Flexible flocked dressing

Abstract

A wound surface is protected by a wound dressing consisting of a moisture permeable elastomeric film whose moisture permeability is in the order of that of the intact human skin to which is adhesively flocked a layer of tissue compatible and tissue absorbable fibers, such as polyglycolic acid. All tissue contacting material is absorbable by living tissue so that any material which is trapped within the wound is absorbable.

Description

BACKGROUND OF THE INVENTION

The primary concerns is with the treatment of human patients and, to some extent, animals, which have incurred severe burns or tissue damage which leaves a substantially exposed wound. One purpose is to convert the contaminated and open wound to a clean and closed wound in the shortest time possible.

It has been customary to use cadaver skin or porcine skin among others to protect wounds and to aid in the development of granulation tissue prior to autografting.

The wound dressing should decrease pain, reduce protein loss, reduce evaporative heat and water losses from the wound surface and prevent further contamination. It is desirable that the use of the dressing results in decreasing existing bacterial growth in the wound. At times a bleeding wound or wound losing plasma rapidly is present as a part of a larger wound and the dressing should aid in minimizing blood or plasma loss. It is desirable that the dressing remain flexible and adherent to the wound at all times and be sufficiently flexible to permit at least some flexing of the wound surface. The desired degree of flexing to some extent varies with the location of the wound. For example, a wound surface adjacent a joint should preferably have greater flexibility than a wound adjacent a less flexed area such as the chest or back.

In general, the requirements for a wound dressing, particularly a burn dressing, are known and recognized.

DESCRIPTION OF THE PRIOR ART

The use of polyglycolic acid is disclosed in a series of patents and applications to Schmitt, et al.:

U.S. Pat. No. 3,297,033, Schmitt and Polistina, Jan. 10, 1967, SURGICAL SUTURES, discloses polyhydroxy-acetic ester absorbable sutures. The material is also called polyglycolic acid, and is disclosed as permitting small quantities of comonomers to be present, such as dl-lactic acid, its optically active forms, homologs and analogs. A small quantity is recognized by the art as up to 15%, as shown by U.S. Pat. No. 2,668,162, Lowe, Feb. 2, 1954, PREPARATION OF HIGH MOLECULAR WEIGHT POLYHYDROXY-ACETIC ESTER.

U.S. Pat. No. 3,463,158, Schmitt and Polistina, Aug. 26, 1969, POLYGLYCOLIC ACID PROSTHETIC DEVICES, discloses surgical uses of polyglycolic acid, and incorporates definitions of some terms.

U.S. Pat. No. 3,620,218, Schmitt and Polistina, Nov. 16, 1971, CYLINDRICAL PROSTHETIC DEVICES OF POLYGLYCOLIC ACID, lists many uses of polyglycolic acid.

U.S. Pat. No. 3,736,646, Schmitt and Epstein, June 5, 1973, METHOD OF ATTACHING SURGICAL NEEDLES TO MULTIFILAMENT POLYGLYCOLIC ACID ABSORBABLE SUTURES, discloses surgical elements of a copolymer containing from 15 to 85 mol percent glycolic acid and 85 to 15 mol percent lactic acid.

U.S. Pat. No. 3,739,773, Schmitt and Polistina, June 19, 1973, POLYGLYCOLIC ACID PROSTHETIC DEVICES, claims particularly bone pins, plates, nails and screws of polyglycolic acid.

U.S. application Ser. No. 365,656, Schmitt and Polistina, May 31, 1973, SURGICAL DRESSINGS OF ABSORBABLE POLYMERS, now U.S. Pat. No. 3,875,937 Apr. 8, 1975, discloses additional subject matter on surgical dressings of polyglycolic acid.

U.S. Pat. No. 3,739,773, supra, lists a number of U.S. patents on methods for preparing polyglycolic acid and starting materials therefor.

In U.S. Pat. No. 3,620,218, supra, in Column 2 are listed a number of medical uses of polyglycolic acids, including in Column 2; line 52, knitted or woven fibrillar products, including velours, and mentioning specifically in line 53, burn dressings; line 57, felt or sponge for liver hemostasis; line 63, foam as absorbable prosthesis; and in lines 74 and 75, burn dressings (in combination with other polymeric films).

The use of gauzes, felts, and knitted fabrics as a wound dressing is quite conventional. The use of collagenous products as a sponge or pad has been disclosed. The requirements for surgical dressings are varied and more satisfactory dressings than presently available are constantly in demand.

U.S. Pat. No. 3,526,224, R. M. Potts, Sept. 1, 1970, DRESSING, discloses an occlusive dressing designed to act as a synthetic skin which has an elastomeric polyurethane film having a water vapor transmission rate of 150 to 500 g/m.sup.2 /24 hrs. laminated to a knitted velour fabric. A tricot fabric of 30 denier textured 6.6 nylon yarn is suggested. The pile or nap side of the knitted velour forms the wound-contacting side of the dressing.

Studies are being made by and for governmental agencies on burn protection. One such "Development of a Synthetic Polymer Burn Covering" prepared by Dynateck R/D Company, for the Office of Naval Research, June 1973, National Technical Information Service AD-761,631 discloses the use of polymeric films, including lactic acid polymers, and 75/25 lactic/glycolic copolymers, and the disadvantages of flat, solvent cast films. A normal insensible water loss from the human body is given as 2.2 mg/hr cm.sup.2, quoting Treger, "Physical Functions of the Skin", Academic Press, New York.

The complete disclosures of the above patents and articles are hereby herein incorporated by this reference thereto.

SUMMARY OF THE INVENTION

This invention relates to a wound dressing, particularly adapted for major burns in humans in which at least a part of the skin has been destroyed or removed and which underlying tissue is subject to moisture and liquid loss and bacterial contamination which dressing comprises an exterior surface of an elastomeric material such as polyurethane which has a moisture permeability of the order of that of the intact human skin and to which is adhesively flocked a layer of fibers of a tissue compatible and absorbable material which fibers are preferably predominantly at about right angles to the elastomeric layer and which are so spaced as to permit the invasion of granulation tissue and which can be removed from the granulation tissue without pulling off such granulation tissue and with minimum damages to the developing granulation tissue to leave a bed for autografting or other subsequent treatment.

The fibers themselves are absorbable by living tissue so that any of the fibers which are trapped within the wound are absorbed by the living tissue without deleterious effects.

The present wound dressing may be used on almost any type of wound in which the skin is broken and body fluids, particularly blood and serum, are released by the wound. It is primarily designed for major burns in which a substantial area of the skin of a human is destroyed, a third degree burn, leaving underlying tissues which are either contaminated, or subject to contamination by bacteria, or other contaminants, and which wound is of such a size that immediate protection of the tissue surface is required. It is desirable to change the wound from a contaminated and open wound to a clean and closed wound in the shortest time possible, to decrease pain, and to minimize protein loss, reduce evaporative heat and water losses, and prevent further contamination during the time required for the underlying tissues to build up a granulating surface which will accept a skin autograft.

By skin autograft is meant skin taken from another area of the subject, and which is living so that when placed on the granulating tissue, the skin will graft to the granulating tissue and grow providing a skin surface at the wound area. With rare exceptions, the skin of any other subject will be rejected and not graft to the wounded subject. The subject's own skin grafts to properly prepared granulating tissue and will grow so as to enlarge the skin covered area. With major burns, a sufficiently large portion of the subject may be burned so that sites for donor skin are limited and it is necessary to protect burned areas for a prolonged period until graft donor sites can regenerate and be used for a subsequent graft.

The generalized subject of burn treatment of this type is fairly well recognized as are many of the requirements for such a wound dressing. The medical profession recognizes the need for improvements in burn site protection during burn treatment. Survivability after major burns has been improving -- the present invention contributes towards such improvement.

The use of a synthetic tissue absorbable dressing eliminates many disadvantages of prior art dressings, particularly as to availability, and represents a substantial step forward in burn treatment.

The dressing should conform to the surface of the tissue. Conformation comprises an assessment of the suppleness, resiliency, anad dressing's ability to mimic the topography of the wound in such a fashion that there is a minimum gap between the tissue and the dressing which minimizes air gaps and pools of liquid. If pools of liquid build up, whether of serum or blood, such pools become sites for the growth of undesirable microorganisms. If the dressing conforms adequately to the surface of the wound, the body's own defense mechanisms are effective up to the zone of contact with the dressing, and bacterial contamination is minimized. In many instances, the body's defense mechanisms can clean a protected contaminated wound and permit the growth of granulation tissue even though the wound was initially contaminated.

In modern hospital technology, any area not known to be surgically clean must be regarded as contaminated or at least suspect, and treated as if contaminated.

For proper protection of the tissue surface, the gross escape of liquids such as serum or blood needs to be prevented by the dressing and the tissue needs to be protected from the atmosphere, but at the same time just as natural skin permits the escape of a certain amount of moisture, a wound dressing must permit the escape of at least some moisture to prevent the dressing from being lifted by the underlying flow of fluids. If the rate of moisture loss is too high, there is a cooling effect from the heat required to convert the liquid to vapor; and electrolytes, proteins, and other materials in the underlying fluid concentrate and crust on the surface, or under the dressing, which leads to complications. It is desirable that the permeability be of at least approximately that of the intact human skin (which is found to be about 2.2 mg./sq. cm./hr.) and may be several times this value. A permeability of 4.7 mg./sq. cm./hr. has been found effective under many conditions. The values are approximate as different skin areas lose moisture at a different rate and, depending upon the temperature of the subject, the temperature of the atmosphere, the movement of ambient air and under other variables, the natural skin has a considerable range of skin moisture loss. The natural skin is adaptable to a wide range of environmental conditions so that if the wound dressing has a moisture loss which is approximately that of the intact human skin and remains within this range of acceptable conditions, the underlying tissues are protected and regenerate. There is a fine and, perhaps, unascertainable line between the regenerative processes of the tissue when protected from adverse effects and the increase that might be caused by dressing characteristics and environmental factors. It is not necessary to ascribe the rate of healing to any special set of factors. It is merely found that by using the present wound dressing, rapid healing is encouraged.

For adequate conformation, the wound dressing must be flexible so that it can conform to the topography of the wound and at the same time it must be sufficiently flexible that as the tissues move, the wound dressing can move with them. For instance, if the skin adjacent to a joint is injured, flexing of the joint and movement of the underying tissues requires that the wound dressing have some flexibility. The minimum required flexibility is exceeded by the present dressing and the dressing is sufficiently flexible for tissue movement over joints and other areas.

Basically, the tissue-contacting portion of the dressing is a flock of tissue compatible material which is substantially absorbed by living tissue within a period of about 90 days and which fibers maintain their integrity for at least about 3 days.

A flock of fibers of the order of 0.5 to 12 denier and from 10 to 30 mils long which are flocked onto an elastomeric layer gives protection to the wound surface.

It is desirable that the fibers be absorbable by living tissue as characteristics of a flocked surface are such that some fibers are not tightly held, and some of the fibers may remain in the wound, and non-absorbable materials can be the source of undesirable side effects.

A preferred tissue absorbable polymer is polyglycolic acid, such as described in the Schmitt patents above and which is meeting with commercial success as a suture. Polymers in which tissue absorption results from the hydrolytic degradation of glycolic acid ester linkages give good results. Because strength of the fibers is not a major requirement, a copolymer containing considerable lactic acid makes a good dressing. Such polymers are disclosed in U.S. Pat. No. 3,736,646, supra.

A polymer having an ordered configuration of glycolic acid units and lactic acid units which is tissue absorbable is described at length in Ser. No. 435,365, Jan. 24, 1974, Augurt, Rosensaft, and Perciaccante, UNSYMMETRICALLY SUBSTITUTED 1,4-DIOXANE-2,5-DIONES.

Another absorbable polymer which may be used for the graft is poly(N-acetyl-D-glucosamine) such as described in U.S. Ser. No. 441,717 filed Feb. 11, 1974, Richard Carl Capozza, POLY(N-ACETYL-D-GLUCOSAMINE) PRODUCTS.

The important thing about the tissue absorbable polymer is that it be of a material which is not deleterious to living human tissue and that it be spinnable as a fiber which forms a fine structure such that blood and other fluids do not flow rapidly therethrough and it has sufficient strength to maintain its integrity during the manufacture of a flock and that it maintains its integrity in contact with the tissue long enough for granulation tissue to form and yet is absorbable within a reasonable length of time, for instance, about 90 days, so that it does not remain as a foreign body after the wound has healed.

The above two patent applications, the disclosures of which are herein incorporated by this reference thereto, give examples of such materials.

Inasmuch as the useful characteristics of such materials are largely as a function of size, shape and structure, these materials may be substituted for the polyglycolic acid fibers described in more detail in the following examples.

The fibers which conveniently are spun in about 1 to about 12 denier are adhesively flocked to the elastomeric backing layer. By using an electrostatic charge, as is conventional in flocking systems, the fibers are caused to stand on end and are predominantly at right angles to the elastomeric layer. The fibers may be adhesively united to the elastomeric layer by using the adhesive characteristics of the elastomeric layer as it is formed. More conveniently, when the elastomeric layer is formed, a separate adhesive layer is placed thereon and the flocked fibers are placed on such adhesive layer and caused to stand on end elastrostatically.

The elastomeric layer may be any material which is permeable to moisture, has a low Young's modulus and is thus readily conformable to the wound surface. A particularly useful material is polyurethane. A soft, flexible elastomeric layer of polyurethane of the order of 2 mils thick provides a barrier to excessive water loss, is permeable to moisture within the range of that of the intact human skin, which is approximately 2.2 mg./sq. cm./hr., to two to four times this value, which permits moisture to pass through the backing layer at such a rate that formation of liquid pools under the dressing is minimized, and yet the water loss is within a desirable range as regards heat loss and concentration of dissolved components in the body fluids which are underneath the dressing.

At the time of use, the wound should be debrided in accordance with usual techniques and substantially dried so that there is no standing liquid on the surface of the wound. Then, the soft flocked surface of the wound dressing is placed in contact with the wound, being sure that it conforms to the topography of the wound surface so that there are no gaps or spaces between the tissue and the dressing; with the dressing being held in place by adhesive tape, additional bandages, or suturing. A low pressure bandage may be used to hold the dressing in place, depending upon the location of the dressing and the condition of the patient. The dressing is permitted to remain in place for approximately seven days. If less than 4 days in most subjects, there is not sufficient time for adequate granulation tissue to grow under a dressing and if more than 14 days, too much granulation tissue may grow and result in scar tissue. At times a wound must have a first dressing applied and be permitted to heal so that granulation tissue is formed in part on the wound and then additional debridement or other treatment is undertaken in other areas, requiring a second wound dressing application to encourage the growth of additional granulation tissue. There are times when many treatments are required before the wound is in condition for autografting or before skin for autografting becomes available. For major burns or traumatic tissue damage, prolonged treatment may be required before the wound is ready for final grafting.

In other instances, a wound may be fairly minimal and the present wound dressing may be applied even though a less adequate wound dressing could have been used and a single application permits substantial healing. Different areas of the same wound may require different treatment.

The present wound dressing in particular functions as a temporary synthetic skin, giving a protective covering to any area of a body from which the skin is removed and the underlying tissues are exposed with the covering not interfering with normal physiological processes conducive to wound healing and autograft conditioning.

The composite structure provides both a good moisture barrier and bacteria barrier. The conformability resulting from the elastomeric backing permits conformation to nearly any wound topography while the short fibers protruding from the flocked surface insure intimate contact and wetting at the wound surface which provides an intimate contact with the tissue absorbable fiber during the healing process. Because the flocked surface is absorbable, there is no problem resulting from biological rejection of the flocked material and there can be no deleterious entrapment in regenerating tissue in tangled fibers, as can be the case of a sponge or woven web.

As shown in the attached drawing, a polyurethane such as described in U.S. Pat. No. 3,582,423, Wang, June 1, 1971, PROCESS FOR COATING POROUS SUBSTRATES, and sold as Helastic 13141 polyurethane, is cast on a release coated paper to form a film with a thickness of 2 mils. The material is a reaction product of a hydroxy terminated polyester such as diethylene glycol adipate and p,p'-methylene dianilane and a mixture of 2,4- and 2,6-toluene diisocyanates, at about 25% solids. The polyester type segmented polyurethane is permitted to harden to form a water vapor permeable elastomer layer, and then coated with an additional half a mil thickness of the same polyurethane.

The polyurethane structure may be graphically described as:

NH.sub.2 --R.sub.1 -- NH--CO--NH--R.sub.2 --NH--CO--O--R.sub.3 --O--CO--NH--R.sub.2 --NH----CO--NH--R.sub.1 ].sub.n NH.sub.2

where, ##SPC1## ##EQU1## or --CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 -- O--CH.sub.2 --CH.sub.2 --CH.sub.2 --CH.sub.2 ].sub.m

The polyurethane film is cast by pouring the resin dissolved in solvent on a release paper such as a silicone coated release paper, which is pulled through rollers set to leave about 4 mils of 25% solids solution on the release paper, so that when dry a 2 mil layer remains. After a second pass to leave an additional adhesive coat which dries to about 0.5 mil thickness, there are flocked 2 denier polyglycolic acid fibers approximately 25 mils long with the fibers being subjected to a strong electrostatic field, in accordance with conventional procedures, to cause the fibers to stand at approximately right angles to the field and, hence, at right angles to the backing, while the polyurethane adhesive layer cures. The thus formed flock is shaken and then blown with air to remove any loose fibers, after which the flocked sheet is cut into 2 inch .times. 3 inch rectangles for individual dressings.

As a surgical device, it is obviously desirable, almost mandatory, that the wound dressing be sterile at the time of use. The wound dressing may be sterilized by an appropriate sterilizing cycle using ethylene oxide as a sterilizing agent. Radiation sterilization may be used, as may heat sterilization.

If ethylene oxide is used to sterilize, it is convenient that the ethylene oxide be diluted with carbon dioxide or a chlorofluoroalkane to such an extent that the sterilizing gas is non-explosive. For storage stability, it is desirable that the wound dressing be protected from atmospheric influences. Because the wound dressing contains hydrolyzable polyglycolic acid ester linkages, the linkages can be hydrolyzed by ambient moisture under room storage. The wound dressing requires that the flocked fiber retain sufficient strength to be separated from the wound when the dressing is changed. Preferably, it should retain strength at least 10 days to 2 weeks. It is desirable that such storage conditions be used as to maintain the wound dressing in a dry environment so that whether used immediately after packaging or after a storage period of several years, the wound dressing has the same characteristics and, hence, has known predictable attributes as far as the using surgeon is concerned.

A good method of sterilizing and storage is the same as is used for polyglycolic acid sutures on a commercial scale and as disclosed in U.S. Pat. No. 3,728,839, Arthur Glick, Apr. 24, 1973, STORAGE STABLE SURGICALLY ABSORBABLE POLYGLYCOLIC ACID PRODUCTS. As there described, the polyglycolic acid product is stored in a moisture proof envelope in which conveniently the product is packaged except for one open side and sterilized using ethylene oxide diluted so as to be non-explosive, and then while protecting sterility, the product is vacuum dried and the envelope sealed. By having the foil envelope hermetically sealed, as there taught, the wound dressing may be maintained in a usable form with consistent characteristics for a period of at least several years. Conveniently, but not necessarily, the wound dressing may be placed between two sheets of paper, or a single sheet of paper with a fold, so that the wound dressing is held in flat condition between the sheets during storage and service to the using surgeon.

A single envelope can be used, which, on stripping, releases the wound dressing folded in a sheet of paper. Such a single envelope package is shown in U.S. Pat. No. 3,017,990, Singerman, Jan. 23, 1962, STERILE PACKAGE FOR SURGICAL FABRIC.

For large sheets, the wound dressing may be folded, but for sheets up to 3 inches .times. 5 inches it is conveniently placed in an envelope large enough to hold the sheet flat. A plurality of sheets may be packaged in a single envelope if desired. Single sheets of about 3 inches .times. 5 inches are a surgically acceptable size, with the wound dressing being cut to size if necessary by the surgeon, or an assistant, at the time of use. For many surgical procedures, a single sheet is all that is required. For major burned areas, either a number of smaller sheets or a single layer sheet of the wound dressing gives good results. A series of smaller dressings gives more conformity on irregular areas. A single large sheet reduces the number of seam lines. Conveniently, the wound dressing is made available in sterile form in sheets 3 inches .times. 5 inches, 3 inches .times. 12 inches, 3 inches .times. 18 inches, 3 inches .times. 24 inches and continuous rolls, about 12 inches wide. Other sizes and shapes can be provided to supply the using surgeon with a choice of sizes, consistent with reasonable inventory demands.

At the time of use, the enclosure is stripped open, the individual dressing removed and placed in contact with the wound surface. For burn areas with adjacent whole skin, the wound dressing may be held in place by adhesive strips.

On burn test subjects, the wound is cleaned from burned tissue and other contaminants, in accordance with conventional debriding proceedings, and the wound covered by the wound dressing. After approximately 7 days, the wound dressing is removed from the wound gently to avoid stripping granulation tissue, and the wound is ready for grafting, or additional treatment.

The treatment of the wound before applying the wound dressing may include antibacterial agents, anesthetics, etc.

The time before dressing change varies with the location of the wound, and the general condition of the patient. Some heal more rapidly than others. The surgeon in charge must adapt the treatment to the specific patient.

Claims

I claim:

1. A wound dressing for the surface of living tissue from which at least part of the skin has been removed and which tissue is subject to moisture loss, and bacterial contamination, which dressing is sufficiently flexible that it will conform and adapt to the surface of the tissue to minimize pools of fluid or air between the dressing and the tissue surface, which pools generate problems of infection, and which has a permeability to moisture of the order of that of the intact human skin (approximately 2.2 mg/sq. cm./hr.) which comprises: an elastomeric layer which elastomeric layer has adhesively flocked to its surface a layer of fibers and which fibers are of a tissue compatible material which is substantially absorbed by living tissue within about 90 days, and which fibers maintain their integrity for at least about 3 days.

2. A wound dressing for the surface of living tissue from which at least part of the skin has been removed and which tissue is subject to moisture loss, and bacterial contamination, which dressing is sufficiently flexible that it will conform and adapt to the surface of the tissue to minimize pools of fluid or air between the dressing and the tissue surface, which pools generate problems of infection, and which has a permeability to moisture of the order of that of the intact human skin (approximately 2.2 mg/sq. cm./hr.), which comprises: an elastomeric layer of the order of 2 mils thick, and which elastomeric layer has adhesively flocked to its surface a layer of fibers of the order of 1 to 12 denier, and about 10 to 30 mils long, and which are predominantly at about right angles to the elastomeric layer, and which fibers are of a tissue compatible material which is substantially absorbed by living tissue within about 90 days, and which fibers maintain their integrity for at least about 3 days.

3. The wound dressing of claim 2 in which the tissue compatible material is a polymer subject to hydrolytic degradation to non-toxic, tissue compatible absorbable components, said polymer having glycolic acid ester linkages.

4. The wound dressing of claim 3 in which the tissue compatible material is homopolymeric polyglycolic acid.

5. The wound dressing of claim 3 in which the tissue compatible material is a polymer of 3-methyl-1,4 dioxane-2,5-dione.

6. The wound dressing of claim 2 in which the tissue compatible material is a polymer of N-acetyl-D-glucosamine.

7. A sterile wound dressing package comprising an interiorly sterile strippable laminate container having therein

a wound dressing for the surface of living tissue from which at least part of the skin has been removed and which tissue is subject to moisture loss, and bacterial contamination, which dressing is sufficiently flexible that it will conform and adapt to the surface of the tissue to minimize pools of fluid or air between the dressing and the tissue surface, which pools generate problems of infection, and which has a permeability to moisture of the order of that of the intact human skin (approximately 2.2 mg/sq. cm./hr.) which comprises:

an elastomeric layer which elastomeric layer has adhesively flocked to its surface a layer of fibers and which fibers are of a tissue compatible material which is substantially absorbed by living tissue within about 90 days, and which fibers maintain their integrity for at least about 3 days.

8. A method for protecting the surface of living tissue during a healing process which comprises: during a preliminary period, covering and protecting the surface of damaged tissue by emplacing thereon

a wound dressing for the surface of living tissue from which at least part of the skin has been removed and which tissue is subject to moisture loss, and bacterial contamination, which dressing is sufficiently flexible that it will conform and adapt to the surface of the tissue to minimize pools of fluid or air between the dressing and the tissue surface, which pools generate problems of infection, and which has a permeability to mositure of the order of that of the intact human skin (approximately 2.2 mg/sq. cm./hr.), which comprises: an elastomeric layer of the order of 2 mils thick, and which elastomeric layer has adhesively flocked to its surface a layer of fibers of the order of 1 to 12 denier, and about 10 to 30 mils long, and which are predominantly at about right angles to the elastomeric layer, and which fibers are of a tissue compatible material which is substantially absorbed by living tissue within about 90 days, and which fibers maintain their integrity for at least about 3 days,

permitting granulation tissue to regenerate thereunder to give a clean wound closed by said dressing,

stripping off said dressing to expose granulation tissue,

then autografting living skin to said exposed granulation tissue.

9. The process of claim 8 in which the tissue compatible material is homopolymeric polyglycolic acid.