Device and Method Employing Shape Memory Alloy

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.

1 . A medical device for pumping a fluid, comprising:
 a plunger having reciprocal movement in a displacement cavity between a first limit and a second limit;   a shape memory alloy wire attached to the plunger for pulling the plunger in a first direction in the displacement cavity;   a digital timing circuit for activating the shape memory alloy wire including an electrical energy storage device for providing electrical energy to the shape memory alloy wire to thermally phase transform the wire; and   a reservoir containing a fluid and being in fluid communication with the displacement cavity so that as the shape memory alloy wire is activated, the shape memory alloy wire phase transforms and shortens, and pulls the plunger in the first direction thereby pulling a predetermined volume of fluid from the reservoir into the displacement cavity.   
     
     
         2 . The medical device of  claim 1 , where in the electrical energy storage device is a capacitor. 
     
     
         3 . The medical device of  claim 2 , wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         4 . The medical device of  claim 1 , wherein the electrical energy heats the shape memory alloy wire to a transition temperature thereby causing a phase transition and the wire to shorten. 
     
     
         5 . The medical device of  claim 1 , wherein the plunger moves to the first limit corresponding to a maximum volume within the displacement cavity. 
     
     
         6 . The medical device of  claim 4 , wherein the shape memory alloy wire cools and a biasing spring associated with the wire moves the plunger to the second limit corresponding to the minimum volume within the displacement cavity. 
     
     
         7 . The medical device of  claim 1 , wherein the digital timing circuit is programmable. 
     
     
         8 . The medical device of  claim 1 , wherein the rate of fluid delivery is controlled by varying the period of time between activations of the shape memory alloy wire. 
     
     
         9 . The medical device of  claim 1 , wherein the medical device is disposable with the exception of the electronics including the digital timing circuit and the shape memory alloy wire. 
     
     
         10 . The medical device of  claim 1 , wherein the plunger includes a rigid, dielectric material. 
     
     
         11 . The medical device of  claim 10 , wherein the plunger is electrically connected to the digital timing circuit via the shape memory alloy wire, and the rigid, dielectric plunger acts as a ground. 
     
     
         12 . The medical device of  claim 11 , wherein the device includes an elastomeric diaphragm attached to the plunger and facing the displacement cavity, and wherein the elastomeric diaphragm electrically insulates the plunger, digital timing circuit, and shape memory alloy wire from the fluid. 
     
     
         13 . The medical device of  claim 1 , wherein the plunger is connected to a diaphragm, and flexing in the diaphragm caused by the plunger movement acts on the displacement cavity to increase and decrease a volume thereof. 
     
     
         14 . The medical device of  claim 13 , wherein the diaphragm includes a non-wetted surface facing the plunger. 
     
     
         15 . The medical device of  claim 13 , wherein the device includes a biasing spring acting on the plunger, and wherein when the shape memory alloy wire is deactivated, the biasing spring pushes on the plunger in a second direction restoring the shape memory alloy wire to an initial length and compressing the displacement cavity to expel the fluid through an outlet. 
     
     
         16 . The medical device of  claim 11 , wherein the displacement cavity includes an inlet and an outlet, and an inlet check valve and an outlet check valve located away from the displacement cavity and in communication with the displacement cavity via the inlet and outlet, respectively. 
     
     
         17 . A medical device for pumping a fluid, comprising:
 an actuator being disposed adjacent a chamber, the chamber having a diaphragm, the actuator being in contact with the diaphragm;   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 a fluid and being in fluid communication with the chamber so that as the shape memory wire imparts movement to the actuator, the diaphragm reacts to the movement of the actuator to expand and thereby pull a predetermined volume of fluid from the reservoir into the chamber.   
     
     
         18 . The medical device of  claim 17 , wherein the electrical energy heats the shape memory alloy wire to a transitional temperature thereby causing the wire to shorten. 
     
     
         19 . The medical device of  claim 18 , wherein the actuator moves a predetermined amount corresponding to a maximum volume within the chamber. 
     
     
         20 . The medical device of  claim 18 , 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. 
     
     
         21 . The medical device of  claim 17 , wherein the digital timing circuit is programmable. 
     
     
         22 . The medical device of  claim 17 , wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         23 . The medical device of  claim 17 , wherein the rate of fluid delivery is controlled by varying the period of time between actuations of the shape memory alloy wire. 
     
     
         24 . The medical device of  claim 17 , wherein the medical device is disposable with the exception of the electronics including the digital timing circuit and the shape memory alloy wire. 
     
     
         25 . A medical device for pumping a fluid, comprising:
 an actuator being disposed adjacent a chamber, the chamber having a diaphragm, the actuator being in contact with the diaphragm and having reciprocal movement;   a shape memory alloy wire attached to the actuator to impart movement to the actuator via phase changes;   a digital timing circuit for activating the shape memory alloy wire phase changes including an electrical energy storage device for providing electrical energy to the shape memory alloy wire; and   a reservoir containing a fluid and being in fluid communication with the chamber so that as the shape memory wire imparts movement to the actuator, the diaphragm reacts to the movement of the actuator to expand and thereby pull a predetermined volume of fluid from the reservoir into the chamber.   
     
     
         26 . The medical device of  claim 25 , wherein the electrical energy storage device is a capacitor. 
     
     
         27 . The medical device of  claim 25 , wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         28 . The medical device of  claim 25 , wherein the electrical energy heats the shape memory alloy wire to a transition temperature thereby causing the wire to shorten. 
     
     
         29 . The medical device of  claim 28 , wherein the actuator moves a predetermined amount corresponding to a maximum volume within the chamber. 
     
     
         30 . The medical device of  claim 28 , 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. 
     
     
         31 . The medical device of  claim 25 , wherein the digital timing circuit is programmable. 
     
     
         32 . The medical device of  claim 25 , wherein the rate of fluid delivery is controlled by varying the period of time between actuations of the shape memory alloy wire. 
     
     
         33 . The medical device of  claim 25 , wherein the medical device is disposable with the exception of the electronics including the digital timing circuit and the shape memory alloy wire. 
     
     
         34 . The medical device of  claim 25 , wherein the reservoir has a variable internal capacity. 
     
     
         35 . A medical device for pumping a fluid, comprising:
 an actuator being disposed adjacent a chamber, the chamber having a flexible diaphragm, the actuator being in contact with the diaphragm and having reciprocal movement to flex the diaphragm;   a shape memory alloy wire, having a high temperature phase with a first transition temperature and a low temperature phase with a second transition temperature, attached to the actuator to impart movement to the actuator via phase changes;   a digital timing circuit for activating the shape memory alloy wire phase changes including an electrical energy storage device for providing electrical energy to the shape memory alloy wire; and   a reservoir containing a fluid and being in fluid communication with the chamber so that as the shape memory wire imparts movement to the actuator, the diaphragm reacts to the movement of the actuator to expand and thereby pull a predetermined volume of fluid from the reservoir into the chamber.   
     
     
         36 . The medical device of  claim 35 , wherein the shape memory alloy wire includes a nickel-titanium alloy for which the high temperature phase is the austenitic phase and the low temperature phase is the martensitic phase. 
     
     
         37 . The medical device of  claim 35 , wherein each phase change of the shape memory alloy wire causes a respective, reversible, dimensional change in the shape memory alloy wire. 
     
     
         38 . The medical device of  claim 35 , wherein the shape memory alloy wire alloy includes a first transition temperature of an ambient temperature + about 70° C., and a second transition temperature of slightly above the ambient temperature. 
     
     
         39 . The medical device of  claim 35 , wherein the diaphragm includes an elastomer. 
     
     
         40 . The medical device of  claim 35 , wherein the actuator includes a rigid dielectric material.