Centrifuges: Adding Safety and Versatility to High-Speed Separations.

When it comes to common technology in a laboratory, centrifuges rise toward the top of the list. If a scientist wants the liquid at the bottom of the tube, but it’s distributed along the sides in droplets, centrifuge it. Need to separate the cells from a suspension? Centrifuge it. This tool also comes into play in a wide range of other workflows, including purifying DNA, RNA, or proteins. As Dr. Lars Borrmann, group marketing manager at Eppendorf (Hauppauge, NY), says, “It’s very common technology.”

To meet so many applications, centrifuges come in many forms. Microcentrifuges can spin 1.5- to 2-milliliter tubes at speeds that provide 20,000 times the force of gravity (g). Molecular biologists use this kind of centrifuge when purifying nucleic acids or proteins. Many researchers use a multipurpose centrifuge. These come in benchtop or floor models and provide considerable versatility. For example, it might spin tubes that range in volume from 1.5 milliliters to 1 liter. These can even spin multiwell plates. For faster spinning, researchers use an ultracentrifuge, which can spin tubes at speeds that generate 100,000 to 1,000,000 x g. “This could be used to separate proteins based on their mass,” says Borrmann. So-called flow-through centrifuges provide nonstop spinning, which comes in handy when someone needs to spin down large volumes—up to a few thousand liters—from a bioprocessing fermenter or tank. “You can spin the entire liquid through,” says Borrmann, “and it separates the cells from the liquid in a continuous flow.”

Increasing comfort

Anyone who ever used an ultracentrifuge years ago knows that “easy to use” did not describe that device. After loading tubes in the rotor, you screwed down the top; it felt like reaching into the bottom of a washing machine to get the rotor in place. The process is a little easier now.

“There are lots of factors you can improve,” says Borrmann. For example, giving the device a lower profile provides easier access. Instead of using a screw that requires several turns to tighten, Borrmann says they have a QuickLock rotor that “closes in a quarter turn and is safely closed.”

These features also play a part in what Borrmann calls an overall trend toward making centrifuges more user-friendly. His company even makes sure that the lid closes easily. “It’s like a door on a Cadillac closing,” he says. “It’s a soft-touch approach that gently closes and locks automatically.”

More from less

As labs require more equipment, space grows increasingly valuable. That impacts the design of centrifuges. “Size is important,” says Borrmann. “Today’s centrifuges save space.”

Also, researchers prefer platforms that perform multiple functions when possible. Thinking along those lines, Eppendorf developed its crossover centrifuge 5430. “It’s between a micro centrifuge and a multipurpose one,” says Borrmann. “It has the size of a micro centrifuge but can do some of what a multipurpose centrifuge can do, like spinning plates.”

Other centrifuges also include new features. For example, Borrmann points out a trend toward refrigerated centrifuges. “They protect samples better from the heat generated during spinning, and they ensure a more consistent environment during the process,” he says.

Safer spinning

Some of the enhanced safety features of modern centrifuges can be heard but not seen. For example, quieter devices make life in the lab more pleasant while the centrifuge runs.

Noise, however, does not generate a centrifuge’s biggest danger. If work is being done on biological agents and a tube breaks during spinning, the agent can be released into the air. That’s just what happened at a biosafety level 3 (BSL-3) laboratory at Yale University in 1994, and a scientist contracted the Sabia virus, which can cause internal bleeding. Although the Yale scientist recovered, today’s centrifuges guard against such an accident.

For example, some centrifuges provide aerosol-tight containment. So if a researcher is spinning bacterial cells, a virus, or radioactive samples and a tube leaks, the material cannot escape the rotor.

Nonetheless, Brandy J. Nelson, biological safety officer at the University of Kentucky, points out that researchers might buy a centrifuge without the aerosoltight feature because they plan to use the device in a BSL-1 or -2 lab. “Then they might move to working with viral vectors and need that containment.” She says that some manufacturers offer an upgrade to an aerosol- tight rotor, but some don’t. “Manufacturers could do better at that,” she says.

In addition, after a broken tube, the rotor traps just the potentially infectious or hazardous substance. It’s safe only if a researcher opens the rotor in a biosafety cabinet. Nelson would like to see a sensor that tells you ahead of time that a tube leaked. Maybe the sensor could just detect liquid in the rotor.

Rather than place all of the safety responsibility on the manufacturers, Nelson adds that training could be improved in labs that use centrifuges. “They’re very common equipment in labs, and people don’t always get training and information on hazards,” she says.

Managing maintenance

Nelson’s other top requests involve maintenance. First, she’d like to see easy-to-clean rotors and buckets. “It’s very hard to decontaminate them after a spill,” she says. “In microcentrifuges, for example, it’s really hard to clean where you put the 1.5-milliliter tubes.”

Nelson’s second request involves ordinary wear. “In some centrifuges, the rotor is exposed to such high force that it wears down over time, and you have to change the speed rating.” She says that some centrifuges digitally track the usage of rotors so you know when to set back the speed rating on them. “It would be nice if they all did that,” Nelson says.

With the advances in centrifuges since the hand-cranked ones in the 19th century, we can surely expect an increasing array of capabilities and applications. Likewise, tomorrow’s centrifuges should be even safer than today’s.

For additional resources on centrifuges, including useful articles and a list of manufacturers, visit www.labmanager.com/centrifuges