Abstract:
The invention relates to a device ( 22 ) for changing the pH of a solvent in which a substance is dissolved. The device includes a housing ( 24 ) in contact with the solvent through a housing wall ( 26 ) that is permissive to the solvent and the substance. The housing contains enzymes adapted for converting the substance in order to provide hydrogen or hydroxyle ions; the housing wall being non-permissive to the enzymes.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for varying the pH of a solution. 
     DISCUSSION OF PRIOR ART 
     For certain applications, it is desirable to be able to modify the pH of a solution. An example of application is the regulation of a physico-chemical phenomenon occurring in a solution and having a speed which varies according to the pH of the solution, for example, the variation of the solubilization of a substance in a solution where the pH is varied. Another example of application is the regulation of chemical or mechanical properties of a solution which vary according to the pH. One such property for example is the osmolarity of the solution. 
     The pH of an initial solution can conventionally be modified by mixing of an additional acid or basic solution with the initial solution. The pH of the solution finally obtained after mixing stabilizes at a value which depends on the pH of the initial solution, on the pH of the additional solution, and on the volumes of the initial and additional solutions. 
     However, for certain applications, it would be desirable to be able to modify the pH of a solution without having to add an acid or basic solution thereto. As an example, it would be desirable to be able to modify the pH of a solution contained in the human body, called biological solution hereafter, while limiting as much as possible any intervention on the human body to perform the pH modification. 
     SUMMARY OF THE INVENTION 
     The present invention aims at a method and a device for varying the pH of a solution which do not require the addition of an acid or basic solution. 
     Another object of the present invention is to provide a method for varying the pH which is likely to be implemented in a human body and a device for varying the pH which is likely to be implanted in a human body. 
     To achieve these objects, an aspect of the present invention provides a device for varying the pH of a solvent in which a substance is dissolved, comprising an enclosure in contact with the solvent via an enclosure wall permeable to the solvent and to the substance, the enclosure containing enzymes capable of transforming the substance to release hydrogen or hydroxyl ions, the enclosure wall being non-permeable to enzymes. 
     According to an embodiment, the substance is D-glucose and the enzymes are glucose oxidase enzymes capable of causing the releasing of hydrogen ions by oxidation of the D-glucose. 
     According to an embodiment, the substance is L-glucose and the enzymes are L-fucose dehydrogenase enzymes capable of causing the releasing of hydrogen ions by oxidation of the L-glucose. 
     According to an embodiment, the substance is urea and the enzymes are urease enzymes capable of causing the releasing of hydroxyl ions by ureal degradation. 
     Another aspect of the present invention provides an actuator comprising a device for varying the pH such as described hereabove; a first chamber connected to the device for varying the pH or corresponding to the enclosure of the device for varying the pH, and at least partially containing solvent, the device for varying the pH being capable of bringing the pH in the first chamber within a given pH range; and a second deformable chamber connected to the first chamber, the first chamber containing means capable of transferring solvent between the first chamber and the second chamber when the pH in the first chamber is within the given pH range. 
     According to an embodiment, the first chamber contains a solute and is separated from the second chamber by a chamber wall non-permeable to the solute and permeable to the solvent, the transformation of a precipitate of said solute into said solute or the solute precipitation being promoted when the pH in the first chamber is within the given pH range to vary the osmotic pressure in the first chamber and the second deformable chamber is capable of changing volume under the action of the solvent displacing between the first chamber and the second chamber by osmosis. 
     According to an embodiment, the first chamber contains a solute and is separated from the second chamber by a chamber wall non-permeable to the solute and permeable to the solvent, the transformation of a precipitate of said solute into said solute being promoted when the pH in the first chamber is within the given pH range to vary the osmotic pressure in the first chamber and the first chamber is intended to be arranged in contact with the solvent, the second chamber being capable of increasing its volume under the action of the solvent penetrating into the first chamber by osmosis. 
     According to an embodiment, the first chamber comprises a material capable of changing volume when the pH in the first chamber is within the given range, the material surrounding a deformable envelope containing solvent and connected to the second chamber. 
     An aspect of the present invention provides a motor comprising an actuator such as described previously, in which the first chamber is at least partly deformable and is connected to the second chamber at the level of the chamber wall, the transformation of the precipitate of said solute into said solute being promoted for a pH within a given acid pH range, and the precipitation of said solute being promoted for a pH within a given basic pH range, the device for varying the pH being capable of bringing the pH in the first chamber within the given acid pH range, the motor further comprising an additional device for varying the pH connected to the first chamber and capable of bringing the pH in the first chamber within the given basic pH range. 
     An aspect of the present invention provides a motor comprising an actuator such as described previously, in which the second chamber comprises return means which oppose the volume increase of the second chamber and controllable means for lowering the osmotic pressure in the second chamber. 
     An aspect of the present invention provides a motor comprising an actuator such as described previously, in which the material is capable of decreasing its volume for a pH ranging within a given acid pH range, and of increasing its volume for a pH within a given basic pH range, the device for varying the pH being capable of bringing the pH in the first chamber within the given acid pH range, the motor further comprising an additional device for varying the pH connected to the first chamber and capable of bringing the pH in the first chamber within the given basic pH range. 
     According to an embodiment, the second chamber is intended to surround a hollow organ of a mammal, especially the urethra, the stomach, the anus, or the heart, a volume increase of the second chamber causing a constriction of said organ. 
     An aspect of the present invention provides a system for purifying a substance comprising a device for varying the pH such as described hereabove, intended to be implanted in a human body in contact with a biological solvent containing said substance. 
     An aspect of the present invention provides a purifying system comprising a device for varying the pH such as described hereabove; a first controllable valve arranged between the enclosure wall and the solvent; a second controllable valve capable of having the enclosure of the device for varying the pH communicate with a drain; and means capable of cyclically decreasing the volume of the enclosure of the device for varying the pH when the second valve is open and the first valve is closed, whereby the content of the enclosure of the device for varying the pH is discharged through the drain, and increasing the volume of the enclosure of the device for varying the pH when the first valve is open and the second valve is closed, whereby the solvent is sucked into the enclosure of the device for varying the pH through the enclosure wall. 
     An aspect of the present invention provides a cell comprising an enclosure containing first and second electrodes, a reduction or oxidation reaction being likely to occur at the level of the first and of the second electrode according to the pH; a device for varying the pH capable of bringing the pH at the level of the first electrode within a given pH range promoting one of the reduction or oxidation reactions; and means capable of bringing the pH at the level of the second electrode within a second given pH range different from the first range, promoting the other one of the reduction or oxidation reactions. 
     According to an embodiment, the cell is intended to be arranged in contact with a solvent, said means corresponding to a valve likely to have the content of the enclosure communicate with the solvent at the level of the second electrode. 
     According to an embodiment, the means are an additional device for varying the pH such as described hereabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, among which: 
         FIG. 1  shows a first embodiment of a device for varying the pH according to the invention; 
         FIG. 2  shows a second embodiment of the device for varying the pH according to the invention; 
         FIGS. 3A and 3B  show two operating steps of an embodiment of an osmotic actuator implementing the device for varying the pH according to the first embodiment; 
         FIGS. 4A to 4D  show four operating steps of a first embodiment of an osmotic motor implementing the first embodiment of the device for varying the pH according to the present invention; 
         FIGS. 5A and 5B  show two operating steps of a second embodiment of an osmotic motor implementing the second embodiment of the device for varying the pH according to the present invention; 
         FIGS. 6A and 6B  show two operating steps of a variation of the second embodiment of the osmotic motor; 
         FIGS. 7A and 7B  show two operating steps of a purifying device implementing the first embodiment of the device for varying the pH according to the invention; 
         FIGS. 8A to 8D  show four operating steps of a third embodiment of an osmotic motor implementing the first embodiment of the device for varying the pH according to the invention; 
         FIGS. 9A and 9B  show two operating steps of a first embodiment of an electric cell implementing the first embodiment of the device for varying the pH according to the invention; 
         FIG. 10  shows a second embodiment of an electric cell implementing the first embodiment of the device for varying the pH according to the present invention; and 
         FIG. 11  illustrates a processing method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The same elements have been designated with the same reference numerals in the different drawings. For clarity, only those elements which are useful to the understanding of the invention have been shown in the drawings and will be described hereafter. 
     The present invention provides promoting a first series or a second series of chemical reactions in a solution where the pH is desired to be modified, the first series of chemical reactions decreasing the solution pH while the second series of chemical reactions increases the solution pH. 
     Any reaction leading to the forming of H +  ions, and thus to a pH decrease, may be appropriate for the first series of reactions. Such is in particular the case for the oxidation of D-glucose, or D stereoisomer of glucose, by the glucose oxidase enzyme, which results in the forming of gluconic acid (likely to release an H +  ion) and hydrogen peroxide. Hydrogen peroxide is further degradable by the catalase enzyme or the peroxidase enzyme to provide additional H +  ions. The implemented reactions are the following: 
     
       
                 
         
             
             
         
      
     
     The first series of reactions may correspond to the oxidation of L-glucose, or L stereoisomer of glucose, by the L-fucose dehydrogenase enzyme. The implemented reactions are the following: 
                                
where compound NADP is nicotinamide adenine dinucleotide phosphate and where NADPH is the same compound once reduced.
 
     The second series of reactions implemented by the present invention to basify a solution may correspond to the degradation of urea by the urease enzyme, which results in the forming of ammonium ions NH 4   +  and of hydroxyl ions OH − , that is, in a pH increase. The implemented reactions are the following: 
     
       
                 
         
             
             
         
      
     
     Reactions (1) and (3) have the advantage of being directly implementable with a biological solution which naturally contains D-glucose, which is the glucose taking part in glycemia, and urea. Reactions (2) can easily be implemented with a biological solution which naturally contains the NADP compound. L-glucose then only needs to be added to the biological solution. 
       FIG. 1  shows a first embodiment of a device  10  for varying the pH according to the present invention. Device  10  is arranged in a solution having a pH which is desired to be modified, for example, a biological solution. Device  10  comprises a tight enclosure  12  and a valve  14  which, when open, puts the content of enclosure  12  in communication with the external solution. Device  10  may be connected to a system, not shown, having an operation which requires a solution having a pH within a determined range. For this purpose, device  10  comprises a valve  16  which, when open, puts the content of enclosure  12  in communication with the system to be supplied. Device  10  comprises a membrane  18  arranged between valve  14  and enclosure  12  and a membrane  20  arranged between valve  16  and enclosure  12 . Membranes  18  and  20  have given cut-off thresholds, generally expressed in Daltons, that is, they let through particles having a molecular mass substantially smaller than the cut-off threshold. 
     When the solution contained in enclosure  12  is desired to be acidified, the glucose oxidation, for example, according to reactions (1), can be promoted in enclosure  12 . For this purpose, device  10  is placed in a solution containing D-glucose, for example, a biological solution, and glucose oxidase enzymes and the catalase or peroxidase enzymes are placed in enclosure  12 . Membranes  18  and  20  have cut-off thresholds such that they enable to retain the glucose oxidase enzymes and catalase or peroxidase enzymes in enclosure  12 . Further, membrane  18  has a sufficiently high cut-off threshold to let glucose through. As an example, membranes  18  and  20  have a cut-off threshold on the order of a few hundreds of Daltons. 
     The operation of the first example of device  10  according to the present invention will now be described for a pH decrease operation. Initially, valve  16  is closed and valve  14  is open, enabling D-glucose to diffuse into enclosure  12 . Valve  14  is then closed. The D-glucose contained in enclosure  12  is then oxidized to provide H +  ions and gluconic acid according to the previously-described reactions (1). The pH of the solution contained in enclosure  12  thus decreases. The obtained acid solution can then be used by the system connected to enclosure  12  by opening valve  16 . The applicant has shown that for an aqueous solution having an initial D-glucose concentration of 5.5 mmol/l, which corresponds to the average glucose concentration in the human body, a glucose oxidase enzyme concentration of 1 mg·ml −1 , that is, 47 units and an initial pH of 7, a pH equal to 5 is obtained within one hour and a pH of 3.5 is obtained after three hours in enclosure  12 . 
     The gluconic acid resulting from the glucose oxidation tends to form salts, or gluconate, with the dissolved substances. If it is not desirable for the gluconate to penetrate in the system connected to device  10 , membrane  20  is selected with a sufficiently low cut-off threshold to retain the gluconate in enclosure  12  when valve  16  is open. The cut-off threshold of membrane  20  then is on the order of 100 Daltons. At the next opening of valve  14 , the gluconate diffuses outside of enclosure  12 . In the case of a medical application for which device  10  is placed in the human body, it is desirable for the catalase or peroxidase enzymes to be placed at the level of membrane  18  to avoid the releasing of free radicals resulting from the D-glucose oxidation into the human body. Further, the releasing of gluconate into the human body is not dangerous since it is naturally discharged by the kidneys. 
     For a solution acidification operation, L-fucose dehydrogenase enzymes, retained by membranes  18  and  20 , may be arranged in enclosure  12 . Device  10  is then placed in a solution containing L-glucose, the device operation being identical to what has been previously described. A human biological solution does not naturally comprise L-glucose. In the case where device  10  is placed in the human body, a step of addition of L-glucose to the biological solution, for example by intravenous injection, may be provided. 
     Device  10  according to the first embodiment of the invention may also be used to obtain a pH increase. Device  10  is then arranged in a solution containing urea, for example a biological solution, and the degradation of urea into ammonia and into carbonic acid according to reactions (3) is promoted in enclosure  12 . Since ammonia reacts with water to provide ammonium ions, a pH increase is thus obtained. For this purpose, urease enzymes are placed in enclosure  12 . In this case, membranes  18  and  16  have a sufficiently low cut-off threshold to retain the urease enzymes in enclosure  12 . Further, membrane  18  has a sufficiently high cut-off threshold to let through urea, which has a 60 g/mol molecular mass. As an example, membrane  18  has a cut-off threshold of a few hundreds of Daltons. The operating cycle of device  10  is then identical to what has been previously described. The applicant has shown that for a solution having a 3 mmol/l urea concentration, which corresponds to the average urea concentration in the human body, and an initial pH of 7, a pH equal to 8.2 is obtained within two hours and a pH of 9.2 is obtained after one night in enclosure  12 . In the case of a medical application for which device  10  according to the invention is placed in the human body, the carbon dioxide resulting from reactions (3) is naturally exhaled. Further, the ammonium ions resulting from reactions (3) are metabolized by the liver. 
       FIG. 2  shows a second embodiment of a device  22  for varying the pH according to the invention. Device  22  comprises an enclosure  24  formed of a bundle of hollow fibers with a semi-permeable wall  26 , for example of the type used for dialysis operations. Each fiber for example has a diameter on the order of 200 μm. Fiber bundle  26  is maintained at a first end by a first connection ring  28 , for example, via a gluing area  30 . Ring  28  comprises an opening  32  closed by a plug  34 . The second end of fiber bundle  26  is maintained by a second connection ring  36 , for example, via a gluing area  38 . Second ring  36  comprises an opening  40  closed by a plug  42 . 
     Device  22  is intended to be immersed in the solution where the pH is desired to be modified. The diameter and the length of the fibers are adapted according to the desired exchange surface area between fiber bundle  26  and the solution in which device  22  has been immersed. If the pH is desired to be decreased, glucose oxidase and catalase or peroxidase enzymes are placed in fibers  26  via openings  32 ,  40 , which are then closed by plugs  34 ,  42 . The wall of fibers  26  then has a cut-off threshold such that it does not let through glucose oxidase enzymes and catalase or peroxidase enzymes, which are retained in fiber bundle  26 , while it lets through D-glucose and gluconate. If the pH is desired to be increased, urease enzymes are arranged in fibers  26  via openings  32 ,  40  which are then closed by plugs  34 ,  42 . The wall of fibers  26  then has a cut-off threshold such that it does not let through urease enzymes, which are retained in fiber bundle  26 , while it lets through urea. 
     When device  22  is implanted in the human body to acidify a biological solution, the catalase or peroxidase enzymes are preferably fixed on the internal wall of fibers  26  while the glucose oxidase enzyme can be left free in fiber bundle  26 . Such an arrangement enables to avoid for the free radicals created by the degradation of glucose by the D-glucose oxidase enzymes to cross the wall of fibers  26  and spread in the biological solution. 
     When device  10 , or device  22 , is used to acidify a solution implementing the oxidation of D-glucose, it simultaneously enables the suppression of part of the D-glucose contained in the solution. Indeed, the reactions implemented in enclosure  12  or in fiber bundle  26  (reactions (1)) result in the transformation of glucose into gluconic acid, which provides gluconate. Such a device  10  (or  22 ) may be implanted in the human body to suppress an excess of D-glucose, generally associated with a type-I or type-II diabetes or with an overweight. Several locations of implantation of device  10  (or  22 ) can then be envisaged. As an example, device  10  (or  22 ) may be placed at the level of the peritoneum or of a fatty peri-cellular space. An implantation close to the peritonea has the advantage of a rich vascularization and of a high D-glucose concentration. An implantation in a fatty space decreases risks of inflammatory responses. Device  10  (or  22 ) may also be implanted at the level of a muscle, by a puncture performed by means of a medical trocart. 
     As soon as it has been implanted in the human body, device  22  according to the present invention daily transforms a quantity of D-glucose into gluconate which is naturally removed by the kidney. Device  10  itself enables, by the controlling of valves  14 ,  16 , to control the amount of D-glucose transformed into gluconate. Via valves  14 ,  16  (respectively openings  32 ,  40 ), it is possible to have access to the content of enclosure  12  (respectively of fibers  26 ) to renew the enzyme population contained in enclosure  12  (respectively in fibers  26 ) if necessary. The implantable chambers conventionally used for chemotherapies allow a very easy percutaneous puncture, due to which this renewal can be performed. This enables to overcome a lower enzymatic activity. Further, the access to the content of enclosure  12  (respectively of fibers  26 ) also enables to regulate the enzyme population to control the consumed glucose amount. 
       FIGS. 3A and 3B  show an embodiment of an osmotic actuator  50  implementing the first embodiment of device  10  for varying the pH according to the invention. Osmotic actuator  50  comprises a tight deformable envelope  52  filled with a solvent and connected to device  10  at the level of valve  16 . Envelope  52  is further connected via a membrane  54  to a cylindrical body  56  in which a piston  58  can slide. Piston  58  and cylindrical body  56  define an expansion chamber  60 . Envelope  52  may be arranged in a rigid housing  64  which is perforated so that deformations of envelope  52  are not hindered by a vacuum which might install between envelope  52  and housing  64 , if the latter was tight. 
     Expansion chamber  60  contains a substance A, dissolved in the solvent and osmotically active and at a concentration enabling an osmotic balance with the inside of envelope  52 . Membrane  54  has a sufficiently low cut-off threshold to block substance A. As an example, substance A is dextrane. Device  10  for varying the pH is of the type enabling to basify the solution that it contains, as described previously. Envelope  52  contains an osmotically-active substance Z. Membrane  54  has a sufficiently low cut-off threshold to block substance Z. As an example, substance Z is chitosan, which is soluble in water at an acid pH, and insoluble at a basic pH. The pH variation of the solution thus causes a variation of the number of dissolved molecules and accordingly of the osmolarity of the solution. 
     The operation of osmotic actuator  50  according to the present invention will now be described. It is a single-stroke actuator. 
       FIG. 3A  shows osmotic actuator  50  in the state which precedes the actuator operation. Valve  16  is then closed. Envelope  52  has a maximum volume while expansion chamber  60  has a minimum volume. The concentrations of substances A and Z are initially selected so that the osmotic pressures in expansion chamber  60  and in envelope  52  are balanced, with piston  58  remaining idle. Before the operation of actuator  50 , device  10  for varying the pH is controlled, as described previously, so that enclosure  12  contains a basic solution. 
     When osmotic actuator  50  is desired to be operated, valve  16  is opened. The OH −  ions contained in enclosure  12  expand into envelope  52 , thus increasing the pH of the solvent contained in envelope  52 . When the pH in envelope  52  has increased up to the desired value, valve  16  is closed. The precipitation of substance Z is then promoted. The osmotic pressure in envelope  52  decreases with respect to the osmotic pressure in expansion chamber  60 , which does not vary. A solvent transfer thus occurs, with solvent passing from envelope  52  to expansion chamber  60  through membrane  54 , thus causing a displacement of piston  58 . Piston  58  is in its upward phase. 
       FIG. 3B  shows osmotic actuator  50  at the end of the upward phase of piston  58 . Expansion chamber  60  then has a maximum volume. Piston  58  may be connected to an external element to which mechanical power is desired to be transmitted. 
     In the previously-described example of actuator  50 , device  10  is of a type enabling to basify the solution that it contains. However, actuator  50  may also be implemented with a device  10  capable of acidifying the solution that it contains. In this case, initially, expansion chamber  60  may have a maximum volume and envelope  52  may have a minimum volume, as shown in  FIG. 3B . When valve  16  is opened, the pH of the solvent in envelope  52  and expansion chamber  60  decreases, promoting the solubilization of substance Z present in envelope  52 . The osmotic pressure in envelope  52  increases with respect to the osmotic pressure in expansion chamber  60 , which does not vary. A solvent transfer thus occurs, with solvent passing from expansion chamber  60  into envelope  52  through membrane  54 , causing, by suction, a displacement of piston  58 . Piston  58  is then in its downward phase until expansion chamber  60  has a minimum volume, as shown in  FIG. 3A . 
     An example of application of actuator  50  is the inflating of a joint associated with an endoprosthesis corresponding to a small spring, or stent, slid into a cavity of the human body (arteries, for example) to maintain it open. Indeed, joints may be provided at the ends of the stent and may be inflated by means of actuator  50 , after the stent has been installed, to maintain the tightness at the stent ends in the case of a subsequent unwanted deformation of the cavity containing the stent. 
       FIGS. 4A to 4D  show a first embodiment of an osmotic motor  70  according to the invention. Osmotic motor  70  comprises certain components of actuator  50  shown in  FIGS. 3A and 3B  and the corresponding reference numerals are kept. Return means  72 , for example, a spring, exerts on piston  58  a pulling force tending to bring it back to an idle position. Motor  70  comprises two devices for varying the pH, noted  10  and  10 ′. In the following description, dashed reference numerals are used to designate the elements of device  10 ′ for varying the pH, to differentiate them from the elements of device  10  for varying the pH. Envelope  52  is connected to device  10 ′ at the level of valve  16 ′. Device  10  is of the type enabling to decrease the pH of the solution that it contains and device  10 ′ is of the type enabling to increase the pH of the solution that it contains. 
     Envelope  52  contains, as described previously, substance Z likely to solubilize in the presence of H +  ions, the inverse reaction according to which substance Z precipitates being likely to occur in the presence of OH −  ions. As described previously for osmotic actuator  50 , expansion chamber  60  contains an osmotically-active substance A, dissolved in the solvent. Membrane  54  has a sufficiently low cut-off threshold to prevent the passing of substance A and Z. 
     An operating cycle of motor  70  according to the invention will now be described. 
       FIG. 4A  shows motor  70  at the beginning of a cycle. Envelope  52  has a maximum volume and chamber  60  has a minimum volume. The concentrations of substances A and Z are initially selected so that the osmotic pressures in expansion chamber  60  and in envelope  52  are balanced, with piston  58  remaining idle. During the opening cycle of valves  16  and  16 ′ which will now be described, devices  10 ,  10 ′ are controlled so that enclosures  12 ,  12 ′ contain solutions having the desired pH. 
     Valve  16  is closed and valve  16 ′ is opened. The OH −  ions disseminate into envelope  52 , thus increasing the pH of the solvent contained in envelope  52  and in expansion chamber  60 . When the pH in envelope  52  has increased up to the desired value, valve  16 ′ is closed. The precipitation of substance Z is then promoted. The osmotic pressure in envelope  52  decreases with respect to the osmotic pressure in expansion chamber  60 , which does not vary. A solvent transfer thus occurs, with solvent passing from envelope  52  into expansion chamber  60  through membrane  54 , thus causing a displacement of piston  58 . Piston  58  is in its upward phase. 
       FIG. 4B  shows motor  70  at the end of the upward phase of piston  58 . Chamber  60  thus has a maximum volume. 
     In  FIG. 4C , valve  16  has been opened to put the content of envelope  52  in communication with the content of enclosure  12 . H +  ions disseminate into envelope  52 , thus causing a decrease in the pH of the solvent contained in envelope  52  as well as in expansion chamber  60 . When the pH is sufficiently acid, valve  16  is closed. The solubilization of substance Z is then promoted, thus causing an increase in the number of dissolved osmotically-active particles in envelope  52 . With the osmotic pressure increase in envelope  52 , a new solvent transfer occurs, with solvent passing from expansion chamber  60  into envelope  52  via membrane  54 . The action of spring  72  promotes the discharge of the solvent from expansion chamber  60 . However, spring  72  might be absent, and piston  58  would then only be displaced by suction. Piston  58  is said to be in its downward phase. 
       FIG. 4D  shows motor  70  at the end of the downward phase of piston  58 , which closes the cycle. The concentrations of substances Z and A, respectively in envelope  52  and in expansion chamber  60 , are then substantially identical to the concentrations at the beginning of a cycle. 
       FIGS. 5A and 5B  show a second embodiment of an osmotic motor  75  implementing the second embodiment of device  22  for varying the pH according to the invention and certain elements of osmotic motor  70 . Motor  75  comprises two devices for varying the pH, noted  22  and  22 ′. In the following description, dashed reference numerals are used to designate the elements of device  22 ′ for varying the pH, to differentiate them from the elements of device  22  for varying the pH. Each device  22 ,  22 ′ for varying the pH communicates with expansion chamber  60  at the level of membrane  54 ,  54 ′ which replaces plug  34 . Further, device  22  for varying the pH is contained in a tight enclosure  67  which connects connection rings  28  and  36 , and device  22 ′ for varying the pH is contained in a tight enclosure  67 ′ which connects connection rings  28 ′ and  36 ′. A valve  69 ,  69 ′ is provided at the level of enclosure  67 ,  67 ′. Enclosures  67 ,  67 ′ are contained in an semi-permeable envelope  71  which is connected to cylindrical body  56  and to connection rings  36 ,  36 ′ of devices  22 ,  22 ′ for varying the pH. Cylindrical body  56  comprises a discharge valve  73  which connects the expansion chamber to the outside of motor  75  via a membrane  76 . 
     As an example, device  22 ′ is of the type enabling to decrease the pH of the solution in which it is arranged according to the previously-described reactions (1), glucose oxidase enzymes being arranged in fibers  26 ′. Device  22  is of the type enabling to increase the pH of the solution in which it is arranged according to the previously-described reactions (3), urease enzymes being arranged in fibers  26 . 
     Compound Z, such as previously described, likely to solubilize in an acid medium, is further arranged in envelope  71 . The cut-off threshold of fibers  26  enables to prevent the passing of substances A and Z and of urease enzymes. The cut-off threshold of membrane  54  enables to prevent the passing of urease enzymes but lets through substance A. Further, the cut-off threshold of fibers  26 ′ enables to prevent the passing of substances A and Z and of glucose oxidase enzymes. The cut-off threshold of membrane  54 ′ enables to prevent the passing of glucose oxidase enzymes but lets through substance A. The cut-off threshold of envelope  71  enables to prevent the passing of substance Z. The cut-off threshold of membrane  76  enables to prevent the passing of substance A. 
     In normal operation, motor  75  is placed in a solution containing glucose and urea. The cut-off threshold of fibers  26 ′ is sufficiently high to enable the passing of glucose and the cut-off threshold of fibers  26  is sufficiently high to enable the passing of urea. Further, the cut-off threshold of envelope  71  is sufficiently high to enable the passing of the solvent, of glucose, and of urea. The concentrations of substances A and Z are initially selected so that the osmotic pressures in expansion chamber  60  and in envelope  71  are balanced, with piston  58  remaining idle. 
     An operating cycle of motor  75  will now be described. 
       FIG. 5A  shows motor  75  at the beginning of a cycle. Piston  58  is in idle position, the volume of expansion chamber  60  being minimum. Discharge valve  73  is closed, valve  69 ′ is closed, and valve  69  is open. As soon as motor  75  is placed in the solution containing urea, the urea crosses envelope  71  and expands into fibers  26 . The ureal degradation provides OH −  ions which disseminate into envelope  71 . The pH increase in envelope  71  promotes the precipitation of substance Z, which tends to lower the osmotic pressure in envelope  71 . The osmotic pressure variation creates a liquid flow from the inside of envelope  71  to expansion chamber  60  via fibers  26 , thus displacing piston  58 . The displacement  58  stretches spring  72 , thus enabling to store mechanical power. 
     In  FIG. 5B , expansion chamber  60  is shown in maximum expansion. Valve  69  is then closed and valve  69 ′ is open. Further, discharge valve  73  is open. The pressure within expansion chamber  60  equalizes with the ambient pressure. Spring  72  brings piston  58  back to its idle position, thus chasing, through discharge valve  73 , the solvent from expansion chamber  60  in to the environment. The mechanical power stored in spring  72  is thus recovered. Further, valve  69 ′ being open, glucose penetrates into fibers  26 ′. The degradation of glucose provides H +  ions which disseminate into envelope  71 . The pH decrease in envelope  71  promotes the solubilization of substance Z, which enables to return to the concentrations of substance Z of the beginning of the cycle. Valve  73  is finally closed, thus ending the motor stroke. 
     In the present embodiment, expansion chamber  60  is defined by a cylindrical body  56  in which a piston  58  slides. Depending on the desired use of motor  75  according to the present invention, expansion chamber  60  may be different. 
       FIGS. 6A and 6B  show an osmotic motor  75 ′ implementing an alternative structure of expansion chamber  60  of motor  75  of the preceding embodiment. According to this variation, expansion chamber  60  corresponds to the space defined between an inner envelope  77  and an outer envelope  78 , just like an air tube. Inner envelope  77  is deformable and extensible and surrounds a deformable body  79 . Outer envelope  78  is flexible and inextensible. It closes back onto inner envelope  77  and is connected to cylindrical body  56 . As an example, in a medical application of osmotic motor  75 ′ according to the present invention, deformable body  79  may be a hollow organ of the human body such as the stomach, the urethra, the anus, or the heart and envelopes  77 ,  78  may define bead-shaped expansion chambers  60  surrounding the hollow organ. The osmotic motor then behaves as a mover of an artificial sphincter (when the hollow organ is the urethra or the anus) or of an adjustable gastric band (when the hollow organ is the stomach). 
     A cycle of motor  75 ′ according to the present variation will now be described. 
       FIG. 6A  shows motor  75 ′ at the beginning of a cycle. The volume of expansion chamber  60  is minimum, deformable body  79  being in maximum expansion, which may correspond to a urethra or to an anal canal or to a stomach at maximum “opening” or to a heart in diastole. Discharge valve  73  is closed, valve  69 ′ is closed and valve  69  is open. The urease enzymes promote the ureal degradation and the pH increase in envelope  71 , which promotes the precipitation of substance Z. This causes, by osmosis, the introduction of solvent into expansion chamber  60 . Inner envelope  77  deforms and compresses deformable body  79 . 
     In  FIG. 6B , deformable body  79  is at maximum compression, which may correspond to a “closed” urethra, to a “closed” anal canal, to a stomach at minimum “opening”, or to a heart in systole. Valve  69 ′ is then open and valve  69  is closed. At the opening of discharge valve  73 , the solvent leaves expansion chamber  60 , thus enabling the expansion of deformable body  79 , which ends the cycle. 
     According to another variation of the invention, the expansion chamber is formed of an additional resilient envelope enclosing fibers which are for example arranged in a spiral and which are connected at an end to cylindrical body  56 . When solvent penetrates into the fibers, said fibers tend to straighten up and to deform the resilient envelope. At the opening of valve  73 , the pressure within the fibers decreases and the additional envelope tends to recover its initial shape. 
     According to another variation of the invention, the device for varying the pH may be connected to the deformable chamber by a flexible duct. This enables to advantageously arrange the device for varying the pH in an environment suitable for the supply of a solvent in which the used substances (glucose or urea, for example) are dissolved by the enzymes contained in the device for varying the pH, and to place the expansion chamber at a location where mechanical power is desired to be available. In the case of a medical application, the device for varying the pH may be arranged in a fatty tissue, or on the vascular network. In this last case, the fibers may be arranged to form a hollow tube, leaving at its center a cylindrical space enabling the flowing of a fluid such as blood. The connection rings may be torus-shaped and placed against the wall of a blood vessel. One of the toric connection rings communicates with the expansion chamber by the flexible duct which perforates the blood vessel. 
       FIGS. 7A and 7B  show a variation of device  10  for varying the pH according to the first embodiment of the invention. According to such a variation, a piston  81  capable of sliding in enclosure  12  is provided in enclosure  12 . Piston  81  is driven by a motor (M)  82 , for example, osmotic motor  70  described in relation with  FIGS. 4A to 4D . Reference  84  designates an element of connection between piston  81  and motor  82 , for example, return means. Piston  81  and enclosure  12  define a chamber of variable volume  86 . A drain  88  is connected to valve  16 . 
     The privileged reaction in chamber  86  is the pH increase by ureal degradation (reactions (3)). Urease enzymes are then arranged in chamber  86 . Membranes  18 ,  20  have a cut-off threshold enabling to retain urease enzymes in chamber  86 . Device  80  is adapted to an application according to which, in parallel with the pH increase, excess urea is desired to be removed from the solution in which device  80  is placed. 
     An operating cycle of device  80  according to the invention will now be described. 
       FIG. 7A  shows device  80  at the beginning of a cycle. The volume of chamber  86  is maximum, valve  14  is open and valve  16  is closed. The solution contained in chamber  86  substantially corresponds to the solution in which device  80  is arranged. Valve  14  is then closed. The urea degradation reaction takes place in chamber  86 , thus increasing the pH of the solution contained in chamber  86 . Motor  82  is then actuated to displace piston  81 , thus decreasing the volume of chamber  86 . Valve  16  is open during the displacement of piston  81 , thus causing the discharge of the solution contained in chamber  86  via duct  88 . 
       FIG. 7B  shows device  80  at the end of the upward phase of piston  81 . Chamber  86  then has a minimum volume. Valve  16  is then closed. Motor  82  is then actuated to displace piston  81 , thus causing a volume increase of chamber  86 . Valve  14  is open during the displacement of piston  81 , causing the suction into chamber  86  of the solution in which device  80  is placed. The cycle ends when chamber  86  has a maximum volume. 
     Such a device  80  may be implanted in the human body for the removal of excess urea. The ammonium ions obtained in ureal degradation are then likely to react with elements such as magnesium, calcium, and potassium present in a biological solution to form solid compounds. It may then not be desirable to reject such solid compounds outside of device  80  into the biological solution. For this purpose, drain  88  is connected to a region likely to receive the waste resulting from ureal degradation, for example, at the level of the colon. 
       FIGS. 8A to 8D  show a third embodiment of an osmotic motor  90  according to the invention. Osmotic motor  90  comprises certain components of the first example of osmotic motor  70  shown in  FIGS. 4A to 4D  and the corresponding reference numerals are kept. 
     As compared with osmotic motor  70 , envelope  52  and membrane  54  are no longer present. Housing  64  contains a polymer gel  92  capable of changing volume according to the pH. It for example is a polymer gel reversible according to the pH such as described in the works of Y. Osada (Polymer Gels and Networks, Yoshihito Osada and Alexi R. Khokhlov, New York, Marcel Dekker Inc., 2001, 400 p.), which increases volume when the pH increases. A tight envelope  94  is arranged in housing  92  and communicates with expansion chamber  60 . Envelope  94  and expansion chamber  60  are filled with a solvent, for example, an aqueous solution. 
     An operating cycle of motor  90  will now be described. 
       FIG. 8A  shows motor  90  at the beginning of a cycle. Gel  92  takes up a minimum volume. Envelope  94  thus has a maximum volume and chamber  60  has a minimum volume. In parallel to the opening cycle of valves  16  and  16 ′ which will now be described, devices  10 ,  10 ′ are controlled so that enclosures  12 ,  12 ′ contain solutions having the desired pH. 
     Valve  16  is closed and valve  16 ′ is open. OH −  ions disseminate into housing  64 , thus increasing the pH. Gel  92  then increases volume and compresses envelope  94 . When the pH in envelope  52  has increased up to the desired value, valve  16 ′ is closed. The volume decrease of envelope  94  causes a solvent transfer from envelope  94  into expansion chamber  60 , thus causing the displacement of piston  58 . Piston  58  is in its upward phase. 
       FIG. 8B  shows motor  90  at the end of the upward phase of piston  58 . Chamber  60  then has a maximum volume. 
     In  FIG. 8C , valve  16  has been opened to put the content of housing  64  in communication with the content of enclosure  12 . H +  ions disseminate into housing  64 , thus decreasing the pH in housing  64 . When the pH is sufficiently acid, valve  16  is closed. The volume decrease of gel  92  is then promoted, thus causing the volume increase of envelope  94 . A new solvent transfer occurs, with solvent passing from expansion chamber  60  into envelope  94 . The action of spring  72  promotes the discharge of the solvent from expansion chamber  60 . However, spring  72  may not be present, and piston  58  would then only be displaced by suction. Piston  58  is said to be in its downward phase. 
       FIG. 8D  shows motor  90  at the end of the downward phase of piston  58 , which ends the cycles. 
     The use of gel  92  having a volume which varies according to the pH may be implemented to form a single-stroke actuator. As an example, as compared with motor  90 , only device  10 ′ is present. The actuator operation is then identical to what has been previously described for motor  90  in relation with  FIGS. 8A and 8B . According to another example, as compared with motor  90 , only device  10  is present. The actuator operation is then identical to what has been previously described for motor  90  in relation with  FIGS. 8C and 8D . 
     According to a variation of previously-described actuators and osmotic motors  70 ,  90 , membranes  20 ,  20 ′ and  54  may be replaced with a bundle of fibers or a similar system if the exchange surface area between the content of enclosure  12 ,  12 ′ and the content of housing  64  or between the content of envelope  52  and the content of expansion chamber  60  is desired to be increased. 
       FIGS. 9A and 9B  show a first embodiment of a cell  100  implementing the first example of the device for varying the pH according to the invention. Cell  100  is intended to operate in a biological solution. It comprises a tight enclosure  102  comprising two regions  104 ,  106  which communicate together. A valve  108 , when opened, puts in communication the content of enclosure  102 , on the side of region  104 , with the external solution. A valve  110 , when opened, puts in communication the content of enclosure  102 , on the side of region  106 , with the external solution. Cell  100  comprises a membrane  112  arranged between valve  108  and enclosure  102  and a membrane  114  arranged between valve  110  and enclosure  102 . 
     Cell  100  comprises a first device  10  for varying the pH, arranged at the level of region  104 , for which, with respect to what has been shown in  FIG. 1 , valves  14  and  16  are confounded and membranes  18 ,  20  are confounded. Further, cell  100  comprises a second device for varying the pH, arranged at the level of region  106 . In the following description, dashed reference numerals are used to designate the elements of the device for varying the pH to differentiate them from the elements of first device  10  for varying the pH. Devices  10  and  10 ′ are of the type enabling to decrease the pH of the solution that it contains. As an example, devices  10 ,  10 ′ enable an acidification of the solution contained in associated enclosure  12 ,  12 ′ according to the previously-described reactions (1). 
     A conductive element  120  connects region  104  of enclosure  102  and region  106  of enclosure  102  via a load C intended to be powered by cell  100 . Conductive element  120  is continued by an electrode  122  that may for example be made of ferric hydroxide Fe(OH) 3  in region  104  of enclosure  102  and by a ferric hydroxide electrode  124  in region  106  of enclosure  102 . 
     Cell  100  is placed in a solution containing D-glucose, for example, a biological solution, and having a substantially neutral or possibly slightly acid or basic pH. Membranes  112 ,  114  are capable of letting through D-glucose and gluconate. However, membranes  112 ,  114  do not let through positive ions. For this purpose, membranes  112 ,  114  may be positively charged. An example of positively-charged membranes may be obtained by techniques such as those used by ASTOM corporation. Membranes  112 ,  114  thus let through negative ions of small dimensions, such as hydroxyl ions OH −  and bicarbonate ions HCO 3   − . 
     According to a variation, membranes  20 ,  20 ′,  112 , and  114  may be replaced by a fiber bundle or an analog system if the exchange surface area between the content of enclosure  12 ,  12 ′ and the content of housing  102  or between the content of housing  102  and the environment is desired to be increased. Further, several valves (and the associated membranes) controlled in the same way as valve  108  may be distributed on housing  102  at the level of region  104 . Similarly, several valves (and the associated membranes) controlled in the same way as valve  110  may be distributed on housing  102  at the level of region  106 . Further, several valves (and the associated membranes) controlled in the same way as valve  14  may be distributed on enclosure  12  of device  10 . Similarly, several valves (and the associated membranes) controlled in the same way as valve  14 ′ may be distributed on enclosure  12 ′ of device  10 ′. 
       FIG. 9A  shows cell  100  in a first operating phase. Valve  108  is open and valve  110  is closed. Further, valve  14  is closed and valve  14 ′ is open. D-glucose thus penetrates into enclosure  12 ′ of device  10 ′. Previously-described reactions (1), which take place in enclosure  12 ′, cause the release of H +  ions which disseminate outside of device  10 ′, into region  106  of enclosure  102 , and in particular at the level of electrode  124 . The cell operation is based on oxidation-reduction reactions which are more or less promoted according to the pH. More specifically, in the first operating phase, electrode  124  behaves as a cathode. The presence of H +  ions at the level of cathode  124  promotes the following reduction reaction:
 
Fe(OH) 3 +3H +   +e   − →Fe 2+ +3H 2 O  (4)
 
     Since valve  14  is closed, device  10  releases no H +  ions into region  104  of enclosure  102 . Further, since valve  110  is closed and valve  108  is open, the establishment of a pH gradient between region  104  and region  106  of enclosure  102  is promoted, the pH being higher in region  104  than in region  106 . Indeed, the H +  ions which propagate to region  104  for example tend to react with OH −  hydroxyl ions present in the biological solution and crossing membrane  112  to form water or with HCO 3   −  bicarbonate ions to form water and carbon dioxide. 
     The Fe 2+  ions which form at cathode  124 , are trapped in enclosure  102  and migrate to electrode  122  which behaves as an anode. The communication with the outside through valve  108  enables the pH to remain close to neutrality, which promotes, at anode  122 , the following oxidation reaction:
 
Fe 2+ +3H 2 O→Fe(OH) 3 +3H +   +e   −   (5)
 
     An electron transfer from anode  122  to cathode  124  through conductive element  120  and thus through load C to be powered can thus be observed. 
     Reaction (4) thus causes the consumption of the ferric hydroxide Fe(OH) 3  of cathode  124 . To enable a long-term operation of cell  100 , it is advantageous to provide a regular inversion of the polarity of cell  100 . 
       FIG. 9B  shows cell  100  in a second operating phase. Valve  108  is closed and valve  110  is open. Further, valve  14  is open and valve  14 ′ is closed. Previously-described reactions (1) which take place in enclosure  12  cause the releasing of H +  ions which disseminate outside of device  10 , into region  104  of enclosure  102 , and in particular at the level of electrode  122 , which then behaves as a cathode. The presence of H +  ions at the level of cathode  122  promotes previously-described reduction reaction (4). 
     Since valve  14 ′ is closed, device  10 ′ releases no H +  ions into region  106  of enclosure  102 . Further, since valve  108  is closed and valve  110  is open, the establishment of a pH gradient between region  106  and region  104  of enclosure  102  is promoted, the pH being higher in region  106  than in region  104 . Indeed, the H +  ions which propagate to region  106  tend to react, for example, with OH −  hydroxyl ions present in the biological solution and crossing membrane  114  to form water or with HCO 3   −  bicarbonate ions to form water and carbon dioxide. 
     The Fe 2+  ions, which form at cathode  122 , are trapped in enclosure  102  and migrate to electrode  124 , which then behaves as an anode. The previously-described oxidation reaction (5) is thus promoted at anode  124 . 
     An electron transfer from anode  124  to cathode  122  can thus be observed through conductive element  120  and thus through load C to be powered. 
     The operating phases previously described in relation with  FIGS. 9A and 9B  are alternated to enable restoring the Fe(OH) 3  stock at the level of electrodes  122 ,  124 . 
       FIG. 10  shows a second embodiment of a cell  130  implementing the first example of a device for varying the pH according to the invention. Cell  130  can operate without being immersed in a biological solution. As compared with cell  100 , cell  130  comprises four devices for varying the pH such as described previously in relation with  FIG. 1 . In the following description, suffixes “A”, “B”, “C”, and “D” are added to designate the elements respectively associated with devices  10 A,  10 B,  10 C, and  10 D for varying the pH. Valves  16 A and  16 B of devices  10 A,  10 B emerge at the level of region  104  of enclosure  102  and valves  16 C and  16 D of devices  10 C,  10 D emerge at the level of region  106  of enclosure  102 . 
     Devices  10 A and  10 C are of the type enabling to decrease the pH of the solution that they contain. As an example, devices  10 A and  10 C enable to acidify the solution contained in the associated enclosure  12 A,  12 C according to previously-described reactions (1). Devices  10 B and  10 D are of the type enabling to increase the pH of the solution that they contain. As an example, devices  10 B,  10 D enable an alkalizing of the solution contained in the associated enclosure  12 B,  12 D according to previously-described reactions (3). 
     An example of operation of cell  130  is the following. In parallel with the opening cycle of valves  16 A to  16 D which will now be described, devices  10 A to  10 D are controlled so that the associated enclosures  12 A to  12 D contain solutions having the desired pH. During a first operating phase, valve  16 A is open, valve  16 B is closed, valve  16 C is closed, and valve  16 D is open. H +  ions are then released by device  10 A, the decreasing the pH at the level of electrode  122  and OH −  ions are released by device  10 D, thus increasing the pH at the level of electrode  124 . A pH gradient is then obtained between regions  104  and  106  of enclosure  102 . The presence of H +  ions at the level of electrode  122  promotes previously-described reduction reaction (4) and the presence of OH −  ions at the level of electrode  124  promotes previously-described oxidation reaction (5). An electron transfer from anode  124  to cathode  122  through conductive element  120  and thus through load C to be powered can thus be observed. During a second operating phase, valve  16 A is closed, valve  16 B is open, valve  16 C is open and valve  16 D is closed. H +  ions are then released by device  10 C, thus decreasing the pH at the level of end  124  and OH −  ions are released by device  10 B, thus increasing the pH at the level of electrode  122 . The presence of H +  ions at the level of electrode  124  promotes previously-described reduction reaction (4) and the presence of OH −  ions at the level of electrode  122  promotes previously-described oxidation reaction (5). An electron transfer from anode  122  to cathode  124  through conductive element  120  and thus through load C to be powered can thus be observed. 
     In the previously-described cell examples, it is possible to use, instead of ferric hydroxyl, several sorts of electrodes, provided that their potential depends on the pH. The electrode potential being imposed by the electronic exchange between the two forms of a redox pair, it is possible to envisage different electrode structures: the two forms may be soluble, one form may be soluble and the other insoluble, and finally, both forms may be insoluble. In this last case, it may be advantageous to use electrodes formed of an electro-active polymer obtained, for example, from a condensation of phenols and thiols. An example of a polymer having a redox capacity is described in document Ion Exchange, Friedrich Helfferich, 1962 McGraw-Hill Book Company, Chapter 12: Electron Exchangers and Redox Ion Exchangers, pages 551 to 568. 
       FIG. 11  illustrates the steps of an example of a targeted enzyme therapy method. An example of a targeted enzyme therapy method is described in document “Lysosomal Enzyme Delivery by ICAM-1-Targeted Nanocarriers Bypassing Glycosylation- and Clathrin-Dependent Endocytosis” by Sylvia Muro, Edward H. Schuchman, and Vladimir R. Muzykantov (Molecular Therapy vol. 13, n o  1, January 2006, pages 135 to 140). 
     At step  150 , a monoclonal antibody B recognizing an antigen A of the target cell is determined. As an example, antigen A corresponds to the carcinoembryonic antigen or CEA, the prostate specific antigen (PSA), or the prostate specific membrane antigen (PSMA). An antibody B adapted to the PSA antigen is, for example, the antibody marketed by Cytrogen Corporation under trade name Prostascint (Capromab Pendetide). 
     At step  152 , a complex X combining monoclonal antibody B and an enzyme G is formed. Enzyme G is capable of promoting a reaction implementing a substance D. Complex X is such that the affinity of antibody B with antigen A remains strong and that the activity of enzyme G on substance D also remains strong. Substance D is, for example, L-glucose and enzyme G corresponds to an L-glucose oxidase enzyme, for example, D-threo-aldose 1-dehydrogenase. Such an enzyme has the advantage of being inactive on D-glucose. According to another example, substance D is mannitol (C 6 H 8 (OH) 6 ) and enzyme G corresponds to a mannitol oxidase enzyme. 
     At step  154 , complex X is injected into the patient&#39;s body. The injection of complex X is, for example, intravenous. Complex X then tends to fix on antigen A via antibody B. It is then expected for complex X flowing in the patient&#39;s body to be eliminated. 
     At step  156 , substance D is injected into the patient&#39;s body. The injection of substance D is, for example, intravenous. In the case where enzyme G is an L-glucose oxidase, L-glucose is injected into the patient&#39;s body. L-glucose then freely diffuses into the organism. L-glucose being harmless for the human body, the L-glucose concentration may be high (for example on the order of the blood glucose concentration, that is, several millimoles per liter). In the case where enzyme G is a mannitol oxidase, mannitol, for example, the D stereoisomer of mannitol, is injected into the patient&#39;s body. 
     In the case of an L-glucose injection, since human cells are not capable of metabolizing L-glucose, only enzymes G of complexes X will promote the previously-described reactions (2), causing, the production of H +  ions from the L-glucose and, accordingly, a local pH decrease. Such a local pH decrease may provide a direct therapeutic effect, causing the death of the target cell, or may cause an inflammatory response causing the death of the target cell. 
     In the case of a mannitol injection, enzymes G promotes the reaction in which mannitol reacts with dioxygen to provide mannose (C 6 H 7 O(OH) 5 ) and hydrogen peroxide, or perhydrol (H 2 O 2 ), according to the following reaction: 
     
       
                 
         
             
             
         
      
     
     The local production of hydrogen peroxide may provide a direct therapeutic effect, causing the death of the target cell, or may cause an inflammatory response causing the death of the target cell. 
     An aspect of the present invention thus provides a therapeutic method comprising the steps of forming a complex comprising an antibody of an antigen of a target cell and an enzyme capable of promoting a reaction which produces a second substance from a first substance, the second substance being noxious for the target cell; introducing the complex into the patient&#39;s body, whereby the antibody of the complex fixes onto the target cell; and introducing the first substance into the patient&#39;s body, whereby the enzyme of the complex promotes the production of the second substance at the target cell level. 
     According to an embodiment, the first substance is L-glucose, the enzyme is the L-glucose oxidase enzyme, and the second substance is the H +  ion. 
     According to an embodiment, the first substance is mannitol, the enzyme is the mannitol oxidase enzyme, and the second substance is hydrogen peroxide. 
     According to an embodiment, the antigen is an antigen from the group comprising the carcinoembryonic enzyme, the prostate specific antigen or the prostate specific membrane antigen. 
     Of course, the present invention is likely to have various alterations and modifications which will occur to those skilled in the art. In particular, the alternative embodiment of the expansion chamber of the osmotic motor described in relation with  FIGS. 6A and 6B  may be applied to the osmotic motor described in relation with  FIGS. 4A to 4D .