Polyethylene terephthalate (PET) is a widely used material for the manufacture of balloon-type medical devices where a "non-compliant" balloon is required. Unlike "compliant" balloons, which continue to expand as internal pressure in the balloon is increased, a "non-compliant" balloon will attain and maintain a substantially constant configuration regardless of the internal pressure. For an analogy in a non-medical field, the typical party balloon is an example of a compliant balloon which continues to expand as it is being blown up. In fact, such a balloon will generally continue expanding under increased pressure until it bursts. On the other hand, a hot air balloon can not be compliant. In order to be safe and effective for its intended use, a hot air balloon must generally maintain its predetermined configuration once it has been inflated. Therefore, it is properly considered as an example of a non-compliant balloon.
In the medical field, depending on the particular application or use, it may be preferable to use either a compliant balloon or a non-compliant balloon. It happens, however, that for some medical procedures and applications it may be preferable to use a balloon which is neither typically compliant nor typically non-compliant. Such a balloon is subsequently referred to herein as being a "semi-compliant" balloon.
A well known use in the medical device field for non-compliant inflatable balloons involves the performance of angioplasty procedures. When used for this purpose, the balloon is first positioned across a stenosis in an artery. It is then inflated under relatively great pressure to a final balloon configuration to dilate the artery. The object is to use the predictable final configuration of the non-compliant balloon to dilate the artery to only a known extent. This, of course, will also breakup the plaque which is causing the stenosis in the artery and, thereby allow for the subsequent flow of blood through the previously blocked artery. Importantly, the balloon can not assume an uncontrolled or unpredictable configuration when inflated. This is so because, if left unchecked, the balloon could cause unwanted damage to the arterial system. A balloon intended for such use is disclosed in U.S. Pat. No. Re. 33,561 Which issued to Levy for an invention entitled "Balloon and Manufacture Thereof".
Use of balloons for stent placement is typically done in situations where it is necessary that a stent act as a structural support for the arterial wall in order to prevent a restenosis or collapse of the artery. The placement of a stent in an artery, however, can be an extremely complicated procedure due to the fact that arteries typically do not have constant diameter lumens and, instead, typically have arteries whose diameters vary significantly over even short distances.
Not surprisingly, the placement of a stent in an artery requires skill and dexterity. Specifically, when placing a stent in an artery it is necessary to generate forces which can be applied to various parts of the stent over controllable and predictable distances to shape and conform the stent to the artery. This, of course, must all be done in situ. Thus, a truly non-compliant balloon which has a fixed inflated configuration would be inefficient because of its inability to vary in configuration during sizing and placement of a stent. On the other hand, a truly compliant balloon would also be inefficient due to its tendency to reconfigure itself into areas of least resistance and, thereby, not necessarily apply forces at the required locations on the stent.
In light of the above it is an object of the present invention to provide a method for manufacturing and using a semi-compliant PET balloon which will expand into predictable configurations that correspond to selectively controlled inflation pressures. It is another object of the present invention to provide a method for manufacturing and using a semi-compliant PET balloon which can be manipulated in an artery and inflated to position, configure and anchor a stent into the arterial wall to prevent collapse of the arterial wall. Still another object of the present invention is to provide a method for manufacturing and using a semi-compliant PET balloon which is simple to employ, and relatively cost effective.