Patent Publication Number: US-2019184102-A1

Title: Administration apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application, and claims benefit under 35 U.S.C. §§ 120 and 365 of PCT Application No. PCT/JP2017/029983, filed Aug. 22, 2017, which is hereby incorporated by reference. PCT/JP2017/029983 also claimed priority to Japanese Patent Application No. 2016-162872, filed Aug. 23, 2016, the entire contents of which are incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     The described technology generally relates to an administration apparatus that administers a substance to be administered to an administration target area. 
     Description of the Related Technology 
     An example of an administration apparatus that administers a substance to be administered includes an injector. There are cases where gunpowder is used as a pressurization source in a needleless injector that performs injection without the intervention of an injection needle (see, e.g., Japanese Translation of PCT Application No. 2004-532049). In the needleless injector described in Japanese Translation of PCT Application No. 2004-532049, a detonator and explosive charge are provided, the detonator is pierced with a hammer, and the detonator ignites, whereby thermal energy generated by the ignition is transmitted to the explosive charge. Subsequently, the explosive charge is combusted, whereby an injection solution is pressurized. As the explosive charge described above, nitrocellulose-based single gunpowder is used. 
     Combustion energy of gunpowder is used as a power source for pressurization also in a field different from the field of the injector. For example, U.S. Pat. No. 6,397,595 discloses a technique related to an actuator for driving a control member via a membrane by using the combustion energy of the gunpowder to interrupt the flow of a medium in a channel. In the technique, the elastically deformable membrane sandwiched between the control member and a housing receives the combustion pressure of the gunpowder and is thereby deformed, a cylinder portion attached to the membrane is displaced, and the control member is thereby driven. 
     SUMMARY 
     In the case where the combustion energy of the gunpowder is used as the power source for pressurization, it is necessary to consider influences of combustion products generated by the combustion such as combustion gas and a combustion residue. For example, in the case where the gunpowder is used as the pressurization source for an object in the administration apparatus that administers the substance to be administered, it is not preferable that the combustion product is mixed into the substance to be administered serving as a pressurization target. 
     On the other hand, as in the conventional art, in the case where a space in which the combustion of the gunpowder is performed is separated from a space where the substance to be administered that is pressurized is disposed by the elastically deformable membrane, and the combustion energy of the gunpowder is transmitted to the substance to be administered via the deformation of the membrane, the membrane is elastically deformed sharply at the time of the combustion. In addition, for the pressurization, the membrane needs to secure a desired deformation amount in the deformation. However, in the conventional art, the membrane needs to be elastically deformed significantly toward the control member by the combustion of the gunpowder, and it is feared that the membrane may be damaged or torn in some situations. When the membrane is damaged, it becomes difficult to seal the combustion product in the space on the side where the combustion is performed. In addition, the elastically deformable membrane according to the conventional art is deformed so as to stick to a specific surface in an internal space. However, depending on the deformation of the membrane, the membrane cannot necessarily press the control member adequately, and adequate transmission of the combustion energy to the control member may be hindered. 
     To cope with this, in view of the above problem, an object of the described technology is to prevent, in an administration apparatus that administers a substance to be administered using gunpowder combustion, a combustion product generated by the gunpowder combustion from acting on the substance to be administered and suitably transmit energy for administration to the substance to be administered. 
     In order to solve the above problem, the described technology has adopted a configuration in which a sealing member, which separates a space in an apparatus body into the side of an ignition device and the side of a piston portion, seals a combustion product generated by the ignition device in the space on the side of the ignition device. With this configuration, it is possible to prevent the combustion product from being mixed into a substance to be administered. In addition, the sealing member is formed of a metal plate-like member, whereby the sealing member is suitably deformed by gunpowder combustion in the ignition device, and the shape of the sealing member after the deformation is easily maintained because the sealing member is made of metal. As a result, it is possible to transmit combustion energy of the gunpowder to the substance to be administered more reliably. 
     Specifically, one embodiment of the described technology is an administration apparatus that administers a substance to be administered to an administration target area, and the administration apparatus includes: an apparatus body having a through hole that is formed in an axial direction; a piston portion disposed so as to be slidable in the through hole; a syringe portion disposed on a side of a tip of the apparatus body, the syringe portion having an accommodation chamber that is capable of accommodating the substance to be administered, a plunger that pressurizes the substance to be administered in the accommodation chamber in response to a slide of the piston portion, and a nozzle portion that includes a channel in which the substance to be administered in the accommodation chamber pressurized by the plunger flows, and ejects the substance to be administered from an ejection outlet formed at a tip of the channel; an ignition device that is disposed on a side of a base end of the apparatus body, that combusts gunpowder, and that supplies ejection energy for ejecting the substance to be administered from the nozzle portion using gunpowder combustion in the ignition device; and a sealing member that is formed of a metal plate-like member, that separates a space in the apparatus body into a first space in which the ignition device is disposed and a second space in which the piston portion is disposed, and that seals a combustion product generated by the ignition device in the first space. A peripheral edge portion of the sealing member is fixed to an inner wall that defines the space in the apparatus body, and the sealing member is deformed by the gunpowder combustion in the ignition device such that a central portion of the sealing member is displaced to a side of the piston portion, to thereby press the piston portion against the plunger using the central portion. 
     In the administration apparatus according to the described technology, combustion energy generated by the gunpowder combustion in the ignition device is used as the ejection energy, and the central portion of the sealing member is deformed so as to be displaced to the side of the piston portion, whereby the piston portion is pressed against the plunger and slides in the through hole. Subsequently, pressure is applied to the substance to be administered accommodated in the accommodation chamber of the syringe portion via the plunger by the slide of the piston portion, and the substance to be administered is thereby ejected to the outside of the apparatus from the ejection outlet. Note that, in the case where the displacement of the central portion of the sealing member is caused by the combustion of the gunpowder, it is possible to appropriately adopt configurations such as a configuration in which the ejection energy is caused to directly act on the piston portion via the central portion of the sealing member, and a configuration in which the ejection energy is caused to propagate to another gas, liquid, or solid once and is then caused to indirectly act on the piston portion via the central portion. 
     As long as the substance to be administered can be ejected by using the ejection energy, the accommodation state of the substance to be administered in the administration apparatus may be any accommodation state, and the specific physical form of the substance to be administered such as fluid such as liquid or gel, powder, or a granular solid may be any physical form. The substance to be administered may contain an ingredient that is expected to be efficacious inside the administration target area. For example, in the case where the administration apparatus is an injector that injects the substance to be administered into a living body area, the substance to be administered contains an ingredient to be delivered to the administration target area of the living body, and the ingredient may be present in a state in which the ingredient is dissolved in the substance to be administered or in a state in which the ingredient is not dissolved therein but is simply mixed with the substance to be administered. Examples of the ingredient to be delivered include vaccine for strengthening an antibody, protein for beauty treatment, and cultured cells for hair regeneration. The substance to be administered is formed by causing fluid such as liquid or gel to contain the above ingredient such that the ingredient can be ejected. The injector may be a type of the injector that supplies the substance to be administered to the administration target area via a needle, or may also be a type of the injector that supplies the substance to be administered to the administration target area without the intervention of the needle. 
     In the administration apparatus according to the described technology, the ignition device that combusts the gunpowder may be the ignition device in which the gunpowder accommodated in the ignition device is ignited by execution of the ignition device and the combustion product of the gunpowder is generated, and may also be the ignition device in which a known gas generating agent (e.g., single-base smokeless gunpowder) is further combusted by the ignition of the gunpowder and the combustion products of the gunpowder and the gas generating agent are generated, and the specific configuration of the ignition device is not limited in the administration apparatus of the described technology. 
     When the gunpowder is combusted in the above ignition device, the combustion product is diffused in the space in the apparatus body and typically transmits the ejection energy to the piston portion via pressure or heat, and, as described above, the energy serves as a power source for ejection of the substance to be administered. The administration apparatus according to the described technology includes the sealing member, and hence the combustion product is sealed in the first space, and does not enter the second space. Consequently, it is possible to prevent unfavorable action of the combustion product on the substance to be administered. In order to obtain the sealing effect, the sealing member needs to have a certain level of resistance to the combustion of the gunpowder. On the other hand, it is not preferable that the transmission of the ejection energy to the piston portion be hindered by the presence of the sealing member. Accordingly, the sealing member needs to achieve both of suitable sealing of the combustion product and suitable transmission of the ejection energy to the piston portion. 
     To cope with this, the sealing member provided in the administration apparatus of the described technology is formed of the metal plate-like member. The sealing member is formed of the plate-like member, whereby, when the gunpowder is combusted in the ignition device, the generated combustion energy can be received by the surface of the plate-like member. As a result, the displacement amount of the central portion of the sealing member is increased, and it becomes easier to press the piston portion. Further, the sealing member is made of metal, whereby, in the case where the sealing member receives the combustion energy of the gunpowder and is deformed, the state after the deformation is maintained more easily than in the case where the sealing member is made of, e.g., an elastic resin such as rubber. That is, when the metal sealing member receives the combustion energy of the gunpowder, the metal sealing member is plastically deformed and does not return to its original state easily, and it becomes possible to substantially maintain the deformed state. This is extremely useful in the administration apparatus that transmits the combustion energy to the side of the piston portion via the sealing member and uses the combustion energy as the ejection energy for the substance to be administered. This is because the returning of the sealing member to the original state after the deformation means that the combustion energy to be transmitted to the side of the piston portion is lost. In view of the foregoing, in the administration apparatus according to the described technology, it becomes possible to achieve both of the sealing of the combustion product and the suitable transmission of the ejection energy to the piston portion. 
     The administration apparatus described above may be configured such that the sealing member is curved such that the central portion is positioned on a side of the ignition device with respect to the peripheral edge portion in a state before the gunpowder combustion in the ignition device, and the sealing member is curved such that the central portion is positioned on a side opposite to the side of the ignition device with respect to the peripheral edge portion by the gunpowder combustion in the ignition device. Thus, when the sealing member is deformed such that the position of the central portion of the sealing member with respect to the peripheral edge portion is displaced from the side of the ignition device, which is the side before the gunpowder combustion in the ignition device, to the side opposite to the side of the ignition device after the gunpowder combustion in the ignition device, it is possible to secure the large displacement amount of the sealing member in the direction of the slide of the piston portion at the time of the combustion. As a result, it becomes possible to efficiently transmit the ejection energy to the piston portion via the sealing member. 
     In addition, in the administration apparatus described above, with approach to the central portion of the sealing member from the ignition device along a central axis of the apparatus body, a cross-sectional area of the space in the apparatus body in a direction perpendicular to the central axis may be reduced. According to this configuration, it is possible to apply the combustion energy of the gunpowder in the ignition device intensively to the sealing member. As a result, it is possible to secure the large displacement amount of the central portion of the sealing member by the gunpowder combustion. In addition, in the case where the large displacement amount of the central portion is secured, as described above, the sealing member is made of metal, and hence the central portion is formed so as not to return to the original state easily, and the efficient transmission of the ejection energy to the piston portion is thereby implemented. 
     Further, in the administration apparatus described above, the ignition device may have a release portion that releases the combustion product generated by the gunpowder combustion and, in this case, the central portion of the sealing member is disposed so as to face the release portion. According to this configuration, it is possible to effectively apply the combustion energy of the gunpowder to the central portion of the sealing member, which contributes to the efficient transmission of the ejection energy to the piston portion. 
     Furthermore, in the administration apparatus described above, an end portion of the piston portion may be in contact with the central portion of the sealing member in the state before the gunpowder combustion in the ignition device. According to this configuration, it is possible to efficiently transmit the energy from the sealing member that receives the combustion energy of the gunpowder and is deformed to the piston portion. 
     According to the described technology, in the administration apparatus that administers the substance to be administered using the gunpowder combustion, it is possible to prevent the combustion product generated by the gunpowder combustion from acting on the substance to be administered, and suitably transmit energy for administration to the substance to be administered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  are views showing the schematic configuration of an injector according to a first embodiment of the described technology. 
         FIG. 2  is a view showing the details of a piston of the injector shown in  FIGS. 1A-1C . 
         FIG. 3  is a view showing the schematic configuration of an initiator (ignition device) mounted to the injector shown in  FIGS. 1A-1C . 
         FIGS. 4A and 4B  are views in which, in the injector shown in  FIGS. 1A-1C , a state before gunpowder combustion in the initiator and a state after gunpowder combustion therein are compared with each other and shown. 
         FIG. 5  is a view showing the schematic configuration of the injector according to a second embodiment of the described technology. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinbelow, description will be made by taking, as an example, a needleless injector  1  (hereinafter simply referred to as an “injector  1 ”) with no injection needle that serves as an example of an administration apparatus according to the described technology with reference to the drawings. Note that the configurations of the following embodiments are shown by way of example only, and the described technology is not limited to the configurations of the embodiments. 
     First Embodiment 
       FIG. 1A  is a cross-sectional view of the injector  1 , and  FIG. 1B  is a view when the injector  1  is viewed from the side of a nozzle portion  9  from which an injection solution is ejected. Note that, in the following description of the present application, a substance to be injected that is injected into an injection target area of an object by the injector  1  is collectively referred to as an “injection solution”. That is, the substance to be injected is the substance that is administered to the injection target area, and corresponds to a substance to be administered of the described technology. However, this is not intended to limit the content and form of the injected substance. In the substance to be injected, an ingredient to be delivered to a skin structure may or may not be dissolved. In addition, as long as the substance to be injected can be ejected to the skin structure from the nozzle portion  9  by pressurization, the specific form of the substance to be injected may be any form, it is possible to use various forms such as liquid, gel, and gunpowder. 
     The injector  1  has an injector body  2  constituted by a first housing  3  and a second housing  4 , and a syringe portion  5  is disposed on the side of the tip of the injector body  2  (the side of an end portion of the second housing  4  opposite to an end portion thereof connected to the first housing  3 ). The first housing  3  and the second housing  4  are fixed to each other with a screw and are thereby integrated with each other. Inside the first housing  3 , a combustion chamber  31  that is an internal space extending in an axial direction of the first housing  3  is formed and, inside the second housing  4 , a through hole  33  that is an internal space extending similarly in an axial direction of the second housing  4  is formed. Although the combustion chamber  31  and the through hole  33  are separated from each other by a sealing member  8 , they are the internal spaces that are continuously disposed inside the injector body  2 . The sealing member  8  is formed of a metal plate-like member. Note that the sealing member  8  also serves as a member that transmits energy of gunpowder combustion in an initiator  20  serving as an ignition device described later to a piston  6  as ejection energy, and the movement of the sealing member  8  at the time of the transmission will be described later. 
     The syringe portion  5  provided on the side of the tip of the injector body  2  has a syringe portion body  11  that has an accommodation chamber  35  that accommodates an injection solution ML inside the syringe portion body  11 , the nozzle portion  9  in which a channel in which the injection solution flows is formed, and a nozzle body portion  10  in which the nozzle portion  9  is provided. The nozzle body portion  10  is mounted, via a gasket  13 , to the syringe portion body  11  by a nozzle holder  12 . The syringe portion body  11  is screwed with and mounted to the end portion of the second housing  4  of the injector body  2  and, in the mounting state, the through hole  33  in the second housing  4  and the accommodation chamber  35  in the syringe portion body  11  form continuous space. Note that, in the mounting state, the injection solution ML is accommodated in the accommodation chamber  35  fluid-tightly by a plunger  7 , and the plunger  7  is exposed on the side of the through hole  33 . The plunger  7  is disposed so as to be slidable in the accommodation chamber  35  and pressurizes the injection solution ML by sliding, and ejection of the injection solution from the nozzle portion  9  is thereby performed. The plunger  7  is formed of a rubber member, the surface of which is thinly coated with silicon oil so as to be able to smoothly slide in the accommodation chamber  35 . 
     Next, the metal piston  6  is disposed in the through hole  33  in the second housing  4  of the injector body  2 , and is held so as to be slidable in the through hole  33 .  FIG. 2  shows the details of the piston  6  such that the positional relationship between the piston  6  and the second housing  4  can be grasped. The piston  6  is formed into a substantially shaft-like shape that extends along an axial direction of the through hole  33 , and has an end portion (hereinafter referred to as a “first end portion”)  6   a  on the side of the combustion chamber  31  and an end portion on the side of the syringe portion  5 , i.e., an end portion (hereinafter referred to as a “second end portion”)  6   b  that comes into contact with the plunger  7  disposed in the syringe portion  5 , and O-rings  6   c  are disposed around the piston  6  such that the piston  6  can slide smoothly in the through hole  33 . In a state in which the injector body  2  is formed by mounting the first housing  3  (indicated by a dotted line in  FIG. 2 ) and the second housing  4  to each other, and the gunpowder combustion is not yet performed in the initiator  20  (hereinafter referred to as a “pre-ignition state”), the first end portion  6   a  is substantially protruded to the side of the combustion chamber  31  from an end surface of a fitted portion  4   a  of the second housing  4  that is fitted in the combustion chamber  31  of the first housing  3 . A diameter dl of the first end portion  6   a  is smaller than a diameter d 0  of the through hole  33 . Consequently, when the piston  6  slides to the side of the syringe portion  5  in the through hole  33 , a specific gap is formed between a side surface (a surface extending along an axial direction of the piston  6 ) of the first end portion  6   a  and an inner wall surface of the through hole  33 . 
     In the pre-ignition state shown in  FIGS. 1A-1C , the sealing member  8  is fixed such that a peripheral edge portion  8   b  of the sealing member  8  is disposed on the end surface of the fitted portion  4   a  of the second housing  4  that is part of an inner wall of the injector body  2 , and the peripheral edge portion  8   b  is buried in the first housing  3  in the vicinity of the fitted portion  4   a . In addition, in the pre-ignition state, a central portion  8   a  of the sealing member  8  is in contact with an end surface of the first end portion  6   a  of the piston  6 . As described above, in the pre-ignition state, the first end portion  6   a  is disposed so as to be protruded in the first housing  3 , and hence, as a result, the sealing member  8  is fixed in the injector body  2  in a state in which the sealing member  8  is curved to the side of the initiator  20  in the pre-ignition state. The sealing member  8  is the plate-like member formed of a metal material and separates the space in the injector body  2  into a space including the combustion chamber  31  positioned on the side of the initiator  20  (corresponds to a first space according to the described technology) and a space including the through hole  33  positioned on the side of the piston  6  (corresponds to a second space according to the described technology), and a combustion product generated by the gunpowder combustion in the initiator  20  is thereby sealed in the combustion chamber  31 . Note that the movement of the sealing member  8  by the gunpowder combustion in the initiator  20  will be described later. 
     An example of the initiator  20  will be described based on  FIG. 3 . The initiator  20  is an electrical ignition device, and a space for disposing gunpowder  22  is defined in a cup  21  by the cup  21 , the surface of which is covered with an insulating cover. A metal header  24  is disposed in the space, and a tubular charge holder  23  is provided on an upper surface of the metal header  24 . The gunpowder  22  is held by the charge holder  23 . A bridge wire  26  that electrically connects one of conductive pins  28  and the metal header  24  is disposed at a bottom portion of the gunpowder  22 . Note that the two conductive pins  28  are fixed to the metal header  24  via an insulator  25  so as to be insulated from each other when voltage is not applied. Further, an open port of the cup  21  from which the two conductive pins  28  supported by the insulator  25  extend is protected by a resin collar  27  in a state in which insulation characteristics between the conductive pins  28  are properly maintained. 
     In the thus configured initiator  20 , when a voltage is applied between the two conductive pins  28  by an external power source, a current flows to the bridge wire  26 , and the gunpowder  22  is thereby combusted. At this point, the combustion product generated by the combustion of the gunpowder  22  is jetted from an opening portion of the charge holder  23 . The cross section of an initiator cap  14  is formed into a flange-like shape such that the initiator cap  14  is caught on an outer surface of the initiator  20 , and the initiator cap  14  is fixed to the first housing  3  by using a screw. With this, the initiator  20  is fixed to the first housing  3  by using the initiator cap  14 , and it is possible to prevent the initiator  20  itself from being disconnected from the injector body  2  by pressure generated at the time of the ignition in the initiator  20 . 
     An example of the gunpowder  22  used in the injector  1  preferably includes a gunpowder containing zirconium and potassium perchlorate (ZPP), a gunpowder containing titanium hydride and potassium perchlorate (THPP), a gunpowder containing titanium and potassium perchlorate (TiPP), a gunpowder containing aluminum and potassium perchlorate (APP), a gunpowder containing aluminum and bismuth oxide (ABO), a gunpowder containing aluminum and molybdenum oxide (AMO), a gunpowder containing aluminum and copper oxide (ACO), a gunpowder containing aluminum and iron oxide (AFO), or a gunpowder obtained by combining a plurality of the gunpowders. Each gunpowder exhibits a characteristic that the gunpowder generates high-temperature high-pressure plasma during the combustion immediately after the ignition but, when the temperature is reduced to normal temperature and the combustion product condenses, generated pressure is sharply reduced because no gas component is contained. Note that another gunpowder other than the gunpowders described above may be used. 
     Nothing is disposed in the combustion chamber  31  shown in  FIGS. 1A-1C , but a gas generating agent that is combusted by the combustion product generated by the combustion of the gunpowder  22  and generates gas may be disposed in the combustion chamber  31 . In the case where the gas generating agent is disposed in the combustion chamber  31 , an example of the gas generating agent includes single-base smokeless gunpowder containing 98 mass % of nitrocellulose, 0.8 mass % of diphenylamine, and 1.2 mass % of potassium sulfate. In addition, it is also possible to use various gas generating agents that are used in a gas generator for an air bag and a gas generator for a seat belt pretensioner. In the combined use of the gas generating agent and the gunpowder, unlike the case where only the gunpowder  22  is used, specific gas generated during the combustion contains the gas component even at normal temperature, and hence the reduction rate of the generated pressure is low. Further, combustion completion time at the time of the combustion of the gas generating agent is significantly longer than that of the above gunpowder  22 , but it is possible to change the combustion completion time of the gas generating agent by adjusting the dimensions, the size, the shape, and particularly the surface shape of the gas generating agent when the gas generating agent is disposed in the combustion chamber  31 . Thus, by adjusting the amount, the shape, and the disposition of the gas generating agent, it is possible to appropriately adjust the generated pressure in the combustion chamber  31 . 
     Note that a plurality of the nozzle portions  9  may be formed in the nozzle body portion  10 , or one nozzle portion  9  may be formed in the nozzle body portion  10 . In the case where a plurality of the nozzle portions are formed, the channels corresponding to the individual nozzle portions are formed such that the released injection solution ML is sent to the individual nozzles as uniformly as possible. Further, in the case where a plurality of the nozzle portions  9  are formed, as shown in  FIG. 1C , it is preferable that the individual nozzle portions be disposed so as to be exposed at regular intervals around the central axis of the injector  1 , and be fixed by the nozzle holder  12 . The diameter of the channel of the nozzle portion  9  is configured to be smaller than the inner diameter of the through hole  33 . With this, it is possible to suitably increase the ejection pressure of the injection solution at the time of the ejection. 
     The ejection state of the injection solution in the injector  1  will be described based on  FIGS. 4A and 4B  together with the movement of each of the sealing member  8  and the piston  6  when the gunpowder  22  in the initiator  20  is combusted.  FIG. 4A  shows the configuration of the injector  1  in the pre-ignition state, while  FIG. 4B  shows the configuration of the injector  1  in a state in which the ejection of the injection solution is completed (hereinafter referred to as an “ejection completion state”). 
     In a pre-combustion state, the peripheral edge portion  8   b  is disposed on the end surface of the fitted portion  4   a  and the sealing member  8  is fixed on the side of the first housing  3  and, at this point, the sealing member  8  is curved such that the central portion  8   a  of the sealing member  8  is positioned on the side of the initiator  20  with respect to the peripheral edge portion  8   b , and the central portion  8   a  of the sealing member  8  is in contact with the end surface of the first end portion  6   a  of the piston  6 . In addition, the central portion  8   a  of the sealing member  8  is positioned so as to face the cup  21  of the initiator  20 . With this disposition, the sealing member  8  receives pressure by the combustion product released from the initiator  20  using its plate-like surface. In particular, the central portion  8   a  of the sealing member  8  is disposed at the position where the central portion  8   a  receives the pressure directly, and hence, as will be described later, it becomes easier for the central portion  8   a  to press the piston  6 . 
     When the gunpowder  22  is combusted in the initiator  20 , the combustion product is diffused in the combustion chamber  31 , and the pressure in the combustion chamber  31  is increased. With this, the pressure is also applied to the sealing member  8 . At this point, the central portion  8   a  is positioned in the central part of the plate-like sealing member  8 , and hence the central portion  8   a  is the portion that is most likely to be deformed in the sealing member  8  of which the peripheral edge portion  8   b  is fixed. Accordingly, when the pressure is applied to the sealing member  8  by the gunpowder combustion, the sealing member  8  is deformed such that the central portion  8   a  presses the first end portion  6   a  of the piston  6  to the side of the tip of the injector  1 . In other words, the sealing member  8 , which is curved such that the central portion  8   a  is positioned on the side of the initiator  20  with respect to the peripheral edge portion  8   b , is deformed so as to be curved such that the central portion  8   a  is positioned on the side opposite to the side of the initiator  20  by the gunpowder combustion. By causing the central portion  8   a  to move in response to the movement of the sealing member  8 , it is possible to secure the large displacement amount of the central portion  8   a  of the sealing member  8  by the gunpowder combustion, and efficiently press the injection solution ML. Further, in the pre-combustion state, the central portion  8   a  is in contact with the first end portion  6   a , and hence it is possible to effectively convert the displacement of the central portion  8   a  of the sealing member  8  by the gunpowder combustion to the slide of the piston  6 . 
     In addition, the sealing member  8  is formed of the metal material, and hence, when the pressure is applied sharply to the sealing member  8  by the gunpowder combustion in the initiator  20 , the sealing member  8  is substantially plastically deformed when the central portion  8   a  is displaced from the side of the initiator  20  to the side opposite to the side of the initiator  20  with respect to the peripheral edge portion  8   b , as described above (see the ejection completion state in  FIG. 4B ). That is, when the sharp pressure change is caused by the gunpowder combustion, the pressure that exceeds the yield point of the metal material forming the sealing member  8  is applied to the sealing member  8 , and the sealing member  8  is plastically deformed. This means that the central portion  8   a  of the sealing member  8 , which has been displaced to the side opposite to the side of the initiator  20  with respect to the peripheral edge portion  8   b , cannot easily return to the side of the initiator  20 . Consequently, when the sealing member  8  presses the piston  6  using the gunpowder combustion, the sealing member  8  can be deformed while adequately resisting reaction from the piston  6 , and hence it becomes possible to effectively pressurize the injection solution ML via the piston  6  and the plunger  7 . 
     In the injector  1  configured to allow the ejection of the injection solution ML described above, the piston  6  is pressed by the sealing member  8  and the entire piston  6  is thereby caused to slide, whereby the ejection energy is transmitted directly to the plunger  7 . In particular, the sealing member  8  is made of metal and is formed into the plate-like shape, and hence the effective pressurization of the injection solution ML by the central portion  8   a  is allowed. In addition, in the injector  1 , the sealing member  8  is disposed so as to separate the combustion chamber  31  and the through hole  33  that are the internal spaces of the injector body  2  from each other, and seal the combustion product generated by the initiator  20  in the combustion chamber  31 . With this configuration, the combustion product does not enter the through hole  33 , whereby it is possible to prevent unfavorable action of the combustion product on the injection solution ML. 
     Second Embodiment 
       FIG. 5  shows a second embodiment of the described technology.  FIG. 5  shows the schematic configuration of the injector  1  according to the present embodiment in the pre-combustion state. Note that, in the present embodiment, configurations substantially identical to those in the first embodiment described above are designated by the same reference numerals, and the detailed description thereof will be omitted. 
     In the injector  1  of the present embodiment, a narrowed portion  3   a  is formed inside the first housing  3  such that the inner diameter of the combustion chamber  31  formed inside the first housing  3  is reduced with approach to the central portion  8   a  of the sealing member  8  from the side of the initiator  20  along the central axis of the injector  1 . With the narrowed portion  3   a , the inner diameter of the combustion chamber  31  at a position where the inner diameter is smallest becomes substantially equal to dl that is the outer diameter of the first end portion  6   a  of the piston  6 , and a passage  3   b  having a diameter of about dl is formed in the combustion chamber  31  at a position facing the first end portion  6   a . In the case where the combustion chamber  31  is formed in this manner, when the gunpowder is combusted in the initiator  20 , it becomes easier for the pressure by the combustion product to act intensively on the central portion  8   a  of the sealing member  8 . As a result, it becomes possible to efficiently bring the sealing member  8  in the pre-combustion state into the ejection completion state shown in  FIG. 4B , and the amount of gunpowder used in the initiator  20  can be thereby reduced. 
     Note that, in order to allow the combustion product concentrated as described above to act on the central portion  8   a  of the sealing member  8  that is in contact with the first end portion  6   a  of the piston  6 , it is preferable that a clearance between an end portion of the passage  3   b  on the side of the piston  6  and the central portion  8   a  of the sealing member  8  with which the first end portion  6   a  is in contact be as small as possible. Also, by forming the narrowed portion  3   a  such that the inner diameter of the passage  3   b  is smaller than dl, it becomes possible to cause the combustion product to act on the central portion  8   a  of the sealing member  8  more intensively. 
     Other Embodiments 
     According to the injector  1  of the described technology, in addition to the above-described case where the injection solution is injected into the skin structure, for example, in the field of regenerative medicine for humans, it becomes possible to inoculate cultured cells or stem cells into cells and scaffold tissue (scaffold) serving as injection targets. For example, as described in Japanese Patent Application Publication No. 2008-206477, it is possible to inject, by using the injector  1 , cells that can be appropriately determined by those skilled in the art according to a portion subjected to transplantation and the purpose of cell regeneration such as, e.g., an endothelial cell, an endothelial precursor cell, a myeloid cell, a preosteoblast cell, a chondrocyte cell, a fibroblast cell, a skin cell, a muscle cell, a liver cell, a kidney cell, an intestinal tract cell, and a stem cell, as well as every cell considered in the field of regenerative medicine. More specifically, by accommodating a solution (cell suspension) containing the cell to be inoculated in the accommodation chamber  35  and pressurizing the solution, a specific cell is injected and transplanted into the portion subjected to transplantation. 
     Further, the injector  1  according to the described technology can be used for delivery of DNA or the like to cells and scaffold tissue (scaffold) described in Japanese Translation of PCT Application No. 2007-525192. In this case, the use of the injector  1  according to the described technology is more preferable than the use of a needle in the delivery because the injector  1  can reduce influences on cells and scaffold tissue (scaffold). 
     Further, the injector  1  according to the described technology is suitably used in the case where various genes, cancer suppressing cells, or lipid envelopes are directly delivered to target tissue and in the case where an antigen gene is administered in order to enhance immunity against a pathogen. In addition, the injector  1  can also be used in the field of medical treatment of various diseases (field described in Japanese Translation of PCT Application No. 2008-508881 or Japanese Translation of PCT Application No. 2010-503616) and the field of immunological medical treatment (field described in Japanese Translation of PCT Application No. 2005-523679), and the field in which the injector  1  can be used is not intentionally limited. 
     Another example of the administration apparatus to which the described technology can be applied includes a catheter device. The catheter device has a catheter portion that can enter a living body, and is a device that ejects a desired chemical solution or the like to the living body from its tip portion. The invention of the present application can be applied to the configuration of the chemical solution ejection from the tip portion of the catheter portion. That is, in a state in which the catheter portion is inside the living body, by applying the described technology to the configuration thereof for the ejection of the chemical solution from the tip portion, it is possible to efficiently transmit energy by the gunpowder combustion in the initiator  20  to the chemical solution, and prevent the combustion product from acting on the chemical solution.