Polymeric blends with zwitterionic groups

Details Polymeric blends with zwitterionic groups Polymeric blends with zwitterionic groups

1994-12-05

1998-01-27

Merriam, Andrew E. C.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

523106, 525183, 525217, 524515, 524547, 524916, 526277, C08L10102, C08L10100

Patent

active

057123268

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to new polymeric materials, especially suitable for use in biomedical applications, processes for their production, articles formed from such materials and processes for modifying the physical and biological properties of plastic materials.
The medical device industry frequently employs a range of thermoplastic, elastomeric and thermoset materials in medical devices. Many of these polymers were originally developed as engineering materials and their physical and mechanical properties reflect this. Thus a plastic may be employed as a medical device because it possesses physical and mechanical properties suitable for use in a biological environment. However, until recently little attention was paid to the biological properties of these materials. This has resulted in a number of problems with current device materials as a result of adverse biological reactions. Silicone rubbers have been shown to leach toxic silicones when implanted, polyurethanes have been found to degrade by macrophage attack and natural rubbers have caused severe allergic reactions. In addition, PVC, a widely used polymer for medical devices, often contains large quantities of the plasticiser bis-(2-ethylhexyl)phthalate and many studies now show this to be toxic. It is clear, therefore, that many materials possess properties which render them unsuitable for use in biological applications.
Previous attempts to prepare biocompatible materials have mimicked the surface of platelet cells which under normal circumstances exist in the blood without causing any adverse reactions. These cell membranes comprise a phospholipid bilayer with the phosphorylcholine group dominating the external membrane surface. It is believed this outer surface avoids adverse reaction with other biological components. Lipids containing phosphorylcholine groups have been coated on to the surface of device materials and bloodclotting studies showed that they rendered the surface more biocompatible (J. A. Hayward & D. Chapman, Biomaterials, Vol. 5, 135, 1984). These phospholipids have also been used as plasticisers in commercial polymers and have again improved the biocompatibility of the base material (WO-A-87/02684). However these two approaches nevertheless possess disadvantages.
Coating the surface of a finished device has a number of problems, one being the difficulty in coating devices with complex shapes or multiple components; in practice a multi-component device can be impossible to coat. In addition the degree of biocompatibility is dependent on the quality of the coating and how strongly it is bound to the surface; thus defects or scratches in the coating will reduce its effectiveness. The use of a lipid as a plasticiser goes some way to overcome these problems, but the lipid is free to move through the material and can eventually leach out of the system. This can again lead to a reduction in the level of biocompatibility. The lipid also has in addition no mechanical strength and can therefore only be used to soften the base polymer.
We have now devised new blended polymeric materials which seek to overcome these disadvantages. The blends combine the desirable physical and/or mechanical properties of an engineering polymer with the biocompatible properties of a polymer bearing pendant zwitterionic, for example phosphoryl choline, groups.
The present invention accordingly provides a polymer blend comprising:
The extent to which a polymer bearing zwitterionic pendant groups (A) renders a further polymer biocompatible in a blend may be assessed as a combination of factors such as reduction in the extent to which the blend causes blood platelet activation and protein adsorption (for instance as judged by absorption of fibrinogen from human plasma).
The polymer bearing zwitterionic pendant groups may be either a homopolymer or a copolymer. Preferably it is a polymer of residues of one or more radically polymerisable monomers, more preferably ethylenically unsaturated monomers. Preferably the polymer bears zwitterionic pendant groups by

REFERENCES:
JP-A 55-48261, Jun., 1980.

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