A Review of Dressing Materials Used for the Treatment of Raw Areas in Plastic Surgery.

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A REVIEW OF DRESSING MATERIALS USED FOR THE TREATMENT OF RAW AREAS IN PLASTIC SURGERY. J. M. PORTER Locum Consultant and Hand Fellow. Plastic Surgery and Burns Unit, Aberdeen Royal Infirmary. INTRODUCTION Hu.man beings have a deep rooted instinct to cover wounds with a dressing and the instinct is equally strong in patients and ·their medical attendants. In the earliest times the choice of dressing materials was probably empirical, based on the accumulated experience of generations. At the time from which the first records of surgical dressings survive, the practice of medicine was also influenced by superstition and the dictates of various religious bodies. During the period of time between the fall of the Roman Empire and the Reformation, the writings of authorities such as Galen achieved the status of holy writ and were therefore rarely questioned. Even after the Reformation wound management on scientific and rational grounds made slow progress t;z. As far as is known, wounds were most often covered with cotton orlinencloths, which were frequently reused if the materials were in short supply. After the discovery that wound infection was caused by microorganisms, there was a need for sterile dressings and a variety of new materials were introduced. These dressings were required to soak up infected wound discharge, give mechanical protection, prevent bacteria gaining access to the wound and to act as carriers for various antiseptic agents. The most successful were made from cellulose fibres, derived from plant sources 3 and these materials are still in everyday use today. The old dressing materials did not affect the wound healing process and in certain circumstances may have hindered it. During the last 30 years the process of wound healing has become better understood and new dressings have evolved, which aim to provide the best possible environment at the wound surface for healing to proceed. 4 In 1825 Syme deplored surgeons 'who will hardly be induced to abandon the old established customs in which they have been educated' 2 • Surgeons have traditionally been conservative in their choice of dressings and the surgeon of 100 years ago would have no difficulty in recognising many of the materials that are still in common usage today. The choice of dressings at the present time, is usually based on the surgeon's experience rather than on the results of laboratory experiments, clinical trials or knowledge of how the dressing material affects the wound healing process. A recent textbook on wound healing for surgeons 5 considers the effect of dressings on wound healing in 7 pages out of 344. Plastic Surgeons are frequently asked to re-surface large skin defects. When first seen, many of these defects are unsuitable for immediate closure with skin grafts or skin flaps, due to infection or the presence of devitalised tissue in the wound. Dressings are required which will promote the separation of dead tissue, enhance the development of granulation tissue,

remove discharge from the wound surface and prevent further tissue loss through desiccation of the wound. Burns, ulcers, soft tissue injuries and pressure sores all have specific dressing requirements. Split skin grafts require dressings which will immobilise, protect and, if the graft has been meshed, promote re-epithelialisation. Split skin graft donor areas likewise require dressings which will allow re-epithelialisation to progress unimpeded. In the present article, the effects of the older dressing materials on wound healing and their common uses in Plastic Surgery are reviewed. The role of the new dressing materials has yet to be defined, therefore only materials which are useful for treating large skin defects are considered. CELLULOSE BASED DRESSING MATERIALS. In 1880 Samson Gamgee discovered that cotton wool, from which all traces of oily material had beenremoved by bleaching, was highly absorbent 6 • The dressing pads, which now bear his name, are pads of absorbent cotton wool, wrapped in a few thicknesses of gauze. Similar dressings can be made up in large sheets for covering burns 7 • Gauze and cotton wool are made from cellulose, derived from various plant sources, mainly cotton or wood pulp. The cellulose fibres may be carded (cotton wool) or woven into a loose cloth, with a warp and weft (gauze). At the present time, most wounds are dressed using these by now traditional materials.

The effect of cellulose based dressings on the healing of an open wound is not fully understood. It has been shown in experimental wounds that fragments of gauze can become embedded into wounds, causing a foreign body inflammatory response 8 • It is probable that the main effect of gauze dressings on wound healing is due to the dry environment which is created at the wound surface. Gauze dressings are only a barrier to the passage of microorganisms if dry. A cellulose based dressing is permeable to micro-organisms, if it is allowed to become wet through with exudate from· the wound 9 • This phenomenon is known as strike-through. Cotton wool impregnated with an antiseptic, has been shown to prevent the passage of bacteria, after strikethrough has occurred 10• The amount of exudate that can be absorbed before strike through occurs varies with the properties of the cellulose fibres, gravity, the physical properties of the exudate, the rate of fluid discharge from the wound and compression of the dressing due to bandages and body weight. Cotton wool has been shown to absorb less fluid when compressed, whereas gauze will absorb the same amount of fluid at low and high compression 3•

The Journal of Tissue Viability April Vol 1 No 2 Gauze and cotton wool are most commonly used to cover raw surfaces in Plastic Surgery. Bums 7• 11 , meshed split skin grafts, skin graft donor areas, discharging leg ulcers, wounds and pressure sores all require dressings which will remove exudate from the wound surface; cellulose based dressing fulfil this function effectively, if applied in sufficient quantity. However, the tendency of the gauze to stick to the wound is a constant problem, even if the gauze is coated with greasy substances. Removal of an adherent dressing is painful and may damage newly grown epithelium. AGENTS ADDED TO CELLULOSE BASED DRESSINGS. Cellulose based dressings are frequently used as carriers for various lotions or ointments and the effect of gauze dressings on wound healing cannot be considered in isolation from the effect of the agents added to the gauze. All too often, antiseptics are applied to raw surfaces with the intention of destroying bacteria but with no consideration of their effects on the process of wound healing 12• Bacterial colonisation of the wound surface does not delay wound healing 8 and bacteria are only harmful if they cause inflammation of the tissues surrounding the wound.

Hypochlorites. Since the introduction of Dakin's solution during the first world war, cellulose based dressings soaked with hypochlorites have often been applied to raw wounds, with the objectives of cleaning the wound, encouraging the separation of dead tissue and promoting the formation of granulation tissue. A variety of different solutions are available (Eusol, Milton, Chlorosal, Dakin's solution).

Hypochlorites are weakly bactericidal in a watery medium but rapidly lose their bactericidal action when diluted in serum, blood or pus 13 • Hypochlorites have no effect on bacteria within the tissues 13 • In the laboratory, hypochlorites have been shown to destroy leucocytes 13 stop capillary blood flow within granulation tissue 14 delay the production of collagen 15 , prolong the inflammatory response15 and delay the re-epithelialisation of partial thickness skin wounds 8 • Eusol and Milton have been shown to have no effect on the bacterial colonisation of wounds 13 burns 16 and venous ulcers 17 • Hirshowitz et al have shown that irrigation with Milton expedites the separation of burn eschar; this observation was not controlled 16 • Irrigation of wounds with a hypochlorite solution does not achieve a bactericidal effect at the wound surface 8 ; the promotion of eschar separation was probably due to the wet environment at the wound surface. Hypochlorites have been sanctified by prolonged clinical use but the decision to apply a hypochlorite to a raw surface is usually made on empirical grounds. Hypochlorites appear to be effective in cleaning wounds, although any beneficial effect may really be due to the frequent changing of the dressing. Hypochlorites have an 'antiseptic' smell and this characteristic odour is more acceptable to patients and their doctors than the smell of a suppurating wound. Some patients experience considerable pain when hypochlorites are applied to raw surfaces.

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Hypochlorites are widely used in Plastic Surgery, as they are in most other branches of surgery. Gauze dressings soaked with hypochlorites are usually effective in £leaning discharging wounds in preparation for flap closure or skin grafting but the dressings have to be changes frequently to be effective. When the wound surface has been successfully cleaned, the available laboratory evidence would suggest that the application of hypochlorites should be discontinued. Although hypochlorites are widely used in surgery and dermatology, there is hardly any evidence of their actual effect from a controlled clinical trial in the human subject. Petroleum Jelly. Cellulose based dressings are widely available, impregnated with petroleum jelly. These preparations are commonly known as paraffin gauze or 'Tulle Gras', which has been defined as a 'fabric ... , (with) weft and warp threads of cotton and/or viscose yarn, impregnated with white or yellow soft paraffin)' 18 • The soft paraffin is intended to render the dressing non-adherent. Tulle Gras tends to dry the wound surface, adhere and become difficult to remove. If the dressing sticks to the wound surface, its removal can damage regrowing epithelium. Tulle Gras is less likely to adhere if a generous amount of paraffin is added to the gauze but the film of paraffin tends to obstruct the passage of exudate from the wound surface.

USP petrolatum has been shown in the pig model to retard reepithelialisation of partial thickness skin wounds, although low melting point petrolatum did not have the same effect 19 • Apart from this investigation, there is no compelling laboratory evidence that petrolatum inhibits epithelial migration and most surgeons substitute Tulle Gras for hypochlorite soaked gauze dressings, when discharging wounds have been cleaned. Tulle Gras and similar preparations are widely used in Plastic Surgery. Due to the problem of adherence, they are not as frequently used for donor sites as formerly. Almost all skin grafts are dressed with paraffin gauze, which is highly conformable and can be used to pack grafts into irregular wound cavities. Paraffin gauze is also mildly adhesive and can therefore immobilise skin grafts. As Tulle Gras dressings act as a barrier to the absorption of wound exudate, they are not suitable for dressing exuding wounds, ulcers and pressure sores. Antiseptics and antibiotics Commercial paraffin gauze preparations, medicated with chlorhexidine and various antibiotics are widely available. Antibiotic creams and antiseptics can also be added to unmedicated gauze, prior to placing the gauze in contact with the wound. As a number of these substances have been shown to affect wound healing in the laboratory but corresponding evidence in the human subject is scanty.

In the laboratory, 0.05% chlorhexidine has been shown to have no effect on capillary circulation 14 or collagen production 15 but the growth of neoplastic and non-neoplastic cell lines is inhibited after 60 minutes exposure 20• 0.5% chlorhexidine has been shown to inhibit the formation of granulation tissue in the guinea pig 21 and 0.2% chlorhexidine has been shown to delay

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The Journal of Tissue Viability April Voll No 2

the re-epithelialisation of partial thickness skin wounds in the pig 8 • In both the guinea pig and in man, Tulle Gras impregnated with 0.5% chlorhexidine has been shown to decrease the rate of colonisation of burns with staphylococcus aureus, when compared to unmedicated Tulle Oras 22 • The healing rated of burns under Tulle Gras medicated with chlorhexidine and nonmedicated dressings are similar. The development of bacterial resistance to chlorhexidine does not seem to be a problem 22 • Nitrofurazone is an antibacterial which can be added to Tulle Gras. It is effective against a wide range of organisms, although not against pseudomonas. In the pig, nitrofurazone has been shown to inhibit the spread of epidermal cells across partial thickness skin wounds 19 • Nitrofurazone Tulle Gras has been most commonly used for the treatment of burns. In burn wounds this dressing is effective in producing a clean granulating surface but can cause considerable pain on application. A number of paraffin gauzes have been marketed, medicated with antibiotics. The use of these dressings has been restricted, due to the problems of skin sensitisation and the development of antibiotic resistant organisms 23 • Antibiotic creams have been shown to improve the re-epithelialisation of experimental wounds, but this effect can also be seen if the wound is covered with the cream base 19 • Only in burns have antibacterial creams been shown to decrease the incidence of wound infection 11 .24. Reports as to whether providone iodine delays healing in experimental partial thickness skin wounds are variable. Providone iodine has been shown to inhibit the formation of granulation tissue in the guinea pig, although the effect was less than the effect of 0.5% chlorhexidine 25 • In the pig wound model, providone iodine has been shown to delay healing and not to achieve a bacterial concentration at the wound surface 8 •

The New Dressing Materials. Gauze and cotton wool dressings can be considered to be 'passive products' in that they take no part in the wound healing process. During the last 30 years, new dressing materials have been designed specifically to provide optimum conditions for wound healing. These dressings have been classed as 'interactive' 4 • In 1962, Winter showed, in the large white domestic pig, that excised partial thickness skin wounds occluded with sterile polythene sheeting re-epithelialised more rapidly that control wounds exposed to the air 26 • The occluded wounds were found to heal in a different manner to the exposed wounds. The wounds, which were left exposed to the air, dried out and formed a scab. The scab was formed from the outermost layer of the wound and the regrowing epidermis spread beneath the scab to cover the wound. The occluded wounds did not form a scab and the epithelium was found to spread directly over the surface of the wound. These findings have been duplicated in experimental wounds in man 27 • Polythene sheeting is not suitable for wound dressing, as it obstructs the passage of blood and wound exudate from the surface of the wound. Winter showed subsequently, in the same pig model, that epidermal wound healing under an absorbent polyurethane foam dressing is similar to epidermal healing under polyurethane sheeting 28 •

Following the results of these laboratory experiments, dressing materials were devised, which were designed to create a moist environment at the healing wound surface. Performance criteria for these new materials have been outlined by Turner 4 • The new dressing materials have generally failed to replace the traditional materials in Plastic Surgery. Some of the new materials have proved to be difficult to use and to be more expensive than cellulose based dressings, although the overall cost of the new dressings can be decreased if the dressing changes are infrequent. Some surgeons have yet to accept that moisture at the wound surface is advantageous and continue to believe that the wound surface should not be allowed to become 'macerated'. The following list of the new materials is by no means exhaustive; only materials which have immediate relevance in Plastic Surgery are discussed.

Polyurethane Film Dressings. Polyurethane film dressings (Opsite) were first developed as skin drapes for operative surgery and were subsequently used as wound dressings 29 • These materials maintain a moist environment at the wound surface by retaining wound exudate. Polyurethane films are impermeable to bacteria and water but are permeable to water vapour and oxygen. There is some evidence that leucocytes are active in the exudate under the dressing 30 • Polyurethane film dressings have been used in Plastic Surgery to dress split skin graft donor sites 29• Donor sites have been shown to heal more rapidly under these dressings than under Tulle Gras or fine mesh gauze and with less pain 31 •32• The main practical problem with polyurethane film dressings is the difficulty of avoiding messy and smelly leakage of wound exudate from beneath the dressing. Polyurethane film dressings are most convenient for dressing buttock donor areas, particularly in children. If leakage occurs the dressing is relatively easy to change.

Alginates Calcium sodium alginate (Kaltostat) is a naturally derived polysaccharide, which is produced from brown seaweed. Alginates were first developed as haemostatics 33• 34 and were subsequently adapted for use as surgical dressings 35 • Alginate dressing materials are supplied as non-woven mats. When brought into contact with a raw wound surface, the alginate is transformed into a hydrophilic gel, by an ion exchange reaction between calci urn in the alginate and sodium in blood and wound exudate. The gel is non-adherent, non-toxic and bio-degradable. If the alginate is applied dry to a raw wound surface, difficulties may be encountered in getting the gel to form; if this process fails the dry alginate sticks firmly to the donor area and does not separate until the wound has healed 36 • This is not necessarily to the patient's disadvantage, but the time taken for the wound to be free from dressings is prolonged by comparison to the time taken after dressing with hydrocolloids and a premature attempt at removing the dressing can damage the ,wound surface 36 •

The Journal of Tissue Viability April Voll No 2 Calcium alginate dressings are haemostatic 34, as the release of free calcium ions provides an essential factor for the clotting cascade. Commercially available alginate products have been shown to increase the division rate of fibroblasts 4 • In Plastic Surgery, alginates have been widely used for dressing split skin graft donor areas, which heal more rapidly under alginate dressings than under Tulle Gras 35 • Alginate dressings are easy to apply in the operating theatre and require little aftercare; they are highly suitable for dressing donor areas in outpatients 36 • Alginates are excellent dressings after facial dermabrasion, after surgery for rhinophyma and for grazing wounds of the face. Alginates have also been used for packing pressure sores and dressing ulcers. There is as yet no conclusive evidence that they offer any advantage over traditional dressings in the treatment of these problems. Alginates are freely permeable to wound exudate once saturated with blood or wound exudate and have to be covered with layers of absorbent cellulose based dressings to prevent strike through.

Hydrocolloids. Hydrocolloid dressings (such as Granuflex) are supplied as membranes, which are composed of two layers. The outer layer is a polyurethane foam sheet, which is impermeable to gases, bacteria, water vapour and fluids. The inner layer is a hydrocolloid polymer complex, which also contains elastomeric and adhesive compounds. The inner layer is adhesive, when in contact with normal skin, but when in contact with a raw wound surface the hydrocolloid reacts with the wound exudate to produce a non-adherent gel, which maintains a moist environment at the wound surface. Hydrocolloid dressings have been shown to stimulate angiogenesis 37 and fibrinolysis 38 • There is no evidence that the moist environment under the dressing encourages the proliferation of pathogenic bacteria 39 and viable leucocytes have been shown to be present in the gel 29 • Split skin graft donor areas have been shown to heal more rapidly under hydrocolloid dressings than under conventional gauze dressings but healing is not improved by comparison with polyurethane film dressings 40 • Hydrocolloid dressings have been used successfully to treat advanced venous ulceration 41 • Partial thickness bums have been shown to heal more rapidly under hydrocolloid dressings than under cadaver skin 42 or silver sulphadiazine cream 40 • 42 but hydrocolloid dressings have no advantages over medicated Tulle Gras in the treatment of outpatient bums 43 • Pre-tibial lacerations have been shown to heal at a similar rate if treated with hydrocolloid dressings or paste bandages 44 • There is some evidence that split skin graft donor areas heal more rapidly under hydrocolloid dressing than under algi nates 36 • If continuous adhesion to the surrounding skin can be maintained all around the pool of gel, hydrocolloid dressing can be left in place for a prolonged period of time. If the gel leaks out from beneath the dressing, the result is an evil smelling discharge, which is usually mistaken for a wound infection. In this event, the correct course of action is to remove the dressing and to substitute a fresh hydrocolloid dressing. This can easily be

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accomplished if the patient is still in hospital but if the patient has been discharged from hospital, another visit may be necessary for a fresh dressing to be applied. The problem of wound leakage limits the usefulness of hydrocolloids, if there is a copious amount of wound discharge.

Hydrogels. Hydrogel dressing (Geliperm) are supplied as transparent, jelly like sheets which consist of a gelable polysaccharide and the cross-linked absorbent polymer of an acryl derivative, in 9697% water. When in contact with raw surfaces these materials need to be kept in place with an overlying absorbent dressing pad. Hydrogels are absorbent until they are saturated with water but are impermeable to bacteria. They can be used as a vehicle for various medicaments. Hydrogels cannot maintain a moist wound surface unless they are regularly wetted with saline; if allowed to dry out the dressing will adhere to the wound surface. In this respect they are inferior to hydrocolloids, which will maintain wetness at the wound surfa¥e without any further attention, for a prolonged period of time. Hydrogel dressings are slippery and are therefore difficult to handle. They are effective in relieving wound pain. Hydrogels have been used in Plastic Surgery for dressing split skin graft donor areas but donor areas have been shown to heal no more rapidly than under paraffin gauze 43 • They are effective dressings for split skin grafts if the hydrogel is not allowed to dry out; dressing adherence may lead to loss of the graft 43 • The need for continuous attention limits their usefulness. Hydrogels have also been used to treat a variety of ulcers and raw areas. Possibly hydro gels are most useful as a temporary dressing for exposed periosteum or dura mater. If the hydrogel sheet can be kept moist, the exposed structures can be prevented from drying out, while they await definitive flap cover.

Recently introduced dressing materials. Hypoallergenic polyamide membrane (Tegapore) has recently been marketed as a transparent sheet, which is claimed to be non-adherent but able to permit the passage of exudate into an overlying absorbent dressing. A flexible double polymer membrane (Flexipore 6000) has also recently been introduced. This material is claimed by the manufacturers to combine the pain relieving and haemostatic properties of the alginates with the controlled and moist wound environment of the hydrocolloids. This material is particularly useful for hand dressings as it is thin and highly conformable. Both these products have obvious potential for dressing donor areas, open wounds and ulcers. They await evaluation in controlled trials in comparison with established dressing materials. CONCLUSION. It is now well established in the laboratory, that partial thickness skin wounds kept in a moist environment heal more rapidly than wounds, which have been allowed to dry and to form a scab. It has also been shown that many of the traditional materials, which are still applied to wounds, do not promote healing and may be harmful if inappropriately used. However the results of this experimental work are not widely known to clinicians and have had little impact in clinical wound man-

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The Journal of Tissue Viability April Vall No 2

agement. Although new dressing materials have been designed to provide optimum conditions for wound healing, these new materials have in some instances proved to be expensive and difficult to use in clinical situations. All to often, the manufacturers of the new dressings have offered anecdotal evidence for their effectiveness. Although there is experimental evidence that dressings of all types affect the wound healing process, there is a lack of corresponding clinical evidence. More research is required to elucidate the effects of the older dressing materials on wound healing in man. There is also a need for comparative studies, in which the new dressing materials are compared with the older materials and with one another, in the human subject. Clinical trials have not always given clear results, as open wounds in the human subject cannot be standardised, with the possible exception of split skin graft donor areas. An additional problem is the difficulty of measuring the progress of wound healing, in a manner that is objective and can be subjected to statistical analysis. The precise time of wound healing is particularly difficult to assess, as most dressings conceal the wound surface and the wound can therefore only be observed during a dressing change. These difficulties should not absolve clinicians from attempting research into wound healing. Until more information is available from trials in the human subject, the choice of dressing materials for surgical wounds will usually remain empirical. ACKNOWLEDGEMENTS. I am much indebted to Mr IFK Muir for his help and advice in the preparation of this paper. I am also grateful to Squibb ConvaTec, Smith and Nephew, the 3M Company, Geistlich and BritCair for supplying information about their products. REFERENCES. 1 Forrest RD. Early history of wound treatment. J Royal Soc Med ,1982; 75:198-205. 2 Bishop WJ. A History of Surgical Dressings.Robinson and Sons Ltd. Chesterfield. 1959. 3 Piskozub ZT. The efficiency of wound dressing materials as a barrier to secondary bacterial contamination. Br J Plast Surg ,1968; 21: 387-401. 4 Turner TD. The development of wound management products. Wounds ,1989; 1:155-71. 5 Bucknall TE. Ellis H (Ed). Wound healing for Surgeons. Bailliere and Tindall. 1984. 6 Gam gee JS. Absorbent and medicated surgical dressings. Lancet., 1880; 1:127-8. 7 Davis JH, Artz CP, Reiss E, Amspacher WH. Practical technics in thecaseoftheburnpatient.AmerJSurg, 1953; 86: 713-7. 8 Archer GA, Barnett S, Irving S, Middleton KR, Seal DV. A controlled model of moist wound healing: comparison between semi-permeable film, antiseptics and sugar paste. J Exp. Path.,1990; 71: 155-70. 9 Colebrook K, Hood AM. Infection through soaked dressings. Lancet 1948; 2: 682-3 10 Lowbury EJL, Hood AM. A disinfectant barrier in dressings applied to burns. Lancet ,1952; 1: 899-901. 11 Muir IFK, BarclayTL, SettleJAD. Burns and their Treat-

ment. (3rd Ed) 1987: 67-74. 12 Branemark PI, Albrextsson B, Lindstrom J, Lindborg G. Localtissueeffectsofwounddisinfectants.ActaChirScand Suppl., 1966; 357: 166-76. 13 Fleming A. The action of chemical and physiological antiseptics in a septic wound. Br J Surg, 1919; 7: 99-129. 14 Brennan SS, Leaper DJ. The effect of antiseptics on the healing wound: a study using the rabbit ear chamber. Br J Surg, 1985; 72: 780-2. 15 Brennan SS, Foster ME, Leaper DJ. Antiseptic toxicity in wounds healing by secondary intention .IH osp. Inf., 1986; 8: 263-7. 16 Hirshowitz B, Moscona AR, Lefler E. Milton for the treatment of burns using the irrigation technique. Burns, 1979; 5: 282-4. 17 Daltrey DC, Cunliffe WJ. A double-blind study of the effects of Benzoyl peroxidase 20% and Eusol and Liquid Paraffin on the microbial flora of leg ulcers. Acta Derm Venereol1981; 61: 575-7. 18 British National Formulary. 1990; 19: 416. 19 Eaglstein WH, Mertz PM. Effect of topical medicaments on the rate of repair of superficial wounds. The Surgical Wound. Ed Dineen P, Hildick-Smith G. Lea and Fabiger Philadelphia 1981; 150-70. 20 Blenkharn Jl. The differential cytotoxicity of antiseptic agents. J Pharm Pharmacal, 1987; 39:477-9. 21 Neidner R, Scoph E. Inhibition of wound healing byantiseptics. Br J Dermatol ,1986; 115 (Suppl31): 41-4. 22 Lawrence JC. The treatment of small burns with a medicated chlorhexidine Tulle Gras. Burns, 1977; 3: 239-44. 23 Leaper DJ, Simpson RA. The effect of antiseptics and topical antimicrobials on wound healing. J Antimicrobial Chemotherapy, 1986; 17: 135-7. 24 Fox CL Jr.Silver sulphadiazine- a new topical therapy for pseudomonas infections in burns. Arch Surg ,1968; 96: 184-8. 25 Gruber RP, Vistnes L, Pardoe D. The effect of commonly used antiseptics on wound healing. Plast Reconstr Surg. 1975; 55: 472-6. 26 Winter GD. Formation of the scab and rate of epithelialisation of superficial wounds of the skin of the young domestic pig. Nature, 1962; 193: 293-4. 27 Hinman CD, Maibach H, Winters GD. Effect of air exposure and occlusion on experimental human skin wounds. Nature, 1963; 200: 377-8. 28 Winter GD. Epidermal wound healing under a new polyurethane foam dressing. Plast Reconstr Surg, 1975; 56: 531-7. 29 James JH, Watson ACH. The use of Op-Site, a vapour permeable dressing on skin graft donor sites. Br J Plast Surg. 1975; 28: 107-10. 30 Varghese MC, Balin AK, Carter DM, Caldwell D. Local environment of chronic wounds under synthetic dressings. ArchDermatol, 1986; 122: 52-7. 31 Barnett A, Berkovitz RL, Mills R, Vistnes LM. Comparison of synthetic adhesive moisture vapor permeable and fine mesh gauze dressings for split thickness graft donor sites. Am J Surg 1983; 145: 379-81. 32 Blight A, Fatah MF, Datubo-Brown DD, Mountford EM, Cheshire IM. The treatment of donor sites with cultured epithelial cells. Br J Plast Surg. 1991; 44: 12-4. 33 Blaine G. Experimental observations on absorbable alginate products in surgery. Ann Surg 1947; 125: 102-114.

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34 Groves AR, Lawrence JC. Alginate dressings as a donor venous stasis ulceration. An environment for healing; the site haemostat Ann R Coli Surg Engl. 1986; 68: 27-8. role of occlusion. Ed Ryan TJ. Royal Society of Medicine 35 Attwood AI. Calcium alginate dressing accelerates split International Congress and Symposium Series. No 88; 99skin graft donor site healing. Br J Plast Surg 1989; 42: 103. 373-9. 42 Hermans MHE. Comparison of a hydrocolloid dressing, 36 Porter JM. A comparative investigation ofreepithelialisation silver sulphadiazine and cadaver skin in the treatment of of split skin graft donor areas after application of burns. An environment for healing: the role of occlusion. hydrocolloid and alginate dressings. Br J Plast Surg In Ed Ryan TJ. Royal Society of Medicine International press. Congress and Symposium Series No 88; 129-32. 37 Cherry GW, Ryan TJ. Enhanced wound angiogenesis with '43 Phipps AR, Lawrence JC. Comparison of hydrocolloid a new hydrocolloid dressing. An Environment for Healing, dressings and medicated Tulle Gras in the treatment of the role ofocclusion. Ed Ryan TJ. Royal Society of Medicine outpatient burns. Beyond occlusion; wound care proceedInternational Congress and Symposium Series No 88. 61-8. ings. Ed Ryan TJ. Royal Society of Medicine International 38 Lydon MJ, Cherry GW, Cederholm-Williams SA, Congress and Symposium Series No 136; 121-5. Pickworth JJ, Cherry C, Scudder C, Johnson ER, Ryan TJ, 44 Paskins JR, Crosby AC, Ferguson DG, Hockey M. A Fairbrother JE. Fibrinolytic activity of hydrocolloid multicentric prospective trial of Granuflex dressings vs dressings. Beyond Occlusion: Wound care proceedings. paste bandages in the treatment of pre-tibial lacerations. Ed Ryan TJ. Royal Society of Medicine International Beyond occlusion: wound care proceedings. Ed Ryan TJ. Congress and Symposium Series. No 136; 9-17. Royal Society of Medicine International Congress and 39 Hutchinson JJ. Prevalence of wound infection under occluSymposium Series. No 136; 137-40. sive dressings: a collective study ofreported research. Wounds 45 Knapp U, Rahn HD, Schauwecker F. Clinical experience 1989; 1: 123-33. with a new gel-like wound dressing following skin graft 40 Madden MR, Nolan E, Finkelstein JL, Yurt RW, Smeland Akt Traumatol, 1984; 14: 275-81. J, Goodwin CW, HeftonJM, Staiano-Coioco L. Comparison of an occlusive and a semi-occlusive dressing and the effect of the wound exudate on keratinocyte proliferation. J Trauma 1989; 29: 924-31. 41 Ryan TJ, Given HF, Murphy JJ, Hope-Ross M, Byrnes G. The use of a new occlusive dressing in the management of

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