Patent Application
20050228428
This invention relates to balloons for medical devices such as balloon catheters, and also to manufacturing such balloons using a heating and stretching process that uses laser energy for the heating.
Balloon catheters are used to perform various medical procedures within the body. One example is a percutaneous transluminal coronary angioplasty (PTCA). To perform a PTCA, a physician guides a balloon catheter through the vascular system over a guide wire until the catheter's balloon is positioned across a thrombus, commonly referred to as a lesion, that has reduced or completely blocked blood flow through a vessel. Once placed, the balloon is inflated radially, or that is, outwardly, to a pre-determined diameter, for example 9 millimeters, to reestablish blood flow through the vessel.
To maneuver a distal end of the balloon catheter through the vascular system to treat a lesion that has a very small opening requires the balloon catheter to have a small crossing profile, which is the largest cross-sectional diameter of the balloon portion of the balloon catheter. One portion of the crossing profile is the diameter of the catheter's shaft, which must be large enough to allow a guide wire to pass freely through a guide wire lumen in the shaft in a longitudinal direction. Catheters that use a guide wire with a larger diameter will have a larger catheter shaft and vice-versa. Existing catheters typically use guide wires that have cross-sectional diameters in the range of fourteen thousandths of an inch (0.014) up to 35 thousandths of an inch (0.035). Smaller guide wires make it easier to maneuver the balloon catheter through the body. Consequently, many doctors that perform cardiac procedures prefer using balloon catheters with a 0.014 inch guide wire.
Another portion of a balloon catheter's crossing profile is the thickness of the folded balloon, particularly at the balloon's folded cone and waist portions. Catheter balloons typically have a body portion near the center of the balloon, which is the portion of the balloon that expands. The balloon's waist portions are located at the balloon's proximal and distal ends, and the cone portions are located between the balloon's body portion and the waist portions. Typically, the wall thickness of the entire balloon is restricted to the dimensions of the original tubing material, or parison, from which the balloon is formed. Thus, an overall reduction in the wall thickness of the parison to reduce the thickness of the cone and waist portions will also result in a similar reduction of the wall thickness of the parison in the body portion. A reduced body portion wall thickness, however, limits the diameter to which the balloon may be inflated while maintaining a satisfactory hoop strength, which is a measure of a balloon's ability to withstand internal pressure. Consequently, there have been continuing efforts to form balloons made of materials suitable for cardiac procedures, such as Nylon 12, PEBAX, PET, and PEEK, that have large inflation diameters, for example 9 millimeters, and small crossing profiles.
One method of forming balloons with body portions that have a greater wall thickness and waist portions that have a reduced wall thickness is to physically remove, or grind away, the undesired thickness of the waist portions. This method may be performed, for example, by using a laser ablation process utilizing UV excimer lasers or ultrashort lasers. The physical removal of the wall, however, has not been able to produce a balloon that has an inflation diameter of greater than six millimeters for use on a catheter having a 0.014 inch guide wire.
The wall thickness of a polymer tube may also be changed by a stretching, or “drawing down,” process. Using this process, the wall thickness of the tubing may be locally reduced in the cone and waist portions of the balloon. Heating is advantageous during the stretching process because polymers have certain thermophysical characteristics that cause them to soften and flow upon heating. Thus, with the use of heat, it is possible to target a specific portion of a polymer tube for stretching. Various heating methods are used to heat polymer tubes for stretching. These methods include passing a polymer tube through a heated ring and putting the tube in a hot oil or hot water bath. These methods, however, result in a large heating area and do not provide the ability to target small areas of the polymer tube for stretching. For example, the heating area of a heated ring is typically greater than five millimeters along the axial direction. The heating area of a hot oil or hot water bath is even greater. Thus, these methods that essentially provide heat from the outside of the tube are not suitable to vary the amount of stretching of a coronary balloon, which is typically one to two centimeters in length (the cone and waist portions being only a few millimeters in length). Moreover, it takes several seconds to change the amount of heat applied to the polymer tube using these methods.
The invention features balloons, catheters, and methods of manufacturing balloons for balloon catheters using lasers. The use of lasers for heating allows small areas of a polymer tube to be targeted for stretching. Lasers also allow the heat to be delivered uniformly throughout the bulk of the polymer tube instead of relying on heat conductivity from the tube's outer layers. In addition, lasers provide the ability to instantaneously change the amount of heat applied during the process to precisely vary the amount of stretching in the various portions of the polymer tube. The ability to instantaneously change the heat provided during stretching also allows the molecular orientation of the balloon to be varied throughout its length.
In one aspect, the invention features a method of manufacturing a balloon for a balloon catheter. The method includes heating and longitudinally stretching a first portion of an elongate polymer to form a first reduced diameter portion of the tube that serves as a first end portion for the balloon. A second portion of the tube is heated and longitudinally stretched to form a second reduced diameter portion of the tube that serves as a second end portion for the balloon that is opposite the first end portion. A body portion located between the first and second end portions is expanded radially to form the balloon.
In embodiments, the heating of the first and second portions may be performed by a laser, which may emit a beam in the infrared frequency range to heat the first and second portions. In some implementations, the elongate polymeric tube may have a uniform diameter before the method is performed.
The balloon may have an inflatable body portion with sufficient hoop strength for use in an angioplasty procedure. The inflated outer diameter of the balloon may be more than about six millimeters, for example, about 9 millimeters. In implementations where the first end portion of the balloon includes a first waist section and the second end portion of the balloon includes a second waist section, the first and second waist sections may have an inner diameter such that the balloon may be affixed to a catheter shaft that has an inner lumen sized appropriately to accommodate a guide wire having a diameter of at most about 0.014 inches. The first and second waist sections may have an inner diameter that is, for example, no more than 0.028 inches. In some implementations, the formed balloon may have an inflatable body portion that has a longitudinal length suitable for use in an angioplasty procedure. In other implementations, the inflatable body portion of the balloon may have a longitudinal length of no more than about 30 millimeters.
In another aspect, the invention also features a catheter that includes an elongate shaft having a lumen that extends longitudinally through the shaft. The lumen is sized appropriately to accommodate a guide wire having a diameter of at most about 0.014 inches. An inflatable polymeric balloon is affixed circumferentially about the shaft near the distal end of the shaft, and has an inflated outer diameter of more than about 6 millimeters.
In embodiments, the balloon may be formed by heating and longitudinally stretching a first portion of an elongate polymeric tube to form a first reduced diameter portion of the tube that serves as a first end portion for the balloon, and heating and longitudinally stretching a second portion of the tube to form a second reduced diameter portion of the tube that serves as a second end portion for the balloon that is opposite the first end portion. A body portion located between the first and second end portions may be expanded radially to form the balloon. In some implementations, before the balloon is formed, the elongate polymeric tube has a uniform diameter. The heating of the first and second portions may be performed by a laser, which may emit a beam in the infrared frequency range to heat the first and second portions.
In some embodiments, the balloon's body portion may have an inflated outer diameter of 9 millimeters and may be suitable for use in an angioplasty procedure. The balloon may have a first end portion that includes a first waist section and a second end portion that includes a second waist section. The first and second waist sections may have an inner diameter of no more than about 0.028 inches.
In another aspect, the invention features an inflatable polymeric balloon for a balloon catheter. The balloon includes a waist portion having an inner diameter that fits circumferentially around and is affixable to an elongate shaft that has an inner lumen sized appropriately to accommodate a guide wire having a diameter of at most about 0.014 inches. The balloon's body portion has an inflated outer diameter, the ratio of the outer diameter of the body portion to the inner diameter of the waist portion being at least 12.5 to 1.
In embodiments, the balloon may be formed by heating and longitudinally stretching a portion of an elongate polymeric tube. The polymeric tube from which the balloon is formed may have a uniform diameter before the heating and stretching. The heating of the tube may be performed by a laser, which may emit a beam in the infrared frequency range. In some embodiments, the inner diameter of the waist portion may be about 0.028 inches or less. The balloon may also have an inflated outer diameter of more than about 6 millimeters, for example, about 9 millimeters. Further, the balloon may have an inflatable body portion with sufficient hoop strength for use in an angioplasty procedure.
In another aspect, the invention features a method of processing an elongate polymeric material for use in a medical device that is placed inside a body. The method involves heating a portion of the polymeric material with a laser while longitudinally stretching the portion of the polymeric material.
In embodiments, the laser may emit a beam in the infrared frequency range to heat the polymeric material, which may be Nylon 12, PEBAX, PET, or PEEK. The laser may have a heating area of approximately two millimeters or less. The method may also include cooling the heated portion of the polymeric material after it has been longitudinally stretched to the desired dimension. A control system may be used to control the heating and stretching of the polymeric material.
In another aspect, the invention features an inflatable balloon for a balloon catheter constructed of a single polymeric material and having first and second regions. The polymeric material in the first section is oriented in a fashion that results from the balloon's body portion being stretched while being heated by a laser. The polymeric material in the second region is oriented differently from the first region.
In embodiments, the balloon may have an inflatable body portion that has a longitudinal length suitable for use in an angioplasty procedure. In other implementations, the balloon may have a longitudinal length of at most about 30 millimeters. The laser may emit a beam in the infrared frequency range to heat the polymeric material, which may be Nylon 12, PEBAX, PET, or PEEK.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
In this example, it will be appreciated that a leading portion 24 of the tube 10 located between the tube's leading end 26 and the target portion 22 has already been heated and stretched, whereas a trailing portion 20 of the tube 10 located between the tube's target portion 22 and the unwinding spool 12 has not yet been heated and stretched. Therefore, the leading portion 24 of the tube 10 is shown to have a smaller cross-sectional diameter than that of the tube's trailing portion 20.
A temperature sensor 28 is positioned to sense the temperature of the tube's target portion 22 as it is heated by lasers 16 and 17. An optical filter (not shown) may be placed between the temperature sensor 28 and the lasers 16 and 17 to eliminate reflection from the lasers 16 and 17 into the sensor 28. A diameter sensor 30 is positioned to sense the diameter of the tube 10 at a portion of the tube 10 that has most recently been stretched. In this example, the diameter sensor 30 senses the diameter at a portion of the tube's leading portion 24 that is near the target portion 22. The system also includes a tension sensor 34 to measure the tension in the tube 10 caused by the difference in the pulling speed of the winding system 14 and the speed at which the tube 10 is provided by the unwinding spool 12. A cooling device 32 is positioned to cool a heated and stretched portion of the tube's leading portion 24. The cooling of the heated portion of the tube 24 may prevent the tube 24 from stretching beyond a desired range as the longitudinal force continues to be applied to the tube 24 by the winding system 14 during the stretching process. The cooling device 32 may be placed distal to the sensors 28 and 30, as shown in
A controller 36 is connected to the temperature sensor 28, the diameter sensor 30, and the tension sensor 34. The controller receives the temperature readings of the heated portion 22 of the tube 10 from the temperature sensor 28, cross-sectional diameter readings from the diameter sensor 30, and tension readings from the tension 34 sensor. The controller is also connected to the unwinding spool 12, the winding system 14, the lasers 16 and 17, and the cooling device 32 to control the operation of each. Thus, the entire processing of the polymer tube 10 to reduce the diameter of selected portions of the tube 10 may be under computer control with feedback.
In the
The laser beams 18 may have a heating area that can range from as small as a micron to as much as a centimeter and may be expanded or reduced in precise amounts throughout the stretching process. By changing the heating area of the laser beams 18, the size of the tube's target portion 22 may be varied during the stretching process. Further control of the stretching process may be provided by changing the heat intensity of the laser beams emitted by the lasers 16 and 17. Increasing the heat intensity of the laser beams 18 will cause greater softening and greater longitudinal stretching of the polymer tube 10, assuming a constant longitudinal force is being applied by the winding system 14. Likewise, lowering the heat intensity of the laser beams 18 will result in less softening and thus less stretching.
The ability to vary the heat intensity of the laser beams 18 may also be used to change the molecular orientation, and thus the physical characteristics, of the polymer tube 10. For example, if the polymer tube 10 is stretched under elevated temperatures (a hot stretch), the stretched tube 10 will have a lower molecular orientation and will be more elastic. If the polymer tube 10 is stretched after little or no heating (a cold stretch), the stretched tube 10 will have a high molecular orientation and will be more stiff.
The winding spool system 14 may include conventional linear motor to control the pulling force applied to the tube 10. In other examples, a clamp, jaw, or other suitable mechanism may be used to create the pulling force on the tube 10. Alternatively, the winding spool could be a pulley system through which the tube 10 is passed and placed in a vertical alignment. A dead weight may then be secured to the tube's leading end 26 to stretch the tube 10. In other implementations, the unwinding spool and motion system 12 may be replaced with another pulling device similar to winding system 14. For example, the unwinding spool may be a linear motor that can feed the polymer tube 10 to the lasers 16 and 17 for heating. In a system where the unwinding system 12 and winding system 14 both include linear motors, the polymer tube 10 may be stretched from either direction, or both directions, by changing the direction and relative speeds of the linear motors. Alternatively, the unwinding and winding systems 12 and 14 could include two clamps to stretch the tube 10. Clamps may be particularly useful when only a small length of polymer tube 10 is being processed by the system, such as a parison for making a balloon.
The controller 36, which is connected to the unwinding system 18, winding system 20, and the lasers 16 and 17, may be used to precisely control the polymer tube's cross-sectional diameter and molecular orientation. The controller 36 may also be used to control the speed of the overall stretching process. For example, by controlling the rate at which the polymer tube 10 is released from the unwinding system 12, it is possible to control the heat intensity and heating area of the lasers 16 and 17, and the speed and longitudinal force applied by the winding system 14. The controller 36 may also cool the heated portion of the tube's leading end 24 with the cooling device 32. The cooling device may be a nozzle that emits super-cooled nitrogen, or another suitable fluid. Alternatively, the cooling device may be a liquid or oil bath through which the leading end 24 of the tube may pass after it is heated and stretched. In other implementations, the cooling device 32 may be omitted.
The controller 36 may further control the stretching process with feedback provided by the temperature sensor 28, the diameter sensor 30, and the tension sensor 34. The temperature sensor 28 may be an infra-red sensor, thermistor, or other suitable type of sensor. Feedback provided to the controller 36 by the temperature sensor may allow the controller 36 to continually adjust the intensity of the heat provided by the lasers 16 and 17. The diameter sensor 30 may measure the cross-sectional diameter of the polymer tube 10 ultrasonically, optically, or some other technique. Feedback may be provided to the controller through the sensor 28 to allow the controller to continually adjust the parameters of the stretching process. The tension sensor may be of a conventional three-roller or on-line sensor. Alternatively, the tension sensor 34 may be a torque sensor that is built into the control systems of most modern motion control systems. For example, in implementations where the winding system 14 is a servo motor, the motor may include a torque sensor that allows the torque of the motor, and thus the longitudinal force applied to the tube 10, to be changed throughout the process. In other implementations, the positions of the sensors 28, 30, and 34 may be changed. Yet in other implementations, the sensors 28, 30, and 34 may be omitted.
Referring to
Once the tube's target portion has been heated to the desired temperature, shown at data point 206, the velocity of the winding system is increased and the velocity of the unwinding system is decreased to apply a longitudinal force to the tube and stretch the tube's target portion. A constant force is applied by the pulling of the winding system using feedback from the tension sensor (shown in
As the method is applied to subsequent portions of the tube, the controller may use the feedback provided by the diameter and tension sensors to further fine-tune the stretching process. For example, the diameter sensor may indicate the amount of reduction in the diameter of the tube's target portion based on the amount of tension applied by the winding system. Using the information provided by the amount of tension applied by the winding system may be varied to achieve the precise amount of stretching desired. Alternatively, feedback from the temperature sensor may be used to fine-tune the stretching process. Rather than adjusting the amount of tension applied by the winding system to vary the amount of stretching, the amount of stretching may be increased or decreased by the changing the amount of heat applied by the lasers, and thus, the temperature of the tube's target portion.
In the example of
Equilibrium may be achieved through the use of the controller 36 and the feedback provided by sensors 28, 30, and 34 (shown in
The process illustrated in
Now, turning to a more detailed description of the process,
The cone and waist sections 50 and 52 may be formed in a number of different ways using the heating and stretching method of
Next, referring to
In the example of
Once the parison 40 is formed to the configuration shown in
The catheter 100 includes an elongate shaft 103 that extends through the longitudinal center of the balloon 102. The balloon 102 has a proximal waist section 104, a body portion 106, and a distal waist section 108. A guide wire 110 extends longitudinally through a lumen in the catheter shaft 103 so that the catheter 100 may be guided through vessels in the body. The balloon may be constructed of Nylon 12, PET, PEBAX, PEEK, or a similar material.
In the
In the
The balloon also includes waist sections 104 and 108 that are typically welded to the catheter shaft 103 and secure the balloon 102 attaches to the catheter shaft 103 at the balloon's waist sections 104 and 108. The inner waist diameter is the inside diameter of the waist sections 104 and 108 of the balloon 102, and is slightly larger than the outer diameter of the catheter's shaft 103. In this example, the balloon may have an inner waist diameter (indicated by dimension B) that ranges from 0.022 inches, which is typical for a catheter using a 0.014″ guide wire, to 0.028 inches. In other examples, the inner diameter may be increased or decreased depending on the size of the catheter shaft 103. In an example where the inflated body portion 106 of the balloon 102 (dimension A) is seven millimeters and the inner waist diameter is 0.022 inches (dimension B), the ratio between these dimensions is approximately 12.5 to 1. In an example where the inflated diameter of the balloon is increased to 9 millimeters, the ratio increases to approximately 16.1 to 1. As the dimensions A and B either increase or decrease in other examples, the ratio between the inflated body portion 106 and the inner waist diameter may vary.
In the
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
