Method for making biocompatible medical article

A method for making a biocompatible medical article, and preferably, a blood compatible medical article, through the use of a copolymer coating. The copolymer coating is synthesized using methacrylate or acrylate monomers with a functional group (primary amino group) for subsequent attachment of heparin. Synthesis of the copolymer coating is carried out using the proper proportion of hydrophobic monomer/hydrophilic monomer/functional monomer in order to optimize the solubility of the copolymer in alcohol, its insolubility in water (before and after heparin coupling), the heparin coupling efficacy and heparin bioactivity. Once the copolymer coating is fashioned, a medical article is coated with it. The coating is thereafter dried and heparin attached. In such a manner the present invention provides for a method for making a biocompatible medical article, and preferably, a blood compatible medical article.

FIELD OF THE INVENTION
 This invention relates to a method for making a biocompatible medical
 article, and preferably, a blood compatible medical article. In
 particular, this invention relates to a method of making blood compatible
 medical articles through the use of an alcohol-based polymer carrier
 suitable for the subsequent attachment of a bioactive molecule, such as
 heparin.
 BACKGROUND OF THE INVENTION
 The development of medical articles that contact physiological fluids,
 particularly blood, is a rapidly developing area of medicine. This has
 been hampered, however, by the lack of suitable synthetic materials that
 are stable when contacted with such fluids.
 Adverse reactions between materials and blood components are predominant
 factors limiting the use of synthetic materials that come into contact
 with physiological fluids. For example, catheters, vascular grafts, and
 the like, tend to serve as a nidus, or focus, for the formation of thrombi
 (blood clots). Initial contact of such materials with blood results in
 deposition of plasma proteins, such as albumin, fibrinogen,
 immunoglobulin, coagulation factors, and complement components. The
 adsorption of fibrinogen onto the surface of the material causes platelet
 adhesion, activation, and aggregation. Other cell adhesive proteins, such
 as fibronectin, vitronectin, and von Willebrand factor (vWF) also promote
 platelet adhesion. As a result, the continual use of anticoagulants in
 conjunction with the introduction of such materials to the body is often
 necessary.
 Furthermore, complement activation occurs when materials are introduced
 into blood. Adsorption of large amounts of IgG, IgM, and C3b onto surfaces
 causes activation. Subsequently, complexes may be formed which contribute
 to undesirable immune responses, such as proteolysis, cell lysis,
 opsonization, anaphylaxis, and chemotaxis. As a result, these responses
 render such materials incompatible with the living body.
 A number of approaches have been suggested to improve the biocompatibility,
 and even blood compatibility, of medical articles. One approach which has
 met with some success is to couple anticoagulants to the surface of
 biologically inert materials to impart antithrombogenic characteristics to
 the materials. Among the anticoagulants bound to the surface is heparin.
 It has been found generally that heparinized surfaces greatly reduce the
 generation of thrombus and thus cellular activation of blood contacting
 them, because heparin is a potent inhibitor of thrombin generation.
 Although many different methods have been disclosed for heparinizing a
 surface, the problem still exists to combine in one method the following
 features: (I) technological simplicity and wide applicability in terms of
 the substrate materials; (II) stability/durability of coating, (III) high
 bioactivity of attached heparin. (I) The most simple and universal method
 of surface modification of a medical article is a dip coating (or pumping
 through) the device in a solution of the proper polymer, followed by the
 solvent evaporation. Since the organic solution should be preferably used
 for the good wetting and coating of plastics, the haemocompatible polymer
 must be soluble in a non-toxic, chemically not aggressive organic solvent,
 such as, for example, ethanol. (II) Such a polymer, however, has to be
 insoluble in water, because the coating should be stable upon the contact
 with blood. (III) The polymer must include heparin in its structure or
 must have the functional chemical group, which is required for subsequent
 heparin coupling. Preferably, the polymer must be a copolymer, having both
 hydrophobic and hydrophilic segments. The hydrophobic segments are
 required to anchor the polymer to the substrate surface, while hydrophilic
 segments must provide an extra mobility to heparin molecule, which is
 important to achieve a high biological activity of heparin.
 It is thus an object of the present invention to provide a method of
 producing a haemocompatible coating from a polymer or copolymer as the
 primary layer which is soluble in a non-toxic, chemically not aggressive
 organic solvent, such as, for example, ethanol.
 It is a further object of the present invention to provide a method of
 producing such a polymer or copolymer which is also insoluble in water and
 will thus be stable upon the contact with blood.
 It is a further object of the present invention to provide a method of
 producing such a polymer or copolymer which has a functional chemical
 group, which is required for subsequent heparin coupling.
 It is a further object of the present invention to provide a method of
 producing such a polymer or copolymer which has both hydrophobic and
 hydrophilic segments.
 SUMMARY OF THE INVENTION
 The present invention meets these and other objects by providing a method
 for making a biocompatible medical article, and preferably, a blood
 compatible medical article, through the use of a copolymer coating. The
 copolymer coating is synthesized using methacrylate or acrylate monomers
 with a functional group (primary amino group) for subsequent attachment of
 heparin. Synthesis of the copolymer coating is carried out using the
 proper proportion of hydrophobic monomer/hydrophilic monomer/functional
 monomer in order to optimize the solubility of the copolymer in alcohol,
 its insolubility in water (before and after heparin coupling), the heparin
 coupling efficacy and heparin bioactivity. Once the copolymer coating is
 fashioned, a medical article is coated with it. The coating is thereafter
 dried and heparin attached. In such a manner the present invention
 provides for a method for making a biocompatible medical article, and
 preferably, a blood compatible medical article.

DETAILED DESCRIPTION OF THE DRAWINGS
 As already discussed above, the biocompatibility of materials used in
 medical articles can be improved by attaching a biomolecule, preferably
 heparin, to the relevant surface(s) of the medical article. According to
 the present invention such a biomolecule may be attached through the use
 of a copolymer coating, the copolymer coating synthesized using
 methacrylate or acrylate monomers with a functional group (primary amino
 group) for subsequent attachment of the biomolecule. Using this method,
 the extent and severity of adverse reactions between the substrate and
 bodily fluids, particularly blood, is reduced.
 Blood compatibility is much more complex than the compatibility of a
 material with other bodily fluids or tissues. This is because of the
 complex mixture of red cells, white cells, platelets, inorganic ions, and
 plasma proteins such as albumin, fibrinogens, and globulin in blood. Blood
 forms a clot or thrombus when injury occurs or when it is contacted by a
 foreign substance. Almost all materials set off this clot-forming process,
 and generally soon thereafter become coated with an irreversible clot of
 varying size. Such clots could have an adverse effect on the utility of
 such materials. Thus, particularly preferred materials of the present
 invention are particularly advantageous because they do not cause any
 significant coagulation or reaction of natural blood components as would
 occur in vivo, such as blood platelet activation and thrombin generation.
 The materials of the present invention include a substrate and a
 biomolecule attached through the use of a copolymer coating, the copolymer
 coating synthesized using methacrylate or acrylate monomers with a
 functional group (primary amino group) for subsequent attachment of the
 biomolecule in an amount and orientation effective to provide an improved
 nonthrombogenic surface relative to the substrate without either the
 copolymer coating or the copolymer coating and the biomolecule. The
 contact between blood and a foreign surface initiates a complex process of
 thrombogenesis that involves platelet adherence, aggregation, and granular
 release; thrombin generation; and fibrin formation. As a consequence,
 there are a number of parameters that can be selected as a measure of a
 material's thrombogenicity. Thus, evaluation of the reactions at the
 blood-material interface therefore typically involves a multi-parameter
 (i.e., multi-assay) approach (e.g., platelet factor 4 (PF4) assay for
 platelet activation, thrombin-antithrombin (TAT) assay for thrombin
 generation, and clotting time test for general antithrombogenic
 properties) used herein can be sufficient to show the improvements
 resulting from the method of the present invention.
 The blood compatibility of the material of the present invention can be
 demonstrated by reduced platelet activation and thrombin generation rate
 upon interaction with blood when compared to the material without the
 biomolecule attached through the copolymer coating synthesized using
 methacrylate or acrylate monomers with a functional group (primary amino
 group). By this it is meant that for a substrate to which there is a
 biomolecule, such as heparin, attached through copolymer coating
 synthesized using methacrylate or acrylate monomers, there is a reduction
 in the clotting time relative to the same substrate without the
 biomolecule and the copolymer coating synthesized using methacrylate or
 acrylate monomers with a functional group (primary amino group) for
 subsequent attachment of the biomolecule attached thereto when contacted
 with human blood according to the procedure outlined in the Examples.
 Preferably, the substrate surface of this invention is substantially
 nonthrombogenic, i.e., it has longer clotting time. Herein, a
 substantially nonthrombogenic substrate has clotting time at least 30%
 longer than conventional surface being tested at the conditions described
 elsewhere.
 Platelet activation can also be determined by the release of Platelet
 Factor 4. For a substrate to which there is a biomolecule, such as
 heparin, attached through a copolymer coating synthesized using
 methacrylate or acrylate monomers, there is a reduction in the amount of
 Platelet Factor 4 released relative to the same substrate without the
 biomolecule attached through a copolymer coating synthesized using
 methacrylate or acrylate monomers when contacted with human blood
 according to the procedure outlined in the Examples. Preferably, this
 reduction is in an amount of at least about 20%, and more preferably, at
 least about 50%.
 The blood compatibility of the material of the present invention can also
 be demonstrated by reduced thrombin-antithrombin (TAT) formation upon
 interaction with blood when compared to the material without the
 biomolecule attached through a copolymer coating synthesized using
 methacrylate or acrylate monomers. By this it is meant that for a
 substrate to which there is a biomolecule, such as heparin, attached
 through a copolymer coating synthesized using methacrylate or acrylate
 monomers with a functional group (primary amino group), there is a
 reduction in the number of thrombin-antithrombin (TAT) complexes formed
 relative to the same substrate without the biomolecule attached through a
 copolymer coating synthesized using methacrylate or acrylate monomers when
 contacted with human blood according to the procedure outlined in the
 Examples. Preferably, this reduction is in an amount of at least about
 30%, and more preferably, at least about 50%.
 The blood compatibility of the material of the present invention can be
 demonstrated by the increased clotting time upon interaction with blood
 when compared to the material without the biomolecule attached through a
 copolymer coating synthesized using methacrylate or acrylate monomers. By
 this it is meant that for a substrate to which there is a biomolecule,
 such as heparin, attached through a copolymer coating synthesized using
 methacrylate or acrylate monomers, there is a reduction in amount of
 elastase formed relative to the same substrate without the biomolecule and
 the copolymer coating synthesized using methacrylate or acrylate monomers
 with a functional group (primary amino group) for subsequent attachrment
 of the biomolecule thereto when contacted with human blood according to
 the procedure outlined in the Examples. Preferably, this increase in
 clotting time is in an amount of at least 50%, and more preferably, at
 least about 100%.
 FIG. 1A illustrates the basis upon which the present invention of a
 copolymer coating synthesized using methacrylate or acrylate monomers with
 a functional group (primary amino group) for subsequent attachment of the
 biomolecule rests. As seen, the extracellular side of the membrane mostly
 consists of phosphoryl choline (PC) containing phospholipids such as
 phosphatidylcholine and sphingomielin. The phospholipids are assembled
 along the membrane in such a way that only polar PC groups are exposed to
 the extracellular space. Because the membrane of blood cells are not
 naturally thrombogenic, it is reasonable to conclude that a properly
 oriented PC group would be a biocompatible coating for medical articles.
 Past attempts have been made to use phospholipid polar groups to obtain a
 biocompatible material. For example, 2-methacryloyloxyethyl
 phosphorylcholine (MPC) was offered in Japanese laid-open patent
 application 54-63025. This polymer has been suggested for use for the
 short term contact with blood, such as blood bags and the like.
 Nonetheless, polymers containing MPC have not, to date, proven wholly
 satisfactory for the long term contacting with blood or, further, in use
 with medical articles in contact with blood. In particular, several
 patents and patent application (e.g. the above-referenced Japanese
 application JPA-54-63,025 published May 21, 1979; U.S. Pat. Nos.
 5,466,853; and 5,368,733) state MPC containing copolymers can be used on
 medical article as blood compatible coatings. Several recent studies on
 coating of oxygenators and stents with MPC copolymers did not lead to
 marketing of coated devices. The main drawback of MPC coating is that it
 is passive coating. Although it can reduce platelet adhesion, it does not
 reduce thrombin generation rate and it does not reduce platelet and
 leukocyte activation in blood measured by release of PF4 and elastase,
 respectively. It is a coupling of particular bioactive substances, e.g.
 heparin, that alters the properties of MPC copolymers rendering them with
 truly antithrombogenic properties. Nakabayashi U.S. Pat. No. 5,658,561
 "Method Of Producing Anti-Thrombogenic Material And Material Produced
 Thereby" and assigned to Biocompatibles Limited, Uxbridge, England, for
 example, mentions the use of MPC and heparin, although the specific
 implementation of heparin grafting to MPC is not disclosed. Moreover, the
 method disclosed relates to the graft of such to regenerated cellulose,
 and requires a subbing layer, in the case of silicone medical articles,
 for example. There is, in fact, evidence that MPC copolymers do not
 influence the rate of thrombin generation and, in general, the rate of
 blood activation, presented in the tables below I and II. The present
 invention, in contrast, provides a coating which uses a MPC copolymers
 having heparin attached thereto so as to provide much improved
 biocompatibliity, reduce thrombin generation rate and platelet activation
 in blood measured by release of PF4, also seen in the tables I and II
 below.
 FIG. 1B depicts a block representation of a suitable copolymer coating used
 in the present invention. As seen, the copolymer coating consists
 essentially of three groups, each group having a particular characteristic
 with regard to either water or the subsequent attachment of biomolecules.
 In particular, the copolymer coating has a first group 1 comprised of a
 hydrophilic moiety, a second group 2 comprised of a hydrophobic moiety and
 a third group 3 comprised of a functional moiety provided for the
 subsequent attachment of a biomolecule thereto.
 The hydrophilic block 1 may be provided by the synthesis or polymerization
 of any number of possible suitable monomers or polymers including one or
 more monomers selected from the group consisting of acrylic or methacrylic
 monomers which have a hydrophilic moiety (which makes the monomer soluble
 in water and the copolymer formed therefrom wettable) including
 methacryloyl oxyethyl phosphorylcholine (MPC), acrylamide, poly(ethylene
 glycol) methacrylate, hydroxyethyl methacrylate, hydroxypropyl
 methacrylate, acrylic acid, methacrylic acid, 2,3-dihydroxypropyl
 acrylate, 2,3-dihydroxypropyl methacrylate, 3-sulfopropyl methacrylate,
 methacrylamidopropyltrimethylammonium chloride, or any of the homologues
 thereof. In the preferred embodiment the hydrophilic group is provided
 using methacryloyl oxyethyl phosphorylcholine (MPC).
 The hydrophobic block 2 may be provided by the synthesis or polymerization
 of using any monomers which are not soluble in water, monomers or polymers
 including one or more monomers selected from the group consisting of butyl
 methacrylate, butyl acrylate, dodecyl methacrylate, dodecyl acrylate,
 heptyl acrylate, hexadecyl methacrylate, octyl methacrylate or any of the
 homologues thereof. In the preferred embodiment the hydrophobic monomer is
 provided using butyl methacrylate.
 The functional group 3 may be provided by the synthesis or polymerization
 of any suitable monomers selected to provide the functional group for the
 subsequent attachment of a biomolecule, the functional group further being
 provided to synthesize and thus form the copolymers with the hydrophobic
 and the hydrophilic blocks. A suitable functional group may be provided
 from one or more monomers selected from the group consisting of
 2-aminoethyl methacrylate hydrochloride, N-(3-aminopropyl)methacrylamide
 hydrochloride) or similar monomer with primary amino group or the group,
 which is convertible to the amino group. In addition, any of the
 homologues thereof may also be used. In the preferred embodiment the
 monomer is 2-aminoethyl methacrylate hydrochloride.
 FIG. 1C illustrates the structure of a copolymer coating synthesized using
 methacrylate monomers with a functional group for the subsequent
 attachment of a biomolecule according to the present invention. As seen in
 this illustrated example, the hydrophobic group is provided through a
 butyl group, the hydrophilic group is provided by MPC while the functional
 group is provided by an aminoethyl group.
 FIG. 2 depicts the basic steps for providing a medical article with the
 biocompatible coating of the present invention. First at step 100 the
 surface of the article is cleaned. This may be accomplished in any
 acceptable manner according to the specific material from which the
 article is constructed. For a silicone article, for example, the surface
 is cleaned by supercritical fluid extraction, while for a polyurethane
 article the surface is cleaned with ethanol. Next at step 112 an organic
 solvent-based solution of the copolymer coating synthesized using
 methacrylate or acrylate monomers with a functional group (primary amino
 group) for subsequent attachment of the biomolecule is applied. Specific
 details concerning the creation of the copolymer coating are discussed
 below with regard to FIG. 3. The article is then dried at step 114,
 driving off the organic solvent and leaving a coating of copolymer. Once
 such a coating is present, the copolymer coating is further treated at
 step 116 so as to achieve a desired level of biocompatibility. In the
 preferred embodiment this is accomplished by coupling heparin to the
 coating. Specific details concerning the coupling of heparin are discussed
 below with regard to FIG. 3
 FIG. 3 depicts the steps used to create an acceptable copolymer coating
 used in the present invention. First at step 120 an acceptable mixture of
 hydrophobic monomer/hydrophilic monomer/functional monomer is created. As
 discussed above, the monomers are selected in order to optimize the
 solubility of the copolymer in an organic solvent (preferably ethanol),
 its insolubility in water (before and after heparin coupling), the heparin
 coupling efficacy and heparin bioactivity. In the preferred embodiment the
 copolymer coating is synthesized using methacrylate or acrylate monomers
 with a functional group (primary amino group) for subsequent attachment of
 heparin. An acceptable copolymer coating may be formed by selecting the
 monomers n-butyl methacrylate (BMA); 2-methacryloyloxyethyl
 phosphorylcholine (MPC); and 2-aminoethyl methacrylate in the relative
 molar proportions of 65:20:15. The selected monomers are mixed together at
 step 122 and the polymer is synthesized at step 124 by conventional free
 radical polymerization. An acceptable synthesis conditions are typically
 using ethanol at 60.degree. Celsius for 24 hours. Synthesis results in a
 copolymer coating which is soluble in alcohol, insoluble in water and to
 which heparin may be readily coupled. Thereafter the copolymer is ready
 for application to the medical article.
 FIG. 4 depicts the steps used to coat the surface of a medical article with
 the copolymer coating of the present invention. After preliminary cleaning
 of the surface of medical article at 200, alcohol solution of the polymer
 contacts the surface by either pumping of the solution through the device
 or immersing the device into the solution at 202. The time, during which
 surface is in contact with solvent should be in the range from several
 seconds to several minutes. The surface of the medical article is then
 dried at 204 (i.e., removing the alcohol carrier). This can be done by a
 variety of methods. Preferably, they are carried out in one step by
 flushing the surface of the substrate with moist air (e.g., greater than
 50% relative humidity).
 FIG. 5 depicts the steps used to couple a biomolecule to the copolymer
 coating. One particularly preferred method is to couple heparin using an
 oxidation method involving the use of periodate. The basic steps of the
 preparation of such a solution are shown. These steps consist of admixing
 heparin with a periodate solution shown as 210; reacting the admixture
 shown as 212; and adding cyanoborohydrate to the admixture at 214.
 Essentially, the prepared heparin solution used to couple heparin to the
 copolymer coating is described in Verhoeven et al. U.S. Pat. No. 5,679,659
 Method For Making Heparinized Biomaterials assigned to the assignee of the
 present invention and incorporated herein by reference. The heparin, is
 contacted with a periodate in a buffered aqueous solution and allowed to
 react. This controlled oxidation provides a limited number of reactive
 aldehyde groups per molecule. The periodate is a water-soluble periodate,
 preferably, an alkali metal periodate, such as sodium periodate. When the
 biomolecule is heparin, the amount of periodate used is sufficient to
 react with no more than two of the sugar units in the heparin molecule
 (i.e., the basic disaccharide residues constituting the structure of the
 glycosaminoglycan). If the periodate used is sodium periodate and the
 heparin used is a commercially available injectable form of heparin (e.g.,
 its sodium salt with activity of 160 units/milligram), the weight ratio of
 heparin to periodate should be about 30:1 or less in order to react with
 no more than two of the sugar units in the heparin molecule. It will be
 appreciated by those skilled in the art that the amount of periodate
 required for other periodate compounds and other forms of heparin can be
 determined by conventional calculation and empirical tests.
 The reaction between heparin and periodate takes place in an aqueous buffer
 solution. Generally, buffers having a pH in a neutral to slightly acidic
 range of about 4.5 to about 8 can be used. A lower pH (e.g., an acetate
 buffer at pH 4.5) is preferred if a rapid reaction is desired while a more
 neutral pH (e.g., a phosphate buffer at pH 6.88) is preferred for a slower
 reaction with a longer storage life. With the acetate buffer at a pH of
 4.5, the reaction should proceed for about 3 hours, while with a phosphate
 buffer at a pH or 6.88, the reaction should proceed for about 16 hours. If
 desired, the reacted mixture may then be stored prior to use at about
 5.degree. C.
 The reacted mixture is diluted and the pH adjusted in order to bring the pH
 of the mixture to a pH that is favorable for the coupling reaction between
 the biomolecule and the copolymer coating synthesized using methacrylate
 or acrylate monomers with a functional group (primary amino group). A mild
 reducing agent, such as sodium cyanoborohydride, is added to the diluted
 mixture to effect the reduction of the bonds formed between the reactive
 aldehyde groups on the oxidized biomolecule and the amine functional
 groups on the copolymer coated on the substrate surface. The substrate
 surface being treated is then contacted with (e.g., immersed in or flushed
 with) the diluted mixture at a sufficient temperature and for a sufficient
 time to complete the reaction (i.e., attach the biomolecule). This time
 can range from about 30 seconds to about 2 hours at temperatures ranging
 from about 20.degree. C. to about 60.degree. C.
 Once the heparin solution is prepared it is used to couple heparin to the
 medical article. In particular, the heparin solution is brought into
 contact with the MPC copolymer coated surface of the medical article. For
 example, the 2000 ml of the heparin solution prepared according to the
 above is carefully dispensed in a reactor glass chamber. The temperature
 of the water circulation bath is set at 50.degree. C., while same pumping
 speed is maintained. Next, The reactor chamber is filled in such a way
 that desired article may be immersed in the heparin solution. Stirring is
 started so as to prevent that a strong vortex is formed. The immersion of
 the medical article in the heparin solution is allowed to continue for 120
 minutes at 50.degree. C. Next, the article is dried in the way described
 above.
 The method of the present invention is particularly applicable to stents.
 The term "stent" refers to any device capable of being delivered by
 catheter. FIG. 6 is an illustration of a stent 10 (shown around a balloon
 15) treated with the copolymer coating synthesized using methacrylate or
 acrylate monomers with a functional group (primary amino group) for
 subsequent attachment of the biomolecule according to the present
 invention. Stent 10 includes lumen wall-contacting surface 12 and
 lumen-exposed surface (not shown). Where the stent is shaped generally as
 a tube-like structure, including a discontinuous tube or ring-like
 structure, the lumen-wall contacting surface is the outside surface of the
 tube and the lumen-exposed surface is the inner surface of the tube. When
 in place, the outer surface is in contact with a portion of a wall of a
 lumen, and the inner surface is in contact with blood. Stent 10 is coated
 with the copolymer coating synthesized using methacrylate or acrylate
 monomers with a functional group (primary amino group) with a biomolecule,
 thus forming blood compatible surface 14. Typically, both the lumen
 wall-contacting surface 12 and the lumen-exposed surface are coated with
 the copolymer coating synthesized using methacrylate or acrylate monomers
 with a functional group (primary amino group) and biomolecule, although,
 depending on the materials used to make the stent, only the lumen-exposed
 surface would need to be. Balloon 15 is positioned adjacent the
 lumen-exposed surface of the stent to facilitate delivery of the stent.
 Other suitable stents include a deformable metal wire stent useful as a
 stent framework, such as that described in U.S. Pat. No. 4,886,062
 (Wiktor), which discloses preferred methods for making a wire stent. Other
 useful metallic stents include those of U.S. Pat. No. 4,733,665 (Palmaz)
 and U.S. Pat. No. 4,800,882 (Gianturco). Other suitable stents include the
 Palmaz-Schatz coronary stent (Johnson & Johnson Interventional, Warren,
 N.J.) and stents from memory-shaped metals such as self-expanding nitinol
 stents including that available under the trade designation CARDIOCOIL
 from Medtronic, Eden Prairie, Minn., and disclosed in U.S. Pat. No.
 5,372,600. Preferred stents for use in this invention should be flexible
 to navigate lumens during insertion, biocompatible, and reliably expand
 and embed in the lumen wall.
 The method of the present invention also is particularly applicable to
 blood gas exchange devices, e.g., oxygenators. This includes both sheet
 and hollow fiber (or tubular) forms of membrane oxygenators, which are
 well known in the art. Hollow fibers suitable for use with oxygenators are
 made blood compatible, typically by exposing the hollow fibers to the
 alcohol solution of the copolymer synthesized using methacrylate or
 acrylate monomers with a functional group (primary amino group) for
 subsequent attachment of the biomolecule; drying with moist air to remove
 solvent and excess compound; and then exposing it to an aqueous
 biomolecule solution for a time sufficient to couple the biomolecule to
 the polymer and to form blood compatible hollow fibers.
 FIG. 7 illustrates a simplified diagram of a blood oxygenator 20, wherein a
 plurality of hollow fibers 22 is disposed within hollow housing 24. Though
 depicted in a linear arrangement, it is to be understood that the fibers
 could be arranged in a variety of configurations, including a circular or
 spiral arrangement, as well as being wrapped around a core or the like.
 The fibers are supported within housing 24 by end walls 25 and 26. Blood
 flow inlet 28 permits the passage of blood through fibers 22, as depicted
 in FIG. 8, and thereafter out through blood flow outlet 29. Although these
 FIGS. depict blood flow through the fibers, it is to be understood that,
 depending upon the desired characteristics of the oxygenator, blood can
 flow either through or over the hollow fibers. Gas (e.g., oxygen) flows
 into housing 24 via gas inlet port 31. The gas flows over the fibers and
 out of housing 24 via gas outlet port 32. The hollow fibers 22 and other
 surface of the oxygenator would be made blood compatible by exposing the
 entire surface of the fibers to the copolymer coating synthesized using
 methacrylate or acrylate monomers with a functional group (primary amino
 group); drying to remove solvent and excess compound; and then exposing it
 to a biomolecule for a time sufficient to couple the biomolecule to the
 silicon and form a biocompatible membrane, as represented by layer 36 in
 this FIG. 8.
 Although the examples described below involve treatment on polymeric films
 or tissue culture plates as the substrate surfaces, it is not intended
 that this invention be so limited.
 EXPERIMENTAL EXAMPLES
 Synthesis of MPC-BMA-AEMA Copolymer
 The MPC, BMA and AEMA monomers in the proportion 20:65:15, respectively,
 were dissolved into ethanol (analytical grade) to the total solids
 concentration of 1 mole/L. Glass ampoules (100 ml) were filled with
 monomers solution and 2,2'-azobisisobutyronitrile (AIBN) was dissolved to
 a concentration of 1 mmole/L at room temperature. Argon gas was bubbled
 through the solution to displace the oxygen, and then the ampoule was
 sealed. The polymerization was carried out at 60.degree. C. for 1 hour.
 After cooling to the temperature of 30.degree. C. or lower, the content of
 the ampoule was poured into 2 L of the mixture of diethyl ether and
 N,N-dimethylformamide (DMF) (9:1 by volume) to remove unreacted monomer
 and to precipitate the copolymer formed. The precipitated copolymer was
 filtered off with the glass filter (pores size of 5 .mu.m) and dried in
 vacuo. The dry copolymer was kept in refrigerator at 4.degree. C. until
 use.
 Thereafter to apply the copolymer to the surface of medical article, the
 copolymer is dissolved in ethanol to the concentrations from 0.1 wt % to 5
 wt %, preferably 1.0% and this solution is ready for application to the
 medical article.
 Application to the Medical Article
 Copolymer solution is pumped through the Medtronic PVC, PU tubing, Maxima
 hollow fibers oxygenators for one minute and then the tubing is dried by
 blow of the air through the tubing for 1 h. Medtronic Wiktor stents and
 Medtronic DLP's PVC cannulae are dip coated at the lifting speed from 10
 cm to 100 cm per minute. The coated devices are dried at room temperature
 for 12 h in air.
 Immobilization of a Biomolecule
 The heparin, is contacted with a periodate in a buffered aqueous solution
 and allowed to react. If the periodate used is sodium periodate and the
 heparin used is a commercially available injectable form of heparin (e.g.,
 its sodium salt with activity of 160 units/milligram), the weight ratio of
 heparin to periodate should be about 30:1 or less in order to react with
 no more than two of the sugar units in the heparin molecule. The reaction
 between heparin and periodate takes place in an aqueous buffer solution.
 With the acetate buffer at a pH of 4.5, the reaction should proceed for
 about 3 hours. The reacted mixture is diluted and the pH adjusted in order
 to bring the pH of the mixture to a pH=9 that is favorable for the
 coupling reaction between the biomolecule and the copolymer coating
 synthesized using methacrylate or acrylate monomers with a functional
 group (primary amino group). A mild reducing agent, such as sodium
 cyanoborohydride, is added to the diluted mixture to effect the reduction
 of the bonds formed between the reactive aldehyde groups on the oxidized
 biomolecule and the amine functional groups on the copolymer coated on the
 substrate surface. This time is about 2 hours at temperature of about
 60.degree. C.
 Blood Testing
 We have performed two types of tests aiming at the determination of blood
 activation and have observed the similar tendency in both experiment: A
 surface coated with the present invention, that is a surface having a
 copolymer coating synthesized using methacrylate or acrylate monomers with
 a functional group a biomolecule attached thereto provided a superior
 blood compatible surface as compared to any of the other surfaces tested.
 These other surfaces included both uncoated polymers as well as polymers
 coated with MPC, but without the attachment of a biomolecule, as taught by
 the present invention.
 TABLE 1
 Clotting time test using recalcified human Plasma Rich Protein (PRP).
 Material Clotting time, sec
 Polypropylene (PP) 595 .+-. 38
 PP-(MPC-DMA) 619 .+-. 25
 Polyurethane (PU) 592 .+-. 12
 PU-(MPC-BMA) 623 .+-. 9
 PU-(MPC-BMA-PMBU) 636 .+-. 8
 PU-(MPC-BMA-Heparin) 1350 .+-. 30
 "PMBU" stands for Polymethoxyacryloyloxyethyl butylurethane
 "DMA" stands for dodecyl methacrylate.
 Table 1 shows the results for several surfaces of a clotting time test
 using recalcified human PRP performed in accordance with the teachings of
 "Platelet Procoagulant Surface As An Essential Parameters For The In Vitro
 Evaluation Of The Blood Compatibility Of Polymers," J.
 Mater.Sci.Mater.Med.6, 367 (1995). In particular six surfaces where tested
 including both uncoated polymers as well as polymers coated with MPC, but
 without the attachment of a biomolecule, as taught by the present
 invention. The six surfaces treated were: Polypropylene (PP);PP-(MPC-DMA);
 Polyurethane (PU); PU-(MPC-BMA), PU-(MPC-BMA-PMBU) and
 PU-(MPC-BMA-Heparin.) As shown in Table 1 the MPC copolymers without
 heparin attachment did not increase the clotting time of PP and PU.
 Attachment of heparin resulted in a two-fold increase of the clotting time
 and, therefore, MPC-Heparin combination is superior to any other MPC
 copolymers in terms of preventing thrombin generation in blood. Data,
 shown in Table 2 also supports this conclusion.
 TABLE 2
 Ratios of blood activation parameters (coated/non-coated) from loop
 studies. Flow condition:pulsatile flow (pulse frequency = 1Hz; Average
 shear rate at surface = 133 s.sup.-1). Human blood was heparinized
 (0.6-0.8 IU/ml).
 Material .beta.TG TAT
 PU--(MPC--PMB--PMBU)/PU 0.56 .+-. 0.41 0.80 .+-. 0.38
 PP--(MPC--DMA)/PP 1.1 .+-. 0.56 2.0 .+-. 2.7
 PU--(MPC--PBM-Heparin)/PU 0.58 .+-. 0.36 0.39 .+-. 0.11
 PP--(MPC--PBM-Heparin)/PP 0.15 .+-. 0.09 0.27 .+-. 0.09
 Table 2 shows the ratios of blood activation parameters (coated/non-coated
 from the loop studies. The loop studies were performed with pulsatile flow
 (pulse frequency=1 Hz; Average shear rate at surface=133 s.sup.-1). Human
 blood was heparinized (0.6-0.8 IU/ml). Thrombin-antithrombin complex (TAT)
 is a marker of thrombin generation. The higher is its concentration in
 blood, the higher is activation of coagulation system. Clearly, the was no
 statistically significant difference in terms of TAT concentration upon
 coating of PU and PP with MPC copolymers, unless the heparin was coupled
 to such copolymers. .beta.TG is a marker of platelet activation. Although
 MPC copolymers did reduced platelet adhesion and activation, the coupling
 of heparin to MPC coating on PP resulted in the further reduction of
 platelet activation, as shown in this table.
 Results
 The surface featuring a copolymer coating synthesized using methacrylate or
 acrylate monomers with a functional group (primary amino group) and to
 which a biomolecule is attached clearly improves the hemocompatibility and
 reduces the propensity to inflammation of the surface, as compared to both
 untreated surfaces and surface coated with the monomer
 2-methacryloyloxyethyl phosphorylcholine (MPC,) only.
 The relative superiority of the present invention compared to uncoated
 surfaces and surface coated only with MPC may be further seen in FIG. 9.
 FIG. 9 depicts the relative difference between the present invention and
 materials not featuring the present invention in reference to thrombin
 generation. In particular, three thrombin generation curves from
 recalcified platelet rich plasma are shown. The three curves correspond
 with three separate materials, the first designated PU being an untreated
 75D-type polyurethane (a suitable 75D polyurethane is available as
 PELLETHANE 75D from Dow Chemical Corp.), the second curve designated
 PU-MPC being a 75D polyurethane surface treated using an MPC-type coating,
 the MPC-type coating provided by the above-described process of providing
 a copolymer coating synthesized using methylacrylate or acrylate monomers
 with a functional group, but without the functional group being
 heparinized. Finally, the third curve depicts the polyurethane surface
 treated with a copolymer coating as described above and in which the
 functional group has had heparin coupled thereto. As seen, thrombin
 generation occurs quickest and in the greatest relative amount for the
 untreated polyurethane surface while the PU-MDC heparinized surface,
 according to the present invention, exhibits the least amount of thrombin
 generation in the greatest relative time. This is an important and crucial
 difference in that, from a patient's perspective, much less thrombin in
 the blood stream is generated overall using the present invention as
 compared to prior surfaces. In particular regards to a PU-MPC surface
 without heparinization, the present invention is almost half as
 thrombogenic while requiring much greater time.
 Although as discussed above ethanol is the preferred solvent for the
 copolymer solution according to the present invention, it should be
 understood other organic solvents may also be used, including isopropyl
 alcohol, acetone, butanone, hexane, n-octane, isooctane, cyclohexane,
 benzene, toluene, methyl, ethyl, and isopropyl formate, methyl, ethyl, and
 isopropyl acetate, methyl, ethyl, and isopropyl propionate, and ethyl
 acetate. What is most important is that the organic solvent selected is
 such that it will permit the selected monomers to readily dissolve but not
 the polymer or polymeric substrate to which the copolymer solution is
 coated. Moreover, as used herein "polymer" or "polymeric surface"
 generally may include polymeric materials such as silastic or other
 silicone-based materials, polyethylene tecephtalate (PET), dacron, knitted
 dacron, velour dacron, polyglacin, chromic gut, nylon, silk, bovine
 arterial graft, polyethylene (PE), polyurethane (PU), PMMA [poly-(methyl
 methacrylate), latex, poly vinyl] alcohol (PVA), poly (hydroxyethyl
 methacrylate (PHEMA), poly (glycolic acid), poly (acrylonitrile) (PAN),
 floroethylene-co-hexafluoropropylene (FEP), polypropylene (PP),
 polyvinylchloride (PVC), and polyvinylidenefluoride (PVDF), and teflon
 (PTFE). Medical articles made using these materials can be coated or
 uncoated, and derivatized or underivatized, prior to being coated with the
 copolymer coating synthesized using methacrylate or acrylate monomers with
 a functional group (primary amino group).
 As used herein a "medical article" is defined as any article or device that
 has surfaces that contact tissue, blood, or other bodily fluids in the
 course of their operation, which fluids are subsequently used in patients.
 This can include, for example, extracorporeal devices for use in surgery
 such as blood oxygenators, blood pumps, blood sensors, tubing used to
 carry blood and the like which contact blood which is then returned to the
 patient. This can also include endoprostheses implanted in blood contact
 in a human or animal body such as vascular grafts, stents, pacemaker
 leads, heart valves, and the like that are implanted in blood vessels or
 in the heart. This can also include devices for temporary intravascular
 use such as catheters, guide wires, and the like which are placed into the
 blood vessels or the heart for purposes of monitoring or repair.
 A "biomolecule" is defined as a biologically active molecule. As used
 herein this term includes, for example: antibacterial and antimicrobial
 agents; anticoagulant and antithrombotic agents; platelet agents;
 anti-inflammatories; enzymes; catalysts; hormones; growth factors; drugs;
 vitamins; antibodies; antigens; nucleic acids; dyes (which act as
 biological ligands); DNA and RNA segments; and proteins and peptides. The
 biomolecules can be synthetically derived or naturally occurring. These
 biomolecules include heparin, prostaglandin E.sub.1 (PGE1), ticlopidine,
 plasmin, urokinase, TPA, polyethylene oxide (PEO), and FUT-175. Heparin
 inhibits the coagulation of blood by interacting with antithrombin III and
 thrombin to inhibit the conversion of fibrinogen to fibrin. Ticlopidine
 and prostaglandin E.sub.1 inhibit the activation of platelets. Plasmin,
 urokinase, and TPA are serin proteases which lyse protein deposits and
 networks. Polyethylene oxide minimizes protein adsorption, and FUT-175
 inhibits the formation of thrombin.
 A "biocompatible" material is one that does not generally cause significant
 adverse reactions (e.g., toxic or antigenic responses) in the body,
 whether it degrades within the body, remains for extended periods of time,
 or is excreted whole. Ideally, a biocompatible material will not induce
 undesirable reactions in the body as a result of contact with bodily
 fluids or tissue, such as tissue death, tumor formation, allergic
 reaction, foreign body reaction (rejection) or inflammatory reaction.
 A "blood compatible" material is one that will not induce undesirable
 reactions in the body as a result of contact with blood, such as blood
 clotting. This can be demonstrated by reduced thrombin generation, for
 example.
 It will be appreciated by those skilled in the art that while the invention
 has been described above in connection with particular embodiments and
 examples, the invention is not necessarily so limited and that numerous
 other embodiments, examples, uses, modifications and departures from the
 embodiments, examples and uses are intended to be encompassed by the
 claims attached hereto. The entire disclosure of each patent and
 publication cited herein is incorporated by reference, as if each were
 individually incorporated by reference.