Single-use Technology Matures
“I think we will start to see multimode, or hybrid, single-use bioreactors that use multiple actions, particularly for mammalian cell culture,” says Kevin Auton, Ph.D., chief executive of Cellexus Biosystems (www.cellexusbiosystems.com). This reflects a change from a one-size-fits-all mentality. Combination modes may incorporate two different mixing strategies or combine perfusion with mixing, for example.
In May, Cellexus launched the CellMaker Lite2, a range of bioreactors that rely on aeration to mix the contents of the company’s disposable Cellexus Bag. “The reactor’s unusual shape allows for mixing with minimum energy input,” says Auton. Mammalian cells, and especially CHO cells, prefer low oxygen levels when growing at low concentrations, Auton explains. The geometry of the CellMaker Lite vessel, compared to a cylindrical reactor, allows for “slow stirring, with aeration purely from gas exchange into the headspace.”
As cell concentrations increase and higher oxygen levels are needed, the company’s CellMaker Hybrid system, introduced in July and having both airlift and stirred tank mixing technology, can switch to a mixed mode, combining airlift and stirred mixing in the HybridBag™. At high cell concentrations, the reactor relies on airlift alone.
“Most of the market is pushing toward high cell concentrations for use in inoculating large stirred-tank bioreactors,” says Auton. Using a passive aeration strategy characteristic of flask-based or rocking culture systems, it is difficult to get enough oxygen into the culture to achieve these high densities, he says.
In September, the company will release the CellMaker PLUS™, initially available in two size ranges, 1–8 liters and 10–50 liters. The system will include disposable sensors for dO2 and pH, dO2 control using both air and nitrogen, automated blending of CO2, and independent gas feeds to the headspace and integrated sparge tube.
Whereas current Cellexus systems all have a maximum working volume of 50 L, by the end of the year the company plans to introduce reactor bags ranging from 100 to 500 L, which, due to the vertical positioning of the reactor bags in the housing, will have a smaller footprint than a similar volume in a rocking system.
Appropriate Technical Resources (ATR; www.atrbiotech.com) has added the Cellexus CellMaker Lite2 to its U.S. distribution line. New to ATR’s Infors line of traditional bioreactor technology is the X-Controller microprocessor-based control system. It can control up to 16 parameters, linking up to three Multifors units and providing independent control of up to six vessels.
Wave Biotech, a parent of the rocking platform, single-use, bag-based Wave Bioreactor, was acquired in April by GE Healthcare (www.gehealthcare.com). Prior to the acquisition of Wave, GE’s presence in the cell culture arena focused primarily on its Cytodex microcarrier beads.
Ann O’Hara, general manager of GE Healthcare BioProcess, points to the growing emphasis on Lean Six Sigma in biopharmaceuticals production as a driving force behind GE’s move into the disposable bioreactor space. The company believes that bag-based culture systems offer the potential to minimize the three main forms of waste in manufacturing—time, cost, and defects (out-of-spec product).
Specifically, O’Hara points to the reduced time and cost associated with installation and operation of a facility containing single-use reactors, including elimination of the need to install, run, and validate clean-in-place/SIP systems. The potential to minimize product defects relates to consistency of results and reduced dependence on hardware quality over time, according to O’Hara.
With the acquisition of Wave, GE adds to its product offerings the company’s rocking bioreactor technology and a host of ancillary products for making sterile connections, transporting fluids pre- and post-process, and in-process analytical devices for measuring and monitoring conditions in the bag to facilitate process optimization.
Often, downstream purification equipment sits idle awaiting completion of large batches, says O’Hara. The use of 1,000-L to 2,000-L disposable bioreactors for processing small batches in parallel can help optimize utilization of downstream capacity in a production facility, she contends.
Sartorius’ (www.sartorius.com) most recent entry into the disposable bioreactors space, the Biostat® CultiBag RM, relies on rocking motion mixing technology licensed from Switzerland-based Wave Biotech AG (www.wavebiotech.net) and integrates it with Sartorius BBI controllers. The closed, bag-based, rocking systems include preinstalled, disposable, optical chemical sensors and are available in working volumes ranging from 0.5–1 L, 1–25 L, up to 50–100 L, and up to 300 L. The large bags incorporate scalable mixing and are contained in a stainless steel housing.
“Users will be able to operate the new systems in batch, fed-batch, or perfusion mode,” says Millie Ullah, Sartorius’ product manager in North America for disposable bioreactors. “We have disposable perfusion membrane technology for use with rocking devices, in addition to a number of external perfusion devices,” she adds. Sartorius’ BioWelder™ and BioSealer™ products are designed for sterile fusing and sealing of thermoplastic tubing.
“We are currently not looking to go beyond 300-L working volume with traditional rocking devices,” notes Ullah. “We will focus our larger-scale efforts on disposable stirred-tank bioreactor systems,” and plan to launch a range of systems by the end of 2007. These will initially be intended for cell culture applications and will have a stirring shaft and motor for mixing, with capacities up to 2,000 L.
The systems will incorporate disposable sensors for monitoring pH and dissolved oxygen, heating and cooling capability, over-pressure control (which shuts off the gas when the pressure limit in the bag is reached and then restarts the gas flow when the pressure drops back below the defined upper limit), and will interface with standard controllers. “The 2,000-L mark seems to be the current limit for single-use bag systems,” says Ullah. “The industry wants to drive volumes higher,” but that will require engineering enhancements to improve oxygen transfer, she adds.
Contract manufacturer Xcellerex (www.xcellerex.com) provides process development and GMP-manufacturing services for biotherapeutics and vaccines using its single-use bioreactor technology. Xcellerex also markets its 1,000-L working volume XDR™ disposable stirred tank bioreactor system, XDM™ stirred tank mixing systems, and PDMax™ high-throughput process development service platform.