Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Shape memory actuated microvalve

The valve concept is based on a pincher pressing on an elastic tube. To obtain minimal dimensions and a minimal number of parts, classic joints were avoided and replaced by elastic joints; screwed clamps were replaced by gluing, melting and soldering. Following these design rules, a prototype was built with only three parts per valve: the body, the shape memory wire, and a screw for adjusting the initial wire length. The plastic body contains two elastic joints: one for the opening and closing movement of the valve and another for the pretensioning system of the wire. The valve is normally closed and opens when it is elastically deformed by actuation of the shape memory wire. Thereafter, the valve closes again by the elasticity of the joint. The valve measures about 5 x 8.5 x 2 mm{3}.

For experimental purposes, a full drug delivery system is made consisting of a refill system, reservoirs, tubes, two microvalves, antenna and housing. The refilling system consists of an injection port sealed by a plug of silicone rubber. The reservoirs are moulded in silicone rubber. The main reservoir of the proposed prototype has a capacity of about 1 ml. The tubes were tested with air pressure and they resisted a pressure of 200 kPa (all pressure values are relative to the environment).
In this system the valves had the following performance:
Leakage: the valves were tested with compressed air. Pressure was raised up to the maximum strength of the tubes (200 kPa), without any leakage.
Life-time: the smoothness of the tips pressing on the tubes is of extreme importance: with a smooth surface, 10 000 cycles were obtained without any problem. No leaks occurred and the shape memory wire pretensioning system of the valve had not to be adjusted. These 10 000 cycles correspond to 3 injections a day, 9 years long, or 5 injections a day, 5 years long.
Power consumption: the resistance of the shape memory wire is 750 mOhms. When driven with current peaks of 400 mA during 660 ms, this results in a power consumption of 120 mW per cycle and per valve. This system has been successfully powered with a transcutaneous transformer working at 1 MHz and with a power density of 10 mW/cm{2}. Dosing accuracy: depending on the internal pressure, the dose leaving the system each cycle is between 5 and 25 µl, allowing 40 to 200 doses.


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