A FEEDBACK-CONTROLLED SILICON MICROPROBE FOR QUANTITATIVE MECHANICAL STIMULATION OF NERVE AND TISSUE

The ability to apply and control the force and force velocity of mecha nical stimulation is essential for the study of mechanoelectric transd uction and adaptation processes. Silicon micromachining technology was used to produce miniature (20-70 mu m wide) mechanical microprobes. P assive polysilicon, piezoresistive, force sensing elements were deposi ted onto the boron-doped epitaxial silicon and the individual devices were chemically etched from the bulk wafer. These microprobes display a linear force versus output voltage relationship. Stimulation forces upto 2 mN can be generated with a measurement resolution of 1.5 mu N T he probes were mounted onto circuit board holders and their output sen t to a proportional-integral controller which drives an electromagneti c actuator. By using this force-feedback control circuit coupled to a PC it is possible to define any stimulus wave form pattern and indepen dently control and measure the actual stimulus force and velocity. A c omputer controlled 3-axis stepper motor (0.025 mu m step capability) m anipulator is used to position the silicon microprobe-actuator assembl y relative to the mechanoreceptive field. Sensor feedback control coup led to the 3-axis stepper motor manipulator allows automatic touchdown control and/or preloading of the probe prior to stimulation. Three-di mensional topographic manipulator feedback position control allows aut omated receptive field mapping.