it has now been found that hydrophilic crosslinked polyetheramidoamine polymers have surprisingly shown haemocompatible heparin - adsorbing properties , which have improved hydrophilic and elastic characteristics with respect to the crosslinked polyamidoamine of the above cited prior art . hydrogels of the invention are formed by polymeric polyetheramidoamine and / or polyamidoamine chains ending with acryl groups , hereinafter named as &# 34 ; prepolymers &# 34 ;, in their turn crosslinked with suitable crosslinking agents . the prepolymers are obtained by a michael &# 39 ; s like nucleophilic polyaddition , starting from bisacrylamido bifunctional monomers named [ aa ], of formula ( i ), ## str1 ## wherein : r 1 is hydrogen ; [ d ] is c 1 - c 12 straight or branched alkylene unsubstituted or substituted with one or more hydroxy groups , optionally interrupted by oxygen atoms , or [ d ], together with n &# 39 ; and n &# 34 ;, forms a piperazine ring , in which case r 1 is absent ; which are reacted with α - ω - diamino bifunctional monomers , named [ bb ], of formula ( ii ): ## str2 ## wherein : r 2 is c 1 - c 10 straight or branched alkyl , optionally substituted with one or more hydroxy groups ; [ e ] is c 1 - c 12 straight or branched alkylene unsubstituted or substituted with one or more hydroxy groups , optionally interrupted by oxygen atoms ; or the monomers [ aa ] are reacted with monofunctional monomers , named [ b ], of formula ( iia ): wherein [ f ] has the same meanings as [ e ] and it can also be interrupted by tertiary amino groups . preferred alkylene groups [ d ] are included in the following formula ( iii ): ## str3 ## wherein a , b , c , d , e and f are numbers 0 to 12 , r 3 is methyl , hydroxy , c 1 - c 12 alkyl , optionally substituted with one or more hydroxy groups ; particularly preferred alkylene groups [ d ] are those which , together with the nitrogen atoms n &# 39 ; and n &# 34 ;, form the polyoxyalkylenediamines known under the commercial name jeffamine ®, manufactured by texaco chemical company . even more preferred monomers are monomers [ aa ], in which [ d ] is a group of formula ( iii ) wherein r 3 is methyl , r 4 is hydrogen , r 5 is methyl , a and b are 1 , c is an integer 2 to 12 included , d , e , f are 0 ; or : r 3 , r 4 and r 9 are methyl , r 5 - r 8 are hydrogen , a and b are 1 , c is about 8 . 5 , d is 0 , the sum e + f is about 2 . 4 ; a , d , f are 0 , b is 2 , c and e are 1 , r 4 - r 7 are hydrogen . particularly preferred are bisacryloylpiperazine ( bap ), methylene - bis - acrylamide ( bac ), dihydroxyethylenebisacrylamide ( dheba ). particularly preferred compounds of formula ( ii ) are those in which r 2 are both 2 - hydroxypropyl , [ e ] has the following formula : ## str4 ## in some particular cases monofunctional monomer ( iia ) are used as chain extending agents between two monomers [ aa ]. wherein x and y are numbers comprised between 1 and 50 selected to have prepolymers with a maximum molecular weight mw 20 , 000 . the cross - linking of the resulting prepolymer can take place through two reaction mechanisms : a ) by michael nucleophilic polyaddition ; b ) radicalically . in the case of cross - linking by nucleophilic polyaddition , at least tetrafunctional crosslinking agents are used , of formula ( iv ): [ g ] is c 2 - c 12 straight or branched alkylene , unsubstituted or substituted with one or more hydroxy groups , optionally interrupted by oxygen atoms and / or & gt ; nr 10 amino groups , wherein r 10 is hydrogen or c 1 - c 4 alkyl . preferred compounds are those of formula ( iv ), wherein [ g ] represents the polyoxyalkylene residues comprising jeffamine ® of the m , d , ed , c - 346 , du , edr - 148 and t series , described in the publication by texaco chemical company &# 34 ; the jeffamine ® polyoxyalkyleneamines &# 34 ;, 1987 . the stoichiometric ratio , considered in equivalents , of the monomer [ aa ] to the sum of the monomer [ bb ] with the crosslinking agent must be such as to the number of acryl bonds on [ aa ] be the same as the number of the hydrogen atoms bound to the amino nitrogen atoms , i . e ., each molecule [ aa ] corresponds to one molecule [ bb ] and to half a molecule of the crosslinking agent . in case cross - linking is carried out radicalically , monomers with unsaturated end groups such as [ aa ], or bisacrylates , bismetacrylates or diallyl compounds can be used . cross - linking by michael nucleophilic polyaddition can be carried out according to two different methods . a ) in two steps , first preparing the prepolymer {[ aa ] [ bb ]} x , which , optionally after recovering it , is reacted with the crosslinking agent ; b ) in a single step , wherein the monomers and the crosslinking agent / s are reacted simultaneously . the reaction medium consists of a polar solvent or a mixture of polar solvents , such as water or water - miscible alcohols . the reaction temperature ranges from 0 ° to 60 ° c ., preferably from 20 ° to 40 ° c . the radicalic reaction can be carried out in aqueous or water - alcohol solvents , with radical promoters , such as ammonium persulfate , at a temperature from 20 ° to 40 ° c . otherwise , the reaction can be carried out in organic solvents with radical promoters , such as organic peroxides , dibenzoyl - peroxide and azobisisobutyronitrile , at a temperature higher than 60 ° c . the hydrogel will have different cross - linking degrees , depending on the desired physical characteristics . the final product will be elastic and have a swelling capability in water from 50 to 500 %. 1 . 65 g ( 11 . 44 mmoles ) of dimethylhexanediamine ( dmesa ) were reacted with 2 . 11 g ( 9 . 8 mmoles ) of methylene - bis - acrylamide ( bac ), in 10 ml of distilled water at room temperature . the mixture was left to react for 3 days shielding from light , to give a polyamidoamine prepolymer , mainly ending with vinyl groups . after that , the prepolymer was cross - linked directly by adding the reaction mixture with 170 mg ( 1 . 144 mmoles ) of jeffamine edr - 148 . the reaction was carried out for 3 days at room temperature . when the reaction was over , the product was repeatedly washed with water and methanol to remove the unreacted compounds . an elastic opaque white gel was obtained ( 89 % yield ). 2 g ( 13 . 86 mmoles ) of dmesa were dropped into a solution containing 2 . 56 g ( 16 . 60 mmoles ) of bac in 12 ml of distilled water and left to react at room temperature for 3 days . after the reaction , the prepolymer was recovered by evaporation of the solvent under vacuum at 30 ° c . the dried product was dissolved in chcl 3 ( 1 g / 5 ml chcl 3 ) and the solution was dropped into 300 ml of ethyl ether under magnetic stirring . the precipitate was washed twice with ethyl ether , filtered and dried . the control with hplc ( eluent buffer phosphate , ph 6 . 8 ; bio - gel tsk20 and tsk40 columns ) and with tlc ( chcl 3 : meoh 95 : 5 , developer k 2 co 3 -- kmno 4 ) evidenced the absence of unreacted starting products . the prepolymer was dissolved in water to obtain a 20 % w / v solution . subsequently 57 mg ( 13 . 86 mmoles ) of jeffamine edr - 148 were added and the cross - linking reaction was carried out for 3 days at room temperature . the product was recovered as in example 1 , to obtain a transparent elastic gel ( 96 % yield ). with a process similar to the one described in example 1 , and using 1 . 01 g ( 7 mmoles ) of dmesa , 1 . 51 g ( 9 . 8 mmoles ) of bac in 8 ml of distilled water and subsequently 207 mg of edr 148 , a transparent elastic gel was obtained ( 84 % yield ). a gel was prepared for comparison purposes , starting from the prepolymer of example 1 , which was cross - linked with 69 mg ( 1 . 144 mmoles ) of ethylenediamine , according to the procedure de scribed in u . s . pat . no . 3 , 865 , 723 . a brittle opaque gel was obtained ( 69 % yield ). 3 . 57 g ( 10 . 32 mmoles ) of jeffamine c346 , 4 g ( 20 , 64 mmoles ) of bap in 10 ml of distilled water were reacted , according to the method described in example 1 , for 4 days , shielding from light and at room temperature . at the end of the reaction , 10 . 31 g ( 5 . 16 mmoles ) of jeffamine d 2000 and 15 ml of methanol were added . the cross - linking reaction was carried out for 7 days at room temperature . an elastic light yellow gel was obtained , which was washed with water and methanol to remove the unreacted products ( 70 % yield ). 1 . 8 g ( 5 . 2 mmoles ) of jeffamine c346 in 2 ml of distilled water were treated with 1 . 11 g ( 5 . 72 mmoles ) of bap . the reaction was carried out for 2 days at room temperature and shielding from light . at the end of the reaction , the mixture was deareated under vacuum and nitrogen was introduced . after that , 60 mg of radicalic promoter azobisisobutyronitrile , suspended in 15 ml of water were added . the cross - linking was carried out at 60 ° c . for 3 hours . a brittle light yellow gel was obtained ( 60 % yield ). with a process similar to that described in example 6 , 1 . 66 g ( 4 . 79 mmoles ) of jeffamine c346 and 1 . 21 g ( 6 . 23 mmoles ) of bap were reacted in 2 ml of distilled water . a brittle light yellow gel was obtained ( 63 % yield ). the procedure of the example 7 was repeated and the amount of unreacted bap was analyzed by hplc , which amount corresponded to about 9 % w / w compared with the starting amount , then the reaction mixture was added with 0 . 292 g of bap ( 10 % by weight on jeffamine c346 ), nitrogen was repeatedly removed and bubbled therein and 5 ml of a 5 % w / w ammonium persulfate solution were added . cross - linking took place immediately : the white opaque gel was washed with distilled water and repeatedly with methanol ( 93 % yield ). hydrogel from prepolymer [ jeffamine c346 / bap ] crosslinked with bac ( jc 10 aps ) with a procedure similar to the one of the example 8 , except bac ( 1 . 56 g at the beginning of crosslinking and further 0 . 292 g after 8 days ) was used . at the end of the 8 th day , unreacted bac was about 9 % ( 83 % yield ). the gel prepared as described in the above examples were tested for heparin adsorption and release by means of the ptt test ( clotting test ). the tests were carried out on the gels obtained in the examples 1 and 2 , namely da1 / 2jr and da1 / 2 + jr , respectively , and on the gels obtained in the examples 3 , 4 and 5 , namely da1 / 4jr , da1 / 2ed and jajd . the samples were heparinized according to the procedure described in tanzi , levi , j . of biomed . mater . res . 23 ( 1989 ), 863 . the samples were immersed in heparin sodium salt solutions , 150 . 000 iu / g ( sarsyntex ) having 0 . 1 % and 1 % concentrations in acetate ( ab , ph 4 . 8 ) or phosphate ( pbs , ph 7 . 4 ) buffers . immersion lasted 16 hours , then the samples were extracted and twice washed with distilled water . the treatment with 1 % heparin ( see table 1 , n . 1 ) was the well known one in the case of the polyamidoamines . the treatment with 0 . 1 % heparin ( see table 1 , n . 4 and 5 ) was carried out in order to evaluate if the whole heparin could be completely adsorbed from a diluted solution . the treatment with heparin in pbs ( table 1 , n . 3 ) was intended to verify heparin absorption at physiological ph . the evaluation of heparin release in pbs was carried out by stirring the eparinized samples for several intervals , until heparin disappeared from eluates , each interval was 30 minutes long . the evaluation of heparin release in naoh solution was carried out by immersing the same sample in 0 . 1n naoh solution , until heparin disappeared from eluates . in this way , &# 34 ; weakly &# 34 ; adsorbed heparin , i . e . by means of electrostatic interactions , was released and could be evaluated in pbs , whereas more stably adsorbed heparin , i . e . by means of strong ionic interaction , was released only after treatment with naoh ( wherein tertiary nitrogen atoms deprotonate ). heparin amount was calculated with aptt test ( activated partial thromboplastin time ), with an elvi logos digiclot coagulometer and logos reagents , by additions of 50 μl of bovine serum to 50 μl of both known and unknown solutions . two calibrations curves were considered : the one with pbs and the other with 0 . 1n naoh ( neutralized with hcl and containing a final nacl concentration of 0 . 9 %). the results are shown in the following table 1 . table 1______________________________________heparin adsorption . aptt test : evaluation of heparinrelease from heparinized samples , both in physiological ( pbs ; ph 7 . 4 ) and alkaline ( 0 . 1 n naoh ) conditions . residue heparin released heparin heparini - in solu - pbs naohsample zation tion ( mg ) ( mg ) ( mg ) ______________________________________1 .) da1 / 2jr 1 % hep . in ˜ 7 g 0 . 26 16 ab over - (& lt ;& lt ; 1 %) ( 53 %) night ( tot . 30 mg ) 2 .) da1 / 2jr 0 % hep . in 0 . 0017 (*) ab over - night3 .) da1 / 2jr 1 % hep . in 0 . 180 g 0 . 236 19 pbs over - ( 1 . 2 %) ( 95 %) night ( tot . 20 mg ) 4 .) da1 / 2jr 0 . 1 % hep . in 0 . 22 g 0 . 044 2 . 8 ab over - ( 1 . 5 %) ( 93 %) night ( tot . 3 mg ) 5 .) da1 / 2 + jr 0 . 1 % hep . in 0 . 015 g 0 . 0805 2 . 7 ab over - ( 2 . 7 %) ( 90 %) night ( tot . 3 mg ) 6 .) da1 / 2ed 0 . 1 % hep . in 34 μg 0 . 100 (& gt ; 0 . 100 )(**) ab over - night ( tot . 2 mg ) 7 .) da1 / 4 jr 1 % hep . in 0 . 443 13 . 5 ab ( tot . (& lt ; 1 %) ( 45 %) 30 mg ) 8 .) jajd 1 % hep . in 3 . 22 167 . 5 ab ( tot . ( 1 . 6 %) ( 83 . 5 %) 200 mg ) ______________________________________ ab = acetate buffer ( ph = 4 . 6 ) pbs = phosphate buffer (*) = blank for the heparinization procedure (**) = non homogeneous gel , highly swollen in acetate buffer . the obtained results confirm these gels are interesting as potential materials sequestering heparin even from solutions having physiological ph , and also as heparinizing materials for coating the surfaces of devices or protheses to be contacted with blood . in the above table , points 1 to 4 show the results of the heparinization of the gels obtained without isolating the prepolymer . it can be seen that heparin remains adsorbed not only after acid buffer treatment ( ab ), but also after physiological ph treatment ( pbs , ph = 7 . 4 ). heparin , which is initially present in the solution is completely adsorbed , both in 1 % and in 0 . 1 % one . the release occurs partly in pbs , but mostly in alkaline conditions ( 0 . 1n naoh ). the data obtained by using a gel prepared from a previously isolated prepolymer ( point 5 ) confirm the ones obtained with the previous gel , which was prepared without isolating the prepolymer . in the comparison with a product , which was crosslinked with other than jeffamine , but with a diamine like ethylenediamine ( described in u . s . pat . no . 3 , 865 , 723 ), it should be noticed that the gel is not homogeneous , is poorly stable and reliable data may not be obtained ( see table 1 , n . 6 ).
polymeric polyetheramidoamine hydrogel materials , which are capable of complexing heparin in physiological conditions are herein described . said materials are useful in the manufacturing of medical devices .