential collagen band in the constructs, and elastin was evident from its characteristic autofluorescence, Verhoff's stain, and amino acid analysis of insoluble remnants after hot alkali digestion. All constructs had a confluent cellular lumen with cells well-dispersed throughout the scaffolds. At physiologic pressures, the compliance of the 8-week construct was comparable to human arteries as observed in pressure-diameter testing. Combination of elastomeric scaffolds, co-culture of EPC and SMC, and mechanical conditioning appears to encourage the expression of a more natural extracellular matrix and lead to physiologically-relevant compliance; both are major challenges in blood vessel tissue engineering.