Table 7.1 Functions (desirable characteristics) of wound dressings
Desirable characteristic Clinical significance to wound healing Debridement (wound
cleansing)
Enhances the migration of leukocytes into the wound bed and supports the accumulation of enzymes. Necrotic tissue, foreign bodies and particles prolong the inflammatory phase and serve as a medium for bacterial growth
Provide or maintain a moist wound environment
Prevents desiccation and cell death, enhances epidermal migration, promotes angiogenesis and connective tissue synthesis, and supports autolysis via the rehydration of desiccated tissue
Absorption. Removal of blood and excess exudate
In chronic wounds, there is excess exudate, containing tissue- degrading enzymes, which block the proliferation and activity of cells, and break down extracellular matrix materials and growth factors, thus delaying wound healing. Excess exudate can also macerate the surrounding skin
Gaseous exchange (water vapour and air)
Permeability to water vapour controls the management of exudate.
Low tissue oxygen levels stimulate angiogenesis. Raised tissue oxygen stimulates epithelialization and fibroblasts
Prevent infection:
protect the wound from bacterial invasion
Infection prolongs the inflammatory phase and delays collagen synthesis, inhibits epidermal migration and induces additional tissue damage. Infected wounds can have an unpleasant odour
Provision of thermal
insulation Normal tissue temperature improves the blood flow to the wound bed and enhances epidermal migration
Low adherence. Protects
the wound from trauma Adherent dressings may be painful and difficult to remove, and cause further tissue damage
Cost-effective low frequency of dressing change
Dressing comparisons based on treatment costs rather than unit or pack costs should be made (cost-benefit-ratio). Although many dressings are more expensive than traditional materials, the more rapid response to treatment may save considerably on the total cost Reproduced with permission from J.S. Boateng, K.H. Mathews, H.N.E. Stevens,
G.M. Eccleston in Journal of Pharmaceutical Sciences, 2008, 97, 8, 2892.
©2008, John Wiley & Sons [1]
Traditional dressings, such as gauze and tulle dressings, account for the largest market segment and are passive products. Interactive products are comprised of polymeric films and foams, which are mostly transparent, permeable to water vapour and oxygen but impermeable to bacteria; these films are recommended for low exuding wounds. Bioactive dressings deliver substances active in wound healing either via the delivery of bioactive compounds or the dressing is constructed from material which has endogenous activity; these materials include proteoglycans, collagen, noncollagenous proteins, alginates or chitosan. The various types of wound dressings clinically applied are provided in Table 7.2.
Table 7.2 Commercially available bioactive and interactive wound dressing products
Dressing Type Company Material
Bioclusive® Film Johnson & Johnson Polyurethane
Mitraflex® Film BritCair Polyurethane
Omiderm® Film Iatro Medical Polyurethane
Opsite® Film (transparent) Smith & Nephew Polyurethane
Spyrosorb® Film PolyMedica Polyurethane
CarraFilm® Film (transparent) Carrington Laboratories, Inc. Polyurethane Polyskin™ Film (transparent) Kendall (Covidien) Polyurethane
Tegasorb® Bioactive 3M Health Care Hydrocolloid
Bursamed® Bioactive SAM Medical Products Hydrocolloid
Comfeel® Bioactive Coloplast AS Hydrocolloid
Cutimed® Bioactive BSN Medical, Inc. Hydrocolloid
DermaFilm® Bioactive DermaRite Industries, LLC Hydrocolloid
Duoderm® Bioactive ConvaTec Hydrocolloid
Exuderm Bioactive Medline Industries, Inc. Hydrocolloid GranuDerm® Bioactive SciVolutions Medical, Inc. Hydrocolloid
Hydrocol® Bioactive Mylan Bertek
Pharmaceuticals, Inc. Hydrocolloid
MediPlusTM Bioactive MediPurpose, Inc. Hydrocolloid
KendallTM Alginate Bioactive Coviden Hydrocolloid
Restore Bioactive Hollister Incorporated Hydrocolloid
Lyofoam® Foam Seton Polyurethane
Allevyn® Foam Smith & Nephew Polyurethane
Tielle® Foam Johnson & Johnson Polyurethane
PolydermTM Foam DeRoyal Polyurethane
CurafoamTM Foam Kendall Polyurethane
MitraflexTM Foam Mölnlycke Health Care Polyurethane
Vigi-Foam® Foam Bard Polyurethane
Biopatch® Foam Johnson & Johnson Polyurethane
Actisorb plus® Deodorising Johnson & Johnson Activated charcoal cloth with silver
Carbonet® Deodorising Smith & Nephew Activated charcoal cloth
Kaltocarb® Deodorising BritCair Activated charcoal cloth
with alginate
Granuflex® Deodorising ConvaTec Activated charcoal cloth
with alginate
Tegasorb® Deodorising 3M Health Care Activated charcoal cloth with alginate
Granugel® Bioactive ConvaTec Hydrogel
Intrasite Gel® Bioactive Smith & Nephew Hydrogel
Nu-Gel® Bioactive Johnson & Johnson Hydrogel
Sterigel® Bioactive Seton Hydrogel
Algisite® Bioactive Smith & Nephew Alginates
Kaltostat® Bioactive ConvaTec Alginates
Tegagel® Bioactive 3M Health Care Alginates
Comfeel SeaSorb® Bioactive Coloplast AS Alginates
Mepore® Traditional Mölnlycke Nonwoven polyester fabric
Alginate wound dressings are one of the most widely used and commercially available.
They are highly absorbent, degradable and haemostatic, and available in different forms, such as fibres, films foams and so on. Dressing changes are easier with these dressings and they can be used as packs in cavity wounds, particularly dressings made of fibrous materials. Alginates have inherent bacteriostatic properties and should be safe to use on infected foot ulcers. Foam dressings are particularly useful for nonhealing ulcer wounds as they have high absorbency and good thermal insulation.
These dressings can be cut into suitable sizes and shapes in order to accommodate difficult-to-apply to sites; these foams can be incorporated with silver to make them antibacterial. Hydrocolloid dressings are occlusive film-type dressings that contain gel-forming agents in an adhesive material laminated onto a water-resistant backing layer. Some dressings contain alginates and chitosan to increase absorption, and are available in pre-cut shapes suitable for different locations. They maintain a moist wound environment, provide thermal insulation and require less frequent dressing changes; however, these dressings are not suitable for heavily exudating wounds and highly infected wounds. Similarly, hydrogel dressings are also highly absorbent and can also donate moisture to dry wounds; therefore, if applied to a heavily exudating wound they can cause maceration. They also help in the autolysis of necrotic tissue and will not support bacterial growth. Silver dressings are usually used for acute as well as chronic wounds and are particularly indicated for burn wounds. The silver is normally delivered as silver nitrate or silver sulfadiazine; however, a high concentration of silver ions exerts cytotoxic effects on host cells.
7.2.1 Paraffin Gauze Dressing
Paraffin gauze is bleached cotton or a combination of cotton and rayon cloth impregnated with yellow or white soft paraffin, and is the basic form of wound dressing. It is nonadherent and used to dress denuded areas for the treatment of ulcers, burns, skin grafts and various traumatic injuries. The cotton gauze is specially coated with soft paraffin jelly so that the spaces between the threads are free of paraffin. A paraffin gauze dressing functions by reducing the fluid loss while the water barrier layer is reforming. The two properties of the paraffin gauze that are most useful are those of nonadherence and semiocclusiveness. It is also used as a packing material to promote granulation. Gauze dressings are also available which have been impregnated with povidone iodine, chlorhexidine, sodium fusidate and framycetin sulfate, although they are not popular due to the possibility of developing resistant strains of infective organisms. Some commercial gauze dressings are Jelonet by Smith & Nephew, Paranet™ by Synergy Health, Inadine™ by Johnson & Johnson and so on.
7.2.2 Hydrogel Dressings
Hydrogels are hydrated polymeric dressings that were originally developed in 1950s and contain about 90% water in a gel base. Hydrogel dressings are available in three forms; as amorphous hydrogels that are free-flowing packaged in tubes and spray bottles, which may vary in viscosity, as impregnated hydrogels that are saturated onto gauze pads, nonwoven sponges, rope or strips and as sheet hydrogels usually supported by a thin fibre mesh and available with or without adhesive borders.
Hydrogel dressings provide a moist environment which promotes granulation, epithelialization and autolytic debridement. These dressings will not adhere to the wound which allows comfortable dressing changes. The high water content in the dressing provides a soothing effect and also produces pain relief; these dressings are also clear or translucent, making the wound visible from outside. Hydrogel dressings are normally indicated for dry or slightly moist wounds, painful wounds, partial- and full-thickness wounds, for abrasions and minor burns and for wounds with granulation tissue, eschar or slough. However, they require a secondary dressing for support as they are mechanically weak, hence making it difficult to secure. In addition, in some cases it can dehydrate, causing periwound maceration, and may require frequent dressing changes. An example of a polymeric hydrogel dressing applied to a minor burn wound is shown in Figure 7.1.
Figure 7.1 A polymeric hydrogel dressing applied to a minor burn. The hydrogel dressing can provide a moist environment but its strength is low
7.2.3 Hydrocolloid Dressings
A hydrocolloid dressing is similar to a hydrogel dressing. It is a wafer-type dressing containing gel-forming agents in an adhesive compound which is laminated with a flexible water-resistant polymer layer. Many hydrocolloid dressings use alginate and chitosan to increase the absorption capacity of the dressing for exudates. These dressings are available with or without adhesive borders and in various shapes suitable for difficult-to-apply to body areas. Hydrogel dressings are occlusive and hence provide a moist wound-healing environment which promotes autolytic debridement and insulation of the wound. They are impermeable to bacteria and do not adhere to the wound, making removal easy. These dressings can be worn for several days, however they are not suitable for heavily exudating wounds and are indicated for noninfected wounds with moderate drainage, necrotic or granular wounds, dry wounds, partial- and full-thickness wounds and are also used to protect an intact or newly healed wound. Various commercial hydrocolloid dressings are detailed in Table 7.2.
7.2.4 Alginates
Alginate dressings are available in the form of freeze-dried porous sheets or foams, or as flexible fibres. They are produced from calcium or sodium salts of alginic acid, comprising mannuronic acid and guluronic acid residues. Alginate dressings have inherent antibacterial properties and have the ability to form gels upon contact with wound exudates. Dressings that are rich in mannuronic acid components form soft gels upon the absorption of exudates, whereas guluronic-acid-rich alginates form firm gels. Upon the absorption of exudates that contain calcium ions a sodium alginate dressing forms a film of calcium alginate gel over the wound. The density of crosslinking of the alginate network in the presence of calcium ions depends upon the ratio of mannuronic acid to guluronic acid, which determines the flexibility of the formed gel. An alginate dressing can absorb about 20 times its weight of exudates and is normally weak mechanically; therefore, a secondary dressing is required for support. Alginates have inherent haemostatic potential which enables haemostasis.
Alginate dressings are indicated for sloughy wounds, heavily exudating wounds, such as leg ulcers, cavity wounds, epithelializing wounds and so on. Alginates are not recommended for dry wounds, eschar covered wounds, surgical wounds or third-degree burns. The removal of alginate dressings is easy as alginate can be easily rinsed away with saline.
7.2.5 Foam Dressings
Foam dressings are normally made up of porous polyurethane foam or foam films, and are available with adhesive borders. They are highly hydrophilic and highly absorbent dressings which allow them to be used for a longer duration. Because of the high absorption capacity and high vapour transmission rate, the possibility of maceration of the surrounding tissue is avoided. These dressings are best suited for heavily exudating wounds, deep cavity wounds, ulcers such as venous stasis ulcers, pressure ulcers and even minor burns. If the drainage is very low there may be a possibility of drying of the wounds.
7.2.6 Composite Dressings
Composite dressings are simple adhesive bands with a central adsorbent pad covered with a simple perforated wound contact layer, similar to Band-Aid®, and can be used for both chronic and acute wounds. They are indicated for low to moderate exudating wounds in the majority of cases and for heavily exudating wounds with composite dressings containing super absorbers such as Viasorb®. Some classic examples are Alldress® (Mölnlycke), Coversite™ (Smith and Nephew) and CoverDerm® (DeRoyal).
Composite dressings are available in a variety of sizes with the basic Band-Aid shape.
The application of a composite dressing is very simple which makes it popular;
this simple wound dressing can be used for surgical wounds and can be used as an inexpensive secondary dressing in many cases.
7.2.7 Activated Charcoal Dressings
Activated charcoal dressings are made from viscose fabric which is coated with activated carbon and impregnated with silver. The carbonised fibre is enclosed in a pocket of nonwoven nylon to reduce particle and fibre loss. The dressing absorbs toxins and wound degradation products as well as the volatile amines and fatty acids responsible for the production of wound odour, along with killing the bacteria present in the wound exudates as a result of the wide spectrum activity of silver. Activated charcoal dressings are indicated for the management of malodorous, infected wounds, including fungating lesions, faecal fistulae, infected pressure sores and heavily exuding leg ulcers. Clinical data indicate that activated charcoal impregnated with silver may help to remove fluids and toxins that impair the healing process, hence this type of dressing is useful in the management of chronic wounds [3]. Examples of activated charcoal dressings are Actisorb® by Johnson & Johnson, InvaSorb by Hasti Medic, Tecasorb by FWDS Research Company a.s. and so on.
7.2.8 Transparent Film Dressings
Transparent film dressings are usually made of thin sheets of polyurethane coated with an adhesive. Although these dressings have a low absorption capacity for exudates, they provide a moist healing environment and promote autolytic debridement, and protect the wound from mechanical trauma and bacterial infection. They are waterproof and highly water vapour permeable, allowing the passage of CO2 and excess exudates away from the wound. They are normally indicated for partial- thickness wounds with minimal wound exudates, superficial wounds, covering blisters and so on. They are mostly used as a protective dressing, to secure IV catheters and to secure the primary dressing. They have the disadvantage of potentially causing skin tear upon dressing removal.
7.2.9 Antimicrobial Dressings
Silver ion containing dressings are widely used for the management of infected wounds, or wounds at risk of infection. It is recommended that silver dressings should be used for wounds where infection is already established or an excessive wound bioburden is delaying healing. Silver treatment will reduce the wound bioburden and prevent systemic spread, hence promoting wound healing. However, silver wound dressings as such do not improve the healing rate as concluded in many controlled trials [4, 5]. Low levels of silver ions are ineffective and high levels of silver ions are cytotoxic to cells [6], therefore, the ion release is optimised so that it is effective as an antibacterial agent, but noncytotoxic to cells. The role of silver as an antimicrobial agent is attractive, since it has a broad spectrum of antimicrobial activity and is less likely, compared with antibiotics, to induce resistance due to its activity at multiple bacterial target sites. Topical creams and solutions containing silver are available commercially and have long been used in wound management for burn patients who are susceptible to infection. The main disadvantage of creams is that they can stain the intact skin and can be toxic. A wide range of antimicrobial dressings containing silver are now available for clinical use, but they differ in their silver content, release mechanism and chemical properties. Silver is found in dressings in a variety of forms;
as silver metal and nanocrystalline silver, as organic compounds such as silver oxide, silver phosphate, silver chloride, silver sulfate, silver zirconium compound and so on, and as organic complexes such as silver-zinc allantoinate, silver alginate, silver carboxymethyl cellulose and so on. It can be incorporated into wound dressings in the form of coatings, within the structure of the dressing or as a combination. In vitro studies have shown that even low levels of silver ions, i.e., in the range of 1 part per million or less is effective as an antibacterial drug [7]. However, in clinical settings the actual levels of silver ions which demonstrate antibacterial action is unknown.
It is always suggested that silver wound dressings need to be used initially for the duration of 2 weeks.
7.2.10 Honey-based Dressings
Honey is known as an ancient remedy for the treatment of wounds and burns, and for fighting infection. It is believed that the Egyptians used honey in wound treatment as early as 3000 BC. The ‘three healing gestures’, i.e., washing the wounds, making the plasters and bandaging the wound, described in 2400 BC, includes honey as an integral part. The first plasters are believed to be have been made from honey, animal fat and vegetable fibre. Honey was first recognised as a topical antibacterial agent in 1892 [8]. The US Food and Drug Administration (FDA) in 2007 authorised the usage of a honey-based medical product in the USA. MEDIHONEY® antimicrobial honey dressings (Derma Sciences) are a new and unique line of dressings. Active Manuka Honey (Leptospermum scoparium) has been reported to have powerful and long- lasting antimicrobial activity similar to that of ionic silver; however, there seems to be no associated toxicity as found with ionic silver. This dressing has been reported to significantly improve the rate of healing, reduce the risk of methicillin-resistant Staphylococcus aureus and effectively assist in debridement. It also helps in managing the moisture balance and controlling the odour often associated with infected or highly colonised wounds. Honey gelled with calcium alginate forms a rubbery sheet similar to hydrocolloids; this rubbery sheet forms a softer gel when absorbing exudates and keeps a layer of honey in contact with the wound. The MEDIHONEY® gel sheet and ApinateTM dressings (Comvita®, honey-impregnated mechanically bonded calcium alginate fibre), and Algivon® dressings (Advancis) create a barrier against antibiotic- resistant strains and other wound pathogens, hence reducing the risk of infection.
The outflow of exudates, induced by osmotic action, removes the wound bacteria, endotoxin debris and slough. An optimal healing environment enhances granulation and epithelialization, and is suitable for the treatment of leg ulcers, burns, donor graft sites and infected wounds. However, it has also been reported in the Cochrane Database that there is insufficient evidence in the usage of honey to guide clinical practice, although honey may be superior to some conventional dressings [9]. In the latest study on human burns, ulcers and other wounds, honey seems to be a dressing which stimulates wound healing [10].
7.2.11 Iodine-based Dressings
Iodine is an antiseptic used clinically for wound cleansing and debridement. It kills bacteria and pathogens, and is used for the prevention and treatment of infection.
It has also been reported that releasing iodine into the wound environment may
enhance the healing of chronic leg ulcers [11]. The suggested potential mechanism involves a pro-inflammatory stimulus within the wound tissue by activation of the resident macrophage population, which generates pro-inflammatory cytokines and subsequently an influx of monocytes and T-lymphocytes into the wound that may trigger the wound into the healing phase [11]. The two types of formulations available for clinical use are povidone iodine and cadexomer iodine. Povidone iodine is available as liquid formulations and as impregnated tulle dressings, whereas cadexomer is available in powder form and as ointments and dressings. Cadexomer iodine is a starch-based porous material in the form of spherical particles which contain 0.9%
iodine. The Iodosorb dressing by Smith & Nephew effectively removes the barriers of bacteria, slough, debris and excess exudates, and is effective for the treatment of chronic exudating wounds. The broad spectrum antimicrobial action is provided by the sustained release of iodine and the desloughing action is provided by the unique cadexomer matrix. Iodosorb is also available in gel and powder form. Inadine® are povidone iodine dressings by Johnson & Johnson consisting of knitted viscose fabric impregnated with a polyethylene glycol base containing 10% povidone iodine. This low adherent dressing is indicated for the prophylaxis and treatment of infection in minor burns, leg ulcers, superficial skin-loss injuries and as a dressing for adjunctive therapy in the treatment of infected ulcerative wounds.
7.2.12 Polyhexamethylene Biguanide Antimicrobial Dressings
Polyhexamethylene biguanide (PHMB) is a commonly used antiseptic, and is also known as polyhexanide and polyaminopropyl biguanide. It is used in a variety of products including wound-care dressings, contact lens cleaning solutions, perioperative cleansing products and swimming pool cleaners. It has been reported to be very effective if packing the dressing into the wound is required [12]. It has also been reported that PHMB promoted contraction and aided wound closure to a significantly greater extent than octenidine and placebo [13]. Kerlix™ AMD antimicrobial gauze and Curity™ AMD antimicrobial gauze sponge by Covidien are examples of PHMB- impregnated dressings. Clinical studies suggest that this dressing is an effective barrier against bacterial colonisation. Suprasorb® X + PHMB wound dressings by Lohmann
& Rauscher support moist wound management and contain 0.3% PHMB.