Defense announcement on 3/16 monday

Title: Development of Piezoresistive Microcantilever based Force Feedback System for Study of Mechanotransduction in C. elegans

University Oral Examination
Sung-Jin Park
Department of Mechanical Engineering
Stanford University
Advisor: Beth Pruitt and Miriam Goodman

Date: Monday, March 16, 2009
Time: 10AM (Refreshments served at 9:45AM)
Location: Building 300- room 300 (Auditorium) (map attached)

Abstract:

 

Cellular mechanotransduction, the conversion of force into to an electrical or biochemical signal, is a fundamental process essential to normal life, including hearing, touch and balance. Among these, touch sensation is the least understood. The nematode Caenorhabditis elegans is one of the most powerful model organisms in which to analyze the mechanism of touch sensation. Few techniques exist to provide forces and displacements appropriate for such studies. To address this technological gap, we developed a metrology using piezoresistive cantilevers as force-displacement sensors coupled to feedback system in order to apply and maintain defined load profiles to micron-scale animals. This thesis presents 1) design and optimization of piezoresistive cantilever, 2) integration and development of force clamp system, and 3) biological studies of C. elegans mechanotransduction.

 

We developed and validated an analytical model to predict the force sensitivity and force resolution of a piezoresistive cantilever. We systematically analyzed the effects of process parameters on the sensitivity and resolution of the cantilevers to optimize their design. This optimization technique produced optimal cantilever with minimum resolution such as 69 pN at 1-1000 Hz bandwidth. This analytical model and optimization technique are very useful to design piezoresistive devices with complex design conditions for biological applications.

 

We conducted biological studies of C. elegans mechanotransduction by integrating the developed force probe with force and displacement feedback system. We measured body stiffness of wild type and mutants which alter body shape and cuticle proteins. The analysis of C. elegans body mechanics suggests that shell mechanics dominates stiffness rather than hydrostatic pressure. We also conducted the behavioral response of C. elegans to touch stimuli by utilizing the system in force-clamping mode. We applied a 100 nN to 10 mN force to freely-moving wild type and mec-4 mutant which has loss of touch receptor neuron. The behavioral result agrees with our prior in-vivo work which suggests that electrical responses of wild type to touch saturate near a force threshold, between 100nN and 1mN. These studies form a part of the bigger puzzle of how body mechanics affect locomotion and force sensing.