Sutures, staples, and adhesives Wound Closure Sutures, staples, and adhesives Some material taken from http://www.vetmed.auburn.edu/~hendera/guide/guide1.htm#outline

Historical Background – Sutures Use of textiles goes back at least 4000 years Linen (earliest) Other Fe wire, Au, Ag, dried gut, horse hair, strips of hide, bark fibers, silk, and tendon Up until 1930, catgut and silk Stainless wire and polymers (nylon, polyester, polypropylene) during and after WW II 1970s Dexron® (polyglycolic acid) and Vicryl® (polyglactic acid) resorbable Controlled degradation

The “Ideal” Suture Material Universal applicability – only difference in diameter Limp – easy to handle, no kinks, coiling, twisting, or levitating Biocompatible Inert Strong Frictionless surface to glide through tissue High friction for secure knotting Sterlizable without composition changes Complete absorption, no residue, after healing is complete – no matter how long it takes

Suture Classification Physical/Mechanical Handling Biocompatibility Biodegradation Size (diameter) Number of Filaments Tensile strength and elongation Elastic modulus Bending stiffness Stress relaxation and creep Capillarity Swelling Coefficient of friction Pliability Packaging memory Knot tie-down Knot slippage Tissue drag Inflammatory reaction Propensity toward wound infection, thrombi formation, carcinogenicity, and allergy Tensile breaking strength and mass loss Biocompatibility of degradation properties

Absorbability Lose 50% of breaking strength within 60 days of implanting Monofilament, braided, or twisted Natural or synthetic Natural – enzymatic attack Synthetic – hydrolysis More stable mechanism Rapidity commonly rated as percentage of breaking strength – breaking strength rate (BSR) Can be modified in synthetic sutures

BSRs for Some Absorbable Sutures Natural Fiber Synthetic Fiber BSR Monofilament Poly(glycolide-co-ε-caprolactone) (Monocryl)* Poly(p-diaxonone) (PDS II)* Poly(glycolide co-trimethylene carbonate) (Maxon)+ 7 35 Braided Polyglactin 910 (Vicryl)* Polyglactin 910 (Vicryl Rapide)* Polyglycolic acid (Dexon)+ 15 5 12 Twisted Plain Surgical Gut Light Surgical Gut Medium Surgical Gut Heavy Surgical Gut 1 4 8 11 BSR = Approximate days after placement when 50% of breaking strength remains. *Ethicon Inc., +Davis & Geck Inc.

Nonabsorbable Retain majority of breaking strength for more than 60 days Three classes Class I – silk, monofilament, and sheathed Class II – cotton and linen Class III – metallics Classes I and III most common as Class II are prone to contamination and infection

Common Nonabsorbable Sutures Monofilament Polypropylene (Prolene* & Surgilene+) Nylon (Ethilon* & Dermalon+) Braided Polyester (Mersilene*) Silk Nylon (Surgilon* & Nurolon+) Braided & Coated Polyester & Polybuterate (Ethibond*) Polyester & Silicone (Tichron+) Polyester & Teflon (Tevdek#) Silk & Beeswax Multifilament Sheathed Multistrand Nylon & Polyethylene Sheath (Supramid$) *Ethicon Inc., +Davis & Geck Inc., #Deknatel Inc., $S. Jackson Inc.

Suture Sizes – Two Systems United States Pharmacopœia (USP) Complex relationship between diameter, tensile strength, and knot security Precise criteria vary with suture class, natural or synthetic, and absorbability Whole numbers from 5 to 12-0 Allows comparison among different types European Diameter in mm Differences in tensile strength of materials make comparisons difficult Sutures function best when their strength and tissue strength are similar.

Examples of Suture Sizes for Use in Pet Animals Suture Sizes/Use Examples of Suture Sizes for Use in Pet Animals 10-0 - 8-0 7-0 - 5-0 4-0 - 3-0 2-0 - 0 1 - 2 Microvascular Corneal Ophthalmic Neural Vascular Skin & Subcutis Bowel Bladder Abdominal Fascia Stomach Hernia Rib Retention Cutaneous Stents Increase or decrease abdominal fascia and retention sutures appropriately based on weight & suture pattern

Tensile Strength of Sutures Dependent upon Material Size/diameter Condition Wet Dry Knotted Absorption of bodily fluids Hydrophobic Hydrophilic “Abuse” Heat history – “re-autoclaving”

Knot Strength vs. Tensile Strength Strength of a knotted suture generally significantly less than strength of a straight yarn (~ 50%) Knotting induces stresses in the suture due to bending and twisting As knotted suture pulled compressive stress develops increasing residual stress and lowering overall strength values

Sizes and Breaking Strengths of Dry 2-0 and 3-0 Sutures Straight Pull Knotted Pull Dia. inches No. 3-0 No. 2-0 3-0 2-0 lbs. psi. Surgical Gut Dexon Vicryl PDS II Maxon 0.0125 0.0100 0.100 - - 0.0160 0.0127 0.0130 0.0130 0.0153 6.7 6.1 - - - 54600 77800 - - - 9.8 9.6 - 11.5 14.8 48000 75900 - 80000 80000 3.8 3.9 5.0 - - 30900 49700 - - - 5.7 6.4 7.9 - 10.8 28000 50300 - 50000 58000 Silk Cotton Polypropylene Nylon Polyester 0.104 0.0103 - - 0.0097 0.0131 0.0128 0.0123 0.0131 0.0131 5.3 4.0 - - 8.5 62400 48000 - - 115000 8.2 5.5 7.6 9 14.5 60900 40200 63000 67000 107600 3.4 2.7 3.8 4.3 3.7 40000 32400 - - 50100 4.8 3.5 5.5 6.5 6.8 35600 27200 46000 48000 50400

Coating Materials Facilitate handling Nonabsorbable coatings Ease of passing through tissue Ease in sliding knots down But can result in poor knot security Nonabsorbable coatings Beeswax Silicone Paraffin wax Poly(tetrafluoroethylene) Absorbable Must be absorbable like the suture Water soluble Water insoluble – break down by hydrolysis

Problems Associated with Surgical Sutures Time-consuming nature of secure knot tying Need for knot security under all conditions with all sutures Risk of suture breakage during surgery Loss of control due to needle slippage or rotation within the needle holder Postsurgical slippage of the knotted suture Early or pathologically induced degradation of absorbable suture

Ligating Clips Essentially “clips” to replace sutures when occluding (closing) the lumen (central canal) of a vessel or tubular organ Blood vessels Gynecological & urological (GU) procedures Metallic or polymeric Requirements Nontoxic and biocompatible Absence of allergic and immunogenic effects Tolerated by wide range of tissue types High strength and low solubility Finite longevity Secure

Metallic Clips First – Cushing neurosurgery clip, 1910 Ag wire formed in the shape of a “U” and closed around blood vessel Tantulum (1940) Tubule ligation Others Co-Cr Titanium Stainless Steel “Memory metal” – Ni-Ti alloy Desirable properties in metallic clips High strength Malleability & ductility – can make fine wire Capacity for work-hardening Corrosion resistance Some problems Allergic reaction Radio-opaque – can cause problems with CT, X-ray, and MRI examinations

Polymeric Clips Absorbable and non-absorbable Viscoelastic Creep Stress-relaxation

Surgical Stapling Introduced in the late 1970s Used widely in human and veterinary medicine Gynecological Cardiovascular Gastrointestinal Esophageal Pulmonary Staples originally stainless but now Ti and polymeric used Polymeric – 2 parts “U”-shaped fastener Figure “8” retainer

Surgical Staples Staple Staple Gun Staple Remover

Staples & Clips vs. Sutures Speed Convenience Reduced infection rate Lower cost If done properly, no cosmetic difference

Tissue Adhesives Sterilizable Easy in preparation Before Curing After Curing Sterilizable Easy in preparation Viscous liquid or liquid possible for spray Nontoxic Rapidly curable under wet physiological conditions (pH 7.3, 37°C, 1 atm) Reasonable cost Strongly bondable to tissues Biostable union until wound healing Tough and pliable Resorbable after wound healing Nontoxic Nonobstructive to wound healing or promoting wound healing

Natural Tissue – Fibrin Glue First reported in 1940 Mimics blood clot – major component fibrin network Excellent tissue adhesive but insufficient in amount for larger wounds Nontoxic if human protein sources are used to obtain fibrin

Synthetic Systems: Poly-Alkyl-2-Cyanoacrylates Discovered in 1951 “Crazy Glue” H2C=C―CO2―R CN R = alkyl group CH3 (methyl) H3CCH2 (ethyl) Release small amount of formaldehyde when curing amount lessens with length of alkyl chain

Characteristics of Currently Available Adhesive Systems Fibrin Glue Cyanoacrylate Handling Excellent Poor Set time Medium Short Tissue bonding Good Pliability Toxicity Low Resorbability Cell infiltration

Other Experimental Systems Gelatin-based adhesives Mimic coagulation but without fibrin Polyurethane (-HNOCO-) based adhesives Capped with isocyanate to rapidly gel upon exposure to water More flexible than current cyanoacrylate adhesives Collagen-based adhesives