Periodic Reporting for period 3 - HOLOMAN (Holographic acoustic assembly and manipulation)
Berichtszeitraum: 2022-02-01 bis 2023-07-31
Acoustic waves in the form of ultrasound are used for sensing and detection, for instance as distance sensors in a car or for medical imaging. However, ultrasound can also exert forces and interact with materials. Examples include ultrasonic cleaning baths, ultrasonic welding setups, as well as devices to destroy kidney stones and ablate biological tissue. The latter are important applications in medicine. Ultrasound can also exert small forces to move particulate matter and even living cells. The aforementioned applications would all benefit from technologies that can precisely shape an ultrasonic wave. For instance, it would be a major advance, if it were possible to project ultrasound to form well-controlled pressure zones in a defined volume. In medical ultrasound it would, for instance, be beneficial if one could match the focal volume of the ultrasound to the precise shape of a tumor. This has thus far not been possible with high resolution. This ERC project HOLOMAN is developing technologies, computational models and applications that are based on our invention of the acoustic hologram, which permits sophisticated sound patterns to be formed. The hologram is used to control the phase and amplitude across an ultrasound beam with a specially designed mask, such that pressure images can be formed in space. Our goal is to develop the tools to compute the holograms that will yield pressure distributions (images) in 2D and 3D. These pressure distributions can exert forces on microparticles and/or cells, and a major goal of the ERC project is to realize the contactless, parallel assembly of an object from particulate matter “in one shot”. Another goal is to develop technologies that allow the dynamic projection of ultrasound patterns and images, i.e. a projector for ultrasound (pressure) movies. We will use our tools to investigate the interaction of ultrasound microrobotic systems and biological matter.
Within the ERC project HOLOMAN we have already achieved a number of our goals. In particular, we have shown that we can assemble living cells into shapes defined by the hologram. The acoustic images generated by the hologram are ‘line drawings’ in solution, where the lines represent regions of high (or low) pressure. Cells in suspension experience forces because of the pressure gradients and will move to assemble along the patterns defined by the pressure image. We could show that the assembly works extremely well in a biocompatible hydrogel and is more efficient than originally expected. We have examined the forces that act on the cells. After the assembly the cells continue to grow, which opens the possibility to realize complex cell assembly by exposing a cell suspension to ultrasound. Another major advance is a technology that permits us to update the hologram through which the ultrasound wave propagates. Thus far, we have mainly used static holograms. The new technology developed, as part of this ERC project, utilizes a CMOS chip with 10,000 electrodes to generate microbubble patterns. The bubbles can locally block ultrasound, which results in an amplitude hologram. This spatial ultrasound modulator can thus be used to project dynamic ultrasound patterns. Both advances open the possibility to study the interaction of ultrasound with matter and to explore exciting applications.
We expect that we can realize the first 3D pressure distributions with our hologram technology. We plan to assembly an object in 3D “in one shot” using these ultrasound pressure patterns. We also expect that we can develop more efficient computational tools to calculate the form of the holograms that are needed to obtain arbitrary (designed) pressure patterns. Another expected result is that we can achieve the dynamic projection of complex ultrasound patterns and images.