GB2448153A

GB2448153A - Coated Implantable Medical Devices

Info

Publication number: GB2448153A
Application number: GB0706532A
Authority: GB
Inventors: Gerhard Anthony Symons; David Robert Hampton
Original assignee: CAMSTENT Ltd MBE
Current assignee: CAMSTENT Ltd MBE
Priority date: 2007-04-04
Filing date: 2007-04-04
Publication date: 2008-10-08
Anticipated expiration: 2027-04-04
Also published as: GB2448153B; GB0706532D0

Abstract

Coated implantable medical devices where the surface can be both hydrophobic and oleophobic. Device such as catheter, vascular graft, cardiac pacer lead, heart diaphragm suture, needle, angioplasty device, artificial joint heart valve, neurological stimulators or drug pump, stents with biofilm, sirolimus-eluting stent, paclitaxel-eluting stent and device reducing thrombosis. Repellent coating such as calixarenes and resorcarene can be used.

Description

Coated Medical Devices The present invention relates to implantable

medical devices, such as stents, that have a biorepellant coating that is both oleophobic and hydrophobic, said coated S devices being useful for reducing thrombosis associated with such implants.

Every day, thousands of people suffer heart attacks caused by underlying coronary artery disease. Coronary artery disease (CAD) is mankind's most widespread and lethal disease, affecting over 14 million Americans. Of these, one million will suffer a subsequent acute myocardial infarction (AMI) each year, with a five year mortality of nearly 30%.

CAD is a disease of the coronary arteries, in which the vessels supplying blood to the heart muscle become narrowed by atherosclerotic plaques. This stenosis restricts blood flow and, in severe cases, the oxygen delivery to cardiac tissue, causing myocardial ischemia and anginal pain. Total occlusion of these arteries, caused by plaque rupture, is the underlying cause of a heart attack, and results in permanent tissue death: an AMI.

A common and safe coronary intervention carried out to prevent heart attacks or to relieve the blockage associated with AMI is to thread a catheter into the blocked artery and expand the channel with an inflatable balloon. A stent, consisting of a wire mesh tube, is then placed in the artery to hold the artery open and to restore adequate blood flow. The arterial wall heals over the stent, incorporating it as a permanent solution, but this process fails in up to 1/3 of patients as the artery wall overdevelops as a result of neointimal proliferation (restenosis). Furthermore, clots can form on or around the stent itself due to inflammation and increased platelet adhesion, leading to abrupt occlusion of the open vessel through thrombosis. Thus, it is not surprising that with over 500,000 stent procedures a year, restenosis and thrombosis are major health and cost burdens.

Drug-eluting stents, e.g. CypherTM, are used as one solution to the problem of neointimal growth. A bare-metal stent is coated with an inert polymer that slowly releases embedded deposits of sirolimus, an antibiotic with immunosuppressive properties, at the artery wall. This drug slows the multiplication and growth of epithefial cells, reducing the thickness of the lumen as it heals. Clinical trials have shown that the two existent drug eluting stents, CypherTM and TaxusTM, have achieved a decrease of up to 80% in revascularization procedures needed to relieve restenosis. However, these drugs also make the vessels more prone to processes that lead to the formation of a blood clot. Administration of anti-platelet and anticoagulant drugs may prevent platelet and fibrinogen interaction with the endothelial wall while it heals, but it raises the risk of haemorrhage. Thus, up to 2% of patients receiving drug-eluting stents may suffer thrombosis, a potentially fatal complication, which in addition to the risk of haemorrhage associated with current therapies, constituting a major concern for interventional cardiologists.

Recent attempts to address the issues of protein adhesion and thrombus formation have centred on the possibility of using another drug, such as heparin, instead of and possibly in addition to the current immunosuppressive drug in the stent coating to directly prevent thrombosis. However, hepann exerts its effect against circulating blood components, not on cells in adjacent tissue. Thus a strategy of slow release from the stent itself would not result in therapeutic quantities accumulating in the blood flowing through the coronary arteries. Secondly, if the rate of release is increased to achieve therapeutic concentrations, then the amount of drug in the stent is exhausted before the healing process is complete. Late-stage thrombosis would thus remain a problem. Thirdly, the spread of antiplatelet agents beyond the immediate vicinity of the stent could pose a risk of haemorrhage to tissues of the heartand lungs.

There is a need, therefore, for an alternative coating that provides a solution to the problems of foreign body reaction and irritation leading to excessive inflammation, and subsequent thrombus formation. Ideally, such a coating will be: 1. Biologically inert: -will not exacerbate inflammation -will not carry risk of side-effects.

2. Durable: -will remain part of the stent surface, effective for duration of the stents life-time.

3. Thin-film coating: -will form a smooth monolayer over the stent, decreasing turbulence caused by surface roughness, a factor which has been implicated in coronary thrombosis.

4. Non-pharmacologic: -will not incur any drug-drug interactions with immunosuppressive already coupled to the stent.

-will not require control of elution rates -will not require characterization or testing for drug stability, availability, release, or degradation.

5. Localized effect: -can be applied preferentially to the luminal side of the stent, facing the blood stream, while the endothelial side could still be coated with the conventional drug-eluting combination, achieving an optimal combination.

It is therefore an object of the present invention to provide a stent which is less irritating and repels protein and thrombotic deposits and has long-term benefits for patients, physicians and payers.

The present invention accordingly provides an implantable medical device having a coating comprising an outer surface that is both oleophobic and hydrophobic. Such a coating will be able to resist adhesion platelets and protein factors involved in clotting and subsequent thrombus formation, making stents safer as well as decreasing the need for high doses of antiplatelet drugs.

Preferably, with such a stent, the luminal side comprises a coating comprising an outer surface that is both oleophobic and hydrophobic and the endothelial side is bare metal or is coated with a drug-eluting composition.

The inner surface of said coating may be hydrophilic or be modified so as to preferentially bind to the substrate. The coating would preferably form a monolayer over the device, thus providing a smooth surface that would decrease turbulence.

In order to provide an outer surface that is both oleophobic and hydrophobic, said coating may comprises long chain hydrocarbon or fluorocarbon groups, or long chain polyether groups, each having from 1 to 18 carbon atoms in the chain. The hydrocarbon or fluorocarbon groups preferably have from 5 to 15 carbon atoms in the chain. Preferably, the hydrocarbon and fluorocarbon groups are saturated or unsaturated alkyl and fluoroalkyl groups, respectively.

The invention encompasses any implantable medical device and in particular covers a medical device which is a stent, catheter, vascular graft, cardiac pacer lead, heart diaphragm, suture, needle, angioplasty device, artificial joint, heart valve, neurological stimulator or drug pump. Stents are the most preferred medical devices to which the invention is directed.

In a preferred embodiment of the invention, the oleophobic and hydrophobic coating is applied to the luminal side of the stent only. In another preferred embodiment the endothelial side of the stent is coated with a drug-eluting composition.

Any drug may be used and is preferably an immunosuppressant, antibiotic or an antiplatelet or anticoagulant agent. Alternatively, the drug etuting composition may comprise a stem-cell eluting composition. Most preferred drugs for coating the stent are sirolimus or paclitaxel.

Accordingly the invention provides a stent wherein the luminal side comprises a coating comprising an outer surface that is both oleophobic and hydrophobic and the endothelial side is bare metal or is coated or impregnated with a drug-eluting composition.

In another preferred embodiment the entire stent is coated with a coating comprising an outer surface that is both oleophobic and hydrophobic wherein the endothelial side of the stent is additionally coated or impregnated with a drug-eluting composition.

According to a preferred embodiment of the invention the coating comprises a calixarene.

Calixarenes are macrocyclic molecules based on the hydroxyalkyation product of a phenol and an aldehyde and whose general structure is that of a molecular bowl on legs with the rim of the bowl lined by hydroxyl groups and the legs consisting of long-chain alkyl groups. A detailed review of the different types of calixarenes and their methods of manufacture is given by Bohmer, Angew. Chem. lnt. Ed. EngI. 1995, 34, 713-745. The surface properties of the calixarenes may be suitably modified to impart the desired properties by altering the substituents on either the nm or the legs.

There are three main types of calixarene, prepared respectively from phenols, from resorcinols (resorcarene) and from pyrogaUols and aldehydes. The present invention is applicable to all these types of calixarenes, and encompasses devices having a coating derived from any one of them. Preferably, the invention covers a device wherein the calixarene is a resorcarene.

In a preferred embodiment the calixarene, preferably a resorcarene, provides a surface that is both oleophobic and hydrophobic, said calixarene comprising long chain hydrocarbon or fluorocarbon groups, or long chain polyether groups, each having from 1 to 18 carbon atoms in the chain. The hydrocarbon or fluorocarbon groups preferably have from 5 to 15 carbon atoms in the chain. Preferably, the hydrocarbon and fluorocarbon groups are saturated or unsaturated alkyl and fluoroalkyl groups, respectively.

In a preferred embodiment of the invention, the medical device has a coating which comprises a resorcarene of formula (I) x

R K y V /\ \/

Y (R I \ (I)

wherein X is hydrogen, C1-C4 alkyl, NH2, NH(C1-C4 alkyl), or N(C1-C4 alkyl)2; Y is OH or OCH2COOR', where R' is C,-C4 alkyl; R is a C5-C15 fluoro-substituted alkyl group; n is 1 or 3, and wherein each X, Y, R' and R group can be the same or different.

Preferably, the devices are coated with a resorcarene of formula (1) wherein X is hydrogen and R is-CH2C8F17.

The calixarenes of the invention may be suitably modified in order to provide an outer surface that is both oleophobic and hydrophobic, said modification may comprise incorporation of long chain hydrocarbon or fluorocarbon groups, or long chain polyether groups, each having from I to 18 carbon atoms in the chain. The hydrocarbon or fluorocarbon groups preferably have from 5 to 15 carbon atoms in the chain. Preferably, the hydrocarbon and fluorocarbon groups are saturated or unsaturated alkyl and fluoroalkyl groups, respectively.

Methods for the preparation of the resorcarene of formula (I) and processes for coating materials are disclosed in WO 97/39077 and at http:I/www.rsc.org/pdf/mcgfshefcotes.pdf. Other suitable methods for coating medical devices such as stents are known to those skilled in the art and include, e.g. methods described in WO 2005/112570, US 6702850, US 6602287, US 5053048, US 7070798 and US 2002/0102405. The surface of the medical devices may also be subject to treatment to modify the surface properties prior to coating such as disclosed in US 4445998 and Kim, Surface and Coatings Technology, 171, 2003, 312-316.

Claims

Claims 1. An implantable medical device having a coating comprising an

outer surface that is both oleophobic and hydrophobic.

2. A device according to claim 1 wherein the inner surface of the coating is hyd rophil ic.

3. A device according to either claim 1 or claim 2 wherein the coating forms a monolayer over the device.

5. A device according to any one of claims 1 to 3 wherein the outer surface of the coating comprises long chain hydrocarbon or fluorocarbon groups, or long chain polyether groups, each having from 1 to 18 carbon atoms in the chain.

6. A device according to claim 5 wherein the hydrocarbon and fluorocarbon groups are saturated or unsaturated alkyl and fluoroalkyl groups, respectively.

7. A device according to any one of claims 1 to 6 which is a stent, catheter, vascular graft, cardiac pacer lead, heart diaphragm, suture, needle, angioplasty device, artificial joint, heart valve, neurological stimulator or drug pump.

8. A device according to claim 7 which is a stent.

9. A stent according to claim 8 wherein the oleophobic and hydrophobic coating is applied to the luminal side of the stent only.

10. A stent according to either claim 8 or claim 9 wherein the endothelial side is coated with a drug-eluting composition.

11. A stent according to claim 10 wherein the drug is an immunosuppressant, antibiotic or an antiplatelet or anticoagulant agent, or the drug-eluting composition is a stem-cell eluting composition.

12. A stent according to claim 11 wherein the drug is sirolimus or paclitaxel.

13. A stent wherein the luminal side comprises a coating comprising an outer surface that is both oleophobic and hydrophobic and the endothelial side is bare metal or is coated with a drug-eluting composition.

14. A device according to any one of claims I to 13 wherein the coating comprises a calixarene.

15. A device according to claim 14 wherein the calixarene is derived from phenols, from resorcinols (resorcarene) and from pyrogallols and aldehydes.

16. A device according to claim 15 wherein the calixarene is a resorcarene.

17. A device according to claim 16 wherein the resorcarene is a compound of formula (I)

N

R R /_\

Y \ x (I)

wherein X is hydrogen, C1-C4 alkyl, NH2, NH(C,-C4 alkyl), or N(C1-C4 alky))2; V is OH or OCH2COOR', where R' is C1-C4 alkyl; R is a C5-C15 fluoro-substituted alkyl group; n is I or 3, and wherein each X, Y, R' and R group can be the same or different.

18. A device according to claim 17 wherein X is hydrogen and R is-CH2C8F17.