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The present invention relates to a novel antithrombogenic polyurethane
polymer and process for making the same. More particularly the invention
relates to a polyurethane polymer having an antithrombogenic material
covalently bonded thereto so that the material is permanently affixed to
the polymer and remains virtually nonleachable when the products made from
the reaction product are in use.
Extensive investigations have been undertaken over many years to find
materials that will be biologically and chemically stable towards body
fluids. This area of research has become increasingly important with the
development of various objects and articles which can be in contact with
blood, such as artificial organs, vascular grafts, probes, cannulas,
catheters and the like.
Artificial materials are being increasingly used as blood contact devices
and may be subject to potential generation of thrombus. When blood
contacts a foreign material, a complex series of events occur. These
involve protein deposition, cellular adhesion and aggregation, and
activation of blood coagulation schemes. Considerable research effort has
been focused on this blood-material-interaction in the last twenty years.
The overall objective of these investigations has been to minimize the
potential for thrombus formation on the foreign materials, such as the
device when introduced into the body upon contact with blood.
Early work by R. I. Leininger and R. D. Falb, U.S. Pat. No. 3,167,344, was
based on binding quaternary amines to a polymer surface and subsequently
ionically binding heparin thereto. In contrast, H. M. Grotta established a
method in U.S. Pat. No. 3,846,353 in which heparin was complexed with a
quaternary amine on a polymer surface. Both Leininger et al. and Grotta
methods have the disadvantage of being non-permanent or leachable systems.
In general, ionically bound systems have limited viability due to their
inherent leachability. J. Love and G. W. Holmes patented a method for the
preparation of antithrombogenic surfaces in U.S. Pat. No. 3,616,935
wherein polyalkylenimines are used to irreversibly absorb the
antithrombogenic compound to cellulose, cellulose esters, silicone rubber,
polypropylene, polycarbonate and glass through the formation of ionic
bonds. The Love et al. technique, however, was not able to overcome the
deficiencies of the prior techniques, notably leaching of the
antithrombogenic material rendering the system non-permanent and
ineffective for long term internal use in the body.
U.S. Pat. No. 3,826,678 of A. S. Hoffman and G. Schmer relates to a
covalent bonding method involving the use of "soft" hydrogel surfaces
wherein radiation grafting is employed with a reactable compound selected
from polymers and copolymers on an inert polymeric substrate and
thereafter a biologically active compound is chemically bound to the
reactable compound. "Soft" gel-like surfaces are not appropriate for
devices such as catheters or other medical devices which require a "hard"
polymer surface. The "soft" hydrogel or hydrophilic surface of the Hoffman
et al. patent would be subject to being stripped off catheters and in case
of other blood contact devices, be devoid of the mechanical properties
required. "Hard" polymers would provide the mechanical strength required
in such applications.
U.S. Pat. No. 4,326,532 to Hammar discloses a layered medical article
having an antithrombogenic surface wherein a natural or synthetic
polymeric substrate is reacted with chitosan and the antithrombogen is
then bonded to the chitosan. Hammer discloses on column 3, lines 10 to 49
that the antithrombogenic material may be ionically bonded to the chitosan
or covalently bonded using boron hydrides.
In contrast to the aforementioned techniques, Larm et al. disclosed in "A
New Non-Thrombogenic Surface Prepared by Selective Covalent Bonding of
Heparin via A Modified Reducing Terminal Residue," Biomat., Med. Dev.,
Art. Org.," (283) pages 161-173 (1983) a new method for binding heparin to
artificial surfaces. The procedure described involved partially degrading
heparin and coupling the fragments through their reducing terminal units.
Heparin was then ionically and covalently coupled to different surfaces
with best results achieved using polyethylenimine containing primary,
secondary and tertiary amino groups.
It would be desirable to provide a material which has excellent biological
and chemical stability towards body fluids, namely blood, and which
retains its antithrombogenic agent in a permanent and non-leachable
fashion when in contact with blood. It would also be desirable to provide
materials which, while being biocompatible, are also bifunctional, that
is, materials which have biological activity in a variety of functions.
The present invention accomplishes all of these needs by use of a specific
covalently bonded antithrombogenic agent to a solid support. More
particularly the invention involves an antithrombogenic polyurethane
polymer having (a) a support substrate; (b) a protonated amine rich
polyurethane-urea bonded to said support substrate and (c) an aldehyde
containing antithrombogenic agent reacted with the amine functionality of
said polyurethane-urea to form a covalently bonded antithrombogenic
material.
In another embodiment, the present invention involves a process for
imparting antithrombogenic activity to polyurethane polymer materials
which comprises (a) treating the surface of a solid support with a
solution of a protonated amine rich polyurethane-urea so that the
polyurethane-urea is bonded to the support substrate; (b) removing solvent
from the treated substrate to form a layer of the polyurethane-urea upon
the support substrate; (c) activating the amine functionality on the
polyurethane-urea by use of an alkaline buffer to form free amine groups;
and (d) reacting the free amine groups with an aldehyde containing
antithrombogenic agent to covalently bond the antithrombogenic agent to
the polyurethane-urea in the presence of a reducing agent.
The term antithrombogenic agent or material as used herein refers to any
material which inhibits thrombus formation on its surface, such as by
reducing platelet aggregation, dissolving fibrin, enhancing passivating
protein deposition, or inhibiting one or more steps within the coagulation
cascade. Illustrative antithrombogenic material may be selected from the
group consisting of heparin, prostaglandins, urokinase, streptokinase,
sulfated polysaccharide, albumin and mixtures thereof. The
antithrombogenic material may be used in varying amounts depending on the
particular material employed and ultimate desired effect. Preferred
amounts have generally been found to be less than about 5% by weight of
the final products and may range from about 0.2% to about 5% by weight.
The support structure used in the invention is not critical and may be
selected from a wide variety of materials that are compatible with a
polyurethane-urea formulation. Exemplary support surfaces may be prepared
from thermoplastic polyurethanes, thermosetting polyurethanes, vinyl
polymers, polyethylene, polypropylene, polycarbonates, polystyrenes,
polytetrafluoroethylene, polyesters, polyvinyl chlorides and the like. The
particular structures do not constitute a critical aspect of this
invention other than to serve as a support substrate for the
antithrombogenic agent. The supports are preferably performed into the
desired shape or structure for the particular application prior to
treatment according to the invention. Of significant importance is the
ability of the support to bind the modified polyurethane-urea compound
with the antithrombogenic agent in order to effect irreversible coupling.
It has been found that any support may be used which has an average
molecular weight different from the polyurethane-urea compound used to
form the coupling complex and which does not dissolve in the organic
solvent for the complex. This distinction is critical to enable bonding of
performed supports without deformation while permitting a layer of
polyurethane coupler to be bonded to the support structure. In this
manner, an integral unit is formed which will not easily separate upon
use.
The first step in the process of the invention involves treating the
surface of the solid support with a solution of a protonated amine rich
polyurethane-urea so that the polyurethane-urea material is bonded to the
support substrate. The polyurethane-urea materials of the invention may be
selected from a wide variety of compounds prepared by reacting a
polyurethane prepolymer with a diamine.
Polyurethane-ureas are known in the art. They are generally made by chain
extending the reaction product of a diisocyanate and a high molecular
weight glycol (urethane prepolymer) with a diamine. Without being limited
there to, one particularly preferred procedure of the present invention
involves adding diamine in excess, that is from about 0.6 to 1 mole of
diamine and preferably 0.75 to 1 mole for each free isocyanate group in
the prepolymer to produce a polyurethane-urea with primary amine end
groups. Use of ratio's below 0.6 have been found unsuitable to prepare an
amine rich polyurethane-urea compound to enable sufficient reaction with
the antithrombogenic agent. Ratios above about 1.0 result in the presence
of nonreactive excess diamine which must be removed from the solution for
adequate processing.
The urethane prepolymer can be based on a variety of diisocyanates.
Suitable diisocyanates include; 1,4-cyclohexane diisocyanate;
dicyclohexylmethane 4,4'-diisocyanate; xylene diisocyanate;
1-isocyanate-3-isocyanatomethyl-3,5,5-trimethylcyclohexane; hexamethylene
diisocyanate; 1,4-dimethylcyclohexyl diisocyanate;
2,4,4-trimethylhexamethylene diisocyanate; isocyanates such as m-phenylene
diisocyanate; mixtures of 2,4-and 2,6 hexamethylene-1,5-diisocyanate;
hexahydrotolylene diisocyanate (and isomers), napthylene-1,5-diisocyanate;
1-methoxyphenyl-2,4-diisocyanate; diphenylmethane 4,4'-diisocyanate;
4,4'-biphenylene diisocyanate; 3,3'-dimethoxy-4,4-biphenyl diisocyanate,
3,3'-dimethyl-4,4'-biphenyl diisocyanate, and 3,3' dimethyl
diphenylmethane-4,4' diisocyanate and mixtures thereof. The aliphatic and
alicyclic diisocyanates employed in the process of this invention and the
products made therefrom generally exhibit good resistance to the
degradative effects of ultraviolet light.
The high molecular weight glycols useful in the present invention may be a
polyether diol or polyester diol and range in number average molecular
weight from about 400 to about 3,000 and preferably about 500 to about
2,000. The low molecular weight glycols may also be used to prepare the
prepolymer which materials may have from about 2 to 10 carbon atoms.
Exemplary of the low molecular weight glycols which may be employed to
prepare polyester polypols are 1,6-hexanediol, neopentyl glycol,
trimethylolpropane, ethylene glycol, diethylene glycol, triethylene
glycol, 1,4-butanediol, 1,4-cyclohexanediol, 1,2-propanediol,
1,3-propanediol, 1,3-butylene glycol, 1,4-cyclohexane dimethanol,
1,6-hexanediol, and the like, and mixtures thereof.
The polyethers containing at least 2 hydroxyl groups used in accordance
with the invention are also known per se and are obtained, for example, by
polymerizing epoxides, such as ethylene oxide, propylene oxide, butylene
oxide, tetrahydrofuran, styrene oxide or epichlorohydrin on their own, for
example, in the presence of BF.sub.3, or by adding these epoxides,
optionally in admixture or in succession, to starter components containing
reactive hydrogen atoms, such as water, alcohols, or amines, for example,
ethylene glycol, 1,3- or 1,2-propylene glycol, 4,4'-dihydroxy diphenyl
propane, aniline, ammonia, ethanolamine or ethylene diamine. The most
preferred polyether diols are poly(tetramethylene ether)glycols.
The use of trihydric alcohols can be employed when branched polymers are
desired to improve coating properties. Examples are glycerin,
trimethyolpropane, adducts of trimethylolpropane or glycerin with ethylene
oxide, or epsilon-caprolactone, trimethylolethane, hexanetriol-(1,2,6),
butanetriol (1,2,4) and pentaerythritol.
Illustrative polyesters may contain hydroxyl groups, for example, reaction
products of polyhydric alcohols reacted with divalent carboxylic acids. It
is also possible to use the corresponding polycarboxylic acid anhydrides
or corresponding polycarboxylic acid esters of lower alcohols or mixtures
thereof, for producing the polyesters. The polycarboxylic acids may be
aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally
be substituted, for example, by halogen atoms and/or unsaturated. Examples
of polycarboxylic acids of this kind include succinic acid, adipic acid,
suberic acid, azelaic acid, sebacic acid, phthalic acid, phthalic acid
anhydride, tetrachlorophthalic acid anhydride, endomethylene
tetrahydrophthalic acid anhydride, glutaric acid anhydride, maleic acid,
maleic acid anhydride, fumaric acid, dimeric and trimeric fatty acids such
as oleic acid, optionally in admixture with monomeric fatty acids,
terephthalic acid dimethyl ester and terephthalic acid bis-glycol ester.
Examples of suitable polyhydric alcohols are ethylene glycol, 1,2-and
1,3-propylene glycol, 1,4- and 2,3-butylene glycol, 1,6-hexanediol,
octanediol, neopentyl glycol, cyclohexane dimethanol (1,4-bis-hydroxy
methyl cyclohexane), 2-methyl-1,3-propanediol, also diethylene glycol,
triethylene glycol, tetraethylene glycol, polyethylene glycols,
dipropylene glycol, polypropylene glycols, dibutylene glycol and
polybutylene glycols. Polyesters of lactones, for example,
.epsilon.-caprolactone or hydroxy carboxylic acids, for example,
.omega.-hydroxycaproic acid, may also be used.
The prepolymer is prepared by heating polyols and diisocyanate with
agitation in solvent under an inert atmosphere to 60.degree.-100.degree.
C. The ratio of NCO to hydroxyl (OH) groups in the prepolymer is from 1.5
to 2:1 with a ratio of 2:1 preferred. The higher NCO to OH ratio limits
the molecular weight of the prepolymer and results in higher levels of
amine functionality from the diamine reaction later.
The diol molecular weight can vary from 400-3000 molecular weight.
Molecular weights of about 800 to about 1500 give a combination of good
film formation with adequate levels of amine functionality at the end of
the reaction sequence. A catalyst may be employed but is not required. The
reactants are heated for a period sufficient to react all the hydroxyl
groups. The reaction time is generally 2-6 hours, however catalysts may
shorten the reaction time to as little as 5 minutes. Suitable catalysts
include tin salts such as dibutyltin dilaurate, stannous octoate or
tertiary amines.
The prepolymer reaction is preferably carried out in solvent and in a
solvent which is unreactive to NCO. Alternatively, the prepolymer may be
formed neat and solvent added after the prepolymer is formed. Convenient
solvents used in preparation of the prepolymer are aromatic hydrocarbons,
ketones, esters, methylene chloride or tetrahydrofuran. Certain solvents
have potential reactivity with amines and therefore must be evaporated
prior to the addition of amines; examples of such solvents include ketones
and methylene chloride.
A diamine solution is made by dissolving the amine in an appropriate
solvent. Isopropanol was selected because the diamine dissolves (or
disperses) readily in it and it is a secondary alcohol with a low
probability of competing for available NCO groups with the amine groups.
One particularly preferred final solvent mixture of toluene-isopropanol
(2:1 by wt.) has the ability to solvate the highly polar
polyurethane-urea.
In additon to isopropanol, methanol, ethanol, propanol, butanol,
isobutanol, tert-butanol and diacetone alcohol or mixtures of alcohols may
also be used.
Amines useful for this invention are: ethylene diamine, 1,3-propylene
diamine, 1-4 butanediamine, 1-6 hexanediamine, 1,7-heptanediamine,
1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine,
1,12-dodecanediamine, piperazine, phenylene diamine, tolylene diamine,
hydrazine, methylene bis aniline, methylene bis 4 aminocyclohexane,
isophorone diamine, 2,2,4 trimethyl-1,6-hexanediamine, menthane diamine,
polyoxypropylene diamines and polyoxyethylenediamines known as
"Jeffamines" from Jefferson Chemical Company, U.S.A.
The prepolymer solution may be prepared at a concentration of 10-60%, with
30-40% being preferred (wt/wt). A solution of diamine and solvent such as
isopropanol is made with a concentration of 1-30%, with 5-15% being
preferred (net weight). The prepolymer is slowly added to the diamine
solution with good stirring, maintaining the temperature at 30.degree. C.,
in a nitrogen environment. After the reaction solution has been mixed well
and the reaction is complete, a preferred optional procedure involves
adding an acid slowly to the amine rich polyurethane-urea solution. A
sufficient amount of acid is added to protonate the amine functionality of
the amine-rich polyurethane-urea. The solution concentration is adjusted
to an appropriate concentration of 5-50 weight percent, where 10-30% is
preferred and 15-25% is most preferred.
The preferred acid addition technique used according to the invention
prevents premature reaction of the free amine groups with carbon dioxide
and other oxidizing agents present in the reaction. This is achieved by
converting the amine groups into salt radicals by reaction with a
protonating acid. Suitable acids include acetic acid, hydrochloric acid,
phosphoric acid, formic acid, citric acid, butyric acid, toluene sulfonic
acid, methane sulfonic acid and so forth. The reaction permits the
amine-rich polyurethane-urea compound to be stored for long periods. It
has been unexpectedly found that when this protective step was not
employed, a sharp variation in results was evidenced due to variable and
often relatively low amounts of antithrombogenic material bond to the
polyurethane.
The choice of polyurethane-urea solvent for coating the substrate is an
important factor. Many combinations of the previously listed solvents
could be found useable by a coatings chemists skilled in the use of
solubility parameter theory. Although the solvent mixture of toluene and
isopropanol has the proper characteristics, many other combinations are
useable.
Other solvents can be substituted by volatilizing the original reaction
solvent and reconstituting to 5-40% by weight where 15-25% is preferred.
Exemplary solvents include toluene, methanol, ethanol, propanol,
isopropanol, acetonitrite, and the like. The solvent system is important
to the invention but not critical or limiting.
Once prepared, the protonated polyurethane-urea is dispersed or dissolved
in a solvent at the appropriate concentration of about 5% to about 40% and
is contacted to form a layer upon the substrate by conventional flow or
dip coating processes. Once contacting is complete, the structure is
placed in a gaseous environment, preferably nitrogen, to remove the
solvent. The structure is then ready for reaction with the
antithrombogenic agent. Prior to reacting the protonated amine group with
the antithrombogenic agent it will be necessary to activate the amine
functionality on the polyurethane-urea. Activation may be conveniently
performed with an alkaline buffer. The particular buffer is not critical
even though it is preferred that the pH of the buffer be above about 8.0.
Suitable buffers include, but are not limited to, sodium borate, sodium
5:5-diethylbarbiturate-HCl, Clarks and Lubs solution (NaOH, KCl and
H.sub.3 BO.sub.3), and sodium bicarbonate.
It is essential according to the invention that the antithrombogenic agent
be modified to contain a reactive aldehyde moiety which does not inhibit
the bioactivity of the antithrombogenic agent when coupling is complete.
The formation of aldehyde containing agents may be achieved by conventional
methods. For example when using heparin as the antithrombogenic agent,
heparin may be partially depolymerized by deaminative cleavage with
aldehyde inducing compounds such as sodium periodate and nitrous acid.
This cleavage converts an amine bearing carbohydrate residue to a
2,5-anhydro-D-mannose residue. One preferred method to produce an aldehyde
modified heparin involves the reaction of sodium heparinate with sodium
periodate at a pH of between 3-7 with a preferred range of 4-5. The pH of
the reaction mixture is maintained by an appropriate buffer. The reaction
is carried out with the reaction vessel protected from light with constant
stirring. Upon completion of the reaction, an excess of glycerin is added
to neutralize the remaining unreacted periodate. The aldehyde modified
heparin is then optionally dried in a nitrogen environment. The dried
aldehyde modified heparin may then be simply reconstituted in an
appropriate acidic buffer to pH 3.0-8.0 where 4-7 is preferred and a
reducing agent such as sodium cyanoborohydride is added at weight percent
of 1-40%, where 5-30% is preferred, and 5-15% most preferred. This
solution is then exposed to the amine rich polyurethane-urea coated
substrate. The aldehyde functional groups on the heparin are then reacted
with the free amine groups to give a Schiff base formation that may be
reduced to provide stable secondary amines. Exemplary reducing agents
include sodium borohydride, sodium cyanoborohydride, and
tetrahydrofuran-borane. This reaction results in covalently bonding of the
antithrombogenic agent to the polyurethane-urea.
Upon completion of the antithrombogenic coupling reaction, the surface may
be washed with water to remove loosely bound or unreacted antithrombogenic
agent. Washing may be optionally performed with an isotonic solution. The
resulting covalently bonded heparin demonstrates high antithrombogenic
activity as well as permanency and nonleachability.
The invention will be further illustrated by the following nonlimiting
examples. All parts and percentages given throughout the Specification are
by weight unless otherwise indicated.
EXAMPLE 1
This example illustrates the synthesis of a preferred amine rich
polyurethane-urea.
29.61 g of trimethylolpropane and 215.14 g of a low molecular weight
polyether polyol such as Teracol.TM. 650 (poly(oxytetramethylene)glycol)
were added together in a mixing vessel (1.0 equivalent of each) and heated
at 70.degree. C. After equilibrating, 346.90 g (4.0 equivalents) of
hydrogenated diphenyl methylene diisocyanate was added and mixing
continued. 0.09 g of dibutyl tin dilaurate (0.015%) was added to the
mixing solution. After at least 5 minutes of mixing the reactants were
transferred to a 90.degree. C. oven for 60 minutes. After one hour the
prepolymer was removed and the percent free NCO groups was titrated and
calculated. Typical values ranged from 8.0-9.5%. The prepolymer was then
purged with nitrogen gas and stored.
60 g of the previously prepared prepolymer (with NCO content of 8.46%) was
added to 120 g of toluene to make a 33% wt/wt solution. A diamine solution
was prepared by adding 14.72 g of 1,6-hexanediamine to 80 g of isopropanol
and 40 g of toluene. The diamine solution was stirred vigorously with a
magnetic stir bar. The prepolymer solution was then added dropwise to the
diamine solution over a two hour period. The reaction was stirred for an
additional two hours. Glacial acetic acid (10 g) was then added dropwise
to the reaction mixture. The resulting amine rich polyurethane-urea
polymer was then dried with nitrogen gas and finally with vacuum. The
amine rich polyurethane-urea polymer was then dissolved in methanol to a
20% wt/wt solution for coating.
EXAMPLE 2
This example demonstrates the preparation of an aldehyde modified heparin.
Heparin (1.0 g) was added to a sodium acetate buffer which was prepared by
dissolving 0.5 g of sodium acetate in 300 ml distilled water. The pH of
this solution was then adjusted to 4.5 with glacial acetic acid.
0.1 g of sodium periodate (NaIO.sub.4) was added and the solution was
reacted for 20 minutes in a light protected reaction vessel with constant
stirring. Thereafter, 3.0 g of glycerol was added to neutralize any
remaining periodate. The solution was concentrated by drying under
nitrogen gas. The final solution was reconstituted to 1% wt/wt.
EXAMPLE 3
This example is illustrative of the preparation of an antithrombogenic
surface according to the present invention.
An amine rich polyurethane-urea polymer of Example 1 was dissolved in
methanol to a 20% wt/wt solution. A polyurethane substrate was coated with
the amine-rich polyurethane-urea. After coating, the substrate was placed
in nitrogen atmosphere for 60 minutes at ambient temperature. The samples
were then placed in sodium borate buffer of pH 9.2, which was prepared by
dissolving 57.21 g of sodium borate in 15 liters of distilled water, and
stored until reaction with heparin.
The samples were then placed in a mixing vessel and aldehyde-modified
heparin of Example 2 was added to a concentration of 1%. The reaction was
performed in a pH 4.5 sodium acetate buffer at 50.degree. C. Sodium
cyanoborohydride (0.05 g) was added as a reducing agent. After 2 hours the
samples were removed and placed in a 3M saline solution to remove any
loosely bound or adsorbed heparin. Initial radiolabel assays showed that
117.2 ug.+-.3.4 ug of heparin was bound per cm.sup.2 of surface area.
After 384 hours washing in a dynamic 3M saline solution, essentially no
heparin was leached or lost. The radiolabel assay showed 112.5 ug.+-.6 ug
of heparin was still bound per cm.sup.2. This demonstrates the permanency
of the covalent bonded heparin of this invention.
EXAMPLE 4
Various length diamines can be used in the synthesis of the amine rich
polyurethane-urea. This example demonstrates the use of an eight carbon
diamine.
29.61 g of trimethylolpropane and 215.14 g of a low molecular weight
polyether polyol such as Teracol.TM. 650 (poly(oxytetramethylene)glycol)
were added together in a mixing vessel (1.0 equivalent of each) and heated
at 70.degree. C. Thereafter, 346.90 g (4.0 equivalents) of hydrogenated
diphenyl methylene diisocyanate was added. 0.09 g of dibutyl tin
dilaurate, a catalyst, (0.015%) was added to the mixing solution. After at
least 5 minutes of mixing the reactants were transferred to a 90.degree.
C. oven for 60 minutes. After one hour the prepolymer was removed and the
percent free--NCO groups were titrated and calculated. Typical values
ranged from 8.0-9.5%. The prepolymer was then purged with nitrogen gas and
stored.
15 g of the previously prepared prepolymer (with NCO content of 8.16%) was
added to 30 g of toluene to make a 33% wt/wt solution. A diamine solution
was prepared by adding 5.09 g of 1.8-octanediamine to 45 g of 2:1
isopropanol/toluene (by wt.) solvent mixture. The diamine solution was
stirred vigorously with a magnetic stir bar. The prepolymer solution was
then added dropwise to the diamine solution over a two hour period. The
reaction was stirred for an additional two hours. 2.23 g of glacial acetic
acid was then added dropwise. The resulting amine rich polyurethane-urea
was then dried with nitrogen gas and finally with vacuum.
The amine rich polyurethane-urea polymer was then dissolved in propanol to
a 15% wt/wt solution for coating.
EXAMPLE 5
This example demonstrates the effectiveness of the present invention in
using longer chain diamines in the amine rich polyurethane-urea and the
subsequent bonding of antithrombogenic agents.
An amine rich polyurethane-urea polymer of Example 4 was dissolved in
propanol to a 15% wt/wt solution. A polyurethane substrate was coated with
the amine rich polyurethane-urea. After coating, the substrate was placed
in a nitrogen atmosphere for 60 minutes at ambient temperature. The
samples were then placed in sodium borate buffer of pH 9.2 and stored
until reaction with heparin.
The samples were then placed in a mixing vessel and
aldehyde-modified-heparin, similar to that of Example 2, was added to a
concentration of 1%. The reaction was performed in a pH 4.5 sodium acetate
buffer at 50.degree. C. Sodium cyanoborohydride (0.05 g) was added as a
reducing agent. After 2 hours the samples were removed and placed in a 3M
saline solution to remove any loosely bound or adsorbed heparin. Initial
radiolabel assays showed that 113.6 ug.+-.8.2 ug of heparin was bound per
cm.sup.2 of surface area. After 24 hours in a dynamic water wash, the
radiolabel assay showed 90.7 ug.+-.4.9 ug of heparin was still bound per
cm.sup.2. This demonstrates the permanency of the covalent bounded heparin
of this invention.
The invention being thus described, it will be obvious that the same may be
varied in many ways. Such variations are not to be regarded as a departure
from the spirit of scope of the invention and all such modifications are
intended to be included within the scope of the claims.
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