The development towards producing biotherapeutics faster, in greater scales, and to a more consistent quality is great news for the industry and an exciting time for companies that support it. Progress, however, breeds challenges. One challenge that I find particularly interesting is preparation of samples containing high levels of aggregates.
Meeting the scale requirements
Visiting customers across the USA, I heard about major breakthroughs in cell culturing. Cells are being programmed to produce a wider range of biomolecules to a more consistent quality. Also, cell growth and productivity are being increased. However, as culture densities hit the 100 million cells per mL mark, removal of unwanted debris released after cellular lysing is becoming a real speed bump. Such samples are too particle-laden for chromatographic purification, they can cause traditional depth filters to get clogged, and sample preparation by centrifugation is slow and cumbersome. While sample clearance still tediously relies on a combination of all three of these techniques, I heard a few best practices for syringe-based sample preparation that are worth sharing:
1. Check your membrane first. Sometimes, the perception that a sample is hard to filter is simply caused by trying to run an aqueous sample through a hydrophobic membrane like a polytetrafluoroethylene (PTFE) membrane. Using a hydrophilic membrane is a step in the right direction, but make sure to choose a membrane that exhibits low protein binding, such as polyethersulfone (PES) or regenerated cellulose membranes, to avoid sample loss.
2. Use a pre-filter, or even a pre-filter stack, to extend syringe filter life. Choose a device that has a depth filtration pre-filter stack that traps coarse particles, leaving the main membrane to deal only with the finer particles. Pre-filters are generally made from either glass microfibers or polypropylene. Your choice of which to use should come down to whether ionic extractables from the glass will interfere with your downstream work or not.
3. Always think of scale. While laboratory-scale sample volumes can be as small as some a few microliters, production of a successful biotherapeutic will always berequires scale up. Whatever filter is used; make sure that the same type of membrane/pre-filter combination exists in multiple formats, from vial-based, syringe-based, capsule-based, and beyond. Planning for scale-up will make sure that your filtration optimization does not come at the expense of more work later on.
Until next time, may all your filtrations go according to plan.