The EN 13726 series of standards cover test methods for primary wound dressings:
BS EN 13726-1 - Aspects of Absorbency
The majority of wound dressings are applied to remove excess wound fluid (exudate) from the immediate vicinity of the wound. This standard contains a series of test methods which assess absorbency, fluid handling capacity and dispersion characteristics:
Section 3.2 Free-Swell Absorptive Capacity
This test is intended to measure the absorbency of fibre-type wound dressings such as alginates (e.g. Kaltostat, Sorbsan etc.) and gelling fibres (e.g. Aquacel, Durafibre etc.) which are used on moderate to heavily exuding wounds where total absorptive capacity is an important feature.
Dressings are sectioned into 5x5cm samples, weighed and then incubated in artificial exudate at 37°C. The free-swell absorbency following 30 minutes incubation is subsequently calculated.
This test is only appropriate for dressings which remain physically intact and which reach their absorptive capacity within 30 minutes under the test conditions.
As the dressings need to be sectioned prior to testing, this test method is not appropriate for super-absorbent containing wound dressings (SMTL have alternative test methods for super-absorbent wound dressings which are outlined in SMTL TM-404 and TM-414).
Similarly, wound dressings which have duel action of handling exudate via absorbency and moisture vapour transmission are not appropriate for this test, and should be tested for Fluid Handling Capacity.
Section 3.3 Fluid Handling Capacity
This test is designed to measure the removal of exudate from the wound by wound dressings which handle the exudate through absorbency and permeability (also known as moisture vapour transmission) e.g. foam and hydrocolloid wound dressings.
Dressings are sectioned and applied to a Paddington cup (see image). Artificial exudate is introduced into the cup and a lid applied to form a closed system. The cup is pre-weighed and then incubated at 37°C. Following 24 or 48 hours incubation, the cup is weighed to calculate exudate handled via moisture vapour transmission. The lid of the cup is then removed and remnant exudate drained from the cup. The cup is then re-weighed to calculate the mass of exudate absorbed by the wound dressing.
This test is only appropriate for waterproof wound dressings.
Testing is often performed using a 72 hour incubation period for slow fluid handling wound dressings such as hydrocolloids.
Section 3.4 Fluid Affinity of Amorphous Hydrogels
Amorphous hydrogels are designed so that they absorb or donate fluid depending on the environment of the wound. This test measures the ability of the hydrogel to donate or absorb exudate when incubated in a relatively dry (gelatine) and moist (agar) environment respectively.
Section 3.5 Gelling Characteristics
This test is designed to distinguish between fast and slow gelling fibre dressings when in the presence of excess exudate. The formation of a gel between the dressing and the wound exudate can reduce adherence to the wound and helps create a moist environment. Knowledge about the rate of gelling can assist in selecting the most appropriate dressing for a particular wound.
A sample of the dressing is grated and introduced to artificial exudate for 1 minute. The solution is then processed via a series of filtrations and the final residue examined for the presence of a gel.
Section 3.6 Dispersion Characteristics
This test is designed to distinguish between fibre wound dressings which readily lose integrity and disperse, and those which stay intact.
A sample of the dressing is placed into a flask with artificial exudate and gently swirled for 1 minute. The contents of the flask is then visually examined and an assessment made whether the dressing is a dispersal (separation of fibres leaving no evidence of the original fabric structure) or non-dispersal dressing (clear evidence of the dressing original fabric structure).
Section 3.7 Dispersion/Solubility of Hydrogel Dressings
This test is useful to determine the physical properties of amorphous hydrogels wound dressings in the presence of copious quantity of exudate.
Hydrogel is introduced into a stoppered flask containing artificial exudate and the flask shaken for 2 minutes to allow dressing dispersion/dissolution. The flask is then allowed to stand for 2 hours and then inspected and an assessment made whether the dressing is soluble (has dissolved into the test solution), dispersible (remains in two distinct phases or disperses to uniformly and then settles out to form two distinct layers) or if the dressing is a non-dispersal product (retains its original structure).
BS EN 13726-2 - Moisture Vapour Transmission Rate (MVTR) of Vapour Permeable Film Dressings
MVTR forms an important part of the fluid handling properties of a dressing. It influences both the hydration of the wound and that of surrounding tissues where maceration may be a problem. This test is intended to be performed on wound dressings which handle wound exudate through permeability alone (e.g. film wound dressings) when:
Section 3.2 MVTR of a Wound Dressings When In Contact With Water Vapour
Designed for wound dressings which are not in direct contact with wound exudate.
Section 3.2 MVTR of a Wound Dressings When In Contact With Liquid
Designed for waterproof wound dressings which are in contact with wound exudate.
Dressings are sectioned and applied to a Paddington cup. Artificial exudate is introduced into the cup and a lid applied to form a closed system. The cup is pre-weighed and then incubated at 37°C. Following 4 -24 hours incubation, depending on the test method, the cup is weighed to calculate exudate handled via moisture vapour transmission.
BS EN 13726-3 - Waterproofness
The ability of a dressing to maintain a waterproof barrier is important to prevent possible transmission of bodily fluids into the wound. This test measures the ability of the outer surface of the dressing to act as a waterproof barrier under a hydrostatic pressure.
Dressings are sectioned and applied to a test cell containing deionised water so that the outer surface of the dressing is in contact with the water. Filter paper is placed on the wound contact layer surface of the dressing and a hydrostatic head of 0.5 meters is applied to the test cell for 5 minutes. The filter paper is then examined for the penetration of water through the wound dressing.
BS EN 13726-4 Conformability
Dressings that are applied around joints or to other areas of tissue subject to movement or distortion must, to some degree, accommodate this without causing excessive pressure, or in the case of adhesive products, shearing forces that can cause skin trauma.
In this method the dressings are sectioned into 25mm widths and marks made on the sample 100mm apart (L1). The samples are then positioned within a tensometer then extended 20% and the maximum load recorded, so that the extensibility can be calculated (N per cm-1). The sample is held at this extension for 1 min, then removed from the tensometer. The 2 marks on the sample are then re-measured (L2) and the percentage permanent set is calculated.
Even though the EN 13726-4 is termed conformability, in reality this is an assessment of extensibility/permanent set test rather than an assessment of dressing conformability. Therefore the SMTL have developed other test methods to assess dressing conformability.