HYDROGEL & HYDROFIBER DRESSINGS
Overview
Hydrogel dressings consist of insoluble polymers with a high water content, enabling them to facilitate autolytic debridement of necrosis and slough. They are produced in tubes or as flat sheet dressings and selection would depend on the wounds position and depth. Hydrogels are better for dry necrotic wounds that require hydration and debridement, whilst hydrocolloids debride tissue in sloughy, exuding wounds. A secondary dressing which does not affect the ability of the hydrogel to donate water to the wound bed is required. Examples: Activheal, Intrasite and Cutimed. Indications: dry and slightly exuding wounds, soothing painful wounds, radiation skin damage. Hydrogel sheets are used for reducing hypertrophic scarring. Pros: Creates optimal moist environment rehydrating wound bed and removing dead tissue, soothing to patient, easy application and removal, reduces wound pain, conforms to wound. Cons: Potential to macerate surrounding tissue, requires additional secondary dressing to secure due to poor mechanical strength, costly and needs frequent application. Notes: should be avoided in moderate to heavily exuding wounds, superficial wounds (8).
Description of System
These are two component systems, where one is a hydrophilic polymer, insoluble in water because of the 3D network, and the second is water. These systems may swell in water to reach equilibrium and retain their original shape therefore providing a moist environment needed for an ideal dressing. They may be chemically stable or may eventually disintegrate and dissolve. They are called reversible or physical gels where the networks are held together by molecular entanglements and/or by secondary forces including ionic and hydrogen bonding and also called permanent or chemical gels when they have covalently cross-linked networks (8).
Some known methods of making them include physical methods (repeated freezing and thawing), and chemical method using chemicals like borax, boric acid and formaldehyde. They are beneficial for burns patients as they reduce the loss of body fluid and maintain the high humidity in the wound. To overcome poor mechanical strength, composite membranes (where a textile material is coated with the polymer solution are used. The fabric reinforcement provides strength to the dressing and the drug loaded dressings offer precise control of the release behaviour. Hydrogel dressings consist of 90% water in a gel base and serves to help monitor fluid exchange from within the wound surface. By keeping the wound moist, the hydrogel dressing assists in protecting the body from wound infection and promotes efficient healing (8). The sheets do not need a secondary dressing and due to their flexible nature, can be cut to fit around the wound (8).
Mechanisms Involved
The hydrogel creates a moist wound healing environment which assists with natural autolytic debridement whilst the alginate component enhances its absorptive capabilities. The gel can be used to soften and hydrate eschar by facilitating rehydration of the wound (8).
Costs and Evidence
Some RCTs assessed hydrogels against larval therapy and surgical debridement. It was suggested that hydrogels are significantly more effective in healing diabetic foot ulcers (62). They are relatively inexpensive, factoring unit costs only. An example by Advanced Medical Solutions Ltd includes ActivHeal Hydrogel (Hydrogel containing guar gum and propylene glycol) priced at £1.41 (54).
Image 44 - An example of a polymeric hydrogel sheet wound dressing (8)
Overview
Hydrofiber dressings contain sodium carboxymethyl cellulose of which the sodium component is formed into textile fibres. Depending on the levels of exudate the dressings can stay in place for up to 3 days and can aid debridement (40). Example: Aquacel. Indications: moderate to heavy exuding wounds, cavities. Pros: Minimal pain during wear and dressing removal as its non-adherent, easy application and removal and worn up to 7 days. Cons: May require a second dressing. Notes: Should be avoided on dry eschar, nonexudating wounds, third-degree burns and heavy bleeding (63).
Description of System
A Hydrofiber is a soft, sterile, non-woven pad or ribbon dressing composed of sodium carboxymethylcellulose, which is incorporated in the form of a fleece held together by a needle-bonding process. This conformable material absorbs large amounts of exudate, and then transformed into a soft gel, creating a moist environment to support the body’s healing process. The gel also aids the removal of non-viable tissue from the wound (autolytic debridement), without damaging newly formed tissue. Hydrofibers are versatile and can be incorporated into different dressing formats. They are neither hydrocolloids nor alginates, but a separate category incorporating the benefits of both, while also addressing their weaknesses (e.g. cohesive gelling and aggressive adhesion).
The first Hydrofiber dressing to be launched was Aquacel® in 1997. By the mid-2000s new formulations were introduced for different clinical situations and these now include antimicrobial ionic silver, or the use of Hydrofiber as a specific layer in composite dressings. Hydrofiber dressings also come in a variety of formats for different wound types and situations, for example Aquacell Hydrofiber ribbon can be used in deep cavity wounds. Different shapes and sizes of dressings are also produced for various anatomical areas.
In vitro tests have also demonstrated the hydrophilic properties of Hydrofiber dressings and their ability to absorb fluid from a petri dish (representing the wound bed), wicking it away from the surface. Importantly, the fluid did not wick across the length of the dressing, but remained confined to the fluid-soaked area, unlike conventional dressings (gauze or alginate), where the fluid is wicked laterally across the dressing. This ability to lock in fluid may help prevent maceration by limiting the lateral spread of wound fluid (63).
Mechanisms Involved
It’s a moisture-retention dressing consisting of soft non-woven sodium carboxymethylcellulose fibres which forms a gel on contact with wound exudate; similar to alginates. The gel promotes a moist wound-healing environment yet retains wound exudates by vertical absorption. Fibrin collects between the dressing and wound surface and acts as an adhesive, fixing the dressing in place and providing adherence of the dressing to the wound without ingrowth of tissue into the dressing (64).
Costs and Evidence
In a 12-week evaluation of 131 community patients with leg ulcers, Aquacel demonstrated better results than other dressings in terms of overall performance, wear time and cost-effectiveness. In wounds of mixed aetiology, it achieved healing or substantial healing in over 75% of patients after just four weeks. It also reduced pain during treatment and on removal and resulted in fewer dressing changes compared with patients previously managed with other dressings. Another randomised controlled trial of patients who had undergone orthopaedic surgery compared Aquacel covered with Tegaderm against another dressing. The Aquacel was 5.8 times more likely to result in a complication-free wound.
Aquacell with silver (Aquacell Ag): A prospective multicentre study of 134 patients with non-ischaemic diabetic foot ulcers compared Aquacell Ag with a calcium alginate dressing. The study found that Aquacel Ag reduced average healing time and healed or improved more patients over eight weeks. Another randomised study examined patients with burns for 21 days. Aquacel Ag was compared to a standard treatment of silver sulfadiazine cream under a gauze dressing. In patients with partial thickness burns, Aquacel Ag was associated with less pain and anxiety at dressing change, fewer dressing changes, less nursing time and fewer procedural medications (63). They can be expensive. Aquacel by ConvaTec Ltd (Soft non-woven pad containing hydrocolloid-fibres) ranges in price from £1.01 - £4.53 (54), factoring unit costs only. Concerns relating to the cost of care arose with advanced silver-impregnated dressings. Silver-containing dressings are relatively expensive, although the higher cost is partially offset by; reduced use of secondary gauze, retention dressings, and improved wound healing together with the reduced costs of other care. Cost-effectiveness calculations comparing Aquacel Ag® to standard of care in patients with acute and chronic wounds showed favourable results using Aquacel Ag (64).
