Patent Publication Number: US-2021162134-A1

Title: Microsyringe unit

Description:
TECHNICAL FIELD 
     The present invention relates to a microsyringe unit including a microsyringe and a needle guide. 
     BACKGROUND ART 
     There has been proposed a microsyringe for injecting a liquid such as a drug or a tissue piece or therapeutic cell preparation composition into a target area of a patient&#39;s brain (refer to Patent Literature 1). With the tip of a cylindrical needle in the liquid such as a drug, the plunger that is passed through the inside of the needle moves backward from the tip of the needle, by which the liquid is inhaled inside the needle. With the needle that is passed through the needle guide constituting the needle guide whose tip is inserted into the patient&#39;s brain, the plunger passed through the needle moves forward, by which the liquid is ejected from the tip of the needle. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Utility Model Application Laid-Open No. S51-44389 
     SUMMARY OF INVENTION 
     Technical Problem 
     If, however, the liquid ejected from the tip of the needle comes into contact with the tip of the needle guide, the liquid is more likely to spread outward in the radial direction of the needle accordingly, by which it may be difficult to accurately eject the liquid in front of the needle and thus to accurately inject the liquid into the target area in the brain. 
     Therefore, it is an object of the present invention to provide a microsyringe unit capable of improving the accuracy of the injection position of liquid in a brain. 
     Solution to Problem 
     The present invention relates to a microsyringe unit composed of a microsyringe that includes a cylindrical needle and a plunger that is passed through the needle, and a cylindrical needle guide. 
     According to an aspect of the present invention, there is provided a microsyringe unit wherein the base portion of the needle abuts on a guide base portion that supports the needle guide, thereby causing the tip of the needle to protrude from the tip of the needle guide in a first specified state in which forward movement of the needle passed through the needle guide is stopped. 
     According to the microsyringe unit having the above configuration, the tip of the needle is separated from the tip of the needle guide in the first specified state, thereby ensuring that the liquid such as a drug ejected from the tip of the needle does not come into contact with the tip of the needle guide to spread in the radial direction of the needle. This allows the liquid ejected from the tip of the needle to be accurately ejected in front of the needle and thus the liquid to be accurately injected into a target area in a brain. 
     In the microsyringe unit of the present invention, preferably the tip of the needle has a convex curved surface whose outer diameter gradually decreases toward the tip. 
     According to the microsyringe unit having the above configuration, a gap is secured between the convex curved surface at the tip of the needle and a tissue of the brain, thereby enabling the liquid ejected from the tip of the needle to be retained in the gap to suppress the radial spread of the liquid. This further ensures that the liquid does not come into contact with the tip of the needle guide to spread in the radial direction of the needle. 
     In the microsyringe unit of the present invention, preferably the surface roughness of the convex curved surface of the tip of the needle is greater than the surface roughness of the outer side surface of the needle. 
     According to the microsyringe unit having the above configuration, the tip of the needle is hydrophilic, thereby enabling the wetness of the outer side surface of the tip to be lower than the wetness of the convex curved surface, the liquid ejected from the tip of the needle to be retained in the gap between the convex curved surface of the tip of the needle and the tissue of the brain, and the liquid to be prevented from spreading radially along the outer side surface of the needle. This more reliably prevents the liquid from coming into contact with the tip of the needle guide and spreading in the radial direction of the needle. 
     In the microsyringe unit of the present invention, preferably the tip of the needle guide has a convex curved surface whose outer diameter gradually decreases toward the tip, and the radius of curvature of the convex curved surface of the tip of the needle is greater than the radius of curvature of the convex curved surface of the tip of the needle guide. 
     According to the microsyringe unit having the above configuration, a large gap is secured between the convex curved surface of the tip of the needle and the tissue of the brain due to the radius of curvature of the convex curved surface of the tip of the needle greater than the radius of curvature of the convex curved surface of the tip of the needle guide accordingly, thereby enabling more liquid to be retained in the gap to prevent radial spread of the liquid. Moreover, the radius of curvature of the convex curved surface of the tip of the needle guide is smaller than the radius of curvature of the convex curved surface of the tip of the needle, thereby reliably preventing the tip of the needle guide from damaging the brain tissue accordingly. 
     In the microsyringe unit of the present invention, preferably the microsyringe unit further includes a stylet that is passed through the needle guide and is columnar at least in the tip, wherein the base portion of the stylet abuts on the guide base portion that supports the needle guide, thereby causing the tip of the stylet to protrude from the tip of the needle guide in a second specified state in which forward movement of the stylet passed through the needle guide is stopped. 
     According to the microsyringe unit having the above configuration, the tip of the stylet protruding from the needle guide that is fixed while entering the patient&#39;s brain deviates the tissue of the brain in the second specified state, thereby enabling formation of a space for the tip of the needle protruding from the needle guide to enter in the first specified state that is implemented after the second specified state. 
     In the microsyringe unit of the present invention, preferably the tip of the stylet has a convex curved surface whose outer diameter gradually decreases toward the tip and the radius of curvature of the convex curved surface of the tip of the stylet is greater than the radius of curvature of the convex curved surface of the tip of the needle guide. 
     According to the microsyringe unit having the above configuration, the radius of curvature of the convex curved surface of the tip of the stylet is greater than the radius of curvature of the convex curved surface of the tip of the needle guide, thereby preventing the tissue of the brain from being damaged accordingly with the brain deviated by the tip of the stylet protruding from the needle guide that is fixed while entering the patient&#39;s brain in the second specified state. 
     In the microsyringe unit of the present invention, preferably the protruding length of the stylet from the tip of the needle guide in the second specified state is equal to or greater than the protruding length of the needle from the tip of the needle guide in the first specified state. Thereby, a cell injection space can be secured since a space is formed in the brain for the volume caused by a difference in protruding length between the stylet and the needle. 
     According to the microsyringe unit having the above configuration, the tip of the stylet deviates the brain&#39;s tissue as described above, thereby enabling a sufficient space for the tip of the needle to be formed. 
     In the microsyringe unit of the present invention, preferably the tip of the plunger has a convex curved surface whose outer diameter gradually decreases toward the tip and the radius of curvature of the convex curved surface of the tip of the plunger is smaller than the radius of curvature of the convex curved surface of the tip of the needle. 
     According to the microsyringe unit having the above configuration, the radius of curvature of the convex curved surface of the tip of the plunger is smaller than the radius of curvature of the convex curved surface of the tip of the needle, thereby enabling a gap between the tip of the plunger and the inner side surface of the needle to be reduced accordingly with the tip position of the plunger matching the tip position of the needle. Therefore, when the plunger is pushed in until the tip position of the plunger matches the tip position of the needle, the amount of liquid that stays in the gap is reduced and thus the amount of liquid ejected from the tip of the needle can be accurately adjusted. 
     In the microsyringe unit of the present invention, preferably at least a part of the needle is composed of a transparent member. 
     According to the microsyringe unit having the above configuration, when the plunger passed through the needle whose tip is in contact with the liquid moves backward, whether the liquid has been properly contained in the internal space of the needle can be seen from the part composed of a transparent member of the needle. 
     In the microsyringe unit of the present invention, preferably the microsyringe unit further includes a cylindrical packing that is arranged so as to abut on the side wall of a through hole penetrating the base portion of the needle and having a narrow portion that narrows toward the tip inside the through hole and so as to abut on the narrow portion at the tip and that the plunger is passed through. 
     According to the microsyringe unit having the above configuration, the liquid can be prevented from entering the space on the rear side of the packing in the internal space of the needle. 
     In the microsyringe unit of the present invention, preferably the needle guide has at least one stepped portion where its outer diameter decreases discontinuously from the rear end side to the tip side. 
     Thereby, in the needle guide, the outer diameter of the tip side part that is thinner than the rear end side part across the stepped portion and is continuous with the tip can be designed within an appropriate numerical range from the viewpoint of being inserted into the brain. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram related to the configuration of a microsyringe unit as an embodiment of the present invention. 
         FIG. 2  is an enlarged explanatory diagram of a part A in  FIG. 1 . 
         FIG. 3  is an enlarged explanatory diagram of a part B in  FIG. 1 . 
         FIG. 4  is an enlarged explanatory diagram of a part C in  FIG. 1 . 
         FIG. 5  is an explanatory diagram related to the configuration of a syringe outer cylinder and a plunger guide. 
         FIG. 6  is an explanatory diagram related to the configuration of a plunger and a syringe inner cylinder. 
         FIG. 7  is an explanatory diagram related to the configuration of a stylet. 
         FIG. 8  is an explanatory diagram related to a combination usage of the stylet and the needle guide. 
         FIG. 9  is an enlarged explanatory diagram of a part D in  FIG. 8 . 
         FIG. 10  is an enlarged explanatory diagram of a part E in  FIG. 8 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     (Configuration) 
     A microsyringe unit as an embodiment of the present invention, which is illustrated in its entirety in  FIG. 1  and whose essential parts are respectively illustrated in  FIGS. 2 to 4 , is composed of a microsyringe  100  and a needle guide  200 . For description, the right side of  FIGS. 1 to 4  is defined as the tip side or front side of the microsyringe  100  and of the needle guide  200 , and the left side is defined as the rear end side or rear side of the microsyringe  100  and of the needle guide  200 . 
     As illustrated in  FIG. 1 , the microsyringe  100  includes a needle  110 , a plunger  120 , a needle base portion  130 , a syringe outer cylinder  140 , an outer cylinder  151 , and a syringe inner cylinder  152 . Each of the needle  110 , the plunger  120 , the needle base portion  130 , the outer cylinder  151 , and the syringe inner cylinder  152  is made of metal such as stainless steel. The syringe outer cylinder  140  is made of transparent glass, synthetic resin, or the like. 
     As illustrated in  FIG. 2 , the needle base portion  130  is composed of a first base element  131 , a second base element  132 , and a third base element  133 . The first base element  131  is a substantially truncated cone-like part extending along the central axis line and having a through hole whose diameter is substantially equal to or slightly smaller than the outer diameter of the needle  110 . The second base element  132  is a substantially cylindrical part having an inner diameter that is greater than the diameter of the through hole of the first base element  131  and having an outer diameter that is locally expanded at the rear end. The third base element  133  is a substantially cylindrical part having an inner diameter that is substantially equal to or greater than the outer diameter of the second base element  132  and having an outer diameter that is substantially equal to the rear end of the second base element  132 . The first base element  131 , the second base element  132 , and the third base element  133  are arranged coaxially and formed integrally so that the tip of the second base element  132  is continuous with the rear end (or lower bottom) of the first base element  131  and the tip of the third base element  133  is continuous with the enlarged diameter portion at the rear end of the second base element  132 . 
     As illustrated in  FIG. 1 , the needle  110  has a substantially cylindrical shape or has a cross section that is formed in a substantially annular linear shape, and is fixed to the needle base portion  130  with its rear end inserted into the through hole of the first base element  131 . As illustrated in  FIG. 4 , the tip of the needle  110  may be R-processed so that the outer diameter of the tip of the needle  110  gradually decreases or becomes thinner toward the tip, thereby forming a convex curved surface (R surface). The radius of curvature R 110  of the convex curved surface of the tip of the needle  110  is designed to be, for example, within the range of R0.05 to 0.15 mm. 
     The surface roughness of the convex curved surface of the tip of the needle  110  may be designed to be greater than the surface roughness of the outer side surface of the needle  110 . For example, the surface roughness Ra of the convex curved surface of the tip of the needle  110  is designed to be within the range of 1.0 to 6.0 μm, preferably 1.0 to 4.0 μm, and more preferably 1.0 to 2.0 μm, while the surface roughness Ra of the outer side surface of the tip of the needle  110  is designed to be within the range of 0.04 to 1.0 μm, preferably 0.04 to 0.50 μm, and more preferably 0.04 to 0.10 μm. In this case, it is preferable to make the tip of the needle  110  hydrophilic. For example, the tip of the needle  110  can be made hydrophilic by imparting a hydrophilic functional group to the needle  110  made of SUS or of synthetic resin by plasma treatment or the like. 
     As illustrated in  FIG. 3 , the plunger  120  has a diameter slightly smaller than the inner diameter of the needle  110  and is formed in a substantially columnar shape longer than the needle  110  or in a linear shape with a substantially circular cross section, and the plunger  120  is passed through the internal space of the needle  110 . As illustrated in  FIG. 4 , the tip of the plunger  120  may be processed (R-processed) so that the diameter of the plunger  120  gradually decreases as it approaches the tip to form a convex curved surface (R surface). The radius of curvature R 120  of the convex curved surface of the tip of the plunger  120  is designed to be, for example, within the range of R0 to 0.15 mm. A substantially columnar plunger holder  122  is attached to the rear end of the plunger  120 . 
     As illustrated in  FIG. 2 , the syringe outer cylinder  140  is made of substantially cylindrical transparent glass, synthetic resin, or the like having an outer diameter substantially equal to the inner diameter of the third base element  133  of the needle base portion  130 . Similarly, as illustrated in  FIG. 2 , the inner diameter of the syringe outer cylinder  140  is substantially equal to the inner diameter of the second syringe base portion, and the syringe outer cylinder  140  is fixed to the needle base portion  130  with the tip inserted into the third base element  133  of the needle base portion  130 . As illustrated in  FIG. 1 , a substantially flat-shaped plunger guide  142  having a through hole is fixed to the rear end of the syringe outer cylinder  140 . 
     As illustrated in  FIG. 5 , the plunger guide  142  is formed in a shape in which the outer part of a chord (a shape like the alphabetical letter “D”) of a circle is cut out from the circle when facing the microsyringe  100  in the front-back direction. On the outer peripheral surface of the syringe outer cylinder  140 , a scale  1402  may be provided to indicate the amount of liquid inhaled by the needle  110  (or the amount of advance and retreat of the plunger  120  with respect to the needle  110 ) in the outer peripheral surface region corresponding to the side opposite to the chord with respect to the center of the circle in the cross section of the plunger guide  142  or in the outer peripheral surface region deviated in the circumferential direction therefrom. 
     As illustrated in  FIG. 2 , the outer cylinder  151  is formed in a substantially cylindrical shape having an inner diameter greater than the diameter of the plunger  120  and having an outer diameter substantially equal to the inner diameter of the second base element  132  of the needle base portion  130 . Also as illustrated in  FIG. 2 , the outer cylinder  151  is fixed to the needle base portion  130  in a state where the plunger  120  penetrates the internal space of the outer cylinder  151  and a tip-side part of the outer cylinder  151  is partially passed through the internal space of the second base element  132  of the needle base portion  130 . 
     As illustrated in  FIG. 2 , in the internal space of the second base element  132  of the needle base portion  130 , there is provided a syringe packing  134  that abuts on the step between the tip of the outer cylinder  151  and the through hole of the first base element  131 . As illustrated in  FIG. 2 , the syringe packing  134  is made of a cylindrical and flexible material such as synthetic resin that has an outer peripheral surface shaped so that the diameter gradually decreases from the tip to the center and then gradually increases from the center to the rear end or has a drum-shaped outer peripheral surface and that has an inner diameter substantially equal to the diameter of the plunger  120 . 
     The syringe inner cylinder  152  is formed in a substantially cylindrical shape having an inner diameter that is substantially equal to or slightly greater than the diameter of the plunger  120  and having an outer diameter that is substantially equal to the through hole of the plunger guide  142  (and smaller than the outer diameter of the outer cylinder  151 ). As illustrated in  FIG. 6 , the syringe inner cylinder  152  is fixed to the plunger holder  122  at the rear end by the plunger  120  penetrating its internal space on the rear side of the outer cylinder  151 . As illustrated in  FIG. 1 , the syringe inner cylinder  152  penetrates the through hole of the plunger guide  142 . Therefore, when the plunger holder  122  moves forward and backward relative to the syringe outer cylinder  140 , the plunger  120  and the syringe inner cylinder  152  move forward and backward integrally through the through hole of the plunger guide  142  (see  FIGS. 1 and 6 ). 
     As illustrated in  FIG. 2 , with the tip of the syringe inner cylinder  152  and the rear end of the outer cylinder  151  in contact with each other, the tip of the needle  110  and the tip of the plunger  120  are aligned in the same position in their axial directions. 
     As illustrated in  FIG. 8 , the needle guide  200  is composed of an inner needle guide  210  and an outer needle guide  220  and is supported by a guide base portion  230 . The inner needle guide  210 , the outer needle guide  220 , and the guide base portion  230  are each made of metal such as stainless steel. At least one of the inner needle guide  210 , the outer needle guide  220 , and the guide base portion  230  may be made of thermosetting resin. 
     As illustrated in  FIG. 9 , the guide base portion  230  is formed in a substantially cylindrical shape in which an internal space on the front side is formed in a substantially columnar shape and an internal space on the rear side contiguous thereto is formed in a substantially truncated cone-like shape. As also illustrated in  FIG. 9 , the internal space on the rear side of the guide base portion  230  has an upper bottom with a smaller diameter than the internal space on the front side and than the upper bottom of the first base element  131  of the needle base portion  130 , has a lower bottom with a greater diameter than the lower bottom of the first base element  131 , and has an inner side surface shape that follows the outer side surface shape of the first base element  131 . 
     As illustrated in  FIG. 9 , the inner needle guide  210  is formed in a substantially cylindrical shape having an outer diameter smaller than the diameter of the internal space on the front side of the guide base portion  230  and having an inner diameter substantially equal to the outer diameter of the needle  110 . As illustrated in  FIG. 10 , the tip of the inner needle guide  210  may be processed (R-processed) so that the outer diameter of the inner needle guide  210  gradually decreases as it approaches the tip to form the convex curved surface (R surface) (see  FIG. 4 ). The radius of curvature R 210  of the convex curved surface of the tip of the inner needle guide  210  is designed to be, for example, within the range of R0.05 to 0.15 mm. 
     There may be a magnitude relation between the radius of curvature R 110  of the convex curved surface of the tip of the needle  110 , the radius of curvature R 120  of the convex curved surface of the tip of the plunger  120 , and the radius of curvature R 210  of the convex curved surface of the tip of the inner needle guide  210  as represented by the relational expression (1). 
       R 120 &lt;R 210 &lt;R 110    (1)
 
     As illustrated in  FIG. 9 , the outer needle guide  220  is formed in a substantially cylindrical shape, which is shorter in the axial direction than the inner needle guide  210 , having an outer diameter substantially equal to the diameter of the internal space on the front side of the guide base portion  230  and having an inner diameter substantially equal to the outer diameter of the inner needle guide  210 . Therefore, the needle guide  200  has a step in the outer diameter as illustrated in the part B of  FIG. 1  and in  FIG. 3 . The outer needle guide  220  may be processed (R-processed) so that the outer diameter gradually decreases or becomes thinner as approaching the tip in the tip part. 
     Each of the inner needle guide  210  and the outer needle guide  220  has a wall thickness that ensures enough strength to prevent bending thereof as it is longer in the axial direction. In the case where each of the inner needle guide  210  and the outer needle guide  220  is made of, for example, stainless steel, its wall thickness is designed to be, for example, within the range of 0.1 to 1.0 mm, preferably 0.1 to 0.5 mm, and more preferably 0.2 to 0.5 mm. 
     As illustrated in  FIG. 9 , the inner needle guide  210  is fixed to the outer needle guide  220  in a state that the rear side part of the inner needle guide  210  is passed through the internal space of the outer needle guide  220  so that the rear end of the inner needle guide  210  is located at the same position as the rear end of the outer needle guide  220  in the axial direction. Also illustrated in  FIG. 9 , the outer needle guide  220  is fixed to the guide base portion  230  with its rear end passed through the internal space on the front side of the guide base portion  230 . 
     The microsyringe unit as an embodiment of the present invention may further include a stylet  400  illustrated in  FIG. 7 . As illustrated in  FIG. 7 , the stylet  400  includes a substantially columnar shaft  410  that is passed through the inner needle guide  210  and a substantially columnar base portion  420  that has a diameter greater than the diameter of the shaft  410  and supports the shaft  410 . As illustrated in  FIG. 8 , the stylet  400  is passed through the needle guide  200 . 
     As illustrated in  FIG. 9 , the base portion  420  of the stylet  400  abuts on the guide base portion  230  supporting the needle guide  200 , thereby stopping forward movement of the stylet  400  passed through the needle guide  210  and of its shaft  410 . In this state (second specified state), the tip of the shaft  410  of the stylet  400  protrudes from the tip of the needle guide  200  as illustrated in  FIG. 10 . As illustrated in  FIG. 10 , the tip of the shaft  410  of the stylet  400  may have a convex curved surface (R surface) such that the outer diameter gradually decreases toward the tip (see  FIG. 10 ). There may be a magnitude relation represented by a relational expression (2) between the radius of curvature R 410  of the convex curved surface of the tip of the shaft  410  of the stylet  400  and the radius of curvature R 210  of the convex curved surface of the tip of the inner needle guide  210 . 
       R 210 &lt;R 410    (2)
 
     (Functions) 
     At the time of brain surgery, the needle guide  200  in the second specified state is inserted into a brain, first. At this time, the tip position and posture of the needle guide  200  are determined by the needle guide  200  supported by a support mechanism (not illustrated). In the “second specified state,” the substantially columnar stylet  400  is passed through the internal space of the needle guide  200  (that is, the inner needle guide  210 ), and the base portion  420  of the stylet  400  abuts on the guide base portion  230 , by which forward movement of the stylet  400  is stopped (see  FIGS. 8 and 9 ). In the second specified state, the tip of the shaft  410  of the stylet  400  protrudes from the tip of the needle guide  200  by a protruding length p (see  FIG. 10 ), and the tip of the shaft  410  of the stylet  400  deviates a tissue of the patient&#39;s brain, by which a minute space is secured in the brain by that amount. The stylet  400  is then pulled out of the needle guide  200  supported by the support mechanism. 
     Subsequently, the needle  110  of the microsyringe  100  with a liquid containing a therapeutic composition inhaled at the tip in advance is passed through the needle guide  200  supported by the support mechanism. The substantially truncated cone-like lateral inner side surface that defines the internal space on the rear side of the guide base portion  230  constitutes a tapered surface that approaches the central axis line of the guide base portion  230  as it goes forward in the longitudinal section (See  FIG. 2 ). Due to this tapered surface, the needle  110  is smoothly guided to the internal space of the inner needle guide  200 , and the first base element  131  of the needle base portion  130  is smoothly guided to the internal space on the rear side of the guide base portion  230 . 
     The needle base portion  130  and the guide base portion  230  are moved relative to each other so that they are closer to each other with the needle  110  passed through the needle guide  200 , by which the tip of the second base element  132  of the needle base portion  130  abuts on the rear end of the guide base portion  230  (see  FIG. 2 ). In addition thereto, the outer side surface of the first base element  131  of the needle base portion  130  may abut on the inner side surface of the internal space of the rear side of the guide base portion  230 . Thereby, there is implemented a “first specified state” in which forward movement of the needle  110 , which is passed through the needle guide  200 , is stopped (see  FIG. 1 ). 
     In the first specified state, a part of the needle  110  protrudes from the tip of the needle guide  200  (that is, the inner needle guide  210 ) (see  FIG. 4 ), and then the needle  110  enters the minute space in the brain secured by the tip of the shaft  410  of the stylet  400  as described above. At this time, the plunger  120  is located behind the position illustrated in  FIG. 4 , and the internal space of the needle  110  is filled with a liquid such as a cell preparation composition on the tip side of the plunger  120 . 
     The protruding length q of the needle  110  is equal to or similar to the protruding length p of the shaft  410  of the stylet  400 . The protruding length q of the needle  110  is within the range of 1d to 30d, for example, with respect to the maximum wall thickness d of the inner needle guide  210 , and when d=0.15 mm, q=0.15 to 4.5 mm. The protruding length q of the needle  110  is preferably within the range of 2d to 15d, more preferably 5 to 10d. The protruding length p of the shaft  410  of the stylet  400  is within the range of 1d to 30d, for example, with respect to the maximum wall thickness d of the inner needle guide  210 , and when d=0.15 mm, q=0.15 to 4.5 mm. The protruding length p of the stylet  400  is preferably within the range of 3d to 16d, more preferably 6 to 11d. 
     When the plunger holder  122  moves forward relative to the syringe outer cylinder  140  in this state, the plunger  120  moves forward and a liquid such as a cell preparation composition is injected into the minute space in the brain from the opening at the tip of the needle  110  (see  FIG. 4 ). Since the tip of the needle  110  is separated from the tip of the needle guide  200  in the first specified state (see  FIG. 4 ), a liquid such as a cell preparation composition ejected from the tip of the needle  110  comes into contact with the tip of the needle guide  200  (that is, the inner needle guide  210 ), thereby reliably preventing the situation in which the liquid spreads in the radial direction of the needle  110 . This allows the liquid ejected from the tip of the needle  110  to be accurately ejected in front of the needle  110  and thus the liquid to be accurately injected into a target area in the brain. 
     (Other Embodiments of the Present Invention) 
     At least a part of the needle  110 , especially the tip thereof, may be formed of an acrylic or other transparent member. Thereby, when the plunger  120  inserted into the needle  110  whose tip is in contact with the liquid moves backward, whether the liquid has been properly contained in the internal space of the needle  110  can be seen from the part composed of the transparent member of the needle  110 . 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           100  Microsyringe 
           110  Needle 
           120  Plunger 
           122  Plunger holder 
           130  Needle base portion 
           134  Syringe packing 
           140  Syringe outer cylinder 
           142  Plunger guide 
           151  Outer cylinder 
           152  Syringe inner cylinder 
           200  Needle guide 
           210  Inner needle guide 
           220  Outer needle guide 
           230  Guide base portion 
           400  Stylet 
           410  Shaft 
           420  Stylet base portion