Autoinjector

Details Autoinjector Autoinjector

1999-10-04

2001-08-07

Mendez, Manuel (Department: 3763)

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

Reexamination Certificate

active

06270479

ABSTRACT:

TECHNICAL FIELD
An autoinjector for replaceable containers of syringe type, comprising a barrel of axially roughly constant cross-section, a front opening with or for an injection needle and at least one movable rear piston, optionally with a plunger connected thereto, inserted in the barrel for the displacement of a container content, the autoinjector comprising a) a housing, b) a container carrier, arranged for reception of the container and arranged movably in relation to the housing in container axial direction between a rear, needle-covering, position and a forward, needle-exposing, position, c) an autopenetration mechanism, comprising at least a penetration head and a penetration drive, the penetration head being arranged for movement of the barrel or carrier in the forward direction and the penetration drive being operable to apply force between the housing and the penetration head, d) an autoinjection mechanism, comprising at least an injection head and an injection drive, the injection head being arranged for movement of the piston or plunger in the forward direction and the injection drive being operable to apply force between the housing or the carrier and the injection head, e) optionally an autoreturn mechanism operable to apply force between the housing and the barrel or carrier for movement thereof in the rearward direction and f) a control system for sequencing the operation of at least the autopenetration and autoinjection mechanisms, at least comprising a releasable penetration lock for the autopenetration mechanism and a releasable injection lock for the autoinjection mechanism.
BACKGROUND
Autoinjectors are designed to facilitate injection procedures over those required by manual use of common syringes and to secure a proper injection result highly independent of operational circumstances. Autoinjectors are typically used in non-hospital environments, sometimes in emergency situations, and by non-professionals like unskilled assistants or the patients themselves, which operator groups may include sick, disabled, elderly and child persons. The autoinjectors provide at least an automatic injection step in which stored energy, for example from a compressed spring, is released by a trigger to act on a syringe piston or plunger for expulsion of syringe content. Frequently the autoinjectors also provide an automatic penetration step in which stored energy is used for propulsion of the syringe from a rear position, in which the needle is hidden, to a front position, in which the needle is at least partially exposed, to thereby relieve the patient from the, sometimes fearful, task of inserting the needle through the skin and to secure an always appropriate penetration depth once the autoinjector front has been placed against the skin. Autopenetration and autoinjection may take place concurrently, e.g. in simple devices or for the intentional purpose of allowing for an over depth distributed injection. Normally it is desirable to limit injection until the needle has reached or is close to its target location. Still some known injectors try to obtain this feat with a single force system acting on syringe piston or plunger for both purposes, relying for sequencing on the normally lower needle penetration resistance than fluid ejection flow resistance. Yet impact, propulsion inertia and friction cannot prevent at least some leakage during penetration but above all, in case the penetration movement is prevented or jams, injection will entirely fail with preparation expelled on the skin or at improper depth. Hence more advanced injectors applies penetration force directly or indirectly on the syringe barrel, with single or dual drive systems, which requires some control mechanism disabling injection force application during most of the penetration phase and enabling injection force only after proper penetration. Autoinjectors may also provide an automatic needle retraction step in which stored energy, typically stored during the penetration movement in a weaker return counter-spring, acts to push the syringe back into the autoinjector after completed injection in order to relieve the user from the task and risk of withdrawal, to verify sequence completion to the user and to prevent inadvertent needle pricks after use. Again, this function may need a control mechanism enabling action of the return spring only after completed injection, normally accomplished by separation of the penetration and injection forces from the syringe at a certain forward extreme for the piston or plunger, freeing the return spring for action.
Most known autoinjectors are designed for use with a single syringe type or even a single specialized and adapted syringe type container in order to meet the various tolerance in dimensions, sizes and forces involved and these requirements become more pronounced when more of the advanced features outlined above are included in the injector. Yet there is a need for autoinjectors able to operate with a variety of syringe sizes, filling degrees, preparation viscosities, aging properties, temperature conditions, needles and flow characteristics. A manufacturer of a broad range of preparations may need a device useful for many container types and doses. Low cost preparations in particular cannot support development of a unique device or syringe container of its own and furthermore may require use of cheap standardized syringe types on the market with a selected minimum size for each dose. Patients on prescription of several pharmaceuticals may benefit from replacement of several devices for a single universal one. Manufacturers of injectors may find a broader market for their autoinjectors if compatible with container variations.
The above objects meet with numerous problems. Variations in size first require a syringe seat or carrier, not only able to accommodate and guide the various container movements with small lateral deviations, but also to secure appropriate start and end positions with respect to both the injector front and the injector mechanism. Variations in length or filling degree means differences in start positions for penetration and injection, either requiring a complicated device with adaptable start positions or long worst case dead runs for the mechanism, creating strong and potentially destructive impact forces or painful injection rates. The force requirements are highly variable. Variations in diameter, for example, means variations in injection force due to differences in piston cross-section surface, even at similar hydraulic flow pressures, as well as differences in piston to wall friction. Further broadening in force requirements is caused by differences in flow characteristics, such as resistance and obstructions in syringe opening, needle lengths or diameters as well as receiving tissue, and by differences in piston to wall friction, even at constant diameter, due to manufacturing tolerances and aging, typically resulting in increased friction due to an ongoing depletion of lubricant in the piston to wall contact surface. It is also well known that the first piston displacement requires a much higher “break-loose” force than continued motion. An again increased force may be desirable at the piston bottoming out to fully squeeze out container content, of special value at precise dosing or for expensive preparations. If the autoinjector drive systems are proportioned for the highest force required by all the abovesaid factors combined, they tend to be excessively strong for less demanding combinations, besides becoming generally bulky and ungainly. Applied in the penetration step the forces may damage or destroy smaller or weaker glass containers and counteract a safe penetration due to vibrations, shaking, recoil and rebound effects. Applied to the injection step extreme pressures may damage the container itself, deform the piston or blow away front sealing or attachments and most probably cause pain and bruises in the receiving tissue. As indicated above all these problems are exaggerated if the high forces are combined with inertia

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