US 2006001.3853A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2006/0013853 A1 Richard (43) Pub. Date: Jan. 19, 2006 (54) MEDICAL DEVICES HAVING CONDUCTIVE Publication Classification SUBSTRATE AND COVALENTLY BONDED COATING LAYER (51) Int. Cl. A6IF 2100 (2006.01) (76) Inventor: Robert E. Richard, Wrentham, MA (52) U.S. Cl. .............................................................. 424/423 (US) (57) ABSTRACT Correspondence Address: MAYER, FORTKORT & WILLIAMS, PC The present invention provides a medical device comprising 251 NORTHAVENUE WEST an electrically conductive Substrate and a coating layer that 2ND FLOOR covers at least a portion of the electrically conductive WESTFIELD, NJ 07090 (US) Substrate, wherein the coating layer comprises a polymer that is made by a process that comprises (a) electrochemi cally linking a initiator to a Surface of the electrically (21) Appl. No.: 10/894,391 conductive Substrate and (b) conducting a free radical poly merization reaction in the presence of one or more free (22) Filed: Jul. 19, 2004 radical polymerizable monomers. Patent Application Publication Jan. 19, 2006 Sheet 1 of 2 US 2006/0013853 A1 O E. O d s O On 8 S. C ATRP of styrene PS-1a(C FIG 1 Patent Application Publication Jan. 19, 2006 Sheet 2 of 2 US 2006/0013853 A1 US 2006/OO13853 A1 Jan. 19, 2006 MEDICAL DEVICES HAVING CONDUCTIVE they may lack mechanical integrity Since they envelop the SUBSTRATE AND COVALENTLY BONDED device, but do not necessarily chemically adhere to it. COATING LAYER Another potential drawback is that Spray coatings and dip coatings are physical, rather than chemical, coatings. FIELD OF THE INVENTION Because they rely upon the Spray or dip equipment and not 0001. The present invention relates generally to medical upon chemical interactions at a molecular level for control devices which contain polymeric Surface coatings. The ling the coating process, precision in terms of thickneSS and present invention also relates to methods for producing conformity with the substrate surface has been difficult to covalently bonded polymeric coatings for medical devices, achieve with these techniques. particularly for insertable or implantable medical devices. 0006 Attempts have been made to address the poor adhesion problem, including first coating the metal Surface BACKGROUND OF THE INVENTION with one or more “primer layers,” followed by application of the polymeric coating of interest. One obvious disadvantage 0002) Numerous polymer-based medical devices have of Such a primer is that it introduces another layer which been developed for the delivery of therapeutic agents to the does not aid, and may even hinder, the drug delivery body. In accordance with Some typical delivery Strategies, a functions of the polymeric coating. In addition, the polymers therapeutic agent is provided within a polymeric carrier or materials Suitable for use as a primer layer may not layer and/or beneath a polymeric barrier layer that is asso necessarily possess the desired mechanical or biocompatible ciated with a medical device. Once the medical device is characteristics, and thus the range of materials that may be placed at the desired location within a patient, the therapeu utilized as part of a coating System for a medical device may tic agent is released from the medical device at a rate that is dependent upon the nature of the polymeric carrier and/or be limited. barrier layer. 0007. In view of the above, it would be advantageous to provide coatings that have desirable biostability and/or 0003. Materials which are suitable for use in making biocompatibility properties, while also having improved implantable or insertable medical devices typically exhibit one or more of the qualities of exceptional biocompatibility, mechanical properties. It would also be desirable to provide extrudability, elasticity, moldability, good fiber forming tenacious coatings which exhibit improved adhesion to the properties, tensile Strength, durability, and the like. More Surfaces of common medical device Substrates. over, the physical and chemical characteristics of the device materials can play an important role in determining the final SUMMARY OF THE INVENTION release rate of the therapeutic agent. 0008. These and other challenges of the prior art are 0004. As a specific example, block copolymers of poly addressed by the present invention which provides a medical isobutylene and polystyrene, for example, polystyrene-poly device comprising an electrically conductive Substrate and a isobutylene-polystyrene triblock copolymers (SIBS copoly coating layer that covers at least a portion of the electrically mers), which are described in U.S. Pat. No. 6,545,097 to conductive Substrate. The coating layer comprises a poly Pinchuk et al., hereby incorporated by reference in its mer, which is made by a process that comprises (a) electro entirety, have proven valuable as release polymers in chemically linking a free radical polymerization initiator to implantable or insertable drug-releasing medical devices. AS a Surface of the electrically conductive Substrate and (b) described in Pinchuk et al., the release profile characteristics conducting a free radical polymerization reaction in the of therapeutic agents Such as paclitaxel from SIBS copoly presence of one or more free radical polymerizable mono mer Systems demonstrate that these copolymers are effective CS. drug delivery Systems for providing therapeutic agents to 0009. The present invention is advantageous in that Sites in Vivo. These copolymers are particularly useful for coated medical devices are provided in which the coating is medical device applications because of their excellent covalently bonded to the surface of the medical device, Strength, biostability and biocompatibility, particularly thereby providing a strong, conformal coating. within the vasculature. For example, SIBS copolymers exhibit high tensile Strength, which frequently ranges from 0010 Another advantage of the present invention is that 2,000 to 4,000 psi or more, and resist cracking and other implantable or insertable medical devices are provided, forms of degradation under typical in Vivo conditions. which result in controlled release of a therapeutic agent. Biocompatibility, including vascular compatibility, of these 0011 Yet another advantage of the present invention is materials has been demonstrated by their tendency to pro that methods of coating medical devices are provided which voke minimal adverse tissue reactions (e.g., as measured by avoid various limitations of Standard dip and Spray coating reduced macrophage activity). In addition, these polymers proceSSeS. are generally hemocompatible as demonstrated by their ability to minimize thrombotic occlusion of small vessels 0012. These and other embodiments and advantages of when applied as a coating on coronary Stents. the present invention will become immediately apparent to those of ordinary skill in the art upon review of the Detailed 0005 Currently, technologies used to prepare coatings on Description and claims to follow. medical devices having metal Surfaces, which are typical of coronary Stents and many other medical devices, include BRIEF DESCRIPTION OF THE DRAWINGS Spray and dip coating. While these processes are capable of producing effective coatings, there is a need for a more 0013 FIG. 1 schematically illustrates a two-step process efficient and precise coating method. One major drawback of for the grafting of polystyrene to an electrically conducting the coatings produced using these prior art methods is that Substrate. US 2006/OO13853 A1 Jan. 19, 2006 0.014 FIG. 2 is an SEM image of polystyrene grafted to more polymers and is made by a process that includes (a) a Steel Substrate Surface. electrochemically linking an initiator to a Surface of the electrically conductive Substrate and (b) conducting a free DETAILED DESCRIPTION OF THE radical polymerization reaction in the presence of a free INVENTION radical polymerizable monomer, or two or more free radical polymerizable comonomers. 0.015 The present invention relates to medical devices having polymeric coating layers wherein covalent bonds 0019. The technology for linking the initiator to the exist at the interfaces between the coating layers and the electrically conductive Surface, for example, a StainleSS Steel substrates on which they are formed, and to methods for Surface, includes electrografting processes Such as those producing Such coating layers. Specifically, the present disclosed by Claes et al., Polymer Coating of Steel by a invention relates to processes for chemically linking (e.g., Combination of Electrografiing and Atom-Transfer Radical covalently bonding) a polymer to a Substrate Such as an Polymerization, Macromolecules, Web release No. electrically conductive Substrate (e.g., a metal Surface) by 0217130, published Jul. 19, 2003, the contents of which are electrochemically attaching an initiator Species to the Sub hereby incorporated by reference in their entirety. Strate followed by a monomer polymerization reaction Such 0020. The usually weak and short-term adhesion between as atom-transfer radical polymerization (ATRP). The pro organic polymers and radically different materials. Such as ceSSes of the present invention can be used for a number of metals, glass, and carbon have presented Special challenges purposes, including the preparation of passive device coat in formulating Suitable coatings. For example, proper adhe ings, hydrophilic device coatings, and