Drug coating with topcoat

Abstract

A coating and method for a coating an implantable device or prostheses are disclosed. The coating includes an undercoat of polymeric material containing an amount of biologically active material, particularly heparin, dispersed herein. The coating further includes a topcoat which covers less than the entire surface of the undercoat and wherein the topcoat comprises a polymeric material substantially free of pores and porosigens. The polymeric material of the topcoat can be a biostable, biocompatible material which provides long term non-thrombogenicity to the device portion during and after release of the biologically active material.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a Continuation-In-Part of co-pending application Ser. No. 08 / 633,518, filed Jun. 13, 1996.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates generally to providing biostable elastomeric coatings on the surfaces of implants which incorporate biologically active species having controlled release characteristics in the coating and relates particularly to providing a non-thrombogenic surface during and after timed release of the biologically active species. The invention is particularly described in terms of coatings on therapeutic expandable stent prostheses for implantation in body lumens, e.g., vascular implantation. [0004] 2. Related Art [0005] In surgical or other related invasive procedures, the insertion and expansion of stent devices in blood vessels, urinary tracts or other locations difficult to otherwise access for the purpose of preventing restenosis, prov...

AI Technical Summary

Benefits of technology

[0027] It is desirable that the topcoat be substantially free of connected pores or porosigens (materials which can elute during implantation and form pores). The addition of a porous membrane as a top coat will increase the coating thickness and reduce the overall drug loading. Also, the release of porosigens into the body can be undesirable since it introduces additional foreign materials into the body, which can cause the patient to have adverse reactions.

[0032] The coating may be applied by dipping or spraying using evaporative solvent materials of relatively high vapor pressure to produce the desired viscosity and quickly establish coating layer thicknesses. The preferred process is predicated on reciprocally spray coating a rotating radially expanded stent employing an air brush device. The coating process enables the material to adherently conform to and cover the entire surface of the filaments of the open structure of the stent but in a manner such that the open lattice nature of the structure of the braid or other pattern is preserved in the coated device.

[0052] The desired release rate profile can be tailored by varying the coating thickness, the radial distribution (layer to layer) of bioactive materials, the mixing method, the amount of bioactive material, the combination of different matrix polymer materials at different layers, and the crosslink density of the polymeric material. The crosslink density is related to the amount of crosslinking which takes place and also the relative tightness of the matrix created by the particular crosslinking agent used. This, during the curing process, determines the amount of crosslinking and so the crosslink density of the polymer material. For bioactive materials released from the crosslinked matrix, such as heparin, a denser crosslink structure will result in a longer release time and reduced burst effect.

[0053] It will also be appreciated that an unmedicated silicone thin top layer provides some advantage and additional control over drug elution.

Problems solved by technology

Moreover, drug elution rates for a coating containing a hydrophilic or a lipophobic drug is usually very fast initially when the coated device contacts body fluid or blood.

Even though the method might be quite successful to control the drug release, it increases the coating thickness, reduces the effective drug loading and introduces undesirable additional foreign materials into the patient.

With regard to stents, polymeric stents, although effective, may have mechanical properties that are inferior to those of metal stents of like thickness and weave.

A polymer material of comparable strength requires a much thicker-walled structure or heavier, denser filament weave, which in turn, reduces the cross-sectional area available for flow through the stent and / or reduces the relative amount of open space in the weave.

Also, it is usually more difficult to load and deliver polymeric stents using catheter delivery systems.

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