A hollow fibre module is a bundle of porous tubes that lets a culture be filtered continuously without a pump shearing the cells, which is what makes perfusion practical. The same separation appears as a dialysis device at bench scale and as an ultrafiltration skid downstream.
A hollow fiber filter and hollow fiber membranes
A hollow fiber filter is a cartridge of hollow fiber membranes with the feed flowing inside the lumen, which is what makes it tolerant of cells and solids compared with a flat sheet, and the specification is the pore rating, the fibre diameter and the membrane area. Flux and transmembrane pressure together tell whether a module is fouling.
perfusion systems and what they hold constant
perfusion systems exchange medium continuously while retaining the cells, which holds nutrient and metabolite levels steady and lets a culture run at high density for weeks. The retention device, the bleed rate and the medium exchange rate are what a process is controlled on, and the cell specific perfusion rate is the number that transfers between scales.
n-1 perfusion and why the seed train uses it
n-1 perfusion runs the stage before the production reactor in perfusion so the inoculum arrives at a much higher density, which shortens the production culture and raises its final titre. It is the commonest single change that increases output without a new reactor, and it moves the process risk into the seed train.
ultrafiltration devices and the cut-off that defines them
ultrafiltration devices are specified by a nominal molecular weight cut-off rather than a pore size, and the cut-off is a distribution, so a membrane rated well below the target protein is what actually retains it. Concentration polarisation at the membrane, not the rating, usually sets the achievable flux.
dialysis tubing 6 in, and what the width means
dialysis tubing 6 in describes the flat width of the tubing, which fixes its volume per length, and the other half of the specification is the cut-off. Tubing needs wetting and often a rinse before use, since the glycerol and sulphur compounds it is shipped with will otherwise enter the sample.
A dialysis kit and when a device beats tubing
A dialysis kit puts the membrane in a cassette or a tube with a defined volume, which makes a small sample recoverable and the buffer exchange reproducible, where tubing clamped at both ends loses material and is hard to standardise. For volumes under a millilitre a device is the only practical format.
bioreactor components around the filter
The bioreactor components a perfusion process adds are the retention device, its pump and the tubing set, the level and weight control that balance feed against permeate, and the sensors that report the culture between samples. Single use assemblies make the set a purchased item rather than a built one, which changes the validation rather than the physics.
A 5/16 barb fitting and sizing to the tubing
A 5/16 barb fitting is sized to the tubing's inner diameter rather than to a thread, and the fit is made by the ridges gripping the bore under a defined clamp. A size chosen from the tubing's outside diameter is the commonest ordering error, and an over clamped joint causes the leak it was meant to stop.
Questions people ask about hollow fiber filters
Why hollow fibre rather than flat sheet?
Feed flows inside the lumen, so it tolerates cells and solids and shears them far less.
What transfers between scales in perfusion?
Cell specific perfusion rate, not volumetric flow.
Tubing or a cassette?
A cassette below a millilitre, and wherever recovery has to be reproducible. Tubing loses material.