A cell-culture apparatus forms an extra-capillary space between at least one hollow fiber and an enclosed chamber. Cells are placed in the extra-capillary space to grow. A media reservoir holds a cell-culture medium. The cell-culture medium is allowed to pass through a lumen of the at least one hollow fiber and to pass nutrients through the walls of the at least one hollow fiber to the cells in the extra-capillary space. Flow through the at least one hollow fiber is produced by action of gravity when a rocking or rotating motion is imparted to the media reservoir.