Abstract:
The present invention provides an apparatus and process for improving the properties of braided ligature by hot stretching the braid.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus and process improving the properties of braided fibers, more particularly an apparatus and process for hot stretching braided surgical ligatures. 
     BACKGROUND OF THE INVENTION 
     Multifilament sutures are generally made by braiding yarns into a braided structure. Appropriate braided constructions for surgical sutures have been described in U.S. Pat. Nos. 5,019,093; 4,959,069 and 5,059,213 (all incorporated by reference herein). After the braided construction has been made the braid is cleaned by scouring and generally compacted by hot stretching the braid multifilament. 
     One suitable means for hot stretching braided constructions is illustrated in FIG. 1. A spool of braided multifilament is attached to a tensioning device. The braided multifilament is then wound around feed rolls ( 4  and  6  respectively) and threaded through heated plates  8 . The braided multifilament is then drawn by draw rolls  10  and  12  and collected on take up spool  14 . The drawing is accomplished by rotating the draw rolls faster than the feed rolls to stretch the braided multifilament. Generally the braided multifilament are drawn in the range of from about 10 to about 20 percent. The amount that the suture is to be drawn depends on the size of the suture, the material the suture is made of and the braid construction. Similarly the temperature and residence time for the braided multifilament would have between the heated plates would also depend on these same factors. 
     Unfortunately, this process and apparatus although effective in providing a hot stretched braided suture resulted in two potential defects being introduced into the braided multifilament sutures. The first defect is slight increase in the number of sutures that do not pass quality assurance strength tests. The second defect is a tendency for the braid to have irregular bunching in the braid. 
     Therefore, it is an object of the present invention to provide a method and apparatus for hot stretching braided multifilament sutures that results in little or no strength loss associated with hot stretching. Alternatively, it is an object of the present invention to provide an apparatus and process for hot stretching braided multifilament sutures which reduces or eliminates bunching in braided multifilament sutures. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved process for hot stretching braided multifilaments. This process comprising advancing a braided multifilament to a first heating zone, then drawing the braided multifilament while heating the braided multifilament thereafter heat setting the braided multifilament to provided a braided suture. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 illustrates a prior art apparatus for hot stretching braided multifilament ligatures. 
     FIG. 2 illustrates the improved hot stretching apparatus, which both draws and relaxes the multifilament sutures and which is described in the Detailed Description. 
    
    
     DETAILED DESCRIPTION 
     The present invention is illustrated in FIG.  2 . As shown in FIG. 2, a braided ligature  200  is taken from feed roll  202  by take-off device  205 . The feed roll  202  may have a functional brake to facilitate even feeding of the braid to the take-off rolls. Take-off device  205  is not heated and generally will be comprised of one or more rolls, which have multiple wraps of the braided ligature  200  wrapped around the rolls to avoid slippage. The braided ligature  200  is advanced by take-off device  205  which, in a preferred embodiment of this invention, is composed of one or more rolls (i.e., take-off rolls  204  and  206 ) to a first heating zone, which includes as illustrated, a first set of heated rolls  208  and  210  which are run at substantially the same speed as take-off device (i.e.,  204  and  206 ). Preferably, the braided ligature will be wrapped around heated  208  and  210  to avoid slippage and improve heat transfer. The braided ligature  200  is then advanced to a third heated roll  212  which is rotated a speed faster than the first two heated rolls ( 208 ,  210 ). The second set of heated roll  212  and  213  stretches the ligature  200 . The braided ligature is preferably wrapped several times around the third heat roll to avoid slippage and improve heat transfer. The stretched braided ligature  200  is then advanced to the third set of heated rolls. The third set of heated rolls preferably comprises a fifth and sixth heated rolls  214 ,  216  that are rotated at a speed slower than the second set of heated roll  212  and  213  to control the relaxation of the braided ligature  200 . Alternatively the heated rolls  214  and  216  can be rotated at a higher rate of speed to stretch the braided suture a second time. The braided ligatures will preferably be wrapped multiple times around the fifth and sixth heated rolls in a FIG. 8 pattern. The braided ligature  200  is then advanced to tensioning device  218  and proceeds to take up roll  220 . 
     The speed at which the braided ligature travels through the rolls and temperature which the rolls are heated, depends on the size of the braid, braid construction, number of wraps per roll and materials which the braid ligature is made. Generally the overall stretch (i.e., the approximate percent difference in the initial length of the braid as compared to the final length of the braid after the process is finished) will be in the range of from about 3 percent to about 25 percent greater than the initial length of the braid, preferably from about 6 percent to about 20 percent and more preferably from about 10 percent to about 16 percent greater than the initial length of the braid. These percentages are based on the relative speeds between the heated rolls, therefore, are approximate values. 
     The temperature at which the first three heated rolls are maintained at will be sufficient to facilitate the stretching of the braided ligature. This temperature will generally be in the range of about 150° F. to about 50° F. below the melting temperature of the braided ligature material. As an example, for ligatures made from polyethylene terephthalate, the temperatures will be in the range of from about 150° F. to about 50° F., preferably in the range of from about 125° F. to about 50° F. and most preferably from 100° F. to about 50° F. 
     After stretching, the braided ligature will then be heat set (and optionally relaxed) by the fifth and sixth heated rolls. The relaxation may be accomplished by matching the speed of the second set of heated rollers ( 212  and  213 ), the speeds of the fifth and sixth heated rolls  214  and  216  will be in the range of from about 0 percent to about 15 percent slower than the speed of the second set of heated roller and preferably will be in the range of from about 5 percent to about 15 percent slower than the speed of the second set of heated roller. The percent of relaxation will be approximately the same as the percent reduction in relative speed. Those skilled in the art will appreciate that the individual braided yarns may not be capable of relaxing to the maximum amount specified, in which case the upper limit of the relaxation should be viewed as being the maximum amount that the braid will relax or shrink under the specified conditions or 15 percent whichever is less. 
     Alternatively, the fifth and sixth heated rolls can perform a heat set and second stretch. The second stretch may be accomplished by increasing the speed of the fifth and sixth heated rollers relative to the speed of the second set of heated roller ( 212  and  213 ). For example, for sizes 4/0 through size 2 (USP suture sizes) the hot stretch process could be performed in two or more separate stretching operation as described in the table provided below. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 DOUBLE DRAW CONDITIONS 
               
               
                 % STRETCH 
               
             
          
           
               
                 USP 
                 RANGE 
                 PREFERRED 
                 MORE PREFERRED 
               
             
          
           
               
                 SUTURE SIZE 
                 DRAW 1 
                 DRAW 2 
                 DRAW 1 
                 DRAW 2 
                 DRAW 1 
                 DRAW 2 
               
               
                   
               
               
                 4/0 - 2 
                 about 2 
                 about 2 
                 about 6 
                 about 4 
                 about 8 
                 about 4 
               
               
                   
                 to about 
                 to about 
                 to about 
                 to about 
                 to about 
                 to about 
               
               
                   
                 14% 
                 10% 
                 12% 
                 8% 
                 12% 
                 8% 
               
               
                   
               
             
          
         
       
     
     As will be appreciated by those skilled in the art the process of the present invention could be conducted by placing unheated rolls inside an oven or using a heat transfer medium (such as steam) to elevate the temperature of the braided multifilament as it stretched and subsequently heat set using draw rolls. 
     This process can be used with a variety of biocompatible multifilament braided sutures. Suitable biocompatible multifilament braided sutures may be made from a biocompatible nonabsorbable polymers selected from the group consisting of but not limited to polyethylene, polypropylene homopolymers and copolymers and polymer blends containing polypropylene (such as those described in U.S. Pat. Nos. 3,359,983, 4,520,822, 4,557,264, 4,620,542, 4,621,638 and 4,911,165 hereby incorporated by reference), polyesters such as polyethylene terephthalate, polyamides (i.e. nylon 6, nylon 66, nylon 610 and nylon 4) and combinations thereof. Suitable absorbable materials for the manufacture of multifilament braided sutures may be selected from the group consisting of but are not limited to lactic acid, lactide (including L-, D-, meso and D,L mixtures), glycolic acid, glycolide, caprolactone, p-dioxanone (1,4-dioxan-2-one), trimethylene carbonate (1,3-dioxan-2-one), delta-valerolactone, beta-butyrolactone, epsilon-decalactone, 2,5-diketomorpholine, pivalolactone, alpha, alpha-diethylpropiolactone, ethylene carbonate, ethylene oxalate, 3-methyl-1,4-dioxane-2,5-dione, 3,3-diethyl-1,4-dioxan-2,5-dione, gamma-butyrolactone, 1,4-dioxepan-2-one, 1,5-dioxepan-2-one, 6,6-dimethyl-dioxepan-2-one, 6,8-dioxabicycloctane-7-one and combinations thereof. 
     Additionally, the braids can be made up of combinations of absorbable and non-absorbable yarns, as well as, from yarns that are combinations of different absorbable and/or different non-absorbable filaments. 
     Following heat stretching the braided ligatures can be annealed, scoured, coated (i.e. with lubricants, drugs etc.), tipped, attached to needles (or other surgical devices), sterilized and/or packaged using conventional technology. 
     The following non-limiting examples are illustrative of the principles and practice of this invention. Numerous additional embodiments within the scope and spirit of the invention will become apparent to those skilled in the art. 
     EXAMPLE 1 
     This example describes a comparative test between the hot stretch machines depicted in FIGS. 1 and 2. 
     A size 2/0 braided polyester suture was braided using a 16 carrier New England Butt braider. The carrier yarn was nominally 55 denier (2.3 denier per filament polyester fibers) which had been twisted to a nominal level of 8 twists per inch (tpi), and dyed. The yarn used was Trevira™, type 712 from Hoechst Celanese or Hoechst AG. A single core yarn of a nominal 110 denier also twisted to about 8 tpi which was also dyed. The core fiber is threaded in to the braider using a tensioning control device. After the braid was made the braid was taken up on a spool. 
     The braid was then doffed and wound onto a flexible spring dyer tube for scouring. The braid was scoured in a pressurized vessel with an aqueous detergent under acidic conditions at elevated temperature (165-270° F.) for about three hours. After scouring the braid was dried and a coating was applied to the braid, then the braid was hot stretched. 
     The braided polyester was hot stretched on the machines described in FIGS. 1 and 2 under the conditions described below in Table 1. 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 2-PLATEN 
                  HEATED ROLL 
               
               
                   
                 AVG./S.D. 
                 AVG./S.D. 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 IN PROCESS 
                   
                   
               
               
                   
                 TENSILE(lbs) 
                 13.84/0.389 
                 13.86/0.202 
               
               
                   
                 ELONGATION % 
                 13.28/0.747 
                 17.105/0.341 
               
               
                   
                 KNOT (lbs) 
                 7.643/0.188 
                 7.21/0.188 
               
               
                   
                 FINISHED 
               
               
                   
                 TENSILE (lbs) 
                 14.72/0.27 
                 14.59/0.27 
               
               
                   
                 ELONGATION % 
                 12.45/0.99 
                 17.4/0.39 
               
               
                   
                 KNOT (lbs) 
                 7.64/0.33 
                 7.54/0.43 
               
               
                   
                 BUNCH 
                 5 failures 
                 0 failures 
               
               
                   
                   
                 from 200 lots 
                 from 60 lots 
               
               
                   
                   
               
             
          
         
       
     
     As can be seen from the data the number of suture failures per lots because of bunching was reduced.