Jurg Dual

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

Inverse finite element characterization of soft tissues

In this work a tissue aspiration method for the in vivo determination of biological soft tissue material parameters is presented. An explicit axisymmetric finite element simulation of the aspiration experiment is used together with a Levenberg-Marquardt algorithm to estimate the material model parameters in an inverse parameter determination process. An optimal fit of the simulated experiment and the real experiment is sought with the parameter estimation algorithm. Soft biological tissue is modelled as a viscoelastic, non-linear, nearly incompressible, isotropic continuum. Viscoelasticity is accounted for by a quasi-linear formulation. The aspiration method is validated experimentally with a synthetic material. In vivo (intra-operatively during surgical interventions) and ex vivo experiments were performed on human uteri.

Forthcoming Lab on a Chip tutorial series on acoustofluidics: Acoustofluidics—exploiting ultrasonic standing wave forces and acoustic streaming in microfluidic systems for cell and particle manipulation

Forthcoming lab on a chip tutorial series on acoustofluidics : Acoustofluidics - Exploiting ultrasonic standing wave forces and acoustic streaming in microfluidic systems for cell and particle manipulation

Manipulation of micrometer sized particles within a micromachined fluidic device to form two-dimensional patterns using ultrasound

Ultrasonic manipulation, which uses acoustic radiation forces, is a contactless manipulation technique. It allows the simultaneous handling of single or numerous particles (e.g., copolymer beads, biological cells) suspended in a fluid, without the need for prior localization. Here it is reported on a method for two-dimensional arraying based on the superposition of two in-plane orthogonally oriented standing pressure waves. A device has been built and the experimental results have been compared with a qualitative analytical model. A single piezoelectric transducer is used to excite the structure to vibration, which consists of a square chamber etched in silicon sealed with a glass plate. A set of orthogonally aligned electrodes have been defined on one surface of the piezoelectric. This allows either a quasi-one-dimensional standing pressure field to be excited in one of two directions or if both electrodes are activated simultaneously a two-dimensional pressure field to be generated. Two different operational modes are presented: two signals identical in amplitude and frequency were used to trap particles in oval shaped clumps; two signals with slightly different frequencies to trap particles in circular clumps. The transition between the two operational modes is also investigated.

Contactless micromanipulation of small particles by an ultrasound field excited by a vibrating body

A method is presented to position and displace micron-sized particles of a diameter between 10 and 100 microm without contact to solid instruments. An ultrasound field is utilized for this purpose. It is excited in a fluid-filled gap between a harmonically vibrating body and a rigid plane surface of an arbitrary other body, e.g., an object slide or a wafer. In this ultrasound field a force field is established, which acts on the particles suspended in the fluid and moves them to certain positions. The advantage of the method is that it is possible to manipulate single particles or many particles in parallel on any surface, for example, on a structured wafer. Theoretical calculations of the force field and experimental results including three principles to displace particles with micrometer accuracy are shown. The method might be used for microassembly or cell manipulation and treatment.

Micro-manipulation of small particles by node position control of an ultrasonic standing wave

For the controlled positioning of small particles with ultrasound a standing wave in a fluid is used. The standing wave is implemented in a resonator, that consists of a fluid filled tube and two piezoelectric transducers on each end. A one-dimensional model of a piezo-device including the fluid-loading on one side and a backside support is introduced. This model allows the calculation of the transmitted wave as a function of the applied electric voltage and the incident wave. In addition, when an electrical impedance is connected to the piezo-device, the reflection coefficient can be varied in amplitude and phase, so that the parameters of the reflected wave can be controlled completely. The resonator itself, consisting of a piezo-device on each end and the fluid between, is included in the model. Several methods to shift the nodes of the standing wave in the resonator are investigated and the ability to position particles is discussed.

High-resolution analysis of the complex wave spectrum in a cylindrical shell containing a viscoelastic medium. Part I. Theory and numerical results

In this study the relation between frequency and complex wave number of axisymmetric wave modes in an isotropic, thin-walled, cylindrical shell containing a linear viscoelastic medium is derived. Shell wall bending and longitudinal motion are coupled in an empty cylindrical shell. When a viscoelastic medium is enclosed, the shell motion is affected by the complex bulk and shear modulus, as well as by the density of the medium enclosed. A Maxwell model is used for both complex Lame constants λ and μ to describe the constitutive equations of the medium. By varying the complex moduli, the medium can be modeled as an inviscid fluid, an elastic material, or anything between these two extremes. The interaction of the thin-walled linear elastic shell and the viscoelastic medium is discussed numerically by calculating the complex dispersion relation. Numerical results are presented for an empty shell and a shell filled with three types of core material: an inviscid fluid, a shear dissipative fluid, and a shear el...

Sensitivity improvement of a pump–probe set-up for thin film and microstructure metrology

This investigation deals with various new aspects of the sensitivity improvement of a pump-probe laser based acoustic method. A short laser pulse is used to excite a mechanical pulse thermo-elastically. Echoes of these mechanical pulses reaching the surface are causing a slight change of the optical reflectivity. The surface reflectivity is scanned versus time with a probe pulse. Thus the time of flight of the acoustic pulse is measured. The quantity to be measured i.e. the optical reflectivity change deltaR caused by acoustic pulses, is rather small. A set-up having an estimated sensitivity deltaR/R of about 10(-5) has shown to be sufficient to detect up to the fifth echo in a 50 nm aluminum film on sapphire substrate. A key challenge is the reduction of optical and electrical cross-talk between the excitation and the detection. Therefore the concepts of double-frequency modulation, cross-polarization, and balanced photodetection are implemented. Practical aspects like beam guiding, modulation techniques, beam focus minimization, and beam focus matching are discussed. Measurements for single- and multi-layer metallic films demanding higher sensitivity are presented.

High-resolution analysis of the complex wave spectrum in a cylindrical shell containing a viscoelastic medium. Part II. Experimental results versus theory

The complex frequency spectrum of axisymmetric wave modes in a circular cylindrical shell containing various viscoelastic media is measured. A new measurement technique has been developed for this purpose by combining a high-resolution laser interferometer with modern spectrum estimation methods. To decompose the complex wave-number dependence, a complex spectrum estimation method has been implemented. Up to 40 dispersion curves of traveling, axisymmetric modes are decomposed simultaneously in a frequency range between 1 kHz and 2 MHz. The guided structural waves are excited by piezoelectric transducers. Linear elasticity can be considered as an extreme case of viscoelasticity (long relaxation times compared with the deformation periods). To ascertain the validity of the theory, dispersion curves are calculated for a shell containing a viscoelastic material behaving like the elastic shell and are compared with the measured curves of an isotropic aluminium rod. The phenomenon of “backward wave propagation,...

A high density microchannel network with integrated valves and photodiodes

We have realised a microchannel network with integrated valves, which allows parallel processing of nanoparticles with very high throughput. With the latest prototype, we could show for the first time, that integrated photodiodes are capable of detecting particles moving through the channels. In previous work, we have shown that manipulation of particles is possible. The size of the particles the system is designed for ranges from a few hundred nm to a few microns, which allows using the system for applications demanding the manipulation of biological cells or bacteria. Compared to related work on microvalve arrays with valve densities of around 100 valves in/sup -2/, our systems feature densities of up to 2150 valves in/sup -2/. This was achieved with a 3 microns thick silicone valve membrane. This is a factor of 10 less than thicknesses achieved in related work on thermopneumatic actuation with silicone rubber membranes.