The biomechanical efficacy of a dressing with a soft cellulose fluff core in prophylactic use

Abstract

In this work, we developed an experimental-computational analysis framework which facilitated objective, quantitative, standardised, methodological, and systematic comparisons between the biomechanical efficacies of two fundamentally different dressing technologies for pressure ulcer prevention: A dressing technology based on cellulose fibres used as the core matrix was evaluated vs the conventional silicone-foam dressing design concept, which was represented by multiple products which belong in this category. Using an anatomically-realistic computer (finite element) model of a supine female patient to whom the different sacral dressings have been applied virtually, we quantitatively evaluated the efficacy of the different dressings by means of a set of 3 biomechanical indices: The protective efficacy index, the protective endurance, and the prophylactic trade-off design parameter. Prior rigorous experimental measurements of the physical and mechanical behaviours and properties of each tested dressing, including tensile, compressive, and friction properties, have been conducted and used as inputs for the computer modelling. Each dressing was evaluated for its tissue protection performances at a new (from the package) state, as well as after exposure to moisture conditions simulating wet bedsheets. Our results demonstrated that the dressing with the fluff core is at least as-good as silicone-foams but importantly, provides the best balance between protective performances at its "new" condition and the performance after being exposed to moisture. We conclude that preventative dressings are not equal in their prophylactic performances, but rather, the base technology, the ingredients, and their arrangement in the dressing structure shape the quality of the delivered tissue protection.

Keywords: finite element model; moisture; pressure injury; pressure ulcer; prevention.

FIGURE 1

The anatomically‐realistic finite element (FE) computational modelling of the buttocks, based on the MRI‐acquired female subject anatomy: A, The skeleton of the pelvis including the details of the sacral region from a posterior view. B, The relevant skeletal muscle structures added onto the skeleton. C, Adipose and skin tissues added to form the complete anatomical reconstruction, including the hard and soft tissue details. D, The latter geometrical model meshed into elements for the FE modelling process, with a magnified region to show details of the meshing grid

FIGURE 2

The multi‐layered structure of the Resposorb silicone border dressing. The mechanical properties of the marked layers (excluding the “protective sheet” which is not an integral part of the dressing structure) are reported in Table 2

FIGURE 3

The compressive force‐displacement curves of all the tested dressing products, fitted to a tri‐linear function (for which the coefficients resulting from the best fits to the test data of each dressing product are provided in Table 3), for dry (A) and moist (B) test conditions. The stiffness relationships shown here should be considered as representing an area of 1 mm² of each dressing. SF, silicone‐foam; RSB, resposorb silicone border

FIGURE 4

The two steps of loading the model variants for simulating the application of a prophylactic sacral dressing and then further calculating the tissue loading state in a resting supine body position. p = the minimal pressure level (up to 0.2 kPa) simulating the pressure applied on the dressing by a skilled nurse during the action of dressing application, to attach the dressing to the skin surface while maintaining it smooth and free of folds or wrinkles. F = the reaction force between the mattress and the supine body which is increased gradually (until reaching 40% of the bodyweight which simulates full weight‐bearing based on anthropometrical data). The loading process is shown here from an inferior view, so that the sacral prophylactic dressing can be seen

FIGURE 5

The volume of interest (VOI) in the modelling (with dimensions of 9 × 9 × 9 cm³) containing the soft tissue structures located directly under the sacrum and coccyx, which are at the highest risk for development of a sacral pressure ulcer in a supine position

FIGURE 6

The stress exposure histogram (SEH) charts of the different dressings under dry (left column) and moist (right column) test conditions, for the skin and pooled soft tissue layers (skin, adipose and skeletal muscle tissues considered together) in the upper and lower panels, respectively, for the softer (10 kPa) mattress (A) and the stiffer (30 kPa) mattress (B). The SEH data in the sacral volume of interest (VOI; demarcated in Figure 5) are shown on a semi‐logarithmic scale. The no‐dressing SEH charts (continuous red lines, plotted starting from the median stress value on the horizontal axes) were considered the basal condition for the calculations of the protective efficacy index (PEI), protective endurance (PEN) and prophylactic trade‐off design parameter (PTOD) values (detailed in Tables 5, 6 and 7, respectively) for each tested dressing product. SF, silicone‐foam; RSB, resposorb silicone border

FIGURE 7

The protective efficacy index (PEI) of the Resposorb silicone border (RSB) dressing vs the corresponding mean PEI of the silicone‐foam (SF) dressings for skin only (A) and the pooled soft tissues (B) (skin, adipose and skeletal muscle tissues considered together). The error bars denote the standard errors of the means (n = 4 SF dressings)

FIGURE 8

The protective endurance (PEN) (A) and prophylactic trade‐off design parameter (PTODP) (B) of the Resposorb silicone border (RSB) dressing vs the corresponding means of the silicone‐foam (SF) dressings for skin and the pooled soft tissues (skin, adipose and skeletal muscle tissues considered tgether) on the softer (10 kPa) and stiffer (30 kPa) mattresses. The PTODP data are plotted on a semi‐log scale. The error bars denote the standard errors of the means (n = 4 SF dressings)