Abstract:
The invention relates to a method of releasing chemical compounds. The method includes distributing containers encapsulating a chemical compound over hair, said containers being configured to release the chemical compound upon reaching a transition temperature, and heating the hair to a predetermined temperature equal to or higher than the transition temperature. The heating of the hair enables heat transfer from the hair to one or more of the containers that are in proximity of the hair,whereby the one or more containers reach the transition temperature and release the chemical compound. In this manner, only those containers that are in close proximity to the hair can be heated up to their transition temperature and release the compound. Consequently, the compound is only released locally where the hair is present, while other skin areas where the hair is not present are protected against the potentially negative side effects of the compound.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the present invention relate generally to the field of hair treatments, and, more specifically, to methods and systems for releasing chemical compounds onto hair. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Historically, a number of techniques have been used in eliminating unwanted hair on various body parts. One technique commonly utilized for the removal of hair on arms and legs relies on the use of depilatory creams containing bio active ingredients, such as thioglycolates. Weakening of the hair occurs by the oxidation of the disulfide bridges of keratin, resulting in easy removal of the hair. One drawback of this technique is that, since the epidermis contains a high content of keratin, damaging and irritation of the skin occurs if the thioglycolate mixture is applied for an extended period of time. Another drawback is that thioglycolate-based creams, for instance Veet®, cannot be used in the face, due to the fact that facial hair dissolves too slowly using thioglycolates, giving rise to unacceptable damage of the skin. 
         [0003]    Other techniques are based on thermolysis of hair achieved by irradiation of hair with light. For example, WO97/38638 and WO2009/073017 describe methods of permanent hair removal which rely on preferentially depositing additional quantities of melanin, a naturally occurring element in the skin and hair follicles, at the follicle sites or in their proximity. The preferential deposition is achieved by encapsulating melanin-based compounds in liposomes specifically selected and formed to bind to specific sites in the proximity of or inside the hair follicles. After a medium containing such liposomes has been applied topically to the skin, laser light of a frequency which is readily absorbed by the melanin is directed to the skin. As a consequence of the added quantity of melanin, a greater proportion of the incident light is absorbed at the hair follicles, causing thermolysis and death of the follicles. One drawback of this approach is that melanin-containing liposomes may also be deposited on areas which are not necessarily in the proximity of hair follicles, leading to undesirable increased absorption of light in those areas. 
         [0004]    What is needed in the art is a method of providing chemical compounds for hair removal, hair coloring, or other treatment in a manner that reduces at least some of the drawbacks described above. 
       SUMMARY OF THE INVENTION 
       [0005]    According to one aspect of the invention, a method of releasing a chemical compound onto hair is disclosed. The method includes distributing containers encapsulating the chemical compound over hair, where the containers are configured to release the chemical compound upon reaching a transition temperature. The method also includes heating the hair to a predetermined temperature that is equal to or higher than the transition temperature. The heating of the hair enables heat transfer from the hair to one or more of the containers that are in proximity of the hair, whereby the one or more containers reach the transition temperature and release the chemical compound. In turn, the released chemical compound that is in contact with the hair may e.g. treat the hair. 
         [0006]    The invention is based on the recognition that encapsulating a chemical compound into containers, distributing the containers over the hair, and selectively heating the hair in a manner that avoids or minimizes direct heating of the containers results in the hair being heated to a temperature higher than that of the containers and, therefore, enables heat transfer from the heated hair to the containers. When such containers are temperature-sensitive so that they are configured to release the compound upon reaching a certain transition temperature, and when the hair is heated to a temperature that is equal to or higher than the transition temperature of the containers, then the heat transfer from the heated hair to the containers will, eventually, heat the containers to their transition temperature and they will release the compound. In this manner, only those containers that are in close proximity to the hair, preferably adjacent to or in contact with the hair, can be heated up, via the heat transfer from the hair, to their transition temperature and are able to release the compound. Consequently, the compound is only released locally where the hair is present, while other skin areas where the hair is not present are protected against the potentially negative side effects of the compound. 
         [0007]    In one embodiment, selective heating of hair may be achieved by irradiating the hair with light, the wavelength or the range of wavelengths of said light being selected so that a portion of the light absorbed by the hair is greater than a portion of the light absorbed by the containers and the chemical compound in order to ensure that the hair is heated up by the light to a higher temperature than the containers and that the containers only reach their transition temperature via the heat transfer from the hair. For safety reasons, the wavelengths of the light are preferably  400  nanometers (nm) or higher. In various embodiments, such light could be generated by one or more of a laser, a laser diode, a light emitting diode (LED) or an intense pulsed light (IPL) source such as a flash lamp. 
         [0008]    In an alternative embodiment, selective heating of hair may be achieved using a pressure wave source, such as e.g. an ultrasound transducer. 
         [0009]    In an embodiment, the temperature-sensitive containers could be in the form of carriers comprising a lipid bilayer shell. Particularly, such shells could enclose a cavity, and be semi-permeable, typically comprising phospholipids. The carriers could be microcarriers, having a particle size whose diameter is of the order of several microns to tens of microns, and nanocarriers, having a particle size of the order of tens to hundreds of nanometers. In the context of the invention, the carriers are hereinafter referred to as “liposomes”. Liposomes are typically spherical vesicles comprising a bilayer membrane enclosing a cavity (referred to as a “lumen”). The bilayer can be made up of at least one phospholipid and may or may not comprise cholesterol. Temperature-sensitive liposomes (TSLs) release encapsulated molecules at the melting phase transition temperature (T m ) of the lipid bilayer. 
         [0010]    In an embodiment, the containers could be distributed over the hair in the form of a topical formulation such as e.g. a cream, a spray, a gel, a suspension, or a solution carrying the containers. 
         [0011]    In an embodiment, the step of distributing the containers over the hair could comprise distributing the containers over a skin area comprising the hair. Such containers would be selectively opened, releasing the chemical compound stored in them, only near the hair where sufficient heat is available but will remain closed at other locations. This enables easy application of the containers while protecting the skin against the chemicals. 
         [0012]    In an embodiment, the chemical compound could be a compound for treatment of the hair that is in contact with the released compound, such as e.g. hair coloring, hair conditioning, hair removal, or any other treatment. For example, the chemical compound could include water-soluble components such as enzymes, hormones or other chemicals like e.g. thioglycolate. 
         [0013]    According to another aspect of the invention, an assembly for releasing a chemical compound onto hair is provided. The assembly includes a topical formulation for distribution over hair and a heat source. The topical formulation comprises containers encapsulating the chemical compound, the containers being configured to release the chemical compound upon reaching a transition temperature. The heat source is configured for heating the hair to a predetermined temperature equal to or higher than the transition temperature, whereby heat transfer from the hair to one or more of the containers that are in proximity of the hair is enabled, causing the one or more containers to reach the transition temperature and release the chemical compound. Such an assembly could be used in e.g. a light-based hair treatment product, such as a photoepilation device, or light-based shavers or groomers. 
         [0014]    Hereinafter, embodiments of the invention will be described in further detail. It should be appreciated, however, that these embodiments may not be construed as limiting the scope of protection of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In all figures, the dimensions as sketched are for illustration only and do not reflect the true dimensions or ratios. All figures are schematic and not to scale. 
           [0016]      FIG. 1A  illustrates a temperature-sensitive container below its transition temperature, encapsulating a chemical compound, according to an embodiment of the present invention; 
           [0017]      FIG. 1B  illustrates the temperature-sensitive container of  FIG. 1A  at or above its transition temperature, releasing the chemical compound, according to an embodiment of the present invention; 
           [0018]      FIG. 2  illustrates removal of hair by temperature-induced release of bioactive ingredients from temperature-sensitive containers, according to an embodiment of the present invention; 
           [0019]      FIG. 3  illustrates the release of hair dyes, conditioner or therapeutics, e.g. for hair coloring, from temperature-sensitive containers, according to an embodiment of the present invention; 
           [0020]      FIG. 4  illustrates enhanced photoepilation, according to an embodiment of the present invention; and 
           [0021]      FIG. 5  illustrates experimental proof of light-induced release of fluorescent chemical compound encapsulated in temperature-sensitive liposomes. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention. 
         [0023]      FIGS. 1A and 1B  each illustrate a temperature-sensitive container  100 , according to one embodiment of the present invention. When the container  100  is at a temperature below its transition temperature, the container  100  is closed and encapsulates a chemical compound  110 , as shown in  FIG. 1A . In this state, preferably, the chemical compound  110  does not escape from the container  100  at all, or, at least is not released from the container  100  in significant amounts. However, when the container  100  is heated to its phase transition temperature, the container  100  is configured so as to open and release the compound  110 , as is shown in  FIG. 1B . While  FIG. 1B  illustrates that the container  100  opens to release the compound  110  from one side (the right side in  FIG. 1B ), persons skilled in the art will recognize that, in other embodiments, the container  100  could release the compound  110  in other manners, all of these manners being within the scope of the present invention. For example, when the container  100  reaches its transition temperature, the walls of the container  100  could become porous, so that the compound  110  can sip out through the walls. Alternatively, upon reaching its transition temperature, the container  100  could partially or completely dissolve, thereby also releasing the compound  110 . 
         [0024]    The present invention provides a method of releasing the compound  110  from the container  100  onto hair in a manner that minimizes the amount of the compound  110  released onto anything other than the hair, e.g. the skin. 
         [0025]    The method begins with distributing a plurality of containers  100  over hair. Upon distribution, the containers  100  are at a temperature that is below their transition temperature and, therefore, are closed. In various embodiments, the containers  100  could be distributed by being included in any kind of topical formulation such as e.g. a cream, a spray, a gel, a suspension, a solution, or a powder. For easy application, in an embodiment, the containers  100  could be distributed over the entire skin area comprising the hair, as opposed to being e.g. spread only onto hair and not onto the skin area near and/or under the hair. 
         [0026]    Once the containers  100  are distributed over the hair, the hair is selectively heated. As used herein, the expression “selective heating” describes heating of the hair in such a manner that the temperature of the hair increases faster than the temperature of the containers  100  and the chemical compounds  110  therein. 
         [0027]    In one embodiment, selective heating of hair may be achieved by irradiating the hair with light, the wavelength or the range of wavelengths of the light being selected so that a portion of the light absorbed by the hair is greater than a portion of the light absorbed by the containers  100  and the chemical compound  110 . In a preferred embodiment, the containers  100  and the chemical compounds  110  do not absorb any light or absorb only a small amount, e.g. less than 10%, of the light incident on the containers and chemical compounds, while the hair readily absorbs the light, e.g. more than 50% of the light incident on the hair. The absorption behavior of the containers  100  and the compounds  110  could be adjusted by tuning their chemical composition so that they do not absorb light of the wavelength(s) of the available light source. In various embodiments, the light source could include one or more of a laser, a laser diode, an LED or an IPL source. For reasons of skin safety, the wavelengths of the light are preferably 400 nm or higher. 
         [0028]    Selective heating of hair results in the hair being heated up to a higher temperature than that of the containers  100  and the compounds  110  encapsulated therein. Because of the temperature differences between the hair and the containers  100 , some of the heat from the hair is transferred to the containers  100  that are in thermal contact with the hair, until the hair and the containers  100  are in thermodynamic equilibrium. Since the temperature of the containers  100  is not increased directly (or onlyat a lower rate) by the heat source providing the selective heating, such selective heating of the hair ensures that the containers  100  may only reach their transition temperature via the heat transfer from the hair. 
         [0029]    The thermal contact between the hair and the containers  100  could be established e.g. by the containers  100  being adjacent to, i.e. in contact with, the hair. The heating of the containers  100  could also be established when the containers  100  are not in direct contact with the hair but are in close proximity of the hair, so that heat transfer from the hair to the containers  100  is enabled via e.g. convection. In some applications of the present invention, the latter type of thermal contact is preferably minimized to ensure that only the containers  100  that are in direct contact with the hair are able to receive sufficient heat from the hair to be heated up to their transition temperature and release the compounds  110 . This could be achieved by e.g. selectively heating the hair to a sufficiently high temperature but only for a short period of time. In this manner, the sufficiently high temperature of the hair would enable heat transfer to the containers  100  that are in direct contact with the hair, so that these containers release the compounds  110  encapsulated therein, but the heat transfer to the containers  100  that are not in direct contact with the hair would not be sufficient to heat those containers to their transition temperature. Consequently, the containers  100  that are not in direct contact with the hair would remain closed. 
         [0030]    When some of the containers  100  distributed over hair reach, via the heat transfer from the hair, their transition temperature (e.g. hyperthermia temperature of 40-45° C.), these containers release the chemical compound  110  encapsulated in them. The chemical compound  110  could be e.g. a compound for hair treatment such as hair removal, hair coloring, and/or hair conditioning. Such a compound could be configured to react with the hair tissue in order to degrade, color, or condition the hair tissue, when the compound is in contact with the hair. 
         [0031]    In a preferred embodiment, the containers  100  are selected or modified such that their transition temperature is sufficiently far above the body temperature in order to avoid the containers reaching their transition temperature by being in contact with the body and uncontrollably releasing the compound  110 . While the transition temperature should be above the body temperature and, particularly, above the skin temperature, it should also be below the maximum temperature reached by the hair exposed to selective heating. The maximum temperature may vary, depending on the particular application of the disclosed method of releasing the chemical compound  110 . For example, in a method where the hair is merely heated by light, the maximum temperature could be as low as 35-50° C. However, in applications where the hair is cut by the heat, such as e.g. laser shaving, the temperature of the hair may locally reach the melting and/or evaporation temperature of the hair, which is typically much higher than 50° C. 
         [0032]    In an embodiment, the containers  100  could be in the form of temperature-sensitive liposomes capable of triggered-release of a bioactive ingredient (i.e., the chemical compound) from their lumen. These heat-sensitive vessels release encapsulated molecules at the melting phase transition temperature (T m ) of the lipid bilayer. At T m , structural changes in the lipid membrane occur as it transfers from a gel to the liquid-crystalline phase. Liposomal membranes in the gel (i.e. solid-like) phase are less permeable to water and drugs compared to the liquid-crystalline phase. At the melting phase transition temperature, the membrane permeability of the lipid bilayer increases by several orders of magnitude, thereby facilitating the release of the chemical compound previously encapsulated therein. 
         [0033]    The T m  of the liposomes could be adjusted by tuning the chemical composition of the lipid bilayer, as is known in the art. For example, incorporation of lyso-phosphatidylcholines (lyso-PCs) in the bilayer of liposomes has a pronounced effect on the release properties of the heat-sensitive container. In this manner, low temperature-sensitive liposomes (LTSLs) composed of lyso-PC/DPPC/DPPE-PEG2000 could be created that release encapsulated aqueous solutes in a matter of seconds at 39-42° C. 
         [0034]    Some examples of the chemical compound  110  that could be encapsulated in the containers  100  include water-soluble components such as enzymes, hormones or other chemicals like e.g. thioglycolate. 
         [0035]      FIGS. 2-4  provide some exemplary applications of the method of releasing the chemical compound onto hair, according to various embodiments of the present invention. However, a person skilled in the art will recognize that many further applications are possible, e.g. applications where the released chemical compound does not directly result in treatment of hair, but may serve as a pre-cursor for such treatment later on, all of these applications being within the scope of the present invention. 
         [0036]      FIG. 2  illustrates removal of hair by temperature-induced release of bioactive ingredients from temperature-sensitive containers, according to an embodiment of the present invention. As shown in step ( 1 ) of  FIG. 2 , first the containers  100  (indicated by means of the round dots) are distributed over the hair and the skin. In step ( 2 ) illustrated in  FIG. 2 , the hair is locally heated with a light source (shown as a rectangle). The local heating of the hair results in temperature-mediated release of the chemical compound from the containers, illustrated in step ( 3 ) of  FIG. 2 , which reduces the disulfide bridges of keratin in the hair. In step ( 4 ) of  FIG. 2 , the hair is removed and the remainder of the containers and the released chemical compounds could be wiped off. This approach could be used in a depilation product, such as an IPL photoepilation device, or a shaving product. 
         [0037]      FIG. 3  illustrates release of hair dyes, conditioner or therapeutics from temperature-sensitive containers, according to an embodiment of the present invention. As shown in step ( 1 ) of  FIG. 3 , first the containers  100  (again, shown by means of the round dots) are distributed over the hair and the skin. In step ( 2 ) illustrated in  FIG. 3 , the hair is locally heated with a light source (shown as a rectangle), which results in the release of the dye, conditioner or therapeutic from the containers. The released dye could have a cosmetic function, e.g. when it is used for coloring of the hair, or may serve to enhance the efficacy of a photoepilation treatment. 
         [0038]      FIG. 4  illustrates enhanced photoepilation, according to an embodiment of the present invention. This embodiment combines photoepilation with temperature-triggered release of bioactive ingredients to the hair. Step ( 1 ) of  FIG. 4  illustrates the original state of the hair and the skin. Step ( 2 ) of  FIG. 4  illustrates pre-shaving of the hair, resulting in remaining stubble. Step ( 3 ) of  FIG. 4  illustrates that the containers  100  (again, shown by means of the round dots) are distributed over the hair and the skin. Step ( 4 ) of  FIG. 4  illustrates a light source (shown as a rectangle) locally heating up the hair and the hair follicle, thereby locally triggering the release of the hair-attacking chemical compound encapsulated in the containers  100 . Step ( 5 ) illustrates the released chemical compound dissolving the hair, which results in smoother skin compared to pre-shaving treatment only, as shown in step ( 6 ) of  FIG. 4 . 
         [0039]    For the proof of principle, temperature-triggered release of fluorescent molecules from the aqueous lumen of a temperature-sensitive liposome (TSL) in the presence of hair was investigated using a long-pulse commercial photoepilation device and a short-pulse commercial photoepilation device. The long-pulse device was a device characterized by a pulse length between 140 and 360 ms, fluence between 10 and 35 J/cm 2 , and wavelength of 810 nm. The short-pulse device was a device characterized by a pulse length of  2  ms, fluence between 3 and 6 J/cm 2 , and wavelength between 570 and 1200 nm. 
         [0040]    The release of encapsulated molecules from the TSL was probed by fluorescence spectroscopy. As shown in  FIG. 5 , quantitative release of the fluorescent molecule from the TSL was observed after the application of 20 light pulses using the long-pulse commercial photoepilation device, where pulse duration is of the order of hundreds of milliseconds (ms). As expected, no release of the fluorescent molecule from the TSL was observed after the application of 20 light pulses using the short-pulse photoepilation device, because the pulse duration in that device is only 2 ms. Moreover, control experiments with TSLs and photoepilation devices in the absence of hair didn&#39;t show any release of the fluorescent molecules. In conclusion, the release of encapsulated fluorescent probes from TSLs has been demonstrated by heating up the hair by light using a long-pulse photoepilation device. 
         [0041]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Therefore, the scope of the present invention is determined by the claims that follow.