A PUMP AND A FLUID DISPENSING DEVICE INCORPORATING A PUMP

Abstract: A pump (2) for use in an implantable drug delivery system for ambulatory patients meets the requirement for small size by comprising a piezoelectric disc element bonded to a diaphragm member forming one wall of a pump chamber (18), and a battery (26) and electrical circuits (22) for cyclically applying electrical voltage to the piezoelectric member whereby to induce pumping movement in the diaphragm member to pump drugs from a reservoir (12) via a valve (14) to a delivery catheter (20) via a valve (16). A gas spring (30) is provided to move the pump (18) to maintain adequate pressure in the drug reservoir.

Description: A PUMP AND A FLUID DISPENSING DEVICE INCORPORATING A PUMP This invention relates to pumps of a small size particularly though not exclusively implantable pumps which are sufficiently small for use within the human body. Pumps of small dimensions are used in im¬ plantable drug dispensing devices where a medicament is to be dispensed to an ambulatory patent on a regular or intermittent basis over an extended period of time, as where insulin is dispensed in the treatment of diabe¬ tes, or where chemotherapeutic drugs are dispensed in the treatment of cancer. In these circumstances it is advantageous in the treatment with the drug to perform an automatic dispensation o the drug without having to rely upon pills or injections. Thus a unit is im¬ planted within the patient comprising a reservoir of the drug and a pump, the pump being under control of a control circuit which may be coupled by an electromag¬ netic transmitter and receiver to an external control source. Such a device for delivering the drug must be reliable in operation, sealed against body fluids and must hold a sufficient quantity of medication so as to avoid the need for frequent refills and must be refill- able when empty. Furthermore, such dispensing systems must be physically small, so as to be readily implant¬ able without unnecessary disturbance of the baby. It is known to employ in such dispensing devices pumps such as the peristaltic type or solenoid type. Peri- staltic pumps operate by responding to blood pressure within the bodv and solenoid pumps operate under control of an internal battery connected to a solenoid for operating a suitable pump mechanism. However such pumps are relatively large, and considering their size, are inefficient within the context of implantable units. The present invention is based on the concept of a pump whicti incorporates a mechanism which is actuated by means of a piezo electric element. Such a pump can be made of a very small size and is therefore suitable for use in an implantable drug delivery system. However such a pump may be of use in whatever application where the requirement is for a pump of very small size. The present invention therefore provides in general term.s a pump comprising a source of electric power connected to means for cyclically applying electrical voltage to a piezo electric element whereby to induce periodic changes in dimension in the piezo electric element . the piezo electric element being ohysically contiguous with and directly coupl to a movable pump element whereby changes in dimension of the piezo electric element induces pumping movement into the movable pump member. Thus since all that is required to provide t-he pump motive power is a piezo electric element and a source of electrical power such as for example a battery, and that furthermore since the piezo electric element is contiguous with and directly coupled with the movable pump element , with no intervening shaft or push rod, the piezo electric pump may be made very small in dimensions. The electrical power supplied to the piezo electric element from the battery may be in pulsed d.c. form or alternatively and as preferred for efficiency it may be AC. with a suitable inverter circuit being provided. The " movable pump member may be of any suitable type rotatable o displaceable , and the piezo electric element - may be coupled to the pump member in such a way as to induce the required type of movement. In a preferred embodiment , the movable pump member comprises a flexible , membrane move¬ ment of which increases or decreases the size of a pump chamber which is coupled to a drug reservoir and an outlet port by suitable one way valves. Thus a decrease in volume of the pump chamber causes a drug within the pump chamber to be expelled through the valve of the outlet port, the valve at the inlet port remaining closed, whereas when the volume of the pump chamber is increased by movement of the membrane, the one way valve at the outlet port is closed whereas the one way valve at the inlet port is opened to permit further- drug to be introduced into the pump chamber. As preferred the piezo electric element comprises a planar element extend- ing over a substantial or major part of the surface area of the membrane and being firmly affixed to the surface thereof. Thus when dimensional changes are induced in a suitable direction in the piezo electrical element, this causes the piezo electric element to curve in one or two opposite directions from the plane in which it is disposed and the consequent bowing effect of the element causes a correspond¬ ing deformation of the membrane resulting in similar type of movement of the membrane. Thus the pump may be configured as essentially a flat disc-like element, with the piezo electric element , the membrane forming the movable pump mem¬ ber and the pump chamber all being of essentially planar form A preferred embodiment of the invention will now be described with reference to the accompanying drawings wherein : Figure 1 is a view in elevation of the exterior of an implantable dispenser incorporating a pump according to the invention: Fi ure 2 is a schematic cross-sectional view of the dispenser of Figure 1 ; Figure 3 is a view in cross-section of the pump of the implantable dispenser; and Figure is a block diagram of the electrical control circuit of the implantable dispenser. Referring now to the drawings there is shown an implantable dispenser 2 for use in a drug delivery system where the dispenser is implanted into the body of a human being and is operative to dispense into the body suitable quantities of a drug at intervals under control of a circuit within the dispenser and as required under external control by means of a receiver/transmitter arrangement. The dispenser 2 as shown in Figure 1 compr ses an outer casing 3 of bio-compatible material, for example titanium alloy or stainless steel or biologically compatible silicone rubber. The dispenser body comprises a main portion 4 which is circular in elevation with a diameter of 3-5 cm (this dim¬ ension and the dimensions quoted below are approximate). The depth of the main portion is 2.5 cm. A lobe portion 6 is provided having a w r idth as measured from the circumfer¬ ence of " the circular portion 4 of 1.5 cm and having a depth of 1.5 cm. The overall configuration of the implantable dis¬ penser is shown in Figures 2 and 3 as comprising a septum δ mounted in lobe portion 6 and containing a radially comp¬ ressed block of silicone rubber, an inlet being provided for external access and a passageway 10 to a. ain drug reservoir region 12. In use. the reservoir 12 is filled by insertion of the hypodermic needle of a syringe into the silicone rubber insert via a passageway 9 , so that the drug flows into the main reservoir region 12 via a passageway 10. Extraction of the needle when the reservoir is filled auto¬ matically closes the silicone block. Valves 14. 16 are provided, inlet valve 14 permitting entry of the drug into a pump lδ and outlet valve 16 permitting exit of the drug from the pump body to a delivery catheter 20 which extends from the dispenser body to a suitable location within the - ύ - human body. The pump is connected to an electronic control circui by means of electrical leads 24, the electronic circuit bein powered by a battery 26. A gas spring is provided in the area 0 between the pump and the electronic circuit 22 with- in the volume enclosed by a bellows 32. The function of the gas spring is to maintain an essentially constant press¬ ure in reservoir 12 as the quantity of drug decreases during infusion. By selecting a suitable mixture of "Freon '' -type hydrocarbons which liquify at about one ' bar pressure, the pressure in the gas spring can be made to remain effectively constant (apart from the spring characteristics of the bellows ' ) as the drug is used up and the bellows 3 opens. The pump is shown in more detail in Figure 3 as being of generally flat and planar shape being 3.0 cm in diameter and 2 mm thick. Thepump comprises two plate members 3 , 2 of pressure moulded titanium alloy and an intermediate plate 34 is also formed of titanium alloy. These plates define a port 36 for inlet valve 14 housing a freely movable valve member 38 and communicating with a passageway 40. Passageway 4 formed in intermediate plate 34 communicates with a pump chamber 42 and a further channel 44 formed in plate member 34 communicates with an outlet valve having a freely movable valve member 40 which is mounted in a recess 48 which communicates with outlet 5 . Titanium plate 32 defines a movable member to which is bonded a circular plane piezo electric sheet 52. Suitable seals are provided (not shown) surrounding the valv members, the seals and valve members being made of biologic¬ ally compatible materials, for example silicone rubber. The three plates 30, 32, 34 are sealed together by a tech¬ nique such as electron beam welding or diffusion bonding. The piezo electric element 52 is mounted on plate 32 using a conductive epoxy filled with silver. In operation, when an electric voltage is applied across the thickness of the piezo electric element 52. this creates a bowing, resulting in the central part of the piezo electric element moving out of the plane of the element a certain amount whereby to cause a corresponding deformation in plate 3 and thus causing an expansion or contraction of volume of the pump chamber. Where expansion is caused, this creates a suction effect causing valve member 3& to be moved downwardly allowing drug from reservoir 12 to flow into the valve chamber. Outlet valve member 46 is main¬ tained against passage 44 during this movement. Upon con- traction of the space of the pump chamber caused by inward movement of plate 32, valve member 46 is pushed upward by permitting a drug to flow through the outlet valve 16. Referring now to Figure 4 there is shown the elec¬ tronic circuitry for controlling the pump comprising an inductive loop antenna 60 which receives electrical signals from external control apparatus. This is connected to a receiver and transmitter 62, 64 which in "turn provide and receives signals from a central control logic 66. A lithium battery 26 is coupled via a battery checking circuit 65 to control logic 66. Electronics circuits 70 are pro¬ vided coupled to sensors which are situated within the pump to monitor conditions such as battery charge, critical operating voltages , _internal humidity, pump/valve monitoring, quantity of drug in reservoir and rate of dispensation, clock settings and stored operating system. In .addition sensors may be " situated at parts of the human body to deter¬ mine from biological conditions whether a drug should be administered. The control logic is also coupled to an oscillatory driver 72 which includes an inverter circuit and which provides alternating current to the pump for causing a pumping action of the pump. It may thus be seen that the pump can be ' controlled in any suitable manner to provide a regular or intermittent flow or drug to a person having this dispenser device implant-therewithin , the pump being controlled either internally by sensor devices mounted within the patient or externally by means of signals trans¬ mitted electromagnetically from an external control device. The pump as described delivers very small quantitie of fluid, as shown about 0.1 micro litres per pump sample. The advantages of the pump as described are its very small size and its cheapness as compared with peristaltic pumps or solenoid pumps and the pump is therefore very suitable for applications where accurate quantities of liquid must be pumped in small amounts and where a pump of small size is required.

Claims: CLAIMS : - <? - 1. A pump comprising a piezoelectric element (52) physically contiguous with and directly coupled to a movable pump element (32) whereby changes in dimen¬ sion of the piezoelectric element induces pumping movement in the movable pump element, and a source of electrical power (26) connected to control means (22) for cyclically applying electrical voltage to the piezoelectric element (52) whereby to induce periodic changes in dimension in a piezoelectric element. 2. A pump as claimed in claim 1 , wherein the movable pump element (32) comprises a flexible dia¬ phragm forming part of the wall of a pump chamber (42). 3. A pump as claimed in claim 2 , and comprising a one way valve member (38) being connected between a fluid reservoir (12) and the pump chamber (42) to permit flow of a fluid from the reservoir 'into the pump chamber upon movement of the flexible diaphragm (32). 4. A pump as claimed in claim 3, including a further one way valve member (46) connected between the pump chamber (42) and an outlet (50). 5. A pump as claimed in any one of claims 2, 3 or 4, wherein the source of electric power is a battery in the shape of a disc and the control means (22) in the shape of a planar member, wherein the battery, control circuit and pump chamber are stacked one upon another to permit the pump to be formed as a disc-like device. 6. A pump as claimed in any preceding claim, wherein the control means (22) includes receiver means arranged to respond to remotely transmitted electromag¬ netic waves to actuate the pump. . pump as c a me n c a m , an nc u ng means for checking the condition of the source of electric power. 8. A dispensing device comprising a housing (3) forming a reservoir (12) for fluid to be dispensed and a pump (18) located within the reservoir (12) for dispensing the fluid, the pump being constructed in accordance with any one of the preceding claims. 9. A dispensing device according to claim 8 and comprising means (32) for maintaining constant the pressure of fluid in the reservoir as the fluid is being dispensed. 10. A dispensing device according to claim 9, wherein the pressure maintaining means comprises an expandable member (32) within the reservoir. 11. A dispensing device according to claim 10, wherein the pump (18) is disposed within the expandable member (32 ) . 12. A dispensing device according to any one of claims 8 to 11 , and comprising an inlet chamber (8) connected to the reservoir (12 | ) and sealed by an elastomeric member (9) whereby to permit injection of fluid into the reservoir by means of an hypodermic- syringe.

Inventors: COX ROBERT EDWARD LATIMER, DAMHUIS EDWARD HENDRIKUS JOHAN, LABBE JEAN-MARIE, COX, ROBERT, EDWARD, LATIMER, DAMHUIS, EDWARD, HENDRIKUS, JOHANNES, LABBE, JEAN-MARIE
Applicants: KABIVITRUM AB
Application year: 1988
Main classification: A61M5
IPC codes: A61M5, F04B43