Graft polymerization of substrate surfaces

Details Graft polymerization of substrate surfaces Graft polymerization of substrate surfaces

1999-09-10

2002-03-19

Beck, Shrive P. (Department: 1762)

Coating processes

Medical or dental purpose product; parts; subcombinations;...

Implantable permanent prosthesis

C427S002250, C427S002280, C427S002300, C427S002310, C427S487000, C427S372200, C427S301000, C427S302000, C427S303000, C427S399000, C427S400000

Reexamination Certificate

active

06358557

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods for grafting polymers and copolymers onto polymer substrates.
BACKGROUND OF THE INVENTION
It is desirable for substrates such as those used in certain medical devices, including but not limited to catheters and tubes which are inserted into blood vessels, body cavities or tissues, or into the respiratory tract including the trachea, or inserted through other catheters or tubes, to have smoothness to ensure that such devices may be introduced without causing trauma to tissue encountered during their placement. The surfaces may be further enhanced by having lubricity for preventing injury or inflammation of mucous membranes or other surrounding tissues that may be caused when the devices remain in place.
In some instances, it is advantageous for medical device surfaces to have the capability to serve as a depot for various physiologically or pharmacologically active agents. Antithrombogenic materials, such as complexes of heparin with quaternary ammonium compounds, have been used on medical device surfaces to prevent thrombus formation on the surface of a medical device, as described in U.S. Pat. No. 5,069,899. In order to control nosocomial infections, anti-microbial agents including penicillins, cephalosporins, fluoroquinolones, aminoglycosides, silver compounds, phenols, biguanides, and others, have been proposed for use in surface coatings on the surfaces of implanted prostheses, as described in U.S. Pat. Nos. 5,069,899 and 4,442,133.
Many of the plastic materials of which such devices are ordinarily constructed are not easily treated with conventional surface enhancing methods. Materials used to make catheters are mostly hydrophobic and resist to one degree or another treatments designed to make them more biocompatible. Polymers such as silicones, latex rubbers, polyolefins, and many polyesters and polyamides have very low surface energies, often less than 40 dynes/cm
2
. Furthermore, these surfaces are often very resistant to dissolution in or swelling by solvents that ordinarily are used in the coating industry. Also, these surfaces often lack functional groups susceptible to interactions such as hydrogen bonding or Van der Waals forces, which are commonly utilized to promote improved adhesion of surface layers. Technologies that have been proposed to overcome these shortcomings fail to address a number of the difficulties associated with the surface treatment of such medical devices.
Flame treatments are widely applied in surface modification to introduce oxygen-containing functions at polyolefin surfaces, mainly to improve printability or paintability. (F. Garbassi, M. Morra, E. Occhiello,
Polymer Surfaces, From Physics to Technology,
John Wiley & Sons, Chichester, (1994)). Active species formed by the high temperatures include radicals, ions, and molecules in excited states. Such treatments have not been used widely in the medical device industry. The harsh conditions of flame treatments generally could be harmful to the relatively fragile devices, and they have not been useful in treating device lumens.
Corona treatments exploit the corona affect, i.e. the formation of high energy electromagnetic fields close to thin wires or points, with consequent ionization in their proximity, even at atmospheric pressure and relatively low temperatures. Excited species (ions, radicals, electrons, molecules in excited states, etc.) are present in the ionized region, and are active in surface modification, typically the introduction of oxygen-containing functions. (F. Garbassi, M. Morra, E. Occhiello,
Polymer Surfaces, From Physics to Technology,
John Wiley & Sons, Chichester, (1994)). Although this process may be suitable for treating film webs, it is not suitable for treating device lumens and has not found wide application in the medical device industry.
“Cold Plasma” treatments require low pressure to be sustained at low temperatures. An ionized region is formed, including high energy photons, electron, ions, radicals, and excited species, with its composition depending on a gas feed. Low pressure plasmas can be employed for surface activation by the introduction of oxygen-containing functional groups, etching by formation of gaseous species (e.g., carbon oxides or fluorides in CF
3
/O
2
plasmas), or coating deposition by plasma polymerization (e.g., of fluorine or silicon-containing monomers). (F. Garbassi, M. Morra, E. Occhiello,
Polymer Surfaces, From Physics to Technology,
John Wiley & Sons, Chichester, (1994)). Cold plasma treatments have been used in the medical device industry but generally have not been effective at treating device lumens that are long or of small diameter.
“Hot Plasma” treatments are performed at atmospheric pressure at very high temperatures (5,000 to 10,000° K.). While these treatments have gained widespread use in the metallurgy industry, they generally are not useful with polymeric medical devices because of the extremely high temperatures that are required.
Ultraviolet (UV) treatments employ photons, usually having low wavelength and high energy, which are used to activate a variety of chemical reactions. A typical example of UV action on polymer surfaces is surface degradation by sun exposure. UV lamps have been used for the treatment of polymer surfaces, with the apparatus involving a lamp and sample illumination devices. A review of literature on UV-cured coatings can be found in C.-M. Chan, T.-M. Ko, and H. Hiraoka,
Surf. Sci. Rep.,
24,1 (1996), and R. R. Rye,
J. Polym. Sci. Phys.
Ed. 26, 2133 (1988). UV-induced graft polymerization is used to treat and modify medical devices. However such treatment has limited application. Many medical devices are deliberately treated to make them opaque to such radiation, and it is difficult to treat device lumens, especially smaller, longer lumens, unless the device is transparent to the UV radiation.
Free radical graft copolymerization has been used to modify material surfaces. Highly reactive free radical transferring creates reactive radical sites on the substrate surface, which are able to initiate copolymerization with available monomers, or reactive oligomers, thereby generating a graft polymer layer. Two major difficulties with such an approach are the ability to create a substantial number of substrate radicals, and to significantly reduce the amount of homopolymerization initiated by initiator radicals along with the graft copolymerization. (M. P. Stevens, Polymer chemistry: an introduction, Addison-Wesley, London(1975)).
Graft polymerization of medical catheters and other medical devices has been utilized to provide surfaces having different properties from the bulk polymers forming the body of the device. Such treatments typically use plasma or UV as a source of energy to promote the graft polymer formation and attendant covalent bonding to the surface.
In U.S. Pat. No. 5,447,799, Loh, et al. describe a process for depositing polymeric materials on surfaces, first by providing a layer of polymeric material on the surface by glow discharge polymerization of a mixture of silane and a vaporizable hydrocarbon monomer or a vaporizable organosilane monomer, and then providing a second layer of another polymeric material, on the first polymeric material, by vapor deposition polymerization of aromatic hydrocarbons or unsaturated hydrocarbons.
Kolesinski et al. U.S. Pat. No. 5,211,993 describes a method of preparing chromatographically active support material by coating surfaces of a comminuted inorganic substrate material with a monomer which, when polymerized, has chromatographic properties. Such monomers are said to include vinyl stearate, polyethylene glycol 1000 monomethacrylate, and stearyl methacrylate. Such treatments have the shortcoming of requiring expensive plasma generating apparatus to modify the device surface.
U.S. Pat. No. 5,741,551 describes methods for providing a polymer coating on a solid substrate by applying a coating of reactive chemicals having photo-activatable ketones covalently bonded to them, and irradi

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