Spontaneous Helical Alignment of Smooth Muscle Cells to Form a Medial Layer for Engineered Microvasculature

Microscale small resistance vessels (SRVs) are key regulators of local vascular resistance and tissue perfusion, yet, compared to efforts toward engineering capillaries ("exchange vessels") and vascular grafts ("conduit vessels"), there has been limited effort devoted to engineering SRVs with appropriate architecture and function. Natural SRVs rely on a medial layer of helically arranged contractile smooth muscle cells (SMCs) to modulate lumen diameter, thereby regulating local fluidic resistance. However, current SRV-scale engineered vasculature either lacks an SMC layer or contains unaligned or non-contractile SMCs, rendering such constructs incapable of recapitulating the essential function of natural SRVs. Here, we demonstrate that appropriate choice of fabrication parameters can promote spontaneous helical alignment of SMCs seeded on the walls of SRV-sized channels within a hydrogel (without any patterning of topography or binding sites). The resulting alignment angle is sensitive to the composition of extracellular matrix proteins coating the attachment surface, SMC seeding density, and channel diameter. SMCs within these constructs exhibit functional and morphological hallmarks of a contractile phenotype, including biochemical response to vasoconstrictor endothelin-1 (ET-1). Establishing an aligned, contractile phenotype SMC layer represents a critical step toward engineering SRVs with vasoreactive functionality mimicking that of natural vessels.