Acoustic tweezers manipulate cells with sound waves

An illustration of the surface acoustic wave generators, with the generated 3-D trapping nodes. The inset indicates a single particle within a 3-D trapping node, which can be manipulated independently along x, y, or z axes.

Technique could enable 3-D printing of cellular structures for tissue engineering.

Engineers at MIT, Penn State University, and Carnegie Mellon University have devised a way to manipulate cells in three dimensions using sound waves. These “acoustic tweezers” could make possible 3-D printing of cell structures for tissue engineering and other applications, the researchers say.

Designing tissue implants that can be used to treat human disease requires precisely recreating the natural tissue architecture, but so far it has proven difficult to develop a single method that can achieve that while keeping cells viable and functional.

“The results presented in this paper provide a unique pathway to manipulate biological cells accurately and in three dimensions, without the need for any invasive contact, tagging, or biochemical labeling,” says Subra Suresh, president of Carnegie Mellon and former dean of engineering at MIT. “This approach could lead to new possibilities for research and applications in such areas as regenerative medicine, neuroscience, tissue engineering, biomanufacturing, and cancer metastasis.”

Suresh, Ming Dao, a principal research scientist in MIT’s Department of Materials Science and Engineering, and Tony Jun Huang, a professor of engineering science and mechanics at Penn State, are senior authors of a paper describing the device, published the week of Jan. 25. in the Proceedings of the National Academy of Sciences.

The paper’s lead author is Penn State graduate student Feng Guo. The team also includes Penn State researchers Zhangming Mao, Yuchao Chen, James Lata, Peng Li, Liqiang Ren, Jiayang Liu, Zhiwei Xie, and Jian Yang.

3-D control

The new acoustic tweezers are based on a microfluidic device that the researchers previously developed to manipulate cells in two dimensions. This device produces two acoustic standing waves, which are waves with a constant height. Where the two waves meet, they create a “pressure node” that can trap single cells. By altering the wavelength and another wave property known as the phase, the researchers can move the node and the cell trapped within it.

The research team previously used a similar approach to separate cancer cells from healthy cells, which could be useful for detecting rare tumor cells in a patient’s bloodstream and predicting whether the tumor will spread.

In the new study, the researchers added a third dimension of control: Once the cells are trapped in a horizontal plane, they can be moved up and down by altering the acoustic waves’ power, that is, the rate at which sound energy is emitted. Boosting the power allows the researchers to lift the cells from the surface in a type of “acoustic levitation,” then place them in a specific location, Dao says.

The researchers also developed equations that allow them to accurately predict how changes in the wavelength, phase, and acoustic power will affect cells’ positions.

“We now have a good idea of what to expect and how to control the 3-D positioning of the acoustic waves and the pressure nodes, enabling validation of the method as well as system optimization,” Dao says.

“Innovative approach”

In this study, the researchers demonstrated their device on polystyrene particles as well as mouse fibroblast cells. They were able to move the cells, one at a time, into specific positions on a surface and create patterns. They could also stack cells on top of each other.

“This is an exceptionally innovative approach of manipulating particles and single cells in 3-D in fluids,” says Taher Saif, a professor of mechanical science and engineering at the University of Illinois at Urbana-Champaign, who was not part of the research team. “Since acoustic energy is used for this manipulation, the approach is noninvasive and the cells maintain their viability. Overall, the method presented will be of significant interest for a broad community, from biologists to bioengineers.”

The researchers have filed for a patent on the technology and plan to continue developing it for tissue engineering and other applications.

ORIGINAL: MIT News

Anne Trafton | MIT News Office 

January 25, 2016

The first photo of light as both particle and wave

Since the days of Einstein, scientists have been trying to directly observe how light behaves both as a particle and a wave at the same time. Now, the first-ever snapshot of this dual nature has been captured, potentially opening up a new route towards quantum computing.

Scientists at École Polytechnique Fédérale de Lausanne (EPFL) have designed an experiment that makes use of the way electrons interact with light to take a photograph of its dual nature. (Image: © Fabrizio Carbone/EPFL.)

When UV light hits a metal surface, it causes an emission of electrons. Albert Einstein explained this ‘photoelectric’ effect by proposing that light – thought to only be a wave – is also a stream of particles.

But no experiment has ever been able to capture both of these ‘split personalities’ of light at the same time. The closest researchers of quantum mechanics have come is seeing either wave or particle, but always at different times.

Now, researchers at École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and Trinity College and the Lawrence Livermore National Laboratory in the US have done an experiment with a clever twist: using electrons to image light. The team is the first to capture a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle. The breakthrough work, spearheaded by Fabrizio Carbone at EPFL, was published today in the journal Nature Communications.

A new take on a classic effect 
The experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves travelling in opposite directions meet each other, they form a new wave that looks like it’s standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.

The imaging was done at EPFL’s ultrafast energy-filtered transmission electron microscope – one of only two in the world. (Photo: EPFL.)

This is where the experiment’s trick comes in: The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using an ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualise the standing wave, which acts as a fingerprint of the wave-nature of light.

While this phenomenon shows the wave-like nature of light, it also simultaneously demonstrates its particle aspect. As the electrons pass close to the standing wave of light, they ‘hit’ the light’s particles – the photons – thereby either accelerating or slowing down their speed. This change in speed appears as an exchange of energy ‘packets’ (quanta) between electrons and photons. The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle.

New route towards quantum computing?

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. As Carbone explains: “Being able to image and control quantum phenomena at the nanometre scale like this opens up a new route towards quantum computing.”

Adapted from article by Nik Papageorgiou, EPFL Mediacom  

ORIGINAL: Technologist.eu
Technologist Online
Mar 2, 2015