CA1192492A - Composite wound dressing - Google Patents

Abstract

Abstract A composite wound dressing having controlled permeability, is highly absorbent toward blood and exudate and comprises a polytetrafluoroethylene fibril matrix, hydrophilic absorptive particles enmeshed in the matrix, and a partially occulsive film coated on one surface of the matrix.

Description

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COMPOSITE WOUND DRESSING

Technical Field The present invention rela es to a composite wound dressin~ which is ~i~hly absorbent towards bloocl and exudate, yet non-adherent to the wound surface, having controlled water vapor permeability.

Background Art It has been recognized in the prior art tha~ a satisEactory wound dressing creates a suitable micro-climate Eor rapid and efective healing. A good wounddressing preven~s dehydration and scab formation, is permeable to oxygen, is s~erili~able, absorbs blood and exudate, protects against secondary infection, supplies mechanical protection to the wound, is non-adherent, is non-toxic, is non-allergenic or sensitizing, does not shed loose material into the wound, conforms to anatomical contours, resists tearlng~ resis~s soilin~, is not i.nl:l~m-mable, has constant properties in a range of temperatures and humidities encountered in use, has long shelf life, has small bulk/ is compatible with medicaments, and is economical.
Layered dressings are known in the art. ~.S.
Patent No. 4,203,435 discloses a five~layered wound dressing haviny two permeable, non~adherent outer layers, the next two layers being cellulosic fiber absorbent layers, and the inner-most layer comprising a powder of modified starchO U~S. Patent No. 3,888,257 provides a layered disposable, absorbent article for management of body Eluid Elow, in which a central zone oE a matrix o:E
fiberized wood pulp incorporates a three-dimensional dispersion of hydrocolloid polymer particles.
Great ~ritain Patent No. 1,~5~,055 clisclose.s a preparation, such as.a bandage, for treating a fluid-di;cl~clr~Jing s~ surEace, which comprises a w~ter-insoluble hydrophilic macromolecular swellable material such as crosslinked dextran, carboxymethylc3extran, starch or hydroxyethyl s~arch ~or absorbance oE low molecul~r weight constituents o~ blood plasma in admixture with a dermatologically suitable carrier. The swellable material ~ay be dextran, or a derivative thereof, and the carrier ma~ comprise ~ibrous material. This patent discloses no fibrous materials having submicron diameters nor does it disclose a partial mois~ure barrier in the preparation to prevent the wounc3 Erom drying out.
A crosslinked dextran derivative which ls sold by Pharmacia of Sweden under the tradename "Debrisan", is primarily used as a wound treating powder. ~harmacia's ~rade literature on Debrisan~ asserts the following advantages or the use of the powder: "continuously absorbs wound exudate and bacteria, cleanses the wounds, l~reven~s cr~l-;t Eormation, reduces inflammation and oedema and does not cause sensitization". The trade literature which states that no side effects have been reportec3 also ~ives the following limitations on the product: "1) do not leave Debrisan~ for more than 24 hours on wounds with a very low exudation rate as it may dry and form a crust which may be difficult to wash of, ~) occlusive dressings may lead to maceration of skin around the wound und~r treatment, 3) when deep infected wounds are treated~ care must be taken to wash Debrisan~ from the depths of the woun~3, and 4) no side effects have been reported.
Warning: Debrisan~ spillage can render surfaces very slippery. Clear spillages promp~ly." Thus, it appears that although the dextran derivatives have excellent absorptive capacities, there are problems associated with their use relating to moisture loss, adhesion, contalnitlation oE the wound, ~nd handlinc~ ha~ar~l.S.

Disclosure of Invention The present invention overcomes some of these problems by providin~ a composite wound-dressing which is sheet material comprising:
(a) a polytetrafluoroethylene ~PTFE) Eibril ma-trix;
(b) Q.5 to 10 parts of hydrophilic absorptive particles per part 3f PTFE by weight enmeshed in said matrix, the absorptive particles having absorptive capacity grea~er than 0.5 ~rams of water per gram of dry particles; and (c) optionally, a partially occlusive film coated on one surface of said matrix.
By "occlusive ~ilm" is meant a layer o material havin~ controlled permeability or porosity.
When the par~ially occlusive film i5 present, such a coating has controlled permeability and it reduces the rate of evaporation of moisture out of the dressing to the atmo.sphere thereby reducing the tendency for Eormation o~ a har~enecl scab over~ ~he wound. Scab ~oelnati.on i..s undesirable because it retards healing and enhances scar formation. In addition, by slowing the moisture loss from the wound surace, the moisture barrier imparts to the wound dressing of the instant invention superior non-adheren~ properties.
The absorpti~e particles o~the present inven-tion are thoroughly enmeshed in the PTFE fibrils so that substantially all of the particles are contained in the ~brils and do not slough in the wet or dry state. Con-tamination of the wound from particulate matter ori~inating in the dressing is thereby prevented.
The composite wound dressing of the present invention has many desirable characteristics. For example, it provides an ideal microclimate Eor healin~ in tha~ i~ is highly permeable, therehy allowin~ oxygen ~o permeate the membrane. The bandage is sterilizable~ The composite is a good absorbent for blood and exudate ~.see Example 2) ancl does not adhere to the wound ~urface.

These properties exist because the absorptive particles are not in direct contact with the wound but are separated thererom by an intertwining coat of polytetraEluoro-ethylene fibrils. The dressing is particularly advanta~eous in tha-t it need not be changed every day.
The wound dressing affords rapid absorption o~ exudate and thereby draws bacteria away from the wound, he~ping to protect ayainst wound sepsis, as will be discussed below~
Dressings of the present invention can provide water absorptive capabilities as high as about 40 grams of water per gram of dressing. When a partially occlusive film is present as the outermost layer on the PTFE fibril matrix, tlle moisture transmi~sion is controlled so that th~ wouncl stays moist enough to prevent scab formation and adherence o~ the dressing to the wound surface and to permit rapid epidermal wound healing.
The composite wound dressing of the present invention consisting of a PTFE fibril matrix in which absorptive particles are enmeshed, but which has no moisture controllin~ coatin~, also has many of these desirable characteristics. Such dressings are most use~
in treating wounds which produce large amounts o~ exudate, for example highly infected wounds. In such a situation, it is desirable to change the dressing frequently, since the absorptive capacity of the dressing tends to be quickly exhausted. However, rapid evaporation of moisture prolongs the length of time ~he dressing remains absorbent on the wound. Thus, dressings both with and without moisture evaporation retarding coatings are useful, depending on the rate at which a wound is producing exudate. It is most desirable to use a dressing which absorbs exudate at approximately the rate the wound is producing exudate to prevent either dehydration o the wound or excessive accumulation oE exudate on the wound surface.
The composite dressing, a chamois-like material, is very conformable yet tough enough to provide some protecti~n against the abrasive and penetratin~ efEects of foreign objects. It maintains its physical integrity ~nder normal handlin~ condltions, is not soiled due to its chemical inertness and low surEace tension, does not physically or chemically degrade (i.e., it has good shel~
life) and the chemical and physical properties are not adversely afected by changes in temperature from -~O~C to 120C. PolytetraEluoroethylene is presente-3 at the surface directly adjacent to the wound~ The absorptive particles are not on the surface o~ the composite but are s~rongly enmeshed in ~ough PTFE Eibrils. Therefore, there is very little chance that any absorptive particles will s]ough of~ and get into the wound. The PTFE Eibrillated surface is not rendered adhesive by other materials because it is non-absorptive and non-wetted due to its unusually low sur~ace tension despite the ~act that the composite is very hydrophillic. In addition, PTFE is non-toxic, non-allargenic and nonsensitizingO
In summary, the physical properties o the wound dressing are considerably superior to ~hose of the prior art.

srief Description of Drawin~
The drawing shows a cross-sectional view, greatly enlarged, of a composite wound dressing o~ the present invention.

Detailed Description The present invention provides a co~posite wound-dressing which is a sheet material, optionally havin(~ conkrolled porosity, comprising:
(a) a polytetraEluoroethylene fibril matrix;
(b) 0.5 to 10 parts of hydrophilic absorptive particles per part o~ PTFE by wei~ht enmeshed in saicl matrix, said absorptive particles having absorptive capacity greater than 0.5 grams of water per yram of dry particle; and (c) optionally, a partially occlusive film coated on one surface oE the matrix;
wherein substantially all of ~he hydrophilic absorptive par~icles are unavailable for sloucJhing.
FIG. 1 shows one embodimen~ o a composite wound dressing 10 according to the present invention having occlusive film 12 coated on one surface of the matrix 14 vf PTFE Eibrils 16 in which are enmeshed hydrophilic absorptive par~icles 18.
To prepare the composite wound-dressing the hydrophilic particles are incorporated into a PTFE
emulsion to form a paste, which is subjected to a great amoun~ of shear causing the PTFE to fibrillate and enmesh :l5 ~he particles into a fibrillar matrix. There are many processes of Eibrillating PTFE and virtually all non-sintering processes are adaptable to the method of making the coml~o~site o the instant invention. The m~.st suitable, however, is that described by Ree et al. in U.S Patenk No.
4,153,661. Basically, the fibrillation i~volves the forma-tion of a paste of water swollen particulate material and PTFE particles, intensive mixing at 50 to 1~0C, biaxial calendering, and a drying step. This results i~ a membrane with PTFE ~ibrils having a thicXness in the range oE about 0.025 to 0.5 micrometers.
The size of the absorbent-type particles are within a broad range of 0.1 to 300 micrometers when dry.
Preferably, the particle size range oE the hydrophilic polymer absorbent is 1.0 to 80 micrometers. The particles which are insoluble in a wound environment have an absorp tive cal~aci~y c~eater than 0.5 (i.e., in tlle range o~ 0.5 ancl 40 grams) of water per gram of dry particles.
Because of its high absorptive capacity, the wound dressillcJ may be usecl to cleanse the surfaces of contaminated or in-~ected wounds. Such wounds include traumatic wounds, cuts, lacerations and abrasions, hurns, indolent wounds, pressure sores, and ulcers which may be contaminat~cl with Eoreign matter, deacl tis~ue, and micro-organisms such as bacteria and Eungi. For this cleansing purpos~ dressings oE the instant invention may be remove~
and replaced as of ten as necessary ~o remove contaminating 5 ma~erial, and then a final similar dressin~ may be lef t in place undisturbed on the cleansed surface until the wound heals. Al~ernatively, if the wound is too d~ep to heal spontaneously, after clPansing the woun~ surace in the above manner, it may be grafted~ It is to be noted that some of the cleansin~ action is brought about by the activities of cells, (e.~., leukocytes and ma~rophages) in the tissues of the body, aided by appropriate conditions oE hydration and oxygen availability brought about by the dressing. The breakdown products are removed by the I r~ c~h.50r:belll. ;.n the dressing, thus comp3eting the cl~ansing process. ~ particular advantage of the wound dressing having a partially occlùsive film of the instant invention ~ ml?~e~ wil:h other means o~ wound debri~ement is that the controlled wound environment provided herein is an intrinsic part o the dressing by reason o its controlled permeability and, therefore, there is no danger that the wound is made too soggy or is dehydrated, both of which conditions adversely afect wound repair.
The hydrophilic absorbent ma~ be particles comprised of alginic acid, polyacrylate-cellulose graft copolymer, collagen, chitin, chitosan, clay, casein~ zein, dextran, carboxymethyldextran, starch/ modified starch, hydroxyethyl starch, hydrolyzed polyacrylonitrile, s~archr methacrylonitrile polymer, polyacrylamide, hydrolyzed polyacrylamide (Separan~ AP-30 from the Dow Chemical Co.), cellulose, carboxymeth~lcellulose, an~ derivatives or mix-tures oE the aforementioned materials. The most pre~erred material is a crosslinked dextran ~erivative, having a water absorptive capacity between 2 g and 10 g of water per gram o dry material. The thickness of dressings pro-viding satisfactory volume absorption is in the range of 0.1 to 10 mm, preferably in the range oE 0.25 mm to 5 mm~

- s -Hyclrophilic absorbent particLes may he admixed with inert less~absorptive diluent particulates which ran~e in size rom 0.1 to lO0 micrometers to improve the feel and handling characteristics oE the composites and to acilitate their manufacture. Examples of diluent particles include powdered polymers such as polyethylene, polypropylene, ancl polystyrene, kaolin, talc, silica, bentonite, ai~ vermiculite.
The particulate material accounts for from 40 to 90 percent, and perferably 80-90 percent, by weight o~ the total composition, of which up to 50 percent can be inert diluent particles~ The most prefarred amount of total particulates is about 85 percent by weight.
~s noted above, if the uncoated PTFE-absorptive l5 particulates composite membrane is used as a wound- ;
treating material for extencJed periods o~ time, ~tlsre i~ a tendency ~or Eormation of a hardened scab over the wound due to excessive moisture transmission out of the dressing to the atmosphere. Thus, to render the dressing satis-~actory Eor long periods, evaporation rates must be reduced by means of a coating on one side of ~he ~andage. No coating is required for short (1-4 hours) application times, especially for wounds which produce large amounts of exudate.
The surface coating must be 1exible and not totally occlusive, e.g., a film which controls the evaporative loss to a rate which allows low levels of moisture to remain in the bandage. Coatings which allow water transmission through the wound dressing in the range of 240 to 2400 g/m2/24 hours, in vivo, measured by the desiccant method, 37~C, 75 percent relative humic]ity, modified ASTM E96-66 (reapproved 197~), Procedure A, are useful. The thickness of dressings providing these rates of water transmission is generally in the range of 0.1 to 5 millimeters, the thickness of the coating on the surface of tlle dressing bein~3 in the range o~ 2 to 200 microns~
Suitable coatings can be achieved with any material that wi.l l. res~r.i~ he passage o~ water moleculPs, incluc7ing s.il icol~e, ure thane, and acrylate polymers .
Medicaments which may be useful in promoting wound healin~ or reducin~ infection of wounds can be 5 incorporated in the composite wound dresslngs. These can include but are not limited to antibacterial agents, such as the penicillins, the aminoglycosides, iodine and other well known an~ibiotics useful in reducing infection;
antiEungal agents such as nystatin and undecylenic acid;
hemostatic agents such as microcrystalline cellulose, chitosan, thrombin, and fibrin; and, wound-healing promoting a~ents such as epidermal growth factor, ascorbic acid, collagen, and aluminum salts such as aluminum acetate and aluminum chlorohydrate.
Objects and advantages of this invention are Eurther illustrated by the following examples, but the particular materials and amounts thereoE recited in these examples, as well as other conditions and details, should no~ be construed to unduly limit this invention.

EXAMPLE 1 - Preparation and Characterization of Composite Dressing Materials The general procedures disclosed in UOS. Patent 4,153,661, mentioned above, were used to prepare the composite dressing materials. The specific methods used were as follows:
Fifty grams of Sephadex~ G-25-80 ~crosslinked dextran derivative, particle size ~0-80 microns, available ~rom Sigma Chemical Co., St. Louis, MO) and 50 gm of water were mixed in a one-liter beaker. The Sephadex~ absorbed all ~he wa~er and swelled from 60 cc to a total volume oE
21G cc. Sixty grams of water and ~0 grams of polytetra-fluoroethylene (PTFE) resin dispersion (Teflon~ 30B, Dupont) were Inixed and added to the swollen Sephadex~ in 10 ml por-tions with intermittent vigorous stirring. Af ter these ingredients had been thoroughly rnixed, a semi-coherent material w~s formed with enough physical -~10--inte~rity to allow the entire contents to be removed from the beaker as a sin~le mass.
The above mass was passed through two rollers kept at 50C and spaced about 0.4 cm apart to ~ive a strip of cohesive material which barely supported its own weight of dimens.ions approximately 14 cm x 0.~ cm x 42 cm. The resulting strip was folded to three thicknesses o~ a mater-ial having dimensions of 14 cm x 1.2 cm x 14 cm and then passed through the rollers after a 90 rota~ion rom the previous pass. The cyclic process of three-layer folding and re-rolling in the direction 90 rom the direction of the preceding pass was repeated a total of 1~ times to give ~ tou~h, ~strong, ~lat piece oE material o~ ~imensions 14 cm x 0.4 cm x 42 cm. The material was then calendered along the long axis through a set of ten rollers which were spaced at successively smaller distances apart to give a continuous ribbon of dimensions 14 cm x .04 cm x ~0 ~-~n. 'L'll~ ~ibl~on was folded ~o give a 32-laycre-l l?iece of dimensions 14 cm x 1.3 cm x 15 cm. The 32-layered piece was then calendered as before along the 14 cm axis (90~ from the calendering direction.used previously) to give a ribbon of dimensions 15 cm x .05 cm x 350 cm~ By calendering using varying spaced rollers~ different degrees of compaction oE the mass could be obtained and various thicknesses of ribbon, as desired, realized. The calendered sheet of material was washed in a water bath and then allowed to dry in air for 48 hours. It was then stretched to a width o~ 20 cm to ~ive it a so~ter, more comfortable feel. The resultin~ dressing material was then coated with a semi~occlusive polymeric film.
Tl~e serni-occlusive Eilm was prepared Erom nine gra~s of a vinyl functional polydimethylsiloxane material (3M?

C1~l3 CH3 Cl~3 CH~
CH2=CH--SiO~SiO)'1~5iO)~Si--CH=CH2 containing 50 ppm of platinum catalyst, (pyridine) PtC12~C~H,~), one gram of polymethylhydro siloxane ( PS 1~0, 30 ctsks, available from Petrarch Systems, Inc., Levittown, PA), and 40 grams o methyl ethyl ketone. This solution was sponge dabbed onto the dressing material until a coating of the desired weight percent was ~ormed. The methyl ethyl ketone was allowed to evaporate ~ncl the material was cured at 80C for ten minutes. The final composition of the dressing was 73O3 percent Sephadex~ G-25-80, 18~3 percent PTFE, and 8.4 percent silicone coating.
Th~ dressing material, which had a chamois-like appearance and -feel, was then cut into 5 cm x 5 cm squares, packaged, and sterilized. Two or three squares were used for tes~ing ~he physical characteristics of the dressings.
The tensile strength oE the dressings was measured according to ASTM 638. The measurements were made on strips of material cut parallel to the longitudinal axis of the final calendering step. The tensile strength was about 300 psi ~2 megapascals). R
tensile strengtll in the range o 20 to 1000 psi can ~e obtained by variation of the preparation procedures.
The water vapor permeability o~ the dressing was measured according to AST~ E 96-66, P~rocedure B, at 23C
with an 81 percent relative humidity gradient across the dressing. A 5.7 cm~ area of clressiny was evaluated. The data showed that the permeability of the test dressings was 400 grams H20/m2/24 hours.
The rate of evaporative water loss was determined according to ASTM E 96-66, Procedure BW, at 23C with a 100 percent relative humidity gradient across the test dressing ma~erial. The rate of evaporative water loss was Eound ~o be 2 x 103 gm H20/m2/24 hrs.

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To determine the water ab~orption, small pieces o dressing m~terial ( O .1 to O. 5 g ) were weighed and placed in water for 2 hours. They were removed, blotted wi~h a paper towel to remove non-absorbed water, and reweighed. The dressing materials absorbed 2.5 g H20 per gram of dry dressing.

~X~M~L~ valuation o~ P'rl`~ Composite Dre~sing on shallow wounds of pigs.
Three materials were tested.
Dressing A - PTFE composite material with Sephadex~ particulate filler coated on one side with silicone made by the method described in Example 1.
Dressin~ B - PTFE composite material with Sephadex~ ~iller, not coated~ The PTFE composite material was made by the process of Example 1 to ~he exclusion o ~he coating process.
~ ont~ol - Polyethylene ~ilm ~natur~] ~ri~-le, low density) 37.5 micrometers thick.

The dressings were double packed and sterilized by ethylene oxide gas followed by degassing ~24 hours in an aerator).
The hair on the back of the pigs was clipped with electric clippers 48 hours prior to the start of the surgical procedure. Protective guards were put on the animals at this time. At the start of the procedure, the anaesthetised pigs were shaved, taking care not to damage the skin. Sterile techniques were used throughout the procedure and all operatives wore masks, hats, sterilized gowns and gloves. Care was taken to rinse any ~love powder from the gloves.
Twelve standard shallow wounds, each measuring

2.5 cm x 2.5 cmt were made on each animal using sharp round-bellied scalpel blades. The scalpel was held in the plane oE the skin and the epidermis and papillary layer of the dermis were cut away. When a]l 12 wounds had been made, the dressings were applied. Four wounds were covered with ~ressing A, four with B, and four with the control.
Biopsy specimens were obtained after one, three, and six days from each of the 12 wounds. Using a template measuring approximately l cm x 4 cm, cuts were made throu~h the dressinc3 to the wound surface and extended the Eull thickness of the skin. The specimens were placed in lO~ buf~ered formal saline.
A~ter 24 hours fixation the biopsy specimens were trimmed to yield ~our blocks. For e~ch wound, two o the blocks spannin~ the entire width of the wound were em~edded in wax and serial sections prepared using a rotary microtome set to cut at lO microns. Every Eifth section was mounted on glass slides to provide a series of sections for staining with H & E, Weigert and van Geison's stain and Masson's trichrome method.
Sections were examined under the microscope and the wound surfaces of the control and Sample A and B
dressings were compared.
Comparison of the results using the composite dressing with and without a covering of silicone to control the water vapor permeability clearly confirmed ~the validity of the hypothesis concerning the advantages o~ controlling the hydration of the wound by means oE a properly de igned dressing. The events within dressing A and B, as seen histologically, were interpreted to mean that both dressings ini~ially absorbed the fluid blood and exudate present on the wound surface when the dressings were applied. It is known that because of the inflammatory reaction and increased vascular permeability, the wouncls continue to ooze proteinaceous exudate for at least 24 hours after injury. Evidently, in the dressing lacking a silicone top coat ~dressing B), the exudate filling the lower third oE the dressing soon dried, blocking the pores and preventing ~urther uptake. Further loss oE water vapor dehydrated the surface of the wound, damaging the exposed f~

tissue and causing a scab to develop. In consequence, epidermal wound healing was delayed.
~ rl~e opposite ef~ect was seen under the occlusive polyethylene film control dressing. The exudate remained hydr~ted for at leas~ three days, no scab formed, an~ the epidermis migrated through the moist exuda e between the polyethylene film and the wo~nd surface. Bacteria proliferated in the exudate and their presence stimulated an outpouring of leucocytes. The natural defense mechanisms were adequate to control the in~ection, but the presence of numerous bacterial colonies at three days in areas where the new epidermis prevented access o leuco-cytes to the infection, the occurrence of micro-abcesses at six days and the persistence o acute inflammation, indicated that this was a borderline septic situation~ It is anticipated that the presence of more virulent organisms or a less adequate leucocytes response would result in septic wounds and delayed healing.
The condition of the wounds under those composite dressin~s which were provid~d with a silicone coating ~dressing A) to control the water vapor permeability approached the ideal. The wound surface did not dry and el>ide~ al re~Jeneration was at least as rapicl as uncler polyethylene. The perceived advantages compared with the control are that blood and exudate were absorbed, no gross in~ection dcveloped and there was a remarkable reduction in inflammation. The epidermis migrated directly in contact with the injured dermis and, in consequence, ~he new epidermis was less hypertrophied on the sixth day.
Whereas under the occlusive polyethylene Eilm dressing a mesh of ibrin was clearly seen in the exudate, no fibrin network was visible in the exudate within the composite dressing. This agrees with the findings of Aberg et al [Alberg, M., Hedner, U., Jacobson, S. and Rothman, U., "Fibrinolytic Activity in Wound Secretion", Scand. ~.
Plast. Recon. Surg. 1~, pp. 103-105 (1~76)] that %

exudate absorbed by dextran polymer has high fibrinolytic activity.
It is concluded that the composite dressing that incorporated beads of dextran polymer in a matrix of polytetrafluoroethylene fibrils having a coating to control water vapor ~ransmission provided beneficial e-~fects on donor site wounds.

Two scalds were made, one on ei~her side of the back of a young pig. The injury was created with runnin~
water at 80C applied for 35 seconds over a circular area o~ 16.6 cm2. The dead epidermis was removed ~rom the ~urns surfaces. Ten days later the eschar, which comprised the skin tissue which had been killed by scalding, was removed with a proteolytic enzyme prepara-tion. Loose debris was scraped rom the surface. The debrided burns were then treated with sterile composite dressings, i.e., sample A of Example 2 - PTFE membrane with Sephadex~ particulate Eiller ~oated one side with silicone made by the method described in ~xample 1. The dressings were changed after ~ hours, 17 hours, 25 hourst 33 hours, 44 hours, and 56 hours after enz~matic debride-ment. The wounds were grafted ater an additional 30 hours. Autografts were cut with an air-powered der~atome and were sutured in place on the wounds. The graEted burns were covered with povidone-iodine ointment (Betadine~, Purdue Frederick Co., Norwalk, CT~ on a pa~ of gauze secured to, a sheet of plastic adhesive film (Tegaderm~, 3M) and polyvinylchloride foam (Microfoam, 3M), and held in place with adhesive tape (~lenderm~ 3M).
This dressing was changed aEter 2 days and replaced by Betadine~ gauze and Tegaderm~ which was left in place for a further ~ days by which time it was judged that the grafted wounds no longer required the protection of a dressing.
The pig was sacrificed 14 days after grafting and biopsy d L~

specimens o~ the ~rafted b~rns were processed ~or microscopic examination~
On the ri~ht side oE the wound, a 0.8 mm thick ~raEt was healthy and was covered by an intact epidermis.
The Eibrous repair tissue ~eneath the graft was about 2 mm ~hick. There were a .~ew bireEringen~ foreign bodies embedded in the repair tissue which had provoked a giant cell reaction.
On the left side of the wound, there was a healthy graft about 1. 0 mm thick with intact epidermis on the surface o~ repair tissue measuring about 1 mm deep.
There was ne abnormal inflammation or other adverse reactions. By histological criteria this was an ideal result.
These results indicated that the composite dressing was efficacious in preparing the surfaces of contaminated wounds to accept a skin graft.

Eighty grams of corn starch IFisher Scientific Co.) were thoroughly mixed with 60 ml oE water. Thirty ml of PTFE resin dispersion ~TeElon~ 30B) were added, with mixin~, to ~orm a viscous solution. rrhen, 30 g~ams oE corn starch were added slowly with vigorous mixing to ~orm a thick paste. This paste was subjected to shear orces on a rubber mill operatiny at 50C until a solid cohesive mass Eormed. This mass was subjected to 10 cycles of 3-layer folding and rerolling at an angle of 90 as described in Example 1. It was then calendered, folded and recalendered also as described in Example 1. The final shee t of rnaterial was 0.6 mm thick. The composition of this material was 80.1 percent corn starch and 19~ percent PTFE. The material was coated with pol~neric films to control water vapor permeability as is described in Example 6, below.

9~:
~17-Ten ml o PTFE resin di~persion tTeflon~ 30B) were aclded with mixing to 20 grams o polyethylene powder (Micro~herle~ - USI Industries). The dou~h-like mixture which res~lted was milled and calendered as described in Example 1. The final product was 0~15 mm thick. The composition of this material was 31~ percent PTFE and 68.8 percent polyeth~lene. The material was hydrophilic due to the presence of residual surfactant from the PTFE
~ dispersion, but after a thorough rinsing in distilled water, it became hydrophobic and would not a~sorb water or be wet by water.

Samples o composite dressing materials compo~ed L5 oE p~rF~-seplladex~ PTFE-Corn Starch and PTFE-Polyethylene mixtures were prepared by the procedures disclosed in Examples 1, 4, and ~, respectively. These unzoated dressings were then coated with semi-occlusive polymeric films with a variety of water vapor permeabilities. The coated dressings were used in animal trials to determine the useful range of dressing water vapor perme~bilities and ~o establish a correlation between the ~n vitro permeability and in v _ water loss rates.

Three samples were prepared as follows: 5 Dressing C- PTFE-Sephadex~ composite material was prepared as ~lescribed in Example 1 exclusive o~ the silicone coating procedure. The Einal compo-sition was 19~4 percent PTFE and 80.6 percent Sephadex~ G-25-80 and was 0.4 ~nm thick. 0 Dressing D- PTFE-Corn Starch material was prepared according to Example 4. The final composition was 20 percent PTFE and 80 percent Corn Starch and was 0~6 mm thiGk.
Dre~ssin-3 E- P'l'FE-Polyethylene material was prepared according to Example 5. The final composition wa~ 20 percent PTFE and 80 percent polyethylene ~1~

and was 0~150 mm thick.
These composite dressin~s were then coated according to one of the ollowing procedures:
1 ~ A 28.0 micron thick shee~ of polyurethane ~Estane~, B~ F~ Goodrich), coate~ with an acrylate pressure sensitive adhesiv~ was pressed onto the upper surface of the composite dressing ma ter i a 1 .
2 - A 50 micron thick shee'c of poly(dimethyl, diphenyl~ siloxane was coated on its upper surface with a 30 micron film of 1:1 (by weight) mixture of Type A Silastic ~dical Adhesive ~Dow Corning) and toluene. The composite dressing material was applied to this surface and the adhesive was allowed to cure overnight at room temperatureO

3 - R 23 micron sheet o polyurethane (Estane~) was coated on one surface with a 30 micron Eilm o~ a 1:1 mixture (by weight) of Type A Silastic Medical Adhesive (Dow Corning) and t~luene. The composite dressing material was p~essed onto this surface and the adhesive was allowed to cure overnight at room temperature.

4 - A 168 micron film of a 2:1 mixture ~y weight) of Tyue ~ Silastic Medical ~dhesive and toluene was cast onto a TeElon~ (Dupont) surace. AEter five minutes a piece of composite dressing material was pressed onko the adhesive film.
After curing overnight, ~he composite dressing with an adherent silicone film were removed from the Teflon~ surface. ~he thickness of the silicone film is estimated at 112 microns~

5 - This procedure is identical to Procedure 4, except a 135 micron film o a 1:1 mixture ~by weight~ of Type A Silastic Medical Adhesive ~Dow Corniny) and toluene was initially cast onto the Teflon~ surface~ The thickness oE the resulting silicone :Eilm is estimated at 68 micron.

6 - This procedure is identical to Procedure ~, except a 10~ micron ilm oE a 1:1 mixture tbY
weight) of Type A Silastic Medical Adhesive (Dow Corning) and toluene was initially cast onto the Te~lon surEace. The thickness o~ th~e resulting silicone film is estimated at 51 mi~ron.
Permeability of water vapor was mea~ured in vitro through the dry dressings according to ~STM ~ethod E96 Procedure B
with these exceptions:
a) a 4.9 cm2 ar~a of dressing was expo~ed b) the incubation temperature was 37 ~ 1C.
c) the relative humidity o~ the incubation chamber was held at 24 ~ ~ percent~
Permeability o~ water vapor through the dressings when wetted and in contact with liguid water was measured according to ASTM Method E96 Procedure BW with the excep~ions a, b, and c above. These results are reported i n TABLE I .
Dressing s~uares ~5 cm x 5 cm~ were packaged, sterilized and handled as described in Example 1. Twelve dre~sing samples, with various compositions as shown in TAB~E I, were usPd to cover twelve wounds on each of two pigs. Details of the animal trials were as described in Example 2. The actual rates of water vapor loss from the various dressings on the shallow wounds were determined at one day and three days after application with an evaporimeter (Model Epl, Servo Med AB, S~ockholm, Sweden).
Results are reported in TABLE I.
Wound healing was measured as ~he percen~age oL
the wound surEace recovered with epidermal cells (Winter, G~D. 1972. _ Epidermal Wound Healing, H~ ~aibach and D.
T. Rovee, eds. Chicago: Yearbook Medical Publishers).
Data is recorded in TABLE I.

-2o~ 3 x I ~ o ~ r~ n ~ ~ cr~

a U~
O
~a o o o o o ~ o o o C~
X X X X X X X X X X ~C X

.C ~ O O O O O O O C ~ o ~.1 , i C I ~1 -1 a~ u, V O
~OOOOOOO~OOC:O
O ~) X X X X X ~C X ~ ~ X
~ ~ ~ ~ n ~ cr~ ~D o o~
~ ~ ~ ~ Ln er CS~
O
o o o o C~ ~ o o o o C ~1 ~ O

4 ~, 3 O O O O O C:~ O C:~ O O C:~ O ttS
m .c _ o x X x X X X x ~ x X X x n ~¢ ~ ~ ~S.J ~) r-- O ~ ~ ~ ~ O r~ J a~
o o ~ ~D Ln ~ ~ u~ Ln . . . . . . O
I~ ~ ~D --I O ~ ~ ~ ~ ~ O ~ ~ ~ C

N , J.
O
OO O O O O Q o ~ O
X ~ I ~ X X X I I X ~c X
~ o m L~ n~
Q) ~ ~O OD q~ ~ ~ ~ o . . . . . . . .
H cn O -1 0 -1 0 .,~ ,,~
~
a~
' ~
~ ~ r Ln ~9 .-1 ~ ~ ~ ~9 o ~ ~ 5 c~ z v) n ~
o n~ ~3 ~
:~: W V W C~ W C ? Q a a ~ a ~: ~ q P~

The water vapor permeabilities measurecl by ~STM
Methocl E96 Procedure ~W (the wet dressing method) compared wi th the in vivo rate of water 105s at one day showed ~hat there was a c~ef irli ~e correlation between the in ltro and ln vlvo measurements Water vapor permeabilities measured by procedure BW were superior to those measured by ASTM
Method E96, Procedure ~t in predicting in vivo performance.
~ lso, as shown in TABLE I, all dressings having a coating permit~ed wound healing to progress to at least 64 percent in three days whereas wound healing under the uncoated dressing was no mcre than 39 percen~ in the same time. ~ dried, fibrous surface to the wound was observed under the uncoated dressing. Histological observations of the wound under the uncoated dressing were similar to those oE Dressing B at 3 days of healing previously reported in Example 2. The histological appearance of all other wounds, i.e., those under coated dressings, were similar to those o~ Dressing A at 3 days of healing reported in Example 2.

Samples of composite dressing materials were prepared from mixtures of PTFE tTeflon 30B) and various hydrophilic particulate materials, according to the procedures disclosed in Example l. TABLE II contains the amounts of particulate material, water and PTFE used in each mixture. The thickness of the dressings varied from 0.1 mm to 2.0 mm. ~ll dressings were useful in the practice of the present invention.

TABLE I T

Particulate Weight of ~olume Volume Composition o_ ~ried Proauct Material Particulaie of Wa~er ~eflon~ 30B(i) (Amount in parenthesis is in percenr) Chitosan (a) 40-0 g89. ml 15. ml (25) PTFE, (75) Chitosan ~lginic Ac~d (b)60.0 g120. ml 25. ml (27.5) PTFE, ~72.5~ Alginic Acid Collagen (c) 8.0 g 8. ml ~. ml (31) PT~E, (69~ Collagen Kaolin ~d) 8S.Q gS0. ml 30. ml ~24) PT~E, (76) ~aolin Xaolin - Derivatized 50.0 9 100. ml 30. ml (21) PT~E, (39.5) Kaolin sta~ch (e) of each (39.5) Derivatized Starch Sepharose~ (f) 20.0 9140. ml 10. ml (31~ PTFE, (69) Sepharose Cellulose (g~ 20.0 920. ml 10. ml (31) PTFE, (69~ Cellulose Diethyl Amino Ethyl 10-0 g 150. ml 20. ml (64.5) PTFE, (35.5) Diethyl Amino Sephadex (h) Ethyl Sephadex Calcium Carbonate30.0 920. ml 15. ml (313 PTFE, 16g) Calcium Carbonate (~t Chitosan - Kytex Mt ~ercules (b) Alginic Acid - Type III, Sigma Chem. Co.
(c) Colla~en - purified rrom rat-tail tendon (d) ~aQli~-Kaopaque (e) Derivatized Starch - SGP 5125, General Mills Chemicals (f) Sepharose~ - Type aB-20Q, Sigma Chem. Co.
(9) Cellulose - ~licrocrystalline, Type 20, Sigma Chem. Co.
~h) Diethyl aminoethyl Sephandex~ - A-50-120, Sigma Chem. Co.
(i) Polytetrafluoroethylene - Teflon~ 30B, Dupont EXAMPLE ~3 Samples of composite dressing materials c(~ntaining various medicaments wh,ich may promote wound healing, reduce wound infecti~n or be hemostatic were prepared according to the procedures ~isclosed in Example l. The compositions of these dressings are presented in TABLE III. The medicaments were introduced into the ~ressin~Js ~y three methods. Method A - Medicaments were added to ~he PTFE-particulat~ mixture before fibrillation of the PTFE on the two roll mill, thus ensuring the medicaments were thoroughly enmeshed in the fibrillated PTFE matrix. Method B - The fully manufactured dressing sample was soaked in an aqueous solution of medicament, allowing the sample to absorb medicament and then was dried, trappin~ the medicament in the sample. Method C - A
solution of medicament,was coated onto the surface of the sample and then allowed to dry.

TABLE III
Dressing Preparation 20 Composition* Medicaments* Procedure PTFE (24.3) Ascorbic Acid (2.0) Method A
Sephadex~ Boric Acid (0O4) G-25-80 (72.9~ Aluminum Acetate (0.4) PTFE (20) Neomycin Sulate (0.2) Method B
25 Sephadex~ (antibacterial) G-25-80 (79.8) PTFE (20) Nystatin Method C - An Seyhade~x'l~ (antifungal) a~ueous solution G-25-80 (80) conta~ning lO0,000 units was coated onto the dressing sur~ace and allowed ~o dry.

PTF~ (21) Iodine Method B - Soakecl ~aolin (39.5) (antibacterial) in 0.5 percent KI3 SGP 5125 aqueous solution.
Derivatized Material turned 5 Starch (39.5) characteristic gun-metal blue.

PT~E (25) Chitosan Method A
Chitosan (75~ (hemost~tic agent~

PTFE (20) Povidone ~lethod B - The lO Sephadex~ Iodine dressin~ was G-25-8Q soaked in a lO
percent Povidone-Iod ine solution and dried.

* (amount is in parenthesis and i5 in percent~

The data show that all of the dressings were useEul in treatment of wounds.

Various modifications and alterations o this invention will become apparent to those skilled in the art without departing rom the scope and spirit of this inven-tion, and i~ should be understood that this invention is not to be unduly limited to the illustrative e~bodiments set forth herein.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A composite wound-dressing which is a sheet material, comprising:
(a) a polytetrafluoroethylene fibril matrix, and (b) 0 5 to 10 parts of hydrophilic absorptive particles per part of polytetrafluoroethylene by weight enmeshed in said matrix, the absorptive particles having absorptive capacity greater than 0.5 grams of water per gram of dry particles, wherein substantially all of said hydrophilic absorptive particles are unavailable for sloughing.

2. The composite wound-dressing according to Claim 1 further compris-ing a partially occlusive film coated on one surface of said matrix.

3 The composite wound-dressing according to Claim 1 wherein said hydrophilic absorbent particles are alginic acid, polyacrylatecellulose graft copolymer, collagen, chitin, chitosan, dextran, a cross-linking dextran deri-vative, clay, casein, zein, carboxymethyldextran, starch, hydroxyethyl starch, hydrolyzed polyacrylonitrile, starch-methacrylonitrile polymer, polyacrylamide, hydrolyzed polyacrylamide, cellulose, carboxymethylcellulose, or derivatives or mixtures thereof.

4. The composite wound-dressing according to Claim 1 further comprising diluent particles admixed with said hydrophilic absorptive particles.

5. The composite wound-dressing according to Claim 4 wherein said hydrophilic and diluent particles comprise 40-90 percent oh the weight of the said composite wound-dressing

6. The composite wound-dressing according to Claim 1, 2 or 3 wherein said hydrophilic absorbent particles range in size from about 0.1 to 300 micrometers and wherein said fibril matrix comprises fribrils having a thickness in the range of about 0.025 to 0.5 micrometers.

7. The composite wound-dressing according to Claim 1, 2 or 3 wherein said partially occlusive film is a polymer of silicone, urethane, or acrylate having a thickness in the range of 2 to 200 micrometers.

8. The composite wound-dressing according to Claim 1, 2 or 3 wherein said dressing has a thickness in the range of 0.1 to 10 mm and wherein the rate of transmission of moisture through said dressing is in the range of about 240 to 2400 g/m2/24 hrs., at 37°C and 75 percent relative humidity.

9. The composite wound-dressing according to Claim 1, 2 or 3 further comprising medicaments selected from antibacterial agents, antifungal agents, hemostatic agents, and wound-healing agents.