“Ultrasonic hands” grip microparticles

Ultrasonic waves can be used to grab several microparticles at a time, effectively creating a pair of invisible ultrasonic hands that can move tiny objects like cells under a microscope. Using tiny polystyrene spheres the size of biological cells – between 45 and 90-?m in diameter – researchers from the Universities of Bath, Bristol and Dundee found that objects could be moved along independent paths and carefully brought together. The research, published in Applied Physical Letters, could help biologists and medics perform a variety of delicate tasks, such as sorting or assembling cells into patterns for tissue engineering, stem cell work, and regenerative medicine. “We have shown that sophisticated microparticle manipulation is possible using a relatively simple desktop apparatus that can be used with a standard microscope system,” said Dr Charles Courtney, a Lecturer in Mechanical Engineering at the University of Bath. “We believe this has the potential to radically improve results in bioscience labs where pinpoint positioning of cells is a useful research tool.” The researchers used a specially developed circular array of 64 ultrasonic loudspeakers to generate a complicated pattern of ultrasonic waves needed to create three separate particle traps, in which particles are confined by a sound field, and move those traps independently of each other. “When an object scatters an acoustic wave there is a resulting force on the object called the acoustic radiation force. In standing waves the forces act to move small objects to regions of low pressure amplitude (pressure nodes) and away from regions of high pressure amplitude,” Courtney told Laboratory News. “We exploit this by using an ultrasonic array to produce standing waves with nodes at points surrounded by regions of high pressure (the particular pressure distributions we use are called Bessel functions). The high-pressure forces the objects to the nodes and grips them there. We can then move the nodes to shift the particles to the locations we want.” “It is currently a big challenge to move tiny things like cells around under a microscope,” said Professor Bruce Drinkwater from the University of Bristol. “Our ultrasonic hands can grip and move microscopic cells without damaging them. There are a huge number of applications for this technology.” Independent trapping and manipulation of microparticles using dexterous acoustic tweezers