Coating for use with medical devices and method of making same

Details Coating for use with medical devices and method of making same Coating for use with medical devices and method of making same

2001-08-15

2004-07-27

Page, Thurman K. (Department: 1615)

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Implant or insert

C424S423000, C424S422000, C424S425000

Reexamination Certificate

active

06767551

ABSTRACT:

BACKGROUND
1. Technical Field
The present disclosure relates to a coating for silicone based medical devices, and more particularly, to a coating which allows a pharmaceutical agent to be released from an internal and/or external surface of such medical devices.
2. Background of the Related Art
Various medical devices that are inserted into body cavities of humans and animals can unfortunately introduce bacterial, viral and fungal infections into these body cavities. Numerous coatings are available for medical devices that employ polyurethane or urethane pre-polymers to act as lubricants, drug delivery systems and the like. Known coatings applied to surfaces of medical devices include coatings of polyvinylpyrrolidone, polyurethane, acrylic polyester, vinyl resin, fluorocarbons, silicone rubber, and combinations of these substances. For example, U.S. Pat. Nos. 4,100,309 and 4,119,094 to Micklus et al., relate to a hydrophilic coating of polyvinylpyrrolidone-polyurethane interpolymer formed using polyisocyanate. To prevent infections, various anti-microbial methods and compositions have been disclosed in U.S. Pat. Nos. 4,054,139; 4,592,920 and 4,603,152. Additionally, U.S. Pat. No. 3,939,049 to Ratner et al. relate to a method of grafting hydrogels for lubrication to polymeric substrates using radiation, U.S. Pat. No. 3,975,350 to Hudgin et al. relate to hydrophilic polyurethane polymers for use as lubricants and U.S. Pat. No. 3,987,497 to Stoy et al. relate to a tendon prosthesis having a lubricant hydrogel coating.
While the above coatings are appropriate for application to urethane, polyvinylchloride (PVC), steel or polyesters, these systems offer poor adherence to silicone medical devices unless the silicone surface is subjected to corona or plasma treatment. The need to pre-treat these silicone based medical devices limits coatings to surfaces that are pre-treated by the above methods, resulting in additional manufacturing process steps, additional costs and variability of the medical device. Additionally, the above methods have not been adequate as performance of the coatings has been unsatisfactory over flexible or expandable segments of medical devices such as catheter balloons.
Known silicone medical devices have been coated by a co-extrusion of silicone rubber and by room temperature vulcanizing (“RTV”) silicone. Silane coupling agents have also been employed to attach coatings and compounds to silicone rubber medical devices. However, these methods do not overcome the inherently poor drug delivery properties of silicone. These problematic silicone drug delivery properties include poor diffusion of the drug in a hydrophobic environment and surfaces that resist subsequent application of a hydrophilic bolus coating or lubricious coating.
To solve these and other potential disadvantages of known methods for coating silicone medical devices, a coating is needed that will allow effective drug delivery from surface areas of silicone medical devices. Desirably, the coating is flexible to retain adhesion over an expandable portion of a silicone medical device. Coatings are needed for silicone medical devices having a broad range of applications, including accommodating the proper delivery of medicinal agents ranging from inorganic silver salts to antibiotics. Furthermore, it is desirable to produce a coating that will eliminate additional manufacturing steps that require surface pre-treatment resulting in excessive cost.
SUMMARY
The inventive coating may be employed to deliver a pharmaceutical agent to a targeted tissue, releasing a pharmaceutical agent from the surface of a coated medical device, the surface of which is in contact with the target tissue. Therefore, the inventive coating may incorporate additives such as anti-microbial, anti-fungal and phytochemical having medicinal or like properties. Methods are provided for manufacture of the inventive coating and its application to medical device surfaces.
As is described in greater detail below, the present disclosure provides a coating composition including a combination of RTV silicone and urethane. The combination of RTV silicone and urethane produces an inventive coating that facilitates drug delivery and enhances adherence to a flexible silicone medical device. The inventive coating provides adherence over highly expanded surfaces such as, for example, catheter balloons, etc.
The present disclosure provides a method of making the subject coating that adheres to a wide variety of flexible silicone devices. The coating is chemically stable, bio-compatible and eliminates additional manufacturing requirements for surface pre-treatment. The coating allows effective drug delivery from a flexible silicone medical device that accommodates a broad spectrum of medicinal agents ranging from inorganic silver salts to antibiotics.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The disclosed exemplary embodiments and examples of use and operation are discussed in terms of medical device coatings, and more particularly, in terms of coatings for the internal and/or external surfaces of silicone-based medical devices which facilitate release of pharmaceutical agents from such coated surfaces to targeted tissues. The inventive medical device coatings are useful in a wide variety of coatings and devices employable in the medical field including, those used during invasive procedures, as well as, topical, dental and veterinary coatings and devices.
The following discussion describes inventive coatings for deformable surfaces of silicone-based medical devices and coatings that facilitate release of medicinal agents from such coated surfaces. Reference will now be made in detail to the non-limiting exemplary embodiments of the disclosure, which are illustrated herein and in the accompanying examples.
The inventive coatings include a combination of RTV, silicone and urethane. The combination advantageously provides a coating that is flexible and retains adhesion with a deformable surface of the silicone-based medical device. The coating adheres to the deformable surface during flexure or expansion of the device, such as, for example, catheter balloons, etc. Solvent selection in preparing the inventive coatings is based on providing adequate solubility and compatibility to the urethane, silicone and additives. The urethanes in the coatings are selected from the group of aromatic urethanes, including, but not limited to those derived from 4,4-methylenediphenol diisocyanante, 1,4-butanediol and polytetramethylene glycol (i.e., Pecoflex®). Additional polyurethanes include: Pellethane®, an aromatic ether polyurethane manufactured by Dow Chemical; Hyrothane®, manufactured by CardioTech International; and Tecoflex®, an aliphatic urethane manufactured by Thermedics, Inc. Other known urethanes are contemplated.
Polyurethane in the coating increases the binding strength and controls the rate of release of any active ingredient, permitting release rates for anti-microbial or other medicinal additives to be engineered to perform within desired parameters and rates. The polyurethane imparts adherence properties to the coating allowing its adhesion to deformable surfaces of silicone based medical devices. Since different urethanes have different properties and may require different solvent systems, appropriate solvent selection and blend ratio is desirable to ensure adequate solubility and compatibility to urethane and additives.
Without limitation, preferred RTV silicones are moisture-cure elastomers desirably derived from acyloxy-, alkoxy-, and methoxy-curing systems. The examples include but are not limited to methyltri-methoxy silane (GE RTV 142) or methyltri-acetoxy silane (GE RTV-108). Additional RTV silicones include, but are not limited to, Dow Corning 3140 RTV, Wacker RTV SWS951 and Nusil Med10-6605. Other alternative silanes include tetrachlorosilane, vinyl trimethoryl silane, organosilane ester tris[3-(trimethoxysilyl)propyl] isocyanurate, bis[trimethoxysilyl)propyl] amine and gamma-ureidopropyltrimethoxy silane. While the

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