Blood separation means

Abstract: A blood separation means received in blood collection tubes characteristically comprises, as such a gel-like material that is the main ingredient of the means, a copolypolymer of sebacic acid with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol. The separation means may further comprise a thixotropic agent blended with the copolymer. The copolymer renders stable and less flowable the blood separation means during storage, allowing it to form a stable partition barrier in each collection tube when centrifuged, and the blood cells above barrier are prevented from remaining within the serum, without any amount of harmful oily substance being released from the separation means.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blood component-separating composition ( hereinafter referred to as "blood separation means" ) which is employed in the centrifugal separation method to separate-serum or plasma from whole blood, wherein the difference in specific gravity between them is utilized. 2. Prior Art Many kinds of blood separation means which have been proposed are useful in the centrifugal method. Those prior art separation means contain as their main ingredient a gel-like material such as silicone oil, chlorinated polybutene, acrylic polymer or copolymer of α-olefin and diester of maleic acid (see e.g. EP-A-0 076 051 and EP-A-0 384 331). Typical additives blended with the main ingredient are: a thixotropic agent enhancing important properties to the gel-like material (see e.g. EP-A-0 075 119); and an inorganic substance. The thixotropic agent causes the gel-like material not to flow within blood collection tubes but stay on its bottom while being transported. When centrifugal force is applied to the collection-tubes filled with blood, the gel-like material moves upwards and forms a partition barrier between the serum ( or plasma ) and the clot. The thixotropic agent also enhances a stable strength to the partition barrier. On the other hand, the inorganic substance such as titanium dioxide and calcium carbonate is blended with the gel-like material so as to adjust its specific gravity. However, the prior art gel-like materials are disadvantageous in that it is not easy to adjust the viscosity and specific gravity to their level desirable for the blood separation means. Consequently, it has been necessary to add to the gel-like material a large quantity of a thixotropic agent and/or specific density-adjusting agent, with the former agent adjusting the thixotropic property of the blood separation means. Thus, the actual specific gravity of the blood separation means cannot be kept at a constant level but varies among production lots thereof and in course of time. In addition, some fractions of the separation means are likely to be dispersed in the serum phase ( or plasma phase ) which will be obtained by centrifugal separation of blood samples. Said fractions will form an oily substance which floats in the serum or plasma and thus are likely to clog the nozzles in an automatic analyzer. Further, because of insufficient strength of the partition barrier, perfect centrifugal isolation of the serum ( or plasma ) from the clot is not ensured. A number of blood cells will remain in the serum phase above the partition, thus impairing the separation accuracy. US-A-4 101 422 and WO-A-91/08246 disclose copolymeric gels for use in blood separation which comprise a fatty acid component, a dicarboxylic acid (e.g. sebacic acid) component and a diol (e.g. a mixture of 2,2-dimethyl-1,3-propanediol and 1,2-propanediol) component. Therefore, an object of the present invention is to provide a blood separation means free from the aforementioned drawbacks of the prior art separation means. The blood separation means provided in the invention comprises characteristically as a gel-like material a copolymer of sebacic acid with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol, the gel-like material being a main ingredient of the blood separation means. THE PREFERRED EMBODIMENTS The inventors have conducted to achieve the object a series of researches and found that the copolymer of sebacic acid with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol as said main ingredient is effective to easily realize the specific gravity and viscosity of a level desirable to the blood separation means. The blood separation means has a high separating capability even though it does not contain such a large amount of thixotropic agent or specific gravity-adjusting agent, and is therefore of a higher practical value. Now, the invention will be summarized below more in detail. The copolymer of sebacic acid polymerized with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol is the gel-like material contained as the principal ingredient in the blood separation means in accordance with the present invention. A copolymerization ratio of 1 mole of sebacic acid to 1.02 - 1.07 moles of a mixture of 2,2-dimethyl-1,3-propanediol and 1,2-propanediol is desirable in the invention. A lesser amount of sebacic acid below 1 mole in 1 mole of the copolymer will bring about an undesirably low viscosity of the gel-like material, whereas an excessively larger amount of said acid above 1 mole will raise the viscosity to an undesirable extent. A ratio of 2,2-dimethyl-1,3-propanediol to 1,2-propanediol is preferably 0.85 : 0.15 - 0.75 : 0.25. If the former is contained at a lower ratio, then the specific gravity of said gel-like material will become too high, while a higher ratio of the former diol will undesirably render low the specific gravity. On the other hand, a ratio of the latter diol below the limit will cause an undesirably high melting point which makes waxy the material, but a ratio of the latter diol above that limit makes it difficult to handle the material. Molecular weight of the copolymer is to be 1,000 - 10,000, and more desirably 2,000 - 8,000. A lower molecular weight below this limit will excessively decrease both the viscosity and specific gravity of the copolymer to an unacceptable degree, whereas a higher molecular than the limit will contrarily raise the viscosity and specific gravity to a high level which is not adequate for the blood separation means. The preferably specific gravity of the copolymer is 1.035 - 1.055 and the preferable viscosity thereof is 30,000 - 150,000 mPa.s (cP), at 25 °C. With the specific gravity below 1.035 and the viscosity lower than 30,000 mPa.s (cP), the blood separation means is too mobile to stand still within the tubes when gravitational force or the like is imparted to it during storage. In detail, the separation means in this case may move close to a rubber stopper sealing an open top of the previously evacuated blood collection tube, even if received therein to rest on the bottom thereof at first. Consequently, it will not only be mixed with and thus contaminate a centrifugally separated serum or plasma, but also be left sticking to the rubber stopper, thus making it difficult to obtain a pure sample of serum or plasma. Such a separation means will rise ( or "ascend" ) from the bottom at an accelerated timing so that the partition barrier is formed too early to prevent the blood cells from completely sinking below the barrier. Thus, the blood cells remaining within a fraction above the barrier will impair its separating capability. On the contrary, a specific gravity above 1.055 in combination with a viscosity higher than 150,000 will disable the smooth rising of the separation means, also failing to enhance a desirable capability of separation. The excessively high viscosity will cause further disadvantages such as difficult handling and allocation of the separation means to a number of collection tubes. A thixotropic agent may be added to the blood separation means so that it is easily controlled of its thixotropic property. Though any conventional thixotropic agents may be used, preferable ones are fatty acid amides, silica, clay and the like. The fatty acid amides are inert to blood, and a small amount of the amides may be blended with the gel-like material in order to improve its gel property needed for the blood separation means to form a partition barrier. Any of fatty acid amides having 10 - 25 carbon atoms, or more desirably 16 - 18 carbon atoms per molecule, or any mixture thereof may be employed herein. 0.5 - 7 parts by weight, or more desirably 1 - 4 parts by weight of the fatty acid amides may be added to 100 parts by weight of the copolymer. In a case wherein the fatty acid amides as the thixotropic agent is added at a ratio falling within this range, the gel-like material will have a desirable flowability which improves the shape stability and reservability of the material, thus providing an blood separation means which is excellent in its "ascendability" and its partition strength. The blood separation means in the invention may readily be produced for example by conducting the steps of: heating to a temperature between 60 °C and 80 °C a given amount of the gel-like material, i.e., the copolymer of sebacic acid with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol; adding thereto an appropriate amount of the thixotropic agent, e.g., the fatty acid amide(s); and continuing to stir this mixture with a sufficient shearing stress, while keeping the temperature, until the amide(s) is completely dissolved in the gel-like material. The blood separation means prepared in this manner in the invention need have a specific gravity intermediate those of the serum or plasma and the clot. The separation means put in blood collection tubes usually rests on the bottom thereof. Therefore, a larger difference in specific gravity between the separation means and the clot or blood cells is advantageous in that the centrifuged separation means can ascend within the tubes more smoothly and more rapidly. On the other hand, such a separation means as having an overall specific gravity not exceeding 1.035 includes its fraction whose specific gravity is much lower than 1.035. This fraction may undesirably migrate from said means into the centrifugally separated serum phase or plasma phase. Besides the specific gravity as prescribed above, the blood separation means which is composed of the gel-like material and the predetermined amount of thixotropic agent preferably has a viscosity from 100,000 to 400,000 mPa.s (cP) at 25 °C ( when measured in the same manner as will be described for the Examples given below ). The specific gravity as well as viscosity of the separation means may be adjusted, if necessary, by further adding an amount of an inorganic substance such as such as titanium dioxide or calcium carbonate. Examples The following Examples are given only by way of example, with no intention of delimiting thereto the scope of the present invention. Viscosity of the Examples was measured using "E-Type Viscometer" which is a rotary viscometer ( with a cone angle of 3° and a diameter of 28 mm, made by TOKYO KEIKI CO., LTD. ). Specific gravity was measured according to the Cupric Sulfate Method using cupric sulfate solutions of different concentrations. One drop of each sample was put in the solutions, in order to find which of them neither caused the drop to rise to the surface nor sink to the bottom. The thus found solution ought to have the same specific gravity as the tested sample. -- Preparation of copolymers -- Copolymer No. 1 Copolymer of sebacic acid may be produced by any conventional method known in this field of art. Polymerisation was carried out in a quatre-mouthed flask comprising a stirrer, a thermometer, an N₂ gas-introducing tube and a Vigreaux column. This Vigreaux column of a medium length comprised in turn a distillation head and a condenser which was composed of a thermometer and a receptacle. The condenser was arranged to distill water and/or an amount of excessive diol, under atmospheric or reduced pressure. Reactants which were involved in this process are as follows. 202 grams of sebacic acid, 89 grams of 2,2-dimethyl-1,3-propanediol and 16 grams of 1,2-propanediol were put in the quatre-mouthed flask to thereby form a reaction mixture. This mixture was heated up to about 225 °C, by continuously removing water therefrom while maintaining the vapor temperature almost constant to fall within a range of about 100 - 120 °C. Upon detection of a reduced rate of water generation after about 4 hours from the start of reaction, a little amount of a titanium compound as esterification catalyst ( at a ratio corresponding to 0.005 % of initial weight of the reactants ) was added. At the same time, the reaction system pressure was reduced to 933 1333 kPa (70 - 100 mmHg), and reaction was continued for 5 hours under this condition. Subsequent to this phase of process, the pressure was reduced below 67 kPa (5 mmHg) for a further reaction for 3 hours. A highly viscous product was discharged from the flask and cooled to room temperature to give a yield of 98 %. This product's viscosity was 35,000 mPa.s (cP), and specific gravity was 1.041 at 25 °C, with its molecular weight being 3,800. Copolymer No. 2 202 grams of sebacic acid, 87 grams of 2,2-dimethyl-1,3-propanediol and 15 grams of 1,2-propanediol were put in the quatre-mouthed flask to form another reaction mixture. Reaction to produce a copolymer was carried out in the same manner as for the copolymer No. 1, except that the total reaction time was 15 hours including the last phase for 3 hours with a pressure kept at 20 kPa (1.5 mmHg). The yield of copolymer No. 2 obtained in this manner was 95 %, its viscosity being 150,000 mPa.s (cP) with a specific gravity of 1.041 at 25 °C, with its molecular weight being 6,600. Copolymer No. 3 202 grams of sebacic acid, 88 grams of 2,2-dimethyl-1,3-propanediol and 16 grams of 1,2-propanediol were put in the quatre-mouthed flask to form still another reaction mixture. Reaction to produce a copolymer was carried out in the same manner as for the copolymer No. 1, except that the total reaction time was 15 hours including the last phase for 3 hours with a pressure kept at 20 kPa (1.5 mmHg). The yield of copolymer No. 3 obtained in this manner was 95 %, its viscosity being 68,000 mPa.s (cP) with a specific gravity of 1.041 at 25 °C, with its molecular weight being 4,400. -- Preparation of blood separation means -- Example No. 1 This example of blood separation means was prepared by blending 2 parts by weight of stearamide ( containing a small mixed amount of palmitamide ) with 100 parts by weight of the copolymer No. 1. Example No. 1 showed a viscosity of 140,000 mPa.s (cP) and specific gravity of 1.043 at 25 °C. Example No. 2 3 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 1 to give Example No. 2 of blood separation means having a viscosity of 187,000 mPa.s (cP) and specific gravity of 1.042 at 25 °C. Example No. 3 2 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 2 to give Example No. 3 of blood separation means having a viscosity of 260,000 mPa.s (cP) and specific gravity of 1.041 at 25 °C. Example No. 4 3 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 3 to give Example No. 4 of blood separation means having a viscosity of 156,000 mPa.s (cP) and specific gravity of 1.042 at 25 °C. Example No. 5 4 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 3 to give Example No. 4 of blood separation means having a viscosity of 187,000 mPa.s (cP) and specific gravity of 1.042 at 25 °C. Reference No. 1 0.01 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 3 to give a reference of blood separation means having a viscosity of 80,000 mPa.s (cP) and specific gravity of 1.041 at 25 °C. Reference No. 2 10 parts by weight of stearamide were blended with 100 parts by weight of the copolymer No. 2 to give another reference having a viscosity of 460,000 mPa.s (cP) and specific gravity of 1.044 at 25 °C. Reference No 3 4 parts by weight of stearamide as well as 4 parts by weight of fine silica ( "Aerosil R972", a trademark of Nippon Aerosil Co., Ltd. ) were blended with 100 parts by weight of a copolymer of α-olefin and maleic acid to prepare still another reference having a viscosity of 360,000 mPa.s (cP) and specific gravity of 1.039 at 25 °C. -- Comparison of examples with references -- Examples Nos. 1 - 5 as well as References Nos. 1 - 3 were tested of their stability during storage and their capability of dividing blood phases. (1) Stability during storage Blood collection/separation tubes made of glass and those made of polyethylene terephthalate, having an inner diameter of 13.6 mm, were used. A small amount of blood separation means of "Example" or "Reference" weighing 1.5 grams was put in each tube, and after kept at 25 °C for 24 hours, "flow distance" of said means was measured at different temperatures. The "flow distance" is a distance between an initial position of the blood separation means and a final position thereof which was measured after predetermined hours of storage had passed. A result of this test is given on Table 1. As will be seen on the table, the blood separation means of the present invention was stabler even if stored for a long time, and less flowable when transported or handled otherwise, than the prior art blood separation means represented by the References. (2) Capability of dividing blood phases Similarly, blood collection/separation tubes made of glass and or polyethylene terephthalate, having an inner diameter of 13.6 mm, were used. A small amount of blood separation means of "Example" or "Reference" weighing 1.7 grams was put in each tube, and kept therein at 25 °C for 24 hours after storage at 40 °C for 336 hours. 9 ml of human whole blood was put in each tube, and after complete coagulation thereof, they were centrifuged with 1,300 G for 10 minutes ( "G" being the gravitational acceleration ). Performance or capability of the blood separation means was evaluated as to the following items, according to the standards given below. The term "ascendability" used herein indicates the extent to which the blood separation means can rise in the centrifuged collection tube previously filled with a given amount of human blood. A rating symbol "+++" ('excellent') was allotted to the separation means which completely rose within the blood collection tube, while another symbol "++" ('good') means a little amount of said means remaining on the tube bottom. A further rating symbol "+" ('poor') represents a significant amount of the blood separation means which was left on the bottom, whereas a still further symbol "±" ('worse') denotes the quite unsatisfactory rising of the separation means which fully remained on said tube bottom. Further, the "stability of partition barrier" between the serum and the clot was judged based on the state of said barrier sticking to the tube wall, when 24 hours had passed after centrifugal separation process. Similarly to the "rising" property, the rating symbols "+++" (excellent), "++" (good), "+" (poor) and "±" (worse) respectively indicate: the perfectly sticking barrier; partially loosened barrier; significantly loosened barrier; and thoroughly loosened barrier. The "released amount of oily substance" from the separation means was inspected by observation of the serum surface. "Reddishness" of the serum was checked to determine whether or not any significant number of blood cells had been left in the serum, and also to determine whether or not hemolysis had occurred. Test results are given on Tables 2 and 3 respectively for the glass tubes and for the polyethylene terephthalate tubes. It will be seen on Tables 2 and 3 that in the blood phase-separating operation using the separation means provided in the invention, not only ascendability but also stability of partition barrier are excellent and satisfactory. Besides, there is neither observed any amount of oily substance released nor any extent of hemolysis or any number of blood cells remaining in the serum. It will now be apparent from the foregoing that the blood separation means provided by the invention is advantageous in its high separating capability and its good stableness which are not affected by a long time reservation or the like. It does neither move adversely within the collection tubes during transportation thereof, nor change in its minimum shear stress and its rising property in the centrifugal process, thus maintaining its high capability of separating blood phases. Further, the separation means is inert to blood so that blood is neither absorbed nor hemolysis is caused by it. Radiation sterilization using gamma-ray or the like will not give rise to any physical or chemical change of the separation means. Further, the separation means will not release any oily substance which will give undesirable influence on the operation of testing apparatuses.

Claims: A blood separation means comprising, as a main ingredient thereof: a gel-like material which is a copolymer of sebacic acid with 2,2-dimethyl-1,3-propanediol and 1,2-propanediol. A blood separation means as defined in claim 1, wherein the copolymerisation ratio of sebacic acid to a total of 2,2-dimethyl-1,3-propanediol and 1,2-propanediol falls within the range from 1 : 1.02 - 1 : 1.07. A blood separation means as defined in claim 2, wherein the ratio of 2,2-dimethyl-1,3-propanediol to 1,2-propanediol is from 0.85 : 0.15 - 0.75 : 0.25. A blood separation means as defined in claim 1, 2 or 3, wherein the molecular weight of the copolymer is from 1,000 - 10,000. A blood separation means as defined in claim 4, wherein the molecular weight of the copolymer is from 2,000 - 8,000. A blood separation means as defined in claim 5, wherein the copolymer has a specific gravity of 1.035 - 1.055 and a viscosity of 30,000 - 150,000 mPa.s (cP) at 25 °C. A blood separation means as defined in claim 6, further comprising, as a thixotropic.agent, 1 - 4 parts by weight of fatty acid amides blended with 100 parts by weight of the copolymer, whereby the blood separation means has a viscosity of 100,000 - 400,000 mPa.s (cP) at 25 °C.

Inventors: MURAKAMI KAZUNORI, TAGUCHI TETSUO, MURAKAMI, KAZUNORI, TAGUCHI, TETSUO
Applicants: NISSHO KK, NISSHO CORPORATION
Application year: 1992
Main classification: G01N33
IPC codes: A61L33, G01N33