Function and uses of a medical centrifuge

Medical centrifuges come in various sizes and apply to many different applications, making them an extremely useful device, whether in a doctor’s office, hospital, or laboratory.

Modern centrifuges are basically compact, made of plastic or metal, and are visually appealing; they typically sit on a countertop on rubber feet so they won’t move while in operation. The bottom can be weighted to make it stable while in use. The size will determine how many test tubes or glass vials it can hold at one time. They are controlled by a timer and have at least two speeds, low and high. Many also have the ability to keep the interior cool, so that when the appliance is running, especially at high speed, the contents will remain cold instead of heating up as would normally happen when centrifugal force is applied.

There are many medical applications for a medical centrifuge, including studies of viruses, proteins, polymers, nucleic acids, and blood. They can separate both serum and plasma from blood and solids from liquids. The uses are many and are not limited solely to the medical field.

Having a timer is convenient when uses include long periods of time required for ingredient separation. The high speed spin creates an artificial gravity that, depending on the substance, will separate the ingredients quickly or slowly.

Medical centrifuges can spin at amazing speeds, especially the variable speed models. They can produce anywhere from eight hundred revolutions per minute (RPM) to two and a half million RPMs. The average use and application for most centrifuges with a minimum of two speeds (low and high) is two thousand RPM up to sixty thousand RPM. Most uses require higher speeds but for shorter periods of time.

It is a difference in density that causes most substances to separate when cycled in a medical centrifuge. High-speed drives are called ultracentrifuges and are typically benchtop drives that require some means of securing them to the counter or bench top so they stay in place while in use. Uses for ultracentrifuges include the separation of gases to determine the molecular weight of certain liquids. They are used as a uranium 235 separation medium for nuclear reactors. Temperature requires close control in many of these applications due to the sensitivity of the ingredients. They will get very hot at high revs which is actually a form of friction.

While the average medical centrifuge can cost anywhere from a few hundred to several hundred thousand dollars, there is an example of an efficient device created by chemists at a university that costs just two dollars. The device is basically an old-fashioned egg beater to which plastic tubes held together with duct tape have been added. It is capable of creating a low speed centrifugal force that will actually separate blood cells from plasma and has proven useful for simple laboratory tests where no laboratory or equipment is available. It shows that human ingenuity can do many wonders.