Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1999-01-29
2001-09-11
Seidel, Richard K. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S265000, C424S422000, C424S423000
Reexamination Certificate
active
06287285
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of therapeutic, diagnostic, or hydrophilic coatings for intracorporeal medical devices.
The use of a medical device within a patient may be facilitated by the presence of a therapeutic, diagnostic, or hydrophilic agent on the device surface. For example, intravascular devices, such as catheters and guidewires, are more easily maneuvered within a patient's vasculature when the friction between the walls of the vessel and the intravascular device is reduced. The friction may be reduced by coating the device with a hydrophilic compound which becomes slippery after adsorbing an appreciable amount of water. Consequently, the hydrophilic coating provides lubricity when the coated device is exposed to aqueous solution, as when the coated device is exposed to water prior to insertion in the patient or to the patient's blood during use. Alternatively, coatings, such as fluoropolymers, and silicone, provide lubricity to the surface of an intracorporeal device without the need for exposure to aqueous solution. However, the degree of lubricity may vary greatly depending on the nature of the lubricious coating. Hydrophilic coatings provide superior lubricity compared to hydrophobic coatings, such as silicone, when tested against a biological tissue countersurface.
In addition to lowering the coefficient of friction of the coated device, an effective lubricious coating must strongly adhere to the device surface. The lubricious coating should remain adhered to the device surface during potentially extended periods of storage, as well as in response to abrasive forces encountered during preparation and use. Poor adhesive strength is undesirable because the lost coating may be left behind inside the patient during use, with detrimental affects and a corresponding decrease in the lubricity of the device. Typically, a trade off exists between a coating's lubricity and the coating's adhesive and cohesive strength, so that attempts to increase the adhesive strength of lubricious coatings may inadvertently decrease the lubricity of the coating. Consequently, one difficulty has been providing a highly lubricious coating that strongly adheres to a device surface.
Similarly, various medical devices, such as stents or catheters, have been coated with therapeutic or diagnostic agents, to provide localized and possibly extended exposure of the tissue to the agent. For example, drugs which prevent the proliferation of smooth muscle cells, or which promote the attachment of endothelial cells, can be coated on a stent which is then implanted at the site of a stenosis within a patient's blood vessel, to thereby inhibit restenosis following an angioplasty or stent implantation procedure. However, the agent must be strongly adhered to the device surface for effective delivery within the patient. Moreover, controlled release of the agent from the device surface within the patient may be required as part of the therapeutic or diagnostic regime.
It would be a significant advance to provide a hydrophilic coating which strongly adheres to a surface of a medical device, or a therapeutic or diagnostic coating strongly, but potentially releasably, adhered to the surface of a medical device. The present invention satisfies these and other needs.
SUMMARY OF THE INVENTION
The invention is directed to a method of providing a coating on an intracorporeal medical device, and the coated medical device produced thereby. A durable coating is provided on the medical device which modifies the device surface with a therapeutic, diagnostic, lubricious or other active agent. The coating of the invention may be used on a variety of medical devices including stents, catheters, guidewires, cardiac pacing leads, and vascular grafts.
In one embodiment, the coating on the intracorporeal medical device generally includes a base coat and a top coat. The base coat has a binding component and a grafting component, and is used to strongly adhere to the surface of the device and also to strongly bond to the top coat. Specifically, the binding component binds to both the top coat and to the grafting component, and the grafting component adheres to the device surface. The base coat containing the grafting component and binding component in a suitable carrier such as a solution is first applied to the surface of the device. The base coat is preferably polymerized, e.g., exposed to polymerizing radiation to polymerize the grafting component, and the grafting component is bonded to the binding component and adhered to the surface of the device to form a base coat on the device. The device is then coated with a top coat containing a desired therapeutic, diagnostic, or hydrophilic agent. The top coat may be applied in a solution which is allowed to evaporate, to form a top coat with a therapeutic, diagnostic, or hydrophilic agent. In another embodiment, the device is coated with a top coat comprising a linking agent, and the linking agent is exposed to the therapeutic, diagnostic, or hydrophilic agent to form a complex therewith, to thereby form the therapeutic, diagnostic or hydrophilic coating of the invention. Because the top coat bonds to the base coat, the therapeutic, diagnostic, or hydrophilic coating produced will not readily wear off.
In one embodiment, the base coat comprises a binding component which is a homofunctional compound having homofunctional groups which covalently bond to functional groups in the top coat. In a preferred embodiment, the homofunctional binding component is grafted to the grafting component by a hydrogen abstraction mechanism, in which the grafting component is activated by initiators and covalently bonds to the binding component. In another embodiment, the base coat comprises a binding component which is a heterofunctional compound having a first functional group for covalently bonding with the grafting component, and a second functional group for covalently bonding to functional groups in the top coat.
As mentioned above, the binding component of the base coat bonds to the top coat. In one embodiment, the therapeutic, diagnostic, hydrophilic or other active agent has functional groups which directly bond to functional groups of the binding component. In another embodiment, the therapeutic, diagnostic, or hydrophilic agent is bound to the binding component by a linking agent in the top coat. The linking agent may inherently have functional groups, or may be modified to include functional groups, which bond to functional groups of the binding component. The linking agent may be bound to the base coat and thereafter exposed to the therapeutic, diagnostic or hydrophilic agent, or alternatively, the linking agent may be exposed to the agent before or during the binding of the linking agent to the base coat.
A variety of suitable linking agents may be used, including avidin-biotin complexes, and functionalized liposomes and microsponges and microspheres. Avidin is a polypeptide composed of at least 128 amino acid residues. Typically however, the single polypeptide chain is a subunit associated with three essentially identical polypeptide chains, forming a tetramer. Avidin as a receptor is typically used in conjunction with its highly specific ligand, biotin, C
10
H
16
N
2
O
3
S. An avidin tetramer will bind 4 biotin molecules in solution in a noncovalent interaction which has a binding constant of about 10
15
M
−1
, a half-life in vivo of about 89 days, and which is essentially undisturbed by organic solvents. Biotinylation, or the process of covalently binding biotin to another molecule, typically takes place by N-hydroxysuccinimide binding. Spacer molecules may be inserted between the avidin and the base coat, or between the biotin and the therapeutic or diagnostic agent, as is known in the art, to facilitate avidin-biotin binding or improve the activity of the therapeutic or diagnostic agent. The avidin or the biotin molecule may be chemically altered to decrease the binding constant, to thereby tailor the dissociation r
Bigus Stephen J.
Buchko Christopher J.
Michal Eugene T.
Advanced Cardiovascular Systems Inc.
Heller Ehrman White & McAuliffe
Seidel Richard K.
Thanh Loan H.
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