Optimized suspension culture: the rotating-wall vessel

Suspension culture remains a popular modality, which manipulates mechanical culture conditions to maintain the specialized features of cultured cells. The rotating-wall vessel is a suspension culture vessel optimized to produ ce laminar flow and minimize the mechanical stresses on cell aggregates in culture. This review summarizes the engineering principles, which allow opt imal suspension culture conditions to be established, and the boundary cond itions, which limit this process. We suggest that to minimize mechanical da mage and optimize differentiation of cultured cells, suspension culture sho uld be performed in a solid-body rotation Couette-flow, zero-headspace cult ure vessel such as the rotating-wall vessel. This provides fluid dynamic op erating principles characterized by 1) solid body rotation about a horizont al axis, characterized by colocalization of cells and aggregates of differe nt sedimentation rates, optimally reduced fluid shear and turbulence, and t hree-dimensional spatial freedom; and 2) oxygenation by diffusion. Optimiza tion of suspension culture is achieved by applying three tradeoffs. First, terminal velocity should be minimized by choosing microcarrier beads and cu lture media as close in density as possible. Next, rotation in the rotating -wall vessel induces both Coriolis and centrifugal forces, directly depende nt on terminal velocity and minimized as terminal velocity is minimized. La st, mass transport of nutrients to a cell in suspension culture depends on both terminal velocity and diffusion of nutrients. In the transduction of m echanical culture conditions into cellular effects, several lines of eviden ce support a role for multiple molecular mechanisms. These include effects of shear stress, changes in cell cycle and cell death pathways, and upstrea m regulation of secondary messengers such as protein kinase C. The discipli ne of suspension culture needs a systematic analysis of the relationship be tween mechanical culture conditions and biological effects, emphasizing cel lular processes important for the industrial production of biological pharm aceuticals and devices.