Overview

Alginate dressings contain calcium or sodium alginate derived from seaweed by treatment with aqueous alkali solutions, typically Sodium hydroxide. When it contacts wound exudates, a hydrophilic gel is formed; facilitating easier dressing removal. The calcium component acts as a haemostat and is therefore useful in bleeding wounds. Alginate ribbon and rope are available and are particularly useful in packing wound cavities (53). Indications: Moderate to highly exuding wounds, leg ulcers, pressure ulcers, diabetic foot ulcers, acute wounds: donor sites and abrasions. Examples: Sorbsan, Kaltostat. Pros: Reduces pain, packs cavities, is absorbent in exudative wounds and haemostatic. Cons: May require secondary dressing and gel can be confused with slough or pus in wound. Notes: should be avoided in dry wounds and wounds with hard eschar (11).

 

Description of System

Alginate hydrogels have been particularly attractive in wound healing, drug delivery, and tissue engineering applications, as they are structurally similar to the extracellular matrices in tissues and are easily manipulated. It has been extensively investigated and used for many biomedical applications, due to its biocompatibility, low toxicity, relatively low cost and mild gelation by adding divalent cations. Alginate hydrogels can be prepared by various cross-linking methods. (53)

 

Traditional wound dressings (e.g. gauze) have acted as a barrier, keeping the wound dry by allowing evaporation of wound exudate while preventing entry of pathogen into the wound. In contrast, modern dressings (e.g. alginate dressings) provide a moist wound environment and facilitate wound healing. Alginate dressings are typically produced by ionic cross-linking of an alginate solution with calcium ions to form a gel, followed by processing to form freeze-dried porous sheets (i.e. foam), and fibrous non-woven dressings (53).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Mechanisms Involved

These dressings maintain a moist microenvironment, minimize bacterial infection, and facilitate healing. Drug molecules, (small chemical drugs to macromolecular proteins) can be released from alginate gels in a controlled manner, depending on the cross-linker types and cross-linking method. Whilst dry, it absorbs wound fluid to re-gel. The gel can then supply water to a dry wound, maintaining a moist microenvironment and minimizing bacterial infection at the wound site. These functions can also promote granulation tissue formation and rapid epithelialization. Alginate is a whole family of linear copolymers containing blocks of (1,4)-linked β-D-mannuronate (M) and α-L-guluronate (G) residues. Only the G-blocks of alginate participate in intermolecular cross-linking with divalent cations (Ca2+) to form hydrogels. The composition (i.e., M/G ratio), sequence, G-block length, and molecular weight are therefore critical factors affecting its physical properties and its resultant hydrogels (53).

 

Costs and Evidence

All the alginate dressings in BNF 70 are impregnated with silver and are relatively inexpensive. An example product by Aspen Medical Europe Ltd is Sorbsan Silver Flat (Calcium alginate fibre, highly absorbent, flat non-woven pads, with silver). Prices range from £1.57 - £7.26) (54), factoring unit costs only. Several literature reviews have shown the value of the alginate dressing in management of a wide variety of wounds including those heavily colonised with pathogenic bacteria.

 

A review that assessed the evidence for the effectiveness of alginate dressings compared to other dressings reported the following results: Leg ulcers: 73% of leg ulcers treated with alginate showed overall improvement compared with 43% treated with paraffin tulle. With ydrocolloid dressings and Class III compression stockings, no statistically significant differences in healing was detected but significantly lower pain scores were reported by those using alginates. When alginate dressings were compared with dextranomer paste used on full-thickness pressure ulcers, significantly higher rates of wound area reduction in a shorter period of time were reported in the alginate dressing group. Surgical wounds: At dressing change, alginate dressings yielded reduced bacterial counts, were easier and less painful to remove compared with proflavine soaked gauze/saline-soaked gauze/paraffin gauze/cotton gauze roll in the management of cavities arising following drainage (55).