Watertight, low-power micro-actuator probes brain, in-vivo

Leuven, Belgium — Using the principal of hydrophobia, scientists at IMEC have overcome the problem of making their ultra-low-power 'inch-worm' micro-actuator watertight, thereby opening up a wide range of in-vivo biomedical applications, including recording the activity of individual neurons in the brain.

The announcement (download the full presentation) was made here at IMEC's annual media gathering and according to Piet De Moor, IMEC's manager of heterogeneous component integration, the actuator in itself is a micro electromechanical systems (MEMS) device fabricated using silicon-on-insulator (SOI)-based micromachining. (*More at end.)

Key features include low-voltage operation (6 V), a range of +/- 50 micron, and a force of +/- 195 microNewtons. The latter allows it to accurately position micro-needles or in-vivo brain electrodes in close proximity to individual neurons. To date, the problem of fluid intrusion has kept probes external to the brain.

IMEC's inchworm actuator has 6 pull-in actuators; 4 are used for latching and 2 for driving. By proper latching, unlatching, and driving the shuttle, the actuator can drive a bidirectional step-like movement.

However, to enable the neural sense-and-record, IMEC's prototype has an integrated micro-needle, which can be steered by the actuator. That poses a problem: How do you allow an external needle, controlled by an actuator, to move back and forth while still maintaining the package hermeticity required for in-vivo applications?

To achieve this, De Moor prepped the needle channel with a coating of hydrophobic material (Teflon) so that an bubble of air would be trapped and separate the inside of the actuator from the external body fluid.

The low-power actuator can be combined with a needle to enable in-vivo medical applicitions, but a hydrophobic coating was needed for hermeticity.

While De Moor has confidence in the actuator itself, which he said has a lifespan of 20 million steps, he told EETimes that the hydrophobic-enabled in-vivo application still needs to be studied. Potential issues include the natural adhesion of body cells to the device and the unknown effects--if any--of water vapor on the inside of the needle cavity where corrosion may occur.

*A micro-actuator is a MEMS-device (micro-electromechanical system) that converts energy into micro-movements, allowing it to position or control elements with a high precision, and with steps of a few micrometers or even nanometers. IMEC's actuator is an electrostatic inchworm actuator, having 6 arms that selectively latch, unlatch, and drive. Today, micro-actuators are already used in medical applications where biological objects or their environment need to be controlled at the microscopic scale. Examples are micro-manipulators, micro-surgery tools, micro-pumps, and micro-needles. One particular biomedical application of micro-actuators is to integrate them with microprobes for brain applications. Today, actuators for brain implants are already used during brain research; but they are placed outside the body.