Effects of cyclic stretch on three-dimensional vascular smooth muscle cell rings

Vascular grafts are used to repair, replace, or bypass diseased arteries, and there is a growing need for tissue-engineered blood vessels (TEBVs) as replacement grafts. However, TEBV utility is often limited by underdeveloped mechanical integrity. Thus, the purpose of this research was to design, manufacture, and validate a cyclic circumferential stretch bioreactor to mechanically stimulate engineered vascular tissue and improve tensile strength. The bioreactor consists of a closed cam-syringe-tubing system that forces fluid into the tubing with each rotation of the cam, thereby distending and relaxing the tubing. Various-sized cams were fabricated to vary the stretch magnitude. Self-assembled human SMC rings were cultured for six days and then placed on the tubing in the bioreactor. Circumferential stretch applied to both the tubing and SMC tissue ring wall were measured using a high speed camera and speckle tracking program. We observed a 31-56% decrease in peak strain values between the tubing and the tissue ring regions; this variation may reflect differences in wall thickness and modulus in the tissue rings. To assess the effects of cyclic distension, 7-day-old SMC rings were cultured dynamically for 7 days and exposed to 0, 5%, 7.5%, 10%, or 15% cyclic stretch (1 Hz). Stretched rings exhibited a reduction in UTS and MTM compared to unstretched control samples.