US 6979420 B2
An apparatus for molding balloon catheters is disclosed. The balloon may be molded by providing a polymeric tube within a mold having an interior cavity in the shape of the desired balloon. Microwave energy, which may be generated by a gyrotron, may then be directed toward the mold, to heat the polymeric material without heating the mold. Once heated, pressurized fluid may be injected into the tube to blow the polymeric material against the interior cavity whereupon the material can cool to form the balloon or can be further heatset by additional microwave energy and be cooled to form the balloon.
1. A method of molding balloon catheters, comprising:
positioning a parison within a mold, the mold having an interior cavity for forming a balloon;
heating the parison using microwave energy for forming the balloon, the microwave energy being generated by a gyrotron;
monitoring the temperature of the parison and adjusting the power of gyrotron based on the measured temperature; and
directing fluid pressure into an interior of the parison when the parison reaches a predetermined temperature level, the fluid pressure expanding the parison into the interior cavity of the mold to form the balloon.
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16. A method of molding balloon catheters, comprising:
providing a parison of polymeric material;
subjecting the parison to microwave radiation generated by a gyrotron and being transmitted to the parison by way of at least two optical lenses comprising a focusing lens and a scanning lens;
monitoring the temperature of the parison;
injecting fluid pressure into the parison upon the temperature of the parison reaching a predetermined level to form a balloon; and
cooling the balloon.
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The disclosure generally relates to balloon catheters and, more particularly, relates to methods of manufacturing balloon catheters.
Angioplasty is an effective medical procedure performed to expand constricted sections of blood vessels. In such a procedure, an angioplasty balloon or balloon catheter is navigated to the site of the constriction. The balloon is inflated upon reaching the site, by way of fluid pressure injected into the balloon, to thereby expand its dimension. The expansion of the balloon exerts pressure on the vessel walls to thereby widen the vessel and alleviate constriction to blood flow.
Conventionally, such balloons are manufactured from a polymeric material and are molded in a blow molding procedure. More specifically, a cylinder or tube of polymeric material, known as a parison, is placed within a mold having an interior cavity in the desired shape of the balloon. The mold is then heated, with the heat of the mold being conducted to the parison, such that upon introduction of fluid pressure into the parison the polymeric material deforms into the shape of the mold cavity. The mold is then cooled to cause the polymeric material to harden into the shape of the mold.
Typically, the mold is provided in a clam shell design wherein each half of the mold includes half of the interior cavity forming the balloon. The mold can therefore be wrapped around the parison and easily removed to facilitate production. The parison itself can be heated by immersing the entire mold within a hot water, oil, glycerin or other fluid bath and allowing the mold and parison to be heated via conduction. One problem associated with such a process is that heating of the parison is less than optimal. Heating via conduction, by its very nature, is a relatively slow process. Moreover, the tubular shape of the parison lends itself toward a substantial heat flow axially along the parison which itself tends to heat portions of the polymeric material at which balloon deformation is not desired. Accordingly, such systems typically need to employ some sort of cooling mechanism, such as a cold air jet, to keep the areas of the parison, outside of the mold, cool. One problem stemming from such a system is that temperature control or distribution across the entire polymeric tube is difficult. For bigger balloon sizes, in which the gap between the polymeric tube and mold wall is too large to give sufficiently fast transfer of heat, small amounts of water are often injected inside the mold between the parison and the mold for better heat conduction.
Moreover, with such conventional systems, it is not possible to heat different axial sections of the polymeric tube to different temperatures. For example, this may be advantageous when it is desired to create different physical properties within the balloon itself such as multiple areas of varying diameter, wall thickness, or multiple areas consisting of different materials to be heated to different temperatures. Although a section of the mold can be kept above the fluid bath, having the effect of a cooler section in the mold, still because of the slow heating process, a sharp temperature transition is not possible. It is also not possible to set the metal mold to a different temperature than that to which the polymeric tube is heated. The mold must therefore be cooled down before the balloon can be removed.
In accordance with one aspect of the disclosure, a method of molding balloon catheters is provided which comprises the steps of positioning a cylinder of polymeric material within a mold, the mold having an interior cavity, heating the cylinder of polymeric material using microwave energy, and injecting fluid pressure into an interior of the cylinder of polymeric material with the fluid pressure expanding the cylinder into the interior cavity of the mold.
In accordance with another aspect of the disclosure, a balloon catheter molding apparatus is provided which comprises a microwave source, a mold, and a fluid pressure source. The microwave source is adapted to emit a microwave band, while the mold is positioned proximate to the microwave band. The fluid pressure source is operatively associated with the mold and adapted to direct pressurized fluid through a polymer tube positioned within the mold.
In accordance with another aspect of the disclosure, a balloon catheter molding apparatus is provided which comprises a gyrotron, a mold, a waveguide, and at least one lens. The gyrotron is adapted to generate microwave radiation, while the mold includes a cavity adapted to receive a parison. The waveguide is positioned to transmit the microwave radiation from the gyrotron to the mold. The lens is adapted to focus the microwave radiation onto the mold.
These and other aspects and features of the disclosure will become more apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings.
While the disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the disclosure to the specific examples disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined by the appended claims.
Referring now to the drawings, and with specific reference to
Referring again to
Referring now to
Preferably, the mold 24 is manufactured from a microwave-transparent material having a low dielectric loss characteristic, such as a ceramic material or quartz material, although many other types of non-metallic materials, including but not limited to Teflon®, or boron nitride, can be employed with similar efficacy. If the mold 24 is made of Teflon®, for example, or another microwave transparent material that is a poor thermal conductor, application of the microwave beam will allow the temperature of the balloon to be raised to the heatset temperature by applying further microwave energy after the balloon has been blown.
With regard to the microwave source 22, it may be provided in the form of a gyrotron adapted to emit microwave energy at a frequency within the range of 10 gigahertz to 110 gigahertz, and a wavelength within the range of 2.7 mm to 30 mm. As shown in
For example, using a magnetron injection-type electron gun with the cathode 54 potential at ten kilovolts and a magnetic field 59 of twelve Tesla will result in the electrons being gyrated in a spiral with a radius of 30 micrometers and a cyclotron frequency of 330 GHz. Changing the magnetic field 59 enables the frequency to be changed accordingly. In order to obtain a high frequency wave, the resonant cavity should be designed in such a way that its geometric size matches a harmonic of the wavelengths created by the gyrating electrons. The electromagnetics transmitted through the radio frequency (RF) window 62, and by means of a waveguide 63, can be transported to the target. Manufacturers of gyrotron systems deliver such gyrotrons with built-in mode converters to convert the beam to a gaussian-shaped He11 mode, which can be guided through a circular wave guide with low loss. For example, Insight Product Company of Brighton, Mass. provides such a system. The He11 mode radiated from an open-ended circular waveguide has an axisymmetric narrow Gaussian beam with well-defined polarization and direction, and low-side lobe level enabling the use of simple optical components like metal mirrors and HDPe lenses to focus the beam on a target.
With regard to the power level required to heat the workpiece 36, if the parison is manufactured of Pebax®, in order to bring the workpiece 36 from room temperature to 140° Celsius, and be able to blow a balloon, the required energy can be calculated according to the following. By way of example only, a typical parison tube can be, for example, 1 mm in an outer diameter, and 0.6 mm in the inner diameter, and have a length of 32 mm. The volume of such a tube therefore is 12.8 cubic mm. Taking a CP value of 1500 Joules per kilogram degree Celsius and a density of 1.1 grams/cm3, this means that 2.54 Joules are required to heat the parison from room temperature to 140° Celsius. A commercial low power gyrotron, for example, that manufactured by Insight Product Co., which offers a 24 GHz continuous wave gyrotron with the output power being continuously regulated in the range of 0.1–3 kW by varying the electron beam voltage, up to a maximum of 12 kV, can be defocused roughly to its wavelength, i. e., 12 mm. Therefore when the parison is placed in the focus of the beam about 1/12 of the beam will hit the target. Assuming a 50% absorption of the energy, this means that at 0.1 kW CW output power, it will take about 2.54 Joules/(100 (Joules))/24)=0.6 seconds to heat the parison.
Referring again to
To control the power output of the gyrotron the pulse links of the input voltage on the cathode 54 could be adjusted. By doing so, it would be possible to, for example, operate a 10 kilowatt gyrotron at an average power level of 5 watts or even lower. If the end temperature should be controlled within plus or minus 2° F., the rise of the temperature should be less than 2° for every pulse in between the sensor readings. Therefore, there should be at least 60 readings in between 20 and 140° Celsius assuming a constant absorption coefficient of the polymer material as a function of the temperature. The update frequency of the Heitronics IR sensor is 200 Hz. Taking the earlier calculated 0.6 seconds to rise the parison 120° Celsius into account, which is 200° Celsius per second, and assuming for the time being a simplistic model of a linear rise, reading the IR sensor at 200 Hz will result in an accuracy of 1° Celsius. This demonstrates that it is not unrealistic with existing equipment and sensors to realize a control temperature rise in the parison to 140° Celsius with a precision of ±2° within less than 2 seconds.
In an alternative embodiment, the gyrotron beam could be defocused so that only a small percentage of the beam impinges upon the sample. For example, this could be done using a cylindrical lens. In so doing, a much smaller temperature rise could be achieved and the gyrotron could be stopped once the required temperature is reached. Similarly, the current of the cathode could be reduced thereby reducing the output power of the gyrotron. In a still further embodiment, use of a power splitter such as a polarizing splitter could be used to enable a 50/50 power split. Three of these such splitters in series would enable the power level to be reduced to 12.5%. One could also use the 50/50 splitting operation to do multiple balloon blowing at the same time. Defocusing the laser beam would also allow to heat multiple parisons at the same time.
In order to focus the microwave output upon the workpiece 36 and provide an even heating profile across the balloon 34, the embodiments depicted in
Alternatively, the beam could be scanned along a part of the tube to achieve a more uniform temperature distribution. This can be done by focusing the beam on a mirror which makes an angle, e. g., 45°, with the optical axis and which rotates around that optical axis as shown in
As shown in
Turning now to
Based on the foregoing, one of ordinary skill in the art will readily understand that the teachings of this disclosure can be employed to create a system for effectively and quickly molding medical devices such as balloon catheters.
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