|United States Patent Application
;   et al.
July 22, 2004
Microbial-derived cellulose amorphous hydrogel wound dressing
A microbial-derived cellulose wound dressing is provided which is in the
form of a hydrogel which can be used to treat chronic wounds and burns.
Serafica, Gonzalo; (Langhorne, PA)
; Mormino, Richard; (San Antonio, TX)
; Hoon, Russell A.; (Doylestown, PA)
|Correspondence Name and Address:
FOLEY AND LARDNER
3000 K STREET NW
|Assignee Name and Adress:
January 16, 2003|
|U.S. Current Class:
|U.S. Class at Publication:
||A61L 015/00; A61L 015/16|
What is claimed is:
1. A microbial-derived cellulose amorphous gel wound dressing comprising a
cellulose content by weight selected from the group consisting of about
1.0% to about 99%, about 2.5% to 65%, about 3.0% to 50%, 3.5% to about
12%, 4% and 7%.
2. The wound dressing of claim 1, comprising about 4% or 7% cellulose.
3. The wound dressing of claim 1, further comprising an ingredient for
4. The wound dressing of claim 1, further comprising a preservative.
5. The wound dressing of claim 1, further comprising one or more active
6. The wound dressing of claim 3, wherein the ingredient for flow
modification is a polyol.
7. The wound dressing of claim 6, wherein said polyol is present in the
dressing from about 5 to about 50 wt % and is selected from the group
consisting of propylene glycol, glycerol, polyethylene glycol and
8. An amorphous gel dressing of claim 4, wherein the preservative is one
or more of the following group: chlorhexidine digluconate,
polyhexamethylene biguanide hydrochloride or silver compounds.
9. An amorphous gel dressing of claim 5, wherein the one or more active
agents are selected from the group consisting of antimicrobials,
antibiotics, antivirals, enzymes, proteins and growth factors.
10. An amorphous gel dressing of claim 9, wherein the antibiotic,
antimicrobial or antiviral active agent is selected from the group
consisting of bacitracin, polymixin B, gentamicin, chloramphenicol,
mupirocin neomycin, silver sulfadizine, gramicidin, ofloxicin,
tetracycline, streptomycin, fluoroquinolones, ganciclovir,
acyclovir,clindamycin, clortimazole, econazole, ketoconazole, miconazole,
nystain, terbinafine, tolnaftate, undecylenic acid, gentamycin
sulfadiazine, dapsone, ampicillin, amphotericin B, silver halides, silver
protein, colloidal silver
11. An amorphous gel dressing of claim 9, wherein the enzymes, proteins
and growth factors are selected from the group consisting of collagenase,
papain, fibrinolysin, desoxyribonuclease, platelet derived growth
factor(PDGF), epidermal growth factor (EGF), acidic and basic fibroblast
growth factors (FGF-1 and FGF-2), insulin-like growth factors 1+2(IGF-1
and IGF-2), vascular endothelial growth factor (VEGF), nerve growth
factor (NGF), tumor angiogenesis factor (TAF), corticotropin releasing
factor (CRF), interleukin-8 (IL-8), granulocyte-macrophage colony
stimulating factor (GM-CSF), transforming growth factors alpha and beta
(TGF-alpha and TGF-beta), bone morphogenetic protein (BMP), interferons,
interleukins and albumin.
12. The amorphous gel dressing of claim 1, where the microbial-derived
cellulose dressing donates 40 to 85% of its liquid weight and absorbs 10
to 50% of its weight.
13. The amorphous gel dressing of claim 1, wherein the microbial-derived
cellulose dressing donates 50 to 65% of its liquid weight and absorbs 15
to 35% of its weight.
14. A method for preparing a microbial-derived cellulose amorphous gel
wound dressing comprising: production of a microbial cellulose pellicle;
isolation of a pellicle with a cellulose content by weight in the range
of about 0.5 to about 1%; and wet milling the pellicle to produce an
amorphous gel with a cellulose content by weight of 0.5% to 5%.
15. The method as claimed in claim 14, wherein the microbial cellulose
pellicle is obtained from Acetobacter xylinum.
16. A method for treating chronic wounds or burns comprising: applying a
nonpyrogenic, biocompatible microbial-derived cellulose amorphous gel
wound dressing to a wound site.
17. A method as claimed in claim 16, further comprising filling the wound
with the gel dressing, covering with a secondary film dressing, and
changing the cellulose gel dressing from twice daily to weekly, wherein
said microbial-derived cellulose amorphous gel dressing comprises a
cellulose content selected from the group consisting of about 1.0% to
about 99%, about 2.5% to 65%, about 3.0% to 50%, 3.5% to about 12%, 4%
18. The method of claim 16, wherein the microbial-derived cellulose
amorphous gel dressing further comprises an ingredient for flow
19. The method of claim 16, wherein the microbial-derived cellulose
amorphous gel dressing further comprises a preservative.
20. The method of claim 16, wherein the microbial-derived cellulose
amorphous gel dressing further comprises one or more active agents.
21. A method of claim 18, wherein the ingredient for flow modification is
present in the dressing about 5 to about 50 wt % and is a polyol selected
from the group consisting of propylene glycol, glycerol, polyethylene
glycol and sorbitol.
22. A method of claim 19, wherein the preservative is at least one
selected from the group consisting of chlorhexidine digluconate, glycerol
monolaurate or polyhexamethylene biguanide hydrochloride.
23. A method of claim 20, wherein the one or more active agents are
selected from the following groups: antimicrobials, antibiotics,
antivirals, enzymes, proteins and growth factors.
24. A method of claim 23, wherein the antibiotics, antimicrobial or
antiviral are selected from the group consisting of bacitracin, polymixin
B, gentamicin, chloramphenicol, mupirocin, neomycin, silver sulfadizine,
gramicidin, ofloxicin, tetracycline, streptomycin, fluoroquinolones,
ganciclovir, acyclovir,clindamycin, clortimazole, econazole,
ketoconazole, miconazole, nystain, terbinafine, tolnaftate, undecylenic
acid, gentamycin sulfadiazine, dapsone, ampicillin, amphotericin B,
silver halides, silver protein, colloidal silver
25. A method of claim 23, wherein the enzymes, proteins and growth factors
are selected from the group consisting of collagenase, papain,
fibrinolysin, desoxyribonuclease, platelet derived growth factor (PDGF),
epidermal growth factor(EGF), acidic and basic fibroblast growth factors
(FGF-1 and FGF-2), insulin-like growth factors 1+2 (IGF-1 and IGF-2),
vascular endothelial growth factor (VEGF), nerve growth factor (NGF),
tumor angiogenesis factor (TAF), corticotropin releasing factor (CRF),
interleukin-8 (IL-8), granulocyte-macrophage colony stimulating factor
(GM-CSF), transforming growth factors alpha and beta (TGF-alpha and
TGF-beta), bone morphogenetic protein (BMP), interferons, interleukins,
26. A method of claim 16, wherein the microbial-derived cellulose dressing
donates 40 to 85% of its liquid weight and absorbs 10 to 50% of its
27. The method of claim 16, wherein the microbial-derived cellulose
dressing donates 50 to 65% of its liquid weight, while absorbing 15 to
35% of its liquid weight.
FIELD OF THE INVENTION
 The invention relates to a wound dressing comprising
microbial-derived cellulose in an amorphous hydrogel form.
BACKGROUND OF THE INVENTION
 There are numerous wound dressings that demonstrate effectiveness
to aid in the healing of wounds. The components of these include various
polymeric systems, cellulosic materials derived from plants and bacteria,
and collagen. Each has its mode of action to assist the wound healing
process. Many rely on either the donation of fluid to hydrate a wound
surface and aid in removal of necrotic tissue through autolytic
debridement or the absorption of excess fluid termed exudate.
 Microbial-derived cellulose dressings are composed of bacterial
cellulose and water. The processing of which, results in a dressing that
possesses unique characteristics. Not only can it donate moisture which
is associated with the dressing but its multi-layered three-dimensional
structure, that distinguishes it from plant-derived cellulose, creates a
material with a water-holding capacity up to 700 times its own dry
weight, as described in U.S. Pat. No. 4,942,128. Microbial cellulose also
demonstrates excellent wet tensile and compression strength. Lastly, by
adjusting the cellulose to liquid ratio in processed microbial cellulose,
the amount and rate of both fluid donation and absorption can be
 Because of its superior characteristics, use of microbial cellulose
in the medical industry has been previously investigated. For example,
U.S. Pat. Nos. 4,588,400, 4,655,758 and 4,788,146 to Ring et al. disclose
the possible use of microbial-derived cellulose in liquid-loaded medical
pads. The patents to Ring et al focus on using statically produced
microbial cellulose pads loaded with various liquids and medicaments.
These pads were detailed as well as the production and cleaning method to
produce the starting cellulose material. Also described in these patents
are examples detailing methods of fabrication of various pads, wherein
the method involves a series of pressing and soaking steps to adjust the
physical properties, mainly with respect to the liquid to cellulose
ratio, to yield a desired product. As an example, these patents
illustrate a highly hydrated pad (80 to 1 fluid to cellulose ratio) that
is able to provide a cooling capability ideal for bum applications. In
particular, the '146 patent describes the use of such liquid loaded pads
as wet dressings for use as an ulcer dressing capable of providing
moisture to the wound over an extended period of time. The same '146
patent mentions that the wet dressings described in the examples have the
additional ability to absorb large quantities of fluid from the wound
site when the dressing is applied in a less than saturated condition.
However, the wound dressings of Ring et al. fail to mention a singular
dressing having both the ability to be a source of moisture for wounds as
well as the ability to absorb fluid. The Ring et al. patents also fail to
describe the effective liquid to cellulose ratio to fabricate a dressing
having the dual fluid handing capability. Furthermore, the Ring et al.
patents do not describe microbial-derived cellulose wound dressings in an
amorphous gel form.
 Amorphous hydrogel dressings, for example IntraSite Gel (Smith &
Nephew), differ from other dressings in their ability to add moisture to
a dry wound and as such have been shown to be useful for debriding
necrotic dry tissue found in chronic and bum wounds. Since these
hydrogels have not been cross-linked and therefore do not take a fixed
shape, they have been termed amorphous (Ovington, L. G., Amorphous Gels
Can Help Dry Escharic Wounds, Wound Care Institute Newsletter,
July/August 1997, Volume 2, No. 3).
 Rhodes, in U.S. Pat. No. 5,662,924, describes a wound dressing that
contains a water-insoluble water swellable cross-linked cellulose
derivative, water and a polyol. This dressing, in the form of an
amorphous gel, is believed to enhance moisture penetration of necrotic
tissue and thereby facilitate wound healing by speeding up debriding
 The present inventors have developed a flowable cellulose-based gel
wound dressing that possesses this novel fluid handling capability of
absorption and donation. Surprisingly, production of a microbial-derived
cellulose wound dressing in an amorphous gel form enhances the moisture
donating aspect of the wound dressing relative to the unprocessed
microbial cellulose starting film material. This fluid handling
capability is an end result of the processed microbial cellulose that
contains the proper cellulose content for the intended purpose. The
resulting wound dressing can donate fluid if the wound surface is dry and
found to be particularly useful for dry wounds covered with dry necrotic
tissue or eschar. Here it acts to autolytically debride the wound: the
necessary first step in healing of a chronic wound.
 Surprisingly, at the optimal cellulose content, the same dressing
is also capable of absorbing fluid away from the exuding wound bed.
Typically, chronic wounds such as venous ulcers tend to exude large
amounts of fluids during the healing process. At this stage the dressing
of the present invention is able to absorb the fluid exudate while
maintaining a moist surface for epithelial cells to migrate. The
epithelial migration is essential for eventually closing the wound.
 Furthermore, the flowable nature of this material allows this
dressing to fill areas that a pad cannot effectively treat. The amorphous
gel dressing can be delivered to the entire wound bed surface. The
intimate contact of the gel dressing with the entire wound surface
further enhances the moisture donation and absorption quality of
microbial-derived cellulose and thereby improves wound healing. When it
is necessary to change the dressing the amorphous gel dressing can be
easily removed without upsetting the newly forming tissue. Also, since it
can be removed en bloc, the wound cleansing process, required for other
gel dressing products, is greatly simplified.
SUMMARY OF THE INVENTION
 It is an object of the present invention to provide
microbial-derived cellulose wound dressings in an amorphous gel form,
comprising 1% to 10% cellulose by weight. In a preferred embodiment, the
microbial-derived cellulose is biocompatible and nonpyrogenic.
 It is another object of the present invention to provide an
effective wound dressing comprising microbial cellulose in an amorphous
gel form that is capable of enhanced donation of moisture for improved
 Further, it is an object of the present invention to provide an
effective wound dressing comprising microbial cellulose that can flow to
fill an area and then be easily removed when changing is necessary.
 Other objects, features and advantages of the present invention
will become apparent from 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.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Unless otherwise specified, "a" or "an" means "one or more".
 The preferred biosynthesized cellulose for the amorphous gel is
produced by cellulose-producing organisms, such as Acetobacter xylinum,
and is subjected to a series of chemical wash steps to render it
non-pyrogenic. Once grown the typical processing uses hydroxide solutions
at concentrations of 0.5-20% by weight. Preferably, sodium hydroxide is
used at a concentration of not less than 1% by weight and most preferably
about 2% to about 4% by weight in order to dissolve the cells. In
addition, the present invention provides hydrogen peroxide washing
capable of whitening and sanitizing the non-pyrogenic films.
 Cellulose pellicles are typically composed of greater than 98%
water and from 0.2 to 2% cellulose by weight. Subsequent to chemical
processing, the pellicles are wet milled to produce the amorphous gel
form with a cellulose content roughly equivalent to that of the starting
material but which can be adjusted to any desired concentration through
the addition or removal of fluids. The amorphous gel wound dressing
obtained from the milling and grinding of the intact microbial cellulose
pellicles has a primary structure of ultra fine fibers that are known to
be about 200 times finer than cotton fibers. The secondary structure,
which is a non-woven pattern of interpenetrating cellulose fibers, is
also not completely disrupted.
 Typical cellulose content of the present invention ranges from
about 1.0% to about 99% cellulose by weight, preferably about 2.5% to 65%
by weight, more preferably about 3.0% to 50% by weight and most
preferably 3.5% to about 12% by weight. In an especially preferred
embodiment, the cellulose content is about 4% or about 7% by weight.
 The amorphous gel dressings of the invention can be used for
donation of liquid to wounds as well as absorbing liquid from wounds.
Typically, the microbial-derived cellulose dressing can donate between
about 40 to 85% of its liquid weight and can absorb between about 10 to
50%, more preferably the dressing can donate about 50 to 65% of its
liquid weight and absorb about 15 to 35% of its weight in liquid.
 The flowable nature of the wound dressing can be manipulated by the
addition of an ingredient for flow modification. Such ingredients include
but are not limited to polyols. The polyols include propylene glycol,
glycerol, polyethylene glycol and sorbitol and the like.
 The rheological properties of the gel are easily adjusted by
addition of liquids or solids such as polyols, i.e., polyethylene glycol,
sorbitol, mannitol, glycerol, and propylene glycol or other flow
modification agents such as lecithin and aloe vera. The concentration of
these additives in the microbial cellulose gel may vary from 1% to 50% by
weight depending on the properties of the specific additive and on the
desired flow characteristics of the resulting gel.
 Liquid materials which can be loaded into the gel include but are
not limited to water, isotonic saline, synthetic polymers such as
polyethylene oxide, polyvinylpyrrolidone, aqueous solutions of molecules
including proteins, such as platelet derived growth factor (PDGF),
epidermal growth factor (EGF), fibroblast growth factor (FGF),
insulin-like growth factor (IGF), Transforming growth factor-beta
(TGF-.beta.), bone morphogenetic protein (BMP), vascular endothelial
growth factor (VEGF), nerve growth factor (NGF), tumor angiogenesis
factor (TAF), corticotropin releasing factor (CRF), interleukin-8 (IL-8),
granulocyte-macrophage colony stimulating factor (GM-CSF), and other
growth factors, and enzymes such as collagenase, papain and fibrinolysin
desoxynuclease. Additionally the dressing may contain one or more active
agents like antibiotics, such as bacitracin, polymyxin B, gentamicin,
chloramphenicol, mupirocin, neomycin, silver sulfadiazine, gramicidin,
and the like: topical anesthetics, such as lidocaine hydrochloride,
benzocaine, dibucaine, tetracaine hydrochloride and the like: antifungal
agents, such as clotrimazole, econazole, ketoconazole, miconazole,
nystain, terbinafine, tolnaftate, undecylenic acid and the like;
antiseptics and preservatives, such as polyhexamethylene biguanide,
chlorhexidine digluconate, benzalkonium chloride, silver-based
antimicrobials, copper-based antimicrobials and the like; antiviral
agents, such as gentamycin sulfadiazine, dapsone, ampicillin,
amphotericin B, silver halides, silver protein, colloidal silver,
erythromycin and the like.
 Compared to the intact microbial cellulose pellicles, the amorphous
gel form can be formulated to enhance the donation and/or absorption
characteristics of the gel. The content of microbial-derived cellulose
present in the amorphous gel dressing can be manipulated depending upon
the method of preparation and the eventual end use of the wound dressing.
 The present invention also relates to a method of treatment of
wounds using the inventive wound dressing. In a preferred embodiment,
chronic wounds or burns are treated with the inventive wound dressing.
The method comprises applying the wound dressing to the wound site,
filling the wound with the hydrogel dressing, and covering the wound with
a secondary film layer. The frequency of changing the dressing is readily
determined by one skilled in the art. In one embodiment, the dressing is
changed twice daily to weekly.
 The present invention will be illustrated through the following
1. Production of Microbial Cellulose
 In preparing the microbial cellulose amorphous gels of the
invention, a microbial cellulose film is prepared. The film is prepared
by using microorganisms such as Acetobacter xylinum which are cultured in
a bioreactor containing a liquid nutrient medium at 30 degrees .degree.
C. at 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, and corn
steep liquor as nutrient source coupled with a proprietary trace elements
supplement, which varies from the original Schramm & Hestrin medium
(1954) used by those skilled in the art. This proprietary trace elements
supplement is quantified in the following table:
 Trace Element Solution
 Composition Per Liter
EDTA Tetrasodium Salt 570 mg
7H.sub.2O 200 mg
ZnSO.sub.4 7H.sub.2O 10 mg
H.sub.2O 26 mg
H.sub.3BO.sub.3 30 mg
6H.sub.2O 20 mg
NiCl.sub.2 6H.sub.2O 3.2 mg
(NH.sub.4).sub.6Mo.sub.7O.sub.14 4H.sub.2kp[O 2.4 mg
 Two ml of this solution is added per liter of media.
 Suitable bioreactors are selected which minimize evaporation and
provide adequate oxygen-limiting conditions. Oxygen-limiting conditions
may be varied depending upon the desired water content and thickness of
the cellulose film. Generally, under oxygen-limited conditions, oxygen is
present in an amount of 5%-21% of the total gas present at the air liquid
interface. The bioreactor is composed of plastic box fitted with an
airtight cover or a limited gas-permeable cover. Dimensions of the
bioreactor can vary in configuration (cube or cylinder) depending on the
shape and size of the cellulose film being produced. For example, a six
inch diameter cylinder will produce a six inch diameter dressing, which
can be used as is or cut to conform to the wound to be treated, prior to
application. By limiting the amount of oxygen in the fermentation medium,
it is hypothesized that the Acetobacter utilizes the carbon available in
the medium to produce more cellulose instead of using it for
reproduction, thereby increasing the total yield of cellulose.
 The fermentation process under static conditions was allowed to
progress over for a period of about 7-30 days, during which the bacteria
in the culture medium produced an intact cellulose pellicle containing
the microorganisms. Depending on the desired thickness, which corresponds
to a certain cellulose content per unit area, the fermentation is stopped
and the pellicle is removed from the bioreactor. The excess medium
contained in the pellicle is then removed by standard separation
techniques such as compression or centrifugation prior to chemical
cleaning and subsequent processing of the pellicle to yield a wound
dressing with a cellulose to liquid ratio of about 1:10 to about 1:65.
The raw cellulose pellicle has an increased sugar:cellulose yield of
about 35%, compared to literature values of 10%. This increased yield
coupled with an inexpensive nitrogen source resulted in a 40-fold
reduction in production-cost of the raw cellulose film as compared to
cellulose films produced according to the original Schramm & Hestrin
medium [1954, J. Gen. Micro, 11:123-129].
2. Processing and Depyrogenation Procedures
 After the cellulose film has been produced, the cells have to be
removed from the cellulose pellicle for purification. Fontana et al.
(1990, Appl. Biochem. Biotech, 24: 253-264) have described the cells as
being apyrogenic, however, the unpurified cellulose pellicle has tested
positive for pyrogens using the Limulus Amebocyte Lysate (LAL) test kit.
This result necessitated the removal of the cells by chemical processing
discussed here in order to pass the standard pyrogenicity test and
qualify the microbial cellulose wound dressing as nonpyrogenic.
 The cellulose pellicle is subjected to a series of chemical wash
steps to convert the raw cellulose film into a medical grade and
non-pyrogenic wound dressing material. Typical processing uses hydroxide
solutions at concentrations of 1-20% by weight. Preferably, sodium
hydroxide is used at a concentration of not less than 3% and most
preferably about 3% to about 5% in order to dissolve the cells. In
addition, the present invention provides hydrogen peroxide washing
capable of bleaching and sterilizing the pyrogen-free films.
Concentrations of about 0.05% to about 10% peroxide by weight are useful
to effect whitening of the films. Preferably the amount of peroxide used
in about 0.1% to about 0.5%. Other bleaching agents such as hypochlorite,
hypobromite, and perborate may also be used.
 Purification processes using various exposure times, concentrations
and temperatures were conducted on the raw fermentation product.
Processing times of 1-4 hours have been studied in conjunction with
temperature variations of 30-100 degrees centigrade to optimize the
process. The resulting films from each of the different operating
conditions were tested for their respective pyrogen levels and physical
characteristics. The process condition that yields a nonpyrogenic product
in the least amount of time and lowest chemical concentration was then
selected for economic reasons. The time involved in this process can be
as much as 4 hours at about 90.degree. C., preferably the time involved
is about 1-2 hours at about 60.degree. C. to about 80.degree. C.
 The amount of cellular debris left in the cellulose pad after
processing may be measured by Limulus Amebocyte Lysate (LAL) test as
outlined by the U.S. Food and Drug Administration (FDA) in 21 CFR10.90.
The instant cleaning process outlined above provided a nonpyrogenic
cellulose pad (<0.05 EU/ml). The allowable pyrogen content in Class I
medical devices is 0.5 EU/ml (FDA LAL test Guideline). The steps of the
LAL test are defined by the test kit manufacturer and can simply be
followed to yield the pyrogen level in the cellulose film.
Production of a Microbial Cellulose Amorphous Gel
 This example presents a method for making an amorphous gel material
from microbial cellulose sheets. The cellulose sheets were processed
using the method described in Example 1 to remove pyrogens and other
contaminants, and compressed to obtain a cellulose content of
approximately four percent.
 A 500 g quantity of the processed and depyrogenated microbial
cellulose was placed in a 1 gal blender. To this 2500 ml of deionized
water was added, and the mixture was processed using a 3 hp motor at high
speed for 5 min to ensure consistency. The resulting mixture was decanted
into a draining bin, and excess water was allowed to drain. After
draining for 15 min, the mixture was pressed until the weight of the gel
again reached 500 g.
 Two 20 g samples of the gel were removed and dried to determine the
cellulose content of the gel. The average dry weight was 0.85 g,
indicating a cellulose content of 4.25% by weight
Modification of Flow Properties
 This example demonstrates how the viscosity and flow properties of
a microbial cellulose amorphous gel can be modified through the addition
of an ingredient for flow modification.
 Amorphous gel was produced by the method described in example 1,
and the final cellulose content was determined to be 3.95% by drying of
20 g aliquots. Using this gel, nine 50 g samples were prepared containing
0 to 40 percent propylene glycol by weight. The gels were mixed
thoroughly to distribute the propylene glycol and then packed into
identical 5 cc disposable syringes with 1.5 mm tip openings.
 The maximum force required to discharge the material from the
syringes was measured with a compact force gauge and was plotted versus
the propylene glycol content. This image is shown in FIG. 1. The
discharge force initially dropped rapidly with the addition of the flow
modifying agent, but the cumulative effect diminished as the
concentration was increased. At around 25% propylene glycol the force
leveled off at 4.5 N, with higher concentrations showing no discernible
Addition of Active Agents
 This example shows how the properties of a microbial cellulose
amorphous gel can be changed through the addition of active agents. The
amorphous gel used for this example was produced using the method
described in example 1.
 The 500 g gel was divided in half. The first half was modified with
the addition of polyhexamethylene biguanide (PHMB) in sufficient quantity
to give a 0.25% concentration. The second half of the gel was kept
unchanged. Both gels were sterilized by gamma irradiation at 30-35 kGy.
The samples then underwent antimicrobial testing. 10 g samples of each
gel were inoculated with 10.sup.5 cultures of either Staphylococcus
aureus or Esherichia coli and incubated at 30.degree. C. Organism
populations were measured at time zero and again after 24 hr, and the
totals of the PHMB-treated gel were compared with the untreated control.
Bacterial Inhibition by PHMB-Containing
Population Count (cfu/ml)
Time 0 Time 24 hr
Sample S. aureus E. coli S. aureus E. coli
PHMB-treated 1.5 .times. 10.sup.5 2.0 .times. 10.sup.5 <10 <10
Untreated 1.5 .times. 10.sup.5 2.0 .times. 10.sup.5 3.7 .times.
10.sup.2 6.2 .times. 10.sup.4
 The amorphous gel treated with 0.25% PHMB reduced the bacterial
population of both species by 99.99%, whereas the untreated amorphous gel
resulted in significantly less reduction.
Preparation of an Amorphous Gel Wound Dressing
 This example demonstrates the method of producing a wound dressing
comprised of microbial cellulose amorphous gel. This dressing will have
the ability to both donate moisture to or absorb moisture from a wound
site, depending on the state of the wound.
 Amorphous gel was produced following the method described in
example 1. Using the 500 g gel as a base material and assuming the
initial cellulose content to be 4%, eight samples were created ranging
from 1 to 10 percent cellulose according to the following table:
Composition of Amorphous Gel Samples
Cellulose Mass of Water (g) Cellulose
Gel (g) Addition Subtraction Total Weight (actual*)
37.5 -- 50 1.17
2 25.0 25.0 -- 50 2.41
3 37.5 12.5 -- 50
4 50.0 -- -- 50 4.71
5 62.5 -- 12.5 50 5.48
75.0 -- 25.0 50 6.39
8 100 -- 50.0 50 8.87
10 125 -- 75.0
*A sample of each was dried to determine the exact
 These samples were then tested for absorption from a saturated
sponge and donation to a dry surface. For the absorption test, a 5 g
sample of the gel was spread evenly over a 2 in circular area on a sheet
of filter paper. The paper was placed on top of a sponge sitting in a
0.9% saline bath at room temperature. The liquid level was maintained at
the level of the sponge. Samples were removed after 24 hr and reweighed
to determine the quantity of saline absorbed by the gel, and the
absorption was reported as a percentage of the initial weight of the
sample. FIG. 2 shows the absorption profile for this set of amorphous
gels. As can be seen, gels containing less than 3% cellulose lost weight
during the test, indicating that moisture was donated to the wet sponge.
The inflection point on the curve occurred at approximately 5.5%
cellulose by weight, and increased rapidly from there as the cellulose
 Donation testing was performed by spreading a 5 g sample of gel
evenly over a 2 in diameter circular area on a 3 in.times.3 in piece of
pre-weighed smooth leather. Samples were removed after 2 hr and the
leather was reweighed to determine the quantity of moisture donated to
the dry surface. Donation results were reported as a percentage of the
initial weight of the sample, and are shown graphically in FIG. 3.
Donation decreased nearly linearly up to 6% cellulose by weight, and then
decreased more slowly up to the 11% by weight.
 Using FIGS. 2 and 3, a wound dressing can be devised to accommodate
both absorption and donation. In order to have measurable absorption, the
gel would need to possess a minimum of 4% cellulose, and the gel would
need less than 6% cellulose to donate significantly. Therefore, a wound
dressing gel should contain between 4 and 6 percent cellulose to optimize
the natural fluid handling ability of the microbial cellulose matrix.
 Each of the references cited above is incorporated herein in its
entirety to the same extent as if each reference was individually
incorporated by reference.
 Though the invention has been described with reference to
particular embodiments, it is recognized that variations and equivalents
of these embodiments may be used without departing from the scope or
spirit of the invention.
* * * * *