Anti-adhesion cellulose acetate wound dressing comprising a very low content of Siloxane

0001The invention is directed to a cellulose acetate anti-adhesion wound pad or dressing, and in particular to a cellulose acetate anti-adhesion pad having a low level of siloxane finishing agent applied thereto. The pad has use in the medical arts area for application to wounds, particularly burns.

0002Numerous injuries, and particularly burns, require the application of some type of pad, gauze, cloth, dressing or similar covering (herein collectively called a "dressing") to protect the wound while it is healing. Wounds, especially burns, sometimes have difficulty in healing and are frequently prone to infection because natural protective skin barriers are disrupted and are slow in repairing themselves. The most commonly used dressing material has been cotton because it is both inexpensive and readily available. However, as those who have used cotton dressings are aware, they tend to stick to the injured area, even when the surface of the area is covered with a lubricant such as petroleum jelly ("petrolatum") or similar substance, or a medicinal which contains a lubricant. Developments in the medical arts have resulted in some improvements in medical dressings, two of which are represented by Johnson & Johnson's ADAPTIC™ brand non-adherent dressings and the Curity® brand TELFA® sterile pads sold by Kendall-Futuro Company. The ADAPTIC™ brand dressing was found to consist of a cellulose acetate pad which has been soaked in petrolatum or similar substance to impart anti-adhesion properties. While the petrolatum reduces adhesion to a wound, it's use results in a pad that is greasy and messy to handle compared to a pad without petrolatum. The TELFA® dressing consists of a polyethylene terephthalate (PET) shell and a caustic washed cotton insert, the anti-adhesion properties being imparted by the PET shell.

0003Another dressing is disclosed in China Patent No. CN 87 101 823 A, published August 31, 1988, to Tie Han et al. This Chinese patent describes a "Medicinal Anti-Adhesive Dressing" prepared using plain cellulose acetate to make a spun and woven gauze, or a non-woven fabric having a weight of 50-80 g/m². No additional information is given concerning treatment of the cellulose acetate material before, during or after preparation of the dressing. The dressing did not contain a biostat nor was use of a biostat suggested.

0004United States patents disclosing the use of cellulosic materials and siloxane materials in wound dressing include: <ul id="ul0001" list-style="bullet" compact="compact"><li>US-A-5,372,739 to B. Shriram which describes fibers, including cellulose acetate fibers, having polyethylene glycol fatty acids thereon to reduce adhesion;</li><li>US-A-4,984,570 to Langen et al. which describes a wound dressing having a cellulose acetate absorbent pad and a hydrophobic man-made fiber covering over the pad which covering is in contact with the wound;</li><li>US-A-4,546,027 to Holvoet which describes the use of a non-woven corrugated fabric for medical and surgical compresses, which compresses include the use of plastic reinforced cellulose fibers;</li><li>US-A-5,635,201 to Fabo which describes the use of a curable siloxane material coated on a carrier surface and heat cured to form a siloxane gel; and</li><li>US-A-5,685,832 to Chen et al. which describes a wound dressing comprising a woven cellulose acetate substrate and a partial solvent thereon, which dressing releases, in a controlled manner, acetic acid to act as a therapeutic agent.</li><li>US-A-3,285,245 to Eldridge et al. which describes an absorbent wound dressing having an absorbent backing and a non-absorbent facing.</li></ul>

0005These dressing, while having various qualities which may reduce adhesion or provide other benefits, incorporate lubricants and/or fluids or fluid releasing agents, and use fibers other than cellulose acetate to provide non-adhesion properties.

0006Adhesive dressings and methods of preparing adhesive dressings are well known in the art as exemplified by US-A-4, 595,001, and patent references cited therein, to Potter (a surgical dressing which carries an adhesive layer for securing a dressing to a body), all of whose teachings are incorporated herein by reference.

0007DE-A-2007449 discloses a non-woven fabric (Rayon) which is coated with at least 1 wt.-% siloxane and can contain a bactericide.

0008While the above dressings represent improvements in reducing dressing adhesion to wounds, further improvements in the field is highly desirous. In particular, an improved dressing of cellulose acetate would be useful in the medical arts because cellulose acetate is both chemotactic for attracting white blood cells and hydrophilic. The white cell chemotactic property of cellulose acetate fibers is desirable in a wound dressing because white blood cells aid in fighting infection. The hydrophilic property is desirable because it aids in removing excess fluids which may ooze from the surface of a wound during the healing process. Accordingly, the present invention is directed to providing such improved dressing.

0009It is an object of the invention to provide a wound dressing made of cellulose acetate which has improved non-adhesion characteristics.

0010It is a further object of the invention to provide a wound dressing made of cellulose acetate and a low level of a siloxane finishing agent, which dressing has improved non-adhesion characteristics.

0011It is an object of the invention to provide a self-adhesive bandage having a wound dressing pad attached thereto, which pad is made of cellulose acetate with a low level of a siloxane finishing agent, and which pad has improved non-adhesion characteristics.

0012It is an additional object of the invention to provide a biostat containing wound dressing and/or self-adhesive bandage having a wound dressing attached thereto, which dressing is comprised in part or wholly of cellulose acetate, and has a low level of a siloxane finishing agent applied thereto; and which dressing has improved non-adhesion characteristics.

0013Thus the invention relates to <ul id="ul0002" list-style="none" compact="compact"><li>(1) A fabric comprising cellulose acetate fibers and cellulose acetate fibers having a selected quantity of a biostat therein, and a siloxane; wherein the biostat-containing fibers are from 1% to 100% of the fibers in the fabric, the siloxane is from 0.01 % to 0.0001 % and said fabric is selected from the group consisting of woven and non-woven fabrics;</li><li>(2) The fabric according to (1), wherein said fabric is a non woven fabric, said biostat-containing fibers are from 1% to 30% of the total fibers, and said biostat-containing fibers contain from 0.01% to 5% biostat;</li><li>(3) The fabric according to (1) or (2), wherein the cellulose acetate and biostat-containing cellulose acetate fiber are from 1.1 to 55 dtex pro filament (1 to 50 dpf).</li></ul>

0014The invention is directed to a wound dressing which does not adhere to a wound surface or which has improved non-adhesion characteristics relative to the wound dressings known to the art. In the one embodiment, the invention comprises a woven or non-woven cellulose acetate dressing. In a preferred embodiment, the invention comprises a non-woven cellulose acetate web, and a particularly preferred non-woven dressing comprises a spunlace material having a weight of about 20 to about 90 g/m² (grams per square meter). These embodiments further comprise such additional substances as low levels of siloxane materials to finish the dressing or the fibers used to make the dressing and additionally impart further adhesion-reduction characteristics; and anti-biologics such as bactericides and fungicides which can be incorporated into the cellulose acetate before it is formed into a filament for use in producing the dressing or such anti-biologics incorporated into a fiber which can be used in conjunction with cellulose acetate fibers to produce the dressing.

0015In another embodiment, the invention is directed to an article of manufacture comprising an adhesive strip having an adhesive on one side thereof and a wound dressing adhering to a portion of the adhesive side of said strip, wherein said wound dressing comprises one or a plurality of layers of a fabric comprising cellulose acetate fibers, biostat-containing cellulose acetate fibers having a biostat content of 1 % to 5%, and a siloxane in the amount of 0.01 % to 0.0001 %; wherein the amount of biostat-containing fibers in the dressing is from 1% to 100% of the total fiber in the dressing.

0016The term "anti-biologic" or "biostat", and variations thereof, as used herein means any substance which has an effect on a biological organism, and in particular means bactericides, antibiotics, fungicides, herbicides, antimicrobials and similar substances which effect biological organisms, both animal and plant.

0017The term "dressing" as used herein means any material applied to protect, cushion, cover, and generally guard a wound from either further injury or from any undesirable contacts. The material may be in any form such as a pad, gauze, cloth, sheet, or similar form as might be used in the medical arts. The dressing may be used by itself or in conjunction with a medicinal or other substance applied thereto or contained therein, and may comprise multiple layers of the cellulose acetate materials of which the dressing is made.

0018The terms "non-stick," "no-stick," "anti-adherent," "non-adherent", "anti-adhesion" and variations thereof, and similar terms, may be used interchangeably to signify a dressing which either does not stick or adhere to a wound, or which exhibits a reduced tendency to stick or adhere to a wound relative to other dressings.

0019The dressing may be made of either a woven or a non-woven cellulose acetate; non-woven being preferred. Further, the dressing may be made of cellulose acetate alone or in combination with another filament or fiber suitable for use in medical dressings, including polyesters, polyolefins, polyamides and cotton; polyesters being preferred.

0020All percentages herein are weight percentages unless specified otherwise.

General Preparative Methods

0021The cellulose acetate containing dressing of the invention may be a knitted, woven or non-woven material, non-woven being preferred. The spinning process used to produce a cellulose acetate dressing can be either dry spinning or wet spinning as those terms are understood by one skilled in the art. A description of cellulose acetate filaments and fibers (hereafter collectively called "fibers"), and the materials and processes used to make such fibers, can be found in the "Encyclopedia of Chemical Technology, 4th Ed." (Wiley-Interscience, John Wiley &amp; Sons, New York), Vol. 10, pages 204-253 (non-woven fabrics), 598-624 (cellulose esters) and 696-726 (regenerated cellulosics), and are well known to those skilled in the art. The making of knitted and woven fabrics is well known to those skilled in the art.

0022The process used to incorporate anti-biologics into a fiber is well known in the art as exemplified by US-A-3,959,556 and US-A-4,343,853 to Morrison which describe incorporating an antimicrobial agent into a thermoplastic resin to produce a fiber having the antimicrobial intimately mixed with the resin. Cellulose acetate is a thermoplastic substance.

0023Woven fabrics can be prepared using cellulose acetate fibers by conventional weaving procedures known to those skilled in the art. Such techniques can be used to produce either a cellulose acetate (only) fabric or a fabric comprising cellulose acetate and a second fiber having an anti-biologic intimately mixed with the fiber resin.

0024Non-woven fabrics can be prepared using cellulose acetate fibers by conventional non-woven techniques known to those skilled in the art. In the preferred embodiment of the invention the non-woven fabric is prepared according to the spunlace method. The spunlace method can be used to produce either a cellulose acetate (only) fabric or a fabric comprising cellulose acetate and a second fiber having an anti-biologic intimately mixed with the fiber. In the preferred embodiment the anti-biologic containing fiber is cellulose acetate and the anti-biologic containing fiber is present in the fabric in an amount of greater than zero percent to 100% of the total fiber of the fabric.

0025The fibers used to produce woven or non-woven fabric are made using spinnerets having 50 to about 250 openings therein for producing filaments of 1.1 to 55 dtex pro filament (1 to 50 denier per filament (dpf)), with 1.1 to 5.5 dtex (1-5 dpf) being preferred. Heavier dpf materials are used when multiple "layers" are desired in a non-woven fabric, for example, for strength imparted by a layer of heavier fibers, or when it is desired to give any fabric more "body." The fabrics, and particularly the spunlace fabric, are preferably produced in a weight range of 20 to 90 g/m². After fabric forming, the fabric is then needled or punched to yield a fabric having from 10 to 200 openings per square centimeter. Alternatively, the fabric may be used as formed and not punched or needled to form openings. Subsequent to fabric forming and needling, the fabric may undergo optional additional treatments such as washings. In preferred embodiments of the invention, the fabric is washed and treated with a siloxane containing solution comprising 2.27 kilograms (Kg) of 70 % Sentry NF30 and 30% Nuwet® 500 (both from Witco Chemicals, Greenwich, CT ,USA) in about 226 liters of deionized or distilled water (5 lbs. per 60 gallons). Those skilled in the art are familiar with the foregoing siloxane materials and the invention hereby teaches that similar silicone materials from other sources can be substituted. Siloxane treatment time is typically in the range of 10-30 minutes, and with 15 minutes being a typical treatment time. Following siloxane treatment the fabric is optionally water washed to remove excess silicone and dried. The amount of siloxane on the fabric after washing and drying is from 0.01 % to 0.0001 %. The fabric may then be folded, cut and otherwise processed and packaged for sale to the end user. Fabric is sterilized by any sterilization method known in the art, for example, by gamma irradiation whereby typically 27-34 KGy is delivered. When applied to wounds, a dressing may consist of one or more layers of the fabric of the invention. Typically, one to twenty layers may be used, the exact number being determined by the nature and/or severity of the wound.

Example 1: Cellulose Acetate Fabric Containing Siloxane and No Biostat

0026Using the general procedures described above, 3 dpf filaments were extruded from a plurality of spinnerets to produce a fiber subsequently used in the spunlace method to produce a non-woven fabric of 77g/m² weight with 24 openings per square centimeter. The fabric was washed, treated with the siloxane solution, dried, packaged and sterilized using gamma radiation. Alternatively, a fabric can be prepared by conventional weaving using spun yarn from cellulose acetate staple, e.g., a 1x1 plain weave pattern at comparable fabric weight. The siloxane content is 0.01 % to 0.0001 %

Example 2: Cellulose Acetate Fabric Containing Siloxane and a Biostat

0027Using the general procedures described above, 3 dpf fibers were extruded from spinnerets, and the resulting fibers used to produce a non-woven spunlace fabric of 77g/m² weight. One or a plurality of fibers used in producing the fabric was a fiber containing the biostat Microban® [2,4,4'-trichloro-2'-hydroxydiphenyl ether, or alternatively, 5-chloro-2(2,4-dichlorophenoxy)phenol], a chlorinated phenoxy material identical to one of those disclosed in the Morrison patents (US-A-3,959,556 or US-A-4,343,853). The Microban® containing fiber used in preparing the fabric of this Example was Microsafe® cellulose acetate fiber available from Celanese Acetate LLC, Charlotte, NC, U.S.A. Other biostat fibers useful in practicing the invention include polyolefin, polyamide, polyester, polyacrylate, polyvinyl alcohol and similar fibers known to those skilled in the art. Generally, the biostat may be incorporated into the fabric resin in an amount of 0.01 % to 5 %. As used in this Example, the biostat amount incorporated into the fiber was 2%.

0028The amount of biostat-containing fiber incorporated into a woven or non-woven fabric may be from 1% to 100%. Preferably, the amount may be from 1% to about 50% and most preferably from 3% to 30%. As used in this Example, the amount of biostat-containing fiber in the spunlace fabric was 30%. The needled fabric was washed, treated with the siloxane solution, dried, packaged and sterilized using gamma radiation. The siloxane content is 0.01% to 0.0001%

FIELD TESTS

0029Field tests were conducted at four hospitals in China, all major burn centers, because burns are a common occurrence in China where kerosene heaters are commonly used for indoor heating during the winter months and open fires are used for cooking year around. As a result, an evaluation of the dressing of the invention and other dressings could be made more quickly because of a readily available pool of patients. In addition, because of cost consideration, dressings are generally left on the burns for longer periods of time before they are changed, unless medical necessity or circumstances dictate otherwise.

0030The Clinical Directors of each hospital burn center were asked to help design a single study protocol that would be used to evaluate the dressing of the invention against other burn dressings commonly used in China.

0031Four different dressings were used in the field tests. These are: <ul id="ul0003" list-style="none" compact="compact"><li>1. Cotton gauze;</li><li>2. Kangda, a commercially available dressing in China</li><li>3. CAYX, a commercially available "plain" cellulose acetate dressing from Yong Xing Company; and</li><li>4. CAM, the cellulose acetate dressing of the invention prepared according to Example 2.</li></ul>

0032The Kangda dressing is a nylon netting having cotton stuffing. The CAYX dressing is "plain" cellulose acetate having no discernible other material such as petrolatum, siloxane or biostat, and is similar to that of China published patent 87 1 01823 A cited above. The CAM dressing was prepared according to Example 2.

0033The dressings were applied in a standardized manner to a sufficiently large body area on each patient which would accommodate all four dressings. A drawing was made of each burn site on the patient evaluation sheet to record the order of application and the location of each dressing. Each dressing sample was a minimum of 10x10 cm² and sixteen (16) layers thick. Prior to placing the dressing on the burn surface, a thin layer of Silvadene™ cream was applied to either the burn site or the dressing. The Silvadene was reapplied at each subsequent dressing change. After application, the dressings were overlapped with a standard material such as cotton gauze in order to hold the dressing in place.

0034To minimize any differences which might be caused by having multiple physician evaluators, each Field Test site designated one physician to be the primary evaluator who would complete the Patient Evaluation form. This form was completed at every dressing change by the primary examining physician. Dressings were initially changed after 24 hours, and the changing was later extended to 48 hours as the wounds healed. Each dressing change results in a separate Evaluation.

0035The participants were patients who were hospitalized with a minimum of second degree burns on less than 50% of the body. The patients were between 15 and 55 years of age and were free from any medical conditions such a diabetes, HIV and other immunosuppressed conditions that would effect wound healing. A target number of 30 participants of either sex were selected for the field test at each hospital site. A total of 270 patients from all hospital sites were collected in the trials. The Field Test Results are given in Tables 1-5.

0036Pain was evaluated using a 1-10 scale with one (1) being no pain and ten (10) being the worst pain. Adherence was also evaluated using a 1-10 scale with one (1) being no adhesion and ten (10) signifying that the dressing was stuck to the wound. Wound appearance was evaluated using a scale of 10-100, with 100 indicating worst appearance. The "P" Value (Pain Value) is defined at 99% and for the invention is significantly less than cotton. <tables id="tabl0001" num="0001"><img file="EP0940147B1_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0940147B1_D0002.tif" /></tables>

0037The results of Table 1, Pain, indicate that the CAM dressing containing Microsafe® fibers and having a siloxane treatment caused significantly less pain when removed than any of the other dressings. The CAM dressing had an average score of 2.02 out of a total of 262 readings (dressing changes) in contrast to an average score of 2.70 for the next best dressing, CAYX. The Pain Score for CAYX, the plain cellulose acetate dressing was about 35% higher than that of CAM, the dressing of the invention. Cotton dressing had the highest pain score, about double that of CAM. There were no difference in the results when the age and sex of the patients was considered.

0038The overall trend in scores remained consistent when the scores were separated by participating hospital as shown in Table 2, indicating that the statistical data is accurate and that there were no anomalies. <tables id="tabl0003" num="0003"><img file="EP0940147B1_D0003.tif" /></tables><tables id="tabl0004" num="0004"><img file="EP0940147B1_D0004.tif" /></tables>

0039The results of Table 3, Adherence Scores, indicate that the CAM dressing containing Microsafe® fibers and having a silicone treatment was significantly less adherent to a wound than any of the other dressings. The CAM dressing had an average score of 2.01 out of a total of 262 readings (dressing changes) in contrast to an average score of 2.83 for the next best dressing, CAYX. The Adherence Score for CAYX, the plain cellulose dressing, is about 40% higher than that of CAM, the cellulose acetate dressing of the invention. Cotton dressing had the highest adherence score, about double that of CAM. There were no differences in the results when the age and sex of the patients was considered.

0040The overall trend in scores remained consistent when the scores were separated by participating hospital as shown in Table 4, indicating that the statistical data is accurate and that there were no anomalies. <tables id="tabl0005" num="0005"><img file="EP0940147B1_D0005.tif" /></tables>

0041While judging the appearance of wounds is often very subjective, but the clinicians involved in the study wished to include this as one of the factors being evaluated. Appearance was judged after the dressings were removed and were assessed on the amount of healthy appearing wound surface observed. The greater the amount of healthy wound surface observed, the lower the score.

0042The results of Table 5, Wound Appearance Score, indicate that the CAM dressing containing Microsafe® fibers and having a siloxane treatment resulted in the lowest score and hence was deemed indicative that the wound was healing properly. The CAM dressing had an average score of 18.58 in contrast to an average score of 20.25 for the next best dressing, CAYX. Cotton dressing had an Appearance Score of 25.60. There were no difference in the results when the age and sex of the patients was considered

0043If an ideal wound dressing could be designed, it would protect the wound surface, while not disturbing the healthy granulating tissue when removed, absorb blood and other fluids, help promote wound healing by chemotaxis of leukocytes, reduce the overall risk of infection and be inexpensive when compared to other commercially available dressings. While cotton has long been the standard dressing for use in burns and other healing wounds, largely due to its availability and low cost, it does not of itself promote the healing process. Microscopically, cotton is a fiber that possesses an irregular surface with numerous tiny protuberances on the surface of the fiber. It is these protuberances that cause cotton fibers to stick uncomfortably to a wound's surface. In contrast, cellulose acetate dressings, and in particular the CAM dressing described herein, possess advantages over cotton. Cellulose acetate fibers generally have a smooth surface without breaks or protuberances to catch in a wound surface. In view of this fact, it is not surprising that cellulose acetate is less adhesive than cotton or other materials.

0044It is noted that although both the CAYX and CAM dressings are made of a cellulose acetate fabric, the CAM dressing of the invention is superior to the CAYX in all categories. Without being held to any particular theory or explanation, this is believed to the result of CAM including both a biostat and a siloxane.

0045While this invention has been described with an emphasis on the preferred embodiments, it will be apparent to one of ordinary skill in the art that variations of the preferred embodiments can be used and it is intended that the invention can be practiced otherwise than as specifically described herein, in both the medical and non-medical arts. In the medical field, polyester or polyolefin fibers containing biostat as indicated herein could be used in place of the biostat-containing cellulose acetate fibers.