Surgery – Instruments – Light application
Utility Patent
1998-08-11
2001-01-02
Dvorak, Linda C. M. (Department: 3739)
Surgery
Instruments
Light application
C606S043000
Utility Patent
active
06168590
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related generally to hair removal and relates more particularly to the use of electromagnetic energy for the selective modification and/or removal of hair.
BACKGROUND OF THE INVENTION
As is well known, the human skin contains a number of components. For example, vascular and lymphatic channels provide for nutrition, healing and transport. Sweat and sebaceous glands provide respectively for temperature control and lubrication. Pigmented structures provide for sun protection. Hair follicles and their associated hairs provide for insulation and protection.
The components and function of human hair can be understood by reference to FIG.
1
. Growth of each hair is originated by germinative fibroblast cells in the basal layer of the epidermis
152
. The hair grows both outwards and inwards (towards the lower dermis
154
and hypodermis
158
) during its growth cycle, and the follicle
100
develops as an encapsulating pouch extending beyond the epidermis and down several millimeters in depth into the subcutaneous fat. Each hair remains attached to the hair bulb
102
at the base of the follicle, where a capillary network develops to provide nourishment.
During an anagenic growth phase, hair matrix cells divide rapidly and migrate upwards to form the hair shafts
104
within the hair ducts
120
. A subsequent catagenic phase is marked by cessation of mitosis, and the re-absorption of the lower part of the follicle. Capillary nourishment is greatly reduced during this phase. In this or a final telogenic (resting) phase, the hair falls out and a new hair may replace it in a new growth cycle. At any particular time, approximately 10% of scalp hairs will be in telogenic phase.
The growth cycle varies with anatomical location from as little as 3 months for facial hair to as much as 7 years on the scalp. Hair in the pubic area is typically retained by the body as protection and may not shed at all.
The hair follicle consists of a mixture of germinative cells and melanocytes. Sebaceous cells from the sebaceous glands empty into the follicle, providing a lipid-rich environment.
The follicle is typically about 0.1 to 0.2 mm in diameter and may extend up to about 4 mm in depth. The average hair shaft diameter within the follicle is about 60 to 75 &mgr;m. The hair shaft itself is generated as an accumulation of dead (keratinized) cells. Structurally it consists of two or three discrete layers: The outer cuticle layer consists of a single layer of overlapping flat cells like the scales of a fish. This acts as a protective barrier. An inner cortex layer contains any pigment which may be present. Pigments may also reside in melanocytes which line the follicle
100
. Pigments may exist as two melanin forms. Eumelanin is responsible for brown/black coloration and pheomelanin is responsible for red/blonde coloration. Larger, fully developed hairs also contain a core known as the medulla.
In the lower region of the follicle, a bulge is formed where the arrector pili muscle
110
contacts the follicle. This muscle controls movement and orientation of the hair and may, under some stimuli, render the hair vertical with respect to the skin surface. The bulge area has one of the fastest rates of cell division found in mammals, stimulated by growth factors from the lower papilla
112
area.
Because dermal thickness varies greatly over the body, the papillae may be superficial (as in, for example, the eyelids and scrotum), but for many areas of interest for the practice of the present invention (e.g., the face, axillae, and legs), the papillae are located at depths of approximately 4 to 7 mm beneath the epidermal surface.
Located a few tenths of a millimeter below the papillae are neurovascular bundles which serve the metabolic and other needs of a hair matrix.
The hair matrix is the region of rapidly growing keratinizing cells, located in the papilla
112
, which produce the hair shaft
104
.
It is important to note that the matrix, papillae, and their associated neurovascular bundles are necessary for hair growth. By destroying or modifying these anatomical structures, hair growth is mitigated. Thus, the matrix, papilla, and the corresponding vascular bundle represent the follicular targets to be destroyed. According to the present invention, during the treatment of these regions, the depilatory effects are localized so that damage is confined to a small region of dermis surrounding each follicle.
The extent of damage should preferably be much less than half the distance between neighboring follicles (typically between about 1 and 4 mm). If it is significantly greater than this, the injury may result in a third-degree burn.
While the follicle and hair contained therein function at several different levels, excess body hair does present a cosmetic problem for hirsute females, and some males as well. As a consequence, many individuals undergo hair removal treatments. Conventional hair removal techniques, including electrolysis, shaving, wax epilation and tweezing, are often painful and temporary.
Electrolysis is used by an estimated 1 million women in the United States. Two techniques dominate the electrolysis field. Galvanic (DC) current can be passed down a fine needle inserted into the follicle. This technique converts tissue saline locally to sodium hydroxide, which destroys the follicle. Alternatively, the thermolysis technique utilizes an AC current to directly heat and thereby destroy the papilla. Some clinicians utilize a combination approach of these two electrolysis technique. Electrolysis methods are only used to treat follicles one at a time. This is an undesirably painful procedure which can require analgesia. Disposable needles are used in this frequently nonpermanent, time consuming, multiple treatment technique.
Several contemporary photonics techniques have also been evaluated. In 1993, Thermotrex Corporation was assigned two Hair Removal Device and Method patents (U.S. Pat. Nos. 5,226,907 and 5,425,728) based on the use of an externally applied chromophore to enhance local absorption of laser light. In these patents, a topically applied substance is said to penetrate to the full depth of the root of the follicle. The substances cited include permanent hair dyes, suspensions of carbon particles and photosensitizing compounds. A subsequent application of laser light is said to induce a reaction which destroys the follicle and a surrounding tissue area. The compounds cited by ThermoLase in their patents will probably demonstrate follicular selectivity. Many other topical compounds, and some systemic compounds, exist as candidates. Liposomal or lipophilic compounds may favor the lipid rich environment. Alternatively, solvents such as ethanol may be used to de-lipidize or re-organize the saburra, and thereby open the follicular passageways.
Deposition of hydrophilic drugs may be facilitated by the action of wetting agents such as sodium lauryl sulfate, which may promote the creation of an emulsion. Particle size clearly plays a role in terms of ability to penetrate through narrow epidermal structures and along the follicular duct. The approach cited in this issued patent may work, although its practice involves the use of light absorbing topical compounds and short pulse durations which may result in explosive events with significant collateral damage to adjacent skin tissue. Furthermore, the approach cited in this patent involves non-selective deposition of the absorbing compound along the entire follicle with a correspondingly non-selective deposition of laser energy. This, in turn, may prevent effective destruction of the follicle sustaining tissue. Indeed doubts exist as to effectiveness of this invention as a permanent method for hair removal.
A second technique has been studied and reported by Drs. Rox Anderson, Melanie Grossman, and William Farinelli (U.S. Pat. No. 5,595,568) whereby single high energy normal mode ruby laser pulses are applied to the skin in the absence of an externally applied chromophore. In this method, the optical targ
Christie Parker & Hale LLP
Dvorak Linda C. M.
Y-Beam Technologies, Inc.
Yarnell Bryan K.
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