The Gravity of it All
Centrifuges separate particles and structures suspended in liquid by applying thousands of gravitational force equivalents to the sample through spinning. Laboratories use centrifuges to clarify suspensions, separate liquids, isolate suspended particles, perform density measurements and for many other applications.
Many users, and some manufacturers, specify centrifuges and centrifugation in terms of rotor revolutions per minute (rpm), but as Dr. Lars Borrmann, group marketing manager at Eppendorf (Hauppauge, NY), notes, rpm is a vague term that says nothing about separation power.
“Customers still ask about rpm, but that only tells you what the motor can do and nothing about the force being applied.”
The operative term these days is RCF, relative centrifugal force, which is a function of rotor radius and the square of the rotational speed. Two centrifuges with the same RCF provide comparable resolving power. Transferring methods between centrifuges is difficult without knowing the instruments’ RCF values.
Ergonomics and usability
Dr. Borrmann places centrifuges into two basic categories: inexpensive instruments that provide basic speed and capacity, and units designed to ergonomic and “eco-friendly” specifications.
Labs tend to be noisy places, with numerous devices contributing to the din. A loud centrifuge can tip the noise balance into the intolerable range. “You don’t want a screaming loud instrument right next to where you’re working,” Dr. Borrmann tells Lab Manager Magazine.
Accessibility is another often-overlooked ergonomic issue. Larger benchtop units may require operators to stand on a step stool to access samples. Coupled with poorly designed lids whose operation requires extreme force, these units are recipes for injury. Dr. Borrmann therefore advises potential purchasers to consider units with a low profile and easy-open-and-close lids.
The final ergonomic consideration is ease of operation. Eppendorf, for example, engages the services of a German institute that specializes in human- machine interaction to provide “a highly satisfactory experience with our centrifuges, beyond speed and capacity,” according to Dr. Borrmann. “Centrifuges should be fun to work with.”
Materials lead the way
For Maurizio Merli, senior product manager for benchtop centrifuges at Thermo Fisher Scientific (Milford, MA), improved materials of construction have been the most significant trend in centrifugation. New materials and designs provide levels of biological and workplace safety that did not exist 15 years ago.
“Centrifuges generate a lot of energy,” Mr. Merli notes. When a centrifuge spinning at tens of thousands of rpm crashes, the device becomes a kind of centrifugal fragment bomb that can destroy a lab and cripple or kill anyone nearby. Most units today employ high-quality covers and paneling to keep flying metal inside.
Manufacturers have paid special attention to rotor design to minimize the effects of a crash, particularly for high-speed units. Aluminum alloys and lightweight metal amalgams provide mechanical integrity and high performance. Composite rotor materials, which Thermo has pioneered, do an even better job by providing the highest strength-to-weight ratings ever.
Most use glass-reinforced plastics, similar to materials used to make surfboards and aircraft. Carbon fiber-based composites do an even better job, according to Mr. Merli, who calls them “an extraordinary material that completely changes how we design rotors.” Carbon fiber rotors are stronger than metal of equivalent weight, contain potential biological hazards better than do conventional rotor designs, and resist corrosion—a major source of catastrophic failure and centrifuge crashes.
“These extremely light products can spin as fast as you want, and [they] change the rules of the game with respect to safety,” Mr. Merli tells Lab Manager. Because they are lightweight, carbonfiber rotors do not generate as much energy as metal rotors do.
Industrial and regulated applications are driving the application of data logging in centrifugation, observes Randy Pawlovich, strategic marketing manager at Beckman Coulter (Indianapolis, IN). “In the old days the traditional customers were research and academic labs, and data wasn’t a big deal.” Today, he says, regulated industries (like diagnostics) routinely collect centrifuge operation data.
Even in nonregulated settings, companies facing tight budgets are paying close attention to who uses instruments, and for how long, and what mishaps may have occurred during a particular run. In situations where centrifuges are shared among several laboratories, usage data permits allocation of related expenses.
Performance and ease of use are critical purchase factors for centrifuges, but, as Mr. Pawlovich notes, all reputable manufacturers can deliver these adequately. To differentiate their products, vendors need to innovate around specific workflows, particularly with disposable labware that streamlines operations. “All manufacturers have to be more creative, more innovative, because labs tend to hold on to centrifuges for a long time.”