To enable the rapid point-of-care analysis promised by "lab on a chip" technology, doctors need the whole lab. Previous efforts to design lab-on-a-chip systems have managed to shrink the devices used to gather medically relevant data, but have failed to replicate the beakers, pipettes and various tools that transform biological samples into usable forms. Utilizing the propensity of plastic to deform under stress, a team of Taiwanese scientists has figured out how to make a centrifuge small enough to work in lab-on-a-chip situations.
The Taiwanese-designed centrifuge works mechanically and has few moving parts, making large scale industrial scale production easier than other similar solutions. By combining the ability to separate blood plasma at very small volumes with a practical, cheap design, these micro-centrifuges aim directly for the medical device market, as opposed to other, more complex and theoretical, lab-on-a-chip devices.
"Therefore, a simple, robust, and affordably manufacture-able decanting method is desired. In this study, we present a novel approach to decant supernatant by manipulating the centrifugally induced pressure and the elastic behavior of the plastic lids of the chamber," said the recent paper in the journal Biomicrofluidics discussing the centrifuges.
The paper, titled "Supernatant decanting on a centrifugal platform," details how the entire process relies on the fact that the plastic deforms faster than blood cells and blood plasma can mix.
The spin cycle beings with the centrifuge spinning up towards its maximum speed of 4,000 rpm. During this initial period, centrifugal force pulls the sample out of its reservoir chamber and into the first part of the two section decanting chamber. The wall separating the two sections of the decanting chamber is short enough for liquids to flow from the first section to the next section when at rest, but too tall for the liquids to cross during the spin cycle.
When the centrifuge reaches its maximum speed of 4000 rpm, the blood cells and the blood plasma separate as in a standard centrifuge. However, since the volume of the plastic container has expanded under the stress of spinning, both liquids remain pulled beneath the lip of the first section of the decanting chamber.
As the spin cycle slows down and ends, the decanting chamber returns to its original shape, pushing the liquid over the wall and into the second section of the decanting chamber. Since spinning had divided the liquid plasma from the blood cells, only the plasma flows into the second part of the decanting chamber, effectively separating the two constituents for analysis.
The available spin speed and the mechanical properties of the materials needing separation dictate the size and shape of the chambers. Although the authors of the Biomicrofluidics paper focused on medical applications, and shaped their chambers to separate blood plasma, this method could provide lab-on-a-chip centrifugal separation for any mixture in any field. Far from an exclusively medical advance, these centrifuges could parse soil samples, test water samples, or monitor the efficiency of a wide range of industrial processes.