--- title: Up or Down? description: Many cells grow on tiny beads (microcarriers) that float in the bioreactor. The stirrer has to keep every bead off the floor, but each extra turn per minute also means more stress for the cells. So the goal is the slowest speed at which nothing stays on the bottom. image: https://www.p4b.io/hubfs/raw_assets/public/p4b/images/og-default.png --- [![p4b](https://www.p4b.io/hubfs/raw_assets/public/p4b/images/p4b-logo-white.svg) ![p4b](https://www.p4b.io/hubfs/raw_assets/public/p4b/images/p4b-logo-navy.svg)](https://www.p4b.io/) Products [**pDS inserts**Large-scale conditions in your lab bioreactor](https://www.p4b.io/pds) [**Advanced CFD**Gradients, lifelines and cell experiences](https://www.p4b.io/cfd) [**DREAM-bio**Find the best geometry for your bioreactor](https://www.p4b.io/dream-bio) [**Ambr 250 vs. 2,000 L**Interactive CFD comparison of the mixing](https://www.p4b.io/compare) [Case studies](https://www.p4b.io/case-studies) [Insights](https://www.p4b.io/insights) [Events](https://www.p4b.io/events) [About](https://www.p4b.io/about) [Contact](https://www.p4b.io/contact) [Request a quote](https://www.p4b.io/contact#quote) [Home](https://www.p4b.io/) / [Insights](https://www.p4b.io/insights) CFD · 4 Nov 2026 # Up or Down? Many cells grow on tiny beads (microcarriers) that float in the bioreactor. The stirrer has to keep every bead off the floor, but each extra turn per minute also means more stress for the cells. So the goal is the slowest speed at which nothing stays on the bottom. [← All insights](https://www.p4b.io/insights) Get in touch ## Let's find out how your process reacts to scale Tell us your system and target scale - we come back with a proposal for your insert set. [Request a quote](https://www.p4b.io/contact#quote)[Book a 30-min call](https://www.p4b.io/contact#meeting) ![Lena Achleitner](https://www.p4b.io/hs-fs/hubfs/website/team/lena-avatar.webp?width=84&height=84&name=lena-avatar.webp) **Lena Achleitner**Senior Bioprocess Engineer, Key Account Manager[lena.achleitner@p4b.io](mailto:lena.achleitner@p4b.io) ### Get new insights by email CFD results, case studies and new insert systems when we publish them. 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