the delivery of treating agents such as medicaments , nutritional agents and moisturizers to parts of the body is important for comfort and medical reasons . current systems , as described above , have not entirely met the needs of users . the inventors have found a novel composition which is simple , easy to apply and that may be used to deliver other agents . because the compositions of this invention are long lasting , they allow for the controlled release of additional treating agents . the release of the active agent over a period of time , is an important requirement for many effective treatments . the composition of the invention , though primarily directed toward use with the human body , may also be used in veterinary applications , particularly for mammals . the application of the invention to animals will , of course , require modification of the amounts of ingredients to compensate for different body temperatures and will also require tailoring the amounts of any additional ingredients so that they will be effective . dogs , for example , have a normal body temperature of about 38 . 5 ° c . such modification is within the contemplated scope of the invention and within the ability of those skilled in the art . this invention is concerned with the gelling of the inventive composition in response to temperature , i . e ., thermo - gelling , rather than other factors , since it is a more general characteristic than others , ( i . e . ; it doesn &# 39 ; t vary as greatly throughout the typical mammalian body as do ph and ionic composition ). as used herein , the term “ gel ” is defined as a colloid in which a disperse phase has combined with a continuous phase to produce a viscous , jelly - like product . generally speaking , the disperse phase will be a solid and the continuous phase will be an aqueous liquid . the gels formed according to the present invention may be relatively “ stiff ” and can be characterized as a semisolid containing a certain quantity of water . a colloidal solution with water is often also called a “ hydro - sol ”. as used herein , the term “ themo - gel ” or “ thermo - gelling ” refers to a colloidal system that responds to temperature changes by changing from a liquid to a gel . for purposes of the present invention , the “ thermo - gel ” refers to colloidal systems that change from a liquid to a gel upon an increase in temperature . the colloidal systems of the present invention are different from more well known colloidal systems that change from a liquid to a gel upon a decrease in temperature . the system of this invention uses a thermo - gelling composition that includes a base of water , methylcellulose or hydroxypropyl methylcellulose ( hereinafter referred to collectively as methylcellulose ) and citric acid and salts thereof . desirably , the aqueous liquid is de - ionized water . it is contemplated that water may be combined with small amounts of other compatible liquids such as , for example , glycerin . the thermo - gelling composition is a suitable base to which may be added various “ treating agents ” which may be medicinal agents , cosmetic agents , nutritional agents , adjuvants , moisturizers and other ingredients as desired without appreciably changing the gelling properties of the base . the resulting therapeutic compositions have a wide range of uses and applications . as noted above , temperature responsive or thermo - gelling solutions respond to temperature changes , in this case temperature increases , by changing from a liquid to a gel . the temperature range of interest for the invention is between about 25 and 40 ° c ., more particularly between about 35 and 39 ° c . or still more particularly around that of the human body ( 37 ° c .). compositions that change state at about this temperature are useful because they will remain in a body cavity , for example , after they have been delivered . a liquid would have difficulty in remaining in place in many locations of the body , particular with movement of the individual . therapeutic compositions containing the thermo - gelling base of the invention may be used on any mucosal surface location of the body such as in vaginal , rectal , oral cavity , ophthalmic and nasal locations . it may also be used a topical and transdermal composition and as an injectable in - situ gelling composition for subcutaneous or intramuscular applications to deliver specific medicaments where needed . in the case of injectable applications , after injection , the thermo - gelling composition along with the active ingredients becomes a semisolid gel and forms a drug “ reservoir ” in contact with body fluid and so enables the sustained release of the active ingredients . this approach helps to lower the injection frequency and hence improves patient compliance , which is especially important for drugs currently only available through injection . this includes drugs such as protein / peptide ( e . g . insulin and growth hormones ) drugs , for example . it has also been found that the thermo - gelling composition may be used as a soft tissue replacement in , for example , foot cushions , articular cartilage , and wound dressings . in these applications , the thermo - gelling composition is applied as a liquid to minimize disturbance to the site and to accommodate the configuration of the target site . it then solidifies in situ to provide mechanical support and barrier functionality . methylcellulose ( fig1 ) and hydroxypropyl methylcellulose ( fig2 ) have a polymeric backbone made of cellulose , a natural carbohydrate that contains a basic repeating structure of anhydroglucose units . these polymers are commercially available from a number of sources including the dow chemical company of midland , mich . the inventors have found that the molecular weight of the methylcellulose is important to the success of the composition , particularly that it be relatively low , i . e ., producing a viscosity for a 2 weight percent water solution which should be less than 1000 mpa · s at 20 ° c . methylcellulose concentration should be relatively high , i . e ., between 0 . 5 and 10 weight percent . a solution of methylcellulose may be made in cold water ( about room temperature or below ) by simply mixing the desired amount of methylcellulose in water with mild agitation . alternatively , the methylcellulose may be first dispersed in hot water ( about 50 - 90 ° c . ), and cold water added to the suspension to dissolve the methylcellulose . citric acid ( 2 - hyroxy , 1 , 2 , 3 propanetricarboxylic acid ) is colorless , odorless and acidic tasting . citric acid is also commercially available from numerous manufacturers . citric acid can be in its acid form ( hydrate or anhydrate ) or salt form ( e . g . sodium potassium salts ). it is desired that the thermo - gelling composition of this invention have from a positive amount to about 6 weight percent of citric acid and salts thereof and from about 0 . 5 to 10 weight percent of methylcellulose with the balance water ( preferably de - ionized ) as a base . any optional medicaments , moisturizers and other ingredients may be added as desired . more particularly the citric acid and salts thereof can be present in an amount between a 0 . 5 and 3 weight percent and the methylcellulose in an amount between about 2 and 7 weight percent with the balance water and any medicaments and / or moisturizers . the final composition should have a ph ranging from 2 to 9 . the additional treating agents mentioned above include active agents and medicaments selected generally from the classes of medicinal agents , ( i . e ., pharmaceutically active agents ), cosmetic agents , moisturizers , adjuvants and nutritional agents , as well as other desirable ingredients . the treating agent may be used singly or as a mixture of two or more such agents . exemplary medicinal agents include agents for treating infections such as antibacterial , anti - fungal and antibiotic agents ; for treating cardiovascular conditions such as chlorothiazide ( diuretic ), propranolol ( antihypertensive ), hydralazine ( peripheral vasodilator ), isosorbide or nitroglycerin ( coronary vasodilators ), metoprolol ( beta blocker ), procainamide ( antiarrythmic ), clofibrate ( cholesterol reducer ) or coumadin ( anticoagulant ); agents for treating internal conditions such as conjugated estrogen ( hormone ), tolbutamide ( antidiabetic ), levothyroxine ( thyroid conditions ), propantheline ( antispasmodic ), cimetidine ( antacid ), phenyl propanolamine ( anti - obesity ), atropine or diphenoxalate ( anti - diarrheal agents ), docusate ( laxative ), or prochlorperazine ( antinauseant ); agents for treating mental health conditions such as haloperidol or chlorpromazine ( tranquilizers ), doxepin ( psychostimulant ), phenytoin ( anticonvulsant ), levo dopa ( anti - parkinism ), benzodiazepine ( anti - anxiety ) or phenobarbital ( sedative ); anti - inflammatory agents such as fluorometholone , acetaminophen , phenacetin , aspirin , hydrocortisone , or predisone ; anti - histamines such as diphenhydramine hydrochloride or dexchlorpheniramine maleate ; antibiotics such as sulfanilamide , sulfamethizole , tetracycline hydrochloride , penicillin and its derivatives , cephalosporin derivatives or erythromycin ; chemotherapeutic agents such as sulfathiazole , doxorubicin , cisplatin or nitrofurazone ; topical anaesthetics such as benzocaine ; cardiac tonics such as digitalis or digoxin ; antitussives and expectorants such as codeine phosphate , dextromethorphan or isoproterenol hydrochloride ; oral antiseptics such as chlor hexidine hydrochloride or hexylresorcinol ; enzymes such as lysozyme hydrochloride or dextronase ; birth control agents such as estrogen ; ophthalmic treating agents such as timolol or gentamycin , and the like . in addition , medicinal treating agents may also include whole proteins such as the vp3 capsid protein ( also known as the vpthr and vp1 capsid proteins in other nomenclature systems ) as described in u . s . pat . no . 4 , 140 , 763 , insulin or interferon ; polypeptide treating agents such as endorphins , human growth hormone , or bovine growth hormone , or still lower molecular weight polypeptides or conjugates of those polypeptides linked protein carriers . exemplary cosmetic agents include sunscreens such as p - dimethylaminobenzoic acid or glyceryl p - aminobenzoate , a skin softener such as urea , keratolytic agents such as salicylic acid ; acne treating agents such as benzoyl peroxide or sulfur ; perfumes , and the like . the composition can be used as a moisturizing formulation with or without out pharmaceutically active ingredients . suitable moisturizers are known in the art and include vitamin e , aloe , glycerin , propylene glycol , alpha - hydroxy acid . one or more adjuvants may also be included with another treating agent , and when so used , an adjuvant is included in the meaning of the phrase “ treating agent ” as that phrase is used herein . exemplary of useful adjuvants are chelating agents such as ethylenediaminetetracetic acid ( edta ) that bind calcium ions and assist in passage of medicinal agents through the mucosa and into the blood stream . nutritional agents such as vitamins and / or minerals like riboflavin and iron , respectively , and combinations thereof may also comprise useful treating agents herein . the composition can also include effective amounts of other desirable ingredients ( other than methylcellulose , citric acid , and other active ingredients ) including ph adjusting acids / bases , e . g . hydrochloric acid or sodium hydroxide , tonicity adjusters , e . g . sodium chloride and mannitol , preservatives , e . g . parabens , benzoic acid , and benzalkonium chloride , antioxidants , e . g . ascorbic acid , and polymeric thickeners / viscosity adjusters , e . g ., alginate and chitosan and combinations thereof . if present , these are generally effective in amounts from a positive amount to about 5 weight percent . the treating agent or medicament is present in the compositions of this invention in an amount that is sufficient to prevent , cure and / or treat a condition for a desired period of time for which the composition of this invention is to be administered , and such an amount is referred to herein as “ an effective amount ”. as is well known , particularly in the medicinal arts , effective amounts of medicinal agents vary with the particular agent employed , the condition being treated and the rate at which the composition containing the medicinal agent is eliminated from the body , as well as varying with the species in which it is used , and the body weight of that individual . consequently , effective amounts of treating agents may not be defined for each agent . thus , an effective amount is that amount which in a composition of this invention provides a sufficient amount of the treating agent to provide the requisite activity of treating agent in or on the body of the treated individual for the desired period of time , and is typically less than that amount usually used . since amounts of particular treating agents in the blood stream that are suitable for treating particular conditions are generally known , as are suitable amounts of treating agents used in cosmetics , it is a relatively easy laboratory task to formulate a series of controlled release compositions of this invention containing a range of such treating agents to determine the effective amount of such a treating agent for a particular composition . while the effective amount for all treating agents cannot be stated , typical compositions of this invention may contain about one microgram to about one gram of treating agent per dose administered . the following embodiments illustrate the invention in varying scope . all the following example formulations were tested for their thermogelation property by the inverting - flow test method . in this test method , glass vials ( about 12 . 7 mm diameter ) containing the formulations are maintained at a given temperature for a specific time period , and are then inverted to see the flow behavior . a gel was defined as systems without notable flow by this method . aqueous solutions of 10 weight percent methocel a15lv methylcellulose ( dow chemical ) in de - ionized water were prepared using the hot / cold technique described above . methocel a15lv methylcellulose has a viscosity of 15 mpa · s measured at 2 weight percent concentration in water at 20 c . a 15 weight percent citric acid solution was prepared by mixing 15 . 8 grams citric acid and 4 . 3 grams sodium hydroxide into 85 ml de - ionized water at room temperature . these stock solutions were used in the following examples at varying amounts . the specific solutions were made by mixing the desired amount of the two solutions and then diluting with de - ionized water . the solutions were then kept overnight ( about 18 hours ) at 4 ° c ., then placed in another area at room temperature for 1 hour and finally placed in an oven at 37 ° c . the samples ( about 1 ml ) were in glass vials in the oven for 30 minutes ( table 1 ) and 2 hours ( table 2 ) and then inverted in the oven for two minutes as described above . the results are given in tables 1 and 2 where the methylcellulose concentration ( mc %) is given horizontally across the bottom of each table ( x - axis ), the citric acid concentration is given in the first vertical column ( y - axis ) and the result is in the box at the intersection of the desired solution . as used in the following tables , the term “ gel ” means the solution remained inverted for at least two minutes without running and the term “ not ” means the solution did not gel sufficiently to pass the inverting - flow test . a series of sample solutions were prepared similar to those in example 1 , with different methylcellulose and citric acid concentrations . benzoic acid was added to these samples as a preservative with weight concentration of 0 . 2 %, and all the solutions were adjusted to ph 4 . 0 ± 0 . 1 by naoh . the test was similar to that in example 1 except that a 37 ° c . water bath was used instead of an oven , and the samples were removed from the water bath and held at room temperature for the inversion tests which were done for 5 - 10 seconds instead of 2 minutes because of the reduced testing temperature . the result is shown in table 3 . a series of sample solutions were prepared similar to those in example 1 , with different methylcellulose and citric acid concentrations . methocel a4c methylcellulose ( dow chemical ) was used for these experiments in de - ionized water containing benzoic acid as a preservative at a weight concentration 0 . 2 %. solutions were prepared with differing amounts of citric acid by first dispersing the methylcellulose in hot water between about 50 - 90 ° c . and then adding cold water to dissolve the methylcellulose . methocel a4c methylcellulose has a viscosity of 400 mpa · s measured at 2 weight percent concentration in water at 20 ° c . all the solutions were adjusted to ph 4 . 00 ± 0 . 25 by naoh . a 37 ° c . water bath was used as in example 2 . samples were inverted for 5 - 10 seconds to observe flow behavior . the results are shown in table 4 . the preceding examples show the invention to be effective in gelling at the desired temperature range . such a composition is useful in delivering other desirable compounds to the body and for soft tissue replacement . as will be appreciated by those skilled in the art , changes and variations to the invention are considered to be within the ability of those skilled in the art . examples of such changes are contained in the patents identified above , each of which is incorporated herein by reference in its entirety to the extent it is consistent with this specification . such changes and variations are intended by the inventors to be within the scope of the invention .
there is provided a new thermo - gelling composition made with methylcellulose and citric acid . this composition may also have an effective amount of a treating agent , which may be a medicinal agent , cosmetic agent , moisturizer , adjuvant , nutritional agent , other ingredients and combinations thereof . the composition is useful in delivering moisturizers or pharmaceutically active agents to the user in a controlled release manner through the mucosal tissues in a body cavity , or on body surfaces , or as a subcutaneously injected medicament . the composition may also be used as a replacement for the soft tissues of the body as in , for example , the foot cushion and cartilage repair .