VASCULAR PROSTHESES APPARATUS AND METHOD OF MANUFACTURE

Abstract: A vascular prosthesis including a tubular material segment is protected against fraying, suture pullout or dilation by the inclusion of a thin-line binder that fuses or adheres to the surface of the thread fibers. Typically, the tubes are polyester or polytetrafluoroethylene and the thin-line binder is a polypropylene monofilament properly overlaid and then melted or softened in place. In a spirally crimped structure (10), which applies to many woven and knit structures, the monofilament (20) is laid into the root of the crimp (12). The root-to-crest dimension of the crimp (12) exceeds the thickness of the monofilament (20) or other thin-line binder, resulting in virtually no appearance or feel change of the structure (10) or modification of porosity. For knitted or other tubular substrates that are not spirally crimped, the thin-line binder is overlaid and attached in a helical, double helical or an axial pattern, preferably before crimping. The crimping pattern and the overlay pattern in such event are not related. The stabilizing by an appropriate thin-line binder of a tubular construction that is not crimped at all is also possible.

Description: VASCULAR PROSTHESES APPARATUS AND METHOD OF MANUFACTURE Background of the Invention This invention pertains to vascular prostheses and particularly to stabilizing vascular prostheses to render them non-fraying, resistant to suture pullout and resistant to dilation, all without otherwise damaging their other properties. Description of the Prior Art Vascular prostheses or grafts have been employed in vascular surgery for the replacement and by-pass of arteries for about 30 years. Such prostheses are generally tubular in shape; made of polyester, especially polyethylene terephthalate (e.g., DacrorP) or TeflorP, especially polytetrafluoroethylene, material; are either woven or knitted; and are crimped to provide resistance to kinking and to permit some elongation or stretching by the surgeon at the critical time of performing the surgery. Such tubular prostheses are constructed in several shapes, typically straight, bifurcated and tapered. A comprehensive review of vascular prostheses on the market is set forth in an article entitled "Designing Polyester Vascular Prostheses for the Future", M. W. King, R. G. Guidoin, K. R. Gunasekera and C. Gosselin, appearing in the Spring 1983 issue of Medical Progress Through Technology, pages 217-226, which article is incorporated herein for all purposes. Typical fabric constructions that are employed include a plain warp/weft interlaced weave, a plush weave known as a velour weave (wherein an extra thread or filament is included which is interlaced or "floats" over a plurality of threads in the opposite orientation or direction to add plushness to one or both the internal and external surface of the graft) and a knit (wherein single or multiple threads are interlaced with respect to themselves in a regular interlocking pattern) . The threads or filaments used in the construction of vascu¬ lar prostheses have been flat, texturized and single or multiple ply and have been round and trilobal in cross- section. Tube sizes for textile based artificial vascular grafts vary from about 4 mm internal diameter to about 35 mm. They vary in "porosity" (actually, in water permeability) from about 50-1500 ml/min/cm 2 for woven grafts and from about 1000-4000 ml/min/cm 2 for knitted grafts. The nominal wall thickness of the materials vary from about 0.5 mm to about 1.5 mm. Crimping dimension varies from about 2.0 mm for some knit grafts to a dimension under 0.5 mm for some woven grafts. Crimping is normally provided in a helix or spiral pattern or a circular pattern. The above is not necessarily all-inclusive, but covers a great percentage of the textile based artificial graft products currently on the market. Some vascular prostheses in the past have also included reinforcement spiral and circular rings or loops, particularly at locations where the anticipated use indicates a bend or turn in the tubular material, thereby subjecting the material to the danger of possible kinking or compression. Such rings or loops are slipped over the outside of the tube. They are usually of an appreciable dimension, on the order of 0.6-1.2 mm in diameter, and are applied as individual rings spaced along the length or as loops of a spiral wrap. They may or may not be permanently fixedly secured to the tube. The number of rings or spiral loops employed has no relation to the number of crimpings, there usually being only two or three rings or loops per linear inch of tube, whereas there may be a dozen or more crimps per linear inch. Such rings or loops employed in the past have been employed with respect to both crimped and uncrimped prostheses. The vascular prostheses employed in the past have had three related shortcomings. In use, the stock, which comes in relatively long lengths, are cut and trimmed for a particular application. When this is done, particularly when the end of the tubular material is cut on a bias, the end frequently frays. Related to this propensity to fraying just due to handling, is the particularly aggravating propensity to fray or pullout when the material is sutured near the cut end of the tube. Because of this propensity, surgeons do not suture as near to the ends as they would otherwise prefer. Finally, knitted grafts in the past have had a propensity to diliate or gradually open up or expand in one or more directions over a period of time. Such propensity can even result in hemorrhaging. Therefore, it is a feature of the present invention to provide an improved vascular prosthesis including a thin in-line binder secured to the interstices of the tubular segment to reduce the propensity , of the tubular segment from fraying, to increase the suture holding capability of the prosthesis and to virtually eliminate harmful dilation, all without appreciable loss in porosity handling. It is another feature of the present invention to provide an improved vascular prosthesis including an integrated external surface structure that reduces the fraying propensity of the tubular material without changing its external appearance or feel. It is still another feature of the present invention to provide an improved vascular prosthesis having a non-fraying structure over an appreciable length, usually over its entire length, so that the tubular material can be cut and trimmed at any location without resulting in end fraying. SUMMARY OF THE INVENTION A woven and spirally or helically crimped vascular prosthesis is provided in a preferred manufactur¬ ing procedure with a very thin polypropylene monofilament which is wrapped in the root of the crimps. The monofila¬ ment has a diameter less than the root-to-crest diameter of the material. It is heated at a temperature that is just enough to soften the monofilament without melting or burning the substrate or base tubular material,, the softened monofilament material fusing with the external surface fibers of the tubular material. Hence, the monofilament becomes an overlaid or integral thin-line binder. The external feel of the tube does not change since the monofilament is entirely confined within the helical groove of the crimp. Furthermore, the addition of the softened monofilament does not interfere with the elongation or the elasticity provided by the crimping nor does it appreciably affect the porosity. Alterna¬ tive means to a melted monofilament are also available to provide a similar non-fraying overlaid and involved structure, such as by spraying and by gluing. Other embodiments of the invention employ a thin-line binder that is not related to the crimping structure, which is particularly useful for tubular vascular grafts that are circularly crimped, rather than spirally crimped, which is often employed with knit grafts. Thin-line binders can be laid axially, helically or in a double helical pattern prior to crimping or with respect to a graft that is left uncrimped. In either of such cases the added thin-line binder is not confined to a crimp groove at all, but the dimension is small enough not to appreciably change the feel or appearance of the knitted surface. It should be noted that knitted and velour surfaces are usually more textured and porous than a woven surface, and, therefore, more forgiving in this regard. The monofilament can also be included as an integral part of the textile fabric. That is, one or more plys of the monofilament can be included in the plys of the yarn in weaving or knitting the material. In a woven structure, such ply or plys can be included in either or both the warp or weft (fill) yarn. Subse¬ quent heating will soften the onofilaments to cause them to bind to the substrate material, as described above with respect to an overlaid monofilament. BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above-recited features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular descrip¬ tion of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only preferred embodi¬ ments of the invention and are, therefore, not to be considered limiting of its scope for the invention may admit to other equally effective embodiments. In the Drawinσs: Fig. 1 is a side view of a straight tubular vascular prosthesis in accordance with a preferred embodiment of the present invention. Fig. 2 is a side view of the embodiment shown in Fig. 1 showing a bend. Fig. 3 is an oblique view of a tubular vascular prosthesis in accordance with the present invention being sutured. Fig. 4 is a close up view of a typical woven construction of a vascular prosthesis in accordance with an embodiment of the present invention prior to overlay¬ ing with a thin-line binder. Fig. 5 is a close up view of the vascular prosthesis shown in Fig. 4 following overlaying with a thin-line binder. Fig. 6 is a pictorial view showing a helical pattern for overlaying a thin-line binder on a vascular prosthesis in accordance with the present invention; Fig. 7 is a pictorial view showing a double helical pattern for overlaying a thin-line binder on a vascular prosthesis in accordance with the present invention. Fig. 8 is a pictorial view showing an axial pattern for overlaying a thin-line binder on a vascular prosthesis in accordance with the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Now referring to the drawings and first to Fig. 1, a tubular segment of a typical vascular prosthe¬ sis or graft 10 is shown. Such a segment can be part of a standard long tubular stock or can be a part of a more complex structure, such as a bifurcated or branched structure. When a tube or tubular segment, is referred to herein, it refers to any of such structures. The structure is crimped typically in a spiral fashion in connection with a woven structure at crimps 12, as shown. Although not critical to the invention, it is usual for there to be a dozen or so crimps per inch, which provides the tubular structure with the ability to be selectively elongated and bent, as required. Now referring to Fig. 2, the vascular prosthesis shown in Fig. 1 is illustrated in a bent configuration. Please note that the bending of prosthesis 10 does not result in kinking due to the crimping of the tubular material. Reference now is made to Fig. 4, which illustrates a typical woven pattern. The illustration is a magnified illustration of the actual filaments or individual plys employed in the respective thread bundles. It will be seen that each of warp thread bundle 14 comprises a plurality of individual thread filaments. The thread filaments are typically polyester threads, most notably polyethylene terephthalate, such as Dacron ® . Other polymers have also been employed, such as Teflon ® , especially polytetrafluoroethylene. Interlaced with the warp thread bundles just described are weft (i.e., fill) thread bundles 16 and overlapping bundles 18 similarly bundled from a plurality of indivi¬ dual filaments or plys. It should be noted that the thread structure illustrated in Fig. 4 is representative of structures used for vascular prostheses in general. Other common structures are plain woven structures (without an overlap thread bundle) and knitted structures, which utilize a single multiple thread bundle which interlaces on itself in a locking pattern. The knitted structures are not limited to one particular knit pattern, however. It should be further noted that the illustration of Fig. 4 is highly magnified. The mean filament diameter of a typical thread bundle used in the woven structure shown in Fig. 4 is 12-13 micrometers. Now referring to Fig. 1 again, it will be noted that the spiral crimp which is shown provides a root-to-crest dimension on the order of 0.5-2.0 milli¬ meters for a thickness of material of 0.35 millimeters. A very thin line monofilament of polypropylene 20 is laid into the root of the crimp of vascular prosthesis 10. The diameter of the monofilament is less than the root-to-crest dimension of the crimp so that to the feel there is no appreciable change in texture to the texture before the monofilament was added. The monofilament is fused into the interstices of the tube by applying a controlled amount of heat to the monofilament. Such heat is obviously less than enough to melt or scorch the surface of the substrate or base material, but adequate to soften the binder. As is shown in Fig. 5, monofilament 20 fuses with all of the substrate threads it crosses, including the warp threads, the weft threads and the overlap threads wherever contact between the monofilament and these threads occurs. Although the structure which has just been described utilizes a monofilament thin-line binder and heat for causing attachment of the thin-line binder to the overall material, the thin-line binder may be connected by gluing the binder to the surface. Alter¬ natively to heat sealing or gluing a polypropylene monofilament in place, it is possible to provide a thin-line binder to the surface by spraying polypropylene or other suitable material in a fine jet spray to accomplish this same structure shown in Fig. 5. The above description pertains to a vascular prosthesis which includes a spiral crimp prior to securing a thin-line binder to the external surface thereof. As mentioned in the prior art section above, knitted or woven vascular prosthesis tubes can be crimped in a circular manner rather than in a spiral manner or left uncrimped. It is not necessary to wrap each circular crimp root in order to obtain the benefits of the thin-line binder attached structure as described above. In such a construction, the alternatives illus¬ trated in Figs. 6, 7 and 8 are available. The substrate or base tube shown in Figs. 6 and 7 are knitted tubes 22. The tube is wrapped in a helical pattern with an appropriate monofilament 24 in Fig. 6 and in a double helical pattern with an appropri¬ ate monofilament 26 and 28 in Fig. 7. Monofilament 26 is wrapped in a first direction and monofilament 28 is wrapped in the opposite direction, which may be conven¬ iently done by wrapping the tube with the same monofilament thread running first in one direction and then in the return direction. Following the wrapping which is shown in Fig. 6 or Fig. 7, the tube is crimped in the manner which is well known in the art for crimping such tubes. Also, such technique could be applied to tubes that are not crimped at all. It should be noted that the location of the thin-line binder of Figs. 6 and 7 are unrelated to the location of the crimping and therefore it is expected that in some cases- the overlaid monofilament line runs up and over a crest portion of the crimp. The textured surface of the overall tube is such that such a construct¬ ed overlaid and attached thin-line binder will not be appreciable noticed either by feel or by appearance. Now referring to Fig. 8, a structure is shown wherein a monofilament line 30 is overlaid in an axial direction with respect to the vascular prosthesis tube. Additional monofilament lines 32 can be overlaid at different locations around the periphery, if desired. The overlaying may be done prior to crimping or after crimping, as desired. Now referring again to Fig. 4, as an alternative to overlaying the tube in any fashion, a thread bundle used for one or more of a warp bundle, weft (fill) bundle, or overlap bundle for a woven tube or the knit bundle for a knitted tube can include one or more filaments of plys 15 of polypropylene or other suitable thin-line binder material. With the subsequent applica¬ tion of controlled heat, such a thin-line binder will adhere to the substrate or base material in the same fashion as described above. Referring to Fig. 3, it will be seen that a vascular prosthesis 10 with fraying protection provided by a thin-line binder in any of the manners previously discussed is shown in use. A surgical tool 34 is shown inserting a suture near the end thereof in order to make the stitching of the vascular prosthesis in place as the surgeon desires. It is very important that the suture be located as close to the end as possible so that an excess amount of material will not be unnecessarily involved with the part of the anatomy to which the prosthesis is attached. By having the fraying and suture holding protection provided by a thin-line binder, this location can be quite near the end, as illustrated, without pulling out. In fact, such thin- line binder protection makes it possible to trim the prosthesis on a bias and to handle the prosthesis extensively without causing fraying just by the manual manipulation thereof. Furthermore, its presence does not interfere with its suturability, its elongation properties, or its flexibility, only in reducing its propensity to fray, in enhancing its resistance to suture pullout and its resistance to dilation. The term "stability" is used herein to refer to enhancing a tube in the manner described above to provide one or more of these enhanced properties. Because of the very thin nature of the overlaid thin-line binder with respect to the materials which are involved, the appearance and texture or feel of the overall suture is not materially changed. In addition to increasing the stability of the material, the porosity or water permeability of the material is not materially reduced by processing in any of the above manners, probably well less than 10%-15%, even with the double helical wrap shown in Fig. 7. It should be apparent that the securing of a thin-line binder, either by employing a monofilament or otherwise as discussed above, may readily be automated. Although it is normal to provide an entire tubular stock with non-fraying protection in the above manner, only a portion or segment thereof may be so protected, if desired. In any event, the results are an integrated and substantially similar structure to the structure prior to treatment, only with stability added to the structure. While particular embodiments of the invention have been shown and described, and modifications or alternatives have been discussed, it will be understood that the invention is not limited thereto since modifica¬ tions can be made and will become apparent to those skilled in the art.

Claims: WHAT IS CLAIMED IS: 1. A vascular prosthesis, comprising at least one tubular segment of interlaced threaded construction, and a thin-line binder secured to the interstices of said tubular segment at least near an end thereof to substantially increase the stability of said tubular segment. 2. A vascular prosthesis in accordance with claim 1, wherein said tubular segment is woven. 3. A vascular prosthesis in accordance with claim 1, wherein said tubular segment is a woven velour. 4. A vascular prosthesis in accordance with claim 1, wherein said tubular segment is knitted. 5. A vascular prosthesis in accordance with claim 1, wherein said thin-line binder is externally overlaid said tubular segment. 6. A vascular prosthesis in accordance with claim 5, wherein said thin-line binder is an overlaid polypro¬ pylene monofilament melted to fuse with the external surface fibers of said tubular segment. 7. A vascular prosthesis in accordance with claim 5, wherein said overlaid tubular segment is spirally crimped, and said overlaid thin-line binder is located in the root of the spiral crimp. 8. A vascular prosthesis in accordance with claim 6, wherein the root-to-crest dimension of said spiral crimp is greater than the thickness of said overlaid thin-line binder. 9. A vascular prosthesis in accordance with claim 5, wherein said overlaid tubular segment is uncrimped. 10. A vascular prosthesis in accordance with claim 1, wherein said overlaid thin-line binder is laid at least largely axially of said tubular segment. 11. A vascular prosthesis in accordance with claim 1, wherein said overlaid thin-line binder is laid helically of said tubular segment. 12. A vascular prosthesis in accordance with claim 1, wherein said overlaid thin-line binder is laid in a double helix with respect to said tubular segment. 13. A vascular prosthesis in accordance with claim 1, wherein said thin-line binder is assembled with the substrate during the making of the interlaced threaded construction. 14. A vascular prosthesis in accordance with claim 1, wherein said tubular segment is polyester. 15. A vascular prosthesis in accordance with claim 1, wherein said tubular segment is polyethylene terephtha- late. 16. A vascular prosthesis in accordance with claim 1, wherein tubular segment is polytetrafluoroethylene. 17. The method of making a vascular prosthesis, which comprises the steps of fabricating the vascular prosthesis to include at least one tubular segment of inter¬ laced threaded construction, spirally crimping said tubular segment, and securing .a thin-line binder into the root of said spiral crimp at least near the end thereof so that it adheres to the external surface fibers of said tubular segment. 18. The method of making a vascular prosthesis in accordance with claim 17, wherein said height of said thin-line binder is less than the root-to-crsst dimension of said spiral crimp. 19. The method of making a vascular prosthesis in accordance with claim 17, wherein said thin-line binder is a polypropylene thread, and said securing includes the steps of laying said polypropylene thread into the root of said spiral crimp, and heating said thread so that it fuses with the external fibers of said tubular segment. 20. The method of making a vascular prosthesis in accordance with claim 17, wherein said thin-line binder is adhered to the root of said spiral crimp. 21. The method of making a vascular prosthesis, which comprises the steps of fabricating the vascular prosthesis to include at least one tubular segment of inter¬ laced construction, securing a thin-line binder to adhere to the external surface fibers of said tubular segment at least near the end thereof, and crimping said tubular segment including said thin-line binder. 22. The method of making a vascular prosthesis in accordance with claim 21, wherein said thin-line binder is laid at least largely axially of said tubular segment. 23. The method of making a vascular prosthesis in accordance with claim 21, wherein said thin-line binder is laid helically of said tubular segment. 24. The method of making a vascular prosthesis in accordance with claim 21, wherein said overlaid thin- line binder is laid in a double helix with respect to said tubular segment. 25. The method of making a vascular prosthesis in accordance with claim 21, wherein said crimping is circular. 26. The method of making a vascular prosthesis, which comprises the steps of making up a bundle of plys including at least one ply of a thin-line binder material, fabricating the vascular prothesis to include at least one tubular segment of interlaced construction using said bundle for at least one of the interlacing components, and controllably heating the tubular segment to cause said thin-line binder materials to adhere to the fibers of the tubular segment.

Inventors: LALOR GABRIEL P, SNYDER ROGER W, WEINBERG STEVEN L, LALOR, GABRIEL, P., SNYDER, ROGER, W., WEINBERG, STEVEN, L.
Applicants: ADVANCED VASULAR TECHNOLOGIES, ADVANCED VASCULAR TECHNOLOGIES, INC.
Application year: 1987
Main classification: A61F2
IPC codes: A61F2, A61L26, A61L27