WO1997047250A1

WO1997047250A1 - Liquid crystals in dermatological treatments using light energy

Info

Publication number: WO1997047250A1
Application number: PCT/US1997/010399
Authority: WO
Inventors: Thomas L. Mehl, Sr.
Original assignee: Mehl Thomas L Sr
Priority date: 1996-06-13
Filing date: 1997-06-13
Publication date: 1997-12-18
Also published as: ZA975263B; AU3311897A

Abstract

A method of treatment of tissue is provided which uses the unique properties of liquid crystal compounds. Liquid crystal compounds (10) are introduced into, onto, or adjacent a targeted tissue region. Light energy (12) is then passed through the liquid crystal before striking the targeted tissue. The properties of the selected liquid crystal are such that the light energy is altered or filtered to enhance the effectiveness of the light energy in treatment. Methods are provided in which liquid crystals are used to automatically match the incident light to increase absorption. These methods are used in depilation. Liposome delivery is provided for delivery of the liquid crystals to specific tissues.

Description

DESCRIPTION

LIQUID CRYSTALS IN DERMATOLOGICAL TREATMENTS USING LIGHT ENERGY

Background of the Invention

The present invention pertains to processes and devices used to destroy human tissue by application of light energy. In particular, the present invention involves a process by which light energy projected onto the skin for the purpose of killing hair follicles is first filtered or modified by a liquid crystal. Destruction of other tissues, such as lesions and cancerous cells, are similarly accomplished. The invention may be applied to remove skin tissue accomplishing exfoliation, resurfacing, or removal of skin wrinkles.

Photothermolysis as a method of depilation is typically limited by the potential collateral damage occurring to the skin surrounding the targeted hair follicles. This damage is a consequence of the inevitable absorption by the skin of the light energy directed at the hair follicle. This is particularly a concern in processes for hair removal from large portions of the body as compared to processes aimed at removing individual hairs. Prior methods in the art have attempted to increase the relative absorption by the hair follicle by using a light source of a wavelength particularly absorbed by cells in the vicinity of the hair follicle (see Zaias, U.S. patent No. 5,059,192) or providing a secondary target by introducing contaminants (see Tankovich, U.S. patents 5,226,907 and 5,425,728). However, because of the potential for collateral skin damage, these methods have been constrained to light sources producing light energy of a limited wavelength band - those most readily absorbed by the targeted tissues. Liquid crystals are a class of chemical compounds and mixtures which exhibit the mechanical properties of liquids and the optical properties of solids. As well, liquid crystals are known for their own unique properties such as optical behavior which is dependent on applied external energy fields. In particular, it is possible to select a liquid crystal whose optical properties are dependent on, or controllable by, the liquid crystal temperature, applied electrical fields, or the characteristics of the incident light itself.

What is needed is a process in which the unique properties of liquid crystal compounds can be utilized so that any light source of sufficient intensity may be filtered, or modified, to provide energy for photothermolysis while limiting collateral damage.

Summary of the Invention It is an object of the present invention to provide a method for altering light energy projected at human tissue to enhance absorption of light energy by specific cells in the skin.

It is another object of the invention to provide a method for filtering light energy projected at tissue such as to increase the relative absorption of such light by specific cells thereby leading to the destruction of those cells while leaving surrounding tissue relatively unaffected.

It an another object of the present invention to provide a method for altering the characteristics of light energy projected at the human skin thereby enhancing photothermolysis of tissue. It is yet another object of the present invention to provide an enhanced photothermolysis target material which is capable of absorbing light energy of any of a broad spectrum of wavelengths.

It is a further object of the present invention to provide an enhanced target material which responds or tunes to incident light to increase the target material's absorptivity of that incident light.

It is yet a further object of the invention to provide a method of depilation in which liquid crystals are used to filter a projected light beam to increase the relative absoφtion of the projected light energy by the melanin in the proximity of the hair follicles. The present invention makes use of the particular properties of liquid crystals to achieve these objects. Liquid crystals are a family of compounds known for their unique properties. In particular, some liquid crystals have nonlinear optical properties. That is, their optical properties change with external energy fields. The present invention is a method by which liquid crystals are introduced between a selected tissue region and incident light energy. The liquid crystal is used to direct or alter the light energy to more efficiently effect the desired result. Because of liquid crystals ability to reflect light in multiple of directions, liquid crystals are also used to redirect incident light toward or away from selected tissues.

In one application, liquid crystals are used as a target material in photothermolysis. A liquid crystal is selected with the ability to "tune" itself to absorb a variety of wavelengths of light energy. By introducing such a liquid crystal into a targeted tissue, a variety of light sources may be directed at the targeted tissue to effect photothermolysis. In another application, a liquid crystal is introduced between a selected tissue and a light source. The liquid crystal filters or alters the light energy as it passes through the liquid crystal. In another application, a liquid crystal is introduced in the proximity of the hair follicle. This liquid crystal reflects the applied incident light energy such as to direct it toward the hair shaft or germative cells of the hair. In a separate application, liquid crystals are applied to the skin surface. The liquid crystal acts as a blocker of deleterious light energy such as UV sunlight, reflecting the energy away from the skin surface. In these uses, liquid crystals are generally topically applied to the skin surface or applied to be absorbed into a targeted tissue. A liposome encapsulated liquid crystal is provided to deliver liquid crystal to specific tissues. An alternative method is to provide the liquid crystal in a carrier structure such as a thin plastic film which is held adjacent or on the skin surface.

Description of the Figures

Figure 1 is a cross section of a skin region showing several embodiments of the invention as applied to the skin tissues.

Details of the Preferred Embodiments Liquid crystals are a class of chemical compounds and mixtures which exhibit the mechanical properties of liquids and the optical properties of solids. Liquid crystals are known for their own unique properties such as optical behavior which is dependent on applied external energy fields. In particular, it is possible to select a liquid crystal whose optical properties are dependent upon the liquid crystal temperature, applied electrical fields, or the characteristics of the incident light itself. The nonlinear optical properties of liquid crystals are discussed in detail in Liquid Crystals - Physical Properties and Nonlinear Optical Phenomena: Iam-Choon Khoo; 1995; John Wiley & Sons, Inc.

In the present invention, liquid crystals are selected to alter the characteristics of a projected light beam such that the resultant light energy, when striking targeted tissue, causes photothermolysis or otherwise destroys the unwanted tissue. The characteristics of the incident light is altered or filtered such that the light energy striking the targeted tissue is absorbed to a greater extent than would be the projected light. As a consequence, destruction of the targeted tissue is accomplished while reducing the exposure and destruction of surrounding tissue. In Figure 1 a liquid crystal material 10 is shown introduced in a variety of ways. Liquid crystal 10 may be introduced at the skin surface or within the epidermis 16 to intercept light incident on the skin. Alternatively, the liquid crystal is selected to act as an absorber of the light energy, causing thermolysis by conduction of the energy to the surrounding tissue, while reducing direct absorption by the surrounding tissue. Without some such means of altering or filtering the incident energy of projected light, many light sources are unusable for selective tissue destruction due to the inevitable absoφtion by untargeted cells and consequential collateral damage.

In an example application, a liquid crystal is selected for its absoφtivity of a broad range of light wavelengths. Essentially, the liquid crystal itself is altered by the incident light in a manner to increase the liquid crystal absoφtivity in the particular wavelength range of the incident light. The liquid crystal "tunes" itself in this manner over a broad range of wavelengths, thereby acting as a very effective photothermolysis target. Because the liquid crystal tunes itself to the applied light, selection of the light source is not as critical. Any light source producing light energy within the wavelength range of the liquid crystal's ability to "tune in" may then be used for photothermolysis and tissue removal. The liquid crystal will absorb the light energy and conduct it to the targeted tissue.

In another application, a liquid crystal is provided which can modify the characteristics of light energy used for photothermolysis. Light energy which would otherwise be detrimentally absorbed by protected tissue is caused to pass through a specifically selected liquid crystal. The liquid crystal alters or modifies the light energy characteristics such that it is not absorbed by the protected tissue. The modified light energy instead is absorbed preferentially by the targeted tissue, thereby effecting the desired result without causing unwanted damage to the protected tissue. Preferably, the liquid crystal is selected such that its properties are dependent on the wavelength of the light itself. In this manner the liquid crystal tunes itself to cause the desired effect not just at a single wavelength, but instead can cause the same result regardless of the wavelength of the projected light, within a broad range.

Liquid crystal compounds can also be effected by external electrical fields. In an alternative application of the invention, a liquid crystal is provided together with a means of applying to it an electrical field. By altering the electrical field, the liquid crystal optical properties are modified to those desired for the specific application. In this manner, the liquid crystal properties may be altered to allow transmission to the tissue of only a specific wavelength of light regardless of the frequency content of the projected incident light.

In one embodiment of the invention, the liquid crystals are applied in the form of a patch. This patch is a thin sheet or sheets of a material such as plastic in which, or on which, the appropriate liquid crystal is contained. In use, the patch is attached to, or otherwise located adjacent to, the surface of the tissue to be treated. In Figure 1 , a patch 26 is shown above the skin surface. The light energy is projected through the patch 26 allowing the liquid crystal 10 to modify the light energy characteristics to that required to effect the target tissue as desired. A light beam 12 is shown passing through a patch

26. It emerges 14 with altered characteristics. In this embodiment, an electrical field may be applied to the patch to modify the liquid crystal optical properties to meet the requirements of the specific light source to be used.

The liquid crystals are applied in a variety of ways depending upon the specific function. In depilation through photothermolysis the liquid crystal is delivered as close to the germative and growth cells of the hair follicle and papilla as possible. This may be accomplished by topical application with a means of encouraging the liquid crystal into the hair follicle. Mechanical encouragement such as by using ultrasonic devices may be used. In the figure, a liquid crystal 10 is shown introduced into the hair follicle walls 22 where they reflect light toward the hair shaft 18, papilla 20 and germative cells of the hair. Where it is desired that light energy striking only specific targeted cells be effected by the the liquid crystal, the liquid crystal is first encapsulated in a liposome. A liposome is selected to migrate and bond preferentially to the specific targeted cells carrying with it the liquid crystal. The liposome acts as a carrier to direct the liquid crystal to the targeted tissue. In one application, the liposome is applied topically to a tissue surface such as the epidermis. Once the liquid crystal has been delivered to the target cell site by the liposome, light energy is projected at the targeted tissue and in passing through the liquid crystal is effected in a manner to enhance thermolysis of the tissue. For depilation a liposome preferably binding to the epidermal cells is used. As shown in Figure 1, the epidermis 16 is the portion of the skin tissues making up the skin's outermost layer. The epidermis also forms the lining of the hair follicle walls 22.

By depositing a liquid crystal 10 in the epidermis, it is concentrated surrounding the hair shaft and adjacent the papilla 20 and other growth cells of the hair. The reflective properties of the liquid crystal there help retain the light energy in this proximity rather than allowing transmission to other tissues. In an alternative embodiment the liposome encapsulated liquid crystal is first freeze-dried to enhance shelf-life and delivery. A general discussion of liposomes and liposome technology can be found in a three volume work entitled Liposome Technology edited by G. Gregoriadis, 1993, published by CRC Press, Boca Raton, Florida. The pertinent portions of these references are incoφorated herein by reference. Although lasers (depicted 28 symbolically in the figure) are the preferred light energy source, the present invention is equally applicable to noncoherent light sources. Where the light source has a broad band, or multiple, of wavelengths, selecting a liquid crystal capable of filtering or tuning to cause the desired effect may be a complex problem. Tissue is intended to be inteφreted very broadly as used in this discussion. The application of the present invention may be directed to many different human, as well as other animal, physiological structures. In one particular application, the tissue of interest is the germative cells responsible for hair growth. In U.S. Patent 5,059,192 to Zaias, incoφorated herein by reference, removal of human hair by photothermolysis is disclosed. Hair follicle death and removal is effected by photothermolysis of the germative cells which initiate and sustain hair growth. A limitation of this, and similar methods, is the collateral damage occurring to the skin cells surrounding the targeted germative cells. Zaias teaches that light of a particular wavelength range will effect death of the germative cells without undue collateral skin damage. Light sources of other wavelengths are not normally practical in this application due to unacceptable damage. However by application of liquid crystals by the methods outlined above, light energy of a broader range of wavelengths may be applied. In this application a specific liquid crystal and controlling parameters are selected such that projected light energy would be directed such that an increased proportion of energy would effect photothermolysis of the targeted cells while a decreased proportion would strike the surrounding skin tissue. To accomplish this the light energy characteristics are altered to a form not as readily absorbed by the tissues surrounding the target cells. Alternatively, the liquid crystal filters a broad band light source to allow only light energy which is preferably absorbed by the target cells. In this manner depilation may be accomplished with a minimum of collateral damage. This method of tissue destruction can also be applied where selective destruction of tissues is desired. Destruction of cancerous cells, lesions, or similar unwanted tissue may be effected without undue damage to surrounding skin. For these puφoses the liquid crystal is delivered preferably by a liposome which binds to the target cells. Similarly this method may be applied to removal of unwanted skin tissues to accomplish exfoliation, resurfacing, or removal of skin wrinkles. In a separate embodiment, liquid crystals may be employed to protect rather than destroy tissue. A selected liquid crystal may be applied to the skin surface. As applied on the skin surface, the proper liquid crystal has the ability to reflect incident light energy in the UV spectrum away from the skin surface. Applied before exposure to sunlight, the liquid crystal acts as an effective sunscreen.

Depilation can be effected through application of various forms of electric fields. In one embodiment of the present invention liquid crystal compounds are introduced to enhance the DC or radio frequency electromagnetic reception of the hair. For this puφose the liquid crystal is introduced to the hair follicle or adjacent tissues, preferably by liposome delivery as previously discussed above. Alternatively, the liquid crystal is introduced to the skin surface, in contact with the hair. Surface contact may be accomplished through use of a thin patch applied to the skin surface. By tuning the hair to the applied field, death of the hair may be effected with a reduced energy input.

Claims

I claim: 1. A method of destroying selected human tissue comprising the steps of: a. introducing a liquid crystal adjacent to a selected tissue, b. projecting light energy through said liquid crystal, said liquid crystal effecting said light energy such that at least an increased portion of said light energy is of a wavelength preferentially absorbed by the selected tissue, c. allowing said portion of said light energy to be absorbed by the selected tissue thereby effecting destruction of at least a portion of said tissue.

2. The method according to claim 1, including the step of: incoφorating said liquid crystal into a flexible patch.

3. The method according to claim 1, including the step of: encapsulating said liquid crystal within a liposome.

4. A method of destroying selected human tissue comprising the steps of: a. selecting a light energy source, said source producing light energy of a wavelength causing a minimum of damage to a protected tissue when projected on said protected tissue; b. introducing a liquid crystal in the proximity of a selected tissue, said liquid crystal being capable of tuning itself to the wavelength of said light energy such that the liquid crystal absorbs an increased portion of said light energy; c. directing said light energy source at said liquid crystal such that said liquid crystal absorbs a portion of said energy and causes destruction of said selected tissue; and whereby damage to protected tissue is minimized.

5. The method of claim 4 including the step of: encapsulating said liquid crystal within a liposome.

6. A method of depilation comprising: a. introducing a liquid crystal into the proximity of hair growth tissue; b. directing a light energy source into said liquid crystal and said liquid crystal alters said light energy; whereby said altered light energy causes death of the hair growth tissues.