Hydrocolloids are a type of dressing containing gel-forming agents, such as sodium carboxymethylcellulose (NaCMC), pectin and gelatin. In many products, these are combined with elastomers and adhesives and applied to a carrier - usually polyurethane foam or film, to form an absorbent, self adhesive, waterproof dressing.

The primary physical functions of hydrocolloid dressings are to:

  • produce a moist wound environment thus facilitation of autolytic debridement

  • management of exudate

  • provision of a barrier to micro-organisms

In the presence of wound exudate, hydrocolloids absorb liquid and form a gel, the properties of which are determined by the nature of the formulation. Some dressings form a cohesive gel, which is largely contained within the adhesive matrix; others form more mobile, less viscous gels which are not retained within the dressing structure. In the intact state most hydrocolloids are impermeable to water vapour and thus increase the wound bed moisture content and can facilitate autolytic debridement. However, as the gelling process takes place, the dressing becomes progressively more permeable and the loss of water through the dressing in this way enhances the ability of the product to cope with exudate production. There are many differences in structure, flexibility, dimensions, and fluid handling properties between commercially available hydrocolloid dressings (Thomas et.al 2004).

The original test methods to assess the physical performance of hydrocolloid dressings were published in the British Pharmacopoeia 1993 Addendum 1996. The published monographs for Semi-permeable hydrocolloid dressings include test to assess uniformity of weight, waterproofness, adhesiveness, extensibility, pH and fluid handling capacity and sterility. The fluid handling capacity and waterproofness where subsequently published as European Standards in BS EN 13726-1 Aspects of absorbency and BS EN 13726-3 Waterproofness respectively.

The following characteristics of hydrocolloids can be tested by SMTL :

SMTL hydrocolloid dressing testing to British Pharmacopoeia 1993 Addendum 1996 - Semi-Permeable Hydrocolloid Dressings

  • Uniformity of weight

  • Waterproofness (UKAS accredited)

  • Adhesiveness (UKAS accredited)

  • Extensibility (UKAS accredited)

  • pH

  • Fluid Handling Capacity (UKAS accredited)

 

SMTL hydrocolloid dressing testing to BS EN 13726 Test methods for primary wound dressings

  • Fluid Handling Capacity - EN 13726-1 Section 3.2 (UKAS accredited)

  • Waterproofness - BS EN 13726-3 (UKAS accredited)

  • Conformability (Extensibility and Permanent Set) - BS EN 13726-4 (UKAS accredited)

 

SMTL in-house developed hydrocolloid dressing testing to BS EN 13726 Test methods for primary wound dressings

  • Conformability - SMTL TM-16

  • Conformability SMTL/Queen Method - SMTL TM-16 modified

 

The in-house methods have been used for major dressing companies and the NHS since its development in the late 1980's and uses the waterproofness apparatus (which is listed in the BP and BS EN 13726-2).  The wound dressing under test is clamped over the apparatus and then pressurised.  The pressure required for the dressing to dome up to a specific height (2cm) is recorded via a pressure transducer.  The pressure required to dome the dressing is inversely proportional to the conformability i.e. the higher the pressure required to reach the 2cm height, the less conformable the dressing.

The SMTL/Queen method is a miodificatoin of TM-16 and is based on the publication Queen et.al 1987 Biomaterials.  Wound dressings are set up as above, and then inflated to 40mmHg.  The height which the dressing reaches is proportional to the conformability of the dressing i.e. the higher the dressing height, the higher the dressing conformability.  It is also possible to calculate the radius of curvature from the dressing inflation height.

Conform Upright

Conform Close up

 

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