The centrifuge-operated slide stainer (COSS) is a conceptual self-contained system that could be attractive for use in a variety of histological and cytological procedures in both microgravity and normal Earth gravity. The COSS was conceived specifically for use in staining blood smears on glass slides in order to enable differential white-cell counts (DWCCs) on astronauts during spaceflight. (The differential white-cell count is a standard technique for distinguishing between a healthy condition and any of a number of viral or bacterial infections.) In addition to overcoming microgravitational obstacles to the staining process, the COSS would do most of the routine and tedious processing steps that heretofore, have been performed manually in conventional terrestrial preparation of blood samples. On Earth, the COSS could be useful at remote medical research field stations, military field hospitals, and biomedical research facilities.
In a terrestrial setting, preparation of a sample of blood for a DWCC involves (1) smearing blood on a glass slide, (2) fixing the cells in the smear to the surface of the slide, (3) staining the cells with a histochemical stain, and then (4) washing the slide in a clean buffer solution. After step 4, the smear is viewed under a microscope and the DWCC is made according to morphological criteria. While it is fairly easy to handle the fixative, dye, and buffer solutions under normal Earth gravitation, the difficulties of handling these or any liquids in microgravity makes it impractical to perform DWCCs in spaceflight. Several prior cell-staining apparatuses have been developed for use in microgravity, but have proved inadequate for various reasons.
The design of the COSS would not only largely automate the staining process but would also eliminate the liquid-handling difficulties through the elimination of microgravity: as the term "centrifuge-operated" suggests, the COSS would be mounted in a standard laboratory centrifuge and would be operated only during operation of the centrifuge. The COSS (see figure) would comprise a cell-staining apparatus within a sealed shell. All the required fixer, buffer, and staining solutions would be contained in disposable cartridges that would be sequentially emptied into a staining chamber by centrifugal force. The sequential emptying of cartridges would be triggered by the timed removal of retaining pins from weighted plungers.
Air displaced from the staining chamber would be vented to the space previously occupied by each cartridge plunger. After the sample had been exposed to each solution, that solution would be drained from the staining chamber, into a disposable waste container, by activation of a one-way valve at the base of the staining chamber. Air displaced by draining would be vented back to the staining chamber. After each draining, the one-way valve to the waste chamber would be closed to enable filling the chamber with the next solution. During operation, air would be vented within the centrifuge via a gravity-operated ring seal valve; this valve would be open during a centripetal acceleration greater than normal Earth gravitation and would close upon return to microgravity once the centrifuge stopped spinning.
The COSS could be operated relatively easily, with minimal training and minimal human intervention. The only action required of the operator would be to place a blood-smear slide into the staining chamber, sealing the COSS shell, placing the COSS in the centrifuge, and switching on the centrifuge. The COSS would contain a microprocessor that would control the releases of solutions into, and draining of the solutions from, the staining chamber at the designated times.
Because the COSS would operate as a sealed unit, there would be minimal risk of escape of solutions. The waste container and the cartridges containing the solutions could be disposable. The remainder of the COSS could be reused. The volumes of the solutions could be kept to a minimum because the hypergravitational effect of centrifugation would cause the solutions to spread over the slide as intact liquid sheets without air bubbles. Minimization of volumes of solutions is desirable aboard spacecraft for minimizing the mass of material that must be lofted and the amount of waste material that must be stored after use. Minimization of volumes of solutions is also desirable in terrestrial applications in which the required solutions are very expensive. The "hands-free" aspect of the preparation of DWCC blood smears by use of the COSS would make the COSS attractive for use by nontechnical personnel at remote medical facilities.
This work was done by Daniel L. Feeback of Johnson Space Center and Mark S. F. Clarke of University Space Research Association. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Bio-Medical category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Mark S. F. Clarke, Ph.D.
University Space Research Association, DSLS
3600 Bay Area Blvd.
Houston, TX 77058
Refer to MSC-22949, volume and number of this NASA Tech Briefs issue, and the page number.