BIODEGRADABLE STENT HAVING AN ACTIVE COATING

Abstract

A stent having a main body made of a biodegradable material and an active coating applied to the main body, which comprises a biodegradable carrier matrix and at least one pharmaceutically active substance embedded in the carrier matrix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is explained in the following on the basis of an exemplary embodiment and the attached drawings.

FIG. 1 shows a schematic top view of a detail of a biodegradable implant having a coating according to the present disclosure; and

FIG. 2 shows a section through the main body of the stent in area of active coating.

DETAILED DESCRIPTION

For purposes of the present disclosure, the term “biodegradable” relates to a material which is degraded in vivo, i.e., loses its mechanical integrity. The degradation products do not necessarily have to be completely resorbed or excreted by the body. For example, small particles may also remain at the location of application. For purposes of the present disclosure, biodegradation relates, in particular, to hydrolytic, enzymatic, and other degradation processes in the living organism caused by the metabolism, which result in gradual dissolving of at least large parts of the materials used. The term biocorrosion is frequently used synonymously with biodegradation. For purposes of the present disclosure, the term bioresorption additionally comprises the subsequent resorption of the degradation products.

For purposes of the present disclosure, an “active coating” comprises a biodegradable carrier matrix and at least one pharmaceutically active substance embedded therein. Optionally, the active coating may also contain further auxiliary materials to improve adhesion capability and processability and the release of the substance, for example. In addition, polymers of natural origin come into consideration as materials for the carrier matrix, such as hyaluronic acid, poly-L-lactide, poly-D-lactide, collagen, and the like.

The carrier matrix used is preferably based on a biodegradable polymer. Biodegradable polymers have been known for some time and are also used for oral applications and injections. Many different polymer classes have been used for medical purposes, each of which have properties custom tailored for the corresponding use. The polymer system used must be examined in relation to the physiological effect; the degradation products may not be toxic and/or form toxic substances by reaction with bodily substances. Furthermore, it is to be ensured that a potential of the polymer systems for initiating infections because of foreign body reactions of the immune system is as low as possible. Finally, an interaction between the active ingredient and the polymer matrix must be taken into consideration; the polymers may neither lose their biodegradable properties by interaction with the active ingredient nor may the active ingredient be deactivated by reaction of the active ingredient with the polymer matrix. Therefore, one skilled in the art will take the cited parameters into consideration when selecting a specific system made of polymer matrix and active ingredient.

For purposes of the present disclosure, a “pharmaceutically active substance” includes, but is not limited to, a vegetable, animal, or synthetic active ingredient which is used at suitable dosing as a therapeutic agent for influencing states or functions of the body, as a replacement for natural active ingredients generated by the human or animal body, and for removing or making harmless pathogens or bodily foreign materials. The release of the substance in the implant surroundings has a positive effect on the course of healing and/or counteracts pathological changes of the tissue as a result of the surgical intervention.

For purposes of the present disclosure, the “release of pharmaceutically active substance” is the removal of the substance from the carrier matrix. A partial process for the release of pharmaceutically active substance is the dissolving of absorbed substances out of the solid or gel-type carrier matrix with the aid of media present in the body, such as blood.

A release speed is determined as follows: a half-life is detected, in which 50 weight-percent of the substances released, and a (mean) release speed is determined on the basis of the half-life for assumed linear release kinetics.

A degradation speed of the carrier matrix and the main body is detected in that, first a half-life is ascertained, in which 50 weight-percent of the material forming the main body and/or the carrier matrix is degraded, and then a (mean) speed of the degradation processes calculated on the basis of this half-life for an assumed linear course of the degradation.

The main framework of the stent comprises all components necessary for ensuring the mechanical integrity and main functionalities of the implant. In addition, the stent may have marker elements, for example, which are bonded to the main body in a suitable way. The main framework provides a surface which is used for applying the active coating. An area of the coating may be established individually; preferably, only an outwardly directed part of the main framework is coated.

FIG. 1 shows a section of the main body 10 of the stent which is molded from a biodegradable material. The metallic material forms a filigree framework of struts connected to one another, whose design is only of subordinate significance for the present disclosure. An active coating is applied to an external surface 12 of the main body 10. As is obvious, the coating area is divided into an uncoated partial area and a partial area coated with the active coating.

The active coating is implemented as multiple coating islands 14 which comprise a biodegradable carrier matrix 15 and at least one pharmaceutically active substance 16 (shown here as a triangle) embedded in the carrier matrix 15. The coating islands 14 are applied to the surface 12 of the main body 10 in such a way that the coated partial area, i.e., the coating islands 14, cover approximately 10-15% of the surface 12 of the coating area.

The main body 10 comprises the magnesium alloy WE43, and the carrier matrix is high-molecular-weight poly-L-lactide (molar mass greater than 500 kD). A degradation speed of the polymer material of the carrier matrix 15 is approximately 10 to 15 times the degradation speed of the material of the main body 10.

The individual coating islands have a mean diameter of approximately 50 to 70 μm. A distance of an arbitrary point of the surface in the coated partial area to the closest uncoated partial area is thus less than 35 μm. If the coating islands are uniformly round, the distance from an arbitrary first boundary point of the surface of the coated partial area to a second boundary point, which is furthest away from the first boundary point, is approximately 50 to 70 μm.

The following procedure may be used for applying the coating islands 14.

The stent is pre-mounted on a balloon or catheter. A solution or extremely fine dispersion of the biodegradable polymer and the at least one active substance is provided in a reservoir. Subsequently, droplets of defined size are applied in selected areas of the main body via a controllable microinjection system. The solvent is withdrawn by vaporization and the coating islands of defined diameter are formed.

Claims

1. A stent having a main body, comprising: (a) a biodegradable material, and(b) an active coating applied to the main body, the coating comprising a biodegradable carrier matrix and at least one pharmaceutically active substance embedded in the carrier matrix, wherein the active coating has a degradation speed less than a degradation speed of the main body; and wherein the active coating is applied on a coating area of the surface of the main body provided for this purpose such that the coating area is divided into an uncoated partial area and a partial area coated with the active coating, the coated partial area covering 5% to 80% of the surface of the coating area; a distance of an arbitrary point of the surface in the coated partial area to the closest uncoated partial area is less than 35 μm; and a distance of an arbitrary first boundary point of the surface in the coated partial area to a second boundary point in the same coated partial area, which is furthest away from the first boundary point, is at most 400 μm.

2. The stent of claim 1, wherein the degradation speed of the main body is 1.1 to 50 times the degradation speed of the active coating.

3. The stent of claim 1, wherein the coated partial area covers 5% to 20% of the surface of the coating area.

4. The stent of claim 1, wherein the distance of an arbitrary point of the surface of the coated partial area to the closest uncoated partial area is less than 30 μm.

5. The stent of claim 1, wherein a release speed of the pharmaceutically active substance is greater than the degradation speed of the carrier matrix, but less than the degradation speed of the main body.

6. The stent of claim 1, wherein the active coating comprises multiple coating islands.

7. The stent of claim 6, wherein the coating islands have a mean diameter of 10 to 100 μm.

8. The stent of claim 1, wherein the uncoated partial area is divided into multiple partial surfaces, and partial surfaces having a size of up to 1000 μm2 occupy at least 70% of the total surface of the uncoated partial area.