all illustrations of the drawings are for the purpose of describing selected versions of the present invention and are not intended to limit the scope of the present invention . polyanhydrides are a class of biodegradable polymers characterized by anhydride bonds that connect repeat units of the polymer backbone chain . the main application of polyanhydrides is in the medical device and pharmaceutical industry . the characteristic anhydride bonds in polyanhydrides are usually decomposed in water . this decomposition results in two carboxylic acid groups which are biodegradable components easily metabolized by the body . biodegradable polymers such as polyanhydrides are capable of releasing physically entrapped or encapsulated drugs by well - defined kinetics . due to their biocompatibility and drug encapsulating properties , polyanhydrides are ideal polymers used in drug delivery . therefore , the majority of prior art thoroughly exploited the drug delivery aspect of polyanhydrides . for example , prior art ep0223524b1 and ep0200508b1 are dermal and oral bandages that utilize a polyanhydride as a drug delivery component . the present invention , however , utilizes a polyanhydride to stop chemical absorption into the skin organ and membranes . additionally , these prior art utilize polycarboxylic acid polymer alone or with maleic anhydride . the present invention , however , utilizes only a single polyanhydride polymer . the present invention is a transdermal retardant composed of a single polyanhydride derivative polymer named poly ( 1 , 3 - bis ( p - carboxyphenoxy ) propane - sebacic acid ) in low molecular weight polymer ( lmwp ) forms and high molecular weight polymer ( hmwp ) forms . the polyanhydride derivative polymer named poly ( 1 , 3 - bis ( p - carboxyphenoxy ) propane - sebacic acid ) has the chemical structure shown in fig6 , where m and n are integers from 2 to 200 . moreover , the polyanhydride derivative polymer named poly ( 1 , 3 - bis ( p - carboxyphenoxy ) propane - sebacic acid ) has the molecular weights ranging from 15000 to 75000 . the transdermal retardant comprises not only the aforementioned polyanhydride derivative , but also various variations of the poly ( 1 , 3 - bis ( p - carboxyphenoxy ) propane - sebacic acid ) and its polyanhydride family , which has the general chemical structure shown in fig5 , where r is a linear or branched organic moiety , and m and n are integers from 2 to 200 the polymer has been used as a model from polyanhydride family as a transdermal retardant . the creation of the transdermal retardant is claimed along with methods of preparing and applying the transdermal retardant . the transdermal retardant has been manufactured using the solvent casting method for preparation of an invisible nanofilm on the skin . the method of preparing and applying the transdermal retardant commences with mixing the transdermal retardant with chloroform and ether to formulate the final product , wherein 2 % and 4 % w / v of the transdermal retardant is mixed in chloroform . subsequently , the final product is applied to skin and allowed the chloroform to evaporate in warm air in less than 10 minutes . finally , the transdermal retardant is allowed to settle into skin while chloroform and ether evaporate . in the preferred embodiment , the thickness of the transdermal retardant is 100 μl / cm 2 or 1 millimeter . chloroform serves as a solvent and a carrier of the polyanhydride polymer . additionally , ether serves as a stabilizer to the transdermal retardant . the transdermal retardant may be formulated in various forms such as solvent , aerosol and semisolid . as reported in summary of invention and examples thereinafter , both low molecular weight polymer ( lmwp ) and high molecular weight polymer ( hmwp ) forms of the poly ( 1 , 3 - bis ( p - carboxyphenoxy ) propane - sebacic acid ) retard transdermal diffusion of nitrofurazone , nicotine , and nitroglycerin . therefore , the results illustrate the efficacy of the polyanhydride as a transdermal retardant . the retardation effect of lmwp and hmwp against the percutaneous absorption of nitrofurazone through rat skin is demonstrated in this example . the study was performed ex vivo on a male wistar rat skin . each rat was euthanized with chloroform vapor and the abdominal hair was gently removed with an electric clipper . the abdominal skin excised as full - thickness and was cleaned of extraneous tissue . for the experiments the skin was placed in home - made vertical franz - type glass diffusion cells , while the stratum corneum was facing the donor compartment . each diffusion cell was allowed to equilibrate with the receptor fluid for 24 hrs prior to experiments at ambient temperature . our preliminary studies showed that distilled water cannot provide a perfect sink condition for nitrofurazone , therefore , two other systems of a ) tween 20 aqueous solution ( 1 % w / v ) and b ) a mixture of distilled water , acetonitrile and triethylamine buffer ( 79 : 20 : 1 ) were investigated and the latter was chosen as the receptor phase for nitrofurazone . this mixture is suggested as mobile phase for hplc assay of nitrofurazone by usp ( 35 ) and the effect of this mixture as an enhancer was investigated here . results showed that this system did not change the nitrofurazone flux through rat skin when used in both donor and receptor phases . this solution could provide sink condition . solubility of nitrofurazone in this receptor phase was measured to be 668 μg / ml . after the 24 hr equilibration phase , receptor phases were replaced with fresh phases and its temperature was set at 37 . 0 ± 0 . 1 ° c . to provide surface temperature of 32 ° c . the retardants were applied to the donor phase as 2 and 4 % w / v solution in chloroform ( 100 μl / cm 2 ) and the solvent evaporated in less than 10 min using warm air . the systems were left to settle and the final residues of chloroform to evaporate ( as much as possible ). permeants were then applied to the donor phase as aqueous solutions of 200 μg / ml . interval sampling was performed for 24 hrs . donor phase was replaced with fresh one at 13 hours . permeated nitrofurazone of all samples was measured by uv spectrophotometry at 385 nm . the results are shown in fig2 and summarized in table 1 below . as shown in table 1 above and fig2 , nitrofurazone showed a permeation flux of 11 . 4 ± 1 . 6 ( μg / cm 2 / hr ) and lag - time of 3 . 5 ± 0 . 4 ( hr ) in control samples . retardant treatment decreased nitrofurazone flux and increased its lag - time up to 4 . 7 and 2 . 6 times , respectively . the effects of both polymers at all concentration on nitrofurazone flux retardation ( 2 . 2 - 4 . 7 times ) were statistically significant ( p & lt ; 0 . 00 ). for the lag - time however , while lmwp at 2 % did not show a significant effect ( p & gt ; 0 . 05 ), hmwp at both 2 % and 4 % was able to increase the lag time significantly ( p & lt ; 0 . 00 ) by about 2 . 0 and 2 . 6 times , respectively . in studies with lmwp , there was no delay in the appearance of penetrants in the receptor compartment , which indicates that the preparation did not form a physical barrier on the skin . however , after pretreatment with hmwp , the appearance of penetrants was delayed . these results suggest that this composition also acted as a physical barrier . the retardation effect of lmwp and hmwp against the percutaneous absorption of nicotine through rat skin is demonstrated in this example . the procedures in example 1 were repeated using distilled water as the receptor phase and aqueous nicotine solution of 500 μg / ml as the donor phase . permeated nicotine of all samples was measured by uv spectrophotometry at 260 nm . table 2 and fig3 summarize the effects of different concentrations of low and high molecular weight polymers on percutaneous absorption of nicotine through rat skin at 32 ° c . control ( untreated ) skin exhibited a nicotine steady - state flux of 40 . 00 ± 6 . 97 μg / cm 2 / hr . the presence of polymeric film from 2 % ( w / v ) lmwp reduced the flux of nicotine significantly ( p = 0 . 006 ) by about 2 times . application of 2 % hmwp showed a higher retardation effect for permeation of nicotine ( 2 . 6 times , p = 0 . 001 ). when the hmwp concentration was increased to 3 %, it showed a low but detectable amount of nicotine in the receptor phase at 2 and 3 hours , which stayed constant until the end of the experiments . at 4 %, hmwp stopped permeation of nicotine through rat skin completely , as no nicotine was observed in the receptor compartment throughout the experiment . it was decided here to study the effect of penetrant concentration on the retardation effect of lmwp and hmwp , based on the hypothesis that the complexation mechanism is affected by permeant concentration , while a simple barrier effect does not . as nicotine and nitrofurazone have similar sites for nucleophilic attack , only one of these permeants ( nitrofurazone ) was used to investigate this hypothesis . the retardation effect of lmwp and hmwp against the percutaneous absorption of 100 , 200 μg / ml and saturated solutions of nitrofurazone through rat skin is demonstrated in this example . an absorption rate of 5 . 11 ± 1 . 39 μg / cm 2 / hr was measured with 100 μg / ml nitrofurazone in aqueous solution , and this increased further to 11 . 44 ± 1 . 62 μg / cm 2 / hr and 18 . 24 ± 1 . 51 μg / cm 2 / hr with 200 μg / ml and saturated nitrofurazone in aqueous solution . this model penetrant also showed concentration - dependent lag time profile . the profile of the relationship between flux retardation ratio and concentration of nitrofurazone indicated that flux retardation ratio increased significantly with decreasing concentration of nitrofurazone ( table 3 ). the same profile , although to a lesser extent , was observed about hmwp between lag time elongation ratio and nitrofurazone concentration ( table 4 ). the retardation effect of lmwp and hmwp against the percutaneous absorption of nitroglycerin through rat skin is demonstrated in this example . the procedures in example 2 were repeated using aqueous nitroglycerin solution of 200 μg / ml as the donor phase . the amount of permeated nitroglycerin was measured using the bell spectrophotometric method ( 37 ). nitroglycerin was chosen as a model penetrant that does not have nucleophilic sites . table 5 and fig4 summarize the effect of low and high molecular weight polymer on percutaneous absorption of nitroglycerin through rat skin . penetration of nitroglycerin was not significantly changed in the presence of polymeric film from 2 % ( w / v ) lmwp ( p = 0 . 803 ). however , application of 2 % hmwp led to a decrease of flux by 1 . 6 ( p = 0 . 036 ). cumulative amount absorbed after 24 hrs in presence of lmwp and hmwp has not changed compared to untreated skin ( p = 0 . 293 ). in this example the utilization of higher molecular weight of this polymer which was synthesized in our lab ( data not shown ) could be highly advantageous . although the invention has been explained in relation to its preferred embodiment , it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed .
the present invention relates to a protective agent suitable to protect the human skin against toxic materials , particularly against chemicals with nucleophilic sites . the active moiety is a polyanhydride derivative . the active transdermal retardant offers a barrier property and chemically and / or physically reacts with harmful chemicals to decrease percutaneous absorption . in the preferred embodiments , polyanhydride in its low molecular weight form reduced flux of nicotine and nitrofurazone significantly . additionally , polyanhydride in its high molecular weight form prevented nicotine absorption and decreased nitrofurazone permeation dramatically . moreover , the polyanhydride in its high molecular weight form reduced nitroglycerin flux to a lesser extent .