Design of a SMA-actuated implantable drug delivery system

Shape memory alloy actuators offer the advantage of extremely high power to volume ratio´s, which can be an advantage in miniature applications. This paper describes the design of an implantable drug delivery system based on shape memory alloy actuated micro-valves. The operating principle is based on a precisely controlled, discontinuous release from a pressurized reservoir. The reservoir is pressurized using a two-phase fluid providing constant pressure at body temperature. The volume of one dose can be controlled with an accuracy up to 5 microlitres. The system is remotely powered and controlled using a transcutaneous transformer. A refilling possibility based on transcutaneous injections is also provided. The design of the valves is such that they can be mounted on a printed circuit board (PCB) together with the other electrical components. Furthermore, the design is optimised towards aspects like biocompatibility, low cost production, ease of assembly, lifetime, safety, and minimal dimensions. Also possible improvements based on thin film shape memory alloy melt spun ribbons will be discussed. The design is aiming at patients that need multiple injections per day over a long period of time. The current design could already reduce the number of injections by a factor of 200, but by further miniaturisation a reduction by a factor of 3000 could be obtained