Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Producing multilayer work or article
Reexamination Certificate
2000-09-26
2001-12-11
Dye, Rena L. (Department: 1772)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Producing multilayer work or article
C264S515000, C264S516000, C264S209500
Reexamination Certificate
active
06328925
ABSTRACT:
BACKGROUND OF THE INVENTION
Balloons mounted on the distal ends of catheters are widely used in medical treatment. The balloon may be used to widen a vessel into which the catheter is inserted or to force open a blocked vessel. The requirements for strength and size of the balloons vary widely depending on the balloon's intended use and the vessel size into which the catheter is inserted. Perhaps the most demanding applications for such balloons are in balloon angioplasty in which catheters are inserted for long distances into extremely small vessels and used to open stenoses of blood vessels by balloon inflation. These applications require extremely thin walled, high strength, relatively inelastic balloons of predictable inflation properties. Thin walls are necessary because the balloon's wall and waist thicknesses limit the minimum diameter of the distal end of the catheter and therefore determine the limits on vessel size treatable by the method and the ease of passage of the catheter through the vascular system. High strength is necessary because the balloon is used to push open a stenosis and so the thin wall must not burst under the high internal pressures necessary to accomplish this task. The balloon must have some elasticity so that the inflated diameter can be controlled, enabling the surgeon to vary the balloon's diameter as required to treat individual lesions, but that elasticity must be relatively low so that the diameter is easily controllable. Small variations in pressure must not cause wide variation in diameter.
The compliance characteristics of angioplasty balloon materials are described in U.S. Pat. No. 5,447,497, incorporated herein by reference. A variety of low-compliant materials have been employed in angioplasty balloons, including polypropylene, polyimides, polyamides, and polyesters, such as PET and PEN. Such low compliant materials can generally be fabricated into higher strength balloons than balloons made of more compliant materials. The use of low compliant materials, however, has been associated with a number of minor but undesirable problems, such as poor refold characteristics, pinhole development, difficulty in bonding to the catheter structure and high friction coefficient.
To address some of these problems a number of balloon structures have been proposed in which a layer of low compliant polymer material is coated or coextruded with an over or underlying layer of another polymer material less prone to one or more of the problems occasionally encountered with low compliant balloons. Exemplary of this approach are U.S. Pat. No. 5,270,086 (Hamlin), U.S. Pat. No. 5,195,969 (J. Wang, et al.) and U.S. Pat. No. 5,290,306 (Trotta, et al), which pertain to co-extruded structures and U.S. Pat. No. 5,490,839 (L. Wang, et. al) which pertains to coated balloon structures wherein the balloon coating imparts refold and soft pliable surface characteristics. The balloons of these references are unitary structures whose compliance and burst profiles are determined primarily by the non-compliant polymer layer, with little or no contribution by the second polymer layer. However, balloons made from coextruded tubes with soft polymer material on the top layer do provide rewrap, abrasion and puncture resistance, and reduced tracking resistance.
It is also known to prepare catheter balloon structures which include two separate concentrically arranged balloon elements mounted on a catheter. References which describe such structures include U.S. Pat. No. 4,608,984, in which an outer balloon element of a highly elastic material such as latex having a deflated circumference less than the diameter of the associated catheter is disclosed for use in refolding the inner working balloon after it has been inflated and deflated; and U.S. Pat. Nos. 5,447,497, 5,358,487 and 5,342,305, in which a non-linear compliance curve is obtained from two different sized balloon elements or from use of an inner balloon which bursts at some pressure below the burst pressure of the outer element. The dual concentric balloon structures, are made of materials of quite different strength characteristics and tend to give balloons whose burst strength is little different from to the burst strength of the strongest member element (typically PET or nylon).
SUMMARY OF THE INVENTION
This invention will provide a linear and noncompliant balloon expansion curves. In the case both balloons have almost the same diameters.
In one aspect the invention comprises a laminate balloon comprising at least two layers of separately oriented thermoplastic polymer material, which are coextensive over the body of the balloon. The two layers are preferably made of different polymer materials. Suitably, the layers are sufficiently adherent to each other so that the laminate balloon is a unitary structure even when the balloon is deflated. Most preferably the balloon has an underlying layer made of a low compliant, high strength polymer and an overlying layer of a softer and more flexible polymer material relative to the first polymer material. The inventive balloon structures have an additive burst pressure, meaning that they are stronger than a first single-layer reference balloon corresponding to the underlying polymer layer. The additive strength of the balloons of the invention is exhibited typically by burst strengths greater than the first reference balloon by at least 50%, and commonly at least 75%, of the strength of a second single-layer reference balloon corresponding to the overlying relatively soft flexible polymer layer. Optimal balloons of the invention give burst strengths which exceed the strength of the first reference balloon by about 100% or even more of the strength of the second reference balloon.
The preferred inventive balloons have good flexibility and surface softness, allowing catheters to track down into lesions relatively easily, good puncture resistance, good abrasion resistance and good refold characteristics, all contributed by the soft material top layer. Furthermore they also have a low compliance profile with a burst strength which exceeds the strongest PET angioplasty balloons currently commercially available.
A second aspect of the invention comprises a preferred method of making a laminate balloon which includes the steps of
a) providing a first tubing segment of a first polymer material;
b) stretching the first tubing segment at a first stretch ratio to produce a first stretched tube having an outer diameter;
c) providing a second tubing segment of a second polymer material having an inner diameter greater than the outer diameter of the first stretched tube;
d) inserting the first stretched tube into the second tubing segment;
e) stretching the second tubing segment at a second stretch ratio to produce a second stretched tube, the first and second stretched tubes being brought into direct annular contact during the stretching of said second tubing segment, to form a laminate stretched tubing structure; and
f) forming the laminate balloon by pressurizing the laminate stretched tubing structure at a temperature and pressure above ambient so as to expand the laminate stretched tubing structure.
A still further aspect of the invention is an alternative process for forming a laminate balloon which includes the steps of:
a) providing a first tubing segment of a first polymer material;
b) stretching the first tubing segment at a first stretch ratio to produce a first stretched tube;
c) blowing the first stretched tube in a mold to produce a first layer structure, said first layer structure including waist, cone and body portions, the waist portion having an inner diameter;
c) providing a second tubing segment of a second polymer material;
d) stretching the second tubing segment at a second stretch ratio to produce a second stretched tube having an outer diameter less than the inner diameter of the waist portion of said first layer structure;
e) inserting the second stretched tube into the first layer structure and
f) forming the laminate balloon by pressurizing the secon
Chen Jianhua
Lee Nao
Wang Lixiao
Dye Rena L.
Sci-Med Life Systems, Inc.
Vidas Arrett & Steinkraus P.A.
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