title: Piezoresistive cantilever force-clamp system.
abstract: We present a microelectromechanical device-based tool, namely, a force-clamp system that sets or "clamps" the scaled force and can apply designed loading profiles (e.g., constant, sinusoidal) of a desired magnitude. The system implements a piezoresistive cantilever as a force sensor and the built-in capacitive sensor of a piezoelectric actuator as a displacement sensor, such that sample indentation depth can be directly calculated from the force and displacement signals. A programmable real-time controller operating at 100 kHz feedback calculates the driving voltage of the actuator. The system has two distinct modes: a force-clamp mode that controls the force applied to a sample and a displacement-clamp mode that controls the moving distance of the actuator. We demonstrate that the system has a large dynamic range (sub-nN up to tens of μN force and nm up to tens of μm displacement) in both air and water, and excellent dynamic response (fast response time, <2 ms and large bandwidth, 1 Hz up to 1 kHz). In addition, the system has been specifically designed to be integrated with other instruments such as a microscope with patch-clamp electronics. We demonstrate the capabilities of the system by using it to calibrate the stiffness and sensitivity of an electrostatic actuator and to measure the mechanics of a living, freely moving Caenorhabditis elegans nematode.
authors.affiliation: Department of Mechanical Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Park
authors.forename: Bryan C
authors.initials: BC
authors.lastname: Petzold
authors.forename: Miriam B
authors.initials: MB
authors.lastname: Goodman
authors.forename: Beth L
authors.initials: BL
authors.lastname: Pruitt
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000502:physiology; D002138:Calibration; D004867:Equipment Design; D055595:Mechanical Phenomena; D008853:Microscopy; D009068:Movement; D018511:Systems Integration; D013997:Time Factors