Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
1997-07-03
2001-10-16
Nguyen, Anhtuan T. (Department: 3763)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S209000
Reexamination Certificate
active
06302869
ABSTRACT:
The invention relates to flexible piston rods for injection syringes.
Injection syringes are mainly provided with a rigid piston rod by which a piston is pressed into one end of a cartridge to press out the content of said cartridge through an injection needle mounted at the other end. Such injection syringes will mainly have a length which is at least twice the length of the cartridge.
To provide shorter syringes flexible piston rods have been proposed. As used in the specification and claims, the term “flexible piston rod” refers to a piston rod which may be deflected so that its; outer end lies parallel with the cartridge next to this cartridge and not in axial continuation thereof.
WO 95/09021 describes a flexible piston rod for a syringe comprising a cartridge holder and a dose setting part. Set doses are pressed out of the cartridge by a flexible piston rod which is deflected 180° by a piston rod guide placed immediately behind the cartridge. As the syringe is of the type in which an empty cartridge may be replaced by a new one after the piston rod has been retracted from the empty cartridge, the piston rod guide must be so designed that it can support the piston rod both when a pressure and a drag is transmitted through this piston rod. This is obtained by using a piston rod guide having the shape of a curved tube supporting all sides of the piston rod which is made as a tight wound steel spring.
For use in a disposable syringe with a flexible piston rod the piston rod guide only have to support the piston rod during its transmission of pressure to a piston in the cartridge and consequently a more simple piston rod guide may be used. Further it is wanted to manufacture the piston rod from a material of the same kind as the material from which the disposable syringe is made, i.e. plastic as combination of metal parts and plastic parts reduces the recycling possibilities. Also the piston rod shall compromise between the need for a piston rod which is sufficiently rigid to not bend out and the wish for a minimised consumption of material.
From EP 110 687 it is known to use a flexible pusher tape to drive a piston into a cartridge. The tape is made of a plastic such as moulded polypropylene and the needed stiffness is obtained by giving the tape a curved cross section and by beads along the lateral edges of the tape. The curved shape of the cross section corresponds to the curving of the inner wall of the cartridge so that the tape may abut this inner wall in its full width.
However, when a tape with a curved cross section is deflected to follow an arc of a circle, the tape have to assume a linear cross section. Furthermore plastic possesses a memory so that a cross section which has for some time been kept linear will not automatically attain the original curved shape when the part in question is no longer following an arc of a circle. Consequently a cross section which is intended to follow the curve shape of the inner wall of a cartridge cannot be relied on.
It is the object of the invention to provide a flexible piston rod made of plastic and which may be deflected outside a cartridge and used for pressing a piston into a cartridge without bending out within this cartridge.
This is obtained by a piston rod which comprises a tape shaped body which is along its length provided with supporters projecting from at least one side of the tape, the tape having a width and the supporters a length so that the sides of the tape and the ends of the supporters abuts the inner wall of an ampoule in at least three positions along the inner perimeter of the ampoule with not all the supporting points lying in the same half of the circular cross section.
In a preferred embodiment of a piston rod according to the invention the tape shaped body has a width corresponding to the length of a chord spanning an arc of about 120° of the circular inner cross section of the ampoule and supporters projecting perpendicularly from the side of the tape facing the axis of the ampoule abuts the inner wall of this ampoule in a position 120° displaced form each of the sides of the tape shaped body.
According to the invention the supporters may be provided with a spacing allowing the piston rod to be deflected to the side carrying the supporters. Supporters may be provided on both sides of the tape to enhanced the stiffness of the piston rod in the ampoule. By such piston rods the piston rod guide must be provided with a slot in the moving directions of the piston rod to accommodate projecting supporters.
Alternatively the supporters may be placed adjacent to each other so that the piston rod can only be deflected to the side away from the supporters. The piston rod guide must the be designed with a slot which may accommodate the projecting supporters.
In an embodiment of the piston rod according to the invention the supporters may have the shape of plates oriented in the longitudinal direction of the piston rod body perpendicular to this body and connected to the piston rod body by connections having a small length in the longitudinal direction of the piston rod. This construction possesses enhanced stiffness and as the connections of the plates to the piston rod is small, e.g. of the same order of size as is the thickness of the tape forming the piston rod, in the longitudinal direction of this rod they will not reduce the flexibility of this piston rod.
In another embodiment of the piston rod according to the invention this rod may be composed by tape shaped pieces each having a plate shaped supporter fixed to it along the whole length of the piece, the pieces being connected by hinges allowing deflection of the pieces to the side not carrying the supporters. In this embodiment the tape shaped pieces forming the piston rod has obtained a good stiffness on the account of the overall flexibility of the piston rod.
For the advancing of the piston rod according to the invention racks may be provided either on a side carrying no supporters or next to such supporters along the edge of the piston rod on the same side as these supporters. In embodiments with stiffened tape pieces the rack may be composed of sector shaped racks matching a drive pinion.
REFERENCES:
patent: 4787893 (1988-11-01), Villette
patent: 4846797 (1989-07-01), Howson et al.
patent: 4908017 (1990-03-01), Howson et al.
patent: 5304152 (1994-04-01), Sams
patent: 5368572 (1994-11-01), Shirota
patent: 5380295 (1995-01-01), Vacca
patent: 5672155 (1997-09-01), Riley et al.
patent: WO 95/09021 (1995-04-01), None
Nguyen Anhtuan T.
Novo Nordisk A S
Skadden, Arps, Slate, Meagher & Flam LLP
Thompson Michael M
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