Biocompatible lubricious hydrophilic materials for medical...

Details Biocompatible lubricious hydrophilic materials for medical... Biocompatible lubricious hydrophilic materials for medical...

1998-06-26

2001-09-11

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C525S303000, C525S330100, C525S330600, C526S320000

Reexamination Certificate

active

06287707

ABSTRACT:

BACKGROUND OF THE INVENTION
In recent years there has been an increased awareness of the need for biocompatible materials for medical devices. Currently medical devices are typically made from synthetic polymeric materials such as polyvinylchloride (PVC), polyurethanes (PU), polybutadienes (latex), polyamides (PA) and others. It has also been recognized that hydrophilic materials offer good biocompatibility to medical devices when in-contact with biological fluids or living tissue. These hydrophilic materials significantly reduce adsorption of proteins and of cellular components such as platelets, leucocytes, erythrocytes and fibroblasts, and also reduce activation of intrinsic and extrinsic blood clotting pathways.
In addition to the biocompatibility of the material, the lubricity of the coating is also important, as it minimises patient trauma, and allows ease of insertion and removal of the device. An example of an important application of a biocompatible lubricious hydrophilic material is during chest drainage, which occurs after cardio-thoracic surgery. In this chest drainage procedure, preformed blood clots and whole blood is able to slide down the medical device such as thoracic drain catheter. This is achieved because of the lubricious (slippery) nature of the coated device. A biocompatible lubricious hydrophilic medical device can be used in other wound drain applications.
It has been well recognized that polyethylene oxide (PEO) (also called polyethylene glycol or PEG) when bound to a medical device offers good biocompatibility, lubricity and hydrophilicity. U.S. Pat. No. 4,424,311 discloses a polymerizable PEO monomer having polyethylene oxide unit with a carbon-carbon double bond which is grafted on to PVC or vinyl chloride-vinyl acetate copolymer or vinyl chloride-vinyl acetate-ethylene terpolymer. Disadvantages of grafting PEO are that it is a lengthy procedure and the grafted PEO units are unevenly distributed. Therefore, homogenous coverage on the surface is not achieved, which results in reduced biocompatibility and lubricity.
In another U.S. Pat. No. 5,075,400, PEO containing a polymerizable carbon-carbon double bond is polymerised, in toluene, with methyl methacrylate or ethyl methacrylate. The resultant polymer, which is referred to as supersurfactant, is predominantly water soluble and is adsorbed onto various polymeric surfaces from water, water/ethanol mixtures, or ethanol. A disadvantage of these polymers is that they act as surfactants, are adsorbed on to the surface and therefore would be readily de-sorbed from the surface when they are in contact with biological fluids such as blood, as blood has surfactant properties. Similarly, the lubricious properties would also be lost since the adsorbed surfactant is not stable on the surface. Another disadvantage is that the polymer supersurfactant is synthesized by solution polymerization in toluene and as a result high molecular weight polymer containing PEO would be difficult to produce, since PEO polymers have limited solubility in toluene.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to mitigate or overcome some of the aforementioned disadvantages encountered in the prior art.
The present invention is concerned with biocompatible, lubricious, hydrophilic materials suitable for use in medical devices or otherwise. It is proposed that the materials may be used to coat a substrate such as a medical device or may be blended into a polymer composition prior to formation of the medical device or other article. The invention extends to polymers, their production methods, and their uses as coatings or components of articles of manufacture.
In one aspect of the present invention a biocompatible, lubricious, hydrophilic material for medical devices or other applications can be produced by aqueous emulsion polymerization to yield a polymer with the desired hydrophobic and hydrophilic domains, not conventionally obtained by solution polymerization, wherein the emulsion polymer produced is a stable emulsion having high molecular weight.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with a more specific aspect of the invention, there is provided a biocompatible, lubricious, hydrophilic material comprising a terpolymer of 5 to 25 mole percent of a polymerizable monomer (1) having a polyethylene oxide unit with an average degree of polymerization from 5 to 18 and a polymerizable carbon-carbon double bond, 5 to 30 mole percent of a polymerizable monomer (2) having a polyethylene oxide unit with an average degree of polymerization from 19 to 65 and polymerizable carbon-carbon double bond, and 45 to 90 mole percent of an alkyl methacrylate (3):
[CH
2
═C(R)—CO—[—O—CH
2
—CH
2
—]
n1
—O—R]CH
2
═C(R)—CO—(—O—CH
2
—CH
2
—)
n1
—O—R
1
  (1)
where n1 is from 5 to 18, and [each] R and R
1
are [is] independently H or CH
3
[CH
2
═C(R)—CO—[—O—CH
2
—CH
2
—]
n2
—O—R]CH
2
═C(R)—CO—(—O—CH
2
—CH
2
—)
n1
—O—R
1
  (2)
where n2 is from 19 to 65, and [each] R and R
1
are [is] independently H or CH
3
 CH
2
═C(CH
3
)—CO
2
—(CH
2
)
m
—CH
3
  (3)
where m is from 3 to 17.
Monomers (1) and (2) are hydroxy or, preferably, methoxy polyethyleneglycol acrylates or, preferably, methacrylates, and provide the hydrophilic moieties in the terpolymer. Monomer (3), ranging from butyl to octadecyl methacrylate, provides the hydrophobic moieties.
The preferred molar proportions of (1), (2) and (3) are about 15% each of (1) and (2) and 70% of (3). In weight terms, proportions of 6 to 20% of (1), 40 to 80% of (2) and 10 to 50% of (3) are generally appropriate.
It is preferred that monomer (1) has polyethylene oxide units with a degree of polymerization n1 from 5 to 12, more especially a degree of polymerization n1 from 5 to 10.
It is preferred that monomer (2) has polyethylene oxide units with a degree of polymerization n2 from 20 to 50, more especially a degree of polymerization n2 from 22 to 48.
It is preferred that monomer (3) is n-butyl methacrylate.
The incorporation of significant proportions of monomer (2) of higher molecular weight than monomer (1) allows the formation of a solid dry powdery product with advantageous properties of handling, processing and storage.
The production of a terpolymer by polymerizing monomers (1), (2) and (3) may be carried out in water to produce an aqueous emulsion polymer which is stable, having high molecular weight.
The production of the terpolymer in water differs significantly from production in organic solvents in two respects.
a) Higher molecular weights of the terpolymer can be achieved by emulsion polymerisation than by solution polymerisation in organic solvents, as PEO solubility decreases with increasing molecular weight for polymerisation carried out in organic solvents such as toluene, ethyl and butyl acetate, alcohols etc.
b) Aqueous emulsion polymerisation allows polymers to be produced where the hydrophobic monomer (3) is phase separated to a certain degree to produce a polymer having hydrophilic and hydrophobic domains. This allows the polymer to be adsorbed, solvent welded or blended with PVC, polyurethanes, polybutadienes and the like. Polymerisation of the above three monomers (1), (2) and (3) in organic solvents produces polymers which are random, and phase separated domains of hydrophilic and hydrophobic do not occur. This results in poor adhesion of the polymer on to PVC, polyurethanes, polybutadienes and the like.
Aqueous emulsion polymerisation of monomers (1), (2) and (3) can be initiated by conventional water soluble initiators such as potassium persulphate. After polymerisation, the terpolymer is dialyzed against water to remove unreacted monomer and the resultant polymer is freeze dried, spray dried or treated by other means to obtain a dry powder.
The resultant terpolymer may then be dissolved in organic solvents, such as alcohols, acetone or tetrahydrofuran (THF) or mixtures thereof, and coated on to prefabricated devices, or

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