Testing the effectiveness of a polymeric membrane dressing in modulating the inflammation of intact, non‐injured, mechanically irritated skin

Abstract

We investigated the inflammatory (IL‐1 alpha) and thermal (infrared thermography) reactions of healthy sacral skin to sustained, irritating mechanical loading. We further acquired digital photographs of the irritated skin (at the visible light domain) to assess whether infrared imaging is advantageous. For clinical context, the skin status was monitored under a polymeric membrane dressing known to modulate the inflammatory skin response. The IL‐1 alpha and infrared thermography measurements were consistent in representing the skin status after 40 min of continuous irritation. Infrared thermography overpowered conventional digital photography as a contactless optical method for image processing inputs, by revealing skin irritation trends that were undetectable through digital photography in the visual light, not even with the aid of advanced image processing. The polymeric membrane dressings were shown to offer prophylactic benefits over simple polyurethane foam in the aspects of inflammation reduction and microclimate management. We also concluded that infrared thermography is a feasible method for monitoring the skin health status and the risk for pressure ulcers, as it avoids the complexity of biological marker studies and empowers visual skin assessments or digital photography of skin, both of which were shown to be insufficient for detecting the inflammatory skin status.

Abbreviations

FE

finite element

IRT

infrared thermography

PIs

pressure injuries

PMD

polymeric membrane dressing

PUs

pressure ulcers

1. INTRODUCTION

Chronic wounds such as pressure ulcers/injuries (PUs/PIs) and diabetic foot ulcers initially form as a microscopic deformation‐induced cell and tissue damage, which deteriorates, scales up and then fails to heal in a timely manner. ¹ , ² , ³ Focusing on PUs/PIs, the initial cell and tissue damage is escalated by inflammatory oedema, which rises the interstitial tissue pressures in tissue regions sandwiched between rigid skeletal structures and a support surface (or a medical device), thus progressively worsening the state of cell deformations and lowering the available vascular supply and lymphatic function. ⁴ Inflammation is the initial phase in the normal wound healing process, which prepares the wound for tissue regeneration, by promoting migration of tissue‐repairing cells and formation of neovasculature. ⁵ In PUs/PIs, however, the cell deformation‐related death triggers an inflammatory response that, depending on the characteristics of the specific patient and wound, may become excessive and prolonged and may not fade away to allow the wound to progress to the regenerative phases, leading to chronicity. ⁵ , ⁶

Millions of people internationally are affected by such non‐healing PUs/PIs, which negatively impact their quality of life and become a burden to healthcare professionals and organizations, in both the therapeutic and financial aspects, costing tens of billions of dollars annually to health service systems. ⁷ , ⁸ It is therefore a broad consensus that effective PU/PI prevention strategies need to be implemented in health organizations, to avoid entering the vicious cycle of PU/PI formation and deterioration and the associated vast labour and cost resources that PUs/PIs typically consume in addition to the suffering of patients and families. There are many traditional clinical prevention approaches, for example, repositioning, use of support surfaces that provide good immersion and envelopment and visual skin assessments.

In addition, emerging clinical technologies, including, for example, subepidermal moisture scanner measurements and infrared thermography (IRT) imaging, are currently being integrated into hospital prevention programmes to prevent and early detect PUs/PIs, and these may be further powered by machine learning in the near future. ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁴ , ¹⁵ An additional important component in contemporary preventative bundles is the use of prophylactic dressings, which may provide local alleviation of mechanical stresses in skin and subdermal tissues to protect from PUs/PIs, typically at the sacral and heel regions. ¹⁴ , ¹⁶ , ¹⁷ , ¹⁸ However, the prophylactic use of dressings is still in its early days, particularly because the dressings that are currently used for prevention were in fact developed for treating wounds, and hence, their properties relevant for prevention, for example, management of perspiration and thermal performance to release metabolic heat from the skin, are still subject to bioengineering laboratory research. ¹⁹

Modulating and focusing the inflammatory process within the relevant tissue space and time frame to help heal wounds while avoiding excess or stalled inflammation is an established concept in wound care, ²⁰ , ²¹ , ²² which requires monitoring of the inflammatory process, its intensity and time course behaviour. A relatively recent laboratory research approach for early identification of an inflammatory response in skin is the measurement of the concentration of IL‐1 alpha, an inflammatory cytokine (small signalling protein molecule) thought to be involved in the pathogenesis of chronic inflammatory diseases. ²³ , ²⁴ The monitoring of IL‐1 alpha levels is based on physical collection of this biomarker from the skin surface. Previous studies have shown that the IL‐1 alpha cytokine is highly expressed among subjects with chronic inflammatory disorders ²³ , ²⁵ and it has been further demonstrated that inflammatory cytokines are elevated in chronic, non‐healing wounds, causing a pro‐inflammatory environment and degradation of growth factors and various tissue‐building proteins. ²⁶ , ²⁷

The local skin temperature magnitudes and distributions also relate to the inflammatory status of the skin and thereby, indirectly, to the susceptibility to superficial PUs/PIs at the relevant anatomical location. ²⁸ The spatial skin temperature can be acquired non‐invasively by means of contactless IRT, a quantitative, robust and cost‐effective method for skin temperature mapping using a thermal camera. ¹⁴ , ¹⁵ , ²⁹ , ³⁰ Our previously published work revealed that entropy, a measure of the degree of randomness of pixels in an IRT image of skin (extracted using an image processing algorithm), effectively identifies skin irritation conditions through the thermal response of the tissue, even if visual signs of skin surface redness are not (yet) present. ¹⁴ In other words, an IRT image of a skin with a high entropy number denotes a complex or noisy thermographic appearance with a wide range of pixel values and is characteristic to irritation and inflammation, whereas a low entropy value of a skin IRT image denotes a more uniform and, therefore, healthy skin condition. ¹⁴

Of note, collecting IL‐1 alpha cytokines from skin and measuring their levels requires expensive biological laboratory equipment, is relatively labour intensive, difficult to implement clinically and the results cannot be obtained in real time. In contrast, the use of IRT for detecting the skin inflammatory status is inexpensive, provides real‐time data and being contactless and therefore non‐disturbing for patients, can potentially be conducted at the bed‐side as part of the clinical routine of PU/PI risk assessment and early detection. However, no studies have assessed these technologies (with IRT further augmented by image processing) on the same group of subjects, to systematically explore their pros and cons in potential use for clinical PU/PI prevention, including when applied under prophylactic dressings, that is, towards integration in future clinical PU/PI preventative bundles.

Accordingly, in this study, we investigated the inflammatory (IL‐1 alpha) and thermal (IRT) reactions of the skin of healthy subjects to sustained, irritating mechanical loading delivered to the sacral region. In addition to the skin IRT images (taken at the infrared domain), we acquired corresponding digital photographs (at the visible light domain) to assess whether the infrared imaging is indeed necessary or advantageous over conventional digital photography. For clinical context, the skin status was monitored under a polymeric membrane dressing (PMD), which is known to modulate the inflammatory response of skin and, therefore, has a potential unique prophylactic benefit for PU/PI prevention. ¹⁴ , ³¹ , ³² , ³³ , ³⁴ To further assess the inflammation modulation function of the PMDs, we used a placebo foam dressing with identical shape and size at the contralateral sacral side. The specific research questions addressed in the current work were therefore: (i) Are IL‐1 alpha and IRT measurements consistent in measuring the inflammatory status of mechanically irritated sacral skin? (ii) Is IRT imaging advantageous over conventional digital photography as a contactless optical device producing data for image processing, in order to extract information on skin irritation? (iii) Do PMDs offer a prophylactic benefit in the aspect of inflammation reduction at the mechanically loaded sacral region over standard medical polyurethane foam?

2. METHODS

2.1. Subjects

Ten healthy adult subjects of both genders, in the age range of 20–40 years, were recruited for this study from the university community. The experimental protocol described below was approved by the ethics committee of Tel Aviv University (TAU ethical approval number: 2‐0003183). Subjects with abnormal haemoglobin A1c levels, smokers, those who reported significant emotional stress, or those on antibiotic medications and pregnant women were excluded. Prior to the experiments, each participant provided their written consent to be tested and for potential publication of the acquired skin images.

2.2. Experimental set‐up and related computational model

The method of mechanically irritating the skin at the sacral region was adopted from the published work of Soetens and colleagues. ³⁵ Specifically, to examine the inflammatory skin response to non‐damaging mechanical irritation at the sacral region, each subject was positioned lying in prone on a standard flat foam mattress. Two identical cylindrical stainless‐steel weights, weighing 1.4 kg and 36 mm in diameter each (causing localized skin pressure of 100 mmHg), were located to the left and right of the sacral bone (Figure 1). These weights were covered with polyester fabric to minimize the heat transfer between the weight and the irritated skin, and were tied using zip ties to an adjustable aluminium frame that was fixed above the bed frame. The vertical rods of the frame were inserted inside 3D printed bases, which were placed on the floor for more efficient stabilization (Figure 1). The mechanical load was delivered to the sacral region through the pair of weights for 1 h and digital photographic, IRT and biological data were collected prior to the loading session and after 20, 40 and 60 min of mechanical loading. The experimental sessions were conducted under controlled ambient temperature (20 ± 2°C) and relative humidity of (40 ± 5%). Two types of dressings were used in this experiment ¹ : non‐adhesive clinically used PMD, which is indicated for inflammation reduction (Ferris Mfg. Corp., Fort Worth, TX, USA); and ² standard single‐layer conventional medical‐grade polyurethane foam material (hereinafter referred to as ‘placebo foam’). Importantly, the placebo foam dressings lacked the specific active PMD components, which act synergistically to result in the focusing and modulation of wound‐related inflammation as stated by their manufacturer. ³² , ³³ , ³⁶ , ³⁷ , ³⁸ , ³⁹ , ⁴⁰ Both dressing types were cut to standard circular specimen dimensions of 36 mm in diameter and 3 mm in thickness, and were located between the weights and the sacral skin of the subjects to compare their protective performance (Figure 1).

FIGURE 1.

A schematic of the experimental set‐up (A) and the location of the loaded areas at the sacral region (B). PMD, polymeric membrane dressing.

A computational model of the above experiments was developed using the finite element (FE) method to provide better characterization of the loading state of the sacral skin and subcutaneous tissues during the subject trials (Figure 2). The anatomy of the pelvic region in the modelling was based on magnetic resonance imaging (MRI) slices of the buttocks of a 28‐year‐old healthy woman, as described in detail in our published work. ⁴¹ The tissue constitutive models and the mechanical properties assigned to each tissue type are also reported in our previous published works ⁴² , ⁴³ (Figure 2A). The mechanical properties of the placebo and PMD were measured in another previous work and the respective experimentally obtained elastic moduli of 33.5 and 15.5 kPa ³⁶ were further fed into the current model. The model revealed that in the sacral skin, the peak strains were 37%, 38% and 42.5% for the placebo, PMD and no dressing conditions, and the maximal stresses were 45.9, 46.8 and 51.9 kPa for the placebo, PMD and no dressing conditions (Figure 2B,C). In the subcutaneous adipose tissue, the peak strains were substantially greater, 78.5%, 79.6% and 81.1% for the placebo, PMD and no dressing conditions, and the maximal stresses were 7, 7.3 and 8.3 kPa for the placebo, PMD and no dressing conditions. Overall, the modelling indicated that the tissue strains and stresses were similar between the placebo and PMD (that is, the tissue strains differed by 1% maximally and the tissue stresses differed by less than 1 kPa). However, both dressing types reduced the peak tissue stresses considerably with respect to the no dressing condition, by 10% for skin and by 14% subcutaneously.

FIGURE 2.

The computational finite element model of the subject trials (A) and resulting tissue stresses from top (B) and cross‐sectional (C) views. PMD, polymeric membrane dressing. The horizontal and vertical displacements of the weight are 11.4 and 31.3 mm, respectively.

2.3. Data collection

An Optris Xi‐400 IR camera (Optris GmbH, model Xi 400, Berlin, Germany) operating with Optris PIX Connect software (Optris GmbH, Berlin, Germany) was connected to a computer for obtaining digital IRT images demonstrating the temperature distribution of the irritated sacral skin. An Apple iPhone 13 phone camera (Apple, Cupertino, CA, USA) was used to further obtain digital images of the irritated sacral skin (use of a smartphone camera, as opposed to a specialized digital camera, was tested here to explore the prospects of using accessible and available equipment for routine image processing‐aided, digital photography‐based skin assessments). Both the infrared and smartphone cameras were fixed above the subject throughout the experiment to acquire images of the irritated skin regions at each time interval. Sub‐epidermal moisture (SEM) measurements were also performed, using the commercial Provizio® SEM Scanner (Bruin Biometrics LLC, Los Angeles, CA, USA), to obtain the SEM‐delta subject‐specific risk assessment measure for a PU/PI during the trials, as per the instructions for use provided by the manufacturer. In addition, sebum was collected from under each dressing type using Sebutape 1 (CuDerm Corp., Dallas, TX, USA). The skin was carefully checked for blanching prior to each collection of sebum, to ensure that there were no visible signs of skin damage, such as continuous (non‐blanchable) redness, visible scratches or dermatographia. The sebutapes were applied to the skin for 2 min for the collection periods, using gloved hands and tweezers to avoid potential cross‐contaminations.

2.4. Recovery of sebum proteins from the sebutape

For the current sebum protein content analyses, we again followed the methodology reported by Soetens et al. ³⁵ Specifically, for batch analyses, the frozen sebutape specimens were first thawed to room temperature and submerged in 1 mL of saline. Using forceps, the sebutape specimens were arranged in culture tubes so that the entire skin sampling surface of each tape was immersed in the extraction saline for at least 1 h. Next, the tubes with tapes were placed on a roller mixer for 1 h, then sonicated for 10 min at room temperature and lastly re‐frozen in an −80°C freezer for storage until performing an enzyme‐linked immunosorbent assay (ELISA). Prior to the ELISA tests, the tape extracts were thawed, vortexed and then centrifuged for 1 min to recover the total extract from the tapes. The tapes were then removed from the sample vials and discarded.

2.5. Evaluation of the total protein extracted from the sebutape

The QuantiPro™ BCA assay kit (SIGMA Aldrich, QPBCA, St. Louis, MO, USA) was used for quantitative evaluation of the total protein extracted from the sebutape. First, all the reagents and samples were brought to room temperature. Next, the samples, blanks and protein standards were mixed in a ratio of 1:1 with the working reagent, and the solution was then incubated at 37°C for 2 h and read in a plate reader using a 562 nm wavelength. The concentration of total protein in the samples was calculated based on the calibration curve, as per the instructions for use for this kit.^* The calculated total protein concentrations were used in the next step to normalize the inflammatory marker levels detected using the ELISA, as described below.

2.6. Evaluation of the interleukin‐1 alpha inflammatory marker levels

All the reagents and samples were first brought to room temperature. A human IL‐1 alpha ELISA kit (Millipore, provided by SIGMA Aldrich, RAB0269) was used to detect the IL‐1 alpha concentrations in the samples. The samples and the cytokine standards were read using a 450 nm wavelength in the plate reader. Using the standard curve and calibration equation obtained by performing standardization with the kit, as described by the manufacturer,^† we calculated the IL‐1 alpha concentrations in the samples acquired from the subjects, resulting in quantitative and comparative results for the presence of this marker in their sebum.

2.7. Digital and infrared thermography image processing

Processing and analysis of the digital skin and IRT images were performed using dedicated computer codes developed in a Python environment (version 3.8.12). The regions of skin irritation to the left and right of the sacral bone were determined as the regions of interest (ROIs) for all further analyses. Both the digital skin and IRT images were pre‐processed through the following steps: (1) cutting the ROIs out of the original images; (2) converting the ROIs to grayscale; (3) resizing the resulting images to a unified size of 250 × 250 pixels; and (4) normalizing the pixel intensities to a range of 0–1.

The temperature values for the ROIs were extracted from the acquired IRT images using the Optris PIX Connect software (Optris GmbH). Histograms of the pre‐processed ROIs from both the digital skin and IRT images were also obtained for feature extraction. Entropy, a texture feature quantifying the randomness of the pixel intensity distribution in an image, was calculated from the histograms as follows:

$$E\left(I\right)={\sum }_{k=0}^{N-1}p\left(x_k\right)\mathit{lo}{g}_{2}p\left(x_k\right)$$ (1)

where I is the image, N is the number of pixel intensities in the image and $p\left(x_k\right)$ is the probability of occurrence of the value $x_k$ in image I. The weighted average of the grayscale intensities was also calculated as:

$$\overline{X}=\frac{{\sum }_{k=0}^{N-1}{W}_i{x}_i}{{\sum }_{k=0}^{N-1}{W}_i}$$ (2)

where $W_i$ is defined as the probability of occurrence of the grayscale intensity $x_i$ (as appearing in the histogram). It was decided to use the weighted average here (Equation 2) rather than the simple average, since the probabilities of occurrence of the grayscale intensities in the acquired images are non‐uniform, causing a bias of the simple average. ⁴⁴

2.8. Statistical analysis

Data for the group of 10 subjects are presented as means ± standard deviations. Two‐way analysis of variance (ANOVA) for the factors of time and the dressing type (PMD and placebo) followed by pairwise comparisons where significant differences were detected by the ANOVA were performed, separately for each reported outcome measure, to identify potential statistically significant differences. Outliers were considered as Z ≥ 3 using the Z‐score outlier test. The level of statistical significance was set as p < 0.05.

3. RESULTS

3.1. Evaluation of the skin inflammatory marker levels

The IL‐1 alpha measurements from all subjects and at all times were always at normative levels, that is, near or below baseline (Figure 3), as opposed to the at least twofold greater than normal and potentially several‐fold changes in dermatological diseases or injured skin. ⁴⁵ , ⁴⁶ , ⁴⁷ , ⁴⁸ This experimental observation was consistent with the SEM‐delta measurements of all subjects, which always fluctuated below the 0.6 threshold, as stated by the manufacturer and relevant literature to indicate healthy sacral skin. ⁴⁹ , ⁵⁰ , ⁵¹ The medians of the IL‐1 alpha data for the placebo foam and PMD were similar and near the onefold baseline level at the 20‐ and 40‐min time points. However, mild differences appeared between the placebo and PMD at the 60‐min end point where the fold‐change was approximately 20% lower for the PMD with respect to the placebo (without statistical significance) (Figure 3).

FIGURE 3.

Changes in IL‐1 alpha over the course of the experiment. PMD, polymeric membrane dressing.

3.2. Evaluation of the skin image data

The processed digital and IRT images of the loaded sacral skin regions (Figure 4) visualized the colour changes of the irritated skin over time, corresponding to the skin temperature changes. The average temperature of the sacral skin increased over time under both the placebo dressing and PMD (Figure 5), with the steepest increase occurring after 20 min under the placebo (p < 0.05), but more moderately under the PMD where a significant difference with respect to baseline was recorded after a longer time, that is, 40 min (p < 0.05). The average grey level calculated from the digital skin images after 20, 40 and 60 min was lower under both the PMD and the placebo dressing (Figure 6A) with respect to the average grey level at time zero (without statistical significance), which is consistent with the appearance of darker grey areas (i.e., lower grey level pixels) in the digital images after 20, 40 and 60 min of irritation (Figure 4). The entropy measures calculated from the digital skin images (acquired in visible light) did not show consistent trends nor did they indicate statistically significant differences throughout the course of the experiments (Figure 6B ), and likewise, the average grey level of the IRT images did not demonstrate a consistent trend over time (Figure 7A). However, the entropy levels of the IRT images demonstrated statistically significant increases under both the placebo and PMD dressings compared with the baseline, such that the entropy values at each time point after time zero were statistically significantly greater than the respective baselines at both the placebo and PMD locations (p < 0.05 at least) (Figure 7B). Moreover, while the average entropy values for the placebo dressing increased monotonically over time, those for the PMD decreased at the 60‐min time point with respect to the 40‐min point and were lower than those of the placebo at all time points (without statistical significance) (Figure 7B). Noteworthy is that the decrease in the average entropy level for the PMD from 40 to 60 min (Figure 7B) was consistent with the decrease in the IL‐1 alpha inflammatory marker for the same time points and experimental (PMD) condition (Figure 3).

FIGURE 4.

Examples of digital (A) and infrared thermography (IRT) (B) images of the sacral skin collected from one subject (female, 26 years old) throughout the experiment. The redness (indicating skin irritation) caused by the sustained mechanical loading is identifiable in both the visible light and IRT images. PMD, polymeric membrane dressing.

FIGURE 5.

Changes in the temperature of the sacral skin over the course of the experiment measured through infrared thermography (N = 10 and *p < 0.05, **p < 0.01). PMD, polymeric membrane dressing.

FIGURE 6.

Changes in the grey level, where 0 refers to black pixels and 1 refers to white pixels (A), and entropy values (B) of the digital images of the sacral skin throughout the course of the experiment. PMD, polymeric membrane dressing.

FIGURE 7.

Changes in the grey level (A) and entropy (B) of the infrared images of the sacral skin throughout the course of the experiment (N = 10 and *p < 0.05, **p < 0.01, ***p < 0.001). PMD, polymeric membrane dressing.

4. DISCUSSION

In this study, we investigated visual, biological and thermal responses of sacral skin to sustained mechanical irritation over time. Skin inflammatory marker levels (IL‐1 alpha) as well as temperature values and distributions along with skin colour changes in the visible light were analysed via sebum analysis, thermal imaging and digital image processing, respectively. These physiological parameters were extracted and compared before the loading was applied and after 20, 40 and 60 min of mechanical irritation, under PMDs versus placebo foam dressings.

The results first demonstrated that as opposed to the expected upregulation of IL‐1 alpha when a clinical skin injury occurs, that is, when there is visible loss of structural integrity of skin, ⁴⁵ the inflammatory marker levels from all subjects fluctuated within the normal range at all times (Figure 3). This indicated that no identifiable skin damage occurred to any of the participating subjects throughout the experiments. In this context, no noticeable fold‐change differences were observed between the PMDs and placebo dressings, excluding a non‐statistically significant but notable reduction in the IL‐1 alpha measurements for the PMD after 60 min of skin irritation (Figure 3), which supports the claims of a prophylactic quality of PMDs through inflammatory modulation. ³⁷ , ³⁸ These IL‐1 alpha results were further consistent with the subepidermal moisture scanner measurements, which, likewise, always fluctuated below the threshold stated by the manufacturer to be characteristic of undamaged sacral skin.

The current digital and thermal image processing analyses further revealed that both visual and thermal responses had occurred as a result of the mechanical skin irritations: Visible redness developed at the irritated areas (demonstrated as darker grey areas and lower average grey levels calculated from the digital skin images), particularly at the perimeters of the irritated circles where shear due to the weights was maximal as the computational FE modelling demonstrated (Figures 2 and 4). The intensity of skin irritation indeed corresponded to the mechanical stress magnitudes on skin at both the visible light and infrared domains (Figures 4 and 6A). In addition, the skin temperatures showed consistent and statistically significant increase over time under both the PMDs and placebo dressings (Figure 5); however, the temperatures under the PMDs always remained lower with respect to those under the placebo dressings (though without statistical significance), suggesting that the relatively high thermal conductivity of the PMD characterized in our published work facilitated better thermal energy release from the sacral skin to the environment, which again supports the use of PMDs in PU/PI prophylaxis. ⁵² This is because lower heat accumulation reduces perspiration moisture trapping between the skin and the dressing that may eventually macerate the skin. ⁵³

Interestingly, the median IL‐1 alpha skin inflammatory biomarker levels decreased below baseline for the PMD but not for the placebo at the 60‐min end point of the experiments (Figure 3). Corresponding to this, the entropy levels of the skin IRT images decreased at 60 min for the PMD with respect to the 40‐min time point, whereas the entropy levels of the IRT images of skin for the placebo condition continued to increase between the 40‐ and 60‐min time points (Figure 7B). While these experimental results related to the IL‐1 alpha and entropy of the IRT skin images were not statistically significant as stand‐alone measurements (Figures 3 and 7B), it is highly unlikely a coincidence that these two independent and orthogonal laboratory methods agreed in demonstrating a similar inflammatory response of the skin under the PMD with respect to the placebo condition over time, and, in particular, towards the end point of the trials. Collection of IL‐1 alpha from sebum is an established laboratory method for quantifying the skin inflammatory status, ²³ , ²⁵ , ²⁶ , ²⁷ and similarly, the entropy levels of IRT images of skin increase with the variability in spatial skin temperatures due to transition from a baseline homogenous skin perfusion to an irritated skin condition where irregular inflammatory blood vessel dilation occurs due to the inflammatory signalling. ¹⁴ Given the above consistent trends between the IL‐1 alpha and IRT measurements at the 40‐to‐60‐min time points of the experiments, an inflammatory modulation effect of the PMD on mechanically loaded sacral skin has been demonstrated in the current work.

The importance and utility of IRT imaging in evaluating the skin response to sustained, bodyweight‐related mechanical loading was already reported by our research group. ¹⁴ In the aforementioned published work, skin temperature distributions at the sacral area under PMD and placebo foam dressings were evaluated for the recovery period of the skin after continuous mechanical irritation through still, supine lying for 1 h. In the current study, the entropy of skin temperature distributions consistently demonstrated statistically significant increases over time under both the PMD and placebo dressings for the first 40 min (Figure 7B), as the entropy values at each time were statistically significantly greater than the value obtained before the application of the mechanical load (at time zero). The temperature distribution in the loaded area became less homogeneous over time under both types of dressings, indicating that the dressings applied under sustained mechanical loading caused heat trapping between the skin and the dressing, which should be considered in the context of assessment of the prophylactic performance. ³³ , ⁵³ , ⁵⁴ Nonetheless, more homogeneous skin temperature distributions were evident under the PMD compared with the placebo dressing at all times (including at the 40–60 min period; Figure 7B), indicating better microclimate under the PMD in a prophylactic context compared with the placebo. In future translational work and towards clinical implementation, the IRT entropy studies should be extended from healthy subjects to examinations of at‐risk patients in a hospital setting.

To conclude, the current bioengineering study provided the following answers to our three specific research questions put forward in the Introduction section: (i) The IL‐1 alpha and IRT measurements were consistent in measuring the inflammatory status of the mechanically irritated sacral skin after 40 min of continuous irritation (Figures 3 and 7B). (ii) The IRT method was proven to be advantageous over conventional digital photography as a contactless optical device producing data for image processing, as it revealed skin irritation trends that were not detectable through digital photography in the visual light, not even with the aid of advanced image processing (Figure 7). (iii) The PMDs were shown to offer important prophylactic benefits over simple polyurethane foams, both in the aspect of inflammation reduction at the mechanically loaded sacral region (Figures 3 and 7B) and with regard to microclimate management (Figure 5). Overall, the current study also points to the potential of IRT as a cost‐effective, contactless and clinically feasible method for monitoring the skin health status and the individual risk for PUs/PIs. The IRT and the associated image processing to extract the entropy measure avoids the complexity of biological marker studies and empowers visual skin assessments (i.e., the unassisted vision of a clinician) or digital photography of skin, both of which were shown to be insufficient for detecting the inflammatory status of the skin.

CONFLICT OF INTEREST STATEMENT

Author AG is ascientific advisor to Ferris Mfg. Corp. (Fort Worth TX, USA) whose polymericmembrane dressing technology is studied in this article. Ferris Mfg. Corp. hasnot controlled the research reported here and had no influence on its findingsor conclusions. All the other authors declare no conflict of interest.

Dabas M, Kreychman I, Katz T, Gefen A. Testing the effectiveness of a polymeric membrane dressing in modulating the inflammation of intact, non‐injured, mechanically irritated skin. Int Wound J. 2024;21(1):e14347. doi: 10.1111/iwj.14347

DATA AVAILABILITY STATEMENT

The data that support the findings of this study are available from the corresponding author upon reasonable request.