i . membranes comprising a support made of polycarbonate covered with hydroxypropyl methylcellulose ( hpmc ) alone ( control membranes ) the following solutions are prepared at least the day before the treatment by dissolving 2 g of hpmc ( e4m from dow chemical ) in 1 l of water for injection or an equivalent ratio in order to obtain a concentration of 0 . 2 % hpmc . the solution is left overnight with stirring ( magnetic stirrer ) at room temperature . the support membranes made of polycarbonate pokalon ( lonza ) are cleaned beforehand with water for injection . the treatments of the polycarbonate support membranes are carried out in a clean room with a branson plasma machine ; the following treatment is applied : ar — 50 w — 10 minutes . the polycarbonate support membranes thus treated are immediately immersed in the hpmc solution and are then allowed to dry at 45 ° c . in an oven . ii . membranes functionalized with vegf in hpmc according to the invention a 0 . 1 % hpmc solution ( 1 g / l ) is prepared in water for injection . 1 ml of this hpmc solution is diluted in 100 ml of dpbs phosphate buffer , giving an hpmc concentration of 0 . 001 %. the preparation of a vegf solution ( tebu - bio sas ) at 10 μg / ml ( that is 10 mg / l ) is carried out by adding 1 ml of dpbs to the vial containing 10 μg of vegf . the whole of this vegf solution ( that is 1 ml therefore comprising 10 μg of vegf ) is mixed with 4 ml of hpmc solution ( comprising 40 μg of hpmc ) in order to prepare a solution which comprises 25 parts of vegf per 100 parts of hpmc . the mixture is introduced into a 50 ml flask and diluted in order to obtain final concentrations of 0 . 2 μg / ml for vegf and 0 . 8 μg / ml for hpmc . according to the same principle , solutions comprising hpmc / vegf ratios of 100 / 50 and 100 / 10 are prepared . these steps are carried out as described at point i . b with the exception of the drying which is carried out at room temperature . iii . membranes functionalized with heparin in ethyl cellulose ( ec ) with an ec / heparin ratio of 100 / 25 according to the invention the ec solution is prepared as follows : ec exists in the form of a paste ( surelease from colorcon , at 25 % that is 25 mg / 100 mg ); it is diluted in water for injection at 1 g / l , that is 250 mg / l of ec . this solution is diluted a second time in water for injection in order to give a solution at 10 mg / l of ec . commercial heparin solution ( heparin choay 25000 iu sanofi - aventis ) has a heparin concentration of 200 mg / 5 ml ; it is diluted in water for injection until a heparin concentration of 10 μg / ml is obtained . 1 ml of the heparin solution ( containing 10 μg of heparin ) is mixed with 4 ml of the ec solution ( containing 40 μg of ec ) to give a solution having a ratio of 25 parts of heparin per 100 parts of ec . this solution is introduced into a 50 ml flask and diluted in order to bring the concentrations back to 0 . 2 μg / ml for heparin and to 0 . 8 μg / ml for the ec . these steps are carried out as described at point i . b with the exception of the drying which is carried out at room temperature . iv . membranes functionalized with heparin in ec and vegf in hmpc according to the invention the solutions of heparin in ec and of vegf in hpmc are prepared as indicated at points iii . a and ii . a respectively . the plasma treatment is carried out as described at point i . b . immersion of the polycarbonate support in the ec / heparin solution and then drying at room temperature ; then immersion of the support functionalized with heparin in the hpmc / vegf solution and then drying at room temperature . v . preparation of the device according to the invention with a silicone support devices according to the invention may be prepared with a silicone support . these supports constitute a complementary part of the semi - permeable membranes according to the invention . the silicone supports ( nusil ) are plasma - treated beforehand under the following conditions : ar — 100 w — 7 . 5 minutes . next , the application of the functionalized layers is carried out as described in the protocols of parts ii , iii and iv ; it being possible for the water for injection to be replaced with distilled water . trials for permeability to glucose and to immunoglobulins ( igg ) of the preprepared membranes are carried out as follows : materials : diffusion chamber consisting of a top compartment and a bottom compartment separated by a membrane whose permeability it is desired to test ( imperviousness between the two compartments is provided by a seal ), glucose ( prolabo ), nacl ( sigma , ref . s3014 ), igg ( sigma , ref . 196640 ), distilled water . 3 ml of physiological saline are introduced into the bottom compartment of the diffusion chamber , the membrane whose permeability it is desired to test is placed on top of the physiological saline while avoiding the presence of air bubbles . 3 ml of glucose solution are introduced into the top compartment , the diffusion chamber is closed with parafilm and is then incubated at 37 ° c . for glucose : 1 ml of the solution present in the top compartment of the diffusion chamber is collected after gentle homogenization . the membrane is then removed and placed in a petri dish and 1 ml of the solution in the bottom compartment is collected after homogenization . the enzymatic assay of glucose is carried out with the aid of the glucose rtu kit ( biomérieux , reference 61 269 ). the results ( expressed as glucose content in the bottom compartment as a function of time ) are presented in the graph of fig3 . comparison of the permeability to glucose of the functionalized membranes according to the invention ( 126 . 3 , 126 . 4 and 126 . 5 ) in relation to the membranes of the state of the art whose preparation is described in example 1 point i ( 126 . 1 and 126 . 2 ) demonstrates that the treatment intended to functionalize the membranes does not reduce permeability to glucose . for the iggs : 1 ml of the solution present in the top compartment of the diffusion chamber is collected after gentle homogenization . the membrane is then removed and placed in a petri dish where it is rinsed with 1 ml of distilled water . the rinse water is preserved . 1 ml of the solution in the bottom compartment is collected after homogenization . the assay of the iggs is carried out by the bradford method ( bradford , 1976 & amp ; wright et al ., 1996 ). the semi - permeable membranes according to the invention are completely impermeable to the iggs ; they thus advantageously prevent penetration of the encapsulation chamber for cytokines and chemokines . the membranes prepared as described in example 1 are implanted into the peritoneal cavity of healthy wistar rats . in the remainder of the experimental part , the membranes are coded as follows : 126 . 1 and 126 . 2 : “ control ” membranes ( prepared as described in part i of example 1 ); 126 . 3 : “ vegf / hpmc ” membrane ( ratio : 25 / 100 , prepared as described in part ii of example 1 ); 126 . 4 : “ heparin / ec ” membrane ( ratio : 25 / 100 , prepared as described in part iii of example 1 ); 126 . 5 : “ vegf / hmpc + heparin / ec ” membrane ( for both layers , the ratio is 25 / 100 , the membrane is prepared as described in part iv of example 1 ). male wistar rats of 230 - 250 g are anesthetized with gas ( isoflurane ). a 3 cm laparotomy in the left iliac fossa allows the implantation of the membrane . the incision is then closed . the rats are then placed in cages with food and water ad libitum ( each membrane is implanted in three rats ). after one week , the rats are anesthetized with an imalgene / rumpun mixture , and incised in order to recover the membrane and the epiploic tissue surrounding it . the membrane is then placed in 2 . 5 % glutaraldehyde while the tissue is fixed in 3 % paraformaldehyde prepared in a pbs buffer for 3 h . the epiploic tissue collected is embedded in paraffin for histological analysis according to the following protocol : 1 flask of 500 ml of 36 % formaldehyde ( reference sigma — f8775 — 500 ml ). 1 flask of 500 g of powdered paraformaldehyde ( reference : sigma — 30525 - 89 - 4 ) which should be stored in a refrigerator . 1 flask of 10 ml of 25 % glutaraldehyde ( reference : sigma — g5882 — 10 × 10 ml ) 1 flask of 500 ml of pbs ( reference : gibco — 14190 - 094 ). 1 flask of 500 ml of pbs x10 ( reference : gibco — 14200 - 067 ). because of the toxicity of the products used , the following steps are carried out in a safety cabinet with gloves . formaldehyde makes it possible to preserve the tissue surrounding the membrane during collection for 4 h maximum ; it is also used for the eosin / hematoxin stainings . in a 100 ml flask , put 100 ml of pbs ; add 8 . 3 ml of formaldehyde at 36 %; mix . the solution of paraformaldehyde at 4 % may be used in place of the formaldehyde solution ; it makes it possible to fix the tissues up to 24 h and is used for the immunocytochemical staining . prepare an alkaline solution by dissolving 1 sodium hydroxide pellet in 2 to 3 ml of distilled water ; put 8 g of paraformaldehyde in suspension in 100 ml of distilled water ; in a safety cabinet , heat the suspension on a heating magnetic stirrer ; when the suspension simmers ( at about 80 ° c . ), add a few drops of alkaline solution until the mixture becomes completely clear ; rapidly cool in ice . this solution should be used immediately or stored at − 20 ° c . in 20 ml fractions ready to use . the paraformaldehyde solution at 4 % is prepared by dilution with pbs ( introduction of 20 ml of paraformaldehyde solution at 8 % into 20 ml of pbs and then mixing ). in a 100 ml flask , put 100 ml of distilled water . add 10 ml of glutaraldehyde at 25 %. 1 flask of 500 ml of pbs ( reference : gibco — 14190 - 094 ). 1 flask of 500 ml of pbs x10 ( reference : gibco — 14200 - 067 . 1 bottle of 1 l of toluene ( reference : fisher scientific — code : t / 2250 / 17 ), toluene is very toxic and volatile and should be stored and handled in a safety cabinet . 1 bottle of 1 l of 70 % ethanol . 1 bottle of 1 l of 95 % ethanol . 1 bottle of 1 l of 100 % ethanol . paraffin ( reference : tyco / healthcare — ref : 8889501006 ). 1 standard cassette for incorporation histosette 2 ( reference : m . 492 , ref 039753 or m . 485 , ref 039775 in the dutscher catalog ). 1 dish for incorporation 37 × 24 mm ( reference : richard allan scientific — catalog no . 58953 ) 3 beakers of 50 ml . 2 beakers of 600 ml . 1 pair of forceps . aluminum . rubber gloves . in an empty pbs flask ( 500 ml ), put 50 ml of pbs x10 ; adjust with 450 ml of distilled water ; mix . in a 1 l bottle , put 700 ml of ethanol ; adjust with 300 ml of distilled water ; mix . in a 1 l bottle , put 950 ml of ethanol ; adjust with 50 ml of distilled water ; mix . in the 2 beakers of 600 ml , pour the paraffin pellets ; place the 2 beakers at 62 ° c .- 65 ° c . in the oven in the histology room ; keep the beakers in the oven . on the worktop : place 9 containers comprising the solutions in the following order : 2 pbs containers and 7 ethanol containers . in the chemical safety cabinet , place 3 beakers of 50 ml of toluene and in the oven , place 3 paraffin containers . pour liquid paraffin into the incorporation dish ; put the tissue to be incorporated in the dish ; apply the incorporation cassette and pour the paraffin over it for a uniform covering ; allow to cool for a few minutes at room temperature , and then place in a refrigerator for 24 h minimum . incorporation cassette microtome permafrost slides 75 × 25 mm ( reference : 045796 , in the dutscher catalog ). 1 disposable transfer pipette 1 container containing distilled water 2 brushes : 1 large brush + 1 fine brush 2 tools for collecting the sections slide heater 1 bottle of 1 l of 95 % ethanol 1 bottle of 1 l of 100 % ethanol 1 bottle of toluene ( reference : fisher scientific — code : t / 2250 / 7 5 hellendahl type staining tanks rubber gloves . the sections are produced with the aid of the leica rm2265 microtome according to the recommendations of the manufacturer . this step makes it possible to remove the paraffin present on the slide while preserving the tissue , the slide is treated with the following baths : permafrost slide 76 × 26 mm , with the fixed section . 1 bottle of 1 l of eosin . 1 bottle of 1 l of alcohol - acid . 1 bottle of 1 l of ammonia water . 1 flask of harris hematoxylin ( reference : surgipath — 01562 e ). 1 bottle of 500 ml of 100 % ethanol . 1 toluene bath . 1 tube of adhesive ( reference : eukitt ). cover glass 25 × 75 mm ( reference : esco no . 2951 ). 13 tanks with lids ( reference : 068506 , in the dutscher catalog p . 187 ). 2 baskets ( reference : 068507 , in the dutscher catalog p . 187 ). absorbent paper . rubber gloves . 1 coffee filter . eosin 225 ra2 : 3 . 125 g ( reference : reactif ral — 312730 - 0100 ); erythrosine ra2 : 1 . 875 g ( reference : reactif ral — 312820 - 0100 ); distilled water : 1 l 96 % alcohol : 990 ml ; hydrochloric acid ( hcl ): 10 ml ( reference : prolabo — 20 . 246 . 298 ) ( to be handled with gloves and safety goggles ) in a 1 l bottle , put 960 ml of pure ethanol ; adjust with 40 ml of distilled water and mix . 20 % ammonium hydroxide 2 . 5 ml ( ref . : fisher scientific — code ; a / 3367 / 17 ) distilled water : 1 l the staining of the tissues is carried out using successive baths : immersion in harris hematoxylin for 1 minute and 30 seconds ; two baths in water ; immersion in the alcohol - acid solution with stirring two to three times ; two baths in water ; immersion in ammonia water until the tissue becomes blue ; one bath in water ; immersion in eosin for 10 seconds ; one bath in ammonia water ; 3 successive baths in 96 % ethanol ; final bath in toluene the baths in water and ethanol consist of 2 - 3 rapid stirrings . apply the adhesive to the tissue taking care not to damage it ; apply the cover glass and press well in order to remove any air bubbles ; roughly remove excess adhesive ; rapidly dip the slide in toluene and immediately remove it ; wipe with absorbent paper taking care not to move the cover glass ; repeat the operation 2 to 3 times until complete removal of the adhesive residues is obtained . the harris hematoxylin allows red - violet staining of the basophilic elements of the tissue . the alcohol - acid allows mild destaining and the production of an orange tint . the 0 . 20 % nh4 ammonia water allows violet staining of the cell nuclei . the 3 96 % ethanol baths allow destaining to be carried out . the toluene bath makes it possible to fix the tissue and to remove the excess dye . the counting of the blood vessels , the measurement of their diameter and the determination of the distance between the module and the first blood vessels are carried out under a binocular lens with the aid of a micrometer ; 5 fields are counted for each section at the rate of three sections per tissue . the images of the sections prepared 7 days or 1 month after the implantation of the membranes are reproduced in fig4 and 5 . fig6 represents the mean of the number of blood vessels counted in 5 fields of the sections after 7 days , 14 days or 1 month for the various membranes tested . fig7 represents the mean distance between the semi - permeable membrane and the first blood vessels counted in 5 fields of the sections after 7 days or 1 month for the various membranes tested . fig8 represents the mean diameter of the blood vessels measured in 5 fields of the sections after 7 days or 1 month for the various membranes tested . these trials show that vegf induces a long - term formation of blood vessels . heparin also exhibits a vascularization - inducing effect . it is interesting to note that these two compounds have a synergistic effect .