A Medical Microactuator based on a Electrochemical Principle

Glaucoma is a disease causing damage to the optic nerve head due to a too high eye pressure. This damage will lead to visual field loss, and finally to blindness. The current surgery treatment improves the drainage of the eye fluid by introducing a draining device. The problem is that one cannot predict in advance the value of the eye pressure after surgery and it cannot be adjusted to the optimum eye pressure of the patient, after surgery. A continuous adjustment of the eye pressure would simplify and improve the present treatment. The goal of this research is to develop a micromachined actuator that could be combined with existing glaucoma implants. This microactuator, that acts as an active valve would allow the eye pressure to be adjusted continuously around a desired value. The actuator can be used to adjust the eye fluid pressure, for patients suffering from glaucoma, by changing the fluid resistance of an implanted flow channel due to deflection of an integrated membrane. To obtain a low energy consumption and to have the possibility of discontinuous supply of power, it was opted for electrochemical actuation, which is based on the electrolysis of an aqueous electrolyte solution. The reversible electrochemical reactions, which are driven by an external current source, lead to gas evolution or gas reduction (depending on the direction of the current). In a closed system the corresponding gas pressure rise or drop is used to change the deflection of a flexible membrane, which in turn can close or open a liquid channel. If such an electrolytic cell is operated under open-circuit conditions, the pressure and thus the deflection state of the diaphragm will, ideally, be maintained. This means that no energy is required to maintain the state of the valve. It has been proven that relatively large pressures (up to tens of bar) and large deflections can be reached in this electrochemical actuator with a low energy consumption. The complete microactuator system should have a maximum size of 5x5x2 mm3 and will be powered by wireless energy supply. The energy is transmitted by using a pair of coils which are inductively coupled; one coil is implanted and the other one is outside the body.