NZ723205B2 - Systems and methods for tissue healing - Google Patents
Systems and methods for tissue healing Download PDFInfo
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- NZ723205B2 NZ723205B2 NZ723205A NZ72320515A NZ723205B2 NZ 723205 B2 NZ723205 B2 NZ 723205B2 NZ 723205 A NZ723205 A NZ 723205A NZ 72320515 A NZ72320515 A NZ 72320515A NZ 723205 B2 NZ723205 B2 NZ 723205B2
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- New Zealand
- Prior art keywords
- wound
- fluid
- wound bed
- ester
- negative pressure
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Abstract
Systems, methods and devices are provided for use in a negative pressure wound therapy system for healing a wound in a patient. Various aspects may include an ester-based material adapted to be directly applied to the wound, such as a smooth muscle fistula, without substantially damaging tissue in the wound during dressing changes. The ester-based material may have an affinity for the wound bed surface and/or wound fluid. In addition various aspects may include a device adapted to close the wound, such as a smooth muscle fistula. he wound during dressing changes. The ester-based material may have an affinity for the wound bed surface and/or wound fluid. In addition various aspects may include a device adapted to close the wound, such as a smooth muscle fistula.
Description
SYSTEMS AND METHODS FOR TISSUE HEALING
CROSS-REFERENCE TO RELATED APPLICATIONS
The present disclosure claims the benefit of U.S. Provisional Patent Application Serial
No. 61/940,245, filed February 14, 2014, the contents of which are hereby incorporated by
reference in their entirety.
BACKGROUND
Negative pressure wound therapy is a therapeutic technique used to promote healing
and closure of various types of acute or chronic wounds in the human body. Negative
pressure wound therapy is a wound bed management technique that creates an environment
of sub-atmospheric pressure over the wound bed to draw fluid out of the wound. The effect of
the sub-atmospheric pressure environment is to reduce inflammation and increase blood flow
within the wound, providing a more oxygen rich environment to the wound and improve the
delivery of wound-healing white blood cells, proteins, carbohydrates, and growth factors.
Generally, the wound is irrigated with saline and/or antibiotics, and may be covered with
a non-adherent material that adapts to the contours of the wound. An absorptive dressing is
applied over the non-adherent material and an occlusive material is applied over the dressed
wound to form an air-tight seal. A vacuum tube is connected to an opening in the occlusive
material. A vacuum pump applied to the vacuum tube provides the negative pressure needed
to draw fluid through the wound for collection and removal. The non-adherent material and/or
the absorptive dressing may be changed according to various factors such as the amount of
fluid output from the wound, the patient’s age, clinical objectives, and the like.
The absorptive dressing may include any one of a number of materials that are chosen
as a function of the type of wound, clinical objectives, and the comfort of the patient. For
example, the absorptive dressing may include cotton gauze for shallow wounds such as
pressure sores or diabetic ulcers of the skin. The absorptive dressing may include a foam
material for open cavity wounds such as gunshot wounds, leg ulcers, and surgically created
cavities. These wounds may be lightly, moderately, or heavily exuding wounds that may
benefit from the high absorption capacity of foam material. The foam material may be cut to fit
the margins of the open cavity wound and placed inside the wound. Conventional foam
materials generally have pore diameters in the range of approximately 100µm – 600µm and
are consistently used with a protective layer, typically petrolatum gauze, between the foam
material and the wound bed in wounds involving fistulas, tendons, nerves or sensitive tissues.
SUMMARY
Various embodiments of the invention provide dressings, systems and methods for a
negative pressure wound therapy system for healing a wound in a patient. Dressings, systems
and methods according to various aspects of the present invention may include an ester-based
material adapted to be directly applied to the wound, such as a smooth muscle fistula, without
substantially damaging tissue in the wound during dressing changes. The ester-based
material may have an affinity for the wound bed surface and/or wound fluid. Under pressure,
the ester-based material may promote uniformity of wound fluid movement through the wound
and dressing and regulate temperature within the wound.
In addition, systems and methods according to various aspects of the present invention
may include a device adapted to close a wound such as a smooth muscle fistula.
According to one aspect, the present invention provides a negative pressure treatment
system for the treatment of a wound bed including a smooth muscle fistula, the negative
pressure treatment system comprising:
an absorptive dressing comprising an ester-based foam adapted to be placed directly
against the wound bed and to contact smooth muscle without causing substantial cellular
disruption or damage in the negative pressure environment, the foam having primary structural
features comprising pores with a width of about 0.1μm to about 50μm and secondary structural
features adapted to direct a flow of wound fluid from the wound bed;
a vacuum pump configured to apply negative pressure to the absorptive dressing to
thereby withdraw wound fluid from the wound bed; and
an interface layer adapted to be placed between the absorptive dressing and the wound
bed.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be derived by referring to
the detailed description when considered in connection with the following illustrative figures. In
the following figures, like reference numbers refer to similar elements and steps throughout the
figures.
Elements and steps in the figures are illustrated for simplicity and clarity and have not
necessarily been rendered according to any particular sequence or scale. For example, steps
that may be performed concurrently or in different order are illustrated in the figures to help to
improve understanding of embodiments of the present invention. In addition, graphical
representations of structural features have been simplified for the purposes of illustration.
The figures described are for illustration purposes only and are not intended to limit the
scope of the present disclosure in any way. Various aspects of the present invention may be
more fully understood from the detailed description and the accompanying drawing figures,
wherein:
Figure 1 schematically illustrates a simplified cross-section of a negative pressure
wound therapy treatment system including an absorptive dressing according to an embodiment
of the present invention;
Figure 2 schematically illustrates a simplified cross-section of a negative pressure
wound therapy treatment system including an integral vacuum according to another
embodiment of the present invention;
Figure 3A schematically illustrates cell sacrifice in relation to the pore size of a
conventional absorptive dressing;
Figure 3B schematically illustrates cell sacrifice in relation to the pore size of the
absorptive dressing of the embodiment of Figures 1 and 2;
Figure 4 schematically illustrates a detailed pore structure of the absorptive dressing of
the embodiment of Figures 1 and 2;
Figures 5A-5C schematically illustrate simplified cross-sections of absorptive dressings
with various pore sizes and/or multiple layers according to further embodiments of the
absorptive dressing of Figures 1 and 2;
Figure 6 schematically illustrates a simplified cross-section of another embodiment of a
negative pressure wound therapy treatment system including an absorptive dressing having
preformed flow paths to direct wound fluid flow;
Figure 7A schematically illustrates a simplified cross-section of a further embodiment of
a negative pressure wound therapy treatment system including an absorptive dressing having
barriers to direct wound fluid flow;
Figure 7B representatively illustrates a simplified cross-section of a barrier of Figure 7A;
Figure 8A schematically illustrates a simplified cross-section of a further embodiment of
a negative pressure wound therapy treatment system including an absorptive dressing having
a radial housing to direct wound fluid flow;
Figure 8B representatively illustrates a simplified perspective view of the radial housing
of Figure 8A;
Figure 8C representatively illustrates a simplified cross-sectional view of the radial
housing of Figure 8B;
Figure 8D representatively illustrates a simplified cross-sectional view of the radial
housing of Figure 8C along line I - I’;
Figure 9 schematically illustrates a simplified cross-sectional view of a negative
pressure wound therapy treatment system including a healing layer that may be incorporated
into the embodiments of the negative pressure wound therapy treatment system.
DETAILED DESCRIPTION
The present invention may be described in terms of functional block components and
various processing steps. Such functional blocks may be realized by any number of
components configured to perform the specified functions and achieve the various results. For
example, the present invention may employ various process steps, apparatuses, systems,
methods, etc. In addition, the present invention may be practiced in conjunction with any
number of systems and methods for treating open wounds. Further, the present invention may
employ any number of conventional techniques for wound treatment, wound bed preparation,
treating or preventing infection of wounds, reducing inflammation, extracting fluid from wounds,
changing wound dressings, and preventing the advancement of wound edges.
The particular implementations shown and described are illustrative of the invention
and its best mode and are not intended to otherwise limit the scope of the present invention in
any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation,
and other functional aspects of the system may not be described in detail. Furthermore, the
connecting lines shown in the various figures are intended to represent examples of functional
relationships and/or steps between the various elements. Many alternative or additional
functional relationships or physical connections may be present in a practical system.
The terms “comprises”, “comprising”, “includes” or “including” or any variation thereof,
are intended to reference a non-exclusive inclusion, such that a process, method, article,
composition, system, or apparatus that comprises a list of elements does not include only
those elements recited, but may also include other elements not expressly listed or inherent to
such process, method, article, composition, system, or apparatus.
Expressions such as “at least one of,” when preceding a list of elements, modify the
entire list of elements and do not modify the individual elements of the list. Further, the use of
“may” when describing embodiments of the present invention refers to “one or more
embodiments of the present invention.”
When a first element is described as being “coupled” or “connected” to a second
element, the first element may be directly “coupled” or “connected” to the second element, or
one or more other intervening elements may be located between the first element and the
second element.
Spatially relative terms, such as “beneath”, “below”, “lower”, “downward”, “above”,
“upper” and the like, may be used herein for ease of description to describe one element or
feature’s relationship to another element(s) or feature(s) as illustrated in the figures. It will be
understood that the spatially relative terms are intended to encompass different orientations of
the device in use or operation in addition to the orientation depicted in the figures. For
example, if the device in the figures is turned over, elements described as “below” or “beneath”
other elements or features would then be oriented “above” the other elements or features.
Thus, the exemplary term “below” can encompass both an orientation of above and below.
The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the
spatially relative descriptors used herein interpreted accordingly.
It will be understood that, although the terms “first”, “second”, “third”, etc., may be used
herein to describe various elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be limited by these terms.
These terms are only used to distinguish one element, component, region, layer or section
from another element, component, region, layer or section. Thus, a first element, component,
region, layer or section discussed below could be termed a second element, component,
region, layer or section, without departing from the spirit and scope of the inventive concept.
The terminology used herein is for the purpose of describing particular embodiments
only and is not intended to be limiting of the inventive concept. As used herein, the singular
forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context
clearly indicates otherwise.
As used herein, the term “substantially,” “about,” and similar terms are used as terms of
approximation and not as terms of degree, and are intended to account for the inherent
deviations in measured or calculated values that would be recognized by those of ordinary skill
in the art.
Various representative implementations of the present invention may be applied to any
area of damaged tissue on the body of a human or animal. In some embodiments, the
damaged tissue may include a penetrating wound that may expose underlying tissue where
wound closure is desired. In one embodiment, the present invention may be applied to
incisional wounds. The penetrating wound may also include wounds caused by surgery and/or
trauma, fistulas including smooth muscle fistulas, lacerations, thermal injuries such as burns,
chemical wounds, electrical wounds, and the like. For example, the damaged tissue may
include one or more fistulas. Fistulas may result from various traumas, including gunshot
wounds, Caesarean sections, Crohn’s disease, and various other diseases, injuries or surgery.
Fistulas can occur between two epithelialized surfaces, such as blood vessels, skin, intestines
or other hollow organs. One type of commonly occurring fistula is an enterocutaneous fistula,
which occurs between the intestine and the skin surface. However, the present invention is not
limited thereto, and may be applied to a various types of fistulas, including other fistulas of the
digestive system or fistulas located in other systems of the body.
In some embodiments, various representative implementations of the present invention
may be applied to any system for promoting healing of a wound bed including smooth muscle
tissue. Certain representative implementations may include, for example, any suitable system
or method for providing an at least partially or fully occlusive wound dressing for the treatment
and healing of fistulas in smooth muscle tissue using negative pressure wound therapy. In one
embodiment, a negative pressure wound therapy system may include an absorptive dressing
applied directly in contact with the wound bed for absorbing wound fluid. In some
embodiments, one or more of a healing layer may optionally be applied to a wound bed
including smooth muscle tissue beneath the absorptive dressing and may further encourage
wound closure and healing. The healing layer may be overlaid with the absorptive dressing for
absorbing wound fluid from the wound bed. An occlusive seal may overlay the absorptive
dressing and the wound edge. A vacuum pump may be coupled to a vacuum tube that may be
connected to the occlusive seal with communication of the negative pressure through the
absorptive dressing to the wound bed. Activation of the vacuum pump may cause withdrawal
of the wound fluid from the wound bed into the absorptive dressing for removal with dressing
changes.
A smooth muscle fistula may be an open cavity wound including exposed smooth
muscle tissue. Unlike cardiac and skeletal muscle, which include firm and relatively coarse
tissue, smooth muscle is fragile, friable, and easily damaged or stripped when touched with a
foreign object. Negative pressure wound therapy using any conventional absorptive dressing
such as foam or gauze are contraindicated in the treatment of certain fistulas due to the fragile
nature of, for example, cardiac tissue, nerve tissue, tendon, exposed blood vessels, and
smooth muscle tissue. Specifically, the clinical standard of practice does not allow direct
contact of the foam or gauze or any conventional absorptive dressing to any wound including
smooth muscle because such direct contact is known to cause damage to smooth muscle
tissue, aggravating the wound and preventing healing. Without being bound by theory, it is
believed that such systems inappropriately draw wound fluid non-uniformly from the fistula,
increase the down growth of tissue into the wound, and cause undesirable cell sacrifice during
dressing changes. For at least these reasons, fistulas are generally treated with mechanical
attempts to close the wound by methods such as suturing, gluing, and/or stapling the fistula
closed. Such mechanical wound closures have marginal success in promoting the healing of
fistulas.
Referring to Figure 1, a negative pressure treatment system 100 may include an
absorptive dressing 101. In one embodiment, the absorptive dressing 101 may be placed in
direct contact with a wound bed 120. The wound bed 120 may include smooth muscle tissue
121 surrounding a smooth muscle fistula 122. The absorptive dressing 101 may also contact
various tissues 123 adjacent to the fistula 122 and in the wound bed 120, including skeletal
and smooth muscle tissue, bone (not shown), and other tissues. An occlusive material 130
may overlay the absorptive dressing 101 and adhere to skin 124 flanking the edges 125 of the
wound bed 120. The application of the occlusive material 130 may provide an airtight seal
over the wound bed 120. The occlusive material 130 may include any suitable airtight material,
such as plastic. In one embodiment, an adapter 131 may be coupled to the occlusive material
130 to provide an access point through the occlusive material 130 for the passage of gas or
wound fluid while maintaining the airtight seal of the occlusive material 130 over the wound bed
120. A conventional vacuum tube connector 132 may be coupled to the adapter 131. A
vacuum tube 133 may be coupled to the vacuum tube connector 132 and to a vacuum pump
134. The vacuum pump 134 may include any suitable conventional vacuum pump used with
negative pressure therapy systems such as a piezoelectric pump, a sound wave pump, and/or
a mechanical pump. Such conventional vacuum pumps may be capable of applying negative
pressure in the amount of 0-200mm Hg. Activation of the vacuum pump 134 may provide a
reduced pressure environment over the wound bed 120.
In use, medical personnel, such as a doctor, may apply the absorptive dressing 101
directly to the wound bed, which includes the smooth muscle fistula 122. Wound fluid may
begin to be absorbed into the absorptive dressing 101. An occlusive material 130 may be
overlaid on the absorptive dressing 101 such that it fully covers the edges 125 of the wound
bed 120. Medical personnel may then exert pressure on the occlusive material 130 until it
adheres to the skin 124 and creates an airtight seal over the wound bed 120. The adapter 131
may be connected to a source of negative pressure, for example, a vacuum pump 134. The
vacuum pump 134 may be assembled with the vacuum tube connector 132 and the vacuum
tube 133 in order to connect to the adapter 131. The adapter 131 may also be connected to
the access point in the occlusive material 130 to allow negative pressure to flow from the
vacuum pump 134 to the absorptive dressing 101. Upon activating the vacuum pump 134,
negative pressure may be applied to the absorptive dressing 101 thereby withdrawing wound
fluid from the absorptive dressing 101 and the wound bed 120.
In the alternative embodiment of Figure 2, a negative pressure treatment system 200
may include a vacuum pump 234 integrated into the absorptive dressing 101. In this
embodiment, the vacuum tube 133 or vacuum tube connector 132 may not be needed. The
integral vacuum pump 234 may allow a patient with the smooth muscle fistula 122 to have
improved freedom of movement or allow the patient to be fully ambulatory while using the
negative pressure treatment system 100. Such movement may be restricted when the vacuum
tube 133 is connected to the external vacuum pump 134 as shown in Figure 1. This
embodiment functions similar to the embodiment of Figure 1, however, medical personnel need
not assemble a separate vacuum tube connector, vacuum tube or adapter in order to apply
negative pressure to the absorptive dressing 101.
In various embodiments of the present invention, the absorptive dressing 101 may
include any biocompatible absorptive material suitable for direct contact with wounds, such as
wounds including smooth muscle. In one embodiment, the biocompatible absorptive material
may have an affinity for living tissue and/or wound fluid. The wound fluid may include exudate,
transudate, extracellular matrix, blood, and/or any other type of fluid coming from the wound
having a variety of viscosities. In some embodiments, the biocompatible absorptive material
may be capable of absorbing and/or suspending wound fluid having the variety of viscosities.
In some embodiments, the biocompatible material may be adapted to contact smooth muscle
121 without causing substantial cellular disruption or damage in a reduced pressure
environment and/or during dressing changes. In some embodiments, the absorptive dressing
101 may include an ester-based material.
The ester-based material may be formed into a foam suitable for trimming to fit the
boundaries of the wound bed 120, such as fitting to the edges 125. The ester-based material
may include ester functional groups that may be exposed to and/or directly contact the surface
of the smooth muscle 121. The ester functional group is a carboxylic acid derivative having the
general
chemical formula R–CO–OR’ [ ]. Esters may be derived from an inorganic
acid or organic acid in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl
(alkoxy) group. The carbonyl oxygen of the ester functional group may have a partial negative
charge with a delocalized carbocation. The ester functional group may be capable of at least
three chemical reactions. First, the electrophilic carbocation may be vulnerable to nucleophilic
attack by another molecule, such as hydroxide, resulting in addition of the nucleophile to the
carbocation. Such nucleophilic attack may result in hydrolysis of the ester. Second, an
electrophile may be accepted by the highly electronegative carbonyl oxygen. The electrophile
may be a hydrogen ion. Accordingly, the carbonyl oxygen may participate in intermolecular
hydrogen bonding. Third, the carbon adjacent to the carbocation may undergo deprotonation
by a base and leave a negative charge on the adjacent carbon or the carbonyl oxygen, as
stabilized by resonance structures.
In various embodiments, any one or more of these ester functional group reactivities
may participate in the affinity of the ester-based material for living tissue and/or the wound
fluid, in particular when applied directly to the smooth muscle tissue 121. The ester functional
group may have an affinity for a variety of molecules in the wound bed 120, including polar
groups on cells in the wound bed 120 such as the phospholipid bilayer of cell membranes, the
water component of wound fluid produced by the wound bed 120, and the water component of
fluid coming through the smooth muscle fistula 122, such as intestinal fluid.
As described above, the ester functional groups may interact with the smooth muscle
tissue 121 through hydrogen bonding, nucleophilic addition, including hydrolysis, and/or base
deprotonation. Without being bound by theory, it is believed that these chemical interactions
may form along the interface between the absorptive dressing 101 and the smooth muscle
tissue 121, evenly spreading a lifting force of negative pressure over the exposed surface of
the smooth muscle tissue 121, creating a consistent and uniform pull upward.
At least one or more of the presence of the chemical interaction of the tissue in the
wound bed 120 with the ester functional groups of the absorptive dressing 101 and/or the
interface layer 902 (discussed with respect to Figs. 8A-8B below) and negative pressure from
the vacuum pump may promote a uniform upward and/or inward pull of the wound bed 120.
As a result of this uniform pull upward and/or inward, the ester-based material may produce
little to no detrimental changes or damage to the geometric environment of the wound bed 120,
may promote the uniform movement of wound fluid through the wound bed 120, and may
reduce the flow of wound fluid out of the wound bed 120. The reduction of fluid and/or the pull
of tissue inward may lead to closure and healing of the wound bed 120.
The reactivity of the ester functional group with the smooth muscle tissue 122 in
combination with the negative pressure environment provided by the vacuum pump 134 may
have a variety of effects on the wound bed 120. Without being bound by theory, it is believed
that the ester functional group may promote at least one or more of: an optimal geometric
environment of the wound, the formation of granulation tissue, temperature regulation, at least
partial reversal of tissue downgrowth, optimal fluid management, and induction of cell growth.
The geometric environment of the wound bed 120 impacts certain physiological
phenomenon including the migration of cells, such as epithelial cell growth and capillary
endothelial cell migration, and the movement of exudate through the wound carrying growth
factors, nutrients, and proteins. As discussed further below, without being bound by theory,
non-uniform movement of wound fluid can lead to the pooling of wound fluid at the wound bed.
This pooling may disrupt cell-to-cell interactions and may lead to cell distortion or damage. It is
believed that the ester-based material limits such cellular distortions and maintains an optimal
or improved geometric environment for wound healing and closure. This may be due to the
chemical interactions of the ester functional groups with the tissue of the wound bed 120.
Granulation tissue may include new connective tissue and the formation of new blood
vessels on the surface of the wound bed 120, facilitating the healing process. The growth of
granulation tissue may fill the wound bed 120 and assist in closure of the wound and/or the
reduction of exudate output. The application of the ester-based material to the wound bed 120
including the smooth muscle fistula 122 may stimulate tissue granulation.
Maintaining a normal temperature in the wound bed 120 may prevent vasoconstriction
and hypoxia and may decrease the risk of infection. The small pore diameter 111 of the ester-
based material which provides an even distribution and movement of the exudate throughout
the absorptive dressing 101 may effectively regulate the normal temperature of the wound bed
120 by reducing evaporation and/or uneven airflow through the ester-based material.
Evaporation and/or uneven airflow, such as that exhibited by ether- based materials, may
cause the wound temperature to drop which may increase tissue metabolism and decrease
pH. These changes in the wound tissue metabolism and pH may cause bleeding, disruption of
granulation tissue formation, and pain for the patient.
The absorptive dressing 101 including the ester-based material in combination with
continuous or intermittent negative pressure may provide enhanced temperature regulation of
the wound bed 120. In various embodiments of the present invention, the ester-based material
may provide temperature regulation in one or more locations on the ester-based material.
First, the interface between the surface of the ester-based material and the tissue of the wound
bed 120 where the ester functional groups make direct contact and react with the tissue may
consistently maintain a substantially normal body temperature. Second, the remaining portion
of the ester-based material may evenly distribute and interact with the exudate pulled from the
wound bed 120, forming chemical bonds such as hydrogen bonds with the exudate as the
exudate moves through the ester-based material towards the source of negative pressure.
The exudate in the ester-based material may establish a temperature equilibrium which may be
lower than body temperature and may provide a layer of insulation over the ester-based
material to tissue interface. As described above, effective regulation of the temperature of the
wound bed may positively affect healing providing an optimal temperature for cellular
metabolism and pH maintenance. Additionally, the ester-based material may provide a thermal
buffer to increase the temperature of incoming instillation fluids such as saline that may be
applied to the negative pressure treatment system 100, such as for the addition of antibiotics to
the wound, and may prevent or reduce a low temperature shock to the wound bed 120.
The chemical interactions of the ester functional groups in the ester-based material with
the tissue of the wound bed 120 may result in improved fluid management as compared to
non-ester based materials. The evenly distributed affinity of the ester functional groups for the
tissue and exudate may allow exudate to move through the wound in an even and orderly
manner toward the source of negative pressure, despite the effect of microstrain distortions of
the surface of the wound bed 120 in response to the negative pressure. This affinity may
promote consistent collection of exudate fluid in folds and contouring lines of the wound bed
120. The effect of the uniform movement of exudate provides efficient removal of exudate,
fluids, and materials and promotes the uniform orientation of cell growth throughout the surface
of the wound bed 120. Without being bound by theory, the uniform affinity of the ester
functional groups may also prevent or decrease the formation of cavities or undermined tissues
due to the closer connection between the tissue and the ester-based material. Further, the
uniform affinity of the ester functional group for the tissue may require less cellular work to
orient and re-orient during physical movements of the patient and changes in the negative
pressure treatment system 100. Thus, systems used in the industry, such as the instillation of
external fluids, soak, vacuum pause cycles, and/or dressing changes, to abate issues of fluid
pooling may not be as necessary or may lead to even further improved results when used with
the ester-based material.
An upward pull induced by the interaction of the ester functional groups with the tissue
on the surface of the wound bed 120 may reduce and/or at least partially reverse naturally
occurring tissue down growth into the wound bed 120. Down growth of epithelial tissue and
deeper tissue into the wound bed 120 may occur naturally in incisions and wounds. However,
an upward pull provided by the ester-based material on the wound bed 120 may uniformly
distribute pressure over the surface of the wound bed 120 and cause migrating cells to move
toward the surface of the wound bed 120.
In one embodiment, the ester-based material may be a polymer of polyurethane,
specifically polyester. As compared to conventional ether-based foams, ester-based foams are
more rigid, have a smaller open-reticulated cell structure, and have a higher tensile strength.
Ester-based foams also suspend moisture substantially evenly and allow fluid to flow evenly
throughout the foam due to its small cell structure and/or chemical affinity for moisture.
Conventional foams are typically ether-based foams, including polymers of polyether
triol, and have a larger pore diameter. Without being bound by theory, it is believed that these
relatively large pore sizes, as compared to the sizes of individual cells with which the foam
material was used, such as smooth muscle cells, are responsible for the damage caused to
wound beds when conventional foam material is placed in direct contact with the wound.
Figure 3A representatively illustrates an example of pore diameters 311 of conventional foam
materials 301 compared to smooth muscle cells 321.
In addition, without being bound by theory, it is believed that the large pore diameter of
ether-based foams reduces the foam’s ability to suspend moisture and allow moisture to pass
through the foam easily. The ease of movement of moisture through the ether-based foam has
the practical result of promoting fluid collection in the portion of the foam having the lowest
center of gravity, leading to an uneven distribution of moisture throughout the ether-based
foam. The poor ability of ether-based foams to retain moisture renders them inappropriate for
use in negative pressure therapy applications because the ether-based foam provides
inadequate temperature regulation to the wound bed, poor delivery of additives to the wound
bed such as antibiotics, and limits ambulation of a patient due to the uneven distribution and
pooling of moisture in a sealed system when the patient moves.
Additionally, the basic chemical structure of the ether linkage in ether-based
polyurethane foams is R-O-R’. The central oxygen may be substantially unreactive, incapable
of appreciable hydrogen bonding, and significantly less polar than the oxygen of ester
functional groups. Without being bound by theory, it is believed that the stability of the ether
linkage renders them incapable of forming the same types of chemical interactions or reactions
as ester-based foams including hydrolysis and reactions with acids, oxidizing agents, reducing
agents, bases, and active metal species. The chemical and resultant structural differences
between ether-based foams and ester-based foams impact the performance of these materials
in different applications. In healing applications using negative pressure therapy systems, the
temperature regulation and even distribution of moisture provided by the various embodiments
of the ester-based material described may optimize wound healing and closure.
The absorptive dressing 101 including the ester-based material may be manufactured
and/or further processed to obtain any desired physical properties. In some embodiments, the
desired physical properties may optimize pore size and structure such as pore density, pore
geometry, pore reticulation, permeability of pores to wound fluid, dry tensile strength, and/or
wet tensile strength. Processing of the ester-based material may further optimize the ability of
the ester-based material to maintain a saturated volume of suspended fluid. For example, the
ester-based material of the absorptive dressing 101 applied to the wound bed 120 may
ultimately become saturated with wound fluid coming through the smooth muscle fistula 122.
Wound fluid may be continually removed from the absorptive dressing 101 through the vacuum
tube 133 and, at the same time, wound fluid may continually be entering the absorptive
dressing 101 from the smooth muscle fistula 122. As a result of the ester-based material’s
affinity for the wound fluid, a saturated absorptive dressing 101 may allow a substantially equal
volume of wound fluid and/or number of wound fluid molecules into the ester-based material as
is exiting the ester-based material through the vacuum tube 133. Accordingly, wound fluid
removal may not substantially affect the saturated volume of wound fluid retained by the
absorptive dressing 101 under clinically relevant negative pressures of 0-200mm Hg. Without
being bound by theory, it is believed that this environment where the volume in is substantially
equal to the volume out (referred to simply at times as a “one molecule in/one molecule out”
environment) as provided by a substantially saturated absorptive dressing 101 promotes a
plurality of benefits to wound healing such as effective temperature regulation, even distribution
of negative pressure, and maintaining an even distribution of wound fluid despite movement of
the patient.
In other applications, the geometry of the pores of the absorptive dressing 101 may
include a shape that provides for increased surface area inside the pores 110, such as a round
shape. Such increased surface area may increase contact of the ester functional groups with
the wound bed 120 and may benefit the healing of the smooth muscle fistula 122. The
increased surface area may be particularly beneficial for a wound with a high wound fluid flow,
such as an intestinal fistula. In other embodiments, the geometry of the pores 110 of the
absorptive dressing 101, shown in Fig. 3B, may be configured to correlate with the general
shape of the primary cell type in the wound bed 120, such as epithelial cells, skeletal muscle
cells, and/or smooth muscle cells. In addition, the pores may be configured to correlate with
the size and/or diameter of any of the cells or other material of the exudate from the wound
bed. For example, the pores 110 may have an elongated shape to correlate with the elongated
dimensions of skeletal or smooth muscle cells. Example dimensions and shapes of cell types
that may be in the wound bed are shown in Table 1 below. The pores 110 may be configured
to correlate with the diameter, shape and/or length of any of the cells types below, in addition
to the diameter, shape and/or length of other cell types in the wound bed 120. However, the
pores 110 may have a variety of shapes, including octagonal, hexagonal, diamond or trigonal.
TABLE 1
Cell Type General Cell Diamete Length
Shape r
MUSCLE varies varies varies
CELLS
Cardiac Short, narrow 10µm ̶ 80µm ̶
Muscle Cells cell 15µm 100µm
Smooth Short, 0.2µm ̶ 20µm ̶
Muscle Cells elongate, fusiform cell 2µm 200µm
Skeletal Large, elongate 10µm ̶ Up to
Muscle Cells cell 100µm 100cm
EPITHELIAL varies varies varies
CELLS
(including
endothelial cells)
CONNECTIVE varies varies varies
TISSUES
NERVE varies varies varies
CELLS
In some applications, the pore diameter and/or size of the absorptive dressing 101 may
be customized to promote the interaction of the pore struts with the cells in the wound bed 120.
For example, the pore diameter and/or size may be substantially equivalent to the diameter
and/or size of a primary cell type in the wound bed 120. In some embodiments, the pore width
may be about 0.1µm to about 100µm, in order to correlate with the size of smooth muscle cells.
In other embodiments, the pore width may be about 0.1µm to about 50µm.
Without being bound by theory, it is believed that reducing the size of the pores 110 to
be substantially equivalent to the diameter of smooth muscle cells leads to a reduction in cell
sacrifice, as representatively illustrated in Figures 3A-3B. An example of pore 310s of a
conventional ether-based foam 301 is illustrated in Figure 3A. Pores 310 may have a diameter
311 of about 400µm to about 600µm. In general, smooth muscles cells 321 adjacent to pores
310, shown in the illustration of a portion of a wound bed 320, may be removed (e.g.,
sacrificed) during dressing changes. Without being bound by theory, it is believed that the
sacrifice of cells 321 may be caused by the formation of weak cell-to-cell contacts, such as cell
junctions, that form as damaged tissue regrows to fill a wound bed 120. The struts or edges of
pores 310 in conventional ether-based foams may contact some smooth muscle cells 321 and
destroy weak cell junctions formed as the smooth muscle cells 321 divide as part of wound
healing. Pore 110 of the ester-based foam of an embodiment of the present invention may be
illustrated in Figure 3B. In some embodiments, pore 110 may have a diameter of about 30µm
or less and be close to the diameter of a smooth muscle cell. As a result, the pores 110 may
make many contacts along the length of each smooth muscle cell 121. In this fashion, it is
believed that the pores 110 may function as a scaffold to support closer and/or stronger cell
junctions as the smooth muscles cells 121 divide. The smooth muscle cells 121 may therefore
remain intact during dressing changes, with no appreciable loss of the smooth muscle cells
121 at the foam-tissue interface that may disrupt wound healing.
Referring to Figure 4, in various embodiments of the present invention, the size of the
pores 110 in the absorptive dressing 101 including the ester-based material may be adapted to
reduce the sacrifice of the smooth muscle tissue 121. In one embodiment, the size of pores
110 may be reduced to any pore size that is less than the pore size of conventional ester-
based foam of approximately 100µm – 600µm. In some embodiments, the pore diameter 111
may be substantially equivalent to the diameter of smooth muscle cells. Smooth muscle cells
include short, elongate, and fusiform shapes that may be about 0.2µm – 20µm in diameter and
approximately 20µm – 200µm in length. In one embodiment, the average pore diameter 111
may be approximately less than or equal to 30μm. For example, the average pore diameter
111 may be about 0.2-30µm, or 0.2-2µm.
Further, the pores 110 of the ester-based material may be reticulated pores.
Reticulation refers to the open nature of the pores 110 such that the lumen 112 of the pores
110 communicates with adjacent pores 110, such as through channels 113. The struts or
edges of the pores 110 where contact is made with adjacent pores 110 remain intact in
reticulated foam. Without being bound by theory, the open-celled and substantially uniform
pore size of the reticulated absorptive dressing 101 may facilitate substantially uniform
diffusion of nutrients, oxygen, bioactives, and allow for negative pressure across the entire
wound bed 120, and efficient removal of exudates upon application of negative pressure
wound therapy.
In various embodiments of the present invention, the size of the pores 110 of the
absorptive dressing 101 including an ester-based material may be less than the pore size of
conventional ester foams and/or substantially similar to the diameter of smooth muscle cells
121. In one embodiment, the pores 110 may be created in an ester-based material using any
suitable process such as using molds including fiber-optic molds, stamping methods,
bombardment methods such as ion beam or ultrasound bombardment, chemical etching,
chemical baths, and/or laser irradiation of the ester-based material.
In one embodiment, the pores of conventional ester foam may be reduced to a desired
size in any suitable process such as felting. The felting process may include thermal,
mechanical, or chemical compression of the ester-based material, resulting in permanently
compressing the pores 110. The felting process may include heating the ester-based material
during the manufacturing process of the polyurethane ester foam, followed by the application of
a degree of compression to produce a desired pore density, a desired fluid dynamic within the
foam, and/or an increase in tensile strength. In various embodiments, the biocompatible foam
may be processed to obtain any desired physical properties such as any desired pore size,
porosity, density, reticulation of pores, permeability and/or tensile strength.
In various embodiments, the ester-based material may be manufactured and/or further
processed to obtain any desired chemical properties such as affinity for wound fluid, elasticity
of the ester-based material to allow contraction of the absorptive dressing 101 under negative
pressure, even wound fluid suspension and/or absorption within the ester- based material,
and/or retention and/or delivery of additives. In some embodiments, the ester-based material
may be customized to promote healing of a particular type of wound bed 120. For example, a
wound bed 120 including the smooth muscle fistula 122 of a highly acidic nature, such as a
biliary fistula, may benefit from an absorptive dressing 101 with an altered chemistry such as
impregnation with a neutralizing composition such as bicarbonate. In another embodiment, the
ester-based material may include alcohols, antibiotics, pharmaceutically active compounds,
and the like. Accordingly, the chemistry, pore size, and/or the pore geometry within the
absorptive dressing 101 may be optimized and/or customized to provide a maximum healing
benefit to any particular type of wound bed 120. Additionally, in some embodiments, the ester-
based material may include a plurality of horizontally arranged layers with the desired physical
properties that are coupled to form a single cohesive piece of foam.
In further embodiments, as illustrated in Figs. 5A-5B, the absorptive dressing may
include more than one layer of foam where each layer includes a substantially uniform pore
size and/or pore geometry within each layer, but has a different pore size and/or pore geometry
relative to an adjacent layer or layers. For example, referring to Figure 5A, an absorptive
dressing 501a may have a first layer 540 including pores 541 having a diameter that may be
larger than the pores 551 of a second layer 550. Referring to Figure 5B, an absorptive
dressing 501b may include the second layer 550 overlaid with the first layer 540 and the first
layer 540 may be overlaid by an additional second layer 550. The absorptive dressing 501b
may include as many alternating layers 540/550 as desired. In various embodiments, the
pores 541 and 551 may be approximately the size and/or diameter of the cells with which the
absorptive dressing 501a, 501b will be used. For example, the pores 551 may be about 0.1µm
to about 10µm and the pores 541 may be about 10µm to about 100µm, or about 20µm to about
100µm. Accordingly, many pores 541 and/or pores 551 may extend the length of any smooth
muscle cells in the wound bed 120. However, the pores 541 and 551 may also have any of the
characteristics of the pores 110 discussed above, including any of a variety of shapes, sizes,
diameters or reticulation as discussed above.
Without being bound by theory, it is believed that having such alternative layers of 540
and 550 will create a better seal via the smaller pores 551 at the wound bed 120 while still
allowing for higher levels of absorption and compressibility (to compensate for peristalsis and
other movements by the patient) at the larger pores 541. In addition, in the absorptive dressing
501b, having the second layer 551 on both the top and bottom of first layer 540 allows the
absorptive dressing 501b to be reversible, facilitating its use by medical personnel. In such an
embodiment, the pores 551 may be about 0.1µm to about 50µm and the pores 541 may be
about 10µm to about 300µm. In some embodiments, the first layer 540 may have a thickness
of about 0.1mm to about 2mm and the second layer 550 may have a thickness between 2mm
and 8mm.
Referring to Figure 5C, describing another embodiment of the absorptive dressing, in
an absorptive dressing 501c, the pores 541 and the pores 551 may be combined within the
same layer, such as a layer 560. For example, smaller pores 551 may be interspersed
between larger pores 541 where each pore 551 is surrounded by larger pores 541.
Additionally, the absorptive dressing 501c may include pores having a limited reticulation to
reduce the volume and/or rate of wound fluid flow through the absorptive dressing 501c. The
pores of layer 501c may also have any of the characteristics of the pores 110 discussed above,
including any of a variety of shapes, sizes, diameters or reticulation as discussed above. For
example, the pores of layer 560 may have a size of about 0.1µm to about 300µm.
Without being bound by theory, by interspersing different sized pores, it is believed that
the wound fluid would travel through pathways including large pores 541 and smaller pores
551, increasing the resistance to fluid flow. In some embodiments, the interspersion of small
pores 551 with large pores 541 may increase the resistance of the absorptive layer 501c to
wound fluid, creating a tighter seal over the wound bed 120 as compared to an absorptive layer
having a uniform or larger pore 541 structure. This tight seal or layer of pressure resistance
may lead to lower wound fluid production and output from the wound bed 120 and/or increased
wound fluid flow back through the source of the fistula, such as an intestine. Additionally,
without being bound by theory, it is believed that selection of the size of small pores 551 and/or
large pores 541 may provide a filtration function to facilitate removal of pre-selected particles
from the wound fluid while encouraging lower wound fluid production and/or redirection of flow.
For example, the size of small pores 551 and/or large pores 541 may be similar to the size of
various cell debris and/or bacteria, which are generally substantially smaller than eukaryotic
cells.
Layer 560 may include the entire absorptive dressing 501c, or may be layered with
additional layers having interspersed large and small pores or may be layered with additional
layers of uniform pores, such as first and second layers 501a and 501b. In further
embodiments, any of absorptive dressings 501a, 501b and 501c may be layered with a foam
having a larger pore size, such as conventional foams having a pore size between 100µm –
600µm. In addition, any of absorptive dressings 501a, 501b and 501c may have the physical
and chemical properties of the various embodiments of absorptive dressings discussed herein,
for example, the absorptive dressing 101.
In various embodiments, the absorptive dressing including horizontally stacked layers,
such as the layers 540, 550 and 560, may include a junction 545 between two adjacent layers,
as shown in Figs. 5A. The junction 545 may be treated with any suitable additive to provide or
improve a desired physical and/or chemical property of the absorptive layer 501a, 501b, 501c.
For example, a solution including one or more additives may be painted, sprayed, wiped,
sponged, or otherwise applied to the junction 545. The additives may include biocompatible
material such as an antibacterial agent, a pharmaceutically active agent, a vitamin, a semi-
occlusive substance, an emollient, a humectant, medicament, and the like. The absorptive
dressing 501a, 501b, 501c may be soaked and/or saturated in the additive prior to or upon its
application onto the wound bed 120.
The method or use for the absorptive dressings 501a, 501b and 501c is the same as
the method of use for the embodiment of Figure 1. However, in embodiments in which the
absorptive dressings 501a, 501b and 501c are not reversible, i.e., in which the outermost
layers of the absorptive dressings 501a, 501b and 501c have different pore sizes, the
outermost layer with the smallest pore size may face the wound bed in order to create a tighter
seal over the wound bed 120.
In further embodiments, additional structural features (which may also be referred to as
secondary structural features whereas the pores of the absorptive dressing may be referred to
as primary structural features) may be introduced into the absorptive dressing to encourage
wound closure by directional wound fluid flow through the absorptive dressing. Such structural
features may direct wound fluid flowing from the edges 125 of the wound bed 120, particularly
the edges 626 of the fistula 122, toward a central area above the fistula 122 to promote a pull
of the tissues toward a midline of the fistula 122. Conventional absorptive dressings, such as
ether-based foams, do not discretely or intentionally employ structural features that influence or
guide the direction of wound fluid through the absorptive dressing. Any suitable method for
creating directional fluid flow may be implemented within the absorptive dressing.
In one embodiment, an example of which is illustrated in Figure 6, the structural
features may direct wound fluid flowing from the edges 125 of the wound bed 120, particularly
the edges 626 of the fistula 122 toward the center of an absorptive dressing 601 to promote a
pull of the tissues toward a midline of the fistula 122. The absorptive dressing 601 may have
the physical and chemical properties of the various embodiments of absorptive dressings
discussed herein, for example, the absorptive dressings 101, 501a, 501b and 501c. The
absorptive dressing 601 may also include preformed flow paths 614 of large diameter pores
through a scaffold 615 of small diameter pores to encourage wound fluid to primarily move
through the preformed flow paths 614. The preformed flow paths 614 may include pores
having one or more diameters different from the pore size(s) of the scaffold 615 (e.g., greater
than the pore size of the scaffold) or may include hollow pathways, e.g., from the side of the
absorptive dressing 601 closest to the wound bed 120 to the opposite side farthest from the
wound bed 120. The preformed flow paths 614 may be arranged in an hourglass-like shape,
such as a top heavy hourglass shape as shown in Fig. 6, or the preformed flow paths 614 may
have a symmetrical or bottom-heavy hourglass-like shape. The hourglass-like shape may be
three-dimensional, such that a cross-section of the absorptive dressing 601 in a horizontal
direction may show the preformed flow paths 614 as circles of different sizes corresponding to
the level of the hourglass-like shape at which the cross-section is taken. In further
embodiments, the preformed flow paths 614 may have a cone-shape, with the larger opening
of the cone-shape facing the fistula 122. In such embodiments, the smaller opening or apex of
the cone-shape may face the vacuum pump 134 located above it.
In some embodiments, more than one vacuum pump 134 may be included, for
example, two to five vacuum pumps 134, at the upper ends 616 of the preformed flow paths
614. Alternatively, a vacuum pump capable of creating a circular negative pressure flow above
the upper ends 616 of the preformed flow paths 614 can be used. The lower ends 617 of the
preformed flow paths 614 may be positioned between the edges 626 of the fistula 122 so that
the negative pressure of the vacuum pump 134 directs the fluid flow and the edges 626 of the
fistula 122 inwardly to aid in the closure of the fistula 122. Prior to use, the absorptive dressing
601 may be cut in order to have the lower ends 617 of the preformed paths 614 correctly sit
between the edges 626 of the fistula 122. Without being bound by theory, it is believed that in
use, negative pressure created by the vacuum pumps 134 may pull both the wound fluid and
the edges 626 of the fistula 122 upwards and because of the lower pressure of the preformed
flow paths 614, the wound fluid and the edges 626 will be pulled towards the preformed flow
paths 614. The directionality of the movement of the edges 626 will aid in the closure of the
fistula 122. Further, as the edges 626 of the fistula 122 grow closer together, a further
embodiment of the absorptive dressing 601 can be used in which lower ends of the preformed
flow paths 614 are positioned closer together than in previously used absorptive dressing 601,
so that the edges 626 of the fistula 122 are still being directed inwardly during the use of the
vacuum pumps 134. This process can be repeated until the fistula is closed or until the edges
of the fistula are too close together for preformed flow paths to create an inward pull.
In use, the absorptive dressing 601 including the preformed flow paths 614 may be
applied to the wound bed 120 including the smooth muscle fistula 122. The absorptive
dressing 601 may be positioned such that the lower ends 617 of the preformed flow paths 614
are between the edges 626 of the fistula 122. An occlusive material 130 may be overlaid on
the absorptive dressing 601 such that it fully covers the edges 125 of the wound bed 120.
Medical personnel may exert pressure on the occlusive material 130 until it adheres to the skin
124 and creates an airtight seal over the wound bed 120. The adapter 131 may be connected
to a source of negative pressure, for example, a vacuum pump 134. The vacuum pump 134
may be assembled with the vacuum tube connector 132 and the vacuum tube 133 in order to
connect to the adapter 131. However, more than one set of the vacuum pumps 134, vacuum
tube connectors 132, the vacuum tubes 133 and adapters 131 may be assembled as shown in
Figure 6. The adapter 131 may be connected to the access point in the occlusive material 130
to allow negative pressure to flow from the vacuum pump 134 to the absorptive dressing 601.
If more than one vacuum pump 134 is used, each adapter 131 associated with each vacuum
pump 134 may have its own access point in the occlusive material 130. Upon activating the
vacuum pump 134, negative pressure may be applied to the absorptive dressing 601 thereby
withdrawing wound fluid from the absorptive dressing 601 and the wound bed 120. Without
being bound by theory, negative pressure created by the vacuum pump or vacuum pumps 134
may pull both the wound fluid and the edges 626 of the fistula 122 upwards and towards the
preformed flow paths 614.
Other embodiments, as shown in Figures 7A-7B, may include structural features that
create pressure gradients and/or physical barriers to direct fluid flow. Such structural features
may include barriers 770 composed of plastic, metal or other materials, such as biocompatible
materials. However, because the barriers 770 may be incorporated into an absorptive layer
701 and not in direct contact with tissue, non-biocompatible materials may also be used. The
absorptive dressing 701 may have the physical and chemical properties of the various
embodiments of absorptive dressings discussed herein, for example, the absorptive dressings
101, 501a, 501b and 501c.
The barriers 770 may have a wing-like shape, such as an airplane wing-shape. For
example, as shown in Fig. 9C, the barriers 770 may be asymmetrical along a chord line 771
connecting the leading edges 772 and the trailing edges 773 of the barriers 770 creating a
camber in which the inner portions 774 of the barriers 770 have a thickness t greater than the
thickness t of the outer portions 775 of the barriers 770. The inner portions 774 are directed
towards an area of the absorptive dressing 701 above the center of the fistula 122 and the
outer portions 775 are directed away from the area of the absorptive dressing 701 above the
center of the fistula 122. The leading edges 772 may also have an angle of attack α relative to
the direction of fluid flow 776 from the fistula 122. Without being bound by theory, it is believed
that the wing-like shape of the barriers 770 and the angle of attack α take advantage of the
Bernoulli Principle to create a pressure gradient in which the pressure between the inner
portions 774 of the barriers 770 is lower than the pressure surrounding the outer portions 775
of the barriers 770. With the application of negative pressure from the vacuum pump 134,
wound fluid flowing from the fistula 122 along with the edges 626 of the fistula 122 will be
directed towards the area of low pressure between the inner portions 774, constricting the
opening of the fistula and aiding in wound closure.
The barriers 770 may be a single piece structure or multiple pieces. For example, the
barriers 770 may be a single and/or monolithic donut-shaped structure when viewed from
above or the barriers 770 may be multiple overlapping wings arranged in a circle around the
area above the fistula 122. In further embodiments, the barriers 770 may vary in size. Without
being bound by theory, it is believed that by varying the size of the barriers 770, for example,
incrementally from small to large around the circumference of the barriers 770, the
directionality of the fluid flow can be controlled.
The barriers 770 may have a height from the leading edges 772 to the trailing edges
773 of about 5mm to about 40mm. In some embodiments, the barriers 770 may have a height
from the leading edges 772 to the trailing edges 773 of about 10mm to about 30mm. The
barriers 770 may have a width, including the thickness t of the inner portions 774 and the
thickness t of the outer portions 775, of about 1mm to about 10mm. In some embodiments,
the barriers 770 may have a width, including the thickness t of the inner portions 774 and the
thickness t of the outer portions 775, of about 1mm to about 3mm.
In use, the absorptive dressing 701 including the barriers 770 may be applied to the
wound bed 120 including the smooth muscle fistula 122. The absorptive dressing 701 may be
positioned such that the leading edges 772 of the barriers 770 are above or between the edges
626 of the fistula 122. An occlusive material 130 may be overlaid on the absorptive dressing
701 such that it fully covers the edges 125 of the wound bed 120. Medical personnel may
exert pressure on the occlusive material 130 until it adheres to the skin 124 and creates an
airtight seal over the wound bed 120. The adapter 131 may be connected to a source of
negative pressure, for example, a vacuum pump 134. The vacuum pump 134 may be
assembled with the vacuum tube connector 132 and the vacuum tube 133 in order to connect
to the adapter 131. The adapter 131 may also be connected to the access point in the
occlusive material 130 to allow negative pressure to flow from the vacuum pump 134 to the
absorptive dressing 701. Upon activating the vacuum pump 134, negative pressure may be
applied to the absorptive dressing 701 thereby withdrawing wound fluid from the absorptive
dressing 701 and the wound bed 120. Without being bound by theory, negative pressure
created by the vacuum pump 134 may pull both the wound fluid and the edges 626 of the
fistula 122 upwards and towards the area between the inner portions 774 of the barriers 770.
Further embodiments, examples of which are shown in Figures 8A-8D, may include
structural features including suitable devices for drawing in wound fluid from the wound bed
120 in an upward and spiral pattern that may promote lifting and, at the same time, gentle
twisting of the tissues in the wound bed 120. The lifting and twisting motion of the tissue as
wound fluid is withdrawn through the device may further encourage the wound edges to be
drawn together toward the midline of the wound bed 120 and promote ultimate wound closure.
As shown in Fig. 8A, the structural features may include a radial housing 880 that may be
incorporated into an absorptive dressing 801. The absorptive dressing 801 may have the
physical and chemical properties of the various embodiments of absorptive dressings
discussed herein, for example, the absorptive dressings 101, 501a, 501b and 501c. The radial
housing 880 may be positioned such that a central axis C of the radial housing 880 is above
the center of the fistula 122. The radial housing 880 may include a substantially hour-glass
shaped hollow structure. Alternatively, the radial housing 880 may include one or more tubes
spirally wound to form a cone-shaped structure where the larger opening of the cone-shaped
structure faces the fistula 122. Without being bound by theory, it is believed that by virtue of its
shape and structure, the radial housing 880 is capable of spinning a fluid moving through the
radial housing 880 at a suitable pressure. The fluid may include a gas, a liquid or a
combination of both. For example, the fluid may include filtered air and/or saline.
In some embodiments, the fluid may be delivered into the radial housing 880 under
pressure through a delivery tubing 885, such as by an air compressor, or by creating a twisted
Venturi effect where wound fluid moving through a central area 886 of the radial housing 880
draws gas though the delivery tubing 885 by a vacuum pressure. The radial housing 880 may
include a radial tubing 881 that is capable of receiving the fluid from the adjacent delivery
tubing 885. The fluid may then be delivered from the radial tubing 881 into the central area
886 of the radial housing 880 via injection ports 887. The central area 886 may be defined by
the radial tubing 881 of the radial housing 880. The injection ports 887 may have varied
diameters along the length and/or height of the radial housing 880 to promote the rotation and
upward force of the wound fluid and resultant toroidal twist of the tissue. For example, the
injection ports 887 may be larger at the inferior opening 882 and smaller at the flow constriction
zone 883. Alternatively, the injection ports 887 may be smaller at the inferior opening 882 and
larger at the flow constriction zone 883. In addition, the walls 888 of the injection ports 887
may be angled to direct the flow of the fluid. The walls 888 of the injection ports 887 may be
angled such that the fluid is directed to the center of the central area 886.
In some embodiments, the radial housing 880 may include a single continuous radial
tubing 881, as shown in Fig. 8B, or may include multiple pieces of radial tubing coupled
together. The radial tubing 881 may include a flexible, biocompatible, and/or biodegradable
material. For example, the radial tubing 881 may include a polymeric material where each
layer of the radial tubing 881 may be flexible in relation to adjacent layers and/or may be
flexible in relation to its contact with the wound bed 120 to provide for patient ambulation. In
one embodiment, each layer of the radial tubing 881 may be offset as the radial tubing 881
ascends to achieve the hourglass shape. Accordingly, the radial housing 880 may include at
least three blended zones, each of which may have a different diameter. For example, the
three blended zones may include at least an inferior opening 882, a superior opening 884, and
a flow constriction zone 883.
In some embodiments, the wound fluid may enter the central area 886 of the radial
housing 880 from the wound bed 120 (including the smooth muscle fistula 122), through the
inferior opening 882, and may exit the superior opening 884 to the vacuum pump 134.
However, in some embodiments, the radial housing 880 may be symmetrical such that either
the inferior opening 882 or the superior opening 884 may function as the fluid inlet or outlet.
Accordingly, either end of the radial housing 880 may be applied to the wound bed 120. In
such embodiments, as shown in Figure 8C, the side of the radial housing 880 facing downward
and touching the wound bed 120 may function as the inferior opening 882 and the side facing
upward toward the vacuum source including the vacuum tube 133 may function as the superior
opening 884.
In some embodiments, the delivery tubing 885 may have valves, for example, one-way
valves, such as butterfly valves or valves similar in function and/or structure to a revolving
door, for preventing a reversal of flow. In other embodiments, the radial housing 880 may have
one-way valves at the delivery tubing 885 to prevent wound fluid from exuding up into the
vacuum tube 133 or vacuum pump 134 after the vacuum pump 134 is turned off.
As also shown in Figure 8C, in some embodiments, the walls 888 of the injection ports
887 may be angled such that the fluid is directed to the center of the flow constriction zone
883. However, for the injection ports 887 closest to the inferior opening 882, the injection ports
887 may be angled perpendicular to the central axis C of the radial housing 880 in order to
push the fluid towards the central axis C of the radial housing 880 and resultantly push the
edges 626 of the fistula 122 closer together.
In some embodiments, as shown in Figure 8D, the walls 888 of the injection ports 887
may be angled in a circumferential direction. Without being bound by theory, it is believed that
by angling the injection ports 887 in a circumferential direction, the fluid will be rotated in a
helical pattern up the radial housing resulting in a toroidal twist of the fluid and of the edges
626 of the fistula 122 facilitating closure of the fistula 122.
In various embodiments of the present invention, the radial housing 880 may comprise
a flexible, biodegradable material that may be compressed under the negative pressure
provided by the vacuum pump 134. For example, the radial housing 880 may be made of a
composition that can dissolve, such as sugar crystals and/or a chromic gut polymer. In some
embodiments, one or more additives may optionally be applied to the inside of the radial
housing 880 to interact with the wound fluid entering through the inferior opening 882. For
example, the additives may optimize at least one of the adhesion or cohesion of the wound
fluid as it travels through the radial housing 880 and may encourage the toroidal twist of the
wound fluid. In some embodiments, additives may be added to facilitate or slow the rate of
dissolution of the radial housing 880, depending the desired resulted in view of the
characteristics of the fistula 112. For example, for a radial housing 880 made of sugar crystals,
additives may be added to slow the rate of dissolution so that the dissolution of the radial
housing 880 correlates with the rate of wound healing.
In some embodiments, the radial tubing 881 may taper in diameter toward the flow
constriction zone 883. In other embodiments, the diameter of the radial tubing 881 may remain
constant or may increase toward the flow constriction zone 883. The radial tubing 881 may
have a diameter between about 0.5mm and about 5mm. The injection ports 887 may be
circular in shape and have a diameter of about 0.1mm to about 0.7mm. However, the injection
ports 887 need not be circular and may have any other geometric shape.
The radial housing may have a diameter at the inferior opening 882 sufficient to
completely encircle the fistula 122. For a stomatized fistula, the radial housing may have a
diameter at the inferior opening sufficient to completely encircle the fistula 122 including the
stomatized walls surrounding the fistula. For example, the radial housing 880 may have a
diameter of about 10mm to about 40mm. In some embodiments, the radial housing 880 may
have a diameter of about 15mm to about 25mm.
In further embodiments, the radial tubing 881 of the radial housing 880 may be a single
hourglass shaped structure. For example, the radial tubing 881 may include a double-walled
structure that receives fluid from the delivery tubing 885 and have injection ports on the inner
pane of the double-walled structure so that the fluid can enter the central area 886.
The delivery tubing 885 may be a single tube on one side of the radial housing 880, or it
may be multiple tubes on opposite sides of the radial housing 880, as shown for example in
Figures 8C-8D. The delivery tubing 885 may include two or more tubes spaced around the
periphery of the radial housing 880. Alternatively, the radial housing 880 may be a double-
walled hollow cylindrical structure surrounding the radial housing 880 and capable of delivering
fluid around the entire circumference of the radial housing 880 at the inferior opening 882. The
delivery tubing 885 may have a diameter similar to the radial tubing 881 of the radial housing
880. For example, the delivery tubing 885 may have a diameter between about 0.5mm and
about 5mm.
In use, the absorptive dressing 801 including the radial housing 880 may be applied to
the wound bed 120 including the smooth muscle fistula 122. The absorptive dressing 801 may
be positioned such that the inferior opening 882 of the radial housing 880 encircles the fistula
122. An occlusive material 130 may be overlaid on the absorptive dressing 601 such that it
fully covers the edges 125 of the wound bed 120. Medical personnel may exert pressure on
the occlusive material 130 until it adheres to the skin 124 and creates an airtight seal over the
wound bed 120. The adapter 131 may be connected to a source of negative pressure, for
example, a vacuum pump 134. The vacuum pump 134 may be assembled with the vacuum
tube connector 132 and the vacuum tube 133 in order to connect to the adapter 131. The
adapter 131 may also be connected to the access point in the occlusive material 130 to allow
negative pressure to flow from the vacuum pump 134 to the absorptive dressing 801. Upon
activating the vacuum pump 134, negative pressure may be applied to the absorptive dressing
801 thereby withdrawing wound fluid from the absorptive dressing 801 and the wound bed 120.
Without being bound by theory, negative pressure created by the vacuum pump 134 may pull
both the wound fluid and the edges 626 of the fistula 122 upwards and towards the central
area 886.
Referring to Figure 9, in some embodiments of the present invention, a negative
pressure treatment system 900 may further include a wound bed interface layer 902 between
the absorptive dressing 101 and the wound bed 120. The interface layer 902 may be used
with any of the embodiments of the absorptive dressings 101, 501a, 501b, 501c, 601, 701 and
801 described above. The wound bed interface layer 902 can be a healing layer having an
affinity for living tissue and/or wound fluid produced by the wound. The interface layer 902
may form chemical interactions, such as chemical bonds and/or attractions, with the tissue in
the wound bed 120 at the interface of the interface layer 902 and the wound bed 120. In one
embodiment, the interface layer 902 may form a “chemical seal” where the chemical
interactions effectively promote closure of the wound bed 120. Closure of the wound bed 120
may reduce or eliminate the flow of wound fluid out of the wound bed 120. For example, where
the wound bed 120 includes an enteric fistula as the smooth muscle fistula 122, the flow of
intestinal material out of the wound bed 120 may slow and ultimately stop due to the chemical
seal.
In some embodiments, the interface layer 902 may provide normalization of negative
pressure at the wound bed 120. The vertical distribution of negative pressure through the
absorptive dressing 101 between the source of vacuum pressure at the occlusive material 130
and the bottom of the absorptive dressing 101 that contacts the wound bed 120 or the interface
layer 902 may be variable depending on the thickness of the absorptive dressing 101.
Application of the interface layer 902 between the absorptive dressing 101 and the wound bed
120 may enhance fluid management of exudate from the wound bed 120 by creating a uniform
layer of negative pressure at the wound bed 120. The uniformity of pressure provided by the
interface layer 902 may improve closure of difficult to close wounds such as stomatized
wounds where the inner walls of the wound may become thickened and may resist closure.
In various embodiments, the interface layer 902 may be placed over the smooth muscle
fistula 122 in the wound bed 120. The absorptive dressing 101 may then be placed over the
interface layer 902. In various embodiments, the interface layer 902 may be at least partially
coupled to the absorptive dressing 101. In some embodiments, the interface layer 902 may
include an ester-based material, for example an ester-based material with the physical and
chemical properties discussed above with regards to the absorptive dressing 101. In one
embodiment, the interface layer 902 may include a bio-absorbable material. The bio-
absorbable material may include a hydrophilic material that may have an affinity to the tissue of
the smooth muscle fistula 122. In one embodiment, the bio-absorbable material may include a
suture material such as absorbable surgical plain gut suture. Plain gut suture is composed of
purified connective tissue and may absorb in the body within a few days by enzymatic
dissolution as part of the body’s response to a foreign object. In some embodiments, the bio-
absorbable material may include a longer lasting absorbable material that dissolves more
slowly than plain gut sutures, such as chromic gut sutures or Vicryl™. The ester-based
material and/or the bio-absorbable material may resist tissue ingrowth from the smooth muscle
fistula 122.
In another embodiment, the interface layer 902 may include a hydrophobic non-
absorbable material. For example, the hydrophobic material may comprise a petroleum
emulsion such as Adaptic® or a silicone wound dressing such as Mepitel®. Such hydrophobic
material may also resist tissue ingrowth from the smooth muscle fistula 122.
In some embodiments, the interface layer 902 may be a thin sheet having a thickness.
In one embodiment, the thickness may be about the thickness of a sheet of printer paper, such
as about 100µm. The interface layer 902 may include a plurality of pores to allow wound fluid
produced by the wound bed 120 to flow through the interface layer 902 and into the absorptive
dressing 101. The diameter of the pores may be similar to the width/diameter of smooth
muscle cells, such as between about 1µm to about 20µm. In one embodiment, the interface
layer 902 may include a single layer of pores. In some embodiments, the interface layer 902
may include more than one layer of pores where each layer includes a substantially uniform
pore size and/or pore geometry within each layer, but a different pore size and/or pore
geometry than an adjacent layer or layers. For example, the interface layer 902 may include a
layer structure and/or pore structure as described with reference to the absorptive dressings
501a, 501b and 501c and Figures 5A-5C above. For example, the interface layer 902 may
include multiple alternating layers in which the layers between layers of smaller pore size and
larger pore size, such as discussed regarding Figs. 5A-5B. In various embodiments, the
smaller pores may be about 1µm to about 10µm and the larger pores may be about 10µm to
about 20µm. In some embodiments, the interface layer 902 may include a layer with larger
pores sandwiched between two smaller pore layers, such as described with reference to Fig.
5C. This configuration provides for a reversible interface layer 902 which may facilitate use by
medical staff. The interface layer 902 may also have smaller pores interspersed between
larger pores as described with respect to Fig. 5C above. Additionally, the interface layer 902 of
this embodiment may include pores having a limited reticulation to reduce the volume and/or
rate of wound fluid flow through the interface layer 902. In embodiments in with the interface
layer 902 has multiple layers, the total width of all layers of the interface layer 902 combined
may be about 100µm. In some embodiments, the interface layer 902 may be a thin film or
sheet having a thickness.
In use, the interface layer 902 may be applied to the wound bed 120 including the
smooth muscle fistula 122 prior to application of any of the embodiments of the absorptive
dressings 101, 501a, 501b, 501c, 601, 701 and 801 described above.
Example 1
A female patient diagnosed with Crohn’s disease was hospitalized having three
enterocutaneous fistulas at the biliary junction. Various conventional treatments were
attempted, but her fistulas persisted, having a fluid drainage rate of 1000-2000ml per day. The
patient was informed that her body would not heal this fistula on its own and was declared
terminal. The patient agreed to an experimental procedure in which an ester-based foam was
placed directly on the fistulas. The ester-based foam was composed of reticulated
polyurethane ester foam with a pore size of 133-600µm sold under the trade name V.A.C.
VeraFlo Cleanse™ Dressing by Kinetic Concepts, Inc. The ester-based foam was felted such
that the size of the pores varied directionally within the foam, where the pore size was greater
along the length of the foam than along the direction of felting (i.e. the thickness). The foam
was placed directly on the fistulas, with the width of the ester-based foam perpendicular to the
fistulas and a flat surface of the ester-foam in direct contact with the fistula, covered with an
occlusive material and attached to a vacuum pump via a vacuum tube, as exemplified in Fig. 1.
A second vacuum tube and pump was positioned at the opposite end of the wound from the
fistulas to collect exuded drainage fluid not collected by the first vacuum pump. The ester-
based foam was replaced every three days. Within about 12 hours of the experimental
procedure, the fluid drainage had decreased to a rate of approximately 500ml/day. In the
proceeding days, the fluid drainage decreased to approximately 200ml/day. In addition, the
overall coloration, texture and smell of the wound improved within three days. The tissue at
the wound bed improved from a yellowish slough-covered tissue to a red, beefy granular
tissue. In addition, likely do to the decrease in fluid drainage, the smell of bile at the wound site
decreased within the first three days of the experimental procedure as well.
In the foregoing description, the invention has been described with reference to specific
embodiments. Various modifications and changes may be made, however, without departing
from the scope of the present invention as set forth. The description and figures are to be
regarded in an illustrative manner, rather than a restrictive one and all such modifications are
intended to be included within the scope of the present invention. Accordingly, the scope of
the invention should be determined by the generic embodiments described and their legal
equivalents rather than by merely the specific examples described above. For example, the
steps recited in any method or process embodiment may be executed in any appropriate order
and are not limited to the explicit order presented in the specific examples. Additionally, the
components and/or elements recited in any system embodiment may be combined in a variety
of permutations to produce substantially the same result as the present invention and are
accordingly not limited to the specific configuration recited in the specific examples.
For example, while certain embodiments of the methods and systems described above
disclose the withdrawal of body fluid without introducing any other fluid in order to promote
healing, such embodiments may be modified to optionally introduce a carrier fluid such as air,
water, saline, or other solutions or fluids into the wound to further encourage a desired flow of
body fluid, and thereby promote healing.
Benefits, other advantages and solutions to problems have been described above with
regard to particular embodiments. Any benefit, advantage, solution to problems or any
element that may cause any particular benefit, advantage or solution to occur or to become
more pronounced, however, is not to be construed as a critical, required or essential feature or
component.
Other combinations and/or modifications of the above-described structures,
arrangements, applications, proportions, elements, materials or components used in the
practice of the present invention, in addition to those not specifically recited, may be varied or
otherwise particularly adapted to specific environments, manufacturing specifications, design
parameters or other operating requirements without departing from the general principles of the
same.
The present invention has been described above with reference to specific
embodiments. However, changes and modifications may be made to the above embodiments
without departing from the scope of the present invention. These and other changes or
modifications are intended to be included within the scope of the present invention.
Claims (3)
1. A negative pressure treatment system for the treatment of a wound bed including a 5 smooth muscle fistula, the negative pressure treatment system comprising: an absorptive dressing comprising an ester-based foam adapted to be placed directly against the wound bed and to contact smooth muscle without causing substantial cellular disruption or damage in the negative pressure environment, the foam having primary structural features comprising pores with a width of about 0.1μm to about 50μm and secondary structural 10 features adapted to direct a flow of wound fluid from the wound bed; a vacuum pump configured to apply negative pressure to the absorptive dressing to thereby withdraw wound fluid from the wound bed; and an interface layer adapted to be placed between the absorptive dressing and the smooth muscle fistula in the wound bed.
2. The negative pressure treatment system of claim 1, wherein the interface layer comprises an ester-based material.
3. The negative pressure treatment system of claim 1 or claim 2, wherein the interface 20 layer comprises a film having pores with a width of about 0.1μm to about 50μm.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US201461940245P | 2014-02-14 | 2014-02-14 | |
US61/940,245 | 2014-02-14 | ||
PCT/US2015/015968 WO2015123609A1 (en) | 2014-02-14 | 2015-02-13 | Systems and methods for tissue healing |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ723205A NZ723205A (en) | 2021-09-24 |
NZ723205B2 true NZ723205B2 (en) | 2022-01-06 |
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