Freestanding hydrogel lumens for biological assays

Lumen structures exist throughout the human body, and the vessels of the circulatory system are essential in carrying nutrients and oxygen and regulating inflammation. Vasodilation, the widening of the blood vessel lumen, is important to the immune response as it increases blood flow to a site of inflammation, raises local temperature, and enables optimal immune system function. A common method for studying vasodilation uses excised vessels from animals; major drawbacks include inconsistencies, time-consuming procedures, the need to sacrifice animals, and differences between model animal and human biology. We have developed a simple, user-friendly in vitro method to form freestanding cell-laden vessel-like structures from collagen and quantitatively measure the effects of vasodilators on the size of the structure. The hydrogel rings are composed of collagen I laden with human vascular smooth muscle cells, a major cellular and structural component of blood vessels; we also demonstrate the ability to line the lumen with endothelial cells. The methods presented include a 3D printed device (which is amenable to future fabrication by injection molding) and commercially available components (e.g., Teflon tubing or a syringe) used to form hydrogel rings between 2.6-4.6 mm outer diameter and 0.79-1.0 mm inner diameter. The rings enable the measurement of dynamic changes when vasodilators are added; here we demonstrated a significant difference in ring area in the presence of a known vasodilator, fasudil (p<0.0001). Our method is easy to implement and provides a medium-throughput solution to generating blood vessel-like model structures for future investigations of the fundamental mechanisms of vasodilation (e.g., studying uncharacterized endogenous molecules that may have vasoactivity) and testing vasoactive drugs.