Abstract: Embodiments relate to a unique design of a cell growth vessel stack system that provides for inter-communication of cell growth levels arranged in a parallel configuration so to facilitate environmental uniformity of the inter-connected growth surface tiers. The unique design also facilitates a fine-tuning of optimized gas and media flow to each cell growth level within the vessel stack. The unique architecture facilitates media refreshment at conveniently scheduled intervals and/or allows constant perfusion from a media reservoir that can be replenished without interrupting the cell proliferation rate. The perfusion rate, nutrient medium condition, CO2 content and osmolality can be controlled to optimize the desired cell proliferation rate, thereby improving cell quantity, quality, and viability.