From geometry to biology for cell therapy manufacturing
THE CHALLENGE Design an impeller for a bench top stirred-tank bioreactor that delivers rapid, homogeneous mixing, maintains peak shear below 0.5 Pa and minimises dead zones at the bottom of the vessel, all while remaining manufacturable using simple airfoil-style blade profiles welded to a central shaft.
WHY IT MATTERS Suspension cell cultures are extremely sensitive to the hydrodynamics inside a stirred-tank bioreactor. Bioreactors must balance gentle mixing with efficient nutrient delivery, while protecting fragile cells and aggregates, and maintaining uniform conditions.
Even small geometric changes - from blade length to impeller position - can disrupt flow patterns, create concentration gradients, and generate damaging shear stress, often causing low yields and inconsistent cell viability in conventional bioreactor designs.
Generative Approach
Parametric Model: Automated impeller generation (blade pitch, blade count, blade length, blade twist, chord length, thickness factor, impeller position, rotational speed, airfoil profile).
CAD-to-Simulation: Integrated with SimScale for CFD propagation, automatically creating a transient CFD simulation of the stirred tank with an initial passive scalar concentration, saving setup time.
Physics Validation: Multiphase flow, rotating impeller zones, turbulence, and shear mapped; validated against 250 mL prototype data.
Automated Exploration: 150+ configurations simulated, extracting KPIs - global mixing normalised variance, mixed volume fraction and peak shear stress - with trade-offs visualised in real time.
Generative Impact
Used multiple mixing metrics under a shear constraint, optimising designs that mixed quickly, avoided dead zones, and stayed within cell-friendly shear limits.
Determined impeller height was a dominant driver of mixing performance; raising the impeller increased the well-mixed volume, while low-mounted impellers created persistent dead zones beneath the hub.
Converged on longer blade lengths through optimisation, maintaining a high mixing index while remaining within the shear limit.
Identified a rotational-speed threshold, with rotational speeds above 3.0 rad/s often exceeding the 0.5 Pa shear limit.
Refined blade geometry—adjusting chord length, blade pitch, and airfoil profile—to reduce dead zones and local shear peaks.
