How Should Clinical Wound Care and Management Translate ...

How Should Clinical Wound Care and ManagementTranslate to Effective Engineering Standard TestingRequirements from Foam Dressings? Mappingthe Existing Gaps and Needs

Amit Gefen,1,* Paulo Alves,2 Dimitri Beeckman,3 Breda Cullen,4

Jose Luis Lazaro-Martınez,5 Hadar Lev-Tov,6 Bijan Najafi,7

Nick Santamaria,8 Andrew Sharpe,9

Terry Swanson,10 and Kevin Woo11

1Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel.2Centre for Interdisciplinary Research in Health, Catholic University of Portugal, Porto, Portugal.3Skin Integrity Research Group (SKINT), University Centre for Nursing and Midwifery, Ghent University and Swedish

Centre for Skin and Wound Research, School of Health Sciences, Orebro University, Orebro, Sweden.4RedC Consultancy, Bradford, United Kingdom.5Diabetic Foot Unit, Universidad Complutense de Madrid, Madrid, Spain.6Dr. Phillip Frost Department of Dermatology and Cutaneous Surgery, University of Miami Hospital Miller School

of Medicine, Miami, Florida, USA.7Interdisciplinary Consortium on Advanced Motion Performance (iCAMP), Michael E. DeBakey Department of Surgery,

Baylor College of Medicine, Houston, Texas, USA.8School of Health Sciences, University of Melbourne, Melbourne, Victoria, Australia.9Podiatry Department, Salford Royal NHS Foundation Trust, Salford Care Organisation, Salford, United Kingdom.10Nurse Practitioner, Warrnambool, Victoria, Australia.11School of Nursing, Queen’s University, Kingston, Ontario, Canada.

Significance: Wounds of all types remain one of the most important, expensive,and common medical problems, for example, up to approximately two-thirdsof the work time of community nurses is spent on wound management. Manywounds are treated by means of dressings. The materials used in a dressing,their microarchitecture, and how they are composed and constructed form thebasis for the laboratory and clinical performances of any advanced dressing.Recent Advances: The established structure/function principle in material sci-ence is reviewed and analyzed in this article in the context of wound dressings.This principle states that the microstructure determines the physical, mech-anical, and fluid transport and handling properties, all of which are criticallyimportant for, and relevant to the, adequate performances of wound dressings.Critical Issues: According to the above principle, once the clinical requirementsfor wound care and management are defined for a given wound type andetiology, it should be theoretically possible to translate clinically relevantcharacteristics of dressings into physical test designs resulting specific metricsof materials, mechanical, and fluid transport and handling properties, all ofwhich should be determined to meet the clinical objectives and be measurablethrough standardized bench testing.Future Directions: This multidisciplinary review article, written by an Inter-national Wound Dressing Technology Expert Panel, discusses the translationof clinical wound care and management into effective, basic engineering

Amit Gefen, PhD

Submitted for publication November 16, 2021.

Accepted in revised form February 20, 2022.

*Correspondence: Department of Biomedical

Engineering, Faculty of Engineering, Tel Aviv

University, Tel Aviv 6997801, Israel

(e-mail: [email protected]).

ª Amit Gefen et al., 2022; Published by Mary Ann Liebert, Inc. This Open Access article is dis-tributed under the terms of the Creative Commons License [CC-BY] (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium,provided the original work is properly cited.

j 1ADVANCES IN WOUND CARE, VOLUME 00, NUMBER 002022 by Mary Ann Liebert, Inc. DOI: 10.1089/wound.2021.0173

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standard testing requirements from wound dressings with respect to material types, microarchitecture,and properties, to achieve the desirable performance in supporting healing and improving the quality oflife of patients.

Keywords: treatment, laboratory testing methods and standards, test fluid,fluid handling and retention, exudate management

BACKGROUNDScope and significance

Wounds remain one of the most important, ex-pensive, and common medical problems, and manywounds are treated using dressings. The materialsthat make an advanced wound dressing, their mi-croarchitecture, and how they are composed andconstructed form the basis for its laboratory andclinical performances. This multidisciplinary re-view article discusses the translation of clinicalwound care and management into effective, basicengineering standard testing requirements fromwound dressings with regard to material types,microarchitecture, and properties, to achieve thedesirable performance in supporting healing andimproving the quality of life of patients.

Translational relevanceThe established structure/function principle in

material science states that the microstructuredetermines the physical, mechanical, and fluidtransport and handling properties, all of which arecritically important for the adequate performancesof advanced wound dressings. Accordingly, oncethe clinical requirements for wound care are de-fined for a given wound type and etiology, it shouldbe theoretically possible to translate the clinicallyrelevant characteristics of dressings into physicaltest designs resulting specific metrics of materials,mechanical, and fluid transport and handlingproperties, all of which should be determined tomeet the clinical objectives and be measurablethrough standardized bench testing.

Clinical relevanceClinicians should adopt critical thinking con-

cerning dressing technologies and specifications.Laboratory test data should be routinely requestedfrom manufacturers to verify that the dressingbeing considered is capable of managing the exu-date fluids that are relevant to the wound etiologiesto be treated, for example, the expected exudatevolumes, flow rates, and viscosities.

Requiring manufacturers to agree upon andimplement standardized, clinically relevant testmethods, resulting in peer-reviewed, publishedtest data will facilitate informed selection of thesafest and best performing dressings. Clinically

relevant testing standards would also ultimatelyallow objective, standardized, and quantitativecomparisons between dressing brands, therebyoptimizing personalized treatment decisions.

The critical role of laboratory test standardsin dressing performance evaluations

Wounds and skin injuries of all types, includingtraumatic injuries and burns, surgical woundsand hard-to-heal (including chronic) wounds, suchas pressure ulcers/injuries, venous leg ulcers, anddiabetic foot ulcers, are one of the most impor-tant, impactful, expensive, and common medicalproblems.

For example, up to approximately two-thirds ofcommunity nursing time is spent on the provisionof wound care and management, the majority ofwhich is due to delayed healing.1–3 All seriouswounds and some of the mild ones are treated bymeans of dressings. The materials currently usedin modern wound dressings, their microarchitecture,and how they are composed and constructed in adressing structure form the basis for the perfor-mance of dressings in contemporary, clinical woundcare.

The established structure/function principle inmaterial science states that the microstructuredetermines the physical, mechanical, and fluidtransport and handling properties of a givendressing product (Fig. 1). All these properties areimperative and relevant to the laboratory testing ofwound dressings and, more importantly, are criti-cal to the clinical performance of dressings in sup-porting wound healing (Fig. 2).

Therefore, once the clinical requirements forwound care and management are defined for a gi-ven wound type and etiology, it should be theoreti-cally possible to translate the clinically relevantcharacteristics of wound dressings into a physicaldesign with specific metrics of materials, mechani-cal, and fluid transport and handling properties thatare all determined to meet the clinical objectivesand that are measurable through standardizedbench testing.

This multidisciplinary critical review article,written by an International Wound Dressing Tech-nology Expert Panel (IWDTEP), discusses the

2 GEFEN ET AL.

translation of clinical wound care and managementinto the requirements from an effective wounddressing and how such clinical requirements shoulddetermine the types, behavior, and properties ofdressing materials to achieve the desirable dressingperformances, as well as the need for clinically rel-evant laboratory test methods.

The IWDTEP appreciates that the translation ofclinical wound care and management to the engi-neering requirements from effective dressings is amassively broad theme, even if being restricted tofoam dressings. Accordingly, a long-term series ofcomprehensive scientific publications are planned,with the current work being the cornerstone andproviding context and structure to the plannedseries of works.

THE CONDENSED HISTORY OF WOUNDDRESSINGS

Wound dressings are most likely the oldest typeof medical device. In the ancient world and medi-eval times, mud, salts, feathers, leaves, cobwebs,various plant extracts, honey, and lint were com-monly used to cover wounds.4–6 The discov-ery of microorganisms changed the design andmanufacturing of wound care products. In the late19th century, the Johnson & Johnson companybegan producing sterile surgical dressings (made ofcotton and gauze) using dry-heating and pressur-ized steam.7

Further advances were made during World WarI, when the first nonadherent dressings, whichconsisted of fabrics impregnated with soft paraffin

Figure 1. The established structure–function principle in material science is that the microstructure determines the properties, such as the mechanical andfluid handling characteristics (a). For wound dressings, ‘‘function’’ encompasses the mechanical, fluid transport, and retention properties (altogether). Thefocus of the vast majority of the existing testing standards for wound dressings is on the properties and function of the tested dressing products, not theirstructure or microstructure. In a multilayer foam dressing, for example, each layer of the dressing has its own set of the above properties, and accordingly, the‘‘function’’ of the whole dressing structure is determined by the contribution of each of the material components, for example, to the effective permeability ofthe dressing structure (b).

TRANSLATING WOUND CARE TO DRESSING REQUIREMENTS 3

oil, appeared to solve the problem of cotton andgauze dressings adhering to wounds, resulting invery painful dressing changes. These nonadherentdressings then evolved into two-layered dressings,a cotton fabric facing the wound that contained theparaffin and a balsam for nonadherence, and asecond gauze layer on top to allow drainage byabsorbency, introducing the concept of a multilayerdressing for the first time.8

During World War II, purified, whitened,bleached woven gauzes were developed for a vari-ety of wound care applications and these are stillused today, however, the advent of flexible poly-urethane (PU) foams and the development of theirmass production methods in the 1950s had againrevolutionized the world of wound dressings.

Foams can absorb fluids, are vapor permeable,but retain moisture; provide mechanical cushioningand thermal insulation; and are easy to apply andremove; all of which are necessary to support effec-tive wound healing. Altogether, these propertieshave progressively made foams a core dressingtechnology in modern wound care.

As of the 1980s, the single-foam design evolvedinto multilayer foam dressings based on theaforementioned historical concept of nonadherence

through use of multiple layers in the dressingstructure. Furthermore, other modern materi-als, particularly silicone, were added to the foamdressing structure, to form encased (also known as‘‘bordered’’) foam dressings, which are dressingscomprising a wound contact foam pad surroundedby an adherent silicone rim.9–11

Today, many advanced dressings have siliconecoating across their entire contact area to preventdressing adherence, thereby minimizing the risk ofdamage to the wound and periwound skin uponremoval. Although other advanced dressing typeshave been developed during the recent decades,such as superabsorbent, hydrocolloid-based, andhydrogel-based dressings, foam dressings remain acommon choice for many wound care applications,and are therefore the focus of this review.

THE PRIMARY CLINICAL ROLESOF DRESSINGS AND THEIR RELATIONSHIPAND CONTRIBUTION TO THE PROCESSOF WOUND HEALINGThe concept of moist wound healing

Odland12 observed that the skin epithelializesfaster under unbroken blisters compared with

Figure 2. The fluid handling (or mass transport) performance of a certain wound dressing (as detailed in Table 1), which can be measured in a bioengineeringlaboratory setting, determines the likelihood of that dressing to successfully manage exudates, or alternatively, to fail in the more challenging clinical scenariosrequiring, for example, the absorbency of high volume of exudation or of a viscous exudate; treatment of infected wounds; and protection of fragile periwoundskin. Hence, the mass transport performance of the dressing eventually determines both the patient and the financial outcomes.

4 GEFEN ET AL.

beneath broken ones. Just a few years later, Win-ter13 presented his theory of moist wound healing,which was based on the observations of a porcinewound healing model. Winter’s seminal work,which Hinman and Maibach14 subsequently con-firmed in humans, indicated that maintaining amoist wound environment was conducive to heal-ing, which is the concept still used today.{

The advantages of a moist versus a dry woundbed environment include the following: preventionof tissue dehydration and cell death, faster epi-dermal cell migration, accelerated angiogenesis,increased breakdown of dead tissues and fibrin,potentiation of growth factor interactions withtheir target cells, and reduction of pain.16 Inter-estingly, all of these factors are associated with thebenefits of the foam dressing technology, so thatthe introduction of semiocclusive foam dressings

(which keep the wound bed moist) and the devel-opment of the moist wound healing paradigmcross-fertilized each other.

Clinical performance categories for wounddressings

From a clinical perspective, the primary roles ofa wound dressing are to address the symptoms ofthe wound, that is, (i) manage exudate and, in ad-dition, provide (ii) mechanical and (iii) biologicalprotection to the wound, thereby substituting forthe lack of a native functional skin.17 Any existingor new dressing can be evaluated with respect tothe above fundamental three clinical require-ments, based upon more specific performancecategories that are listed in Table 1.

Each of the factors listed under the fundamentalrequirements in Table 1 is essential to the healingprocess and deviation from these requirementsmay delay, reverse, or otherwise harm the healing.For example, the fluid handling characteristics allrelate to the removal of excess exudate so that thewound bed remains moist, but not wet, at all times.

Table 1. The primary clinical roles and functions of adequately performing wound dressings and the associated requirementsfrom dressing materials and structures

Fundamental Clinical Requirements for Wound and Skin Protection and Repair

Other Requirements

Physical and Engineering

BiologicalFluid Handling Mechanical Behavior

Effectively absorb a variety of woundexudates (e.g., having differentviscosities) while maintaining anoptimally moist wound environment

Be compliant (i.e., flexible) to conform tovarious contours of the body surface

Not be toxic, sensitizing, allergenic, orotherwise irritating to the woundarea; not abnormally change the skinpH

Be acceptable in appearance to patients,family members, health careprofessionals, and others

Effectively retain absorbed exudatesunloaded and under gravity,bodyweight, or any sustained orsudden external forces

Be reasonably strong and stiff tomechanically protect the wound butnot rigid; to not abrade the wound

Be sterile Have long storage life across a widerange of conditions

Effectively release retained fluids intothe environment through the backingmaterial/film as vapor, to facilitateadditional absorbency

Not release any particulates or debrisinto the wound bed

Resist the penetration of bacteria,viruses, and fungi through thedressing into the wound, or theirescape from the wound

Have low inflammability to keep patientssafe near fire sources

Stay in place once attached but notforcefully adhere to the woundsurface or to the periwound skin toallow easy removal and preventstripping damage

Cost-effective material components,construction, and manufacturingprocess

Minimum change of mechanicalproperties when exposed to body andwound fluids (endurance)

Be easy to apply and discard, forexample, through easy release fromthe package

Not change mechanical properties whencontacting other topical therapeuticagents

Desirably include indicators for when thedressing needs to be changed orremoved as it approaches its capacityto manage exudate or due to otherfactors that affect the life cycle

Minimize frictional forces and shearstresses that potentially apply at thewound region to reduce potentialwound tissue distortions

{For example, in the TIME model—a widely used practicalguide to wound management developed by a global team of woundcare experts, which relates clinical observations and interventionsto the underlying wound pathology in several aspects, includingmoisture imbalance.15


Failure of a dressing to absorb the wound fluidsand retain these fluids effectively under the influ-ence of expected (e.g., gravity or weight-bearing, orcompression therapy) or unexpected (e.g., unin-tentional contact with objects) mechanical forces,or ineffective fluid release into the environmentthrough evaporation, may lead to backflow (reflux)of fluids into the wound area. Such wetting of thewound (potentially, with aggressive or infectedexudate fluids) may cause inflammation and mac-eration, which are, of course, not conducive tohealing.

From a biological perspective, any adverse re-sponse of the wound or periwound tissues to thedressing materials, or failure to prevent infectionof the wound by pathogens, consumes the (alreadylimited) inflammatory and healing resources fromthe wound and invests them elsewhere, for exam-ple, in an allergen response or in attacking invad-ing bacteria. Specifically, an adverse reaction of thewound/periwound tissues to the dressing materialsmay provoke an excessive inflammatory response.

In theory, this should be detected before thedressings being placed on the market according tothe ISO-10993-118 testing standard (‘‘Biologicalevaluation of medical devices’’). Another cause ofexcessive inflammation may be the invadingpathogens, which are the primary cause of chro-nicity and nonhealing.{,19,20

CLINICALLY RELEVANT CHARACTERISTICSOF WOUND DRESSINGS RELATE TO THEIRPHYSICAL (MICRO-)STRUCTURE

All the three fundamental requirements listed inTable 1 strongly relate to the structure of thedressing and more specifically, to the microstruc-tural architecture and features of its materialcomponents (Fig. 1a).

Wound fluids flow into a dressing structure dueto one or a combination of the following factors: (i)capillary bed pressure from the wound, which pu-shes the fluid into the wound cavity and from thereinto the dressing; (ii) gravity, which causes themass of the fluid to be transported into the dress-ing; and (iii) capillary action (sorptivity), whichtransfers the fluid, possibly against the direction ofthe gravity vector, from the wound into the dress-ing, due to intermolecular forces between the fluidand the surrounding solid surfaces.21

Once the fluid has penetrated the dressingstructure, the fluid handling and the intrinsic ab-sorption capacity of an applied foam dressing are

facilitated by the microporous structure of the foam(Fig. 1b). The porosity of the foam and the level ofinterconnectivity between the micropores in thefoam are very likely to influence the fluid transportproperties of a foam dressing.

However, it is important to note that the existinglaboratory test methods, including those specifiedin the European test standard 13726-1,22 are notdesigned to capture the time course of fluid trans-port. Therefore, there is a clear need to include newtest methods in the future, improved testing stan-dards, to measure and record the performance ofwound dressings as they are used clinically, over atime course, during the indicated period of use.

The microstructure of foam dressingsand the potential effects on performance

Absorbency in foam dressings is achieved bytransport of exudate into the open cells of the foamstructure, through interconnecting channels, andhence, the absorbency capacity of foam dressings isdetermined largely by the porosity of their foams(i.e., the volume fraction of the micropores). Thefluid handling characteristics of foam dressings areconstituted by the interaction of this absorbencycapacity with the moisture-vapor transmissionrate (MVTR) that is determined by the perme-ability of the backing material/film. That is, afterthe initial fluid uptake into the foam structure viaabsorbency, evaporation of the fluid through thebacking material/film largely controls the fluidmanagement of the dressing.

The MVTR keeps the dressing from becomingsaturated, and an adequate MVTR level of thedressing will maintain the wound bed moisturethrough the use period. As evaporation takesplace through the backing material/film, additionalmoisture can be removed from the wound throughabsorption into the foam. Accordingly, throughevaporation, the total amount of moisture removedfrom a wound can exceed the absorbency capacity ofthe foam. More permeable backing materials/filmspermit higher evaporation rates from the dressing,thus providing the potential for longer wear times.

On the contrary, if the MVTR is set too low inthe design of the dressing, then at a certain timeduring usage, newly inflowing exudate arrivingfrom the wound will not have space in the mi-cropores, resulting in leakage from the dressingand maceration.

Of note, unlike superabsorbent wound dressingsthat actively retain and ‘‘lock in’’ fluid throughhydrogen bonding with water molecules, foamshold in the exudate passively in their voids, andhence, will release fluid under the influence of

{Chronic wounds fail to heal because they do not progress fromthe proinflammatory state.

6 GEFEN ET AL.

mechanical forces such as bodyweight or externalforces that substantially deform the dressing. Inother words, deformations of the dressing bybodyweight or external forces decrease the size ofthe micropores, squeezing fluid out of the dressing(as in a squashed sponge), which may compromisethe wound or periwound.

Foams used in commercial wound dressings havevariable pore sizes, ranging from 25lm to over1,000 lm.23 Smaller pore sizes and interconnectingchannels allow for greater fluid retention proper-ties. Larger pore sizes typically facilitate increasedfluid absorption from the wound into the dressing,better handling of viscous fluids, and greater evap-oration from the dressing to the environment.24

The downside though is that larger pores andconnecting channels allow immune and tissue-repairing cells such as fibroblasts to migrate intothe dressing structure, instead of remainingwithin the wound bed,25 which in turn impairshealing. Furthermore, fibroblasts infiltrating theporous dressing structure may synthesize colla-gen within the dressing, near the wound surface,which would effectively lead to connective tissue(micro-)ingrowth into the dressing, resulting intraumatic and painful dressing removals.

Even if the pore sizes are not large enough forcells to infiltrate into the dressing, they may besufficiently large to facilitate fibrin deposition atthe wound contacting layer (as fibrin is present inthe exudate at the early healing stages). The de-posited fibrin may then cause dressing adherence(acting like a fibrin glue), especially if the dressingwas in situ for multiple days.26

Many of these historical problems related totissue ingrowth into dressings and fibrin deposi-tion, resulting in dressing adherence (leading totissue trauma and pain to the patient on dressingremovals), have been addressed by the introduc-tion of dressings with silicone at the skin andwound interfaces.27–33 Yet, discomfort and painduring dressing removals remain a clinical issue,for example, because for dressings in which softsilicones are used to provide the adhesive borderonly, the wound contact layer (not covered by the sili-cone) might adhere to some degree to the wound bed.32

Accordingly, the above considerations highlightthe complexity of choosing the correct porosity andconnectivity for the microstructures of foams inwound dressings. Given the existing wide varietyof porosities in foam dressing products,23 what isan ideal porosity that perfectly balances betweenabsorbency, retention, and occlusion of tissue in-growth into the dressing, or fibrin deposition, ob-viously remains an open question.

Further complications arise from the fact that, forfoam dressings, porosity and connectivity affecttheir mechanical (strength and flexibility) charac-teristics. For example, smaller pores indicate great-er density of the dressing and, correspondingly, astiffer material behavior.34,35 A foam dressing that isexcessively stiff may indent the skin and causedeformation-inflicted tissue damage.36

A clinical case demonstrating this phenomenonis shown in Fig. 3, which documents a wound of a67-year-old man with a history of obesity andchronic leg ulcers due to venous lymphedema. Thispatient developed a pretibial ulcer with a moderateamount of drainage. A rectangular foam dressingwas applied under compression therapy that waschanged every 5 to 7 days. Not only was the choiceof the foam dressing material too stiff in this case,but the dressing was also applied under a two-layercompression system, which caused an ‘‘imprint’’ ofthis overly stiff dressing into the skin under thecompressive forces.

Figure 3. A clinical documentation of the effect of an excessively stifffoam dressing on the periwound skin. The image shows the wound of a 67-year-old man with a history of obesity and chronic leg ulcers due to venouslymphedema. This patient developed a pretibial ulcer with moderate amountof drainage. A rectangular foam dressing with sharp corners (white arrowmarking) was applied under a two-layer compression therapy system for atleast five consecutive days. The deep indentation on the periwound skin,which was also associated with pain, is clearly visible. Of note, the dressingmay not have been appropriately chosen by the clinician caring for thiswound. The documentation of this case is courtesy of author K.W.


The selection of the dressing, with its sharpcorners that induced mechanical stress concen-trations in skin and underlying soft tissuesx (Fig. 3;white arrow marking), indicates that this was notan optimal compression treatment, and the dress-ing itself may not have been appropriately chosenby the clinician caring for this wound. Indeed, thisdressing left a deep, well-demarcated indentationon the periwound skin, which was also associatedwith pain (Fig. 3). The patient case presented inFig. 3 exemplifies how an inadequate engineeringdressing property (excessive material stiffness inthis case) and the dressing geometry with its sharpcorners may lead to an adverse event and failure ofthe dressing in clinical practice.

In contrast to the above, larger pores (i.e., lowerdensity of the foam) mean more entrapped air andless solid polymer phase, resulting in lowerstrength and stiffness of the foam.34,35 While lowstiffness is theoretically beneficial for a wounddressing, as it minimizes abrasion of the wound orindentation of the dressing into the periwoundskin (Fig. 3), the associated decreased strengthmay, in theory, allow occasional low-intensityforces to damage and degrade the dressing mi-crostructure (Table 1).

Consideration of the strength, stiffness, andfluid transport and handling properties for eachmaterial component in the design optimization ofmultilayer foam dressings (as relevant to their clin-ical performance) greatly increases the complexityof the dressing’s structural optimization task.

Permeability and breathability of the externaldressing surfaces

The design of an adequate backing material/filmof a dressing can be similarly considered an outcomeof an engineering optimization problem. On the onehand, the backing material/film should have suffi-cient permeability to achieve an adequate MVTR, sothat fluids are constantly removed from the dress-ing reservoir by evaporation to the environment(thereby making space for additional exudate, asexplained above) (Table 1).38

On the other hand, the backing material/filmshould have a sufficiently low permeability to pre-vent pathogens and other irritants from enteringthe wound (and from there, into the circulation)(Table 1). Furthermore, the MVTR is affected bythe ambient temperature, relative humidity, and

air velocity at the vicinity of the applied dressing,as well as by any additional coverage of the dress-ing, such as by clothing or bedsheets.39

Once again, the ideal permeability for the backingmaterials/films of wound dressings is currently un-known,40 although some manufacturers introduceda ‘‘moisture control layer’’ in their foam dressings tomodulate the MVTR through the backing material/film under varying wound conditions.38

Of note, foam dressings may also include a soft,porated silicone sheet over the wound contact lay-er, to allow absorbency of exudates into the dress-ing, in which case the pore size and density in thesilicone sheet will affect both the rate and theamount of the absorbed and retained exudates(also, while some bacteria are known to adhere tosilicones, that can be minimized through surfacetreatments/preconditioning and/or by embeddingsilver ions in the foam layer).

EXUDATE MANAGEMENT AND DRESSINGFUNCTION ACROSS THE RANGE OF ACUTEAND CHRONIC WOUNDS

Themost relevantphysical lawgoverning themodeof action of all foam dressings is Darcy’s Law. Thisphysical law, which generally applies to relativelyslow-moving flows, determines that the rate of theexudate flow into a foam dressing is inversely pro-portional to the viscosity of the inflowing exudate.41,42

According to Darcy’s law, aqueous exudates with arelatively low viscosity flow into a dressing faster thanmoreviscousexudatesmanagedbythesamedressing.

Therefore, the effective permeability of thedressing structure, which is influenced by the den-sity, porosity, and interconnectivity of the micro-pores in the foams that make up each layer of thedressing, should be considered in the context of theexudate viscosity, and is the key performance pa-rameter that ultimately determines absorbency.

If the permeability of any of the layers in thedressing to an exudate of certain viscosity (typi-cally high viscosity) is insufficient, more viscousexudates will not be able to effectively penetratethe inner dressing layers and the dressing willtherefore not absorb and retain a sufficient amountof wound fluids. In such cases, exudate pooling mayoccur or the exudate might flow back into thewound area and accumulate, causing further in-flammation and/or maceration, thereby potentiallyincreasing the wound size.

In addition, if the exudate contains solid parti-cles such as blood clots, or aggregates of dead cellsor proteins, the dressing could act as a filter, ab-sorbing the fluid components from the exudate but

xIt is well established in the biomechanical engineering theorythat stress concentrations in tissues occur due to sudden geo-metrical changes or irregularities in a contacting object, includingsharp corners, which steeply increase the intensity of the localtissue stresses.37

8 GEFEN ET AL.

leaving the solid particles at the wound bed, wherethey would (similarly to excess fluid) compromisethe healing.

Clinical cases illustrating this type of dressingfailure in acute care are documented in Fig. 4a andb. The first image (Fig. 4a) is of a wound of a 73-year-

old female poststroke with left hemiparesis and im-paired mobility and sensibility, who also suffereddepression and malnourishment, where the appliedPU foam dressing had failed to absorb the viscoushematic wound fluids from her highly exuding heelpressure ulcer.

Figure 4. Clinical documentations of dressing failures due to poor absorbency of viscous fluids in the care of acute and chronic wounds: (a) A highly exudingheel pressure ulcer where the polyurethane foam dressing had failed to absorb the viscous hematic exudate. The documentation of this case is courtesy ofauthor PA. (b) A 60+ year-old male patient who underwent a left knee repair was at risk of postoperative bleeding. A conventional postoperative dressing wasapplied, but clearly failed (the images were taken at day 4 postsurgery), because the dressing needed to handle a relatively large amount of whole blood, whichis considerably more viscous than plasma exudation. While appreciating that ideally, hemostasis of the wound should be achieved before applying a dressing,and therefore, bleeding into a dressing presents a considerable challenge for its fluid management and handling performance, in these two cases shown here,the absorption rate into the dressing was too slow and the rate of the incoming blood flow was too high, resulting in pooling of blood under the dressing (asopposed to the absorption and retention that a dressing is expected to achieve). The documentation of this case is courtesy of author TS. (c) An 82-year-oldmale patient with multiple venous leg ulcers on the same leg that release exudates with different viscosities. The dressing was clearly unable to absorb themore viscous exudate. The documentation of this case is courtesy of author P.A.


Similarly, in the second illustrative case(Fig. 4b), a male patient older than 60 years un-derwent a left knee repair procedure and was atrisk of postoperative bleeding. A conventionalpostoperative dressing was applied in the lattercase, but it failed because the dressing had tohandle a relatively large amount of whole blood,which is substantially more viscous than plasmaexudation (by approximately fivefold21).

While appreciating that ideally, hemostasis ofthe wound should be achieved before applying adressing, and therefore, bleeding into a dressingpresents a considerable challenge for its fluidmanagement and handling performance, in theabove two documented cases, the rate of absorptioninto the dressing was too slow and the rate of theincoming blood flow was too high, resulting in anaccumulation of blood under the dressing.

This stands in contrast to the fundamentalclinical requirement that a dressing should achieveabsorption and retention in all cases—both foraqueous and viscous exudates. Another similarclinical case of a dressing that had failed to absorb aviscous exudate, this time in the context of care ofchronic wounds, is shown in Fig. 4c. This lattercase is an 82-year-old male patient with multiplevenous leg ulcers on the same leg that releasedexudates with different viscosities. The applieddressing clearly failed to absorb the more viscousdischarge.

All of these clinical cases of dressing failuresdescribed above, together with the human factorsthat were involved in each case (Figs. 3 and 4), ledto medical device-related adverse events. Un-fortunately, however, in clinical practice, suchdressing failure events are often left unreportedor are considered minor issues, which preventsor delays regulatory actions (contrarily, for ex-ample, to problems observed with implantabledevices that are promptly reported to regula-tory bodies through a Medical Device Reportingprocess).

THE REQUIRED DRESSING-WOUND/SKININTERFACE CONDITIONS DURING THE USEAND REMOVAL OF DRESSINGS

An adequately performing wound dressing must‘‘stay in place’’ over the periwound skin during use,even in a moist environment, but should also allowfor easy, atraumatic, painless, and as convenient aspossible removal when a change is required.43 Ad-hesive dressings may strip layers of the periwoundskin.44 This causes discomfort or pain during re-movals and further compromises the integrity of

the skin (particularly the stratum corneum), ad-versely affects transepidermal water loss, andpromotes inflammation.45–47 The above processesare repetitive, as skin damage accumulates eachtime a dressing is removed from the wound.48

In people with sensitive skin (e.g., the elderly orinfants), excessive adhesion of a dressing to theskin near the wound can cause skin tears.49 Inaddition, painful episodes during dressing chan-ges can cause chronic psychological stress in pa-tients, which in itself delays wound healing.50

The requirements of ‘‘stay in place’’ and ‘‘no skinpeeling’’ are seemingly contradictive and againrequire careful optimization of wound dress-ing designs, which is another bioengineeringchallenge.

From a patient’s perspective, a dressing that isnot adhesive enough may slip and move duringwear, hindering its ability to manage exudate andnot facilitating showering for the user. Sincechronic wounds are typically present for manyweeks or months, the ability of a person to showerregularly with the dressing remaining in place isalso a necessary property for their quality of life.Related to that, and from an engineering testingpoint of view, the adhesive strength of a dressingonto a skin-mimicking material can be measuredusing a laboratory ‘‘peel test,’’ which is designed todetermine the adhesive bond strength or the tackyproperty between the dressing and a (dry or wet)skin simulant.

Nevertheless, despite decades of research, nosuitable material to optimally mimic skin has beenfound that would allow for reproducible adhesionforce testing and determination of which forceswould be considered being comparable with whatnative skin is exposed to clinically when dressingsare removed. Traditionally, glass and steel platesare therefore commonly used as a substrate for peeltests; for reproducibility, however, efforts are un-derway to develop more biomimetic skin substi-tutes for this purpose, for example, based on blendsof natural proteins in gelatin, to better representthe interactions occurring at the skin/adhesive in-terface with respect to conventional substrates forpeel tests.51

In physical terms, laboratory peel tests measurethe resistance forces to separation of the dressingfrom the skin substitute (or in some cases, on theskin of study subjects), to determine if these forcesare sufficient or perhaps excessively high.52 Tocontrol these separation forces, engineers designtextured adhesive surfaces so that only a portion ofthe surface (with the higher surface topography)makes contact with the skin. A relevant test

10 GEFEN ET AL.

standard for these measurements is ASTM D903-98.53 Of note, the specific substrate to measureagainst is not stipulated in the aforementioned teststandard, despite the choice of the substrate beingimportant for determining the clinical relevance ofthe method, as indicated above.

There are several other problems associatedwith laboratory evaluations of dressing removals.For example, it is extremely difficult to correlatemeasured force values with expected levels of dis-comfort or pain, because discomfort/pain is alwayssubjective and influenced by numerous patient-specific conditions such as the nature of the wound,medications, sedation, hyperalgesia, allodynia, andneuropathy, as well as the anatomical location ofthe wound (as some body areas are more sensitivethan others).

Second, the technique of removing a dressinghas a strong effect on the measured separationforces, as both skin simulants and dressing mate-rials are viscoelastic and the state of contactstresses between the dressing and the skin there-fore depends on the speed of removal.

Once a health care professional begins to removea dressing from the skin, the contact area betweenthe skin and the dressing continues to decreaseuntil the dressing completely detaches from theskin. Since the amount of mechanical stress on theskin at the wound site depends on the ratio be-tween the separation (removal) force and the(continuously decreasing) contact area, a clinicianwould need to lower the removal force in proportionto the remaining contact area between the skin andthe dressing, to avoid applying too much mechan-ical stress on the skin at the wound site, but this isdifficult to control manually and requires skill andexperience.

Moreover, appreciation and knowledge of how toapply such bioengineering principles to the bedsideare lacking, and are not commonly taught.

In addition, the viscoelasticity of the skin anddressing will increase the stresses on skin at thewound site with an increased rate of peeling,which is the scientific rationale for the medicalrecommendation to remove dressings slowly.49,54

All of these real-world factors that point to theinfluence of dressing removal techniques (in termsof clinical skills), as well as to the skin healthstatus, are not considered in the current labora-tory work. Similar to the other aspects discussedabove, more clinically relevant testing standardsthat consider real-world conditions should be de-veloped to represent the real-life factors related towound dressing removals in laboratory perfor-mance evaluations.

THE HOSTILE BIOPHYSIOLOGICALENVIRONMENTS WHERE DRESSINGS MUSTFUNCTION AND THEIR POTENTIALIMPACT ON DRESSING PERFORMANCESThe pH of wound exudates and their potentialinfluence on foam dressings

The biochemical state of a wound, and in par-ticular, the pH level in the wound bed, has beenshown to have a significant impact on various as-pects of the healing cascade including cell prolif-eration and migration, the proteolytic environmentincluding the metalloproteinase enzyme levels,angiogenesis, and antimicrobial activity.55–57 De-pending on its material composition and the level ofocclusion provided, a dressing can alter the pH ofthe wound,58 and should remain structurally andfunctionally tolerant to highly acidic or alkalinewounds.

For example, the pH of exudates in burns rangesfrom 5 (which is in the middle range of normal skinpH) to as high as 10, and such elevated pH valuesare typically associated with local infections.59

Combined with mechanical forces that occasionallyact on a dressing and the enzymatic agents inwound exudates, extreme alkaline pH values canchallenge the chemical resistance of some PUfoams, thereby leading to the release of dressingmaterials into the wound or a breakdown in thestructure of the dressing.60,61

Cell biology and microbiology aspectsAnother important and relevant consideration is

that the presence of a wound dressing may interactwith the coordinated and combined efforts of thecells involved in the wound healing process, forexample, keratinocytes, fibroblasts, endothelialcells, neutrophils, and macrophages. The migra-tion, infiltration, proliferation, and differentiationof these cell types are triggered and regulated bycomplex molecular signaling involving growthfactors, cytokines, and chemokines.

Numerous research articles and textbooks werepublished concerning the involvement of specificgrowth factors in these coordinated efforts, such asthe fibroblast growth factor, epidermal growthfactor, transforming growth factor-beta, connec-tive tissue growth factor, vascular endothelialgrowth factor, granulocyte macrophage colonystimulating factor, platelet-derived growth factor,and tumor necrosis factor-alpha families, to men-tion a few, as reviewed by Field and Kerstein16 andthe references cited therein.

Likewise, members of the interleukin family ofcytokines are known to be involved in controllingthe intensity of the inflammatory process in the


wound and its surroundings, through signalingbetween cells of the same phenotype and acrossdifferent cell groups. Accordingly, the materials ofthe dressing must not affect the molecular confor-mation, intermolecular interactions, or chemicalstability of any of these proteins.

The presence of infection is another critical bio-logical aspect, affecting the clinical management ofwound care. Foam dressings can also be manu-factured to release antibacterial and antifungalagents such as silver ions for antimicrobial pro-tection, as wound infections, particularly in com-bination with neuropathy and/or ischemia, forexample, as in a diabetic foot ulcer, may lead togangrenes and amputations. As potential leakageof infected exudate from a dressing may transferthe infection to other body regions, using silver-containing foams, in addition to frequent dressingchanges, can also mitigate the risk of spread of theinfection beyond the existing wound.

In this context, Davies et al. recently reportedthe results of a global electronic survey in whichthey found that dressing changes are typicallyperformed 1–2 days earlier in infected woundsthan in noninfected wounds with a correspondingetiology.62 The more frequent dressing changes forthe infected wounds may be associated with eitherthe need for change of a wet dressing, or be-cause the clinician is more concerned about an in-fected wound and would want the dressingchanged more frequently (many dressing manu-facturer’s recommend daily dressing changes forinfected wounds, due to the greater risk associatedwith infected wounds and the need to ensure thatthe wound is not deteriorating).

Regardless of the clinical reasoning for the fre-quent dressing changes, the effects of the presenceof microorganisms on the structure and function ofa dressing must be taken into account in engi-neering design endeavors and bioengineering lab-oratory evaluations of existing and new wounddressings.

The quality of attachment of the dressing to thewound site. Another important challenge in awound dressing design is premature detach-ment due to moisture from the wound exudate orperspiration in the wound environment, whichcompromises the adhesive/tacky function of thewound-facing aspect of the dressing.63 Prematuredetachment of wound dressings is common andcan occur as early as the day after application ofthe dressing, with the occurrence increasing overthe next few days (up to day 5, which was the end-point of the work by Rippon et al.63).

Global surveys of nurses found that a dressing ischanged at least once every*3 days if the wound isinfected, or at most every *6 days if the woundis not infected, regardless of the wound etiology.62

Therefore, if the design of the dressing is such thatbody fluids are trapped at the edges of the dress-ing and cannot effectively escape by evaporation,the dressing will detach earlier than expected bythe wound care professional (as documented in thework of Rippon et al.63).

In other words, the absorptive and retentiveproperties of a foam dressing are also key to reduc-ing the risk of premature detachment of dressings.Such premature dressing detachments not onlycause additional health care labor and costs associ-ated with the more frequent than necessary dress-ing changes, but also jeopardize the goal ofundisturbed healing, which is a consistent require-ment in contemporary wound care practice.43,64

ADDITIONAL IDENTIFIED GAPS IN THEEVALUATION AND TESTING OF WOUNDDRESSING PERFORMANCE WITH RESPECTTO CLINICAL NEEDSEvaluating pain and discomfort during woundcare procedures

Pain and discomfort during common wound careprocedures are considered a primary patient-centered outcome, particularly in the context ofdressing changes, which are often a painful expe-rience for patients. Gardner et al. reported thatdressing changes caused considerable pain in 74%of the patients in their study, half of whom definedthat pain as being severe.65

While many of the historical problems of tissueingrowth into dressings and dressing adherence(leading to tissue trauma and pain to the patienton dressing removal) have been addressed by theintroduction of foam dressings with siliconewound/skin interfaces,27,66 pain and discomfortduring dressing removals continue to be a sourceof stress and anxiety for patients, who oftenmention these issues as a major quality-of-lifeindicator.50,67

Price et al.68 conducted a survey among 2018patients with wounds across 15 countries, andfound that *40% of their study participants indi-cated that the pain at dressing change was theworst part of living with a wound.

Importantly, there is a strong association be-tween the pain and discomfort during suchdressing changes and poor exudate managementperformance of the relevant dressing (e.g., asdemonstrated in Fig. 4). For example, excess exu-

12 GEFEN ET AL.

date that dries on the periwound skin or thedressing may increase the pain sensation duringremovals of the chosen dressing type.

Some recent studies used heart rate variability(HRV) analyses of electrocardiographic measure-ments to quantify pain and discomfort duringdressing changes. This had been based on litera-ture demonstrating that pain episodes are associ-ated with a decrease in the power spectral analysisof the HRV, which serves as a measure of the ac-tivities of the sympathetic and parasympatheticcomponents of the autonomic nervous system.69

Using an HRV-based method, Razjouyan et al.reported that high-intensity pain causes substantialmental stress for patients that may negatively affecttheir wound healing outcomes.70 Clearly, the selec-tion of a dressing type, its materials, structure, andcomposition, has an important role in potentiallyreducing the discomfort and pain during dressingchanges, which in turn, influences the healing rate.70

Gaps between laboratory fluid handling testsand real-world exudate management

Another common problem in evaluating theperformance of wound dressings with respect to themechanism of failure, shown in Fig. 4, is that lab-oratory tests conducted by industry and academiaoften consider only the fluid management proper-ties of wound dressings tested by exposure tosaline, Ringer’s solution, or similar solutions pre-pared by dissolving salts in water.71 In the Euro-pean standard 13726-1,22 the test fluid is specifiedas ‘‘Solution A,’’ a water solution of sodium chlorideand calcium chloride. Exudates in the real worldcontain proteins, ions, and cells that make themsubstantially more heterogeneous and viscousthan water.21,71–73

Therefore, a dressing that exhibits adequateabsorbency and retention capabilities in a labora-tory test performed with such aqueous solutionsmay fail in a clinical scenario where it must man-age viscous fluids that barely penetrate the firstlayer of the dressing facing the wound and hardlyever reach the core of the dressing, effectively dis-abling the absorbency and retention features ofthis failing dressing (Fig. 4).

Furthermore, multilayer foam dressings evalu-ated in laboratory studies are often subjected tosoaking tests, such as in the absorbency tests de-scribed in the European test standard 13726-122 forprimary wound dressings (critically reviewed byGefen and Santamaria74). Such soaking tests ig-nore the basic mode of action of multilayer foamdressings, where fluid penetration and absorptioninto the different dressing layers progress from the

layer in contact with the wound to the deeper lay-ers of the dressing. This progression of fluid doesnot necessarily occur at equal rates across thelayers of the dressing.

When a dressing is soaked in fluid and broughtto a fully saturated state, no information can beobtained about the extent of absorbency in each ofthe individual dressing layers, and how the fluidhas progressed within the dressing over time.74

Importantly, the types of dressing failures docu-mented in Fig. 4 cannot be captured in a soakingtest because if fluid can penetrate the dressingfrom all sides, the information concerning theclinically relevant time course of the fluid pene-tration into the dressing, and of the transportprocess within the dressing, is lost completely. Thismeans that a dressing may ‘‘pass’’ the aforemen-tioned 13726-1 test, but fail clinically.

SUMMARY AND CONCLUDING REMARKS

The objective of this review article is to describethe interplay between the structure and function ofwound dressings and identify relevant gaps inknowledge. More specifically, we demonstratedthat multilayer (or even single-layer) foam dress-ings are not all created equal, but rather, theirperformance is based on their specific materialcomposition and construction. To be clinically ef-fective, a foam dressing must be able to handle awide range of exudate viscosities associated withdifferent wound etiologies, or with the same woundat different stages of healing.

Current industry test standards often useaqueous solutions (with different salinity levels),without proteins to test dressing performance,which is unrealistic and oversimplifies the com-plexity of the clinical demands of real-worldwounds. There are a few examples for academicresearch and companies reporting the use of pro-tein containing test liquids75,76 and more viscoustest fluids.21,77–80 However, since these testsolutions are not included in the EN 13726-122

standard, the tests are often not eligible for con-sideration in hospital formularies.

Bioengineering studies in the area of dressingefficacy research are therefore essential to advancethis field, for example, by measuring the ranges ofexudate viscosities for different wound etiologiesand stages of healing toward establishing stan-dards for test fluids. Ultimately, the industrywould need to develop a range of exudate substi-tute fluids capable of representing the existing di-versity of native biological exudates, to enableclinically relevant laboratory testing and the


formulation of new testing standards for wounddressings. This work is ongoing in the first author’s(A.G.) research group.21,74,80

Finding the ideal balance between feasible, ro-bust, and reproducible laboratory testing of wounddressings versus the need to reflect the vast clinicalcomplexity in such engineering tests will continueto be a challenge for bioengineers. The variety ofwound etiologies, patient characteristics, and un-derlying diseases requires that bioengineers inacademia and industry work closely with woundcare clinicians to develop realistic yet practicalbench tests that would optimize the quality andreproducibility of these tests with respect to theclinical practice.

The IWDTEP recommends that for foam dress-ings, such bench tests will be designed to quanti-tatively acquire the basic engineering performancemetrics detailed in Table 2, based on mapping thegaps between existing testing standards for wounddressings and real-world clinical conditions, aslisted in Table 3. This table lists the fundamentaland quantifiable parameters (through engineeringlaboratory testing) as a core conceptual frameworkfor the design and evaluation of existing and newfoam dressings.

In some of the patient cases shown (Figs. 3 and 4),the selected dressings were likely not the appropri-ate or optimal choice for the treated wounds, whichwas the root cause for the failure. Nevertheless, the

Table 2. Description of the basic engineering performance metrics required from a foam dressing that can be quantitativelymeasured in laboratory settings

Fluid Handling Mechanical Biological

Manage a rangeof viscosities

The dressing should absorb and retainexudate effectively and consistently interms of volume and mass over theclinically relevant time course, acrossthe entire reported range of possiblehuman biofluid viscosities, without theoccurrence of spillovers or pooling

Stiffness The dressing stiffness should notsubstantially exceed the skin andsubcutaneous tissue stiffnessesrelevant to the location, etiology, andseverity of the wound, at either itsnew (straight-from-the-package)condition, or post a usage period, toavoid indentation damage

Permeabilityto pathogens

The dressing should preventpenetration or release ofparticulates at sizesrepresentative ofbacterial, viral, and fungalpathogens through theexternal dressing surface

Body position,wound location,and interactionwith additionalwound caretreatments

The dressing should absorb and retainexudate effectively and consistentlyacross all the possible positions of thebody and wound with respect to thegravity vector, for example, when thedressing is vertical to the ground(such as when treating a venous legulcer), or when the dressing issubjected to sustained or repeatedbodyweight forces (as in a nonoff-loaded wound). Addition of externalcompressive forces, such as duringapplication of multilayer compressionbandaging and other forms of legcompression treatments applied forthe management of venousinsufficiency or venous leg ulcersshould minimally affect theabsorbency and retentionperformance of the applied dressing

Strength The dressing should be durable to theexpected compressive, tensile, andshear force magnitudes associatedwith the bodyweight, including anypotential body movements againstsurfaces (in single or repeatedevents), and to the pull-out forceswhen the used dressing is removed,at its new (straight-from-the-package;also considering storage duration andconditions), or post a usage period

Consistent fluidevaporationto the environment

The dressing should constantly andconsistently release the retained fluidto the environment, via evaporation,for the ranges of clinically relevanttemperatures and humidity valuesrepresenting the ambient conditionsat the potential or the intendedgeographical regions of use (e.g., inan extremely moist or an extremelydry environment)

Adhesiveness The borders of the dressing shouldprovide consistent adhesivenessthroughout the intended period of use,that is, the dressing should stay inplace under the expected regimens ofthe bodyweight and external forces,as well as under the influence of skinmoisture conditions, but should notrequire excessive peeling forcesduring removal to avoid periwoundskin stripping damage. Contrarily, thewound pad should never adhere to thewound bed (i.e., for the wound pad,measured peeling forces should beextremely low)

14 GEFEN ET AL.

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 13726-1Test methods for primary

wound dressings—Part 1:Aspects of absorbency

(specifies laboratory testmethods recommendedfor the evaluation ofabsorbency of primarywound dressings)

� Does not consider physiological directional flows(from the wound-bed into the wound pad), as itutilizes free-swell measures for dressingssubmerged in excess test fluid� Does not consider the combined effects of gravity

and bodyweight-induced or other forces on theflow conditions, such as the variable roles ofnatural convection versus capillary motion(depending on the specific wound and dressingorientations with respect to the ground), and anypotential distortion and reduction of the availabledressing reservoir for absorbency and retention bybodyweight or external forces� Does not address the protein contents and the

associated range of fluid viscosities that exist forbiological wound exudates (as this test utilizes anaqueous test fluid, i.e., salts dissolved in watertermed ‘‘Test Solution A’’) for the absorbencymeasures specified therein


wound dressings—Part 4:Conformability (describes a

laboratory test methodfor measuring theconformability of primarywound dressings)

� Does not consider the real-world, clinically relevantshape conformation phenomena that involve bendingand shearing, for example, of wound dressings appliedto irregularly curved body regions (such as theposterior heel, the nasal bridge, or the ears), as thetest is limited to tensile elasticity only

� Does not consider mechanical durability (also knownas ‘‘fatigue’’) factors or real-world wear-and-tearphenomena, and their potential effects on thestructural integrity of wound dressings

� There is no consideration of the stiffness matchingbetween the tested dressing materials and native skin(or underlying soft tissues), in the context ofpreventing indentation damage to the periwound skin


wound dressings—Part 2:Moisture-vapor transmission

rate of permeable filmdressings

� Does not consider protein contents in the testfluid, and, as a result, neglects the possiblymodified kinetics of evaporation of protein-richfluids (as proteins may have hydrophobic regionson their surface, which in turn, may affect theirevaporation kinetics)

ISO 29862:2007(en)Self-adhesive tapes—

Determination of peeladhesion properties(concerns the laboratorymeasurements ofseparation forcesrequired to peel a strip ofadhesive tape fromindustrial steel plates)

� Does not consider the deformability of human skin,and hence is poorly relevant to either healthy or fragileskin response. Specifically, as steel is rigid (i.e., notdeformable and viscoelastic as native skin is), it is notrepresentative of the complex biomechanicalphenomena that occur during removal of wounddressings. For example, the level of deformability ofthe surfaces that are subjected to separation stronglyaffects the dynamic separation forces that formbetween the separating surfaces. A faster peelingaction applied by a wound care clinician would inducea higher deformation rate of the skin, and, due to theviscoelasticity of hydrated skin that would result ingreater peeling forces (which are associated with therate of deformation). A rigid steel substrate cannotrepresent this complex mechanical behavior of thebiphasic (solid-fluid) skin tissue

� Does not consider the microtopography features ofskin. Specifically, as the industrial steel platesubstrates are relatively smooth, and do not containthe inherent roughness and possible wrinkling ofhuman skin, the realistic contact area of the dressingadhesives with skin is not adequately represented,which again biases the peeling force measurements


wound dressings—Part 3:Waterproofness (describes a

laboratory test methodfor the evaluation of thewaterproofness ofprimary wound dressingswhen such claims aremade)

� Does not consider the influence of the body andwound temperatures, and thereby, the effect ofthe resulting (temperature-dependent) fluidsurface 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 thefluid repellent or interact differently with thedressing materials. This is particularly importantfor nonwatery, protein-rich fluids (not consideredin the test but representative of the majority ofbiological exudates), where a rise in the pH canchange the protein conformation, and thereby, thesurface tension interactions

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

j 15

examples that were provided demonstratethat foam-based or other types of dressingsmay be challenged in terms of fluid man-agement, for example, by wounds withthick and viscous exudates, or prove to beoverly stiff for the type of treatment (suchas in compression therapy), and the failurecases could have been prevented by notselecting these specific dressings for thetasks.

Clearly, control over hemostasis isfundamental in wound care and spansbeyond the dressing choice, but the fail-ure cases that were presented, namelycompromised management of highly vis-cous fluids and the excessive stiffness ofthe dressing with respect to that of thewound and periwound, are points that cliniciansshould be aware of, and consider when choosing aspecific dressing for a specific wound and treat-ment approach. For example, with regard to thecase shown in Fig. 3, while the key foams used inwound dressings are either PU or polyvinyl alcohol(PVA), PU foams generally exhibit more uniformpore sizes and better interconnectivity between thepores, as well as substantially less swelling, andhence, lower stiffness at their wet condition withrespect to the PVA foams.81,82

The latter implies that PVA foam dressingsshould not be used under compression therapy,which again exemplifies that foam dressings mayvary considerably in their clinical performance, de-pending on the specific foam materials and micro-structures.

Pain associated with dressings may be related toadherence of the dressing to the wound bed, or toperiwound skin stripping damage during remov-als, or be related to failure of the dressing to man-age the exudate, leading to maceration due topooling or spillover of the exudate. The depth oftissue loss may be associated with the intensityof the resulting pain, because the density ofnociceptors—the neural sensory receptors thatdetect signals from damaged tissues—differsacross tissue types (cutaneous tissues are generallymore densely innervated than deeper soft tissues).

The seminal position document of the EuropeanWound Management Association concerning painat wound dressing changes indicated that a dressingshould maintain moist wound healing to (among theother factors reviewed in our current work) reducefriction at the wound surface, and thereby lower thefrictional rubbing against the wound.83

In addition, the dressing should also remain at-tached for longer times, to reduce the need for fre-

quent dressing changes.83 In this regard, Alvarezet al. commented that compared with dressings withtraditional adhesives, the use of dressings incorpo-rating soft silicone can minimize traumatic injuriesto the wound-bed and periwound skin, reducedressing-associated trauma, and thereby, reducethe discomfort and pain.84

Finally, clinicians should adopt proactive criticalthinking and inquire about the specifications offoam dressing technologies that are being offered tothem. Laboratory test data should be requestedfrom manufacturers, to verify that the dressingbeing considered is capable of handling the fluidsrelevant to the wound etiologies that are treated,such as the expected exudate volumes, flow rates,and viscosities.

Requiring manufacturers to agree upon and im-plement standardized clinically relevant test meth-ods for their wound dressing products, and thenprovide peer-reviewed, published laboratory testdata basedonthe implemented testing standardswilllead to informed clinical decision-making regardingthe selection of the safest and best performing foamdressings.

Such dialogue between clinicians and industrywill further positively impact patient safety, qual-ity of care, and the overall cost-effectiveness oftreatments. Furthermore, it is essential for optimalcare to use appropriate wound dressings that caneffectively absorb exudates, are resistant to themechanical and biochemical wound environment,remain in place for the required treatment periodbut can be easily removed, and are acceptable toboth patients and health care professionals.

The only way for clinicians to fully trust wounddressing products is to develop clinically relevantlaboratory test standards that result in compre-hensive performance metrics for dressings. Suchclinically relevant testing standards would allow

TAKE-HOME MESSAGES

� It is essential for optimal wound care to use appropriate dressings thatcan effectively absorb exudates, are resistant to the mechanical andbiochemical wound environment, remain in place for the requiredtreatment period but can be easily removed, and are acceptable to bothpatients and health care professionals.

� The only way for clinicians to fully trust wound dressing products is todevelop clinically relevant laboratory test standards that result in com-prehensive performance metrics for dressings.

� Clinically relevant testing standards would facilitate objective, stan-dardized, and quantitative comparisons across wound dressing productsand brands, leading to informed treatment decisions, and thereby tobetter patient outcomes.

16 GEFEN ET AL.

objective, standardized, and quantitative com-parisons between wound dressing products andbrands, leading to informed decisions.

ACKNOWLEDGMENTAND FUNDING SOURCES

The current work of the International WoundDressing Technology Expert Panel was supportedby an educational grant from Molnlycke HealthCare (Gothenburg, Sweden).

AUTHOR DISCLOSUREAND GHOSTWRITING

The authors have no conflicts, financial or oth-erwise, to disclose. A.G. conceived the idea for thiswork and its structure, reviewed the literature,and drafted the article and its revisions. P.A., D.B.,B.C., J.L.L.-M., H.L.-T., B.N., N.S., A.S., T.S., andK.W. reviewed the literature and the article draftsand edited the texts. In addition, P.A., T.S., andK.W. provided clinical case documentations. Noghostwriters were used in writing this article. Thecontent of this article was expressly written by thelisted authors.

ABOUT THE AUTHORS

Amit Gefen, PhD, is a Professor with the Fa-culty of Engineering, Tel Aviv University, and theBerman Chair in Vascular Bioengineering.

Paulo Alves, PhD, is an Assistant Professor ofNursing and Tissue Viability at the UniversidadeCatolica Portuguesa, Porto, Portugal.

Dimitri Beeckman, PhD, is a Professor ofNursing at Ghent University, Belgium and OrebroUniversity, Sweden.

Breda Cullen, PhD, is a biochemist and inde-pendent consultant at RedC Consultancy.

Jose Luis Lazaro-Martınez, PhD, is a Pro-fessor at the Complutense University of Madrid,Spain.

Hadar Lev-Tov, MD, is an Assistant Professorat the University of Miami Department of Derma-tology and Cutaneous Surgery, FL, USA.

Bijan Najafi, PhD, is a Professor and Directorof Clinical Research at the Department of Surgery,Baylor College of Medicine, TX, USA.

Nick Santamaria, PhD, is a Professor ofNursing Research, Translational Research, SkinIntegrity, and Wound Care at the University ofMelbourne and the Royal Melbourne Hospital,Australia.

Andrew Sharpe, MSc, is a podiatrist workingfor the National Health Services of the UnitedKingdom.

Terry Swanson, NP, is a specialist in woundmanagement working in a wound clinic in Warr-nambool, Australia.

Kevin Woo, PhD, is a Professor at Queen’sUniversity, Schools of Nursing and Rehabilitation,Kingston, Canada.

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Abbreviations and Acronyms

HRV ¼ heart rate variabilityIWDTEP ¼ International Wound Dressing

Technology Expert PanelMVTR ¼ moisture-vapor transmission rate

PU ¼ polyurethanePVA ¼ polyvinyl alcohol




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