BR112020009713B1 - PROPHYLACTIC DRESSING - Google Patents

Abstract

The present invention generally relates to a medical dressing for preventing pressure ulcers. The dressing comprises a gel coating having a low pressure resistance; i.e., from 5 kPa to 60 kPa at 50% strain, as measured by the compression test described in the specification. The dressing reduces shear and compression forces on the skin and underlying soft tissue layers and prevents or mitigates the development of pressure ulcers.

Description

Technical Field

[001] The present invention relates to a medical dressing comprising a gel coating. The dressing is suitable for preventing pressure ulcers.

Background

[002] A pressure ulcer is a localized wound in the skin and/or underlying tissue over a bony protuberance that results from sustained pressure, often in combination with friction and shear. The main factors that result in pressure ulcers or pressure injuries are pressure, shear, friction and unfavorable microclimate. Other factors, intrinsic to the patient, can also increase the likelihood of pressure ulcer development, for example, poor perfusion, reduced sensation and inadequate nutrition. Pressure ulcers frequently occur among people who are bedridden for various reasons, such as due to prolonged hospitalization or other causes of immobility. Pressure ulcers also occur under medical devices, such as nasogastric tubes, ventilation masks and tracheostomy tubes, which are applied for diagnostic or therapeutic purposes. The rigid materials used in these devices can cause abrasion of the skin and create pressure on the soft tissues.

[003] A pressure ulcer does not always start at the surface of the skin. What is seen on the skin is often only a small part of the wound, and this can lead the patient and/or their caregiver to believe that there is only a minor problem.

[004] Pressure ulcers often develop in the soft tissue beneath the skin covering bony areas of the body (so-called "bony protuberances"), for example the heels, ankles, hips or sacrum. Pressure and shear forces cause blood vessels to become compressed between the skin surface and the bone. Thus, the muscles and tissue beneath the skin, close to the bone surface, typically suffer the most damage. Accordingly, any pressure ulcer that is apparent on the skin, no matter how small, should be considered critical due to the likely damage beneath the skin surface.

[005] A pressure ulcer can be classified into four categories: in category one, the skin appears pink, red or discolored, and may feel hard and warm to the touch. In category two, the skin breaks down and an ulcer, which may look like a blister, forms. At this stage, the skin may be damaged beyond repair or may die. A category three pressure ulcer is an ulcer that extends into the tissue beneath the skin, forming a small crater. In category four, the pressure wound is very deep, reaching into the muscle and bone and causing extensive damage to the deeper tissue and tendons. Serious complications, such as infection of the bone or blood, may occur if the pressure ulcer progresses.

[006] One of the first signs that a pressure ulcer has developed or is about to develop is a red, discolored, or darkened area of skin. To determine whether a pressure ulcer has developed, caregivers typically use what is called a "blanch test," in which a finger is used to press on the darkened or reddened area. The area should turn white, and when pressure is removed, the area should return to its red or dark color within a few seconds, which is an indication of good blood flow. If the area remains white, blood flow is impaired and damage has begun.

[007] In a hospital or care facility, caregivers adhere to specific protocols to prevent pressure ulcers from occurring. An important part of the prevention regimen is regular skin inspection.

[008] In some hospitals, caregivers apply dressings to wounds in areas at risk of pressure ulcer development, for example, on the sacrum, heels or under medical devices such as oxygen masks, and feeding tubes, tracheostomy and nasogastric tubes. The dressings used are not primarily designed for prophylactic purposes.

[009] In addition, when a dressing is applied, the skin beneath the dressing should be inspected regularly, typically at least twice daily, to assess the condition of the skin and ensure there are no signs of damage. This requires the dressing to be removed to allow assessment of the skin. The dressing may need to be opened and reapplied several times a day. The adhesive capacity of the dressing is thus compromised.

[0010] Pressure ulcers are a global problem and preventability is desirable, both to reduce human suffering and to avoid unnecessary costs. The average cost for a category 3 or 4 pressure ulcer is estimated at between $75,000 and $125,000 per patient.

[0011] In summary, there is a need to provide a dressing having an improved prophylactic effect, i.e. a dressing that targets both preventing a pressure ulcer from occurring in the first place and preventing an existing pressure ulcer from progressing. Furthermore, there is a need to provide a proactive and cost-effective means of minimizing the burden on caregivers and staff dealing with pressure ulcers.

Summary

[0012] According to at least one aspect of the invention, there is provided a medical dressing having a first side and a second opposing side, wherein the first side has a skin-facing surface adapted to detachably adhere the medical dressing to a dermal surface; the dressing comprising a gel coating, wherein the gel has a compressive strength of 5 to 60 kPa at 50% strain, as measured in accordance with the compression test described herein.

[0013] According to at least one alternative aspect of the invention, there is provided a medical dressing having a first side and a second opposing side, wherein the first side has a skin-facing surface adapted to detachably adhere the medical dressing to the dermal surface; the dressing comprising a gel coating, wherein the gel has a compressive strength of 1 to 14 kPa at 25% strain, as measured in accordance with the compression test described herein.

[0014] According to at least one alternative aspect of the invention, which may also be combined with two other aspects highlighted above, there is provided a medical dressing having a first side and a second opposing side, wherein the first side has a skin-facing surface adapted to detachably adhere the medical dressing to a dermal surface; the dressing comprising a gel coating, wherein the gel has a water content of less than 15% by weight.

[0015] Any of these (alternative) embodiments may be combined, independently, with any of the subsequent embodiments, including the embodiments of the claims.

[0016] The medical dressing is particularly useful for pressure ulcer prevention and/or pressure ulcer mitigation. The gel coating of the dressing is soft and deformable and has a consistency that mimics the soft tissue of a human being. The inventors have discovered that by applying a gel dressing, having a compressive strength that resembles the compressive strength of human soft tissue, to the skin surface, critical compression and shear forces on the skin and underlying tissue can be reduced. Accordingly, epithelial cells and soft tissue cells are protected from becoming deformed, which can mitigate and/or prevent the onset of pressure ulcers. The gel coating is considered to act as an additional protective soft tissue layer that absorbs pressure, shear and friction forces and distributes them evenly throughout the gel coating. The dressing of the invention allows for improved protection of the soft tissue beneath the skin. Furthermore, the soft and deformable gel conforms to the skin and compensates for body asymmetries.

[0017] In embodiments, the gel has a compressive strength of 5 to 40 kPa at 50% strain, as measured according to the compression test described herein.

[0018] In embodiments, the gel exhibits a compressive strength of 2 to 12 kPa, preferably 2 to 8 kPa, at 25% strain, as measured according to the compression test described herein.

[0019] A gel coating having a compressive strength in this range provides improved soft tissue reproduction and prevents soft tissue damage. If the gel is too soft, the coating may lose its effectiveness and crack or flatten in critical areas.

[0020] A dressing, in use, for example applied to the sacrum region of a patient, is exposed to pressure, shear and compression forces and therefore needs to maintain a low compressive strength at increased stress. It is important that the elastic behavior of the gel does not result in a dramatic increase in compressive strength at higher pressures. The compressive strength of the gel should increase in a generally smooth manner with pressures and up to 50%, so that the dressing can still compress at higher loads. It is desirable that compression occurs in the dressing and thus reduces compression and stresses in the tissue. A stiffer dressing does not deform as easily and the deformation can therefore be transferred to the tissue, which is not desirable.

[0021] In embodiments, the gel has a water content of less than 10% by weight, preferably less than 5%.

[0022] This allows the dressing to be stored at ambient conditions without requiring special packaging (such as hermetically sealed foil packets, etc.), and without compromising the properties of the gel and dressing. If the water content is too high, the gel may dry out when stored at ambient conditions, which may harden the gel. Instead, standard packaging and ethylene oxide (EtO) sterilization can be used to sterilize the product.

[0023] The gel according to the present invention can be manufactured by polymerizing: - 15 to 50% by weight of a hydrophilic acrylic monomer; - 50 to 85% by weight of a hydrophilic softening agent; - 0.001 to 0.5% by weight of a crosslinker; - 0.05 to 0.5% by weight of a polymerization initiator.

[0024] The hydrophilic acrylic monomers are preferably selected from 4-hydroxybutyl acrylate, methoxy polyethylene glycol acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate or combinations thereof.

[0025] The monomers are chosen so that the copolymer formed is hydrophilic, soft, elastic and compatible with the softening agent. The components of the mixture are chosen so that the gel maintains its low compressive strength and softness.

[0026] The hydrophilic softening agent is any additive that increases the softness of the gel. In embodiments of the invention, said hydrophilic softening agent is a low volatility liquid or a solid compound.

[0027] In embodiments, the dressing is substantially transparent.

[0028] The gel liner, and, if present, additional dressing components, are preferably transparent. This should allow visual inspection of the skin beneath the dressing. The softness and flexibility of the gel, combined with the transparency, allow a caregiver to perform a blanching test on a patient without having to remove the dressing. A finger can be used to press the skin through the deformable gel liner, and the blanching and/or redness of the skin can be monitored through the dressing. Although the dressing may still need to be removed from time to time, the transparency of the dressing reduces the frequency of detachment and reapplication to a user's skin. Accordingly, the inventive dressing will have a longer useful life, and the patient will be less exposed to invasive examinations. This means time savings and a greater likelihood of compliance in a hospital or community care setting. Furthermore, marks can be made on the dressing (or photographs can be taken) to allow comparison of the extent of the redness at the next assessment. The transparency of the dressing allows the patient and/or their relatives to carry out the inspection, and the chances of early detection of damage are greater.

[0029] In embodiments, the gel coat has an opacity of less than 25%, preferably less than 15%, as measured by the opacity test described herein.

[0030] This allows for optimal inspection of the skin under the dressing and any discoloration or reddened skin can be detected.

[0031] In embodiments, the dressing comprises a backing layer and an adhesive body contact layer; the gel coating being disposed between the backing layer and the body contact layer.

[0032] In embodiments, the dressing adheres to the skin during use, both to increase the adhesion capability of the dressing and to prevent undesirable friction between the patient's skin and the dressing. The skin-facing surface of the gel may be adhesive per se, but the dressing may also comprise an additional body-contacting adhesive layer. The body-contacting adhesive layer reduces or eliminates friction on the patient's skin.

[0033] In embodiments, the backing layer extends beyond the periphery of the gel coat to define a border portion around the contour of the coat.

[0034] The dressing may comprise an edge portion to prevent the deformable gel from bulging outwards at the edges (due to compression or swelling) and to improve the wear of the dressing.

[0035] In embodiments, the dressing comprises an anisotropic layer having a first (x) direction and a second (y) direction, where the anisotropic layer has a higher tensile strength at 15% strain in the second (y) direction than in the first (x) direction, as measured by the tension test described herein.

[0036] Accordingly, the dressing will have a higher tensile strength in the second (y) direction. In use, the dressing should be applied so that its second (y) direction corresponds to the direction in which the patient is exposed to the most shear forces. For example, when the dressing is applied to the sacrum region of a bedridden patient, the dressing is stiffest in the direction in which the patient slides in bed. This is typically along the length of the patient. The inventors have discovered that in order to withstand the pressure and shear forces imposed on a patient lying in a hospital bed (e.g., a bedridden patient), the dressing must be stiffer, i.e., have a higher tensile strength in the direction in which the patient slides. On the other hand, the first (x) direction of the dressing is preferably more deformable and may exhibit a lower tensile strength. This is beneficial because the first direction (x) of the dressing corresponds to the direction in which the patient wearing the dressing will be turned and repositioned by the nursing staff. The dressing is advantageously more stretchable in the first direction (x). A bedridden patient at risk of developing pressure ulcers should be turned and repositioned at regular intervals. It is therefore advantageous for the dressing to conform to this lateral movement and remain on the skin.

[0037] Furthermore, when the dressing is more stretchable in the first (x) direction, it prevents the skin and underlying tissues from becoming "overly constrained", which might otherwise be the case when the dressing is rigid in both the first (x) and second (y) directions.

[0038] In embodiments, the anisotropic layer has a 15% strain tensile strength that is at least 6 times greater, preferably at least 10 times greater, in the second (y) direction than in the first (x) direction, when measured in accordance with the tensile test described herein.

[0039] The prophylactic effect of the dressing is thereby enhanced, and the skin cells and underlying soft tissue cells are protected from extensive damage. The structural integrity of the dressing is enhanced, and the pressure and shear forces inflicted on a patient are reduced. Stiffness in the direction of critical shear exposure protects the skin cells and deeper tissue layer cells from stretching, and thus from deformation. Sustained deformation of skin cells and tissue can affect the tissue in a number of ways; i.e., impaired cell metabolism resulting from vascular occlusion resulting in ischemia, impaired membrane transport of individual deformed cells, tears between cells, all of which can result in tissue and cell damage resulting in the formation of pressure ulcers.

[0040] The sacral region is an area at particular risk for pressure ulcers. Therefore, in the modalities, the dressing has a shape that conforms to the anatomy of the sacrum.

[0041] Thus, the dressing has a lateral extension (x) and a longitudinal extension (y); the covering being symmetrical about a longitudinal centerline and the dressing comprising a first lobe-shaped portion on one side of the longitudinal centerline and a second lobe-shaped portion on the other side of the longitudinal centerline.

[0042] In embodiments, the anisotropic layer is arranged such that the first direction (x) of the anisotropic layer corresponds to the lateral extent (x) of the dressing, and the second direction (y) of the anisotropic layer corresponds to the longitudinal extent (y) of the dressing.

[0043] As explained so far, the dressing protects the skin cells and the cells of the deeper tissue layer against stretching and deformation. It also improves the adhesion capacity of the dressing if the dressing is more stretchable in the lateral (x) direction, allowing the patient to turn and reposition without the dressing being removed.

[0044] In embodiments, the medical dressing is divided into three separate zones along the longitudinal extent (y) of the dressing: a central zone and two lateral zones, wherein the overall coating comprises a plurality of notches, at least in the central zone of the dressing.

[0045] The central zone of the dressing is the area exposed to the most stress, especially in the lower part of the central zone, which is arranged to cover the coccyx region of a patient. The notches allow for localized softening of the gel coating while preserving the overall properties of the gel dressing. The inventors have discovered that the skin and underlying soft tissue are best protected by providing notches in the central zone.

[0046] In embodiments, the medical dressing is divided into three separate zones along the longitudinal extent (y) of the dressing: a central zone and two lateral zones, where the compressive strength of the gel in the central zone is lower than that in the lateral zones.

[0047] Accordingly, the dressing may be formed into different regions having different properties; i.e., compressive strengths. As mentioned, the central zone is exposed to the greatest stresses when the dressing is in use. The inventors have discovered that this region may be softer, i.e., have a lower compressive strength to prevent the soft tissue cells from becoming deformed and damaged. Accordingly, the central zone of the dressing may have a compressive strength in the range specified above, and the lateral zones of the dressing may have a higher compressive strength. This may be beneficial in preventing flattening of the gel coating at the edges.

[0048] The medical dressing may still need to be opened from time to time. Therefore, to facilitate inspection of the skin, the dressing may comprise at least one gripping tab, wherein the tab is coplanar with and projects outwardly from the periphery of the dressing.

[0049] The grip tab directs the caregiver to lift the dressing, inspect the skin beneath the dressing, and then reapply the dressing to the skin.

[0050] In another aspect, the present invention relates to a dressing as described above, for use in preventing or mitigating pressure ulcers.

[0051] Additional features and advantages of the present invention will become apparent upon studying the appended claims and the following description. Those skilled in the art will realize that the different features of the present invention can be combined to create embodiments other than those described below, without departing from the scope of the present invention.

Brief Description of the Drawings

[0052] Figures 1a and 1b illustrate, schematically, how pressure, shear and friction contribute to the development of pressure ulcers.

[0053] Figure 2 illustrates the compression behavior of the two dressings according to the invention compared to two stiffer dressings according to the prior art.

[0054] Figure 3 illustrates a medical dressing, according to at least one illustrative embodiment of the invention, applied to the sacral region of a human body. Figures 3a to 3c are enlarged views of the dressing and illustrate a caregiver performing the blanching test on the patient's skin.

[0055] Figure 4a is a cross-sectional view of a dressing, according to an illustrative embodiment of the present invention.

[0056] Figure 4b is an exploded view of a dressing, according to an illustrative embodiment of the present invention.

[0057] Figure 4c illustrates the anisotropic properties of a dressing, according to an illustrative embodiment of the present invention.

[0058] Figure 5 illustrates a bedridden patient exposed to pressure and shear forces when the patient's head is tilted upwards when no dressing is being used (5a), and when a dressing of the invention has been applied to the patient's sacrum region (5b).

[0059] Figure 6 illustrates an illustrative embodiment of the dressing according to the invention.

[0060] Figure 7 illustrates a dressing, according to an illustrative embodiment, comprising three lateral coating zones, where the central zone comprises notches in the form of openings.

[0061] Figure 8 illustrates stress curves for five different types of anisotropic layers in the second (y) direction (Figure 8a) and in the first (x) direction (Figure 8b).

[0062] Figure 9 illustrates the mean pressure distribution (hydrostatic stress) on the skin arising from compression in a Finite Element (FE) model simulation, when no dressing is used (Figure 9a), a dressing comprising a stiffer gel, according to the prior art (Figure 9b) and a dressing, according to an illustrative embodiment of the present invention (Figure 9c).

[0063] Figure 10 illustrates the mean pressure distribution (hydrostatic stress) on the skin arising from compression and shear in a Finite Element (FE) model simulation, when no dressing is used (Figure 10a), a dressing comprising a stiffer gel, according to the prior art (Figure 10b), and a dressing, according to an illustrative embodiment of the present invention (Figure 10c).

[0064] Figure 11 illustrates a Von Mises stress distribution in muscle arising from compression and shear in a Finite Element (FE) model simulation, when no dressing is used (Figure 11a), a dressing comprising a stiffer gel, according to the prior art (Figure 11b), and two dressings, according to illustrative embodiments of the present invention (Figures 11c and d).

[0065] Figure 12 illustrates the shear stress distribution in muscle near bones arising from compression and shear in a Finite Element (FE) model simulation, when no dressing is used (Figure 12a), and two dressings, according to illustrative embodiments of the present invention (Figures 12b and c).

[0066] Figure 13 illustrates two simulated dressings with a central lining zone comprising openings (13a and 13b), and a lower compressive strength region (13b).

[0067] Figure 14 illustrates the Von Mises stress distribution in the muscle arising from compression in a Finite Element (FE) model simulation, when no dressing is used (Figure 14a) and the dressings illustrated in Figure 13, respectively (Figures 14b and c).

Detailed Description

[0068] The present invention will now be described more fully with reference to the accompanying drawings, in which presently preferred embodiments of the present invention are illustrated. The present invention may, however, be embodied in many different forms and should not be considered limited to the embodiments set forth herein; rather, these embodiments are provided for the sake of completeness and completeness, and to convey more fully the scope of the present invention to those skilled in the art.

[0069] Figures 1a and 1b conceptually illustrate how pressure, shear and friction contribute to the development of pressure ulcers.

[0070] When a patient, in contact with a support surface 100, moves, friction 101 between the skin 102 and the contact surface 100 tends to hold the skin 102 in place, and a shear force 103 occurs displacing and deforming the deeper tissues (muscle 104 and adipose tissue 105). The deeper tissue layers 104 and 105 are subjected to the worst effect of the shear, since these layers, in closer proximity to the bones 107, cannot move in a manner similar to the skin layer 102. Instead, these layers are stretched, yet are "glued together." In addition, the blood vessels 106 are distorted and compressed (Figure 1a). Compression of the blood vessels 106 by pressure and/or shear can reduce blood flow to the tissues. This can result in tissue hypoxia, accumulation of metabolic wear products, and eventually tissue damage.

[0071] Referring to Figure 1b, when a force 107 is applied perpendicularly to the surface of the skin, pressure is exerted on the skin 108 and subcutaneous tissues 109. The pressure 107 compresses the tissues 109 and may distort or deform the skin and soft tissues (e.g., subcutaneous fat and muscle). Shear 110 may also occur in and between layers 111 of the deeper tissues as a result of tissue deformation caused by pressure on a bony protuberance 112. Muscle, in particular, is prone to damage by shear. Compressive stresses 113 occur on the axis perpendicular to the direction of the muscle fibers, and stresses 114 occur when the tissue is stretched and deformed along the fiber direction. Arrows 115 represent surface pressure. Soft tissue deformation is greatest when pressure is applied over a bony protuberance 112. Damage in this way often occurs initially in the soft tissue, i.e. at the interface between muscle and bone, with skin breakdown and pressure wound formation occurring later in the process. Thus, when assessing a pressure wound, the full extent of the damage may not be clear or visible.

[0072] Figure 2 illustrates the compressive behavior of two gel dressings according to the present invention and two prior art dressings comprising stiffer gel coatings at different pressures. Compressive strength (y-axis) refers to the amount of stress required to deform a material at a given stress (x-axis).

[0073] The inventive gels A and B follow a compressive strength curve that closely resembles, respectively, the behavior of soft tissue. At lower pressures, soft tissue exhibits a linear compressive behavior with a compressive strength closer to 2 kPa at 20% strain, but its compressive strength increases dramatically at higher pressures (above 40%), due to the hyperelastic properties of soft tissue. The inventive gels A and B in Figure 2 illustrate a similar linear behavior at lower pressures, and the compressive strength curves remain substantially linear even at strains up to 50%.

[0074] This behavior is advantageous for the purposes of preventing and/or mitigating pressure ulcers. The soft tissue beneath the dressing is protected from damage and deformation, and the gel coating can reduce the pressure, shear and friction forces occurring on the skin and soft tissue layers. The gel dressings of the present invention allow compression at high loads. The low compressive strength of the gel at higher pressures (50%) prevents the deformation (resulting from compression) from being transferred to the underlying skin and soft tissue. Instead, the deformation resulting from the high load is occurring within the dressing.

[0075] Measuring compressive strength at 50% strain is a particularly useful point on the compressive strength (stress) curve (see Figure 2), since compression at this stress represents the compression to which a bedridden patient is typically exposed in a clinical setting.

[0076] Figure 3 illustrates a dressing 300, in accordance with an illustrative embodiment of the present invention, applied to the skin in the sacrum region of a patient. The medical dressing 300 has a first side 301 and a second opposing side 302, wherein the first side 301 has a skin-facing surface 303 adapted to detachably adhere the medical dressing 300 to a dermal surface; the dressing comprising a gel coating 304, wherein the gel has a compressive strength of 1 to 14 kPa at 25% strain, as measured in accordance with the compression test described herein.

[0077] In embodiments, the gel has a compressive strength of 5 to 60 kPa, preferably 5 to 40 kPa at 50% strain, as measured according to the compression test described herein.

[0078] More preferably, the compressive strength of the gel is less than 25 kPa at 50% strain, as measured in accordance with the compression test described in the specification.

[0079] Suitably, the compressive strength is 2 to 12 kPa, or 2 to 8 kPa at 25% strain, as measured in accordance with the compression test described herein.

[0080] As used herein, the term "compressive strength" refers to the amount of stress required to deform a material at a given stress. Compressive strength is calculated by dividing the load by the original cross-sectional area of a specimen. Compressive strength, as defined herein, is independent of the ultimate compressive strength before fracture (i.e., the maximum stress a material can withstand before breaking). Compressive strength is measured as described in the Examples section.

[0081] In embodiments of the present invention, the gel as described herein has a water content of less than 15 wt %, preferably less than 10 wt %, still preferably less than 5 wt %. In embodiments, the gel has a water content of from 0.5 wt % to 15 wt %, preferably from 1 wt % to 13 wt %, still preferably from 3 wt % to 12 wt %.

[0082] It is believed that conventional hydrogels, that is, gels containing a significant amount of water, as described in the art, are generally not suitable for use as gels in accordance with the present invention.

[0083] The composition of the gel as described above allows the dressing to be stored at ambient conditions without the need for special packaging (such as hermetically sealed foil packets, etc.) and without compromising the properties of the gel and dressing. If the water content of the gel is too high, the gel may dry out when stored at ambient conditions. As a result, the gel may become stiffer and harder. Instead, standard packaging may be used and ethylene oxide (EtO) sterilization may be used to sterilize the product.

[0084] The gel according to the present invention can be manufactured by polymerizing: - 15 to 50% by weight of a hydrophilic acrylic monomer; - 50 to 85% by weight of a hydrophilic softening agent; - 0.001 to 0.5% by weight of a crosslinker; - 0.05 to 0.5% by weight of a polymerization initiator.

[0085] The hydrophilic acrylic monomers are preferably selected from monomers resulting in a homopolymer with a low glass transition temperature, Tg, such as less than -10° Celsius, preferably less than -20° Celsius.

[0086] In embodiments, the hydrophilic acrylic monomer is selected from 4-hydroxybutyl acrylate, methoxy polyethylene glycol acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate, or combinations thereof.

[0087] The monomers are chosen so that the copolymer, as formed, is hydrophilic, soft, elastic and compatible with the softening agent. The monomers are typically present in an amount of 15 to 50% by weight, suitably 20 to 35% by weight of the total mixture.

[0088] In embodiments, the polymerization mixture further comprises 0.1 to 5% of an acidic group-containing monomer or salts thereof. In embodiments, said monomer is acrylic acid or, more preferably, 2-acryloamido-2-methylpropane sulfonic acid (AMPS) or salts thereof are used. The acidic group-containing monomers or salts thereof may improve the absorption capacity of the gel.

[0089] In embodiments, a comparatively low amount of the acidic group-containing monomers or their salts, e.g., 2-acryloamido-2-methylpropane sulfonic acid sodium salt (Na-AMPS), is used, such as from 0.1 to 5 wt %, e.g., from 0.1 to 3 wt %, e.g., from 0.1 to 2 wt %. Acrylic acid and AMPS typically result in homopolymers having a higher glass transmission temperature, Tg. Thus, if present in very high amounts, the resulting gel may be very hard.

[0090] The hydrophilic softening agent may be selected from polyethylene glycol, glycerol and/or urea or combinations thereof. The total amount of softening agent is 50 to 85 wt%, suitably 65 to 80 wt%.

[0091] The crosslinker is preferably selected from dysfunctional acrylates, such as polyethylene glycol diacrylate. A small amount, such as 0.001 to 0.5 wt% is typically used, preferably 0.001 to 0.2 wt%. A low degree of crosslinking is desirable to maintain the smoothness of the gel.

[0092] A polymerization initiator may be a UV initiator selected from 1-hydroxycyclohexyl-phenyl ketone, 2-hydroxy-2-methylpropiophenone, and combinations thereof. The UV initiator enables the gel to be curable in a UV curing process.

[0093] In the embodiment illustrated in Figure 3, the gel coating 304 and the dressing 300 are substantially transparent.

[0094] As used herein, the term "substantially transparent" means that the dressing is sufficiently transparent to permit visual inspection of the skin; that is, to monitor for potential changes in skin color or ulcer formation without having to remove the dressing from the skin.

[0095] Suitably, the gel coat 304 has an opacity of less than 25%, preferably less than 15%, as measured by the opacity test described herein.

[0096] The opacity of the gel coating reflects the degree of "non-transparency" of the gel. When the gel coating has an opacity of 0%, the gel is completely transparent. If the gel coating has an opacity of 100%, the gel coating is not transparent; that is, no light can be transmitted through the material. The opacity of the gel coating illustrates the degree to which the skin can be clearly seen through the gel coating. When the opacity is less than 25%, any change in the color or appearance of the skin can be observed through the dressing. Opacity is measured according to the ASTM D2244-11 standard method as described in the Examples section.

[0097] Assessment of potential tissue damage includes an observation of the skin for changes in color compared to the surrounding skin. Figure 3 illustrates palpation of the skin or the so-called "blanch test" on a patient. Redness of the skin that may be bleached (erythema) may signal impending tissue damage. In Figure 3a, a reddened area 305 can be seen beneath the dressing. In a patient with a pressure ulcer, the redness may result from the release of pressure causing ischemia.

[0098] An erythematous lesion that loses all redness when pressed is called "blanchable." Blanchable erythema is initially red, but turns white when pressed with a fingertip (Figure 3b), and then returns to red when pressure is removed (Figure 3c). Palpation of the skin can be performed through the gel coating 304 without having to remove the dressing 300 from the skin. The caregiver can press his or her finger 306 through the soft, pliable gel 304 and note the color of the skin when the pressure of the finger is removed (Figure 3c). The gel 304 is so soft and pliable that when a finger 306 is pressed into the coating portion, it "sinks" into the gel 304, as can be seen in Figure 3b. Tissue exhibiting blanchable erythema typically returns to its normal color within 24 hours and does not suffer any long-term damage. The longer it takes for the tissue to recover from the pressure of the finger, the greater the risk that the patient will develop pressure ulcers.

[0099] On the other hand, non-blanchable erythema may be an early sign of tissue destruction. The redness associated with non-blanchable erythema is more intense and does not change when compressed with a finger. If recognized and treated early, non-blanchable erythema is reversible. The medical dressing of the present invention allows such early recognition.

[00100] The thickness of the gel coating may vary depending on where the dressing is to be applied. Dressings are available in a variety of sizes and shapes suitable for different anatomical locations. Different anatomical locations vary in terms of skin properties, shape of the underlying bony protuberance, and thickness and types of subcutaneous tissue present. For example, a heel dressing may be thicker than a dressing applied to the sacrum or to a patient's face or head.

[00101] In embodiments, the thickness of the gel coating is in the range of 2 to 10, e.g., 2 to 6 mm, suitably 2 to 4 mm. A gel coating that is too thick causes increased stresses in the soft tissue.

[00102] Figure 4a illustrates a cross-sectional view of an illustrative embodiment of the present invention. The dressing comprises a backing layer 401 and a body contact adhesive layer 402; the gel coating 403 being disposed between the backing layer 401 and the body contact layer 402.

[00103] As used herein, the term "body contact layer" means the layer that is in contact with the skin of a user. The body contact surface of the gel may be adhesive per se, but may also comprise an additional adhesive layer. In the field of medical dressings, in particular wound dressings, an adhesive film or layer for adhering to the patient is often referred to as a wound contact layer. The present invention is primarily intended for the prevention of pressure ulcers, that is, for use on an area of the human body that does not necessarily require wound treatment. Therefore, in this application, the adhesive film or layer will be referred to as a body contact layer. However, it should be understood that although the primary use of the invention is the prevention of pressure ulcers, if nursing staff decide to use it as a wound dressing, the body contact layer may be applied to a wound or scar.

[00104] In embodiments, the body-contacting adhesive layer 402 of the dressing covers at least 60% of the surface of the covering 403. Suitably, the body-contacting adhesive layer 402 covers at least 75% of the surface of the covering.

[00105] It is beneficial to have an even distribution of adhesive across the surface of the covering in order to hold the dressing in place during use. In addition, a greater coverage of adhesive on the surface of the covering assists in preventing undesirable frictional forces that may form between the skin and the dressing as a patient slides in bed.

[00106] The body contacting adhesive layer 402 has a body-facing surface 405; that is, a surface oriented toward the user's skin, and a non-body-facing surface 406, that is, a surface oriented opposite to the adhesive surface when fitted to a user.

[00107] The body contact adhesive layer 402 may comprise a film covered by an adhesive layer (not shown). The film to which the adhesive layer is applied may be comprised of a thin plastic film, or a laminate comprising a thin plastic film, e.g., a thin polyurethane film having a thickness of 15 to 100 μm, e.g., 20 to 80 μm, preferably 45 to 60 μm.

[00108] The adhesive is preferably skin-friendly, and sufficiently adherent to the skin so that the dressing remains in place and maintains its adhesion with repeated removal and reapplication. The adhesive should be easy to remove without causing trauma and is suitably silicone-based. In embodiments of the invention, the adhesive may comprise a soft silicone gel.

[00109] Examples of suitable silicone gels include the two-component RTV systems such as Q72218 (Dow Corning), and SilGel 612 (Wacker Chemie AG) mentioned herein, in addition to NuSil silicone elastomers. In embodiments of the invention, the adhesive may comprise a soft silicone gel having a softness (penetration) of 8 to 22 mm, for example 12 to 17 mm, as measured by a method based on ASTM D 937 and DIN 51580, the method being described in European patent application No. 14194054.4. The thickness of the adhesive layer is preferably at least 20 μm.

[00110] The body contact adhesive layer may be perforated or not. The body contact adhesive layer is preferably substantially transparent.

[00111] The medical dressing may comprise an edge portion 407. In embodiments, at least the backing layer 401 extends beyond the periphery of the gel coating 403 to define an edge portion 407 around the contour of the coating 403. In Figure 4 , the backing layer 401 and the body contacting adhesive layer 402 extend beyond the periphery of the gel coating 403 to define an edge portion 407 around the contour of the coating 403. The body contacting layer 402 is typically coextensive with the backing layer 401, and has the same external dimensions. The edge portion 407 forms a closed path around the contour of the coating 403, and the backing layer 401 and the body contacting layer 402 are joined to each other in those areas of both layers that extend beyond the periphery of the coating. The adhesive can be a thin acrylic adhesive.

[00112] In order to achieve sufficient adhesion properties, the edge portion 407 has a width of 5 to 50 mm and extends along the contour of the coating 403. A smaller sized dressing may have a smaller edge portion than a larger sized dressing. Preferably, the edge portion has a width of 10 to 25 mm and extends along the contour of the coating. This allows easy handling and application of the product while still maintaining sufficient adhesion after application.

[00113] The backing layer 401 may be a thin film, sheet or membrane that is vapor permeable and impermeable to water. Examples of suitable materials for the backing layer include, but are not limited to, polyurethane, polyethylene or polyamide films, silicone films, polyester-based nonwoven materials, and laminates of the polyester-based nonwoven materials, and polyurethane films. Suitably, the backing layer is a polyurethane film having a thickness of 5 to 40 μm, for example, 15 to 25 μm. The backing layer 401 may be partially or fully bonded to the coating 403, for example, by an adhesive, such as a pressure-sensitive adhesive (e.g., an acrylic adhesive).

[00114] Preferably, the backing layer 401 is substantially transparent.

[00115] In illustrative embodiments, dressing 400 comprises an anisotropic layer 408.

[00116] As used herein, the term "anisotropic layer" means a layer that has anisotropic stiffness properties; that is, the stiffness (or stretchability) of the layer is different in the first (x) and second (y) directions. In the present description, the "anisotropic layer" is stiffer in the second (y) direction and more stretchable in the first (x) direction.

[00117] The anisotropic layer 408 has a first (x) direction and a second (y) direction, where the anisotropic layer has a greater tensile strength at 15% strain in the second (y) direction than in the first (x) direction, as measured by the tension test described herein.

[00118] The tensile strength at 15% strain in the second direction (y) may be at least 6 times greater, preferably at least 10 times greater, than in the first direction (x), as measured by the tensile test described herein.

[00119] The anisotropic layer 408 may be a film or layer having a tensile strength at 15% strain of at least 4 N, preferably at least 10 N, and more preferably at least 15 N in the second (y) direction, as measured by the tensile test described herein.

[00120] The anisotropic layer 408 may be selected from a variety of materials, such as nonwoven materials, films, textile materials, polymeric webs as long as they exhibit the desired anisotropic stiffness properties. The anisotropic layer 408 may comprise a plurality of reinforcing fibers or filaments that provide the layer with high tensile strength in the longitudinal (y) direction. Films and webs made of, for example, polyethylene, polypropylene, polyester, polyurethane, or silicone may be used as long as these materials have sufficient strength in the longitudinal (y) direction and sufficient anisotropic properties.

[00121] In embodiments, the anisotropic layer 408 comprises a nonwoven material. Suitable nonwoven materials for use as the first anisotropic layer are meltblown, wound, wound lace, or carded nonwoven fabrics.

[00122] In illustrative embodiments, the anisotropic layer is an oriented fibrous non-woven layer having greater than 50% of the fibers oriented in the longitudinal (y) direction. Thus, the fibers oriented in the longitudinal (y) direction will provide reinforcement in that direction.

[00123] Examples of polymers suitable for use in nonwoven materials are polyethylene, polyesters, polypropylenes, and other polyolefin homopolymers and copolymers.

[00124] For example, nonwoven fabrics comprising thermoplastic fibers of polypropylene and polyethylene fibers or blends thereof may be used. The fabrics may have a high thermoplastic fiber content and contain at least 50%, e.g. at least 70%, thermoplastic fibers. The nonwoven material may be a blend of polyethylene and viscose, e.g. in a ratio of 70:30. Natural fibers, e.g. cotton, may also be used provided they provide the desired properties. The basis weight of the nonwoven material may be in the range of 10 to 80 g/m2, e.g. 13 to 50 g/m2. The anisotropic first layer may also be a wind-melt-blown or wind-melt-wind-melt (SMS) fabric.

[00125] Preferably, the anisotropic layer 408 is substantially transparent, so that it does not obstruct the transparency of the gel dressing 400. The anisotropic layer may comprise additives to achieve the desired transparency/opacity. For example, organic or inorganic matrices, coloring agents, or whitening agents may be used.

[00126] The anisotropic layer 408, when present, affects the anisotropic stretch properties of the entire dressing. As illustrated by the arrows in Figure 4c, the dressing 400 is stiffer in the second (y) direction and more stretchable in the first (x) direction.

[00127] The effect of this feature can be explained with reference to Figure 5.

[00128] Figure 5 illustrates a patient 501 positioned on an adjustable bed 502, where the head of the bed has been elevated and the patient 501 has been placed in a more upright condition. When no dressing is used (Figure 5a), the patient 501 is subjected to pressure compression of the tissue, and to shear forces 503 distorting or deforming the soft tissue layers 504. The individual tissue cells 505 are thus subjected to both pressure and compression, and also to shear forces 503 arising from the patient 501 sliding on the layer 502. This has a negative impact on the soft tissue, and the tissue cells 505 have a greater tendency to deform, which may ultimately result in the formation of a pressure ulcer.

[00129] In Figure 5b, a dressing 500 in accordance with the present invention has been applied to the sacrum region of patient 501 such that the second stiff direction (y) corresponds to the direction from which the tissue is exposed to the most shear and stretch (i.e., a patient's gliding direction). When a dressing is applied to the sacrum region, pressure forces are reduced by the dressing 500 and distributed over a larger area. This results in redistribution of pressure and reduced magnitude of critical forces on the skin and underlying tissues. Shear forces 503 are reduced by the dressing 500 since the dressing is stiff in the direction in which patient 501 glides on the bed 502. Therefore, the stiff dressing 500 "locks" the skin and underlying tissues so that they do not stretch excessively in the region where the dressing 500 has been applied. The fact that the dressing is flexible in the first direction (x) is advantageous, as it prevents the tissues from becoming "overly restricted". Instead, the sacral gluteus can spread gently and naturally. The individual tissue cells 505 in the sacral region of the patient 501 are thus kept relatively intact. Skin stretching can still occur in the areas of the skin outside the dressing (areas that are less at risk of pressure ulcer formation due to deformation, pressure and shear). In this way, pressure forces, shear forces and tension and stretching of the skin cells and the underlying tissue cells are minimized.

[00130] An illustrative embodiment of this aspect of the present invention is illustrated in Figure 6. The shape of the dressing is suitable for application to the sacral area of a patient.

[00131] The medical dressing 600 has a lateral extension (x) and a longitudinal extension (y); the covering 601 being symmetrical about a longitudinal centerline 602 and the dressing comprising a first lobe-shaped portion 603 on one side of the longitudinal centerline 602 and a second lobe-shaped portion 604 on the other side of the longitudinal centerline 602.

[00132] The anisotropic layer (not shown) is arranged so that the first direction (x) of the anisotropic layer corresponds to the lateral extent (x) of the dressing 600, and the second direction (y) of the anisotropic layer corresponds to the longitudinal extent of the dressing 600. Thus, the dressing is stiffer in the longitudinal (y) direction than in the lateral (x) direction.

[00133] The edge portion 605 may be substantially heart-shaped, such that the first 603 and second 604 lobe-shaped portions form part of the lobe-shaped upper sides of a heart shape. Suitably, the first and second lobe-shaped portions are separated by a branched portion 606 that replaces the pointed lower portion of a heart shape. The branched portion 606 comprises a protuberance on each side of an interstice located coaxially with the longitudinal centerline.

[00134] The shape of the medical dressing 600 is adapted to fit the sacral region of a human body. The branched portion 606 allows for improved adhesion capability in the region of the gluteal cleft. It is important that the dressing remains adhered in this region since otherwise body fluids (e.g. as a result of incontinence) may enter the dressing and impair adhesion to the skin.

[00135] The coccyx is an area exposed to a great deal of pressure and shear. It is therefore important to protect this part of the body, and the dressing is appropriately shaped to allow for such protection.

[00136] In this way, the skin 601 can be divided by a lateral centerline 607 into an upper skin region 608 having an upper lateral edge 609 and a lower skin region 610 having a lower lateral edge 611. The width, x1, of the lower lateral edge 611 is between 10 and 40% of the maximum width, x2, of the skin 601 in the lateral (x) direction.

[00137] The maximum width, x2, of the dressing liner 600 is typically in the range of about 12 to 30 cm, preferably 15 to 20 cm. The width, x1, of the lower side edge may be in the range of about 1 to 7 cm, e.g., 2 to 4 cm, depending on the size of the dressing.

[00138] In embodiments, dressing 600 comprises at least one gripping tab 612; gripping tab 612 being coplanar with and projecting outwardly from the periphery of dressing 600.

[00139] The grip tab 612 directs the caregiver to lift the dressing, inspect the skin beneath the dressing, and then reapply the dressing to the skin (if the skin appears good). Inspection of the skin may still be necessary, although less frequently, when the dressing is transparent. Since skin inspection typically occurs where the patient is lying on their side in bed, it is beneficial to have at least two grip tabs so that the caregiver can lift the dressing regardless of which side the patient is lying on. In FIG. 6, the grip tab 612 is coplanar with and projects outwardly from the edge portion of one of the lobe-shaped portions 603 and 604.

[00140] As illustrated in Figure 7, the coating 701 can be divided into three separate zones along the longitudinal extent (y) of the dressing 700: a central zone 702 and two lateral zones 703.

[00141] The central zone 702 of the dressing 700 is the area exposed to the greatest pressure and shear stresses, especially in the lower portion 704 of the central zone 702, which is arranged to cover the coccyx region of a patient. In the embodiment envisioned in FIG. 7, the gel coating comprises a plurality of indentations 705 at least in the central zone 702.

[00142] As used herein, the term "notches" means areas of reduced coating thickness. Notches may be openings that extend through the gel coat.

[00143] The notches 705 allow for localized softening of the gel coating while preserving the overall properties of the gel dressing. The inventors have discovered that the skin and soft tissue underneath are best protected by providing notches 705 in the central zone.

[00144] In embodiments, the liner 701 may be divided into three separate zones along the longitudinal extent (y) of the dressing 700: a central zone 702 and two lateral zones 703 where the compressive strength of the gel in the central zone 702 is lower than in the lateral zones.

[00145] Accordingly, the dressing may be formed of different regions having different properties; i.e., compressive strengths. The inventors have discovered that the central zone 702 may be softer, i.e., have a lower compressive strength to prevent soft tissue cells from becoming deformed and damaged. In embodiments, the central zone of the dressing 702 may have a compressive strength in the range specified above, and the lateral zones 703 of the dressing may have a higher compressive strength.

[00146] In another aspect, the invention relates to a dressing as described above for use in preventing pressure ulcers.

[00147] However, although the primary use of the invention is directed to prevention, such a dressing can also be used in the treatment of ulcers or pressure wounds, especially low-exuding wounds.

[00148] Although the dressing of the present invention is primarily intended for prophylactic use, it is preferable that the dressing exhibit sufficient absorbency, as illustrated in the Examples section below. A prophylactic dressing must be capable of handling low-exuding wounds and body fluids, such as sweat, small amounts of blood, and pus.

Examples Preparation of gels according to the invention. Gel A

[00149] 23 g 4-hydroxybutyl acrylate, 3 g AMPS, 0.02 g PEG400 diacrylate (from Sartomer), 50 g glycerol, 30 g PEG400 (from Sigma-Aldrich) and 0.15 mg Omnirad 1000 (from IGM Resins) were placed in a speed mixer jar, where Omnirad UV initiator was added last to the mixture. The ingredients were then mixed in the speed mixer for 2 minutes at 2400 rpm.

[00150] After mixing, the jars were allowed to rest for at least 3 hours in a dark box in order to get rid of air bubbles from the gel solution.

[00151] Thin gels (up to 5 mm) were then cured for 20 seconds in UV light to measure absorption and opacity. Thicker gels (25 mm) were cured for 1 minute in UV light to perform compression testing and compressive strength analysis.

[00152] The water content of gel A was 9 wt%.

Gel B

[00153] 29.75 g MPEG450A (from Sigma Aldrich), 0.25 PEG400diA (from Sartomer), 70 g Glycerol/urea (70/30 mixture), and 0.1 Omnirad 1000 (from IGM Resins) were placed in a speed mixer jar, where Omnirad UV initiator was added last to the mixture. The ingredients were then mixed in the speed mixer for 2 minutes at 2400 rpm.

[00154] After mixing, the jars were left to rest for at least 3 hours in a dark box in order to get rid of air bubbles from the gel solution.

[00155] Thin gels (up to 5 mm) were then cured for 20 seconds in UV light for absorption and opacity measurements. Thicker gels (25 mm) were cured for 1 minute in UV light for compression testing and compressive strength analysis.

[00156] The water content of gel B was 4 wt%.

Absorption capacity of gels

[00157] To analyse the absorption capacity of the gels, Solution A (according to EN 13726-1:2002) diluted with distilled water in a ratio of 1:5 was used. The dry weight of the gels was recorded. The gels were allowed to absorb liquid from a wet surface without being immersed in the liquid at room temperature. The surface used was Mesorb®, cut to approximately the same size as the gels (1-2 mm excess material on each side due to swelling of the gel). The Mesorb® pieces were soaked with 20 ml of liquid (this is how much the piece can hold) and the gel was placed on top of this. A beaker was covered with Parafilm® to prevent evaporation of the liquid. After four hours, 10 ml more liquid was added to the Mesorb® piece to ensure that it remained saturated. The set-up was then left to stand for a further 18 hours. In total, the gels were allowed to absorb liquid for 22 hours. After swelling, the weight of the gels was recorded again.

Opacity of gels (determined according to ASTM standard 224411)

[00158] After the gels were wetted and swollen, the opacity was measured with a Minolta Chroma CR 300 Meter, according to ASTM D2244-11 to study opacity after exposure to liquid.

[00159] The method measures the Yxy color space values on the specimens that cannot be used to calculate the opacity number. Apparatus: Chroma meter CR-300 and Data Processor DP-301. Sample preparation: The specimen with an initial height of 4 mm is allowed to absorb the liquid according to the method described above. Procedure: The Yxy color space values are measured on the wet test specimens. The Chroma meter is calibrated according to the instructions of the apparatus. The apparatus is set up to measure the color space values. The specimens are first located on a black background and the tip of the measuring head is placed flat against the surface of the specimen. When the measuring head lamp is on, the measuring button is pressed. 5 measurements are performed on each specimen. The specimens are then moved to a background arm and the tip of the measuring head is located flat against the surface of the specimen. 5 measurements are performed on each specimen.

[00160] The following results are measured in the method: - Y x y color space values - Opacity number, Yblack/Ywhite (expressed as %) Compressive strength of the gels (Determined according to ASTM standard D3574-11, test C) Apparatus: insight MTS Tensile tester connected to a computer Cross speed: 50 mm/min Plate distance: 37.5 cm Specimen preparation: The specimen area should be at least 2500 mm2 (50 mm*50 mm) with a height of at least 20 mm, preferably 25 mm. The specimens are conditioned for 24 h at 50% RH plus or minus 5% RH and 23 °C plus or minus 2 °C, prior to testing. Procedure: The tensile tester is calibrated according to the apparatus instructions and set to zero. The distance between the upper and lower plate is set to 37.5 mm. The specimen is centered on the support plate of the apparatus. The compression foot presses down and the thickness at 140 Pa is determined. The specimen is compressed to 50% of its thickness at a speed of 50 mm/min and then the upper plate is raised directly again.

[00161] The following results are expressed by the tension tester/computer: - Load [N] - Specimen thickness at 14 Pa [mm] - Young's modulus at 20% tension and 50% strain [kPa]

[00162] Compressive strength is calculated by dividing the specific stress load by the original cross-sectional area of the specimen. Compressive strength, as defined herein, is independent of the maximum compressive stress prior to fracture (i.e., the maximum stress a material can withstand before breaking).

[00163] The results of the absorption, opacity and compressive strength tests for the gels of the present invention and commercially available gels, such as those used in medical coatings, are summarized in the table below. Table 1: Characteristics of the inventive and commercially available gels * Measured at 45% strain since the load cell limit (250 N) was reached before 50% strain (since the gel was too stiff). Tensile force (determined according to ASTM D882-12) Equipment: Tensile tester for e.g. insight MTS Tensile tester connected to a computer Cross-section speed: 50 mm/min Grip separation: 100 mm Specimen preparation: Test specimens are punched out of the material. The width of the specimens is 25 mm and the length is at least 50 mm longer than the grip separation, if possible. It is important that the edges of the specimens are homogeneous and without break notches. The specimens are conditioned for at least 24 hours at 50% RH, plus or minus 5% RH, and 23 °C, plus or minus 2 °C prior to testing. Procedure: The tension tester is calibrated according to the instrument instructions and set to zero. The specimen is then mounted on the clamps and the backlash and pre-tension should be minimized. The tension tester is started and the specimen is stretched to breakage or until 100% elongation is reached, the tensile force (load) X elongation is recorded. Measurements resulting from premature failure (i.e., the specimen breaks in the clamp, or is damaged during setup) are ignored if possible.

[00164] The following results are expressed by the tension tester/computer: - Strain [%], calibration extension/length - Load with specific strain (e.g. with 15% strain).

[00165] Five different anisotropic layers were tested, and their tension curves are illustrated in Figure 8. Figure 8a illustrates the tension curves in the second (y) direction, and Figure 8b illustrates the tension curves in the first (x) direction. Sample A was Eschler's M33116-A (polyamide), sample B was Eschler's M33116-B (polyamide), sample C was Eschler's 322223 (polyester), sample D was DEKA Medical's 114160 Delstar (polyamide sample), and sample E was a 40 gsm non-woven wrapped lace comprising viscose and polyethylene (70:30).

Finite Element (FE) Modeling

[00166] The mechanisms that result in pressure ulcers are not fully understood. Pressure sensor mats can provide information about the pressure present in mattresses under the skin surface, but they do not inform about the behavior within the soft tissues at the origin of the damage. Therefore, the Finite Element (FE) method offers a great alternative to study the biomechanisms of action for pressure ulcers.

[00167] The FE method is a numerical and computational technique used to solve multiphysics problems by solving partial differential equations using different types of discretization. The FE method subdivides a larger problem or large 3D model into smaller parts called finite elements. Analysis is performed within each element and the assembly provides a solution to the entire problem.

[00168] The workflow for an FE analysis can be explained as follows: creation of a 3D model consisting of finite elements, definition of material properties of the model, definition of boundary conditions and loads to be applied to the model, according to the problem, computational solution of the problem, and analysis of the results through visualization and calculations.

Finite Element (FE) Configurations and Anatomical Model

[00169] In order to understand the effect of the dressing according to the present invention, Finite Element (FE) models of a pelvis and a dressing according to the invention were created and analyses were performed to study the effect of pressure and tension on the skin and deep tissue layers. The volunteer was a healthy, non-smoking, adult male, 31 years of age at the time of the study (year of birth 1984, height: 1.83 m, weight: 77 kg).

[00170] The FE models were prepared in ANSA 16.0.1 and 17.1.0 (BETA CAE) and the analysis performed in ABAQUS 14.0 (DASSAULT SYSTEM). The FE model of the pelvis was segmented from MRI scans of the pelvis in order to ensure the highest anatomical accuracy.

[00171] Soft tissues were represented by nonlinear materials (muscles were placed together as a single material, fat and skin were placed together as a compression material), bones as the rigid body. Soft tissue deformation caused by body hair compression was used to validate the FE model and its material properties with ABAQUS 14.0 (DASSAULT SYSTEM). Validation was performed by comparing soft tissue thickness before and after compression between the model and MRI data.

[00172] Soft tissue deformation was performed by simulating a clinical setup in which a patient is lying on a mattress. A soft mattress (30 kPa) was added under the pelvis and the equivalent of body weight was applied to induce contact and compression of the pelvis on the mattress.

[00173] The deformation of the soft tissue, resulting from pure compression, was simulated with a vertical displacement of the body on the mattress, while the additional effect of the shear force was induced by a subsequent horizontal displacement of the body on the mattress to reproduce the elevated position.

[00174] The following soft tissue layers were investigated for stress distribution, and the following stresses were analyzed: Table 2: Soft tissue layers and simulated stresses.

[00175] "Stresses in compression" means the stresses arising from compression, i.e. defined as the vertical displacement of the body on a mattress in order to reproduce the compression of the pelvis when the patient is lying horizontally on a mattress.

[00176] "Stress in compression + shear" means the stresses arising with shear added after compression, i.e. defined as the horizontal displacement of the body on a mattress to reproduce the sliding of the pelvis after compression, when the patient is lying on an inclined mattress.

[00177] Mean pressure (or hydrostatic stress) and Von Mises stresses provide an overview of the effort energy density and help capture the origin of stresses and strains in tissues.

[00178] "Shear stresses" means stresses in the plane, parallel to the coronal plane or dressing plane, and arising from shear forces that are applied to the cross-sectional area, parallel to the direction of the force.

[00179] Von Mises stresses (VMS) are defined in Distortion Energy Theory and represent a common criterion widely used in engineering. VMS can be defined as: The mean pressure (or hydrostatic stress) can be defined as: σHyd = 1/3 (σxx+σyy+σzz)

[00180] The stress energy density is separated into different components in order to isolate hydrostatic stresses and shear stresses. Shear stresses are represented by VMS and combine stresses in different directions into an equivalent stress, which will take into account normal stresses, shear stresses and shear. Combined with hydrostatic stresses, VMS can provide an overview of separate components of the stress energy density and help to capture the origin of stresses and strains in tissues.

[00181] The physical and mathematical relationship between force, tension, displacement and effort is as follows:

[00182] Stress ε is defined as "deformation of a solid due to stress" and can be expressed as: ε = dl/L0 Where dl = change in length or displacement (mm) L0 = initial length (mm) Young's modulus E (MPa) is a material property and can be defined as: E = σ/ε Shear stresses are stresses parallel to the plane and can be expressed as: T = Fp/A Where T = shear stress (MPa) Fp = parallel component force (N) A = area (mm2)

[00183] There are no critical stress values, as these vary between individuals due to their physiological parameters, health, age and duration of exposure to stress. Therefore, the evaluation of the effect of dressings is based on qualitative values. In Figures 9 to 14, the dark areas illustrate higher stresses (critical stress values). Critical stress values were defined as a high stress value showing the difference without "any dressing" and with dressings.

[00184] The critical value of the stresses corresponds to about 1 kg per 10 cm2 (around 10 kPa), except for the shear stresses, where a lower value of the critical stresses was used, corresponding to about 100 g for 10 cm2 (around 1 kPa), since the stresses are applied parallel to the muscle fibers and, therefore, against a more natural compression behavior.

Effect on inventive gel dressing

[00185] A dressing having the properties according to the invention (low compressive strength) was created from the technical CAD drawings and was designed to correspond to the properties of the dressing according to claim 1. The compressive strength of the gel at 25% strain was 4.2 kPa, and the Young's modulus, E, was 0.008 MPa. The inventive dressing is called "Dressing A".

[00186] For comparison purposes, a stiffer gel according to the prior art was designed and inserted into the model. This dressing is referred to as "Dressing B". Dressing B had a gel coating with a compressive strength at 25% strain of 14.6 kPa and a Young's modulus, E, of 0.03 MPa, corresponding to the properties of the Elastogel® dressing.

[00187] The remaining components and properties of dressings A and B were identical to those in the simulations; that is, they had identical shapes and both comprised a simulated backing layer and a border portion surrounding the gel coating. In the simulations, the skin-facing surface of the dressings was fully adhered to the skin. For all dressings, the gel coating material was assumed to be a linear elastic isotropic material and nearly incompressible.

[00188] The material properties of the different dressings were defined by actual laboratory measurements in tension and compression based on ASTM D 882-12 and ASTM D 3574-11.

[00189] Simulations were performed to analyze compression and compression + shear stresses. The simulated model used: no dressing, dressing A and dressing B, respectively.

[00190] Figures 9 and 10 illustrate the mean pressure on the skin of the sacrum region after exposure to pressure and compression (Figure 9) and when shear was added; that is, the patient was subjected to both compression and shear (Figure 10). The black dots in Figures 9 and 10 illustrate the areas exposed to critical pressure. The critical value of the stresses corresponds to about 1 kg per 10 cm2 (about 10 kPa).

[00191] As can be seen in Figure 9c, the inventive dressing drastically reduces the critical compressive stresses on the skin compared to when no dressing is used (Figure 9a) and when a more rigid dressing is used (Figure 9b). Indeed, when a dressing according to the invention is applied, there are no critical stresses present on the skin.

[00192] Figures 10a-c illustrate the mean skin pressure in the sacrum region when shear has been added, simulating, for example, a patient sliding in bed. As can be seen in Figure 10c, the inventive dressing removes all critical tension compared to when no dressing is used (Figure 10a) or when a dressing, according to the prior art, is used (Figure 10b).

[00193] One way to evaluate the performance of dressings is to define their ability to reduce tissue volume under critical stresses. Critical stress values are defined as high stress values showing the difference between "without dressing" and with dressings. As mentioned, for Von Mises stresses, the critical stress value corresponds to about 1 kg per 10 cm2 (around 10 kPa).

[00194] Dressing performance can therefore be defined as the percentage reduction in the volume of tissue under critical tension when compared to no dressing: Reduction (%) = (Vnd - Vd)/Vnd x 100 With reduction (%) = percentage reduction in the volume of tissue under critical tension With Vnd = volume of tissue under critical tension without dressing With Vd = volume of tissue under critical tension with dressing

[00195] Von Mises stresses within the soft tissue (muscles) of the sacral area under the dressing were analyzed and compared between No Dressing, Dressing A, and Dressing B. The table below summarizes the volume of soft tissue subjected to critical stresses. Although already illustrated in Figures 9 and 10, the reduction in skin volume under critical mean pressure is also included in Table 3 below. Table 3: Percentage reduction in muscle and skin volume under critical VMS tension

[00196] The volume of muscle under critical VMS tension was substantially reduced when a dressing of the present invention was used. Notably, critical VMS tensions actually increased with the prior art dressing (Dressing B); that is, the dressing created more tensions in the tissue compared to when no dressing was used.

Effect of gel dressing with support layer

[00197] The effect of incorporating an anisotropic layer was also studied. A simulated anisotropic layer, in accordance with sample E above, was inserted into the dressing concept. The simulated anisotropic layer refers to a wrap with properties similar to a layer that has a tensile strength at 15% strain of 20.6 N in the second (y) direction, and 0.3 N in the first (x) direction. This dressing concept is referred to as Dressing C.

[00198] In Figure 11, the Von Mises stresses in the muscle when the model was subjected to compression and shear are presented. Figure 11a illustrates the situation in which no dressing is used, Figure 11b illustrates Dressing B, Figure 11c illustrates Dressing A, and Figure 11d illustrates Dressing C, that is, Dressing A with an anisotropic layer.

[00199] As observed, VMS stresses in the muscle are substantially reduced with the inventive Dressing A (Figure 11c), and almost all stresses are removed in the coccyx region. Dressing C completely reduces VMS stresses across the sacrum area (Figure 11d), and it can be concluded that the anisotropic layer is particularly beneficial when the body is exposed to shear; resulting, for example, from patient sliding.

[00200] The results are also presented in Table 4 below in terms of the dressings' ability to reduce tissue volume under critical stresses for a simulated compression + shear configuration (mirroring the results of Figure 11). Table 4: Percentage Reduction in Muscle Volume Under Critical VMS Stress with Inventive Dressings A and C

[00201] Shear stress in muscle near bone can also be studied. Shear stresses occur in tissue in various configurations and are due to shear forces, which have been identified as a major cause of pressure ulcers. For shear stresses, the critical stress value corresponds to about 100 g per 10 cm2 (about 1 kPa), since the stresses are applied parallel to the muscle fibers and therefore against a more "natural" compression behavior.

[00202] Figure 12 illustrates the effect of the inventive dressings A (figure 12b) and C (figure 12c), with respect to reducing shear stresses in the muscle near the bones in the sacrum area, compared to no dressing (figure 12a).

[00203] As illustrated in Figure 12b, the inventive Dressing A substantially reduces detrimental shear stresses, and the volume reduction under critical shear stresses was calculated to be 91%. Notably, the inventive Dressing C completely removed the critical shear stresses in the muscles near the sacral bone (Figure 12c) and the calculated volume reduction under critical shear stresses was 100%. This clearly illustrates the effect of the gel, and in particular the positive effect of an anisotropic layer when subjected to detrimental shear forces.

Effect of gel having openings and/or a lower compressive strength in the central zone

[00204] Two additional inventive dressing concepts were investigated; i.e., Dressing D and Dressing E. Dressing D, illustrated in Figure 13a, was similar to Dressing C in construction, but further comprised openings in the central zone of the liner (through the liner and through the anisotropic layer). Dressing E, illustrated in Figure 13b, was similar in construction to Dressing D, but further comprised a region in the central zone of the dressing (near the coccyx) with a lower compressive strength, i.e., 3.1 kPa at 25% strain. The remaining liner exhibited a compressive strength in agreement with the other dressing concepts (4.2 kPa at 25% strain).

[00205] The ability of the dressings to reduce tissue volume under critical tensions in a simulated compression setting was studied and the results are presented below. Table 5: Percentage reduction in muscle volume under critical VMS tension with inventive dressings A, D and E

[00206] The effect of the inventive dressings D and E is also illustrated in Figure 14, which illustrates the Von Mises stresses in the muscle under compression conditions similar to that of a pelvis without any dressing (Figure 14a), a pelvis when Dressing D was applied (Figure 14b), and a pelvis when Dressing E was used (Figure 14c). In other words, Figure 14 illustrates the effect of soft tissue (muscles) after exposure to pressure and compression.

[00207] As can be seen, providing openings and/or a coating region having a lower compressive strength significantly reduces critical stress areas (e.g. black spots).

[00208] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification or practice of the invention described herein. It is intended that the specification and examples be considered as illustrative only, with the true scope of the invention being indicated by the following claims.

Claims (14)

1. A medical dressing (300), wherein the medical dressing (300) has a first side (301) and a second opposing side (302), wherein the first side (301) has a skin-facing surface adapted to detachably adhere the medical dressing (300) to a dermal surface; the dressing (300) comprising a gel coating (304), characterized in that the gel has a compressive strength of 5 to 60 kPa at 50% strain, as measured according to the compression test described in the specification, and wherein the gel has a water content of less than 15% by weight, preferably less than 10% by weight, preferably less than 5%, or wherein the gel has a water content of 0.5% by weight to 15% by weight, preferably from 1% by weight to 13% by weight, more preferably from 3% by weight to 12% by weight, wherein the gel is manufactured by polymerizing: - 15 to 50% by weight of a hydrophilic acrylic monomer, preferably selected from 4-hydroxybutyl acrylate, methoxy polyethylene glycol acrylate, 2-hydroxyethyl acrylate, hydroxypropyl acrylate or combinations thereof; - 50 to 85% by weight of a hydrophilic softening agent; - 0.001 to 0.5% by weight of a crosslinker; and - 0.05 to 0.5% by weight of a polymerization initiator. 2. Medical dressing (300) according to claim 1, characterized in that the gel has a compressive strength of 1 to 14 kPa at 25% strain, as measured according to the compression test described in the specification, preferably 2 to 12 kPa, more preferably 2 to 8 kPa. 3. Medical dressing (300) according to claim 1 or 2, characterized in that the gel has a compressive strength of 5 to 40 kPa at 50% strain, as measured according to the compression test described in the specification. 4. Medical dressing (300) according to any one of the preceding claims, characterized in that the dressing (300) is substantially transparent. 5. The medical dressing (300) of claim 4, wherein the gel coating (304) has an opacity of less than 25%, preferably less than 15%, as measured by the opacity test described in the specification. 6. Medical dressing (300) according to any one of the preceding claims, characterized in that the dressing (300) comprises a backing layer (401) and a body contact adhesive layer (402); the gel coating (304) being disposed between the backing layer (401) and the body contact layer (402). 7. Medical dressing (300) according to any one of the preceding claims, characterized in that at least the backing layer (401) extends beyond the periphery of the gel coating (304) to define a border portion (407) around the contour of the coating (304). 8. Medical dressing (300) according to any one of the preceding claims, characterized in that the dressing (300) comprises an anisotropic layer (408) having a first direction (x) and a second direction (y), wherein the tensile strength at 15% strain of the anisotropic layer (408) is greater in the second direction (y) than in the first direction (x), when measured in accordance with the tensile test described in the specification. 9. Medical dressing (300) according to claim 8, characterized in that the tensile strength at 15% strain of the anisotropic layer (408) in the second direction (y) is at least 6 times greater, preferably at least 10 times greater than in the first direction (x), when measured according to the tensile test described in the specification. 10. Medical dressing (300) according to any one of the preceding claims, characterized in that the medical dressing (300) has a lateral extension (x) and a longitudinal extension (y); the covering (304) being symmetrical about a longitudinal centerline (602) and the dressing (300) comprising a first lobe-shaped portion (603) on one side of the longitudinal centerline (602) and a second lobe-shaped portion (604) on the other side of the longitudinal centerline (602). 11. Medical dressing (300) according to claim 10, characterized in that the anisotropic layer (408) is arranged so that the first direction (x) of the anisotropic layer (408) corresponds to the lateral extent (x) of the dressing (300), and the second direction (y) of the anisotropic layer (408) corresponds to the longitudinal extent of the dressing (300). 12. Medical dressing (300) according to claim 10 or 11, characterized in that the medical dressing (300) is divided into three separate zones along the longitudinal extension (y) of the dressing (300): a central zone (702) and two lateral zones (703), wherein the gel coating (304) in at least the central zone (702) comprises a plurality of notches (705). 13. Medical dressing (300) according to any one of claims 10 to 12, characterized in that the medical dressing (300) is divided into three separate zones along the longitudinal extension (y) of the dressing (300): a central zone (702) and two lateral zones (703), wherein the compressive strength of the gel in the central zone (702) is lower than that in the lateral zones (703). 14. Medical dressing (300) according to any one of the preceding claims, characterized in that the dressing (300) comprises at least one gripping tab (612), which gripping tab (612) is preferably coplanar with and projecting outwardly from the periphery of the dressing (300).