Abstract:
Suture material that includes an exterior braid of more than 50% ultra-high molecular weight polyethylene fibers, defining a lumen having a lumen diameter. In addition, the suture material includes an interior core, comprised of fibers and having a diameter that is less than 55% of the diameter of said lumen.

Description:
BACKGROUND 
       [0001]    Suture material is preferably strong and can be easily formed into durable knots. Some stiffness is also desirable, as sutures must sometimes be threaded through holes, and it is easier to push a material that has some stiffness. 
         [0002]    Suture material typically includes an outer braid and an inner braided or twisted core of fibers. Ultra-high molecular weight polyethylene (UHMWPE), due to its exceptional strength, is a popular material for both outer braid and inner core. Although this construction appears to be the most popular for suture material, at least two problems have been noted. 
         [0003]    First, UHMWPE is very strong, but also very hard. Accordingly, when tied in a knot, very hard material of a first fiber has a tendency to cut through a second fiber into which the first fiber is pressed, in the knot. It appears that the hard inner core may play a role by providing a hard backing to the outer braid, permitting a contacting fiber to cut through more easily, just as a cutting board permits a knife to more easily cut through a fibrous vegetable. 
         [0004]    Second, it has been noted that the inner core is bulky and causes knots formed in the suture to have a higher profile and take up a greater volume. Anything taking up space inside the body can potentially conflict with tissue growing back and attempting to claim some of the same volume. The core of a suture, in particular, may interfere with tissue ingrowth, which is a health promoting process. 
         [0005]    Although a suture with an outer braid alone addresses some of these problems, it does so at a price of reduced stiffness. It has a tendency to fold on itself in a somewhat unpredictable manner, making surgical handling more difficult. 
       SUMMARY 
       [0006]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements. 
         [0007]    In a first separate aspect, the present invention may take the form of suture material that includes an exterior braid of more than 50% ultra-high molecular weight polyethylene fibers, defining a lumen having a lumen diameter. In addition, the suture material includes an interior core, comprised of fibers and having a diameter that is less than 55% of the diameter of said lumen. 
         [0008]    In a second separate aspect, the present invention may take the form of suture material that includes an exterior braid of more than 50% ultra-high molecular weight polyethylene fibers, defining a lumen having a lumen diameter. Also, the suture material includes an interior core comprised of fibers that are entangled together. 
         [0009]    In a third separate aspect, the present invention may take the form of suture material that includes an exterior braid of more than 50% ultra-high molecular weight polyethylene fibers, defining a lumen. Also, the suture material includes an interior core comprised of fibers, at least some of which are bio-absorbable fibers. 
         [0010]    In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic cross-section view of suture material according to the present invention. 
           [0012]      FIG. 2  is a side view drawing of the braided exterior of a suture. 
       
    
    
       [0013]    Exemplary embodiments are illustrated in referenced drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Definitions 
       [0014]    “Filament” is a single strand of material. 
         [0015]    “Fiber” is an industry term of art, meaning an element of a braid or of a group that is twisted together. One fiber may include a collection of filaments. 
         [0016]    Referring to  FIG. 1 , in a preferred embodiment a suture  10  comprises an outer braid  12  defining a lumen  14  containing an inner core  16 . The diameter of the inner core  16  is substantially less than that of the lumen  14 , thereby permitting lower profile and volume knots to be formed in the suture material, compared with suture material having a core that fills the lumen. But core  16  helps to prevent the otherwise hollow outer braid from unpredictably folding over on itself and generally increases the stiffness of the suture  10 , thereby improving handling qualities.  FIG. 2  shows a side view of outer braid  12 . 
         [0017]    In various preferred embodiments the diameter of inner core  16  is 55%, 50%, 45%, 40% or less than the diameter of the lumen  14  (which is equal to the inner diameter of braid  12 ). The core may be made of a single fiber, two fibers twisted together, three or four or more fibers. Also, the core  16  may be made of UHMWPE fibers twisted, air tangled or braided with fibers of poly ester or polyethylene terephthalate both of which are more elastic than UHMWPE and will therefore not break, but stretch slightly and continue to help the overall suture  10  bear a load under stress. The smaller the core  16  is in comparison with the lumen  14  width and the greater percentage of core  16  material that is softer and more elastic and flexible than UHMWPE, the less core  16  interferes with knot tying and the lower the knot profile that is achievable. But a smaller diameter core  16  that has a higher percentage of softer material will also contribute less to the strength and stiffness of the suture. Accordingly, in one embodiment, a system of grading is established, where suture material is rated according to stiffness, strength and knotting characteristics. 
         [0018]    In another alternative embodiment the core  16  may be made at least in part of fibers of a bio absorbable material, such as poly butyl succinate (PBS); polydioxanone (PDO); poly glycolic acid (PGA); poly lactic acid (PLA); poly glycolic-co-lactic acid (PGLA); or poly glycolide-co-caprolactone (PGCL). These materials also can accept a dye and, accordingly, can be used as tracer elements on the suture exterior braid  12 , to help distinguish one suture from another. The bio-absorbable material permits the suture to shrink in dimension as it remains in the body, as the fibers of bio absorbable material are gradually absorbed. As new body tissue grows after a surgery in which sutures are placed, the full strength of the original suture is no longer needed as a portion of the stress on the suture is taken up by the newly formed body tissue. This process is beneficial to the patient, as foreign material left in the body is generally harmful to a patient. 
         [0019]    In one preferred embodiment of the suture material  10 , the fibers of the core  16  are air tangled together, in a known technique of blowing air into the fibers as they are brought into proximity. In alternative preferred embodiments they are twisted together or braided together. 
         [0020]    The sutures described above, in which a core  16  fills only a portion of a lumen defined by a braided exterior, may be made in size 0 to size 10, or larger, the limitation being that for the smallest size sutures, it may be difficult to define a lumen and there may be little space for any space about a core. The suture material described herein may be produced on a maypole braiding machine having 4, 8, 12, 16 or 32 carriers. The air entangled core suture embodiment and the partially bio-absorbable core suture embodiment may be made in any size larger than 3-0. 
         [0021]    While a number of exemplary aspects and embodiments have been discussed above, those possessed of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.