Abstract:
Polyurea systems comprising: (a) an amino-functional aspartic ester of the general formula (I) 
     
       
                 
         
             
             
         
       
     
     wherein X represents an n-valent organic radical derived from a corresponding n-functional primary amine X(NH 2 ) n , R 1  and R 2  each independently represent an organic radical having no Zerevitinov active hydrogens and n represents an integer of at least 2; and (b) an isocyanate functional prepolymer having a residual monomer content of less than 1% by weight, the prepolymer prepared by reacting: (b1) an aliphatic isocyante; and (b2) a polyol component having a number average molecular weight of ≧400 g/mol and an average OH functionality of 2 to 6, wherein the polyol component comprises one or more constituents selected from the group consisting of polyester polyols, polyester-polyether polyols and mixtures thereof; processes for making the same; postoperative adhesions barriers prepared therewith and dispensing systems for such polyurea systems.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Adhesions are among the most frequent complications after interventions in the abdominal and pelvic region. Adhesions are fibrous bands which generally form within the first seven days after an operation, in the course of the healing process. They cause tissues and organs which are normally separated from one another to grow together, which can give rise to a multiplicity of complications such as, for example, chronic pain, infertility or a life-treating intestinal occlusion. Products able to reduce the formation of adhesions have been developed in recent years to avoid such complications. Success has so far been limited, however. 
         [0002]    Methods of preventing adhesions are peritoneal cavity lavage; the use of pharmacologically active agents such as anti-inflammatories or fibrinolytics; and also the application of mechanical barriers to separate the tissue. Adhesion barriers consist of an inert or absorbable material which is applied to the organs in question. Research has been done on a multiplicity of materials such as polysaccharides (U.S. Pat. No. 4,886,787, U.S. Pat. No. 5,356,883), hyaluronic acid U.S. Pat. No. 4,141,973, U.S. Pat. No. 5,246,698), alginates (U.S. Pat. No. 5,266,326), chitin (U.S. 5,093,319), chitosan (U.S. Pat. No. 4,532,134, U.S. Pat. No. 5,679,658), xanthan (U.S. Pat. No. 4,994,277), dextran (U.S. Pat No. 5,605,938), cellulose and derivatives thereof (Journal of spinal disorders &amp; techniques (2006), 19(4), 270-5), human serum albumin (U.S. Pat. No. 5,583,114), collagen (US 2005175659), glucosamine (U.S. Pat. No. 5,462,976), polyoxyalkylene copolymers (U.S. Pat. No. 4,911,926, U.S. Pat. No. 5,366,735, U.S. Pat. No. 5,135,751, U.S. Pat. No 5,681,576), polyester (U.S. Pat. No. 5,612,052, U.S. Pat. No. 6,136,333), etc. A large proportion of these materials have not been commercialized for lack of efficacy, lack of bioabsorbability or because of interactions with the wound-healing process. 
         [0003]    Commercially available products in membrane form such as INTERCEED™ (Johnson &amp; Johnson), SEPRAFILM™ (Genzyme Corp.) and REPEL-CV™ (Life Medical Corp.), are absorbed within 28 days. However, since the barriers are laid onto the organ in question, there is a risk of slippage. 
         [0004]    Barriers which like the hyaluronic acid derivative SEPRACOAT™ (GenzymeCorp.) and LUBRICOAT™ (Lifecore Biomedical Inc.) are applied as a liquid are often too quickly degraded by the body, limiting their barrier effect. In addition, there is a risk of migration and hence of no protective effect at all. 
         [0005]    Hydrogels are water-containing polymers whose chains are linked covalently to form a three-dimensional network. In water, they swell rapidly and with a substantial increase in volume. Owing to their high water content, they are being investigated for use as adhesion barriers. As well as the hydrogels based on natural polysaccharides (alginates, hyaluronic acid) it is in particular hydrophilic polyethylene glycol-based systems (US 2005266086, DE-A 69929278, U.S. Pat. No. 7,025,990, U.S. Pat. No. 6,514,534, US 2003/0077242), such as the commercially available SPRAYGEL™ (Confluent Surgical), which have been the subject of intensive research. Disadvantages found include the occasionally excessive rate of degradation and the acidity of the degradation products of lactic acid-based polyesters. As well as the polyethylene glycol-based hydrogel formation, there are frequent mentions (WO 0009087, US 20030077242, US 20050271727) of the redox-initiated free-radical polymerization. Redox initiators used include ascorbic acid and peroxides. As well as possible tissue irritation, one of the problems which arises is the aqueous consistency of the two reactants which is responsible for the absence of bonding to the organ in question. 
         [0006]    Isocyanate-capped polymers such as polyester- and polyether-urethanes are described in US 2004/0068078 and WO 2004/021983 for uses including as postoperative adhesion barriers. Isocyanates used are preferably TDI (toluylene diisocyanate) and IPDI (isophorone diisocyanate), the prepolymers containing 0.05 to 1 mEq of low molecular weight polyisocyanaes such as monomeric TDI to promote adherence to the tissue being treated. In the presence of significant biological fluid, or in adherence to certain types of tissue, greater amounts thereof should preferably be present. Adherence develops inter alia through reaction of the isocyanate with the tissue. However, monomeric isocyanates, as well as tissue irritation, are known to lead to a sensitization and hence to allergic reactions. The reaction rate of the prepolymer on the tissue is substantially slowed when aliphatic isocyanates such as HDI are used, and therefore such a system is not practicable for clinical use. 
         [0007]    U.S. Pat. No. 7,129,300 describes the production of absorbable 2-component systems consisting of a polyethylene oxide having two or more amine substituents and a biodegradable diisocyanate or an isocyanate-capped polyethylene oxide with an absorbable diamine. 
         [0008]    WO 2006/010278 describes the production and use of polyurethane prepolymers and polyurethane acrylates based on aliphatic isocyanates such as HDI. Chain extenders (curatives) used are low molecular weight diols, diamines, triols, triamines or oligomers and also physiologically active compounds. Organic zinc, tin, magnesium and iron compounds are used as a catalyst. The invention is useable inter alia as an adhesion barrier but also for various implants. However, the use of a catalyst generally leads to a substantial acceleration in the rate of curing of the polymer and hence to an increased evolution of heat. Usefulness for internal organs is limited as a result. 
         [0009]    EP-A 1719530 describes the use of isocyanate-capped polyester macromers based on aliphatic dicarboxylic acids and dihydroxy components such as polyalkylene oxides or polyethylene glycols. Aromatic, aliphatic and alicyclic isocyanates are described as possible isocyanates. Prepolymers formed from aromatics-based isocyanates such as TDI (as recited in the examples) have a reported crosslinking time on tissue of 1-10 min. However, the use of aromatics-based isocyanates in the body where, like the adhesion barriers, the product is fully degraded must be considered problematical because of the cleavage products which form. Systems based on aliphatic isocyanates are known from experience to have insufficient reactivity and hence too slow a cure time for practicable use in vivo. In addition, the viscosities of the compounds recited in EP-A 1719530 are too high at an average of 60 000 mPas for application, and therefore a solvent has to be used. 
         [0010]    WO 2007/067624 describes a bioabsorbable 2-component system consisting of an isocyanate prepolymer based on glycolide, lactide, ε-caprolactone, p-dioxanone, trimethyl carbonate and polyalkylene oxide (for example polyethylene glycols). The second component used is a polyamine. On application of the two components to tissue a gel is formed that is useful as an adhesive or as an adhesion barrier. However, the prepolymers have an extremely high viscosity and therefore are difficult to apply without added solvent. Possible solvents mentioned include water, alcohols and ketones. Hydroxyl-containing solvents, however, present the problem of rapid reaction with the prepolymer, so that there is a risk of gelling. Processing time, moreover, can become extremely rapid and thereby make processing problematical. The use of solvents in vivo must generally in most cases be considered problematical on account of possible cytotoxicity and also interaction with the tissue. 
         [0011]    That aspartic esters are suitable in principle for crosslinking prepolymers is known in the prior art in the context of surface coatings and described in DE-A 10246708 or EP-A 1081171. 
         [0012]    European patent application No. 07021764.1, unpublished at the priority date of the present invention, already describes wound adhesives based on a combination of hydrophilic polyisocyanate prepolymers and aspartates as hardeners. The prepolymers are based on polyether polyols and therefore are not biodegradable within 6 to 12 months. In addition, the systems described are strong adhesives and therefore unsuitable for use as an adhesion barrier. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present invention relates to novel adhesion barriers based on hydrophilic polyisocyanate prepolymers for use in surgery. 
         [0014]    Various embodiments of the present invention can provide adhesion barriers which: form a flexible film on the organs/tissue to be protected; adhere to the organs/tissue to be protected; are biodegradable in a time window of up to 6 months; are biocompatible; form degradation products without cell and tissue toxicity; solidify rapidly in keeping with the use; display no significant, tissue-damaging exotherm in curing; are easy to apply and unable to penetrate into deeper layers of tissue. 
         [0015]    Tissue in the context of the present invention is to be understood as meaning cell assemblages consisting of cells of the same shape and function such as epithelial tissue, myocardial tissue, connective or stroma tissue, muscles, nerves and cartilage. Also included are all organs constructed of cell assemblages such as the liver, kidneys, lungs, heart, uterus, etc. 
         [0016]    It has now been found that such advantageous adhesion barriers can be achieved by a combination of isocyanate-functional polyester prepolymers based on aliphatic isocyanates having residual monomer contents of less than 1% by weight in combination with amino-functional aspartic esters. Crosslinking catalysts are not needed for crosslinking on the tissue. 
         [0017]    The present invention accordingly provides polyurea systems comprising 
         [0018]    A) amino-functional aspartic esters of the general formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    where X is an n-valent organic radical obtained by removal of the primary amino groups of an n-functional amine, R 1 , R 2  are the same or different organic radicals devoid of any Zerevitinov-active hydrogen and n is an integer of at least 2 and 
         [0019]    B) isocyanate-functional prepolymers having residual monomer contents of less than 1% by weight, preferably less than 0.1% by weight and more preferably less than 0.03% by weight, obtainable by reaction of
       B1) aliphatic isocyanates with   B2) a polyol component having number average molecular weights of ≧400 g/mol and average OH functionalities of 2 to 6 which contains polyester polyols and/or polyester-polyether polyols and also optionally polyether polyols and       
 
         [0022]    C) optionally, organic fillers having a DIN 53019 viscosity at 23° C. in the range from 10 to 6000 mPas, and 
         [0023]    D) where appropriate, reaction products of isocyanate-functional prepolymers as per the definition of component B) with aspartic esters as per component A) and/or organic fillers as per C). 
         [0024]    One embodiment of the present invention includes a polyurea system comprising: 
         [0025]    (a) an amino-functional aspartic ester of the general formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein X represents an n-valent organic radical derived from a corresponding n-functional primary amine X(NH 2 ) n , R 1  and R 2  each independently represent an organic radical having no Zerevitinov active hydrogens and n represents an integer of at least 2; and 
         [0026]    (b) an isocyanate functional prepolymer having a residual monomer content of less than 1% by weight, the prepolymer prepared by reacting:
       (b1) an aliphatic isocyante; and   (b2) a polyol component having a number average molecular weight of ≧400 g/mol and an average OH functionality of 2 to 6, wherein the polyol component comprises one or more constituents selected from the group consisting of polyester polyols, polyester-polyether polyols and mixtures thereof.       
 
         [0029]    Another embodiment of the present invention includes a process for preparing a polyurea system, the process comprising: 
         [0030]    (i) providing (a) an amino-functional aspartic ester of the general formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein X represents an n-valent organic radical derived from a corresponding n-functional primary amine X(NH 2 ) n , R 1  and R 2  each independently represent an organic radical having no Zerevitinov active hydrogens and n represents an integer of at least 2; 
         [0031]    (ii) providing (b) an isocyanate functional prepolymer having a residual monomer content of less than 1% by weight, the prepolymer prepared by reacting:
       (b1) an aliphatic isocyante; and   (b2) a polyol component having a number average molecular weight of ≧400 g/mol and an average OH functionality of 2 to 6, wherein the polyol component comprises one or more constituents selected from the group consisting of polyester polyols, polyester-polyether polyols and mixtures thereof; and       
 
         [0034]    (iv) mixing the (a) amino-functional aspartic ester and the (b) isocyanate functional prepolymer in a ratio of free or blocked amino groups to free NCO groups of 1:1. 
         [0035]    Another embodiment of the present invention includes a dispensing system comprising a first chamber and a second chamber; wherein the first chamber comprises (a) an amino-functional aspartic ester of the general formula (I) 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    wherein X represents an n-valent organic radical derived from a corresponding n-functional primary amine X(NH 2 ) n , R 1  and R 2  each independently represent an organic radical having no Zerevitinov active hydrogens and n represents an integer of at least 2; and wherein the second chamber comprises (b) an isocyanate functional prepolymer having a residual monomer content of less than 1% by weight, the prepolymer prepared by reacting: 
         [0036]    (b1) an aliphatic isocyante; and 
         [0037]    (b2) a polyol component having a number average molecular weight of ≧400 g/mol and an average OH functionality of 2 to 6, wherein the polyol component comprises one or more constituents selected from the group consisting of polyester polyols, polyester-polyether polyols and mixtures thereof. 
         [0038]    Yet another embodiment of the present invention includes a method comprising: (i) providing cell tissue to be treated; (ii) providing a polyurea system according any of the various embodiments of the invention; and (iii) contacting the cell tissue to be treated with the polyurea system. 
         [0039]    Still other embodiments of the present invention include postoperative adhesion barriers and films comprising polyurea systems according any of the various embodiments of the invention. 
         [0040]    For the definition of Zerevitinov-active hydrogen, reference is made to Römpp Chemie Lexikon, Georg Thieme Verlag Stuttgart. Groups having Zerevitinov-active hydrogen are preferably understood as meaning OH, NH or SH. 
     
    
     DESCRIPTION OF THE INVENTION 
       [0041]    As used herein, the singular terms “a” and “the” are synonymous and used interchangeably with “one or more” and “at least one,” unless the language and/or context clearly indicates otherwise. Accordingly, for example, reference to “an aliphatic isocyanate” herein or in the appended claims can refer to a single aliphatic isocyanate or more than one aliphatic isocyanate. Additionally, all numerical values, unless otherwise specifically noted, are understood to be modified by the word “about.” 
         [0042]    Preferred meanings in the formula (I) are:
       R 1 , R 2  are the same or different optionally branched or cyclic organic radicals devoid of any Zerevitinov-active hydrogen and having 1 to 20 and preferably 1 to 10 carbon atoms, more preferably methyl or ethyl,   n is an integer from 2 to 4, and   X is an n-valent organic optionally branched or cyclic organic radical having 2 to 20, preferably 5 to 10 carbon atoms, obtained by removing the primary amino groups of an n-functional primary amine.       
 
         [0046]    It will be appreciated that mixtures of two or more aspartic esters can also be used, and therefore n in the formula (I) may also be a non-integral mean value. 
         [0047]    The amino-functional polyaspartic esters A) can be prepared in a known manner by reaction of the corresponding primary at least difunctional amines X(H 2 ) n  with maleic or furmaric esters of the general formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0048]    Preferred maleic or fumaric esters include dimethyl maleinate, diethyl maleinate, dibutyl maleinate and the corresponding fumaric esters. 
         [0049]    Preferred primary at least difunctional amines X(NH 2 ) n  include ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,3-diaminopentane, 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, 1,6-diaminohexane, 2,5-diamino-2,5-dimethylhexane, 2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane, 1,11-diaminoundecane, 1,12-diaminododecane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4- and/or 2,6-hexahydrotoluylenediamine, 2,4′- and/or 4,4′-diaminodicyclohexylmethane, 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, 2,4,4′-triamino-5-methyldicyclohexylmethane and polyetheramines having aliphatically attached primary amino groups having a number average molecular weight M n  in the range from 148 to 6000 g/mol. 
         [0050]    Particularly preferred primary at least difunctional amines are 1,3-diaminopentane, 1,5-diaminopentane, 2-methyl-1,5-diaminopentane, 1,6-diaminohexane, 1,13-diamino-4,7,10-trioxatridecane. 2-Methyl-1,5-diaminopentane is very particularly preferred. 
         [0051]    In some preferred embodiments of the invention, R 1 =R 2 =ethyl and X is based on 2-methyl-1,5-diaminopentane as n-functional amine. 
         [0052]    The preparation of the amino-functional aspartic esters A) from the starting materials mentioned can be effected according to U.S. Pat. No. 5,243,012, the entire contents of which are hereby incorporated herein by reference, preferably within the temperature range from 0 to 100° C., the starting materials being used in such ratios that for each primary amino group there is at least one, preferably exactly one, olefinic double bond, any starting materials used in excess being removable by distillation after the reaction. The reaction can be carried out without a solvent or in the presence of suitable solvents such as methanol, ethanol, propanol, dioxane or mixtures thereof. 
         [0053]    The systems according to the present invention can be obtained by mixing the prepolymers B) with the amino-functional aspartic esters A) and also where appropriate the components C) and/or D). The ratio of free or blocked amino groups to free NCO groups is preferably 1:1.5 and more preferably 1:1. 
         [0054]    Immediately after the individual components have been mixed together, the systems according to the present invention have a DIN 53019 shear viscosity at 23° C. of preferably 500 to 20 000 mPas and more preferably 500 to 8000 mPas. 
         [0055]    The time for complete crosslinking and curing of the adhesion barrier typically is in the range from 30 s to 10 min at 23° C., preferably in the range from 30 s to 8 min and more preferably in the range from 1 min to 5 min. 
         [0056]    The isocyanate-functional prepolymers used in B) can be obtained by reaction of isocyanates B1) with polyols B2) in the presence or absence of catalysts and also auxiliary and additive materials. 
         [0057]    The isocyanates or isocyanate mixtures used in B1) preferably have an average NCO functionality in the range from 2 to 2.6 and more preferably in the range from 2 to 2.4. B1) may utilize as isocyanates, for example, monomeric aliphatic or cycloaliphatic di- or triisocyanates such as 1,4-butylene diisocyanate (BDI), 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 2,2,4- and/or 2,4,4-trimethylhexamethylene diisocyanate, the isomeric bis (4,4′-isocyanatocyclohexyl)methanes or their mixtures of any desired isomeric content, 1,4-cyclohexylene diisocyanate, 4-isocyanatomethyloctane 1,8-diisocyanate(nonane triisocyanate) and also alkyl 2,6-diisocyanatohexanoate(lysine diisocyanate) having C 1 -C 8 -alkyl groups. 
         [0058]    As well as the aforementioned monomeric isocyanates, it is also possible to use their higher molecular weight descendent products of uretdione, isocyanurate, urethane, allophanate, biuret, iminooxadiazinedione or oxadiazinetrione structure and also mixtures thereof. B1) preferably utilizes isocyanates of the aforementioned kind with exclusively aliphatically or cycloaliphatically attached isocyanate groups or mixtures thereof. Hexamethylene diisocyanate is very particularly preferred for use in B1). 
         [0059]    Polyol component B2) preferably utilizes polyols having an average OH functionality in the range from 2.3 to 4. B2) preferably utilizes polyether ester polyols and preferably their mixtures with polyether polyols. 
         [0060]    Such preferred polyether ester polyols having a hydroxyl number of 30 to 140 mg KOH/g, preferably 35 to 130 mg KOH/g, and also an acid number of 0.05 to 10 mg KOH/g, preferably 0.1 to 3 mg KOH/g and more preferably 0.15 to 2.5 mg KOH/g. 
         [0061]    Polyether esters essential to the present invention are liquid at room temperature and have a DIN 53019 shear viscosity at 23° C. of 200 to 8000 mPas, preferably 400 to 4000 mPas. 
         [0062]    Such polyether ester polyols are preferably prepared by polycondensation of polycarboxylic acids, anhydrides of polycarboxylic acids and also esters of polycarboxylic acids with volatile alcohols, preferably C1 to C6 monools, such as methanol, ethanol, propanol or butanol, with (in molar terms) excess, low molecular weight and/or higher molecular weight polyol; the polyol used comprises polyols containing ether groups with or without other polyols free of ether groups. 
         [0063]    It will be appreciated that polyether ester synthesis may also utilize mixtures of the higher molecular weight polyols and of the low molecular weight polyols. 
         [0064]    Such (in molar terms) excess low molecular weight polyols are polyols having molar masses of 62 to 299 daltons, having 2 to 12 carbon atoms and hydroxyl functionalities of at least 2, which may further be branched or unbranched and whose hydroxyl groups are primary or secondary. These low molecular weight polyols can also have ether groups. Typical representatives are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, cyclohexanediol, diethylene glycol, triethylene glycol and higher homologues, dipropylene glycol, tripropylene glycol and higher homologues, glycerol, 1,1,1-trimethylolpropane and also oligotetrahydrofurans having hydroxyl end groups. It will be appreciated that mixtures can also be used within this group. 
         [0065]    Higher molecular weight polyols excess in molar terms are polyols having molar masses of 300 to 3000 daltons, which are obtained by ring-opening polymerization of epoxides, preferably ethylene oxide and/or propylene oxide, and also by acid-catalysed, ring-opening polymerization of tetrahydrofuran. Ring-opening polymerization of epoxides may utilize either alkali metal hydroxides or double metal cyanide catalysts. 
         [0066]    Useful starters for ring-opening polymerization of epoxides include all at least bifunctional molecules from the group of the amines and the abovementioned low molecular weight polyols. Typical representatives are 1,1,1-trimethylolpropane, glycerol, o-TDA, ethylenediamine, 1,2-propylene glycol, etc. and also water, including mixtures thereof. It will be appreciated that mixtures can also be used within the group of excess higher molecular weight polyols. 
         [0067]    The construction of the higher molecular weight polyols comprising hydroxyl-terminated polyalkylene oxides formed from ethylene oxide and/or propylene oxide may be effected randomly or blockwise, in which case mixed blocks can be present as well. 
         [0068]    Polycarboxylic acids are aliphatic and aromatic carboxylic acids which can be cyclic, linear, branched or unbranched and which have between 4 and 24 carbon atoms. 
         [0069]    Examples are succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid. Preference is given to succinic acid, glutaric acid, adipic acid, sebacic acid, lactic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, pyromellitic acid. Particular preference is given to succinic acid, glutaric acid and adipic acid. 
         [0070]    The group of the polycarboxylic acids further comprises hydroxy carboxylic acids or inner anhydrides thereof, for example caprolactone, lactic acid, hydroxybutyric acid, ricinolic acid, etc. Also included are monocarboxylic acids, in particular those having more than 10 carbon atoms, such as soybean oil fatty acid, palm oil fatty acid and groundnut oil fatty acid, subject to the proviso that their proportion of the total reaction mixture constructing the polyether ester polyol does not exceed 10% by weight and additionally the resulting lesser functionality is compensated by co-use of at least trifunctional polyols, whether as part of the low molecular weight polyols or as part of the high molecular weight polyols. 
         [0071]    The preparation of the polyether ester polyol can be effected in accordance with known methods at elevated temperature in the range from 120 to 250° C., initially under atmospheric pressure, later by applying a vacuum of 1 to 100 mbar, preferably but not necessarily with use of an esterification or transesterification catalyst, the reaction being completed to such an extent that the acid number decreases to values in the range from 0.05 to 10 mg KOH/g, preferably 0.1 to 3 mg KOH/g and more preferably 0.15 to 2.5 mg KOH/g. 
         [0072]    Furthermore, an inert gas can be used as part of the atmospheric pressure phase before a vacuum is applied. It will be appreciated that liquid or gaseous entrainers can also be used alternatively or for individual phases of the esterification. For example, the water of reaction can be removed using nitrogen as a carrier gas, but also with the use of an azeotropic entrainer, for example benzene, toluene, xylene, dioxane, etc. 
         [0073]    The polyether polyols optionally used in B2 as a blending component have a molecular weight in the range from 100 to 2000 g/mol, preferably in the range from 100 to 1000 g/mol and more preferably in the range from 100 to 400 g/mol and consist wholly or partly of polyethylene oxide polyols. 
         [0074]    When B2 utilizes polyether polyols alongside the polyesters or polyether esters, their proportion will comprise not more than 70% by weight and preferably not more than 50% by weight based on the entire component B2. 
         [0075]    Preferably the mass fraction of the entire component B2 that is attributable to ethylene oxide is preferably in the range from 40% to 95% by weight and more preferably in the range from 60% to 90% by weight. 
         [0076]    Component B2 preferably has an ester group concentration (in moles per kg) of 0.5 to 5.5 and more preferably 1 to 3.5. 
         [0077]    The prepolymers prepared from B1 and B2 have a DIN EN ISO 11909 average NCO content of 2% to 10% by weight and preferably 2.5% to 8% by weight. 
         [0078]    The organic liquid fillers used in C) are preferably non-cytotoxic as per ISO 10993 cytotoxicity measurement. 
         [0079]    Useful organic fillers include for example 23° C. liquid polyethylene glycols such as PEG 200 to PEG 600, their monoalkyl and dialkyl ethers such as PEG 500 dimethyl ether, liquid polyether and polyester polyols, liquid polyesters such as, for example, Ultramoll (Lanxess AG, Leverkusen, Germany), and also glycerol and its liquid derivatives such as, for example, Triacetin (Lanxess AG, Leverkusen, Germany). 
         [0080]    The organic fillers of component C) preferably comprise hydroxy- or amino-functional, preferably purely hydroxy-functional compounds. Particular preference is given to polyols. Preferred polyols are polyethers and/or polyester polyols and more preferably polyether polyols. The preferred organic fillers preferably have average OH functionalities in the range from 1.5 to 3, more preferably in the range from 1.8 to 2.2 and more preferably 2.0. The preferred organic fillers of component preferably have repeat units derived from ethylene oxide. The viscosity of the organic fillers is preferably in the range from 50 to 4000 mPas, more preferably in the range from 50 to 2000 mPas at 23° C. measured to DIN 53019. 
         [0081]    Certain preferred embodiments of the invention utilizes polyethylene glycols as organic fillers. These polyethylene glycols preferably have a number average molecular weight in the range from 100 to 1000 g/mol and more preferably in the range from 200 to 400 g/mol. 
         [0082]    The weight ratio of the filler component C) to the aspartate component A) is generally in the range from 0:1 to 20:1 and preferably in the range from 0:1 to 12:1. 
         [0083]    The weight ratio of the filler relative to the total amount of the mixture of A, and B is generally in the range from 0 to 100% and preferably in the range from 0 to 60%. 
         [0084]    To further reduce the average equivalent weight of all the compounds used for prepolymer crosslinking, based on the NCO-reactive groups, it is also possible, in addition to the compounds used in A), to prepare the amino- or hydroxy-functional reaction products of isocyanate-functional copolymers with aspartic esters and/or organic fillers, provided the latter are amino- or hydroxy-functional, in a separate prereaction and then to use these reaction products as higher molecular weight curative component. 
         [0085]    The pre-extending step preferably utilizes ratios of isocyanate-reactive groups to isocyanate groups in the range from 50:1 to 1.5:1 and more preferably in the range from 15:1 to 4:1. 
         [0086]    The isocyanate-functional prepolymer to be used for this can correspond to that of component B) or else be constructed differently from the components listed as possible constituents of the isocyanate-functional prepolymers in the context of this application. 
         [0087]    Modification through pre-extension has the advantage that the equivalent weight and equivalent volume of the curative component is modifiable within distinct limits. As a result, commercially available 2-chamber dispensing systems can be used for application in order to obtain an adhesive system which, given existing ratios for the chamber volumes, be fine tuned to the desired ratio of NCO-reactive groups to NCO groups. 
         [0088]    The invention further provides a process for preparing the urea systems of the invention and also their use as an adhesive or coating for sealing, uniting or covering cell tissues. Covering cell tissues is preferably understood as meaning preparing postoperative adhesion barriers. 
         [0089]    In the case of coatings for preparing postoperative adhesion barriers, it can be sensible to colour one or more of the components A) to D) used to make the barrier easier to see. 
         [0090]    In the in vivo application of a coating to produce a postoperative adhesion barrier, the necessary components are applied, with the aid of a two-chamber dispensing system and a suitable applicator, to the organ to be protected and there form a protective polymeric film within 10 minutes. This polymeric film adheres to the organ surface without penetrating into the tissue. The film can be mechanically removed without damaging the tissue. The invention further provides the present urea systems for preparing means for sealing, uniting or covering cell tissues. Similarly, films and composite parts are obtainable using the urea systems of the present invention. 
         [0091]    The invention will now be described in further detail with reference to the following non-limiting examples. 
       EXAMPLES 
       [0092]    Unless stated otherwise, all percentages are by weight. 
       Example A 
     Aspartate Synthesis 
       [0093]    To 2 mol of diethyl maleate was gradually added dropwise 1 mol of 2-methyl-1,5-diaminopentane under nitrogen atmosphere such that the reaction temperature does not exceed 60° C. The reaction mixture was then heated at 60° C. until diethyl maleate was no longer detectable in the reaction mixture. 
       Example B 
     Polyester Synthesis 
     Raw Materials 
       [0094]    Polyether 1 is a 1,2-propylene glycol-started, KOH-catalysed polyether glycol from BMS AG having a hydroxyl number of 56 mg KOH/g and having about 50% by weight each of ethylene oxide and propylene oxide units, the chain ends being tipped with ethylene oxide. 
         [0095]    Polyether 2 is a 1,2-propylene glycol-started, KOH-catalysed, hydroxyl-terminated polyethylene oxide from BMS AG having a hydroxyl number of 190 mg KOH/g. 
         [0096]    Polyether 3 is a 1,1,1-trimethylolpropane-started, KOH-catalysed, hydroxyl-terminated polyethylene oxide from BMS AG having an hydroxyl number of 550 mg KOH/g. 
         [0097]    The ester group concentration portrayed in Table 1 corresponds to the number of moles of carboxyl groups used for 1 kg of product. 
         [0098]    The reported “fraction of ethylene oxide groups” computes from the ethylene oxide group content of the starting polyether 1 (50% by weight), polyether 2 (100%), polyether 3 (100%) and diethylene glycol (100%), or their proportion of the starting materials of the polyester recipe. 
         [0099]    In a 6 l flask equipped with thermometer, column, reflux divider with head thermometer, descending condenser and 1 l receiver, 98 g (1.07 mol) of glycerol, 935 g (0.47 mol) of polyether 1, 1615 g (2.73 mol) of polyether 2 and 467 g (3.2 mol) of adipic acid were gradually heated to 200° C. at atmospheric pressure and under nitrogen with stirring, while water of reaction distilled off. After 5 hours, 68 mg of tin dichloride dihydrate were added and at the same time vacuum was applied to ultimately produce a pressure of 15 mbar. After a further 20 hours, the reaction had ended. Analysis gave the values recited in Table 1. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Synthesis and characterization of inventive polyester polyols, batch size per 3 kg of product 
               
             
          
           
               
                   
                 Example 
               
             
          
           
               
                   
                 B-1 
                 B-2 
                 B-3 
                 B-4 
                 B-5 
                 B-6 
                 B-7 
                 B-8 
                 B-9 
                 B-10 
               
               
                   
                   
               
             
          
           
               
                 adipic acid 
                 [g] 
                 467 
                 426 
                 218 
                 289 
                 562 
                   
                 733 
                 493 
                 201 
                 292 
               
               
                 succinic acid 
                 [g] 
                   
                   
                   
                   
                   
                 473 
               
               
                 glycerol 
                 [g] 
                 98 
                   
                 118 
                 98 
                   
                   
                   
                   
                 99 
                 82 
               
               
                 TMP 
                 [g] 
                   
                   
                   
                   
                   
                   
                   
                 256 
               
               
                 polyether 1 
                 [g] 
                 935 
                 931 
                 1527 
                 2150 
                   
                   
                 954 
                 937 
                 2748 
                 2148 
               
               
                 polyether 2 
                 [g] 
                 1615 
                 906 
                 1191 
                 534 
                 1735 
                 1829 
                 326 
                 1179 
                   
                 546 
               
               
                 Polyether 3 
                 [g] 
                   
                 842 
                   
                   
                 842 
                 842 
                 842 
                 256 
               
               
                 diethylene glycol 
                 [g] 
                   
                   
                   
                   
                   
                   
                 326 
               
               
                 tin dichloride dihydrate 
                 [mg] 
                 68 
                 68 
                 68 
                 68 
                 68 
                 68 
                 68 
                 68 
                 68 
                 68 
               
               
                 functionality 
                   
                 3 
                 3.5 
                 2.5 
                 3 
                 3.5 
                 3.5 
                 3.5 
                 3.5 
                 3 
                 3 
               
               
                 OH number exp. 
                 [mg KOH/g] 
                 52.1 
                 121.4 
                 98.3 
                 43.5 
                 122 
                 121 
                 120 
                 115 
                 44.4 
                 38.4 
               
               
                 acid number 
                 [mg KOH/g] 
                 0.9 
                 0.3 
                 0.3 
                 1.2 
                 0.2 
                 0.3 
                 0.2 
                 0.3 
                 0.6 
                 0.7 
               
               
                 viscosity 
                 [mPas, 75° C.] 
                 620 
                 180 
                 100 
                 440 
                 2110 
                 2490 
                 3230 
                 1850 
                 2340 
                 4450 
               
               
                 fraction of ethylene 
                 [% by weight] 
                 67 
                 71 
                 64 
                 52 
                 82 
                 85 
                 69 
                 61 
                 45 
                 53 
               
               
                 oxide units 
               
               
                 ester group concentration 
                 [mol/kg] 
                 2.13 
                 1.95 
                 1.00 
                 1.32 
                 2.56 
                 2.67 
                 3.35 
                 2.25 
                 0.92 
                 1.33 
               
               
                   
               
             
          
         
       
     
       Example C 
     Prepolymer synthesis 
     Example C-2a 
       [0100]    236.95 g of HDI and 0.4 g of benzoyl chloride were placed as initial charge in a 500 ml four-neck flask. 162.6 g of polyester 2 from Example B-2, dewatered at 100° C., were added at 80° C. during 2 h and subsequently stirred in for 1 h. Then, thin film distillation at 140° C. and 0.1 Torr was used to distil off excess HDI (hexamethylene diisocyanate) to leave 280 g of the prepolymer having an NCO content of 5.67%. The residual monomer content was &lt;0.03% of free HDI. 
       Example C-2b 
     Prepolymer-Synthesis 
       [0101]    281.88 g of HDI and 0.4 g of benzoyl chloride were placed as initial charge in a 500 ml four-neck flask. A mixture of 96.75 g of polyester 2 from Example B-2 and 20.97 g of polyethylene glycol of molar mass 200 Da (PEG 200), dewatered at 100° C., were added at 80° C. during 2 h and subsequently stirred in for 1 h. Then, thin film distillation at 140° C. and 0.1 Torr was used to distil off excess HDI to leave 311 g of the prepolymer having an NCO content of 7.88%. The residual monomer content was &lt;0.03% of free HDI. 
       Example C-2c 
     Prepolymer-Synthesis 
       [0102]    267.82 g of HDI and 0.4 g of benzoyl chloride were placed as initial charge in a 500 ml four-neck flask. A mixture of 91.92 g of polyester 2 from Example B-2 and 39.85 g of PEG 400, dewatered at 100° C., were added at 80° C. during 2 h and subsequently stirred in for 1 h. Then, thin film distillation at 140° C. and 0.1 Torr was used to distil off excess HDI to leave 302 g of the prepolymer having an NCO content of 7.57%. The residual monomer content was &lt;0.03% of free HDI. 
       Example D 
     Production of Adhesion Barrier 
     Example D 
       [0103]    10 g of prepolymer B were thoroughly mixed in a beaker with equivalent amounts of the amino-functional aspartic ester (aspartate A). The reaction mixture was immediately thereafter applied thinly to kidneys, liver and muscle tissue. Cure time and temperature and also adherence to the tissue were determined. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Example 
               
             
          
           
               
                   
                 D-1 
                 D-2a 
                 D-2b 
                 D-2c 
                 D-3 
                 D-4 
               
             
          
           
               
                   
                 prepolymer of polyester 
               
             
          
           
               
                   
                 C-1 
                 C-2a 
                 C-2b 
                 C-2c 
                 C-3 
                 C-4 
               
               
                   
               
               
                 NCO content of prepolymer 
                 3.06 
                 5.67 
                 7.88 
                 7.57 
                 4.38 
                 2.57 
               
               
                 [%] measured to DIN 
               
               
                 EN ISO 11909 
               
               
                 cure time [min] 
                 2 
                 1 
                 2 
                 1.5 
                 3 
                 3 
               
               
                 cure temperature [° C.] 
                 35 
                 40 
                 41 
                 40 
                 42 
                 35 
               
               
                   
               
             
          
           
               
                   
                 Example 
               
             
          
           
               
                   
                 D-5 
                 D-6 
                 D-7 
                 D-8 
                 D-9 
                 D-10 
               
             
          
           
               
                   
                 prepolymer of polyester 
               
             
          
           
               
                   
                 C-5 
                 C-6 
                 C-7 
                 C-8 
                 C-9 
                 C-10 
               
               
                   
               
               
                 NCO content of prepolymer 
                 5.95 
                 5.92 
                 6.0 
                 5.72 
                 2.01 
                 2.07 
               
               
                 [%] 
               
               
                 cure time [min] 
                 1.5 
                 1 
                 1 
                 1.5 
                 2 
                 3 
               
               
                 cure temperature [° C.] 
                 41 
                 43 
                 42 
                 47 
                 28 
                 37 
               
               
                   
               
             
          
         
       
     
         [0104]    A shiny, transparent film had formed at the reported times in all recited examples. Good adherence without penetration of the polymer into the tissue was observed in all cases. The barriers could be mechanically removed without damaging the tissue. 
       COMPARATIVE EXAMPLES 
     Example 1 
       [0105]    When prepolymer A-1 was applied to tissue without aspartate admixture, no cure took place within 30 min. 
       Example 2 
       [0106]    Prepolymer A-1 was prepared as described in Example B using TDI instead of HDI. The prepolymer obtained was admixed with different amounts of water and applied to tissue. No cure took place within 15 min. 
       Example 3 
     Synthesis of Polyether Polyol Prepolymer from EP 07021764.1 
       [0107]    465 g of HDI and 2.35 g of benzoyl chloride were placed as initial charge in a 1 l four-neck flask. 931.8 g of a polyether having an ethylene oxide content of 63% and a propylene oxide content of 37% (each based on total alkylene oxide content) started on TMP (3-functional) were added at 80° C. during 2 h and subsequently stirred in for 1 h. Then, thin film distillation at 130° C. and 0.1 Torr was used to distil off excess HDI to leave 980 g (71%) of the prepolymer having an NCO content of 2.53%. The residual monomer content was &lt;0.03 % HDI. 
       Example 4 
     Adhesion Barrier 
       [0108]    10 g of the prepolymer of Example 3 were thoroughly stirred in a beaker with equivalent amounts of the amino-functional aspartic ester (aspartate A). The reaction mixture was immediately thereafter applied thinly to kidneys, liver and muscle tissue. A cure took place within 2 min to form a transparent film. In the process, the polymer penetrated into the tissue and could not be removed without damage. 
         [0109]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.