Abstract:
The invention is directed to an inflatable member for intralumenal catheter which has been formed by vapor and/or gas cover deposition and a balloon formed by the method. Multi-furcated inflatable members can be made with essentially no pin holes and other defects.

Description:
This application is a continuation of copending application Ser. No. 08/848,592, filed Apr. 28, 1997, now U.S. Pat. No. 6,013,054 which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is directed to the formation of inflatable members and particularly to inflatable balloons for dilatation catheters used in angioplasty procedures, commonly referred to as percutaneous transluminal coronary angioplasty (PTCA). 
     In a typical PTCA procedure a dilatation balloon catheter is advanced over a guidewire to a desired location within the patient&#39;s coronary anatomy where the balloon of the dilatation catheter is properly positioned within the stenosis to be dilated. The balloon is then inflated to a predetermined size with radiopaque liquid at relatively high pressures which can generally range from 4-20 atmospheres to dilate the stenosed region of the diseased artery. One or more inflations may be needed to effectively dilate the stenosis. The catheter may then be withdrawn from the stenosis or advanced further into the patient&#39;s coronary anatomy to dilate additional stenoses. 
     The catheters used to insert stents into a patient&#39;s blood vessel are very similar to the catheters employed for angioplasty. The stent is mounted onto the balloon of the catheter in a contracted or otherwise unexpanded state, the catheter with the stent is advanced through the patient&#39;s vasculature until the balloon and stent thereon are disposed within a desired region of the patient&#39;s vasculature, such as a coronary artery. The balloon is inflated to expand the stent into position within the desired region of the patient&#39;s blood vessel. 
     Presently used balloons are formed of a polymer such as polyethylene terephthalate (PET), polyethylene (PE), nylon and the like. The strength requirements for balloons whether for dilatation and stent delivery has tended to increase over the years. But it has become more difficult with conventional manufacturing procedures to form high strength balloons with thin walls of uniform thicknesses without pin holes. Typical procedures involve blowing of a tubular parison, usually within a mold having an interior surface corresponding to the desired inflated shape of the balloon. 
     Dilatation balloons of non-standard shapes, such as bifurcated balloons shown in U.S. Pat. No. 4,456,000, are difficult to manufacture without seams, flow lines, flash or other defects. What has been needed and heretofore unavailable is a method of forming balloons having high strength, thin walls and low incidence of pin holes and in a variety of shapes and sizes without the prior defects. The present invention satisfies these and other needs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method of forming a thin walled high strength balloon for dilatation, stent delivery and implacement and the like, which has little incidence of pin holes and which is without seams, flow lines, flash or other defects. 
     In one presently preferred embodiment of the invention, a balloon is formed by deposition of a thermoplastic polymeric material or thermoplastic elastomeric material onto a mandrel of desired shape in a vacuum or low pressure environment and preferably under cover of an inert or non-reactive gas such as argon, nitrogen and the like. The mandrel has an exterior shape which corresponds to the desired inflated shape of the balloon. One presently preferred method of depositing the polymeric material onto the mandrel is radio frequency (RF) sputtering. Another method is plasma coating. Other vacuum or vapor deposition methods may also be employed to deposit polymeric material onto a mandrel to form a balloon. Suitable polymeric materials which may be vacuum deposited onto a mandrel to form a balloon include conventional dilatation balloon materials such as polyethylene, polyvinyl chloride, polyethylene terephthalate, nylon and other polyamides and zinc and sodium ionomers (e.g. Surlyn). Balloons formed of other less conventional materials such as polypropylene, polyimide, various fluoropolymers and proprietary polymeric materials such as Parylene and Parylast which are available from Advanced Surface Technology, Inc. of Billerica, Mass., may also be made with the method of the invention. Blends of polymeric materials are also suitable for deposition. Composite balloons and other catheter parts with separate layers of different polymeric materials may also be formed by the vacuum deposition of the polymeric materials. For example, a first component such as a balloon can be formed in the manner of the invention, and then be assembled with a suitable inner tubular member and catheter shaft. After the assembly, the balloon can be first coated in the manner of the invention with a suitable material such as Parylene and then Parylast is applied to further secure the balloon to the catheter shaft. 
     Generally, the vacuum deposition is conducted within a chamber that has a vacuum level of about 10 −2  to about 10 −10  torr, preferably about 10 −3  to about 
     10 −6  Torr. The gas cover is preferably argon for RF sputtering and nitrogen for plasma deposition. Other relatively inert or otherwise non-reactive gases may likewise be employed in this regard. 
     The balloon of the invention can be formed with a wall thickness which is uniform and accurate. Wall thicknesses between about 0.3 to over 2 mils (0.008-0.05 mm) and typically from 0.5 to about 1.5 mils (0.013-0.038 mm) can be readily formed with variations from 0.05 to 0.3 mils (0.0013-0.008 mm), typically about 0.1 to about 0.2 mils (0.0025-0.005 mm). Moreover, the balloon is essentially pin hole free and has no seams, flow lines, flash or other defects. The method of the invention is particularly adaptable to the manufacture of balloon shapes other than conventional cylindrical working sections with tapered ends, e.g. multi-furcated balloons, i.e. balloons with multiple distal portions which extend distally a angles from one another. These and other advantages of the invention will become more apparent from the following detailed description of the invention, when taken in conjunction with the accompanying exemplary drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross-sectional view of a dilatation catheter with a bifurcated balloon structure within a patient&#39;s blood vessel position to dilate an accumulation of plaque at an arterial branch. 
     FIG. 2 is a perspective of the bifurcated balloon shown on the catheter depicted in FIG.  1 . 
     FIG. 3 is an elevational view, partially in section, of a bifurcated mandrel with a bifurcated balloon deposited thereon in accordance with the present invention. 
     FIG. 4 is a schematic view of a system for the vacuum deposition of a polymeric layer onto a suspended mandrel to form a bifurcated balloon by RF sputtering. 
     FIG. 5 is a schematic view of a system for the vacuum deposition of a polymer material onto a suspended mandrel to form a bifurcated balloon by plasma deposition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to FIG. 1 which illustrates the distal portion of a dilatation catheter  10  having a bifurcated balloon  11  within a forked branching of a patient&#39;s coronary artery  12  for dilating plaque  13  at the branch point  14  of the artery. The catheter  10  has an outer tubular member  15 , a Y-shaped inner tubular member  16 , a bifurcated balloon  11  having a proximal end  17  secured to the distal end of the outer tubular member  15  and distal ends of each of the bifurcated portions secured to the distal ends of the Y-shaped inner tubular member. A guidewire  18  is slidably disposed within the inner lumen  20  which extends within the inner tubular member  16 . 
     The bifurcated balloon  11  is best illustrated in the perspective view shown in FIG.  2 . FIG. 3 illustrates a bifurcated mandrel  21  onto which a layer  22  of polymeric material has been vacuum deposited to form the bifurcated balloon  11  as shown in FIG.  2 . 
     FIG. 4 illustrates a system for depositing a polymer film  22  onto a bifurcated mandrel  21  as shown in FIG.  3 . This system includes a vacuum chamber  23  in which the mandrel  21  is suspended. A body  25  of target material, e.g. polyethylene, is suspended within the vacuum chamber  23  and is electrically connected to a RF source  26  through cable  27 . A suitable pump  28  is connected to the vacuum chamber  23  through conduit  29  to develop a vacuum within the chamber  24  at the desired levels. A source  30  of inert or non-reactive gas, e.g. argon or nitrogen, is likewise connected to the vacuum chamber  23  through a conduit  31 . A vent line  32  is provided with a valve  33  to vent the chamber  23  at the end of the process. 
     The system shown in FIG. 4 is operated in the following manner. The mandrel  21  is suspended within the chamber  23  and the body  25  of target material is supported within the chamber electrically connected by cable  27  to an RF electrical energy source  26 . The chamber  23  is closed and the pump  28  is actuated to develop a vacuum within the chamber of about 10 −7  torr. An inert gas, in this case argon, is injected into the chamber  23  from the source  30  to serve as the bombardment source. After stabilization of the vacuum within the chamber  23  at a desired level of about 10 −4  torr, the RF power is turned on. A plasma is generated within the chamber  23  between the polyethylene body  25  and the mandrel  21  by the ionized argon gas which bombards the polyethylene body causing dislocation of atoms and molecules of target material from the surface of the polyethylene body and the deposition thereof onto the surface of the mandrel  21 . On the surface of the mandrel  21 , the deposited material reacts to form a polymeric film similar to the original target material. When the desired film thickness is reached, the power to the RF source  26  is turned off. The vacuum chamber  23  is then vented through conduit  32  by opening the valve  33 . When the chamber reaches atmospheric pressure, the chamber is opened and the coated mandrel  21  is removed. The mandrel  21  may be separated from the bifurcated balloon  11  formed on the surface thereof by a variety of means. For example the mandrel  21  may be made of material which is easily dissolvable by a suitable solvent which does not effect the polymeric layer on the mandrel. The proximal and distal ends of the balloon  11  are clipped to a desired length and the balloon then assembled onto the catheter shaft in a conventional manner. The balloon has a uniform thickness and no pinholes seams, flow lines, flash or other defects. 
     FIG. 5 illustrates an alternative system for depositing a polymer film  22  onto a bifurcated mandrel  21  as shown in FIG.  3 . This system includes a vacuum chamber  34  in which the mandrel  21  is suspended. A suitable pump  35  is connected to the vacuum chamber  34  through conduit  36  to develop a vacuum within the chamber  34  at the desired levels. A vent line  37  is provided with a valve  38  to vent the chamber  34  at the end of the process. A vaporizing vessel  41  is filled with an appropriate amount of dichloro-p-xylylene dimer. A pyrolyzer vessel  42 , in fluid communication with the vaporizing vessel  41  through conduit  43 , is heated to a temperature of about 700° C. When the temperature of the pyrolyzer vessel  42  is stabilized, the dimer in the vaporizer  41  is vaporized by heating the dimer to 200° C. Valve  44  in the conduit  43  is opened allowing the vaporized dimer to flow into the pyrolyzer vessel, where the dichloro-p-xylylene is heated and then into the pyrolyzer chamber  45  through conduit  46 , where the dichloro-p-xylylene is cleaved into two reactive monomeric species of monochloro-p-xylylene. The reactive monomers are directed through conduit  47  to the vacuum chamber  34  which has been pumped down to a desired vacuum level of about 10 −4  torr by pump  36 . Within the vacuum chamber  34  the monomers polymerized at room temperature as a film of Parylene C on the surface of the mandrel  21  disposed in the chamber. When the desired polymer thickness is formed on the mandrel surface, e.g. when a fixed amount of the dimer source is depleted from the vaporizer, the vacuum chamber is vented through line  37  by opening valve  38  as in the previous example and the vacuum chamber opened so that the coated mandrel  21  can be removed. Once removed from the vacuum chamber  34 , the polymer balloon  11  on the mandrel  21  can be separated in a manner as previously described. 
     Suitable deposition systems for the present invention include the CrC Sputtering System, particularly the CrC-150 System with a 200 watt RF power supply, available from Plasma Sciences, Inc. of Lorton, Va. and Specialty Coating System&#39;s (Indianapolis, Ind.) Parylene Coater. 
     Other uses may be made of the present invention. For example, the Y-shaped inner member can be made in essentially the same manner. Other alternatives include forming a Y-shaped tubular member in the manner of the invention and then irradiating the portions of the tubes which are to be blown into balloons, and the blowing the irradiated sections in a conventional manner. The method of the invention can also be employed to apply a layer of material onto a previously formed balloon so as to reap the benefits of a composite construction. Other modifications will become apparent to those skilled in the art. 
     Although individual features of embodiments of the invention may be shown in some of the drawings and not in others, those skilled in the art will recognize that individual features of one embodiment of the invention can be combined with any or all the features of one or more of the other embodiments. Moreover, various changes and modification can be made to the invention without departing from the scope thereof.