Patent Application
20060052719
The skin is a sensory organ, an immune organ, an organ that provides thermoregulation, and a barrier to chemical and biophysical species acting in both directions inwards and outwards. The skin is also a structural organ that interacts with other structural elements such as bones and muscles. The bones are the body's structural elements onto which tissue elements are attached. Muscles surround the bones, and tendons provide attachments between the bones and the muscles allowing forces to be applied onto the bones, which may result in motion or locomotion. The muscles are surrounded by layers of fat that allow changes in volume of the muscles as they flex while maintaining a relatively constant outline. Muscles also serve as insulation and act as shock absorbers to external impulses. The skin is the wrapping that keeps the subcutaneous fat in position and defines in space the body from external elements. The skin, thus, is an element that is generally under tension, allowing flexing and locomotion by adjusting and redistributing internally, as well as externally, applied forces.
The mechanical properties of the skin are of paramount importance in describing the state of the skin as a container of the body, both as a barrier and an enclosure. A number of techniques have been developed to study the mechanical properties of the skin. These techniques are based on the idea that assessing the force necessary to pull or to push the skin allows one to estimate the elastic and plastic properties of the skin since the skin undergoes both elastic and plastic deformations.
It is evident to any observer that the state of the skin changes significantly with age. In particular, it is known that skin generally loses elasticity as it ages. This is attributed to skin thinning and loss of elastin and collagen in the dermal matrix, as well as losses in the subcutaneous tissue (fat layers and muscle mass), which are expressed as sagging of the skin. The mechanical properties of the skin are, in particular, heavily influenced by the microstructural arrangement of collagen and elastin in the dermal matrix. Collagen forms fibrils that appear as fibers and bundles that are believed to be arranged in a chicken wire fence pattern, allowing the dermis to deform due to pressure and, thus, minimizing the possibility of tears. The collagen bundles vary in size as one moves from the upper (papillary) dermis to the deeper (reticular) dermis and are normally under tension that ranges from 0-20 N/m depending on the body site, direction, and posture (Y. Lanir, Skin Mechanics—in: Handbook of Bioengineering eds. Richard Skalak and Shu Chien, MacGraw-Hill Book Co chapter 11 pp 11.1-11.24.).
Collagen production takes place preferentially along the direction of tension of the fibroblasts (the dermal cells that are responsible for the production of collagen). The other structural dermal element is elastin, which appears as bundles and is interspersed in the collagen matrix. Elastin bundles form a two dimensional network within the dermal collagen, and the bundles also reach towards the dermal epidermal junction forming candelabra-like structures.
Such observations regarding the arrangement of collagen and elastin in the dermis, as well the ability of this arrangement to change with age, is consistent with the understanding that tension the skin is under is directional. This has, in fact, been used to advantage in surgical procedures. For example, maximum tension in the skin has been found to orient along Langer's cleavage lines present in the skin. As such, this orientation is typically chosen as the direction along which surgical incisions are made so that the tension across the wound is minimized.
While various instrumental approaches have been described for objectively assessing the elastic or more correctly the mechanical properties of the skin, these approaches have frequently failed to account for anisotropy in mechanical parameters of the skin. One such method employs an instrument that generates suction. The height to which the skin may be pulled under constant suction is determined, and then the rate at which the skin returns to its original shape is also measured. Another method uses two concentric cylinders that are placed in contact with the skin. One of the cylinders applies a constant torque to the skin surface and measures the angular displacement under torque and the rate at which the skin returns to equilibrium once the torque is removed. Yet another method uses an instrument where a small mass located on an arm is allowed to strike the skin with a certain fixed velocity and it determines the speed and the rebound of the mass from the skin thereby assessing the firmness/elasticity of the skin. Unfortunately, while these measurement methods can successfully measure certain elastic properties of the skin, they do not take into consideration the anisotropy that is provided by the arrangement of dermal collagen and elastin. As such, these methods have limitations in both poor sensitivity/resolution and random testing error. These problems make the above methods unreliable and unsatisfying, especially for determining fine or even gross effects from treating the skin with skin care compositions or other treatments.
One tool that attempts to overcome the problems of directional insensitivity of the instruments and methods described above is the Reviscometer® RVM 600 (commercially available from Courage and Khazaka, Cologne, Germany). The instrument measures the time of propagation of an elastic shear pulse in viscoelastic materials such as skin. The principle behind the use of the instrument is that the speed of propagation of elastic disturbances on the skin will depend strongly on its orientation because it depends on both the tension the tissue is under and the density of the tissue. Mechanical vibrations propagate faster the higher the tension. As with a guitar string, the higher the tension, the higher the frequency of oscillation after plucking. A probe that is placed in contact with the skin is composed of two transducers that are spaced apart and mounted on two independent supports. One transducer generates a motion of small amplitude and the second transducer determines when the disturbance generated by the first transducer arrives at its location.
The manufacturer of the Reviscometer in its operations manual recommends measurements at 45° increments in order to assess the variability of skin firmness with skin direction. Unfortunately, this method yields highly inconsistent measurements, and is unable to provide a high degree of resolution with respect to subtle differences in firmness. Thus, it is very difficult to, for example, differentiate the measurement of the firming effect of active topical products versus a placebo control product. Accordingly, there remains a need to overcome the above-mentioned drawbacks.
In one aspect, the present invention features a method of determining skin anisotropy of a subject by measuring rates of propagation of mechanical energy between a mechanical energy generator and a mechanical energy detector along a plurality of directions of an expanse of skin wherein each of the directions are from about 0° to about 10° in separation relative at least one other of the directions and at least two of the directions are from about 30° to about 180° in separation relative to each other.
In another aspect of the invention, the present invention features a method of determining the efficacy of a skin treatment that includes the steps of: (i) measuring a first set of rates of propagation of mechanical energy along a plurality of first directions of an expanse of skin wherein each of the first directions are from about 0° to about 10° in separation relative at least one other of the first directions and at least two of the first directions are from about 30° to about 180° in separation relative to each other; (ii) administering a treatment to the expanse of skin; (iii) measuring a second set of rates of propagation of mechanical energy along a plurality of second directions of an expanse of skin wherein each of the second directions are from about 0° to about 10° in separation relative at least one other of the second directions and at least two of the second directions are at least about 30° in separation relative to each other; and (iv) comparing the first set and the second set.
In another aspect of the invention, the present invention features a method of promoting a product by promoting the use of said product for reducing the appearance of the age of a user's skin wherein the efficacy of said product was determined using the above methods.
Other features and advantages of the present invention will be apparent from the detailed description of the invention and from the claims.
A more particular description of the invention, briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be so noted, however, that the appended drawings illustrate only typical embodiments of the invention and, therefore, are not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding identical reference elements have been used, wherever possible, to designate identical elements that are common to the figures.
It is believed that one skilled in the art can, based upon the description herein, utilize the present invention to its fullest extent. The following specific embodiments are to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Also, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference.
Skin Anisotropy
Embodiments of the present invention relate to a method of determining skin anisotropy. What is meant by “skin anisotropy” is the magnitude or degree to which at least one property of the skin varies depending upon which direction (relative to an arbitrary direction) along which the property is measured. For example, if an arbitrary direction along the skin is defined as 0°, a measurement of a rate of propagation of a mechanical (e.g., sound) wave along 0° and a measurement along an angle other than 0° are taken. If the measurements are significantly different, the skin is said to be anisotropic with respect to sound propagation. The degree to which the measurements differ is a determination of skin anisotropy. By “rate of propagation” it is meant a speed at which a wave or pulse of mechanical energy moves across an expanse of skin, such as a rate at which the mechanical energy moves between two transducers. According to embodiments of the invention described herein, skin anisotropy may be determined by relating, for example, a first rate of propagation of mechanical energy along a first direction of skin to a second rate of propagation of mechanical energy of skin along a second direction of skin. By “relating a first rate of propagation of mechanical energy along a first direction of skin to a second rate of propagation of mechanical energy along a second direction of skin,” it is meant that a graphical or mathematical relationship between such rates is determined.
Measurement Device
According to embodiments of the invention described herein, skin anisotropy of a subject is measured by measuring rates of propagation of mechanical energy along a plurality of discrete directions of an expanse of skin. In one embodiment, the subject is a mammal such as a human. The method of the present invention may be used on both healthy subjects (e.g., to ensure their skin health) as well as subjects who are inflicted at various stages of a skin disorder, including but not limited to intrinsic skin aging, wrinkles, crow's feet, photodamage, swelling (edema), and the like.
A suitable device for measuring rates of propagation of mechanical energy is the Reviscometer® RVM 600 (commercially available from Courage and Khazaka, Cologne, Germany), which is depicted in
The transducer 5 and transducer 7 are electrically coupled, via a connector 9, to a signal unit 11 (shown in phantom in
Note, that while the device described above includes transducer 5 for converting electrical energy to mechanical energy (to generate the energy to be propagated across the expanse of skin) and transducer 7 for converting mechanical energy back to electrical energy (for signal processing), other types of devices, such as those that may be fabricated on integrated circuits may be used. For example, transducer 5 may be a pulsed laser that uses electromagnetic radiation to generate a mechanical wave that is in turn propagated across the skin. Corresponding transducer 7 may include a photo-acoustic or electro-acoustic material such as lead zirconate titanate (PZT) that is capable of converting the mechanical energy that has propagated across the skin into an electrical or optical signal to be processed. In this embodiment, transducer 7 may be a plurality of photo-acoustic detectors each spaced apart, such as in a circular manner at a constant distance from transducer 5 at a particular angle (e.g., 0°, 3°, 6°, 9°, and the like) relative to transducer 5. Each of the plurality of photo-acoustic detectors captures a signal that can be correlated to a rate of propagation of mechanical energy across the expanse of skin 17 in a particular direction. Such a configuration of transducer 5 and transducers 7 may be fabricated, for example, on an integrated circuit using techniques known in the art of integrated circuit manufacture.
Method of Measuring Rate of Propagation of Mechanical Energy Along an Expanse of Skin
In operation, the transducer 5 and transducer 7 are placed in contact with an expanse of skin 17 along a first arbitrary direction 19 as shown in
The mechanical energy may, for example, be in the form of a pulse that propagates from the first transducer 5 across the expanse of skin 17 to the second transducer 7 along a first segment of propagation 25. In one embodiment, the pulse has a frequency in a range from about 0.5 kHz to about 30 kHz. The microprocessor then calculates one or more parameters of the propagation (e.g., that can later be correlated to the density or firmness of the expanse of skin 17). For example, the microprocessor may calculate a time required for the pulse to move from the first transducer 5 across the expanse of skin 17 along first arbitrary direction 19 to the second transducer 7. The time required is referred to as a resonance running time (RRT). Similarly, by factoring in the distance between transducer 5 and transducer 7, the microprocessor may calculate a velocity of propagation of the pulse.
By spacing transducer 5 and transducer 7 apart at a distance from about 1.5 to about 2 mm, the instrument probes the propagation of mechanical energy through the epidermis and superficial dermis. It, however, is believed that useful measurements may also be obtained using a spacing as small as about 0.5 mm or as large as about 5 mm.
As shown in
Referring to
Once the probe head is adjusted, the second measurement is taken. The steps of rotating the probe head 35 and taking an additional measurement is repeated one or more times, such as, for example, to cover span of angles up to at least 30°, but as much as 90°, 120°, or even 180° from the first (arbitrary) direction 19. In general, rates of propagation of mechanical energy are measured between transducer 5 and transducer 7, along a plurality of directions of the expanse of skin 17. Each of the directions are from about 0° to about 10° in separation relative at least one other of the directions, and at least two of the directions are at least about 30° in separation relative to each other. In this manner, one is able to obtain enhanced resolution of anisotropy. See, e.g.,
Note that for embodiments of the invention in which transducer 5 converts optical energy from a pulse of light into mechanical energy which is propagated across the expanse of skin 17, and transducer 7 is a plurality of photo-acoustic detectors each spaced apart in a circular manner (described above in the section, “MEASUREMENT DEVICE”), measurements at various angles are conveniently measured in a simultaneous manner (e.g., no rotation of transducers is required).
Assessing Skin Anisotropy and Calculating Skin Anisotropy Parameters
Skin anisotropy may be assessed by relating the first rate of propagation of mechanical energy along the first direction of the expanse of skin to the second rate of propagation of mechanical energy along the second direction of the expanse of skin. This may be accomplished by plotting resonance running time versus probe angle. In one embodiment of the invention, relating the first rate of propagation of mechanical energy to the second rate of propagation includes calculating a skin anisotropy parameter. The skin anisotropy parameter is generally calculated from the at least two measurements of rates of propagation of mechanical energy. In particular, the anisotropy parameter may be derived from or include a difference, a quotient, or a ratio between (1) the time or velocity of propagation determined by the first measurement and (2) the time or velocity of propagation determined by the second measurement. For example, if time of propagation is measured, the anisotropy parameter may be derived from a ratio of the first time of propagation to the second time of propagation. If numerous measurements are taken, the relationship between time of propagation versus angle may be modeled as a Gaussian or other suitable mathematical function to determine a maximum and minimum time of propagation. A ratio between maximum and minimum RRT may then be used as the anisotropy parameter. Specific examples of how anisotropy parameters may be calculated are discussed below in the section entitled “EXAMPLES.”
The Expanse of Skin
Various locations may be chosen for the expanse of skin 17. In one embodiment of the invention, the expanse of skin is relatively loose and fleshy such as skin located on the upper inner arm, the neck, upper inner thigh, the abdomen, buttocks, or other soft body parts (e.g., where any bone is well buried beneath soft tissue). The skin on the upper inner arm is particularly preferred. In another embodiment of the invention, the expanse of skin is located in a region that is not prone to a high degree of exposure to the sun, such as the upper inner arm or the buttocks.
Skin Treatments
What is meant by a “skin treatment” is a treatment of the expanse of skin with a therapeutic device (e.g., mechanical, optical, or electrical device) or a benefit agent (e.g., delivered via such routes as topical or oral compositions) that may effect the skin's elasticity, density, firmness, number or frequency of wrinkles, or other indications of aging. “Applying a skin treatment” refers administering the therapeutic device to the expanse of skin (e.g., contacting the expanse of skin with a mechanical device or illuminating it with a light source) or applying a benefit agent (e.g., such as by topically applying a composition containing the benefit agent to the expanse of skin). What is meant by a “benefit agent” is a compound (e.g., a synthetic compound or a compound isolated from a natural source) that has a cosmetic or therapeutic effect on the skin, including, but not limiting to, anti-aging agents, firming agents, and anti-wrinkle agents. Examples of benefit agents include, but are not limited to, vitamin A and its derivatives such as beta-carotene and retinoids such as retinoic acid, retinal, retinyl esters such as and retinyl palmitate, retinyl acetate, and retinyl propionate; vitamin C and its derivatives such as ascorbic acid, ascorbyl phosphates, ascorbyl palmitate and ascorbyl glucoside; copper peptides; simple sugars such as lactose, mellibiose and fructose; and alkanolamines such as dimethylaminoethanol (“DMAE”)
Evaluation and Promotion of Skin Treatments
Skin treatments may be evaluated, advertised, or promoted in conjunction with embodiments of the inventive method for determining skin anisotropy described herein. For example, a plurality of pre-treatment rates of propagation of mechanical energy may be measured for an expanse of skin of a subject using a device such as device 1. After this measurement, a skin treatment may be applied the expanse of skin of the subject. After the application of the skin treatment, post-treatment measurements may be made. One or more of the pre-treatment rates of propagation of mechanical energy may then be compared to one or more of the post-treatment rates of propagation of mechanical energy to evaluate the efficacy of the skin care treatment.
In another embodiment of the invention, a relationship is determined between skin anisotropy parameters and other variables such as chronological skin age. The relationship may be determined by, for example, making skin anisotropy measurements of a plurality of subjects who are classified in one or more individual categories such as categories based upon age, sex, ethnicity, skin type, skin condition, or combinations of these categories. An anisotropy parameter associated with a test subject is then determined. The anisotropy parameter of the test subject is then compared to one or more standard anisotropy parameters determined above (e.g., to classify the subject into or compare the subject with a particular age group). A skin treatment may then be applied to the subject and then a post-treatment anisotropy parameter may be determined. The post-treatment anisotropy parameter may then be compared with the standard anisotropy parameter and/or with the pre-treatment anisotropy parameter to classify the subject into or compare the subject with a group or to measure the degree of improvement after the skin treatment.
In another embodiment of the invention, a method of promoting the use of a product, such as a topical composition or skin treatment, includes promoting the use of the product for reducing the appearance of the age of a user's skin, wherein the efficacy of the product was determined using by measuring skin anisotropy in a manner consistent with embodiments of the invention described hererin. What is meant by “promoting” is promoting, advertising, or marketing. Examples of promoting include, but are not limited to, written, visual, or-verbal statements made on the product or in stores, magazines, newspaper, radio, television, internet, and the like. Examples of such statements include, but are not limited to: reduces the appearance of wrinkles and/or fine lines, lifts the skin, firms the skin, reduces the appearance of the age of the skin, provides younger looking skin, and similar statements.
The following is a description of examples of measurements of rates of propagation of mechanical energy (resonance running time), determination of skin anisotropy parameters, and related methods for evaluating and promoting skin treatments. Other methods within the scope of the present invention can practiced in an analogous manner by a person of ordinary skill in the art.
Resonance running time versus probe angle for 239 human subjects was determined using the Reviscometer® RVM 600. The subjects were of varying ethnicity and skin type, from very light Caucasian (Types I and II) to African Americans (Type VI). The volunteers were divided in 5 groups according to their age: 0-2 years old (mean age of 1.8±standard deviation of 1.1); 14-20 years old (17±4.2), 24-40 years old (32.5±10.6), 55-60 y old (57.5±3.5); and 65-75 years old (70±7). Reviscometer readings were taken on the upper inner arm at about 15 cm from the elbow for a range of probe angles that spanned 1000. The measurements were taken in 3° increments, and 0° was (arbitrarily) assigned to the angle that gave the lowest RRT reading. An example of a plot of resonance running time (“RRT”) versus angle for one individual is shown in
After taking these measurements, a 6 term-Gaussian function was fitted to the measured RRT curve as a function the angle using the computer program IDLE (from RSI, Research System Inc., Boulder, Colo.). Two anisotropy parameters were calculated: (1) the ratio of the maximum resonance running time (RRTmax) divided by the minimum resonance running time (RRTmin), referred to hereinafter as anisotropy (“A”); and (2) and the full width at half maximum of the Gaussian distribution, referred to as the Langer's Line Width (“LW”). These anisotropy parameters are illustrated in the example in
The subjects of Example 1 were categorized by age group. A representative example of RRT as a function of angle for each of three age groups is shown in
This fitted expression may be used to calculate a test subject's age based upon his A/LW ratio. Solving for age, one obtains:
The model from Example 2 was used to calculate various subjects' ages based on their particular ratio, A/LW, calculated from the Reviscometer measurements. This was done on 18 subjects with real age varying from 9 up to 63 years old. The actual age in years and the predicted age using the above expression are illustrated in
Skin anisotropy of 84 human subjects was determined using the Reviscometer® RVM 600. The subjects were Caucasian women ranging in age from 40 to 72 years. Reviscometer readings were taken on the neck area half way from the bottom of the ear area to the collarbone, in an interval ranging from 0° up to 100° in 3° increments, where the initial 0° is an arbitrary angle that gives us the lowest RRT reading. Gaussian curves were fitted to the data and the values of the A and LW were calculated. After statistical analysis using ANOVA (general linear model), no statistical significance was found for LW as a function of age (p=0.62) but there was statistical significance for the A (p=0.026). A plot of A versus age category is shown below in
Skin anisotropy of 6 human subjects was determined using the Reviscometer® RVM 600. Reviscometer readings were taken on the upper inner arm at about 15 cm from the elbow in an interval ranging from 0° up to 128° in 3° increments. For each subject, one of six topical skin treatments were separately applied to different expanses of skin (using a dose of 2 μl/cm2). Reviscometer readings were then taken 35 minutes after treatment. The topical treatments that were tested included 0%, 0.5%, 1%, 2%, and 3% dimethyl amino ethanol (DMAE), by weight, formulated in an identical cosmetic base (additional DMAE was compensated for by using less water).
where RRT is the resonance running time (Reviscometer readings) taken at maximum and minimum values.
Definition of the RRT allowed the calculation of a dose response relationship between RRTR and the concentration of DMAE. Applying the same procedure for eight volunteers using the 5 samples determined a dose-response function of the concentration.
Embodiments of the invention described herein are advantageous in that clear and subtle differences in skin elasticity may be determined. For example, by taking measurements with small angle separations, one is likely to include measurements that are closely aligned with the particular Langer lines of the expanse of skin that is being measured. As such, this may permit measuring enormous differences in properties (e.g., a 3 fold, 6 fold or even greater difference in rate of propagation of mechanical energy). Because the various embodiments of the inventive method provide excellent resolution, subtle differences may be measured, thereby allowing the inventive measurement method to (1) be used to promote skin care treatments, including topical treatments; and/or (2) to make assessments regarding chronological age of the skin based on its elastic properties.
It is understood that while the invention has been described in conjunction with the detailed description thereof, that the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the claims.
