piezoresistive cantilever-based force-clamp ... - Stanford University

PIEZORESISTIVE CANTILEVER-BASED FORCE-CLAMP SYSTEM FOR THE STUDY OF MECHANOTRANSDUCTION IN C. ELEGANS

S.-J. Park1, B. Petzold1, M.B. Goodman2, and B.L. Pruitt1 1 Department of Mechanical Engineering, Stanford University, Stanford, CA, USA 2 Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA, USA defined force profiles (e.g. constant, sinusoidal) to C. elegans. We also present initial mechanotransduction studies enabled by the system which reveal new insights into the inner working of the sense of touch in this tiny nematode.

ABSTRACT Understanding how the mechanoreceptor neurons of Caenorhabditis elegans mediate mechanotransduction can unravel how touch works, but new tools are required to quantitatively analyze the relationship between mechanical loading and the physiological response. Here we present a piezoresistive cantilever-based force clamp system that can apply user-defined force profiles to C. elegans. We present a novel MEMS force-clamp system and demonstrate a piezoresistive cantilever with low 1/f noise, low noise floor and high force resolution suitable for these measurements. Initial studies enabled by the system are also discussed.

METHOD Piezoresistive cantilever We designed and fabricated custom microcantilevers of several sizes (1.7 to 6 mm long, 30 to 400 μm wide, 7 to 50 μm thick cantilever with a 200 to 350 μm long and 10 to 20 μm wide U-shaped piezoresistor) using previously discussed microfabrication techniques [3, 4]. We glued completed cantilevers to custom printed circuit boards with epoxy (Devcon, Glenview, IL) and created aluminum wire interconnects between the device bond pads and the circuit board contacts using a wirebonder (Figure 1A). To control the contact area, a glass bead (10μm diameter, Duke Scientific, Palo Alto, CA) was attached to the end of each cantilever with an ultraviolet adhesive (Loctite 352, Henkel Technologies, Germany) (Figure 1B).

INTRODUCTION 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 [1]. C. elegans is extremely simple compared to humans: it has 302 neurons and about 1000 cells. Six touch receptor neurons that innervate the length of its body are responsible for touch sensitivity. The classical method to test for touch sensitivity in C. elegans is to score its response to applied mechanical stimuli. One of us (Goodman) previously used micro-von Frey hairs to touch to freely moving worms until buckling was observed. Each different size probe has different buckling force, so each probe was used to measure touch sensitivity at different force levels. However, this method has the intrinsic issue of precision and accuracy: buckling of the probe is an unstable deformation mode. In addition, it is incapable of delivering forces