Patent Publication Number: US-2020289328-A1

Title: Wound dressing with humidity colorimeter sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Application No. 62/580,853, filed on Nov. 2, 2017, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to a wound dressing and more particularly to a wound dressing configured to monitor moisture level at a wound site. 
     Maintaining a suitable level of moisture at a wound site can promote wound healing. However, it can be difficult to monitor the moisture level at the wound site, except by removing the wound dressing and directly observing the wound. Selecting an appropriate level of absorbency for the wound dressing can be important for several reasons. A wound dressing that is too absorbent can over-dry the wound site, whereas a wound dressing that is not absorbent enough can saturate with wound exudate and result in a wet wound site. It would be desirable to accurately monitor and control the level of moisture of a wound site in order to promote effective wound healing. 
     SUMMARY 
     One implementation of the present disclosure is a wound dressing including a superabsorbent pad, a drape layer, a humidity chamber, a wick, and a humidity colorimeter sensor. The superabsorbent pad is configured to absorb wound fluid and has a first side and a second, wound-facing side. The drape layer is coupled to the first side of the superabsorbent pad and has a first side and a second, wound-facing side. The drape layer is substantially impermeable to liquid and substantially permeable to vapor. The humidity chamber is coupled to the first side of the drape layer opposite the superabsorbent pad. The wick extends through the drape layer and is configured to wick moisture between the superabsorbent pad and the humidity chamber. The humidity colorimeter sensor is located within the humidity chamber and configured to change color responsive to a humidity level within the humidity chamber. 
     In some embodiments, the humidity colorimeter sensor includes a graphene oxide sensor. In some embodiments, the humidity colorimeter sensor includes a non-powered humidity sensor. 
     In some embodiments, the humidity chamber is substantially impermeable to liquid and substantially permeable to vapor. In some embodiments, the humidity chamber is substantially impermeable to both liquid and vapor. 
     In some embodiments, the humidity chamber includes an outer layer having a perimeter adhered to the first side of the drape layer, thereby sealing the humidity colorimeter sensor between the outer layer and the drape layer. In some embodiments, the drape layer is configured to transfer moisture vapor through the drape layer at a first moisture vapor transmission rate and the outer layer of the humidity chamber is configured to transfer moisture vapor through the outer layer at a second moisture vapor transmission rate less than the first moisture vapor transmission rate. 
     In some embodiments, the humidity chamber includes an outer layer and an inner layer positioned between the outer layer and the first side of the drape layer. The inner layer may have a perimeter adhered to the outer layer, thereby sealing the humidity colorimeter sensor between the outer layer and the inner layer. In some embodiments, the wick extends through both the drape layer and the inner layer of the humidity chamber. 
     In some embodiments, the wick includes a first end portion located between the superabsorbent pad and the drape layer, a second end portion located within the humidity chamber, and a middle portion extending through the drape layer and connecting the first end portion and the second end portion. In some embodiments, the first end portion and the second end portion are substantially parallel to the superabsorbent pad and the drape layer. In some embodiments, the middle portion is substantially perpendicular to the superabsorbent pad and the drape layer. 
     In some embodiments, the drape layer includes a polyurethane film. In some embodiments, the drape layer is configured to wick moisture from the superabsorbent pad and distribute the moisture across the first side of the drape layer. 
     In some embodiments, the wound dressing includes an adhesive coating coupled to the second, wound-facing side of the drape layer. In some embodiments, the drape layer extends beyond a perimeter of the superabsorbent pad to provide an adhesive-coated margin configured to adhere the wound dressing to a surface. 
     Another implementation of the present disclosure is a wound dressing including a superabsorbent pad, a humidity chamber, and a humidity colorimeter sensor. The superabsorbent pad is configured to absorb wound fluid and has a first side and a second, wound-facing side. The humidity chamber is located on the first side of the superabsorbent pad. The humidity colorimeter sensor is located within the humidity chamber and configured to change color responsive to a humidity level within the humidity chamber. 
     In some embodiments, the humidity colorimeter sensor includes a graphene oxide sensor. In some embodiments, the humidity colorimeter sensor includes a non-powered humidity sensor. 
     In some embodiments, the humidity chamber is substantially impermeable to liquid and substantially permeable to vapor. In some embodiments, the humidity chamber is substantially impermeable to both liquid and vapor. 
     In some embodiments, the wound dressing includes a wick configured to wick moisture between the superabsorbent pad and the humidity chamber. 
     In some embodiments, the wound dressing includes a drape layer positioned between the superabsorbent pad and the humidity chamber. The drape layer may be substantially impermeable to liquid and substantially permeable to vapor. In some embodiments, the wound dressing includes a wick extending through the drape layer and configured to wick moisture between the superabsorbent pad and the humidity chamber. 
     In some embodiments, the wick includes a first end positioned between the superabsorbent pad and the drape layer, a second end positioned within the humidity chamber, and a middle portion extending through the drape layer and connecting the first end and the second end. In some embodiments, the first end portion and the second end portion are substantially parallel to the superabsorbent pad and the drape layer. In some embodiments, the middle portion is substantially perpendicular to the superabsorbent pad and the drape layer. 
     In some embodiments, the humidity chamber includes an outer layer having a perimeter adhered to the drape layer, thereby sealing the humidity colorimeter sensor between the outer layer and the drape layer. In some embodiments, the drape layer is configured to transfer moisture vapor through the drape layer at a first moisture vapor transmission rate and the outer layer of the humidity chamber is configured to transfer moisture vapor through the outer layer at a second moisture vapor transmission rate less than the first moisture vapor transmission rate. 
     In some embodiments, the humidity chamber includes an outer layer and an inner layer positioned between the outer layer and the drape layer. The inner layer may have a perimeter adhered to the outer layer, thereby sealing the humidity colorimeter sensor between the outer layer and the inner layer. In some embodiments, the wick extends through both the drape layer and the inner layer of the humidity chamber. 
     In some embodiments, the drape layer includes a polyurethane film. In some embodiments, the drape layer is configured to wick moisture from the superabsorbent pad and distribute the moisture across a first side of the drape layer opposite the superabsorbent pad. 
     In some embodiments, the wound dressing includes an adhesive coating coupled to a second, wound-facing side of the drape layer. In some embodiments, the drape layer extends beyond a perimeter of the superabsorbent pad to provide an adhesive-coated margin configured to adhere the wound dressing to a surface. 
     Another implementation of the present disclosure is a system for monitoring humidity of a wound site. The system includes a wound dressing including a humidity colorimeter sensor configured to measure the humidity of the wound site and to emit or reflect light at a wavelength representative of the humidity of the wound site. The wavelength of the light emitted or reflected by the humidity colorimeter sensor is within a spectrum readable by an electronic device to allow the electronic device to determine the humidity of the wound site based on the wavelength of the light. 
     In some embodiments, the humidity colorimeter sensor includes a graphene oxide sensor. In some embodiments, the humidity colorimeter sensor includes a non-powered humidity sensor. 
     In some embodiments, the electronic device includes a photo sensor configured to detect the wavelength of the light emitted or reflected by the humidity colorimeter sensor and a processing circuit configured to determine the humidity of the wound site based on the wavelength of the light detected by the photo sensor. 
     In some embodiments, the electronic device is a smartphone having a camera that includes the photo sensor. The processing circuit includes an application installed on the smartphone. The application may be configured to determine the humidity of the wound site based on the wavelength of the light detected by photo sensor. 
     In some embodiments, the wound dressing includes a superabsorbent pad configured to absorb wound fluid and having a first side and a second, wound-facing side. The wound dressing may include a humidity chamber located on the first side of the superabsorbent pad. The humidity colorimeter sensor may be located within the humidity chamber and configured to change color responsive to a humidity change within the humidity chamber. 
     In some embodiments, the humidity chamber is substantially impermeable to liquid and substantially permeable to vapor. In some embodiments, the humidity chamber is substantially impermeable to both liquid and vapor. 
     In some embodiments, the wound dressing includes a drape layer positioned between the superabsorbent pad and the humidity chamber. The drape layer may be substantially impermeable to liquid and substantially permeable to vapor. 
     In some embodiments, the wound dressing includes a wick configured to wick moisture between the superabsorbent pad and the humidity chamber. In some embodiments, the wick extends through the drape layer. 
     In some embodiments, the wick includes a first end positioned between the superabsorbent pad and the drape layer, a second end positioned within the humidity chamber, and a middle portion extending through the drape layer and connecting the first end and the second end. In some embodiments, the first end portion and the second end portion are substantially parallel to the superabsorbent pad and the drape layer. In some embodiments, the middle portion is substantially perpendicular to the superabsorbent pad and the drape layer. 
     In some embodiments, the humidity chamber includes an outer layer having a perimeter adhered to the drape layer, thereby sealing the humidity colorimeter sensor between the outer layer and the drape layer. 
     In some embodiments, the drape layer is configured to transfer moisture vapor through the drape layer at a first moisture vapor transmission rate and the outer layer of the humidity chamber is configured to transfer moisture vapor through the outer layer at a second moisture vapor transmission rate less than the first moisture vapor transmission rate. 
     In some embodiments, the humidity chamber includes an outer layer and an inner layer positioned between the outer layer and the drape layer. The inner layer may have a perimeter adhered to the outer layer, thereby sealing the humidity colorimeter sensor between the outer layer and the inner layer. In some embodiments, the wick extends through both the drape layer and the inner layer of the humidity chamber. 
     In some embodiments, the drape layer includes a polyurethane film. In some embodiments, the drape layer is configured to wick moisture from the superabsorbent pad and distribute the moisture across a first side of the drape layer opposite the superabsorbent pad. 
     In some embodiments, the wound dressing includes an adhesive coating coupled to a second, wound-facing side of the drape layer. In some embodiments, the drape layer extends beyond a perimeter of the superabsorbent pad to provide an adhesive-coated margin configured to adhere the wound dressing to a surface. 
     Those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting. Other aspects, inventive features, and advantages of the devices and/or processes described herein, as defined solely by the claims, will become apparent in the detailed description set forth herein and taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a wound dressing as would be visible when the wound dressing is adhered to a surface (e.g., a patient&#39;s skin), according to an exemplary embodiment. 
         FIG. 2  is a bottom view of the wound dressing of  FIG. 1  showing the wound-contacting surface of the wound dressing, according to an exemplary embodiment. 
         FIG. 3  is an exploded view illustrating several layers of the wound dressing of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 4  is a cross-sectional view of the wound dressing of  FIG. 1  adhered to a surface, according to an exemplary embodiment. 
         FIG. 5  is an array of graphene oxide (GO) based humidity sensors exposed to various humidity levels, according to an exemplary embodiment. 
         FIG. 6  is a drawing of a thin and flexible sensor which can be used in the wound dressing of  FIG. 1 , according to an exemplary embodiment. 
         FIG. 7  is a drawing of a humidity monitoring system including the wound dressing of  FIG. 1  and an electronic device, according to an exemplary embodiment. 
         FIG. 8  is a block diagram of the humidity monitoring system of  FIG. 7 , according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Overview 
     Referring generally to the FIGURES, a wound dressing with a humidity colorimeter sensor is shown, according to various exemplary embodiments. The wound dressing may include a superabsorbent pad, a drape layer, a humidity chamber, a wick, and a humidity colorimeter sensor. The superabsorbent pad can be configured to absorb wound fluid and may include a first side and a second, wound-facing side. The drape layer may be coupled to the first side of the superabsorbent pad. The drape layer may also include a first side and a second, wound-facing side. In some embodiments, the drape layer is substantially impermeable to liquid and substantially permeable to vapor. The humidity chamber may be coupled to the first side of the drape layer opposite the superabsorbent pad. 
     The wick may include a first end portion located between the drape layer and the superabsorbent pad and a second end portion located within the humidity chamber. The wick may extend through the drape layer and may be configured to wick moisture between the superabsorbent pad and the humidity chamber. The humidity colorimeter sensor may be located within the humidity chamber and configured to change color responsive to a humidity level within the humidity chamber. In some embodiments, an electronic device can be used to measure the color of the humidity colorimeter sensor and determine a humidity level based on the measured color. These and other features of the wound dressing and electronic device are described in greater detail below. 
     Wound Dressing 
     Referring now to  FIGS. 1-4 , a wound dressing  100  is shown, according to an exemplary embodiment. In brief overview,  FIG. 1  is a top view of wound dressing  100  as would be visible when wound dressing  100  is adhered to a surface (e.g., a patient&#39;s skin).  FIG. 2  is a bottom view of wound dressing  100  showing the wound-contacting surface of wound dressing  100 . The broken lines in  FIGS. 1-2  outline the layers of wound dressing  100  that are not visible in each view.  FIG. 3  is an exploded view illustrating several layers  102 - 110  of wound dressing  100 .  FIG. 4  is a cross-sectional view of wound dressing  100  adhered to a surface  130 . 
     In various embodiments, wound dressing  100  can be formed as a substantially flat sheet for topical application to wounds or contoured for application to body surfaces having high curvature. The size of wound dressing  100  can vary depending on the size of the wound to be dressed. For example, it is contemplated that the size of wound dressing  100  can range from 1 cm 2  to 200 cm 2 , and more preferably from 4 cm 2  to 100 cm 2 . However, other shapes and sizes of wound dressing  100  are also possible depending on the intended use. Wound dressing  100  is shown to include superabsorbent pad  110 , a drape layer  108 , a humidity chamber  106 , a wick  104 , and a humidity colorimeter sensor  102 . Each of these components of wound dressing  100  is described in detail below. 
     Superabsorbent Pad 
     Superabsorbent pad  110  can be configured to absorb wound fluid and is shown to include a first side  112  and a second, wound-facing side  114 . When wound dressing  100  is applied to a wound, first side  112  faces away from the wound, whereas second side  114  faces toward the wound. In some embodiments, first side  112  of superabsorbent pad  110  contacts the wound-facing side  118  of drape layer  108 . Similarly, second side  114  of superabsorbent pad  110  may contact a surface  130  to which wound dressing  100  is applied (e.g., a patient&#39;s skin, a wound, etc.). Superabsorbent pad  110  can be configured to wick moisture from the wound and distribute the moisture across first side  112 . 
     In some embodiments, superabsorbent pad  110  includes a superabsorbent layer along first side  112  and a hydrophilic foam layer along second side  114 . The superabsorbent layer can be laminated to the hydrophilic foam layer using a fusible fiber positioned between the superabsorbent layer and the hydrophilic foam layer. In some embodiments, the superabsorbent layer includes a hydrogel or hydrogel composition. Several examples of hydrogels and hydrogel compositions which can be used to form superabsorbent pad  110  are described in detail in U.S. Pat. No. 8,097,272 issued Jan. 17, 2012, U.S. Pat. No. 8,664,464 issued Mar. 4, 2014, and U.S. Pat. No. 8,058,499 issued Nov. 15, 2011. The entire disclosure of each of these patents is incorporated by reference herein. 
     The expressions “hydrogel” and “hydrogel compositions” used herein are not to be considered as limited to gels which contain water, but extend generally to all hydrophilic gels and gel compositions, including those containing organic non-polymeric components in the absence of water. For example, the superabsorbent layer may be formed from a polyurethane that entraps water to form a gel. In some embodiments, the superabsorbent layer is substantially continuous and/or substantially non-porous or non-foamed. The superabsorbent layer may include a flexible plasticized hydrophilic polymer matrix having a substantially continuous internal structure. The density of the superabsorbent layer may be greater than 0.5 g/cm 3 , more preferably greater than 0.8 g/cm 3 , and most preferably from 0.9 to 1.1 g/cm 3 . In some embodiments, the thickness of the superabsorbent layer is from 1 mm to 10 mm, more preferably from 2 mm to 5 mm. 
     In some embodiments, the superabsorbent layer is cross-linked and preferably it is substantially insoluble in water at ambient temperature. However, the structure of the superabsorbent layer absorbs and entraps liquid to provide a highly hydrated gel structure in contrast to the porous foam structure of the hydrophilic foam layer. Preferably, the gel can absorb 1 to 10 g/g of physiological saline at 20°, more preferably 2 to 5 g/g. 
     In some embodiments, the dry weight of the superabsorbent layer is from 1000 to 5000 g/m 2 , more preferably from 2000 to 4000 g/m 2 . In some embodiments, the superabsorbent layer includes from 1% to 30% of water, more preferably from 10% to 20% by weight of water before use. In some embodiments, the superabsorbent layer contains from 1% to 40%, more preferably from 5 to 15%, by weight of one or more humectants, preferably selected from the group consisting of glycerol, propylene glycol, sorbitol, mannitol, polydextrose, sodium pyrrolidine carboxylic acid (NaPCA), hyaluronic acid, aloe, jojoba, lactic acid, urea, gelatin, lecithin and mixtures thereof. The entrapped water and optional humectants give the hydrogel a soft, moist wound-friendly surface for contacting the wound. 
     The hydrophilic foam layer can be positioned between the superabsorbent layer and the wound. In some embodiments, the hydrophilic foam layer is laminated to the superabsorbent layer using a fusible fiber positioned between the superabsorbent layer and the hydrophilic foam layer. The superabsorbent layer can be bonded to the hydrophilic foam layer, for example by an adhesive or by radiation cross-linking. In some embodiments, the superabsorbent layer is bonded to the hydrophilic foam layer by urethane or urea linkages. This can be achieved by applying the hydrophilic foam layer to the superabsorbent layer (substantially without mixing) before polyurethane curing is complete. 
     The hydrophilic foam layer may include a polyurethane foam coupled to the superabsorbent layer. In some embodiments, the hydrophilic foam layer includes a flexible plasticized hydrophilic polymer matrix having an internal cellular structure. Several examples of hydrophilic foams which can be used to form the hydrophilic foam layer are described in detail in U.S. Pat. No. 8,097,272 issued Jan. 17, 2012, U.S. Pat. No. 8,664,464 issued Mar. 4, 2014, and U.S. Pat. No. 8,058,499 issued Nov. 15, 2011. The entire disclosure of each of these patents is incorporated by reference herein. 
     Advantageously, the hydrophilic foam layer may provide enhanced absorbency for liquid exudate. This is because the initial substantially anhydrous condition and porous structure of the hydrophilic foam layer enables it to absorb a larger amount of water by both chemical and physical absorption that is the case for the corresponding hydrogel material. Furthermore, the porous structure of the foam provides for rapid uptake of liquid exudate, in contrast to pure hydrogel dressings. 
     In some embodiments, the hydrophilic foam layer has a thickness of from 1 to 20 mm, more preferably from 1.5 to 5 mm. In some embodiments, the hydrophilic foam layer has a density of from 0.28 g/cm 3  to 0.5 g/cm 3 , and more preferably from 0.32 g/cm 3  to 0.48 g/cm 3 . Preferably, the hydrophilic foam layer has an elongation to break of at least 150%, more preferably from 500% to 1000%. The foam that forms the hydrophilic foam layer may be hydrophilic and can absorb aqueous fluids such as wound exudate with swelling. The hydrophilic foam layer may be highly cross-linked and substantially insoluble in water. 
     In some embodiments, the hydrophilic foam layer has an absorbency of at least 3 grams of saline per gram of foam, and preferably a swellability in water of at least 200%. In some embodiments, the hydrophilic foam layer is constructed using the foam as described in European Patent No. 0541391 issued Jun. 10, 1998, the entire disclosure of which is incorporated by reference herein. In some embodiments, the hydrophilic foam layer includes less than 10% water prior to use as an absorbent, more preferably less than 5% water, and even more preferably it contains less than 2% of water before use. 
     Drape Layer 
     Drape layer  108  is shown to include a first side  116  and a second, wound-facing side  118  opposite first side  116 . When wound dressing  100  is applied to a wound, first side  116  faces away from the wound, whereas second side  118  faces toward the wound. Drape layer  108  supports superabsorbent pad  110  and provides a barrier to passage of microorganisms through wound dressing  100 . In some embodiments, drape layer  108  is a thin layer of polyurethane film. One example of a suitable material for drape layer  108  is the polyurethane film known as ESTANE 5714F. Other suitable polymers for forming drape layer  108  include poly alkoxyalkyl acrylates and methacrylates, such as those described in Great Britain Patent Application No. 1280631A filed Nov. 22, 2002, the entire disclosure of which is incorporated by reference herein. In some embodiments, drape layer  108  includes a continuous layer of a high-density blocked polyurethane foam that is predominantly closed-cell. Drape layer  108  may have a thickness in the range of 10 μm to 100 μm, preferably in the range of 50 μm to 70 μm. In some embodiments, drape layer  108  has a thickness of approximately 60 μm. 
     Drape layer  108  may be substantially impermeable to liquid and substantially permeable to moisture vapor. In other words, drape layer  108  may be permeable to water vapor, but not permeable to liquid water or wound exudate. This increases the total fluid handling capacity (TFHC) of wound dressing  100  while promoting a moist wound environment. In some embodiments, drape layer  108  is also impermeable to bacteria and other microorganisms. Drape layer  108  may have a moisture vapor transmission rate (MVTR) of approximately 300 to 5000, preferably 500 to 2000 at 37.5° C. at 100% to 10% relative humidity difference. In some embodiments, drape layer  108  is configured to wick moisture from superabsorbent pad  110  and distribute the moisture across first side  116 . 
     Side  118  of drape layer  108  may be coated with an acrylic or other adhesive. The adhesive applied to side  118  ensures that wound dressing  100  adheres to surface  130  and that wound dressing  100  remains in place throughout the wear time. In some embodiments, the perimeter of drape layer  108  extends beyond (e.g., circumscribes) the perimeter of superabsorbent pad  110  to provide an adhesive-coated margin for adhering wound dressing  100  to the skin of a patient adjacent to the wound being treated, shown in  FIG. 4  as surface  130 . The adhesive-coated margin may extend around all sides of superabsorbent pad  110  such that wound dressing  100  is a so-called island dressing. In other embodiments, the adhesive-coated margin can be eliminated and wound dressing  100  can be adhered to surface  130  using other techniques. 
     In some embodiments, side  118  of drape layer  108  contacts contact side  112  of superabsorbent pad  110 . Side  118  of drape layer  108  may adhere to side  112  of superabsorbent pad  110  along the portion of drape layer  108  that overlaps with superabsorbent pad  110 . In this way, drape layer  108  and superabsorbent pad  110  may form a closed pocket, sealing end portion  104   b  of wick  104  between drape layer  108  and superabsorbent pad  110 . In some embodiments, drape layer  108  includes an aperture  120  (e.g., a hole, slot, opening, etc.) through which wick  104  passes. Wick  104  may extend through aperture  120  such that end portion  104   a  of wick  104  is located on one side of drape layer  108  (e.g., within humidity chamber  106 ) whereas end portion  104   b  of wick  104  is located on the opposite side of drape layer  108  (e.g., between drape layer  108  and superabsorbent pad  110 ). 
     In some embodiments, the adhesive applied to side  118  of drape layer  108  is moisture vapor transmitting and/or patterned to allow passage of water vapor therethrough. The adhesive may include a continuous moisture vapor transmitting, pressure-sensitive adhesive layer of the type, conventionally used for island-type wound dressings (e.g., a polyurethane-based pressure sensitive adhesive). One example of an adhesive which can be used is a pressure sensitive adhesive based on acrylate ester copolymers, polyvinyl ethyl ether and polyurethane, as described in Great Britain Patent Application No. 1280631A. The basis weight of the adhesive may be 20 to 250 g/m 2 , and more preferably 50 to 150 g/m 2 . 
     Humidity Chamber 
     Humidity chamber  106  may be coupled to first side  116  of drape layer  108 , opposite superabsorbent pad  110 , and may include an outer layer  105  and an inner layer  107 . The perimeters of outer layer  105  and inner layer  107  can be coupled to each other to define humidity chamber  106  between outer layer  105  and inner layer  107 . In some embodiments, layers  105  and  107  of humidity chamber  106  are substantially impermeable to liquid and substantially permeable to vapor. In other embodiments, layers  105  and  107  of humidity chamber  106  are substantially impermeable to both liquid and vapor. 
     As shown in  FIGS. 3-4 , inner layer  107  may be positioned between outer layer  105  and first side  116  of drape layer  108 . The perimeter of inner layer  107  may be adhered to the perimeter of outer layer  105 , thereby sealing humidity colorimeter sensor  102  between outer layer  105  and inner layer  107 . Inner layer  107  can be adhered to first side  116  of drape layer to couple humidity chamber  106  to drape layer  108 . In other embodiments, inner layer  107  can be omitted and the perimeter of outer layer  105  can be adhered directly to first side  116  of drape layer  108 , thereby sealing humidity colorimeter sensor  102  between outer layer  105  and drape layer  108 . 
     In some embodiments, outer layer  105 , inner layer  107 , and drape layer  108  are configured to provide various rates of moisture transfer through their respective layers. For example, drape layer  108  can be configured to transfer moisture through drape layer  108  at a first moisture vapor transmission rate (MVTR), whereas outer layer  105  may be configured to transfer moisture vapor through outer layer  105  at a second MVTR. In some embodiments, the second MVTR is less than the first MVTR (i.e., outer layer  105  is less permeable to moisture than drape layer  108 ). In other embodiments, the second MVTR is greater than the first MVTR (i.e., outer layer  105  is more permeable to moisture than drape layer  108 ). Similarly, inner layer  107  can be configured to transfer moisture vapor through inner layer  107  at a third MVTR. The third MVTR can be different from both the first MVTR and the second MVTR such that each of layers  105 ,  107 , and  108  provides a different MVTR. In other embodiments, the third MVTR can be different from the first MVTR but the same as the second MVTR such that each of layers  105  and  107  provide the same MVTR. 
     Humidity chamber  106  can be configured to enclose a volume within which humidity colorimeter sensor  102  is located. The internal volume of humidity chamber  106  may be maintained at the same humidity level as superabsorbent pad  110  by the operation of wick  104 . In some embodiments, humidity chamber  106  includes an aperture  122  (e.g., a hole, slot, opening, etc.) that extends through inner layer  107 . Wick  104  may pass through aperture  122  such that end portion  104   a  of wick  104  is located on one side of inner layer  107  (e.g., within humidity chamber  106 ) whereas end portion  104   b  of wick  104  is located on the opposite side of inner layer  107  (e.g., outside humidity chamber  106 , between drape layer  108  and superabsorbent pad  110 ). In some embodiments, wick  104  extends through both drape layer  108  (via aperture  120 ) and inner layer  107  (via aperture  122 ) such that both drape layer  108  and inner layer  107  are located between end portion  104   a  and end portion  104   b  of wick  104 . 
     Wick 
     Wick  104  is shown to include a first end portion  104   a  located within humidity chamber  106  and a second end portion  104   b  located between superabsorbent pad  110  and drape layer  108 . Although end portions  104   a  and  104   b  are shown as separate parts in  FIG. 3  (for purposes of illustrating an exploded view), it should be understood that wick  104  may be a continuous structure that includes both end portions  104   a  and  104   b  and a middle portion that connects end portions  104   a  and  104   b . In some embodiments, the middle portion of wick  104  includes a bend or fold (e.g., a 180 degree bend) such that wick  104  has a “C” shape (as shown in  FIG. 4 ). End portions  104   a  and  104   b  can be arranged substantially parallel to each other and offset from each other by the thickness of layers  107  and  108  between end portions  104   a  and  104   b . End portions  104   a  and  104   b  may be substantially parallel to both superabsorbent pad  110  and to drape layer  108 , whereas the middle portion that connects end portions  104   a  and  104   b  may be substantially perpendicular to both superabsorbent pad  110  and drape layer  108   
     Wick  104  may extend through drape layer  108  and/or inner layer  107  and can be configured to wick (e.g., transfer) moisture between superabsorbent pad  110  and humidity chamber  106 . In some embodiments, wick  104  equilibrates the humidity level within humidity chamber  106  with the humidity level of superabsorbent pad  110  and/or the humidity level of the wound site. Accordingly, the humidity level measured by colorimeter humidity sensor  102  within humidity chamber  106  may be the same as the humidity level of superabsorbent pad  110  and/or the wound site. 
     Wick  104  can be made of any material suitable for providing a wicking function to effectively transmit fluid between first end portion  104   a  and second end portion  104   b . For example, wick  104  can be made of rayon or other suitable wicking fabric. Several examples of wicking materials that can be used in wick  104  are described in detail in U.S. patent application Ser. No. 13/009,238 filed Jan. 19, 2011, U.S. Pat. No. 6,936,037 filed Apr. 8, 2003, and U.S. Pat. No. 9,456,930 filed Mar. 17, 2014. The entire disclosure of each of these patents and patent applications is incorporated by reference herein. The wicking properties of wick  104  can be enhanced by using a hydrophilic material to form superabsorbent pad  110 . 
     Wick  104  can be configured to transfer fluid bidirectionally between end portions  104   a  and  104   b . For example, if the humidity level of superabsorbent pad  110  exceeds the humidity level within humidity chamber  106 , wick  104  may transfer fluid from superabsorbent pad  110  to humidity chamber  106 , thereby increasing the humidity level within humidity chamber  106 . Conversely, if the humidity level of superabsorbent pad  110  is less than the humidity level of humidity chamber  106 , wick  104  may transfer fluid from humidity chamber  106  to superabsorbent pad  110 , thereby decreasing the humidity level within humidity chamber  106 . Advantageously, the bidirectional wicking provided by wick  104  may allow the humidity level within humidity chamber  106  to increase or decrease in response to a change in humidity of superabsorbent pad  110  and/or at the wound site. In other words, wick  104  can cause the humidity level within humidity chamber  106  to equilibrate with the humidity level of superabsorbent pad  110  and/or the humidity level at the wound site. 
     The humidity equilibration caused by wick  104  may occur over a period of seconds (e.g., 30-60 seconds), minutes (e.g., 1-2 minutes, 2-5 minutes, 5-10 minutes, etc.), or any other time period. The shape of wick  104  (e.g., length, width, thickness, etc.) and material properties of wick  104  can be varied to adjust the equilibration time. For example, a thicker wick  104  may cause the humidity to equilibrate more quickly, whereas a thinner wick  104  may cause the humidity to equilibrate more slowly. It is contemplated that sensor  102  can respond to a change in humidity significantly faster than the change in humidity occurs such that the humidity level indicated by sensor  102  accurately represents the actual humidity level within humidity chamber  106 . 
     Humidity Colorimeter Sensor 
     Humidity colorimeter sensor  102  may be located within humidity chamber  106  and can be configured to change color responsive to the humidity level within humidity chamber  106 . The color of humidity colorimeter sensor  102  can be read (e.g., by a user or by an electronic device) as an indication of the humidity level within humidity chamber  106 . For example, a user can compare the color of humidity colorimeter sensor  102  to a reference chart in order to interpret the humidity reading provided by sensor  102 . The reference chart may include a range of colors and corresponding humidity values. The user can compare the color of humidity colorimeter sensor  102  and/or the corresponding humidity values to the ends of the range to determine whether the wound is too wet or too dry. An electronic device can measure the color of humidity colorimeter sensor  102  and automatically translate the color into a humidity value. 
     In some embodiments, outer layer  105  of humidity chamber  106  is transparent or substantially transparent to allow humidity colorimeter sensor  102  to be viewed or read through outer layer  105 . Advantageously, humidity colorimeter sensor  102  may be a low-cost, disposable sensor, which is non-toxic and configured to provide a rapid response to a change in humidity within humidity chamber  106 . In some embodiments, humidity colorimeter sensor  102  can respond to a change in humidity level within humidity chamber  106  within seconds (e.g., under 30 seconds, under 10 seconds, etc.) to provide a real-time indication of the humidity level within humidity chamber  106 . 
     Although sensor  102  is described primarily as a humidity colorimeter sensor, it is contemplated that any type of humidity sensor can be used in wound dressing  100 . For example, sensor  102  can be replaced with an electronic sensor configured to measure humidity and output a data signal or visual indication of the measured humidity value. In some embodiments, sensor  102  includes one or more LEDs (e.g., a red LED, a green LED, and a blue LED) that can be selectively powered or unpowered by sensor  102  to electronically create a color similar to the color displayed by a non-powered humidity colorimeter sensor. By increasing or decreasing the intensity of the light output by the colored LEDs, sensor  102  can blend the light output to create any color. Alternatively, sensor  102  can generate an electronic data signal that indicates the measured humidity and can transmit the data signal to an electronic device via a wired or wireless data connection. In some embodiments, sensor  102  is configured to detect the presence of both water vapor and specific other gases and can provide additional readings other than humidity. 
     In some embodiments, humidity colorimeter sensor  102  includes a graphene oxide (GO) humidity sensor or other type of non-powered humidity sensor. GO-based humidity sensors can be configured to provide a direct indication of humidity by changing color based on the humidity level at the location of the GO-based sensor. For example,  FIG. 5  shows an array  140  of GO-based humidity sensors exposed to various humidity levels ranging from 0% relative humidity to 98% relative humidity. The color of each GO-based humidity sensor is different and corresponds to the humidity level of the container within which the GO-based humidity sensor is located. In some embodiments, humidity colorimeter sensor  102  is a GO-based colorimetric sensor configured to respond to humidity levels by changing color that can be easily observed without requiring a power supply or other electronics. 
     In other embodiments, humidity colorimeter sensor  102  is a powered GO-based humidity sensor. One example of such a powered GO-based humidity sensor is described in detail in the non-patent publication “Ultrafast Graphene Oxide Humidity Sensors”  ACS Nano,  2013, 7 (12), pp 11166-11173, published Nov. 9, 2013, the entire disclosure of which is incorporated by reference herein. In some embodiments, humidity colorimeter sensor  102  includes a two-dimensional graphene structure which is highly permeable to water molecules. Accordingly, the response time of humidity colorimeter sensor  102  (e.g., the time required to transition from displaying a color indicating 10% humidity to a color indicating 90% humidity and vice versa) may be less than 100 ms when a two-dimensional graphene structure is used. 
     In some embodiments, the sensing region of humidity colorimeter sensor  102  is thin (e.g., approximately 15 nm thick) and coupled to a physical substrate. The overall thickness of the physical substrate may be between 0.001 inches and 0.010 inches in various embodiments. However, it is contemplated that sensor  102  may be thicker or thinner in other embodiments. The thickness of sensor  102  can be decreased to increase flexibility or increased to make sensor  102  easier to handle and less likely to be damaged. Sensor  102  may be transparent, and/or flexible. An example of such a thin and flexible sensor  102  is shown in  FIG. 6 . 
     Although a power supply and/or other electronics are not required to use humidity colorimeter sensor  102 , it is contemplated that an electronic device can be used to read or measure the color of humidity colorimeter sensor  102  to improve the accuracy of the humidity reading. Such an embodiment is described in greater detail below. Additionally, humidity colorimeter sensor  102  can be used in combination with a power supply (e.g., a battery) and wireless transmitter to transmit the humidity reading to an external device such as a smartphone or therapy unit. The battery and wireless transmitter can be located within wound dressing  100  or as part of an external therapy unit connected to wound dressing  100 . 
     Humidity Monitoring System 
     Referring now to  FIGS. 7-8 , a humidity monitoring system  200  is shown, according to an exemplary embodiment. System  200  is shown to include wound dressing  100  and an electronic device  202 . In some embodiments, electronic device  202  is a mobile device such as a smartphone, tablet, PDA, laptop computer, or other portable computing device. In some embodiments, electronic device is a therapy device such as a negative pressure wound therapy (NPWT) device or other type of medical device. Electronic device  202  is shown to include a communications interface  203 , a processing circuit  212 , a photo sensor  206 , and a user interface  204 . 
     Communications interface  203  may facilitate communications between electronic device  202  and external systems or devices. Communications interface  203  may include wired or wireless communications interfaces (e.g., jacks, antennas, transmitters, receivers, transceivers, wire terminals, etc.) for conducting data communications external systems or devices. In various embodiments, the communications may be direct (e.g., local wired or wireless communications) or via a communications network (e.g., a WAN, the Internet, a cellular network, etc.). For example, communications interface  203  can include an Ethernet card and port for sending and receiving data via an Ethernet-based communications link or network. In another example, communications interface  203  can include a Wi-Fi transceiver for communicating via a wireless communications network or cellular or mobile phone communications transceivers. 
     Processing circuit  212  is shown to include a processor  214  and memory  216 . Processor  214  may be a general purpose or specific purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a group of processing components, or other suitable processing components. Processor  214  is configured to execute computer code or instructions stored in memory  216  or received from other computer readable media (e.g., CDROM, network storage, a remote server, etc.). 
     Memory  216  may include one or more devices (e.g., memory units, memory devices, storage devices, etc.) for storing data and/or computer code for completing and/or facilitating the various processes described in the present disclosure. Memory  216  may include random access memory (RAM), read-only memory (ROM), hard drive storage, temporary storage, non-volatile memory, flash memory, optical memory, or any other suitable memory for storing software objects and/or computer instructions. Memory  216  may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described in the present disclosure. Memory  216  may be communicably connected to processor  214  via processing circuit  212  and may include computer code for executing (e.g., by processor  214 ) one or more processes described herein. When processor  214  executes instructions stored in memory  216 , processor  214  generally configures electronic device  202  (and more particularly processing circuit  212 ) to complete such activities. In some embodiments, memory  216  stores an application  218  which can be run by processing circuit  212 . 
     As discussed above, humidity colorimeter sensor  102  can be configured to measure the humidity of a wound site and emit or reflect light at a wavelength representative of the humidity of the wound site. In other words, the color of humidity colorimeter sensor  102  may represent the humidity of the wound site. Electronic device  202  can use photo sensor  206  (e.g., a camera) to capture an image  220  of humidity colorimeter sensor  102 . In some embodiments, the wavelength of the light emitted or reflected by humidity colorimeter sensor  102  is within a spectrum readable by photo sensor  206 . Accordingly, electronic device  202  can determine the humidity of the wound site based on the wavelength of the light. 
     In some embodiments, electronic device  202  runs an application  218  (e.g., a mobile application) configured to measure or determine the color of humidity colorimeter sensor  102  based on the image  220  captured by photo sensor  206 . Application  218  can be any type of application capable of running on electronic device  202  including, for example, the “iOn HEALING” mobile application by Kinetic Concepts, Inc. Application  218  can be configured to determine the humidity of the wound site based on the color of image  220 . For example, application  218  may use a lookup table, a function, or other stored relationship to determine a humidity value that corresponds to the measured color. In some embodiments, image  220  is presented to a user via user interface  204 . Application  218  can be configured to generate a graphical representation  208  of the humidity value, which can be presented to a user via user interface  204 . In some embodiments, the humidity value is communicated to an external system or device via communications interface  203 . 
     In some embodiments, application  218  is configured to generate a recommendation based on the determined humidity value. It may be desirable to achieve a target level of humidity at the wound site to promote effective wound healing. The recommendation generated by application  218  may suggest a user action which will drive the measured humidity level to the target humidity level. For example, the recommendation may include a recommendation to replace wound dressing  100  with a more absorbent wound dressing if the measured humidity level is above the target humidity level (i.e., the wound site is too moist). Conversely, the recommendation may include a recommendation to replace wound dressing  100  with a less absorbent wound dressing if the measured humidity level is below the target humidity level (i.e., the wound site is too dry). The recommendation can be presented to a user via user interface  204  and/or communicated to an external system or device via communications interface  203 . 
     In some embodiments, application  218  is configured to record multiple data points over a period of time. Each data point may include a humidity value and a corresponding timestamp. Application  218  can use the recorded data points to generate and present a time series or graph that indicates the history of humidity values measured over time. In some embodiments, application  218  uses the history of humidity values to determine the rate at which wound exudate is absorbed by wound dressing  100  over time. Application  218  can determine whether the exudate rate is increasing or decreasing. A decreasing exudate rate after one or more dressing changes may indicate that the wound is healing, whereas an increasing or constant exudate rate over time may indicate that the wound is not healing or healing more slowly than expected. By using the history of humidity values to determine whether the wound is healing, application  218  can provide a quantitative confirmation of caregiver intuition. Application  218  can also use rate at which the exudate is increasing or decreasing to determine and recommend an appropriate level of absorbency for the next wound dressing when wound dressing  100  is removed and a new wound dressing is applied. 
     Configuration of Exemplary Embodiments 
     The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements can be reversed or otherwise varied and the nature or number of discrete elements or positions can be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps can be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure. 
     The present disclosure contemplates methods, systems and program products on any machine-readable media for accomplishing various operations. The embodiments of the present disclosure can be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwired system. Embodiments within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. 
     Although the figures show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps can be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps.