The preclinical and clinical assessment of the physical characteristics of burn wound dressings
Preclinical assessment procedures for wound dressings have been established with the clinical situation in mind, taking into account the important parameters of tensile mechanical properties, conformability to body surfaces, water vapour transmission rate (WVTR) and gaseous transmission (GTR) to 0₂ and CO₂. The mechanical (tensile) properties, the WVTR and the GTR's are measured by modified international standards. These are ASTM D882-81, ASTM E96-81 and BS 2782 respectively. The mechanical test is basically a uniaxial test taken to failure, from which the stress-strain characteristics and the ultimate strength of the material are determined. The WVTR is determined by measuring the rate of water loss from a container, covered with the dressing being evaluated, under controlled humidity conditions. Gaseous transmission, to both oxygen and carbon dioxide, is determined by the British Standard Vacuum technique. This method was used only for the assessment of the hydrophobic dressings. A liquid to gas technique was employed to assess the hydrophilic (water containing) dressings in respect to their transmission characteristics. Conformability is measured by an inflation test. At a pressure of 40 mmHg, a radius of curvature is calculated from the incremental change in height of the central point of a disc of the material under test. Viscoelastic tests were carried out to determine if any of the materials showed viscoelastic behaviour. These properties are of importance in the application of pretensioned dressings. A series of commercial and experimental materials were evaluated using the techniques described above. Some of the materials were assessed as a bi-laminate form, with a Mefix (adhesive bandage) top layer. Such a layer generally proved beneficial with regard to their possible clinical performance. Clinical studies were carried out for both in situ water vapour transmission and conformability. Such studies were carried out to provide a correlation between the laboratory and clinical situations. By providing an indication of possible clinical problems, preclinical assessment is of importance to clinicians and manufacturers.