03 July 2020
The right approach to biological safety cabinets, and collaboration between engineers and those who will operate the equipment, is crucial to preventing cell-culture contamination.
Cell-culture contamination is a common challenge facing cell-culture laboratories, with consequences that range from minor to devastating. Every effort must be made to protect the integrity of cell cultures, both for the experiments that are being performed in the laboratory, as well as to prevent problems later on, downstream. When selected and designed correctly, biological safety cabinets (BSCs) play a critical role in protecting cell cultures, laboratory personnel, and the environment.
Selecting a BSC requires careful consideration of many factors, including the performance criteria important to the laboratory in which it will be used, and the service support that the vendor will provide following installation. In recent years, BSC technology has improved significantly, and vendors are offering more features that allow users to make better decisions, such as enhanced monitoring features (e.g., interfaces that provide a visual depiction of airflow in real time) to help operators maintain an aseptic laboratory environment.
However, the efficacy of a BSC is only as strong as its weakest link in a complex and multi-faceted operating process. This article summarizes the key criteria for assessing BSC performance so that it prevents contamination.
The wide variety of potential biopharmaceutical contaminants and their sources show just how vulnerable cell-culture laboratories are. Contaminants may be classed as biological (e.g., bacteria, fungi, mycoplasma, viruses), chemical (e.g., endotoxins, detergent wash residue, trace concentrations of metal ions, chemical disinfectants), or physical (e.g., fluorescent and ultraviolet light, radiation, vibration) and can be introduced in a variety of ways (e.g., as airborne particles, infected cell lines, contaminated water, or during routine maintenance or operating procedures) (1). Some contaminants require a very proactive approach to detection and management, such as regular quarantine and testing to help avoid the introduction of mycoplasma-infected cell lines. The type, extent, and frequency of contamination determine the severity of the consequences, which drain resources, whether time, samples, or reagents. Repeating work and reinvesting in those resources exacerbate losses, and subsequent experiments typically become more costly as additional precautions are incorporated into their procedures. However, these costs pale when compared with the long-term implications of undetected contamination, where misidentified cell lines and erroneous data can compromise reproducibility and lead to paper retractions (2).
Contamination control is complex and challenging, particularly when laboratory environments are constantly changing, with various components being replaced based on seasonal changes in building ventilation requirements. Efforts to protect cell cultures and experiments must, therefore, be multidimensional and thorough, and BSC use is no exception. BSCs protect the product, environment, and operator through two primary mechanisms of containment: precise control of airflow and high efficiency filtration, which purifies the air that enters the BSC, maintaining an air barrier between operators and their work. High efficiency particulate air (HEPA) filters remove microscopic particles from the air, which is then recirculated within the BSC and discharged elsewhere, depending on the design—into the room or a building’s exhaust system. In Class II Type A2 BSCs, the most common class, approximately 70% of the air is recycled and pushed back into the BSC work area; the remaining 30% is exhausted through the HEPA filter.
In addition to understanding airflow dynamics, the use of BSCs to prevent contamination involves the thoughtful application of scientific knowledge and an integrated approach. Best practices from the quality control field must be applied to reduce or eliminate variation in output. In practice, this requires examining every movement and process and taking steps to support the consistent execution of those processes. For example, designated spaces might be marked out for specific items in a supply tray, so the operator can quickly confirm that he or she has everything required to perform the task at hand. It is easy to underestimate the benefits of these simple steps, but there are significant benefits to supporting the consistent execution of precise processes. Simplified workflows help limit operator distractions, which is particularly important to maintaining an aseptic environment.
Traditionally, the industry has relied heavily on regular BSC testing and certification following purchase and installation in order to respond to gradual filter loading. With earlier models, the gradual build-up of contaminants captured in the filter would result in a subsequent reduction in air velocity, compromising the BSC’s ability to capture contaminants. Design efforts have been directed at overcoming this threat to precise airflow and improving monitoring systems. Modern BSC design features include:
When selecting a BSC, it is important to consider the specific processes and applications in the laboratory in which the cabinet will be used. For example, some laboratories require additional connections for the BSC interior, such as power and data, or piped-in media such as combustible gas. As cramped conditions compromise processes and contamination protection, laboratories with extensive equipment assets would benefit from larger BSCs. While the most common width of a BSC is approximately four feet, other sizes can accommodate smaller spaces, more equipment, or environments in which two people work concurrently in one space.
In addition to performance criteria and monitoring features, safety is another important component to consider. Laboratories working with volatile chemicals or gases may require the installation of a canopy/thimble connection to the top of their BSC, to allow exhaust to be directed to a designated channel. Specialized BSCs are available for those who must contain dangerous substances, such as those preparing hazardous drugs.
To ensure optimal airflow, filters and other systems must be validated and shown to function as vendors claim they do. BSC testing and certification must be performed at the prototype stage in a recognized validation laboratory and then again at the manufacturing factory where the cabinet will be used. This practice increases the likelihood that the BSC will remain effective in preventing cell-culture contamination, because it will permit any design or manufacturing issues to be flagged early. Once the BSC is installed in a laboratory, testing and certification will be implemented by specially trained inspectors whose experience and skills are regularly assessed, before use and then at least annually thereafter.
Prototypes of each BSC design are assessed according to NSF/ANSI 49 (National Science Foundation/American National Standards Institute 49) (1), an internationally recognized standard that assesses quality, compliance, and safety. Assessment examines a wide range of parameters, including equipment design, construction, performance, product and environmental protection, reliability, durability, cleanability, noise level and illumination control, vibration control, and electrical safety (2).
Once the individual BSC arrives in the laboratory, it must be certified on site and periodically thereafter to ensure it is operating as required and that it functions well within that specific laboratory. Although a thorough assessment process can help assure that the BSC will perform properly, the responsibility for performance and cell culture protection ends with the buyer. Following design validation and performance verification at the manufacturing facility and periodically at the laboratory, the performance of the BSC and level of cell culture protection will largely depend on correct use by system operators.
Competent and knowledgeable BSC operators are critical to contamination control, because their actions directly influence airflow and the movement of contaminants. Taking an active approach to BSC operation, the operator should arrange for regular certification of the cabinet and ensure he or she has understood the test results—in particular, those which might require that procedures be altered or improved (3). This active approach must be intertwined with various elements of expertise, including the physical operation of the BSC machinery, interpretation of alarms, and an understanding of the controls, displays, and principles of operation.
Often, problems with BSCs arise from incorrect assumptions and poor practices. In some cases, staffers may not realize the consequences of actions, such as silencing an alarm, which can prevent understanding of risks, preventing identification of any underlying root causes of potential contamination. Other examples of poor practices include failing to arrange materials optimally within the BSC, and too many quick and unnecessary movement of hands and arms near the equipment, which call for limiting the number of times users reach in and out of the BSC. Another frequent cause of problems is failing to wipe down the cabinet’s interior surfaces before commencing work.
Processes within the BSC should be optimized by a process designer together with an operator or technician that will be performing the required processes. The process designer must develop a clear understanding of what is needed for the laboratory’s operations and procedures and create a detailed process workflow so that every operating step has been optimized. Activities, equipment, and resources should be arranged so the workflow sequence can be followed consistently using aseptic best practices.
Streamlining workflows reduces the room for error and reliance on the operator’s attention and should be used to examine every aspect of the process. For example, in the case of decontaminants, the process designer would consider the type, bottle size, and frequency of preparation required to meet lab needs. In the end, system efficacy is only as strong as its weakest link, and robust manufacturing, validation, installation, and service infrastructure is the foundation required for effective laboratory contamination control.
1. NSF, NSF/ANSI Biosafety Cabinetry Certification, nsf.org (2020).
2. C.K. Lincoln, M.G. Gabridge, Method Cell Biology 57, 49–65 (1998).
3. S. Horbach, W. Halffman, PLOS One, 12 (10) (2017).
David Phillips is senior global product technology specialist for Thermo Fisher Scientific’s Clean Air division.Print
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