Method for producing improved medical devices and devices so produced

Medical devices and methods of producing same are provided. The medical device comprising a body member and a coating on at least a portion of the body member comprising an insitu condensation product of a first electrophilically active, high molecular weight polyalkylene oxide and a second high molecular weight polyoxyalkylene derivative.

BACKGROUND OF THE INVENTION
 The present invention relates generally to medical devices and products.
 More specifically the present invention relates to medical devices and
 products that are coated with a material to provide improved
 characteristics.
 There are literally thousands of products that are used in the medical
 industry for a variety of treatments and therapies. The surface
 characteristics of some of these products may be critical to the ability
 of the products to function. Such products run the gamut from membranes
 used in blood and cell separation devices, theracyte devices, dialyzers,
 arterial filters, catheters, wound drains, vascular grafts, and heart
 valve tissues.
 For example, a slippery or low friction surface property is required in
 various medical devices. These devices include wound drains, chest tubes,
 guide wires, catheters, and angioplasty products. A lubricious surface is
 desirable as it reduces pain to the patient during insertion and/or
 removal of the device.
 It is also desirable, on a number of medical products, to provide a surface
 that has anti-microbial properties. Likewise, medical devices that have
 surfaces that are non-thrombogenic are valuable in many applications.
 In certain applications, it is also desirable to provide a surface that
 binds to certain type of cells or agents. For example, such products may
 be desirable for implantable biological tissue such as bioprosthetic
 valves.
 By way of further and more detailed example, in processing whole blood for
 therapeutic administration to patients, it is desirable to separate the
 various cellular components. In particular, it is desirable to remove
 leukocytes because of their role in mediating immunologic reactions which
 can cause adverse clinical events such as allosensitization. For a review
 of adverse clinical sequellae to transfusion, see Sekiguchi, et al.,
 Leucocyte-depleted blood products and their clinical usefulness, Ch. 5,
 pg. 26-33, from The Role of Leucocyte Depletion in Blood Transfusion
 Practice (1988). Furthermore, leukocytes are unessential for therapeutic
 supplementation of cell deficiencies in patients involving platelets and
 red cells. Thus, filter systems have been devised for passaging blood
 cells in order to remove leukocytes while allowing platelets or red blood
 to pass through for subsequent recovery.
 There have been a number of approaches reported for leukocyte depletion.
 U.S. Pat. No. 4,330,410 discloses a packed fiber mass with leukodepletion
 properties comprising fibers of cellulose acetate, acrylonitrile,
 polyamide, or polyester. U.S. Pat. No. 4,925,572 discloses the use of a
 gelatin coating to inhibit red blood cell (RBC) and platelet adhesion.
 Leukodepletion is accomplished primarily through physical entrainment of
 the cells in the fiber body, and adhesion of RBCs and platelets results
 from the gelatin coating. U.S. Pat. No. 4,936,998 discloses a strategy for
 leukodepletion in which a hydrophilic monomer containing hydroxyl or amido
 groups and functional nitrogen-containing groups such as primary or
 secondary amino groups is coated onto a filter matrix of known fibers such
 as polyester, polyamide, etc.
 Modification of fiber surfaces has also been used to obtain materials with
 improved cell separation properties. For example, U.S. Pat. No. 4,130,642
 discloses a packed column in which the packing material comprises an
 Egyptian cotton which has been de-fatted and bleached so that RBC readily
 pass through the column.
 Some separation strategies involve multiple steps. U.S. Pat. No. 4,925,572
 discloses a multistep method comprising an upstream porous element for
 removal of gels, a second element of finer porosity for removal of
 aggregated matter, and a final filtration step involving common fibers to
 which surface tension-reducing and improved wetting are obtained by
 radiation grafting of biocompatible moieties. Further description of
 leukodepletion methods is contained in Rikumaru, et al., Advanced methods
 for leucocyte removal by blood filtration, Ch. 6, pgs. 35-40, from The
 Role of Leucocyte Depletion in Blood Transfusion Practice (1988).
 It is of utmost importance in designing leukodepletion strategies in which
 one goal is to obtain good recoveries of platelets and RBCs, to achieve
 separations without activating platelets or complement. It is also
 important that any coatings utilized to enhance the separations not be
 leached into solution, since the recovered cells are intended for
 intravascular administration to patients. One approach embodies a filter
 composed of a porous polymer material with continuous pore structure
 having a coating combining a nitrogen-containing functional group with a
 polyethylene oxide chain having 2-15 repeating units (See Jap. Kokai Pat.
 Application No. Hei 5 [1993]-194243). This material is said to entrap
 leukocytes while giving high yields of platelets.
 The use of polyalkylene oxide polymers is well-known in the construction of
 biocompatible materials, because of its low biological activity in
 activating cellular and humoral components of blood, and in stimulating
 immune responses. However, the inertness of the polyalkylene oxide
 polymers may also interfere with the degree of separation that can be
 obtained with cell separation filters, unless combined with functional
 groups that enhance separation parameters. A suitable combination of
 coating components has not heretofore been developed which is efficacious
 for cell separations from whole blood as distinct from semi-purified cell
 suspension mixtures.
 Likewise, for a number of other medical products, a suitable material or
 combination for coating products has not been provided.
 SUMMARY OF THE INVENTION
 The present invention provides improved methods for coating medical
 products and devices. Additionally, the present invention provides
 improved coated medical devices and products.
 Summarizing briefly, the present invention provides, in an embodiment,
 medical devices which are coated, at least in part, with a chemical
 condensation product, prepared by reaction in-situ of a first
 electrophilically active, high molecular weight polyalkylene oxide, and a
 second high molecular weight polyalkylene oxide derivative. In an
 embodiment, the derivative can be either a tetraaminopolyalkylene oxide or
 a bifunctional dihydroxy- or diamino- polyoxyalkylene derivative, or
 combination thereof. In another embodiment, the coating may be an
 isopolymer of a high molecular weight tetraacrylatepolyalkylene oxide,
 polymerized by exposure to radiation.
 The condensation reaction occurs in-situ, e.g. after one polymer is placed
 onto a surface, the second polymer is then contacted with the surface and
 specifically the first polymer, and the condensation reaction occurs
 spontaneously at a temperature between 5 degrees and about 200 degrees
 centigrade. The electrophilically active, high molecular weight
 polyalkylene oxide compound has the general structure Y-PEO-R-PEO-Y
 wherein Y is a reactive moiety selected from an oxycarbonylimidazole,
 tresyl-, tosyl-, N-hydroxysuccinimidyl, and p-nitrophenyl-activated
 esters; acrylates; glycidyl ethers; and aldehydes. The
 oxycarbonylimidazole leaving group is preferred, as will be apparent from
 the detailed specification, R is a spacer molecule (a chemical backbone)
 consisting of either bisphenol A (4,4'-(1-methylethylidene)bisphenol) or
 bisphenol B (4,4'-(1-methylpropylidene)bisphenol), and PEO stands for
 polyalkylene oxide.
 In a method of preparing the material of the present invention, a first
 polymer comprising an electrophilically active, high molecular weight
 polyalkylene oxide compound, having terminal leaving groups as indicated
 herein above, oxycarbonylimidazole being preferred, is applied to the
 surface, then drying the first polymer onto the surface, followed by
 applying a second polymer consisting of either a tetraamino-, a diamino-,
 or a dihydroxy- polyalkylene oxide, or combination thereof The reaction
 between the polymers occurs spontaneously, and an incubation at a
 temperature from about 5 degrees to about 200 degrees Centigrade is
 continued for a time sufficient to obtain substantial completion of
 crosslinking.
 To this end, in an embodiment, the present invention provides a medical
 device comprising a body member and a coating on at least a portion of the
 body member comprising an in-situ condensation product of a first
 electrophilically active, high molecular weight polyalkylene oxide and a
 second high molecular weight polyoxyalkylene derivative.
 In an embodiment, the portion of the body member is constructed at least in
 part from polyvinyl chloride.
 In an embodiment, the portion of the body is constructed at least in part
 from silicone.
 In an embodiment, the portion of the body is biological tissue.
 In an embodiment, the coating provides a lubricious surface.
 In an embodiment, the coating includes a third component.
 In an embodiment, the coating includes a functional group that modifies the
 surface.
 In an embodiment, the functional group is chosen from the group consisting
 of anti-coagulants, heparin, hirudin, anti-microbial, proteins, peptides,
 and biopolymers.
 In an embodiment, the coating provides a multilayer structure.
 In an embodiment, the coating provides an anti-thrombogenic surface.
 In an embodiment, the coating provides a noninflammatory surface.
 In an embodiment, the coating provides an anti-bacterial surface.
 In another embodiment, the present invention provides a medical device
 designed to be at least partially inserted into a patient comprising a
 body member that includes on a portion thereof a coating of a polyalkylene
 oxide that is cross-linked with a polyalkylene oxide derivative to form a
 coating that provides a lubricous surface.
 In an embodiment, the coating includes water.
 In an embodiment, the coating includes a functional group that provides a
 modified surface property to the coating.
 In an embodiment, the device is a catheter.
 In an embodiment, the device is a wound drain.
 In an embodiment, the device is a guide wire.
 In an embodiment, the device is a chest tube.
 In an embodiment, the portion thereof is constructed from silicone.
 In an embodiment, the portion thereof is constructed from polyvinyl
 chloride.
 In another embodiment, the present invention provides an implantable
 biological tissue comprising a biological tissue and a coating thereon
 including a multilayer surface including a high molecular weight
 polyalkylene oxide derivative and a biopolymer.
 In an embodiment, the tissue is a vascular graft.
 In an embodiment, the tissue is a heart valve tissue.
 In an embodiment, the tissue is a synthetic membrane.
 In a still further embodiment, the present invention provides a
 bioprosthetic device comprising a biological tissue coated at least in
 part with a coating including a polyalkylene oxide derivative that is
 cross-linked with a polyalkylene oxide derivative.
 Additionally, the present invention provides methods of providing medical
 devices. In an embodiment, the method comprising the steps of providing a
 medical device having a body and coating at least a portion of the body
 with a coating including a polyalkylene oxide derivative cross-linked with
 polyalkylene oxide derivative to modify the surface properties of the
 portion of the body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention provides medical products having a coating applied
 thereto which changes the surface properties. Additionally, the present
 invention provides methods for producing such products.
 Pursuant to the present invention products are provided having a surface
 thereof that includes a PEO cross-linked coated surface. Due to the
 modified PEO surface certain advantages are provided.
 For example, improved bioprosthetic devices can be provided. In this
 regard, the PEO coating technology can be applied to various types of
 biological tissues, such as bovine pericardium or porcine aortic tissues,
 that have been chemically pre-treated with Denacol and/or glutaraldehyde
 for the development of bioprosthetic heart valves. The method is based on
 a preliminary coating of tissue in an aqueous solution containing
 electrophilically active PEO derivatives, preferably a
 bis-oxycarbonyl-diimidazole-active PEO (Imz-PEO), having an average
 molecular weight of 20,000 daltons. The resulting intermediate
 Imz-PEO-activated tissue was further cross-linked with an amino-PEO
 derivative (preferably of the same MW) to form a stable PEO-coated
 surface.
 This intermediate activated Imz-PEO-coated tissue can also be used to
 couple proteins, such as avidin into this matrix. This avidin-PEO-coated
 surface can be further employed to bind biotinylated agents, such as
 peptides like GREDVY, in order to produce surfaces capable of capturing
 endothelial cells.
 PEO-coated tissues prepared by the above techniques have been shown to
 reduce fibrinogen binding, compared to uncoated tissue. Other potential
 advantages of such PEO-modified surfaces include: reduced protein
 adsorption; limit complement activation; eliminate protein aggregation;
 produce specific ligand or cell attachment sites through avidin-biotin
 chemistry; and intermediate activated PEO-coated-tissues can be used for
 attachment sites to other anti-calcification agents such as 2-amino-oleic
 acid or toluidine blue.
 By way of further example, the surface of certain devices such as wound
 drains, chest tubes, guide wires, catheter, and angioplasty products can
 be modified with a PEO coating to make them lubricious. To this end, such
 lubricious surfaces can be produced using a simple surface modification
 technology based on a direct coating of high molecular weight polyethylene
 oxide (PEO) derivatives onto polymeric tubes, using water as a solvent.
 The polymer materials can be varied from polyvinyl chloride (PVC) to
 silicone or other type of polymers that are typically used for medical
 devices. These materials include polyurethane, polyolefine, polyethylene,
 polypropylene, metal or alloy.
 The PEO derivatives are functionalized PEO that could contain an
 electrophilically active compound such as oxycarbonyl-imidazoyl-PEO
 (Imz-PEO) or nucleophilically active such as amino-PEO (NH.sub.2 -PEO).
 This technology provides a coating that generates low-friction or
 lubricious surfaces which also can limit fibrinogen adsorption. It has
 been found that the PEO-coated PVC and PEO-coated silicone tubes are
 stable in saline or plasma at 37.degree. C. for several days. Also, they
 can be sterilized with ETO without loss of lubricity or of low protein
 adsorption properties.
 This technology presents several advantages including a simple coating
 technology that uses water as a solvent. It also allows the production of
 lubricious surface on PVC and/or silicone surfaces. The production of
 products having surfaces with low fibrinogen adsorption. It provides the
 availability of functional groups that allow further surface modification
 (e.g., coupling with anti-coagulant substances, heparin or hirudin) or
 anti-microbial ligand (e.g. chitosan). The technology also provides a
 coating that can be also sterilized with ETO (or gamma) without loss of
 lubricity or low protein binding ability. The technology also provides the
 potential application to a variety of other synthetic polymers
 (polyurethane, polyethylene, polyolefine, and metal or alloy).
 Still further pursuant to the present invention multilayer coating can be
 used to provide new surface modifications. To this end, the present
 invention provides a new surface modification method that is based on
 multilayer coatings between high molecular weight PEO derivatives and
 anti-coagulant biopolymers containing terminal primary amine groups.
 The base material can be a wide variety of materials. For example, the base
 material, could be derived from any biological tissue such as vascular
 grafts or heart valve tissues, or synthetic membranes made from various
 hydrophobic or hydrophilic polymers. Biopolymers containing amino-terminal
 groups can be derived from carbohydrate structures such as heparin
 (glycosaminoglycan family) and chitosan or proteins such as hirudin.
 FIG. 1, and specifically FIGS. 1a-1d, set forth examples of multilayer
 structures that can be produced. In the figures, the base material has
 thereon the multilayer coating. PEO refers of course to the polyethylene
 oxide coating discussed herein. ABP refers to the anticoagulant
 biopolymers.
 These multiple layers of coating may provide numerous advantages. One of
 the advantages is to provide a permanent coating technique that assures
 complete coverage of the base material. Additionally, the multiple layers
 allow the production of a highly anti-thrombogenic surface due to the
 combined presence of PEO and anticoagulants (heparin or hirudin). Further,
 the multiple layers allow the production of a non-inflammatory (e.g.
 non-complement activating) material due to the presence of PEO and
 heparin. Still further the multilayers allow the production of a potential
 anti-bacterial surface because of the presence of chitosan. The multilayer
 coating has applicability to multiple devices, including: membranes;
 theracyte devices; arterial filter membranes, and oxygenators; catheters,
 wound drains; and vascular grafts or heart valve tissues.
 In another embodiment a blood cell fractionation means is provided
 comprising a matrix having a fibrous structure and the matrix further
 characterized in having a coating applied to it which changes its surface
 properties with respect to cellular adherence of blood cell containing
 fluid coming into contact therewith. The matrix can be a packing material
 contained within a column, or a fibrous material compressed into a filter
 and held in a filter housing of conventional design and construction,
 although other configurations of a solid matrix contacting a fluid are
 within the scope of the invention. In an embodiment, the coating of
 polymers and the chemical reactions which are carried out to create a
 generally molecularly continuous polymeric surface on the matrix fibers do
 not require covalent or noncovalent interaction with any chemical moiety
 present on the native surface of the matrix, the coating itself is
 independent of the chemical and physical identity of the matrix. Thus, the
 coating is intended to be universally applicable to any filter available
 in the cell separation art. Examples include, without limitation, filters
 having a high glass content, as in glass fiber mats, filters with less or
 no glass content such as a filter comprising a mixture of glass and
 polyester, and a polyethylene terephthalate platelet filter coated with
 hydroxyethylmethyl-methacrylate.
 Filter housings which may be conveniently used are manufactured
 conventionally. Examples of such housing are Swinney plastic manifolds
 manufactured by Gelman, pediatric Enterprise Housings, or Intermediate
 Enterprise Housings. The correct size correlations of filters to
 correspondingly suitable housings will be apparent to those skilled in the
 art. The only limitation applicable to the blood cell fractionation means
 is a surface which is incompatible with the polymer solutions. Even in the
 instance where molecular wetting is not obtainable with the polymer
 solutions, techniques utilizing emulsifiers and phase penetrants may be
 useful in achieving adequate coating. To Applicants' knowledge, none of
 the blood cell fractionation filter materials currently available
 commercially are to be excluded from applicability to the present
 invention.
 In the method of separating cells using the product of the invention, a
 cell suspension or whole blood is filtered through the filter having the
 polymer coating as disclosed. The leukocytes adhere, and the platelets and
 RBCs pass through the in the filtrate. More generalized methods of
 contacting the filter with a cell containing fluid are contemplated by
 this invention as well. For example, contracting by passaging through a
 packed column, or mixing cells in bulk with dispersed matrix in solution
 may be employed.
 As noted above, the method of the present invention is applicable to a
 number of products and surfaces. For example, manufacturing ease, chemical
 condensation reaction of the respective polymers can be carried out
 insitu, i.e. a first free polymer is laid down on the matrix and dried,
 and then the second is contacted in solution with the matrix. The ensuing
 reaction then produces a skin-like sheet or layer of copolymerized
 material at the surface or the matrix. This reaction in a preferred
 embodiment proceeds spontaneously at temperatures generally in the range
 of 5 to 200 degrees centigrade. It is evident that the time for completion
 of the reaction will be slightly longer at cooler temperatures than for
 higher temperatures in accordance with kinetic thermodynamic principles.
 Generally, these reactions may be carried out at ambient temperatures, as
 disclosed in the Examples, but very little experimentation will be
 required by those skilled in the art to adjust the reaction times to a
 particular desired temperatures of reaction.
 The first polymer to be contacted with the surface is a high molecular
 weight electrophilically active polyalkylene oxide. Electrophilically
 active means that a polyalkylene oxide polymer contains a oxycarbonyl
 moiety reactive with a nucleophilic center such as an amino or hydroxyl
 group contained in a second polymer. In a preferred embodiment, a primary
 amine serving as a nucleophile, reacts with the carbonyl group of the
 imidazole-polyalkylene oxide polymer to form, upon reaction, an
 N-substituted carbamate bond where the carbonyl moiety from a cross-linker
 is incorporated into the new bond. These polymer entities must be high
 molecular weight, in the range of about 13,000 to 24,000 daltons,
 preferably about 20,000 daltons. Thus preferred molecules shown in FIG. 2
 for reaction on surfaces will have n values of about 100-225.
 A first electrophilic polyalkylene oxide polymer will have a terminal
 leaving group reactive with an amine or hydroxyl containing second
 polyalkylene oxide. Suitable leaving groups on the first polymer for
 achieving acceptable chemical condensation are imidazoyl-, tresyl-,
 tosyl-, acryloyl-, and N-hydroxysuccinimidyl-. Additionally the structure
 of the electrophilic polymer can further be defined by the general
 expression: Y-PEO-R-PEO-Y, wherein Y is selected from the following group
 singly or in combination: oxycarbonylimidazole; tresyl-, tosyl-,
 N-hydroxysuccinimidyl-, and p-nitrophenyl- activated esters; acrylates;
 glycidyl ethers; and aldehydes, and R is a spacer defined as a backbone to
 which the two polyalkylene arms are attached, consisting preferably of
 bisphenol A or B. Bisphenol A is preferred, as shown in the structure of
 FIG. 2.
 We have also determined that in certain applications the imidazole derived
 polyalkylene oxides provide excellent results, perhaps because the
 reaction proceeds somewhat better, or perhaps because residual unreacted
 groups improve leukoadhesion. In any event, Applicants do not wish to be
 bound to any particular theory, but disclose the result as a guide to
 those experienced in the art. In general, polyalkylene means polyethylene
 or polypropylene, since these are the most common polyalkylene oxides used
 in biocompatibility applications. However, Applicants consider other
 polyalkylene oxides up to polybutylene oxide to be within the scope of the
 invention.
 In an embodiment, a tetra or diacrylate terminal derivative of polyalkylene
 oxide may be isopolymerized by first contacting with the surface, followed
 by irradiation with UV light or gamma rays to effect free radical
 polymerization. When used for blood filtration, the resulting coated
 filter matrix is leukodepletive with adequate recoveries of platelets and
 red bloods cells, but is not a efficacious as the other embodiments of the
 invention set forth herein.
 In a method of the present invention, insitu chemical condensation can be
 carried out to mold the copolymer skin to the contours of the matrix fiber
 bed. It is important that the electrophilically active polyalkylene oxide
 be deposited on the matrix first, dried, and then further contracted with
 the second amino- or hydroxy- containing nucleophilic polymer. This
 teaching arises from empirical observation as to which method steps give
 best results in terms of platelet and RBC recovery, and leukodepletion,
 and the mechanistic or molecular basis for the observation is unknown to
 Applicants. In the drying step, drying in ambient air is adequate to "fix"
 the polymer in position, but light to moderate heat at various humidities
 down to less than 5% humidity or in vacuo may be applied to hasten the
 drying step in a manufacturing context.
 The copolymerized material is highly stable to leaching, as shown in some
 of the Examples. In contrast to unreacted single polymer labeled with
 .sup.125 I which is readily leached into filtrate, the fully copolymerized
 material made according to a method of the present invention is highly
 resistant to leaching, and is stable for preparation of therapeutically
 acceptable cell fractions.
 By way of example, and not limitation, examples of the present invention
 will now be given.
 EXAMPLE NO. 1
 Oxycarbonyl imidazole-polyethylene oxide (Imz-PEO) with an average
 molecular weight of 20 K daltons (Sigma Chemical Company), was first
 coated onto existing Asahi R-2000 filters by soaking the filter mats in a
 2.5% solution of Imz-PEO. The mats were dried under vacuum. The amount of
 Imz-PEO bound to the mat was about 70 mg/gram of filter mat. Dried
 Imz-PEO-coated mats were cross-linked with bis[polyoxyethylene bis(amine)]
 (TAPEO, 20 K daltons), obtained from Sigma Chemical Company. The
 cross-linking reaction was performed by soaking the Imz-PEO-coated mat in
 a water-methanol (1:1) solution of TAPEO at a 2.5 to 5.0 fold molar excess
 over the bound Imz-PEO. The reaction was allowed to proceed for at least
 24 hours. The mats were dried again under vacuum. Dried cross-linked mats
 were washed extensively by soaking with water several times to remove any
 unbound PEO. After the final wash, the mats were dried again under a high
 vacuum. Cross-linked mats were stored at room temperature until used for
 blood filtration. In this example, the mats were used with pooled (ABO
 compatible), one day old, human whole blood, obtained from Interstate
 Blood Bank. The pooled whole blood was suspended about 3 feet above the
 filter unit, and the blood was allowed to flow by gravity through each of
 the different types of PEO-filter mats. An aliquot of whole blood (20 to
 30 ml) was taken from the unit before filtration and was saved as a
 control (pre-sample). The filtered blood (post samples) and the
 pre-samples were counted for platelets with a Sysmex K-1000 cell counter
 and the WBC concentrations were determined by staining WBC nuclei (after
 lysing the sample) with propidium iodide and analyzing the stained samples
 with a FacScan flow cytometer. The results of WBC depletion and platelet
 recovery are illustrated in FIGS. 3 and 4 respectively. The degree of
 platelet recovery ranged from 75 to 80% with Imz-PEO-coated mats vs 0.5%
 for the uncoated mats. The amount of WBC depletion remained unchanged, in
 the range of 3 to 4 logs for all of the mats (Table 1).
 TABLE 1
 Filtration of Whole Blood Through PEO-Coated And
 Uncoated Asahi R-2000 Filter Mats
 WBC Depletion PLATELET
 Depletion Recovery
 SAMPLE (log) (% Pre)
 Imz-PEG 3.25 80
 (no crosslinking)
 2.5x Crosslinked 3.39 74
 (Mat #1)
 2.5x Crosslinked 3.75 74
 (Mat #1)
 Uncoated 3.73 0.5
 EXAMPLE NO. 2
 In this experiment, variable such as the age of the blood and the storage
 temperature were evaluated. The same PEO coated Asahi R-2000 filter mats
 described above were used for these studies. Units of whole blood were
 obtained fresh in-house, and stored at room temperature until used (about
 2 hours). One day old blood, stored at room temperature or 4 degrees
 centigrade, were also obtained form Interstate Blood Bank. Each unit was
 allowed to flow through each PEO-coated filter and the samples were
 analyzed as described above. The results, summarized in Table 2, suggest
 that despite the utilization of various units of whole blood stored under
 different conditions, the yield of platelets obtained from PEO-coated
 Asahi R-2000 filters is dramatically improved (68 to 83%) as compared to
 uncoated mats (2%).
 TABLE 2
 Filtration Of Whole Blood Through PEO-Coated And
 Uncoated Asahi R-2000 Filters
 WBC PLATELET
 Depletion Recovery
 SAMPLE (log) (% Pre)
 PEO-Cross Linked-Mats:
 Interstate-RT
 (1 day old) #1 -2.63 83
 Interstate-RT
 (1 day old) #2 -4.01 68
 Interstate-4.degree. C.
 (1 day old) #3 -3.22 80
 In-house-RT (.about.2 hrs) #1 -3.25 76
 Uncoated Mats:
 Interstate-RT
 (1 day old) #1 -3.50 02
 EXAMPLE NO. 3
 In this example, tetraacrylate PEO derivatives were obtained either from
 Shearwater Polymer Inc., or synthesized from PEO 20 K daltons obtained
 from Sigma (FIG. 2). The acrylate-PEO derivatives were coated onto
 composite mats by the same procedure as described in Example 1. The dried
 acrylate-PEO-coated mats were subjected to gamma irradiation at a low
 dosage (2 megarads) to facilitate cross-linking of the PEO coating. The
 dried, coated mats were cut into circles of about 1.50 inches, and 3
 layers of mats were placed into a small pediatric-sized housing for whole
 blood evaluation. One day old pooled whole blood, obtained from Interstate
 Blood Bank was used. The final volume of blood used per housing was about
 75 ml. The results of these experiments, summarized in Table 3,
 demonstrate the improvement in platelet recovery upon coating mats with
 the PEO derivatives. However, the improvement in platelet recovery seen
 with the acrylate PEO derivatives is not as good as was observed with the
 Imz-PEO coated mats.
 TABLE 3
 Filtration Of Whole Blood Through Various Crylate-PEO Coated and
 Uncoated Composite Filters
 WBC Depletion PLATELET
 Depletion Recovery
 SAMPLE (log) (% Pre)
 Uncoated -2.20 43
 Sigma-Tetra-Acrylate-20K -1.62 69
 Shearwater-Tetra-ACR-14K -2.04 56
 Sigma-Tetra-Acrylate-20K -1.64 65
 Irradiated
 Shearwater-Tetra-ACR-14K -1.91 65
 Irradiated
 EXAMPLE NO. 4
 The stability of these PEO coatings was investigated using radioactively
 labeled .sup.125 I-Imz-PEO and .sup.125 I-Tetraamino-PEO. The presence of
 the bis phenol A units in the structure of Imz-PEO or Tetraamino-PEO
 derivatives permitted conventional labeling of these molecules using
 .sup.125 I and iodo beads (Pierce Chemical Co.). In the first set of
 experiments, the .sup.125 I-Imz-PEO was first coated onto the mats and was
 cross-linked with unlabeled Tetraamino-PEO. In the second set of
 experiments, unlabeled Imz-PEO was coated onto the mats and then
 cross-linked with .sup.125 I-Tetraamino-PEO. Each .sup.125 I-PEO coated
 mat was evaluated in a Swinney housing (using a filter about 1 cm in
 diameter) with fresh whole blood. Four fractions of blood filtrate
 (.about.1 ml each) were collected and counted for the presence of .sup.125
 I-PEO derivatives with a gamma counter. Each .sup.125 I-PEO-coated filter
 mat was also counted for radioactivity, before and after filtration. The
 amount of labeled PEO recovered on the mats after whole blood filtration
 varied from 87% to 95%. In contrast, 35% of the labeled Imz-PEO was
 leached off filter mats where no crosslinking reaction was performed.
 TABLE 4
 Stability Of PEO-Coated Asahi R-2000 Filter Mats Measured With
 .sup.125 I-Imz-PEO or .sup.125 I-Tetraamino-PEO
 125I-PEO Coated Mats Recovered
 After Filtration
 SAMPLE With .sup.125 I-Label (% Pre Labeled Mat)
 125-Imz-PEO-Tetraamino-PEO 95%
 Imz-PEO-125I-Tetraamino-PEO 87%
 125I-Imz-PEO (not cross-linked) 65%
 EXAMPLE NO. 5
 Various pre and post blood samples from the above experiments were further
 evaluated for complement activation by measuring C3a and C5a (by RIA) and
 for platelet activation by determining the percentage of platelets
 positive for the activation marker CD62. PLS10A platelet filters (Asahi)
 were included in this analysis as a control for comparison. The results
 for C3a and C5a is summarized in Table 5.
 TABLE 5
 C3a And C5a Levels In Blood Exposed To PEO-Coated And
 Uncoated Asahi R-2000 and PLS-10A Filters
 C3a (ng/ml) Post- C5a (ng/ml)
 SAMPLE Pre-Samples Samples Pre-Samples Post-Samples
 Cross-linked 952 1,276 20 54
 Cross-linked 538 614 0 19
 Cross-linked 857 1,047 17 13
 Cross-linked 1,103 1,149 28 34
 Cross-linked 610 619 15 15
 Uncoated 319 248 29 19
 Uncoated 686 716 15 11
 PLS-10A 964 4,057 22 66
 PLS-10A 839 2,169 33 34
 PLS-10A 328 1,727 9 25
 PLS-10A 437 2,572 4 26
 High levels of C3a and C5a were found in blood samples obtained from Asahi
 platelet filter PLS-10A. Although these PLS-10A filters have not been used
 with whole blood, it appears that the PLS-10A produces at least a 2 to 4
 fold increase in C3a and C5a levels as compared to the corresponding
 pre-samples. These levels of C3a and C5a are higher than the amount of C3a
 and C5a produced by the PEO-coated Asahi R-2000 filters are more
 biocompatible than the PLS-10A commercial filter used for platelet
 concentrate.
 The percent of platelets expressing the activation marker, CD62, is a
 sensitive measure of the extent of platelet activation. Samples of whole
 blood were analyzed (pre and post filtration) using a FacScan flow
 cytometer to determine the percentage of platelets positive for CD62. This
 analysis revealed (Table 6) that no elevation in the percentage of CD62
 positive platelets occurred during filtration on any of the mats
 investigated.
 TABLE 6
 Platelet Activation In Whole Blood Samples Exposed To Various Filters
 % CD62 in Post-
 SAMPLE % CD62 in Pre-Samples Samples
 Uncoated 5.45 5.88
 Cross-linked-PEO 4.45 4.78
 Cross-linked-PEO 5.20 5.24
 Not Cross-linked-PEO 5.45 3.27
 Not Cross-linked-PEO 4.05 2.11
 PLS-10A 5.45 2.10
 EXAMPLE NO. 6
 In this group of examples, polyvinyl chloride and silicone tubes were
 coated.
 A. PEO-Coated Polyvinyl Chloride (PVC) Tubes
 PVC tubes (10 or 15 French size) were soaked in a water solution containing
 various concentrations of NH.sub.2 -PEO (1%, 2.5% or 5%). The tubes were
 incubated at 55.degree. C. overnight, then they were removed. The tubes
 were allowed to air dry at room temperature following by another
 incubation at 55 .degree. C. as the curing process.
 The NH.sub.2 -PEO-coated PVC was either used for crosslinking with another
 PEO derivative without further washing or was washed extensively with
 water to remove free PEO. Washed tubes were allowed to air dry at room
 temperature and stored desiccated until analysis. Note that the amount of
 bound PEO was estimated based on the amount of radioactive .sup.125
 I-labeled-PEO tracer that was incorporated in the PEO coating solution.
 B. Cross-Linking Of Amino-PEO-Coated PVC
 Dried NH.sub.2 -PEO-coated PVC (before washing) was soaked in a water
 solution containing Imz-PEO at a concentration of 2.5% (or lower). The
 crosslinking reaction was performed at room temperature for 24 hours.
 The tubes were removed and allowed to air dry at room temperature. The
 tubes were then extensively washed with water to remove free Imz-PEO. The
 washed tubes were dried at room temperature and stored desiccated as
 described above.
 C. PEO-Coated Silicone Tubes
 Silicone tubes (15 French size) were pre-treated with sodium hydroxide
 before being treated with a PEO coating. The sodium hydroxide treatment
 consisted of soaking the tubing in 1N sodium hydroxide for 1 hour,
 following by extensive washing (until neutral pH) of the tubes with water.
 The method of coating PEO derivatives (Imz-PEO or NH.sub.2 -PEO) onto
 silicone tubes was the same as for PVC above, except that all soaking in
 PEO solutions were performed at room temperature. The step that involved
 curing at 55.degree. C. Was omitted. The final washed tubes were stored in
 a desiccated vacuum.
 D. Attachment of Heparin and Imz-PEO onto Silicone Tubes
 Heparin and Imz-PEO can be incorporated into the silicone matrix by either
 reacting heparin with Imz-PEO-coated silicone tubes (a two step process),
 or by mixing Imz-PEO and heparin in the same solution that was used as
 coating solution (a one step process). All heparin attachment was
 performed at 4.degree. C. for 24 hours. The tubes were dried and washed as
 described earlier.
 E. Fibrinogen Binding Assay
 All PEO or Heparin-PEO-coated tubes were tested for fibrinogen binding
 against control uncoated tubes. Each assay was performed with a triplicate
 sample using a small piece of tubing (about 0.4 cm length).
 F. Measurement of Surface Lubricity
 Each tube was cut into about 15 lengths and was placed into a designed
 flow-cell filled with saline (0.9% solution). One end of the tube was
 connected to an Instron instrument that served to pull out the tube from
 the flow-cell. The maximum force required for the Instron to pull the tube
 out determines the surface lubricity of the tube.
 The force used for pulling the control tube (uncoated PVC or silicone) was
 set at 20 lb. The measurement was performed at two time intervals: 1) at
 time zero (t=0) where the tube was pulled as soon as it was loaded into
 the flow-cell; and 2) at rinsed time (t=30 minutes) where the tube was
 allowed to stay in the flow-cell containing saline solution for 30
 minutes. Then, the saline solution in the flow-cell was replaced with new
 saline, and finally the tube was pulled out.
 G. Stability Study of PEO-Coated PVC or Silicone
 This study was performed in saline and plasma solutions, at 37.degree. C.
 up to 7 days, using .sup.125 Imz-PEO or .sup.125 1-NH.sub.2 -PEO-coated
 tubes (the radiolabeled PEO was used as a tracer). Several sets of small
 pieces (about 0.4 cm length) of .sup.125 I-PEO-coated PVC (or silicone),
 and uncoated tubes were soaked in saline or pure plasma solutions. The
 samples were placed on a tube rocker which allows a continuous shaking of
 the samples during the entire incubation period. Each set of tubes (in
 triplicate) was removed from the shaker after day-1 (24 hours), day-3, and
 day-7. Each sample was counted for total radioactivity before removal of
 saline or plasma solution, then it was washed twice with water. The washed
 piece was counted for the remaining radioactivity. The ratio between the
 remaining radioactivity of PEO-coated tubes after washing and the total
 radioactivity was recorded.
 Results
 PEO-Coated PVC: The results of Imz-PEO or NH.sub.2 -PEO-coated PVC tubes
 are illustrated graphically in FIGS. 5 and 6. FIG. 5 illustrates
 graphically bound NH.sub.2 -PEO (mmoles/cm.sup.2) versus NH2-PEO
 concentration in the coating solution. Three solution concentrations are
 illustrated: 1.0%; 2.5%; and 5.0%. As shown in FIG. 5, NH.sub.2 -PEO
 appeared to bind better to the PVC tubes than the Imz-PEO derivative.
 Also, the amount of bound NH.sub.2 -PEO onto PVC increased with increasing
 concentration of the NH.sub.2 -PEO in the coating solutions. However,
 using high concentration of this NH.sub.2 -PEO (e.g. 10%) in a primary
 coating solution is not necessary, because it reduced the amount of bound
 Imz-PEO used in the crosslinked reaction; see FIG. 6, concentration of
 NH.sub.2 -PEO in coating solution (before cross-linking).
 PEO-Coated Silicone: FIG. 7 sets forth two PEO derivatives: Imz-PEO
 (Imz-PEO cross-linked with NH.sub.2 -PEO); and NH.sub.2 -PEO (NH.sub.2
 -PEO cross-linked with Imz-PEO). Illustrated in FIG. 7, both PEO
 derivatives were strongly bound to silicone tubing. The amount of Imz-PEO
 bound was about 4 fold higher than the amount of bound NH.sub.2 -PEO. In
 addition, the results in FIG. 6 suggested that the primary coating of PEO
 was very stable since the level of radioactivity was unchanged after the
 crosslinking reaction.
 Fibrinogen Binding
 The results of fibrinogen binding to PEO-coated PVC tubing are summarized
 in Tables 7 and 8 below.
 As shown in Table 7, PEO-coated PVC exhibited a great reduction in
 fibrinogen binding, compared to control uncoated PVC. Tubings coated with
 a low concentration of NH.sub.2 -PEO (1%) showed the same level of bound
 fibrinogen, compared to other tubings that were coated with higher
 concentrations of NH.sub.2 -PEO (2.5% or 5%), and with or without
 crosslinking with Imz-PEO (Table 7).
 TABLE 7
 Effect Of PEO Coating On Fibrinogen Binding Onto PVC Tubing
 [NH.sub.2 -PEO] in Bound Fg (ng/cm.sup.2) before Bound Fg (ng/cm.sup.2)
 after
 coating solution crosslinked (.+-.SD) crosslinked (.+-.SD)
 Uncoated 670 .+-. 124
 1% 85 .+-. 9 136 .+-. 23
 2.5% 110 .+-. 7 110 .+-. 19
 5.0% 114 .+-. 27 127 .+-. 20
 Also, the results in Table 8 indicated that there was no change in the
 level of fibrinogen binding to the PVC tubing after ETO sterilization.
 TABLE 8
 Effect Of ETO Sterilization On Fibrinogen Binding
 to PEO-Coated PVC Tubing
 Bound Fg (ng/cm.sup.2) Bound Fg (ng/cm.sup.2)
 PVC Tubing before ETO (.+-.SD) after ETO (.+-.SD)
 Uncoated 462 .+-. 43 394 .+-. 65
 NH.sub.2 -PEO (1%) 80 .+-. 19 82 .+-. 26
 Xlink-PEO (0.5% Imz-PEO) 84 .+-. 20 27 .+-. 15
 Xlink-PEO (2.5% Imz-PEO) 69 .+-. 22 46 .+-. 8
 The ability of the PEO coating to reduce fibrinogen binding was also
 demonstrated to be obtained with silicone (see Table 9 below). The level
 of fibrinogen bound to the Imz-PEO or NH.sub.2 -PEO-coated silicone with
 or without crosslinking was about the same. This result suggests that the
 second crosslinking reaction with Imz-PEO derivative may not be necessary
 in this type of coating.
 TABLE 9
 Effect of PEO Coating On Fibrinogen Binding Onto PVC Tubing
 Silicone Tubing & Bound Fg (ng/cm.sup.2) Bound Fg (ng/cm.sup.2)
 PEO Coating Pre-Crosslinked (.+-.SD) Post-Crosslinked (.+-.SD)
 Uncoated 258 .+-. 173
 .sup.125 I-Imz-PEO 82 .+-. 27 52 .+-. 8
 .sup.125 I-NH.sub.2 -PEO 62 .+-. 19 46 .+-. 2
 However, Imz-PEO coating may be used as crosslinker reagent to the
 attachment of heparin, as shown in FIG. 8. The results in FIG. 8,
 indicated that heparin and Imz-PEO can be incorporated onto silicone
 tubing by a one step (S1) or two step (S2) processes to produce low
 fibrinogen binding surface. The activity of immobilized heparin is under
 investigation.
 Surface Lubricity
 The results of the effect of PEO coating on tubing lubricity are summarized
 in Tables 10 and 11 below for PVC and silicone, respectively.
 In this analysis, surface lubricity was measured by applying a maximum
 force to pull out the tube from the flow-cell filled with saline solution.
 The force for the control uncoated was set at 20 lb, on the Instron
 instrument.
 TABLE 10
 Effect Of PEO-Coated PVC On Tubing Lubricity
 Pre-ETO Pre-ETO Post-ETO Post-ETO
 PVC (10 fr.) (t = 0) (t = 30 min.) (t = 0) (t = 30 min.)
 Experiment #1 not not
 (n = 3) done done
 NH2-PEO (1%) 7.6 .+-. 4.3 2.6 .+-. 0.6
 Experiment #2
 (n = 1)
 S1 (NH2-PEO 1%) 0.75 0.56 0.89 0.94
 S2 (Xlink-PEO) 1.71 0.77 1.38 2.27
 (Imz-PEO = 0.5%)
 S3 (Xlink-PEO) 0.78 0.44 0.41 0.59
 (Imz-PEO = 2.5%)
 TABLE 10
 Effect Of PEO-Coated PVC On Tubing Lubricity
 Pre-ETO Pre-ETO Post-ETO Post-ETO
 PVC (10 fr.) (t = 0) (t = 30 min.) (t = 0) (t = 30 min.)
 Experiment #1 not not
 (n = 3) done done
 NH2-PEO (1%) 7.6 .+-. 4.3 2.6 .+-. 0.6
 Experiment #2
 (n = 1)
 S1 (NH2-PEO 1%) 0.75 0.56 0.89 0.94
 S2 (Xlink-PEO) 1.71 0.77 1.38 2.27
 (Imz-PEO = 0.5%)
 S3 (Xlink-PEO) 0.78 0.44 0.41 0.59
 (Imz-PEO = 2.5%)
 The forces required for pulling the PEO-coated PVC or silicone tube were
 much lower than the force necessary for the uncoated materials. For both
 initial force (t=0) or rinsed force (t=30 minutes) PVC tubing coated with
 1% NH.sub.2 -PEO solution showed the same degree of lubricity, compared to
 other coatings (Table 10). These results suggest that NH.sub.2 -PEO can be
 used at low concentration (1%) as a single coating onto PVC tubing.
 Similar results were also observed with NH.sub.2 -PEO-coated silicone
 tubing (Table 11). This derivative by itself can be used alone for coating
 silicone tube to produce surface with low-friction and low fibrinogen
 binding.
 Stability of PEO Coating
 A. PVC Tubing: The results of the stability study of PEO-coated PVC tubing
 in saline and in plasma are summarized in Tables 12 and 13, respectively.
 As set forth in Table 12, all PEO-coated PVC with or without additional
 cross linking are very stable in saline solution, at 37.degree. C. up to 7
 days.
 TABLE 12
 Stability of .sup.125 I-PEO-Coated PVC Tubing in Saline Solution at
 37.degree. C.
 % Of Recovery % Of Recovery % Of Recovery
 PVC Tubing Day-1 (.+-.SD) Day-3 (.+-.SD) Day-7 (.+-.SD)
 .sup.125 I-NH.sub.2 -PEO-1.0% 95 .+-. 9 90 .+-. 9 98 .+-. 2
 .sup.125 I-NH.sub.2 -PEO-2.5% 94 .+-. 7 94 .+-. 3 93 .+-. 5
 .sup.125 I-NH.sub.2 -PEO-5.0% 91 .+-. 6 93 .+-. 4 96 .+-. 3
 Crosslink-1.0% 92 .+-. 5 102 .+-. 3 92 .+-. 5
 Crosslink-2.5% 94 .+-. 8 98 .+-. 4 95 .+-. 4
 Crosslink-5.0% 97 .+-. 4 97 .+-. 5 100 .+-. 7
 Also, these tubings (post saline incubation) showed very good reduction in
 fibrinogen binding compared to control uncoated tubing (see Table 13
 below).
 TABLE 13
 Stability of .sup.125 I-PEO-Coated PVC Tubing in Saline Solution at
 37.degree. C.:
 Effect On Fibrinogen Binding
 Bound Fg Bound Fg Bound Fg
 (ng/cm2) (ng/cm2) (ng/cm2)
 PVC Tubing Day-1 (.+-.SD) Day-3 (.+-. SD) Day-7 (.+-. SD)
 Uncoated 576 .+-. 45 513 .+-. 53 561 .+-. 44
 .sup.125 I-NH.sub.2 -PEO-1.0% 75 .+-. 9 76 .+-. 16 71 .+-. 13
 .sup.125 I-NH.sub.2 -PEO-2.5% 119 .+-. 20 100 .+-. 25 100 .+-. 18
 .sup.125 I-NH.sub.2 -PEO-5.0% 87 .+-. 9 101 .+-. 8 93 .+-. 19
 Crosslink-1.0% 73 .+-. 10 66 .+-. 11 73 .+-. 18
 Crosslink-2.5% 98 .+-. 6 85 .+-. 2 95 .+-. 9
 Crosslink-5.0% 86 .+-. 16 79 .+-. 7 92 .+-. 25
 However, in pure human plasma, the percentage of the recovery of bound
 NH.sub.2 -PEO is in the range of 60% to 90% depend on the initial coating
 concentrations and the duration of the incubation (see Table 14 below).
 TABLE 14
 Stability Of .sup.125 I-PEO-Coated PVC Tubing in Human Plasma at 37.degree.
 C.
 % Of Recovery % Of Recovery % Of Recovery
 PVC Tubing Day-1 (.+-.SD) Day-3 (.+-.SD) Day-7 (.+-.SD)
 .sup.125 I-NH.sub.2 -PEO-1.0% 92 .+-. 2 77 .+-. 10 65 .+-. 5
 .sup.125 I-NH.sub.2 -PEO-2.5% 86 .+-. 5 77 .+-. 20 72 .+-. 1
 .sup.125 I-NH.sub.2 -PEO-5.0% 102 .+-. 27 79 .+-. 5 72 .+-. 4
 Crosslink-1.0% 95 .+-. 4 91 .+-. 19 75 .+-. 3
 Crosslink-2.5% 91 .+-. 1 82 .+-. 6 77 .+-. 6
 Crosslink-5.0% 92 .+-. 2 82 .+-. 2 80 .+-. 7
 B. Silicone Tubing: Similar results were obtained with PEO-coated silicone
 tubing. In saline the coating is very stable, the percentage of PEO
 recovery was all above 95% (see Table 15 below).
 TABLE 15
 Stability Of .sup.125 I-PEO-Coated Silicone Tubing in Saline Solution at
 37.degree. C.
 % Of Recovery % Of Recovery % Of Recovery
 Silicone Tubing Day-1 (.+-.SD) Day-3 (.+-.SD) Day-7 (.+-.SD)
 .sup.125 I-NH.sub.2 -PEO 101 .+-. 1 102 .+-. 3 102 .+-. 5
 .sup.125 I-Imz-PEO 100 .+-. 1 100 .+-. 6 99 .+-. 5
 .sup.125 I-NH.sub.2 -PEO- 98 .+-. 4 94 .+-. 6 92 .+-. 5
 Crosslink
 .sup.125 I-NH.sub.2 -PEO- 93 .+-. 4 98 .+-. 3 88 .+-. 8
 Crosslink
 After saline incubation, all PEO-coated silicone tubing still showed good
 reduction in fibrinogen binding (see Table 16 below).
 TABLE 16
 Stability Of .sup.125 I-PEO-Coated Silicone Tubing in Saline Solution at
 37.degree. C.:
 Effect On Fibrinogen Binding
 Bound Fg Bound Fg Bound Fg
 (ng/cm2) (ng/cm2) (ng/cm2)
 Silicone Tubing Day-1 (.+-.SD) Day-3 (.+-. SD) Day-7 (.+-. SD)
 .sup.125 I-NH.sub.2 -PEO 84 .+-. 21 68 .+-. 24 89 .+-. 17
 .sup.125 I-Imz-PEO 103 .+-. 43 99 .+-. 57 102 .+-. 7
 .sup.125 I-NH.sub.2 -PEO- 70 .+-. 18 50 .+-. 17 55 .+-. 16
 Crosslink
 .sup.125 I-Imz-PEO- 99 .+-. 36 79 .+-. 4 86 .+-. 13
 Crosslink
 In plasma and up to 7 days incubation at 37.degree. C., PEO-coated silicone
 tubes are very stable, since the percent recovery of bound PEO varied
 between 80 and 100% (see Table 17 below).
 TABLE 17
 Stability Of .sup.125 I-PEO-Coated Silicone Tubing in Human Plasma at
 37.degree. C.
 % Of Recovery % Of Recovery % Of Recovery
 Silicone Tubing Day-1 (.+-.SD) Day-3 (.+-.SD) Day-7 (.+-.SD)
 .sup.125 I-NH.sub.2 -PEO 84 .+-. 2 84 .+-. 7 80 .+-. 7
 .sup.125 I-Imz-PEO 99 .+-. 3 94 .+-. 1 91 .+-. 4
 .sup.125 I-NH.sub.2 -PEO- 94 .+-. 5 94 .+-. 6 89 .+-. 10
 Crosslink
 .sup.125 I-Imz-PEO- 101 .+-. 4 95 .+-. 3 97 .+-. 3
 Crosslink
 EXAMPLE NO. 7
 A. Cross-linked-PEO-Coated Tissues
 Various Denacol pre-treated bovine pericardium heart valve tissues (HVT
 obtained from Baxter Edwards) were washed several times with deionized
 water, cut into circles, and pre-coated with an Imz-PEO solution. This was
 followed by a reaction with NH.sub.2 -PEO, at room temperature.
 B. Fibrinogen Adsorption
 PEO-coated and uncoated tissues were soaked in a citrate phosphate buffer
 solution (pH 7.4) containing .sup.125 I-fibrinogen, and incubated at
 37.degree. C. for one hour. Unbound protein was removed by washing
 extensively with PBS, saline and water. The amount of fibrinogen that was
 bound was calculated from the specific activity of the labeled protein and
 expressed as nanogram of fibrinogen per surface area.
 C. Avidin Cross-linking to Imz-PEO-coated-materials
 PVDF flat sheet membranes (or biological tissues) were cut into circles,
 pre-coated with Imz-PEO, and followed by reaction with Avidin, as
 described with NH.sub.2 -PEO above.
 D. Coupling of Avidin-PEO-coated Tissue to LC-Biotin-HSA
 Avidin-PEO-coated PVDF, Uncoated PVDF (Millipore) and Avidin-PVDF (with
 Avidin non specifically bound) were soaked in PBS (pH 7.4) containing
 LC-Biotin-.sup.125 I-HSA. The LC-Biotin-.sup.125 I-HSA was prepared by
 coupling NHS-LC-biotin to .sup.125 I-HSA. Unbound HSA-biotin was washed
 away with PBS and water. The amount of bound HSA was expressed as cpm per
 surface area.
 E. Results
 The results are all illustrated graphically in FIG. 9. These results
 indicate that all cross-linked-PEO-coated tissues (1A, 2A, 3A, 4A) exhibit
 about 10 fold lower fibrinogen binding than the corresponding tissues
 without PEO coating.
 FIG. 10 illustrates graphically the binding of HSA-LC-Biotin to
 Avidin-coated PVDF with and without pre-treatment with Imz-PEO.
 The results of the binding of biotin-HSA to Avidin-PEO-coated PVDF
 membrane, FIG. 10, suggest that Avidin can be covalently attached to the
 Imz-PEO-coated PVDF to improve the binding of Biotin-HSA, compared to
 Avidin-coated membranes without PEO treatment.
 EXAMPLE NO. 8
 A. Cross-Linked Glutaraldehyde-Treated Tissues
 Glutaraldehyde pre-treated bovine pericardium heart valves tissues were
 washed several times with de-ionized water, and pre-treated with an
 Imz-PEO solution. This was followed by a reaction with NH.sub.2 -PEO, at
 room temperature. The reaction with NH.sub.2 -PEO may be optional. The
 result is bovine pericardium tissue treated with PEO.
 "Treated" in this sense is considered broader than "coated", as the PEO
 will tend to diffuse into the tissue rather than merely collecting on the
 surface. Optionally, the tissue may further be treated with a biologically
 active recognition sequence, peptide, or compound during or after the
 reaction with NH.sub.2 -PEO.
 B. Fibrinogen Adsorption
 PEO-treated and untreated tissues were soaked in a citrate phosphate buffer
 solution (pH 7.4) containing 125I-fibrinogen, and incubated at 37.degree.
 C. for one hour. Unbound protein was removed by washing extensively with
 PBS, saline and water. The amount of fibrinogen that was bound was
 calculated from the specific activity of the labeled proteins and
 expressed as nanogram of fibrinogen per surface area.
 C. Calcification Assessment
 8 mm disks of PEO-treated and untreated tissues were implanted into the
 paravertebral muscle of New Zealand albino (NZA) rabbits. After 30 and 90
 days implantation, the disks were removed and their calcium was quantified
 by using known standards, and the results calculated as .mu.g Ca/mg dry
 weight tissue.
 D. Results
 The fibrinogen binding results are provided in Table 18 below. These
 results indicate that cross-linked PEO-treated tissues exhibit about
 six-fold lower fibrinogen binding than the corresponding tissues without
 PEO treatment.
 TABLE 18
 Fibrinogen Binding of both PEO-Treated and Untreated
 Glutaraldehyde-Fixed Tissue
 Bovine Pericardial Tissue Bound Fibrinogen
 Untreated 155 .+-. 43
 PEO-Treated 24 .+-. 3
 Table 19 (below) sets forth the results of the calcium content of a number
 of explanted PEO-treated tissues at 30 and 90 days. It is apparent that
 the average for the three given samples at 30 days is skewed by the second
 tissue explant, and it is believed that the first and third tissue
 explants are more representative. This is borne out by the more closely
 grouped results for the three samples at 90 days.
 In comparison, the results for a number of control samples is provided in
 Table 20 (below). The control samples are glutaraldehyde-treated tissues
 also implanted in the paravertebral muscle of NZA rabbits. The results
 show that the calcium content of PEO-treated tissues is reduced
 significantly compared to glutaraldehyde controls. Indeed, even taking
 into account the seemingly anomalous second PEO-treated tissue sample, the
 average calcium uptake of the PEO-treated tissues was about one-fifth that
 of the untreated tissues at 30 days. The difference at 90 days is even
 more stark, with the average calcium uptake of PEO-treated tissues being
 about 3% of that of the untreated tissues.
 TABLE 19
 Calcium Uptake of PEO-Treated Lutaraldehyde-Fixed Tissue from
 Rabbit Intramuscular Implant Technique
 Time
 Rabbit # Sample # (days) Total .mu.g/mg Ca Average St. Dev.
 703S B2613-05/4 30 2.648 23.209 .+-. 36.581
 705S B2613-05/2 30 65.445
 707S B2613-05/1 30 1.535
 697S B2613-05/4 90 3.41 6.691 .+-. 5.359
 699S B2613-05/2 90 3.788
 701S B2613-05/1 90 12.876
 TABLE 19
 Calcium Uptake of PEO-Treated Lutaraldehyde-Fixed Tissue from
 Rabbit Intramuscular Implant Technique
 Time
 Rabbit # Sample # (days) Total .mu.g/mg Ca Average St. Dev.
 703S B2613-05/4 30 2.648 23.209 .+-. 36.581
 705S B2613-05/2 30 65.445
 707S B2613-05/1 30 1.535
 697S B2613-05/4 90 3.41 6.691 .+-. 5.359
 699S B2613-05/2 90 3.788
 701S B2613-05/1 90 12.876
 It should be noted that the implant methodology wherein the tissues are
 implanted in the muscles of rabbits, or of other mammals, is believed to
 be more effective than traditional subcutaneous implant techniques. That
 is, tissue implanted subcutaneously tends to become rapidly encapsulated
 by the host's natural immune response. Because of this encapsulation, and
 because of the relatively low presence of calcium in such interstitial
 body spaces, the calcium uptake is from passive diffusion and is thus
 relatively slow. Therefore, tissue explanted at 30, 60, and even 90 days
 tends to have a calcium content of around 1 micrograms per milligram dry
 weight tissue. Differentiating between different tissues samples is thus
 problematic because of the relatively low resolution of the subcutaneous
 technique.
 Implanting the tissues directly into the animal's muscle, however, vastly
 increases the exposure of the tissue to body calcium. It is well known
 that calcium flux within muscles is one of the prime physiological causes
 of muscle contraction. Therefore, tissue implanted into the muscle is
 regularly exposed to transitory calcium flows. Because of the increased
 calcium exposure, the tissue more rapidly absorbs the calcium, and thus
 exhibits a much higher calcium content at 30, 60 and 90 days. The
 sensitivity or resolution of this implant methodology greatly facilitates
 differentiation and analysis of the results for different tissue
 specimens. A full disclosure of the muscle implant methodology is provided
 in co-pending U.S. patent application Ser. No. 09/387,468, entitled "In
 vivo Screening Methods for Predicting Calcification of Implantable
 Prosthetic Material" filed on even date herewith.
 It should also be noted that the PEO treatment as disclosed herein may be
 effective in tissues other than bovine pericardium. For example, allograft
 tissue, porcine tissue, equine tissue, or other xenograft tissue may be
 treated with PEO to obtain the benefits mentioned herein, in particular
 calcification mitigation. In addition, although PEO treatment has been
 tested on tissue that has first been pre-treated, or cross-linked, with
 Denacol or glutaralddehyde, the same benefits described herein may also be
 obtained by treating fresh tissue.
 EXAMPLE NO. 9
 In this example, methods and samples having multiple coatings were prepared
 and tested.
 A. PEO-coated Chitosan Surfaces
 1. Attachment of PEO onto Chitosan-mats
 Glass filter mats (GFM) were cut into circles (about 1 cm in diameter). The
 circles were first modified with 1% chitosan solution. The PEO derivatives
 with various lengths (PEO-5K, PEO-18.5K and PEO-20K) were then covalently
 attached to the mats through the amine functional group of the chitosan
 ligand. At the end of the coupling reaction, some mats were treated with
 an NHS-acetate to acetylate the unreacted amine groups of the chitosan
 polymer.
 2. Evaluation with Whole Blood
 Citrated, fresh whole blood was filtered through various PEO-coated
 chitosan mats and uncoated chitosan-mats. Fractions of 1.0 ml (.times.2)
 were collected as post-samples. The number of white blood cells (WBC) and
 platelets were determined on the pre-samples and post samples using a
 Sysmex cell counter.
 3. Results
 PEO-coated chitosan mats showed an improved recovery of platelets and WBC,
 compared to chitosan-coated mats without additional PEO coating.
 N-acetylation of the free amine group of the chitosan molecules appears to
 improve WBC and platelet recovery even further compared to non-acetylated
 materials. Surfaces coated with HMW PEO appear to have performed better
 than surfaces coated with LMW PEO (see FIGS. 11 and 12).
 B. PEO-Coated Heparin-Surfaces
 1. Attachment of PEO onto heparin-fixed denacol-treated pericardial heart
 valve tissues HVT)
 Two types of Heparin fixed Denacol treated tissues (3A and 4A) were
 obtained from Baxter CVG and were used for this study. They were washed
 several times with deionized water and were soaked in an oxycarbonyl
 imidazole-PEO (Imz-PEO) solution (pH=8.3) for 24 hours, followed by
 reaction with an amino-PEO (NH.sub.2 -PEO) at the same pH for at least 24
 hours. Incubations were performed at room temperature.
 2. Biocompatibility Evaluation
 PEO-coated and non-PEO-coated tissues were tested for their ability to bind
 fibrinogen (Fg) from a solution of purified human fibrinogen and from
 fresh whole blood according to the following procedure: PEO-coated and
 uncoated materials were soaked in a citrate phosphate buffer solution
 (pH=7.4) containing .sup.125 I-labeled fibrinogen (Fg), and were incubated
 at 37.degree. C. for one hour. Unbound fibrinogen was removed from the
 materials by washing extensively with saline, then each sample was counted
 in a gamma counter. The amount of protein adsorbed was calculated from the
 specific activity of the fibrinogen and expressed as ng of protein per mg
 (or per surface area) of materials.
 3. Results
 The results indicate that PEO-coated heparinized HVT can significantly
 reduce fibrinogen binding from both sources, a purified solution of human
 Fg and Fg from whole blood, compared to uncoated tissues (see FIGS. 13 and
 14).
 C. Heparin-treated Imz-PEO-coated-HVT
 A Heparin coating procedure, similar to the one described in section 2a
 above, was applied in this study. Heparin solution (prepared in
 bicarbonate buffer pH=8.3) was used instead of amino-PEO to react with
 Imz-PEO-coated HVT.
 It will be understood that various modifications to the presently preferred
 embodiments described herein will be apparent to those skilled in the art
 Such changes and modifications can be made without departing from the
 spirit and scope of the present invention and without diminishing its
 attendant advantages. It is therefore intended that such changes and
 modifications be covered by the appended claims.