BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the utilization of a fluorescent material in surgical sutures. More particularly, the present invention pertains to highly visible, synthetic sutures for external wound repair which fluoresce with a distinctive visible color upon exposure to an ultraviolet light source.

2. Description of the Prior Art

Suture materials for external surgical procedures are generally fabricated from nonabsorbable filaments extruded from such synthetic polymers as polyesters, polyolefins or polyamides, for example. Due to its high flexibility and tensile strength, multifilament nylon particularly finds wide acceptance as a typical nonabsorbable suture material, especially in the field of veterinary medicine. However, multifilament nylon surgical sutures for external wound stitching are usually available only in either clear or white opaque which renders them visually undetectable when utilized on light skinned or coated animals, especially those with white or tan fur. This problem concerning visibility is compounded when animals presented for suture removal exhibit an early regrowth of the light, hairy coat surrounding the wound which has been stitched. Furthermore, the white nylon sutures are often soiled by the animal after application, causing the sutures to turn a dirty brown or darker color which may be practically indistinguishable from the

originally colored coat. This lack of contrasting colors poses serious problems with regard to identification which are not encountered in other surgical applications, such as internal wound repair using absorbable suture materials. For instance, failure to completely remove all fragments of the nonabsorbable suture material after the wound has sufficiently healed may promote tissue irritation which can directly result in stitch abscess or other adverse bodily reactions over an extended period of time. In order to enhance the visibility of surgical ligatures, it has been proposed to provide sterile filaments having a succession of lines or dots of contrasting shades on its surface, as disclosed in U.S. Patent No. 3,949,755 to Vauquois (issued April

13, 1976). The disclosed ligatures may be easily placed in position by the surgeon since the shaded filaments can be readily seen through a film of blood.

While such surgical ligatures are generally effective during internal suturing procedures such as tying small vessels, the aforementioned problems associated with suture identification and removal in external applications remains largely unaddressed.

SUMMARY OF THE INVENTION

It is, accordingly, a primary object of the present invention to provide surgical sutures for external wound repair which are highly visible under normal and ultraviolet lighting conditions to greatly enhance identification and ensure complete suture removal. It is a further object of the invention to provide a method of suturing which utilizes colored suture

filaments that will fluoresce with a bright color upon exposure to ultraviolet light in order to markedly enhance suture visibility.

It is among the additional objects of the present invention to provide a method of preparing monofi lament or multifilament sutures having the desired degree of visibility and flexibility derived from fluorescent dyed synthetic polymers. The present dyed sutures not only retain their mechanical properties for a time sufficient for the wound to heal, but also significantly lessen tissue irritation by increasing suture recognition without leaving harmful residues in the sewn tissue.

These and other objects are accomplished in accordance with the present invention which provides a surgical suture comprising a sterile, synthetic filament containing a colored fluorescent dye, wherein said synthetic filament exhibits a distinctive color under visible light and fluoresces with a bright color of fluorescence during exposure to ultraviolet radiation. The visibly colored sutures of the present invention, particularly synthetic nonabsorbable, multifilament sutures, are especially adapted for external wound repair. For this purpose, it is preferred to use fluorescent dyes with a wide range of desirable shades such as bright yellow, orange, green or fuchsia when viewed under normal and ultraviolet lighting conditions.

In a specific embodiment, the colored fluorescent dyes employed in the invention are incorporated throughout the filament suture material by immersion in a dye bath to provide a brightly colored suture permeated with a fluorescent pigment which is not

removed by abrasion. The colored fluorescent sutures are readily visible for positive identification to enhance suture adjustment or removal and thereby substantially avoid tissue inflammation and other adverse reactions.

The foregoing and other features, advantages and other objects of the invention may be more fully appreciated by reference to the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

As synthetic polymers suitable for the present suture filament, various materials have been considered, the essential requirements being that they possess adequate tensile strength, be capable of sterilization, and exhibit the necessary degree of flexibility, surface smoothness and knot security. The synthetic suture material should also be dimensional ly uniform over a period of time sufficient for the wound to heal and storage-stable in the dry state. In addition, these suture materials should not leave any undesirable residues which may promote adverse tissue reactions. As such, monofi lament and multifilament, synthetic nonabsorbable suture materials of polyethylene terephthalate, polypropylene and nylon, for example, are preferably used. Because of its ready availability, cost and long-standing use by veterinary practi ioners for external surgical procedures, the preferred suture material is nonabsorbable nylon. Nylon is a polyamide of protein- like structure prepared from an aliphatic dicarboxylic acid, such as adipic acid or sebacic acid, and

aliphatic diamines such as hexamethy1ene diamine which can be extruded into filaments. The resulting nylon sutures are usually of braided, twisted or multifilament construction. I n an alternative embodiment, filaments extruded from absorbable suture materials which degrade enzymatical ly can also be used in the present invention if they fulfill the above requirements. The absorbable suture materials should not disappear from the sewn tissue before the wound has completely healed, which may be as long as a year in certain external applications, for example. Those absorbable materials that disappear within a substantially shorter period or prior to wound healing were found to be undesirable since such sutures incorporated with the present dyes may leave a dye residue in the sewn tissue after the suture itself is absorbed. Therefore, extruded collagenous materials such as ordinary catgut are not particularly favorable for the purposes of the invention since they lose their mechanical properties quite rapidly and induce unwanted tissue reactions unless they can be modified to retard their absorption rate, as will be discussed in more detail hereinafter. Synthetic absorbable suture materials which are subject to biodegradation such as polylactide, polyglycol ide, copolymers of lactide and glycolide, po1y(p-dioxanone) , and mixtures of such polymers may be suitable in the present invention if they meet the above prerequisite characteristics, especially regarding absorption rate. The incorporation of fluorescent dyes into these particular absorbable materials alters their chemical properties such that

the biodegradation of the dyed suture product may be significantly retarded for a period sufficient to enable the sutured wound to heal. The present synthetic absorbable sutures may also be coated with conventional suture coating materials such as silicon or beeswax in order to further modify the handling and adsorption rate of the dyed sutures.

In an additional embodiment of the invention, the absorbable suture filament may be coated with a protective sheath consisting of a mixture of the dye material and a resin that is hydrolytical 1y degradable but is enzymatical ly stable. Suitable resins for this specific embodiment are disclosed in U.S. Patent No. 4,433,688 to Bichon. In practice, the dye-resin coating can be modified to have a thickness which varies depending on the particular application. Thus, when an external wound is stitched with the instant coated or sheathed suture filament, the dye-resin coating can be made to partially degrade hydrolytical ly very slowly such that the suture core remains dimensionally stable until the wound heals. Then, when the coating of dye and resin has been partially degraded but clearly visible, the absorbable core is attacked by the body enzymes and is absorbed. As is common with biological systems, the rate of absorption varies from patient to patient and with the thickness or molecular weight of the absorbable core. Thus, a wide range of absorption rates and molecular weights are possible to meet different applications. Care should be taken to ensure that no significant amounts of undesirable residues be left in the tissue.

For practical purposes, any fluorescent dye material which imparts color under visible light to the suture filament and which emits highly visible color in certain wavelength ranges when excited by ultraviolet radiation (UV) may be suitable in the present invention. The color of fluorescence emitted by these dye materials in the solid state may be substantially similar to or completely different from the color exhibited under visible light. As examples of such suitable dye materials,, particular reference is made to the "daylight fluorescent dyestuffs" of the rhodamine, su1forhodamine, naphthal imide or xanthene series. These specific dyestuffs or pigments are well known and are described in the Encyclopedia of Chemical Technology, Second Edition, Vol. 9, (1966), John Wiley and Sons, Inc. Daylight fluorescent pigments are more highly visible than non-daylight fluorescent dyestuffs because the emitted light combines additively with the reflected color to provide sutures having the best possible brilliancy under either visible or UV light. Thus, with the use of these preferred dyes, other nonf1uorescent colorants may not be needed to achieve the desired color under either visible or ultraviolet light conditions. However, it is possible to use a mixture of one or more fluorescent dyes with a nonfluorescent pigment to produce the desired color effect in the visible range. For some purposes, it may be desirable to use fluorescent materials which are colorless when viewed under visible light and emit fluorescent light in a certain range under UV. The daylight fluorescent dyes used in the present invention are commercially available in a variety of bright colors such as red,

blue, yellow, orange, green, purple and pink, for example, from such sources as the Hercules Powder Co., Glen Falls, NY; Lawter Chemicals, Inc., Chicago, IL; Radiant Color Co., Richmond, CA ; and Day-Glo Color Corp., Cleveland, OH.

The sutures of the present invention may be formed by incorporating the fluorescent pigments in the polymeric suture material prior to extrusion or during preparation of the suture product. Thus, an effective amount of a colored fluorescent dyestuff is added to a liquid suture monomer mixture, which is then polymerized to produce individually dyed filaments for the manufacture of the present monofi lament or multifilament sutures. The fluorescent dyes are distributed throughout the mass of the polymer structure and will not leach from the suture material during storage or use. The dyestuff concentration generally ranges between about 0.1 and 10 percent by weight, depending on the degree of brilliancy desired. In a preferred method, the present sutures can be prepared by immersing extruded monofi lament or multifilament synthetic sutures in a dye bath to form a color-permeated suture product in which the fluorescent material is not subject to settling out or being worn off during use. The basic method involves the immersion of the extruded sutures in a bath comprising an aqueous solution of ammonium and sodium sulfate, a surfactant, and an effective amount of the fluorescent dye. The surfactant added to the bath may be any suitable liquid detergent, but it is preferred to use diethylene glycol since this specific surface- active agent results in dyed sutures of greater tinctorial strength. The bath is then heated to

boiling with occasional stirring and acidified by adding glacial acetic acid. The sutures are then removed from the bath, washed, and dried to provide a product in which the fluorescent dye is actually diffused throughout the formed filaments and is not merely on surface thereof.

The amount of fluorescent dye incorporated into the suture material may vary by controlling certain parameters of the method of dyeing, e.g., the concentration of the dye in the bath during boiling, the duration of the dyeing reaction, the suture materials employed, and the like. In general, the concentration of dye in the bath will range from as little as about 1 percent by weight to as much as about 15 percent or higher in some cases. The amount of dye actually distributed throughout the suture filament to produce a fluorescent effect may vary considerably and generally ranges from as low as about 0.000001% up to as much as about 10% by weight of the dyed suture. In most instances, the dye will penetrate sufficiently into the suture structure to give a deep color which is not prone to deterioration. Of course, in dyeing multifilament sutures, it is not necessary that every filament within the suture be individually or completely impregnated with the dye material .

Sterilization of the dyed sutures may be subsequently accomplished by exposure to heat or sterilizing agents such as gamma rays, ethylene oxide gas, cobalt 60, and the like without any significant loss of properties. It is also possible to sterilize the suture material at any time prior to, during or after formation of the final suture structure.

As indicated hereinabove, the surgical sutures of the present invention find wide applications, especially amongst veterinary practitioners for external wound stitching. However, due to their increased visibility and fluorescent properties, the present sutures may find general acceptance amongst dentists, oral surgeons and ophthalmologists for suture identification purposes. As an indirect advantage, pediatric surgeons will no doubt find that the disposition of their young patients will significantly improve from use of the brightly colored sutures of the invention, especially if the children are given the opportunity to select their favorite color. Also, plastic surgeons will appreciate the benefits of the present highly visible sutures and the accompanying assurance of knowing that complete suture removal can be attained by a quick check with any convenient fluorescence-sensing device.

The fluorescent sutures of the present invention will produce visible light of a particular wavelength upon being excited by means of a light source which produces ultraviolet energy within an appropriate spectral band. For practical purposes, any UV light source device such as a small mercury vapor lamp may be utilized in connection with the present invention. The following Examples further illustrate the invention, wherein parts and percentages are by weight unless specifically stated otherwise.

EXAMPLE 1 There were mixed together in a 500 ml . Erlenmeyer flask, 200 ml. of water, 400 mg. of ammonium sulfate, 200 mg. of sodium sulfate and 0.2 ml. of diethylene glycol to form an aqueous solution. To this solution was added 300 mg. of a fluorescent dyestuff of the rhodamine series, available from Day-Glo Color Corp. under the name Grand Yellow D-834. Several strands of multifilament nylon sutures measuring about 6 cm in length each are placed in the dye solution and the resulting mixture is brought to boil by heating the flask over an open burner. The mixture is then boiled gently for 20 minutes with occasional agitation. At this time, 0.2 ml. of glacial acetic acid is added to the mixture, which is boiled for an additional 30 minutes. The suture strands are then removed from the mixture, rinsed in water and allowed to dry.

The above sutures appeared bright yellow when viewed in daylight and exhibited a brilliant yellow color when observed under ultraviolet light.

EXAMPLE 2

The procedure of Example 1 was repeated, except that the fluorescent dyestuff employed was Erio-acid red (acid red-52) available from Burlington Chemical. The dyed nylon sutures of this example showed a pink- tinted color which fluoresces "hot" pink under u1traviolet 1 ight.

Using 150 mg. of the dye of Example 1 in combination with 50 mg. of the above dye, sutures were prepared having a visible orange color. When viewed in ultraviolet light, the sutures fluoresced a brilliant yellowish orange color.

EXAMPLE 3

To a 500 ml. Erlenmeyer flask containing 200 ml. of water, 400 mg. of ammonium sulfate, 200 mg. of sodium sulfate, 0.2 ml. of diethylene glycol and two threads of multifilament nylon sutures, each measuring 8 cm in length, is added 180 m . of the nonf1uorescent pigment Acid Blue #9 available from Pylam Products Co. The resulting mixture is boiled for 10 minutes and 200 mg. of the fluorescent dyestuff Grand Yellow D-834 is then added, whereupon boiling is continued for about 15 minutes with stirring. Glacial acetic acid (0.2 ml.) is added and the mixture is boiled for an additional 30 minutes. The suture threads are then removed from the mixture, rinsed in water and allowed to dry.

The above sutures show a dark green color which under ultraviolet light had a bright yellowish green appearance.

The visible color of the present sutures may be modified by the addition of other nonfluorescent pigments in combination with other fluorescent dyes. Other suitable fluorescent dyes include FDA certified dyes such as Drug and Cosmetic Red #28 (color index name Acid Red 92) and Yellow #8 (color index name Acid Yel low 73) .

It will be apparent that sutures produced in accordance with the foregoing method may be sterilized and finally packed, either dry or in alcohol- containing wrappers, for subsequent use in various external surgical procedures. Thus, it has been found that the brightly colored sutures of the present invention are highly visible for positive identification. The surgical practitioner may then

know immediately upon visual inspection whether all fragments of the suture material have been completely removed and take the necessary action.

The present invention also provides a suture filament which is simple and inexpensive to manufacture. When evaluated under actual use conditions, the present surgical sutures exhibited excellent dye retention and tensile properties. They were further demonstrated to posses an appropriate slick surface to enable quick and easy suture work and, simultaneously, prevent knot slippage.

It should be understood that there may be made various changes and modifications of the representative embodiments herein chosen for purposes of illustration without departing from the spirit and scope of the invention. Accordingly, the forgoing il ustrations are not to be interpreted as restrictive of the invention beyond that necessitated by the fol lowing claims .