The reasons for adopting single-use (aka disposable) bioprocess equipment have not changed since Vijay Singh first conceived of the Wave Bioreactor in the late 1990s. Processing biopharmaceuticals in plastic rather than stainless steel provides speed and flexibility while reducing cross-contamination and eliminating costs associated with cleaning stainless steel bioreactors.
During the early 2000s the economic arguments for disposables were not entirely convincing. Single-use bioreactor volumes remained stuck in the several-hundred-liter range, relegating plastics to bench-scale operations. Connectors and tubing had not been standardized, which was just one factor in complicating the transfer of bioprocesses from bench- to pilot-scale and beyond. For several years the question for single-use was never whether it would work, but at what scales.
Rising protein titers, particularly for monoclonal antibody production, eventually rescued single-use from "tinyland." Today, with some cell systems claiming protein titers above 10 g/L, the emergence of low-dose cellular therapies, the discovery of highly potent antibody-drug conjugates, and the push for personalized medicine, single-use biomanufacturing is no longer solely the property of R&D teams.
The upshot, if one is to trust the impenetrable world of market research, is that single-use bioprocessing is enjoying annual growth of between 12 and 19 percent and will continue to do so for the foreseeable future.
Breaking the size barrier
As expressed antibody titers continue to rise and medicines become more potent, there has been growing opportunity to reduce bioreactor sizes from the traditional stainless steel production scales of 10,000–20,000 liters and utilize single-use technology. At the same time, single-use bioreactor (SUB) vendors have generally been limited to 2,000-liters with overall poorer performance than stainless steel systems, which has resulted in sub-optimal productivity and cost of goods. In September 2020, ABEC introduced a 6,000-liter single-use bioreactor, which will be deployed at BioInno Biosciences' manufacturing facility in Suzhou, China. BioInno uses SUBs to reduce the cost of goods for monoclonal antibody production and for the manufacture of plasmid DNA and viral vectors.
With numerous deployments of 4,000-liter SUBs under its belt, ABEC has been the industry volume leader for some time; the industry standard is currently 2,000 liters.
The company has found a niche in the large-SUB space because, as Brady Cole, ABEC Vice President, Equipment Solutions, says, "demand for large-scale single-use bioreactors and fermenters is strengthening. We have demonstrated process performance in disposable bioreactors comparable to stainless steel systems for both cell culture and microbial fermentations. “The 6,000-liter CSR single-use bioreactor,” says Cole, "will set new benchmarks in cost-of-goods reduction for monoclonal antibody manufacturing."
Single, very large plastic bioreactors are not the only way to achieve volumetric nirvana. With positive economics now firmly established for disposable bioprocessing, and armed with better understanding of the risks of failed batches, bioprocessors also talk of "scaling out" instead of scaling up, meaning it is sometimes more cost-effective to run three 2,000-liter single-use processes than one fixed-tank 6,000-liter process. "And with optimization we can do as much in two thousand liters as we used to do in ten thousand liters," says George Barringer, Ph.D., Product Manager for Small Cultivation Systems at Applikon (now a part of Getinge). "We now have customers running GMP processes in fifty liter single-use bioreactors."
A path to Pharma 4.0?
FDA's Process Analytic Technology (PAT) initiative stressed the need for in-process real-time analytics. Pharma 4.0, dubbed by its proponents as the solution to all that ails "Factories and Supply Chains of the Future," takes this idea a step further with an emphasis on big-data processing, interconnectivity, collaborative robotics, artificial intelligence, etc.
The recent push toward Pharma 4.0 has increased the need for more real-time data, according to Venkatesh Gopal, Product and Market Development specialist at Applikon. "Upstream bioprocessing is highly complex, with a plethora of variables that need to be monitored and controlled for robust process development."
While advanced sensor technology provides a means of measuring physio-chemical attributes like pH, temperature, and other process parameters, the increased adoption of single-use systems requires that sensors and probes developed for stainless steel bioreactors must either be used under sub-optimal conditions or modified in some way.
"Single-use sensors or sensors embedded in the single-use containers or vessels could solve some of the issues," Gopal tells Biocompare. "Fully utilizing the surface areas of single-use containers could allow the installation of more probes to capture real-time data." He refers to "a more meaningful PAT" in which sensor data provides "a path for developing algorithms and models for predictive and prescriptive analysis and eventually to a self-correcting process yielding high-quality product consistently."
But are they safe?
Vendors of single-use bioprocess equipment have solved, or are close to solving, issues related to volume, PAT, and interoperability. One issue that will never go away, however, is concern over injected or infused medicines produced or stored in plastic.
Despite FDA initiatives, the formation of task forces and working groups, and the publication of hundreds of journal articles, bioprocessors are still worried about leachables and extractables (L&Es)—essentially components of polymer processing that wind up in bioprocess streams and, ultimately, in parenteral drugs. "Like bis phenol A from food packaging, the problem persists in single-use bioprocessing," explains Barringer.
L&Es represent a triple whammy for bioprocessors. Monomers, dimers, plasticizers, and other side players in polymerization negatively affect cell populations during expansion and production, challenge manufacturing and scale-up teams with unwelcome analytical problems, and if they wind up at too-high levels in products, can ruin a batch (although that appears to be rare). Manufacturers of single-use bioprocessing equipment are working hard to conform to accepted levels of these substances entering bioprocesses, which is where we are today.
The question of the ages is whether efforts at reducing the impact of L&Es are aimed at actually reducing levels of these contaminants, or merely at becoming better at detecting and quantifying them. In other words, are we mitigating or just testing better? "Manufacturers have a duty to assure that bioprocess vessels are fit for function—that we're not adulterating an injectible drug with a potentially harmful contaminant," Barringer says. "So sure, we're working on improving analysis and assays for leachables and extractables, but we're also working on improving the materials of construction of single-use containers to meet current specifications."