Braided Suture

The accompanying figures are photomicrographs of cross-sectional and linear views of braided sutures both within (FIGS. 3, 4 and 7 to 10) and outside (FIGS. 1, 2, 5 and 6) the scope of this invention, the latter being presented for comparison purposes.

In a preferred embodiment, the braided suture of the present invention is fabricated from a bio-absorbable or biodegradable resin such as one derived from polyglycolic acid, glycolide, lactic acid, lactide, dioxanone, trimethylene carbonate, etc., and various combinations of these and related monomers. Sutures prepared from resins of this type are known in the art, e.g., as disclosed in U.S. Pat. Nos. 2,668,162; 2,703,316; 2,758,987; 3,225,766; 3,297,033; 3,422,181; 3,531,561; 3,565,077; 3,565,869; 3,620,218; 3,626,948; 3,636,956; 3,736,646; 3,772,420; 3,773,919; 3,792,010; 3,797,499; 3,839,297; 3,867,190; 3,878,284; 3,982,543; 4,047,533; 4,060,089; 4,137,921; 4,157,437; 4,234,775; 4,237,920; 4,300,565; and, 4,523,591; U.K. Patent No. 779,291; D. K. Gilding et al., "Biodegradable polymers for use in surgery--polyglycolic/poly(lactic acid) homo- and co-polymers: 1, Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.), Biocompatibility of Clinical Implant Materials, Vol. II, ch. 9: "Biodegradable Polymers" (1981).

The defining characteristics of the braided suture of this invention, apart from the material of its construction, are:

(1) overall suture denier;

(2) the pattern of the interlocking yarns expressed as the pick count, which is to say, the number of crossovers of individual sheath yarns per linear inch of suture;

(3) the number of sheath yarns comprising the braid;

(4) the denier of the individual filaments comprising each sheath yarn; and,

(5) the denier of the core, where present.

The overall denier of the braided suture can vary from about 50 to about 4000. Within this range, the ranges of overall denier for particular sutures are: from about 50 to about 125 denier; from above about 125 to about 200 denier; from above about 200 to about 300 denier; from above about 300 to about 500 denier; from above about 500 to about 800 denier; from above about 800 to about 1500 denier; from above about 1500 to about 2000 denier; and, from above about 2000 to about 3600 denier.

For a suture of any range of overall denier, pick count can vary from about 50 to about 100 crossovers/inch with about 55-80 crossovers/inch being preferred. For sutures constructed within any range of overall denier, as larger numbers of sheath yarns are employed, the pick-count for acceptable sutures will also increase within the above ranges.

For a suture of a particular range of denier and number of sheath yarns, pick count is advantageously established to achieve a balance in the properties desired. In general, with increasing pick count, surface roughness of the suture tends to increase and with decreasing pick count, the ability of the external braided sheath to contain the core (if present) tends to decrease even reaching the point where the braid may become so loose as to result in the core protruding therethrough.

For sutures of any specific denier range and number of sheath yarns, it is preferable to have as low a pick count as possible in order to achieve optimum surface smoothness, consistent, of course, with the need to provide a compact braid which prevents the core (if present) from protruding through the exterior sheath yarn structure.

The number of sheath yarns bears some relation to overall suture denier, the number generally increasing with the weight of the suture. Thus, across the range of suture weight (denier) indicated above, the braided suture of this invention can be constructed with from about 4 up to as many as about 36 individual sheath yarns constructed from individual filaments having the deniers discussed below.

Table I below sets forth broad and preferred ranges for the numbers of sheath yarns which are suitable for the construction of braided sutures of various ranges of overall denier. The pick counts of the sutures vary from about 50 to about 100 and deniers of individual filaments vary from about 0.2 to about 6.0 for the broad range of number of sheath yarns and the pick counts vary from about 55 to about 80 and the deniers of individual filaments vary from about 0.8 to about 3.0, and advantageously from about 0.8 to about 1.4, for the preferred range of number of sheath yarns.

While the sheath yarns need not be twisted, it is generally preferred that they be provided with a twist so as to minimize snagging during braid construction.

The individual filaments comprising each sheath yarn can vary in weight from about 0.2 to about 6.0 denier, preferably from about 0.8 to about 3.0 denier and more preferably from about 0.8 to about 1.4 denier. The number of such filaments present in a particular sheath yarn will depend on the overall denier of the suture as well as the number of sheath yarns utilized in the construction of the suture. Table II sets forth some typical numbers of filaments per sheath yarn for both the broad and preferred ranges of filament weight:

For all but the lowest range of overall denier, the braided suture herein can optionally be constructed around a filamentous core which itself can be braided or which can be provided in some other configuration such as a twist, ply, cable, etc. The filament(s) comprising the core need not be as fine as those comprising the sheath yarns. It is particularly advantageous for sutures of heavier denier to possess a core. Where a core is provided, it is generally preferred that it possess a weight which is significantly greater than that of a core of a known suture of equivalent overall denier.

Table III below provides some typical core deniers for sutures of various deniers.

It can be advantageous to apply one or more coating compositions to the braided suture of this invention to improve such properties as surface lubricity and knot tie=down behavior. A variety of suture coating compositions proposed for either or both purposes is known in the art, e.g., those disclosed in U.S. Pat. No. 4,047,533, the contents of which are incorporated by reference herein.

It is also within the scope of this invention to impregnate the suture with, or otherwise apply thereto, one or more medico-surgically useful substances, e.g.; those which accelerate or beneficially modify the healing process when the suture is applied to a wound or surgical site. So, for example, the braided suture herein can be provided with a therapeutic agent which will be deposited at the sutured site. The therapeutic agent can be chosen for its antimicrobial properties, capability for promoting wound repair and/or tissue growth or for specific indications such as thrombosis. Antimicrobial agents such as broad spectrum antibiotics (gentamycin sulphate, erythromycin or derivatized glycopeptides) which are slowly released into the tissue can be applied in this manner to aid in combating clinical and sub-clinical infections in a surgical or trauma wound site. To promote wound repair and/or tissue growth, one or several growth promoting factors can be introduced into the suture, e.g., fibroblast growth factor, bone growth factor, epidermal growth factor, platelet derived growth factor, macrophage derived grown factor, alveolar derived growth factor, monocyte derived growth factor, magainin, and so forth. Some therapeutic indications are: glycerol with tissue or kidney plasminogen activator to cause thrombosis, superoxide dismutase to scavenge tissue damaging free radicals, tumor necrosis factor for cancer therapy or colony stimulating factor and interferon, interleukin-2 or other lymphokine to enhance the immune system.

In the examples which follow, Comparison Examples 1 to 11 are illustrative of known type sutures while Examples 1 to 12 are illustrative of sutures constructed in accordance with this invention.

The following braided suture configurations are disclosed in U.S. Pat. No. 3,565,077;

Sutures possessing approximately these configurations are relatively inflexible, rough-surfaced and exhibit a relatively high level of chatter and drag.

The following braided suture configurations are those of four commercially available sutures:

Photomicrographs obtained by scanning electron microscopy (SEM) of the suture of Comparison Example 10 (FIGS. 1 and 2: cross-sectional view at 200.times. and linear view at 50.times., respectively) clearly show the structural details of the suture. The suture braid is made up of relatively few sheath yarns and the circumferential indentations, plainly evident in FIG. 1, cause the braid surface to be relatively rough.

These examples illustrate various size braided sutures constructed in accordance with the present invention.

Comparing the details of construction of the foregoing braided sutures with those of the known braided sutures as set forth in Comparison Examples 1-11, it will be noted that for sutures of comparable overall denier, the suture of this invention possesses a significantly greater pick count and number of sheath yarns and a significantly finer denier for the individual filaments making up a sheath yarn than the equivalent characteristics of the known

As a result of their unique construction characteristics, the sutures of this invention exhibit perceptibly improved flexibility and hand and reduced chatter and drag compared with the known sutures of Comparison Examples 1-11.

The following braided sutures were fabricated in accordance with the present invention:

In contrast to the suture of Comparison Example 10, supra, SEM photomicrographs of the suture of Example 11 (FIGS. 3 and 4: cross-sectional view at 200.times. and linear view at 50.times., respectively) show a smooth circumferential surface as the result of the increased number of sheath yarns and smaller diameter of individual filaments.

FIG. 1 as compared to FIG. 3 shows the relatively larger core present in the suture of Example 11 as compared to that of Comparison Example 10.

Comparison between FIGS. 2 and 4 shows the increased number of picks (crossovers/inch) of the suture of Example 11 as compared to that of Comparison Example 10.

The following suture braids were fabricated in accordance with the present invention:

The suture braids were coated to improve suture lubricity and knot tie-down characteristics and compared for physical properties for diameter USP knot-pull and suture tissue drag with the coated commercial suture of Comparison Example 10.

In this tissue drag test, sutures were needled with identical tapered needles to normalize any effect of needle diameter on the test.

Sutures were passed through live animal abdominal fascia tissue. The results of the tissue drag study are shown in Table IV as follows:

These data clearly show that the smoother surface of the braided sutures fabricated in accordance with this invention provide smoother, more resistance-free passage of the suture through tissue thereby resulting in lower tissue drag and chatter. High drag forces make it more difficult for the surgeon to align tissue neatly and increase the time to complete the closure. A visual comparison of the suture of Comparative Example 10 and those of Examples 13 and 14 of this invention are consistent with the tissue drag observations set forth above. Thus, it is evident from a visual comparison of the SEM photomicrographs of FIGS. 5 and 6 (suture of Comparison Example 10 shown in cross-sectional view at 150.times. and linear view at 70.times., respectively) with those of FIGS. 7 and 8 (suture of Example 13 shown in cross-section at 150.times. and linear view at 70.times., respectively) and FIGS. 9 and 10 (suture of Example 14 shown in cross-section at 150.times. and linear view at 70.times., respectively) that the external surfaces of the sutures of the present invention, i.e., those of Examples 13 and 14,are perceptibly smoother than the surfaces of the suture of Comparison Example 10.