Hot compress containing supercooled saline solution and glycerin

Abstract

A heat pack using a supercooled saline solution is disclosed, which resists premature activation at low temperatures. The heat pack comprises two sheets bonded together to form a laminated sheet. The heat pack has first and second compartments. A brittle seal separates the two compartments. One compartment contains a supercooled saline solution. The saline solution contains 15% to 25% glycerol by weight.

Description

Technical Field

[0001] This invention relates to disposable heat packs for therapeutic purposes, and more particularly to heat packs using supercooled saline solution. Background Technology

[0002] It is well known that disposable hot compresses use supercooled saline solutions. These packages typically take the form of flexible plastic containers holding the saline solution. The solution is supercooled, meaning it is prepared in a very pure state and then heated to a high temperature. It is then gradually cooled to a temperature below its normal crystallization temperature. When the package is used, crystallization in the solution can be initiated by exposing the solution to air. As the solution changes from a liquid to a solid phase, the latent heat of crystallization causes the package to heat up. If the correct saline solution formulation is chosen, the phase transition occurs at a constant temperature within a narrow range suitable for warming human skin. This reaction is predictable and stable, and lasts for several minutes—sufficient for the package to perform its function.

[0003] Several methods exist for packaging saline solutions to allow air to be injected upon user triggering. For example, U.S. Patent No. 6,318,359B1, incorporated herein by reference, discloses a heat pack with a ruptureable seal that separates a compartment containing the saline solution from a second compartment containing air.

[0004] One problem with this type of heat pack is premature activation. If a single-use heat pack is activated before reaching the end user, it cannot be used for its intended purpose. In any batch of heat packs, some may be unusable. Therefore, some heat packs using supercooled saline solutions are unreliable. Premature activation also leads to product waste and reduced revenue.

[0005] Premature activation of the packaging is thought to be a result of a rupture or leak in the seal separating the air from the saline solution. However, premature activation has been observed in packaging where the potentially ruptured seals were not damaged. It is unclear why some heat packs survived transport while others activated prematurely.

[0006] Ultimately, it was discovered that low temperatures cause the heating packs to self-activate. It was observed that heating packs placed on the outer layer of the transport container were more likely to be prematurely activated before delivery to the end user compared to those from the central layer. Furthermore, even more heating packs were found to be prematurely activated during colder winter months.

[0007] Typically, saline solutions are prepared to stabilize the supercooled solution at ambient temperatures in homes, hospitals, and their associated storage areas. However, during manufacturing and distribution, the heat packs may be exposed to temperatures below room temperature. In these cases, the saline solution may be prematurely activated.

[0008] While heating packs can be transported in heated vehicles and containers, this solution is both expensive and error-prone. Heating packs stored outside heated trucks may still experience low temperatures. Furthermore, some heating packs may be pre-activated at transfer points within the delivery chain. Premature activation is especially common during colder winters and particularly frigid days. This problem is further complicated by the large number of entities involved in the distribution process; supply chains are often too complex to be properly controlled.

[0009] Some heat packs containing supercooled saline solutions are known to contain organic compounds, but these heat packs disclose organic compound concentrations between 1% and 10% by weight. European Patent No. 2,853,576B1 describes a heat pack containing supercooled aqueous solutions containing 1-9% glycerin. However, test results disclosed in that document appear to indicate that resistance to preactivation decreases when glycerin exceeds 2% of the total solution. In Example J1, a composition containing 2% glycerin by weight was stored at -20°C for 3 to 5 hours under supercooled conditions. In contrast, solutions containing higher concentrations of glycerin showed shorter periods of resistance to preactivation. In Example J5, a solution containing 9% glycerin by weight was stored at -20°C for 2 to 3 hours, while in Example J9, a composition containing 6% glycerin by weight was stored at -20°C for only 1 to 2 hours.

[0010] Existing technology indicates that the ideal concentration of glycerol for maintaining a supercooled state is approximately 2%, and increasing the glycerol concentration to above 2% will make the supercooled saline solution easier to pre-activate.

[0011] Furthermore, organic compounds are believed to reduce the crystallization rate of supercooled salt solutions, thereby reducing the heat released during activation. Because heat packs used for medical or therapeutic purposes must reach a specified maximum temperature (T0). max Therefore, organic compounds may not be suitable as antifreeze agents. Summary of the Invention

[0012] One aspect of the present invention is to provide a heat pack using an ultracooled saline solution that resists premature activation.

[0013] The above-mentioned aspects can be achieved by a heat pack comprising a container having two flexible sheets bonded together to form a laminate. The container has a first compartment and a second compartment. A ruptureable seal separates the two compartments. One compartment contains air, and the other contains a supercooled saline solution. The saline solution contains 15% to 25% glycerol by weight.

[0014] These, along with other aspects and advantages that will subsequently become apparent, are contained in the details of the construction and operation described more fully below and claimed, in which the accompanying drawings containing reference numerals form a part, wherein the same numerals denote the same parts. Attached Figure Description

[0015] Figure 1 This is a top view of an embodiment, showing the salt solution in the first compartment;

[0016] Figure 2 It is along Figure 1 Cross-sectional view of line A;

[0017] Figure 3 yes Figure 1 A top view of an embodiment showing the activated packaging;

[0018] Figure 4 yes Figure 1 The embodiment is shown in a top view in the inactive state, and a fixing mechanism is also shown. Detailed Implementation

[0019] This invention relates to a description of a heat pack having resistance to premature activation of an ultracooled saline solution.

[0020] "1,2,3-Propanetriol" and "glycerol" are used interchangeably in this document to refer to the same polyol compound having the simple formula C3H8O3.

[0021] In this article, "salt" refers to any compound composed of cations and anions.

[0022] In this article, "salt solution" refers to a solution containing water as a solvent and at least one salt as a solute. "Salt solution" and "salt water solution" are used interchangeably.

[0023] In this article, "supercooling" refers to a liquid or gas that has been cooled below its freezing point without turning into a solid.

[0024] In this article, "by mass" refers to a method of indicating the relative composition of a component (or components) in a solution. When the composition of a component is expressed as a percentage "by mass," the mass of the component is measured as a percentage of the total mass of the solution.

[0025] In this article, "fragile" refers to things that are easily broken.

[0026] In this article, "seal" refers to a closed component that prevents liquid from passing through.

[0027] The terms "latent heat of fusion" or "enthalpy of fusion" are used interchangeably in this article to refer to the energy released when a supercooled liquid changes from a liquid to a solid.

[0028] T in this article max Or, "maximum temperature" refers to the maximum temperature reached after the heat pack is activated. The T value of a specific solution... max It is determined by its latent heat of fusion.

[0029] In this article, "sodium acetate" refers to sodium acetate trihydrate.

[0030] Premature activation of the packaging is thought to be a result of a rupture or leak in the seal separating the air from the saline solution. However, premature activation has been observed in packaging where the potentially ruptured seals were not damaged. It is unclear why some heat packs survived transport while others activated prematurely.

[0031] Ultimately, it was discovered that low temperatures cause the heating packs to self-activate. It was observed that heating packs placed on the outer layer of the transport container were more likely to be prematurely activated before delivery to the end user compared to those from the central layer. Furthermore, even more heating packs were found to be prematurely activated during colder winter months.

[0032] Typically, saline solutions are prepared to stabilize the supercooled solution at ambient temperatures in homes, hospitals, and their associated storage areas. However, during manufacturing and distribution, the heat packs may be exposed to temperatures below room temperature. In these cases, the saline solution may be prematurely activated.

[0033] While heating packs can be transported in heated vehicles and containers, this solution is both expensive and error-prone. Heating packs stored outside heated trucks may still experience low temperatures. Furthermore, some heating packs may be pre-activated at transfer points within the delivery chain. Premature activation is especially common during colder winters and particularly frigid days. This problem is further complicated by the large number of entities involved in the distribution process; supply chains are often too complex to be properly controlled.

[0034] Some heat packs containing supercooled saline solutions are known to contain organic compounds, but these heat packs disclose organic compound concentrations between 1% and 10% by weight. European Patent No. 2,853,576B1 describes a heat pack containing supercooled aqueous solutions containing 1-9% glycerin. However, test results disclosed in that document appear to indicate that resistance to preactivation decreases when glycerin exceeds 2% of the total solution. In Example J1, a composition containing 2% glycerin by weight was stored at -20°C for 3 to 5 hours under supercooled conditions. In contrast, solutions containing higher concentrations of glycerin showed shorter periods of resistance to preactivation. In Example J5, a solution containing 9% glycerin by weight was stored at -20°C for 2 to 3 hours, while in Example J9, a composition containing 6% glycerin by weight was stored at -20°C for only 1 to 2 hours.

[0035] Existing technology indicates that the ideal concentration of glycerol for maintaining a supercooled state is approximately 2%, and increasing the glycerol concentration to above 2% will make the supercooled saline solution easier to pre-activate.

[0036] Furthermore, organic compounds are believed to reduce the crystallization rate of supercooled salt solutions, thereby reducing the heat released during activation. Because heat packs used for medical or therapeutic purposes must reach a specified maximum temperature (T0). max Therefore, organic compounds may not be suitable as antifreeze agents.

[0037] A heat pack comprising a container having two flexible sheets bonded together to form a laminated sheet is disclosed. The container has a first compartment and a second compartment. A ruptureable seal separates the two compartments. One compartment contains air, and the other compartment contains a supercooled saline solution. The saline solution contains 15% to 25% glycerol by weight.

[0038] Many salts are suitable for preparing saline solutions, including sodium thiosulfate (Sigma-Aldrich, Oakville, Canada) and sodium acetate trihydrate (Sigma-Aldrich, Oakville, Canada). An effective saline solution for use in heat packs has been found to be an aqueous solution of sodium acetate trihydrate. While the solution strength can vary, a mixture of 100 grams of water and approximately 50 to 100 grams of sodium acetate trihydrate has proven effective. The solution can be heated to 77 to 88 degrees Celsius (170 to 190 degrees Fahrenheit) and then supercooled. The solution can then be placed in a heat pack.

[0039] Solutions within the indicated range have been found to be desirable because they can be readily triggered to provide heat with a substantially constant temperature. If a supercooled solution has been heated to a sufficiently high temperature above its melting point before cooling, it will remain stable in the supercooled state even when cooled below its melting point. The supercooled solution will remain in this state until triggered by mixing the contents of the second compartment.

[0040] Sodium acetate trihydrate is a proven effective chemical for use in solution. Other chemicals with suitable properties can also be used. One requirement is a stable and relatively rapid phase transition once crystallization is initiated. Many applications require a phase transition temperature suitable for warm human skin.

[0041] In one embodiment, the latent heat of fusion of the solution reliably heats the heat pack to a narrow range of approximately 38.3 to 40 degrees Celsius (101 to 104 degrees Fahrenheit), most typically close to 40 degrees Celsius (104 degrees Fahrenheit). In another embodiment, the latent heat of fusion of the solution heats the heat pack to a narrow range of approximately 41.7 to 43.3 degrees Celsius (107 to 110 degrees Fahrenheit). The phase change and heating occur within seconds, and the heat is retained for several minutes. The heat is evenly distributed through gentle kneading.

[0042] Adding glycerol to a saline solution can prevent premature activation, especially at temperatures below -10°C. The concentration of glycerol in the solution can vary depending on the heat released by the desired activation and the required solution stability. Solutions containing approximately 15% to 25% glycerol by mass have proven effective.

[0043] Some embodiments of the heating pad can be used to heat an infant's heel for blood collection. Heating an infant's heel increases capillary blood flow in the infant's foot, thereby promoting blood collection. Therefore, the composition of the saline solution can be chosen to achieve a latent heat of fusion suitable for heating an infant's heel. In one example, the solution may contain glycerol (22% ± 0.5%), water (33.5% ± 0.5%), and sodium acetate (44.5% ± 0.5%) by mass. This solution remains stable at -30°C. In some cases, it remains stable at temperatures below -30°C. When activated, the maximum temperature of the solution may reach 38.3–40°C (101–104°F).

[0044] Other embodiments of the hot compress bag can be used for therapeutic purposes. Therefore, the composition of the saline solution can be selected to achieve a latent heat of fusion suitable for therapeutic purposes. In one example, the solution may contain glycerol (19.1% ± 0.5%), water (34.1% ± 0.5%), and sodium acetate (46.9% ± 0.5%) by mass. This solution remains stable at -30°C. In some cases, it remains stable at temperatures below -30°C. When activated, the maximum temperature of the solution may reach 41.7–43.3°C (107–110°F).

[0045] As mentioned above, other chemicals with different properties and, in particular, different phase transition temperatures can also be used. For some applications, higher temperatures may be required, necessitating the use of chemicals with higher latent heat of fusion. Heat packs are generally used to heat a variety of items other than humans, including other liquids, food, etc. Some of these applications may require heat packs to generate temperatures of 54 to 66 degrees Celsius (130 to 150 degrees Fahrenheit) or higher.

[0046] 1.1 Freezing point of glycerol dilution

[0047] A study was conducted to evaluate the effect of water dilution on the freezing point and boiling point of glycerol. The results are shown in Table 1 below.

[0048] For compositions containing between 66.7% and 100% glycerol, the freezing point decreases as the glycerol-to-water ratio decreases. However, for compositions containing less than 66.7% glycerol, the freezing point increases as the glycerol-to-water ratio decreases. These test results indicate that the freezing point temperature for a glycerol-to-water ratio of 2:5 is -15.6°C.

[0049] Table 1

[0050]

[0051] 1.2 Pre-activation test

[0052] The variable composition of supercooled sodium acetate solution and glycerol was investigated. Each sample was contained in a separate water bag made of polyethylene or polyethylene terephthalate. Five water bags containing 0% glycerol, five water bags containing 5% glycerol, five water bags containing 12% glycerol, five water bags containing 20% ​​glycerol, and five water bags containing 23% glycerol were tested. Sodium acetate comprised 44.5% by weight of each solution, with the balance being water. The total mass of the solution in each water bag was 232 ± 12 g.

[0053] First, the samples were placed in a room at a temperature of 21-24.5°C (70-76°F) until all samples reached room temperature. Next, the samples were simultaneously placed in a high and low temperature test chamber (LNEYA; Wuxi, Jiangsu). The chamber temperature was lowered to -10°C (14°F) over four hours, and pre-activation of the samples was observed. The temperature was further lowered from -10°C (14°F) to -15°C (5°F) over four hours, and pre-activation of the samples was observed. The temperature was further lowered from -15°C (5°F) to -20°C (-4°F) over four hours, and pre-activation of the samples was observed. The temperature was further lowered from -20°C (-4°F) to -25°C (-13°F) over four hours, and pre-activation of the samples was observed. The temperature was further lowered from -25°C (-13°F) to -30°C (-22°F) over four hours, and pre-activation of the samples was observed.

[0054] The test results are summarized in Table 2 below. The checkmark indicates the temperature at which pre-activation was first observed in the corresponding test item.

[0055] Table 2

[0056]

[0057] No solidification occurs at temperatures between room temperature and -10°C (14°F). Solutions containing 0% or 5% glycerol begin to solidify at temperatures between -10°C (14°F) and -20°C (-4°F). Solutions containing 12% glycerol solidify at temperatures between -20°C (-4°F) and -25°C (-13°F). Solutions containing 20% ​​glycerol begin to solidify at temperatures below -25°C (-13°F). Solutions containing 23% glycerol do not solidify at -30°C (-22°F). Therefore, it can be concluded that the pre-activation of supercooled saline solutions is related to temperature and the glycerol ratio.

[0058] 1.3 Long-term freezing test

[0059] This study tested the long-term freeze resistance of a heat pack containing a supercooled saline solution. The heat pack was based on information regarding... Figure 1-4 The packaging method is described later. 162 heat packs were packaged, each containing one of the following four ingredients:

[0060] A. By weight, glycerol (19.1% ± 0.5%), water (34.1% ± 0.5%), sodium acetate (46.9% ± 0.5%);

[0061] B. Water (53.1% ± 0.5%), sodium acetate (46.9%);

[0062] C. By weight, glycerol (22% ± 0.5%), water (33.5% ± 0.5%), sodium acetate (44.5% ± 0.5%);

[0063] D. Water (55.5% ± 0.5%), Sodium acetate (44.5% ± 0.5%).

[0064] The heating pads were stored at -17°C (1.4°F) for 6 consecutive days. The pre-activated heating pads were counted and removed. Then, the heating pads were stored at -27°C (-16.6°F) for 3 consecutive days. The pre-activated heating pads were counted and removed again. The test results are shown in Table 3 below.

[0065] Table 3

[0066]

[0067] Tests showed that adding glycerin to the hot compress formulation lowered the freezing point of the solution. Lowering the freezing point significantly reduced the pre-activation of the supercooled salt solution when samples were stored at extremely low temperatures for extended periods.

[0068] 1.4 Maximum Temperature Test

[0069] Another study was conducted to understand the effect of glycerin on the maximum temperature (T) of a heat pack. maxThe impact of ). According to about Figure 1-4 Multiple heat packs were prepared using the method described later. Three samples with each of the following compositions were tested:

[0070] Composition A: Glycerin (19.1% ± 0.5%), water (34.1% ± 0.5%) and sodium acetate (46.9% ± 0.5%) by weight;

[0071] Composition C: Glycerin (22% ± 0.5%), water (33.5% ± 0.5%) and sodium acetate (44.5% ± 0.5%) by weight.

[0072] Each sample was activated by breaking the fragile seal. The temperature of each sample was then measured every minute for 45 minutes using a resistance temperature detector (RTD) temperature recorder (Omega, Norwalk, USA). The results are summarized in Table 4 below.

[0073] Table 4

[0074]

[0075] Further maximum temperature tests were conducted on the heat packs containing compositions E and F.

[0076] Composition E: Glycerin (22.0%), water (33.5%) and sodium acetate (44.5%) by weight;

[0077] Composition F: glycerol (19.1%), water (34.1%) and sodium acetate (46.9%) by weight.

[0078] In one test, the T of the sample containing composition E max The temperature was found to be 39.48℃ (103.064°F). The results for the eight samples containing composition F are summarized in Table 5 below.

[0079] Table 5

[0080] Sample number The highest temperature reached 1 42.63℃(108.734°F) 2 43.02℃(109.436°F) 3 43.3℃(109.94°F) 4 41.83℃(107.294°F) 5 42.45℃(108.41°F) 6 39.48℃(103.064°F) 7 43.18℃(109.724°F) 8 42.42℃(108.356°F)

[0081] Tests showed that the heat pack containing the above-mentioned supercooled saline solution has a T value within the range suitable for infant heel heaters and therapeutic heat packs. max Value. Ideal T for baby heel warmers. max It may be 38-40℃ (101-104°F). T for testing compositions C and E. max Falling within this range. Ideal for use with therapeutic heat packs. max It is likely 41.7-43.3℃ (107-110°F). As shown in Tables 4 and 5 above, the T values ​​for compositions A and F were tested.max It falls within this range.

[0082] 2.1 Hot compress bag

[0083] Now for reference Figure 1 and 2 The illustration shows a heat pack 10 having a first compartment 12 and a second compartment 14. In this embodiment, the heat pack 10 comprises four sheets 16, 18, 22, and 24, but the heat pack 10 may comprise any suitable number of sheets, more than one. The sheets 16, 18, 22, and 24 are bonded together to form a laminated sheet having internal spaces. The heat pack 10 further includes a fragile seal separating the first compartment 12 from the second compartment 14.

[0084] Sheets 16, 18, 22, and 24 can be configured to form the first compartment 12 and the second compartment 14. Many configurations are suitable for forming the first and second compartments. One possible configuration is... Figure 1-4 As shown in the diagram, the first sheet 22 and the second sheet 24 can be bonded together along their peripheral edges 26 to form a second compartment 14. The third sheet 16 and the fourth sheet 18 can be bonded together along their peripheral edges 20 to form a first compartment 12. The third and fourth sheets 16, 18 can be contained within the second compartment. The third and fourth sheets 16, 18 can be bonded to the first and second sheets 12, 14, or they can be separated from the first and second sheets 12, 14. In this embodiment, the first compartment 12 has the same shape as the second compartment 14, but the first compartment 12 is smaller and therefore suitable for inclusion within the second compartment 14. In this embodiment, one or both of the third sheet 22 and the fourth sheet 24 may contain a brittle seal. The brittle seal may be a weak point or seam in the third and / or fourth sheets 22, 24.

[0085] In another possible configuration (not shown), the first and second sheets can be bonded together along their outer edges to form an internal space. The internal space can be divided into a first compartment and a second compartment. The internal space can be separated by a third sheet or a seam between the first and second sheets 16, 18. If the internal space is separated by a third sheet, the third sheet can contain a brittle seal, which can be a weak point or a seam. If the internal space is separated by a seam, the seam can contain a brittle seal.

[0086] In the illustrated embodiment, the sheets 16, 18, 22, and 24 are generally rectangular in shape and each pair of sheets has approximately the same size and construction, but there are no particular restrictions on the sheets.

[0087] Sheets 16, 18, 22, and 24 may comprise flexible or semi-flexible materials. For ease of manufacture of the heat pack 10, the sheets may be heat-sealable. Many suitable materials exist, including polyester and polynylon. A particularly suitable heat-sealable plastic material is polyethylene. Polyethylene has low to medium density, is inexpensive, and is easily heat-sealable over a wide temperature range. Polyethylene sheet materials are very flexible and easily elongate under tension. In some applications, the use of polyethylene laminates has also been successful. For example, the third and fourth sheets may be made of laminated materials, while the first and second sheets may be made of standard polyethylene material.

[0088] The bonding between the first and second sheets and the third and fourth sheets can create an airtight seal.

[0089] Both the first compartment 12 and the second compartment 14 can be adapted to contain the supercooled brine solution 28 prepared according to the method described above. In this embodiment, the supercooled brine solution is contained in the first compartment 12, but in other embodiments, the second compartment may contain the supercooled brine solution 28. Either compartment not containing the supercooled brine solution 28 may be adapted to trigger solidification of the supercooled brine solution when the fragile seal breaks, such as... Figure 3 As shown. A compartment may contain, but is not limited to: nothing, gas, metal, or atmosphere.

[0090] To trigger the packaging, the user applies steady but reasonable pressure to the outside of the packaging with a squeezing motion. Because solution 28 is typically an incompressible liquid, such as water, the resultant force tends to force the solution out of first compartment 12 by rupturing one or more seams at the edge of first compartment 20, thereby allowing solution 28 to mix with air from second compartment 14. This is sufficient to reliably trigger the crystallization of the supercooled solution, thereby releasing the latent heat of fusion. The heating pack 10 is thus heated and can be applied to the user. The rupture of first compartment 12 in... Figure 3 As shown in the image.

[0091] The sheets can be selected and manipulated so that the force required to break the fragile seal can be easily achieved with one hand. However, due to the fluid nature of the heat pack, any accidentally applied force is unlikely to trigger it. For example, handling during storage and transportation is unlikely to activate the heat pack. If needed, the first compartment 12 can also be secured to the second compartment 14 by heat-sealing all four sheets together along one edge for a distance at a seam. This promotes optimal force distribution when the package is squeezed from the outside, allowing rupture to occur in the most efficient manner.

[0092] If a greater consistency is required in the crystallization solution, such as for larger packaging, a viscosity enhancer or gelling agent can be added to the solution. One such agent that has proven effective is a hydroxyethyl cellulose polymer.

[0093] refer to Figure 4 Optionally, adhesive tape or other fastening mechanisms 30 can be attached to the packaging to help keep the packaging in contact with people or objects for effective heating.

[0094] Many features and advantages of the present invention will be apparent from the detailed description; therefore, the appended claims are intended to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Furthermore, since many modifications and variations will readily occur to those skilled in the art, it is not intended to limit the invention to the exact structures and operations shown and described; therefore, all suitable modifications and equivalents that may be taken fall within the scope of the invention.

Claims

1. A hot pack, characterized by comprising: a first and second sheet adhered together to form a laminated sheet having an interior space; a first and second compartment contained within the interior space; a supercooled brine solution contained in the second compartment, the supercooled brine solution comprising greater than 15% and not greater than 25% by mass of glycerol; and a frangible seal between the first and second compartments.

2. The hot pack of claim 1 wherein, The supercooled brine solution is a solution of a salt of thiosulfate.

3. The hot pack of claim 2 wherein, The solution of a salt of thiosulfate is a solution of sodium thiosulfate.

4. The hot pack of claim 1 wherein, The supercooled brine solution is a solution of a salt of a trihydrate acetate.

5. The hot pack of claim 4 wherein, The solution of a salt of a trihydrate acetate is a solution of sodium trihydrate acetate.

6. The hot pack of claim 1 wherein, The supercooled brine solution has a maximum temperature in the range of 38 to 40 degrees Celsius.

7. The hot pack of claim 1 wherein, The supercooled brine solution has a maximum temperature in the range of 41.7 to 43.3 degrees Celsius.

8. The hot pack of claim 1 wherein, The first compartment contains air.

9. The hot pack of claim 1, further comprising a third sheet adhered to one or both of the first and second sheets, wherein, The third sheet divides the interior space into the first and second compartments, and wherein the third sheet comprises the frangible seal.

10. The hot pack of claim 1 wherein, The first and second sheets are further adhered together to form a seam dividing the interior space into the first and second compartments, and wherein the seam comprises the frangible seal.

11. The hot pack of claim 1, further comprising third and fourth sheets adhered together to form a laminated sheet having the second compartment; wherein, the interior space comprises the third and fourth sheets; and wherein one or both of the third and fourth sheets comprises the frangible seal.

12. The hot pack of claim 1 wherein, The supercooled brine solution comprises 15 to 20% by mass of glycerol.

13. The hot pack of claim 1 wherein, The supercooled brine solution comprises 19% by mass of glycerol.

14. The hot pack of claim 1 wherein, The supercooled brine solution comprises 20 to 25% by mass of glycerol.

15. The hot pack of claim 1 wherein, The supercooled brine solution comprises 22% by mass of glycerol.

16. A method of heating a baby's heel for blood sampling with a hot pack, the method comprising applying a hot pack to the baby's heel, the hot pack comprising: a first and second sheet adhered together to form a laminated sheet having an interior space; a first and second compartment contained within the interior space; a supercooled brine solution contained in the second compartment, the supercooled brine solution comprising greater than 15% to not greater than 25% by mass of glycerol; and a frangible seal between the first and second compartments.

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