March 15, 2008 (Vol. 28, No. 6)
Angelo DePalma Ph.D. Writer GEN
Downstream Is Still Not Single-Use Equipment Friendly, but Firms Are Making Inroads
As the disposables industry consolidates through acquisitions, vendors are combining critical technologies to create products that are more functional and versatile.
Best known for its cell culture and media products, Invitrogen is well positioned to exploit the industry’s need for disposable bioprocess equipment. “Disposables have become a forward-going focus,” says technical area manager Paul Clark. The company’s disposable products range from simple media bags for storage and transport to bioreactor bags stocked with custom media.
Invitrogen’s Gibco® SynerGy™ line of bags include customizable, prefilled bags available in 5-, 10-, and 20-liter sizes. The company’s Universal bags, which according to Clark satisfy 90% of the needs of R&D organizations, are prefilled with any of Invitrogen’s 18 off-the-shelf media. Some are specialty media, but many customers specify classical D-MEM and RPMI classic media.
The Universal line includes bags from 500 mL to 1,000 L in size filled with custom media, with an option for connecting to a disposable mixing system. Additionally, Invitrogen offers cell-culture bags from GE Wave in 10- or 20-liter sizes filled with any custom or catalog media.
From Clark’s perspective, the most significant trends in single-use bioreactor bags are the use of a single film or resin across all sizes, single-layer film construction, and bags with greater optical clarity. “Single-resin product lines allow scale-up without the need to validate new material for biocompatibility,” he notes.
Historically, bioreactor bags are constructed by layering several resin films, each with a unique barrier and mechanical properties. This method of fabrication was a carryover from the medical industry, where plastic bags have been routinely used for decades. Bags extruded in three separate layers result in poor contact between layers and hence, the pooling of media. Invitrogen utilizes single-web film, whereby all three layers are coextruded in one composite structure.
Similarly, Thermo Fisher Scientific has leveraged its position in cell-culture media and nutrients through its Hyclone unit into a robust business in disposables. It began with the manufacture of single-use bags for shipping media and has evolved into providing complete upstream processing systems based on the company’s BioProcess Containers™—sterile, single-use plastic containers referred to as smart-bags.
The key product line for cell culture includes the Thermo Scientific HyClone SUB™ (single-use bioreactor) and SUM™ (single-use mixer). The SUB consists of a BioProcess Container, stainless steel outer vessel for support, a heating jacket, and a disposable mixing mechanism. SUB systems are available in 50, 250, and 1,000 L sizes. Bags of 100 and 500 L will be introduced at “Interphex 2008.”
With protein titers rising and batches generally getting smaller, the need for large stainless steel bioreactors is falling. Rick Sullivan, vp, marketing for Thermo Scientific HyClone products, calls fixed-tank, 20,000-liter bioreactors dinosaurs.
Sullivan believes that personalized medicine and high-titer vaccines are trends that drive the use of disposable upstream equipment. “Many biologicals coming to market will be serving rather small patient populations and therefore, do not require huge manufacturing capacity.”
Sullivan also notes the need among bioprocessors for consistency and continuity of process-fluid surface areas from experimentation through development and manufacturing. Top disposables vendors like Thermo Fisher Scientific guarantee that contact surfaces are the same no matter what the scale, which reduces the need to validate for leachables and extractables.
Single-use downstream equipment is nowhere near as prevalent as upstream, mainly because of the cost of chromatography resins. One could argue that, when a combined buffer and reagent is utilized, time spent in bed packing and regeneration as well as cleaning/cleaning validation are excessively high, discarding the stationary phase might be less expensive than regenerating it. Contract manufacturers are already beginning to think along these lines, especially for extremely time-sensitive production runs.
One area where single-use, downstream products are now flourishing is at the polishing step, which traditionally uses anion-exchange chromatography. In many situations, products like Pall’s Mustang line and Sartorius’ Sartobind anion-exchange membrane-chromatography systems can save significant amounts of time and effort.
Polishing often involves the removal of less than a few hundred grams of contaminant from several thousand liters of process fluid containing tens of kilograms of product.
In this separation, the mass of adsorbent required to bind the contaminant is relatively low, typically less than 5 L, yet the throughput requirements dictate that an oversized chromatography column would often be used simply to achieve the volumetric flow in a reasonable process time. Membrane chromatography enables effective operation at high volumetric flow rates, typically 30–60 times faster than that supported by a packed column of similar volume.
“One big advantage is that membrane-chromatography systems, for example, the Mustang Q XT5000, look and behave a lot like filters,” says Russell Jones, global product manager, membrane chromatography, at Pall. “You don’t need to be an expert chromatographer to use them. Simply plug them into the process to remove trace contaminants. The units also provide some viral clearance.”
Membrane-chromatography cartridges cost approximately the same as the ion-exchange media that a processor would typically use for polishing. Substantial savings accrue from the time required to pack and clean the column and to validate these operations, as well as in buffers used for conditioning, eluting, and cleaning.
Membrane chromatography used in polishing steps are designed for single use and are almost always used in that fashion. “They are, however, ion exchangers, and could be used for capture as well,” points out Peter Levison, Ph.D., technology development director at Pall’s Portsmouth, U.K., facility. In those situations, processors may decide to clean and reuse membranes.
Accurate, inexpensive sensors have been used by numerous industries for at least fifteen years. Some of these devices are now making their way into disposable bioprocessing. PendoTECH sells a microelectromechanical pressure sensor suitable for upstream applications. Another firm, Fluorometrix has entered an agreement with Sartorius to supply its disposable process bags with disposable sensors for detecting multiple parameters.
SciLog claims to be the first vendor to supply smart, disposable sensors suitable for bioprocessing. Although they are designed for single use, SciLog’s sensors may be cleaned/revalidated and reused, depending on the application, with no loss of performance, according to the company.
SciLog develops sensors for conductivity (under the SciCon® brand), pressure (SciPres®), and temperature (SciTemp®). Like most industrial sensors, the company’s are accurate and reliable, but these devices are also smart. Sensors are precalibrated and hold serial number, lot number, and calibration offsets in memory. “They’re almost prevalidated,” comments company president Juliette Schick, Ph.D. While validation is still required, all relevant information is contained in the instrument.
SciLog’s sensors are flow-through devices, meaning the sensor element resides in the flow path that includes a fitting of appropriate dimensions. Polysulfone construction assures compatibility with bioprocess fluids. “What you get is a sensor already in a fitting that you can insert into any flow path,” notes Dr. Schick.
Applications include fluid handling and generating operations such as chromatography, tangential flow filtration, and dispensing/filling. Chromatographers will typically monitor conductivity, pressure, and in some cases, temperature.
SciLog’s philosophy is that disposability on its own is good, but coupling it with automation is even better. “Interest in disposables is accelerating,” says Dr. Schick. “However, you can get the best cost effectiveness when you pair disposability with automation. It’s a whole package.”
Design and End Use
While laboratory and production personnel frequently purchase off-the-shelf equipment and that is certainly possible for disposable process equipment, some applications demand a bit of tweaking.
Primarily a developer of diagnostic instrumentation for medical systems, Invetech recently moved into bioprocess applications to support development of vaccines, cellular therapeutics, and personalized medicines.
Personalized treatments present processors with a conundrum. Manufacturing must be GMP-compliant, but batches are small and numerous. Invetech engineers design and integrate disposable systems to make disposable manufacturing possible without hiring dozens of process engineers or classifying several buildings’ worth of classified space.
“One Class-C room can generally handle as many patient-derived products as we need,” says Ian Fitzpatrick, manufacturing manager.
Invetech often begins with off-the-shelf disposable products, modifies them with sterile single-use bags, tubing, and connectors, then attaches them to controllers to achieve a high level of automation.
Since most of its bioprocess systems are custom-designed, stock disposable equipment must often be modified because vendors are rarely interested in supporting early-stage projects where the design changes frequently. “They’re not set up for a different design every two weeks,” Fitzpatrick notes.
Laureate Pharma is an active contract biomanufacturer that depends in large part on disposable equipment to support its mammalian cell-culture operations.
Laureate generated 15–20 products last year, about 10 kg of protein, in about 30 batches for a dozen customers. “We simply could not be this versatile without disposables,” remarks Larry Mullen, director of manufacturing. “We employ disposables everywhere we can in the manufacturing process. Our culture media comes as 1X liquid formulations prefilled into bags, and we use bags for all buffers and intermediate product holds.” Downstream, disposable products include disposable virus filters from Sartorius and Pall.
Laureate, at times, uses large stainless steel bioreactors. (Its largest holds 2,000 L of working volume.) It is, however, investigating the possibility of switching to Hyclone’s SUB products for 250 and 1,000 L batches under GMP and 50 L for pilot runs.
Vendors of disposable process equipment generally do a good job of providing what industry needs, reports Mullen. One area where improvement would be appreciated is in the sizes of disposable filtration cartridges. “They tend to be on the small side and sometimes when you scale-up you need multiple units of fully disposable products.”
PacificGMP is another CMO that relies heavily on disposable cell-culture technology including the Wave single-use bioreactors, to produce antibodies, vaccines, and other biologicals.
As a midsized biomanufacturer, Pacific runs between 25 and 40 batches per year at reactor volumes up to 500 L. “The disposables give us such an incredibly flexible platform,” says Gary Pierce, founder and CBO. “If a production yield doesn’t meet expectations, we can rapidly scale up by adding more reactors without being tied down to a steel-pipe infrastructure.”
Disposables provide companies like Pacific GMP the ability to jump rapidly into projects at any stage, from early development through manufacturing, and the knowledge that single-use solutions exist all along the way. Pierce noted that Invitrogen sells Wave bioreactors filled with preformulated media. “It eliminates a step. In the past we would use 20 one-liter bottles to get 20 liters of working volume. Now we can order a single bag.”
Pierce thinks that feedback between users and vendors could be a bit better, especially on projects with special needs but he believes that “vendors are doing a good job of supplying bioprocessors with innovative products.”