WO2022115970A1

WO2022115970A1 - Colour migration timer

Info

Publication number: WO2022115970A1
Application number: PCT/CA2021/051741
Authority: WO
Inventors: Nicolas COTTENYE; Gael BOESPFLUG; Alexey TOKAREV; Zeinab Jamila CISSE
Original assignee: Bioastra Technologies Inc.
Priority date: 2020-12-04
Filing date: 2021-12-06
Publication date: 2022-06-09

Abstract

There are provided coloured indicator stickers for tracking usage of personal protection masks and filters and other colour migration timers for measuring exposure to human or environmental stimuli such as humidity.

Description

COLOUR MIGRATION TIMER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from U.S. Provisional Application No. 63/121 ,661 , filed December 4, 2020, the contents of which are hereby incorporated by reference in their entirety.

FIELD

[0002] The disclosure relates generally to colour migration timers useful for indicating exposure time to human or environmental stimuli such as humidity.

BACKGROUND

[0003] Due to the current COVID-19 pandemic, the use of personal protection equipment has reached an all-time high. The demand for masks has exceeded production capabilities and each mask must be used for as long as possible. Furthermore, masks for the general public must be more comfortable and fashionable. These masks are more expensive to produce and thus should be used for a longer time.

[0004] In this context, it is desirable to provide a coloured indicator that will track the usage of a mask or replaceable filter, to maximize its value.

SUMMARY

[0005] The present disclosure relates generally to colour migration timers for tracking exposure to human or environmental stimuli such as humidity, pH, bioanalytes, and the like.

[0006] In a first broad aspect, the present disclosure relates to coloured migration timers for tracking exposure to a stimulus, comprising a coloured ink composition on a substrate, wherein the coloured ink composition migrates on the substrate responsive to exposure to the stimulus, the extent of migration (distance or % migrated) of the coloured ink composition along the substrate indicating time of exposure to the stimulus. A variety of stimuli may be tracked in this way, such as without limitation humidity, pH, a bioanalyte, or a combination thereof. In some embodiments, the stimulus is a human or environmental stimulus. In some such embodiments, the stimulus is in a human breath. For example and without limitation, in one embodiment the stimulus is humidity in a human breath. [0007] In some embodiments, the coloured ink composition comprises: a dye; a stimulus- responsive material; and a thickening agent. Any food-grade dye may be used, such as without limitation Allura Red, Resazurin, and Alizarin Red. In some embodiments, the stimulus-responsive material is a polymer or a monomer. In some embodiments, the stimulus-responsive material is responsive to humidity, e.g., a humectant or a hygroscopic molecule such as without limitation Polyethylene glycol (PEG), Hyaluronic Acid, Polyacrylic Acid, Hydroxypropyl Cellulose, Polyethylene Oxide, glycerol, or a combination thereof.

[0008] In some embodiments, the coloured ink composition further comprises an additive for modifying the kinetics of migration of the dye. For example, an additive may be used to slow or to increase the speed of dye migration in response to a stimulus. In an embodiment, the coloured ink composition comprises a humectant or a hygroscopic additive such as without limitation glycerol.

[0009] In some embodiments, the thickening agent is a cellulosic polymer.

[0010] In some embodiments, the substrate is a porous material such as without limitation nylon or a cellulosic membrane.

[0011] In some embodiments, the coloured ink composition covers from one-fifth to one-half of the substrate before migration.

[0012] The rate, time and direction of migration of the coloured ink composition across the substrate can be varied depending on the desired specifications. In some embodiments, complete migration from one end of the substrate to the other indicates about 2-10 hours of exposure to the stimulus. In some embodiments, complete migration from one end of the substrate to the other indicates about 4-5 hours of exposure to the stimulus. In some embodiments, complete migration from one end of the substrate to the other indicates about 20-50 hours of exposure to the stimulus. In an embodiment, complete migration from one end of the substrate to the other indicates about 4 hours, about 5 hours, 4 hours or more, or 5 hours or more, of exposure to the stimulus. In an embodiment, complete migration from one end of the substrate to the other indicates about 4-10 hours, about 4-8 hours, about 8 hours, or 8 hours or more of exposure to the stimulus. The dye may migrate laterally, orthogonally, or radially on the substrate.

[0013] In some embodiments, the tracker is in the form of a sticker suitable for affixing directly or indirectly to a product such as, without limitation, a personal protective equipment, a face mask, a filter, a surgical mask, a N95 mask, a packaged food, an electronic, a vaccine, a pharmaceutical or an electronic. In particular embodiments, the product is a personal protection mask or filter. [0014] In a second broad aspect, the present disclosure relates to coloured indicator stickers suitable for attachment to a personal protection mask or filter in order to track usage thereof, the sticker comprising the coloured migration timer described herein, and an adhesive support.

[0015] In a third broad aspect, the present disclosure relates to personal protective equipment, e.g., a mask, a shield or a filter, comprising the coloured migration timer or the coloured indicator sticker described herein.

[0016] In another broad aspect, there are provided methods for tracking usage of a personal protective equipment, the method comprising affixing the coloured migration timer or the coloured indicator sticker described herein to the personal protective equipment before use, and monitoring the extent of migration (e.g., distance or % migrated) of the coloured ink composition along the substrate during or after use, wherein the extent of migration along the substrate indicates cumulative time the personal protective equipment has been used.

[0017] In some embodiments, the present disclosure relates to coloured indicator stickers for tracking usage of personal protection masks. The indicator stickers can be used to track usage of a mask. The indicator stickers can also be used to track usage of replaceable filters in a mask. Indicator stickers provided herein allow a user to track the amount of time that a mask is used, based on measuring length of exposure to a certain threshhold of a stimulus such as humidity and/or pH (e.g., humidity in a user’s breath, i.e., in a human breath). The indicator stickers measure cumulative exposure to humidity and/or another stimulus so that exposure is tracked, indicating when a mask or filter must be replaced. This allows optimal usage of masks and filters before replacement to avoid both premature replacement and overuse.

[0018] In order to track the amount of time that a mask is used, an indicator that is sensitive to the high-humidity environment that is present in-between the mask and its user’s mouth is used. The coloured indicator migrates along a blank substrate when in proximity to the mouth and stays at its current position when not in use.

[0019] Depending on the type of the mask or filter that needs to be tracked, it is possible to tune the coloured indicator system so that migration occurs within a desired amount of time. Possible parameters that can be tuned include the nature and porosity of the fabric, the dimensions of the substrates, the fraction of the coloured section of the substrate, the amount of dye that impregnates the substrate, and the nature and quantity of any additive that impacts the viscosity or affinity of the dye-water mixture. [0020] More aspects and features of the technology are described in the detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The patent or application file contains at least one drawing executed in colour. Copies of this patent or patent application publication with colour drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0022] For a better understanding of the invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings, which illustrate aspects and features according to embodiments of the present invention, and in which:

[0023] FIG. 1 illustrates a colour indicator sticker in accordance with one embodiment of the present technology. Numbers indicate size in mm.

[0024] FIG. 2 illustrates a colour indicator sticker in accordance with one embodiment of the present technology. Dye migrates from left to right upon exposure to stimulus.

DETAILED DESCRIPTION

[0025] The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0026] In order to provide a clear and consistent understanding of the terms used in the present specification, a number of definitions are provided below. Moreover, unless defined otherwise, all technical and scientific terms as used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention pertains.

Definitions

[0027] As used herein, the use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one”, but it is also consistent with the meaning of “one or more”, “at least one”, and “one or more than one”. Similarly, the word “another” may mean at least a second or more.

[0028] As used herein, the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “include” and “includes”) and “containing” (and any form of containing, such as “contain” and “contains”), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps. [0029] The term “about” is used to indicate that a value includes an inherent variation of error for the device or the method being employed to determine the value.

[0030] As used herein, when content is indicated as being present on a "weight basis" or at a “weight percent (wt%)” or “by weight,” the content is measured as the percentage of the weight of component(s) indicated by dry basis (by taking moisture percentage in each component into account), relative to the total weight of all components present in a composition.

[0031] The term “derivative” as used herein, is understood as being a substance similar in structure to another compound but differing in some slight structural detail.

[0032] As used herein, the term "polymer" refers to a material that includes a set of macromolecules. Macromolecules included in a polymer can be the same or can differ from one another in some fashion. A macromolecule can have any of a variety of skeletal structures, and can include one or more types of monomeric units. In particular, a macromolecule can have a skeletal structure that is linear or non-linear. Examples of non-linear skeletal structures include branched skeletal structures, such those that are star branched, comb branched, or dendritic branched, and network skeletal structures. A macromolecule included in a homopolymer typically includes one type of monomeric unit, while a macromolecule included in a copolymer typically includes two or more types of monomeric units. Examples of copolymers include statistical copolymers, random copolymers, alternating copolymers, periodic copolymers, block copolymers, radial copolymers, and graft copolymers.

[0033] In some instances, a reactivity and a functionality of a polymer can be altered by addition of a set of functional groups, such as acid anhydride groups, amino groups and their salts, N-substituted amino groups, amide groups, carbonyl groups, carboxy groups and their salts, cyclohexyl epoxy groups, epoxy groups, glycidyl groups, hydroxy groups, isocyanate groups, urea groups, aldehyde groups, ester groups, ether groups, alkenyl groups, alkynyl groups, thiol groups, disulfide groups, silyl or silane groups, groups based on glyoxals, groups based on aziridines, groups based on active methylene compounds or other b-dicarbonyl compounds (e.g., 2,4- pentandione, malonic acid, acetylacetone, ethylacetone acetate, malonamide, acetoacetamide and its methyl analogues, ethyl acetoacetate, and isopropyl acetoacetate), halo groups, hydrides, or other polar or H bonding groups and combinations thereof. Such functional groups can be added at various places along the polymer, such as randomly or regularly dispersed along the polymer, at ends of the polymer, on the side, end or any position on the crystallizable side chains, attached as separate dangling side groups of the polymer, or attached directly to a backbone of the polymer. Also, a polymer can be capable of cross-linking, entanglement, or hydrogen bonding in order to increase its mechanical strength or its resistance to degradation under ambient or processing conditions.

[0034] “Polymerization” is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains. Many forms of polymerization are known, and different systems exist to categorize them, as are known in the art.

[0035] As can be appreciated, a polymer can be provided in a variety of forms having different molecular weights, since a molecular weight (MW) of the polymer can be dependent upon processing conditions used for forming the polymer. Accordingly, a polymer can be referred to as having a specific molecular weight or a range of molecular weights. As used herein with reference to a polymer, the term "molecular weight (MW)" can refer to a number average molecular weight or a weight average molecular weight. Polymers are often referred to in terms of their average MW, for example PEG1000 refers to PEG of average MW of 1000. Polymers may also be referred to in terms of their degree of polymerization (“n”), which can range, generally, from as low as 40 to as high as 5000. In some cases, polymers of different molecular weights may be mixed to give a composition having desired properties. It should be understood that polymers of any molecular weight, or mixtures of polymers of different molecular weights, may be used, as long as the resulting composition has the desired properties or is generally suitable for the uses described herein, as will be determined by the skilled artisan using known techniques.

[0036] As used herein, the term “copolymer” refers to polymers having two or more different divalent monomer units.

[0037] As used herein, the term "chemical bond" refers to a coupling of two or more atoms based on an attractive interaction, such that those atoms can form a stable structure. Examples of chemical bonds include covalent bonds and ionic bonds. Other examples of chemical bonds include hydrogen bonds and attractive interactions between carboxy groups and amine groups. As used herein, the term "covalent bond" means a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds. Attraction-to-repulsion stability that forms between atoms when they share electrons is known as covalent bonding. Covalent bonding includes many kinds of interactions, including sigmabonding, pi-bonding, metal-metal bonding, agostic interactions, and three-center two-electron bonds.

[0038] As used herein, the term "reactive function" means a chemical group (or a moiety) capable of reacting with another chemical group to form a covalent or an electrovalent bond, examples of which are given above. Preferably, such reaction is doable at relatively low temperatures, e.g. below 200 °C, more preferably below 100 °C, and/or at conditions suitable to handle delicate substrates, e.g. textiles. A reactive function could have various chemical natures. For example, a reactive function could be capable of reacting and forming electrovalent bonds or covalent bonds with reactive functions of various substrates, e.g., cotton, wool, fur, leather, polyester, or textiles made from such materials, as well as other base materials.

Coloured migration timers and indicator stickers

[0039] There are provided coloured migration timers for tracking exposure to a human or environmental stimulus such as humidity, pH, bioanalyte(s), combinations thereof, and the like. In some embodiments, the timers are in the form of coloured indicator stickers suitable for fixing to a personal protection mask or filter in order to track usage thereof.

[0040] The coloured migration timers are not particularly limited and may use a variety of materials, so long as they are responsive to human or environmental stimuli such as humidity, pH, bioanalytes, and combinations thereof, allowing measurement of cumulative exposure thereto. In some embodiments, the coloured migration timer is responsive to humidity in a human breath.

[0041] Coloured Indicator system. In a first embodiment, the coloured migration timer is made of a porous-fabric substrate that has been partly impregnated by a dye-containing water-based solution. When dried, this substrate has a coloured section — typically a fifth to a half of its length — where the pores are filled with the dye and other migration-controlling additives.

[0042] In dry conditions, this system is stable and the coloured section will remain constant. In a high-humidity environment, such as between a human mouth and a protective mask, the natural affinity between the substrate and the water vapour will allow for the condensation of liquid water droplets at its surface. When such droplets are present, the dye and additives can mix with the water droplet and migrate to a neighbouring empty pore. Over time, the dye will visibly migrate to cover the blank section of the substrate until the entire surface is coloured.

[0043] Adhesive support. In some embodiments, a coloured indicator sticker includes an adhesive support. In one embodiment, the support for the indicator sticker is a thin flexible white water-proof material coated with a water-proof adhesive on both sides that can adhere permanently to both the dyed substrate and to unwoven filter fabrics or to mask fabrics. Other paper and fabric substrates can also be used. [0044] Substrate. In some embodiments, the substrate for the dye is a thin flexible white porous fabric such as a nylon or cellulosic membrane. The porosity and the nature of the fabric can both be tuned for the desired specifications. In one embodiment, the sticker uses a nylon membrane with a thickness of 0.1 mm and a pore diameter of 3 pm.

[0045] The shape and size of the substrate can vary according to the design of the product and the desired time of migration. Further the fraction of the surface that is dyed can be varied to modify migration time.

[0046] Coloured ink. In some embodiments, the coloured indicator is imbibed into the surface from a water-based solution. This ink is composed of a visible dye in addition to a hygroscopic additive and a thickening agent.

[0047] The dye concentration can be tuned so that the desired amount can be deposited with different production methods. The hygroscopic additive helps with the formation of water droplets on the surface of the substrate, thus increasing migration speed. The thickening agent will influence the viscosity of the ink during production and the dyed-substrate/water-droplet complex formed during use.

[0048] In one embodiment, the ink composition comprises the components shown in Table 1. Other dyes, stimulus-responsive materials or polymers and other thickening agents can be used, depending on the desired specifications. For example, any food-grade dye may be used.

[0049] Table 1. Exemplary ink composition.

[0050] In one embodiment, the ink composition comprises Allura Red; PEG; glycerol; and a cellulosic polymer. [0051] In one embodiment, there is provided a coloured migration timer comprising a strip of a microporous substrate that comprises a dye, a carrier polymer and additives capable of migrating from one end of the strip to the other. The migration time from one end to the other indicates the time that the strip has been exposed to a particular environment or stimulus (humidity, pH, etc.) and therefore provides a humidity-time, or pH-time, etc., indicator, as well as a lateral flow biosensor.

[0052] In an embodiment, the timer comprises a strip of a microporous substrate containing a sensing ink that migrates from one end to the other upon exposure to a certain environmental stimulus (e.g., humidity, pH, etc.). The sensing ink comprises a coloured food-grade dye, an environmentally-responsive polymer, viscosity modifier(s), and additive(s) to stabilise the mixture. The coloured dye can be for example Allura Red, Resazurin, Alizarin Red or any food-grade dye. The environmentally-responsive polymers can respond to humidity, pH, a bioanalyte, or a combination thereof. The migration of the ink can take place over a desired number of hours such as, without limitation, 4 hours, 5 hours, 8 hours, 20 hours or 50 hours. In some embodiments, the migration may take place over 10-50 hours, or 30-50 hours. In other embodiments, the migration time may be such that the entire surface is covered after 2 hours, 4 hours, or 8 hours, for example in the case of a surgical or N95 mask. Migration time can be tailored, for example through microporosity of the substrate, based on recommended guidelines for use of a product to which the timer is attached. The time may indicate that it is time to wash, dispose or replace the product.

[0053] Sensing inks may be prepared using any suitable method known in the art.

[0054] Products include without limitation personal protective equipment, face masks, filters, surgical masks, N95 masks, packaged foods, electronics, vaccines, pharmaceuticals and electronics.

[0055] Stimulus-responsive materials and polymers. Stimulus-responsive materials and polymers are materials and polymers that respond to one or more human or environmental stimulus (such as humidity, pH, presence of a bioanalyte, etc., e.g., in a human breath) by releasing or enhancing flow of the dye across the substrate. The terms “stimulus-responsive” and “environmentally-responsive” are used interchangeably herein.

[0056] Humidity-responsive polymers include without limitation Polyethylene Glycol, Polyvinyl alcohol, polyacrylic acid, and polyvinyl pyrollidone.

[0057] Stabilisers include any suitable component such as without limitation a surfactant molecule. [0058] The Migration Time of Ink corresponds to time of exposure to the environmental stimulus. In some embodiments, a humidity sensor can be integrated into a face mask to capture moist exhaled air from a user’s mouth and nose. It will be appreciated that ink migration speed increases as a function of human activity (e.g., walking vs. running).

[0059] A Substrate can be made of any suitable material such as without limitation Nylon, Cellulose or Teflon.

[0060] Ink can be deposited on the substrate using any suitable method such as without limitation, through flexography.

[0061] Indicator tuning. Depending on the type of the mask or filter that needs to be tracked, it is possible to tune the coloured indicator system so that migration occurs within a desired amount of time. Possible parameters that can be tuned include the nature and porosity of the fabric, the dimensions of the substrates, the fraction of the coloured section of the substrate, the amount of dye that impregnates the substrate, and the nature and quantity of any additive that impacts the viscosity or affinity of the dye-water mixture.

[0062] Coloured ink compositions may optionally comprise further additive(s) to modify the kinetics of dye migration. For example, an additive may speed or slow the rate of migration of the dye across the substrate. In some embodiments, where humidity is the stimulus being detected, an additive which is a humectant or a hygroscopic material (e.g., glycerol) may be used to speed the rate of migration of the dye in response to humidity. Other additives may be used depending on the stimulus, the desired specifications, and the like.

[0063] Indicator sticker design. To maximize the flexibility of the coloured indicator system, a sticker-based approach can be used. In some embodiments, the substrate can have adhesive backing, e.g. to stick as a label onto products. This allows for the placement of an indicator on multiple materials at different stages of production. In one non-limiting embodiment, stickers used a 24 mm by 10 mm stadium-shaped substrate with a dyed section covering a fifth of its length. The substrate had an impermeable frame covering the outer perimeter of the surface and was attached to an adhesive support. This embodiment is illustrated in FIG. 1. In another non-limiting embodiment, a sticker shaped like a shield is used. This embodiment is illustrated in FIG. 2. The shape of the sticker is not limited and any convenient shape may be used. The direction of migration is also not limited and may, for example, be lateral flow, orthogonal flow (e.g., moving up off the substrate), or radial flow. [0064] The means for affixing the coloured indication system onto a product is not particularly limited. In other embodiments, the coloured indicator system may be attached to a product such as a mask by sewing (as in a patch), impregnated or embossed thereto, stamped thereon, and so on.

[0065] Based upon the foregoing, those skilled in the art will readily recognize that various modifications and changes may be made to the various embodiments without strictly following the exemplary embodiments and applications illustrated and described herein. Such modifications do not depart from the true spirit and scope of various aspects of the disclosure, including aspects set forth in the claims.

EXAMPLES

[0066] The present invention will be more readily understood by referring to the following examples, which are provided to illustrate the invention and are not to be construed as limiting the scope thereof in any manner.

[0067] Unless defined otherwise or the context clearly dictates otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It should be understood that any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention.

[0068] Example 1. Migration tests.

[0069] Simulations were made in a humidity chamber to assess the efficiency of a test ink formulation in regard to a fast migration. Two microliters of the test ink was dropped on a nylon substrate, then assembled with sticker material, with final dimensions of 10 x 6 mm. Three separate trials showed a full migration of the ink dye overnight (14h to 16h) in the humidity chamber.

[0070] Samples were studied to assess migration rate and time for full migration. For some samples, migration was obvserved after 1.5 hours; this increased after 4 hours; and a full migration was obtained after about 6.3 hours in the humidity chamber.

[0071] Stickers were also tested in a user trial, in masks. Preliminary results indicated successful migration. Migration was fastest when stickers were placed in the center of the mask rather on the sides. Also migration was reduced significantly if a mask was fitted poorly on the user (e.g., too small). [0072] Although this invention is described in detail with reference to embodiments thereof, these embodiments are offered to illustrate but not to limit the invention. It is possible to make other embodiments that employ the principles of the invention and that fall within its spirit and scope as defined by the claims appended hereto.

[0073] The contents of all documents and references cited herein are hereby incorporated by reference in their entirety.

Claims

CLAIMS What is claimed is:

1. A coloured migration timer for tracking exposure to a stimulus, comprising a coloured ink composition on a substrate, wherein the coloured ink composition migrates on the substrate responsive to exposure to the stimulus, the extent of migration (distance or % migrated) of the coloured ink composition along the substrate indicating time of exposure to the stimulus.

2. The coloured migration timer of claim 1 , wherein the stimulus is humidity, pH, a bioanalyte, or a combination thereof.

3. The coloured migration timer of claim 1 or 2, wherein the stimulus is in a human breath.

4. The coloured migration timer of any one of claims 1 to 3, wherein the stimulus is humidity.

5. The coloured migration timer of any one of claims 1 to 4, wherein the coloured ink composition comprises: a dye; a stimulus-responsive material; and a thickening agent.

6. The coloured migration timer of claim 5, wherein the dye is a food-grade dye.

7. The coloured migration timer of claim 5 or 6, wherein the dye is Allura Red, Resazurin, or Alizarin Red.

8. The coloured migration timer of any one of claims 5 to 7, wherein the stimulus- responsive material is a polymer or a monomer.

9. The coloured migration timer of any one of claims 5 to 8, wherein the stimulus- responsive material is responsive to humidity.

10. The coloured migration timer of any one of claims 5 to 9, wherein the stimulus- responsive material is a humectant or a hygroscopic molecule.

11. The coloured migration timer of any one of claims 5 to 10, wherein the stimulus- responsive material is PEG, Hyaluronic Acid, Polyacrylic Acid, Hydroxypropyl Cellulose, Polyethylene Oxide, Glycerol, or a combination thereof.

12. The coloured migration timer of any one of claims 1 to 11, wherein the coloured ink composition further comprises an additive for modifying the kinetics of migration of the dye.

13. The coloured migration timer of claim 12, wherein the additive slows the speed of dye migration in response to the stimulus.

14. The coloured migration timer of claim 12, wherein the additive increases the speed of dye migration in response to the stimulus.

15. The coloured migration timer of claim 14, wherein the additive comprises a humectant or a hygroscopic molecule.

16. The coloured migration timer of claim 14 or 15, wherein the additive comprises glycerol.

17. The coloured migration timer of any one of claims 5 to 16, wherein the thickening agent is a cellulosic polymer.

18. The coloured migration timer of any one of claims 1 to 17, wherein the tracker is in the form of a sticker suitable for affixing directly or indirectly to a product.

19. The coloured migration timer of claim 18, wherein the product is a personal protection mask or filter.

20. The coloured migration timer of claim 18, wherein the product is a personal protective equipment, a face mask, a filter, a surgical mask, a N95 mask, a packaged food, an electronic, a vaccine, a pharmaceutical or an electronic.

21. The coloured migration timer of any one of claims 1 to 20, wherein the substrate is a porous material.

22. The coloured migration timer of any one of claims 1 to 21, wherein the substrate is nylon or a cellulosic membrane.

23. The coloured migration timer of any one of claims 1 to 22, wherein the coloured ink composition covers from one-fifth to one-half of the substrate before migration.

24. The coloured migration timer of any one of claims 1 to 23, wherein migration of the coloured ink composition across the entire substrate indicates about 2-10 hours of exposure to the stimulus.

25. The coloured migration timer of any one of claims 1 to 23, wherein migration of the coloured ink composition across the entire substrate indicates about 20-50 hours of exposure to the stimulus.

26. The coloured migration timer of any one of claims 1 to 23, wherein migration of the coloured ink composition across the entire substrate indicates about 4-5 hours of exposure to the stimulus.

27. The coloured migration timer of any one of claims 1 to 23, wherein migration of the coloured ink composition across the entire substrate indicates about 4 hours, about 5 hours, 4 or more hours, or 5 or more hours of exposure to the stimulus.

28. The coloured migration timer of any one of claims 1 to 27, wherein the coloured ink composition migrates laterally, orthogonally, or radially on the substrate.

29. A coloured indicator sticker suitable for attachment to a personal protection mask or filter in order to track usage thereof, the sticker comprising the coloured migration timer of any one of claims 1 to 28 and an adhesive support.

30. A personal protective equipment comprising the coloured migration timer of any one of claims 1 to 28 or the coloured indicator sticker of claim 29.

31. The personal protective equipment of claim 30, which is a mask or a filter.

32. A method for tracking usage of a personal protective equipment, the method comprising affixing the coloured migration timer of any one of claims 1 to 28 or the coloured indicator sticker of claim 29 to the personal protective equipment before use, and monitoring the extent of migration (distance or % migrated) of the coloured ink composition along the substrate, wherein the extent of migration along the substrate indicates cumulative time the personal protective equipment has been used.

15