Electric heating – Metal heating – By arc
Reexamination Certificate
1999-02-09
2001-08-21
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
By arc
C219S121690, C623S001210, C623S001210
Reexamination Certificate
active
06278079
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention is related to methods and apparatus for forming a tubular prosthesis, and more specifically, to methods and apparatus for laser cutting a tubular fabric graft.
2. Description of the Related Art
Stents and vascular grafts of various designs are known for the treatment of aneurysms as well as for the treatment of occlusive diseases of the blood vessels or other ducts. A common type of tubular prosthesis includes a graft made of a biocompatible material having mechanical properties that can withstand varying internal pressures. The graft may be supported by an internal or external stent, or by a plurality of expandable circular wires. One such wire-supported intraluminal graft is disclosed in U.S. Pat. No. 5,782,904, issued Jul. 21, 1998.
Many grafts of the prior art, such as in the '904 patent, are made of porous textile material, usually a crimped or resiliently circular-knitted stocking of polymerized ethylene-glycol-terephthalate (Dacron™). Such textile grafts must often be treated blood, or “pre-clotted,” before they are implanted to improve initial leak-resistance and biocompatibility. In recent years, vascular grafts have been made of expanded polytetrafluoroethylene (PTFE) possessing a porosity and flexibility such that no pre-treatment with blood is necessary.
In general, tubular grafts and their respective support and/or attachment means fall into two major categories, self-expanding and pressure expandable. Self-expanding intraluminal tubular prostheses include grafts supported and/or attached via resilient or shape-memory material such as spring steel or Nitinol™. Self-expanding material is capable of being formed in a configuration from which it may be compressed to a radially compact diameter for placement within a damaged vessel. At the time of use, the memory feature of these materials causes them to self-expand from the radially compact diameter to the expanded operative diameter.
Pressure-expandable tubular prostheses include grafts supported and/or attached via plastically deformable material such as stainless steel that is initially formed in its radially compact diameter. This type of material does not have memory, and will remain in the radially compact diameter until manually expanded. Typically, outwardly directed pressure is exerted upon the prosthesis through use of a balloon so as to cause radial expansion and resultant plastic deformation of the material to its operative diameter.
If individual circular wires are used as opposed to a cylindrical stent, consideration must be given to the attachment means between the wires and tubular graft such that uniform and durable support is provided. Some designs stitch the wires to the exterior of the tubular graft. This stitching may ultimately fail, however, and more importantly the support provided to the tube may be inadequate, especially when high negative pressures are present within the lumen of the tube. U.S. Pat. No. 5,782,904 describes the use of thin, stainless-steel undulating wires that are woven through the fabric of the tube such that spaced segments of each wire are outside the tube with the remainder of that wire inside the tube. In this manner, fairly even support is provided to withstand varying pressures in the lumen of the tube. One drawback, however, is the time-intensive nature of weaving a plurality of undulating wires in specific locations along the tube. The weave pattern must be laboriously pre-marked on the outside of the tube. The assembly process is made even more complex if the graft is branched, such as a bifurcated or so-called “trouser graft.”
In the prior art processes for forming grafts, tubular lengths of fabric or PTFE material are cut to individual graft lengths using a heated cautery wire. Shears or other mechanical cutters are unsuitable for fabric grafts because the cut ends tend to fray. The use of a heated wire, however, creates difficulties such as fumes and excessive melting of the material, and is also fairly time-consuming and imprecise.
Lasers are often used for cutting textile material for garments and sailcloth, for example. Examples of the use of lasers in the textile industry can be seen in U.S. Pat. Nos. 4,588,871, 5,200,592, and 5,614,115. However, lasers have not been used for forming grafts, although they have been employed to perforate material for bioprosthetic applications. For instance, U.S. Pat. No. 5,326,356 discloses using a laser to render biocompatible material porous for use in skin grafts, and U.S. Pat. No. 4,729,766 discloses using a laser to form indentations in the exterior surface of an otherwise impermeable tube to encourage tissue ingrowth. In another example, U.S. Pat. No. 5,628,782 discloses the use of a laser to macroscopically perforate an outer tube for covering a fiber-wrapped vascular graft. In all these examples, the goal is to render an otherwise impermeable material porous.
Despite many advances in the field of tubular grafts, there remains a need for an improve method of forming such grafts, and in particular a need to shorten and automate the process for forming which will produce more uniform, and more efficacious, grafts.
SUMMARY OF THE INVENTION
The present invention provides a method of forming a tubular prosthesis including the steps of providing a tube of biocompatible material and fitting the tube on a rotatable mandrel. A laser is directed onto the tube, the laser having sufficient power to cut through the material without excessive melting or burning of the material. A graft portion of the prosthesis is formed from the tube, and a plurality of spaced holes are formed around the circumference of the graft. The graft is then removed from the mandrel, and at least one support wire is weaved through the spaced holes and around the circumference of the graft. In one embodiment, the material is a fabric and the laser is a low-powered, sealed, RF-excited laser operated so as to cut through the fabric material and fuse the cut ends without excessively melting or discoloring the material. In one embodiment, the laser is focused to have a nominal beam width of approximately 0.152 mm (0.006 inches), and the holes formed thereby are between 0.178 mm (0.007 inches) and 0.229 mm (0.009 inches). Preferably, the laser is a CO2 laser, and emits light energy in the infra-red spectrum.
The method may be used for straight grafts, or bifurcated grafts. If bifurcated grafts are being formed, the mandrel comprises a trunk portion and a pair of detachable leg portions. In a first step in the process, the trunk portion is rotated concentrically and the spaced holes are formed in the trunk portion of the graft. Subsequently, the mandrel is reconfigured so that one of the legs rotates concentrically, with the trunk portion rotating off-center, and one of the graft legs is cut to size. By repositioning the graft on the mandrel, the other of the graft legs is cut to size.
The present invention also provides a system for forming bioprosthetic trouser grafts, comprising a frame having a cutting instrument mounted for linear motion thereon. An elongated graft-supporting mandrel is provided including a trunk portion and a pair of removable leg portions. The system includes a rotatable chuck and associated secondary support spaced therefrom, both adapted to be fixed with respect to the frame. The chuck and secondary support are configured to rotate the mandrel therebetween about an axis parallel to and adjacent the linearly movable cutting instrument. The chuck and secondary support are preferably mounted for linear motion on a rail fixed with respect to the frame. The cutting instrument preferably comprises a low-powered, sealed, RF-excited laser positioned to direct a beam of light energy onto the generatrix of the mandrel facing the cutting instrument.
In another aspect, the present invention provides a mandrel kit for forming bifurcated grafts. The kit includes a generally cylindrical trunk portion having a first and a second end. A pair of leg portions removably a
Bye Matthew R.
McIntyre John P.
Cumberbatch Guy L.
Edwards Lifesciences Corp.
Edwards Lifesciences LLC
Gluck Peter Jon
Johnson Jonathan
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