Gel-based temperature indicators

1. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces; and

a first gel coupled to the first face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the first absorbent substrate is configured to allow the first gel upon turning to liquid to diffuse through the first face toward the second face;

wherein the first gel is contained within a second absorbent substrate coupled to the first face of the first absorbent substrate, and

wherein the first gel comprises a first additive that affects the visual appearance of the first absorbent substrate when the first gel diffuses from the second absorbent substrate to the first face of the first absorbent substrate and further diffuses toward the second face; and

wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

2. The gel-based temperature indicator of claim 1 , wherein the first absorbent substrate comprises a second additive and diffusion of the first gel comprising the first additive allows the first and second additives to react with each other in a way that affects the visual appearance of the first absorbent substrate.

3. The gel-based temperature indicator of claim 1 , wherein the first gel goes from gel to liquid with increasing temperature.

4. The gel-based temperature indicator of claim 1 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.

5. A label for a perishable good, comprising a gel-based temperature indicator of claim 1 .

6. A method of protecting a perishable item, comprising:

coupling the perishable item with a gel-based temperature indicator of claim 1 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

7. The gel-based temperature indicator of claim 1 , wherein the first face comprises a marking that is revealed when the first gel diffuses through the first face.

8. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces;

a first gel coupled to the first face; and

a second gel coupled to the first face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the second gel is a gel at the first temperature

wherein the second gel turns to liquid at the second temperature;

wherein the first absorbent substrate is configured to allow the first and second gels upon turning to liquid to diffuse through the first face toward the second face;

wherein the first and second gels interact in the first absorbent substrate to effect a change in the visual appearance of the first absorbent substrate; and

wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

9. The gel-based temperature indicator of claim 8 , wherein the extent of the change in visual appearance of the first absorbent substrate provides an indication of the amount of time that the indicator has been exposed to a temperature greater than or equal to the second temperature.

10. A label for a perishable good, comprising a gel-based temperature indicator of claim 8 .

11. A method of protecting a perishable item, comprising:

coupling the perishable item with a gel-based temperature indicator of claim 8 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

12. The gel-based temperature indicator of claim 8 , wherein the first gel goes from gel to liquid with increasing temperature.

13. The gel-based temperature indicator of claim 8 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.

14. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces;

a first gel coupled to the first face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the first absorbent substrate is configured to allow the first gel upon turning to liquid to diffuse through the first face toward the second face;

wherein the first gel is contained within a second absorbent substrate having a third face positioned adjacent to the first face of the first absorbent substrate; and

wherein a first electrode and a second electrode are positioned in physical contact with the first absorbent substrate so as to not contact each other and so that current does not flow between the first electrode and the second electrode prior to the gel turning to a liquid; and

wherein the first gel comprises conductive particles such that diffusion of the first gel toward the second face allows a current to flow from the first electrode and second electrode through the first absorbent substrate.

15. The gel based temperature indicator of claim 14 , wherein the flow of current between the first and second electrodes causes a signal to be sent to a remote monitoring device.

16. The gel based temperature indicator of claim 14 , wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

17. A label for a perishable good, comprising a gel-based temperature indicator of claim 14 .

18. A method of protecting a perishable item, comprising

coupling the perishable item with a gel-based temperature indicator of claim 14 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

19. The gel-based temperature indicator of claim 14 , wherein the first gel goes from gel to liquid with increasing temperature.

20. The gel-based temperature indicator of claim 14 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.

21. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces;

a first gel coupled to the first face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the first absorbent substrate is configured to allow the first gel upon turning to liquid to diffuse through the first face toward the second face;

wherein the first gel is contained within a plurality of absorbent substrates sized and positioned on the first face of the first absorbent substrate to create a pattern;

wherein diffusion of the first gel toward the second face allows the pattern to be read by a digital code-reading device; and

wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

22. A label for a perishable good, comprising a gel-based temperature indicator of claim 21 .

23. A method of protecting a perishable item, comprising:

coupling the perishable item with a gel-based temperature indicator of claim 21 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

24. The gel-based temperature indicator of claim 21 , wherein the first gel goes from gel to liquid with increasing temperature.

25. The gel-based temperature indicator of claim 21 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.

26. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces;

a first gel coupled to the first face; and

a second gel located at the first face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the second gel is a gel at the first temperature

wherein the second gel turns to liquid at a third temperature;

wherein the first absorbent substrate is configured to allow the first and second gels upon turning to liquid to diffuse through the first face toward the second face; and

wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

27. The gel-based temperature indicator of claim 26 , wherein the first absorbent substrate is configured to prevent the first and second gels from mixing as they diffuse toward the second face.

28. The gel-based temperature indicator of claim 27 , wherein the first and second gels are separated from each other on the first face by a barrier.

29. The gel-based temperature indicator of claim 28 , wherein the first and second gels are located, respectively, in second and third absorbent substrates coupled to the first face of the first absorbent substrate.

30. A label for a perishable good, comprising a gel-based temperature indicator of claim 26 .

31. A method of protecting a perishable item, comprising:

coupling the perishable item with a gel-based temperature indicator of claim 26 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

32. The gel-based temperature indicator of claim 26 , wherein the first gel goes from gel to liquid with increasing temperature.

33. The gel-based temperature indicator of claim 26 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.

34. A gel-based temperature indicator comprising:

a first absorbent substrate having opposing first and second faces;

a first gel coupled to the first face; and

a second gel coupled to the second face;

wherein the first gel is a gel at a first temperature;

wherein the first gel turns to liquid at a second temperature;

wherein the first absorbent substrate is configured to allow the first gel upon turning to liquid to diffuse through the first face toward the second face;

wherein the second gel is a gel at the first temperature and turns to liquid at the second temperature;

wherein the first absorbent substrate is configured to allow the second gel upon turning to liquid to diffuse through the second face toward the first face;

wherein the first and second gels interact to effect a change in the visual appearance of the first absorbent substrate; and

wherein the ratio of the area of the second face in mm 2 to the thickness of the first absorbent substrate in mm is at least 10 mm.

35. A label for a perishable good, comprising a gel-based temperature indicator of claim 34 .

36. A method of protecting a perishable item, comprising:

coupling the perishable item with a gel-based temperature indicator of claim 34 so that the temperature condition indicator is subject to substantially the same temperature conditions as the perishable item.

37. The gel-based temperature indicator of claim 34 , wherein the first gel goes from gel to liquid with increasing temperature.

38. The gel-based temperature indicator of claim 34 , wherein the first gel goes from gel to liquid when the temperature decreases below a low temperature threshold, and the low temperature threshold is below 30° C.