Rheology and coaxial extrusion of acellular and cell-laden hollow conduits of pristine kappa carrageenan and gold–kappa carrageenan nanocomposite hydrogels

This study explores the use of kappa carrageenan (κCG) hydrogels to create cell-laden hollow conduits via multi-material extrusion with a coaxial nozzle. We used an in-house setup with two syringe pumps to extrude both ionically crosslinked κCG and gold–κCG nanocomposite (κCG–AuNP) hydrogels for the conduit shell and a sacrificial core into a crosslinking bath. We tested various κCG compositions and flow rates, finding that the inner filament diameters ranged from 625 to 700 µm and the outer diameters from 1000 to 1030 µm. Perfusion assays showed that 2% (w/v) κCG–AuNP hydrogels extruded at higher flow rates maintained integrity, allowing for uniform perfusion in longer filaments. Rheological analysis indicated that gold nanoparticles (AuNPs) reduced both the storage moduli and the viscosity of the hydrogels, and the crosslinking bath improved storage moduli post-crosslinking. The 2% (w/v) κCG–AuNP hydrogels demonstrated delayed breakage during high-flow rate extrusion, facilitating handling during perfusion. Importantly, the addition of A549 cells did not impact the rheological properties or pinch-off dynamics, and cell viability exceeding 60% was noted within the conduit walls. Thus, the 2% (w/v) κCG–AuNP hydrogel shows promise for rapid fabrication of hollow conduits for in vitro modelling of tubular biological structures.