Process for the manufacture of multilayered wound dressings

Details Process for the manufacture of multilayered wound dressings Process for the manufacture of multilayered wound dressings

2001-12-21

2004-07-20

Lewis, Kim M. (Department: 3764)

Surgery: splint, brace, or bandage

Bandage structure

Skin laceration or wound cover

C602S043000, C602S054000, C602S055000, C602S057000

Reexamination Certificate

active

06765123

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to multilayered wound dressings suitable for the management of especially chronic wounds. More particularly, the invention relates to the manufacture of these dressings in a continuous process such that large quantities of individual dressings can be produced in a repeatable and cost efficient manner.
BACKGROUND OF THE INVENTION
Wound dressings, and in particular, multilayered wound dressings are known to be useful in speeding healing of acute wounds, stimulating healing of chronic non-healing wounds and in reducing wound pain. Wound dressings include transparent adhesive films, primarily constructed of polyurethane, non-transparent adhesives such as hydrocolloids, semitransparent adhesives including hydrogels and non-transparent non-adhesives such as foams.
Hydrocolloid dressings have found widespread use especially for the management of chronic wounds, such as venostasis ulcers and decubitus ulcers. Hydrocolloid dressings also are useful for dressing certain acute wounds such as burns, donor sites and even post-surgical incisions. Hydrocolloid dressings are comprised of a suspension of fluid absorbent fillers in a pressure sensitive adhesive vehicle. Many hydrocolloid adhesive formulations have been described in the prior art. Suitable adhesive formulations may be found, for example, in the following patents, each of which is incorporated herein by reference in its entirety: U.S. Pat. No. 3,339,546; U.S. Pat. No. 4,231,369; U.S. Pat. No. 4,367,732; U.S. Pat. No. 4,477,325; U.S. Pat. No. 4,738,257; U.S. Pat. No. 4,551,490; U.S. Pat. No. 4,192,785; U.S. Pat. No. 4,952,618; WO 99/11728 and WO 99/14282.
Because the hydrocolloid is both adhesive and absorbent, these dressings can be placed in direct contact with the wound and can be adhered to the intact skin surrounding the wound. Generally they need no adjunct fixation and are thus convenient and economical to use. Hydrocolloid dressings are typically occlusive, which means they do not allow the wound to dry out and form eschar. Such dressings maintain the wound in a moist environment so that the cascade of cellular processes involved in wound healing proceeds in an optimal manner. Moreover, the moist hydrocolloid does not adhere to the wound. When a change of dressing is necessary the hydrocolloid dressing can be easily removed from the granulating wound bed without damaging the new tissues.
However, many chronic wounds are highly exudative, and one of the limitations of hydrocolloid dressings arises because of their relatively limited absorption capacity. If the dressing cannot absorb the wound exudate at a rate commensurate with exudate production by the wound, the dressing will quickly become saturated with fluid. This will cause the dressing to leak, and will cause maceration of the skin surrounding the wound. Wound exudate can be highly irritating to intact skin, and can cause the skin to break down and excoriate. Because these chronic wounds can often last for many months and even years, leakage of exudate can cause serious problems for the maintenance of healthy intact skin of the patient, and can therefore compromise effective wound management.
It is predominantly the older population that suffers from venostasis ulcers and decubitus ulcers. The market for dressings for these chronic wounds is therefore a growing one because of the changing demographics especially in developed countries. Considerable effort is being directed to development of improved chronic wound dressings, and this effort is very much directed to improve absorbency by use of composite dressing structures.
A number of approaches have been taken to develop dressings that have enhanced absorption capacity for chronic wounds. Dressings currently on the market that are indicated for heavily exuding wounds can comprise absorbent foams, such as absorbent polyurethane foams, or fibrous absorbents such as are used in dressings containing fibers of calcium alginate, or blends of sodium and calcium alginate, or fibers of sodium carboxymethyl cellulose. Examples of commercially available foam based dressings include Tielle®, sold by Johnson & Johnson, Allevyn®, sold by Smith & Nephew and Lyofoam®, sold by the SSL Company. Examples of fibrous dressings currently on the market include Aquacel®, sold by ConvaTec and Sorbsan®, distributed by Maersk Medical.
However, there are drawbacks with the use of these foam and fiber based dressings. Neither material is inherently adhesive and therefore the fibrous or foam pad must be held in place with adjunct fixation. The Tielle® product from Johnson & Johnson is available with the absorbent foam as an island pad centered on an adhesive coated microporous foam backing. While this dressing has a high capacity for fluid management, this capacity is achieved in part by transmission of water vapor through the microporous backing. Such water vapor transmission can lead to drying out of the wound, especially as the exudate level drops during the intermediate stage of wound healing. Drying of the wound can lead to significant delay in healing and even to deterioration of the wound bed by formation of eschar.
U.S. Pat. No. 5,981,822 addresses this problem. This patent discloses a dressing comprising a wound contact sheet laminated to one side of an absorbent layer of water swellable material such as polyurethane foam. The wound contact sheet is provided with one or more slits. Expansion of the absorbent layer by exudate absorption causes the wound contacting sheet to expand, and the slits to open, thereby allowing passage of high flow rates of exudate. If the flow of exudate falls, then the slits close, thereby avoiding excessive drying of the wound bed.
There are many other examples of composite multilayered wound dressings in the prior art. U.S. Pat. No. 4,793,337 discloses a composite dressing having an absorbent adhesive laminated to a fibrous absorbent such as an alginate. The fibrous absorbent is further laminated to a backing material such as a nonwoven polyester fabric by means of a second adhesive layer in between the fibrous layer and the nonwoven polyester fabric.
WO 00/41661 discloses a multilayered wound dressing having an absorbent layer having a high absorbency but a low lateral wicking rate and a transmission layer having a high moisture vapor transmission rate bonded to the side of said absorbent layer furthest from the wound. The wound dressing may also include an adhesive layer for adhering the dressing to the skin surrounding the wound. The optional adhesive may be a fluid interactive hydrocolloid adhesive and may be provided with perforations to assist transport of exudates through the dressing.
U.S. Pat. No. 6,103,951 discloses a composite dressing having a polymeric cover layer bonded to a fibrous web that contains a mixture of a superabsorbent and a hydrocolloid. The fibrous web is characterized by a glazed surface of fused fibers on to which are deposited particles of hydrocolloid containing adhesive. The selvage edge of the dressing is fused to itself and to the polymeric cover layer. A process for the production of such a dressing is also described.
U.S. Pat. No. 5,681,579 discloses a hydrocolloid having a polymeric support layer which can be continuous or discontinuous, an occlusive backing layer that overlies the support layer, an optional adhesive which may be a hydrocolloid adhesive on the skin contacting surface and an optional absorbent region interposed between the support and the backing layer.
EP 0 617 938 B1 discloses a wound dressing having a non-continuous hydrocolloid-containing polymeric support layer and an occlusive backing layer overlying the polymeric support layer, with an optional adhesive on at least a portion of the wound contacting surface, and an optional absorbent region interposed between the polymeric support and the occlusive layer.
U.S. Pat. No. 5,968,001 discloses a wound dressing having a wound and skin contact layer, an upper occlusive layer with an absorbent layer in between with leak prevention seals which define an ab

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