Wound dressing containing aldehyde-modified regenerated polysaccharide

[0001] The present invention relates to wound dressings containing or fabricated in part from an aldehyde-modified, regenerated polysaccharide, e.g. a biodegradable aldehyde-modified, regenerated cellulose, and to methods of providing coverage and protection to a wound using such wound dressings.

[0002] The control of bleeding is essential and critical in surgical procedures to minimize blood loss, to reduce post-surgical complications, and to shorten the duration of the surgery in the operating room. Oxidized regenerated cellulose, as described herein below and commonly referred to as ORC, due to its biodegradability, bactericidal, and hemostatic properties, has long been used as a hemostatic wound dressing in a variety of surgical procedures, including neurosurgery, abdominal surgery, cardiovascular surgery, thoracic surgery, head and neck surgery, pelvic surgery, and skin and subcutaneous tissue procedures. ORC, as recognized heretofore by those skilled in the art of wound dressings, is carboxylic-oxidized, regenerated cellulose comprising reactive carboxylic acid groups. In other words, the oxidized cellulose is carboxyl-modified to contain a certain amount of carboxylic acid moieties. Examples of hemostatic ORC absorbable hemostats commercially available include Surgicel absorbable hemostat, a knitted fabric of ORC; Surgicel Nu-Knit absorbable hemostat, a dense ORC fabric; and Surgicel Fibrillar absorbable hemostat; all available from Johnson & Johnson Wound Management Worldwide, a division of Ethicon, Inc., Somerville, N.J., a Johnson & Johnson Company. Other examples of commercial absorbable hemostats containing carboxyl-oxidized cellulose include Oxycel absorbable cellulose surgical wound dressing, available from Becton Dickinson, Morris Plains, N.J.

[0003] Conventional oxidized cellulose (OC) and oxidized regenerated cellulose (ORC) hemostats noted above are knitted, woven or non-woven fabrics comprising carboxylic acid groups, as noted above, in amounts effective to provide them with anti-microbial properties. However, the acid-based ORC and OC, due to their acidic pH, also rapidly denatures acid sensitive and hemostatic proteins, including thrombin or fibrinogen, on contact. Thus it is most problematic and has not been suggested in the art to use the OC or ORC as a carrier for acid-sensitive species, such as thrombin and fibrinogen, as well as other acid-sensitive biologics and pharmaceutical agents.

[0004] Cellulose can undergo many modifications in oxidizing media and, accordingly, the properties of oxidized cellulose, generally referred to as oxycellulose, vary widely depending on the oxidation agents used. Oxidation of the secondary alcohol groups of cellulose with periodic acid or its salts to form a aldehyde-modified cellulose has been disclosed in the prior art as a means of characterizing the chemical structure of mono-, oligo- and polysaccharide-based materials.

[0005] The use of cotton gauze that has been modified by oxidation to contain aldehyde, and then further modified by carboxymethylation, sulfonation or phosphorylation, has been disclosed for use in wound dressings. However, such dressings are not regenerated and contain functional groups such as carboxymethly, sulfonyl or phosphonyl, that are acidic.

[0006] To date, aldehyde-modified, regenerated polysaccharides have not been utilized in wound dressings. Methods of producing highly oxidized tricarboxylic acid derivatives of cellulose as hemostic materials, involving two-stage oxidation by successive processing with an iodine-containing compound and nitrogen oxides, has been disclosed in RU2146264 and IN159322. As disclosed in these disclosures, oxidized cellulosic materials were prepared by preliminary oxidation with metaperiodate or periodic acid to yield periodate-oxidized, dialdehyde cellulose to form the intermediate for forming OC. The dialdehyde cellulose intermediate then is further oxidized by NO₂ to yield the OC with a higher carboxylic acid content, which is suitable for use as a hemostatic, anti-microbial and wound healing agent. The disclosures do not, however, suggest or disclose that the periodate-oxidized, dialdehyde cellulose intermediate formed in the first stage oxidation may or should be used in the preparation of wound dressings.

[0007] It would be an advantage to provide wound dressings that are anti-microbial, that aid in covering and protecting a wound, that are compatible with acid-sensitive species and that preferably are essentially free of unnecessary or undesirable reactive moieties.

[0008] The present invention is directed to wound dressings that include a substrate for contacting a wound, which substrate comprises a wound-contacting surface, and which substrate comprises and is fabricated at least in part from a biocompatible, aldehyde-modified, regenerated polysaccharide. The aldehyde-modified, regenerated polysaccharide preferably comprises an amount of aldehyde moieties effective to render the substrate biodegradable. The wound dressings cover and provide protection to a wound. The invention also is directed to methods of covering and providing protection to a wound, which method includes applying to a wound the wound dressing described herein.

[0009] The present invention is directed to wound dressings that provide coverage and protection when applied to a wound. Certain dressings of the present invention may provide effective hemostasis in addition to providing coverage and protection of the wound. Effective hemostasis, as used herein, is the ability to control and/or abate capillary, venous, or arteriole bleeding within an effective time, as recognized by those skilled in the art of hemostasis.

[0010] Certain of the wound dressings of the present invention are particularly useful when conventional procedures to control and/or abate bleeding, such as pressure or suturing, are either ineffective or impractical. Such wound dressings also are useful where one desires to utilize in, or in conjunction with, the wound dressing hemostatic agents, or other biological or therapeutic compounds, moieties or species, particularly those acid-sensitive agents that may be degraded or denatured by, or otherwise detrimentally affected by acidic pH provided by, e.g. carboxylic acid moieties, such as is provided by conventional hemostats.

[0011] The wound dressings may take various physical forms and may include, without limitation, fibrous or non-fibrous, woven or non-woven dressings. In preferred embodiments, the wound dressing may comprise a fiber, including microfibers, a film, a fabric, a foam, a bead, a gel, or combinations thereof. Regardless of the form of the wound dressing, it will comprise a substrate for contacting and/or covering the wound.

[0012] In certain embodiments, substrates may be incorporated into slurries, pastes, dispersions or other mixtures and applied directly to a wound surface. In such instances, additional wound dressings may be applied over such substrates, but are not necessarily required. In some embodiments, the wound dressing could comprise the substrate in a carrier for delivery of the substrate to the wound. For example, polymeric beads, microfibers, or ground foam substrates, all comprising the aldehyde-modified polysaccharides of the present invention, may be dispersed in slurries or dispersions that may be applied directly to a wound or, in certain circumstances, injected subcutaneously or otherwise disposed internally into the body. Gels also may be formulated so as to be applied to a wound or otherwise disposed within the body in order to provide protection of the wound.

[0013] In certain wound dressings, the dressing may consist essentially of the substrate, or may consist of the substrate. This is particularly true where the wound dressing is fabricated from a knitted, woven or non-woven hemostatic fabric that has been oxidized to provide aldehyde modification, as described herein, and which serves as the substrate for the wound dressing. In those cases, while the wound dressing may further include such components as backing layers, adhesive layers, or the like, the wound dressing can include only the hemostatic fabric.

[0014] The wound dressing substrate will comprise a wound-contacting surface. Such substrates may take various physical forms, including, but not limited to, fibrous or non-fibrous, woven or non-woven substrates. In certain embodiments, the wound dressing substrates may comprise a fiber, including microfibers, a film, a fabric, a foam, a bead, a gel, or combinations thereof. In preferred embodiments, the substrate comprises a woven fabric. The fabric may be formed, cut or otherwise shaped to cover the wound surface, thereby providing coverage and protection of the wound.

[0015] Wound dressings of the present invention, and more particularly the wound-contacting substrates thereof, comprise a biocompatible, aldehyde-modified, regenerated polysaccharide. In preferred wound dressings, the regenerated polysaccharide will contain an amount of aldehyde moieties effective to render the modified polysaccharide biodegradable, meaning that the polysaccharide is degradable by the body into components that either are resorbable by the body, or that can be passed readily by the body. More particularly, the biodegraded components do not elicit permanent chronic foreign body reaction because they are absorbed by the body, such that no permanent trace or residual of the component is retained at the implantation site.

[0016] Aldehyde-modified, regenerated polysaccharides used in the present invention may be prepared from biocompatible polysaccharides that are useful in medical devices. Such polysaccharides include, without limitation, cellulose, alkyl cellulose, e.g. methylcellulose, alkylhydroxyalkyl cellulose, hydroxyalkyl cellulose, cellulose sulfate, salts of carboxymethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, chitin, carboxymethyl chitin, hyaluronic acid, salts of hyaluronic acid, alginate, alginic acid, propylene glycol alginate, glycogen, dextran, dextran sulfate, curdlan, pectin, pullulan, xanthan, chondroitin, chondroitin sulfates, carboxymethyl dextran, carboxymethyl chitosan, chitosan, heparin, heparin sulfate, heparan, heparan sulfate, dermatan sulfate, keratan sulfate, carrageenans, chitosan, starch, amylose, amylopectin, poly-N-glucosamine, polymannuronic acid, polyglucuronic acid polyguluronic acid, and derivatives of any of the above. In preferred embodiments, the regenerated polysaccharide is oxidized as described herein to assure that the aldehyde-modified, regenerated polysaccharide is biodegradable. Such biodegrable, aldehyde-modified, regenerated polysaccharides may be represented by Structure I below.

[0017] where x and y represent mole percent, x plus y equals 100 percent, x is from about 95 to about 5,

[0018] y is from about 5 to about 95; and

[0019] R may be CH₂OR₃, , COOR₄, sulphonic acid, or phosphonic acid; R₃ and R₄ may be H, alkyl aryl, alkoxy or aryloxy, and R₁ and R₂ may be H, alkyl, aryl, alkoxy, aryloxy, sulphonyl or phosphoryl.

[0020] In preferred embodiments of the present invention, the biocompatible, biodegradable wound dressing comprises a wound contacting/covering substrate prepared from a biocompatible, biodegradable, aldehyde-modified regenerated cellulose. Regenerated cellulose is preferred due to its higher degree of uniformity versus cellulose that has not been regenerated. Regenerated cellulose is described in, for instance, U.S. Pat. No. 3,364,200, the contents of which is hereby incorporated by reference as if set forth in its entirety.

[0021] In particular, preferred aldehyde-modified regenerated cellulose is one comprising repeating units of Structure II:

[0022] where x and y represent mole percent, x plus y equals 100 percent, x is from about 95 to about 5,

[0023] y is from about 5 to about 95; and R is CH₂OH, R₁ and R₂ are H.

[0024] In certain embodiments according to the present invention, x is from about 90 to 10 and y is about 10 to about 90. Preferably, x is from about 80 to 20 and y is from about 20 to about 80. Even more preferably, x is from about 70 to about 30. Most preferably, x is about 70 and y is about 30.

[0025] The dressings of the present invention also provide anti-microbial activities due to the presence of effective amounts of the aldehyde moieties. It has been shown that in spite of being non-acidic, the aldehyde-modified, regenerated cellulose is anti-microbial in nature. The dressings of the present invention were found to be significantly effective against microorganisms, such as Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, etc. The anti-microbial activities of the non-acidic aldehyde-modified, regenerated cellulose are shown to be comparable to those of the acidic carboxylic oxidized regenerated cellulose conventionally used in wound dressings. The acidic carboxylic oxidized regenerated cellulose loses its anti-microbial activities upon neutralization reaction or over a period of time as the acid groups are neutralized in the body. However, the aldehyde-modified, regenerated cellulose utilized in the present invention is expected to retain its anti-microbial activity over a longer period of time.

[0026] In preferred embodiments of the invention, the aldehyde-modified, regenerated polysaccharide is essentially free of functional or reactive moieties other than aldehyde moieties. By essentially free, it is meant that the polysaccharide does not contain such functional or reactive moieties in amounts effective to alter the properties of the aldehyde-modified, regenerated polysaccharide or to provide the substrate comprising the polysaccharide with a pH of less than about 4.5, more preferably less than about 5, or greater than about 9, preferably about 9.5. Such moieties include, without limitation, carboxylic acid moieties typically present on wound dressings made from OC. Excess levels of carboxylic acid moieties will lower the pH of the substrates and dressings so that they are not compatible for use with those species that may be degraded or denatured by such a low pH, e.g. thrombin. Other undesired moieties include, without limitation, sulfonyl or phosphonyl moieties.

[0027] The hemostat of the present invention exhibits increased thermal stability compared to that of the carboxylic oxidized regenerated cellulose fabric (ORC). The increased thermal stability may be indicative of improved physical shelf-life, compared to ORC or neutralized ORC.

[0028] In certain embodiments of the invention, the fabrics utilized in the present invention may be knitted, woven, or non-woven, provided that the fabric possesses the physical properties adequate for wound dressings. Fabrics oxidized by periodic acid or its salts described in the present invention are expected to retain physical properties and mechanical integrity required for use in wound dressings. Fabrics that are useful in the present invention include those described in U.S. Pat. Nos. 2,773,000, 3,364,200 and 4,626,253, the contents each of which is hereby incorporated by reference herein as if set forth in its entirety. Also useful in wound dressings of the present invention are fabrics useful in adhesion prevention such as those described in U.S. Pat. No. 5,002,551, the contents of which is hereby incorporated by reference herein as if set forth in its entirety.

[0029] In certain embodiments of the invention, the wound dressing of the present invention comprises as the wound contacting/covering substrate a warp knitted tricot fabric constructed of bright rayon yarn that has been oxidized by periodic acid or its salts such that the substrate comprises aldehyde moieties. Both Scanning Electron Microscopic (SEM) images and fabric mechanical properties indicate that the physical characteristics (density, thickness) and physical performance, e.g. fabric tensile strength and mullen burst strength, of the aldehyde-modified, regenerated cellulose in the present invention are comparable to those of the fabric disclosed in U.S. Pat. No. 4,626,253.

[0030] The wound dressing of the present invention remains very flexible, conforms to a wound site, and retains good tensile and compressive strength to withstand handling during application. The aldehyde-modified, regenerated cellulose substrate can be cut into different sizes and shapes to fit the surgical needs. It can be rolled up or packed into irregular anatomic areas.

[0031] Other warp knit tricot fabric constructions which produce equivalent physical properties may, of course, be utilized in the manufacture of the aldehyde-modified, regenerated cellulose hemostatic wound dressings of the present invention, and such constructions will be apparent to those skilled in the art once having the benefit of this disclosure.

[0032] In certain embodiments of the invention, a biologics, a drug, or a combination of pharmaceutical agents, including those that otherwise may be sensitive to the low pH of conventional OC-containing wound dressings, may be incorporated into certain wound dressings of the present invention without having to adjust pH prior to incorporation into the dressing. To fabricate such a wound dressing, a drug or agent first may be dissolved in an appropriate solvent. The fabric is then coated with the drug solution and the solvent is removed. Preferred biologics, drugs and agent include analgesics, anti-infective agents, antibiotics, adhesion preventive agents, pro-coagulants, and wound healing growth factors. The aldehyde groups formed on the polysaccharide matrix during the periodate oxidation reaction can be used to covalently bond amine containing biologics and therapeutic agents. The combination of such biologics, drugs and agents with wound dressings of the present invention using the aldehyde-modified regenerated cellulose substrates can provide improved hemostatic wound dressings, wound healing dressings, drug delivery devices, and tissue engineering matrices.

[0033] While the following examples demonstrate certain embodiments of the invention, they are not to be interpreted as limiting the scope of the invention, but rather as contributing to a complete description of the invention.

[0034] A 15.75 g piece of Nu-Knit rayon fabric was cut in the form of a strip 1.5 inches wide. The strip was wound on a mandrel and suspended in 600 ml of aqueous isopropyl alcohol (IPA) (200 ml IPA/400 ml de-ionized (DI) water). 20.8 g of sodium periodate (Aldrich, Milwaukee, 53201) was dissolved in the solution (1:1 molar ratio) and the mandrel was rotated at moderate rpm in the solution for 21 hours at ambient temperature. It is essential that the oxidation of the fabric be conducted in the dark. The solution pH was 3.8. The solution was discarded after the reaction. The mandrel with the oxidized fabric was washed for 30 minutes in 1 liter of cold DI water containing 50 ml of ethylene glycol. It was then washed with aqueous IPA (50/50) for 15 minutes, followed by a pure IPA wash for 15 minutes. The fabric was dried in ambient air for several hours. Aldehyde content: Ave. 22.83%

[0035] The oxidized fabric then was evaluated for hemostasis as set forth below. Results are provided in Table 1.

[0036] A 10 g piece of cellulose rayon non-woven fabric was cut in the form of a rectangle and placed in an aqueous solution of sodium periodate (Aldrich, Milwaukee, 53201) (1:0.7 molar ratio). The fabric was placed in a container modified to exclude light and soaked in the dark for 24 hours at 37 C. The solution was discarded after the reaction. The fabric was repeatedly washed with DI water until the pH was 6-7. It was then washed with aqueous IPA (50/50) for 15 minutes. The fabric then was washed in pure IPA for 15 minutes. The fabric was dried in ambient air for several hours. aldehyde content: 51.04%

[0037] The oxidized fabric then was evaluated for hemostasis as set forth below. Results are provided in Table 1.

[0038] 10.6 g of powdered cellulose rayon was suspended in an aqueous solution of sodium periodate (Aldrich, Milwaukee, 53201)(13.9 g in 250 ml DI water) and stirred for 7 hours at ambient temperature in the dark. The solution was filtered after the reaction. The filtrate was repeatedly washed with DI water until the pH was in the range of from 6 to 7. It was then washed with aqueous IPA (50/50) and pure IPA for 15 min each. The powder was dried in air for several hours. aldehyde content: 32.8%

[0039] The oxidized powder then was evaluated for hemostasis as set forth below. Results are provided in Table 1.

[0040] 13.67 g of porous cellulose beads are floated in an aqueous solution of sodium periodate (Aldrich, Milwaukee, 53201) (18 g in 250 ml DI water/125 ml IPA) and stirred for 24 hours at ambient temperature. The material was filtered and the filtrate (beads and crushed beads) was repeatedly washed with DI water until the pH was in the range of from 6 to 7. It was then washed with aqueous IPA (50/50) and pure IPA for 15 min each. The material was dried in air for several hours. aldehyde content: intact beads29.86%; crushed beads35%

[0041] The oxidized beads then were evaluated for hemostasis as set forth below. Results are provided in Table 1.

[0042] 100 g of a 5% methylcellulose (Aldrich, Milwaukee, 53201) aqueous solution was combined with 3 g of periodic acid (Aldrich, Milwaukee, 53201) and was then stirred for 5 hours at ambient temperature in the dark. 1.5 ml of ethylene glycol was added to the reaction solution and stirred for 30 minutes. 2000 ml of acetone were added slowly into the reaction solution to precipitate the methylcellulose dialdehyde. The reaction mixture was allowed to stand for 20-30 minutes to separate the liquid phase from the solid phase. The supernatant then was removed and the solid phase centrifuged to precipitate the solids. The solid precipitate was dissolved in 100 ml DI over night followed by dialysis for 72 hours. The final wet mixture was lyophilized to form a sponge/foam.

[0043] The material then was evaluated for hemostasis as set forth below. Results are provided in Table 1.

[0044] 100 g of a 4% sodium carboxymethyl cellulose (Aldrich, Milwaukee, 53201) aqueous solution was added with 2.12 g of sodium periodate (Aldrich, Milwaukee, 53201) and was then stirred for 24 hours at 4 C. in the refrigerator. 200 ml ethanol was slowly added into the reaction solution to precipitate the aldehyde-modified carboxymethyl cellulose. The supernatant was removed and the solid phase mixture centrifuged to precipitate the solids. The solid precipitate was dissolved in 100 ml DI. Precipitation and centrifuging were repeated. The final product was dissolved in 100 ml DI then lyophilized to form a sponge/foam.

[0045] The material then was evaluated for hemostasis as set forth below. Results are provided in Table 1.

	TABLE 1
	Sample	Time to Hemostasis (seconds)
	Example 1 fabric	187 (n 11)
	Example 2	96 (n 5)
	Example 3	120 (n 3)
	Example 4	238 (n 1)
	Example 5	120 (n 2)
	Example 6	360 (n 2)
	Surgical gauze	>720 (n 6)

[0046] A porcine spleen incision model was used for hemostasis evaluation. The materials were cut into 2.5 cm2.0 cm rectangles. A linear incision of 1.5 cm with a depth of 1.0 cm was made with a surgical blade on a porcine spleen. After application of the test article, digital tamponade was applied to the incision for 2 minutes. The hemostasis was then evaluated. Additional applications of digital tamponade for 30 seconds each were used until complete hemostasis was achieved. The fabrics providing hemostasis within 15 minutes, preferably within 12 minutes, were considered to be effective hemostats. Wound dressings comprising aldehyde-modified regenerated cellulose achieved rapid hemostasis compared to the negative control of surgical gauze.

[0047] 1 g of fabric was digested in 10 ml of 0.5N NaOH and 100 ml DI water at ambient temperature for 2 hours. The residual NaOH was back-titrated to a fixed endpoint using 0.1N HCl. The aldehyde content was calculated using the formula:

[0048] where B is the burette reading (in ml) from a blank titration, S is the burette reading (in ml) from a sample and W is the sample weight. Aldehyde content is the number of glucose rings (by mole) containing the dialdehyde functionality.

[0049] Aldehyde content of aldehyde modified regenerated cellulose in the present invention, processed in various physical forms, is substantially consistent in the range of 20-50%.

[0050] Studies were designed to study the effect of the sample against the microbial challenge over a period of time. Aldehyde-modified regenerated cellulose fabric (Example 1), Surgicel NU-KNIT and Surgicel Fibrillar samples were cut to a weight of 165-mg (2-mg). The weighed sample was then placed into a sterile test tube. An aliquot of 11-ml of TSB was added to the test tube containing the sample. Three (3) test tubes were prepared for each aldehyde-modified regenerated cellulose powder and control sample. Each test tube was innoculated with 0.1-L of microorganism from stock cultures. Prepared samples were subsequently diluted and pour plated. This procedure was carried out at time 0 (immediately following innoculation), 1, 6, 24, and 48 hours after innoculation.

[0051] Methicillin-resistant Staphylococcus aureus (MRSA) organisms were grown in Trypticase Soy Broth (TSB) for 24 hours at 30-35 C. Trypticase Soy Agar (TSA) and TSB were the media used in this study. The dilutions used 0.85% saline. All media and solutions were sterile.

[0052] The experiment results demonstrate that periodate oxidized regenerated cellulose hemostats (Example 1 fabric) and the Surgicel Nu-Knit& controls were both effective at significantly reducing the microbial populations of MRSA.