Abstract:
Method of manufacturing a tubular capsule comprising fiber ( 11 ) having a wall delimiting internal compartments ( 11   b ) that are isolated from one another, the wall being made from a solution of at least one polymer and the compartments ( 11   b ) being full of a biologically active medium, the method comprising the steps of: 
     coextruding the solution of at least one polymer and the biologically active medium by simultaneously injecting the polymer solution and the biologically active medium through a die ( 7 ) of determined dimensions; 
     interrupting the injection of the biologically active medium at determined points in time to form in the fiber ( 11 ) successive compartments ( 11   b ) full of the biologically active medium and separated by a solid partition section ( 11   a ) consisting only of the polymer solution; 
     immersing the fiber ( 11 ) in a coagulation liquid as it leaves the die ( 7 ) so as to initiate early coagulation of the polymer solution around the outside of the fiber ( 11 ); and 
     simultaneously driving the fiber ( 11 ) through the coagulation liquid along a determined path.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to the manufacture of a capsule containing a biologically active medium, intended to be implanted in a living organism for therapeutic purposes. In the conventional way, a capsule of this type consists of a core comprising a biologically active medium, which is surrounded by a semipermeable casing. The role of the casing is to isolate the biologically active medium from the tissues of the receiving organism while at the same time allowing substances via which the implanted capsule fulfils its functions to pass through the casing. By way of example, when the biologically active medium is a suspension of cells, the semipermeable casing must act as a barrier to immune reactions, must allow nutrients to diffuse towards the core of the capsule and must allow the substance of therapeutic benefit secreted by the cells (insulin, for example, when the cells are islets of Langerhans) to diffuse towards the organism. 
     From the point of view of the efficiency of the exchanges across the membrane, it would seem that spherical capsules are preferred over tubular capsules. However, spherical capsules have the drawback of being difficult to locate when implanted, which means that at the present time it would not be possible to implant them in a human body from which the implants have always to be able to be extracted for reasons of biological safety. 
     Recent research has therefore been mainly centred on manufacturing tubular capsules, which allow the shaping of implants that are long enough that they can be easily found. In particular, it has been discovered that it is preferable to segment the tubular capsules, that is to say to form therein compartments which are isolated from one another, so that if part of an implanted capsule is damaged, it is possible to separate it from the implant and extract it from the receiving organism. 
     U.S. Pat. No. 5,158,881 describes a method of manufacturing a segmented tubular capsule, comprising the steps of: 
     coextruding a polymer solution intended to form the casing of the capsule and a biologically active medium by simultaneously injecting the polymer solution and the biologically active medium through a die, and 
     interrupting the injection of the biologically active medium at determined points in time to form in the fibre successive compartments full of the biologically active medium and separated by a solid partition section consisting only of the polymer solution. 
     This method does not yield the desired results when the polymer solution is liquid because, when the injection of biologically active medium is interrupted, a drop of polymer solution forms under the die, deforms and breaks under the effect of the weight of the fibre already formed which hangs from the die. 
     The object of the invention is to improve the above-described method in such a way as to make it possible to manufacture a segmented tubular capsule from a liquid polymer solution. Another object of the invention is to shape a tubular capsule into a shape that can be directly implanted. 
     BRIEF SUMMARY OF A FEW ASPECTS OF THE INVENTION 
     To achieve this objective, there is provided, according to the invention, a method of manufacturing a tubular capsule comprising a wall delimiting internal compartments that are isolated from one another, the wall being made from a solution of at least one polymer and the compartments being full of a biologically active medium, the method comprising: 
     coextruding the solution of at least one polymer and the biologically active medium by simultaneously injecting the polymer solution and the biologically active medium through a die of determined dimensions, 
     interrupting the injection of the biologically active medium at determined points in time to form in the fibre successive compartments full of the biologically active medium and separated by a consisting partition section consisting made of of the polymer solution, 
     causing partial early solidification of the fibre as it leaves the die to a sufficient extent to prevent the fibre from breaking at the partition sections. 
     As a preference, partial early solidification of the fibre may include: 
     immersing the fibre in a coagulation liquid as it leaves the die so as to initiate early coagulation of the polymer solution around the outside of the fibre; and 
     simultaneously driving the fibre through the coagulation liquid along a determined path. 
     This method may have at least two major benefits. On the one hand, it makes it possible to envisage industrial-scale or semi-industrial-scale implant production. On the other hand, bringing the fibre leaving the die into early contact with the coagulation liquid allows some of the solvent used to prepare the polymer solution to be extracted, which is something that is particularly desirable when the biologically active medium contains living cells which may be adversely affected by the solvents commonly used. 
     According to one feature of the invention, the method further comprises, at the same time as partially solidifying the fibre, exerting a determined tensile force on the fibre so as to give it at least one geometric characteristic that is independent of the dimensions of the die. 
     By virtue of this arrangement, it is possible to extrude low viscosity polymer solutions. 
     According to another feature of the invention, the method furthermore comprises giving the fibre a permanent shape. For example, the fibre is wound onto a cylindrical mandrel in such a way as to adopt the shape of a spiral, the pitch of which is chosen to be such that each section of fibre comprising a whole number of compartments corresponding to an implantable capsule occupies a determined length of mandrel. 
     By virtue of this arrangement, the dimensions of the implantable capsule can be adjusted to suit the size of the receiving organism. It has been found that the spiral-wound shape was particularly well-suited to implants in that it gave them mechanical robustness, in that it made them easier to handle and in that it made them easier to implant in an organism. 
     Another subject of the invention is a device for manufacturing a tubular fibre comprising a wall delimiting internal compartments isolated from one another and full of a biologically active medium, comprising: 
     extrusion means of determined dimensions for coextruding a solution of at least one polymer and the biologically active medium in such a way as to obtain a tubular fibre having a wall made from the polymer solution and filled with the biologically active medium; 
     means for supplying the extrusion means with the polymer solution and with the biologically active medium; 
     means for controlling the simultaneous supply of the extrusion means with polymer solution and with biologically active medium and for interrupting the supply of biologically active medium at determined points in time so as to form within the fibre successive compartments filled with the biologically active medium and separated by a solid partition section consisting only of the polymer solution; 
     the device being characterized in that it comprises: 
     means for causing partial solidification of the fibre as it leaves the extrusion means, this solidification being enough to prevent the fibre from breaking at the partition sections. 
     As a preference, the solidification means comprise: 
     a bath for a coagulation liquid placed under the extrusion means at a chosen distance so that a fibre flowing out from the die at a given output rate begins to coagulate early from the outside and does not break; and 
     means for driving the fibre through the coagulation liquid along a determined path. 
     According to one feature of the invention, the device further comprises means for exerting a determined tensile force on the fibre so as to give it at least one geometric characteristic that is independent of the dimensions of the extrusion means. 
     In one embodiment of the invention, the driving means and the means for exerting a tensile force comprise a tube passing through the bottom of the coagulation bath and having an upper end inside the bath and a lower end outside the bath, this tube being arranged substantially vertically and its upper end lying below the surface of the coagulation liquid when the bath is filled to a determined operating level. 
     This embodiment is particularly advantageous because it allows several functions to be fulfilled using very simple and inexpensive technical means. Furthermore, it is easy to regulate and allows very low tensile forces to be exerted on the fibre, if appropriate. 
     According to one feature of the invention, the device further comprises means for giving the fibre a determined shape. For example, the shape chosen is a spiral and the means for giving the fibre this shape comprise: 
     a mandrel made up of disassemble portions; 
     means for rotating the mandrel; 
     a guiding device for moving the fibre with a back and forth movement parallel to the mandrel. 
     Advantageously, in operation, the rotational speed of the mandrel and the speed of the back and forth movement of the guiding device are chosen so that the portion of fibre wound in a spiral onto the length of a portion of mandrel corresponds approximately to a determined whole number of internal compartments of the fibre. 
     By virtue of this arrangement, it is possible to limit the handling of the shaped fibre as far as possible: all that is required is to ensure that the length of fibre needed to form an implantable capsule is wound onto each mandrel portion. When the fibre is wound along the entire length of the mandrel, the fibre is cut at the junction between two contiguous mandrel portions and the mandrel portions are separated and can act as supports for the implantable capsules during despatch and storage. 
     Other features and advantages of the invention will become clear from reading the description which follows. Reference will be made to the appended drawings, in which: 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 depicts, diagrammatically, a plan view of a first part of a device for manufacturing a segmented tubular capsule according to the invention; 
     FIG. 2 depicts, diagrammatically, the extrusion and solidification means of the device according to the invention; 
     FIG. 3 depicts, diagrammatically, a view from above of a second part of a device for the manufacture of a segmented tubular capsule according to the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The device of FIG. 1 comprises a first reservoir  1  for containing a biologically active medium, in liquid form, such as a suspension of cells. This reservoir is placed in a temperature control chamber allowing the contents of the reservoir  1  to be kept at constant temperature. There is a second reservoir  2  for containing a polymer solution. The two reservoirs  1  and  2  are hermetically sealed and are connected by pipes  3 ,  4  to a gas-pressure regulating system  5  that allows a constant pressure to be set and maintained in each reservoir. The pressure-regulating system  5  is connected to a control unit  6  which controls the pressure regulation in each reservoir on the basis of datum values communicated beforehand to the control unit  6  by an operator, using a keyboard (not depicted). 
     The reservoirs  1  and  2  and the gas-pressure regulating system  5  constitute the means of supplying extrusion means  7  which have two concentric tubular nozzles, the inner nozzle  71  being connected by pipe  8  to the reservoir  1 , and the outer nozzle  72  being connected by a pipe  9  to the reservoir  3 . 
     In accordance with the invention, means  10  for causing early solidification of a tubular fibre  11  exiting the extrusion means are arranged vertically in line with the concentric nozzles  71 ,  72 . As can be seen in greater detail in FIG. 2, these early solidification means comprise a coagulation bath  101  with a bottom pierced by a hole for the passage of a tube  102 , flared at its top, the central longitudinal axis of which is essentially aligned with the central longitudinal axis of the nozzles  71 ,  72 . As a result Of this layout, the tube  102  has a top end inside the Coagulation bath  101  and a bottom end outside this bath. The Tube  102  is mounted so that it can be slid in a vertical direction, so that the height of water between the top end of the tube  102  and a reference water level in the coagulation bath  102  can be set accurately. 
     The choice of length of the tube  102 , of its inside diameter, and of the height of water between the reference level and the top end of the tube allows the action exerted on the fibre, simple driving or pulling, to be regulated accurately. For the same head of water, and for a tube of the same inside diameter, the longer the tube, the lower the tension. For the same head of water, and for a tube of the same length, the smaller the inside diameter of the tube, the lower the tension. For the same length of tube and the same inside diameter, the lower the head of water, the lower the tension. 
     In the embodiment depicted, the reference water level with respect to which the position of the tube  102  in the bath is regulated, is defined by filling the bath  101  to the very top. In order constantly to maintain the reference level and permanently to renew the coagulation liquid in the bath  101 , the bath  101  is placed in an overflow tank  103  which has an overflow orifice  104 . The coagulation bath  10  is connected by a pipe  12  to a source  13  of coagulation liquid which, during operation, continuously feeds the coagulation bath  101 . 
     A second coagulation bath  14  is arranged vertically in line with the tube  102  to receive the fibre  11  and complete coagulation. The distance between the bottom end of the tube  102  and the level of liquid in the second coagulation bath  14  is set according to the desired tension on the fibre as it leaves the tube  102 . The greater this distance, the greater the tension, which is caused by gravity. Incidentally, the second coagulation bath  14  is used to collect the liquid from the overflow tank  103  of the first coagulation bath  101 . The second coagulation bath  14  is itself also connected to the source  13  of coagulation liquid and is equipped with an overflow pipe  15  allowing its contents to be continuously renewed. 
     The device comprises guide members  16 ,  17  for guiding the fibre out of the second coagulation bath  14  towards a rotary cylinder  18  intended for the temporary storage of the coagulated fibre. The cylinder  18  is arranged in a washing bath  19 . 
     The temperature of the coagulation liquid in the baths  101  and  14 , just like the temperature of the washing liquid in the bath  19  may be set to any datum value by virtue of temperature-regulating means (not depicted). 
     In accordance with the invention, the device also comprises means of shaping the segmented tubular fibre. It has been seen that with certain polymer solutions if, during a determined period of time after the fibre has been removed from the coagulation bath, the fibre is subjected to mechanical deformation over a given time and at a given temperature, this deformation becomes permanent. In the embodiment depicted in FIG. 3, the shaping means comprise a cylindrical mandrel  20  consisting of portions  21  that fit together. This mandrel is mounted removably on a stand  22  so that it can be partially immersed in a second washing bath  25 . One of its ends is coupled to a rotating motor  23  and its other end is supported by a bearing  24  and is free to rotate. The stand  22  further comprises support means (bearings  26 ) to receive the storage cylinder  18 , so that the latter can rotate about its longitudinal axis and be arranged parallel to the mandrel  20 . Between the storage cylinder  18  and the mandrel  20 , there are various mechanical components secured to the stand  22  to allow part of the fibre wound on the cylinder  18  to be transferred onto the mandrel  20 . These mechanical components comprise:—two guides  26 ,  27  allowing the fibre  11  to be kept perpendicular to the cylinder  18  and to the mandrel  20  over part of its length;—a tensioner  28  exerting a vertical thrust on the fibre  11  between the two guides  26 ,  27 ;—a guiding device comprising a rail  29  parallel to the mandrel  20  and a carriage  30  that can move along the rail  29  in a back and forth movement. The moving carriage is equipped with a guide  31  for the fibre  11 . 
     The device just described operates as follows. The entire device is placed in a laminar-flow hood and all the liquids used (coagulation liquid, washing liquid) are sterile. The content of the coagulation baths  101 ,  14  and washing bath  19  are kept at constant temperature. The reservoirs  1 ,  2  are filled, one of them with polymer solution, and the other with a suspension of cells to be encapsulated. The temperature-regulating chamber is regulated to keep the suspension of cells at an appropriate temperature. The various baths  101 ,  14 ,  19  are filled. The value of the gas pressure for each of the reservoirs  1 ,  2  is communicated to the control unit  6 . It is these values which, in particular, determine the rate at which the tubular fibre  11  flows out of the die  7 . When the device has been started up, the control unit  6  controls the gas-pressure regulating system  5  in such a way that the supply of suspension of cells to the die  7  is interrupted at regular moments in time. The fibre which leaves the die is therefore a solid rod  11   a , consisting only of polymer solution. According to the invention, to prevent the fibre  11  from breaking at this solid rod  11   a , which is a drop of liquid, early solidification of the fibre is brought about by immersing it, a short distance from its exit from the die  7 , in a coagulation liquid while driving it vertically downwards using the immersed tube  102 . It has been found that when there is no drive, the fibre, experiencing upthrust in the coagulation liquid, deforms longitudinally into zigzags and exhibits a very uneven cross section, which makes it unusable as an implant. As mentioned above, it is also possible to set the height of the tube  102  in the bath  101  in such a way as to create a tensile force on the fibre  11  that allows the dimensions of the fibre (outside diameter, wall thickness) to be regulated independently of the dimensions of the nozzles  71 ,  72  of the die  7 . As soon as the fibre  11  enters the coagulation liquid, solvent/nonsolvent exchange (which defines coagulation) occurs from the outside of the fibre and limits the undesirable effects of purely internal coagulation which begins as soon as the suspension of cells comes into contact with the polymer solution. In other words, the amount of solvent (which is somewhat toxic to the cells) which is extracted from the fibre from the outside represents so much less solvent liable to migrate into the suspension of cells during the process of coagulation from the inside. 
     The fibre  11  which emerges from the tube  102  is received in the second coagulation bath  14  where it solidifies enough that it can be handled. Note that the coagulation liquid in the baths  101  and  14  is permanently renewed in order to eliminate the solvent. The fibre is then washed and wound onto the storage cylinder  18  to form a single spiral starting and finishing respectively at each end of the cylinder. 
     To shape the fibre, a mandrel  20  is mounted on the rig  22 . One end of the fibre wound onto the cylinder  18  is passed through the guides  26 ,  27  and then into the guide  31  of the carriage  30  of the guiding device and is attached to one end of the mandrel  20 . The length of the disassemble portions  21  of the mandrel  20 , just like their diameter, are designed for the definitive storage and shaping of implantable capsules comprising a determined number of compartments  11   b . The speed of the motor  23  that rotates the mandrel  20 , and the linear speed of the carriage  30  of the guiding device are chosen to be such that a section of fibre comprising a whole number of compartments  11   b  is wound onto each portion  21  of the mandrel  20 , and that there is a section of fibre formed of solid rod  11   a  at each end of each mandrel portion  21 . The rotational speed of the mandrel  20  is increased each time the fibre reaches the end of each mandrel portion  21  so that the formed turns of solid rod are further apart than the rest of the turns and so that separating two adjacent implantable capsules is easier. A single spiral is formed on the mandrel  20 , starting and ending respectively at each end of the mandrel. The implantable capsules can then be separated from one another while at the same time keeping them, for storage and transport, attached to the mandrel portion on which they have been respectively spiral-wound. 
     EXAMPLE 1 
     The reservoir  2  was filled with a polymer solution containing 8% by weight of an acrylonitrile-sodium methallylsulphonate copolymer (known by the trade name AN69),  6 % by weight of physiological saline (solution of sodium chloride in water, at a concentration of 9 g/l) and 86% of dimethyl sulphoxide (DMSO). The contents of the reservoir were at ambient temperature (about 25° C.). 
     The reservoir  1  was filled with a suspension of islets of Langerhans at a concentration of 10 000 EI/ml (EI=equivalent islet, corresponding to a theoretical islet 150 μm in diameter) in agarose (Sigma Type IA-A 0169-batch No.-54 H 0530) at 0.5% (weight/volume) resulting from mixing a suspension of islets in HAM&#39;S F12 (Sigma N8641-batch No.-123 H 2322) and a 0.65% (weight/volume) solution of agarose in physiological saline. The contents of the reservoir  1  were kept at 40.5° C. 
     The coagulation baths  101  and  14  are filled with sterile physiological liquid which is permanently renewed. The die used, manufactured by the company SCP-France had the following dimensions: inside diameter of the outer nozzle 72=1570 μm; outside diameter of the inner nozzle 71=980 μm; inside diameter of the inner nozzle 71=860 μm. 
     The tube  102  of the means for bringing about early solidification of the fibre  11  was a glass tube with an inside diameter of 0.003 m and a length of 0.25 m. The position of the tube  102  with respect to the coagulation bath  101  was adjusted such that the height of water between the top end of the tube  102  and the reference level was 0.005 m. The bottom end of the tube  102  was placed 0.05 m from the level of liquid in the second coagulation bath  14 . 
     The height of the die  7  above the coagulation bath  101  was regulated such that the orifice of the die  7  was 0.002 m from the reference water level. 
     The contents of the coagulation baths  101 ,  14  and washing bath  19  were maintained at 25° C. 
     The datum values for the operating parameters communicated to the control unit  6  were as follows: pressure in reservoir  1 =atmospheric pressure+80 mmHg; pressure in reservoir  2 =atmospheric pressure+100 mmHg; the time for which the injection of the suspension of cells through the die  7  was interrupted was set at 0.40 seconds every 5.8 seconds. 
     Under these operating conditions, and with the hardware described above, there was obtained, after the start-up phase, a segmented tubular fibre with an inside diameter of about 1050 μm, a wall about 150 μm thick, and internal compartments about 0.6 m long. An implantable capsule containing about 30 000 EI, formed with this tubular fibre, was about 3.2 m long (namely five compartments). 
     The fibre  11  was transferred from the cylinder  18  onto the mandrel  20  one hour after the fibre was manufactured. After 18 hours at 37° C., the fibre detached from the mandrel  20  retained a spiral shape. 
     EXAMPLE 2 
     Reservoir  2  was filled with a polymer solution containing 16% by weight of an acrylonitrile-vinyl acetate copolymer and 84% by weight of dimethylformamide (DMF). The contents of the reservoir  2  were at ambient temperature (about 25° C.). 
     The reservoir  1  was filled with a solution of Blue Dextran (Sigma-D5751) at a concentration of 1% by weight in physiological saline. The contents of the reservoir  1  were at ambient temperature. 
     The coagulation baths  101  and  14  were filled with sterile physiological liquid which was permanently renewed. The die used was the same as the one used in Example 1. 
     The tube  102  of the means for bringing about solidification of the fibre  11  was a glass tube with an inside diameter of 0.003 m and a length of 0.10 m. The position of the tube  102  with respect to the coagulation bath  101  was adjusted such that the height of water between the top end of the tube  102  and the reference level was 0.005 m. The bottom end of the tube  102  was placed 0.05 m from the level of liquid in the second coagulation bath  14 . 
     The height of the die  7  above the coagulation bath  101  was regulated such that the orifice of the die  7  was 0.002 m from the reference water level. 
     The contents of the coagulation baths  101 ,  14  and washing bath  19  were maintained at 25° C. 
     The datum values for the operating parameters communicated to the control unit  6  were as follows: pressure in reservoir  1 =atmospheric pressure+39 mmHg; pressure in reservoir  2 =atmospheric pressure+360 mmHg; the time for which the injection of the solution of Blue Dextran through the die  7  was interrupted was set at 0.75 seconds every second. 
     Under these operating conditions, and with the hardware described above, there was obtained, after the start-up phase, a segmented tubular fibre with an inside diameter of about 980 μm, a wall about 180 μm thick, and internal compartments about 0.05 m long. 
     The fibre  11  was transferred from the cylinder  18  onto the mandrel  20  one hour after the fibre was manufactured. After 24 hours at ambient temperature, the fibre detached from the mandrel  20  retained a spiral shape. 
     EXAMPLE 3 
     The reservoir  2  was filled with a polymer solution containing 15% by weight of polyethersulphone (PES), 5% by weight of polyethylene oxide with a molecular mass=10 kdaltons (Sigma-P6667), and 80% by weight of N-methylpyrrolidone (NMP). The contents of the reservoir  2  were at ambient temperature (about 25° C.). 
     The reservoir  1  was filled with a solution of Blue Dextran (Sigma-D5751) at a concentration of 1% by weight in physiological saline. The contents of the reservoir were at ambient temperature. 
     The coagulation baths  101  and  14  were filled with sterile physiological liquid which was permanently renewed. The die used was identical to the one used in Example 1. 
     The tube  102  of the means for bringing about solidification of the fibre  11  was a glass tube with an inside diameter of 0.003 m and a length of 0.10 m. The position of the tube  102  with respect to the coagulation bath  101  was adjusted such that the height of water between the top end of the tube  102  and the reference level was 0.005 m. The bottom end of the tube  102  was placed 0.05 m from the level of liquid in the second coagulation bath  14 . 
     The height of the die  7  above the coagulation bath  101  was regulated such that the orifice of the die  7  was 0.002 m from the reference water level. 
     The contents of the coagulation baths  101 ,  14  and washing bath  19  were maintained at 25° C. 
     The datum values for the operating parameters communicated to the control unit  6  were as follows: pressure in reservoir  1 =atmospheric pressure+50 mmHg; pressure in reservoir  2 =atmospheric pressure+110 mmHg; the time for which the injection of the solution of Blue Dextran through the die  7  was interrupted was set, during a first test, at 0.35 seconds every 1.25 seconds, then during a second test at 0.32 seconds every 0.55 seconds. 
     Under these operating conditions, and with the hardware described above, there was obtained, after the start-up phase, a segmented tubular fibre with an inside diameter of about 900 μm, a wall about 100 μm thick, and internal compartments about 0.08 m long during the first test, and 0.03 m long during the second test. 
     The fibre  11  was transferred from the cylinder  18  onto the mandrel  20  one hour after the fibre was manufactured. After 24 hours at ambient temperature, the fibre detached from the mandrel  20  retained a spiral shape. 
     The invention is not restricted to the embodiment just described and can be varied.