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Contact-free manipulation of multiple microbubbles by means of holographic optical tweezers
Ultrasound contrast agent microbubbles have been recently promoted as potential drug carriers for ultrasound-guided targeted drug administration. A full understanding of their mechanical behaviour is therefore sought. Unfortunately, experiments with bubbles suffer from interference with walls because of buoyancy. In this regard, holographic optical tweezers enable for contact-free positioning of microbubbles in the three-dimensional space. In this project we aim to upgrade an optical tweezers setup to simultaneously trap multiple microbubbles.
The advent of microbubble ultrasound contrast agents (UCA) in medical ultrasound imaging has provided a way to improve the echogenicity (acoustic scattering) of blood and thus visualise and quantify tissue perfusion. UCA are typically 1-10 μm in diameter and comprised of a gas core coated in a thin shell. Beyond imaging and diagnosis, UCA micro-bubbles have shown great potential in facilitating precise, controlled delivery of therapeutic agents to clinical targets. The studies on coated micro-bubbles dynamics performed with videomicroscopy systems have suffered from interference with walls because of buoyancy. To overcome this, holographic optical tweezers can be employed to trap a single microbubble and control its position in the three-dimensional space. Optical tweezing typically involves the use of tightly focussed laser beams and therefore is usually constructed around microscope objective lenses. In addition, trapping micro-bubbles requires a specific topology of the optical trap (Laguerre-Gaussian) that can be crafted by subtly modifying the wavefront of the laser beam by means of a spatial light modulator (SLM). Nevertheless, to study the collective dynamics of microbubble clusters, multiple traps are required.
The advent of microbubble ultrasound contrast agents (UCA) in medical ultrasound imaging has provided a way to improve the echogenicity (acoustic scattering) of blood and thus visualise and quantify tissue perfusion. UCA are typically 1-10 μm in diameter and comprised of a gas core coated in a thin shell. Beyond imaging and diagnosis, UCA micro-bubbles have shown great potential in facilitating precise, controlled delivery of therapeutic agents to clinical targets. The studies on coated micro-bubbles dynamics performed with videomicroscopy systems have suffered from interference with walls because of buoyancy. To overcome this, holographic optical tweezers can be employed to trap a single microbubble and control its position in the three-dimensional space. Optical tweezing typically involves the use of tightly focussed laser beams and therefore is usually constructed around microscope objective lenses. In addition, trapping micro-bubbles requires a specific topology of the optical trap (Laguerre-Gaussian) that can be crafted by subtly modifying the wavefront of the laser beam by means of a spatial light modulator (SLM). Nevertheless, to study the collective dynamics of microbubble clusters, multiple traps are required.
The goal of this project is to upgrade an already existing single-trap holographic optical tweezers system to generate simultaneous multiple traps from a single laser beam. Our strategy is to take full advantage of the SLM capabilities by superimposing the phase pattern encoding for an array of multiple optical traps to the pattern encoding for a Laguerre-Gaussian beam. The phase pattern for multiple traps can be calculated with phase retrieval using iterative algorithm (PRIA method) or directly derived from the propagation and superposition of spherical wavefronts. The two approaches will be compared testing their trapping performance with a microbubble cluster.
The goal of this project is to upgrade an already existing single-trap holographic optical tweezers system to generate simultaneous multiple traps from a single laser beam. Our strategy is to take full advantage of the SLM capabilities by superimposing the phase pattern encoding for an array of multiple optical traps to the pattern encoding for a Laguerre-Gaussian beam. The phase pattern for multiple traps can be calculated with phase retrieval using iterative algorithm (PRIA method) or directly derived from the propagation and superposition of spherical wavefronts. The two approaches will be compared testing their trapping performance with a microbubble cluster.
For additional information, the candidates can contact Marco Cattaneo via email (mcattaneo at ethz.ch)
For additional information, the candidates can contact Marco Cattaneo via email (mcattaneo at ethz.ch)