Fabrication of Endothelialized Capillary-like Microchannel Networks using Sacrificial Thermoresponsive Microfiber Templates

Abstract

In general, cells within living tissue can only survive a few hundred microns away from a source of vital gases and nutrients: within this range the cells’ metabolic needs are met effectively by diffusion. Beyond this range cells begin to starve, waste products build up, and the tissue becomes necrotic. This has traditionally limited development of engineered tissues to geometries where the thickest dimension does not exceed the diffusion limit, such as with organoids and thin-walled organs. In order to, develop a greater diversity of artificial tissues and expand their thickness beyond a few hundred microns, a microvascular network must be engineered to carry nutrients throughout, replicating the scale, architecture, and function of capillary beds responsible for tissue support. Current methods of microvascular engineering are able to produce vessels with a high degree of precision and programmability, such as with bioprinting and optical techniques, but fall short when attempting to produce scalable, organic vessel networks in a three-dimensional context. Here we demonstrate a top-down method of patterning microvessels into hydrogels using sacrificial templates formed from thermoresponsive microfibers whose size and architecture approach those of natural capillaries. Artificial microvessels produced by this method were imaged and quantitatively characterized in order to compare against both human capillaries and murine capillaries, which were analysed in an identical manner. Within the resulting microchannels, we cultured endothelial monolayers that remain viable for over three weeks, covered channels smaller than 13 µm in diameter, and exhibited functional barrier properties. Additionally, we cultured endothelialized microchannels within hydrogels containing fibroblasts and characterized the viability of the co-cultures to demonstrate this approach’s potential when applied to cell-laden hydrogels. This method represents a step forward in the evolution of artificial tissues and a path towards producing viable capillary-scale microvasculature for engineered organs.