HK1060071A1 - Microbial cellulose wound dressing for treating chronic wounds - Google Patents

Description

Microbial cellulose wound dressing for treating chronic wounds

RELATED APPLICATIONS

This application is a continuation-in-part of the application serial No.10/132,171 filed on 26.4.2002. The disclosure of this application is incorporated herein by reference.

Technical Field

The present invention relates to a wound dressing comprising microbially derived cellulose for the treatment of specific types of chronic wounds including pressure sores, venous and diabetic ulcers.

Background

There are a wide variety of materials used to make wound dressings that are used to treat a wide variety of surgical and non-surgical injuries, such as burns and abrasions. Dressings range from simple gauze type dressings to animal derived protein type dressings, such as collagen dressings, the composition of a particular dressing depending on the type of wound being treated. Each of these dressings has advantages in certain types of applications. For example, a gauze type dressing is sufficient to treat simple abrasions and surgical incisions and is very economical.

On the other hand, polymer-based dressings were found to be more effective in the case of chronic wounds. By definition, chronic Wounds are Wounds that fail to undergo a normal recovery process and have typical manifestations of potential problems such as diabetes, venous disease or impaired circulation (Lazarus, G.S. et al Definitions and guidelines for assessessment of Wends and Evaluation of health, Arch. Dermatology, vol.130, page 489-493, 1994). Thus, chronic wounds can be broadly classified as pressure sores (decubitus ulcers), venous and diabetic ulcers, depending on the underlying problem. For this reason, a variety of different types of wound treatment methods and materials are used to address potential problems and promote healing of wounds. Advanced polymeric materials with the ability to maintain a moist wound environment have been shown to be more effective than gauze in treating these difficult to heal chronic wounds.

In the context of polymer-based dressings, various types of polymeric materials have been used in the treatment of skin conditions. Generally, they can be divided into two broad categories, namely synthetic and naturally derived polymeric materials.

Synthetic materials include polyurethane, polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), polyvinyl alcohol (PVA), and Polyacrylonitrile (PAN). These materials may be used in combination with other synthetic or natural polymers to make wound dressings with specific properties, such as moisture retention and high liquid absorption. These properties are generally not present in gauze type dressings, by protecting chronic wounds from infection and maintaining a certain moisture content in the wound to promote healing. Huang, in U.S. patent 6,238,691, discloses a three-dimensionally crosslinked polyurethane hydrogel wound dressing that is absorbent, follows the contours of the wound size and maintains the wound in a moist state to promote healing.

Meyer-Ingold et al, U.S. patent 6,156,334, disclose wound coverings with which to remove interfering factors such as antigens, free radicals, ions, proteins, peptides, lipids and free fatty acids in the wound fluid of chronic wounds. These wound coverings are chemically modified with "capture molecules", such as antibodies, chelators, enzyme inhibitors, enzymes, mimetics, peptides and other proteins, are polyurethanes or plant-derived celluloses.

Similarly, polymers or biopolymers derived from natural sources, such as collagen and alginates, have also been used as wound dressings to exploit desirable polymer properties, such as the high absorptive capacity of alginates or the biocompatible nature of collagen. Each dressing has associated particular advantages, depending on the type of wound and the amount of exudate it produces. However, these dressings also have disadvantages including higher cost, wound adhesion, limited exudate absorption and residual deposits on the wound site.

Hydrocolloid dressings can absorb wound exudate and provide a moist wound healing environment, but also have unwanted residual deposits at the wound site. In addition, unlike the microbial-derived cellulose dressings described herein, hydrocolloid dressings lack the moist environment required to dry chronic wounds with limited exudate. Also, hydrocolloids are known to adhere to the wound bed and can cause secondary damage when removed. The tendency of the hydrocolloid to break down in the wound bed may interfere with the wound healing process.

As an alternative material, the microorganism-derived cellulose has inherent properties effective in promoting wound healing without the disadvantages of those currently available wound dressings. In this regard, microbially derived cellulose has the following physical properties that distinguish it from plant derived cellulose, such as extreme hydrophilicity and a unique multi-layered three-dimensional sheet-like structure that provides its moisture handling capability. As described in U.S. patent 4,942,128, microbial cellulose is very water-absorbent, having a water holding content in the range of 60 to 700 times its own weight. The cellulose of the microorganisms likewise shows good wet strength and does not break under pressure. Finally, because of its multi-layer sheet-like structure, microbial cellulose can be processed to produce films with novel liquid handling capabilities. The processed microbial cellulose has the ability to provide or absorb liquid by adjusting the ratio of cellulose to liquid depending on the surface of the wound in contact with the manufactured film.

Because of the excellent properties of microbial cellulose, its use in the medical industry has been previously investigated. For example, Ring et al in U.S. patent nos.4,588,400, 4,655,758 and 4,788,146 disclose the possibility of using microbially derived cellulose in liquid filled pads. The patent of Ring et al focuses on microbial cellulose pads produced by static methods loaded with various liquids and drugs. Various types of liquids that can be contained in microbial cellulose pads and manufacturing and cleaning processes to produce virgin cellulosic materials are detailed. Examples of detailed methods of making various mats are also described in these patents, wherein the method includes a series of steps of pressing and soaking to adjust its physical properties, primarily with respect to liquid to cellulose ratio, to produce the desired product. As an example, these patents describe a highly hydrated pad (80 to 1 liquid to cellulose ratio) that provides cooling capability, which is desirable for burn applications. In particular, the' 146 patent describes the use of such liquid-filled pads as moist dressings for ulcers, which provide moisture to the wound over an extended period of time. The same' 146 patent also mentions that the moist dressing described in the examples additionally has the ability to absorb large amounts of fluid from the wound when the dressing is in less than saturated conditions. However, the wound dressing of Ring et al does not mention a single dressing that can be used as a source of moisture for chronic wounds while having the dual ability to absorb fluid. The Ring et al patent also fails to describe an effective liquid to cellulose ratio and the production of a wound dressing having dual liquid delivery capabilities.

U.S. patent No.4,912,049 to Farah et al discloses the use of statically produced dehydrated microbial cellulose as an artificial skin graft, separation membrane or artificial leather. The' 049 patent describes the use of acetobacter xylinum, a fibrous film formed by dewatering it as it is stretched. Although the' 049 patent describes the potential use of their invention as artificial skin for treating wounds or injuries, there is no suggestion that these materials could be used for chronic wounds. Furthermore, Farah's dried film has no ability to provide moisture and its absorption capacity is small.

Finally, U.S. patent No.5,846,213 to Wan et al discloses a method for producing microbial cellulose films using raw materials in a stirred bioreactor, rather than a static method. The' 213 patent further describes the use of such cellulosic materials dissolved in a solvent to produce films for use as wound dressings. Because of the dry nature of the resulting film, the film material lacks any ability to provide moisture and limited liquid absorption capacity. In addition, the cellulose film thus produced does not have the three-dimensional multilayer structure described above which is formed only in the statically incubated microbial cellulose.

Although the above patents recognize the potential use of microbial cellulose in medical applications, the prior art fails to provide a method of developing a wound dressing that demonstrates effective wound healing, moisture control capability, and adequate biocompatibility. Thus, there is a need for a wound dressing comprising highly biocompatible microbial cellulose that can treat chronic wounds. Furthermore, wound dressings with a high capacity to provide and absorb moisture are also particularly desirable for optimal wound healing. This two-way moisture management capability of the dressing of the present invention enables the maintenance of a moist wound environment necessary for the healing of chronic wounds. In addition, a high degree of moisture-providing capability is particularly beneficial for dealing with dry, necrotic tissue and closing any wounds into the potentially desirable autolytic debridement. Finally, the wound dressing of the present invention demonstrates the unique ability of the wound dressing to effect wound closure while assisting self-healing by promoting granulation, and the ability to allow epithelial cell transplantation.

Accordingly, the present inventors have developed wound dressings that have novel absorbing and providing fluid management capabilities. This liquid handling capacity is the end result of treating microbial cellulose to contain an appropriate amount of cellulose for its intended purpose. The prepared wound dressing is capable of providing a liquid if the wound surface is dry, and has been found to be particularly beneficial for dry, necrotic tissue or eschar-covered dry, chronic wounds. The same dressing also has the ability to absorb fluids exuded from the wound bed. In addition, unlike hydrocolloid dressings, the microbial cellulose wound dressings described herein do not degrade and leave a residue at the wound site. Removal of the microbial cellulose dressing from the wound site does not damage the tissue because it does not adhere to the wound surface.

The present invention also contemplates microbial cellulose sheets of virtually any shape or size that can be directly synthesized. The fermentation process enables the production of products in very thin and flexible form, which are very robust and permeable to gases and liquids. The shape remains intact even when subjected to extreme environmental conditions, such as autoclaving or gamma-ray sterilization.

Disclosure of Invention

It is an object of the present invention to provide a method of treating chronic wounds with a dressing of cellulose derived from microorganisms, wherein the weight of cellulose is between 1.5% and 9%. In a preferred embodiment, the microbially derived cellulose is biocompatible and non-pyrogenic.

It is another object of the present invention to provide an effective wound dressing comprising microbial cellulose capable of providing and absorbing moisture for optimal wound healing for the treatment of chronic wounds.

It is another object of the present invention to provide the use of a non-pyretic, biocompatible, cellulose dressing derived from microorganisms, wherein the cellulose dressing comprises from about 1.5% to about 9% by weight of cellulose, in the manufacture of a kit for the treatment of chronic wounds.

It is another object of the present invention to provide a kit comprising:

a) a microbial derived cellulose comprising from about 1.5 to about 9% by weight cellulose;

b) a waterproof package comprising cellulose derived from said microorganism; and

c) instructions for administering the microorganism-derived cellulose to a chronic wound.

In a preferred embodiment, the microorganism-derived cellulose in the kit comprises from about 3% to about 7% cellulose. In a more preferred embodiment, the microorganism-derived cellulose in the kit comprises from about 4% to about 6% cellulose. In other preferred embodiments, the kit is sterilized by gamma radiation or by electron beam sterilization. In another preferred embodiment, the water-resistant package containing the microorganism-derived cellulose in the kit comprises a heat-sealable, aluminized plastic coated chevron pouch.

Other objects, features and advantages of the present invention will become apparent in view of the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention provides methods for treating total or localized chronic wounds with microbially derived cellulose. The present invention also provides a biocompatible, non-pyretic, microorganism-derived wound dressing having an appropriate cellulose to liquid ratio, and also having the ability to provide and absorb liquid for optimal wound healing. Unlike hydrocolloids, hydrogels, alginates, collagen, or gauze dressings, the microbial-derived cellulose dressings described herein provide an optimal moist healing environment by providing fluid to a dry surface or absorbing excess fluid secreted from a wound.

The content of the microbially derived cellulose in the dressing may vary depending on the method of preparation and the end use of the wound dressing. In the present invention, the amount of microorganism-derived cellulose in the wound dressing is from about 1.5% to about 9%, preferably from about 3% to about 7%, and more preferably from about 4% to about 6% by weight.

The wound dressing of the present invention may be used to provide moisture. Typically, a dressing wound may provide from about 50% to about 90% by weight of its liquid to the dried substrate. This means that wounds exhibiting dry necrotic tissue can be effectively treated by using a wound dressing containing a liquid. Due to potential problems such as venous insufficiency, most chronic wounds often form a dry surface consisting of dead (necrotic) tissue when they initially form the wound surface. The lack of fresh blood flow in a particular area (usually around the ankle) causes the dermis and epidermis to die subcutaneously and eventually form an ulcerated surface. The liquid contained in the wound dressing pad may be used for dry, necrotic wounds to promote autolytic debridement, which is the primary condition for healing chronic wounds. Liquid materials that may be loaded into the pad include, but are not limited to, water, isotonic saline, glycerol, synthetic polymers, such as polyethylene oxide and aqueous solutions of biomolecules including proteins, Platelet Derived Growth Factor (PDGF), Epidermal Growth Factor (EGF) and enzymes, such as collagenase.

The wound dressing of the present invention may also be used for moisture absorption. Typically, wound dressings are capable of absorbing from about 20% to about 200%, preferably from about 35% to 140%, of their own weight. This means that wounds with exudate can be effectively treated by applying the wound dressing of the present invention, which can absorb excess fluid from the wound. Typically, the chronic wounds of such venous ulcers exude large amounts of fluid during the healing process. The exudation phase usually occurs when the wound begins to form granulation tissue that replenishes the space occupied by the dead dermal tissue. The dressing of the invention is able to absorb exudate at this stage while maintaining a wetted surface for epithelial cell migration. Epithelial migration is the basic condition for eventual wound closure. Thus, the wound dressing of the present invention, due to its dual ability to absorb and provide moisture, provides optimum conditions for wound healing.

1. Production of microbial cellulose under static conditions for a test Process

In the preparation of microbial cellulose of the present invention, a microorganism, such as Acetobacter xylinum, is cultured in a bioreactor containing a nutrient solution medium at 30 ℃ and an initial pH of 3-6. The medium is based on sucrose or other carbohydrates. Preferably, efficient film production is achieved using sucrose as a carbon source, ammonium salts as a nitrogen source, corn steep liquor as a nutrient source, in combination with proprietary additional trace elements, as opposed to the original Schramm and Hestrin media (1954) employed by the skilled artisan. The amount of additional trace elements of this patent is shown in the following table:

composition of microelement per liter of solution

570 mg of Tetrasodium Salt EDTA

FeSO₄·7H₂O200 mg

ZnSO₄·7H₂O10 mg

MnSO₄·H₂O26 mg

H₃BO₃30 mg of

CoCl₃·6H₂O20 mg

NiCl₂·6H₂O3.2 mg

(NH₄)₆Mo₇O₁₄·4H₂O2.4 mg

2 ml of this solution are added per liter of medium.

The appropriate bioreactor is selected to have minimal evaporation and to provide appropriate oxygen limiting conditions. The oxygen-limiting conditions can vary depending on the desired water content and the thickness of the cellulose film. Generally, under oxygen-limited conditions, the amount of oxygen is 5% to 21% of the total amount of gas at the gas-liquid interface. The bioreactor consists of a plastic box equipped with a sealed lid or a limited gas permeable lid. The dimensions of the bioreactor profile (cubic or cylindrical) may vary depending on the shape and size of the cellulose film produced. For example, in prior art applications, a 6 inch diameter cylinder would produce a 6 inch diameter wound dressing that could be used directly or cut to size for the wound to be treated. By limiting the amount of oxygen in the fermentation medium, it is hypothesized that Acetobacter utilizes the carbon in the medium to produce more cellulose rather than using it to propagate, thereby increasing the overall yield of cellulose.

The fermentation process is allowed to proceed under static conditions for a period of more than about 7-30 days, during which time the bacteria in the medium produce an intact cellulose film containing the microorganisms. Depending on the desired thickness, i.e. per unit area corresponding to the determined cellulose content, the fermentation is stopped and the membrane is removed from the bioreactor. Excess medium contained in the film is then removed prior to chemical washing and subsequent processing of the film using standard separation techniques, such as compression or centrifugation, to produce a wound dressing having a cellulose to liquid ratio of about 1: 10 to about 1: 65. The unprocessed cellulose film had an increased sacchari-to-cellulose yield of about 35% compared to the literature value of 10%. And the same as described in original schram & Hestrin medium [1954, j.gen.micro, 11: 123- & 129] these increased yields coupled with an inexpensive source of nitrogen resulted in a 40-fold reduction in the cost of raw cellulose film production compared to cellulose films produced.

2. Processing and depyrogenation process

After the production of the cellulose film, the cells must be removed from the cellulose film for purification purposes. Fontana et al (1990, appl. biochem, Biotech, 24: 253-. This result indicates that the chemical process discussed herein to remove cells is necessary in order to pass standard pyrogenicity tests and cellulose wound dressings that are non-pyrogenic and qualified microorganisms.

The cellulose film undergoes a series of chemical washing steps to convert the raw cellulose film into a raw material for achieving pharmaceutical grade and non-heat generating wound dressings. Typical processing is to use 1-20% strength by weight hydroxide solution. It is preferable to use sodium hydroxide at a concentration of not less than 3%, and more preferably about 3% to about 5% in order to lyse the cells. In addition, the present invention uses a hydrogen peroxide wash that bleaches and disinfects the pyrogen-free film. The bleaching of the film can be achieved with a peroxide concentration of about 0.05% to about 10% by weight. Preferably, the peroxide is used in an amount of about 0.1% to about 0.5%. Other bleaching agents such as hypochlorite, hypobromite, and perborate may also be used.

The raw fermentation product is subjected to various purification processes, such as exposure time, concentration and temperature. A treatment time of 1-4 hours associated with a temperature change of 30-100 degrees celsius was investigated to obtain an optimized process. The films obtained from each of the different operating conditions were tested for their pyrogen content and physical properties. For economic reasons, the process conditions are chosen to produce a non-exothermic product in the shortest time and at the lowest chemical concentration. The time involved in this process may be about 4 hours at about 90 c, preferably about 1-2 hours at about 60 c to about 80 c.

The amount of cell debris remaining in the cellulose pad after treatment can be measured according to the limulus sac cell Lysate (LAL) assay, u.s.food and Drug Administration (FDA) in 21cfr10.90. The direct cleaning procedure outlined above provided a non-heated cellulose pad (< 0.05 EU/ml). The permissible pyrogen level in a Class I medical device is 0.5 EU/ml (FDALAL test guidelines). The steps of the LAL test are defined by the test kit manufacturer and can be easily repeated to obtain the content of pyrogens in the cellulose film.

3. Physical modification of cellulosic dressing of microorganisms

Desirable characteristics of the materials of a wound dressing include the ability to provide a moist environment while also having the ability to absorb excess fluid secreted from the wound or to provide moisture to the wound. Typically, commercially available hydrogel wound dressing products have an approximate composition of 90-95% water and 5-10% polymeric material. However, these products fail to provide adequate moisture to the wound and are not strong enough. In addition, these dressings tend to adhere to the wound. This wound adhesion, when the dressing is removed, can result in the wound being re-injured. However, the dressing of the present invention exhibits excellent wettability and absorbency because it has a three-dimensional structure of a sheet-like multilayer not found in any other wound dressings. Depending on the condition of the wound, the cellulose dressing also shows the ability to control the moisture content of the dressing-wound interface by absorbing excess liquid or providing moisture. This moisture management ability helps promote healing of chronic wounds and is a novel feature of cellulosic wound dressings.

Typically the cellulose film is initially composed of > 90% water and 0.2-1% cellulose, or the ratio of cellulose to water is approximately 1: 100 to 1: 500. This material is subjected to a series of physical treatments to obtain the final wound dressing. The water content of the saturated microbial cellulose pad may be reduced to between 98.5% and 0% to obtain a film with a cellulose to water ratio of approximately 1: 65 to 1: 0, i.e. a completely dry material. This can be accomplished using various drying techniques including mechanical extrusion, centrifugal draining, air drying, vacuum drying and freeze drying.

The obtained dewatering mat was then completely immersed in water for its absorption capacity test. The results show that the ability of the fully dried material to reabsorb water is reduced compared to never-dried material. Completely take offThe maximum amount of 24 hour absorption of a pad of water is only per 100cm²The pad had 30 grams of water, while the non-dewatering pad absorbed 60 grams/100 cm at the same time². In this regard, the wound dressings of the present invention comprise a ratio of cellulose to water of about 1: 65 to 1: 10, more preferably about 1: 24 to about 1: 16. These wound dressings exhibit the ability to provide a moist environment, as well as the dual ability to provide moisture or absorb secreted fluids for optimal wound healing.

4. Packaging and sterilization of products

The packaging material should be impermeable to water to prevent the wetted cellulosic wound dressing from drying out and being able to withstand sterilization procedures. For example, heat sealable, aluminized plastic coated chevron bags can provide sufficient impermeability and moisture retention capability.

Two of the most common sterilization processes used in medical wound dressings, gamma irradiation and electron beam sterilization, have been investigated. The packaged cellulose wound dressing was exposed to various levels of radiation in the range of 5-50 KGy. The sterility of each dressing was then evaluated using USP sterility test standards. The overall appearance and mechanical integrity of the dressing and the packaging material were also checked. The results of the sterility test showed that the cellulose wound dressing was stable at KGy radiation doses of 5-40 and the minimum dose required to ensure sterility of the product was 15 KGray. The cellulose wound dressing products for the biocompatibility, animal and human tests were then completely sterilized at 30KGy (twice the safety factor) to ensure sterility of the product.

Drawings

FIG. 1: expressing the uptake and delivery capacity of the microbial cellulose wound dressing relative to the percentage of cellulose contained in the material. All materials have the same area and similar thickness. The area where the two curves intersect indicates the ideal cellulose content for optimization of both properties.

FIG. 2: denotes the amount of liquid that XCell microbial cellulose wound dressing and hydrogel wound dressing provide to the drying surface. The amounts provided are expressed as a percentage of the original sample weight. The XCell wound dressing is significantly better able to provide fluids than hydrogels.

FIG. 3: the uptake and delivery capacity of XCell microbial cellulose wound dressings is comparable to that of clearsite (ndm) hydrogel wound dressings. The absorption capacity of both is almost the same, but XCell wound dressings have a 6 times greater capacity to provide liquid than hydrogels.

Detailed Description

Biological examples

Example 1 absorption/delivery study

Cellulose films of various thicknesses were produced and processed to remove cell debris. The films were compressed to a uniform thickness of 1.9 mm to produce a series of films having a cellulose content ranging from 1.5% to 10%. These films were tested for their ability to absorb saline from saturated surfaces and provide moisture to dry surfaces.

The same area of the sample weighed was placed on the saturated sponge surface. The sponge was perfused with saline to maintain saturation. After 24 hours, the samples were re-weighed to determine the absorbency performance and then plotted as a percentage of the initial sample weight. To determine the moisture provided, a weighed sample of the same area was placed on a flat, dry leather surface. The leather was weighed before placing the sample. After 2 hours, the sample was removed and the leather was weighed again to determine the amount of moisture provided and plotted as a percentage of the initial sample weight.

Both absorption and data are plotted on a graph to determine the optimum water content for both properties. This data is shown in figure 1. From this figure it can be seen that the percentage of cellulose in the dressing is preferably in the range of 3% to 6% in order to have the ability to absorb and provide. This figure also shows that dressings with enhanced absorption or enhanced delivery capabilities can be produced at the expense of another property.

In order to demonstrate the superior delivery capacity of microbial cellulose wound dressings (Xcell), commercially available conventional hydrogels were tested. The products tested were Clearsite (NDM), Nugel (Johnson & Johnson) and Flexigel (Smith & Nephew). These products were tested using the same procedure described above and the data obtained is shown in figure 2. The data for XCell used is for a material comprising 4.3% cellulose. Clearly, the XCell dressing provides over 75% of its initial weight, rather than providing all competing products with capacities between 9% and 31%.

While providing capacity is important to wound healing, it would be desirable if a wound dressing had the ability to provide and absorb. The previously described absorption process was used for testing of the Clearsite hydrogel wound dressing. This set of data, together with the provisioning data and XCell data, is shown in fig. 3. It can be seen that the absorption of both samples is almost the same, but the Xcell material provides more than 6 times more water than the hydrogel.

Example 2 biocompatibility test

The following biocompatibility tests were performed on sterile cellulose wound dressings: 1) guinea pigs promote receptivity, 2) primary stimulation on wild rabbits and, 3) cellular toxicity. In the test of susceptibility enhancement, 6 guinea pigs were injected with the extract of the product. Body temperature was monitored for any of the guinea pigs that promoted a sensory response over the study period of 8-10 weeks. The results indicate that there is no evidence of prolonged skin contact promoting sensitivity in guinea pigs. Two week primary stimulation test studies were performed using hares. In this test, an extract of the cellulose dressing is injected subcutaneously and the skin is observed for a stimulating response. The results show that there is no evidence of significant irritation or toxicity after subcutaneous injection of the extract into rabbits. The primary irritation index of the cellulose dressing extract was considered negligible. Finally, the dressing was tested for toxicity to mammalian cells using murine L929 cell cultures. The results show that the cellulose dressing extract is non-toxic and does not inhibit cell growth. The cellulosic wound dressing prepared in accordance with the present invention successfully passed all of these tests and therefore the product is believed to be biocompatible, safe and does not inhibit wound healing.

Example 3 wound healing in animal Models (Models)

The objective of preclinical animal studies is to compare the wound healing performance of microbial-derived cellulosic wound dressings in porcine animal models with existing wound dressing products, such as hydrocolloids and hydrogels.

The tests were carried out using The pig model protocol according to The Department of biology of The University of Miami School of Medicine in Association for accession of Laboratory Animal Care (AAALAC).

Briefly, the test was performed on 2 pathogen-free pigs for a period of over seven days. Approximately 140 rectangular wounds (10X 7X 0.3 mm) were made in the paravertebral and thoracic regions of each pig using a special electroplating keratome with a 7 mm blade. The wounds were separated by 15 mm of intact skin. Approximately 35 wounds were randomly assigned to each wound dressing selected from the group consisting of cellulose, hydrocolloid, hydrogel, and dressing-free/air-exposed state. Evaluation of epidermal transplantation was started 2 days later.

In summary, the results indicate that cellulosic wound dressings and hydrocolloid dressings heal locally dense wounds and are superior to hydrogel dressings. Notably, on day four after injury, the cellulosic wound dressing healed 70% of the wound compared to 50%, 20% and 0% healing rates for hydrocolloids, hydrogels and air exposure, respectively. By day 5, both the cellulose and hydrocolloid dressings cured 100% of the sampled wounds, while the hydrogel and air exposed samples cured only 70% and 50%, respectively.

Example 4 clinical efficacy testing in humans in treating chronic wounds

The aim of human clinical testing is to assess the effectiveness of cellulosic wound dressings for the treatment of different types of chronic wounds. A total of 29 patients with 31 different types of chronic wounds were studied. Patients were treated with cellulose wound dressings under the inclusion criteria outlined by institutional ethics committee (IR) approved research protocols. Treatment of the cellulosic wound dressing is carried out for 8 weeks or until the wound is healed. Wounds were observed once a week. Dressing changes were made after the recorded observations. The condition and size of the wound were recorded at the visit once a week, and the study was terminated after wound healing or at eight weeks of treatment.

The results of human studies can be divided into three significant indications based on the performance of cellulosic wound dressings. Cellulosic wound dressings exhibit the strength to remove necrotic slough in deep pressure ulcers. In two wounds that have suffered from such problems, the use of cellulosic wound dressings reduces the highly granulation tissue to the level of its surrounding epithelial cells. Third, it is also of most interest that the cellulosic wound dressing response is observed during treatment of venous ulcers in the leg, especially those of fully dense tissue. The results show that of thirteen (13) leg venous ulcers (two locally dense and eleven fully dense wounds), seven (54%) healed completely, the remainder (46%) showing improvement over the course of the eight week study.

It will be apparent to those skilled in the art that various modifications and variations can be made in the method and composition of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

Claims (22)

1. Use of a non-pyretic, biocompatible cellulose dressing comprising from 1.5% to 9% by weight of cellulose in the manufacture of a kit for the treatment of chronic wounds.

2. The use of claim 1, wherein the microbial-derived cellulose dressing comprises 3% to 7% by weight cellulose.

3. The use of claim 1, wherein the microbial-derived cellulose dressing comprises from 4% to 6% by weight cellulose.

4. The use of claim 1, wherein the chronic wound is a fully or partially dense chronic wound.

5. The use of claim 1, wherein the chronic wound is a venous ulcer.

6. The use of claim 1, wherein the chronic wound is a pressure sore.

7. The use of claim 1, wherein the chronic wound is a diabetic ulcer.

8. Use according to claim 1, wherein the cellulose dressing derived from the microorganism shows a negative in the Limulus Amebocyte Lysate (LAL) test (< 0.5 EU/ml) and is therefore non-febrile.

9. The use of claim 1, wherein the microorganism-derived cellulose shows negative in primary stimulation tests in rabbits, is also negative in cytotoxicity tests using murine L929 cells, passes guinea pig susceptibility-promoting tests and is therefore biocompatible.

10. The use of claim 1, wherein the microbial-derived cellulosic dressing provides from 50% to 90% of its liquid weight and absorbs from 20% to 200% of its weight.

11. A microbial-derived cellulose dressing comprising from 1.5% to 4.3% by weight of microbial cellulose, wherein the cellulose dressing absorbs exudate from a chronic wound and provides greater than 75% of its liquid weight to the dry or necrotic portion of the chronic wound.

12. The microbial-derived cellulosic dressing of claim 11, comprising 3% to 7% by weight cellulose.

13. The microbial-derived cellulosic dressing of claim 12, comprising from 4% to 6% by weight cellulose.

14. A cellulose dressing derived from the microorganism of claim 11, which is shaped into the shape of a wound.

15. The microbially-derived cellulosic dressing according to claim 11, which is capable of providing 50% to 90% of its liquid weight in water to the dried substrate and is capable of absorbing 20% to 200% of its weight.

16. A method of making a microbial-derived cellulosic dressing, comprising: statically producing a microbial cellulose film using acetobacter xylinum; separating the membrane with a ratio of cellulose to water in the range of 1: 100 to 1: 500; the isolated film is dried to achieve a cellulose weight of 1.5 to 9%.

17. A kit, comprising:

a) a microbial derived cellulose comprising from 1.5 to 9% by weight cellulose;

b) a waterproof package comprising cellulose derived from said microorganism; and

c) instructions for administering the microorganism-derived cellulose to a chronic wound.

18. The kit of claim 17, wherein the microorganism-derived cellulose comprises 3% to 7% cellulose.

19. The kit of claim 18, wherein the microorganism-derived cellulose comprises 4% to 6% cellulose.

20. The kit of claim 17, which is sterilized by gamma radiation.

21. The kit of claim 17, which is sterilized by electron beam sterilization.

22. The kit of claim 17, wherein the water-resistant package containing the microorganism-derived cellulose comprises a heat-sealable, aluminum-coated plastic chevron pouch.