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Mar 1, 2013 (Vol. 33, No. 5)

Better Filtration Merges Innovation & Need

  • In other words, a specific filter product might cost twice as much as it did a decade ago, but its greater efficiency could help reduce ancillary costs or even the number of downstream steps. “Users increasingly view filtration as means to lower cost of operating the overall process,” says Mandar Dixit, director field marketing for filtration at Sartorius Stedim Biotech.

    What about performance? According to Watson, forcing a tradeoff between performance and cost would not work very well in the highly competitive marketplace for bioprocess equipment. “It would be inconceivable to introduce new filtration products, in particular, that did not do a better job than the products they’re replacing.”

  • 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.”

  • Following the Industry

    As bioprocessing technology goes, so goes bioprocess filtration. With filtration technology improving, and relieved by single-use filters of significant regulatory burden, end-users now have the luxury of focusing on sourcing and supply chain issues.

    Bioprocessors are increasingly concerned about ready availability of filtration products, in addition to their traceability and validation, says 3M’s Raman. “These regulatory requirements are becoming more and more strict.” Perhaps as a result, end-users are seeking out secondary or backup sources for critical filter components. “They may have validated their process on one system, but to ensure supply chain integrity they will validate it with other filtration equipment to ensure their supply.”

    Customers are looking not just at filter suppliers, but the suppliers’ suppliers to assure supply chain security, adds Dixit. Users try to minimize risk by sourcing through manufacturers with multiple, global manufacturing locations, “preferably on different continents, and with good technical support.”

Readers' Comments

Posted 06/13/2013 by Maik W Jornitz

With interest I read the very interesting and educational up-date on filtration. Indeed filtration innovation is very much driven by application demands and result in enhanced filtration devices and performances as described. However, as much as asymmetric membrane, dominated by polyethersulfon materials, are known as performance filters, test results in a variety of different applications showed that one has to carefully select the filter membrane material and structure to achieve optimal performance. The end-user should rather check the toolbox of filter options and do not rely on the, so much praised, "silver bullet" of all filters, named in this paper as asymmetric. Furthermore, what I missed in the statements made are the fact that unspecific adsorption by the membrane material requires to be evaluated, as it can have a detrimental impact on value losses. In addition, hold-up volume is another value influencer, which means that smaller filter sizes and the elimination of a prefilter causes not only benefits in filter cost reduction, but rather a gains in valuable product.
Filtration is an utmost critical step within the biopharmaceutical industry, one has seen many, extremely favorable advances and this progress will not stop. The filtration step shall never be underestimated. Saving on a filter price and thinking sterilizing filters are a commodity would be a wrong assessment by any means. The right choice of filter, membrane material, structure, dimensions are of utmost importance.
The only blemish sterilizing grade filters can get, are statements as made in the paper of "enhanced sterility". Sterility is and has to be an absolute term.

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