Felix Beyeler

Monolithically Fabricated Microgripper With Integrated Force Sensor for Manipulating Microobjects and Biological Cells Aligned in an Ultrasonic Field

This paper reports an electrostatic microelectromechanical systems (MEMS) gripper with an integrated capacitive force sensor. The sensitivity is more than three orders of magnitude higher than other monolithically fabricated MEMS grippers with force feedback. This force sensing resolution provides feedback in the range of the forces that dominate the micromanipulation process. A MEMS ultrasonic device is described for aligning microobjects suspended in water using ultrasonic fields. The alignment of the particles is of a sufficient accuracy that the microgripper must only return to a fixed position in order to pick up particles less than 100 mum in diameter. The concept is also demonstrated with HeLa cells, thus providing a useful tool in biological research and cell assays

Robotics in the Small, Part I: Microbotics

This article provided an overview of the field of microrobotics, including the distinct but related topics of micromanipulation and microrobots. While many interesting results have been shown to date, the greatest results in this field are yet to come.

Fibronectin forms the most extensible biological fibers displaying switchable force-exposed cryptic binding sites

Rather than maximizing toughness, as needed for silk and muscle titin fibers to withstand external impact, the much softer extracellular matrix fibers made from fibronectin (Fn) can be stretched by cell generated forces and display extraordinary extensibility. We show that Fn fibers can be extended more than 8-fold (>700% strain) before 50% of the fibers break. The Youngs modulus of single fibers, given by the highly nonlinear slope of the stress-strain curve, changes orders of magnitude, up to MPa. Although many other materials plastically deform before they rupture, evidence is provided that the reversible breakage of force-bearing backbone hydrogen bonds enables the large strain. When tension is released, the nano-sized Fn domains first contract in the crowded environment of fibers within seconds into random coil conformations (molten globule states), before the force-bearing hydrogen bond networks that stabilize the domains secondary structures are reestablished within minutes (double exponential). The exposure of cryptic binding sites on Fn type III modules increases steeply upon stretching. Thus fiber extension steadily up-regulates fiber rigidity and cryptic epitope exposure, both of which are known to differentially alter cell behavior. Finally, since stress-strain relationships cannot directly be measured in native extracellular matrix (ECM), the stress-strain curves were correlated with stretch-induced alterations of intramolecular fluorescence resonance energy transfer (FRET) obtained from trace amounts of Fn probes (mechanical strain sensors) that can be incorporated into native ECM. Physiological implications of the extraordinary extensibility of Fn fibers and contraction kinetics are discussed.

A Six-Axis MEMS Force–Torque Sensor With Micro-Newton and Nano-Newtonmeter Resolution

This paper describes the design of a six-axis microelectromechanical systems (MEMS) force-torque sensor. A movable body is suspended by flexures that allow deflections and rotations along the x-, y-, and z-axes. The orientation of this movable body is sensed by seven capacitors. Transverse sensing is used for all capacitors, resulting in a high sensitivity. A batch fabrication process is described as capable of fabricating these multiaxis sensors with a high yield. The force sensor is experimentally investigated, and a multiaxis calibration method is described. Measurements show that the resolution is on the order of a micro-Newton and nano-Newtonmeter. This is the first six-axis MEMS force sensor that has been successfully developed.

A micro-particle positioning technique combining an ultrasonic manipulator and a microgripper

The acoustic radiation force acts on particles suspended in a fluid in which acoustic waves are present. It can be used to establish a force field throughout the fluid volume capable of positioning the particles in predictable locations. Here, a device is developed which positions the particles in a single line by the sequential use of two excitation frequencies which have been identified by a finite element model of the system. The device is designed such that at one end there is an opening which allows the fingers of a microgripper to enter the fluid chamber. Hence the gripper can be used to remove the last particle in the line. The high accuracy of the positioning of the particles prior to gripping means that the microgripper needs just to return to a fixed position in order to remove subsequent particles. Furthermore, the effects of the microgripper fingers entering the fluid volume whilst the ultrasound field is excited are examined. One result being the release of a particle stuck to a gripper finger. It is believed that this combination of techniques allows for considerable scope in the automation of microgripping procedures.

Three-axis micro-force sensor with sub-micro-Newton measurement uncertainty and tunable force range

The first three-axis micro-force sensor with adjustable force range from ±20 µN to ±200 µN and sub-micro-Newton measurement uncertainty is presented. The sensor design, the readout electronics, the sensor characterization and an uncertainty analysis for the force predictions are described. A novel microfabrication process based on a double silicon-on-insulator (SOI) substrate has been developed enabling a major reduction in the fabrication complexity of multi-axis sensors and actuators.

Design of a Micro-Gripper and an Ultrasonic Manipulator for Handling Micron Sized Objects

This work reports on a system consisting of a MEMS (microelectromechanical system) gripper and an ultrasonic manipulator. The gripper is electrostatically actuated and includes an integrated force sensor measuring the gripping force. The device is monolithically fabricated using a silicon-on-insulator (SOI) fabrication process. The resolution of the force sensor is in the sub-micronewton range and, therefore, provides feedback of the forces that dominate the micromanipulation processes. A MEMS ultrasonic device is described which aligns small objects such as biological cells prior to manipulation with the gripper. The concept is demonstrated with polymer spheres, glass spheres and Hela cancer cells, thus providing a useful tool in micro-robotics and biological research

Design and calibration of a MEMS sensor for measuring the force and torque acting on a magnetic microrobot

This paper presents the design, fabrication and calibration of a multi-axis micro force–torque sensor. The sensor and its readout electronics are specifically designed to simultaneously measure two force components and one torque component. The load is measured by capacitive comb drives which provide high sensitivity. The sensor is applied to measure micro-Newton level forces and nano-Newton-meter level torques on a magnetically actuated microrobot. This microrobot is assembled from microfabricated nickel parts and is designed for directed drug delivery inside the human body. The precise knowledge of the forces and torques will help design magnetic position controllers as well as understand the magnetic properties of the electroplated microparts.

Monolithically Integrated Two-Axis Microtensile Tester for the Mechanical Characterization of Microscopic Samples

This paper describes the first monolithically integrated two-axis microtensile tester and its application to the automated stiffness measurement of single epidermal plant cells. The tensile tester consists of a two-axis electrostatic actuator with integrated capacitive position sensors and a two-axis capacitive microforce sensor. It is fabricated using a bulk silicon microfabrication process. The actuation range is +/-16 m along both axes with a position resolution of 20 nm. The force sensor is capable of measuring forces up to +/-60 N with a resolution down to 60 nN. The position-feedback sensors as well as the force sensor are calibrated by direct comparison with reference standards. A complete uncertainty analysis through the entire calibration chain based on the Monte Carlo method is presented. The functionality of the tensile tester is demonstrated by the automated stiffness measurement of the elongated cells in plant hairs (trichomes) as a function of their size. This enables a quantitative understanding and a model-based simulation of plant growth based on actual measurement data.

Adaptive backstepping and MEMS force sensor for an MRI-guided microrobot in the vasculature

A microrobot consisting of a polymer binded aggregate of ferromagnetic particles is controlled using a Magnetic Resonance Imaging (MRI) device in order to achieve targeted therapy. The primary contribution of this paper is the design of an adaptive backstepping controller coupled with a high gain observer based on a nonlinear model of a microrobot in a blood vessel. This work is motivated by the difficulty in accurately determining many biological parameters, which can result in parametric uncertainties to which model-based approaches are highly sensitive. We show that the most sensitive parameter, magnetization of the microrobot, can be measured using a Micro-Electro-Mechanical Systems (MEMS) force sensor, while the second one, the dielectric constant of blood, can be estimated on line. The efficacy of this approach is illustrated by simulation results.