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:
 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 of  claim 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 of  claim 2 , wherein the actuator moves a predetermined amount corresponding to a maximum volume within the chamber. 
     
     
         4 . The medical device of  claim 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 of  claim 1 , wherein the digital timing circuit is programmable. 
     
     
         6 . The medical device of  claim 1 , wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         7 . The medical device of  claim 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 of  claim 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 of  claim 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 of  claim 10 , where in the fluid is insulin. 
     
     
         12 . The medical device of  claim 10 , wherein the capacitor is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         13 . The medical device of  claim 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 of  claim 10 , wherein the actuator moves to a first limit corresponding to a maximum volume within the displacement chamber. 
     
     
         15 . The medical device of  claim 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 of  claim 10 , wherein the digital timing circuit is programmable. 
     
     
         17 . The medical device of  claim 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 of  claim 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 of  claim 10 , wherein the actuator is made from a rigid, dielectric material. 
     
     
         20 . The medical device of  claim 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 of  claim 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 of  claim 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 of  claim 21 , wherein the plunger includes a tapered head at an end thereof that engages the resilient tubing perpendicularly. 
     
     
         25 . The medical device of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 28 , wherein the programmable timing circuit, battery, capacitor, and shape memory alloy wire are connected in parallel. 
     
     
         30 . The medical device of  claim 29 , wherein the digital timing circuit further comprises an inductor in series with the shape memory alloy wire and a diode in parallel therewith.