Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Implant or insert
Reexamination Certificate
1999-07-28
2001-10-30
Azpuru, Carlos (Department: 2165)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Implant or insert
C514S772300, C523S112000
Reexamination Certificate
active
06309660
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to universal, biocompatible coating platforms for medical devices and methods for making same. More specifically, the present invention relates to universal, biocompatible coating platforms compatible with all materials commonly used to fabricate medical devices. In addition, the platforms of the present invention are capable of binding a vast variety of biologically active compounds to the medical device's surface without significantly impacting their activities.
BACKGROUND OF THE INVENTION
The ability of medical scientists to diagnose, treat and repair diseased and damaged tissues has increased dramatically in recent years. As new diagnostic and treatment devices are developed, medical scientists seek the optimum material for each application. The target anatomical site and intended use dictate the physical qualities demanded from candidate materials. Just as the human body has evolved into a variety of different tissue types, each perfectly adapted for its role, medical devices must be composed of equally specialized materials. For example, in vivo medical devices including catheters, cannuals and probes designed for insertion into narrow body structures such as the urethra, arteries, veins, and spinal column must have a minimal diameter, extreme flexibility, resilience and durability. Prosthetic medical devices such as artificial hips and joint replacements must be rigid and capable of surviving severe impact. Extracorpeal devices such as heart-lung machines and kidney dialysis equipment are complex mechanical devices that demand a diversity of functional and structural materials, each optimized for a particular function which may include contact with human tissues and body fluids.
In spite of the ongoing success of such devices, extracorpeal, in vivo, and prosthetic medical devices necessarily have surfaces that come into direct contact with blood and/or other body fluids and tissues, it is essential that the surfaces of these medical device be biocompatible. Thus, such biocompatible surfaces should not stimulate blood clotting (thrombogenesis), induce inflammatory or immune responses, kill or damage host tissues, or release toxic compounds when in contact with blood or living tissues. Of these biocompatibility issues, the most significant problem associated with the surfaces of materials commonly used to produce medical devices is their natural propensity to induce thrombogenesis. When this occurs on the surface of an implanted medical device, or within the chambers of an extracorpeal device, there is a potential risk of thromboembolism—the blocking of a blood vessel by a particle that has broken away from a blood clot—possibly resulting in a heart attack, lung failure, or stroke. Therefore, it has been, and continues to be, a primary focus of materials scientists and biomedical engineers to reduce or eliminate the thrombogenic potentials associated with the materials commonly used in medical device manufacturing.
At present, the most successful techniques known in the art for reducing thrombogenesis have evolved from the observation that certain compounds, when administered systemically, prevent blood clot formation. The most commonly used of these therapeutic anticoagulants is heparin, an acid mucopolysaccharide that acts in conjunction with naturally occurring antithrombin III to inhibit most of the serine proteases in the blood coagulation pathways. However, the use of systemic anticoagulants is not without risks. Heparin, for example, is metabolized through the liver and normally a single therapeutic dose will continue to inhibit blood clot formation in the patient for several hours. Should a traumatic event occur during the time systemic heparin is at therapeutic levels, the patent's ability to control bleeding will be impaired. Therefore, in an effort to reduce the sometimes potentially lethal side effects associated with systemic anticoagulants used in conjunction with medical devices, and to increase surface biocompatibility, materials scientists have experimented with heparin coatings that are intended to inhibit clot formation at its source, rather than systemically.
In addition to the continuing need to improve biocompatibility through reduced thrombogenesis associated with medical devices, there is a developing interest in using implantable or inter-dwelling medical devices as localized drug delivery vehicles as well. For example, the development of stenting techniques to treat cardiovascular disorders and to prevent restenosis (a closing, or narrowing of a previously opened lumenal space) has been on the rise. Typically, in such stenting applications, stents are made from non-reactive metals or polymers treated to have antithrombogenic surfaces and designed to mechanically support, or hold open, a body lumen such as a coronary artery. In spite of their initial success and promise, natural endothelial cell growth (normally lining the blood vessels) surrounding the stent site can be stimulated in response to injuries sustained during stent implantation. Consequently, endothelial cell over-growth itself may lead to neointimal hyperplasia thereby reducing or eliminating the stent's long term effectiveness. To reduce such cell growth and restenosis, early experiments are being conducted with anti-cell growth factors coupled to the stent's surface. Anti-thrombogenic agents and anti-cell growth factors are just two examples of biologically active compounds that materials scientists seek to bind to the surfaces of medical devices in order to improve their performance. Other equally important biologically active compounds that would be desirable to incorporate into medical devices include antibiotics, anti-inflammatory agents, lubricity-enhancing agents, hormones, and immune modulators, just to name a few.
Moreover, the materials that make up modern medical devices can be quite diverse. Examples of these structural and functional compounds include plastics and polymers such as polyethylene, polytetrafluoroethylene, silicone, silicone rubber, natural rubber, polyurethane, Dacron, gelatin-impregnated fluoropassivated Dacron, polyvinyl chloride, polystyrene, nylon, as well as natural rubber latex, stainless steel, other metals, ceramics and glass. Thus, the complexities normally associated with binding a single biologically active compound to the surface of a single material (homologous) device are significantly complicated when single or even multiple biologically active compounds are bound to the surface of a heterologous device (a device composed of more than one type of material, for example, an extracorpeal circuit having polyethylene channels with stainless steel couplers attached thereto).
There are two general methods known in the art for attaching biologically active compounds to such medical device surfaces. The first includes directly bonding the biologically active compound to the device's surface. The second involves indirectly bonding the biologically active compound to the device's surface through an intermediate layer. Each has its own benefits and drawbacks.
For example, providing a prior art medical device with a stable biologically active compound directly bound to its surface generally required the use of covalent chemical bonding techniques. For this to work the material used to make the medical device must possess chemical functional groups on its surface such as carbonyl carbons or primary amines which will form a strong, chemical bond with similar groups on the active compound. In the absence of such chemical bond forming functional groups, prior art techniques required activating the material's surface before coupling the biological compound. Surface activation is a process of generating, or producing, reactive chemical functional groups using harsh chemical or physical techniques. Such physical techniques include radio frequency plasma discharge, ionization, and heating. Similarly, harsh chemical prior art techniques for producing reactive functional groups inclu
Hsu Li-Chien
Hu Can B.
Tong Sun-De
Azpuru Carlos
Cullman Louis C.
Edwards Lifesciences Corp.
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