(437e) Fibril Alignment Induces Alignment of Sprouts From Endothelial Cell Spheroids In Fibrin Gel

The creation of a microvascular network within engineered tissue is an important step toward forming highly metabolic tissues (such as myocardium or liver) large enough for human use. It is critical that this network be aligned, as alignment provides natural inlet and outlet sides for perfusion. One potential method for creating such aligned microvasculature is to harness contact guidance to direct sprout outgrowth from endothelial spheroids. Human blood outgrowth endothelial cell (BOEC) spheroids were entrapped with neonatal human dermal fibroblasts in fibrin gel. The gels were aligned to varying degrees via magnetic fields or mechanically-constrained cell-induced gel compaction. After 7 days of culture, fibril alignment was measured with polarimetry, and spheroids were imaged with confocal microscopy. Sprout lengths and angles were measured in ImageJ, and an anisotropy index was defined (X component of sprout length:Y component of sprout length) to describe sprout alignment. In both alignment conditions, sprout alignment strongly correlated with fibril alignment, and sprout length correlated with both sprout and fibril alignment. Because magnetic fields provide a way to align gels without varying other factors, the data from the magnetically-aligned gels for the first time provide evidence that fibril alignment causes endothelial sprout alignment and that fibril alignment increases sprout lengths. Confounding factors (such as increased fiber density) preclude the same conclusion from the cell-aligned gel data; however those data show that the sprout alignment and lengthening effects can also be achieved using cell-induced alignment, a technique that is technically simpler and more relevant to tissue engineering.