CA1164758A - Pump, and an apparatus incorporating the pump for infusing liquid medicine - Google Patents

Abstract

ABSTRACT

"A Pump, and an Apparatus incorporating such a Pump for infusing Liquid Medicine"
The pump has a chamber in which a piston reciprocates to pump a liquid. The piston is moved by having secured thereto the armature of at least one electromagnet (preferably two). The coil of the electromagnet is suitably external of the pump casing. A control circuit pulses the electromagnet at a predetermined rate to provide a predetermined periodic output.
In a preferred form, the pump is mounted together with a liquid reservoir on a printed circuit board, and the unit is encapsulated for implantation in the human body to infuse a liquid medicine at a controlled rate into the bloodstream.

Description

11~475~

"A Pump, and an Apparatus incorporating such a Pump for This invention relates to a pump and to an apparatus incorporating such a pump for infusing into a su~ject determined quantities of liquid medicine at pre-determined time intervals.
The invention has particular, but not exclusive, relevance to medical applications in which controlled doses of drugs must be administered over long periods of time. For instance, persons su~fering ~rom diabetes melitus require routine administration of insulin, which is normally given by self~injection. Not only does this raise problems of maintaining supplies of stexile needles and the like, ~ut the use of injections tends to limit administration to once or twice daily, and the resulting concentration of insulin in the blood fluctuates widely.
In this and other applications, there is a need for a means of infusing drugs at a controlled rate so as to give relatively small amounts at relatively frequent intervals, say one to four times per hour. Such frequency would preclude conventional injection.
Solenoid actuated piston pumps capable of producing pulsatile continuous flow of discrete volumes of liquid are known from US Patent Specification No. 4102610, GB Patent S~ecification No. 1054366, Federal German Patent Specification No. 2252304 and French Patent Specification No. 609073. ~owever, the valves used in these devices are not tensioned shut and therefore losses from the pumping chamber make them incapable of deli~ering d~screte, accurately metered volumes of liquid.
Although the pumps descri~ed in US Patent Specification No. 2925814, French Patent Specification No. 7043705 and US Patent Specification No. 4152098 have valves which are tensioned shut the resilient ~ ~164758 ---components which provide the holdlrlg force, such as rubber, plastic and springs will change their characteristics as the result ~f ageing, chemical or corrosive attack, and embritt~e-ment due to constant recycling. In the pre~erred fo~n of the present invention highly 6table, cobalt samarium magneks are used to overcome these problem6 and also obviate the need for manufacturing a costly, miniature cage for the powered, captive outlet ball valve as the outlet valve closing magnet also forms a.magnetic cage for this c~mponent.
Another problem arises due to gravitational forces - causing the piston to move, and operate the pump, during normal physical activity such as running and jumping. This is possible in all of the pumps described above as the valves are operated by the pressure changes caused by movement of the pi~ton. It would be p~ssible, as in US Patent Specification No.
4152098~ to 6pring load the piston but this wou:ld greatly increase the amount of energy required to operate the pump. Again.it would be possible to increase the tension on one or both val~e6 of a pump to reduce this problem but this would not only increase the energy requirement of the deYice and 80 reduce battery life, but would also increase the rate of wear of the valve components.
Similarly, to reduce the pos~ibility of an overdosage being caused ~hould tl~e pres6ure in the re6ervoir e2cceed the pressure at the outlet side of the pump, it would be possible to prevent : . 25 the valves from lifting by tensioning ~hem shut with great force at thé cost of increased wear and increased energy usage.
In a pre~erred form of the present invention the provision of hydraulically balanced integral powered valves which open against the flow of liquid mitigates the aforesaid prob~:em. In addition the device of the present invention w~ll hydraulically loclc in the event of elther a rise in outlet pressure or reservoir pressure greater than the limit to which the pump ie designed B tooperate, Objects of the invention are therefore to provide a pump ~4~8 suitable for use in such infusion, and an infusion apparatus incorporating the pump.
According to the first aspect of the present invention,t~ere is provided a pump comprising a casing def~ing an elongate charnber, inlet and outlet valves communicating with the chamber, a piston coaYially movable in the chamber, and an electromagnet controlling mo~rement of the piston via an armature, the. outlet valve al50 being controlled by the electromagnet via a ~alve armature;
characterised in that the inlet and outlet valves are balls made from a material having ferromagnetic properties and seats made of non-magnetic material and magnets tensioning the balls of said inlet and outlet valves against their seats when in a closed . position, and in that power means for opening said balls from their seats, comprise for ~aid inlet valve a force equivalent to Z a hydraulic force caused by coa2~ial movement of the piston in the chsmber, said piston and said outlet valve being operated against the flow of liquid by the excitati~n of the single electro-magnet, a piston lock magnet providing a biasing force on the piston thereby to inhibit unintentional movement of the piston, and 6aid outlet valve remaining closed in response to adverse inlet or outlet pressure condition6 to prevent inadvertant flow of liquid. .
According to a second aspect of the present invention, there is provided an apparatus for infusing into a subject deter-mined quantities of liquid medicine at predetermined time inter~rals, the apparatus comprising a pump in accordance with the preceding paragraph in combination with a reservoir, the pump further including at least one non-return valve for passing liquid pumped from the reservoir to a cannula for infusing timing means for actuating the piston at predetermined regular intervals.
Preferably, two electromagnet coils are wound around the .
casing of the pu~p.
Preferabb also, the apparatu6 together with the cannul~

- 3a-are implantable into the living tissue or cavities OI the ~ubject.
An embodiment of the present invention will now be describedJ by way of example, with reference ts the ..

~ iJ

i, , accompanying drawings, in which:-Fig. 1 is a lengthwise cross-section of.a pump according to the present invention;
Figs. 2 to 5 are respectively cr~ss sectional ~iews of the pump along the lines II - II, III - I~I, IV - IV
and ~ - V of Fig. 1, the ~iews being to the same scale which is larger than that in Fig. l; and Figs. 6A and 6B are respectively a plan view and an end view of an apparatus according to the present invention of a size implantable into the living tissue or cavities of a subject.
Referring to Figs..l to 5 of the drawings, a pump comprises a cylindrical casing 10 whose interior defines an elongate chamber 11. A piston 12 is co-axially - 15 movable in said chamber 11. The piston 12 is an assembly comprising a tube 12A which has on its outside circum~erence two similar rings 14 integral therewith and spaced apart on and pround of its surface. Each ring 14 is adjacent to an end of the piston 12. The lands on the outside of the rings 14 are in sliding engagement with.the inside walls of.the casing 10.
Between the rings 14, piston circumference and the inslde wall of the casing 10, an annular passage 15 is de~ned. Mid-way of the bore 8 of the tube 12A a square inlet valve magnet 16 is in push-fitted engagement (Fig. 4). Symmetrical about the magnet 16, two similar inlet val~es are provided comprising balls 17,17' and seats 18,18'. An axially-bored plug 19,19' secures the balls 17,17' and seats 18,13' in their.positions in the piston. To the outside end wall of the plugs 19,19', a piston armature 20,20' is secured. The armatures.20,20 are bored in axial alignment with the bores in the plugs 19,19' and are both co-axial with the tube 12A and casing 10. Piston lock magnets 9,9' are mounted in axial recesses in outer end walls of piston armatures 20,20'.

1~6~758 -, Two anmatures 21,21' ase s~mmetrically secured in the opposite ends o~ the cas$ng 10 leav~.ng ai~ gaps 22,22' thereby to define the extent of reciprocal movement o~ the pis~on 12. Two similar sleeves 23,23' i 5 are secured around the armatures.21,21' as extensions of the.casing 10. The outer ends of the sleeves 23,23' are closed off by outlet valve plugs 24,24' having axial bores. In the sleeves 23,23' between the armatures 21,21' and plugs 24,24' two valve armatures 25,25' are slida~ly movable. The armatures.25,25' are ~rmed from two materials t~ be defined hereinafter secured together the ~uter parts being 25A,25A'. Two similar outlet va1ves are provided comprising.balls 27,27' and outlet valve seats 26,26'. The seats 26,26' are located in axial recesses and the.inner end of plugs 24,24'.
S~uare outlet valve magnets 28,28' are pr~vided in ' cylindric~l'.recesses in the outer ends of valve armatures 25,25' (Fig. 2). Two coil~s~29,29'. are.provided wound.respectively around the armatures.21,21' as shown in Figs. 1 and 3 and between collars 30,30' and 31,31' and covers 32,32' are provided to fit over the outside of the coils 29,29'. Valve air gaps 33,33' are provlded..between armatures 21,21' and valve armatures ' 25,25'.
An annulus 34 is provided around.the pump casing 10 and seats in collars 30,30! and an annular passage ' 35 is defined between said annulus 34 and casing 10.
Annulus 34 has a port 36 to be s~cured to a.reservoir of fluid, the port 36 communicating with passage 35.
Casing 10 has four equi-spaced ports 37.allowing fluid communicatlon from passage 35 to passage 15, and ~ tube 12A has our e~ui-spaced ports 38 allowing fluid '~ communication from passage 15 to bore 8.
Annulus 34, sleeves 23,23', casing.10, plugs 19,19' , ~ 35 and ports 25A,25A' of valve armatures 25,25' are all of , :

i~64758 -non-magnetic material such as ~c~nel . 600, ~ut can be ~, of non-magnetic stainless steels or plastics. The iron path comprises of the collars 30,3~'; 31,31' and cover 32,32', together with the armature 21,21', the S valve armature 25r25' except parts 25A,25A' referred to above, and the piston armatures 20,20' are all of a material such as Mu-metal, although other materials for example Mu-metal plus, Super Mu-metal, Ortno metal, Super Radio metal or Permendor can be used.
The balls 27,27~ and 17,17~ are of ~ungsten Carbiae~
although they could ~e of a material such as those used above for the armatures 21,21'. The valve seats 26,26' and 18,18' are of synthetic sapphire but can be of ceramics, Inconel 600, non-magnetic stainless steels , 15 or plastics. The magnets 16, 9,9' and 28,28' are all of sintered cobalt - samarium but can be.of Alnico, platinum cobalt, nialco, reco, cunife, or cumico.
Pumping action is achieved by alternately energising the colls 29,29' of the electromagnets to achieve reciprocation of the piston 12. Induction of fluid is achieved by the two inlet valves whose motion is controlled by the hydraulic forces generated by the motion of the piston 12. The outlet valves are powered open by the.,electromagnets... This..is'achieved by having the armature 21,21' to act as a stop in each electromagnet and using a second armature 25,25' to pull the outlet valve open as the piston is pulled into the electromagnet.
Wlth re~erence to Fig. 1, the electromagnet coll 29 is energlse~ causing magnetic flux to set up around the iron path comprised of the collar 30, collar 31 and cover 32, and thus through the valve armature,25, armature 21, and piston.armature 20. This causes the piston armature 20/piston 12 to abut against the armature 21 cl~sing air gap 22 to exhaust a volume of liquid in said air .
i * Trademarks 1164~58 gap equal to the volume of the air gap. The electric p~wer to coil 29 is then switchea off. By causing an electric current to flow in electromagnet coil 29', the air gap 22' will be closed to pump li~uid. The piston 12 is held t n its rest position by the piston locking magnets 9,9' which are mounted in the piston armatures 20,20'. This ensures that the piston 12 will .not drift between strokes as a result of leaks in the valves or piston seals. In considering the inlet valve 10 assemblies, each valve consists of a ball and seat.
.The ball has magnetic properties similar to iron ana the seats are of non-magnetic material as mentioned above.
The balls 17,17', when the valves are not.operating, are tensioned against their seats 18.,1~' by the inlet,valve magnet 16. In Fig. 1, the piston 12 has been pulled across by piston armature 20 being forced to close air gap 22 by a current flowing through coil 29. This causes the air gap 22' to open creating.a negative pressure which is transmitted through the axial bore ln piston armature 20' and hence to the.inlet ball 17'.
~ Thus hydraulic force.overcomes.the magnetic force seating .~ the ball 17' and causes fluid to flow from the reservoir through part 36 into.passage 35 and through..ports 37 into.passage 15 and.thence to fill air.gap 22' by the $1uid passages provided. Once the pressure.is equalised then the ball 17' will seat under the influence of the magnetic force from the inlet valve.magnet 16.
In considering.the outlet valve assemblies, these comprlse the valve armatures 2S,2S'. The parts of the armatures to be under the influence o the electromagnets are made.from materials similar in magnetic properties to iron, the materials being given above. The part of the armature valves housing the outlet valve magnets 28,28' are made from non-magnetic material, details of the materials being given above.. This is to ensure the ,, ~
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~164~7S8 valve armatures 25,25' are not held in the energised positio~ ~y stray ~lux frDm the magnets 28,2~'. The outlet valve ball 27,27' which.are made from a material having ferromagnetic properties will in the on~ case be attracted to the outlet valve magnets.28,28' but will still be free to centralise in the non-magnetic outlet valve seats 26,26' as, being close to the axis of the magnets, there wili be.little lateral force ~ excited on the outlet valve balls. The valves held in the closed position by the outlet valve.magnets 28,28' pulling against the outlet valve plugs 24,24' which have ferromagnetic properties. The closing force on the outlet valves greatly exceeds the closing force on the inlet valves ensuring that they are not moved by the hydraulic forces operating the.inlet valves.
. Outlet valve 27 operates as follows:- Coil 29 is energised. Before the piston with piston armatures moves for piston armature 20 to abut armature 21 thereby closlng air gap 22, piston armature 20' was against armature 21' and held there.by the piston lock magnet 9'. This holding force is of the same order : as the pull exerted on the valve armature 25 by the outlet valve magnet 28 on the outlet valve plug 24.
These forces cancel;each other out. The valve air gap 33 in lts start position..is less than.the piston air gap 22 i~ ~ts stàrt position, thus.the pull on the valve armature 25 will exceed that on the piston armature 20 ensuring the outlet valve 27 will open to allow fluid to be exhausted. Two hydraulic considerations also ensure that the valve will open. The first part o~ the force exerted.on the piston armature.20.will be required to unseat the ball ~alve 17'. Secondly, the hydraulic pressure generated by closing air gap 22.will restrain the motion of the piston 12 by acting on the area bounded by the seal on the piston. The fluid has ~2 V

1~L6475 !3 g free passage around and through the valve armature 25 so the hydraulic force wlll ~e distributed on bot~
faces of this component (less the small area where the ball contact the magnet). The sum of all these ~orce conside~ations mean that the outlet..valve will open. Outlet ~alve 27' operates.i~ a s~milar manner on coil 29' being ener~ised.
The fact that the va~ves in the pump operate on the s2me current pulse as the piston allows.relatively simple driving circuits. The powering of.the valves against the flow of liquid through the pump is a safeguard.against inadvertent flow of liquid. For example, a.rise of pressure at the outlet.greater than the pressure which the pump will work into locks the 1~ inlet valve shut.. 5imilarly a rise in reservoir pressure will locX the outlet valve. Similarly, a.rise in reservoir pressure will lock the outlet valve when the hydrostatic force on the outlet valve ball overcomes the attractive force between this member.and the outlet valve magnet.
An apparatus for.infusing into a subject, namely an animal or human being, determined quantities of liquid medicine at predetermined time intervals is shown in ~igs. 6A and 6B and comprises a printed aircuit base board 40 havlng electronic components.thexeon, a pump as described.above side-by-side w~th a reservoir 41, : power means 42, a liquid crystal ~isual display unit 43, tubing 44 and 45 from both ends of the pump to an outlet 46 to be connected to a cannula (not shown). The reservoir has.a self-sealing bung 48 for.injecting refil li~uid.medicine into the reservoir 41. The power means.42 are lithium batteries but may alternatively be atomic.batteries. The apparatus as shown in the ~ I Figs. 6A and 6B are actual size for implanting 35 subcutaneously or for positioning in cavities in a human body. The apparatus may however be portable ;~ :
.
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in the form of a watch ~o be strapped to the wrist.
Also, the apparatus may be o increased size and usable with existing drip-feed equipment.
The ~mplantable and wrist strap models are primarily for administering liquid medicine such as insulin or heparin but can be used for infusing any liquid medicine while.the human ~eing is going about normal daily life.
The coils.29,29' are of copper wire but for utmost efficiency with the small pumps may be of silver wire, the silver wire version giving on percentage increase in turns per equivalent copper.wire version of 20%.
. If the pump is to be frequently pulsed, then piston locking magnets 9,g' could be omitted since there would not be time for leaks to occur.
The pump as described above can be modified without departing from the scope of the invention in the manner as follows:-(a) The passage 35 can be omitted.
(b) The inlet valve seats 18,18' can be permanent magnets obviating the requirements for for inlet valve magnet 13.
(c) The inlet valve balls 17,17' can be permanent magnets and consequently the valve seats 18,18' are of ferromagnetic or permanent magnetic material.
(d) The non-magnetic plugs 19,19' can be of the same ferromagnetic material as the piston armatures 20,20'. This will effect a holding force between the piston armature 20 or 20' and the armature 21 or 21' and so the piston locking magnets 9,9' can be omitted.
~e) The outlet valve can have the fixed armature secured to lts sleeve. In this case, if ,,,~

1~6~75;~3 the sleeve had ~n ~utside diamete~ that fitted inside the piston armature bore then a scxew-thread between them woul~ a~low the stroke ~f the pump to be altered.
S (f) The pump can be single-acting instead of double-acting as above-descri~ed, in which case the pump will comprise one half of the pump described above i.e. as if it is cut along the line IV-IV and a plate of ferromagnetic material is used to effect a fluid seal. The inlet magnet will then provide a returning force when coil 29 was switched off. In this case, the coil 29 would need to provide more power.
The pump of the invention can be controlled by many forms of electronic control depending on use. For ~' example when used as an implant it may fonm part of a closed loop system, controlled by a sensing device.
An important feature of the pump is that it can easily be interfaced with a wide variety of electronics as it responds to intermittent pulsed information. Also, it has zero ~uiescent,current consumption, the mo~ing components having the magnets as "memories".

Claims (6)

- 12 -

1. A pump comprising a casing defining an elongate chamber, inlet and outlet valves communicating with the chamber, a piston coaxially movable in the chamber, and an electromagnet controlling movement of the piston via an armature, the outlet valve also being controlled by the electromagnet via a valve armature;
characterised in that the inlet and outlet valves are balls made from a material having ferromagnetic properties and seats made of non-magnetic material and magnets tensioning the balls of said inlet and outlet valves against their seats when in a closed position, and in that power means for opening said balls from their seats, comprise for said inlet valve a force equivalent to a hydraulic force caused by coaxial movement of the piston in the chamber, said piston and said outlet valve being operated against the flow of liquid by the excitation of the single electromagnet, a piston lock magnet providing a biasing force on the piston thereby to inhibit unintentional movement of the piston, and said outlet valve remaining closed in response to adverse inlet or outlet pressure conditions to prevent inadvertent flow of liquid.

2. A pump according to claim 1, in which the second electromagnet is spaced apart and axially aligned with the first electromagnet, the armatures of both electromagnets being oppositely linked together by the piston.

3. A pump according to claim 2, in which the electromagnets have coils wound around the casing.

4.. A pump according to claim 3, in which those parts of the casing on which the coils are wound are relatively thin sleeves of non-magnetic material, and each coil is surrounded on its outer surfaces with relatively thick members of low-reluctance magnetic material.

5. An apparatus for infusing into a subject predetermined quantities of liquid medicine at predetermined time intervals, the apparatus comprising a pump as set forth in claim 1 in combination with a reservoir, the pump further including at least one non-return valve for passing liquid pumped from the reservoir to a cannula for infusing the liquid into a subject, and the circuitry including timing means for actuating the piston at predetermined regular intervals.

6. An apparatus according to claim 5, in which the pump casing and the reservoir are mounted side-by-side on a printed circuit board which also carries the circuitry, forming an implantable unit for implanting subcutaneously or in a cavity of the human body.