WO2009021523A1

WO2009021523A1 - Pressure-distributing element of closed cell foam

Info

Publication number: WO2009021523A1
Application number: PCT/DK2008/050200
Authority: WO
Inventors: Jens Hoeg Truelsen
Original assignee: Coloplast A/S
Priority date: 2007-08-14
Filing date: 2008-08-14
Publication date: 2009-02-19

Abstract

When using negative pressure therapy in connection with wound treatment, a pressure-distributing element is preferably used. The invention provides a system for use in connection with negative pressure therapy, which system comprises a pump, a tube, a wound covering and a wound-packing material. A pressure-distributing element is used as a wound-packing material, which element comprises an element of closed cell foam, which is flexible and resilient so as to provide a comfortable wound-packing material. The porosity of the element is only slightly changed during the influence of negative pressure. This gives an improved control over the therapy, as the pressure across the wound packing material will only alter slightly during the therapy. A pressure-distributing element of closed cell foam having perforations in at least two directions is also provided. Perforating in more directions provides more diffuse path-ways for the exudate, which may be advantageous in some situations. Finally a method of treating a wound using a negative therapy system is provided.

Description

Pressure-distributing element of closed cell foam

Field of the Invention

This invention relates to the field of negative pressure wound treatment and to a pressure- distributing element for use as a wound-contacting element.

Background

Applying negative pressure to wounds is particularly useful to promote wound healing of high exudating wounds or wounds, which have difficulty in healing. This process is typically called negative pressure wound therapy (NPWT). For this purpose, a system comprising a pump for providing the negative pressure, a film for covering the wound thereby forming an enclosure and a tube for connecting the pump to the enclosure may be used. When such a system is used it is beneficiary to use a wound-contacting element in form of a pressure-distributing element in connection with the system. When using a pressure-distributing element the negative pressure is distributed over a larger area so suction is applied to almost the complete area covered by the pressure-distributing element. If no pressure distribution were present, suction would only be applied to the area in the near vicinity of the inlet to the tube. If negative pressure were to be applied to a cavity wound without a pressure-distributing element, the edges of the wound may tend to close and heal the wound from the top. In worst case the edges will touch each other and grow together leaving a fistula below. To avoid this situation it is useful to apply a pressure-distributing element into the wound so it also act as a filler preventing collapsing of the wound edges during the negative pressure therapy.

If the exudate stays in the wound for long time the risk of maceration and infection in the wound increases. For chronic wounds there is another risk factor due to the fact that MMP's (Matrix Metallo proteases) then may inhibit optimal wound healing. When the number of MMP's gets too high, as they may in chronic wounds, the MMP will have a tendency to decompose the essential growth factors.

Usually, elements having a high porosity are used so as to be able to remove the exudate from the wound cavity. When using an element of open-celled foam, the porosity will need to be rather high due to comfort reasons. If the porosity gets too low, the open-celled foam element would be rather hard and uncomfortable to wear. However, a high porosity delays transportation of exudate from the wound bed and away, in that sense that the porosity can be considered a delay volume. If a cavity ulcer has volume of 100ml at e.g. 150mmHg negative pressure and is filled with open-celled foam, the porosity of 80% means that the delay volume is 80ml. An exudation of e.g. 20ml per hour will lead to a time for exudate to actually leave the cavity of 4 hours. If, on the other hand the porosity is lower e.g. 40%, the delay volume is just 40ml and the time for exudate to leave the cavity is just 2 hours. In other words, delay volume of the wound dressing is defined as volume fraction where exudate can be flow. Due to this a high porosity during negative pressure therapy is undesirable.

Another problem with the present commercial available dressings is the relatively large compression or contraction of the dressing when negative pressure is applied. The relatively large compression or contraction of the dressing results in reduced porosity, flexibility or conformability and increased hardness. The reduced porosity may result in clotting of the dressing and hence cause a pressure difference across the dressing resulting in an unknown negative pressure for the treatment. The reduced flexibility or the increased hardness may also result in discomfort for the patient or in worse cases in forming of pressure necrosis.

Accordingly, there is still a need for a pressure-distributing element which has a porosity balanced so as to enable the removal of the exudate from the cavity while at the same time prevent the delay volume from being too large during negative pressure therapy. Finally, the element is mechanically flexible and resilient so as to provide for the necessary shape adaptability to the wound cavity.

Description of the Related Art

WO02/43634 provides a thin flexible member comprising a plurality of discrete holes. The member is made of generally non-compressible and non-porous material, e.g. medical grade silicone. The element has channels extending radial from a port for removing exudate, which is provided on the topside of the dressing. Further concentric channels insure an interconnection of the channels.

WO2005091884 provides different wound packings, which is all made of fibres. Examples are: Batting of fibres, corrugated 3-d structure of spun-bonded fibres, spiral wound packing, hollow tubes wound packing. All of the wound packings are resilient, as the material should be able to regain at least most of its initial volume. High void volume is preferred as it makes the wound packing more deformable.

WO2005102234 provides a wound-packing material of felt material e.g. polyester felt material. It may also be weaved or knitted polyester material. Ingrowths are promoted due to "dimples" in the wound-packing material.

Summary of the Invention

The invention provides a system for use in negative pressure therapy, which system comprises a pressure-distributing element for use as a wound-contacting element, where the pressure-distributing element comprises perforated closed-cell foam. By using an element comprising closed-cell foam, the element will have a cushioning effect, as the air- filled closed cells will provide a resistance to compression during influence of negative pressure, which is markedly different from the open-celled foam.

Furthermore, the air-filled cells of the closed-cell foam will not collapse entirely during negative pressure therapy. In use-condition, the closed cells will be only slightly compressed and will substantially maintain their original volume. This means that the pressure-distributing element maintains most of its original porosity during the negative pressure. As the original porosity is almost maintained during the therapy, the original porosity may be lower and still ensure that the exudate from the wound is able to permeate easily through the element during the therapy. Maintaining the original porosity also means maintaining the original flexibility and softness of the dressing and hence reducing the discomfort as a result of a hard element for the patient. Finally, maintaining the porosity of the element during therapy will enable maintaining control of the pressure difference across the element. Thus control of the treatment will be preserved.

Besides the abovementioned advantages, a perforated closed cell foam will also provide for less linting when cutting to match the size and shape of a cavity wound. This is due to the non-porous structure of the closed cell foam.

If granulation ingrowths were to make the pressure-distributing element adhere to the wound bed, the element has to be perforated and granulations would have to grow into at least two perforations, through the perforations to a point, where a connection between the granulations may be established. This amount of ingrowths is very unlikely to occur within the normal stay time of a pressure-distributing element in the wound cavity, hence the element would not adhere to the wound bed and it would be easy and fast to remove from the wound. This would further cause less pain and/or discomfort for the user and the newly formed tissue in the wound will not be torn.

Detailed Description of the Invention One aspect of the invention concerns a negative pressure therapy system comprising a pump, a tube, a wound covering and a wound-contacting element in form of a pressure- distributing element, which pressure-distributing element comprises a closed-cell foam element.

This aspect of the invention provides a negative pressure therapy system (NPWT-system) with improved effects compared to other systems known and in use. Using a closed-cell foam element will help prevent ingrowth into the pressure-distributing element during the NPWT.

As the name implies, closed-cell foams have closed cells - that is individual cells, which has almost no connection to neighboring cells. Of course few of the cells may be connected but most of the cells will be present as individually closed cells in the foam. When an element comprising closed-cell foam is used in connection with NPWT the exudate will only negligibly be able to permeate into the cells so most if not all of the cells will remain air-filled during use. This will provide the element with a cushioning effect.

The pump may be any type of pump well-known in the art and may be motorized or hand- powered.

In an embodiment the system comprises a canister in connection with the pump. This provides for a container for the exudate to be contained in during the therapy.

The pressure-distributing element may comprise perforations in at least one direction through the element. Perforations in the element will enable an easier removal of the exudate through the pressure-distributing element, as the exudate will be able to leave the wound through the perforations.

Preferably, the closed-cell foam element is flexible and resilient. By flexible is meant that the element should be able to conform to the wound cavity so as to provide for a good pressure distribution through out the cavity. In other words the element is bendable. Furthermore, the flexibility of the pressure-distributing element provides a wound-contacting element, which is comfortable and easy for the user to conform to the wound bed.

The resiliency of the element implies that the element will deform elastically at least under the normal in-use condition. This means that the element will deform under influence of pressure but will return to its former shape and configuration when the pressure is removed. In other words there is a linear correlation between the pressure on the element and the deformation of the element - at least during the conditions under which the element will be used.

Furthermore, the element should provide a cushioning effect so as to reduce the discomfort of the wearer during the therapy. That is the element should be slightly compressible but provide a certain resistance to compression. As the element is only slightly compressed during the therapy, the element maintains its flexibility and cushioning effect hence it remains comfortable for the user throughout the therapy. The compressive strength corresponding to 50% compression of the closed cell foam is typically in the range 8 - 100 kPa. The ability to prevent collapse of the element is also particularly useful when negative pressure is applied, as it allows the user to maintain control over the pressure during the therapy.

A closed-cell foam element will almost maintain its original porosity during the therapy due to the cells being only slightly compressible during the in-use condition. Maintaining the porosity during the therapy will lead to a better control of the therapy due to a maintained pressure difference across the element. The original porosity corresponds to the porosity the element has in an un-loaded condition. By unloaded condition is meant a condition in which, the structure is not subjected to any kind of pressure or load. E.g. the condition corresponds to the structure lying on the table under normal atmospheric condition and without being touched by anything. The in-use condition is a condition, where the structure is subjected to negative pressure. Usually negative pressure values between 50 - 200 mm Hg are used.

The porosity of the element as expressed by the amount of air enclosed in the element is preferably between 50% and 95%, more preferred between 60% and 80%. Material used for the closed cell foam is preferably PU-foam (Poly-Urethane foam). Other materials for the foam may be PVA (Poly-Vinyl-alcohol) or EVA (Ethyl-Vinyl-Acetate) or silicone, which is foamed using a gas. Another possibility is to use a thermoplastic elastomeric material such as SEBS (A tri-block copolymer of Styrene-ethylene-butadiene- styrene), SIS (Styrene-lsoprene-Styrene polymer), PIB (Poly-lsobutylene polymer) or PE (Polyethylene polymer). A commercially available example is Pebax ® foam, which is a polyether block amide thermoplastic elastomer (TPE). The TPE Pebax ® is produced by Arkema and is foamed by Sekisui Alveo AG.

The perforations preferably have a circular cross-section but other shapes of the cross- section, such as angular, diamond or oval are also possible. Another possibility is to make the cross-section of the perforations clover-shaped or shaped like a jigsaw piece. The size of the circular, angular, diamond or oval perforations is preferable 1-5 mm in the largest dimension of the cross-section. For the clover-shaped or jigsaw piece perforations the largest dimension of the cross-section is preferably between 2-7 mm. The perforations may be made using one of the following well-known processes: punching, piercing, water- cutting, laser-cutting, inserting heated mandrels or by rolling by spiked drums.

The gaps of the perforations are defined as the point where the perforation communicates with the wound bed in a use-situation - that is the inlet to the perforation at a surface of the pressure-distributing element. The distance between the gap of a perforation and the gap of the perforation adjacent to it may be approximately 1 mm or more. In an embodiment of the invention, the perforations of the pressure-distributing element have gaps at a surface of the pressure-distributing element and the surface of the pressure-distributing element may be deformed between the gaps of the perforations. Usually closed cell foam element will have a smooth or plain surface without any bumps, indentations or other kinds of irregularities. If the surface of the foam element is smooth the exudate, which is between gaps, will move along the surface to a gap nearby and then it will travel along the perforations to the top of the element from where it will be removed by suction. It will be able to move along the smooth surface as the wound bed has indentations and bumps, which will provide the necessary pathways for the exudate. A deformed surface having bumps or indentations can be provided by hot stamping, channeling or calendaring. A bumpy surface may ensure that the element touches the wound bed only in points corresponding to the top of the bumps. Then the exudate will be able to travel between the points and subsequently through a gap into a perforation. More preferred the bumps and indentations are provided such that the surface of the pressure-distributing element is raised between the gaps and has indentations surrounding the gaps. This embodiment ensures that all of the gaps are placed at low points of the surface thereby providing the prime access to the perforations. Furthermore it ensures that all of the gaps are useful for removal of exudate, as none of them will be placed in the contact points between the element and the wound bed.

In an embodiment, the pressure-distributing element has perforations in at least two directions through the element and in a related embodiment the pressure-distributing element has perforations in at least three directions. Perforations in several directions may be advantageous in connection with cavity wounds. It will assist a fast removal of the exudate from the entire wound cavity due to suction being provided over the entire surface of the element, which is in contact with the wound tissue.

The element may be placed in the wound according to the wound cavity. For wounds having a cavity of a few mm's or more the pressure-distributing element may be placed in the wound having the perforations extending mostly from bottom of the cavity to the top of the pressure-distributing element. The pressure-distributing element may also have perforations extending in an oblique angle to this direction for providing suction from the sides of the wound.

For wounds having a larger cavity the pressure-distributing element may be rolled or curved and placed sideways to the regular placing of the element.

The angles between the perforations in different directions are defined as the smaller angle between the two directions that is the angle having a value of between 0 and 90 degrees. Preferably the angles between the directions is between 10 and 80 degrees, more preferred between 20 and 70 degrees such as between 30 and 60 degrees and most preferred between 40 and 50 degrees.

Preferably the perforations of the pressure-distributing element are straight, but they may be curved or bent. For the curved or bent perforations the angle of the direction of the perforation is defined as a straight line through the element between the two gaps making out the inlets to the perforation. Straight perforations will provide the most direct way for the exudate through the element. Furthermore, straight perforations will be easier to make. Another aspect of the invention concerns a pressure-distributing element particularly for use as a wound-contacting element in connection with negative pressure therapy, the element comprising a closed-cell foam element, which closed-cell foam element is flexible and resilient and where the pressure-distributing element has perforations in at least two directions through the element.

An element that is perforated in at least two directions through the element has the advantage that it may be able to provide suction from the entire surface of a wound, particular if the wound is a cavity wound. It will assist a fast removal of the exudate from the entire wound cavity due to suction being provided over the entire surface of the element, which is in contact with the wound tissue.

The pressure-distributing element may also have perforations in at least three directions through the element, which will lead to more diffuse path-ways for the exudate through the element. In a use-situation the pressure-distributing element may in some situations be subjected to pressure in one direction particularly. More diffuse path-ways would in these situations assist in keeping some path-ways for the exudate open such that the exudate can be removed from the wound bed.

A still further aspect concerns a method of treating a wound using negative pressure therapy, the method comprising cutting a pressure-distributing element to fit the wound cavity or flat wound - placing the cut-out element in the wound cavity or at the wound surface covering the element and the wound with a cover film to form an enclosure connecting the enclosure to a pump via a tube applying negative pressure to the wound for a predetermined period

The negative pressure may be applied in several periods during the treatment or it may be applied as a continuous low pressure for a longer period. The periods may be e.g. 5 min under pressure followed by 2 min without pressure followed again by 5 min under pressure and so forth when using the alternating method. A typical period for treatment may be 7-30 days and the pressure-distributing element is typically changed every 1-3 days. During change there is no application of negative pressure.

Brief Description of the Drawings

The invention is disclosed more in detail with reference to the drawings in which Figure 1 illustrates a side view of an element according to the invention provided with perforations in one direction only,

Figure 2 illustrates a side view of an element according to the invention provided with perforations in two directions,

Figure 3 illustrates an element according to the invention provided with perforations in three directions,

Figures 4-6 illustrate the same element as shown in figure 3 with a cutting through different sides thereby illustrating the perforations through the element.

Description of the Preferred Embodiments The invention is now explained more in detail with reference to the drawings showing preferred embodiments of the invention.

Figure 1 illustrates a preferred embodiment of an element 1 according to the invention having perforations 2 in one direction only. Preferably the element is placed with the perforations perpendicular to the wound bed.

The perforations 12 are in this embodiment placed such that they extend mainly perpendicular to the wound bed W. The perforations 13 are placed at an angle β thereto. The angle β defines the smallest angles between the directions of the perforations 12 and 13.

Figure 3-6 illustrate yet another embodiment of an element 21 according to the invention where the element 21 is provided with perforations 22, 23, 24 in three directions. The perforations 22 are preferably placed such that they are perpendicular to the wound bed while the perforations 23 are at angle α thereto and perforations 24 at an angle β thereto. The angle α defines the smallest angle between the direction of the perforation 23 and the direction of the perforation 22 and likewise the angle β defines the smallest angle between the direction of the perforation 24 and the direction of the perforation 22.

Claims

1. A negative pressure therapy system comprising a pump, a tube, a wound covering and a wound-contacting element in form of a pressure-distributing element, which pressure-distributing element comprises a closed-cell foam element.

2. A negative pressure therapy system according to claim 1 further comprising a canister in connection with the pump.

3. A negative pressure therapy system according to any of claims 1 or 2, wherein the pressure-distributing element comprises perforations in at least one direction through the element.

4. A negative pressure therapy system according to any of the previous claims, wherein the closed-cell foam element is flexible and resilient.

5. A negative pressure therapy system according to any of the previous claims, wherein the compressive strength according to 50% compression is between 8 kPa and 100 kPa.

6. A negative pressure therapy system according to any of the previous claims, wherein the air enclosed in the pressure-distributing element in the unloaded condition is between

50% and 95%.

7. A negative pressure therapy system according to any of the previous claims, wherein the size of the perforations of the pressure-distributing element is between 1-5 mm.

8. A negative pressure therapy system according to any of the previous claims, wherein the cross-section of the perforations of the pressure-distributing element are circular.

9. A negative pressure therapy system according to any of the previous claims, wherein the perforations of the pressure-distributing element has gaps at a surface of the pressure-distributing element and where the surface of the pressure-distributing element is deformed between the gaps of the perforations.

10. A negative pressure therapy system according to claim 9, wherein the surface of the pressure-distributing element is raised between the gaps and has indentations surrounding the gaps.

1 1. A negative pressure therapy system according to any of the previous claims, wherein the pressure-distributing element has perforations in at least two directions.

12. A negative pressure therapy system according to any of the previous claims, wherein the pressure-distributing element has perforations in at least three directions.

13. A negative pressure therapy system according to any of the previous claims, wherein the perforations of the element are straight.

14. A pressure-distributing element particularly for use as a wound-contacting element in connection with negative pressure therapy, the element comprising a closed-cell foam element, which closed-cell foam element is flexible and resilient and where the pressure- distributing element has perforations in at least two directions through the element.

15. A pressure-distributing element according to claim 14 wherein the pressure- distributing element has perforations in at least three directions through the element.

16. Method of treating a wound using a negative pressure therapy system according to any of claims 1-13, the method comprising - cutting a pressure distributing element to fit the wound

- placing the element in or at the wound

- covering the element and the wound with a cover film to form an enclosure

- connecting the enclosure to a pump via a tube

- applying negative pressure to the wound for a predetermined period

17. Method of treating a wound according to claim 16 wherein the negative pressure is applied in alternating periods during the treatment.