Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2000-09-15
2003-07-15
Capossela, Ronald (Department: 3744)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S264000, C604S286000, C606S194000
Reexamination Certificate
active
06592550
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to medical devices and, more particularly, to devices for deploying another medical device such as a stent into a patient or for expanding a narrowed or obstructed passage or lumen in a patient.
BACKGROUND OF THE INVENTION
Medical devices which incorporate inflatable or expandable balloons serve a wide variety of purposes. The balloon is carried on or affixed to a catheter shaft for delivery of the balloon to a desired location in the patient. The catheter shaft includes a lumen for introducing an inflation fluid into the balloon. For example, such catheter balloons are widely known to be useful for performing angioplasty procedures or the like, in which narrowings or obstructions in blood vessels or other body passageways are altered in order to increase blood flow through the narrow or obstructed area. More specifically, in a typical balloon angioplasty procedure, a balloon catheter is percutaneously introduced into the patient by way of the arterial system and advanced until the balloon of the catheter lies across the vascular narrowing or obstruction. The balloon is then inflated to dilate the vessel lumen at the site of the narrowing or obstruction. If desired, a stent may be positioned over the balloon and deployed at the site of the narrowing or obstruction to ensure that the dilated vessel lumen remains open. Balloon catheters find utility in a wide range of procedures, including valvuloplasty and urological procedures, among others.
The balloons of prior balloon catheters have been constructed from a wide variety of polymeric materials. These balloons each have their own advantages and drawbacks. Balloons comprising polyethylene terephthalate (PET), for example, have a relatively low degree of distention or expansion once they are inflated. This generally minimizes any potential adverse effects from overinflation or overexpansion of the balloon or any stent carried on it. Semi-distending or non-distending balloons often possess relatively high tensile strength, burst pressure and puncture resistance, qualities highly desirable for dilating tough lesions or for deploying and expanding stents carried over them.
However, body vessels such as arteries are generally tapered, and the locations at which narrowings or obstructions may occur vary, so that a balloon which closely matches the ultimately desired diameter of the vessel may not be readily available. Moreover, it may at times be desirable to be able to increase the diameter of the balloon beyond that which had been contemplated before the balloon procedure was begun. While balloons comprising materials such as polyvinyl chloride can be more distensible than PET or the like, balloons comprising such materials often possess a significantly lower tensile strength, burst pressure or puncture resistance than the less-distensible balloons. Overinflation of such balloons is also possible.
A variety of attempts have been made to construct medical device balloons from materials which yield balloons of good strength (that is, relatively high tensile strength and burst pressure, and good puncture resistance) while retaining an adequate degree of compliance, that is, an acceptable ratio of balloon diameter growth under an applied pressure to that balloon pressure. Each of these attempts possesses its own advantages and disadvantages. Balloons made from materials such as PET may possess excessive crystallinity or may be too stiff, so that such balloons may be resistant to the folding desired to minimize the profile of the catheter in which the balloon is employed; such resistance to folding is particularly problematic when the balloon is deflated following inflation during an in situ application, in order to be retracted into the distal end of the catheter for withdrawal. A minimal catheter profile is a highly desirable characteristic of balloon catheters, however. Some materials do not readily accept coating with drugs or lubricants, and some materials are difficult to fuse or adhere to conventional catheter shafts. Balloons made of some biaxially oriented nylons or polyamides have been asserted to overcome some of these problems.
Catheter balloons comprised of block copolymers have been suggested as a way of achieving an acceptable combination of balloon strength and elasticity. For example, it is known that catheter balloons can be constructed from polyamide/polyether block copolymers, commonly identified by the acronym PEBA (polyether block amide). Many of such copolymers can be characterized by a two phase structure, one being a thermoplastic region that is primarily a polyamide, semicrystalline at room temperature, and the other being an elastomer region that is rich in polyether. Balloons comprising such copolymers are asserted to possess a desirable combination of strength, compliance and softness. Catheter balloons comprising blends of two or more such copolymers are also known, and it has been asserted that irradiating such blends can enhance the properties of the resulting balloons, including increased burst pressures.
It would be highly advantageous to have medical devices which included expandable or inflatable balloons with improved strength, for example, with greater tensile strength, burst pressure and/or puncture resistance, while simultaneously possessing acceptable compliance (in this case, an acceptable ratio of balloon diameter growth to balloon pressure). It would also be highly advantageous to have medical devices made from materials which meet a variety of desirable processing criteria, including thermal stability, non-toxicity, non-volatility, high boiling point (preferably, solid at room temperature), high flash point, insensitivity to moisture and commercial availability.
SUMMARY OF THE INVENTION
Many of the foregoing problems are solved and a technical advance is achieved in an illustrative medical device for positioning an included balloon within a human or veterinary patient, for example, for deploying another medical device such as a stent in the patient or for expanding a passage or lumen in the patient. More particularly, in a first preferred embodiment, the medical device of the present invention comprises a catheter shaft and an expandable balloon carried by the catheter shaft. The medical device of the present invention is characterized in that the balloon comprises an irradiation cross-linked mixture of a polyamide elastomer and at least one additional cross-linking reactant.
This additional cross-linking reactant performs a role which is quite different from that performed by the two reaction promoters disclosed in International Application WO 98/55171. That Application is directed to a cross-linked nylon block copolymer which comprises an irradiation cross-linked copolymer containing a polyamide block and an elastomeric block, including a compound which promotes cross-linking therein. The process disclosed in that application comprises supplying the nylon block copolymer with a cross-linking “promotor” (sic.) and exposing the block copolymer to irradiation sufficient to cross-link the copolymer. Only two promoters are disclosed, triallylcyanurate and triallylisocyanurate, at 2 percent by weight in PEBAX® brand nylon block copolymer (Atochem, Inc., brand of polymers consisting of polyether blocks separated by polyamide blocks). Irradiation is carried out at 5 to 20 megarads (no specific type of irradiation is disclosed), although degradation of the material may take place when total irradiation becomes too high, for example, at 15 or 20 megarads. That Application claims (among others) an improvement in a balloon type catheter having a tubular shaft comprising a nylon block copolymer and an integrally formed balloon section, the improvement comprising irradiation crosslinking the copolymer of the balloon section, wherein the crosslinking lowers the percent elongation of the balloon section as compared to the elongation prior to crosslinking. The only apparent support in the specification for that claim appears to be a single statement that, in
Boatman Scott E.
Burton David G.
Drewes, Jr. David A.
Hoffa Michael C.
Hupcey Maggie A. Z.
Brinks Hofer Gilson & Lione
Capossela Ronald
Cook Incorporated
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