Hypodermic Syringe Assembly

Abstract

A hypodermic syringe assembly comprising a disposable injection unit and a reusable plunger unit adapted to cooperate for dispensing medicament from an elongated cartridge positioned in the injection unit. The disposable injection unit comprises a hub structure, a double pointed needle extending through the hub, and elongated and resilient guides extending rearwardly of the hub to form a barrel for receiving the cartridge. The guides are radially flexible with respect to one another at the rear end of the barrel. The reusable plunger unit comprises a plug having means to simultaneously circumferentially engage the interior and exterior of the barrel at its rear end. The plug is adapted to fit inside the barrel and be locked in circumferential and axial engagement therewith. An elongated plunger is axially movable through said plug and has piston engaging means at its forward end and retracting means at its rear end. The plunger unit also includes flange means for cooperating with the plug to hold the rear ends of the guides in a fixed radial position when the plunger is locked in position in the barrel.

Description

The present invention relates to elongated hypodermic syringes of the type suitable for administering dental anesthesia, and more particularly to such syringes which are adapted to receive a cartridge containing the medicament and dispense the medicament therefrom.

Heretofore this has been accomplished in the dental field, for instance, by utilizing a reusable syringe which must be resterilized before each use along with a cartridge containing anesthetic and a disposable needle. This means that it has been necessary for the dentist, not only to resterilize the syringe, but also to assemble the needle, the syringe, and the cartridge before each use. While some thought has been given to providing a completely disposable syringe and needle unit which is preloaded with the anesthetic, this has not proven to be practicable because the known anesthetics cannot withstand the commercial sterilization procedures necessary to sterilize the syringe prior to packaging. As a result, it has been necessary to load the anesthetic into cartridges in "white rooms" under sterile conditions, and to sterilize the syringe separately as indicated above.

The syringe of this invention comprises a presterilized disposable injection unit which basically consists of a syringe barrel and a double pointed needle affixed at its forward end, and a reusable plunger unit which need not be sterilized at any time. A conventional cartridge containing sterile medicament or anesthetic is inserted in the presterilized injection unit which then is assembled with the plunger unit prior to use. As a result, the cost of sterilizing the syringe before each use is eliminated and the cost of the disposable portion of the assembly is minimized because it does not include the plunger unit which is apt to be the most expensive.

In the hypodermic syringe assembly of this invention the disposable injection unit comprises an elongated barrel closed at its front end and open at its rear end to provide a mouth for receiving the cartridge. The front end of the barrel includes a hub structure which has a double pointed hollow needle passing axially through it in such a way that the front end of the needle extends outwardly of the barrel and the rear end of the needle extends inwardly of the barrel. In its preferred form, the barrel includes a plurality of angularly spaced elongated and resilient guide members extending rearwardly of the hub structure. A corresponding plurality of elongated slots are defined in the barrel in the angular spaces between these guide members. The barrel is formed from a flexible and resilient material such as polypropylene so that the guides themselves are capable of being flexed radially inwardly and outwardly at their rear ends. This facilitates insertion and removal of the cartridge in and from the barrel. Since the cartridge is normally in the form of a cylinder, the guide members normally also are in the form of cylindrical sections which conform to the shape of the cartridge.

The reusable plunger unit comprises a plug and flange combination which is adapted to fit into and over the rear ends of the guide members to fix them in position axially and provide a firm structure for operating the syringe. For this purpose, either the plug or the barrel, i.e. the guide members, is or are recessed to receive a portion presented by the other for locking the plug in position in the barrel. For instance, with the above-described spaced guide members the slots between the guides act as longitudinal recesses for receiving one or more ridges extending radially outwardly from the plug and the guide members include circumferential recesses into which the ridge or ridges may be turned to lock the plug in position in the barrel.

Other and further features and advantages of the invention will appear to one skilled in the art from the following description and claims taken together with the drawings wherein:

FIG. 1 is an exploded view in perspective of a hypodermic syringe assembly according to a preferred embodiment of this invention.

FIG. 2 is a somewhat enlarged view partly in section and partly in elevation of the syringe of FIG. 1 assembled with a cartridge in position therein and with the plunger advancing the piston at the rear end of the cartridge.

FIG. 3 is a similar view partly in section and partly in elevation taken along the line 3-3 of FIG. 2.

FIG. 4 is a more greatly enlarged sectional view taken along the same line as FIG. 5 but showing the position of the respective parts during insertion of the plug in the barrel.

FIG. 5 is a view at the same enlargement as that of FIG. 4 and taken along the line 5-5 of FIG. 3 to show the parts in the locked position of the plug in the barrel.

FIG. 6 is an enlarged sectional view of the front end of the barrel of the embodiment of the foregoing figures showing the structure of the hub prior to insertion of the needle.

FIG. 7 is a sectional view similar to that of FIG. 6, but showing a needle fixed in position in the hub.

Referring to the drawings, there is shown a hypodermic syringe assembly according to a preferred embodiment of this invention which comprises a disposable injection unit D consisting basically of an elongated barrel 11 and a double-ended needle 12, and a reusable plunger unit R consisting basically of a plug or gland 13 and a plunger 14 passing through the plug. The barrel is adapted to receive an elongated cartridge C containing liquid medicament such as a dental anesthetic. The cartridge C, in turn, consists of an elongated vial 15 of glass or other material with a rubber piston 16 closing its rear end and a necked front end closed by a rubber diaphragm 17 which is held in place by a flanged annular sleeve 18 of aluminum or a similar malleable material. As indicated hereinbefore, the cartridge C is presterilized and then filled with the sterile medicament under sterile conditions in a "white room" or the like. The contents of the cartridge then are maintained sterile by the rubber piston 16 at one end and rubber diaphragm 17 at the other end. The diaphragm 17 is adapted to be penetrated by the rear end of the needle 12 when the cartridge is pressed forward into the front end of the barrel, as shown most clearly in FIG. 2. The cartridge and its contents may be conventional in every respect with the exception that the piston 16 may include a threaded bolt 19 which is adapted to be engaged by the front end of the plunger 14, as shown most clearly in FIG. 2. The piston 16 may be molded over the bolt 17 or appropriately recessed to allow the bolt head to be inserted therein. The piston 16, as shown in the drawings, presents a series of three annular pressure rings 21 for contacting the side walls of the cartridge and maintaining tightness with respect thereto.

The barrel 11 of the disposable injection unit is open at its rear end to receive the cartridge C, as shown most clearly in FIG. 1, and closed at its front end by a hub structure 22 through which the double-pointed needle is inserted. The hub structure 22 and the remainder of the barrel are generally cylindrical in shape and the hub 22 is somewhat reduced in diameter to facilitate the positioning of a cylindrical needle cover or shield 23 which is closed at its front end and open at its rear end to fit over the outer surface of the hub. The needle cover 23 is held on the hub 22 by a press fit therewith and thereby protects the pointed end of the needle. As is shown most clearly in FIGS. 6 and 7, the hub 22 defines a generally cylindrical needle receiving opening 24 located approximately on the axis of the syringe. The diameter of this opening 24 is somewhat greater than the outer diameter of the needle 12 throughout most of its length and reduced at its rear end to approximately the outer diameter of the needle. However, the opening does not extend all the way through the hub 22 prior to insertion of the needle, but is separated from the interior of the barrel 11 by a thin membrane 25 until it reaches the desired axial position in the barrel. Then a resin or cement 26 which has a high bonding affinity for the needle is poured into the opening at its front end. The front end of the opening is flared outwardly at 27 for this purpose and the hub 22 includes an annular recess 28 in communication with the opening 24 to provide additional mechanical engagement between the hardened cement 26 and the structure of the hub to secure the needle firmly in position in the barrel. The needle 12 may be a conventional hollow steel hypodermic needle which is pointed at both ends and the barrel and hub structure preferably is formed of a tough and resilient plastic material such as polypropylene which also is flexible for reasons which will be explained hereafter. The cement 26 may be an epoxy or the like which is adapted to bond firmly to the steel of the needle.

The barrel 11 is in the form of an elongated cylinder which defines a pair of opposed longitudinal slots 29 open to the rear of the barrel. These two slots in turn define between them a pair of elongated, resilient and flexible guides 31 in the form of cylindrical sections extending rearwardly from the hub structure 22 and annularly spaced from one another by the slots 29. These guides 31, at their rear ends, define a mouth portion of the barrel which, in turn, is adapted to receive the plug 13 of the reusable plunger unit R. The cylindrical guide sections 31 are capable of radial flexure inwardly and outwardly at their rear ends to facilitate insertion and removal of the cartridge C in and from the barrel 11. Preferably, however, the normal positions of the guides 31 is such that they form an extension of the cylindrical front portion of the barrel, the inner diameter of which is slightly larger than the outer diameter of the cartridge but receives the cartridge snugly therein.

The plug 13 of the reusable plunger unit R is integral with flange means in the form of an annular rim 32 and is connected thereto by a rear portion 33 of the plug. The front portion of the plug 13 is tapered slightly to facilitate insertion of the plug in the barrel 11. The diameter of the plug 13 just rearwardly of the tapered section is such as to normally fit tightly inside the mouth of the barrel when the plug is locked in position in the barrel. However, since the opposed cylindrical guides 31 forming the mouth of the barrel are radially flexible, the annular rim 32 adjacent the rear of the plug 13 is adapted to embrace the ends of the guide members 31 to prevent them from moving radially outwardly away from the plug. To assure that the inner curved surfaces of the guide members 31 are pressed tightly against the plug 13, the corresponding mating outer surface portions 34 of the guide members 31 and the inner surface portions 35 of the annular rim 32 are inclined so that the rim 32 cams the guide members 31 tightly against the plug 13 as the plug is pressed into its final position in the barrel. To assure that the plug 13 remains in position to provide a firm structure for operating the syringe, corresponding locking means are provided on the plug and the guide members 31. These include a pair of opposed ridge portions 36 extending radially outwardly from the plug proper, the opposed axial slots 29 formed between the guide members 31, and correspondingly opposed circumferential recesses 37 in the guide members 31 facing their inner surfaces. Thus, when the plug 13 is being inserted in the barrel 11, the ridge portions 36 ride in the opposed slots 29 between the guide members 31, as shown most clearly in FIG. 4, until the ridges 36 reach the circumferential recesses 37 in the guide members. Then, the plug 13 is rotated about 90.degree. in either direction to turn the ridge portions 36 into the circumferential recesses 37, as shown most clearly in FIG. 5, to lock the plug in position in the barrel. For this purpose, the rearwardly facing surfaces of the ridge portions 36 and the corresponding frontwardly facing surfaces of the circumferential recesses 37 are inclined, as shown most clearly in FIG. 2, to provide an additional camming action in locking the plug 13 in position. The plug may be formed from a suitable metal or from a tough and resilient polymeric material such as nylon, or the like, as shown.

The plunger 14 is in the form of a cylindrical rod which passes through a corresponding cylindrical opening located approximately along the longitudinal axis of the plug 13. The rod is tapped and threaded at its front end for engagement with the threaded bolt 19 extending rearwardly from the rubber piston 16 at the rear of the cartridge C. A cylindrical thumb ring 38 is riveted to the rear end of the plunger rod, as shown most clearly in FIGS. 1 and 2. In addition, corresponding pairs of opposed finger grips 39 and 39' are molded integral with the rear end of the plug 13 and the guide members 31 respectively. The finger grips 39' on the guide members 31 are spaced from the rear ends of the guides by a distance intended to define the desired finger gripping space between the grips 39 on the plug and the grips 39' on the barrel when the plug is locked in position in the barrel, as shown most clearly in FIG. 2.

In operation, the user, such as a dentist, may open a sterile package, now shown, containing the disposable injection unit D only at the rear end of the unit and then insert a medicament-containing cartridge C, obtained from a sterile container, through the mouth of the barrel 11 and at least partially into position therein while holding the injection unit through the partially opened package. Then, the plug 13 of the reusable plunger unit R, which need not be sterilized, may be inserted into the rear end of the barrel in the manner described above and locked in position in the mouth of the barrel. The plunger 14 itself then is rotated to enter into full engagement with the bolt 19 extending rearwardly from the piston 16 in the cartridge. At this point, or prior thereto, the syringe may be removed from the package and the cover 23 may be removed from the front end of the syringe. Now the syringe is ready to operate either for injection or aspiration.

The cartridge C may be pressed forward as it is being placed in the syringe barrel 11 to the point where the rearwardly facing point of the needle 12 will penetrate the rubber diaphragm 17 in the front of the cartridge. However, one of the advantages of the plug-type gland 13 of this invention is that it also is designed to press the cartridge forward to its final position in the front of the barrel as the plug 13 is being inserted into position at the rear end of the barrel.

It will be noted that the position of the finger grips 39' adjacent the rear ends of the guide members 31 and 39 extending outwardly from the rear of the plug 13 make it possible to operate the syringe through these finger grips and the thumb ring 38 at the rear of the plunger, while allowing full insertion of the elongated syringe barrel 11 into the mouth of a patient for anesthesia under the most difficult conditions. It also should be noted that when this is done, it is only the sterile portions of the disposable injection unit D that come into contact with the patient. Another advantage of the syringe of this invention is that the finger grips 39' on the barrel and 39 on the plug are so positioned with respect to the slots 29 in the barrel and the ridges 36 on the plug that the ridges 36 are turned into the recesses 37 in the barrel when the grips 39 on the plug are longitudinally aligned with the grips 39' on the barrel, as shown in FIGS. 2 and 5. Thus, the plug 13 is locked in position in the barrel 11 when the finger grips 39 and 39' are aligned.

Having now described the invention in specific detail and exemplified the manner in which it may be carried into practice, it will be readily apparent to those skilled in the art that innumerable variations, applications, modifications, and extensions of the basic principles involved may be made without departing from its spirit or scope.

Claims

We claim:

1. A hypodermic syringe assembly which comprises a disposable injection unit and a reusable plunger unit adapted to cooperate to dispense medicament from an elongated medicament-containing cartridge positioned in the injection unit; said disposable injection unit comprising an elongated barrel closed at its front end and open at its rear end to provide a mouth for receiving said cartridge, said barrel comprising a hub structure at its front end for receiving a hypodermic needle and a plurality of angular spaced elongated and resilient guides extending rearwardly from the hub structure, said guides being radially flexible with respect to one another at the rear of said barrel, and a double pointed hollow needle mounted in said hub with its front end extending outwardly of the barrel and its rear end extending inwardly of the barrel; said reusable plunger unit comprising a plug having means to simultaneously circumferentially engage the interior and exterior of said barrel at the mouth end and adapted to fit in the mouth of said barrel and be locked in circumferential and axial engagement therewith, and an elongated plunger passing longitudinally through said plug whereby an elongated medicament-containing cartridge having a piston at its rear end axially slideable therein may be inserted in said barrel through said mouth, said plug may be positioned in said mouth in radial and axial engagement therewith, and said plunger may be engaged with said piston for advancing and retracting the piston to aspirate and dispense medicament from the syringe.

2. A hypodermic syringe assembly according to claim 1, wherein said plug has a ridge portion and presents a generally cylindrical outer surface for insertion in the mouth of said barrel and at least one of said guides is circumferentially recessed to receive said ridge portion presented by the plug for locking said plug in position in the barrel, said guides defining an axially extending slot between them for cooperating with said ridge portion in inserting said plug in said barrel.

3. A hypodermic syringe assembly according to claim 2, wherein said means to engage the exterior of said barrel comprises flange means adapted to embrace the rear ends of said guides and prevent their further movement radially outwardly when said plug is locked in position in said barrel.

4. A hypodermic syringe assembly according to claim 3, wherein said flange means is in the form of an annular rim.

5. A hypodermic syringe assembly according to claim 3, wherein said flange means is integral with said plug.

6. A hypodermic syringe assembly according to claim 1, wherein said barrel and said plunger unit each present opposed finger grips adapted to cooperate with one another for operating the syringe when said plug is in position in said barrel.

7. A hypodermic syringe assembly according to claim 6 wherein said finger grips and said ridge portion are so located with respect to the recess in said barrel that the plug is locked in position in said barrel when the finger grips on said barrel are angularly aligned with the finger grips on said plunger unit.