Disposables Still Topical
Arguably, the single most important trend in bioprocess filtration has been single-use membranes. Yet given the difficulty in pleating depth filter media at reasonable packing efficiencies, designing encapsulated single-use depth filters remains technically challenging. Yet some vendors have prevailed.
The design of new large-scale single-use depth filter systems has now enabled the adoption of disposable technology in larger scale processes. “There is greater and greater demand for new technologies in up-front clarification,” says L.P. Raman, manager of marketing development at 3M. “We believe disposable technology for this application is still at an early peak, or perhaps still growing.” Rising product titers, which subject filters to numerous filtration and fouling burdens, exacerbates this need.
This is part of a much newer approach by bioprocessors, particularly with respect to sterile filtration, to consider the overall cost of the unit operation rather than the price for any single piece of equipment. It comes down, Raman says, to throughput, performance, and ease of use. Achieving the correct balance of these characteristics is not easy, given the operational and validation issues associated with depth filtration.
Raman says 3M’s Zeta Plus Encapsulated depth filters solve one critical usability issue while addressing performance and throughput as well. Zeta Plus Encapsulated systems were developed in response to the need for operators to load and unload filter media at waist height, rather than lifting the capsules above their heads and risk exposure to fluid spills when handling used capsules or cartridges. They also save time by being easier to handle than conventional depth media. “You don’t want to spend your entire day loading or unloading lenticular depth filters in large-domed housings gowned in suits,” Raman adds.
Bioprocessors are trending toward implementation of larger-scale, ready-to-use, capsule filters integrally sealed into plastic housings. The largest of these devices can contain 3.5 m2 or more of filter media.
“These filters have creatively eliminated time and expense associated with change-out of filters from traditional stainless steel housings and the associated cleaning and reassembly of the filter/housing system,” says Chuck Capron, director of sales at Meissner Filtration. Additionally, this eliminates cleaning validation concerns for the filter/housing system. Time saved from cleaning and cleaning validation for filters and housings results in less downtime between filtration runs, and improved productivity, Capron adds.
New process methods also allow these filters to be manufactured in continuous lengths from 10-inch to 50-inch sizes to support small filtration campaigns through large-scale production runs. Meissner has developed a configurable platform that allows multiple pre- and final capsule filters to be secured into a presterilized, single-use filtration system for plug and play use (i.e., Meissner’s UltraSnap™ filter assembly), which effectively makes the scale of single-use filters unlimited, according to Capron.
Another trend is the demand for and advancement of high-flow, long-life filter membranes based on asymmetric construction. These have been on the market for well over a decade. Asymmetric pore structures allow for extremely fast flow rates and low pressure drops. The asymmetry of the membrane serves as a final filter with its own built-in prefilter.
Disposable dead-end filtration capsules have been available for quite some time, observes Dixit. “But disposable filtration still lags at larger facilities that have already invested in stainless steel and cleaning infrastructure. We still sell a lot of cartridges and stainless steel housings to legacy processes.” One growth area Dixit notes within single-use are “complete solutions” that are pre-assembled and gamma-sterilized. “We are seeing increasing inquiries into transfer sets—filters plus tubing and connectors, or filter assemblies connected to bags ready to go.”