Patent Publication Number: US-2021169699-A1

Title: Manually-operated negative pressure wound therapy (npwt) bandage with improved pump efficiency, automatic pressure indicator and automatic pressure limiter

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
     This patent application claims benefit of: 
     (1) pending prior U.S. Provisional Patent Application Ser. No. 62/595,398, filed Dec. 6, 2017 by Cornell University and Timothy Johnson et al. for MANUALLY-OPERATED NEGATIVE PRESSURE WOUND THERAPY (NPWT) BANDAGE WITH IMPROVED PUMP EFFICIENCY, AUTOMATIC PRESSURE INDICATOR AND AUTOMATIC PRESSURE LIMITER (Attorney&#39;s Docket No. CORN-50 PROV); and 
     (2) pending prior U.S. Provisional Patent Application Ser. No. 62/611,227, filed Dec. 28, 2017 by Cornell University and Timothy Johnson et al. for MANUALLY-OPERATED NEGATIVE PRESSURE WOUND THERAPY (NPWT) BANDAGE WITH IMPROVED PUMP EFFICIENCY, AUTOMATIC PRESSURE INDICATOR AND AUTOMATIC PRESSURE LIMITER (Attorney&#39;s Docket No. CORN-55 PROV). 
     The two (2) above-identified patent applications are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to bandages in general, and more particularly to negative pressure wound therapy (NPWT) bandages. 
     BACKGROUND OF THE INVENTION 
     Bandages are used to provide wound care during healing. More particularly, bandages generally provide a covering for a wound so as to shield the wound from contaminants and microbes during healing. Most bandages also provide a closure feature to help hold the edges of the wound in close apposition during healing. Bandages also frequently include gauze or the like to receive exudates emerging from the wound during healing. 
     Negative pressure wound therapy (NPWT) bandages apply a negative pressure to a wound during healing. This negative pressure helps reduce the likelihood of contaminants and microbes entering the wound during healing, helps draw exudates from the wound during healing, and can promote beneficial biological responses at the wound site. More particularly, NPWT bandages typically comprise (i) an absorbent dressing configured to make a fully-sealed chamber around the perimeter of a wound (“the wound chamber”), (ii) a source of negative pressure, and (iii) a conduit extending between the fully-sealed wound chamber and the source of negative pressure. As a result of this construction, the absorbent dressing can be applied to a wound so as to create a fully-sealed chamber around the perimeter of the wound, and the source of negative pressure can apply a negative pressure to the fully-sealed wound chamber, such that any contaminants and microbes present at the wound site are drawn away from the wound, exudates are drawn out of the wound, and beneficial biological responses are promoted at the wound site. 
     Most NPWT bandages are part of a large, complex NPWT system, in the sense that (i) the absorbent dressings are generally fairly large (e.g., they are sized to cover large open wounds), (ii) the sources of negative pressure are generally fairly large, and formed and located separate from the absorbent dressings (e.g., the sources of negative pressure typically comprise electrically-powered suction pumps or vacuum canisters), and (iii) the NPWT systems generally require substantial training to use. These NPWT systems also tend to be quite expensive. 
     Efforts have been made to provide a small, simplified and less expensive NPWT bandage where the source of negative pressure is integrated with the absorbent dressing. By way of example but not limitation, efforts have been made to provide an NPWT bandage where a manually-operated suction pump is integrated into the absorbent dressing. Unfortunately, current NPWT bandages integrating a suction pump with the absorbent dressing tend to suffer from a variety of deficiencies, e.g., they have a complex design, and/or are expensive, and/or are complicated to use, and/or are bulky (including having a high profile), and/or cause additional trauma to the wound during use, and/or have poor pump efficiency, and/or lack a way of indicating the level of negative pressure created, and/or lack a way of limiting the level of negative pressure created, etc. In this latter respect it should be appreciated that where too high a level of negative pressure is created, the NPWT bandage can cause trauma to the patient, e.g., blistering, capillary leakage, etc. 
     Thus there is a need for a new and improved NPWT bandage which is simple, inexpensive, easy-to-use, small in size (including having a low profile), is atraumatic to the wound during use, has improved pump efficiency, incorporates an automatic pressure indicator for indicating the level of negative pressure created, and provides an automatic pressure limiter for limiting the level of negative pressure created. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are addressed by the provision and use of a new and improved NPWT bandage which is simple, inexpensive, easy-to-use, small in size (including having a low profile), is atraumatic to the wound during use, has improved pump efficiency, incorporates an automatic pressure indicator for indicating the level of negative pressure created, and provides an automatic pressure limiter for limiting the level of negative pressure created. 
     In one preferred form of the invention, there is provided a negative pressure wound therapy (NPWT) bandage for applying negative pressure to a wound, said NPWT bandage comprising: 
     a membrane configured for disposition over a wound so as to form a wound chamber between said membrane and the wound, said membrane comprising a wound-side surface, an atmosphere-side surface, and an opening extending through said membrane from said wound-side surface to said atmosphere-side surface; and 
     a pump assembly carried by said membrane, said pump assembly comprising:
         a pump body comprising a wall structure disposed about a pump chamber, wherein at least a portion of said wall structure is resilient;   a wound-side passageway extending through said wall structure and communicating with the wound chamber through said opening formed in said membrane;   a wound-side one-way valve disposed in said wound-side passageway, said wound-side one-way valve being configured to allow fluid to flow through said wound-side passageway from the wound chamber to said pump chamber but to prevent fluid from flowing through said wound-side passageway from said pump chamber to the wound chamber;   an atmosphere-side passageway extending through said wall structure and connecting said pump chamber and the atmosphere; and   an atmosphere-side one-way valve disposed in said atmosphere-side passageway, said atmosphere-side one-way valve being configured to allow fluid to flow through said atmosphere-side passageway from said pump chamber to the atmosphere but to prevent fluid from flowing through said atmosphere-side passageway from the atmosphere to said pump chamber;       

     such that when a compressive force is applied to said wall structure of said pump body, fluid within said pump chamber will be forced out of said pump chamber via said atmosphere-side passageway, and when the compressive force applied to said wall structure of said pump body is thereafter reduced, fluid within the wound chamber will be drawn into said pump chamber through said wound-side passageway. 
     Preferably, the NPWT bandage is configured so that when the pressure differential between the pressure of the fluid within said pump chamber and atmospheric pressure is below a predetermined threshold, said pump body of said pump assembly will assume a substantially fully expanded configuration, and when said pressure differential between the pressure of the fluid within said pump chamber and atmospheric pressure is above said predetermined threshold, said pump body of said pump assembly will assume a substantially fully collapsed configuration. 
     Even more preferably, the NPWT bandage is configured so that said pump body abruptly changes state between said substantially fully expanded configuration and said substantially fully collapsed configuration, and between said substantially fully collapsed configuration and said substantially fully expanded configuration, as said pressure differential crosses said predetermined threshold so as to effectively constitute a substantially “binary state” device. 
     In another preferred form of the invention, there is provided a method for applying negative pressure to a wound, the method comprising: 
     providing a negative pressure wound therapy (NPWT) bandage comprising:
         a membrane configured for disposition over a wound so as to form a wound chamber between said membrane and the wound, said membrane comprising a wound-side surface, an atmosphere-side surface, and an opening extending through said membrane from said wound-side surface to said atmosphere-side surface; and   a pump assembly carried by said membrane, said pump assembly comprising:
           a pump body comprising a wall structure disposed about a pump chamber, wherein at least a portion of said wall structure is resilient;   a wound-side passageway extending through said wall structure and communicating with the wound chamber through said opening formed in said membrane;   a wound-side one-way valve disposed in said wound-side passageway, said wound-side one-way valve being configured to allow fluid to flow through said wound-side passageway from the wound chamber to said pump chamber but to prevent fluid from flowing through said wound-side passageway from said pump chamber to the wound chamber;   an atmosphere-side passageway extending through said wall structure and connecting said pump chamber and the atmosphere; and an atmosphere-side one-way valve disposed in said atmosphere-side passageway, said atmosphere-side one-way valve being configured to allow fluid to flow through said atmosphere-side passageway from said pump chamber to the atmosphere but to prevent fluid from flowing through said atmosphere-side passageway from the atmosphere to said pump chamber;   
           such that when a compressive force is applied to said wall structure of said pump body, fluid within said pump chamber will be forced out of said pump chamber via said atmosphere-side passageway, and when the compressive force applied to said wall structure of said pump body is thereafter reduced, fluid within the wound chamber will be drawn into said pump chamber through said wound-side passageway;       

     positioning said negative pressure wound therapy (NPWT) bandage over the wound so as to form a wound chamber between said membrane and the wound; and 
     applying a compressive force to said wall structure of said pump body, and thereafter reducing the compressive force applied to said wall structure of said pump body, so as to apply negative pressure to the wound. 
     In another preferred form of the invention, there is provided a negative pressure wound therapy (NPWT) bandage for applying negative pressure to a wound, said NPWT bandage comprising: 
     a membrane configured for disposition over a wound so as to form a wound chamber between said membrane and the wound, said membrane comprising a wound-side surface, an atmosphere-side surface, and an opening extending through said membrane from said wound-side surface to said atmosphere-side surface; and 
     a pump carried by said membrane and comprising a wall chamber disposed about a pump chamber, wherein at least a portion of said wall chamber is resilient, and further wherein said pump chamber communicates with the wound chamber through said opening formed in said membrane; 
     wherein no part of said pump chamber is defined by the wound. 
     In another preferred form of the invention, there is provided a negative pressure wound therapy (NPWT) bandage for applying negative pressure to a wound, said NPWT bandage comprising: 
     a membrane configured for disposition over a wound so as to form a wound chamber between said membrane and the wound, said membrane comprising a wound-side surface, an atmosphere-side surface, and an opening extending through said membrane from said wound-side surface to said atmosphere-side surface; and 
     a pump carried by said membrane and comprising a wall chamber disposed about a pump chamber, wherein at least a portion of said wall chamber is resilient, and further wherein said pump chamber communicates with the wound chamber through said opening formed in said membrane; 
     wherein said pump does not apply positive pressure to the wound. 
     In another preferred form of the invention, there is provided a negative pressure wound therapy (NPWT) bandage for applying negative pressure to a wound, said NPWT bandage comprising: 
     a membrane configured for disposition over a wound so as to form a wound chamber between said membrane and the wound, said membrane comprising a wound-side surface, an atmosphere-side surface, and an opening extending through said membrane from said wound-side surface to said atmosphere-side surface; and 
     a pump carried by said membrane and comprising a wall chamber disposed about a pump chamber, wherein at least a portion of said wall chamber is resilient, and further wherein said pump chamber communicates with the wound chamber through said opening formed in said membrane; 
     wherein said pump is connected to the wound chamber such that a reduction in the volume of the pump chamber does not cause a change in pressure in the wound chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
         FIGS. 1-4  are schematic views showing a new and improved NPWT bandage formed in accordance with the present invention, with  FIGS. 2 and 3  being exploded views; 
         FIG. 4A  is a schematic view showing, for two different size wound chambers (i.e., a 7.5 mL wound chamber and a 15 mL wound chamber), a maximum negative pressure that may be established with (i) a deformable pump body having two one-way valves (with one one-way valve being disposed on either side of the deformable pump body), and (ii) a deformable pump body having a single one-way valve (note: in the comparison shown in  FIG. 4A , the volume of the pump chamber of the deformable pump body with  1  one-way valve is the same as the volume of the pump chamber of the deformable pump body with  2  one-way valves); 
         FIGS. 5 and 6  are schematic views showing the pump body of the pump assembly of the NPWT bandage shown in  FIGS. 1-4  in its substantially fully expanded configuration ( FIG. 5 ) and in its substantially fully collapsed configuration ( FIG. 6 ); 
         FIG. 7  is a schematic view showing how the pump body of the pump assembly of the NPWT bandage shown in  FIGS. 1-4  abruptly changes state between its substantially fully expanded configuration and its substantially fully collapsed configuration; 
         FIG. 8  is a schematic view showing how the pump bodies of the pump assemblies of prior art NPWT bandages gradually change state between their substantially fully expanded configuration and their substantially fully collapsed configuration; 
         FIGS. 9-16  are schematic views showing exemplary use of the new and improved NPWT bandage shown in  FIGS. 1-4  (note that in  FIGS. 11 and 14-16 , removable cap  100  (see below) is removed from the figures for clarity of illustration); 
         FIGS. 17-20  are schematic views showing another new and improved NPWT bandage formed in accordance with the present invention; and 
         FIGS. 21-25  are schematic views showing another new and improved NPWT bandage formed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention comprises the provision and use of a new and improved NPWT bandage which is simple, inexpensive, easy-to-use, small in size (including having a low profile), is atraumatic to the wound during use, has improved pump efficiency, incorporates an automatic pressure indicator for indicating the level of negative pressure created, and provides an automatic pressure limiter for limiting the level of negative pressure created. 
     The Manually-Operated Negative Pressure Wound Therapy (NPWT) Bandage in General 
     More particularly, and looking first at  FIGS. 1-4 , there is shown a manually-operated negative pressure wound therapy (NPWT) bandage  5  having improved pump efficiency, an automatic pressure indicator for indicating the level of negative pressure created, and an automatic pressure limiter for limiting the level of negative pressure created. 
     NPWT bandage  5  generally comprises a membrane (or sheet)  10  and a pump assembly  15 . 
     As will hereinafter be discussed, membrane  10  is configured to make a fully-sealed chamber around the perimeter of a wound, whereby to define a wound chamber. 
     And as will hereinafter be discussed, pump assembly  15  is configured to apply a negative pressure to the fully-sealed wound chamber, such that any contaminants and microbes present at the wound site are drawn away from the wound, exudates are drawn out of the wound, and beneficial biological responses are promoted at the wound site. Significantly, pump assembly  15  is designed to provide improved pump efficiency, an automatic pressure indicator for indicating the level of negative pressure created, and an automatic pressure limiter for limiting the level of negative pressure created, as will hereinafter be discussed. 
     The Membrane 
     More particularly, membrane  10  comprises a flat planar sheet  20  formed out of a flexible, substantially air-impermeable material, e.g., Tegaderm from 3M Company (which has also been known as the Minnesota Mining and Manufacturing Company), so that it can conform to body contours and form a substantially air-tight chamber around the perimeter of a wound (i.e., the wound chamber). Membrane  10  is characterized by a wound-side surface  25  and an atmosphere-side surface  30 . Membrane  10  is also characterized by an outer perimeter  35  and an inner opening  40 . 
     An adhesive  45  is preferably disposed on wound-side surface  25  of membrane  10 . A release liner  50  is preferably disposed on wound-side surface  25  atop adhesive  45  so as to keep adhesive  45  covered until use. 
     A removable stiffener  55  is preferably disposed on atmosphere-side surface  30  of membrane  10 . Removable stiffener  55  serves to facilitate manipulation of NPWT bandage  5  (and particularly membrane  10 ) during removal of the NPWT bandage from its sterile packaging and during positioning of the NPWT bandage about a wound. Removable stiffener  55  is intended to be removed from membrane  10  once NPWT bandage  5  has been secured about the wound site. Removable stiffener  55  may be provided as a single element or, more preferably, removable stiffener  55  is provided as a pair of elements so as to facilitate removal from membrane  10  after NPWT bandage  5  has been secured about the wound site. 
     The Pump Assembly 
     Pump assembly  15  comprises a pump body  60  having a generally cylindrical shape and comprising a side wall  65  and an inner chamber  70 . Pump body  60  is formed out of a resilient material, e.g., silicone, such that side wall  65  may be compressed inwardly by the application of an external force (e.g., squeezing by the thumb and forefinger of a user) and will then attempt to return to its original uncompressed state when the external force is removed. A pump flange  75  is preferably formed on one side of pump body  60 . As will hereinafter be discussed in further detail, pump body  60  extends through inner opening  40  of membrane  10 , and the upper surface of pump flange  75  is secured to the wound-side surface  25  of membrane  10  so that pump assembly  15  is secured to, and carried by, membrane  10 . Pump flange  75  is preferably formed out of a flexible material so that it can conform (to at least a limited extent) to body contours. In one form of the invention, pump body  60  and pump flange  75  are formed integral with one another out of the same material, e.g., silicone. In one preferred form of the invention, side wall  65  of pump body  60  and pump flange  75  merge at a neck  77  ( FIG. 5 ). And in one preferred form of the invention, neck  77  has a relatively small width relative to the full diameter of pump body  60 , with recesses  78  extending inwardly between membrane  10  and pump body  60 , such that pump body  60  is mounted to pump flange  75  but is still free to radially compress/radially expand with minimal interference from pump flange  75 . A wound-side passageway  80  is formed in pump body  60  and communicates with inner chamber  70 . Wound-side passageway  80  opens on the exterior of pump body  60  at a wound-side port  82 . An atmosphere-side passageway  85  is formed in pump body  60  and also communicates with inner chamber  70 . Atmosphere-side passageway  85  opens on the exterior of pump body  60  at an atmosphere-side port  87 . 
     A wound-side one-way valve  90  is disposed in wound-side passageway  80  and is configured to permit fluid to enter inner chamber  70  through wound-side passageway  80  but to prevent fluid from exiting inner chamber  70  through wound-side passageway  80 . 
     An atmosphere-side one-way valve  95  is disposed in atmosphere-side passageway  85  and is configured to permit fluid to exit inner chamber  70  through atmosphere-side passageway  85  but to prevent fluid from entering inner chamber  70  through atmosphere-side passageway  85 . 
     As a result of this construction, when pump body  60  of pump assembly  15  is manually squeezed (e.g., by applying a compressive force to side wall  65  of pump body  60  with the thumb and forefinger of a user), fluid (e.g., air, liquid, etc.) within inner chamber  70  will be forced out of inner chamber  70  via atmosphere-side passageway  85 , and when pump body  60  of pump assembly  15  is thereafter released (e.g., by relaxing the compressive force applied to side wall  65  of pump body  60  by the thumb and forefinger of a user), fluid (e.g., air, liquid, etc.) below wound-side surface  25  of membrane  10  (e.g., air, liquid, etc. within the wound chamber) will be drawn into inner chamber  70  through wound-side passageway  85  as the resilient side wall of the pump body returns to its uncompressed state. 
     Note that when pump body  60  of pump assembly  15  is manually squeezed, fluid (e.g., air, liquid, etc.) within inner chamber  70  is prevented from exiting inner chamber  70  through wound-side passageway  80  due to the one-way operation of wound-side one-way valve  90 , and when pump body  60  of pump assembly  15  is thereafter released, air from the atmosphere is prevented from being drawn into inner chamber  70  through atmosphere-side passageway  85  due to the one-way operation of atmosphere-side one-way valve  95 . 
     Thus it will be appreciated that repeatedly manually squeezing and releasing pump body  60  of pump assembly  15  will apply suction to the wound chamber disposed below wound-side surface  25  of membrane  10 , whereby to create negative pressure at the wound site. 
     It should be appreciated that the present invention&#39;s approach of providing a pump assembly utilizing two one-way valves disposed on either side of a deformable pump body with an in-line configuration (i.e., wound-side one-way valve  90  and atmosphere-side one-way valve  95  disposed on either side of deformable pump body  60 ) provides a number of significant advantages which are not achievable with the prior art&#39;s approach of providing a deformable pump body utilizing a single one-way valve. 
     More particularly, and as will hereinafter be discussed, the present invention&#39;s approach of providing a pump assembly utilizing two one-way valves disposed on either side of a deformable pump body with an in-line configuration (i.e., wound-side one-way valve  90  and atmosphere-side one-way valve  95  disposed on either side of deformable pump body  60 ) allows substantially the same maximum negative pressure to be established at the wound site regardless of the size of the wound chamber. This is not achievable with the prior art&#39;s approach of providing a deformable pump body utilizing a single one-way valve. 
     In addition, the present invention&#39;s approach of providing a pump assembly utilizing two one-way valves disposed on either side of a deformable pump body with an in-line configuration (i.e., wound-side one-way valve  90  and atmosphere-side one-way valve  95  disposed on either side of deformable pump body  60 ) allows a greater constant selected maximum negative pressure to be achieved at the wound site than can be achieved at the wound site using a deformable pump body with a single one-way valve (which is reflective of the prior art&#39;s approach). 
     More particularly,  FIG. 4A , shows, for two different size wound chambers (i.e., a 7.5 mL wound chamber and a 15 mL wound chamber), a maximum negative pressure that may be established with (i) a deformable pump body having two one-way valves (with one one-way valve being disposed on either side of the deformable pump body), and (ii) a deformable pump body having a single one-way valve (note: in the comparison shown in  FIG. 4A , the volume of the pump chamber of the deformable pump body with  1  one-way valve is the same as the volume of the pump chamber of the deformable pump body with  2  one-way valves). 
     Inherent in  FIG. 4A  are a number of significant aspects of the present invention. 
     First,  FIG. 4A  shows that using a deformable pump body having two one-way valves (with one one-way valve being disposed on either side of the deformable pump body) to evacuate the wound chamber lets you establish substantially the same maximum negative pressure in the wound chamber regardless of the size of the wound chamber (i.e., it yields approximately −150.0 mm Hg for a 7.5 mL wound chamber and approximately −150.0 mm Hg for a 15 mL wound chamber), whereas using a deformable pump body having a single one-way valve does not (i.e., it yields approximately −80.0 mm Hg for a 7.5 mL wound chamber and approximately −50.0 mm Hg for a 15 mL wound chamber). Thus, the NPWT bandage of the present invention allows substantially the same maximum negative pressure to be established at the wound site regardless of the size of the wound chamber, whereas prior art NPWT bandages do not. 
     This unique feature of the present invention is clinically significant, inasmuch as (i) it is generally desirable to establish a selected maximum negative pressure at the wound site (e.g., between about 60 mm Hg and about 180 mm Hg), and (ii) it is generally difficult to know in advance the volume of the wound chamber (e.g., due to variations in medical applications, variations in patient anatomy, etc.). 
     Thus, inasmuch as the NPWT bandage of the present invention allows substantially the same maximum negative pressure to be established at the wound site regardless of the size of the wound chamber, the present invention allows the NPWT bandage to be engineered in advance (e.g., at the time of manufacture) to establish a selected maximum negative pressure at the wound site, whereas prior art NPWT bandages do not. 
     Second,  FIG. 4A  shows that using a deformable pump body having two one-way valves (with one one-way valve being disposed on either side of the deformable pump body) to evacuate the wound chamber lets you establish a substantially higher maximum negative pressure in the wound chamber (i.e., it yields approximately −150.0 mm Hg for a 7.5 mL wound chamber and approximately −150.0 mm Hg for a 15 mL wound chamber) than can be established using a deformable pump body having a single one-way valve (i.e., it yields approximately −80.0 mm Hg for a 7.5 mL wound chamber and approximately −50.0 mm Hg for a 15 mL wound chamber). Thus, the NPWT bandage of the present invention allows a substantially higher maximum negative pressure to be established at the wound site. 
     Note also that the pressure within inner chamber  70  of pump body  60  is generally equal to the pressure below wound-side surface  25  of membrane  10  (i.e., the pressure within inner chamber  70  of pump body  60  is generally equal to the pressure within the wound chamber). 
     In one preferred form of the invention, pump assembly  15  also comprises a removable cap  100 . Removable cap  100  is configured to selectively close off atmosphere-side passageway  85  to fluid flow when removable cap  100  is inserted into atmosphere-side passageway  85  so as to close off atmosphere-side port  87 . 
     Pump assembly  15  is mounted to membrane  10  such that pump assembly  15  is carried by membrane  10 . More particularly, pump assembly  15  is mounted to membrane  10  by (i) passing pump body  60  of pump assembly  15  through inner opening  40  of membrane  10 , (ii) bringing pump flange  75  up against wound-side surface  25  of membrane  10 , and then (iii) adhering pump flange  75  to wound-side surface  25  of membrane  10  (e.g., by bonding, gluing, etc.). Note that pump assembly  15  and membrane  10  make a substantially air-tight connection. 
     Significantly, pump body  60  of pump assembly  15  is carefully configured to provide (i) improved pump efficiency, (ii) an automatic pressure indicator for indicating the level of negative pressure created, and (iii) an automatic pressure limiter for limiting the level of negative pressure created, as will hereinafter be discussed. 
     More particularly, pump body  60  of pump assembly  15  is specifically configured so that the pump body will abruptly change state between (i) a substantially fully expanded configuration where side wall  65  of pump body  60  and inner chamber  70  of pump body  60  have a substantially circular cross-section (see  FIG. 5 ) when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure is below a given threshold, and (ii) a substantially fully collapsed configuration where side wall  65  of pump body  60  bows inwardly (see  FIG. 6 ) when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure exceeds a given threshold. 
     Specifically, when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure is below a given threshold, pump body  60  of pump assembly  15  will assume its substantially fully expanded configuration ( FIG. 5 ), and when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure is above a given threshold, pump body  60  of pump assembly  15  will assume its substantially fully collapsed configuration ( FIG. 6 ). 
     Significantly, pump body  60  of pump assembly  15  is configured so that it will abruptly change state between its substantially fully expanded configuration ( FIG. 5 ) and its substantially fully collapsed configuration ( FIG. 6 ) when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure crosses the aforementioned given threshold. See  FIG. 7 , which is a graph showing the relationship between the diameter of side wall  65  of pump body  60  and the pressure differential between the pressure of a fluid within inner chamber  70  and atmospheric pressure. Thus, pump assembly  15  is specifically configured to essentially behave as a substantially “binary state” device—it is either substantially fully expanded ( FIG. 5 ) or substantially fully collapsed ( FIG. 6 ). In this respect it should be appreciated that, as used herein, the term “substantially “binary state” device” is intended to refer to a device which is inclined to assume either a substantially fully expanded condition or a substantially fully collapsed condition and, as used herein, the term “substantially “binary state” behavior” is intended to refer to the inclination of a device to assume either a substantially fully expanded condition or a substantially fully collapsed condition. 
     Note that the substantially “binary state” behavior of pump body  60  is a consequence of forming the pump body with a side wall  65  having a substantially circular cross-section, which gives the pump body an “over-the-center” deformation characteristic, i.e., the side wall of pump body  60  has a “failure” mode where it abruptly transitions from its substantially fully expanded configuration to its substantially fully collapsed configuration, and has a “restoration” mode where it abruptly transitions from its substantially fully collapsed configuration to its substantially fully expanded configuration. See  FIG. 7 . Note that by forming pump assembly  15  so that side wall  65  of pump body  60  and pump flange  75  merge at a neck  77  ( FIG. 5 ), with neck  77  having a relatively small width relative to the full diameter of pump body  60 , and with recesses  78  extending inwardly between membrane  10  and pump body  60 , pump body  60  has a substantially circular cross-section over substantially its entire circumference, with pump body  60  free to radially compress/radially expand with minimal interference from pump flange  75 , so that pump body  60  can exhibit substantially “binary state” behavior. 
     Note also that the prior art approaches of forming the pump body with dome-like or square pump configurations does not provide the pump body with an abrupt change of state—rather, these prior art dome-like or square pump configurations provide the pump body with a more gradual change of state between an expanded configuration and a collapsed configuration when the pressure differential between the pressure of the fluid within an inner chamber and atmospheric pressure changes. See  FIG. 8 , which is a graph showing the relationship between the diameter of the side wall of a pump body having a dome-like or square configuration and the pressure differential between the pressure of a fluid within an inner chamber of the pump body and atmospheric pressure. 
     As a result of deliberately configuring side wall  65  of pump body  60  of pump assembly  15  to exhibit this abrupt change of state, pump assembly  15  is able to provide improved pump efficiency, an automatic pressure indicator for indicating the level of negative pressure created, and an automatic pressure limiter for limiting the level of negative pressure created. 
     More particularly, by configuring pump body  60  of pump assembly  15  so that it will abruptly change state between its substantially fully expanded configuration and its substantially fully collapsed configuration when the pressure differential between the pressure of a fluid within inner chamber  70  and atmospheric pressure crosses a given threshold, pump assembly  15  effectively returns to its substantially fully expanded configuration as long as the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure is below the given threshold. As a result, so long as the pressure differential between the fluid within inner chamber  70  and atmospheric pressure is below the given threshold, pump assembly  15  returns to its substantially fully expanded configuration between compressions (i.e., squeezes), and hence remains fully efficient as it applies a negative pressure to the wound chamber. This is in contrast to the performance of prior art devices where the pump body exhibits a gradual change of state between an expanded configuration and a collapsed configuration when the pressure differential between the pressure of a fluid within the inner chamber of the pump assembly changes, which makes the pump assembly progressively less efficient as it reduces the pressure within the wound chamber. This is because the pump body will progressively return less and less to its fully expanded configuration as negative pressure is created in the wound chamber, so that the pump assembly is able to evacuate less and less fluid with each squeeze of the pump body. In other words, with prior art devices, the pump assembly becomes less and less efficient as negative pressure is created in the wound chamber. 
     In a related manner, by configuring pump body  60  so that it will abruptly change state between its substantially fully expanded configuration and its substantially fully collapsed configuration when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure crosses a given threshold, pump assembly  15  is able to function as an automatic pressure indicator for indicating the level of negative pressure created, i.e., so long as pump body  60  of pump assembly  15  returns to its substantially fully expanded configuration between squeezes, it will be readily apparent to an observer that the pressure within inner chamber  70  (and hence the pressure within the wound chamber) will be less than a given level. This is in marked contrast to the performance of prior art devices where pump body  60  provides a gradual change of state between an expanded configuration and a collapsed configuration when the pressure differential between the pressure of a fluid within an inner chamber of the pump assembly changes, in which case the pump assembly is not able to function as an automatic pressure indicator for indicating the level of negative pressure created. 
     And also in a related manner, by configuring pump body  60  so that it will abruptly change state between its substantially fully expanded configuration and its substantially fully collapsed configuration when the pressure differential between the pressure of a fluid within inner chamber  70  and atmospheric pressure crosses a given threshold, pump assembly  15  is able to function as an automatic pressure limiter for limiting the level of negative pressure created since, as soon as pump body  60  assumes its substantially fully collapsed configuration, pump assembly  15  is no longer able to pump fluid from the wound chamber, essentially deactivating the pump assembly. This is in marked contrast to the performance of prior art devices where the pump body provides a gradual change of state between an expanded configuration and a collapsed configuration when the pressure differential between the pressure of a fluid within an inner chamber changes, since the pump assembly is not effectively deactivated at a given pressure differential. 
     It should be appreciated that the pressure differential required to transition pump body  60  between its substantially fully-expanded configuration and its substantially fully-collapsed configuration (i.e., the aforementioned “given threshold”) may be “tuned” (i.e., tailored) to a particular level by varying one or more characteristics of pump body  60 , e.g., by forming side wall  65  of pump body  60  out of a material having a particular durometer, by adjusting the thickness of side wall  65  of pump body  60 , by adjusting the diameter of inner chamber  70  of pump body  60 , etc. 
     In general, it has been found that excellent therapeutic results may be achieved when the pressure differential required to transition pump body  60  between its substantially fully-expanded configuration and its substantially fully-collapsed configuration (i.e., the aforementioned “given threshold”) is between about 60 mm Hg and about 180 mm Hg. In other words, it has been found that excellent therapeutic results may be achieved where pump body  60  transitions between its substantially fully-expanded configuration ( FIG. 5 ) and its substantially fully-collapsed configuration ( FIG. 6 ) at a negative pressure of between about 60 mm Hg and about 180 mm Hg. It is believed that where pump body  60  transitions between its two states at a lower pressure (i.e., where pump body  60  transitions at a negative pressure lower than about 60 mm Hg), not enough suction is provided at the wound site to effectively draw contaminants and microbes away from the wound site and/or to effectively draw exudates away from the wound site and/or to promote beneficial biological responses at the wound site. It is also believed that where pump body  60  transitions between its two states at a higher pressure (i.e., where pump body  60  transitions at a negative pressure higher than about 180 mm Hg), the suction provided at the wound site may cause trauma to the tissue (e.g., blistering, capillary leakage, etc.). 
     In one preferred form of the invention, pump body  60  of pump assembly  15  is configured so that it abruptly transitions between its substantially fully expanded configuration and its substantially fully collapsed configuration when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure exceeds 80 mm Hg. Thus, in this form of the invention, as long as the negative pressure within the wound chamber is less than 680 mm Hg (assuming atmospheric pressure is 760 mm Hg), pump assembly  15  returns to its substantially fully expanded configuration between squeezes of the pump body and maintains its pump efficiency as it applies suction to the wound chamber, and as soon as the negative pressure within the wound chamber exceeds 680 mm Hg (assuming atmospheric pressure is 760 mm Hg), pump assembly  15  will assume its substantially fully collapsed configuration, acting as an automatic pressure indicator to indicate that the level of negative pressure created at the wound site has exceeded 80 mm Hg and automatically deactivating pump assembly  15  so that the level of negative pressure created at the wound site cannot exceed 80 mm Hg. 
     Note that inasmuch as pump body  60  of pump assembly  15  has a substantially cylindrical configuration, NPWT bandage  5  has a low profile. 
     Note also that inasmuch as pump body  60  of pump assembly  15  is configured to be squeezed between the thumb and forefinger of a user, the compressive force being applied to pump body  60  is applied parallel to the surface of the skin, so that no trauma is applied to the wound during use (i.e., during pumping of pump assembly  15 ). This is in marked contrast to prior art NPWT bandages which employ a dome-like configuration and require the compressive force to be applied toward the wound. 
     Exemplary Use 
     In one preferred form of the invention, and looking now at  FIGS. 9-16 , NPWT bandage  5  is intended to be used as follows. 
     First, an NPWT bandage  5  is removed from its box. In one form of the invention, each individual NPWT bandage  5  is contained in a separate sterile package, with multiple sterile packages contained in a box. See  FIG. 9 . 
     Next, an NPWT bandage  5  is removed from its sterile package ( FIG. 10 ) so as to be ready for use ( FIG. 11 ). 
     In order to apply NPWT bandage  5  to the wound site, release liner  50  is removed from wound-side surface  25  of membrane  10 . See  FIG. 12 . Then NPWT bandage  5  is positioned against the skin of a patient so that wound-side surface  25  of membrane  10  is positioned against the wound, with adhesive  45  securing NPWT bandage  5  to the skin of the patient, thereby forming a substantially air-tight seal with the skin of the patient about the perimeter of the wound chamber. See  FIG. 13 . 
     Note that when NPWT bandage  5  is applied to the skin of the patient, wound-side port  82  of wound-side passageway  80  of pump assembly  15  is open to the wound chamber. 
     Note also that a layer of gauze (or other absorbent wound dressing)  102  may be placed on the wound site prior to placing NPWT bandage  5  on the skin of the patient, so that the layer of gauze (or other absorbent wound dressing) is interposed between the wound and wound-side passageway  80  of pump assembly  15 . As a result, exudate emerging from the wound will be taken up by the gauze (or other absorbent wound dressing). Note that, if desired, the layer of gauze (or other absorbent wound dressing)  102  may be mounted to (i.e., secured to) the wound-side surface of membrane  10 , e.g., such as at the time of manufacture, so that the layer of gauze (or other absorbent wound dressing)  102  is carried to the wound site by NPWT bandage  5  and is applied to the wound at the same time as the NPWT bandage  5 . 
     Next, with NPWT bandage  5  secured to the skin of the patient, removable stiffener  55  is removed from atmosphere-side surface  30  of membrane  10 . See  FIG. 14 . 
     At this point, NPWT bandage  5  may be used to apply negative pressure to the wound chamber. This is done by squeezing side wall  65  of pump body  60  between the thumb and forefinger of a user so as to compress pump body  60  into its substantially fully collapsed configuration, whereby to expel fluid (e.g., air, liquid, etc.) from inner chamber  70  of pump body  60  via atmosphere-side passageway  85  and atmosphere-side one-way valve  95 . See  FIG. 15 . Note that fluid in inner chamber  70  of pump body  60  is prevented from exiting inner chamber  70  through wound-side passageway  80  due to the presence of wound-side one-way valve  90 . Then side wall  65  of pump body  60  is released, allowing the resilient pump body  60  to return to its substantially fully expanded configuration, thereby creating a negative pressure within inner chamber  70  and wound-side passageway  80 , such that fluid below wound-side surface  25  of membrane  10  (e.g., fluid within the wound chamber) is drawn into inner chamber  70  through wound-side passageway  85  and wound-side one-way valve  90 . Note that air in the atmosphere is prevented from entering inner chamber  70  through atmosphere-side passageway  85  due to the presence of atmosphere-side one-way valve  95 . 
     This process of squeezing and releasing side wall  65  of pump body  60  is repeated until pump body  60  of pump assembly  15  remains in its substantially fully collapsed configuration (i.e., side wall  65  of pump body  60  bows inwardly) even when side wall  65  of pump body  60  is not being manually compressed. See  FIG. 16 . When pump body  60  of pump assembly  15  remains in its substantially fully collapsed configuration even when side wall  65  of pump body  60  is not being manually compressed, an observer will know that the pressure differential between the pressure of the fluid within inner chamber  70  (and the wound chamber) and atmospheric pressure exceeds the desired threshold, indicating that the desired level of negative pressure has been achieved at the wound site. Note that when pump body  60  of pump assembly  15  remains in its substantially fully collapsed configuration even when side wall  65  of pump body  60  is not being manually compressed, pump assembly  15  will have been effectively deactivated, since it will be impossible to continue using the pump assembly with side wall  65  in its substantially fully collapsed configuration. 
     At this point removable cap  100  may be used to seal atmosphere-side port  87  of atmosphere-side passageway  85 . 
     NPWT bandage  5  is left in place on the wound for an appropriate period of time (e.g., a few days) so as to shield the wound from contaminants and microbes during healing, draw exudates out of the wound, and promote beneficial biological responses at the wound site. In the event that leakage should cause the negative pressure created in the wound chamber to fall below the given threshold (which will be apparent to an observer by virtue of the fact that side wall  65  of pump body  60  will return to its substantially fully-expanded configuration), atmosphere-side port  87  of atmosphere-passageway  85  may be unsealed (i.e., by removing removable cap  100 ) and then pump assembly  15  may be used in the manner discussed above to re-establish the desired negative pressure in the wound chamber (i.e., by repeatedly squeezing and releasing side wall  65  of pump body  60 ). 
     When appropriate, NPWT bandage  5  may be removed from the skin of the patient by simply peeling membrane  10  away from the skin of the patient. 
     Pump Body with Notches to Enhance the Substantially “Binary State” Behavior of the Pump Body 
     As noted above, pump body  60  of pump assembly  15  is preferably specifically configured so that the pump body will abruptly change state between (i) a substantially fully expanded configuration where side wall  65  of pump body  60  and inner chamber  70  of pump body  60  have a substantially circular cross-section (see  FIG. 5 ) when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure is below a given threshold, and (ii) a substantially fully collapsed configuration where side wall  65  of pump body  60  bows inwardly (see  FIG. 6 ) when the pressure differential between the pressure of the fluid within inner chamber  70  and atmospheric pressure exceeds a given threshold. 
     As also noted above, this substantially “binary state” behavior of pump body  60  is achieved by forming the pump body with a substantially circular cross-section, which gives the body an “over-the-center” deformation characteristic, i.e., so that the side wall of pump body  60  has a “failure” mode where it abruptly transitions from a substantially fully expanded configuration to a substantially fully collapsed configuration, and has a “restoration” mode where it abruptly transitions from a substantially fully collapsed configuration to a substantially fully expanded configuration. See  FIG. 7 . As noted above, by forming pump assembly  15  so that side wall  65  of pump body  60  and pump flange  75  merge at a neck  77  ( FIG. 5 ), with neck  77  having a relatively small width relative to the full diameter of pump body  60 , and with recesses  78  extending inwardly between membrane  10  and pump body  60 , pump body  60  has a substantially circular cross-section over substantially its entire circumference, with pump body  60  free to radially compress/radially expand with minimal interference from pump flange  75 , so that pump body  60  can exhibit substantially “binary state” behavior. 
     If desired, pump body  60  can be modified so as to enhance the substantially “binary state” behavior of the pump body. 
     By way of example but not limitation, and looking now at  FIGS. 17-20 , notches  105  can be formed in pump body  60  (e.g., at the “9 o&#39;clock”, “12 o&#39;clock” and “3 o&#39;clock” positions) so as to enhance the substantially “binary state” behavior of the pump body by further inducing pump body  60  to assume only its substantially fully expanded configuration or its substantially fully collapsed configuration. Note that the more that pump body  60  exhibits true “binary state” behavior, the more that pump efficiency will improve and the better that pump assembly  15  will serve as an automatic pressure indicator and as an automatic pressure limiter. 
     NPWT Bandage Incorporating Gauze (or Other Absorbent Wound Dressing) and Utilizing an Improved Pump Assembly 
     Looking next at  FIGS. 21-25 , there is shown another negative pressure wound therapy (NPWT) bandage  5  formed in accordance with the present invention. The NPWT bandage  5  shown in  FIGS. 21-25  is substantially the same as the NPWT bandage  5  shown in  FIGS. 1-16 , and the NPWT bandage  5  shown in  FIGS. 17-20 , except that (i) in the construction shown in  FIGS. 21-25 , membrane  10  comprises multiple layers which incorporate gauze (or other absorbent wound dressing), and (ii) in the construction shown in  FIGS. 21-25 , pump assembly  15  has a modified construction and is secured to membrane  10  using a different approach. 
     More particularly, in this form of the invention, membrane  10  comprises a lower skin-contacting polyurethane layer  110  having a center opening  115 , an intermediate foam (or gauze or other absorbent wound dressing) layer  120  for disposition over center opening  115  of lower skin-contacting polyurethane layer  110 , and an upper polyurethane layer  125  for disposition over intermediate foam layer  120  and lower skin-contacting polyurethane layer  110 . In the preferred form of the invention, upper polyurethane layer  125  is formed out of a substantially air-impermeable material. And, in the preferred form of the invention, upper polyurethane layer  125  and lower skin-contacting polyurethane layer  110  have the same size outer perimeter, so that upper polyurethane layer  125  does not contact the skin of the patient. The outer perimeters of upper polyurethane layer  125  and lower skin-contacting polyurethane layer  110  are secured to one another, capturing intermediate foam layer  120  therebetween. Intermediate foam layer  120  has an outer perimeter which is (i) larger than the perimeter of center opening  115  of lower skin-contacting polyurethane layer  110 , and (ii) smaller than the outer perimeter of the outer perimeters of lower skin-contacting polyurethane layer  110  and upper polyurethane layer  125 . In this way, when NPWT bandage  5  has its center opening  115  of lower skin-contacting polyurethane layer  110  positioned over a wound, fluid from the wound can pass through center opening  115  of lower skin-contacting polyurethane layer  110  to reach intermediate foam layer  120 . It will be appreciated that adhesive  45  is positioned on the wound side surface of lower skin-contacting polyurethane layer  110  so that a substantially air-tight seal may be established by NPWT bandage  5  about the perimeter of a wound (i.e., so as to form the aforementioned wound chamber). An opening  130  is formed in upper polyurethane layer  125 , and overlaps center opening  115  of lower skin-contacting polyurethane layer  110 , so that wound-side passageway  80  of pump assembly  15  can access fluid (e.g., air, liquid, etc.) within the wound chamber (i.e., via opening  130  in upper polyurethane layer  125 , the openings in intermediate foam layer  120 , and center opening  115  of lower skin-contacting polyurethane layer  110 ) for evacuation during pumping of pump assembly  15 . 
     The pump assembly  15  utilized in the NPWT bandage  5  of  FIGS. 21-25  is generally similar to the pump assembly  15  described above, except that it comprises a pair of pedestals  135 A,  135 B for mounting pump assembly  15  to membrane  10 . More particularly, pedestal  135 A comprises one end of pump body  60  and is adhered (e.g., by an adhesive  137 ) to the upper surface of membrane  10  (i.e., to the upper surface of upper polyurethane layer  125 ) so that wound-side passageway  80  and wound-side one-way valve  90  are aligned with opening  130  in upper polyurethane layer  125  (and hence in fluid communication with the wound chamber). Pedestal  135 B comprises the other end of pump body  60  and is adhered (e.g., by an adhesive  138 ) to the upper surface of membrane  10  (i.e., to the upper surface of upper polyurethane layer  125 ). The intervening portion  140  of pump body  60  sits suspended between pedestal  135 A and pedestal  135 B, elevated above upper polyurethane layer  125  of membrane  10 , so that a space  145  is formed between intervening portion  140  of pump body  60  and upper polyurethane layer  135  of membrane  10 . Inasmuch as intervening portion  140  of pump body  60  is not mounted directly to membrane  10 , but is instead suspended above membrane  10  by means of pedestals  135 A and  135 B, intervening portion  140  of pump body  60  can be formed with a true circular cross-section, whereby to enhance the substantially “binary state” behavior of the NPWT bandage. It will be appreciated that pump body  60  may incorporate one or more of the aforementioned notches  105  so as to further enhance the substantially “binary state” behavior of the NPWT bandage. 
     Modifications of the Preferred Embodiments 
     It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.