Submerged Robotic Micromanipulation and Dielectrophoretic Micro-objet release.

International audienceThe development of new hybrid microsystems needs new technologies which are able to perform assembly of small micro-objects. Now, the current micromanipulation technologies are still unreliable for micro-objects which typical size is down to hundred micrometers. Consequently, the study and the development of innovative artificial microobject manipulation strategies in these dimensions is particularly relevant. As presented in the literature, micromanipulations are perturbed by the adhesion and surface forces which depend on surrounding mediums. We propose to perform micro-assembly tasks in liquid medium, because adhesion and surface forces applied on submerged micro-objects are less important than in air. The comparative analysis of micro-forces in air and in liquid is presented in this paper. Although the micro-forces reduce in liquid, they stay disturbed the micro-objects release. Thus, we propose to extend the dielectrophoresis micromanipulation principles which are currently done in the biological micromanipulation to submerged artificial objects micro-assembly. The negative dielectrophoresis principle is used to release a micro-object grasped with a micro-gripper. Physical principle and first experimentations is presented in this article. Further works will focus on the optimization of the principle, and on the micro-object release modelling and control

Analysis of forces for micromanipulations in dry and liquid media.

International audienceDuring microscale object manipulation, contact (pull-off) forces and non-contact (capillary, van der Waals and electrostatic) forces determine the behaviour of the micro-objects rather than the inertial forces. The aim of this article is to give an experimental analysis of the physical phenomena at a microscopic scale in dry and liquid media. This article introduces a review of the major differences between dry and submerged micromanipulations. The theoretical influences of the medium on van der Waals forces, electrostatic forces, pull-off forces and hydrodynamic forces are presented. Experimental force measurements based on an AFM system are carried out. These experiments exhibit a correlation better than 40 % between the theoretical forces and the measured forces (except for pull-off in water). Finally, some comparative experimental micromanipulation results are described and show the advantages of the liquid medium

Dynamic modelling of a submerged freeze microgripper using a thermal network.

International audienceManipulating micro-objects whose typical size is under 100 µm becomes an interesting research topic for micro-assembly applications. A comparative analysis of dry and liquid media impacts on surface forces, contact forces and hydrodynamic forces showed that performing manipulation and assembly in liquid surroundings can indeed be more efficient than in dry conditions. We propose a thermal based micromanipulator designed to operate completely submerged in an aqueous medium. The handling principle and the advantages of our proposed submerged freeze microgripper against air working cryogenic grippers are first described. Then, the thermal principle based on Peltier effect, the characteristics of the prototype, and its first micromanipulation tests are reported. In order to manage the heat exchanges in the microgripper, a dynamic thermal model using electrical analogy has been developed for a 3D heat sink of the microgripper. Its validation is presented in the last section.Further works will be focused on the characterization of all parameters and its experimental validation

Micro-factory for submerged assembly : Interests and Architectures.

International audienceThe development of new hybrid microsystems needs new technologies which are able to perform assembly of small micro-objects. Now, the current micromanipulation technologies are still unreliable for micro-objects which typical size is down to hundred micrometers. Consequently, the study and the development of innovative artificial micro-object manipulation strategies in these dimensions are particularly relevant. As presented in the literature, micromanipulations are perturbed by the adhesion and surface forces which depend on surrounding mediums. We propose to perform micro-assembly tasks in liquid medium, because adhesion and surface forces applied on submerged microobjects are less important than in air. An overview of the microforces in air and in liquid is presented in this paper. This paper focuses on the architecture of a submerged assembly cell including the definition of stocks, conveyance systems and workstations. Defining the architecture of the submerged assembly cell is indeed a keypoint of the cell design. The stocks and workstations could be for example place in a large unique liquid medium or in a collection of droplets. Transfers of micro-objects in the submerged assembly cell may be obtained by: (i) moving the micro-objects in an unique liquid medium; (ii) moving the micro-objects through the air from one to another liquid medium; (iii) transfert of micro-objects by movement of the liquid bowl. The analysis of the combination of different transfer types allows the construction of the typical architectures of assembly cell for submerged medium

Single-file escape of colloidal particles from microfluidic channels

Single-file diffusion is a ubiquitous physical process exploited by living and synthetic systems to exchange molecules with their environment. It is paramount quantifying the escape time needed for single files of particles to exit from constraining synthetic channels and biological pores. This quantity depends on complex cooperative effects, whose predominance can only be established through a strict comparison between theory and experiments. By using colloidal particles, optical manipulation, microfluidics, digital microscopy and theoretical analysis we uncover the self-similar character of the escape process and provide closed-formula evaluations of the escape time. We find that the escape time scales inversely with the diffusion coefficient of the last particle to leave the channel. Importantly, we find that at the investigated {\bf microscale}, bias forces as tiny as $10^{-15}\;{\rm N}$ determine the magnitude of the escape time by drastically reducing interparticle collisions. Our findings provide crucial guidelines to optimize the design of micro- and nano-devices for a variety of applications including drug delivery, particle filtering and transport in geometrical constrictions.Comment: 6 pages, 3 figure

Rotating magnetic field actuation of a multicilia configuration

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.The current paper continues the analysis of a completely novel method of fluid manipulation technology in micro-fluidics systems, inspired by nature, namely by the mechanisms found in ciliates. More information on this subject can be found at http://www.hitech-projects.com/euprojects/artic/. In order to simulate the drag forces acting on an array of artificial cilia, we have developed a computer code that is based on fundamental solutions of Stokes flow in a semi-infinite domain. The actuation mechanism consists of a bi-directional rotating excitation magnetic field. The magnetization induced by the magnetic field was calculated in a separate routine based on the Integral Nonlinear Equations Approach with 1D discretization of wire (cilium). Time averaged x-coordinate mass flow rates are computed for several cilium configurations resulting. The outcome and originality of this paper consist on assessing magnetic actuation as a practical tool for obtaining a consistent one-directional fluid flow.This work has been supported through grant ARTIC FP6-2004-NMP-TI4

振動を用いた凝着力緩和とその微細操作への応用

金沢大学理工研究域機械工学系This paper addresses to develop a novel strategy to relax the adhesion forces for picking and placing operation in a micro range. In a micro range, the attracting forces such as the van der Waals, capillary, and electrostatic forces become dominating due to a scaling effect. The attractive forces cause the adhesion between the object and the endeffector. Therefore, it is hard to manipulate an object in a micro range. This paper shows that when an oscillating endeffector approaches to an object, the adhesion between the object and the oscillating endeffector can be reduced. Also, based on the experimental analysis, we clarify the relation between the oscillation and the pushing amount of the endeffector on the object, where the adhesion force can be released effectively. Using this relaxation method and the relation, we develop a strategy for picking and placing operation in a micro range. This strategy provides an accurate manipulation. Some experimental results show the effectiveness of this approach

Akonni Biosystems: Wicking in Microchannels on Biochips

Microfluidics is the science of designing and manufacturing devices and processes for manipulation of extremely small volumes of fluid, typically micro to nanoliters.The most mature application of microfluidics technology is ink-jet printing, which uses orifices less than 100 μm in diameter to generate drops of ink. The complex devices now being developed for biological applications involving the analysis of DNA (in genetics and genomics) and proteins (in proteomics) and bio-defense typically involve aqueous solutions and channels 30 to 300 μm in diameter. Unlike microelectronics, in which the current emphasis is on reducing the size of transistors, microfluidics is focusing on making more complex systems of channels with more sophisticated fluid-handling capabilities, rather than reducing the size of the channels. Although micro- and macro-fluidic systems require similar components including pumps, valves, mixers, filters, and separators, the small size of microchannels causes their flow to behave differently. At micron scales, fluid motions are primarily dominated by surface tension and viscous forces. In the problem under consideration, the issue is one of wicking or leaking of the sample from the reaction reservoir to the waste region at elevated temperatures. A mechanism responsible for this phenomenon was thought to be the "wedge effect," which refers to the tendency of liquids to move along a sharp corner by capillary effects if the conditions are right. The analysis performed during the workshop also mainly focused on this effect. While a definitive solution to this challenging problem posed in the workshop was not identified, it was felt that using a manufacturing process that can affect the corner angles in the channels may hold the most promise, allowing the wicking mechanism to be controlled without surface treatments that insert hydrophobic stops in the channel. For instance by "rounding" the side walls to increase the corner angles from 90 toward 180 degrees, the leaking of the sample away from the reaction chamber might be delayed