Most of our customers have, until now, run the single-use processing equipment manually, says Mani Krishnan, director of process systems, downstream processing business unit of Millipore. “For product contact applications, however, there is an interest in making the process less operator intensive—automation and data acquisition are now being requested. This will drive single-use manufacturers to provide not only the disposable flow path but also the necessary hardware to operate the single-use flow path. These high-value applications require the single-use systems to be designed with sound engineering principles—merely connecting a bag to a piece of tubing and irradiating the assembly is not where the value is.”
Krishnan reports an increasing number of requests from customers for single-use processing systems for product contact applications such as clarification, protein concentration/diafiltration, and final fill/finish. These are “primarily for phase I/II type molecules where the volumes are relatively small or at CMOs where the need for flexibility is the highest. We are also seeing request for medium-to-large scale processing hybrid equipment,” a single-use flow path, and stainless steel contact surfaces.
One of the last hurdles to realizing a totally disposable bioprocess stream is the chromatographic purification step. Large-scale manufacturing yields high-volume fluid streams, which necessitate huge columns and large amounts of specialty resins that are simply too expensive to throw away after a single use.
Pros and Cons
At CHI’s “Peptalk” conference, roundtable panelists including Leigh Pierce, president of PacificGMP, Scott Fulton, cofounder and scientific advisor of Tarpon Biosystems, and Geoffrey Hodge, of Xcellerex, discussed “The Pros & Cons of Disposables.”
PacificGMP has utilized a 100% disposable process stream since its inception four years ago. “We have no steel tanks, no skids,” says Pierce, but “we still need disposable columns and resins.” The increased flexibility that disposable components provide allows the company to “get up and running quickly. Our queues are shorter; our costs are less,” Pierce adds. “We don’t have a water purification system on site; our needs are reduced as we only use WFI for processes, not cleaning.”
PacificGMP is experimenting with continuous feed/perfusion processes to extract the maximum amount of product from a single-use bioreactor bag. The cells are recirculated in a hollow-fiber filtration system. With this continuous-feed approach the company has been able to process 15,000 liters of culture fluid in three runs using a 500 L disposable bag. “I think scale will cease to be an issue with the exception of the downstream component,” says Pierce.
There is a great deal of interest in the disposable chromatography technology being developed by Tarpon Biosystems, according to Fulton. BioSMB™ is a modified form of simulated moving bed (SMB) technology, which is in use in other industries and is now being developed for biopharmaceutical purification applications.
One of the issues in trying to adapt conventional SMB systems for use in an asceptic flow path is the number of valves these systems typically contain, explains Fulton. A typical purification system might contain 8 to 12 columns, with each column having 8 to 9 valves. With the development of a disposable plastic valve block, SMB becomes an economically viable option for disposable chromatographic separation technology.
“With SMB you can maximize use of the resin,” says Fulton. The combination of a substantially larger loading capacity and more rapid cycling allows for purification of large volumes of process fluids in one or two batches, thereby reducing resin and buffer needs by 40–60%.
“SMB makes disposable chromatography feasible,” Fulton states. With cell-culture expression levels increasing to routine yields of 5 g/L and higher, the production bottleneck has shifted downstream to the purification step. “The advantages of SMB grow dramatically as expression levels go up,” says Fulton. Whereas an increase of 1 g/L to 10 g/L would necessitate a ten-fold increase in capacity for traditional chromatographic methods, with SMB, “you can just cycle it faster,” and only a small increase in scale is needed. Tarpon has produced a lab-scale prototype of the BioSMB that can handle the output of a 500–1,000 L bioreactor, he adds.
Limitations still exist in disposable sensor technology for online monitoring. Some sensors such as pressure gauges and dissolved oxygen proves are available, and pH sensors are coming along, according to Pierce, but other detectors such as UV flow cells are still far too costly for one-time use. SciLog recently introduced a family of disposable in-line sensors for monitoring conductivity (SciCon), pressure (SciPres), and temperature (SciTemp). These precalibrated sensors come in five different sizes, ranging from Luer, 3/8" barb, 1/2" barb, 3/4" TC to 1.0" TC.
According to Karl G. Schick, Ph.D., vp of R&D, these sensors accommodate the industry’s need for system scalability.
As part of a program funded by the Defense Threat Reduction Agency to develop technologies and strategies to accelerate biomanufacturing, Xcellerex has investigated an SMB process for purification and reports a reduction in buffer consumption by half or more, contributing to significant cost reductions. The goal of this program is to identify and optimize the technology needed to facilitate a rapid response to a biothreat, enabling quick production of millions of vaccine doses starting from a DNA sequence.
Xcellerex is currently in Phase II of the program, which involves developing a rapid response capability and then demonstrating the manufacture of a subunit vaccine or monoclonal antibody in less than 12 weeks in a live-fire scenario. The company’s FlexFactory™ single-use bioprocessing platform is scalable to a 2,000 L working volume.