Table 3.

Important gaps between existing testing standards for wound dressings and real-world clinical conditions

Fluid Handling		Mechanical
Test Standard	Major Weaknesses	Test Standard	Major Weaknesses
EN 13726-1 Test methods for primary wound dressings—Part 1: Aspects of absorbency (specifies laboratory test methods recommended for the evaluation of absorbency of primary wound dressings)	• Does not consider physiological directional flows (from the wound-bed into the wound pad), as it utilizes free-swell measures for dressings submerged in excess test fluid • Does not consider the combined effects of gravity and bodyweight-induced or other forces on the flow conditions, such as the variable roles of natural convection versus capillary motion (depending on the specific wound and dressing orientations with respect to the ground), and any potential distortion and reduction of the available dressing reservoir for absorbency and retention by bodyweight or external forces • Does not address the protein contents and the associated range of fluid viscosities that exist for biological wound exudates (as this test utilizes an aqueous test fluid, i.e., salts dissolved in water termed “Test Solution A”) for the absorbency measures specified therein	EN 13726-4 Test methods for primary wound dressings—Part 4: Conformability (describes a laboratory test method for measuring the conformability of primary wound dressings)	• Does not consider the real-world, clinically relevant shape conformation phenomena that involve bending and shearing, for example, of wound dressings applied to irregularly curved body regions (such as the posterior heel, the nasal bridge, or the ears), as the test is limited to tensile elasticity only • Does not consider mechanical durability (also known as “fatigue”) factors or real-world wear-and-tear phenomena, and their potential effects on the structural integrity of wound dressings • There is no consideration of the stiffness matching between the tested dressing materials and native skin (or underlying soft tissues), in the context of preventing indentation damage to the periwound skin
EN 13726-2 Test methods for primary wound dressings—Part 2: Moisture-vapor transmission rate of permeable film dressings	• Does not consider protein contents in the test fluid, and, as a result, neglects the possibly modified kinetics of evaporation of protein-rich fluids (as proteins may have hydrophobic regions on their surface, which in turn, may affect their evaporation kinetics)	ISO 29862:2007(en) Self-adhesive tapes—Determination of peel adhesion properties (concerns the laboratory measurements of separation forces required to peel a strip of adhesive tape from industrial steel plates)	• Does not consider the deformability of human skin, and hence is poorly relevant to either healthy or fragile skin response. Specifically, as steel is rigid (i.e., not deformable and viscoelastic as native skin is), it is not representative of the complex biomechanical phenomena that occur during removal of wound dressings. For example, the level of deformability of the surfaces that are subjected to separation strongly affects the dynamic separation forces that form between the separating surfaces. A faster peeling action applied by a wound care clinician would induce a higher deformation rate of the skin, and, due to the viscoelasticity of hydrated skin that would result in greater peeling forces (which are associated with the rate of deformation). A rigid steel substrate cannot represent this complex mechanical behavior of the biphasic (solid-fluid) skin tissue • Does not consider the microtopography features of skin. Specifically, as the industrial steel plate substrates are relatively smooth, and do not contain the inherent roughness and possible wrinkling of human skin, the realistic contact area of the dressing adhesives with skin is not adequately represented, which again biases the peeling force measurements
EN 13726-3 Test methods for primary wound dressings—Part 3: Waterproofness (describes a laboratory test method for the evaluation of the waterproofness of primary wound dressings when such claims are made)	• Does not consider the influence of the body and wound temperatures, and thereby, the effect of the resulting (temperature-dependent) fluid surface tension changes on the waterproofness (as the test solution is used at room temperature) • Does not account for alkaline or acidic fluids where the fluid with non-neutral pH may affect the fluid repellent or interact differently with the dressing materials. This is particularly important for nonwatery, protein-rich fluids (not considered in the test but representative of the majority of biological exudates), where a rise in the pH can change the protein conformation, and thereby, the surface tension interactions

The relevant, widely accepted international test standards are the following: (i) European Standard EN 13726 “Non-active medical devices: Test methods for primary wound dressings”; and (ii) ISO 29862:2007(en) “Self-adhesive tapes—Determination of peel adhesion properties” (which is based on, and improved from the previous EN 1939 standard).