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Using Sound Waves as Tweezers to Move Single Cells

A new acoustic tweezer can pick up, move, and place individual cells in predetermined three dimensional patterns using nothing but sound. This new technology is more accurate and precise than previously available methods and allows cells to be captured and arranged into complex arrays without labels or contact.

The ability to precisely manipulate single cells is important for applications that range from regenerative medicine to biophysics. Using approaches such as magnetic tweezers or geometric constraints scientists have built complex cell patterns and even tissues but these techniques have many limitations. Scientists at MIT, Pennsylvania State University, and Carnegie Mellon now show that sound waves can be used to manipulate cells with much higher accuracy and minimal perturbation. Their 3-D acoustic tweezers use two surface acoustic waves that travel through a microfluidic device. Where these waves meet they create “pressure nodes” that can trap cells or other small objects. The research team had previously demonstrated that by changing wavelength and phase of the waves these nodes and the cells trapped in them could be moved in two dimensions. Guo et al. now show that by altering the power of the sound waves cells can be lifted from the surface. Using their current setup cells can be deposited with an accuracy of 1 µm in the x-y plane and 2 µm in the z-direction, but the authors explain that the placement accuracy is only limited by the optical resolution of the instrument.

These findings show great promise for 3-D bioprinting, where in addition to placement accuracy, maintaining cell integrity is of utmost importance. Unlike other available methods, acoustic tweezers are minimally invasive allowing cells to remain in their native state (e.g. shape, size, polarity, reflective index) and in their original culture medium exposed only to gentle acoustic vibrations. The authors envision applications that range from engineering artificial neural networks to pairing acoustic tweezers with microscopes for a range of imaging and analysis applications.

Source: MIT, Pennsylvania State University, and Carnegie Mellon

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