The Directional Acceleration Vector-Driven Displacement of Fluids (DAVDDOF) system, under development at the time of reporting the information for this article, would be a relatively compact, automated, centrifugally actuated system for staining blood smears and other microbiological samples on glass microscope slides in either a microgravitational or a normal Earth gravitational environment. The DAVD-DOF concept is a successor to the centrifuge-operated slide stainer (COSS) concept, which was reported in "Slide-Staining System for Microgravity or Gravity" (MSC-22949), NASA Tech Briefs, Vol. 25, No. 1 (January, 2001), page 64. The COSS includes reservoirs and a staining chamber that contains a microscope slide to which a biological sample is affixed. The staining chamber is sequentially filled with and drained of staining and related liquids from the reservoirs by use of a weighted plunger to force liquid from one reservoir to another at a constant level of hypergravity maintained in a standard swing-bucket centrifuge.
In the DAVD-DOF system, a staining chamber containing a sample would also be sequentially filled and emptied, but with important differences. Instead of a simple microscope slide, one would use a special microscope slide on which would be fabricated a network of very small reservoirs and narrow channels connected to a staining chamber (see figure). Unlike in the COSS, displacement of liquid would be effected by use of the weight of the liquid itself, rather than the weight of a plunger.
The channel from each reservoir to the staining chamber would be made so narrow that the combination of surface tension of the liquid and friction between the liquid and the channel surface would suffice to prevent the flow of liquid from the reservoir to the staining chamber in the absence of hypergravitational centrifugal acceleration below a specified level. Downstream of the staining chamber, there would be channel for draining each fluid from the staining chamber into a waste reservoir after use; this channel would be wider than the other channels so that draining could be accomplished at a centrifuge speed much lower than that needed for filling the staining chamber from a reservoir. Flow in this channel would be restricted by an electrically actuated microvalve controlled by a microprocessor on the spindle of the centrifuge.
By suitable choice of width of each channel, taking account of properties and amount of each liquid, the threshold centrifugal accelerations for moving the liquids from the reservoirs to the staining chamber would be set at successively greater values in the sequence in which the liquids were required to be used. Then sequential filling of the staining chamber with the various liquids would be achieved by momentarily increasing the speed of the centrifuge to exceed the corresponding threshold accelerations at the required times. Once the sample had been exposed to each liquid for the required time, the valve would be opened to drain the liquid from the staining chamber into the waste reservoir.
The reservoirs, channels, and staining chamber could be created, either on a glass slide or on a uniformly thick coating material on the slide, by one or more of a variety of techniques that could involve photolithography, laser writing, and/or etching. Once a slide had been thus prepared, a sample would be placed on the staining-chamber area of a thin glass cover, then cover would be adhesively or electrostatically bonded to the slide or to the coating material. The liquids would then be dispensed into their assigned reservoirs via access ports and the air displaced from the reservoirs would leave through vent ports. The slide would then be placed on a centrifuge in the form of a spinning disk, and the centrifuge would be operated as described above to expose the sample sequentially to the various liquids.
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, contact the Johnson Commercial Technology Office at (281) 483-3809. 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
University Space Research Association 10227 Wincopin Circle
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Refer to MSC-23179.