The centrifuge, one of the most common lab instruments, is indispensable for separating components of a solution. Frequent lab tasks, such as pelleting cells from suspension, spinning down precipitated nucleic acids or separating components of blood, are accomplished mainly by multipurpose centrifuges—as opposed to microcentrifuges (or microfuges, which typically spin up to 2-ml tubes) and ultracentrifuges (or ultrafuges, which spin samples at greater than 100,000 x g force).
Multipurpose centrifuges come in floor-standing and benchtop varieties. Floor models offer lower speeds (up to about 7,000 x g force) and accommodate sample volumes ranging from those used in routine separation of mixtures to those of large-scale cell-culture preparations from bioreactors. Benchtop centrifuges spin at higher speeds (up to about 25,000 x g force) and offer convenience, space efficiency and a range of features, depending on lab needs. Advances in these lab workhorses are discussed here, as well as important features to consider when choosing a multipurpose centrifuge.
Rotors and sample tubes
An important consideration is a centrifuge’s rotor, along with adaptors that accommodate different sample tubes, bottles and microplates. There are two main types of rotors. Swing-out (or horizontal, or swinging-bucket) rotors spin at relatively lower speeds and are mainly for cell-culture applications or for separating the components of blood (i.e., removing red blood cells from plasma). Fixed-angle rotors, which hold sample tubes at a specific angle, can spin samples at higher speeds than swing-out rotors and are used for many cell and molecular biology applications.
Adaptors make it possible to spin a range of sample tube volumes (from 1.5-ml tubes to 2-L bottles, depending on the rotor/adaptor combination), as well as microplates. Labnet also offers a dedicated microplate rotor, which costs less than a swing-out rotor with microplate adaptors. “This is a good option for a dedicated microplate centrifuge, where it might be overkill to invest in more than what you need,” says Peter Will, product manager at Labnet International (a Corning Life Sciences company).
Many vendors offer benchtop centrifuge models that can accommodate a full range of tube sizes, from 1.5-ml tubes up to different maximum volumes—usually 750-ml bottles. Among the most common sample tubes are the 15-ml and 50-ml conical tubes used in cell-culture work. Eppendorf will soon release the 5920R, a multipurpose benchtop centrifuge that spins from 0.2-ml samples up to 1-L bottles, as well as microplates. The ability to spin 1-L bottles (which are often only spinnable in floor-standing models) is useful for bioprocessing applications, large-scale cell culture or growing bacterial cultures.
Advances have also been made in the materials used to make rotors. Some rotors have special outer coatings that make them resistant to chemical corrosion over time. Rotors made of carbon fiber, such as Thermo Scientific™ Fiberlite™ rotors, are lighter and more resistant to chemical corrosion and structural fatigue than traditional metal alloy rotors. “Carbon fiber vastly increases flexibility and the types of applications that can be achieved,” says Hugh Tansey, global product director of centrifugation at Thermo Fisher Scientific.
Changing rotors can be unnerving considering their high operating speeds. Some vendors offer quick rotor-exchange features to make this process easier while maintaining safety. For example, the Thermo Scientific™ Auto-Lock™ rotor exchange enables users to switch rotors “in as little as three seconds with just the push of a button,” says Tansey. “The centrifuge can change its application setup many times a day within seconds, which is a critical advantage for a busy lab.” NuAire’s patented ClickSpin technology also enables quick, easy and tool-free rotor changes. Another safety feature, Beckman Coulter’s ARIES Smart Balance Rotor technology, automatically corrects for rotor imbalances and is available in Beckman Coulter’s Allegra® line of multipurpose centrifuges.
Footprint and capacity
Two factors affect a centrifuge’s footprint—capacity and refrigeration.
A current trend in centrifuge technology is to increase an instrument’s capacity but not its overall size.
For example, Corning’s new rotors accommodate more tubes with the same centrifuge footprint. “People are looking to spin more tubes without having to go to a floor model or give up more bench space,” says Will. Labnet’s new fixed-angle rotor holds 10 50-ml conical tubes, whereas the former model held only six, for instance. In addition, a new swing-out rotor gives more capacity by increasing sample volume sizes—it holds four 750-ml, instead of 500-ml, bottles.
NuAire offers the largest capacity centrifuge available for the footprint, according to Anthony Locatelli, centrifuge product manager at NuAire; the company hopes this will expand its reach into clinical applications. “Blood centers and hospitals would benefit from the features and robustness of this centrifuge and be able to use these as workhorses,” says Locatelli.
Indeed, centrifuges designed for clinical applications are available in a range of footprints and capacities. Abbexa’s new Clinical Centrifuge for clinical, diagnostic, analytical and veterinary labs is a low-noise benchtop centrifuge with adaptors for 2-, 5-, 7- and 19-ml blood-collection tubes. At the other end of the spectrum, Thermo Fisher Scientific offers floor-model centrifuges for handling large volumes in bioprocessing and blood preparation—“up to 16 liters in bioprocessing and up to 16 500-ml blood-bag capacities for blood banking,” says Tansey.
Refrigeration
Refrigerated centrifuges have a slightly larger footprint than nonrefrigerated models because most house a built-in compressor, which increases their footprint width by several inches. The compressor switches the cooling on and off as needed to regulate the temperature of the centrifuge bowl (much like your refrigerator at home).
Eppendorf’s new 5920R benchtop centrifuge, however, uses a new cooling technology. Instead of a compressor, it utilizes an injection valve to regulate the pressure of refrigerant in the cooling system (much like the way your car engine regulates gasoline flowing to the engine). “This is important because the refrigerant needs to have a certain flow rate to give optimal performance,” says Matt Lieber, product manager in centrifugation at Eppendorf. Injection valve-mediated cooling can result in a steadier temperature in the centrifuge bowl compared with compressor-mediated cooling, which can vary by several degrees per hour, according to Lieber. “If the bowl fluctuates a few degrees, what’s happening to your samples?” he says. Temperature-sensitive samples may benefit from tighter temperature regulation.
Additional features to consider
Many other centrifuge features can smooth your workflow. Touchscreen displays on the NuWind, for example, make for easier and more intuitive use. NuAire centrifuges have an InSight Electronic Control Center—the electronic brain of the instrument—that monitors usage, indicates when preventative maintenance is due and tells the user when the theoretical lifetime of accessories is about to expire.
Built-in noise reduction is another helpful feature—especially for benchtop models that share your lab space. “The last thing you want is a high-pitched noise in your ear, distracting you while you’re trying to work at your desk in the lab,” says Lieber. Noise is the result of vibration, so Eppendorf uses shock absorbers and rubber plating to dampen vibration in the 5920R. NuAire’s NuWind was also built with “vibration shock absorbers to remove the vibrations and make [the instrument] extremely quiet,” says Locatelli.
Ergonomics may also be a factor, particularly in big labs where centrifuges might be used by researchers of multiple heights. A key characteristic here is access height, which is the distance from the benchtop to point of the centrifuge, where you reach in to access the rotor. Eppendorf’s 5920R minimizes access height by building part of the centrifuge bowl into the lid.
Centrifuges continue to evolve technologically while remaining the stalwart workhorses that researchers depend on. Wireless connectivity is likely to become more common, so the instrument can notify a remote user of run status or problems encountered. Will also suggests that in the near future, all centrifuges may have remote service capabilities “where we might be able to dial into the unit and run a remote diagnostic to determine the cause of a failure.” Today’s centrifuges are becoming more versatile than ever, with even more bells and whistles coming soon to assist researchers with their separation tasks.
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