Surface modified blood collection tubes

Abstract: A glass or plastic article, preferably a blood collection tube, has two or more surface regions of different surface chemistry. One region is substantially glass-like and another region is substantially plastic-like. If the tube is glass, a region of the tube adjacent the tube bottom is plastic-like. If the tube is plastic, a region of the tube adjacent the mouth of the tube is be glass-like.

Description: BACKGROUND OF INVENTION 1. Field of the Invention . This invention relates to medical devices and more particularly relates to a blood collection tube having surface regions of different chemistry. 2. Background . Blood samples are routinely taken in evacuated tubes, such as glass VACUTAINER™ tubes (Becton, Dickinson and Company). One end of a double-ended needle is inserted into a patient's vein. The other end of the needle then punctures a septum covering the open end of the VACUTAINER™ tube so that the vacuum in the tube draws the blood sample through the needle into the tube. Using this technique a plurality of samples can be taken using a single needle puncture of the skin. Plastic tubes have also been proposed for blood collection. Plastic offers a number of advantages over glass, such as lower breakage, less weight in shipment, and easier disposal by incineration. During sample collection, the blood comes into contact with the interior surface of the collection tube. The nature of the blood-surface interaction is complex. For example, the blood clotting cascade is activated by contact of the blood with a wettable glass surface and the formed clot does not adhere to the glass, making it easy to separate clot from blood plasma by centrifugation. However, because the clot is non-adherent, it is subject to resuspension in part or whole into the plasma layer during handling or transportation. Thus, in glass tubes, the same surface properties that lead to easy separation of clot from the serum also allow the clot to move freely in the tube. Plastic tubes generally have a nonwettable surface and do not activate the clotting process efficiently. Clots formed in these tubes may be quite gelatinous relative to those in glass. These gelatinous clots adhere tenaciously to plastic surfaces and do not allow for clean separation of serum from clot in conventional hematological centrifuges. However, the adherent clot is not easily disrupted by ordinary handling procedures. Thus, although serum and clot do not separate cleanly in plastic, the clot adheres to the plastic surface, and its mechanical stability is a positive feature not available in glass tubes. Thus, the ideal blood collection tube for serum separation would exhibit both glass-like and plastic-like surface activity. In the present disclosure, the term glass-like is used to describe a surface which is substantially hydrophilic, which is wettable by aqueous liquids, which initiates clot formation and which is non-adherent to the formed clot. The term plastic-like is used to describe a surface which is substantially hydrophobic, substantially nonwettable by aqueous liquids, and which does not initiate clot formation to any significant degree, but which is highly adherent to clot material. Various methods have been proposed for modification of glass and plastic surfaces. In one method, plastic surfaces are coated with a detergent material to render them more glass-like. This approach has the disadvantage of adding a soluble foreign material which contaminates the serum and may interfere with subsequent blood analysis. In US-A-4,967,763 to Nugent et al., plastic microcollection tubes are treated with an oxidative plasma to render the surface more hydrophilic, to achieve faster blood flow and to reduce blood hangup. Conversely, it is known to treat glass surfaces with a plasma to deposit a layer of hydrophobic plastic material. This technology is exemplified in US-A-4,188,426 to Auerbach wherein a fluorine-containing layer is plasma-deposited on a variety of surfaces, including plastic and glass. In these approaches, the entire interior surface of the tube is substantially modified to interconvert glass-like and plastic-like surfaces and thus does not provide surface chemistry having dual functionality for blood collection. Formation of a hydrophobicity gradient on a polydimethylsiloxane film is taught by Golander et al. in Biomaterials 11,32 (1990). The film surface is exposed to an oxygen plasma generated in a planar diode system for various lengths of time as regulated by a cover movably positioned between the plasma and the polymeric surface. Wettability gradients are formed on silicon plates by Elwing et al. in Advances in Colloid and Interface Science , 32,317 (1990). The gradients are formed by diffusion-induced silylation using dichlorodimethyl silane. In US-A-4,257,886 to Kessler, a glass container for blood separation is coated to render it hydrophobic. There is need in the art of blood collection for a tube which promotes clot formation, permits clean separation of clot from serum and enchances strong adherence of the formed clot to minimize mechanical remixing of clot material with serum. The present invention fulfils this need. SUMMARY OF THE INVENTION A plastic article for blood collection has an open end, a closed end, a side wall and a bottom wall. The side wall and bottom wall define an inside wall surface. The inside wall surface has first and second surface regions. The first surface region is adjacent said open end. The first surface region is substantially glass-like and substantially hydrophilic, which promotes clot formation and provides a nonadherent surface to the formed clots. The second surface region is adjacent said bottom wall. The second surface region is of native plastic, substantially hydrophobic, and is highly adherent to clot material. The article can be a tube, flask or dish. For a tube, the the region modified to be glass-like is adjacent the open end of the tube, and the native plastic surface region is adjacent to the bottom wall and may include the bottom wall. Thus the article of the invention has two distinctly different kinds of surface properties which provide a dual clinical functionality. In blood collection tubes, the glass-like surface promotes clotting and provides a nonadherent surface to the formed blood clots. On the other hand, the blood clots adhere strongly to the plastic-like surface region. When a blood sample taken in the tube of the invention is centrifuged, the blood clots at the glass-like region and the clot flows, pellets and adheres to the plastic-like region. A clear serum layer forms above the clot with no fibrin rings and strands suspended in the serum or adhering to the upper region of the tube. The strong adherence of the clot to the plastic-like region prevents mechanical remixing of clot and serum when the centrifuged tube is handled or transported. The location and size of the different regions is easily predetermined by the treatment process so that the total volume occupied by clot and serum within the tube can be controlled by the location of the interface between the regions. BRIEF DESCRIPTION OF THE DRAWING The Figure illustrates the preferred tube of the invention and shows two regions of different surface chemistry. DETAILED DESCRIPTION While this invention is satisfied by embodiments in many different forms, there will herein be described in detail preferred embodiments of the invention, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and is not intended to limit the invention to the embodiments described and illustrated. The scope of the invention will be measured by the appended claims and their equivalents. In accordance with the present invention, an article surface, preferably a continuous surface, is modified to have two or more regions of different chemistry. Regions of different surface chemistry may be formed on a variety of plastic articles, such as flasks, bottles, vials and dishes. The preferred article geometry is a tube, preferably a tube with one closed end. The tube may be combined with a septum over the open end and may be evacuated. Evacuated tubes for blood collection are standard in the art as, for example VACUTAINER™ brand tubes (Becton, Dickinson and Company). The invention will be described in detail for a tube with the understanding that any other article may be treated to have dual surface chemistry regions by the methods described. The plastic tube of the invention may be of any shape or size. The preferred tube may be cylindrical and may be about 25-250, preferably about 75-100 mm long and 10-20 mm in diameter. The tube of the invention will now be further described with the aid of the Figure. A typical tube 10 of the invention has an open end 12, a closed end 14, a side wall 16 and a bottom wall 18. Walls 16 and 18 define an inside wall surface 20 which extends continuously from the top portions 22 and 14 of side wall 16. Wall surface 20 includes a region 26 adjacent the open end of the tube and a region 28 adjacent bottom wall 18 and optionally including the portion of inside wall 20 defined by bottom wall 18. In accordance with the invention, it has been found that a plastic tube may be treated to have a glass-like region on its interior surface. The glass-like region is introduced at the open end. The plastic tube may be of any polymer which can be treated to have a glass-be surface region. Representative polymers are, for example, polyethylene terephthalate, polyethylene, polypropylene, polytetrafluoroethylene, polysiloxane, polyvinyl chloride and preferably polystyrene (PS). Suitable reagents for this embodiment of the invention are chromic acid and preferably sulphuric acid whereby the polymer structure is attacked by the acid with introduction of polar groups. The most preferred tube of the invention is a polystyrene blood collection tube treated with sulphuric acid to have a glass-like surface near the tube mouth to enhance the clotting sequence without clot adherence and the native plastic surface in the area near the closed end to enhance adherence of the clot at the bottom of the tube during centrifugation. This tube is easily made by immersion of the open end of the polystyrene tube in the sulphuric acid solution. From the above disclosure of suitable methods to achieve surface regions of different surface chemistry, it will be apparent that the regions of modified chemistry can be of any size depending merely on how much reagent is added to the tube for bottom-end treatment or how far the mouth of the tube is inserted into the reagent for top end treatment. Thus the glass-like surface region may be from about 10-75, preferably about 50 to 60% of the inside wall surface with the remainder of the surface being plastic-like. EXAMPLE I Polystyrene culture tubes (Becton Dickinson 12x75 mm) were treated with a radio-frequency oxygen plasma (30 Watts 13.56 MHz, planar diode system held at 250 millitorr oxygen) to oxidise the entire interior and exterior surface of the tubes and produce a glass-like surface treatment. Another set of these plastic tubes were filled concentrated sulphuric acid to sulfonate the aromatic ring of the polystyrene. After 30 minutes reaction at room temperature, sulfonated tubes were rinsed with copious amounts of distilled water and air dried. Observation of the shape of water droplets along the tube axis confirmed that the treated region was a hydrophilic, water-wettable surface. The tubes were filled with 4.5 ml of citrated porcine blood containing 0.1 molar calcium chloride and incubated for 30 min at 37°C to allow blood to clot. The tubes were then centrifuged under standard hematological conditions (1380 G, 3300 rpm). It was observed that blood clot did not adhere to the inside wall of the plasma oxidized and sulfonated tubes, behaving in an identical fashion to that of glass control tubes. These experiments verify that surface treatments that render plastic surfaces water-wettable confer a glass-like property with respect to clot adhesion to plastic surfaces. EXAMPLE II Sulphuric acid was carefully added with a pipette into the lower portion of polystyrene tubes. The total height of the glass-like region was varied by varying the total volume of sulphuric acid. The lower portions of the tubes were rendered hydrophilic. The character of blood clots and position relative to the hydrophobic surface region were noted as described in Example I. It was observed that the position of clot adherence along the tube axis positively correlated with the position of the hydrophobic, untreated region on the tube and that the clot was strongly adherent to this layer and did not pellet during centrifugation. Clots on sulfonated region were observed to be pulled away from the wall of the tube wall in a non-adherent manner as in Example I. These experiments illustrate the non-adherence of clotted blood to a glass-like hydrophilic region in a tube of an inherently hydrophobic material to which blood clots do adhere. The Examples show that clot position and adherence within a tube can be controlled by surface treatments that produce glass-like properties.

Claims: A plastic article for blood collection having an open end, a closed end, a side wall and a bottom wall, said side wall and bottom wall defining an inside wall surface, said inside wall surface having a first surface region which is adjacent said open end, which is substantially glass-like and substantially hydrophilic and which promotes clot formation and provides a nonadherent surface to the formed clots, and a second surface region of native plastic which is adjacent said bottom wall, which is substantially hydrophobic and, which is highly adherent to clot material. The article of Claim 1 which is a tube. The article of Claim 1 which is a flask The article of Claim 1 which is a dish. The article of any preceding claim, wherein said plastic is selected from polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl chloride, polyethylene terephthalate, polysiloxane or polystyrene. The article of any preceding claim further comprising a septum over said open end.

Inventors: HARPER GARRY R, VOGLER ERWIN A, HARPER, GARRY R., VOGLER, ERWIN A.
Applicants: BECTON DICKINSON CO, BECTON DICKINSON AND COMPANY
Application year: 1993
Main classification: B01L3
IPC codes: G01N33, B01L3, A61B5