Film dressings often consist of a thin transparent polyurethane membrane surrounded by a layer of adhesive.  Film dressings are usually permeable to both water vapour and oxygen, is impermeable to micro-organisms.  Once in position, the film should provide an effective barrier to external contamination, whilst producing a moist environment at the surface of the wound by reducing water vapour loss from the exposed tissue.  The polyurethane film is usually supported on a removable flexible carrier that can often be drawn upon to provide a record of the size and shape of the wound to which the dressing is applied, and some carriers are printed with a grid to facilitate calculation of the wound area.

Semi-permeable film dressings are typically used on lacerations, abrasions, skin tears and other superficial wounds. They can also be used to cover sutured wounds, graft sites and partial thickness wounds. They may also be used where there are areas of friction to decrease shearing forces between the dressing and the support surface. Because they are waterproof, they may be used to cover wounds and intravenous catheter sites to allow bathing; they may be also be used to cover wounds for ultrasound treatment.

The original test methods to assess the physical performance of film dressings were published in the British Pharmacopoeia 1993. A number of the published monographs for vapour-permeable adhesive film dressings have been subsequently published in the European Standard BS EN 13726 Test methods for primary wound dressings.  The SMTL perform a number of test methods which are appropriate to test the characteristics of semi-permeable film wound dressings:

SMTL semi-permeable film dressing testing to British Pharmacopoeia 1993 

  • Adhesiveness (UKAS accredited)

  • Extensibility (UKAS accredited)

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

  • Water-vapour permeability

 

SMTL semi-permeable film dressing to BS EN 13726 Test methods for primary wound dressings

  • Moisture Vapour Transmission Rate - BS EN 13726-2 Section 3.2 In contact with vapour (UKAS accredited)

  • Moisture Vapour Transmission Rate - BS EN 13726-2 Section 3.3 In contact with liquid (UKAS accredited)

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

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

 

SMTL in-house developed semi-permeable film dressing fibre testing

  • Bacterial/Viral barrier testing

  • 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 modification 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 Close up

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