Abstract:
A leak detection sensor includes a pair of electrodes, each electrode being coated with an electrically insulating coating having fractures formed therein having a breadth of less than 500 nm, whereby a current can flow between the electrodes when the electrodes are exposed to an electrically conductive fluid. An alarm is activatable in response to current flowing between the electrodes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a §371 national stage of International Application PCT/EP2014/066140, filed Jul. 28, 2014, which claims the priority benefit of U.K. patent application Ser. No. 1313721.1, filed Jul. 31, 2013, both of which are hereby incorporated herein by reference in their entireties. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a leak detection sensor for a stoma pouch and a process for making same. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the treatment of certain medical conditions, such as cancer of the colon, it is known to establish an opening in the body for the discharge of body wastes. Such opening is typically known as an ostomy. There are three types, namely urostomy, ileostomy and colostomy, depending upon where such opening is located. A stoma is an outlet from the intestine through the abdominal wall. Such openings are typically connected to an exchangeable bag for receiving the body wastes, such bag typically being known as a stoma pouch. The stoma pouch is typically connected to the ostomy via a flange attachable to the skin around the stoma by means of an adhesive layer. The pouch may be detachable from the flange to permit replacement of the pouch. 
         [0004]    The adhesive layer of the flange gradually loses its effectiveness over time, leading to leakages having unpleasant consequences. Therefore it is desirable to have a reliable and cost effective system capable of detecting the leakage of fluid beneath the adhesive layer of the flange of a stoma pouch to warn the patient that the pouch requires replacement. 
         [0005]    There are approximately 120,000 people in the UK with some form of “ostomy” and it is estimated that 21,000 operations to create them are performed each year. The US has, as expected, a far higher number with more than 650,000 ostomates. The cost to the NHS alone for the cost of accessories (pouches, flanges etc.) for the effective management ranges from £780 to £2300 per person per year with the total annual spend in the region of £200 m. The most pressing complaint raised by patients is not the inconvenience of the pouch system but rather the consequences of its failure, especially in social settings. There is a tremendous psychological burden on the patient when trying to lead a normal, proactive life where there is a constant fear of the pouch leaking and the associated embarrassment. An object of the present invention is to provide an early warning system which will alert the patient to the impending leak and give them sufficient time to take preventative action and thus avoid the debilitating scenario of having to deal with a pouch failure in public. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the present invention there is provided a leak detection sensor comprising a pair of electrodes, each electrode being coated with an electrically insulating coating having fractures formed therein having a breadth of less than 500 nm, and optionally 100 nm or less, whereby a current can flow between the electrodes when the electrodes are exposed to an electrically conductive fluid. 
         [0007]    Optionally, the fractures are formed by a process of laser ablation. 
         [0008]    In one embodiment the electrodes may comprise a pair of intertwined wires. 
         [0009]    Optionally, the electrically insulating coating comprises a polymeric coating, for example a thermopolymer. The polymeric coating may comprise polyvinylacetate, polyimide, polyurethane, or polyester or any other suitable thermopolymer. 
         [0010]    The electrodes may be intertwined with an absorbent wick. 
         [0011]    According to a further aspect of the present invention there is provided a stoma pouch assembly comprising a flange having an opening for receiving an ostomy or stoma, the flange being provided with an adhesive layer for adhering the flange to a patient&#39;s skin, the flange being provided with a leak detection sensor in accordance with the first aspect of the invention for detecting the passage of fluid between the adhesive layer of the flange and the patient&#39;s skin. 
         [0012]    Optionally, the sensor defines a loop encircling the flange opening. 
         [0013]    The leak detection sensor may be coupled to a detection circuit having an alarm, such as a vibration and/or audible alarm, for alerting the patient to the leakage of fluid beneath the adhesive layer of the flange. 
         [0014]    According to a further aspect of the present invention there is provided a method of making a leak detection sensor comprising providing a pair of electrodes each having an electrically insulating coating thereon formed from a thermopolymer, and creating fractures in the coating of the electrodes having a breadth of less than 500 nm, and optionally 100 nm or less, through which fluid may permeate to enable current to flow between the electrodes when exposed to an electrolyte. 
         [0015]    The electrodes may comprise a pair of wires, the method optionally comprising the step of intertwining the wires following creation of the fractures in the respective coating thereof. 
         [0016]    The method may comprise the further step of intertwining an absorbent wick with the wires. 
         [0017]    In another embodiment, the step of creating fractures in the coating of the electrodes may comprise creating successive troughs at spaced intervals in the coating of the electrodes by laser ablation of the coating, exposing the surface of the respective electrode in the troughs, whereby the transmission of heat along the length of the respective electrode during the creation of a respective trough results in the partial melting of the coating surrounding a previously ablated adjacent trough which recovers the previously exposed surface of the electrode, fractures arising in the remelted coating as it solidifies as a consequence of the previous thermal degradation of the coating. 
         [0018]    The laser ablated troughs may have a length of approximately 25 microns and may be created at a spacing of approximately 2 mm. 
         [0019]    These and other objects, advantages and features of the invention will become apparent upon review of the following specification in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:— 
           [0021]      FIG. 1  shows a stoma pouch leak detection assembly in accordance with an embodiment of the present invention; 
           [0022]      FIG. 2  is an electron microscope image of a portion of the leak detection sensor of the assembly of  FIG. 1 ; and 
           [0023]      FIG. 3  is a higher magnification image of the surface of the sensor showing the nanoscale fractures formed in the surface of the insulating coating of the wires thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    In accordance with an embodiment of the present invention, a stoma pouch leak detection assembly comprises a leak detection sensor  10  comprising two intertwined copper wires  12 , 14 , each wire being coated with a thermopolymer, such as polyvinylacetate or polyester, to define an electrically insulating coating, the coating of the wires being treated by laser ablation to create nanoscale fractures  16  (see  FIG. 3 ) in the insulating coating of the wires  12 , 14  through which fluid may permeate, allowing conduction between the wires and thus detection of leaks. The term “nanoscale fractures” used herein is hereby defined as fractures having a breadth of less than 500 nm, or 100 nm or less. The fractures may have a length of between 500 nm and 5 microns. 
         [0025]    The sensor  10  may also include a porous wick (not shown) intertwined with the wires  12 , 14 . This may increase the sensitivity of the device such that, upon a leak emerging at a discrete point, the fluid is transported along the wire network by capillary action and thus contacts a greater proportion of nanoscale fractures  16 , increasing the sensitivity of the sensor  10 . 
         [0026]    As shown in  FIG. 1 , the sensor  10  is shaped and dimensioned to encircle an opening in a flange  2  of a stoma pouch  4  to sit between the skin  24  and an adhesive layer of the flange  2  when the flange  2  is located over a stoma  20  protruding through the skin  24  from the small intestine  22 , such that fluid leaking behind the adhesive layer may be detected by the sensor  10 , triggering a discrete alarm device  18 . 
         [0027]    A process of laser ablation of the insulating coating covering the intertwined copper wires  12 , 14  of the sensor  10  creates nanoscale fractures in the coating through which fluid may permeate to enable the detection of leaks between the adhesive layer and the skin of the patient without the risk of short circuits between the wires  12 , 14 . 
         [0028]    The leak detection sensor  10  of the present invention can be applied to conventional stoma pouch and thereby alert the wear to the early onset of a potential leak. The leak detection sensor  10  may be connected to an alarm device or detector  18 , which may comprise a conductivity circuit connected to a vibration alarm or other user perceptible alert, such as an audible and/or visually perceptible alarm. The leak detection sensor  10  defines a loop encircling the opening in the flange  2  of the stoma pouch  4  to be located between the skin of the patient and the adhesive layer of the flange  2 . 
         [0029]    Fluid draining into the pouch has a tendency to undermine the adhesive layer of the flange  2  and, if left untreated, can lead to the failure of the flange  2  and the release of bowel or bladder contents. The leak detection sensor  10  may be located on or adjacent the adhesive layer, near the periphery of the flange opening such that, upon contact with fluid leaking past the adhesive layer and coming into contact with the sensor, the fluid, defining an electrolyte, completes the detection circuit and activates the vibration alarm, which may provide a discrete alarm signal to inform the patient that the pouch needs to be changed. 
         [0030]    The sensor wires  12 , 14  define two electrodes, such as in the form of intertwined polyvinylacetate copper wires coated with an electrically insulating polymer coating, wherein the coating has been laser treated to create nanoscale factures  16  in the insulating coating, through which the stoma fluid can permeate and hence enable charge transfer between the two wires and thereby raise the alarm. The bulk of the coating however is complete, preventing circuit shorting and avoiding direct contact of the copper wire with the skin and overcomes issues with biocompatibility and peristomal irritation. Acid from the stoma fluid can corrode uncoated copper wires if placed directly in contact with the skin and thus lead to copper ions being mobilised. The copper ions could lead to skin complications and potential copper poisoning. The provision of the coating on the wires  12 , 14  prevents this. 
         [0031]    The insulating coating may comprise polyvinylacetate or any other suitable thermopolymer, such as polyimide, polyurethane or polyester. 
         [0032]    By using laser ablation to create nanoscale fractures  16  in the coating, such cracks allow the permeation of the stoma fluid through to the underlying copper, hence enabling the charge to transfer between the two electrodes. However, the coating remains intact and thus prevents the copper from coming into direct contact with one another and with the patient&#39;s skin, preventing short circuits. The sensor itself lies between the skin and the flange, and thus the provision of an insulating coating eases issues of biocompatibility. While the stoma fluid can still corrode the copper, the surface area of copper exposed via the nanoscale fractures is minimal and transport through the factures of the mobilised copper ion would be significantly restricted (a diffusion based transport process) and thus would be unlikely to cause any irritation issues. 
         [0033]    In one embodiment the nanoscale fractures  16  in the insulating coating may be created by rastering across the polymer coated copper wire using a 25 W carbon dioxide laser to create 25 micron troughs at intervals of 2 mm along the length of the sensor and which partially exposes the underlying metal. The polyvinylacetate (PVAc) coating is a thermopolymer and the laser processing results in the partial ablation of the polymer. A critical issue however is the thermal conductivity of the underlying copper. After removing one segment the laser may be repositioned to remove another. The transmission of heat along the length of the wire however results in the partial melting of the polymer surrounding the previously ablated segment which recovers the metal with molten polymer. When cool, nanoscale fractures  16  arise as a consequence of the previous thermal degradation. 
         [0034]    The copper wires  12 , 14  may then be intertwined with a polyester thread (to create a wick) and the final assembly may serve as a two electrode sensor  10  which can be placed onto the pouch flange around the periphery of the flange opening. The adhesive coating of the pouch flange enables easy positioning of the sensor  10 . The flange plus sensor can then be placed directly over the stoma onto the skin and the sensor connections attached to the detector  18 . It is envisaged that the wire  12 , 14  may be intertwined prior to the process of laser ablation. 
         [0035]    As fluid is released form the stoma, some will begin to seep under the flange and will gradually undermine the adhesive seal. The detector  18  is activated when the fluid reaches the sensor  10  and effectively completes the circuit. The degree of warning can be controlled by the user through the placement of the sensor  10  with respect to the adhesive layer around the flange opening. The closer to the flange periphery, the shorter the period before warning and flange failure. 
         [0036]      FIG. 2  comprises a scanning electron micrograph highlighting the morphology of the sensor structure. The troughs  30  created by the laser are clearly visible in  FIG. 2  but it is important to note that the ablated portion does not reveal the underlying copper. The transmission of heat along the length of the wire however results in the partial melting of the polymer surrounding the previously ablated segment which recovers the metal with molten polymer. When cool, the nanoscale fractures  16  are created in the coating as a consequence of the previous thermal degradation of the coating. The nanoscale fractures  16  can be seen in greater detail in  FIG. 3 . 
         [0037]    The operation of the sensor  10  in accordance with the present invention has been tested ex vivo with stoma fluid. There is a high electrolyte concentration in the stoma output which yields a positive response at the detector. 
         [0038]    The crux of the issue relates to the design of a conductivity sensor that can be mounted onto a biomedical flange which can provide 360° detection of impending leaks. The electrodes of the sensor can be intertwined into a single loop using low cost material and which enables continuous monitoring without inducing skin irritation. 
         [0039]    The detector assembly itself can be re-usable, with the sensor  10  comprising a low cost disposable component. Crucially, the sensor can integrated within existing pouch systems without alteration. The flexible nature of the sensor  10  allows it to be tailored to a wide range of stoma pouches (independent of shape and size) by the patient themselves. 
         [0040]    The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law including the doctrine of equivalents.