Wound Closure

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

2. 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 Historical Background – Sutures

3. 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

4. Suture Classification

5. 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

6. BSRs for Some Absorbable Sutures

7. 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

8. Common Nonabsorbable Sutures

9. 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. Suture Sizes – Two Systems

10. Suture Sizes/Use

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

12. 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

13. Sizes and Breaking Strengths of Dry 2-0 and 3-0 Sutures

14. Coating Materials • Facilitate handling • 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

15. 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

16. 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 Ligating Clips

17. 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 Metallic Clips

18. Polymeric Clips • Absorbable and non-absorbable • Viscoelastic • Creep • Stress-relaxation

19. 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 Stapling

20. Surgical Staples Staple Gun Staple Staple Remover

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

22. 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 Tissue Adhesives Before Curing After Curing

23. 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

24. 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

25. Characteristics of Currently Available Adhesive Systems

26. 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