http://www.freepatentsonline.com/6534016.html

"The control tubes had a light layer of "red-cell" film but did not show any significantly visible adhesion of blood components, such as red cells, in the serum phase of the blood (red-cell hang-up). The prototype tubes containing the additive preparation without the silicone surfactant showed large amounts of film and hang-up. However, when the additive preparation included the silicone surfactant of the present invention, there was very light film in trace amounts, and red-cell hang-up was minimal with just a spot or a trace. The results were equivalent for prototypes #1 and #2. The example illustrates that the surfactant need not be coated on the tube wall to be effective in preventing adhesion of blood components."

http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&Sect2=H...

"Therefore, a need exists for a separator device that (i) is easily used to separate a blood sample; (ii) is non-temperature dependent during storage and shipping; (iii) is stable to radiation sterilization; (iv) employs the benefits of a thixotropic gel barrier yet avoids the many disadvantages of placing a gel in contact with the separated blood components; (v) minimizes red cell film or red cell hang-up of a blood sample; (vi) minimizes cross contamination of the heavier and lighter phases of the sample during centrifugation; (vii) minimizes adhesion of the lower and higher density materials against the separator device; (viii) is able to function in a plastic or glass container; and (ix) can be used with standard sampling equipment. "