Abstract:
An angioplasty balloon and method of manufacture are provided. The balloon has a working length and a taper each having a substantially equivalent thickness. This allows the balloon to be steered easily through vasculature to the site of a stenosis prior to inflation during an angioplasty procedure. The taper thickness in particular is achieved through use of a specially designed multi-tubular slug which is molded to form the angioplasty balloon of the present invention.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to dilation catheters. More particularly, the invention relates to intravascular angioplasty catheter balloons and a method of manufacturing the same. 
     2. Description of the Related Art 
     Angioplasty is a procedure by which stenotic lesions (atheromatous deposits), found in cases of atherosclerosis. During angioplasty, a guidewire is inserted into the cardiovascular system, generally via the femoral artery under local anesthesia. The guidewire is advanced through the patient&#39;s vasculature to the site of the stenosis (stenotic lesion). Placement of the guidewire may be aided by way of fluoroscopic observation. A dilatation catheter, having a guidewire lumen and distensible balloon portion, is then advanced through the vasculature until the balloon portion, at the distal end of the catheter, traverses or crosses a stenotic lesion. The artery is narrowed in the area of the stenotic lesion due to the atheromatous deposits occupying arterial space at the walls of the artery. Once placed, the balloon portion of the catheter is inflated, generally with a fluid, to compress the atheromatous deposits against the walls of the artery. This compression dilates the lumen of the artery leaving an unblocked arterial passage once the guidewire and catheter are removed. 
     Looking back to where the uninflated balloon encounters the stenosis, it must first cross at least a portion thereof in order to reach its distal-most destination. Therefore, a flexible, low profile balloon is preferable. In particular, the ends of the uninflated balloon should taper smoothly and lay low so that the balloon can be threaded into tight passages. It is preferable that the thickness of the balloon material be substantially constant from a working length throughout each taper. In the present context, a thick wall is at least approximately 0.002″ in thickness while a thin wall is approximately 0.001″ in thickness. 
     Unfortunately, current production methods yield a balloon with stiff and bulky tapers. These limitations are related to the behavior of the balloon material during manufacture, where a piece of polymer tubing is stretched to make the balloon. The balloon is made (“blown”) by placing a segment of polymeric tubing in a mold, heating it to a near-molten state, and pressurizing the tubing until it fills the mold. The tubing within the mold forms the balloon. The mold is shaped such that the balloon is comprised of a working length with a taper at each end thereof. Each taper joins an unexpanded segment of tubing outside of the mold, referred to here as a shaft. Because the tapers expand less than the working length, they remain stiffer and bulkier. A thin-walled taper would be more desirable. 
     One approach to thinning the wall of the taper is a process called “pre-necking” in which the segment of tubing that will become the taper is first softened by heating and then subjected to a force which forms a narrowed segment in the tubing, referred to here as a neck. The objective of pre-necking is to form the taper from this neck. As the balloon is blown, the neck expands to form a taper having thinner walls than a taper blown from un-necked tubing. The thin taper terminates at a thin shaft. However, the problem of thick, stiff tapers still remains to a certain extent because the pre-necking is performed in a solid or semi-molten state in which the strain applied to the tubing induces crystallization. In effect, the molecular strands of the polymer become aligned parallel to the load inducing the strain. Once aligned in this manner, the polymer resists further distension. Thus, due to pre-necking, we have exchanged a thicker taper for a somewhat thinner taper which nonetheless remains less expansive than the reminder of the balloon. The remainder of the balloon, which is intended for contacting the wall of a body lumen such as during an angioplasty, is often referred to as the working distance or the working length. In the case of pre-necked balloons we end up with a thin taper which is less expansive than the working length. 
     What is needed, therefore, is an angioplasty balloon having a thin taper terminating at a thin shaft. It is desirable that the thin taper have a wall of substantially equivalent thickness to a wall of the working length. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an angioplasty balloon having a taper thickness substantially equivalent to a working length thickness. 
     It is an object of the present invention to provide an angioplasty balloon having a thin shaft. 
     It is an object of the present invention to provide an angioplasty balloon having a wall thickness no greater than 0.002″, and in one embodiment between 0.0005″ and 0.002″. 
     It is an object of the present invention to provide a slug capable of being molded into an angioplasty balloon having a taper thickness substantially equivalent to a working length thickness. 
     It is an object of the present invention to provide a slug comprising a polymeric inner tube within a shortened polymeric outer tube. 
     It is an object of the present invention to provide a method of manufacturing an angioplasty balloon having a taper thickness substantially equivalent to a working length thickness. 
     In accordance with these objectives an angioplasty balloon  40  is provided having a taper wall thickness  76  substantially equivalent to a working length wall thickness  60 . The angioplasty balloon  40  is manufactured from a slug  100  having an inner tube  106  within a shortened outer tube  102 . The shortened outer tube  102  is fused to the inner tube  106  within a mold until an angioplasty balloon  40  has formed. The working length  44  of the angioplasty balloon  40  has formed from the shortened outer tube  102  while the inner tube  106  forms a taper ( 48 ,  50 ) at each end of the working length  44 . Each taper ( 48 ,  50 ) terminates in a shaft ( 42 ,  46 ). The working length  44 , taper ( 48 ,  50 ), and shaft ( 42 ,  46 ) each have substantially equivalent wall thicknesses ( 60 ,  66 ,  76 ). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective partially sectioned view of the angioplasty balloon of the present invention. 
     FIG. 2 is a side sectional view of the slug of the present invention. 
     FIG. 3 is a side sectional view of the angioplasty balloon of the present invention. 
     FIG. 4 is a flow chart of a method of manufacturing the angioplasty balloon of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, the angioplasty balloon  40  of the present invention is shown partially sectioned. The angioplasty balloon  40  has a working length  44  which extends proximally into a proximal taper  48  and proximal shaft  42 . The working length  44  extends distally into a distal taper  50  and distal shaft  46 . A balloon lumen  52  is surrounded by the angioplasty balloon  40 . The working length  44  has an inner diameter  58 , an outer diameter  56 , and a working length wall thickness  60  there between. The diameters ( 58 ,  56 ) are between 1.5 and 15.0 mm and fairly constant throughout the working length  44  of the angioplasty balloon  40 . The working length wall thickness  60  is between 0.010 mm and 0.045 mm and fairly constant throughout the working length  44  of the angioplasty balloon  40 . 
     Continuing with reference to FIG. 1, the distal shaft  46  has an inner shaft diameter  64 , an outer shaft diameter  62 , and a shaft wall thickness  66  there between. The diameters ( 64 ,  62 ) are between 0.600 mm and 0.720 mm and fairly constant throughout the distal shaft  46  of the angioplasty balloon  40 . The shaft wall thickness  66  is between 0.010 mm and 0.051 mm and fairly constant throughout the distal shaft  46  of the angioplasty balloon  40 . The length of the angioplasty balloon  40 , between the distal shaft  46  and the proximal shaft  42 , generally ranges from 10 mm to 40 mm. However, this is merely a matter of design choice. The proximal shaft  42  is fairly dimensionally equivalent to the distal shaft  46 . However, the proximal shaft  42  is adaptable to communicating with an external supply of fluid pressure and/or delivering such to the angioplasty balloon  40 . 
     The working length  44  adjoins the distal shaft  46  by way of a distal taper  50 . The distal taper  50  has an inner taper diameter  80  and an outer taper diameter  78  which diminish from the working length  44  to the distal shaft  46  providing a smooth transition there between. A taper wall thickness  76  is found between the inner taper diameter  80  and the outer taper diameter  78 . The proximal taper  48  is comparable to the distal taper  50  in dimensions and construction. 
     As configured for angioplasty, the angioplasty balloon  40  is affixed to the distal portion of a catheter (not shown). The balloon lumen  52  communicates with an inflation lumen of the catheter to provide inflation, fluid or otherwise, to the angioplasty balloon  40 . When pressurized, tapers ( 48 ,  50 ) and the working length  44  expand until the full diameters ( 56 ,  58 ,  62 ,  64 ,  78 ,  80 ) are achieved. However, when not pressurized, tapers ( 48 ,  50 ) and the working length  44  lie flattened or folded. When the working length  44  is collapsed to its lowest profile, the tapers ( 48 ,  50 ) are able to collapse to a comparably low profile. Additionally, the flattened tapers ( 48 ,  50 ) have flexibility comparable to that of the flattened working length  44 . These characteristics are advantageous because they lessen the resistance encountered by the uninflated balloon as it is forced through a tight stenosis or sharp curves of vasculature. As a result, the angioplasty balloon  40  can be maneuvered into more difficult stenoses and is less likely to traumatize the artery. 
     Referring to FIG. 2, a cross sectional view of a slug  100  is shown. The slug  100  is made of a shortened outer tube  102  surrounding an inner tube  106  and being in communication therewith. The inner tube  106  has been inserted into the shortened outer tube  102 . The shortened outer tube  102  has an outer proximal end  103  and an outer distal end  104 . The shortened outer tube  102  has an outer tube outer diameter  110 , an outer tube inner diameter  112  and an outer tube wall thickness  114  there between. The shortened outer tube  102  is of a length less than that of the inner tube  106 . The inner tube  106  has an inner proximal end  108  and an inner distal end  109 . The inner tube  106  has an inner tube outer diameter  112 , an inner tube inner diameter  118  and an inner tube wall thickness  120  there between. 
     Referring to FIGS. 2-4, a cross sectional view of an angioplasty balloon  40  formed from the slug  100  is shown. The slug  100  has been placed within a mold (not shown) which defines a desired angioplasty balloon  40  profile. The slug  100  has been heated and pressurized, whereupon the shortened outer tube  102  and the inner tube  106  have filled the mold. During heating, the shortened outer tube  102  and the inner tube  106  have fused. During pressurization, the proximal taper  48  and the distal taper  50  have been formed by expansion of the inner tube  106  and the shortened outer tube  102  within the mold (not shown). Once the tapers ( 48 ,  50 ) have been formed in this manner, the angioplasty balloon  40  has been formed. In particular, the shortened outer tube  102  has formed the working length  44 . The inner tube  106  and the outer distal end  104  have formed the distal taper  50 . The inner tube  106  and the outer proximal end  103  have formed the proximal taper  48 . 
     Continuing with reference to FIGS. 2-4, the tapers ( 48 ,  50 ) form easily as the angioplasty balloon  40  easily expands within the mold due to the configuration of the shortened outer tube  102  and the inner tube  106 . This ease of expansion is due to the substantial disorientation of the molecular structure of the polymer compound of the tubes ( 102 ,  106 ). The tubes ( 102 ,  106 ) are extruded at molten temperatures hot enough to randomize the molecular alignment of the polymer. Generally, this randomization of molecular structure is followed by pre-necking which eliminates the randomization to a degree. However, the present invention provides a slug  100  which allows the reduction or complete elimination of pre-necking. With a reduction or elimination of pre-necking, little or no orientation is imposed upon the polymer and the tubes ( 102 ,  106 ) retain most, if not all, of their distensibility. 
     As a result of the configuration of the slug  100 , less overall tube material is provided to the tapers ( 48 ,  50 ) than to the working length  44 . This corresponds with the fact that the tapers ( 48 ,  50 ) occupy less overall space than the working length  44  in a formed angioplasty balloon  40 . Thus, in the formed balloon  40 , as the diameters ( 78 ,  80 ) of the tapers ( 48 ,  50 ) diminish from the working length  44  to the shafts ( 42 ,  46 ), the taper wall thickness  76  does not increase appreciably. Low profile and flexibility are achieved. This may be further enhanced by utilizing an inner tube wall thickness  120  less than the outer tube wall thickness  114 . Additionally, having a larger diameter shortened outer tube  102  furthers a larger diameter working length  44 , while a smaller diameter inner tube  106  furthers smaller diameter shafts ( 42 ,  46 ). These features contribute to low profile and flexibility of the angioplasty balloon  40 . 
     The shortened outer tube  102  may be fused to the inner tube  106  before or during the formation of the angioplasty balloon  40  within the mold. Fusion prior to molding of the angioplasty balloon  40  may be achieved by various combinations of heat and pressure. Preferably, the temperature during fusion will exceed the glass transition temperature of the polymer. Above the glass transition temperature, the tubing is easily deformed. Below the glass transition temperature, the polymer resists deformation. Additionally, the tubes ( 102 ,  106 ) should be made of compatible materials, especially if fusion is to occur prior to the angioplasty balloon  40  being blown. 
     Generally, the tubes ( 102 ,  106 ) will be made from the same or compatible polymers. For example, both may be made of a polyetherblockamide material, commercially available as PEBAX® 7033 (PEBAX) or a like material, producing an angioplasty balloon  40  of uniform composition. Alternatively, the shortened outer tube  102  may be made of PEBAX while the inner tube  106  is made of a polyamide such as nylon. This will produce a two layer composite working length  44  having nylon shafts ( 42 ,  46 ). The use of a nylon inner tube  106  to produce a two layer composite working length  44  may provide an angioplasty balloon  40  capable of withstanding pressures higher than conventionally possible. If PEBAX-Nylon compositions are utilized where the tubes ( 102 ,  106 ) are fused while the angioplasty balloon  40  is blown, a high temperature (about 235° F.) and high pressure (300 p.s.i. or more) will be required. 
     Other combinations of materials include, for example, polyethylene terephthalate (PET) and a thermoplastic copolyester, commercially available as Hytrel® (a polyether-ester block copolymer) or Arnitel®. Thermoplastic copolyesters can be difficult to blow into a balloon shape because they lose their strength when heated. However, a composite of thermoplastic coplyester with PET (which readily forms a balloon shape) can produce a two layered angioplasty balloon  40 . Alternatively, the tubes ( 102 ,  106 ) may be made of identical or different polyolefins. 
     In addition to the above variations, the slug  100  may be comprised of more than two tubes assembled together to achieve different shaft  42  or working length  44  properties. One of the tubes ( 102 ,  106 , or another) may be a co-extruded tube of two or more layers. The slug  100  may or may not be pre-necked at its outer proximal end  103 , its outer distal end  104 , or both. Diameters ( 56 ,  58 ,  62 ,  64 ) may be constant or variable while the taper diameters ( 78 ,  80 ) may have identical or different characteristics as between the proximal taper  48  and the distal taper  50 .