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 having a portion disposed in a displacement cavity;   a shape memory alloy wire attached to the actuator to impart movement of the actuator in a first direction in the displacement cavity;   a digital timing circuit for activating the shape memory alloy wire including an energy source for providing electrical energy to the shape memory alloy wire; and   a reservoir containing a fluid and being in fluid communication with the displacement cavity so that as the shape memory wire imparts movement to the actuator in the first direction, a predetermined volume of fluid is drawn from the reservoir into the displacement cavity.   
     
     
         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 in the first direction corresponding to a maximum volume within the displacement cavity. 
     
     
         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 in a second direction corresponding to the minimum volume within the displacement cavity. 
     
     
         5 . The medical device of  claim 1 , wherein the digital timing circuit is programmable. 
     
     
         6 . The medical device of  claim 1 , wherein the energy source is an electrochemical capacitor having a high capacitance and low-equivalent series resistance. 
     
     
         7 . The medical device of  claim 1 , wherein the energy source is a battery. 
     
     
         8 . The medical device of  claim 1 , wherein the displacement cavity is shaped like a syringe barrel. 
     
     
         9 . The medical device of  claim 1 , wherein the actuator is pivotably linked to the shape memory alloy wire. 
     
     
         10 . The medical device of  claim 1 , wherein the displacement cavity has a first limit tab and a second limit tab to limit the travel of the actuator in the displacement cavity. 
     
     
         11 . 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. 
     
     
         12 . 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.