GB2600367A

GB2600367A - Shape memory alloy based drug delivery device

Info

Publication number: GB2600367A
Application number: GB2201933.5A
Authority: GB
Inventors: George Webber Dominic
Original assignee: Cambridge Mechatronics Ltd
Current assignee: Cambridge Mechatronics Ltd
Priority date: 2017-05-17
Filing date: 2018-05-16
Publication date: 2022-04-27
Anticipated expiration: 2038-05-16
Also published as: GB2576446A; WO2018210914A1; GB2600367B; GB201707941D0; GB202201933D0; GB2576446B; GB201916342D0

Abstract

A drug delivery device 400 comprising a shape memory alloy (SMA) actuator wire 404 arranged to cause dispensing of a liquid medication from the device, wherein the SMA is controlled by closed-loop control. In a preferred arrangement the device comprises a plunger 406 in fluid communication with a vessel 408 for containing the medicament, with movement of the plunger driven by contraction and expansion of the SMA wire. Resistance measurement circuitry (316, Fig 3) may be coupled to a controller (320, Fig 3) and used to measure the resistance of the SMA wire, for determining plunger positioning. Methods and circuitry for closed-loop control of such a drug delivery device are also taught, the method requiring, and the circuitry being for, determining plunger position from received data (such as resistance data), comparing the determined position of the plunger with a required position thereof, and generating a control signal to adjust the current position of the plunger toward the required position.

Description

Shape Memory Alloy Based Drug Delivery Device The present application generally relates to a drug delivery device, and in particular to a drug delivery device with a shape memory alloy (SMA) based delivery mechanism for precision delivery of medicines or drugs such as insulin.

In a first approach of the present techniques, there is provided a drug delivery device comprising: a vessel for containing a volume of liquid medication or drug; a plunger mechanism in fluid communication with the vessel; an actuation 113 mechanism coupled to the plunger mechanism, the actuation mechanism comprising: a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger in a dispensing direction which dispenses the liquid medication or drug from the vessel; and a controller for closed-loop control of the SMA actuator wire.

In a second approach of the present techniques, there is provided a method for closed-loop control of a drug delivery device comprising a vessel for containing a volume of liquid medication or drug, a plunger mechanism in fluid communication with the vessel, an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger in a dispensing direction which dispenses the liquid medication or drug from the vessel, the method comprising: receiving data for determining a position of the plunger mechanism; determining, using the received data, a current position of the plunger mechanism; comparing the determined current position of the plunger mechanism with a required position; and generating a control signal to adjust the current position of the plunger mechanism towards the required position.

In a third approach of the present techniques, there is provided circuitry for closed-loop control of a drug delivery device comprising a vessel for containing a volume of liquid medication or drug, a plunger mechanism in fluid communication with the vessel, an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger in a dispensing direction which dispenses the liquid medication or drug from the vessel, wherein the circuitry: receives data for determining a position of the plunger mechanism; determines, using the received data, a current position of the plunger mechanism; compares the determined current position of the plunger mechanism with a required position; and generates a control signal to adjust the In a related approach of the present techniques, there is provide a drug 113 delivery device comprising a shape memory alloy (SMA) actuator wire arranged to cause dispensing of a liquid medication or drug from the device, wherein the SMA actuator wire is controlled by closed-loop control.

Preferred features are set out in the appended dependent claims.

In a related approach of the present techniques, there is provided a non-transitory data carrier carrying processor control code to implement any of the methods described herein.

As will be appreciated by one skilled in the art, the present techniques may be embodied as a system, method or computer program product. Accordingly, present techniques may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects.

Furthermore, the present techniques may take the form of a computer program product embodied in a computer readable medium having computer readable program code embodied thereon. The computer readable medium may be a computer readable signal medium or a computer readable storage medium.

A computer readable medium may be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.

Computer program code for carrying out operations of the present 35 techniques may be written in any combination of one or more programming languages, including object oriented programming languages and conventional procedural programming languages. Code components may be embodied as procedures, methods or the like, and may comprise sub-components which may take the form of instructions or sequences of instructions at any of the levels of abstraction, from the direct machine instructions of a native instruction set to high-level compiled or interpreted language constructs.

Embodiments of the present techniques also provide a non-transitory data carrier carrying code which, when implemented on a processor, causes the 113 processor to carry out any of the methods described herein.

The techniques further provide processor control code to implement the above-described methods, for example on a general purpose computer system or on a digital signal processor (DSP). The techniques also provide a carrier carrying processor control code to, when running, implement any of the above methods, in particular on a non-transitory data carrier. The code may be provided on a carrier such as a disk, a microprocessor, CD-or DVD-ROM, programmed memory such as non-volatile memory (e.g. Flash) or read-only memory (firmware), or on a data carrier such as an optical or electrical signal carrier. Code (and/or data) to implement embodiments of the techniques described herein may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code, code for setting up or controlling an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or code for a hardware description language such as Verilog (RTM) or VHDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate, such code and/or data may be distributed between a plurality of coupled components in communication with one another. The techniques may comprise a controller which includes a microprocessor, working memory and program memory coupled to one or more of the components of the system.

It will also be clear to one of skill in the art that all or part of a logical method according to embodiments of the present techniques may suitably be embodied in a logic apparatus comprising logic elements to perform the steps of 35 the above-described methods, and that such logic elements may comprise components such as logic gates in, for example a programmable logic array or application-specific integrated circuit. Such a logic arrangement may further be embodied in enabling elements for temporarily or permanently establishing logic structures in such an array or circuit using, for example, a virtual hardware descriptor language, which may be stored and transmitted using fixed or transmittable carrier media.

In an embodiment, the present techniques may be realised in the form of a data carrier having functional data thereon, said functional data comprising functional computer data structures to, when loaded into a computer system or network and operated upon thereby, enable said computer system to perform all the steps of the above-described method.

Implementations of the present techniques will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a typical liquid drug delivery device in the form of a pen; Figure 2 is a schematic diagram of a typical liquid drug delivery device in the form of a pump; Figure 3 is a block schematic diagram of an SMA-based drug delivery device; Figure 4 is a schematic diagram of an SMA-based drug delivery device; and Figure 5 is a schematic diagram showing the operation of the SMA-based drug delivery device of Figure 4.

Broadly speaking, embodiments of the present techniques provide apparatus and methods for closed-loop control of a shape memory alloy (SMA) based actuator for dispensing a volume of liquid medicine/drug from a device.

Portable drug delivery devices may be used to administer medication or drugs for conditions such as diabetes. In this document, where reference is made to insulin delivery devices or insulin, it will be understood that this is merely one example of a drug that could be dispensed by the drug delivery device of the present techniques. The drug delivery device of the present techniques may be used to dispense any liquid-based medication or drugs.

Known liquid drug delivery devices typically take two forms -'pens' and 'pumps'.

Figure 1 is a schematic diagram of a typical liquid drug delivery device 100 in the form of a pen. The drug delivery device 100 may comprise a vessel 108 for containing a liquid medication/drug. The liquid drug may be ejected from the vessel 108 through a needle 110 into a patient. The drug delivery device 100 may comprise a plunger 106 housed in a body 104 of the device. The liquid drug may be ejected from the vessel 108 by movement of the plunger 106 in the vessel 108. A dosing dial 102 at the distal end of the device 100 relative to the needle 110 may be rotated to select the dose of liquid drug to be dispensed from the vessel 108. The dosing dial 102 may be connected to a mechanism (not shown) to displace the plunger 106 by a distance needed to dispense the selected dose. For example, with respect to insulin delivery devices, insulin doses are typically recorded in 'insulin units' (IU) on the dosing dial 102. Medication delivery may be initiated by depressing a button (not shown) coupled to/at the end of the dosing dial 102, which causes the dosing dial 102 to be pushed toward the body 104 of the drug delivery device 100. A dispense cycle may be completed when the dosing dial 102 returns to its original position relative to the body 104 of the device 100.

Drug delivery devices, such as insulin pens, may be 'disposable' or 'reusable'. Disposable drug delivery devices may be discarded when the vessel 108 containing the liquid drug is empty or contains an insufficient volume of the drug for another dispense cycle. Reusable drug delivery devices may be designed to allow the vessel 108 to be replaced or refilled.

Current drug delivery devices which take the form of a pen may have a number of disadvantages. For example, patients using the drug delivery devices may have impaired dexterity, which may mean that operating the dosing dial 102 and/or applying the necessary force to push the mechanism to deliver the dose is uncomfortable or even impossible in some cases. In another example, the maximum dose selectable on a drug delivery device may be lower than the dose required by some patients, which may require patients to inject themselves several times in order to receive the required dose. For example, an insulin pen may typically be limited to dispensing no more than 80 IU in one dispense cycle. However, some diabetics may require doses in excess of 80 IU and as such, must inject themselves several times to receive the required dose. This may place some burden on the patient to calculate how much medication needs to be dispensed per dispense cycle so that they receive their prescribed dose, or to remember how many dispense cycles they have completed. Similarly, the minimum increment of selectable doses on a drug delivery device (e.g. an insulin pen) may typically be no finer than 0.5 IU. However, some diabetics may require doses in increments of as little as 0.25 IU. To receive the required dose, such patients may need to use a drug delivery device which takes the form of a pump.

Figure 2 is a schematic diagram of a typical liquid drug delivery device 200 in the form of a pump. Pump-type drug delivery devices may be similar in design and function to the pen-type drug delivery devices, but patient interaction with the two devices may be quite different. Patients may select a pump-type drug delivery device over a pen-type drug delivery device for a number of reasons, including dislike of needles regularly piercing the skin. A pump-type drug delivery device may be able to administer medication with complex profiles over time to best manage the patient's condition. Pen-type devices may require a user to interact with the device in order to dispense a dose of medicine (e.g. by pressing a button and injecting themselves with the needle of the device), while pump-type devices may, once attached to a user, may not require any user action to be performed to dispense a dose of medicine. However, pump-type devices are almost permanently attached to a patient via a catheter that is left in the patient and changed infrequently.

The pump-based drug delivery device 200 may comprise a body 204, a motor 202 that is coupled to a plunger 206, a vessel 208 for containing a liquid medicine/drug and a catheter 210 (instead of needle 110 in Figure 1). The dose required by the patient may be input/entered via a digital user interface (not shown), and provided to the pump/motor 202. The drug may be dispensed from vessel 208 using an electrically powered mechanism such as a motorised syringe pump 202. However, there are a number of disadvantages of pump-type drug delivery devices. For example, pump-type devices are typically permanently worn by a user. However, the pump-type devices may, as a result, be quite small, lightweight and quiet during operation. Pump-type drug delivery devices may have complex designs and as a result, a high selling price (e.g. $6000).

The present techniques are now described with reference to Figures 3, 4 and 5.

Figure 3 is a block schematic diagram of an SMA-based drug delivery device or apparatus 300. The drug delivery device 300 may be a disposable or a reusable drug delivery device. The drug delivery device 300 may comprise a vessel 302 for containing a volume of liquid medication or drug. If the drug delivery device 300 is reusable, the vessel 302 may be refillable or replaceable. If the drug delivery device 300 is disposable, once the vessel 302 is empty or near-empty, the whole device 300 may be discarded. The drug delivery device 300 may take the form of a pen or a pump.

The drug delivery device 300 may comprise a plunger mechanism 306 that may be in fluid communication with the vessel 302. The plunger mechanism 306 may be arranged to cause liquid medicine to be dispensed from the vessel 302 -movement of the plunger mechanism 306 in the vessel 302 may impart a force on the liquid in the vessel 302 that causes the liquid to be dispensed from the vessel by a dispensing element 322 that is connected to the vessel 302. The dispensing element 322 may be, for example, a needle or a catheter.

The drug delivery device 300 may comprise an actuation mechanism 324.

The actuation mechanism 324 may be coupled to the plunger mechanism 306 and arranged to move or actuate the plunger mechanism 306, and thereby cause a dose of drug/medicine to be dispensed from vessel 302. The actuation mechanism 324 may comprise at least one shape memory alloy (SMA) actuator wire 304 that is arranged to, on contraction, apply a force to the actuation mechanism 324 to cause the actuation mechanism 324 to advance the plunger 306 in a dispensing direction which dispenses the liquid medication or drug from the vessel 302. The actuation mechanism 324 may comprise a controller 320 for closed-loop control of the SMA actuator wire 304.

Thus, the present techniques provide a drug delivery device 300 that may comprise: a vessel 302 for containing a volume of liquid medication or drug; a plunger mechanism 306 in fluid communication with the vessel; an actuation mechanism 324 coupled to the plunger mechanism 306, the actuation mechanism 324 comprising: at least one shape memory alloy (SMA) actuator wire 304 arranged to, on contraction, apply a force to the actuation mechanism 324 to cause the actuation mechanism 324 to advance the plunger mechanism 306 in a dispensing direction which dispenses the liquid medication or drug from the vessel 302; and a controller 320 for closed-loop control of the SMA actuator wire 304.

The drug delivery device may comprise at least one mechanism for determining a position of the plunger mechanism. The drug delivery device may comprise a resistance measurement circuit or module 316 coupled to controller 320 for determining a position of the plunger mechanism 306. As the SMA actuator wire 304 is heated, it contracts and decreases in length. Thus, the change in length causes a change in the resistance of the SMA actuator wire 304. The resistance of the SMA actuator wire 304 may therefore, be used to determine the position of the plunger mechanism 306.

Additionally or alternatively, the drug delivery device may comprise at least one sensor 314 coupled to the controller 320 for determining a position of the plunger mechanism 306. The position of the plunger mechanism 306 during a dispense cycle relative to a start/initial/original position of the plunger mechanism 306 (i.e. the position of the plunger at the start of a dispense cycle), may be used to determine whether the required dose has been dispensed from the vessel 302. For example, if the plunger mechanism 306 is determined to be at (using data from sensor 314) position A, but the plunger mechanism 306 needs to be at position B in order to dispense the full required dose, then the controller 320 determines that the plunger mechanism 306 may need to be moved further. Thus, the position of the plunger mechanism 306 may feed into the closed-loop control of the SMA actuator wire 304. The at least one sensor 314 may directly determine or sense the position of the plunger mechanism 306, or may indirectly determine the position of the plunger mechanism 306. For example, the at least one sensor 314 may comprise a resistor for measuring the resistance of the SMA actuator wire. The electrical resistance of SMA actuator wires is roughly proportional to their length. The resistance of the SMA actuator wire 304 may be used to determine the position of the plunger mechanism 306.

The resistance of SMA actuator wires may be measured in real-time by driving an electrical current through them and measuring their electrical resistance. Controller or control system 320 may comprise a drive part and a resistance measurement part, and may be used to drive electrical power through the SMA actuator wire(s) 304 and provide closed-loop control. The desired translational position of the plunger mechanism 306 to dispense a particular dose/volume of liquid medicine/drug may be achieved by measuring the resistance of the SMA actuator wire 304 and setting target resistance values for the wire that correspond to the desired positions of the plunger mechanism 306 for each dose.

During a dispense cycle, the controller 320 (which may be entirely hardware-based, entirely software-based, or may comprise hardware and software components), may receive data from the resistance measurement circuit 316 and/or the at least one position sensor 314 and determine, using the received data, a current position of the plunger mechanism. The controller 320 may compare the determined current position of the plunger mechanism 306 with a required position, and if the current position is not equal to the required position (within some acceptable, defined tolerance), generate a control signal to adjust the current position of the plunger mechanism towards the required position. In embodiments, the control signal may cause the power supplied to the SMA actuator wire 304 to be increased in order to cause the SMA actuator wire to contract further and thereby move the plunger mechanism 306 further in the dispensing direction.

In embodiments, the at least one sensor 314 may be used to determine plunger mechanism operation faults. For example, the at least one sensor 314 may be used to detect a system (or plunger mechanism 306) jam where medication is not ejected from the vessel 302 despite the actuation mechanism 324 being operational. If there is a system jam, the SMA actuator wire 304 may be driven (which causes the SMA actuator wire to contract/ reduce in length), but the expected corresponding resistance change may not be sensed, which may indicate a fault with the plunger mechanism 306 (or with another component). If such a fault is detected, the drug delivery device 300 may alert the user (via an interface 326, such as a display) to not use the device 300 until it has returned to its fully functional state.

The drug delivery device 300 may comprise a return mechanism 308 for returning the SMA actuator wire 304 to an extended state at the end of a dispense cycle. The extended state may be the original state of the SMA actuator wire 304 before it is driven/before electrical power is applied to the wire. When the SMA actuator wire 304 is in its extended state, the plunger mechanism 306 may be in its original/start position and ready to push liquid medicine out of the vessel 302 when the next dispense cycle begins.

The return mechanism 308 may be any suitable component or element to cause the SMA actuator wire 304 to extend and the plunger mechanism 306 to move to its start position. The return mechanism 308 may be or comprise a resilient element to oppose the force applied by the SMA actuator wire 304 and push back the plunger mechanism in a direction opposite to the dispensing direction. The return mechanism 308 may be or comprise a spring. The return mechanism 308 may be or comprise a further SMA actuator wire arranged to, on contraction, apply a force to the actuation mechanism 324 to cause the actuation mechanism 324 to advance the plunger mechanism 306 away from the dispensing direction (i.e. apply a force in a direction opposite to the dispensing direction).

The drug delivery device 300 may comprise a power source 310 for supplying power to the SMA actuator wire 304. When electrical power is supplied to SMA actuator wire 304, the SMA actuator wire 304 heats-up, which in turn causes the SMA actuator wire to contract. Cooling of the SMA actuator wire 304 (e.g. by switching off or disconnecting from the power source 310) causes the SMA actuator wire to return to its original extended state. In embodiments, the power source 310 may comprise a battery. In embodiments, the power source 310 may comprise a connection to a mains power supply. In embodiments, the power source 310 may comprise both a battery (which may enable the device 300 to be portable) and a connection to a mains power supply (which may provide a back-up power source or may enable recharging of the battery).

The drug delivery device 300 may comprise a force sensor 312 for detecting and controlling the force used to dispense a dose of medicine from the vessel 302 (and thereby, detect and control the rate of which medicine is dispensed from the vessel 302). The force sensor 312 may be coupled to the controller 320 for determining a rate at which the liquid medication or drug is dispensed from the vessel 302.

In embodiments, a powered pumping system may be used in conjunction with a controller 320 to give the user the ability to vary the rate of drug dispensing, to a preferred balance of discretion, convenience and comfort. The required rate of drug dispensing could be input via a setting or user interface on the device 300 itself, or in the specific case of a pen-type device, the force applied to the dosing dial end button measured by a force sensor connected to the device zo microcontroller.

An alternative means of increasing the pumping force may be to introduce a lever mechanism between the SMA actuator wire 304 and the actuation mechanism 324. This may also reduce the amount by which the actuation mechanism 324 needs to be displaced/moved and therefore, the maximum speed of pumping. This arrangement may have an additional benefit of improving the resolution of dose increment, which may enable relatively small dose volumes to be dispensed.

In embodiments where the drug delivery device 300 comprises a force sensor 312, the controller 320 may: receive data from the force sensor 312; determine, using the received data, a rate at which the liquid medication or drug is being dispensed from the vessel 302; compare the determined rate of dispensing with a required rate of dispensing; and if the determined rate of dispensing is not equal to the required rate of dispensing, generate a control signal to adjust the rate of movement of the plunger mechanism 306.

The drug delivery device 300 may comprise a dosage mechanism 318 coupled to the controller 320 for controlling the volume of liquid medication or drug dispensed from the vessel 302 during a dispense cycle. The dosage mechanism 318 may comprise at least one moveable stop which protrudes from an inner surface of the vessel and is arranged to obstruct the plunger mechanism 306 and thereby control the volume of liquid medication or drug dispensed from the vessel 302 during a dispense cycle.

The drug delivery device 300 may be an insulin delivery device and the liquid medication or drug in the vessel 302 may be insulin.

The dispensing element 322 of the drug delivery device 300 may be or comprise a needle, or may be or comprise a catheter.

The drug delivery device 300 may be an insulin pen.

The drug delivery device 300 may be portable and/or wearable.

The actuation mechanism 324 may be arranged to cause the plunger mechanism 306 to dispense a volume of liquid medication or drug via a single actuation.

The actuation mechanism 324 may be arranged to cause the plunger mechanism 306 to dispense a volume of liquid medication or drug via multiple actuations.

The controller 320 may comprise at least one processor.

Turning to Figure 4, this shows a schematic diagram of an example SMAbased drug delivery device 400. The device 400 comprises a vessel 408 for containing a volume of liquid medication or drug, a plunger mechanism 406 in fluid communication with the vessel 408, and an actuation mechanism 402 coupled to the plunger mechanism 406. The actuation mechanism 402 comprises a length of Shape Memory Alloy (SMA) material 404 -most likely in wire form -which is fixed at one end to a support/static structure 409, and attached at another end to the actuation mechanism 402. When the SMA actuator wire 404 is heated -most likely with an electrical current -it contracts in length. As such, the actuation mechanism 402 will be displaced along the axis of the pump mechanism, and in the dispensing direction (indicated by arrow A). When power is removed from the SMA actuator wire 404, it will cool and may be returned to its original position by a return mechanism 410. The return mechanism may take the form of a spring.

The distance of travel of the actuation mechanism 402 may correspond directly to the quantity of medication delivered to the user. Different users and occasions may require different medication dose quantities, and therefore, the movement/actuation of the actuation mechanism 402 may need to be carefully controlled. The distance of travel of the actuation mechanism 402 may be controlled by controlling the length of the SMA actuator wire 404. The length of the SMA actuator wire 404 may be controlled by measuring its electrical resistance by a microcontroller (or otherwise), and applying the appropriate amount of electrical current to the SMA actuator wire 404. Thus, the SMA actuator wire 404 may be controlled using a closed-loop mechanism, which may use electrical resistance measurements to perform the control. This may allow accurate control of the length of the SMA actuator wire 404 and hence the position of the plunger mechanism 406, allowing variable amounts of medication to be dispensed. The minimum dosage and resolution may be as little as 0.25 IU, or indeed considerably less if required.

The device 400 may dispense a useful amount of medication in a single actuation cycle, for example 10 IU or 20 IU. Larger doses can be dispensed using repeated actuations. An example of a suitable arrangement for this is now described with reference to Figure 5.

Figure 5 is a schematic diagram showing operation of the SMA-based drug delivery device of Figure 4. In embodiments, the amount of contraction of a practical length of SMA actuator wire 404 may not be sufficient to dispense the required dose of liquid medicine from the vessel 408. In this case, a further plunger' part may be required. In this embodiment, the arrangement of the actuation mechanism 402 and plunger mechanism 406 may cause the actuation mechanism 402 to displace the plunger mechanism 406 in the dispensing direction A (i.e. the direction of the contraction of the SMA actuator wire 404)However, when the SMA actuator wire 404 cools and returns to its original position, the actuation mechanism 402 may itself remain stationary. This may allow the contraction and relaxation of the SMA actuator wire 404 to occur repeatedly but cause the actuation mechanism 402 to only move in the dispending direction A. Thus, high doses of medication may be dispensed by multiple actuations of the SMA wire actuator 494.

Figure 5 shows the relative positions of the SMA actuator wire 404, actuation mechanism 402, return mechanism 410 and plunger mechanism 406 during a dispense cycle. At the start of a dispense cycle (step 500), the SMA actuator wire 404 may be in an extended state and the plunger mechanism 406 may be in its start position. During a dispense cycle (step 502), the SMA actuator wire 404 may be driven and caused to contract. Contraction of the SMA actuator wire 404 causes the actuation mechanism 402 to move in the dispensing direction (indicated by arrow A), which in turn causes plunger mechanism 406 to move in the dispending direction into vessel 408. This causes liquid in vessel 408 to be dispensed via a dispensing element. To enable more liquid to be dispensed from the vessel 408, in embodiments, the SMA actuator wire 404 cools and returns to its expanded state, but the actuation mechanism 402 and plunger mechanism 406 may stay in the same position (step 504). Thus, the subsequent contraction of the SMA actuator wire 404 may cause the plunger mechanism 406 to move further into vessel 408, and thereby cause more liquid to be dispensed.

In the case of a reusable device, a mechanism may also be required to allow the plunger to be returned to its original, undisplaced position when replacing the vessel. For instance, the action of opening the delivery device to remove the vessel may allow the mechanism interface between the actuation mechanism and plunger mechanism to become disengaged and allow the plunger mechanism to be pushed to its original position by hand without being hampered by or affecting the position of the advancing member. By closing the delivery device, the mechanism between the actuation mechanism and plunger mechanism would become re-engaged and the mechanism continue to operate as previously.

As mentioned above, one of the key issues users of pen-type drug delivery devices may have with their device is the high force and dexterity required to eject the medication. The SMA based actuation mechanism of the present techniques means the user does not have to apply a high force, and the dose dial does not have to be projected from the body of the pen. This will significantly improve the usability and comfort of use of the product.

Current insulin pens are typically limited to a dose of 80 IU primarily due to the limits of dexterity of users and practical mechanism designs. A powered pumping mechanism is not restricted by these limits and could eject the entire contents of the insulin vessel -typically around 300 IU -in one dose, thus reducing or removing the requirement for multiple injections for a single dose for users that have particularly high requirements for insulin volumes.

Current insulin pens have a limit to the minimum dose size and resolution of the dose -typically 0.5 IU. This is due the design of their internal mechanisms and limits of the manufacturing precision of the parts. The use of an SMA actuator with resistance control would allow much finer and accurate motion, allowing the minimum dosage and resolution to be improved -for instance to 0.25 IU.

The use of an SMA actuator in an insulin pump to replace the current motor would allow significant reductions to the size and weight of the device, making it a more comfortable and less obtrusive to wear. The SMA actuator is also silent in operation and therefore makes it more audibly discrete.

Depending upon the speed of medication ejection, viscosity of medication and details of the medication containment vessel design and materials, a particularly large force may be required from the pumping system. In order to increase the pumping force, thicker diameter SMA wire can be selected. However, this will increase the system power consumption and therefore the wire diameter should be selected to a carefully considered balance of force requirement with minimum power consumption to maximise battery life.

Larger diameter SMA wires will provide greater force and power consumption but also take longer to cool and return to their original position. Using a number of SMA wires in parallel of a relatively narrow diameter will increase the force to that of an SMA wire with relatively thick diameter without compromising the speed of operation of the pump.

Another means of increasing the speed of the pumping system is to use SMA wire in an opposing 'push/pull' arrangement where a heated SMA wire is used to actively return another SMA wire to its original length quickly when cooling, instead of relying on a passive spring component.

Because of the necessity to ensure the quantity of medication delivered is exactly that requested by the user, it may be beneficial to add a further position measurement 'linear encoder' arrangement to the device. Most beneficially this would be added to measure the position of the plunger part. This could be used just to check the expected motion of the plunger has been achieved by the resistance control of the SMA wire or be used as a complementary control element. Appropriate encoder devices include Hall-effect sensors, photo reflectors and other technologies.

Insulin pens typically use the dose dial to set the quantity of medication subsequently delivered. In the case of a powered pump system with a microcontroller, a rotary encoder could be used to advise the pumping system microcontroller of the requested dose. This could result in a more compact mechanism and final product. An appropriate technology would be a rotary potentiometer. Alternatively, the dose dial could be used to displace a hard stop in the pen mechanism that was positioned according to the required displacement of the plunger for the particular medication amount. When the plunger was obstructed by the hard stop, this obstruction would be registered by the change in characteristic of the measured resistance of the SMA wire for a given input current.

Further embodiments of the present techniques are set out in the following numbered clauses: 1. A medication dispenser driven by an SMA wire actuator controlled in closed-loop by electrical resistance measurements.

2. The medication dispenser of clause 1 wherein said medication is insulin.

3. The medication dispenser of previous clauses arranged in the form of a pen and including a needle.

4. The medication dispenser of previous clauses arranged as a wearable device including a catheter.

5. The medication device of previous clauses wherein the SMA wire actuator allows a variable amount of medication to be dispensed within a single actuation.

6. The medication device of clauses 1-4 wherein the SMA wire actuator allows a variable amount of medication to be dispensed by repeated actuations.

Those skilled in the art will appreciate that while the foregoing has described what is considered to be the best mode and where appropriate other modes of performing present techniques, the present techniques should not be limited to the specific configurations and methods disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that present techniques have a broad range of applications, and that the embodiments may take a wide range of modifications without departing from any inventive concept as defined in the appended claims.

Also disclosed is the following: 1. A drug delivery device comprising: a vessel for containing a volume of liquid medication or drug; a plunger mechanism in fluid communication with the vessel; an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising: a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism in a dispensing direction which dispenses the liquid medication or drug from the vessel; and a controller for closed-loop control of the SMA actuator wire.

2. The drug delivery device according to item 1 further comprising resistance measurement circuitry coupled to the controller for determining a position of the 113 plunger mechanism.

3. The drug delivery device according to item 1 or 2 further comprising at least one sensor for determining a position of the plunger mechanism.

4. The drug delivery device according to item 2 or 3 wherein the controller: receives data from the at least one sensor and/or resistance measurement circuitry; determine, using the received data, a current position of the plunger mechanism; compare the determined current position of the plunger mechanism with a required position; and generate a control signal to adjust the current position of the plunger mechanism towards the required position.

5. The drug delivery device according to any one of item 2, 3 or 4 wherein the resistance measurement circuitry and/or the at least one sensor is used to determine plunger mechanism operation faults.

6. The drug delivery device according to any preceding item further comprising 30 a return mechanism for returning the SMA actuator wire to an extended state.

7. The drug delivery device according to item 6 wherein the return mechanism is a resilient element.

8. The drug delivery device according to item 6 wherein the return mechanism is a spring.

9. The drug delivery device according to item 6 wherein the return mechanism is a further SMA actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism away from the dispensing direction.

10. The drug delivery device according to any preceding item further comprising 113 a power source for supplying power to the SMA actuator wire.

11. The drug delivery device according to item 10 wherein the power source comprises a battery.

12. The drug delivery device according to any preceding item further comprising a force sensor coupled to the controller for determining a rate at which the liquid medication or drug is dispensed from the vessel.

13. The drug delivery device according to item 12 wherein the controller: receives data from the force sensor; determine, using the received data, a rate at which the liquid medication or drug is being dispensed from the vessel; compare the determined rate of dispensing with a required rate of dispensing; and generate a control signal to adjust the rate of movement of the plunger mechanism.

14. The drug delivery device according to any preceding item further comprising a dosage mechanism coupled to the controller for controlling the volume of liquid medication or drug dispensed from the vessel during a dispense cycle.

15. The drug delivery device according to item 14 wherein the dosage mechanism comprises at least one moveable stop which protrudes from an inner surface of the vessel and is arranged to obstruct the plunger mechanism and thereby control the volume of liquid medication or drug dispensed from the vessel during a dispense cycle.

16. The drug delivery device according to any preceding item wherein the liquid medication or drug is insulin.

17. The drug delivery device according to any preceding item wherein the device comprises a needle.

18. The drug delivery device according to any preceding item wherein the device comprises a catheter.

19. The drug delivery device according to any preceding item wherein the device is an insulin pen.

20. The drug delivery device according to any preceding item wherein the

device is portable.

21. The drug delivery device according to any preceding item wherein the zo device is wearable.

22. The drug delivery device according to any one of items 1 to 21 wherein the actuation mechanism is arranged to cause the plunger mechanism to dispense a volume of liquid medication or drug via a single actuation.

23. The drug delivery device according to any one of items 1 to 21 wherein the actuation mechanism is arranged to cause the plunger mechanism to dispense a volume of liquid medication or drug via multiple actuations.

24. The drug delivery device according to any preceding item wherein the controller comprises at least one processor.

25. A method for closed-loop control of a drug delivery device comprising a vessel for containing a volume of liquid medication or drug, a plunger mechanism in fluid communication with the vessel, an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism in a dispensing direction which dispenses the liquid medication or drug from the vessel, the method comprising: receiving data for determining a position of the plunger mechanism; determining, using the received data, a current position of the plunger mechanism; comparing the determined current position of the plunger mechanism with a required position; and generating a control signal to adjust the current position of the plunger mechanism towards the required position.

26. The method according to item 25 wherein the data is received from resistance measurement circuitry arranged to measure the resistance of the SMA actuator wire.

27. The method according to 25 or 26 wherein the data is received from at least one sensor for determining a position of the plunger mechanism.

28. A non-transitory data carrier carrying processor control code to implement the method of item 25.

29. Circuitry for closed-loop control of a drug delivery device comprising a vessel for containing a volume of liquid medication or drug, a plunger mechanism in fluid communication with the vessel, an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism in a dispensing direction which dispenses the liquid medication or drug from the vessel, wherein the circuitry: receives data for determining a position of the plunger mechanism; determines, using the received data, a current position of the plunger mechanism; compares the determined current position of the plunger mechanism with a required position; and generates a control signal to adjust the current position of the plunger mechanism towards the required position.

30. A drug delivery device comprising a shape memory alloy (SMA) actuator wire arranged to cause dispensing of a liquid medication or drug from the device, wherein the SMA actuator wire is controlled by closed-loop control.

Claims

CLAIMS1. A drug delivery device comprising: a vessel for containing a volume of liquid medication or drug; a plunger mechanism in fluid communication with the vessel; an actuation mechanism coupled to the plunger mechanism, the actuation mechanism comprising: a shape memory alloy (SMA) actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism in a dispensing direction which dispenses the liquid medication or drug from the vessel; and a controller for closed-loop control of the SMA actuator wire, wherein the drug delivery device further comprises resistance measurement circuitry coupled to the controller for determining a position of the plunger mechanism.
2. The drug delivery device as claimed in claim 1 further comprising at least one sensor for determining a position of the plunger mechanism.
3. The drug delivery device as claimed in claim 1 or 2 wherein the controller: receives data from the at least one sensor and/or resistance measurement circuitry; determine, using the received data, a current position of the plunger mechanism; compare the determined current position of the plunger mechanism with a required position; and generate a control signal to adjust the current position of the plunger mechanism towards the required position.
4. The drug delivery device as claimed in any preceding claim, wherein the resistance measurement circuitry and/or the at least one sensor is used to determine plunger mechanism operation faults.
5. The drug delivery device as claimed in any preceding claim further comprising a return mechanism for returning the SMA actuator wire to an extended state.
6. The drug delivery device as claimed mechanism is a resilient element.
7. The drug delivery device as claimed mechanism is a spring.
8. The drug delivery device as claimed mechanism is a further SMA actuator wire arranged to, on contraction, apply a force to the actuation mechanism to cause the actuation mechanism to advance the plunger mechanism away from the dispensing direction.
9. The drug delivery device as claimed in any preceding claim further comprising a power source for supplying power to the SMA actuator wire.
10. The drug delivery device as claimed in claim 9 wherein the power source comprises a battery.
11. The drug delivery device as claimed in any preceding claim further comprising a force sensor coupled to the controller for determining a rate at which the liquid medication or drug is dispensed from the vessel.
12. The drug delivery device as claimed in claim 11 wherein the controller: receives data from the force sensor; determine, using the received data, a rate at which the liquid medication or drug is being dispensed from the vessel; compare the determined rate of dispensing with a required rate of dispensing; and generate a control signal to adjust the rate of movement of the plunger mechanism.in claim 5 wherein the return in claim 5 wherein the return in claim 5 wherein the return
13. The drug delivery device as claimed in any preceding claim further comprising a dosage mechanism coupled to the controller for controlling the volume of liquid medication or drug dispensed from the vessel during a dispense cycle.
14. The drug delivery device as claimed in claim 13 wherein the dosage mechanism comprises at least one moveable stop which protrudes from an inner surface of the vessel and is arranged to obstruct the plunger mechanism and thereby control the volume of liquid medication or drug dispensed from the vessel lo during a dispense cycle.
15. The drug delivery device as claimed in any preceding claim wherein the liquid medication or drug is insulin.
16. The drug delivery device as claimed in any preceding claim wherein the device comprises a needle.
17. The drug delivery device as claimed in any preceding claim wherein the device comprises a catheter.
18. The drug delivery device as claimed in any preceding claim wherein the device is an insulin pen.
19. The drug delivery device as claimed in any preceding claim wherein thedevice is portable.
20. The drug delivery device as claimed in any preceding claim wherein the device is wearable.
21. The drug delivery device as claimed in any one of claims 1 to 20 wherein the actuation mechanism is arranged to cause the plunger mechanism to dispense a volume of liquid medication or drug via a single actuation.
22. The drug delivery device as claimed in any one of claims 1 to 20 wherein the actuation mechanism is arranged to cause the plunger mechanism to dispense a volume of liquid medication or drug via multiple actuations.
23. The drug delivery device as claimed in any preceding claim wherein the controller comprises at least one processor.