Hydrogel is a blanket term for materials that are able to absorb water and swell in aqueous conditions without dissolving. Most are manufactured from a polymer backbone that provides structure - this is repeated throughout the gel and hydrogen bonds act to retain water within that structure (Thomas, 1998). Hydrogels of this type occur naturally, for example, in the cornea of the eye
or in car tilage. Synthetic hydrogels are normally produced from polyacrylamide or polyethylene oxide.
The type of bonding that occurs within the gel will have an impact on how it performs clinically, with increased cross-linking leading to a more viscous gel. As the cross-linking increases, a sheet of gel will eventually be produced.

Hydrogels have excellent biocompatibility and are used in many medical devices, including electrocardiograph (ECG) contact pads, adhesives, contact lenses and drug delivery devices. As wound dressings, hydrogels are available as amorphous gels, sheet hydrogels and gel-impregnated gauze (Thomas, 1998).

Hydrogels and wound care
Shultz et al (2003) suggested that hydrogels are the best choice for the treatment of dry wounds with
necrotic eschar in situ. Trudgian (2000) and Mulder (1995) found hydrogels reached a 50% debridement level more quickly than wet-to-dry dressings as well as being more cost-effective. Most
hydrogels have the ability to provide moisture to a dry environment and some can absorb limited amounts of exudate from a wound - this can cause the gel to expand and fill a wound (Thomas, 1998).
Wound debridement
Debridement is considered an essential step in the management of chronic wounds as failure to remove necrotic tissue can inhibit healing by providing an environment for bacterial growth and chronic inflammation as well as impeding re-epithelialisation (Schultz et al, 2003). A number of techniques can be used for debridement:
• Surgical/conservative sharp Debridement
• Larval debridement
• Enzymatic debridement
• Autolytic debridement.

Surgical debridement is often viewed as the ‘gold standard’ method of debridement in terms of speed and efficiency, however, not all patients are able to tolerate this or indeed have access to a specialist who can perform the procedure (Timmons, 2003).

Larval therapy is also viewed as a quick and efficient method of debridement, however, it is not suitable for all wound types and may not be acceptable to every patient.

In the case of enzymatic debridement, preparations of proteolytic enzymes such as collagenase or
varidase (a mixture of streptokinase and streptodornase) are applied topically to digest eschar - these can also be crosshatched to aid penetration of the eschar.

Autolytic debridement is one of the most commonly used methods of debridement in the UK. It utilises
proteolytic enzymes produced by cells in the wound tissue, such as macrophages. Its advantage is that the physiological mechanisms involved also allow the macrophages to phagocytose digested debris and remove it from the wound environment. However, autolytic debridement will not
succeed if the eschar is dry. Rehydration with moisture-donating dressings

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