Compression, particles, and protein loss. The peristaltic pump is the default in bioprocessing, and the way it damages product is widely misunderstood. The mechanism is not bulk shear in the flow; it is interfacial contact and cyclic fatigue at the tubing wall.
A peristaltic pump moves fluid by occluding flexible tubing with a roller and dragging the occlusion forward. It is simple, cleanable, and keeps the wetted path inside a disposable tube, which is exactly why it is everywhere. It also subjects the product and the tubing to a specific, repeated mechanical event, and the consequences show up as aggregates and particles in the drug product.
The intuitive story is that the product is torn apart by shear as it squeezes through the occlusion. The peer-reviewed picture is different and more specific. Work on therapeutic protein aggregation during peristaltic pumping shows that the dominant driver is solid-solid interfacial contact at the tubing wall, where the inner surfaces press together and apart on every occlusion, not bulk hydrodynamic shear in the bulk fluid.1 Protein adsorbs at the surface, the surface deforms and separates with each cycle, and that interfacial disruption nucleates aggregation. This matters because the common mitigation, slowing the pump to "reduce shear," does little if the mechanism is contact at the wall.
A roller occludes the tubing and drags the occlusion forward. Every pass presses the tubing walls together, the interfacial contact that nucleates aggregation, and abrades the bore, shedding subvisible particles into the stream.
The tubing is not inert. Repeated compression abrades and fatigues the bore, shedding subvisible particles of the tubing material into the product stream, a process called spallation.3 These particles are a quality concern in their own right and can act as nucleation sites for further protein aggregation. Particle burden rises with the severity of occlusion and the number of cycles, which is why drug-product steps scrutinize tubing selection and pump settings rather than treating the tube as a passive conduit.
The variable that predicts damage is the total number of compression cycles the product and tubing experience, together with how hard each occlusion is, not the instantaneous flow rate. Studies varying tubing characteristics and pumping conditions show particle formation tracking cumulative mechanical loading.2 The practical consequence is counterintuitive: a slow pump run for a long time, or a recirculating step that passes the product through the head hundreds of times, can do more damage than a brief, faster transfer.
For robust proteins the per-cycle damage may be tolerable. For shear-sensitive viral vectors, lipid nanoparticles, and live cells, the same per-cycle insult becomes significant once a TFF step recirculates the product through the pump for hours. The damage was always there; recirculation simply integrates it into a number large enough to see in the yield and the particle count.
Within a peristaltic design, the levers are tubing material and formulation, careful occlusion setting to avoid over-compression, and minimizing total cycles, especially keeping fragile products out of long recirculation where possible. The structural alternative is an architecture that moves fluid without compressing a tube at all, which removes the interfacial-contact and spallation mechanisms rather than managing them. Which path is right depends on the modality and the step, and the way to decide is to measure particle formation against cycle count for your own product rather than to assume.
Not mainly by bulk shear. Peer-reviewed work identifies solid-solid interfacial contact at the tubing wall as the dominant driver of aggregation during peristaltic pumping, with tubing spallation adding subvisible particles. Because the mechanism is contact and cyclic fatigue, simply lowering the flow rate does not reliably prevent it.
Spallation is the shedding of subvisible particles from the inner surface of peristaltic tubing as repeated compression abrades and fatigues it. The particles enter the product stream, are a quality concern themselves, and can nucleate further protein aggregation. Burden increases with occlusion severity and total cycles.
Total compression cycles and occlusion severity predict damage better than instantaneous flow rate. A slow pump over a long run, or a recirculating TFF step that passes product through the head hundreds of times, can cause more aggregation and particle shedding than a brief faster transfer.
Roller occlusion, tubing compression, and flow profile. The mechanics behind the most common pump in bioprocessing.
Shear, cavitation, pulsation, or hold-up? A symptom-to-mechanism framework for finding the real cause of yield or potency loss.
Questions about pump selection for fragile modalities?
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