Brent Bushnell 

One of the hottest trends in bioprocessing today is single-use systems. These disposable systems may replace many types of expensive, stainless steel bioprocessing equipment such as filter housings, hold tanks and transfer lines with disposable filters, bioprocessing bags, and tubing sets. Single-use systems offer many benefits over stainless steel equipment, including faster implementation, reduced validation requirements, and ultimately, cost savings. Finally, single-use products can improve overall production yields as part of a manufacturer's integrated contamination-control strategy. 

This article focuses on how single-use systems effectively control three potential sources of common contamination: cross contamination, microbial contamination and biologic contamination of the process facility. Each contamination type is discussed in detail with specific ways single-use systems may be used to address them. 

In bioprocessing, the potential for cross contamination occurs when process equipment is used to produce more than one protein. Unwanted protein contamination may reduce production yields by requiring additional purification steps, or in the worst possible case, proteins that copurify may result in potentially fatal treatments. 

To prevent cross contamination in stainless steel processing equipment, bioprocess engineers must develop and validate clean-in-place (CIP) procedures that remove all residual proteins between processes. CIP cycles typically use large quantities of caustics, acids and water-for-injection (WFI), and they require regular testing to verify effectiveness. Making simple equipment changes such as adding a new valve may require partial or complete CIP revalidation, increasing time and labor costs.  

Single-use systems can reduce or eliminate the need for CIP by starting with new materials of virgin carbon and silicone polymers. Single-use component and systems manufacturers typically test bacterial endotoxin levels to ensure their products do not introduce harmful pyrogenic proteins into a bioprocess. Since tubing, connectors, bags and filters are used only once, proteins from other processes cannot be introduced. 

One of the greatest threats to bioprocesses is microbial contamination. Once microbes, such as bacteria, yeast, and fungi, enter the nutrient-rich bioprocess environment, they quickly overwhelm mammalian cell cultures, using all available nutrients and secreting unwanted and harmful proteins such as endotoxins. A bacterial contamination can destroy product valued at millions of dollars in a matter of hours. 

To prevent this contamination, manufacturers dedicate enormous resources to developing a sterile bioprocess environment and maintaining aseptic conditions during production and purification. Sterility can be achieved via heat, irradiation, or chemical agents. Bioprocess equipment is primarily sterilized by heat in the form of pressurized steam: autoclaves are used for small scale equipment and steam-in-place (SIP) processes are used for medium and large scale systems. As with CIP, SIP processes must be validated to ensure sterility. 

Single-use systems are sterilized after assembly by irradiation, from cobalt 60 gamma source or e-beam, or using ethylene oxide (EtO) gas as a chemical sterilant. A variety of techniques are used to aseptically connect presterile single-use systems together or to process equipment. Integrated single-use filters may be used to filter sterilize at the point of connection. For quick connectors such as luer fittings or couplings, aseptic connections may be made in Class 100 laminar flow hoods using proper aseptic techniques. For connections in an open or Class 10,000 process environment, tubing welders and aseptic connecting devices such as the "Kleenpak Connector" and "BioQuate DAC" allow single-use to single-use connection. SIP connectors like the "Steam-Thru Connection" effectively control microbial contamination while allowing an aseptic flow path to be created between single-use systems to stainless steel. These systems would be presterilized prior to being introduced into the process. 

Maintaining a clean process facility can be as critical as maintaining an aseptic bioprocess environment. Biologic contaminations within process facilities increase the risk of microbial contaminations within bioreactors and other process equipment. In addition, biologic contamination may pose a health risk for bioprocess technicians, especially in viral vaccine-manufacturing facilities. 

Bioprocess technicians employ a number of systems to maintain cleanliness in Class 10,000 areas. These include cleanroom gowning, regular contamination monitoring and cleaning, rigorous pass-through procedures, and specialized cleaning methods following facility maintenance or suspected contamination.   

Single-use systems provide an excellent means of preventing external contamination from entering a bioprocess facility; however, preventing biologic contamination from bioprocess equipment requires both a sterile connection and an aseptic disconnection. This is an ideal application for the use of single-use SIP connectors that use an SIP cycle to make a sterile connection to the equipment. A second SIP cycle can be used to make a sterile disconnection that minimizes suite contamination when removing the single-use system from process equipment.  

Controlling contamination in bioprocessing facilities is critical. Single-use systems not only offer manufacturers reduced validation, cost savings, and increased production yields, these systems also are an integral part of reducing or eliminating the risks of cross contamination, microbial contamination, and process facility contamination. Specific contamination concerns can be addressed in existing processes by integrating appropriate disposable technologies along with traditional stainless equipment, or in certain cases are best addressed by a redesign to a complete single-use system. These approaches are not limited to upstream or downstream processes, new or existing facilities; the benefits of advanced contamination control can be realized throughout the manufacturing operation.  

 is a Bioprocessing Business Unit Manager at Colder Products Company; and 

 is a Bioprocessing Sales Manager at  Colder Products Company.

Articles

The authors focus on how single-use systems effectively control three potential sources of common contamination: cross contamination, microbial contamination and biologic contamination of the process facility.