Rapid Fabrication of Capillary-Sized Microchannels in Collagen Hydrogel via Thermally Responsive Gelatin Microfiber Templates.

Engineering volumetric three-dimensional tissues requires the rapid establishment of dense, capillary-like microchannels to ensure adequate oxygen and nutrient supply while preventing hypoxic cell necrosis. Sacrificial microfiber templating approaches using lower critical solution temperature (LCST) polymers cannot employ type I collagen hydrogels-a biologically ideal extracellular matrix-because LCST fiber dissolution in cold collagen solutions precedes matrix gelation owing to thermodynamic mismatch. Here, we present a proof-of-concept strategy to rapidly fabricate capillary-sized microchannels within collagen hydrogels using thermoresponsive, physically crosslinked gelatin microfibers as sacrificial templates. Three-dimensional gelatin microfibers with capillary-sized diameters (approximately 10 μm) were fabricated via wet spinning and embedded in a type I collagen aqueous solution (4 °C). Open microchannels throughout the collagen matrix were successfully generated within 1 h of sequential thermal incubation (20 °C for collagen gelation and subsequently 37 °C for gelatin thermal dissolution), without cytotoxic chemicals. Active particle flow confirmed channel patency and fluidic continuity. Additionally, heparinized rat blood readily perfused through the channels, and scanning electron microscopy revealed open microchannel cross-sections (diameter: approximately 10 μm). This simple, thermally controlled approach resolves the limited temperature compatibility between collagen matrices and sacrificial microfibers, serving as a promising biofabrication foundation for engineering tissue constructs.