Patent Publication Number: US-10788795-B2

Title: Microfluidic elapsed time indicator

Description:
RELATED APPLICATIONS 
     The present application is a U.S. National Stage application under 35 USC 371 of PCT Application Serial No. PCT/GB2016/053590, filed on 17 Nov. 2016; which claims priority from GB Patent Application No. 1520229.4, filed 17 Nov. 2015, the entirety of both of which are incorporated herein by reference. 
     FIELD 
     A microfluidic elapsed time indicator is described herein for indicating an elapsed time for use, in particular though not exclusively, in a label. 
     BACKGROUND 
     Microfluidic elapsed time indicators are known which rely upon the use of microfluidic methods to control the rate of movement or flow of a fluid. Some known microfluidic elapsed time indicators use coloured dyes. Other known microfluidic elapsed time indicators rely upon a chemical reaction with a fluid to produce a visible colour change. It is also known to incorporate such microfluidic elapsed time indicators into labels for attachment to an item or for attachment to a container for an item. Such known microfluidic elapsed time indicators may be unreliable or unsuitable for manufacture. Such known microfluidic elapsed time indicators may not provide a quantitative indication of the elapsed time or may not be sufficiently accurate for some fields of use. 
     SUMMARY 
     One or more features of any one of the following aspects may apply alone or in any combination in relation to any of the other aspects. For example, apparatus features may be applied as method features and vice versa. 
     According to an aspect or an embodiment of the present invention there is provided an elapsed time indicator, comprising: 
     a reservoir of a fluid; 
     a porous sheet element; and 
     a fluid port located between the reservoir and the porous sheet element, 
     wherein the porous sheet element defines a predetermined area which is separated from the fluid port by a predetermined lateral distance, 
     wherein the fluid is selectively provided from the reservoir to the porous sheet element through the fluid port whereupon the porous sheet element transmits the fluid laterally through the porous sheet element at a predetermined rate away from the fluid port until the fluid impregnates the predetermined area of the porous sheet element so as to cause the predetermined area of the porous sheet element to become transparent or more transparent after expiry of a predetermined time period. 
     The fluid may be selectively provided from the reservoir to the porous sheet element in response to an activation event. 
     The predetermined time period may be measured from the activation event. 
     The porous sheet element may have first, second and third dimensions, wherein the first dimension is less, for example, significantly less than the second and third dimensions and wherein the lateral direction may refer to a direction which is generally perpendicular to the first dimension. For example, the porous sheet element may have a thickness, a length and a width, wherein the thickness is significantly less than the length and the width and wherein the lateral direction refers to a direction which is generally perpendicular to the thickness. 
     The predetermined time period may be associated with an item with which the elapsed time indicator is to be associated or to which the elapsed time indicator is to be attached. 
     The predetermined time period may comprise a lifetime or a shelf-life of the item or a predetermined proportion of a lifetime or a shelf-life of the item. 
     The fluid may be colourless or clear. 
     The fluid may comprise an oil. 
     The fluid may comprise a silicon oil. 
     The fluid may comprise a mixture of oils. 
     The porous sheet element may be opaque or substantially opaque before receipt of the fluid. 
     In use, such an elapsed time indicator may be attached to a coloured object such as a coloured item or a coloured container for an item such that the coloured object becomes visible or more visible through the porous sheet element when the porous sheet element becomes transparent or more transparent. The coloured object may, for example, be green or red. 
     The elapsed time indicator may comprise an indicator element which becomes visible or more visible through the porous sheet element when the porous sheet element becomes transparent or more transparent. 
     Such a microfluidic elapsed time indicators does not rely upon the use of chemical reactions to produce a visible colour change according to the time elapsed from a manual activation event. Such a microfluidic elapsed time indicator is generally reliable and suitable for manufacture. Such a microfluidic elapsed time indicator may be configured to provide a quantitative indication of time elapsed from an activation event and/or of the time remaining until expiry of a predetermined time period measured from the activation event. 
     The indicator element may be coloured. 
     The indicator element may be green or red. 
     The indicator element may be non-porous and/or impervious to the fluid. 
     The indicator element may have a coloured area. 
     The coloured area may become visible or more visible through the predetermined area of the porous sheet element when the predetermined area of the porous sheet element becomes transparent or more transparent. 
     The elapsed time indicator may comprise a base layer or a substrate. The indicator element may be defined on the base layer or the substrate. 
     The elapsed time indicator may comprise a cover layer defining an opaque area and a transparent window area which is generally aligned with the predetermined area of the porous sheet element so that the predetermined area of the porous sheet element is visible through the transparent window area of the cover layer. 
     The cover layer may be plain in colour. For example, the cover layer may be white. 
     The cover layer may have one or more symbols, characters, letters, numbers or graphical representations printed or otherwise defined thereon. 
     The elapsed time indicator may comprise a microfluidic channel which provides a fluid flow path from the reservoir to the fluid port. 
     The elapsed time indicator may comprise a plurality of microfluidic channels, each microfluidic channel providing a fluid flow path from the reservoir to the fluid port. 
     The elapsed time indicator may comprise a fluid management layer which defines the reservoir of the fluid and the or each microfluidic channel. Defining the reservoir and the or each microfluidic channel in a single fluid management layer may simplify manufacturing and, therefore, reduce manufacturing costs. 
     The fluid port may comprise an inlet fluid port. 
     The elapsed time indicator may comprise an input microfluidic channel which provides a fluid flow path from the reservoir to the inlet fluid port. 
     The elapsed time indicator may comprise an outlet fluid port for receiving fluid from the porous sheet element. 
     The inlet fluid port may be defined at, adjacent or near one end of the porous sheet element and the outlet fluid port may be defined at, adjacent or near the other end of the porous sheet element. 
     The elapsed time indicator may comprise an output microfluidic channel which provides a fluid flow path from the outlet fluid port. 
     The fluid management layer may define the reservoir and the input and output microfluidic channels. Defining the reservoir and the input and output microfluidic channels in a single fluid management layer may simplify manufacturing and, therefore, reduce manufacturing costs. 
     The elapsed time indicator may comprise a body which defines a cavity which defines and/or contains the reservoir of the fluid, the or each microfluidic channel, the or each fluid port and the porous sheet element. 
     The body may comprise one or more layers. 
     The reservoir may be defined by a layer of the body. 
     The reservoir may be defined by more than one layer of the body. 
     The elapsed time indicator may comprise one or more intermediate layers located between the fluid management layer and the porous sheet element. Each of the one or more intermediate layers may be transparent. Each of the one or more intermediate layers may comprise a plastics or a polymer material such as polyethylene terephthalate (PET). Each of the one or more intermediate layers may comprise an adhesive. 
     Each of the one or more intermediate layers may define a corresponding first aperture. Each of the first apertures of the one or more intermediate layers may be aligned so as to collectively define the inlet fluid port. Each of the one or more intermediate layers may define a corresponding second aperture. Each of the second apertures of the one or more intermediate layers may be aligned so as to collectively define the outlet fluid port. 
     The elapsed time indicator may comprise one or more further intermediate layers located between the porous sheet element and the cover layer. Each of the one or more further intermediate layers may be transparent. Each of the one or more further intermediate layers may comprise a plastics or a polymer material such as polyethylene terephthalate (PET). Each of the one or more further intermediate layers may comprise an adhesive. 
     The substrate, the fluid management layer, the one or more intermediate layers and the one or more further intermediate layers may be impervious, non-porous and/or impermeable to the fluid. 
     The reservoir and/or the or each microfluidic channel may be configured to control the rate of transfer of the fluid from the reservoir to the fluid port. 
     The reservoir and/or the or each microfluidic channel may be configured to allow the transfer of the fluid from the reservoir to the fluid port in a predetermined transfer time period. 
     The predetermined transfer time period may constitute a relatively small or negligible proportion of the predetermined time period. 
     When the predetermined transfer time period constitutes a negligible proportion of the predetermined time period, the porous sheet element may become transparent or more transparent on a timescale that is essentially determined by the lateral distance of the predetermined area of the porous sheet element from the fluid port and the predetermined rate at which the porous sheet element transmits the fluid laterally through the porous sheet element away from the fluid port to the predetermined area of the porous sheet element. 
     The predetermined transfer time period may constitute less than one tenth of the predetermined time period, less than 1/20 of the predetermined time period, less than 1/50 of the predetermined time period, less than 1/100 of the predetermined time period, less than 1/1000 of the predetermined time period or less than 1/10000 of the predetermined time period. 
     A shape and/or size of the reservoir may be selected to control the rate of transfer of the fluid from the reservoir to the fluid port. 
     The length and/or cross-sectional dimensions of the or each microfluidic channel may be selected to control the rate of transfer of the fluid from the reservoir to the fluid port. 
     The reservoir and/or the or each microfluidic channel may be configured to control the predetermined rate at which the fluid is transmitted laterally through the porous sheet element. 
     A shape and/or size of the reservoir may be selected to control the predetermined rate at which the fluid is transmitted laterally through the porous sheet element. 
     The length and/or cross-sectional dimensions of the or each microfluidic channel may be selected to control the predetermined rate at which the fluid is transmitted laterally through the porous sheet element. 
     The or each microfluidic channel may have at least one cross-sectional dimension of 100-200 μm or less. 
     The or each microfluidic channel may have a width of 2 mm or less and a height of 10-100 μm or less. 
     The or each microfluidic channel may be straight. 
     The or each microfluidic channel may define at least one straight section. 
     The or each microfluidic channel may define at least one bend. 
     The elapsed time indicator may comprise a deformable membrane which defines the reservoir of the fluid. 
     The cavity may be initially sealed but may be configured to be selectively exposed to an environment external to the elapsed time indicator. 
     The body may define an indicator vent extending from the cavity. The indicator vent may extend from the cavity from a position at or adjacent to the porous sheet element. The indicator vent may extend from an outlet of the output microfluidic channel. 
     The body may define a reservoir vent extending from the cavity. The reservoir vent may extend from the cavity from a position at or adjacent to the reservoir. 
     The reservoir vent may extend from the cavity from a position at, adjacent or near to one end of the cavity and the indicator vent may extend from the cavity from a position at, adjacent or near to the other end of the cavity. 
     The activation event may cause at least one of the indicator vent and the reservoir vent to be unsealed. 
     The indicator vent may be initially sealed but may be configured to be selectively unsealed to provide a fluid flow path from the cavity to the environment external to the elapsed time indicator through the indicator vent. 
     The reservoir vent may be initially sealed but may be configured to be selectively unsealed to provide a fluid flow path from the cavity to the environment external to the elapsed time indicator through the reservoir vent. 
     The indicator vent and the reservoir vent may be configured to be selectively unsealed at the same time. 
     The indicator vent and the reservoir vent may be configured to be selectively unsealed at different times. 
     The indicator vent and the reservoir vent may be configured to be selectively unsealed in response to the activation event. 
     One of the indicator vent and the reservoir vent may be configured to be selectively unsealed in response to the activation event. 
     The elapsed time indicator may comprise a seal member detachably attached to the body so as to initially seal at least one of the indicator vent and the reservoir vent. 
     The indicator vent may be unsealed by detaching the seal member from the body. 
     The body of the elapsed time indicator may be attachable to a first part of a container. The seal member may be attachable to a second part of the container such that opening the container for the first time by relative movement of the first and second parts of the container causes the seal member to be detached from the body and at least one of the indicator vent and the reservoir vents to be unsealed. 
     The elapsed time indicator may comprise a seal member which is detachably attached to the body so as to initially seal one of the indicator vent and the reservoir vent. The indicator vent and the reservoir vent may be connected by an air channel. The air channel may be defined separately from the microfluidic channel such that detaching the seal member from the body unseals both the indicator vent and the reservoir vent. 
     The air channel may be defined by the body. 
     One of the indicator vent and the reservoir vent may be permanently open and the other of the indicator vent and the reservoir vent may be configured to be selectively unsealed to provide a fluid flow path from the cavity to the environment external to the elapsed time indicator through the other of the indicator vent and the reservoir vent. 
     The elapsed time indicator may comprise an indicator vent seal member detachably attached to the body so as to initially seal the indicator vent. 
     The indicator vent may be unsealed by detaching the indicator vent seal member from the body. 
     The elapsed time indicator may comprise a reservoir vent seal member detachably attached to the body so as to initially seal the reservoir vent. 
     The reservoir vent may be unsealed by detaching the reservoir vent seal member from the body. 
     Air in the cavity on a first side of the fluid in the fluid reservoir may be at a first pressure prior to the activation event. For example, air in the cavity above the fluid in the fluid reservoir may be at the first pressure prior to the activation event. Air in the reservoir vent may be at the first pressure prior to the activation event. Air in the cavity on a second side of the fluid in the fluid reservoir may be at a second pressure prior to the activation event. For example, air in the cavity below the fluid in the fluid reservoir may be at the second pressure prior to the activation event. Air in the input microfluidic channel, the inlet fluid port, around the porous sheet element, in the outlet fluid port and in the outlet microfluidic channel may be at the second pressure prior to the activation event. The first pressure may be less than the second pressure. The first pressure may be less than atmospheric pressure. The second pressure may be greater than atmospheric pressure. The presence of air in the cavity on a first side side of the fluid in the fluid reservoir having a reduced pressure prior to the activation event and the presence of air in the cavity on a second side of the fluid in the fluid reservoir opposite the first side prior to the activation event may serve to retain the fluid in the fluid reservoir prior to the activation event. 
     The porous sheet element may comprise a plurality of predetermined areas, each predetermined area being separated from the fluid port by a corresponding predetermined lateral distance such that one of the predetermined areas of the porous sheet element becomes transparent or more transparent after expiry of the predetermined time period and each of the other predetermined areas become transparent or more transparent after expiry of a corresponding intermediate predetermined time period. 
     Each of the intermediate predetermined time periods may be a predetermined proportion of the predetermined time period. 
     Each of the intermediate predetermined time periods may be measured from the time of the activation event. 
     Two or more of the coloured areas may have the same colour. 
     Two or more of the coloured areas may have a different colour. 
     One or more of the coloured areas may be green. 
     One or more of the coloured areas may be red. 
     The cover layer may define an opaque area and one transparent window area for each predetermined area of the porous sheet element. Each transparent window area of the cover layer may be generally aligned with a corresponding one of the predetermined areas of the porous sheet element so that the corresponding predetermined area of the porous sheet element is visible through the corresponding transparent window area of the cover layer. 
     The predetermined rate of transmission of the fluid in the porous sheet element may depend on at least one property of the fluid. 
     The predetermined rate of transmission of the fluid in the porous sheet element may depend on the composition and/or viscosity of the fluid. 
     The predetermined rate of transmission of the fluid in the porous sheet element may depend on at least one property of the porous sheet element. 
     The predetermined rate of transmission of the fluid in the porous sheet element may depend on the composition and/or porosity of the porous sheet element. 
     The porous sheet element may comprise fibres. 
     The porous sheet element may comprise cellulose fibres. 
     The porous sheet element may comprise paper. 
     The porous sheet element may comprise filter paper. 
     The elapsed time indicator may be flexible. 
     The elapsed time indicator may be configured for use in a predetermined orientation. For example, the elapsed time indicator may be configured for use in a predetermined orientation in which the reservoir is located above the porous sheet element. The elapsed time indicator may comprise markings such as “this way up” arrows or the like so as to indicate a required orientation of the elapsed time indicator. For example, the cover layer may have markings such as “this way up” arrows or the like so as to indicate a required orientation of the elapsed time indicator. Orienting the elapsed time indicator so that the reservoir is located above the porous sheet element may cause the fluid to flow from the reservoir towards the porous sheet element under the action of gravity/hydrostatic pressure in combination with capillary action. 
     According to an aspect or an embodiment of the present invention there is provided a label comprising an elapsed time indicator which includes: 
     a reservoir of a fluid; 
     a porous sheet element; and 
     a fluid port located between the reservoir and the porous sheet element, 
     wherein the porous sheet element defines a predetermined area which is separated from the fluid port by a predetermined lateral distance, 
     wherein the fluid is selectively provided from the reservoir to the porous sheet element through the fluid port whereupon the porous sheet element transmits the fluid laterally through the porous sheet element at a predetermined rate away from the fluid port until the fluid impregnates the predetermined area of the porous sheet element so as to cause the predetermined area of the porous sheet element to become transparent or more transparent after expiry of a predetermined time period. 
     The fluid may be selectively provided from the reservoir to the porous sheet element in response to an activation event. 
     The predetermined time period may be measured from a time of the activation event. 
     According to an aspect or an embodiment of the present invention there is provided a container comprising an elapsed time indicator which includes: 
     a reservoir of a fluid; 
     a porous sheet element; and 
     a fluid port located between the reservoir and the porous sheet element, 
     wherein the porous sheet element defines a predetermined area which is separated from the fluid port by a predetermined lateral distance, 
     wherein the fluid is selectively provided from the reservoir to the porous sheet element through the fluid port whereupon the porous sheet element transmits the fluid laterally through the porous sheet element at a predetermined rate away from the fluid port until the fluid impregnates the predetermined area of the porous sheet element so as to cause the predetermined area of the porous sheet element to become transparent or more transparent after expiry of a predetermined time period. 
     The fluid may be selectively provided from the reservoir to the porous sheet element in response to an activation event. 
     The predetermined time period may be measured from a time of the activation event. 
     According to an aspect or an embodiment of the present invention there is provided a method for indicating an elapsed time, comprising: 
     providing a porous sheet element; 
     providing a fluid port; 
     defining a predetermined area of the porous sheet element which is separated from the fluid port by a predetermined lateral distance; and 
     selectively providing a fluid to the porous sheet element through the fluid port whereupon the porous sheet element transmits the fluid laterally through the porous sheet element at a predetermined rate away from the fluid port until the fluid impregnates the predetermined area of the porous sheet element so as to cause the predetermined area of the porous sheet element to become transparent or more transparent after expiry of a predetermined time period. 
     The fluid may be selectively provided to the porous sheet element from a reservoir of the fluid. 
     The fluid may be selectively provided from the reservoir to the porous sheet element in response to an activation event. 
     The predetermined time period may be measured from a time of the activation event. 
     The method may comprise orienting the reservoir of the fluid above the porous sheet element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An elapsed time indicator is described herein by way of non-limiting example only with reference to the following drawings of which: 
         FIG. 1  is a schematic perspective view of a microfluidic elapsed time indicator before activation; 
         FIG. 2( a )  is a schematic plan view of the microfluidic elapsed time indicator of  FIG. 1  immediately after activation; 
         FIG. 2( b )  is a schematic cross-section on AA of the microfluidic elapsed time indicator of  FIG. 2( a )  immediately after activation; 
         FIG. 3( a )  is a schematic plan view of the microfluidic elapsed time indicator of  FIG. 1  immediately after activation; 
         FIG. 3( b )  is a schematic plan view of the microfluidic elapsed time indicator of  FIG. 1  after expiry of a first time period after activation; 
         FIG. 3( c )  is a schematic plan view of the microfluidic elapsed time indicator of  FIG. 1  after expiry of a second time period after activation; 
         FIG. 3( d )  is a schematic plan view of the microfluidic elapsed time indicator of  FIG. 1  after expiry of a final time period after activation; 
         FIG. 4( a )  is a schematic illustration of the microfluidic elapsed time indicator of  FIG. 1  attached to a two-part container before opening of the container for the first time so as to activate the elapsed time indicator; 
         FIG. 4( b )  is a schematic illustration of the microfluidic elapsed time indicator of  FIG. 1  immediately after opening the two-part container for the first time so as to activate the elapsed time indicator; 
         FIG. 5( a )  is a schematic plan view of a first alternative microfluidic elapsed time indicator before activation; 
         FIG. 5( b )  is a schematic plan view of a second alternative microfluidic elapsed time indicator before activation; 
         FIG. 5( c )  is a schematic plan view of a third alternative microfluidic elapsed time indicator before activation; 
         FIG. 6( a )  is a schematic plan view of a fourth alternative microfluidic elapsed time indicator immediately after activation; 
         FIG. 6( b )  is a schematic plan view of the fourth alternative microfluidic elapsed time indicator of  FIG. 6( a )  after expiry of a first time period after activation; 
         FIG. 6( c )  is a schematic plan view of the fourth alternative microfluidic elapsed time indicator of  FIG. 6( a )  after expiry of a final time period after activation; 
         FIG. 7( a )  is a schematic plan view of a fifth alternative microfluidic elapsed time indicator immediately after activation; 
         FIG. 7( b )  is a schematic plan view of the fifth alternative microfluidic elapsed time indicator of  FIG. 7( a )  after expiry of a first time period after activation; 
         FIG. 7( c )  is a schematic plan view of the fifth alternative microfluidic elapsed time indicator of  FIG. 7( a )  after expiry of a final time period after activation; 
         FIG. 8( a )  is an exploded assembly view of a sixth alternative microfluidic elapsed time indicator; 
         FIG. 8( b )  shows the exploded assembly view of the sixth alternative microfluidic elapsed time indicator of  FIG. 8( a )  illustrating a fluid flow path; 
         FIG. 9( a )  is a schematic illustration of the sixth alternative microfluidic elapsed time indicator of  FIGS. 8( a ) and 8( b )  attached to a two-part container before opening of the container for the first time so as to activate the elapsed time indicator; and 
         FIG. 9( b )  is a schematic illustration of the sixth alternative microfluidic elapsed time indicator of  FIGS. 8( a ) and 8( b )  immediately after opening the two-part container for the first time so as to activate the elapsed time indicator. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring initially to  FIG. 1  there is shown a microfluidic elapsed time indicator generally designated  2  including a body  4  and a seal member  6  which is detachably attached to an upper surface  8  of the body  4 . The seal member  6  defines a tab portion  6   a  which is distal from the body  4 . The body  4  includes an adhesive layer (not shown explicitly in  FIG. 1 ) on its lower surface  12  for attachment of the body  4  to an object (not shown) such as a perishable item or a container for a perishable item. The body  4  is flexible to allow the body  4  to conform to the shape of a variety of different objects. The microfluidic elapsed time indicator  2  may be, or may form part of, a label for attachment to the object. As such, one of ordinary skill in the art will understand that the microfluidic elapsed time indicator  2  is illustrated schematically in  FIG. 1  and that the relative proportions of the microfluidic elapsed time indicator  2  may be significantly different to those represented in  FIG. 1 . In particular, the thickness of the microfluidic elapsed time indicator  2  (i.e. the height or dimension of the microfluidic elapsed time indicator  2  in the vertical direction in  FIG. 1 ) has been exaggerated in the interests of clarity. 
     In use, the tab portion  6   a  of the seal member  6  may be pulled until the seal member  6  becomes detached from the body  4 . As will be described in more detail below, detachment of the seal member  6  from the body  4  results in activation of the microfluidic elapsed time indicator  2  which subsequently provides a visual indication of the amount of time elapsed from activation. 
     The microfluidic elapsed time indicator  2  is shown in more detail in  FIGS. 2( a ) and 2( b )  immediately after detachment of the seal member  6  from the body  4 . The microfluidic elapsed time indicator  2  includes a reservoir  20  of a fluid  22 , a display arrangement  30  and a microfluidic channel  40  extending from the reservoir  20  to the display arrangement  30 . As shown in  FIG. 2( b ) , the body  4  includes several different layers which together define the reservoir  20 , the microfluidic channel  40  and the display arrangement  30 . Unless otherwise stated below, one of ordinary skill in the art will understand that the various different layers of the body  4  are impervious, non-porous and/or impermeable to the fluid  22 . 
     The body  4  defines an opening in the form of a reservoir vent  24  which extends from the reservoir  20  to the upper surface  8  the body  4 . Prior to detachment of the seal member  6  from the body  4 , the reservoir vent  24  is sealed by the seal member  6 . Detachment of the seal member  6  from the body  4  unseals or opens the reservoir vent  24  so that the reservoir vent  24  provides a flow path for air from the reservoir  20  to an environment generally designated  26  external to the body  4  as shown in  FIG. 2( b ) . The body  4  defines a reservoir outlet fluid port  28 . The fluid  22  may be a silicon oil having a viscosity in the range of 10 to 5,000 cP. 
     The display arrangement  30  includes a porous sheet element in the form of a paper element  50  which is configured to be initially opaque or generally opaque and to become transparent or more transparent upon impregnation by the fluid  22 . The display arrangement  30  further includes an inlet fluid port  52  in fluid flow communication with the paper element  50 . The microfluidic channel  40  provides a fluid flow path from the reservoir outlet fluid port  28  to the inlet fluid port  52  of the display arrangement  30 . The display arrangement  30  includes a plurality of coloured indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e  and  54   f  defined on an indicator element or layer  56  located below the paper element  50 . Although not shown explicitly in  FIG. 2( a )  and  2 ( b ), the indicator areas  54   a ,  54   b ,  54   c ,  54   d , and  54   e  are green and the indicator area  54   f  is red. 
     The body  4  includes an upper cover layer  60  which defines a plurality of transparent windows  60   a ,  60   b ,  60   c ,  60   d ,  60   e  and  60   f , each window  60   a ,  60   b ,  60   c ,  60   d ,  60   e  and  60   f  being aligned generally above a corresponding one of the coloured indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e  and  54   f  respectively. It should also be understood that the intervening layers of the body  4  located between the paper element  50  and upper cover layer  60  are generally transparent. 
     The body  4  further defines an opening in the form of an indicator vent  62  which extends from the paper element  50  to the upper surface  8  the body  4 . Prior to detachment of the seal member  6  from the body  4 , the indicator vent  62  is sealed by the seal member  6 . Detachment of the seal member  6  from the body  4  unseals or opens the indicator vent  62  so that the indicator vent  62  provides a flow path for air from the paper element  50  to the external environment  26 . 
     It should be understood that the body  4  defines a cavity generally designated  70  which includes the fluid reservoir  20 , the reservoir outlet fluid port  28 , the microfluidic channel  40 , the inlet fluid port  52  of the display arrangement  30  and the paper element  50 . Prior to detachment of the seal member  6  from the body  4 , the cavity  70  is sealed from the external environment  26 . 
     Detachment of the seal member  6  from the body  4  activates the elapsed time indicator  2  by unsealing the reservoir vent  24  thereby exposing the end of the cavity  70  adjacent to the reservoir  20  to the pressure of the external environment  26  and unsealing the indicator vent  62  thereby exposing the end of the cavity  70  adjacent to the paper element  50  to the pressure of the external environment  26 . Following activation by detachment of the seal member  6  from the body  4 , capillary action causes the fluid  22  to move along the microfluidic channel  40  from the reservoir outlet fluid port  28  to the inlet fluid port  52  of the display arrangement  30  on a relatively short timescale which may range from several seconds to several minutes. Air flows in through the reservoir vent  24  to replace the fluid  22  lost from the reservoir  20  and air flows out of the indicator vent  62  to allow the fluid  22  to move towards the paper element  50 . 
     On contacting the paper element  50 , capillary action causes the fluid  22  to move in a lateral direction through the paper element  50  at a predetermined rate which is dependent primarily upon the composition of the paper element  50  and the viscosity of the fluid  22 . As the fluid  22  impregnates the paper element  50 , the paper element  50  becomes transparent or becomes more transparent so that the coloured indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  become visible or become more visible sequentially through the transparent windows  60   a ,  60   b ,  60   c ,  60   d ,  60   e  and  60   f  at predetermined times after activation. 
     As shown in  FIGS. 3( a )-3( d ) , the appearance of the coloured indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  provides a visual indication of the time elapsed from activation. In the interests of clarity,  FIGS. 3( a )-3( d )  omit many of the details of the elapsed time indicator  2 . As shown in  FIG. 3( a )  immediately after activation, none of the coloured indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  are visible through the windows  60   a ,  60   b ,  60   c ,  60   d ,  60   e  and  60   f . As shown in  FIG. 3( a )  following expiry of a first intermediate predetermined time period after activation, the first green indicator area  54   a  closest to the inlet fluid port  52  of the display arrangement  30  becomes visible or becomes distinctly more visible through the window  60   a . Similarly, as shown in  FIG. 3( b ) , following expiry of a second intermediate predetermined time period after activation, the second green indicator area  54   b  adjacent to the first green indicator area  54   a  also becomes visible or becomes distinctly more visible through the window  60   b . As shown in  FIG. 3( d )  following expiry of a final predetermined time period after activation, the red indicator area  54   f  furthest from the inlet fluid port  52  of the display arrangement  30  also becomes visible or becomes distinctly more visible through the window  60   f . The final predetermined time period may be selected according to a lifetime or a shelf-life of an item to which the elapsed time indicator  2  is to be attached. The intermediate predetermined time periods, including the first intermediate and second intermediate predetermined time periods, may comprise a predetermined proportion of the final predetermined time period. The rate at which the fluid moves laterally though the paper element  50  may be selected by selecting the porosity of the paper element  50  and/or the viscosity of the fluid  22 . The lateral positions of the indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  may also be selected so that when the elapsed time indicator  2  is activated at the beginning of the lifetime or shelf-life of the item concerned, the sequential appearance of the green indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e  provides a progressive indication of the time remaining before expiry of the lifetime or shelf-life of the item, whereas the appearance of the red indicator area  54   f  indicates that the lifetime or shelf-life of the item has actually expired. 
     It should be understood that the reservoir  20  and the microfluidic channel  40  are configured to control the rate of transfer of the fluid from the reservoir  20  to the inlet fluid port  52 . Specifically, the reservoir  20  and the microfluidic channel  40  are configured to allow the transfer of the fluid  22  from the reservoir  20  to the inlet fluid port  52  in a predetermined transfer time period which constitutes a relatively small or negligible proportion of the final predetermined time period such that the timing of the appearance of the indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  is essentially determined by the lateral positions of the indicator areas  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  relative to the fluid port and the predetermined rate at which the paper element  50  transmits the fluid laterally through the paper element  50  away from the inlet fluid port  52 . The predetermined transfer time period may, for example, be of the order of minutes and the final predetermined time period may be of the order of several hours or more. The predetermined transfer time period may constitute less than one tenth of the final predetermined time period, less than 1/20 of the final predetermined time period, less than 1/50 of the final predetermined time period, less than 1/100 of the final predetermined time period, less than 1/1000 of the final predetermined time period or less than 1/10000 of the final predetermined time period. Moreover, it should be understood that the configuration of the reservoir  20  and the microfluidic channel  40  also affect the predetermined rate at which the fluid is transmitted laterally through the porous sheet element. Consequently, the shape and/or size of the reservoir  20  and the length and/or cross-sectional dimensions of the microfluidic channel  40  are also selected according to the final predetermined time period. 
       FIGS. 4( a ) and 4( b )  illustrate the use of the microfluidic elapsed time indicator  2  for use in monitoring the time elapsed from opening a container  80  for the first time. As shown in  FIGS. 4( a ) and 4( b ) , the container  80  includes two parts, namely a container body  80   a  and a container lid  80   b . The lower surface  12  of the body  4  includes an adhesive layer for attachment of the lower surface  12  of the body  4  to the container body  80   a . Similarly, the tab  6   a  of the seal member  6  includes an adhesive layer on a lower surface of the tab  6   a  for attachment of the lower surface of the tab  6   a  to the container lid  80   b . The microfluidic elapsed time indicator  2  may be configured as, or may form part of, a label for attachment to the container  80 . On opening the container  80  for the first time and separating the container lid  80   b  from the container body  80   a  for the first time the seal member  6  remains attached to the container lid  80   b  but is detached from the body  4  which remains attached to the container body  80   a  as shown in  FIG. 4( b )  unsealing the reservoir and indicator vents  24 ,  62  and thereby activating the microfluidic elapsed time indicator  2  as previously described above. As such, the microfluidic elapsed time indicator  2  may provide a progressive indication of the time elapsed from opening the container  80  for the first time and/or a progressive indication of the time remaining until expiry of the contents of the container  80 . 
     Alternatively, the container body  80   a  and the container lid  80   b  may be unitary but may still be movable relative to one another so as to detach the seal member  6  from the body  4  on opening the container  80  for the first time. For example, the container body  80   a  and the container lid  80   b  may be unitary but may be pivotable relative to one another so as to detach the seal member  6  from the body  4  on opening the container  80  for the first time. 
     Alternatively, the body  4  could be attached to the container lid  80   b  and the tab  6   a  could be attached to the container body  80   a.    
     Referring to  FIG. 5( a ) , there is shown an alternative microfluidic elapsed time indicator generally designated  102  comprising the body  4  and a modified seal member  106  which is detachably attached to the upper surface  8  of the body  4 . The microfluidic elapsed time indicator  102  of  FIG. 5( a )  is identical to the microfluidic elapsed time indicator  2  of  FIG. 1  in all respects except for the modified seal member  106 . Like the seal member  6 , the modified seal member  106  defines a tab portion  106   a  which is distal from the body  4 . However, unlike the seal member  6 , the modified seal member  106  defines a transparent window or a window recess  106   b  such that the windows  60   a ,  60   b ,  60   c ,  60   d ,  60   e ,  60   f  of the upper cover layer  60  of the body  4  are clearly visible before the seal member  6  is detached from the body  4 . The operation of the microfluidic elapsed time indicator  102  is identical to the operation of the microfluidic elapsed time indicator  2 . 
     Referring to  FIG. 5( b ) , there is shown a further microfluidic elapsed time indicator generally designated  202  comprising a body  204  and a seal member  206  which is detachably attached to an upper surface  208  of the body  204 . The further microfluidic elapsed time indicator  202  of  FIG. 5( b )  is generally similar to the microfluidic elapsed time indicator  2  of  FIG. 1  in many respects. However, unlike the body  4 , the body  204  does not define the fluid reservoir. Instead, the body  204  defines a reservoir chamber  229  which contains a deformable reservoir membrane  227  which contains the fluid  222 . The deformable reservoir membrane  227  defines a reservoir outlet fluid port  228 . The reservoir chamber  229  defines a reservoir vent  224  which is permanently open to an external environment  226 . 
     Like the body  4 , the body  204  defines a display arrangement  230  including windows  260   a ,  260   b ,  260   c ,  260   d ,  260   e  and  260   f . Like the body  4 , the body  204  defines a microfluidic channel  240  which provides a fluid flow path between the reservoir  220  and the display arrangement  230 . Like the body  4 , the body  204  defines an indicator vent  262  which selectively provides a path for air flow to the external environment  226 . Like the seal member  6 , the seal member  206  defines a tab portion  206   a  which is distal from the body  204 . However, unlike the seal member  6 , the seal member  206  only seals the indicator vent  262  and does not seal the reservoir vent  224 . The fluid  222  is retained in the reservoir  220  until the tab portion  206   a  of the seal member  206  is pulled and the indicator vent  262  is unsealed whereupon capillary action causes the fluid  222  to travel along the microfluidic channel  240  to the display arrangement  230  in a manner which is generally similar to that already described above in relation to the microfluidic elapsed time indicator  2 . An indication of elapsed time from activation is then provided via the windows  260   a ,  260   b ,  260   c ,  260   d ,  260   e  and  260   f  in a similar manner to that described above in relation to the microfluidic elapsed time indicator  2 . 
     Referring to  FIG. 5( c ) , there is shown a yet further microfluidic elapsed time indicator generally designated  302  comprising a body  304  and a seal member  306  which is detachably attached to an upper surface  308  of the body  304 . The microfluidic elapsed time indicator  302  of  FIG. 5( c )  is generally similar to the microfluidic elapsed time indicator  2  of  FIG. 1  in many respects. Like the body  4 , the body  304  defines a reservoir  320  of fluid  322  and a display arrangement  330  including windows  360   a ,  360   b ,  360   c ,  360   d ,  360   e  and  360   f . Like the body  4 , the body  304  defines a microfluidic channel  340  which provides a fluid flow path between the reservoir  320  and the display arrangement  330 . Like the body  4 , the body  304  defines an indicator vent  362  which selectively provides a path for air flow to the external environment  326 . However, unlike the body  4 , the body  304  defines an air flow path or channel  325  which extends internally of the body  4  from the reservoir  320  to an indicator vent  362 . Like the seal member  6 , the seal member  306  defines a tab portion  306   a  which is distal from the body  304 . The seal member  306  seals the indicator vent  362 . The fluid  322  is retained in the reservoir  320  until the tab portion  306   a  of the seal member  306  is pulled and the indicator vent  362  is unsealed whereupon capillary action causes the fluid  322  to travel along the microfluidic channel  340  to the display arrangement  330  in a manner which is generally similar to that already described above in relation to the microfluidic elapsed time indicator  2 . The air flow path or channel  325  provides a path for air to flow from the external environment  326  to the reservoir  320  to replace fluid  322  lost from the reservoir  320 . An indication of elapsed time from activation is then provided via windows  360   a ,  360   b ,  360   c ,  360   d ,  360   e  and  360   f  in a similar manner to that described above in relation to the microfluidic elapsed time indicator  2 . 
       FIGS. 6( a ) to 6( c )  illustrate the operation of an alternative microfluidic elapsed time indicator  402  having an alternative display arrangement  430  which includes a first larger transparent window area  460   a  and a second smaller transparent window area  460   b  defined in an upper cover layer  460 . The microfluidic elapsed time indicator  402  further includes a first larger green indicator area  454   a  which is generally aligned with the larger transparent window area  460   a  and a second smaller red indicator area  454   b  which is generally aligned with the smaller transparent window area  460   b . The microfluidic elapsed time indicator  402  includes a porous sheet element in the form of a paper element  450  located between the cover layer  460  and the indicator areas  454   a ,  454   b . Immediately after activation as shown in  FIG. 6( a ) , neither of the indicator areas  454   a ,  454   b  is visible. As time elapses following activation, a fluid progressively impregnates the paper element  450  so as to progressively reveal the first indicator area  454   a  as shown in  FIG. 6( b ) . After expiry of a first predetermined time period following activation, the fluid impregnates the paper element  450  so as to reveal the whole of first indicator area  454   a . After expiry of a second and final predetermined time period following activation, the fluid impregnates the paper element  450  so as to also reveal the second indicator area  454   b  as shown in  FIG. 6( c ) . 
       FIGS. 7( a ) to 7( c )  illustrate the operation of a further alternative microfluidic elapsed time indicator  502  having an alternative display arrangement  530  which includes a single elongate transparent window area  560   a  defined in an upper cover layer  560 . The microfluidic elapsed time indicator  502  further includes a single elongate green indicator area  554   a  which is generally aligned with the transparent window area  560   a . The microfluidic elapsed time indicator  502  includes a porous sheet element in the form of a paper element  550  located between the cover layer  560  and the indicator area  554   a . Immediately after activation as shown in  FIG. 7( a ) , the indicator area  554   a  is not visible or is not clearly visible. As time elapses following activation, a fluid progressively impregnates the paper element  550  so as to progressively reveal the indicator area  554   a  as shown in  FIG. 7( b ) . After expiry of a predetermined time period following activation, the fluid impregnates the paper element  550  so as to reveal the whole of the indicator area  554   a  as shown in  FIG. 7( c ) . 
     A further alternative microfluidic elapsed time indicator  602  is shown in  FIG. 8( a )  which includes a base layer or substrate  604   a , first and second coloured indicator areas  654   a  and  654   b  respectively defined on the substrate  604   a , an upper cover layer  660  defining a plurality of transparent windows  660   a ,  660   b ,  660   c ,  660   d  and  660   e , and a porous sheet element  650  located between the coloured indicator areas  654   a ,  654   b  and the cover layer  660 . The first coloured indicator area  654   a  is green and the second coloured indicator area  654   b  is red. The transparent windows  660   a ,  660   b ,  660   c ,  660   d  are aligned above the first coloured indicator area  654   a  and the transparent window  660   e  is aligned above the second coloured indicator area  654   b . The transparent windows  660   a  to  660   e , the coloured indicator areas  654   a ,  654   b  and the porous sheet element  650  collectively define a display arrangement  630 . The elapsed time indicator  602  includes an intermediate polyethylene terephthalate (PET) layer  604   e  defining an aperture  650   a  which accommodates the porous sheet element  650 . 
     Located between the porous sheet element  650  and the coloured indicator areas  654   a  and  654   b  is a PET fluid management layer  604   b  which defines a fluid reservoir  620 , an input microfluidic channel  640   a  extending from the fluid reservoir  620  to an outlet  621   a  adjacent to the first coloured indicator area  654   a  and an output microfluidic channel  640   b  extending from an inlet  621   b  adjacent to the second coloured indicator area  654   b  to an outlet  621   c  adjacent to the fluid reservoir  620 . 
     The elapsed time indicator  602  includes one or more intermediate transparent layers  604   c , and  604   d  between the fluid management layer  604   b  and the porous sheet element  650 . Each of the intermediate transparent layers  604   c  and  604   d  may include transparent adhesive and/or transparent PET. Similarly, the elapsed time indicator  602  includes one or more further intermediate transparent layers  604   f  and  604   g  between the porous sheet element  650  and the cover layer  660 . Each of the further intermediate transparent layers  604   f  and  604   g  may include transparent adhesive and/or transparent PET. The substrate  604   a , the fluid management layer  604   b , the intermediate layers  604   c - 604   g  and the cover layer  660  collectively define a body  604  of the elapsed time indicator  602 . Unless otherwise stated below, one of ordinary skill in the art will understand that the various different layers  604   a - 604   g  are impervious, non-porous and/or impermeable to the fluid  622 . 
     As shown in  FIG. 8( b ) , each of the intermediate transparent layers  604   c  and  604   d  defines a corresponding aperture  652   a  to permit fluid to flow from the outlet  621   a  of the input microfluidic channel  640   a  to the porous sheet element  650 . The apertures  652   a  collectively define an inlet fluid port  652  at or near one end of the porous sheet element  650 . Similarly, each of the intermediate transparent layers  604   c  and  604   d  defines a corresponding aperture  653   a  to permit fluid to flow from the porous sheet element  650  to the inlet  621   b  of the output microfluidic channel  640   b . The apertures  653   a  collectively define an outlet fluid port  653  at or near the other end of the porous sheet element  650 . 
     Each of the intermediate layers  604   c ,  604   d ,  604   e ,  604   f ,  604   g  between the fluid management layer  604   b  and the cover layer  660  defines a corresponding aperture  624   a . The apertures  624   a  collectively define a reservoir vent  624  which extends from the fluid reservoir  620  to the cover layer  660 . Similarly, each of the intermediate layers  604   c ,  604   d ,  604   e ,  604   f ,  604   g  between the fluid management layer  604   b  and the cover layer  660  defines a corresponding aperture  662   a . The apertures  662   a  collectively define an indicator vent  662  which extends from the outlet  621   c  of the output microfluidic channel  640   b  to the cover layer  660 . 
     It should be understood that the reservoir vent  624 , the fluid reservoir  620 , the input microfluidic channel  640   a , the inlet fluid port  652 , the aperture  650   a  defined by the intermediate layer  604   e , the intermediate layer  604   f , the outlet fluid port  653 , the output microfluidic channel  640   b  and the indicator vent  662  collectively define a cavity  670 . 
     The reservoir  620  is filled with a fluid in the form of silicon oil  622 . 
     The elapsed time indicator  602  further includes a seal member  606  which is initially attached to the cover member  660  so as to seal the reservoir vent  624  and the indicator vent  662  and, therefore, also the cavity  670 , from an environment external to the elapsed time indicator  602 . 
     During manufacture of the elapsed time indicator  602  before the seal member  606  is attached to the cover member  660 , the silicon oil  622  is injected into the reservoir  620  through the reservoir vent  624 . The seal member  606  is then attached to the cover member  660  so as to seal the reservoir vent  624  and the indicator vent  662  and, therefore, also the cavity  670 . After sealing of the cavity  670 , the silicon oil  622  initially moves along the input microfluidic channel  640   b  under capillary action causing a reduction in pressure of the air in the cavity  670  between the reservoir vent  624  and silicon oil  622  and an increase in pressure of the air in the cavity  670  between the silicon oil  622  and the indicator vent  662  until the forces acting on the silicon oil  622  due to capillary action are balanced by the forces acting on the silicon oil  622  due to the differential in the air pressures in the cavity  670  on opposite sides of the silicon oil  622 . One of ordinary skill in the art will understand that this balance of forces may also be affected by the action of gravity/hydrostatic pressure acting on the silicon oil  622  according to the orientation of the elapsed time indicator  602 . 
     The cavity  670  and the silicon oil  622  are configured such that the balance between the forces acting on the silicon oil  622  prevents the silicon oil  622  from reaching the porous sheet element  650  prior to the activation event, regardless of the orientation of the elapsed time indicator  602 . For example, the cavity  670  and the silicon oil  622  may be configured such that the balance between the forces acting on the silicon oil  622  substantially contains the silicon oil  622  within the fluid reservoir  620  prior to the activation event with little or none of the silicon oil  622  being contained within the input microfluidic channel  640   b , regardless of the orientation of the elapsed time indicator  602 . 
     In use, as shown in  FIG. 9( a ) , the body  604  of the elapsed time indicator  602  is initially attached to a body  80   a  of a container  80  and the seal member  606  is attached to a lid  80   b  of the container  80   b . The initial orientation of the elapsed time indicator  602  is such that the reservoir  620  is located generally vertically above the display arrangement  630  which includes the porous sheet element  650 . The cover layer  660  may have markings such as “this way up” arrows or the like so as to indicate a required orientation of the elapsed time indicator  602 . On removing the lid  80   b  of the container  80  from the body  80   a  of the container  80  for the first time, the seal member  606  becomes detached from the body  604  thereby exposing the reservoir vent  624  and the indicator vent  662  to the atmosphere external to the elapsed time indicator  602  as shown in  FIG. 9( b ) . On exposure of the reservoir vent  624  and the indicator vent  662  to the atmosphere, movement of the silicon oil  622  along the input microfluidic channel  640   b  is no longer opposed by the pressure differential on opposite sides of the silicon oil  622  and the silicon oil  622  is free to move by virtue of capillary action possibly in combination with gravity/hydrostatic pressure from the reservoir  620  through the input microfluidic channel  640   a  and the inlet fluid port  652  to the porous sheet element  650  as indicated by the arrow heads in  FIG. 8( b ) . The silicon oil  622  moves laterally along the porous sheet element  650  at a predetermined rate thereby rendering the porous sheet element  650  progressively transparent at a predetermined rate which depends on the nature of the porous sheet element  650  and properties such as the viscosity of the silicon oil  622 . As the porous sheet element  650  becomes progressively transparent in the lateral direction, the first colour indicator area  654   a  is progressively revealed and may be viewed through the transparent windows  660   a  to  660   d  until all of the first colour indicator area  654   a  is revealed and the silicon oil  622  reaches the second colour indicator area  654   b . Thereafter, the silicon oil  622  continues to move laterally along the porous sheet element  650  so as to progressively reveal the second colour indicator area  654   b  which may be viewed through the transparent window  660   e . The rate of movement of the silicon oil  622  laterally along the porous sheet element  650  and the length of the porous sheet element  650  along the direction of travel of the silicon oil  622  may be selected so that the progressive appearance of the first and second coloured indicator areas  654   a  and  654   b  in the transparent window  660   a - 660   e  provides a progressive indication of the time remaining until expiry of a lifetime of the contents of the container  80 . 
     One of ordinary skill in the art will understand that various modifications of the microfluidic elapsed time indicator  2  are possible. For example, different arrangements of the reservoir  20  and the display arrangement  30  and/or different arrangements of the indicator vent and the reservoir vent are possible according to the field of use. The or each microfluidic channel may follow any suitable path to permit fluid to move from the reservoir  20  to the porous sheet element  50  and, optionally, away from the porous sheet element  50 . For example, the or each microfluidic channel may be curved or even define a 180° bend when viewed in plan. 
     One or more symbols, characters, letters, numbers or graphical representations may be printed or otherwise defined on the upper surface  8  of the upper cover layer  60 . In particular, one or more symbols, characters, letters, numbers or graphical representations may be printed or otherwise defined adjacent to each of the windows  60   a ,  60   b ,  60   c ,  60   d ,  60   e ,  60   f  to provide an indication of the elapsed time associated with the appearance of the corresponding indicator area  54   a ,  54   b ,  54   c ,  54   d ,  54   e ,  54   f  in the relevant window  60   a ,  60   b ,  60   c ,  60   d ,  60   e ,  60   f.