Abstract:
A stable composition is provided to treat and/or prevent photo-aged skin and related skin disorders such as sunburn, wrinkles, poor skin tone and skin discoloration by topically applying to the skin the treatment composition containing an effective amount of a compound such as ascorbic acid, derivatives of ascorbic acid and/or extracts containing ascorbic acid, in a pharmaceutically acceptable vehicle containing a substantially anhydrous base having no water added. The anhydrous base stabilizes the compound, so that the compound remains effective for an effective period of time, even in the presence of exposure to water. Preferably, the anhydrous base is a single phase carrier, as opposed to a two phase carrier emulsion.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a composition for stabilizing ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, in a stable delivery system for topical application to the skin. The composition prevents premature aging of the skin of humans, or may be used to treat photo-aged skin and resultant wrinkles and other sequelae. Preferably, the composition is an anhydrous base which is a single phase carrier, such as a dispersion or suspension, as opposed to a two phase emulsion. 
     BACKGROUND OF THE INVENTION 
     Vitamin C is a powerful antioxidant that may help neutralize the damaging effects of free radicals, the unstable chemicals that are a result of air pollution, smoking,stress and sunlight. 
     Studies suggest that Vitamin C has the potential to stimulate the growth of collagen that is important in maintaining healthy skin elasticity and texture. 
     Vitamin C in the form of L-Ascorbic acid is the chemical form of ascorbic acid that is reported to be most effectively utilized by the body. 
     Treatment of photo-aged skin and resultant wrinkles and other sequelae with ascorbic acid and related derivatives has been discussed in the prior art. Among the most common treatment regimen is a topical application of ascorbic acid to affected areas of the skin in lotions, creams and other delivery vehicles, such as discussed in U.S. Pat. No. 5,140,043 of Darr et al for stable ascorbic acid compositions. 
     In Darr &#39;043, it is noted that L-ascorbic acid prevents ultraviolet (UV) damage to the skin. In the discussion of the background art therein, Darr &#39;043 states that ascorbic acid, also commonly known as Vitamin C, acts as an anti-oxidant to counteract the skin damaging effects of superoxide and hydroxyl radicals, which have been known to cause a wide variety of damaged skin conditions ranging from transitory sunburn to permanent wrinkles from photo-aged skin. According to Darr &#39;043, these radicals destroy lipid membranes, break down DNA and inactivate beneficial enzymes which promote healthy skin conditions, citing Cerutti, D. et al, eds. Oxy-radicals in Molecular Biology and Pathology, (Alan Liss, publisher, New York, N.Y. 1988), Hayaishi, O, et al, eds., Biological Role of Reactive Oxygen Species in Skin, (Elsevier Press, New York, N.Y. 1987), Johnson, Jr., J. E. et al, eds., Free Radicals, Aging and Degenerative Diseases, (Alan Liss publisher, New York, N.Y. 1986), Halliwell, B. et al, eds, Free Radicals in Biology and Medicine, (Clarendon Press, Oxford, U.K. 1985), and Sied, H., ed., Oxidative Stress, (Academic Press, 1985), among other cited publications therein. 
     Free radicals from ultraviolet light (UV) are known to increase with air pollution in areas of concentrated populations, thereby magnifying the problem. The free radicals are destructive in that the free radicals hydrolyse elastin fibers in the skin and desynthesize collagen in the lower dermal layers of the skin, thereby causing skin wrinkles and other damaging skin conditions. 
     In contrast, it has also been known that ascorbic acid is effective in counteracting the effects of free radicals upon the skin. Ascorbic acid absorbs ultraviolet (UV) radiation and at the same time stimulates collagen production. 
     However, ascorbic acid, such as Vitamin C, is difficult to stabilize for any significant period of time in pharmaceutical vehicles for topical delivery to the skin. Ascorbic acid loses potency and discolors easily in most delivery vehicles. Furthermore, ascorbic acid hydrolyzes when exposed to water. 
     The term &#34;stable&#34; is defined as a characteristic wherein a composition retains potency for the duration of a predetermined expiration period, as defined by generally accepted pharmaceutical protocols, such as &#34;GMP&#34;, or &#34;good manufacturing practices&#34; as promulgated by various trade conventions, such as for example, the United States Pharmacoepia (USP) convention. 
     For example, for a topically applied skin care formulation, the expected duration of a predetermined expiration period should be at least eight months before the formulation loses significant potency. 
     In contrast, Darr &#39;043 only tested the product described therein for twelve weeks. 
     Moreover, as noted in Darr &#39;043, ascorbic acid washes off easily when exposed to water, so that topical application at a sun-lit beach is generally futile, since swimming washes away the topically applied ascorbic acid. 
     Furthermore, in the past, ascorbic acid has been administered in high dosages to the skin, and has to be made every day because of its instability, thus increasing cost of its use. 
     Darr &#39;043 discloses a method of stabilizing ascorbic acid in a water based delivery system with an ascorbic acid to water/carrier ratio of at least 1:1, preferably 2:1 to 10:1. 
     The ascorbic acid and water mix described in Darr &#39;043 includes both water and a carrier, such as alkylene glycols, or alkylene glycols in combination with one or more derivatives of hydroxyalkyl-cellulose. However, the minimum amount of water in the product disclosed in Darr &#39;043 is fifty (50) percent, since Darr &#39;043 teaches at least a 1:1 ratio of water to carrier, preferably greater than fifty (50) percent, such as sixty seven (67) percent water in a 2:1 ratio, up to ninety two (91) percent water in a 10:1 water/carrier ratio. 
     In general, the carrier is described as being compatible with water, preferably distilled or deionized water without contaminants, which further de-stabilize ascorbic acid. 
     However, the disadvantage of the delivery vehicle in Darr &#39;043 is that it is water-based, and therefore the ascorbic acid is still inherently unstable. 
     For example, while FIG. 1 of Darr &#39;043 shows small drops in potency of L-ascorbic acid of less than 10 percent over seven weeks at room temperature for L-ascorbic concentrations of three (3), five (5) and ten (10) percent respectively, FIG. 1 shows a drop in potency of approximately 30 percent over seven weeks, from 100 percent to 70 percent, of L-ascorbic acid in a concentration of one (1) percent. 
     Moreover, FIG. 2 of Darr &#39;043 shows all four samples of L-ascorbic acid having lost potency of at least ten (10) percent over eight (8) weeks at room temperature, when stored under controlled conditions in the dark. 
     Furthermore, while the testing in Darr &#39;043 was conducted from between seven (7) and twelve (12) weeks duration, any viable over the counter consumer product requires in excess of twelve weeks from manufacture through distribution points to final retail sale, and must still afford the consumer a reasonable time to consume the contents of the product. Therefore, a loss in potency of the magintude as shown in Darr &#39;043 in such a short time span, raises serious questions as to the usefulness of the stability data obtained in predicted the potency of L-ascorbic acid at the time the consumer is able to use the product. 
     Therefore, the response of the ascorbic acid in the epidermis and dermis of the skin is not very effective, because of the presence of substantial amounts of water, which contribute to destabilization of the ascorbic acid. 
     The present invention utilizes a single phase carrier, as opposed to an emulsion, as the anhydrous base. Emulsions are more complicated compositions than single phase carriers, and are discussed in Remington, Remington&#39;s Pharmaceutical Sciences, Mack Publishing Co., Easton, Pa. 1975, pp 327-331, Sagarin, Cosmetics Science and Technology. Interscience Publishers, Inc., New York, N.Y. 1957, pp. 998-1003, Wilkinson et al, Harry&#39;s Cosmetology, Chemical Publishing Co., New York, N.Y. pp 729-741. 
     Such an emulsion for ascorbic acid is shown in U.S. Pat. No. 5,587,149 of Punto et al for a topical emulsion for ascorbic acid. Punto &#39;149 describes two phase emulsions for stabilizing water-soluble active ingredients, such as ascorbic acid. For example, Punto &#39;149 describes a two phase polyethylene glycol-in-oil emulsion. In Punto &#39;149, the glycols are first dissolved in a water phase in a first phase. Secondly, an oil, such as silicone #1, is introduced in a second oil phase. Dispersion agents are then added to create an emulsion between the components of the first water phase and the second oil phase. However, Punto &#39;149 does not describe the making of an anyhydrous base in a single phase carrier, as opposed to a two phase emulsion. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to provide a stable single phase composition and pharmaceutical delivery system for ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid as effective treatments for photo-aged skin and related skin disorders. 
     It is yet another object to provide a topical preparation of ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid for more effective treatment of photo-aged skin and related skin disorders. 
     It is yet a further object to provide a topical delivery vehicle for ascorbic acid, derivatives of ascorbic acid and/or extracts containing ascorbic acid, wherein the delivery vehicle is substantially anhydrous with no water added. 
     It is yet a further object to provide ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, in a composition wherein the ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid remain effective for an extended period of time. 
     It is yet another object to improve over the disadvantages of the prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     In keeping with these objects and others which may become apparent, according to the present invention, a new stable, long-lasting composition is provided as a pharmaceutical delivery vehicle for delivery of ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, to prevent and treat sun-damaged and photo-aged skin, and as a preventative and cosmetic for undamaged skin. 
     Research suggests that ascorbic acid concentrations of 10-15% are preferable to provide enhanced skin care results. 
     For example, the formulation of the present invention 10% maintained 96% of the claimed L-Ascorbic Acid concentration as compared to 34% for other L-Ascorbic Acid products at 10% after 90 days. 
     The formulation of the present invention at 15% maintained 100% of the claimed L-Ascorbic Acid concentration as compared to 20% for other products of L-Ascorbic Acid at 15% after 90 days. 
     A method of preventing and/or treating photo-aged skin, sunburn, wrinkles and related skin disorders is provided by topical application of a lotion, cream, gel or pad applied formulation, preferably a substantially anhydrous composition, with no water added, containing effective amounts of ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, for topical application to the affected area of the skin. The composition of the present invention can also be used to prevent photo-aging of the skin. 
     Ascorbic acid, or its derivatives, such as ascorbic palmitate, sodium ascorbate, potassium ascorbate, ammonium ascorbate, triethanolamine ascorbate, ascorbyl phosphate or magnesium ascorbyl phosphate and related compounds, is applied in a pharmaceutically acceptable vehicle, in a concentration of from 0.1 percent by weight to 95 percent by weight, preferably 10-15 percent by weight, generally by frequent periodic application, such as by a once or twice daily application. 
     Instead of a substantially water based delivery system, the ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid are provided in a substantially anhydrous base, with no added water. Because one or more of the components may have a natural water sub-component, the base is not water free, but is substantially anhydrous, because the pre-existing water concentration does not generally exceed five (5) percent by weight of the total composition. To achieve the substantially anhydrous composition, no water is added, in contrast to the water-based composition in Darr &#39;043. 
     The substantially anhydrous base protects the ascorbic acid, or its derivatives and/or extracts containing ascorbic acid, from degradation, instability, loss of potency and loss of color. 
     The topical pharmaceutical delivery vehicle includes a single phase carrier, such as a mixture, dispersion or suspension, of a base consisting essentially of a substantially anhydrous composition, with no water added, in combination with the ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, wherein the substantially anhydrous composition, with no water added, is provided in a range of from 0.1 percent by weight to 99.8 percent by weight, preferably about 30 percent by weight. 
     The present invention does not rely upon an emulsion, and is not limited by the need to solubize Vitamin C (ascorbic acid) in an aqueous or water miscible phase of an emulsion before proceeding further to try and stabilize ascorbic acid in a second oil phase of the emulsion. For example, standard chemistry, pharmaceutical and cosmetic text books define an emulsion as in Punto &#39;149, in the usual manner. As noted before, Remington&#39;s Pharmaceutical Sciences states &#34;an emulsion is a dispersed system containing at least two immiscible liquid phases. The emulsifying agent is added to the system to improve its stability.&#34; 
     Punto &#39;149 makes use of emulsion technology as described in standard textbooks, whereas the single phase carrier of the present invention utilizes a method that does not rely on emulsion technology. 
     The anhydrous base with a single phase carrier of the present invention teaches a new approach, making it possible to stabilize ascorbic acid without forming an emulsion. This greatly simplifies product manufacturing and removes many of the logistical and long term stability hindrances associated with emulsions. 
     Punto &#39;149 uses a &#34;two phase carrier&#34; emulsion in a gelatin capsule. In contrast, the present invention is a simple &#34;single phase carrier&#34; such as a mixture, suspension or dispersion. 
     In the &#34;background&#34; section of Punto &#39;149, it is stated that ascorbic acid and PEG are in an oil emulsion. Punto &#39;149 solubizes them in an emulsion. In contrast, the present invention forms a single phase carrier suspension. There is no need to solubize the ascorbic acid, and no need to form emulsion. 
     For example, in Punto &#39;149, there are two phases: 
     a primary, solvent or water miscible phase and 
     a secondary, anhydrous oil phase. 
     In contrast, the present invention does not need an emulsion for improving skin feel and luster. Furthermore, some emulsions are incompatible with an anhydrous base. 
     In the preferred embodiment, the substantially anhydrous base includes silicone compounds, which provide a unique, cosmetically elegant smooth, lustrous tactile feel when applied to the skin. 
     Preferably the substantially anhydrous composition, with no water added, includes silicones and derivatives of silicone chemistry. However, other substantially anhydrous compositions, with no water added, may be utilized, such as other emollients, emulsifiers, surfactants, oils and waxes, polyols, binders, polymers, gums, viscosity aids, humectants, anti-oxidants or chelating agents. 
     Other inactive components may include preservatives, humectants, viscosity control aids, pH buffers and carrier solvents. However, certain pH buffers and solvents may also function as a substantially anhydrous base. 
     The resultant mixture is a smooth feeling delivery vehicle which delivers the ascorbic acid or its derivatives to the skin in an effective and stable manner. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the present invention, a stable, long-lasting composition is provided as a pharmaceutical delivery vehicle for delivery of ascorbic acid to sun-damaged and photo-aged skin. 
     A method of treating photo-aged skin, sunburn, wrinkles, dark or uneven pigmentation and related skin disorders is also provided by topical application of a lotion, cream, gel or pad applied formulation, preferably a composition with substantially anhydrous base in the form of a single phase carrier, such as a mixture, suspension or dispersion, composition, with no water added, containing effective amounts of a compound selected from the group consisting of ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, for topical application to the affected area of the skin. 
     In use as a topical agent, ascorbic acid, or its derivatives, such as ascorbyl palmitate, sodium ascorbate, potassium ascorbate, ammonium ascorbate, triethanolamine ascorbate, ascorbyl phosphate or magnesium ascorbyl phosphate, ascorbic acid polypeptides, ascorbyl glucosamine, ascorbic acid polymers, esters of ascorbic acid, amides of ascorbic acid, L-ascorbic acid, known as vitamin C, or other derivatives, or related compounds, including botanical or herbal extracts, such as extract of acerola, citrus extracts, strawberry, which may supply L-ascorbic acid or its derivatives, is topically applied to the skin of a user in a pharmaceutically acceptable vehicle, in a concentration of from 0.1 percent by weight to 95 percent by weight, preferably 10-15 percent by weight, generally by frequent periodic application, such as by a once or twice daily application. 
     Instead of a water based delivery system, or multiphase system in which a water miscible phase is utilized, the compound containing ascorbic acid, ascorbic acid derivatives and/or extracts containing ascorbic acid, is provided in a substantially anhydrous with no water added base. The base provides a unique cosmetically elegant topical vehicle which protects the ascorbic acid or its derivatives from degradation, instability, loss of potency and loss of color. The base includes a single phase carrier, such as a mixture of a substantially anhydrous composition, with no water added, with the compound, instead of a two phase emulsion carrier, wherein the substantially anhydrous composition is provided in a range of from 0.1 percent by weight to 99.8 percent by weight, preferably about 30-45 percent. 
     Preferably the substantially anhydrous composition, with no water added, includes silicones and derivatives of silicone chemistry, including but not limited to cyclomethicones (volatile silicones), linear silicones, dimethylpolysiloxane, dimethicone copolyols, silicone glycols, aminofunctional silicones, polymeric silicones, silicon waxes, such as high molecular weight dimethicones and silicone derivative waxes. 
     When various silicone compounds are used, a lustrous, elegant smooth tactile feel is achieved when the topical composition is applied to the skin. 
     Other substantially anhydrous compositions, with no water added, may be substituted for the silicones, such as other emollients, including but not limited to esters, amides, ethoxylated fats, mineral oil, petrolatum, vegetable fats and animal fats, such as hydrogenated tallow and lanolin. 
     Substantially anhydrous synthetic wax blends, such as triglycerides and tribehenin may be utilized. Polyols such as polyhydric alcohols and solvents such as mineral oil, glycerin and propylene glycol and sorbitol may be used. 
     Emulsifiers such as anhydrous polysorbate and polyethylene glycol, such as PEG 60 hydrogenated castor oil may be employed, as well as anhydrous surfactants such as nonylphenol. 
     Anti-oxidants, such as BHA, BHT, propylgallate, Vitamin E tocopherol, as well as chelating agents such as disodium EDTA, may also be used to further stabilize other substantially anhydrous bases. However, liquid or non-granular anti-oxidants, may be used as a substantially anyhydrous base with ascorbic acid by themselves. 
     Fat soluble vitamins, such as substantially anhydrous Vitamins A, D and E and their esters or derivatives, may also be used as bases for the ascorbic acid based composition. 
     Moreover, pH buffers such as alkaline sodium citrate and magnesium citrate are effective as substantially anhydrous bases for the delivery vehicle. 
     Other inactive components may include preservatives, such as phenoxetol, humectants, viscosity control aids, pH buffers and carrier solvents. However, as noted above, certain pH buffers and solvents may also act as an anhydrous base. 
     The resultant mixture is a comfortable delivery vehicle which delivers the ascorbic acid, its derivatives or extracts containing ascorbic acid to the skin in an effective and stable manner. 
    
    
     The following examples illustrate topically applied skin care products which can be prepared using conventional procedures from the following ingredients with typical ranges of acceptable percentages by weight and typical preferred percentage by weight shown. The formulations are illustrative only, and the preferred range is about the percentage specified: 
     
         ______________________________________Formulation #1:Ingredient    Range (% w/w)                      Preferred (% w/w)______________________________________Ascorbic acid 0.1-95.0     About 10.0Cyclomethicone         0.1-99.8     About 30.0Water (no water           0-5.0      0.0added)Surfactant      0-90.0     About 5.0Methylparaben 0.0-3.0      About 0.2(preservative)Steareth-2    0.0-10.0     About 3.5(emulsifier)Gelene        0.0-95.0     About 36.3(viscosity aid)Bentonite     0.0-25.0     About 5.0(binder)______________________________________ 
    
     
         ______________________________________Formulation #2:Ingredient    Range (% w/w)                      Preferred (% w/w)______________________________________Polyglyceryl  0.0-99.0     About 60.0methacrylate GelAscorbic acid 0.1-95.0     About 15.0Silicone Gylcol         0.1-60.0     About 15.0Water         0.0 to balance                      0.0 to balance(no water added)         of composition                      of composition______________________________________ 
    
     It has also been found that the product is more stable if the cyclomethicone is increased up to about 45% by weight, and the viscosity aid, such as gelene, and the binder, such as bentonite, are excluded, as shown in the alternate embodiment shown in Formulation #3 below: 
     
         ______________________________________Formulation #3:Ingredient   Range (% w/w)                     Preferred (% w/w)______________________________________Ascorbic acid        0.1-95.0     about 5.0Cyclomethicone        0.1-99.8     about 45.0Water (no water          0-5.0      balance of compositionaddedSurfactant     0-90.0     About 5.0Phenoxetol   0.0-5.0      About 0.5(preservative)Dimethicone  0.0-99.8     About 10.0______________________________________ 
    
     Other formulations include the following: 
     
         ______________________________________Formulation #4:Ingredient   Range (% w/w)                     Preferred (% w/w)______________________________________Ascorbic acid        0.1-99.8     About 10.0Petrolatum   0.1-99.8     About 90.0______________________________________ 
    
     
         ______________________________________Formulation #5:Ingredient      Range (% w/w)                       Preferred (% w/w)______________________________________Hydrogenated vegetable           0.1-99.8    About 90.0shorteningAscorbic acid   0.1-99.8    About 10.0______________________________________ 
    
     
         ______________________________________Formulation #6:Ingredient    Range (% w/w)                      Preferred (% w/w)______________________________________Cyclomethicone and         0.0-99.8     About 70.0dimethicone blendAscorbic acid 0.1-99.8     About 15.0Cyclomethicone         0.1-99.8     About 10.0Dimethicone   0.1-99.8     About 15.0______________________________________ 
    
     The composition is made in a single phase, wherein the single phase carrier is an anhydrous base, which is mixed with the ascorbic acid by mixing, dispersing or by suspension, according to techniques known to those skilled in the art. No separate emulsion phases are needed. 
     The present invention therefore includes a method for the prevention and/or treatment of photo-aged skin and related skin disorders, such as wrinkles, sunburn, poor skin tone and skin discoloration. 
     The method comprises steps of the topical application of suitable compositions containing stable ascorbic acid, its derivatives or extracts containing ascorbic acid, in a single phase, substantially anhydrous base, with no water added. 
     In general, the treatment composition suitable for use in accordance with the invention containing ascorbic acid, its derivatives or extracts containing ascorbic acid, may be applied in any dermatologically acceptable vehicle such as a gel, lotion, cream, stick, spray, serum, or pad applied formulation, which may or may not be emulsified and may contain ingredients to improve, modify, or stabilize the formulation physically or cosmetically. Other suitable formulations will be apparent to those skilled in the art. 
     The treatment compositions of the invention will improve the condition of the skin to which it is applied, preferably by frequent periodical application over an extended period of time without undue irritation to the skin or any other side effects. 
     Generally, the topical applications are applied periodically such as one or two times per day. 
     Moreover, Table 1 shows the stability of examples of the composition. Stability tests were conducted of topical skin treatment compositions containing ascorbic acid, specifically L-ascorbic acid at 10%. The compositions were tested for percentage of stability as a function of shelf life in a closed jar at either room temperature or at an elevated temperature of from 40° C. to 45° C. Tests of the containers of the compositions at room temperature were conducted over a six month period and tests of the containers of the compositions at elevated temperature of from 40° C. to 45° C. were conducted over a three month period. 
     
                       TABLE I______________________________________Composition No. 1: a topical facial complex containing10% of L-ascorbic acid.a)  Condition: maintained at room temperature in a 1/2 oz. clear jar    with lined cap.b)  Test: ascorbic acid assay.c)  Recommended Percentage of Stability: 80.0%-110.0%d)  Resultant Percentage of Stability:0 months       3 months 6 months95.6%          90.1%    90.4%Composition No. 1: a topical facial complex containing10% of L-ascorbic acid.a)  Condition: maintained at 40° C. to 45° C. in a 1/2 oz.    clear jar with    lined cap.b)  Test: ascorbic acid assay.c)  Recommended Percentage of Stability: 80.0%-110.0%d)  Resultant Percentage of Stability:0 months 1 month    2 months 3 months95.6%    91.4%      90.4%    84.5%Composition No. 2: a topical hand and body complex containing10% of L-ascorbic acid.a)  Condition: maintained at room temperature in a 2 oz. container.b)  Test: ascorbic acid assay.c)  Recommended Percentage of Stability: 80.0%-110.0%d)  Resultant Percentage of Stability:0 months       3 months 6 months98.5%          92.4%    90.2%Composition No. 2: a topical hand and body complex containing10% of L-ascorbic acid.a)  Condition: maintained at elevated temperature from 40° C. to    45° C.    in a 2 oz. container.b)  Test: ascorbic acid assay.c)  Recommended Percentage of Stability: 80.0%-110.0%d)  Resultant Percentage of Stability:0 months  1 month      2 month 3 months98.5%     95.0%        91.1%   84.0%______________________________________ 
    
     The aforesaid formulations are merely illustrative of the general concepts. Other changes to the present invention may be made without departing from the spirit or scope thereof, when read in conjunction with the appended claims.