US20100100041A1 - Device and Method Employing Shape Memory Alloy - Google Patents

Abstract

A system for the metering and delivery of small discrete volumes of liquid is comprised of a small or minimal number of inexpensive components. One such component is a movable member, such as a miniature precision reciprocating displacement pump head, which is driven by an actuator that comprises a shape memory alloy material. The operating mechanism of the system is of little or minimal complexity. The system facilitates the precise metering and delivery of the small discrete volumes of liquid. Potential applications for the system include subcutaneous, long-term, automated drug delivery, for example, the delivery of insulin to a person with diabetes. In such an application, the small, simple and inexpensive nature of the invention would allow for its use as both a portable and a disposable system.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This is a divisional application of co-pending parent application having U.S. application Ser. No. 12/163,944, filed Jun. 27, 2008, which is a continuation of U.S. application Ser. No. 11/106,256, filed Apr. 13, 2005, now U.S. Pat. No. 7,399,401, which is a continuation-in-part (CIP) of U.S. application Ser. No. 10/683,659, filed Oct. 9, 2003, now U.S. Pat. No. 6,916,159, which claims benefit and priority based on U.S. Provisional Application No. 60/417,464, entitled “Disposable Pump For Drug Delivery System,” filed on Oct. 9, 2002, U.S. Provisional Application No. 60/424,613, entitled “Disposable Pump And Actuation Circuit For Drug Delivery System,” filed on Nov. 6, 2002, and U.S. Provisional Application No. 60/424,414, entitled “Automatic Biological Analyte Testing Meter With Integrated Lancing Device And Methods Of Use,” filed Nov. 6, 2002, each of which is incorporated herein in its entirety by this reference. This non-provisional application is also related to U.S. Pat. No. 6,560,471, entitled “Analyte Monitoring Device and Methods of Use,” issued May 6, 2003, which is incorporated herein in its entirety by reference.
FIELD OF INVENTION
• This invention generally relates to fluid delivery devices, systems, and methods. This invention further relates to small volume, disposable medical devices for the precision delivery of medicines or drugs such as insulin, and associated systems and methods.
BACKGROUND OF THE INVENTION
• Insulin pumps are widely available and are used by diabetic people to automatically deliver insulin over extended periods of time. All currently available insulin pumps employ a common pumping technology, the syringe pump. In a syringe pump, the plunger of the syringe is advanced by a lead screw that is turned by a precision stepper motor. As the plunger advances, fluid is forced out of the syringe, through a catheter to the patient. The choice of the syringe pump as a pumping technology for insulin pumps is motivated by its ability to precisely deliver the relatively small volume of insulin required by a typical diabetic (about 0.1 to about 1.0 cm³per day) in a nearly continuous manner. The delivery rate of a syringe pump can also be readily adjusted through a large range to accommodate changing insulin requirements of an individual (e.g., basal rates and bolus doses) by adjusting the stepping rate of the motor. While the syringe pump is unparalleled in its ability to precisely deliver a liquid over a wide range of flow rates and in a nearly continuous manner, such performance comes at a cost. Currently available insulin pumps are complicated and expensive pieces of equipment costing thousands of dollars. This high cost is due primarily to the complexity of the stepper motor and lead screw mechanism. These components also contribute significantly to the overall size and weight of the insulin pump. Additionally, because of their cost, currently available insulin pumps have an intended period of use of up to two years, which necessitates routine maintenance of the device such as recharging the power supply and refilling with insulin.
• U.S. Pat. No. 6,375,638 of Clyde Nason and William H. Stutz, Jr., entitled “Incremental Motion Pump Mechanisms Powered by Shape Memory Alloy Wire or the Like,” issued Apr. 23, 2002, and naming Medtronic MiniMed, Inc. as the assignee, which patent is incorporated herein in its entirety by this reference, describes various ratchet type mechanisms for incrementally advancing the plunger of a syringe pump. The ratchet mechanisms are actuated by a shape memory alloy wire. The embodiments taught by Nason et al. involve a large number of moving parts, and are mechanically complex, which increases size, weight and cost, and can reduce reliability.
SUMMARY OF THE INVENTION
• A fluid delivery system constructed according to the present invention can be utilized in a variety of applications. As described in detail below, it can be used to deliver medication to a person or animal. The invention can be applied in other medical fields, such as for implantable micro-pump applications, or in non-medical fields such as for small, low-power, precision lubricating pumps for precision self-lubricating machinery.
• In its preferred embodiment, the present invention provides a mechanical insulin delivery device for diabetics that obviates the above-mentioned limitations of the syringe pump namely size, weight, cost and complexity. By overcoming these limitations, a precise and reliable insulin delivery system can be produced with sufficiently low cost to be marketed as a disposable product and of sufficiently small size and weight to be easily portable by the user. For example, it is envisioned that such a device can be worn discretely on the skin as an adhesive patch and contain a three-day supply of insulin after the use of which the device is disposed of and replaced.
• The present invention relates to a miniature precision reciprocating displacement pump head driven by a shape memory alloy actuator. Shape memory alloys belong to a class of materials that undergo a temperature induced phase transition with an associated significant dimensional change. During this dimensional change, shape memory alloys can exert a significant force and can thus serve as effective actuators. The shape memory alloy actuator provides an energy efficiency about one thousand times greater than that of a conventional electromechanical actuator, such as a solenoid, and a force to mass ratio about ten thousand times greater. Additionally, the cost of shape memory alloy materials compares favorably to the cost of electromechanical devices with similar capabilities.
• The device of the present invention is intended to be operated in a periodic dosing manner, i.e., liquid is delivered in periodic discrete doses of a small fixed volume rather than in a continuous flow manner. The overall liquid delivery rate for the device is controlled and adjusted by controlling and adjusting the dosing period. Thus the device employs a precision timing mechanism in conjunction with a relatively simple mechanical system, as opposed to a complex mechanical system, such as that embodied by the syringe pump.
• A precision timing device is an inherently small, simple and inexpensive device. It is an underlying assumption of the invention (and a reasonable conclusion of process control theory) that in the treatment of diabetes, there is no clinical difference between administering insulin in periodic discrete small doses and administering insulin in a continuous flow, as long as the administration period of the discrete dose is small compared to the interval of time between which the blood glucose level is measured. For the present invention, a small dose size is regarded as on the order of 0.10 units of insulin (1 microliter) assuming a standard pharmaceutical insulin preparation of 100 units of insulin per ml (U100). A typical insulin dependent diabetic person uses between 10 and 100 units of insulin per day, with the average diabetic person using 40 units of insulin. Thus the present invention would deliver the daily insulin requirements of the average diabetic person in 400 individual discrete doses of 1 μl each with a dosing period that can be programmed by the user. A pump constructed according to the present invention can have a predetermined discrete dosage volume that is larger or smaller than 1 μl, but preferably falls within the range of 0.5 to 5 μl, and more preferably falls within the range of 1 to 3 μl. The smaller the discrete dose is of a particular pump design, the more energy required by the device to deliver a given amount of fluid, since each pump cycle consumes roughly the same amount of energy regardless of discrete dosage size. On the other hand, the larger the discrete dosage is, the less precise the pump can mimic the human body in providing a smooth delivery rate. A device constructed according to the present invention is also suitable for delivery of other drugs that might be administered in a manner similar to insulin.
• It is further intended that the present invention could be used as a disposable component of a larger diabetes management system comprised of additional disposable and non-disposable components. For example, the present invention could be coupled with a continuous blood glucose monitoring device and remote unit, such as a system described in U.S. Pat. No. 6,560,471, entitled “Analyte Monitoring Device and Methods of Use,” issued May 6, 2003. In such an arrangement, the hand-held remote unit that controls the continuous blood glucose monitoring device could wirelessly communicate with and control both the blood glucose monitoring unit and the fluid delivery device of the present invention. The monitor and pump could be physically separate units, or could share one or more disposable and/or non-disposable components. For example, a disposable pump constructed according to the present invention and charged with a 3-day supply of insulin, a small battery and a disposable glucose sensor could be integrated into a single housing and releasably coupled with non-disposable components such as control electronics, a transmitter/receiver and a user interface to comprise a small insulin delivery device that could be worn on the skin as an adhesive patch. Alternatively, the battery (or batteries) and/or sensor could be replaced separately from the disposable pump. Such arrangements would have the advantage of lowering the fixed and recurring costs associated with use of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• A detailed description of various embodiments of the invention is provided herein with reference to the accompanying drawings, which are briefly described below.
• FIG. 1A shows a schematic representation of a most general embodiment of the invention.
• FIG. 1B shows a schematic representation of an alternative general embodiment of the invention.
• FIG. 2A shows a schematic representation of a preferred embodiment of the invention.
• FIGS. 2B and 2C show enlarged details of a preferred embodiment of the invention.
• FIG. 3 shows a schematic representation of a preferred embodiment of a check valve to be used in the invention.
• FIG. 4 shows a schematic representation of a preferred embodiment of a pulse generation circuit to be used with the invention.
• FIG. 5 shows data from the experimental characterization of the reproducibility of a functional model of the invention.
• FIG. 6 shows data from the experimental characterization of the energy utilization of a functional model of the invention.
• FIG. 7 shows a schematic representation of a first alternative embodiment of the invention.
• FIG. 8 shows a schematic representation of a second alternative embodiment of the invention.
• FIG. 9 shows a schematic representation of a first alternative embodiment of a pulse generation circuit to be used with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• A device of the present invention includes a miniature precision reciprocating displacement pump driven by a shape memory alloy wire linear actuator and controlled by a programmable pulse generating circuit. For purposes of description, the device is divided into three subcomponents, a precision miniature reciprocating displacement pump head, a shape memory alloy linear actuator, and a programmable pulse generating circuit. Each subcomponent is comprised of multiple elements. A schematic representation of a most general embodiment of the invention is shown inFIG. 1A and is described below.
• The miniature precision pump head is comprised of the following elements: arigid substrate101 to which other components may be attached so as to fix their orientation and position relative to one another, afluid reservoir102 for storing the fluid to be pumped103 and a small cavity, henceforth referred to as thedisplacement cavity104, whose volume can be varied between precisely defined limits. The limit corresponding to a state of maximum volume for thedisplacement cavity104 is defined as thefirst limit105 and the limit corresponding to a state of minimum volume for thedisplacement cavity104 is defined as thesecond limit106. Aninlet conduit107 connects thedisplacement cavity104 to thefluid reservoir102 and thus permits fluid flow between the two. Aninlet check valve108 is situated within theinlet conduit107 such that fluid flow is restricted to flowing from thefluid reservoir102 to thedisplacement cavity104. Anoutlet conduit109 connects thedisplacement cavity104 to somepoint111 to which it is desired to deliver the fluid. Anoutlet check valve110 is situated within theoutlet conduit109 such that fluid flow is restricted to flowing from thedisplacement cavity104 to thepoint111 to which it is desired to deliver the fluid.
• The shape memory alloy actuator is comprised of a shape memory allow material, such as a nickel-titanium alloy material, sometimes referred to as “nitinol.” The shape memory alloy material is sensitive to temperature or heat. For example, the material temporarily shrinks at a certain temperature, or shrinkage temperature, such as about 70° C. above ambient temperature for nitinol, and expands at a relatively lower temperature to return to its original condition. In response to being heated to the above-described shrinkage temperature, the shape memory alloy undergoes a dimensional change, such as a change in its length. In this way, a wire composed of a material such as nitinol, can undergo a change in length and a return toward its original length one or more times via temperature treatment or repeated temperature cycling. It is contemplated that a material that expands by going through a phase transition at a certain temperature and shrinks at a different temperature to return toward its original condition could be used.
• In the process of undergoing a dimensional change, as described above, the shape alloy material goes through a reversible phase transition or transformation, or a reversible structural phase transition, upon a change in temperature. Generally, such a transition represents a change in the material from one solid phase of the material to another, for example, by virtue of a change in the crystal structure of the material or by virtue of a reordering of the material at a molecular level. In the case of nitinol, for example, the superelastic alloy has a low temperature phase, or martensitic phase, and a high temperature phase, or austenitic phase. These phases can also be referred to in terms of a stiff phase and a soft and malleable phase, or responsive phase. The particular phase transition associated with a particular alloy material may vary.
• The shape memory alloy actuator is also comprised of the following elements. A movable member is referred to as aplunger112 and is fixed by arigid restraint113 such that it is constrained to a periodic motion of precisely fixed limits. Theplunger112 is situated in relation to and/or attached to thedisplacement cavity104 such that movement of theplunger112 within the limits of its constrained motion will cause the volume of thedisplacement cavity104 to be varied between itslimits105,106. A biasingspring115 is situated relative to therigid restraint113 and theplunger112 such that at equilibrium, the biasingspring115 exerts a force on theplunger112 whose direction is that which would induce thedisplacement cavity104 toward a state of minimum volume, i.e., toward itssecond limit106. A length of shapememory alloy wire114 is connected at one end to theplunger112 and at another end to therigid substrate101. The shapememory alloy wire114 is situated such that its dimensional change will give rise to motion of theplunger112. The shapememory alloy wire114 and the biasingspring115 are both of sufficient dimension such that when the shapememory alloy wire114 is heated so as to induce phase transition and associated dimensional change, the wire will move theplunger112 against the force of the biasingspring115 “in one generally uninterrupted motion” to itssecond limit105 so as to create a state of maximum volume within thedisplacement cavity104, whereas when the shape memory alloy is allowed to cool to ambient temperature, the force imparted by the biasingspring115 will stretch the shapememory alloy wire114 until the point where thedisplacement cavity104 is in a state of minimum volume.
• The programmable pulse generating circuit is comprised of a source ofelectric power116, anelectrical connection117 from the source ofelectric power116 to each end of the shapememory alloy wire114 and a programmablepulse generating circuit118 situated along theelectrical connection117 such that pulses of electricity from theelectric power source116 may be applied to the shapememory alloy wire114 automatically in a preset regular periodic manner.
• Operation of the device proceeds in a cyclic manner. For purposes of description the beginning of the cycle is defined as the following state. All void space within thefluid reservoir102,inlet107 andoutlet109 conduit,inlet108 andoutlet110 check valves anddisplacement cavity104 are completely filled with the fluid103 to be pumped. The shapememory alloy wire114 is at ambient temperature and thus in a state of maximum length. Correspondingly, the position of theplunger112 is such that the volume of thedisplacement chamber104 is at its minimum value. The biasingspring115 is in a compressed state such that it exerts a force on theplunger112 consistent with a state of minimum volume of thedisplacement cavity104. Operation of the device involves first a heating of the shapememory alloy wire114 to a temperature and for a period of time sufficient to induce phase transition and an associated dimensional change. Heating of the shapememory alloy wire114 is accomplished by passing an electric current though it. The duration of the electric heating period is preset and is controlled by the timing and switchingcircuit118. The dimensional change of the shapememory alloy wire114 will result in the movement of theplunger112 against the opposing force of biasingspring115 so as to vary the volume of thedisplacement chamber104 toward itsfirst limit105 and a state of maximum volume. As the volume of thedisplacement cavity104 is increased,fluid103 is drawn into thedisplacement cavity104 from thefluid reservoir102 through theinlet conduit107 andinlet check valve108.Fluid103 is not drawn into thedisplacement cavity104 through theoutlet conduit109 due to the one-way flow restriction of theoutlet check valve110. After the preset duration, the current is then switched off by the timing and switchingcircuit118 allowing the shapememory alloy wire114 to cool below its phase transition temperature. Cooling proceeds via natural convection to the ambient environment. When the shapememory alloy wire114 cools below its phase transition temperature, the force exerted by the biasingspring115 stretches the shapememory alloy wire114 to its original maximum length. This allows the movement of theplunger112 so as to vary the volume of thedisplacement cavity104 toward itssecond limit106 and a state of minimum volume. As the volume of thedisplacement cavity104 is decreased,fluid103 is pushed out of thedisplacement cavity104 through theoutlet conduit109 andoutlet check valve110.Fluid103 is not pushed out of thedisplacement cavity104 through theinlet conduit107 due to the one-way flow restriction of theinlet check valve108. Thus one complete heating and cooling cycle of the shapememory alloy wire114 results in the delivery of a volume offluid103 from thefluid reservoir102 to the end of theoutlet conduit111. The volume of fluid delivered with each cycle is precisely equal to the difference between the maximum and minimum volumes of thedisplacement cavity104 as determined by the precisely definedlimits105,106. The overall rate of fluid delivery is controlled by varying the period of time between actuations of the shapememory alloy actuator104.
An Alternative General Embodiment of the Invention
• A schematic representation of an alternative general embodiment of the invention is shown inFIG. 1B. The alternative general embodiment includes all of the same components and elements as the general embodiment shown inFIG. 1A with the following exceptions. In this embodiment of the invention, heating of the shapememory alloy material114 so as to cause a phase transition associated shortening of its length results in a minimum volume condition for thedisplacement cavity104. This may be achieved, for example, through the use of a pivotinglinkage assembly119 connecting the biasingspring115 to theplunger112.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
• As stated previously, it is an intention of the present invention that it be sufficiently small and sufficiently inexpensive to be practically used as both a portable device and as a disposable device. For example, a device that can be comfortably worn on the skin as an adhesive patch and can be disposed of and replaced after 3 days of use. A preferred embodiment of the invention includes specific embodiments of the various elements and components of the general embodiment that are consistent with this intention.
• A preferred embodiment of the invention is diagrammed schematically inFIGS. 2A,2B and2C and is comprised of all of the same elements and components of the general embodiment of the invention shown inFIGS. 1A and 1B with the following exceptions. In a preferred embodiment of the invention the displacement cavity is comprised of an elastomericdiaphragm pump head201. An enlarged view of the details of thediaphragm pump head201 is shown byFIG. 2B withpump head201 in a state of minimum volume and byFIG. 2C withpump head201 in a state of maximum volume. The diaphragm pump head is comprised of anelastomeric diaphragm202 set adjacent to arigid substrate203 and scaled about a perimeter of theelastomeric diaphragm202. Thedisplacement cavity204 is then comprised of the volume in between the adjacent surfaces of therigid substrate203 and theelastomeric diaphragm202 within the sealed perimeter.
• Separate inlet205 andoutlet206 conduits within therigid substrate203 access the displacement volume of the elastomericdiaphragm pump head201 with theinlet conduit205 connecting thedisplacement cavity204 with afluid reservoir207 and theoutlet conduit206 connecting thedisplacement cavity204 to the point to which it is desired to deliverfluid208. Aninlet check valve209 and anoutlet check valve210 are situated within theinlet conduit205 andoutlet conduit206 respectively, oriented such that the net direction of flow is from thefluid reservoir207 to the point to which it is desired to deliverfluid208.
• Theplunger211 is comprised of a cylindrical length of rigid dielectric material. Theplunger211 is situated within acylindrical bore212 of arigid restraint213 such that the axis of theplunger211 is oriented normal to surface of theelastomeric diaphragm202. The flat head of theplunger211 is functionally attached to the non-wetted surface ofelastomeric diaphragm202 opposite thedisplacement cavity204 such that movement of theplunger211 along a line of motion coincident with its axis will cause the concomitant variation in the volume of thedisplacement cavity204. The biasingspring214 is situated within thecylindrical bore212 of therigid restraint213, coaxial with theplunger211. The relative positions and dimensions of theplunger211, therigid restraint213 and the biasingspring214 are such that at equilibrium the biasingspring214 exerts a force on theplunger211 along a line coincident with its axis such that thedisplacement cavity204 is in a state of minimum volume (FIG. 2A).
• A straight length of shapememory alloy wire215 is situated in a position coincident with the axis of theplunger211. One end of the shapememory alloy wire215 is fixed to therigid restraint203 and electrically connected byconnection216 to the programmablepulse generating circuit217 and theelectric power source218. The other end of the shapememory alloy wire215 along with anelectrical connection219 to that end is connected to the end of theplunger211. The shapememory alloy wire215 and the biasingspring214 are both of sufficient dimension such that when the shapememory alloy wire215 is heated so as to induce phase transition and associated dimensional change, it will pull theplunger211 against the force of the biasingspring214 so as to create a state of maximum volume within thedisplacement cavity204, whereas when the shape memory alloy is allowed to cool to ambient temperature, the force imparted by biasingspring214 will stretch the shapememory alloy wire215 until the point where thedisplacement cavity204 is in a state of minimum volume.
• A preferred embodiment of an inlet and outlet check valve is shown in cross-section inFIG. 3 and is comprised of a molded one-piece elastomeric valve which can be press-fit into the inlet or outlet conduit. An important feature for a check valve appropriate for use in the present invention is that it possesses a low cracking pressure and provides a tight seal in the absence of any back pressure. A preferred embodiment of such a check valve is comprised of a thin-walledelastomeric dome301 situated on top of a thickelastomeric flange302. The top of the dome has asmall slit303 cut through it that is normally closed. A fluid pressure gradient directed toward theconcave side304 of the dome will induce an expansion of thedome301 forcing theslit303 open so as to allow fluid to flow through the valve in this direction. A fluid pressure gradient directed toward theconvex side305 of the dome will induce a contraction of thedome301 forcing theslit303 shut so as to prohibit fluid to flow through the valve in this direction.
• A preferred embodiment of a pulse generating circuit is shown inFIG. 4 and is comprised of a 200 milliamp-hour, lithium-manganese oxideprimary battery401, a high capacitance, low-equivalent series resistance (ESR)electrochemical capacitor402, a programmabledigital timing circuit403, and a low-resistance fieldeffect transistor switch404. The shape memory alloy wire is indicated inFIG. 4 symbolically as aresistor405. Thebattery401 andelectrochemical capacitor402 are electrically connected to each other in parallel and are connected to the shapememory alloy wire405 through thetransistor switch404. Theprogrammable timing circuit403, also powered by thebattery401, sends a gating signal to thetransistor switch404, as programmed by the user in accordance with the user's pumping requirements. During the period of time for which thetransistor switch404 is open, thebattery401 will keep theelectrochemical capacitor402 at a state of full charge. During the period of time for which thetransistor switch404 is closed, power will be delivered to the shapememory alloy wire405, primarily from theelectrochemical capacitor402 rather than from thebattery401, owing to the substantially lower ESR associated with theelectrochemical capacitor402. As such, thebattery401 is substantially isolated from the high current draw associated with the low resistance of the shapememory alloy wire405 and the useful life of thebattery401 is significantly extended.
• A preferred embodiment of afluid reservoir207 appropriate for use with the present invention is one for which the volume of the fluid reservoir diminishes concomitantly as fluid is withdrawn such that it is not necessary to replace the volume of the withdrawn fluid with air or any other substance. A preferred embodiment of afluid reservoir207 might comprise a cylindrical bore fitted with a movable piston, for example, a syringe, or a balloon constructed of a resilient material.
• Operation of the preferred embodiment of the invention proceeds in a manner analogous to that described for the most general embodiment. In addition to its simplicity, the preferred embodiment has the advantage of physically blocking any fluid flow from the fluid reservoir to the point to which it is desired to deliver the fluid when there is no power being supplied to the system. This provides additional protection against an overdose caused by fluid expanding or being siphoned through the check valves when the system is inactive.
DETAILED DESCRIPTION OF A FUNCTIONAL MODEL OF THE INVENTION
• A functional model of a preferred embodiment of the invention has been constructed and its performance has been characterized. The functional model is similar in appearance to the preferred embodiment of the invention shown inFIGS. 2,3 and4 and is described in more detail below. The fixed rigid components of the pump including the rigid restraint and the rigid substrate of the diaphragm pump head are each machined from a monolithic block of acetal. Inlet and outlet conduits are additionally machined out of the same block. Check valves are commercially available one-piece elastomeric valves (for example, Check Valve, Part #VA4914, available from Vernay Laboratories Inc. of Yellow Springs, Ohio). A length of shape memory alloy actuator is 40 mm long and 125 μm in diameter (for example, Shape Memory Alloy Wire, Flexinol 125 LT, available from Mondo-tronics, Inc. of San Rafael, Calif.). Electrical connections to the ends of the shape memory alloy actuator are made with 30 AWG copper wire. The copper wire is twisted to the shape memory alloy wire to effect a good electrical connection. A plunger is machined out of acetal and has an overall length of 10.0 mm and a shaft diameter of 3.2 mm. An elastomer diaphragm is comprised of 0.025 mm thick silicon rubber film (for example, Silicon Rubber Film, Cat. #86435K31, available from McMaster Carr, of Los Angeles, Calif.). The flat head of the plunger is secured to the elastomer diaphragm with epoxy (for example, Epoxy, Stock #14250, available from ITW Devcon, of Danvers, Mass.). The ends of the shape memory alloy wire-copper conductor assembly are connected to the plunger and to the rigid restraint with epoxy. A stainless steel biasing spring has an overall length of 12.7 mm, an outside diameter of 3.0 mm, a wire diameter of 0.35 mm and a spring constant of 0.9 N/mm (for example, Biasing Spring, Cat. #C0120-014-0500, available from Associated Spring, of Dallas, Tex.).
• A pulse generating circuit is comprised of an adjustable analog timing circuit based on a 556 dual timing integrated circuit (for example, 556 Dual Timing Circuit, Part #TS3V556, available from ST Microelectronics, of San Jose, Calif.). Power is supplied by a 3 V lithium-manganese dioxide primary cell (for example, Li/MgO₂Battery, Part #DL2032, available from Duracell, of Bethel, Conn.). Power load leveling is facilitated by the use of an electrochemical supercapacitor (for example, Electrochemical Supercapacitor, Part #B0810, available from PowerStor Inc., of Dublin, Calif.) in parallel with the battery. High-power switching is achieved with a field effect transistor (for example, Field Effect Transistor Switch, Part #IRLZ24N, available from International Rectifier, of El Segundo, Calif.).
• The functional model was characterized with respect to reproducibility, insulin stability and energy consumption. The model was operated by heating the shape memory alloy wire with a short pulse of current and then allowing the shape memory alloy wire to cool. Each heating pulse and subsequent cooling period comprised a single actuation cycle.
• A device that is used to automatically deliver a drug to an individual over an extended period of time should do so with extreme precision. This is particularly critical when the drug being delivered is one that might have dangerous health consequences associated with an inappropriate dose. Insulin is one such drug. An excessive dose of insulin can result in dangerously low blood glucose level, which in turn can lead to coma and death. Thus any device to be used for automatically delivering insulin to a diabetic person must be able to demonstrate a very high level of precision. To characterize the precision with which the invention can deliver insulin, the functional model was repeatedly cycled at a constant period of actuation and the total quantity of liquid delivered was measured as a function of the number of actuation cycles.FIG. 5 shows typical results. The data inFIG. 5 were obtained with an actuation period of 28 seconds and a pulse duration of 0.15 seconds. InFIG. 5 markers show actual data points and the line represents a least squares fit of the data points. Data were collected over 8500 cycles at which point the measurement was stopped. The fit to the data has a slope of 1.997 mg/cycle and a linear correlation coefficient of 0.999 indicating that the functional model delivered extremely consistent volumes of liquid with each actuation over the course of the measurement.
• Another important requirement for any medical device that handles insulin is that the device does not damage the insulin. Insulin is a large and delicate biomolecule that can readily be damaged by the mechanical action (e.g., shear stress) of a pumping device. Three common modes of insulin destruction which result in a loss of bioactivity are aggregation, where individual insulin molecules bond together to form various polymer structures, degradation, where individual insulin molecules are broken apart, and denaturing, where individual molecules remain intact but lose their characteristic conformation. All three modes of insulin destruction are exacerbated by elevated temperatures. Thus, in the development of a practical insulin pumping device, preferably, it should be demonstrated that the device does not damage insulin. To characterize the insulin stability associated with the invention, a quantity of insulin (Insulin, Humalog U100, available from Eli Lilly, of Indianapolis, Ind.) was set up to recycle continuously through the functional model over the course of several days at 37° C. Samples of the insulin were collected each day for evaluation. This resulted in a series of pumped insulin samples with an increasing amount of pump stress. The insulin samples were then analyzed by reverse-phase high performance liquid chromatography. The chromatography indicated a 2% loss of insulin concentration after a single pass through the pump and a further loss of another 5% of the insulin concentration after 3 days of recycling.
• It is desirable for a small and inexpensive insulin delivery device to be able to execute its maximum intended term of use with the energy from a single small inexpensive primary battery. Based on a 0.1 unit dose size and a maximum insulin consumption of 100 units per day for 3 days, a maximum term of use for the inventive device might be considered to be 3000 cycles. To characterize the energy consumption of the invention, the functional model was operated continuously for several days at an actuation period of 85 seconds while the voltage of a 200 milliamp-hour, 2032 lithium/manganese dioxide battery was monitored.FIG. 6 shows typical results. A typical voltage vs. capacity curve for the lithium/manganese dioxide battery is characterized by an initial drop in voltage from about 3.2 V to a plateau voltage of about 2.8 V. The voltage of the battery remains at this plateau level for the duration of its useful life. The battery voltage will then drop precipitously to a value below 2 V when its capacity expires. The data inFIG. 6 indicate that the battery is still at its plateau voltage after 4000 pump cycles and thus the 200 milliamp-hour, lithium/manganese dioxide battery is more than adequate to power the device of the present invention for its intended term of use.
Alternative Embodiments of the Invention
• A first alternative embodiment of the invention is diagrammed schematically inFIG. 7 and is comprised of all of the same subcomponents and elements of the most general embodiment of the invention shown inFIG. 1 with the following exceptions. In a first alternative embodiment of the invention, the displacement cavity, as well as the inlet and outlet conduit, are all comprised of a single length of small-diameter flexible andresilient tubing701. Thetubing701 is situated within a restrainingfixture702 secured to arigid base703 so as to fix the position and orientation of thetubing701 relative to the other elements of the device.Inlet704 andoutlet705 check valves are located within the bore of thetubing701 such that they have a common orientation for flow direction and such that a length ofempty tubing701 exists in between the twocheck valves704,705. The volume within the inner diameter of thetubing701 and in between the twocheck valves704,705 comprises adisplacement cavity706. The volume of thedisplacement cavity706 is varied by compressing theresilient tubing701 with a plunger707 (described below) at a position midway between the twocheck valves704,705. The volume within the inner diameter of thetubing701 and in between the twocheck valves704,705 when thetubing701 is uncompressed defines the maximum volume ofdisplacement cavity706. The volume within the inner diameter of thetubing701 and in between the twocheck valves703,704 when thetubing701 is fully compressed by theplunger707 defines the minimum volume of thedisplacement cavity705.
• Theplunger707 is comprised of a cylindrical length of rigid dielectric material and includes aflange708 and atapered end709. Theplunger707 is situated within acylindrical bore710 of arigid restraint711 such that the axis of theplunger707 is oriented normal to the axis of theresilient tubing701 and such that the taperedhead709 of theplunger707 may be alternately pressed against theresilient tubing701 and removed from contact with theresilient tubing701 with movement of theplunger707 along a line of motion coincident with the its axis. A biasingspring712 is fitted around the shaft of theplunger707 in between therigid restraint711 and theplunger flange708. The relative positions and dimensions of theplunger707, therigid restraint711 and the biasingspring712 are such that at equilibrium the biasingspring712 exerts a force on theplunger707 along a line coincident with its axis that is sufficient to fully collapse theresilient tubing701 and thus create a state of minimum volume of thedisplacement cavity706.
• A straight length of shapememory alloy wire713 is situated in a position coincident with the axis of theplunger707. One end of the shapememory alloy wire713 is attached to therigid base703 and electrically connected byconnection716 to thepulse generating circuit714 and theelectric power source715. The other end of the shapememory alloy wire713 along with anelectrical connection717 to that end is attached to the shaft of theplunger707. The shapememory alloy wire713 is of sufficient length and strength that when heated so as to induce phase transition and associated dimensional change it will pull theplunger707 away from contact with theresilient tubing701 against the opposing force of the biasingspring713.
• A second alternative embodiment of the invention is diagrammed schematically inFIG. 8 and is comprised of all of the same subcomponents and elements of the most general embodiment of the invention shown inFIG. 1 with the following exceptions. Adisplacement cavity801 is comprised of acylindrical shell802 andtube803 arrangement where thetube803 is coaxial with theshell802 and can move freely within theshell802 along a line coincident with that axis. The volume of thedisplacement cavity801 is varied by moving thetube803 relative to theshell802. Movement of thetube803 into theshell802 reduces the volume of thedisplacement cavity801 whereas movement of the tube out of the shell increases the volume of thedisplacement cavity801. Adynamic seal804, for example and elastomer o-ring, seals thedisplacement cavity801 while not interfering adversely with the relative motion of theshell802 andtube803.Outlet805 andinlet806 conduits access thedisplacement cavity801 through the ends of theshell802 andtube803 respectively.Outlet807 andinlet808 check valves are situated within theshell802 andtube803 respectively. A biasingspring809 is situated within thedisplacement cavity801 so as to resist the motion of thedisplacement cavity801 toward a state of reduced volume. A shapememory alloy wire810 is attached between theshell802 and thetube803 along the outside of the assembly such that when the shapememory alloy wire810 is heated so as to induce phase transition and associated dimensional change it will incline thedisplacement cavity801 toward a state of reduced volume. The shapememory alloy wire810 is electrically connected byconnector811 to a programmablepulse generating circuit812 and a source ofelectric power813. Hard stops (not shown) on the limits of the relative positions of theshell802 andtube803 define the maximum and minimum volumes of thedisplacement volume801.
• Operation of both the first and second alternative embodiments of the invention proceed in a manner analogous to that described for the most general embodiment and preferred embodiment of the invention.
• In all of the embodiments described above, a shape memory alloy wire acts as an actuator to drive a movable member to increase or decrease the fluid volume in the pump head, and once the wire cools a spring is used to return the movable member back to its original position. Those of reasonable skill in this field will appreciate that a multitude of other biasing means exist, one or more of which can be used in place of or in addition to the spring. In fact, a shape memory alloy can be constructed in such a way that it drives the movable member in both directions to act as both an actuator and a return biasing element. For example, the shape memory alloy can be coiled much like a spring to drive the movable member in one direction when heated and in the other direction when cooled.
• A first alternative embodiment of a pulse generating circuit is diagrammed schematically inFIG. 9 and is comprised of a 200 milliamp-hour lithium-manganese dioxideprimary battery901, a DC toDC converter902, acapacitor903, a low-resistance fieldeffect transistor switch904, a programmabledigital timing circuit905, aninductor906 and adiode908. The shape memory alloy wire is indicated inFIG. 9 symbolically as aresistor907. The objective of this embodiment of a pulse generating circuit is that the pulses of power delivered to the shapememory alloy wire907 can be of a higher voltage, and thus higher current, than that associated with the preferred embodiment of a pulse generating circuit diagrammed inFIG. 4 and described previously. A high voltage, high current power pulse has the advantage that it can actuate the circuit in a shorter more efficient time period. Additionally, the alternative embodiment of a pulse generating circuit allows the useful life of thebattery901 to be extended to a lower voltage and can prevent other circuitry powered by the battery from resetting when the battery voltage drops as is likely to happen in the preferred embodiment. Thebattery901 andcapacitor903 are electrically connected to each other in parallel through the DC toDC converter902. Thecapacitor903 is further connected to the shapememory alloy wire907 through thetransistor switch904. Theprogrammable timing circuit905, also powered by thebattery901 sends a gating signal to thetransistor switch904 as programmed by the user in accordance with their pumping requirements. During the period for which thetransistor switch904 is open, the DC toDC converter902 draws energy from thebattery901 and stores it in thecapacitor903. Use of the DC toDC converter902 allows the voltage of thecapacitor903 to be charged to a significantly higher value than that associated with thebattery901 and to be charged to the same voltage throughout the life of thebattery901 regardless of the battery voltage. It is intended that thetransistor switch904 may be modulated to send an overall energy pulse as a single pulse or as a sequence of discrete smaller pulses. It is intended that these smaller pulses may be sequenced so as to tailor a custom profile for the overall energy pulse. The custom profile would ensure optimal energy delivery to the shape memory alloy without exceeding its fusing characteristics. The inclusion of theinductor906 anddiode908 allows current to continue to flow through the shapememory alloy wire907 after thetransistor switch904 is opened when the pulse is modulated. This allows further control of the energy delivered to the shape memory alloy.
• Various references, publications, provisional and non-provisional United States patent applications, and/or United States patents, have been identified herein, each of which is incorporated herein in its entirety by this reference. Various aspects and features of the present invention have been explained or described in relation to beliefs or theories or underlying assumptions, although it will be understood that the invention is not bound to any particular belief or theory or underlying assumption. Various modifications, processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed, upon review of the specification. Although the various aspects and features of the present invention have been described with respect to various embodiments and specific examples herein, it will be understood that the invention is entitled to protection within the full scope of the appended claims.

Claims (30)

1. A medical device for pumping a fluid, comprising:

an actuator being disposed adjacent a chamber, the chamber having a resilient tubing, the actuator being in contact with the resilient tubing;

a shape memory alloy wire attached to the actuator to impart movement to the actuator;

a digital timing circuit for activating the shape memory alloy wire including a capacitor for providing electrical energy to the shape memory alloy wire; and

a reservoir containing the fluid and being in fluid communication with the chamber so that as the shape memory wire imparts movement to the actuator, the resilient tubing reacts to the movement of the actuator to expand and thereby pull a predetermined volume of fluid from the reservoir into the chamber.

2. The medical device ofclaim 1, wherein the electrical energy heats the shape memory alloy wire to a transitional temperature thereby causing the wire to shorten.

3. The medical device ofclaim 2, wherein the actuator moves a predetermined amount corresponding to a maximum volume within the chamber.

4. The medical device ofclaim 2, wherein the shape memory alloy wire cools and a biasing spring associated with the wire moves the actuator a predetermined amount corresponding to the minimum volume within the chamber.

5. The medical device ofclaim 1, wherein the digital timing circuit is programmable.

6. The medical device ofclaim 1, wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance.

7. The medical device ofclaim 1, wherein the rate of fluid delivery is controlled by varying the period of time between actuations of the shape memory alloy wire.

8. The medical device ofclaim 1, wherein the pump is disposable with the exception of the electronics including the digital timing circuit and the shape memory alloy wire.

9. The medical device ofclaim 1, wherein the fluid includes insulin.

10. A medical device for pumping a fluid, comprising:

an actuator being disposed adjacent a displacement chamber, the displacement chamber defined by a resilient tubing having an inlet valve and an outlet valve at opposite ends, wherein in an advancement stroke the actuator engages and deforms the resilient tubing to compress the displacement chamber, and in a withdrawal stroke decompresses the resilient tubing enabling the resilient tubing to restore to an original shape decompressing the displacement chamber;

a shape memory alloy wire attached to the actuator to impart movement to the actuator via phase changes in the shape memory alloy wire;

a digital timing circuit including a capacitor connected to and activating the shape memory alloy wire, providing electrical energy to the shape memory alloy wire; and

a reservoir containing the fluid and being in fluid communication with the displacement chamber so that as the shape memory wire imparts movement to the actuator, the resilient tubing reacts to the withdrawal stroke and advancement stroke of the actuator to one of decompressing and compressing the displacement chamber, and thereby one of pulling a predetermined volume of fluid from the reservoir via the inlet valve into the displacement chamber, and pushing the fluid from the displacement chamber through the outlet valve, respectively.

11. The medical device ofclaim 10, where in the fluid is insulin.

12. The medical device ofclaim 10, wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance.

13. The medical device ofclaim 10, wherein the electrical energy heats the shape memory alloy wire to a transition temperature thereby causing a phase change wherein the wire shortens.

14. The medical device ofclaim 10, wherein the actuator moves to a first limit corresponding to a maximum volume within the displacement chamber.

15. The medical device ofclaim 10, wherein the shape memory alloy wire cools and a spring biases the actuator in the direction of the advancement stroke.

16. The medical device ofclaim 10, wherein the digital timing circuit is programmable.

17. The medical device ofclaim 10, wherein the rate of fluid delivery is controlled by varying the period of time between activations of the shape memory alloy wire.

18. The medical device ofclaim 10, wherein the medical device is disposable with the exception of the electronics including the digital timing circuit and the shape memory alloy wire.

19. The medical device ofclaim 10, wherein the actuator is made from a rigid, dielectric material.

20. The medical device ofclaim 10, wherein the shape memory alloy wire includes a nickel-titanium alloy having a high transition temperature of about an ambient temperature+70° C. and a low transition temperature is just above the ambient temperature.

21. A medical device for pumping insulin, comprising:

a resilient tubing having an inlet valve and an outlet valve at opposite ends defining an interior chamber;

a plunger engaging and deforming the resilient tubing at the chamber;

a shape memory alloy wire attached to the plunger to impart reciprocal movement to the plunger to compress and decompress the resilient chamber;

a digital timing circuit for cyclically activating the shape memory alloy wire by providing electrical energy to the shape memory alloy wire; and

a reservoir containing the insulin and being in fluid communication with the chamber so that as the shape memory wire imparts movement to the plunger, the resilient tubing reacts to the movement of the actuator to expand and thereby pull a predetermined volume of insulin from the reservoir into the chamber.

22. The medical device ofclaim 21, wherein the shape memory alloy wire includes a nickel-titanium alloy that has a first transition temperature that is 70° C. higher than a second transition temperature.

23. The medical device ofclaim 21, wherein the resilient tubing is disposed within a restraining fixture surrounding and preventing volumetric expansion of the resilient tubing except for an exposed area that enables the plunger to pass therethrough.

24. The medical device ofclaim 21, wherein the plunger includes a tapered head at an end thereof that engages the resilient tubing perpendicularly.

25. The medical device ofclaim 24, wherein a spring is disposed coaxially with the plunger, and the shape memory alloy wire is attached to an end of the plunger opposite the tapered head, wherein activation of the shape memory alloy wire shortens the wire to withdraw the tapered head away from the resilient tubing against the bias of the spring.

26. The medical device ofclaim 21, wherein the digital timing circuit includes a programmable timing circuit, a battery, and an electrochemical capacitor that supplies primary electrical power to the shape memory alloy wire.

27. The medical device ofclaim 26, wherein the programmable timing circuit, the battery, and the capacitor are wired in parallel to the shape memory alloy wire.

28. The medical device ofclaim 21, wherein the digital timing circuit includes a programmable timing circuit, a 200 milliamp-hour battery, a low resistance transistor, and a capacitor, which circuit supplies a high voltage, high current pulse to the shape memory alloy wire.

29. The medical device ofclaim 28, wherein the programmable timing circuit, battery, capacitor, and shape memory alloy wire are connected in parallel.

30. The medical device ofclaim 29, wherein the digital timing circuit further comprises an inductor in series with the shape memory alloy wire and a diode in parallel therewith.

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