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Method of sterilizing a medical deviceRelated Patent Categories: Chemical Apparatus And Process Disinfecting, Deodorizing, Preserving, Or Sterilizing, Process Disinfecting, Preserving, Deodorizing, Or Sterilizing, Using Direct Contact With Electrical Or Electromagnetic Radiation, In Atmosphere Other Than AirMethod of sterilizing a medical device description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060153732, Method of sterilizing a medical device. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] This invention relates generally to medical devices, and particularly to balloon catheters, including angioplasty and stent delivery balloon catheters. [0002] In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with liquid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom. [0003] In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. [0004] In the design of catheter balloons, balloon characteristics such as strength, flexibility and compliance must be tailored to provide optimal performance for a particular application. Angioplasty balloons preferably have high strength and a high rupture pressure for inflation at relatively high pressure, and high flexibility and softness for improved ability of the catheter to track the tortuous anatomy and cross lesions. The balloon compliance is chosen so that the balloon will have a desired amount of expansion during inflation. Compliant balloons exhibit substantial stretching upon application of internal pressure, whereas noncompliant balloons exhibit relatively little stretching during inflation. [0005] In the manufacture of catheter balloons, a variety of methods have been used to sterilize the catheter before use including exposure to an electron beam (i.e., e-beam) or a sterilizing fluid such as ethylene oxide (i.e., EtO). One difficulty has been sterilizing polymeric materials which degrade substantially in response to a conventional sterilization method. Degradation of the polymeric material will reduce the rupture pressure of the catheter balloon. Increasing the wall thickness of such balloons to provide an acceptably high rupture pressure increases the profile and stiffness of the balloon, and consequently decreases the trackability and crossability of the catheter in the patient's vasculature. Thus, what has been needed is an improved method of sterilizing medical devices. SUMMARY OF THE INVENTION [0006] This invention is directed to a method of sterilizing a medical device component, such as a catheter balloon or shaft, in which an electron beam (i.e., e-beam) is applied to the component in an evacuated or inert gas-filled container. The method of the invention allows for electron beam sterilization without significant degradation of the component polymeric material. It is believed that by minimizing the presence of air during the electron beam sterilization, the method inhibits or prevents the formation of reactive oxygen and nitrogen radicals which would otherwise form from the action of the electron beam radiation on air. Another aspect of the invention is a medical device component, e-beam sterilized according to a method of the invention. A variety of medical device components can be sterilized by the method of the invention, and particularly intracorporeal devices for therapeutic or diagnostic purposes, such as balloon catheters, catheter shafts and balloons, stent covers, and vascular grafts. In one embodiment, the device component is configured to be pressurized or expanded during use, and the method of the invention provides such a device component with a rupture pressure that is not significantly decreased due to electron beam sterilization. Although discussed primarily in terms of a balloon for a balloon catheter, the invention should be understood to include other medical devices. The terminology "medical device component" should be understood to include an independent, complete item such as a vascular graft or balloon catheter, or alternatively, a part of a larger device such as a balloon or a shaft of a balloon catheter. [0007] In one embodiment, the balloon itself, which has typically already been secured to a catheter shaft to form an assembled balloon catheter, is evacuated and/or filled with an inert gas before the electron beam sterilization. In a presently preferred embodiment, the balloon is purged by applying a vacuum to evacuate the balloon and back filling the evacuated balloon with an inert gas. Thus, the air which would have been present inside the balloon and catheter shaft interior is removed and replaced with an inert gas before the electron beam sterilization. As a result, the degradation of the balloon polymeric material due to the electron beam sterilization is minimized. In a presently preferred embodiment, the balloon catheter is purged before being placed inside the container, and before the container is similarly purged by evacuating the container and back filling the container with an inert gas. However, in an alternative embodiment, the balloon catheter is purged after being placed in the container. [0008] The inert gas used for purging in the method of the invention is a gas which when exposed to an electron beam does not form radicals causing oxidative degradation, i.e., hydrogen abstracting radicals. Preferred inert gases are noble gases, and most preferably argon. The heaviness of argon makes it more preferable than helium. However, gases other than the noble gases could be used as the inert gas, provided the gases lack oxygen. Thus, for example, nitrogen could be used as a low cost alternative to argon as the purging gas, because nitrogen is less susceptible than oxygen to the formation of reactive radicals causing oxidative degradation, upon exposure to an electron beam. Thus, the air tight, oxygen- or air-free container sealed with the balloon catheter therein provides an environment for the catheter during electron beam sterilization which does not form reactive radicals which cause significant oxidative degradation of the balloon catheter upon exposure to the electron beam during the sterilization. [0009] In a presently preferred embodiment, the container is filled with inert gas so that the container has a positive pressure which thus prevents or inhibits air leaking into the container in the event that pinholes develop in the container. The inert gas consequently prevents degradation of the balloon polymer during or shortly after the electron beam application and the attendant loss of sterilization if pin holes develop in the container during storage of the catheter. However, in an alternative embodiment, the container is merely evacuated by applying a vacuum to the container and sealing the container, without necessarily filling the container with an inert gas before and the container sealed with the medical device component therein. The container and balloon are evacuated by applying a vacuum to an interior thereof to thereby reduce the internal pressure therein to less than the ambient pressure. For example, the absolute pressure in the evacuated container is typically not greater than about 50 mTorr. After filling with the inert gas, the pressure inside the inert gas-filled container is typically not less than about 1 atm (760 Torr). In a presently preferred embodiment, the container (with the balloon catheter therein) is purged inside a vacuum chamber. Thereafter, the container may be sealed inside the evacuated or inert gas-filled vacuum chamber if the vacuum chamber contains a sealer, or transferred to another vacuum chamber containing a sealer. Alternatively, the purged container may be removed from the vacuum chamber and maintained in an open end-up orientation and sealed outside the vacuum chamber. Inert gas such as argon is heavier than air and will thus prevent air going into the argon-filled container when the container is held with the open end of the container up in an air-filled environment prior to sealing the container. [0010] A catheter polymeric balloon sterilized according to the method of the invention has minimal degradation of the polymer, and consequently, a minimal decrease in rupture pressure due to the sterilization. After the electron beam sterilization according to the method of the invention, the balloon has a mean rupture pressure which is not significantly less than (i.e., not more than 5% to about 25% less than, and preferably not more than about 10% to about 15% less than) the rupture pressure of the balloon before the electron beam sterilization of the method of the invention. Furthermore, the balloon preferably has a high fatigue resistance, i.e., cycles to failure, which is not significantly less than (i.e., not more than about 5% to about 10% less than) the fatigue resistance of the balloon before the electron beam sterilization of the method of the invention. After accelerated aging to simulate shelf life of the balloon in which the balloon is aged at about 45.degree. C. to about 65.degree. C. for about 1 to about 3 weeks, a balloon sterilized according to the method of the invention in an evacuated or inert gas-filled container has a mean rupture pressure which is significantly higher than (i.e., more than about 15% to about 25% higher than) the rupture pressure of a balloon electron beam sterilized in the presence of air although otherwise similarly aged and sterilized, and a fatigue resistance which is significantly higher than (i.e., more than about 1000% to about 1500% higher than) the fatigue resistance of the balloon electron beam sterilized in the presence of air. [0011] The medical device component sterilized according to the method of the invention can be formed of a variety of suitable polymeric materials, and in one embodiment is formed of a polymeric material selected from the group consisting of polyamides and fluoropolymers. In a presently preferred embodiment, the balloon is formed of a polyamide polymeric material such as polyether block amides (PEBAX), available from Atochem. The PEBAX material would typically degrade as a result of an electron beam sterilization in the presence of air. Therefore, in one embodiment, the method of the invention provides an electron beam sterilized PEBAX balloon with a sufficiently high rupture pressure and fatigue resistance, and without requiring an increase in the balloon wall thickness to maintain the rupture pressure and fatigue resistance of the balloon. A catheter balloon of the invention typically has a wall thickness of about 0.0005 to about 0.001 inches (about 0.013 to about 0.03 mm) for a 3.0 mm nominal outer diameter balloon, and a wall thickness of about 0.0008 to about 0.0015 inches (about 0.02 to about 0.04 mm) for a 5.0 mm nominal outer diameter balloon. Similarly, other medical device components sterilized by the method of the invention may be formed of PEBAX or fluoropolymers. For example, in one embodiment, a fluoropolymer such as polytetrafluoroethylene (TEFLON) or polyvinylidiene fluoride (PVDF) forms the catheter shaft, or a layer such as an inner lubricious liner of the catheter shaft, and the method of the invention provides for electron beam sterilization of the shaft without significant degradation of the fluoropolymer. Expanded polytetrafluoroethylene (ePTFE) fluoropolymer will degrade to a lesser degree when electron beam sterilized in the absence of air/oxygen according to the method of the invention, than when electron beam sterilized in the presence of air. [0012] A balloon catheter sterilized according to a method of the invention generally comprises an elongated shaft having a proximal end, a distal end, and an inflation lumen therein, with the balloon secured to a distal shaft section and having an interior in fluid communication with the inflation lumen. The balloon catheter can be used for a variety of applications including PTCA, peripheral angioplasty, stent delivery, arid the like. [0013] The sterilization method of the invention avoids significant degradation of the polymeric material of the medical device component, as a result of sterilizing the medical device component in an evacuated or inert gas-filled container. Consequently, the method provides a sterilized medical device component such as a catheter balloon having a sufficiently high rupture pressure, without requiring an increase in the wall thickness of the balloon. The method thus provides for improved manufacturability of the balloon catheter, and a balloon catheter having excellent performance characteristics such as low profile and flexibility, for excellent trackability, and a desired rupture pressure and fatigue resistance. These and other advantages of the invention will become more apparent from the following detailed description and accompanying exemplary drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 is an elevational view, partially in section, of a balloon catheter for delivering a stent, having a balloon sterilized according to a method that embodies features of the invention. [0015] FIG. 2 is a transverse cross-section of the catheter shown in FIG. 1, taken at line 2-2. [0016] FIG. 3 is a transverse cross-section of the catheter shown in FIG. 1, taken at line 3-3. [0017] FIG. 4 illustrates a balloon catheter in a container during electron beam sterilization according to a method which embodies features of the invention. [0018] FIG. 5 illustrates a stent cover or vascular graft sterilized according to a method that embodies features of the invention. [0019] FIG. 6 is a transverse cross-section of the stent cover or vascular graft shown in FIG. 5, taken at line 6-6. DETAILED DESCRIPTION OF THE INVENTION [0020] FIG. 1 illustrates an over-the-wire type stent delivery balloon catheter 10 embodying features of the invention. Catheter 10 generally comprises an elongated catheter shaft 11 having a proximal end 12, a distal end 13, and an inflatable balloon 14 on a distal shaft section. An expandable stent 16 is mounted on balloon 14 for implanting in the patient's body lumen 18. In the embodiment illustrated in FIG. 1, the shaft 11 comprises an outer tubular member 19 and an inner tubular member 20. As best shown in FIGS. 2 and 3, illustrating transverse cross sections of the catheter 10 shown in FIG. 1, taken along lines 2-2 and 3-3, respectively, outer tubular member 19 defines an inflation lumen 21, and inner tubular member 20 disposed within the outer tubular member lumen 21 defines a guidewire lumen 22 configured to slidingly receive a guidewire 23. Inflatable balloon 14 is disposed on a distal section of catheter shaft 12, having a proximal end sealingly secured to the distal end of outer tubular member 19 and a distal end sealingly secured to the distal end of inner tubular member 20, so that its interior is in fluid communication with inflation lumen 21. An adapter 24 at the proximal end of catheter shaft 11 is configured to provide access to guidewire lumen 22 and to direct inflation fluid through arm 26 into inflation lumen 21. The distal end of catheter may be advanced to a desired region of a patient's body lumen 18 in a conventional manner and balloon 14 inflated to expand stent 16. The catheter 10 is withdrawn after deflating the balloon 14, leaving the implanted stent 16 in the body lumen 18. Continue reading about Method of sterilizing a medical device... Full patent description for Method of sterilizing a medical device Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of sterilizing a medical device patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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