Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – Local application of electrolyte
Reexamination Certificate
2001-09-13
2003-12-16
Nguyen, Nam (Department: 1753)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
Local application of electrolyte
C205S640000, C205S672000, C205S686000, C204S212000, C204S22400M, C204S22400M, C204S275100, C204S297100, C204S297060, C128S898000, C623S001200, C623S901000, C623S902000, C623S903000, C623S909000
Reexamination Certificate
active
06663765
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the manufacture of expandable cylindrical metal meshes for use in expandable stents and in particular to the customized manufacture of expandable metal stents.
BACKGROUND OF THE INVENTION
A cardiologist performing a stent implant procedure requires several stents of various geometrical shapes and lengths in order to be able to quickly choose an optimal stent during the surgery. Depending on the location and degree of damage being repaired, the cardiologist may need as many as eight different pattern stents with lengths ranging from about 6 mm to about 40 mm. During surgery, the cardiologist may have as little as five minutes to select the proper stent. Therefore, hospitals and clinics performing these procedures generally have a substantial number of stents on hand, perhaps as many as 40 or more, for use with a single patient. Given the relatively high cost of stents and their consumption, hospital and clinic expenditures on such operations may be substantial. As a result, many hospitals and clinics without adequate financial resources do not perform surgical procedures involving stent implantation.
There exists, therefore, a need for a system that reduces the number of costly stents required during surgical procedures by allowing a surgeon or clinic staff to select and fabricate a custom stent during a surgical procedure and within a short period of time.
Methods that have previously been used to manufacture stents are described in U.S. Pat. Nos. 4,856,516, 4,907,336, 5,116,365, 5,135,536, and 5,707,386. Stents produced by the methods disclosed therein contain bent wires that are knotted, which introduces stresses into the metal and decreases the quality of the stents. Moreover, these stents are not generally suitable for curved portions of blood vessels. More importantly, these methods only produce stents with a configuration that is tailored to a specific surgical instrument, limiting their usefulness. Other methods that have been used to manufacture stents are described in U.S. Pat. Nos. 5,725,548 and 5,907,893. Stents produced by the methods disclosed therein are joined along a line longitudinal to the length of the stent and then welded. However, at the high temperatures required to weld these joints, the crystalline structure of the metal can be affected and thereby reduce the reliability and strength of the stent and its compatibility in a biochemical environment.
Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,383,896, 4,496,434, 5,030,329, 5,328,587 and 5,772,864. Stents produced by the methods disclosed therein are free from wire knots and welded joints. They are produced using an electrochemical process, which generally produces higher quality stents. However, the methods disclosed, most notably in U.S. Pat. No. 5,772,864, are complex and time consuming. For example, grooves outlining the stent must be etched on very small mandrels with instruments requiring precise control. Then, the cleaned mandrel must be dipped in an electrochemical bath containing a selected metal for up to approximately 12 hours. The stent material must then be carefully removed and further processed and polished. Because the entire process is costly and time consuming, it is not appropriate for use in a hospital or clinical setting during a shunting procedure.
Still other methods of manufacturing stents are described in U.S. Pat. Nos. 4,733,665, 4,776,337, 5,421,955 and 5,514,154. Stents produced by the methods disclosed therein are made using laser technology to directly carve the geometrical contours of stents on tubular blanks. Manufacturing of stents by these methods is associated with formation of sharp edges and burrs on the outside and inside surface of the stent. This can affect the structure of the stent, thereby reducing its reliability. This also requires additional processing to remove these undesirable features. Moreover, the cost and complexity of this technology can limit its use in hospital and clinical settings.
A solution to some of these problems is disclosed in U.S. Pat. No. 5,421,955, where laser technology is used to form a pattern on a mask material that is subsequently etched in an electrochemical process. However, this process requires complex instruments for precise laser control, an etching bath and solution, and extended processing time that may prohibit its use in a hospital or clinical setting.
A proposed solution to the above mentioned problems is disclosed in U.S. Pat. No. 5,902,475 in which much of the stent processing may be carried out prior to its use in a surgical procedure, with the final processing done in the hospital or clinical setting. For example, a tubular blank is coated with a photoresistive polymer over a photo film that contains a stent pattern. It is mounted on a rotatable tube and exposed to ultraviolet rays, thereby creating a negative image of the stent. The film is developed such that the illuminated lines solidify. The film is then placed in an electrochemical bath and the non-illuminated surfaces dissolve. The steps of blank mounting and removing can require up to a total of approximately six minutes to accomplish. The step of transferring and immersing the blank in the electrochemical tank can require up to approximately ten minutes. The step of electrochemically removing the non-illuminated areas can require up to approximately six minutes, with the final step of polishing/processing taking up to approximately 3 minutes. In total, the process described in U.S. Pat. No. 5,902,475 takes about thirty minutes, limiting its usefulness during surgical procedures. Moreover, this process requires, for certain applications, use of cathode made from platinum, gold or their alloys to withstand the strong acidic electrolyte solutions, phosphoric or sulfuric acid. Additional processing steps to prepare the stent for subsequent use may also be required. It is apparent that the additional expense and hazards associated with this method prohibit its use in hospital or clinical settings.
Stents produced by the methods described in U.S. Pat. Nos. 5,421,955, 5,772,864 and 5,902,475 rely on technology that prevents production of high quality stents. For example, the inner surface structure of the holes in the base stent tubes may be nonhomogeneous after the electrochemical treatment, e.g., includes sharp edges, protrusions, etc. Under certain conditions, the stent blank could become contaminated with impurities such as oxides or include other defects. Under these conditions, current supplied to the blank during processing would not be uniform. Further, an additional step is required to process the inner surface of the stent holes. Therefore, it would be desirable to apply the electric current to the external surface of the stent blank during processing rather than the inner surface.
Additionally, the known manufacturing methods may require the use of a diamond dust polishing tool to treat not only the external surface of the final stent but also the internal surface area. This additional step adds to the cost and complexity of the manufactured stent.
Accordingly, prior to the present invention, there have been no described methods of manufacturing stents: that allow surgical or clinical staff to fabricate custom stents as an integral part of the surgical procedure; that require relatively few complicated instruments or dangerous chemicals, that is relatively inexpensive; and that produces stents free from thermal stresses, sharp edges or surface irregularities.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method and device for manufacturing and implanting an expandable stent into a body lumen is carried out by electrochemically forming the expandable stent just prior to implantation. The electrochemical forming includes providing a cathode which includes a pattern for producing the stent; providing a tubular blank adjacent to the cathode; delivering an electrolyte between the cathode and the tubular blank; relative displacing the tubular blank and the c
Blank Rome LLP
Mutschler Brian L
Nguyen Nam
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