A bioreactor and methods for use can include a microfibrous scaffold, that can be made of a composite bioink, and that can have endothelial cells directly embedded within the scaffold using an additive manufacturing process. The scaffold can further be seeded with cardiomyocytes. The hydrogel scaffold can be composed of a plurality of serpentine layers, with each serpentine layers, which can be placed on each other in a cross-hatch configuration, so that the primary axes of successive layers are perpendicular. This configuration can establish an aspect ratio for the scaffold, which can be selectively varied. For greater strength, the successive layers that have a primary axis in the same direction can be placed in the scaffold so that they are slight offset from each other. The scaffold can be placed in the bioreactor with perfusion, for use in cardiovascular drug screening and other nanomedicine endeavors.