Featured Article
Centrifugation forms an integral part of the laboratory workflow, with applications spanning the entire life science spectrum, from research to applied science and clinical studies. Centrifuges can be broadly classified into benchtop and floor-standing systems, with each category featuring a range of capabilities. As their name implies, benchtop centrifuges are compact and can be placed on the bench. These systems are designed to perform separations of small sample volumes of between 0.2 mL and up to several liters, and are mostly suitable for small-scale applications. Floor-standing models can typically accommodate a wide variety of sample containers, from 0.2-mL tubes to 2-L bottles or 500-mL blood bags, with some allowing up to 16 L of sample to be processed in a single run. This capability, combined with high-speed operation, makes these systems ideal for high-throughput applications, or protocols requiring high g-force levels.
With so many different types of centrifuges available, choosing the most appropriate one to meet the needs of an application can be challenging. Informed decisions should be driven by specific application requirements and take into consideration a number of critical factors.
Top considerations for choosing the most appropriate centrifuge
The key driving force behind choosing the right centrifuge is the sample type being processed. Questions to consider include: Is the sample container to be centrifuged a small tube, large bottle, or microplate? Is there a need for high laboratory throughput? The next step is to determine the specific capabilities of the centrifuge that will allow for the efficient and reliable processing of that sample type. These include the speed, g-force, and sample capacity of the system’s rotor, if a refrigerated system is needed, and whether fixed-angle or swinging-bucket separation needs to be performed.
Assess your requirements for rotor speed, g-force, and sample capacity
There are two types of microsample benchtop centrifuges that can process sample volumes of between 0.2 and 5 mL. Those that achieve a g-force of up to 17,000 × g are suitable for routine laboratory work, while models that reach 30,000 × g are ideal for high-end research. Larger-capacity benchtop centrifuges can accommodate sample volumes that vary from under 1 mL up to 4 L, meeting the processing needs of clinical, cell culture, bioproduction, blood separation, and microbiology applications. These systems can operate at g-forces of up to 50,000 × g.
There are several categories based on speeds and g-forces for floorstanding centrifuges that offer g-forces of up to 1,000,000 × g and speeds of up to 150,000 rpm. This range of platforms covers a wide array of applications, including cellular biology, drug discovery, and nanotechnology. For high-throughput blood banking and bioprocessing applications, the systems are designed to accommodate large-volume sample containers. These devices typically operate at a lower speed of between 5000 and 7000 rpm, and are ideal for blood separations, cell harvesting, and vaccine production.
Do you need refrigerated operation?
Clinical and bioprocessing laboratories commonly handle temperature-sensitive samples, such as vaccines and biospecimens, the quality and integrity of which can be compromised by heat generated during centrifugation. These facilities should invest in refrigerated models, which offer a cooling capability that protects samples from degradation due to heat exposure. Some refrigerated centrifuges can reach a temperature as low as –20 °C, although 4 °C is normally low enough for most heat-sensitive samples.
Nonrefrigerated centrifuges are ideal for use with nontemperature-sensitive samples, such as those processed in laboratories performing routine research applications. These devices work by drawing in room temperature air during spin cycles to ensure that ambient conditions are maintained and sample exposure to excessive heat is minimized.
Does your application require fixed-angle or swinging-bucket rotors?
Due to the lack of moving parts, fixed-angle rotors can tolerate an increased centrifugal force. As such, these systems are suitable for processing biological macromolecules such as RNA, DNA, and proteins, which can only be separated when a very high g-force is applied.
Compared to fixed-angle rotors, swinging-bucket rotors offer a higher sample capacity of up to 16 L, making them well-suited to high-throughput applications such as batch harvesting of whole cells from growth media, large-volume tissue culture processing, and high-capacity blood collection tube processing. However, swinging-bucket rotors are generally suited for lower g-force applications.
Tips to ensure sample safety
Preserving the safety of samples is of utmost importance, as sample contamination, degradation, or loss will compromise research outcomes.
Protect your samples from incoming particulates
Biocontainment rotor covers can effectively protect samples from contaminating particles, while high-quality sample containers that have been specified for use with the particular rotor will have a lower risk of failure. Prior to use, the sample tubes should be checked to ensure there are no signs of crazing, cracking, or pitting, which could lead to breakage and sample loss during use. An additional security measure is O-ring sealing mechanisms, which are placed between the tube and cap surfaces to enhance the seal and ensure leak-proof performance.
Install your rotors carefully
Care should be taken when installing rotors, as increased rotor incidence, and subsequent sample leakage, is usually due to improper installation. Some systems feature an automated rotor-locking capability, which eliminates the potential for improper installation. In addition, centrifuges that can automatically identify the rotor and instantly adjust speed and g-force in line with the rotor’s specifications will ensure that both the sample containers and the rotor will not be exposed to unnecessarily high pressure, which could lead to their failure.
Always implement best practices
Laboratories undertaking clinical, cell therapy, and molecular diagnostic research, in particular, are under constant pressure to demonstrate best practices to safeguard sample safety. Thus, these facilities should be using centrifuges that are certified safe for the designated use. Systems can be equipped with data collection software platforms and barcode readers capable of reliably and safely storing sample and patient information for enhanced traceability in compliance with regulatory requirements. This is particularly important when using centrifuges that offer remote monitoring capabilities. Sometimes, regulated protocols require users to prove that centrifugation has been performed correctly, and to do so relevant documentation will need to be generated.
Tips to ensure user safety
As with any application in which equipment poses ergonomic risks, and samples are potentially hazardous, user safety is as much of an issue as sample safety.
Err on the side of caution
In the event of tube breakage, pathogens may be released within the centrifuge and aerosolized into the laboratory environment, where they could contaminate the surrounding surfaces and equipment, or be inhaled by laboratory personnel, posing a health hazard. This risk can be effectively mitigated using rotor covers, which should ideally be transparent so that tubes can be inspected and any leakage identified prior to opening.
Look after your rotors
A lubricated O-ring typically would be securely placed on each rotor to tighten the seal and further protect against sample leakage. Since many detergents and disinfectants used to clean the rotor can remove the lubricant, which protects against corrosion, the O-ring must be relubricated frequently. O-rings tend to degrade after repeated cleaning and autoclaving, and should be replaced once they show signs of cracking or stretching.
Conventional aluminum rotors also need to be regularly inspected because they are prone to stress corrosion cracking. However, high-performance rotors made from carbon fibers eliminate this problem, since they are highly durable, long life, lightweight, and corrosion resistant.
Adhere to ergonomic working practices
Working with large floor-standing models can put strain on users who manually open and close the centrifuge door and rotor lid and lift the heavy rotors in and out of the system. These activities need to be performed repeatedly during a shift, potentially leading to fatigue or repetitive stress injury. To ease the process, newer systems are equipped with automatic doors and rotor lids, which can be opened and closed at the push of a button, saving time and effort. In addition, carbon fiber rotors are much lighter than aluminum models, being easier to lift even when they are fully loaded. Modern floor-standing centrifuges are also a smaller size than previous systems, making them more accessible to users of any height.
Ensuring quality with every spin
Provided that all the right centrifugation capabilities have been matched to the requirements of a specific application, and the appropriate sample and user safety measures have been implemented, the next step is to select a suitable separation protocol.
Optimize your protocol
There are systems that are capable of automatically adjusting run times to compensate for variations in acceleration caused by differences in a full or partial rotor load. This ensures precise, reproducible separations run after run, by applying the same total centrifugal effect to all samples. When there is a need for minimal sample resuspension, cleaner interfaces, and maximized product yields, it is best to opt for a centrifuge that offers different acceleration and deceleration profiles, allowing for customized runs.
Ensure proper care and maintenance
Implementing care and maintenance best practices ensures the centrifuge will remain highly functional and deliver optimal results for a long time. Properly installing and balancing rotors, in particular when they are not fully loaded, will reduce vibration and subsequent wear of the rotor during runs. Thorough cleaning of centrifuges and rotors after each run also ensures longevity, while safeguarding the users and the laboratory, especially when biological or radioactive materials have been processed. Routine maintenance should always include checking the air filters, adjusting door latches, and making sure all sensors work well. Carbon fiber rotors are resistant to corrosion that could be caused by disinfectants and cleaning solutions and, as such, exhibit increased durability in comparison to aluminum rotors.
Conclusion
Centrifugation has changed substantially over recent years. Laboratories can benefit from advances in functionality and performance, as well as ergonomics and ease-of-use. More modern systems have been designed to accommodate larger sample volumes, and operate at higher speeds and g-forces to support varying processing needs. Sample and user safety is ensured, while documentation capabilities are available in line with various regulatory requirements. Choosing the best centrifuge is essentially determining the application and sample types to be run, and matching those requirements to centrifuge speed, g-force, and capacity.
Hugh Tansey is senior business director, Centrifuges, Laboratory Equipment Technologies, Thermo Fisher Scientific, 168 Third Ave., Waltham, MA 02451, U.S.A.; tel.: 781-622-1000; e-mail: [email protected]; www. thermofisher.com