One of the challenges in tissue engineering is to provide adequate supplies of oxygen and nutrients to cells within the engineered tissue construct. Soft-lithographic techniques have allowed the generation of hydrogel scaffolds containing a network of fluidic channels, but at the cost of complicated and often time-consuming manufacturing steps. We report a three-dimensional (3D) direct printing technique to construct hydrogel scaffolds containing fluidic channels. Cells can also be printed on to and embedded in the scaffold with this technique. Collagen hydrogel precursor was printed and subsequently crosslinked via nebulized sodium bicarbonate solution. A heated gelatin solution, which served as a sacrificial element for the fluidic channels, was printed between the collagen layers. The process was repeated layer-by-layer to form a 3D hydrogel block. The printed hydrogel block was heated to 37 degrees C, which allowed the gelatin to be selectively liquefied and drained, generating a hollow channel within the collagen scaffold. The dermal fibroblasts grown in a scaffold containing fluidic channels showed significantly elevated cell viability compared to the ones without any channels. The on-demand capability to print fluidic channel structures and cells in a 3D hydrogel scaffold offers flexibility in generating perfusable 3D artificial tissue composites. Biotechnol. Bioeng. 2010; 105: 1178-1186. (C) 2009 Wiley Periodicals, Inc.