....USWNet....

Mechanical gripping of particles aided by acoustic manipulation (from ETH Zürich): Particles (74 um) randomly distributed in a 1mm wide, 200 um deep micromachined channel are prepositioned along its centerline by the use of acoustic forces, before being removed from it for further handling by means of a microgripper, once the acoustic field has been removed. For better positioning, after a rough alignment at the center at 780 kHz the frequency has been switched to 2.14 MHz to tighten the line. After turning the acoustic field on again, particles are repositioned for the next removal process. (1 MB)From A Neild et al 2006, Journal of Micromechanical Microengineering 16, 1562-1570, doi:10.1088/0960-1317/16/8/017  _______________________________________________________________________________

Continuous flow cell filter: This operates when ultrasound brings cells to the centre of a channel. Once cells have been brought to the centre of the channel clear fluid is stripped away downstream (above) from the field. The filter has been used with cells down to 1μm diameter (bacterial scale). Concentrations from single cells up to 30 % volume have been used.Suitable for the automation of analytical scale filtration without the need for robotization. (1,7 MB) _______________________________________________________________________________

Multi-wavelength system: In this case a 50 mm high tube containing a 5 ml cell suspension, demonstrates how cells form a series of bands at the nodal positions (0.75 mm separation in this 1 MHz field). Initially the bands are discs across the whole circumference of the tube, secondary acoustic forces then concentrate these discs radially. The resulting clumps then sediment much more rapidly than the individual cells.A continuous flow version of this is available called The BioSep, Applikon, for use at high cell concentrations. (493kB) _______________________________________________________________________________

Fixing cells within gel: The cell arrangements created in ultrasound standing waves can be set into more permanent structures in a gel. The gel is formed either by cooling in the field or as in the case shown here a calcium chloride solution is used to set a cell laden alginate stream as it flows out of the sound field. In the flowing system laminar flow maintains the integrity of the cell arrangement. This method will be developed for creating structured tissue-engineering preparations. (850 kB) _______________________________________________________________________________

2D aggregates of cells (from Cardiff University): The Figure shows a 2-D aggregate of neural cells formed in a standing wave and levitated at the node plane. A recently developed ultrasound trap maintains cells in suspension away from any inorganic substratum and allows observation of cell-cell adhesion in a 2-dimensional aggregate developing in suspension.The technique has the following properties, which may aid expression of some aspects of the complex biological reactions occurring in vivo more effectively than do studies on solid substrata:
Sets of cells are brought together away from any solid substratum, therefore no solid surface- specific or elasticity effects are present.The technique is physically non-intrusive on the scale of biomolecular surface receptors, provides real-time microscopic observation of 2-D aggregate development, and the aggregate properties can be studied in situ. (5,7 MB)
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Particle alignment (from CSIC, Spain): Particles are moved to a near quarter-wavelength node (a single node positioned near the right sidewall of the fluid channel). The particle trajectories deviate rapidly towards the node and continue their flow aligned along it and forming a chain perpendicular to the acoustic axis. This favours possible particle interactions (mutual radiation pressure or acoustic wake effect) that could give rise to agglomeration effects. (1,17 MB)  _______________________________________________________________________________

Sorting of polystyrene beads based on size (4,6 and 20um diameters) in deionized water: The video shows the operation of an acoustically induced sorting process in the plastic micro-resonator. (151 kB)