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MEMS Electrolytic Inchworms for Movable Neural Probe Applications


Giacchino, Luca (2011) MEMS Electrolytic Inchworms for Movable Neural Probe Applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GQYY-BM80.


Over decades of cortical neural prosthesis, it was found that "movable" neural probes are important to track neurons for long-term, reliable prostheses. This is challenging because the ideal movable probes require low voltage, small power, bidirectional/latchable movement, and large total traveling distance. The device should also be small enough to entirely fit under the skull after implantation. Many different devices have been demonstrated to move neural probes, but none of them satisfies all the actuation and size requirements.

This thesis presents our work on actuators for movable neural probes that combine MEMS technology with an electrolytic actuation mechanism. Each inchworm is based on two electrolytic balloon actuators. The actuators rely on gas generation by electrolysis inside a sealed balloon, which causes its expansion. When electrolysis is stopped, gas recombination and permeation across the balloon membrane cause the balloon to relax. Electrolytic actuation, although slow, has several advantages: low power, low voltage, and ability to provide large force and displacement. The balloons have been characterized and their behavior mathematically modeled. Innovative salt-shell-based and hydrogel-based processes have been developed to fabricate the balloons and to allow their replenishment by osmosis.

Two balloons are combined into a bidirectional inchworm mechanism. Large traveling distance can be obtained in multiple cycles, the only constraint being the probe length. Displacement of a silicon probe and of a commercial metal probe have been demonstrated in both directions, with a displacement per cycle between 0.5 um and 75 um. The voltage required to drive electrolysis is typically around 3.5 V, with peak power per balloon around 100 uW. The devices were tested in air, water, and saline.

Closed-loop control of the inchworm may be needed for accurate positioning of the probe, and monitoring of the pressure inside the balloons represents a possible source of feedback from the inchworm. Parylene-membrane pressure sensors that are suitable for integration inside balloon actuators have been demonstrated.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:inchworm, balloon, electrolysis, mems, neural probe.
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Tai, Yu-Chong
Thesis Committee:
  • Emami, Azita
  • Yang, Changhuei
  • Burdick, Joel Wakeman
  • Kornfield, Julia A.
Defense Date:16 August 2010
Non-Caltech Author Email:lucagiac (AT)
Funding AgencyGrant Number
Record Number:CaltechTHESIS:01102011-204907918
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6222
Deposited By: Luca Giacchino
Deposited On:18 Feb 2011 00:20
Last Modified:09 Oct 2019 17:07

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