What is Dr. Zubair Khalid's research focus?

Dr. Zubair Khalid specializes in molecular virology, mRNA vaccine development, and computational biology, with a focus on avian pathogens like IBDV and Avian Reovirus.

Where is Dr. Zubair Khalid currently working?

Dr. Zubair Khalid is a Postdoctoral Research Associate at the University of Maryland (UMD), specifically within the Department of Animal and Avian Sciences.

Single-Use Bioreactors: Principles, Applications, and Best Practices

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Introduction to Single-Use Bioreactors

Definition and Basic Concept

A single-use bioreactor (SUB) is a bioprocessing vessel in which all product-contact surfaces—typically the culture chamber, tubing, and connectors—are manufactured from disposable polymeric materials and are intended for one batch of culture before being discarded. The core of the system is a sterile, pre-manufactured plastic bag or rigid plastic vessel that is mounted within a support structure providing mechanical integrity, heat transfer, and process control. Unlike traditional stainless steel systems that require cleaning-in-place (CIP) and sterilization-in-place (SIP) between campaigns, single-use systems arrive pre-sterilized by gamma irradiation and are simply unpacked, installed, and inoculated.

The fundamental value proposition is the elimination of cross-contamination risk between batches and the removal of the capital-intensive cleaning infrastructure. A single-use bioreactor replaces the fixed vessel, agitator assembly, sparger, and associated piping with a consumable. The support hardware—the shell, motor, and control unit—is reused, but the biological contact surface is not. This distinction is critical: the term "single-use" refers to the wetted path, not the entire system.

Historical Context and Adoption

The first commercial single-use bioreactors emerged in the late 1990s, driven by the need for flexible, rapid-response manufacturing in the emerging biologics sector. The earliest systems were wave-type bioreactors, which used a rocking platform to induce mixing in a partially filled bag. These were followed by stirred-tank single-use designs in the mid-2000s, which offered better scalability and higher oxygen transfer rates. Adoption accelerated as the industry recognized that monoclonal antibody (mAb) pipelines required faster turnaround times and lower capital exposure than traditional stainless steel facilities could provide.

By 2020, single-use technology had become the dominant platform for clinical-scale mammalian cell culture, with working volumes ranging from 50 L to 2,000 L. The COVID-19 pandemic further accelerated adoption, as vaccine manufacturers needed rapidly deployable, multi-product facilities. Today, single-use bioreactors are standard for upstream processing in contract development and manufacturing organizations (CDMOs) and are increasingly used in commercial manufacturing for products with annual demand below approximately 1,000 kg.

Design and Construction of Single-Use Bioreactors

Film Materials and Gas Permeability

The culture chamber of a single-use bioreactor is fabricated from multi-layer polymer films, typically 3 to 7 layers thick, with a total thickness of 200 to 400 µm. Each layer serves a distinct function. The product-contact layer is usually polyethylene (PE) or ethylene-vinyl acetate (EVA), chosen for low extractable content and biocompatibility. The gas barrier layer is typically ethylene-vinyl alcohol (EVOH) or polyamide (nylon), which minimizes oxygen ingress and carbon dioxide egress. An outer layer of polyethylene terephthalate (PET) or polyurethane provides mechanical strength and puncture resistance.

Gas permeability is a critical design parameter. The EVOH barrier layer reduces oxygen transmission rates to approximately 10–50 cm³/(m²·day·atm), which is essential for maintaining anaerobic or microaerobic conditions in microbial cultures. However, for mammalian cell culture, the same barrier creates a challenge: carbon dioxide produced by cellular respiration cannot readily escape through the film, leading to CO₂ accumulation in the headspace. This is managed by active headspace gas exchange—continuous sparging with air or oxygen and purging of the headspace with nitrogen or air to strip CO₂.

The film must also withstand gamma irradiation for sterilization. Irradiation causes polymer chain scission and cross-linking, which can alter mechanical properties and generate degradation products. Film manufacturers therefore formulate resins with radiation stabilizers and validate that the irradiated film retains its integrity for the intended storage period, typically 12 to 24 months.

Agitation and Mixing Systems

Agitation in single-use bioreactors is provided by either a top-mounted or bottom-mounted impeller. Bottom-mounted designs are more common in stirred-tank systems because they eliminate the need for a top drive shaft penetrating the bag, which is a potential contamination point. The impeller is typically a pitched-blade or marine-type design, magnetically coupled to an external motor. The magnetic coupling transmits torque through the bag film without a physical shaft penetration, maintaining the sterile barrier.

The impeller and shaft are molded or welded into the bag during manufacture, and the entire assembly is gamma-irradiated as a unit. Impeller designs are optimized for low shear, which is critical for shear-sensitive mammalian cells. Typical tip speeds range from 1.5 to 2.5 m/s, compared to 3 to 5 m/s in stainless steel systems. The lower tip speed is compensated by using larger-diameter impellers and multiple impellers on a single shaft to achieve adequate bulk mixing.

One limitation of bottom-mounted magnetic drives is the torque limit. As the working volume increases, the torque required to rotate the impeller increases, and magnetic couplings can decouple or slip. This imposes a practical scale limit of approximately 2,000 L for stirred-tank single-use systems, beyond which the magnetic coupling becomes unreliable.

Sensors and Single-Use Probes

Traditional bioreactors rely on reusable probes for pH, dissolved oxygen (DO), and temperature, which must be sterilized and calibrated before each run. Single-use systems use pre-sterilized, disposable sensors that are either embedded in the bag or inserted through sterile ports.

Optical pH sensors use a fluorescent dye immobilized on a patch inside the bag. The dye's fluorescence lifetime changes with pH, and an external reader interrogates the patch through a transparent window. The measurement range is typically pH 5.5 to 8.5, with an accuracy of ±0.1 pH units. Optical DO sensors similarly use a ruthenium-based fluorescent dye whose emission is quenched by oxygen. The response time is 30 to 60 seconds, which is adequate for process control but slower than electrochemical probes.

Temperature is measured by a thermocouple or resistance temperature detector (RTD) placed in a thermowell that contacts the bag exterior. Because the film has low thermal conductivity, the sensor reads the temperature of the heat transfer surface rather than the bulk liquid; this is compensated by control algorithms that account for the thermal lag.

Single-use sensors have a finite shelf life and require calibration verification before use. Most manufacturers provide pre-calibrated sensors with a certificate of analysis, but the user must verify the calibration against a reference at the start of each run. Drift over the course of a multi-week culture is a known issue, particularly for pH sensors, which can drift by 0.1 to 0.2 pH units over 14 days.

Mechanism of Operation

Mixing and Mass Transfer

Mixing in a single-use bioreactor serves three functions: homogenizing the culture medium, suspending cells, and dispersing gas bubbles for oxygen transfer. The mixing mechanism depends on the reactor type. In stirred-tank systems, the impeller creates a turbulent flow field with a characteristic mixing time (θ_m) of 10 to 60 seconds, depending on the working volume and agitation rate. In rocking systems, the bag's periodic deformation creates a wave that propagates through the liquid, providing gentler mixing with longer mixing times of 30 to 120 seconds.

Mass transfer of oxygen from gas bubbles to the liquid phase is characterized by the volumetric mass transfer coefficient, kLa. For stirred-tank single-use bioreactors, kLa values range from 5 to 50 h⁻¹, which is sufficient for mammalian cell culture but marginal for high-density microbial fermentation. Rocking systems achieve lower kLa values of 2 to 10 h⁻¹, limiting their use to low-to-moderate cell density cultures.

The mixing and mass transfer performance is influenced by the bag's geometry. Unlike rigid stainless steel vessels, the bag is flexible and can deform under the influence of the impeller, particularly at low fill volumes. This deformation can reduce mixing efficiency and create dead zones. Manufacturers address this by using a rigid outer shell that supports the bag and maintains its shape, or by using internal baffles molded into the bag.

Oxygen Transfer and Aeration

Oxygen is supplied to the culture through sparging—the introduction of gas bubbles through a sparger at the bottom of the bag. The sparger is typically a microporous membrane or a drilled-hole plate that produces bubbles of 0.5 to 3 mm diameter. Smaller bubbles provide a larger surface area for mass transfer but are more easily entrained in the culture and can cause foam.

For mammalian cell culture, oxygen demand is relatively low, typically 0.1 to 0.5 mmol O₂/L/h at cell densities of 1–5 × 10⁶ cells/mL. This demand can be met by surface aeration alone in small-scale rocking systems, but stirred-tank systems require sparging at cell densities above approximately 2 × 10⁶ cells/mL. The sparging gas is typically air enriched with oxygen to maintain the dissolved oxygen concentration at 30% to 50% of air saturation.

Carbon dioxide removal is equally important. CO₂ is produced by cellular respiration at a rate proportional to oxygen consumption, and it must be removed to prevent acidification of the culture. In stainless steel systems, CO₂ is stripped by the sparging gas and exits through the headspace. In single-use systems, the gas-permeable film provides an additional route for CO₂ egress, but as noted, the EVOH barrier layer limits this. Headspace flushing with nitrogen or air at 0.1 to 0.5 vessel volumes per minute (vvm) is therefore standard practice.

Scale-Up Considerations

Scaling up a single-use bioreactor involves maintaining key process parameters—kLa, mixing time, shear rate, and power input per unit volume—while increasing the working volume. The most common scale-up criterion is constant kLa, which ensures that oxygen transfer capacity is maintained. However, maintaining constant kLa requires increasing the agitation rate and gas flow rate, which increases shear stress and can damage cells.

An alternative scale-up criterion is constant power input per unit volume (P/V). This maintains similar mixing and shear characteristics but results in a lower kLa at larger scales. For mammalian cell culture, where oxygen demand is low, constant P/V is often the preferred criterion because it preserves the hydrodynamic environment. For microbial fermentation, where oxygen demand is high, constant kLa is more critical.

The scale-up of single-use systems is also constrained by the physical limits of the bag and impeller. The maximum working volume for a stirred-tank single-use bioreactor is approximately 2,000 L, limited by the torque capacity of the magnetic coupling and the mechanical strength of the bag film. Beyond this scale, stainless steel systems remain the only option. For a detailed treatment of scale-up methodology, see Bioreactor Scale-up.

Types of Single-Use Bioreactors

Stirred-Tank Single-Use Bioreactors

Stirred-tank single-use bioreactors (SUBs) are the most widely used type for mammalian cell culture. They consist of a rigid outer shell, typically made of stainless steel or plastic, that houses a disposable bag. The bag contains the impeller, sparger, and sensor patches, and is connected to the external control system through sterile connectors.

The working volume ranges from 50 L to 2,000 L, with the bag occupying the full volume of the shell. The aspect ratio (height to diameter) is typically 1.5 to 2.5, similar to stainless steel systems. Agitation is provided by one or two pitched-blade impellers, with a maximum tip speed of 2.5 m/s to minimize shear.

Stirred-tank SUBs offer the best mixing and mass transfer performance among single-use designs, with kLa values up to 50 h⁻¹. They are suitable for high-density fed-batch cultures of Chinese hamster ovary (CHO) cells, reaching cell densities of 10–30 × 10⁶ cells/mL and antibody titers of 3–10 g/L. They are also used for perfusion cultures, where a cell retention device is integrated into the bag.

Rocking and Wave Bioreactors

Rocking bioreactors, also known as wave bioreactors, use a rocking platform to induce a wave in a partially filled bag. The bag is placed on a platform that rocks back and forth at a frequency of 5 to 40 rocks per minute, with a rocking angle of 5 to 10 degrees. The wave created by the rocking motion provides mixing and gas transfer.

The key advantage of rocking bioreactors is their gentleness. The wave-induced mixing produces very low shear rates, making them suitable for shear-sensitive cells such as stem cells, insect cells, and primary cells. They are also simpler to operate, with no impeller or sparger to configure.

The main limitation is the low kLa, typically 2 to 10 h⁻¹, which restricts cell densities to below approximately 5 × 10⁶ cells/mL. Working volumes are also limited to 500 L, as the wave amplitude and mixing efficiency decrease at larger scales. Rocking bioreactors are commonly used for seed train expansion, vaccine production, and cell therapy manufacturing.

Other Designs (e.g., Orbitally Shaken)

Orbitally shaken bioreactors use a circular shaking motion to create a toroidal flow pattern in the liquid. The bag is placed on a shaking platform that moves in a circular orbit, creating a centrifugal force that drives liquid up the walls of the bag and creates a central vortex. This design provides good mixing with low shear and is particularly effective for suspension cultures.

Orbitally shaken systems are available in working volumes from 10 L to 250 L and offer kLa values of 5 to 20 h⁻¹. They are simpler than stirred-tank systems, with no impeller or sparger, and are often used for seed train expansion and for cultures that require gentle mixing.

Other emerging designs include vertical-wheel bioreactors, which use a rotating paddle wheel to create a gentle, low-shear mixing environment, and hollow-fiber bioreactors, which use a membrane to provide both oxygen transfer and nutrient delivery. These designs are niche but offer specific advantages for particular applications, such as high-density perfusion culture.

Applications in Bioprocessing

Mammalian Cell Culture

Mammalian cell culture is the dominant application for single-use bioreactors, accounting for the majority of installed systems. The primary cell line is CHO, which is used to produce monoclonal antibodies, fusion proteins, and other recombinant therapeutic proteins. CHO cells are grown in suspension in chemically defined media, typically at temperatures of 36–37°C, pH 7.0–7.2, and dissolved oxygen of 30–50% air saturation.

Fed-batch culture is the most common mode of operation. The culture is initiated at a cell density of 0.3–0.5 × 10⁶ cells/mL in a working volume that is 40–60% of the maximum. Over the course of 12–18 days, concentrated feed medium is added to maintain nutrient levels and support cell growth to densities of 10–30 × 10⁶ cells/mL. The product is harvested at the end of the culture, with typical antibody titers of 3–10 g/L.

Single-use bioreactors are also used for perfusion culture, where fresh medium is continuously added and spent medium is removed while cells are retained in the reactor. Perfusion enables much higher cell densities (50–100 × 10⁶ cells/mL) and longer culture durations (30–60 days), but requires a cell retention device such as an alternating tangential flow (ATF) filter or a settling device. The integration of these devices with single-use bags is an active area of development.

Microbial Fermentation

Microbial fermentation using single-use bioreactors is less common than mammalian cell culture, primarily because of the higher oxygen demand and the need for higher kLa values. However, single-use systems are increasingly used for microbial products such as recombinant enzymes, plasmid DNA, and vaccine antigens.

The key challenge is oxygen transfer. Bacteria such as Escherichia coli can reach cell densities of 50–100 g/L dry cell weight, requiring kLa values of 200–1,000 h⁻¹. Standard single-use stirred-tank bioreactors cannot achieve these values. However, for lower-density fermentations (10–30 g/L dry cell weight), single-use systems with enhanced sparging and agitation can be adequate.

The choice of microbial host is also important. Pichia pastoris (now Komagataella phaffii), a methylotrophic yeast, has lower oxygen demand than E. coli and is more amenable to single-use systems. It is used to produce recombinant proteins, including industrial enzymes and vaccine antigens, at cell densities of 20–50 g/L dry cell weight.

Vaccine Production and Gene Therapy

Single-use bioreactors are widely used in vaccine production, particularly for viral vaccines and viral vectors. The production process involves infecting a susceptible cell line—such as Vero cells, MDCK cells, or HEK293 cells—with the virus or vector, which then replicates and is harvested.

For viral vaccines, the cell culture is typically grown to high density in a single-use bioreactor, then infected with the virus at a multiplicity of infection (MOI) of 0.01 to 0.1 plaque-forming units per cell. The virus replicates over 2–7 days, after which the culture is harvested and the virus is purified. Single-use systems are advantageous here because they minimize the risk of cross-contamination between different vaccine strains.

For gene therapy, single-use bioreactors are used to produce viral vectors such as adeno-associated virus (AAV) and lentivirus. These vectors are produced by transfecting HEK293 cells with plasmid DNA encoding the vector components. The transfection is typically performed in a single-use bioreactor at a cell density of 1–2 × 10⁶ cells/mL, and the vector is harvested 48–72 hours post-transfection. The scalability of single-use systems is particularly valuable for gene therapy, where production campaigns are often small and product demand is uncertain.

Advantages and Limitations

Operational Advantages

The primary advantage of single-use bioreactors is the elimination of cleaning and sterilization. In a stainless steel facility, each batch requires a CIP cycle (typically 1–2 hours) followed by an SIP cycle (typically 1–3 hours). These cycles consume large volumes of water, caustic soda, and steam, and require validation to ensure that cleaning is effective. Single-use systems eliminate these steps entirely, reducing turnaround time between batches from days to hours.

The reduction in contamination risk is a second major advantage. Each batch uses a fresh, sterile bag, eliminating the possibility of carryover contamination from a previous batch. This is particularly important for products where cross-contamination is unacceptable, such as vaccines and gene therapy vectors.

Flexibility is a third advantage. A single-use bioreactor can be used for different products without the need for extensive cleaning validation. This makes them ideal for multi-product facilities, such as CDMOs, where the product mix changes frequently. The lower capital cost of single-use facilities—typically 30–50% less than equivalent stainless steel facilities—also reduces the financial risk of building new manufacturing capacity.

Challenges and Limitations

The most significant limitation is the issue of extractables and leachables. The polymer film and other plastic components can release chemical compounds into the culture medium, particularly at elevated temperatures and in the presence of organic solvents. These compounds can affect cell growth, product quality, or both. The risk is managed through rigorous extractables and leachables testing, but it cannot be entirely eliminated.

Scale is a second limitation. The maximum working volume for a stirred-tank single-use bioreactor is approximately 2,000 L, compared to 20,000 L or more for stainless steel systems. For products with high annual demand, such as blockbuster antibodies, stainless steel remains the only viable option for commercial manufacturing.

Bag integrity is a third concern. The bag is a thin polymer film that can be punctured, torn, or develop leaks during handling, installation, or operation. A leak can result in contamination of the culture or loss of the batch. Manufacturers have reduced the incidence of leaks through improved film formulations and quality control, but the risk remains higher than for rigid stainless steel vessels.

Finally, the cost of consumables is a consideration. Each bag, sensor, and connector set is a single-use item that must be purchased for every batch. For high-volume production, the consumable cost can exceed the cost of cleaning and sterilization in a stainless steel facility.

Regulatory and Quality Considerations

Extractables and Leachables

Extractables are compounds that can be extracted from the polymer material under exaggerated conditions, such as high temperature, prolonged contact, or exposure to aggressive solvents. Leachables are compounds that actually migrate into the culture medium under normal operating conditions. The distinction is important: extractables are a worst-case measure of what could be released, while leachables are what actually is released.

The regulatory expectation is that all product-contact materials are characterized for extractables, and that leachables are assessed under actual process conditions. The testing is typically performed using a model solvent, such as 50% ethanol in water, at elevated temperature (40–70°C) for an extended period (24–72 hours). The extract is analyzed by gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) to identify and quantify the extracted compounds.

Common extractables from single-use bioreactor films include antioxidants (e.g., Irgafos 168, Irganox 1076), slip agents (e.g., erucamide), and oligomers from the polymer itself. The toxicological risk of these compounds is assessed using a safety threshold, typically 0.5 µg/day for genotoxic compounds and 150 µg/day for non-genotoxic compounds. If the leachable concentration exceeds these thresholds, the product may be at risk, and the manufacturer must either change the material or implement additional purification steps.

Validation and GMP Compliance

The use of single-use bioreactors in GMP manufacturing requires validation of the system's performance and integrity. The validation program typically includes:

Installation qualification (IQ): Verifying that the bioreactor system is installed correctly and that all components are present and functional.
Operational qualification (OQ): Verifying that the system operates within specified parameters, including agitation speed, temperature control, and gas flow rates.
Performance qualification (PQ): Verifying that the system produces a product that meets specifications, typically by running a representative culture.

In addition, the bag integrity must be verified before each use. This is typically done by a pressure decay test, where the bag is pressurized to 20–30 mbar and the pressure decay over 10–30 minutes is measured. A pressure decay above a threshold indicates a leak, and the bag is rejected.

The regulatory landscape for single-use systems is evolving. The FDA and EMA have issued guidance on the use of single-use systems, emphasizing the need for extractables and leachables data, bag integrity testing, and risk assessment for the specific product and process. The Bio-Process Systems Alliance (BPSA) and the ASTM International have developed standards for single-use systems, including test methods for bag integrity and extractables.

Common Pitfalls and Best Practices

Selection Pitfalls

A common mistake is selecting a single-use bioreactor based solely on working volume, without considering the oxygen transfer requirements of the specific process. A rocking bioreactor may be suitable for a low-density CHO culture but will fail for a high-density E. coli fermentation. The kLa of the system must be matched to the oxygen demand of the culture, which is determined by the cell density, growth rate, and metabolic activity.

Another pitfall is underestimating the importance of the bag's gas permeability. For cultures that produce large amounts of CO₂, such as high-density CHO cultures, the bag's EVOH barrier can cause CO₂ accumulation, leading to acidification and reduced cell growth. The user must ensure that the headspace gas exchange is adequate for the specific process.

A third pitfall is failing to consider the compatibility of the bag with the specific culture medium. Some media components, particularly lipids and surfactants, can interact with the polymer film and increase the release of leachables. The user should review the extractables data for the specific bag and compare it with the composition of the culture medium.

Operational Best Practices

The following practices are recommended for reliable operation of single-use bioreactors:

Perform a bag integrity test before inoculation. Use a pressure decay test to verify that the bag has no leaks. This is a simple, inexpensive step that can prevent a costly contamination event.
Verify sensor calibration before use. Single-use sensors can drift during storage. Compare the sensor reading with a reference measurement at the start of the run and adjust the process control setpoints accordingly.
Monitor the bag for deformation. The bag can deform under the influence of the impeller, particularly at low fill volumes. If the bag deforms excessively, the mixing efficiency will decrease, and the culture may become heterogeneous.
Use a headspace purge to control CO₂. For mammalian cell cultures, flush the headspace with air or nitrogen at 0.1–0.5 vvm to prevent CO₂ accumulation.
Document the lot number of each bag. If a bag fails, the lot number allows the manufacturer to identify the cause and prevent recurrence.

Troubleshooting Common Issues

Low dissolved oxygen: If the DO falls below the setpoint despite increased agitation and gas flow, the kLa of the system may be insufficient for the cell density. The solution is to reduce the cell density (by reducing the inoculation density or the feed rate) or to switch to a system with higher kLa.

pH drift: If the pH drifts downward, it is likely due to CO₂ accumulation or lactic acid production. Increase the headspace purge to remove CO₂, or add base to correct the pH. If the pH sensor is drifting, verify the calibration against a reference.

Foaming: Excessive foaming can occur at high gas flow rates or when the culture produces surfactants. Add an antifoam agent (e.g., 0.01–0.1% polypropylene glycol) to the culture, or reduce the gas flow rate.

Bag leak: If a leak is suspected, stop the culture immediately and test the bag for integrity. If the leak is confirmed, the batch must be discarded. The cause of the leak should be investigated—common causes include handling damage, impeller contact with the bag wall, and manufacturing defects.

Frequently Asked Questions

What is a single-use bioreactor?

A single-use bioreactor is a bioprocessing vessel in which the product-contact surfaces—the culture chamber, tubing, and connectors—are made of disposable polymeric materials and are discarded after a single batch. The support hardware, including the shell, motor, and control unit, is reused. This design eliminates the need for cleaning and sterilization between batches and reduces the risk of cross-contamination.

How does a single-use bioreactor work?

A single-use bioreactor provides a controlled environment for cell culture or microbial fermentation. The culture chamber is a sterile, pre-manufactured plastic bag that is mounted in a support structure. Mixing is provided by an impeller (in stirred-tank designs) or by rocking or shaking (in wave and orbitally shaken designs). Oxygen is supplied by sparging gas through the culture, and temperature is controlled by a heating/cooling jacket around the shell. The bag contains sensors for pH, dissolved oxygen, and temperature, which are monitored by external readers.

What are the advantages of single-use bioreactors?

The main advantages are the elimination of cleaning and sterilization, reduced contamination risk, greater flexibility for multi-product facilities, and lower capital cost. Single-use systems also reduce turnaround time between batches and require less water, energy, and cleaning chemicals.

What are the limitations of single-use bioreactors?

The main limitations are the risk of extractables and leachables from the polymer materials, the limited maximum scale (approximately 2,000 L for stirred-tank systems), the risk of bag leaks, and the ongoing cost of consumables. The gas permeability of the bag film can also affect CO₂ removal, requiring active headspace management.

What are the main types of single-use bioreactors?

The main types are stirred-tank single-use bioreactors, which use an impeller for mixing and offer the highest kLa; rocking or wave bioreactors, which use a rocking platform to create a wave and are gentler but have lower kLa; and orbitally shaken bioreactors, which use a circular shaking motion. Other designs include vertical-wheel and hollow-fiber bioreactors.

How do you scale up a single-use bioreactor?

Scale-up is performed by maintaining key process parameters, typically constant kLa or constant power input per unit volume (P/V). The choice of criterion depends on the oxygen demand of the culture. For mammalian cells, constant P/V is often preferred to preserve the hydrodynamic environment. The scale-up is also constrained by the physical limits of the bag and impeller, with a maximum working volume of approximately 2,000 L.

What is the difference between single-use and stainless steel bioreactors?

Stainless steel bioreactors are fixed vessels that are cleaned and sterilized between batches using CIP and SIP systems. They can be scaled to very large volumes (up to 20,000 L or more) and have well-characterized performance. Single-use bioreactors use disposable bags that are discarded after each batch, eliminating cleaning and sterilization. They are more flexible and have lower capital cost but are limited in scale and carry the risk of extractables and leachables.

Key Takeaways

Single-use bioreactors eliminate cleaning and sterilization steps, reducing turnaround time and contamination risk, and are now standard for clinical-scale mammalian cell culture.
The culture chamber is a multi-layer polymer film bag with distinct layers for product contact, gas barrier, and mechanical strength; gas permeability and extractables are critical design considerations.
Stirred-tank single-use bioreactors offer the highest mixing and oxygen transfer performance (kLa up to 50 h⁻¹) and are suitable for high-density CHO cell culture, while rocking and orbitally shaken systems are gentler but have lower kLa.
The maximum practical scale for stirred-tank single-use systems is approximately 2,000 L, limited by magnetic coupling torque and bag mechanical strength; beyond this, stainless steel remains necessary.
Extractables and leachables testing is a regulatory requirement for all product-contact materials, and the toxicological risk of leachable compounds must be assessed against safety thresholds.
Bag integrity testing before each use, sensor calibration verification, and active headspace CO₂ management are essential operational practices for reliable performance.
Scale-up of single-use bioreactors should maintain constant kLa or constant power input per unit volume, depending on the oxygen demand and shear sensitivity of the culture.