Use of one or more indicators to trigger the initiation and / or termination of an electrical pulse during control of the operation of a drug delivery pump - Patents.com

Abstract

The present invention relates to the termination of application of an electrical pulse to a shape memory alloy (SMA) element that causes actuation of a drug pump based on the resistance value, where the magnitude of the resistance value, the rate of change of the resistance value, the temperature of the SMA element, the time elapsed since the initial application of the electrical pulse to the SMA element, or a combination thereof, can be used to trigger the termination of application of the electrical pulse to the SMA element.

Description

[Technical Field]

[0001] (Related Applications) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 380508, filed October 21, 2022, the entire contents of which are incorporated herein by reference in their entirety. [Background technology]

[0002] Some conventional drug delivery devices use shape memory alloy (SMA) elements. SMA elements transition between shapes as the temperature of the element changes. The SMA element "remembers" its original shape when the element's temperature reaches a transition temperature. For example, as an SMA wire warms, it may shorten to its original short shape. This feature can be utilized within devices to activate components.

[0003] In one drug delivery device offered by Insulet Corporation of Acton, Massachusetts, an SMA wire drives the actuation of the device's drug delivery pump to deliver the drug. Specifically, an electrical pulse of a predetermined duration is applied to the SMA wire within the device. The application of the electrical pulse heats and shortens the SMA wire. The shortening of the SMA wire moves a component that drives the actuation of the drug delivery pump. Termination of the application of the electrical pulse to the SMA wire is triggered by a mechanical termination mechanism that relies on overshoot of the component that drives the actuation. Summary of the Invention

[0004] According to one aspect of the invention, a drug delivery device for delivering a drug to a user includes a drug reservoir for storing a drug and a drug pump for pumping the drug from the drug reservoir for delivery to a user. The device also includes a power source and a shape memory alloy (SMA) element for causing actuation of the drug pump to deliver the drug. The device further includes a processor configured to initiate application of an electrical pulse from the power source to the SMA element to cause the drug pump to deliver the drug from the drug reservoir. The processor is also configured to determine a resistance of the SMA element over time and, based on the determined resistance of the SMA element over time, determine whether application of the electrical pulse should be terminated. The processor is additionally configured to terminate application of the electrical pulse to the SMA element in response to determining that application of the electrical pulse should be terminated.

[0005] The processor may be configured to determine a rate of change of resistance (RoC) and compare the RoC to a threshold value in determining that application of the electrical pulse should be terminated. The processor may be further configured to determine a magnitude of change in resistance of the SMA element, compare the determined magnitude of change in resistance to a threshold value, and terminate the electrical pulse based in part on the comparison to the threshold value. The processor may be configured to collect voltage and current readings of the SMA element over time, and determining the resistance of the SMA element over time may include the processor calculating the resistance of the SMA element over time from the collected voltage and current readings. The processor may terminate application of the electrical pulse to the SMA element as part of determining that application of the electrical pulse should be terminated by determining a moving average of a subset of the resistance values, determining at least one derivative or approximation of the determined moving average value, and comparing at least one derivative or approximation of the determined moving average value to a threshold value. The SMA element may be an SMA wire. Determining that application of the electrical pulse should be terminated may include determining a second derivative or an approximation of a second derivative of the resistance value or one of the averages of successive ones of the resistance values, and determining that application of the electrical pulse should be terminated based on the second derivative or the approximation of the second derivative.

[0006] According to another aspect of the invention, a drug delivery device includes a drug reservoir for storing a drug, a pump for pumping the drug from the drug reservoir, an SMA element for actuating the pump, and a power source. The device also includes a processor configured to cause electrical pulses from the power source to be applied to the SMA element, causing actuation of the drug pump to expel the drug from the drug reservoir, monitor a resistance of the SMA element, and terminate application of the pulses to the SMA based on a metric reflective of the resistance.

[0007] The drug delivery device may be a wearable insulin pump, and the drug may be insulin. The processor may be configured to perform resistance filtering. The power source may be a battery and / or a capacitor. The SMA element may be coupled to a component that drives operation of the drug pump. The SMA element may contract in length in response to application of an electrical pulse. The indicator reflecting the resistance may be an indicator of RoC over time with respect to the resistance or an indicator of an average of the resistance. The indicator of RoC over time with respect to the resistance may be a derivative of the resistance or the average of the resistance. The indicator of RoC over time with respect to the resistance may be a second derivative of the resistance or the average of the resistance.

[0008] According to a further aspect of the invention, a drug delivery device includes a drug reservoir for storing a drug, a pump for pumping the drug from the drug reservoir, an SMA element for operating the pump, and a power source, and may further include a temperature sensor for sensing the temperature of the SMA element and a clock for outputting an indication of time. The device may further include a processor for causing an electrical pulse from the power source to be initially applied to the SMA element and operating the drug pump to output the drug from the drug reservoir. The processor may also be configured to monitor a temperature value of the SMA element measured by the temperature sensor and to terminate application of the pulse to the SMA element based on the temperature of the SMA element and the time since the initial application of the electrical pulse to the SMA element.

[0009] The SMA element may be one or more SMA wires. Multiple consecutive temperature values ​​may be used to determine that a threshold has been exceeded before terminating the application of pulses to the SMA element. The medication delivery device may be an insulin delivery device.

[0010] According to a further aspect of the invention, a drug delivery system may include a drug reservoir for storing a drug and a pump for pumping the drug from the drug reservoir. The system may include a first SMA element and a second SMA element for actuating the pump. The first SMA element and the second SMA element may be configured to be opposed to each other and alternately actuated to drive the pump. The system may include a power source and a processor. The processor may be configured to monitor the resistance of the first SMA element. An electrical pulse from the power source may have been applied to the first SMA element more recently than the second SMA element. The processor may be further configured to identify when the resistance of the first SMA element reaches a threshold level and, based on the identification, apply an electrical pulse to the second SMA element to activate the second SMA element and drive the pump to deliver the drug from the reservoir to a user.

[0011] The system may include one or more drive wheels coupled to a pump, the drive wheels being driven by a first SMA element and a second SMA element in response to application of an electrical pulse to the first SMA element and the second SMA element. The first SMA element and the second SMA element may be SMA wire. Application of the electrical pulse to the first SMA element may cause the first SMA element to transition from a current state to a more fully austenitic state. The threshold level of resistance may be associated with a state in which the second SMA element has not fully cooled to ambient temperature and is still in a partially austenitic state. Monitoring the resistance of the first SMA element may include measuring a voltage across the first SMA element and determining the resistance of the first SMA element from the voltage measurement. The system may include a current sensor for measuring a current through the first SMA element, and the current measurement may also be used in determining the resistance of the first SMA element. The medication may include at least one of insulin, a glucagon-like peptide (GLP)-1 receptor agonist, or a gastric inhibitory peptide (GIP), or a dual GIP / GLP receptor agonist.

[0012] According to a further aspect of the invention, a drug delivery system may include a drug reservoir for storing a drug and a pump for pumping the drug from the drug reservoir. The system may also include a first SMA element and a second SMA element for actuating the pump. The first SMA element and the second SMA element may be configured to be opposed to each other and alternately actuated to drive the pump. The system may include a power source and a processor. The processor may be configured to initiate application of an electrical pulse from the power source to the second SMA element, causing actuation of the second SMA element by transitioning it from a current state to a more fully austenitic state, thereby actuating the pump to deliver the drug from the reservoir to a user. The processor may also be configured to monitor the resistance of the second SMA element as the electrical pulse is applied to the second SMA element and, based on the monitoring, terminate application of the electrical pulse to the second SMA element.

[0013] Monitoring the resistance of the second SMA element may include measuring the voltage of the second SMA element and the current of the second SMA element and determining the resistance from the voltage and current measurements. The application of the electrical pulse to the second SMA element may be terminated when the temperature of the second SMA element is higher than ambient temperature. The first SMA element and the second SMA element may be SMA wire. The device may include a switch under the control of the processor for initiating the application of the electrical pulse to the second SMA element. The switch may also be configurable to terminate the application of the electrical pulse to the second SMA element. The device may include an additional switch for controlling the application of electricity to the first SMA element.

[0014] According to yet another aspect of the invention, a method may include monitoring, with a processor, the resistance of first and second SMA elements arranged in opposing positions within a medical device and actuated in an alternating manner, and based on the resistance measurements, the method may determine, with the processor, one of the following: that a crimp on one of the SMA elements has a problem, that one of the SMA elements has overheated during application of an electrical stimulus, or that there is a problem with the grounding of the elements of the medical device.

[0015] The medical device may be a drug delivery device. The SMA element may act as an actuator for a pump, causing delivery of drug from the pump. The SMA element may be an SMA wire. The opposing arrangement may be configured to cause a selected one of the SMA elements to elongate the other SMA element as the other SMA element cools. The method may include obtaining voltage and current values ​​and calculating resistance of the SMA element. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates an exemplary drug delivery system of an exemplary embodiment. [Figure 2] FIG. 2 shows the internal components of an exemplary medication delivery device of an exemplary embodiment. [Figure 3] FIG. 3 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on a resistance value for the SMA element. [Figure 4] FIG. 4 shows an exemplary plot of the resistance of an SMA element of a medication delivery device when an electrical pulse is applied to the SMA element. [Figure 5] FIG. 5 is a representative plot showing the resistance and rate of change of resistance (RoC) of an SMA element of a medication delivery device when an electrical pulse is applied to the SMA element. [Figure 6]FIG. 6 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on an RoC for a resistance value. [Figure 7] FIG. 7 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to calculate RoC from the difference between successive resistance values. [Figure 8] FIG. 8 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to calculate RoC as the first derivative of resistance with respect to time. [Figure 9] FIG. 9 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to calculate RoC as the second derivative of resistance with respect to time. [Figure 10] FIG. 10 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on the RoC for the resistance and the magnitude of the change in resistance. [Figure 11] FIG. 11 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on elapsed time. [Figure 12] FIG. 12 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on several factors. [Figure 13] FIG. 13 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on the temperature of the SMA element. [Figure 14] FIG. 14 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to terminate the application of an electrical pulse to an SMA element based on the temperature of the SMA element and elapsed time. [Figure 15] FIG. 15 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to determine the state of an SMA element from its resistance. [Figure 16] FIG. 16 shows an example of status information for an SMA element that can be determined from resistance measurements in an exemplary embodiment. [Figure 17] FIG. 17 shows an example chart of pulse timing for two opposing SMA elements in an example embodiment. [Figure 18] FIG. 18 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to trigger the application of a pulse to an SMA element based on the resistance of the SMA element in an unactuated state. [Figure 19] FIG. 19 shows a flowchart of exemplary steps that may be performed in an exemplary embodiment to trigger the termination of the application of a pulse to an SMA element based on the resistance of the SMA element in an unactuated state. [Figure 20] FIG. 20 shows an example plotted resistance of an SMA element superimposed on the pulse chart diagram of FIG. [Figure 21] FIG. 21 illustrates an exemplary electrical circuit for monitoring the resistance of an SMA element in an exemplary embodiment. [Figure 22A] FIG. 22A shows a flowchart of a first optional example step that may be implemented in an example embodiment to address the voltage offset problem. [Figure 22B] FIG. 22B shows a flowchart of a second optional example step that may be implemented in an example embodiment to address the voltage offset issue. [Figure 23] FIG. 23 shows an alternative electrical circuit for monitoring the resistance for an SMA element in an exemplary embodiment. [Figure 24] FIG. 24 shows another alternative electrical circuit for monitoring the resistance for an SMA element in an exemplary embodiment. [Figure 25] FIG. 25 shows a flow chart of a first optional exemplary step that may be implemented in an exemplary embodiment to determine whether an SMA element has overheated. [Figure 26]FIG. 26 shows a flowchart of a first optional exemplary step that may be implemented in an exemplary embodiment to identify crimp or ground hook problems based on monitored resistance for an SMA element. DETAILED DESCRIPTION OF THE INVENTION

[0017] Unlike conventional approaches that rely on mechanical mechanisms (including mechanical-electrical switch mechanisms) to trigger the termination of application of an electrical pulse, exemplary embodiments can cause drug pump actuation based on resistance to terminate application of an electrical pulse to an SMA element. The magnitude of the resistance, the rate of change (RoC) of the resistance, the temperature of the SMA element, the time elapsed since the initial application of the electrical pulse to the SMA element, or a combination thereof, can be used to trigger the termination of application of an electrical pulse to the SMA element in exemplary embodiments, as described below. It should be recognized that the RoC of the resistance of an SMA element can be captured by the first or second derivative of the resistance with respect to time, as described below. The RoC of the resistance can be a more robust and reliable indicator for accurately triggering the termination of application of an electrical pulse at a desired time than simply relying on the magnitude of the resistance.

[0018] The more precisely timed (i.e., earlier) termination of the application of the electrical pulse to the SMA element in the exemplary embodiments results in less energy use during operation of the drug delivery device. This can be particularly beneficial when the drug delivery device is powered by a finite power source, such as a battery and / or charged capacitor, where lower energy requirements can extend the period before the power source needs to be recharged or replaced. This earlier termination can also result in less mechanical fatigue of the SMA element compared to conventional termination approaches due to the shorter excitation time of the wires that results from earlier termination of the application of the electrical pulse.

[0019] In some exemplary embodiments, the resistance of non-actuated SMA elements (i.e., SMA elements that were most recently actuated but are not currently actuated) may be monitored. This monitoring may be used to determine when to begin applying an electrical pulse to other SMA elements. Furthermore, monitoring the resistance of non-actuated SMA elements may be used to determine when to terminate application of an electrical pulse to other SMA elements. To conserve energy and extend the life of the SMA elements, the initiation of the pulse may occur before the non-actuated SMA elements have completely cooled, and the termination of the electrical pulse may be selected as soon as possible.

[0020] Monitoring the resistance of an SMA element can also identify problems within a device. For example, monitoring the resistance can be used to identify overheating of the SMA element or problems with the crimp or grounding of the component. More generally, monitoring the resistance of an SMA element can provide useful information about the condition of the SMA element.

[0021] 1 shows a block diagram of an exemplary drug delivery system 100 suitable for delivering a drug to a user 108, according to an exemplary embodiment. The drug delivery system 100 includes a drug delivery device 102. The drug delivery device 102 may be a wearable device attached to the body of the user 108 or carried by the user. The drug delivery device 102 may be directly coupled to the user (e.g., attached directly to a body part and / or skin of the user 108 via adhesive, etc.) without using tubing and an injection site directly below the drug delivery device 102, or may be carried by the user (e.g., on a belt or in a pocket) with the drug delivery device 102 connected to an injection site where the drug is injected using a needle and / or cannula. The drug delivery device 102 may include an adhesive on its surface to facilitate attachment to the user 108.

[0022] The medication delivery device 102 may include a processor 110. The processor 110 may be, for example, a microprocessor, logic circuitry, a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or a microcontroller. The processor 110 may maintain the date and time and other functions (e.g., calculations, etc.). The processor 110 may be operable to execute a control application 116 encoded in computer program instructions stored in a memory device 114 that enable the processor 110 to direct the operation of the medication delivery device 102. The control application 116 may be a single program, multiple programs, a module, a library, etc. The processor 110 may also execute computer program instructions stored in the memory device 114 for a user interface (UI) 117, which may include one or more display screens shown on a display device 127. The display device 127 may display information to the user 108 and, in some examples, may receive input from the user 108, for example, when the display device 127 is a touchscreen.

[0023] The control application 116 can control delivery of medication to the user 108 for the control approaches described herein. In an exemplary embodiment, the control application 116 can control termination of an electrical pulse to the SMA element, as described below. The memory device 114 can maintain history 111 about the device and / or user, such as a history of resistance values, resistance RoC values, or a history of basal deliveries, a history of bolus deliveries, and / or other histories, such as a history of meal events, a history of exercise events, a history of glucose levels, etc. Additionally, the processor 110 may be operable to receive data or information. The memory device 114 may include both primary and secondary memory. The memory device 114 may include random access memory (RAM), read-only memory (ROM), optical storage, magnetic storage, removable storage media, solid-state storage, etc.

[0024] The drug delivery device 102 may include a tray or cradle and / or one or more housings for housing its various components, including a pump 113, a power source (not shown), and a reservoir 112 for storing medication for delivery to the user 108. A fluid pathway to the user 108 may be provided, and the drug delivery device 102 may use the pump 113 to expel medication from the reservoir 112 for delivery to the user 108 via the fluid pathway. The fluid pathway may include, for example, tubing connecting the drug delivery device 102 to the user 108 (e.g., tubing connecting a cannula to the reservoir 112) and may include conduits to separate infusion sites. The drug delivery device 102 may have an operating cycle, such as every 5 minutes, in which a basal dose of medication is calculated and delivered as needed. These steps are repeated for each cycle.

[0025] There may be one or more elements for enabling a communication link with one or more devices physically separate from the medication delivery device 102, which may include, for example, a user and / or the user's caregiver's management device 104, a sensor 106, a smart watch 130, a fitness monitor 132, and / or various other devices 134. The communication link may include any wired or wireless communication link operating according to any known communication protocol or standard, such as Bluetooth, Wi-Fi, a near field communication standard, a cellular standard, or any other wireless protocol.

[0026] The drug delivery device 102 can interface with a network 122 via a wired or wireless communication link. The network 122 can include a local area network (LAN), a wide area network (WAN), or a combination thereof. A computing device 126 can interface with the network 122, and the computing device can communicate with the drug delivery device 102.

[0027] The drug delivery system 100 may include one or more sensors 106 for sensing the level of one or more analytes. The sensors 106 may be coupled to the user 108, for example, by adhesive, and may provide information or data regarding one or more medical conditions and / or physical attributes of the user 108. The sensors 106 may be physically separate from the drug delivery device 102 or may be an integral component thereof. The sensors 106 may include, for example, a glucose monitor, such as a continuous glucose monitor (CGM) and / or a non-invasive glucose monitor. The sensors 106 may include a ketone sensor, an analyte sensor, a heart rate monitor, a respiration rate monitor, a motion sensor, a temperature sensor, a sweat sensor, a blood pressure sensor, an alcohol sensor, etc. Some sensors 106 may detect characteristics of components of the drug delivery device 102. For example, the sensors 106 in the drug delivery device may include a voltage sensor, a current sensor, a temperature sensor, etc.

[0028] The medication delivery system 100 may or may not include a management device 104. In some embodiments, a management device is not needed because the medication delivery device 102 can manage itself. The management device 104 may be a special-purpose device, such as a dedicated personal diabetes management (PDM) device. The management device 104 may also be a programmed general-purpose device, such as any portable electronic device that includes a dedicated controller, such as a processor, microcontroller, or the like. The management device 104 may be used to program or regulate the operation of the medication delivery device 102 and / or the sensor 106. The management device 104 may also be any portable electronic device, including, for example, a dedicated device, a smartphone, a smartwatch, or a tablet. In the illustrated example, the management device 104 may include a processor 119 and a memory device 118. The processor 119 may perform processing for managing the user's glucose level and for controlling delivery of medication to the user 108. The medication delivery device 102 may provide data from the sensor 106 and other data to the management device 104. The data may be stored in the memory device 118. The processor 119 may also be operable to execute programming code stored in the memory device 118. For example, the memory device 118 may be operable to store one or more control applications 120 for execution by the processor 119. The control applications 120 may be responsible for controlling the medication delivery device 102, such as controlling automatic insulin delivery (AID) of insulin to the user 108. In some exemplary embodiments, the control applications 120 provide the compatibility described herein. The memory device 118 may store the control applications 120, a history 121 as described above for the medication delivery device 102, and other data and / or programs.

[0029] A display device 140, such as a touchscreen, may be provided to display information. The display device 140 may display a user interface (UI) 123. The display device 140 may also be used to receive input, for example if it is a touchscreen. The management device 104 may also include input elements 125, such as a keyboard, buttons, knobs, etc., for receiving input from the user 108.

[0030] The management device 104 may interface with a network 124, such as a LAN or WAN, or a combination of such networks, via a wired or wireless communication link. The management device 104 may communicate with one or more servers or cloud services 128 via the network 124. Data, such as sensor values, may in some embodiments be sent directly from the medication delivery device 102 to the cloud service / server 128 for storage and processing, or alternatively from the management device 104 to the cloud service / server 128.

[0031] Other devices, such as a smartwatch 130, a fitness monitor 132, and a device 134, may be part of the drug delivery system 100. These devices 130, 132, and 134 may communicate with the drug delivery device 102 and / or the managing device 104 to receive information and / or issue commands to the drug delivery device 102. These devices 130, 132, and 134 may execute computer program instructions, for example, via control applications 116 and 120, to perform some of the control functions otherwise performed by the processor 110 or the processor 119. These devices 130, 132, and 134 may include a display for displaying information. The display may present a user interface for providing input by a user, such as to request a change or pause in dosage, or to request, initiate, or confirm a bolus delivery of a drug, or to display output, such as a change in dosage (e.g., a basal delivery amount), determined by the processor 110 or the managing device 104. These devices 130, 132, and 134 may also have wireless communication connections with the sensor 106 to directly receive analyte measurement data. Other delivery devices 105, such as a medication delivery pen, may be considered or provided for delivering medication to the user 108.

[0032] A wide variety of medications can be delivered by medication delivery device 102 and delivery device 105. The medication can be insulin for treating diabetes. The medication can be glucagon for raising a user's glucose levels. The medication can also be a glucagon-like peptide (GLP)-1 receptor agonist, which lowers glucose or delays gastric emptying, thereby delaying postprandial glucose spikes. Alternatively, the medication delivered by medication delivery device 102 can be one of a painkiller, a chemotherapy drug, an antibiotic, a blood thinner, a hormone, a blood pressure lowering drug, an antidepressant, an antipsychotic, a statin, an anticoagulant, an anticonvulsant, an antihistamine, an anti-inflammatory, a steroid, an immunosuppressant, an anti-anxiety drug, an antiviral, a nutritional supplement, or a vitamin. The medication can also be a combination of two or more of the above medications.

[0033] The functionality described herein for the exemplary embodiments may be under the control of or performed by the control application 116 of the medication delivery device 102 or the control application 120 of the management device 104. In some embodiments, the functionality may be under the control of or performed, in whole or in part, by a cloud service / server 128, a computing device 126, or other enumerated devices, including a smart watch 130, a fitness monitor 132, or other wearable device 133.

[0034] In closed-loop mode, the control application 116, 120 continuously determines the drug delivery rate for the user 108 based on a feedback loop. For insulin delivery devices, the goal of closed-loop mode is to have the user's glucose level at or within a target glucose range.

[0035] 2 shows exemplary components found inside housing 202 of exemplary drug delivery device 200. The components may include a reservoir 204 in which a drug is stored for delivery to user 108, a battery 206 that serves as a power source for drug delivery device 200, and an SMA wire 208 (formed from wire 208A and a second wire 208B, collectively referred to as 208) for causing actuation of drug pump 209. SMA wire 208 may be wrapped around SMA pulley 210. Drive wheel 212 is coupled to drug pump 209 and includes one or more gears 214 and 216. Pivotable drive engagement member 218 has one or more arms 220 and 222 for engaging gears 214 and 216, respectively. SMA wire 208 is coupled to pivotable drive engagement member 218 by integral connector 230, causing pivotable drive engagement member 218 to pivot back and forth, driving drive wheel 212, as will be described below. Drug pump 209 pumps drug from reservoir 204. Drug pump 209 includes a plunger 224 that operates to expel drug from reservoir 204. Drive wheel 212 may be connected to a tube nut 226. Tube nut 226 may be positioned on a lead screw (not shown) on plunger 224, such that movement of drive wheel 212 rotates the lead screw, thereby causing linear displacement of plunger 224.

[0036] To operate exemplary drug pump 209, an electrical pulse is applied to SMA wire 208A to impart an electrical potential to SMA wire 208A. When charged, a first portion of SMA wire 208 contracts, pulling pivotable drive engagement member 218 in a first direction. As pivotable drive engagement member 218 pivots in the first direction, arm 220 engages teeth on gear 214, rotating drive wheel 212 one increment at a time. Pivotable drive engagement member 262 pivots in the first direction. Generally speaking, one of arms 220 and 222 is alternatively engaged by gears 214 and 216 of drive wheel 212. The engaged arms 220 and 222 thus prevent counter-rotation of the drive and eliminate the need for a separate pawl element.

[0037] To initiate another pulse, the control circuit applies a current to SMA wire 208B. When charged, SMA wire 208B contracts, pulling pivotable drive engagement member 218 in a second direction, opposite the first direction. As pivotable drive engagement member 218 pivots in the second direction, arm 222 engages teeth on gear 216, rotating drive wheel 212 one increment. Pivotable drive engagement member 218 pivots in the second direction.

[0038] Each incremental rotation of drive wheel 212 advances a plunger within reservoir 204, dispensing a discrete amount of fluid. The discrete amount of fluid dispensed is a function of the sliding screw pitch (i.e., threads per inch), gear tooth size, and the diameter of the fluid reservoir. In a preferred embodiment, to deliver U100 insulin for the treatment of Type 1 diabetes, the discrete amount of fluid dispensed is between about 0.025 ul and about 0.05 ul. The control circuit alternately energizes SMA wires 208A and 208B until the desired amount of fluid is dispensed.

[0039] The illustration of the exemplary drug delivery device 200 in Figure 2 shows the mechanical overshoot components in place, although these components may be removed or may remain in the exemplary embodiment.

[0040] The optimal time to terminate the application of electrical pulses to SMA wires 208A and 208B corresponds to the point at which active arm 220 or 222 of pivotable drive engagement member 218 disengages from corresponding gear 214 or 216 of drive wheel 212 of drug pump 209. The illustrative embodiments are able to determine and use a termination time that is closer to the optimal termination time than conventional approaches that rely on mechanical overshoot mechanisms.

[0041] As described above, in exemplary embodiments, an indication of resistance (e.g., resistance value, RoC of resistance, etc.) may be used in triggering termination of an electrical pulse that drives actuation of drug pump 113 in drug delivery device 102. FIG. 3 shows a flowchart of exemplary steps that may be performed in exemplary embodiments for using resistance value in triggering termination of an electrical pulse. Termination of the electrical pulse to an SMA element (such as SMA wire 208) causes drug pump 113 to no longer be actuated and delivery of drug to user 108 to cease. At 302, an electrical pulse is applied to an SMA element, such as SMA wire 208A or 208B, causing actuation of drug pump 113 that results in delivery of drug from drug delivery device 102 to user 108. At 304, the resistance of the SMA element is monitored to determine the resistance of the SMA element over time. Based on the determined resistance, a determination is made at 306 that the electrical pulse should be terminated such that the electrical pulse is no longer applied to the SMA element. At 308, based on this determination, the application of the electrical pulse to the SMA element is terminated.

[0042] 4 shows an exemplary plot 400 of the resistance, in ohms, of an SMA element over time during the application of a 0.25 second electrical pulse. In this example, the SMA element is one of SMA wires 208A or 208B. When the electrical pulse is initially applied at 402, the resistance is approximately 16 ohms at its highest level. As electricity flows through SMA wire 208A in response to the electrical pulse, SMA wire 208A or 208B heats up and the resistance of SMA wire 208A or 208B begins to slowly decrease. Thus, at 404, the resistance is decreased relative to 402. As SMA wire 208A or 208B continues to heat, SMA wire 208A or 208B approaches and undergoes a state transition from a martensitic state to an austenitic state. As SMA wire 208A or 208B reaches the transition temperature at which the state transition occurs, the transition progresses and the resistance decreases more rapidly at 406 in plot 400, shortening. Due to the arrangement of the drug pump's actuating components (e.g., gears 214, 216, arms 220, 222, pivotable drive engagement member 218, and the SMA wire connected thereto), actuation of gears 214 and 216 by arms 220 or 222 in response to movement of SMA wire 208A or 208B is completed during this time. Once the transition is completed, SMA wire 208A or 208B is no longer shortening, as suggested by the flat region at 408 in plot 400, and therefore the resistance also remains largely flat.

[0043] FIG. 5 shows plot 500, where earlier or more accurate termination is indicated on the resistance versus time plot. This plot 500 is derived based on the resistance and termination point triggered based on the use of a conventional mechanical overshoot termination mechanism, on the one hand, and based on the use of the resistance-based termination approach of the same device described herein, on the other hand. At 504, as in the exemplary embodiment, application of the electrical pulse to the SMA wire is terminated based on the resistance. As a safety factor, there is some latency between detection and termination, and the termination is not at the optimal termination point. Thereafter, at 506, application of the electrical pulse to the SMA wire is terminated by the mechanical overshoot mechanism employed in conventional systems.

[0044] 5 also shows a plot 502 of RoC in terms of resistance over time, where point 510 corresponds to the time of termination based on resistance value and point 512 corresponds to the time of termination based on a conventional mechanical overshoot termination mechanism.

[0045] The earlier termination of the application of the electrical pulse to the SMA element in the exemplary embodiment results in reduced energy usage during operation of the drug delivery device 102. This can be particularly beneficial when the drug delivery device 102 is battery powered, where lower energy requirements can extend battery life. Earlier termination can also result in less mechanical fatigue of the SMA element due to the reduced wire excitation time that results from earlier termination of the application of the electrical pulse when compared to conventional termination approaches.

[0046] The resistance of an SMA element, such as SMA wire 208A or 208B, can be obtained from a resistance measurement component. Alternatively, the resistance can be obtained by determining the voltage applied to the SMA element and measuring the current through the SMA element. Ohm's law states that I=V / R, where I is current, V is voltage, and R is resistance. Therefore, resistance can be calculated as R=V / I. Therefore, once the voltage and current are obtained, the resistance for the SMA element can be determined.

[0047] A first approach that can be employed to trigger the termination of an electrical pulse to an SMA element is to examine the RoC of the resistance of the SMA element (e.g., SMA wire). In this context, RoC may refer to, for example, the difference in resistance between successively sampled resistance values ​​or the difference in resistance between averages of resistance values, as determined from the first derivative or an approximation of the first derivative of the resistance with respect to time, or the deceleration of change in resistance, as determined from the second derivative of the resistance. The resistance values ​​may be sampled at a predetermined sample time. As described in more detail below, RoC may be one of several factors considered in determining whether to terminate the application of an electrical pulse to the SMA element in some exemplary embodiments.

[0048] 6 shows a flowchart 600 of example steps that may be performed in an example embodiment that uses an RoC for a resistance value to trigger termination of application of an electrical pulse to an SMA element that causes actuation of drug pump 113. At 602, an RoC for a resistance value may be determined. A number of example approaches for determining the RoC are detailed below. At 604, the determined RoC is compared to a threshold value to determine whether application of the electrical pulse should be terminated. If it is not determined that it should be terminated, at 606, application of the electrical pulse is not terminated. If it is determined that it should be terminated, at 608, application of the electrical pulse to the SMA element is terminated.

[0049] FIG. 7 shows a flowchart 700 of example steps that may be performed in an example embodiment to determine RoC (see 602) according to a first approach. In this first approach, at 702, the difference between resistance values ​​at successive times, or the difference between averages, such as rolling averages, over successive times, is determined. At 704, the RoC is calculated from the difference, e.g., set equal to the difference. If the RoC is determined by determining the difference between resistance values ​​or the difference between averages, such as rolling averages of several successive resistance values, over successive times, the comparison at 604 may be whether the RoC is below a threshold value (which may be empirically determined). This is because, as shown in FIG. 4, the resistance of an SMA element does not continue to decrease but may actually increase slightly after actuation in response to an electrical pulse is complete.

[0050] Another approach to determining the RoC value is to determine the first derivative of the resistance value or an approximation of the first derivative as the RoC. FIG. 8 shows a flowchart 800 of example steps that may be performed in an example embodiment. At 802, the first derivative of the resistance with respect to time (i.e., dR / dt) is calculated, or an approximation of the first derivative is calculated. In some embodiments, a curve may be constructed from the obtained resistance values, and interpolation between values ​​may be used to complete the curve. At 804, the calculated or approximated first derivative may be used as the RoC value.

[0051] An additional approach to determining the RoC value is to use the second derivative of the resistance as the RoC. The second derivative determines the RoC of the resistance. FIG. 9 shows a flowchart 900 of exemplary steps that may be performed in an exemplary embodiment for using the second derivative. At 902, the second derivative of the resistance is determined. At 904, a check is made to determine whether the second derivative is less than a threshold. At the inflection point where the state transition is complete and the resistance stops slowing down, the acceleration or deceleration of the resistance change should be zero or near zero because the RoC of the resistance does not change significantly at the inflection point. If the second derivative is not less than the threshold, then at 906, the application of the electrical pulse to the SMA element is not terminated and a recalculation is performed at the next sample time. If the second derivative is less than the threshold, then at 908, the application of the electrical pulse to the SMA element is terminated.

[0052] In some exemplary embodiments, the resistance reference error (ROC) and the magnitude of the change in resistance since the last sampling time are used in conjunction to determine whether to trigger termination of the application of an electrical pulse to the SMA element. Looking at the magnitude of the change in resistance helps avoid premature termination due to noise or other factors. FIG. 10 shows a flowchart 1000 of exemplary steps that may be performed in an exemplary embodiment to trigger termination of the application of an electrical pulse based on the resistance reference error (ROC) and the percentage of change in resistance. At 1002, the resistance reference error (ROC) is determined, as described above. If the resistance reference error (ROC) does not indicate that the application of the electrical pulse should be terminated at 1004, the application of the electrical pulse is not terminated at 1006 and the process is repeated at 1002. If the resistance reference error (ROC) indicates that the application of the electrical pulse should be terminated at 1004, additional steps are performed. At 1008, the percentage of change in resistance between samples is determined, and at 1010, the percentage is compared to a threshold. If the rate is not less than the threshold, the application of the electrical pulse is not terminated at 1006 and the process is repeated at 1002. If the rate of change in resistance is less than the threshold, the application of the electrical pulse to the SMA element is terminated at 1012. It should be appreciated that in some embodiments, a measure of the magnitude of the change may be used rather than the rate of change.

[0053] As an interim measure or alternative approach, in some exemplary embodiments, the time elapsed since the application of an electrical pulse to the SMA element may be used as an indicator for terminating the application of the electrical pulse to the SMA element. FIG. 11 shows a flowchart 1100 of exemplary steps that may be implemented in an exemplary embodiment for using time to trigger the termination of the application of an electrical pulse to the SMA element. At 1102, the time since the start of the application of the electrical pulse to the SMA element is determined using a timer or based on a clock accessible or built into the processor 110. At 1104, a check is made to see if the time exceeds a maximum threshold. The maximum threshold may be a time close to an optimal termination time or may be a fail-safe time for terminating the application of a pulse that would otherwise last longer than desired. If the maximum time has been exceeded, at 1106, the application of the electrical pulse to the SMA element is terminated. If not, the process beginning at 1102 is repeated.

[0054] As described above, in exemplary embodiments, different combinations of indicators and potentially other values ​​may be used to trigger the termination of application of an electrical pulse to an SMA element. FIG. 12 shows a flowchart 1200 of exemplary steps that may be performed in an exemplary embodiment, in which the derivative of the resistance value at a point in time and the rate of change of resistance are used together to trigger the termination of application of an electrical pulse to an SMA element. At 1202, the voltage drop across the SMA element and its current are collected. These values ​​are used to calculate the resistance value at 1204. An exemplary three-point rolling average filter may be applied at 1206 to output a three-point moving average of the most recent resistance value and the two previous resistance values. At 1208, the first derivative is approximated based on the three-point moving average. At 1210, an exponentially weighted moving average filter is applied to the derivative to determine an exponentially weighted moving average of the derivative values. The resulting derivative average is compared to a first threshold at 1212. The rate of change of resistance is determined and compared to a second threshold at 1214. If the derivative of the resistance and rate of change are below the threshold to which they are compared at 1216, the application of the electrical pulse to the SMA element is terminated at 1218. Otherwise, the process is repeated at the next sample time.

[0055] Another alternative factor that can be examined in determining whether to trigger the termination of the application of the electrical pulse to the SMA element is the temperature of the SMA element. When electricity is applied to the SMA element, the temperature of the SMA element increases. A signature temperature value or range can be associated with an inflection point at which actuation of the drug pump 113 is completed. The signature temperature can be used as a trigger for terminating the application of the electrical pulse to the SMA element. FIG. 13 shows a flowchart 1300 of exemplary steps that can be performed in exemplary embodiments using temperature as a trigger. At 1302, one or more temperature readings of the SMA element are obtained from a temperature sensor. In some exemplary embodiments, multiple consecutive temperature readings can be obtained. At 1304, a check is made to see if the one or more temperature readings are greater than or equal to a value suggestive of an optimal endpoint, which can be based on the transition temperature of the SMA element and / or simple experimentation. This check may, for example, involve comparing the average of the last three temperature readings to a threshold, or may involve comparing each of the temperature values ​​to a threshold, or may involve comparing a single temperature value to a threshold. If one or more temperature values ​​(or their average) are greater than or equal to the threshold, application of the electrical pulse to the SMA element is terminated at 1306. If not, the step at 1302 is repeated.

[0056] In other exemplary embodiments, both time and temperature may be examined to determine whether to terminate the application of the electrical pulse to the SMA element. At 1402, one or more temperature readings are obtained from a temperature sensor. If one or more temperature readings are below a threshold temperature at 1404, the steps are repeated at 1402 for the next sample time. If one or more temperature readings are above the threshold, the time since application of the electrical pulse is referenced. Specifically, at 1406, the time since application of the electrical pulse to the SMA element is determined. If the time is greater than the minimum time, as checked at 1408, the application of the electrical pulse to the SMA element is terminated at 1410. Otherwise, the steps are repeated at 1402 for the next sample time.

[0057] In some exemplary embodiments, multiple factors may be examined to determine whether to terminate the application of the electrical pulse to the SMA element. A confidence interval may be defined based on the value of the factor. The termination decision, in some embodiments, may be based on whether the value of the factor falls within a particular confidence interval.

[0058] In some exemplary embodiments, the unactuated SMA element may be monitored to control the time at which a pulse is initiated. Figure 15 depicts a flowchart 1500 illustrating exemplary steps that may be performed in an exemplary embodiment to determine the state of an SMA element, such as an SMA wire. Assume the SMA elements are in an opposing relationship such that they are actuated relative to one another and the SMA elements are actuated alternately. At 1502, the resistance of the unactuated SMA element is measured, such as by measuring the current and voltage and calculating the resistance from those measurements.

[0059] At 1504, the state of the unactuated SMA element can be determined from the resistance measurements. FIG. 16 shows what state information 1600 about an unactuated SMA element can be determined from the resistance. First, the state 1602 of the SMA element can be determined. For example, the resistance can identify whether the SMA element is in the austenite phase, the martensite phase, or a mixture thereof. When the SMA element is in a mixed phase, the resistance can identify where the SMA element is in the transition between phases. The resistance can also identify the length 1604 of the SMA element. The length 1604 is phase-related because the SMA element shortens in the austenite phase and returns to its original length when it returns to the martensite phase. The temperature 1606 of the SMA element can also be determined from the resistance.

[0060] FIG. 17 shows an example of electrical pulses applied to a first SMA wire 1702 and a second SMA wire 1704. As shown, electrical pulses 1706 and 1708 are applied to SMA wire 1702. Between these electrical pulses 1706 and 1708, an electrical pulse 1710 can be applied to the other, opposing SMA wire 1704. The pulse widths (PW) of electrical pulses 1706, 1708, and 1710 are shown. The pulse width represents the time between when the electrical pulse begins (e.g., 1712 for pulse 1710) and when the electrical pulse ends (1714). The pulse-to-pulse (PP) length is shown. The PP length (see arrows labeled PP) represents the length of time between the end of the electrical pulse on one SMA wire and the start of the electrical pulse on the other SMA wire.

[0061] FIG. 18 shows a flowchart 1800 of example steps that may be performed in example embodiments to determine when to trigger the initiation of an electrical pulse to an unactuated SMA element. The selection of when to trigger the initiation of the electrical pulse determines the PP timing. The goal of this timing selection in some example embodiments is to minimize energy loss. Cooling the SMA element completely to ambient temperature is inefficient and results in wasted energy application. In these example embodiments, the initiation of application of the electrical pulse to the unactuated SMA element occurs when the unactuated SMA element has sufficiently cooled (or transitioned from the austenite phase to the martensite phase sufficiently, or has sufficiently lengthened from its contracted length to uncontract or return to its original length), but not to ambient temperature. These embodiments may choose to apply the electrical pulse to the unactuated SMA element when cooling is sufficient to stretch or de-twin the SMA element. This results in a shorter pulse width, saving energy. However, on the other hand, energy is wasted by actuating the SMA element before it has sufficiently relaxed. This ideal window for initiating application of an electrical pulse to an unactuated SMA element may vary between SMA elements and may depend on the material (e.g., alloy) that comprises the SMA element, the length of the SMA element, the age of the SMA element, etc.

[0062] Referring again to FIG. 18 , at 1802, the resistance of the unactuated SMA element is determined, e.g., from voltage and current measurements, as described above. The resistance measurement is taken after the last pulse applied to the other opposing SMA element has terminated. In some examples, a delay may be incorporated before the resistance measurement is collected. At 1804, the resistance measurement is compared to a first threshold. The first threshold may be an empirically derived value that suggests the unactuated SMA element (in this case 2002) has cooled sufficiently so that detwinning has occurred. If the resistance measurement exceeds the threshold (e.g., has exceeded the first threshold since the last pulse was terminated), the process is repeated at 1802. There may be an incorporated delay between successive measurements at 1802. If the resistance measurement exceeds the first threshold, which is an indication that there is sufficient cooling, an electrical pulse is triggered at 1806, resulting in an electrical pulse being applied to the previously deactivated SMA element (i.e., 2004 or 1704 in this example).

[0063] FIG. 20 shows an example of resistance values ​​2000 for the pulse pattern previously shown in FIG. 17. At the end of the pulse 2006 for SMA element 2002 ("Wire 1"), the SMA element 2002 begins to cool as electrical pulses are no longer applied. Resistance changes minimally during this period 2008. When cooling is sufficient, the SMA element begins to transition back to the martensitic phase, and resistance begins to increase rapidly (i.e., more than in other periods), as can be seen at 2010. When the resistance exceeds a first threshold (see 2012), an electrical pulse is applied to the opposing SMA element 2004. The first threshold may be an empirically derived value known to represent such a condition. In other embodiments, the threshold may alternatively be the rate of change of resistance or its derivative over time.

[0064] Exemplary embodiments can also determine when to terminate the electrical pulse applied to the SMA element. Generally, to conserve energy, you want the electrical pulse to end as soon as possible. The strategy of these exemplary embodiments described herein is to terminate the electrical pulse when the unactuated SMA element is still warm but is no longer predominantly austenitic, but before the phase transformation to the martensite phase is complete.

[0065] FIG. 19 shows a flowchart 1900 of example steps that may be implemented in an example embodiment to determine when to terminate the application of an electrical pulse to an SMA element based on the ROC of the SMA element's resistance. This approach is similar to that described above in FIG. 6 for the single wire case. At 1902, the resistance of the SMA element is measured. At 1904, the resistance is checked to see if it exceeds a threshold. This threshold is an empirically derived value at which the electrical pulse should be terminated. If the threshold is not exceeded, the process beginning at 1902 is repeated. In some examples, a delay may be added between 1904 and 1902. If the threshold is exceeded, the application of the electrical pulse to the SMA element is terminated at 1906. It should be appreciated that other approaches, such as using a derivative (see FIG. 8) or a second derivative (see FIG. 9), may be used as well. Additionally, the magnitude of the resistance and the ROC may be used (see FIG. 10), or an approach such as that of FIG. 12 may be used.

[0066] 21 shows an exemplary electrical circuit 2100 of an exemplary embodiment for measuring the resistance of an unactuated SMA element (e.g., SMA2 2104), which in this example is an SMA wire arranged in a facing configuration as described above with another SMA wire (e.g., SMA1 2102). A power supply 2106 supplies power to the circuit 2100. Four switches 2108, labeled S1, S2, S3, and S4, are provided. The resistance of the SMA wires is represented by resistors Rsma1 2110 and Rsma2 2112. The circuit is connected to ground 2114 as shown.

[0067] Applying a voltage to the SMA wires 2102 and 2104 causes current to flow through them. Closing switch S1 applies current to SMA1 2102, and closing switch S4 applies power to SMA2 2104. Closing switches S1 and S3 can deliver current to SMA1 2102 and SMA2 2104, respectively. The delivered current is set to a low level to conserve power and prevent the SMA wires 2102 and 2104 from being activated and experiencing a phase change. The voltage at SMA1 2102 can be measured at V1, and the voltage at SMA2 2104 can be measured at V2. To measure the resistance of SMA2 2104 (the unactuated wire), switch S3 can be closed, causing a current I to flow through SMA2 2104. The resistance of SMA2 2104 can be calculated as V2 / I.

[0068] The voltage generated by the large current in the SMA wire driven through the ground connection can create a voltage offset error due to ground impedance that can affect the calculated resistance of SMA2 2104. FIG. 22A shows a flowchart 2200 of example steps that may be performed in an example embodiment to account for the offset error. First, at 2202, switch S1 may be closed to drive SMA1 2102. At 2204, switch S3 may be opened and the voltage offset may be measured at V2. At 2206, switch S3 is closed, directing a DC current I through SMA2 2104. At 2208, the resistance Rsma2 2112 may be calculated as (V2 - voltage offset) / I.

[0069] 22B. At 2212, switch S1 is closed, allowing current to flow through SMA1 2102. At 2214, switch S3 is closed, allowing current I to flow through SMA2 2104. At 2216, switch S1 is opened, causing a short pause in the drive to SMA1 2102, and the resistance of SMA2 2104 is calculated as the voltage at V2 divided by I. At 2218, switch S1 is closed again, allowing SMA1 2102 to be driven.

[0070] Another alternative to address the voltage offset problem is to add electrical connections to the electrical circuit, as shown in electrical circuit 2300 of Figure 23. Electrical circuit 2300 includes a voltage source 2302, ground 2304, switch 2306, and SMA wires 2308 and 2310, as found in electrical circuit 2100. However, a reference voltage VREF 2312 is used to measure V1 and V2 in a high impedance differential amplifier configuration while removing the voltage offset.

[0071] FIG. 24 shows another alternative electrical circuit 2400 for measuring the resistance of SMA2 2404. The electrical circuit is similar to electrical circuit 2300 shown in FIG. 23, with some notable differences. A large resistor 2406 crosses between SMA wires 2402 and 2406. This resistor 2406 provides a path for current flowing through undriven (or unactivated) SMA wires. With this approach, the number of switches is reduced to only two switches, S1 and S2, and the current source is also eliminated. The configuration of VREF 2408 is as depicted in FIG. 23.

[0072] As described above, the resistance of an SMA element in an unactuated state can be monitored to determine whether the SMA element has overheated by determining the time it takes for the SMA element to cool as reflected in the resistance value. FIG. 25 shows a flowchart 2500 of exemplary steps that may be performed in an exemplary embodiment to identify overheating. At 2502, the resistance of the SMA element is monitored after an electrical pulse is applied to the SMA element. At 2504, the temperature of the wire is determined based on the resistance, and the time it takes for the wire to cool to a particular temperature is determined. At 2506, it can be determined whether the time was sufficient or excessive. If the time is longer than expected given the ambient temperature, a conclusion can be reached at 2508 that the SMA element has overheated. The cause of the overheating can be investigated and addressed.

[0073] As discussed above, monitoring the resistance of the SMA elements can help identify problems related to the crimp, aging, elongation, or other factors. FIG. 26 shows a flowchart 2600 of example steps that may be performed in an example embodiment to identify such problems. At 2602, a baseline resistance of both SMA elements may be determined. At 2604, the resistance of both SMA wires may be measured after the SMA elements have fully cooled. At 2606, a check is made to determine whether the resistance exceeds the baseline or threshold resistance. If the resistance exceeds the baseline or threshold resistance from both SMA elements, it is concluded at 2608 that there is a problem with the crimp or ground hook. If the baseline or threshold resistance is not exceeded, then at 2610, a check is made to determine whether one of the SMA elements has a resistance that exceeds the baseline or threshold resistance. If the baseline or threshold resistance is exceeded, it is concluded at 2612 that there is a problem with the crimp for the problematic SMA element whose resistance is rising, or that some other problem has occurred that significantly increases the circuit impedance. If not, there is no problem identified.

[0074] Although exemplary embodiments have been described herein, it should be recognized that various changes in form and details can be made therein without departing from the scope of the appended claims.

Claims

1. 1. A medication delivery device for delivering medication to a user, said medication delivery device comprising: a drug reservoir for storing the drug; a drug pump for pumping the drug from the drug reservoir for delivery to the user; a shape memory alloy (SMA) element for causing actuation of the drug pump to deliver the drug; Power supply and 1. A processor, comprising: commencing application of electrical pulses from the power source to the SMA element to cause the drug pump to deliver the drug from the drug reservoir; determining the resistance of the SMA element; determining that the application of the electrical pulse should be terminated based on the determined resistance of the SMA element over time; and a processor configured to terminate the application of the electrical pulse to the SMA element in response to determining that the application of the electrical pulse should be terminated.

2. 2. The medication delivery device of claim 1, wherein the processor is configured to determine a rate of change of the resistance and compare the rate of change to a threshold value in determining that the application of the electrical pulse should be terminated.

3. 2. The medication delivery device of claim 1, wherein the processor is further configured to: determine a magnitude of a change in resistance of the SMA element since initiating the electrical pulse; compare the determined magnitude of the change in resistance to a threshold; and terminate the electrical pulse based in part on the comparison to the threshold.

4. 2. The medication delivery device of claim 1, wherein the processor is configured to collect voltage and current readings of the SMA element over time and calculate the resistance of the SMA element over time from the collected voltage and current readings as part of determining the resistance of the SMA element over time.

5. 5. The medication delivery device of claim 4, wherein the processor terminates the application of the electrical pulse to the SMA element as part of determining that the application of the electrical pulse should be terminated by determining a moving average value of a subset of the resistance values, determining at least one derivative or an approximation of the determined moving average value, and comparing the at least one derivative or the approximation of the determined derivative of the moving average value to a threshold value.

6. The medication delivery device of claim 1 , wherein the SMA element is an SMA wire.

7. 2. The drug delivery device of claim 1, wherein determining that the application of the electrical pulse should be terminated comprises determining a second derivative or an approximation of a second derivative of one of the resistance values ​​or an average of successive ones of the resistance values, and determining that the application of the electrical pulse should be terminated based on the second derivative or the approximation of the second derivative.

8. 1. A drug delivery device, comprising: a drug reservoir for storing a drug; a pump for pumping the drug from the drug reservoir; a shape memory alloy (SMA) element for actuating the pump; Power supply and 1. A processor, comprising: causing an electrical pulse from the power source to be applied to the SMA element, causing actuation of the drug pump to expel drug from the drug reservoir; monitoring the resistance of the SMA element; and a processor configured to terminate the application of the pulse to the SMA based on an indicator reflective of the resistance value.

9. 9. The medication delivery device of claim 8, wherein the medication delivery device is a wearable insulin pump and the medication is insulin.

10. The medication delivery device of claim 8 , wherein the processor is configured to perform filtering of the resistance value.

11. The medication delivery device of claim 8 , wherein the power source is a battery or a capacitor.

12. 9. The drug delivery device of claim 8, wherein the SMA element is coupled to a component that drives actuation of the drug pump.

13. 9. The medication delivery device of claim 8, wherein the SMA element contracts in length in response to the application of the electrical pulse.

14. The drug delivery device of claim 8 , wherein the indicator reflecting the resistance value is an indicator of a rate of change of the resistance value over time or an indicator of an average of the resistance value.

15. 15. The medication delivery device of claim 14, wherein the indication of the rate of change of the resistance value over time is a derivative of the resistance value or an average of the resistance value.

16. 15. The medication delivery device of claim 14, wherein the measure of the rate of change of the resistance value over time is a second derivative of the resistance value or an average of the resistance values.

17. 1. A drug delivery device, comprising: a drug reservoir for storing a drug; a pump for pumping the drug from the drug reservoir; a shape memory alloy (SMA) element for actuating the pump; Power supply and a temperature sensor for sensing the temperature of the SMA element; a clock for outputting a display of time; 1. A processor, comprising: an initial electrical pulse applied from the power source to the SMA element actuates the drug pump to output drug from the drug reservoir; monitoring the temperature value of the SMA element measured by the temperature sensor; and a processor configured to terminate the application of the pulse to the SMA element based on the temperature of the SMA element and the time since the initial application of the electrical pulse to the SMA element.

18. 18. The medication delivery device of claim 17, wherein the SMA element is an SMA wire.

19. 18. The medication delivery device of claim 17, wherein a plurality of consecutive temperature values ​​must exceed a threshold before terminating the application of the pulses to the SMA element.

20. 18. The drug delivery device of claim 17, wherein the drug delivery device is an insulin delivery device.

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