Does exudate viscosity affect its rate of absorption into wound dressings?

Abstract

Objective: Exudate is a vital component of healing wounds. There are differences between acute and chronic exudate, with the latter seen as highly toxic to the healing environment. Wound exudate assessment is not easy for clinicians. The viscosity of wound fluid/exudate is as important as its quantity. Wound fluid viscosity increases when it contains more protein. As wound dressings exhibit a variety of fluid-handling mechanisms, it is important to understand how they interact with the different exudate types, which may alter the wound/dressing interface. This knowledge will ensure a healing wound environment that is beneficial, not one that leaves harmful exudate on the wound surface. This study aimed to evaluate if the viscosity of exudate affected absorption time in four wound dressing types. Methods: This study evaluated the viscosities of two solutions and their effect on the absorption times of four dressing types. The viscosities of the solutions were calculated using Ostwald viscometers, then 2 ml of each of these liquids was applied to each of the four dressing types and repeated 10 times for each dressing, as per British Standards Institution requirements. The parameters for temperature and frequency were applied, and the absorption times recorded. A two-way repeated analysis of variance (ANOVA) was conducted to examine if exudate viscosity and dressing type, or their interaction, affected the absorption time. Results: The results indicated that the viscosity of the solution alone had a significant effect on absorption time (p<0.01), and that the combined effect of dressing type and viscosity also affected absorption (p<0.01). The type of dressing alone was found to have a significant effect on absorption time (p<0.01). When looking at the between-subject effects of the dressings (between the four types) the only non-significant finding was between two dressings—the superabsorbent and the moderate (foam) absorbing dressing (p=0.097). All other dressings had a between-subject effect of (p<0.01). Conclusion: A significant difference in absorption times was found in this investigation of dressing types and viscosity of test solutions. The greater the viscosity of the fluid, the longer it took for it to be absorbed into all dressing types tested. This delay was not determined simply by the dressing or by the viscosity of the fluid, but likely to be a combination of the mode of action of the dressing, its pore size and particulate composition of the exudate, all of which require further investigation.

The importance of the simulated wound fluid composition and properties in the determination of the fluid handling performance of wound dressings

“…This new formulation balances the need for standardisation in industry and academic testing, while also incorporating the main biological components. This is primarily done to achieve biochemical realism and a more complex, yet still watery viscosity, which is pivotal for studying the solid-fluid interactions with tested dressings 7,9,14,54 The current work focuses on taking the first steps in developing and characterising SWF A, a well-defined test fluid to simulate a watery chronic wound exudate type for fluid handling testing of wound dressings, for example, according to EN 13726:2023. This SWF A is seen as a platform for potentially adding other components for even more enhanced realism or specific clinical contexts in the future, such as further addition of, for example, nutrients, residual exudate debris, thickener, suspended particles of relevant size, as previously suggested by the Gefen group 26,55 and by Mennini et al 5 in their SWF-related work.…”

Fluid handling by foam wound dressings: From engineering theory to advanced laboratory performance evaluations

“…It explains the increase in viscosity by the increase in nanoscale friction of the relatively large and long protein molecules against each other when flow occurs, which intensifies when more protein molecules are present in the fluid. In infected or surgically debrided wounds, the volume of protein in exudates tends to increase over time, 23,24 rendering the fluid more viscous 9,37 . In addition to the nano‐frictional interactions between protein molecules contributing to a rise in the fluid viscosity, the presence of microorganisms would have a similar and cumulative effect, as individual microorganisms or bacterial aggregates in the liquid culture (as in biofilms) may also frictionally slide against each other or collide during fluid flow (for above‐critical concentrations), which slows down the flow 14 , 72,73 .…”

“…1,13,14,18,[32][33][34] The presence of proteins in an exudate, which is ignored in the EN 17326 standard, strongly influences the surface tension and viscosity of the fluid 6,7 and, in clinical practice, may vary from that of a watery exudate to a thick and tenacious discharge. 15,[36][37][38] Wound dressing performance, influenced by material, structure and manufacturing, varies significantly across manufacturers even within the same sub-class, for example, foam dressings 13,16,17,39 (Figure 2). Optimal functionality requires efficient absorption, spreading, retention and evaporation of diverse exudates during clinical use.…”

“…5 This standard utilizes water solution of sodium chloride and calcium chloride, which completely ignores the above complexity of fluid chemistry, physics and mechanics of real‐world wound exudates 1,13,14,18,32–34 . The presence of proteins in an exudate, which is ignored in the EN 17326 standard, strongly influences the surface tension and viscosity of the fluid 6 , 7 and, in clinical practice, may vary from that of a watery exudate to a thick and tenacious discharge 15,36–38 …”

Fabrication and Properties of the Multifunctional Rapid Wound Healing Panax notoginseng@Ag Electrospun Fiber Membrane

“…Wound healing is a complex pathophysiological process, with four phases: hemostasis, inflammation, proliferation, and remodeling [ 1 , 2 ]. In the inflammatory phase, large amounts of wound exudate are prone to occur at the wound [ 3 , 4 ]. However, excess exudate favors the growth and reproduction of bacteria, which can lead to an intensified inflammatory response, slow down the rate of wound healing, and make wound healing stop in the inflammatory phase [ 5 , 6 , 7 ].…”