Disclosed herein are bioreactors that include a vessel with sides and a bottom, at least one opening in the vessel connected to a means for introducing a gas, and at least one scaffold in the vessel oriented substantially vertically in the vessel. The scaffolds are two substantially parallel sheets that are separated by a distance (dmin). Also disclosed herein are bioreactors that include a vessel with sides and a bottom, at least one opening in the vessel connected to a means for introducing a gas, and at least two scaffolds in the vessel oriented substantially vertically in the vessel. The disclosure also includes methods of culturing cells including incubating a suspension of cells in a disclosed bioreactor and introducing a gas through the at least one opening in the vessel. In some examples, the cells include microalgae, macroalgae, bacteria, fungi, insect cells, plant cells, or animal cells.