Organic acid optimization for the fabrication of centimeter-scale uniaxially aligned capillary networks in cell-laden collagen fiber assemblies

Functional anisotropic tissue reconstruction remains a major challenge in tissue engineering because synthetic polymers lack native extracellular matrix (ECM) functionality, whereas conventional collagen spinning methods often require cytotoxic solvents or chemical crosslinkers incompatible with direct cell encapsulation. We previously developed interfacial spinning technology using collagen and poly (acrylic acid) solutions to fabricate uniaxially aligned cell-laden collagen fibers; however, cell viability was limited using acetic acid (AA) as the collagen solvent. In this study, AA was replaced with lactic acid (LA) or citric acid (CA) to improve cytocompatibility. Both LA and CA preserved fiber-forming capability, collagen assembly behavior, and macroscopic mechanical properties. Cell viability significantly increased from approximately 40% with AA to 80% with LA and CA. Furthermore, co-cultured fibers containing endothelial cells and fibroblasts formed uniaxially aligned capillary networks over centimeter-scale lengths. These findings enable the biofabrication platforms of anisotropic centimeter-scale tissues.