S1 L5 Surgical dressings

1. S1 L5 Surgical dressings Anna Drew NOTES: Linked with carbohydrates (Semester 3 of pharmacognosy) Traditionally plant fibres were used With recent advances in wound-healing many materials of non-vegetable origin are now used

2. Surgical dressings & sutures • Composed of fibres • A solid characterized by • Flexibility • Fineness • High ratio of length: thickness • length at least 1000 times their breadth • Important to: • Forensic science • Pharmacy • For quality control • To determine price v quality for bulk purchasing • Identification • Macroscopical examination • Chemical tests • Performed on a microscope slide • Observed under the microscope

3. Classification of fibres used in surgical dressings

4. Animal fibres • WOOL • From the fleece of the sheep Ovis aries • Treated before use to degrease it • Washed with water, then soap solution, then bleached with sulphuric acid, (acetone removes wool fat), combed, graded • Made of • protein (keratin) [flame tested by burning] • Stretched (unstable) form β keratin • Elastic when let go • Unstretched (stable) form α keratin • Forms peptide links in chain strands • Also contains cysteine in sulphur bridges which give elasticity • [test for sulphur]

6. Uses • Chiropody ie to spread toes • Crepe bandages with cotton/rayon • Wool gives elasticity and warmth • Microscopically • Covered by epithelial scales • Marked; shape and arrangement varies in different breeds • Number of scales per 100 µm length is fairly constant (average 9.7-12.1) in different wools • Counts can distinguish x 130

8. SILK • Prepared fibre from the cocoons of silk worms Bombyx mori • Also from other Bombyx, Antheraea species • China, Japan, India, Asia Minor, Italy, France etc • ‘Wild silks’ • A. mylitta (India) • A. assama (India) • A. pernyi (China) • A. yama-mai (Japan) • Caterpillar -> chrysalis / pupal stage • Secretes an oval cocoon 2-5cm long around itself • Made of continuous thread up to 1200m long! • Chrysalis killed by 60-80ºC few hours or a short steam burst • Graded, hot water, beaten to remove outer layer and soften glue • Loose ends of 2-15 cocoons spun into a single thread • Generally 5 cocoons ie 5 bave, 10 brins (>6 brins too fine)

9. Made of • 2 silk or fibroin fibres • cemented together with silk glue / sericin • Sericin removed by hot soap solution • fully extended chains of alanine and glycine • Non-elastic, don’t double up like wool • Contain no sulphur [negative sulphur test] • Uses • Dressings a bit • eg Oil Silk BPC in surgery • to stop other dressings drying out, cover them • Sutures, ligatures • Non-absorbable • Quite strong • Do not disintegrate when wet • Microscopically • A solid rod-like fibre • Lack of cellular structure • No distinguishing features

11. Animal fibres - different microscopically, differentiated by following chemical tests:

12. Vegetable fibres • COTTON • Cheap and used a lot • USA produces about half; rest Eqypt, India, South America • Source • epidermal trichomes covering seeds of Gossypium herbaceum • Ginning – removes long hairs (better quality) • Linter – removes remaining short hairs • Gives poorer quality cotton (-> cotton wool) • Made into chemical pulp or viscose rayon • Then seeds are pressed to get cotton seed oil • Then seeds used as animal crop

13. Production • Raw cotton has a waxy (fatty) cuticle covering the trichome • Making it fairly non-absorbent • Removed by soaking (or pressure heating) loosened cotton in alkali (NaOH, KOH) • To get absorbent cotton (trichome wall is absorbent) • Then washed, bleached and mechanically loosened ‘scutched’ • Grades • Raw cotton • very impure, only used to absorb spillages • Hospital quality absorbent cotton wool • poorer quality to BPC • BPC • has some impurities • almost impossible to remove all as too expensive • BPC has limits • certain amount of shell & leaf material allowable • Want a minimum for surgical procedures • (rarely used in the body cavity or wrapped in gauze first to prevent loose fibres going into the body)

14. Made of • Primary and secondary cellulose cell walls • Secondary wall constitutes the main bulk of cotton • Raw cotton consists of 90% cellulose • Cellulose molecule made of glucose residues • Repeating unit is ‘cellibiose’ = 2 glucose residues linked by a 1-4β glucosidic bond • Uses • Bandages – gauze linen in very absorbent • Microscopically (of unbleached cotton) • Unicellular hairs look like flattened twisted hose pipes • [Staining with CuOxam -> ballooning]

15. x 130

16. Cotton fibres in longitudinal view (x 250) and transverse section (x 500)

17. CHEMICAL WOOD PULP (WOOD) • Derived from pine and spruce wood ‘off cuts’ • Production • ‘ Delignified wood’ produced by “Sulphite process” to leave the cellulose • Wood chopped into chips – allows penetration • Calcium bisulphite and H2SO4 added to hydrolyse any material other than cellulose • Then washed, bleached, rolled, pressed into board and dried • Composed of cellibiose • Uses • Cellulose wadding BPC • Easily disintegrated • no intinsic structure so falls apart when wet • not used for dressings • but to catch and absorb spillage of wounds, heavy discharge and incontinence • Microscopically • Looks like tracheids with border pits [distinguishes it from cotton]

18. Cellulose wadding (x 130)

19. JUTE • Phloem fibres from stem bark • Corchorus capsularis, C. olitorius, other species • Bengal delta region, Assam, Bihar, Orissa • Fibres separated -> hesian and sacking • Remaining short fibres ‘tow’ – jute in pharmacy • Lignocellulose; nitric acid, potassium chlorate used to disintegrate bundles • FLAX • Pericyclic fibres of Linum usitatissimum stem • Commercial fibres show fine tranverse injuries from preparation • Good quality fibre only lignified in middle lamella • HEMP • pericyclic fibres of Cannabis sativa stem • Mostly cellulose, minimal lignification • Fibre ends bluntly rounded, some forked from injury • Lumen flattened or oval

20. Above: Flax (x 130) Right: Jute (x 300) A. Strand of fibres B. Apices of isolated fibres C,D. Tranverse sections

21. Vegetable fibres: chemical tests, differentiated micropscopically

22. Regenerated fibres • Produced from • naturally occurring, long chain molecules • isolated, controlled and possibly modified • semi-synthetic • VISCOSE RAYON • viscose rayon, viscose, rayon, regenerated cellulose • Made from • Linters, inferior grade of cotton short hairs, or wood pulp • Cellulose is dissolved by adding alkali • and then carbon disulphide to reprecipitate it • Precipitate is forced through a metal sheet with holes • Into a coagulating fluid to produce fibres of required length/diameter • TiO2 is added to the pecipitate solution to delustre rayon (slimey sheen) • Hence specks coating the surface can be seen under microscope • Can get the desired quality free from impurities

23. Delustred viscose rayon filaments in longitudinal view (x 250) and transverse section (x 300) Viscose rayon filaments in longitudinal view and transverse section (x 250)

24. Use • in a mixture with cotton as non-surgical absorbent material • Macroscopically • Its tensile strength varies from 2/3 to 1.5 that of cotton • When wet it loses about 60% of its tensile strength (more than cotton) • If more than a certain amount it used material may need to be made water-repellant Eg cotton crepe bandage • Microscopically • Fibres are solid and transparent • Slight twist with grooves along their length • From being immersed in the regenerating solution • Ends of fibres are abrupt • [Seen in chloral hydrate solution and lactophenol] • [Invisible in in cresol (same refractive index)] • Comparison with cotton: • Impurities in cotton • Waxy material never completely removed from cotton • When stored in a warm temperature pockets of wax move out and coat fibres • therefore absorbency lost on storage

25. CELLULOSE ACETATE • Largely superseded by synthetic fibres • Production: • Cotton linters and delignified wood pulp -> purified cellulose • Partially acetylated by mixing with glacial acetic acid, acetic anhydride and a catalyst • Precipitates as acid-resin flakes • These are dissolved in acetone • Then the solution is filtered and spun down a column of warm air • Produces filaments made of 200-300 ‘glucose’ residue units • Properties: • Less absorbent that viscose rayon • Unsuitable for surgical dressings • Loses less strength when wet • Use: component of plastic splinting bandage • Like Nylon produces static electricity • Macro/microscopically • Similar to viscose rayon

26. ALGINATE Laminaria hyperborea, other sp, Ascophyllum • Alginic acid comes from cell walls of brown algae • Production: • Alginate fibres are produced by a similar process to viscose rayon • Sodium alginate solution is pumped through a spinneret immersed in a bath of CaCl solution (acidified with HCl) • Water insoluble calcium alginate is precipitated as continuous filaments • Collected, washed, dried, reduced to staple form which is processed to calcium alginate wool or a fabric Eg gauze • Composed of • polymers of mannuronic and guluronic acids • Uses • absorbable haemostatic surgical dressings • internal – neurosurgery; external – burns, skin graft sites • bacterial swabs • Microscopy • Similar to viscose rayon (solid grooved rods)

27. Alginate fibres in longitudinal view and transverse section (x 250)

28. Synthetic fibres • Polyamides • NYLON • Condensation polymer • Made of adipic acid and hexamethylene diamine • Polypeptide chain • Like silk structurally • Can be autoclaved • Very strong material • Use: sutures • Polyesters • TERYLENE • Condensation polymer resin • Made of ethylene glycol and terephthalic acid • Can be autoclaved • [Distinguished by chemical tests] • Use: sutures, (preparation of artificial grafts) • POLYPROPYLENE • Addition polymer • Can be autoclaved • Non-absorbable • Use: catheters, sutures

29. Delustred nylon fibres in longitudinal and transverse section (x 750) Delustred terylene fibres in longitudinal and transverse section (x 500)

30. Man-made fibres: solid with limited diagnostic structure, chemical tests more useful