Optical Coherence Tomography (OCT) is a valuable tool for label-free imaging with micrometer resolution. However, conventional approaches to OCT typically image a sample from a single direction or angle, which limits its ability to image structures placed behind strongly attenuating material or deep inside the object. Here we introduce a solution to this problem by adding a small chamber to a spectral-domain OCT setup. Acoustic actuation enables a contact-free levitation and stepwise reorientation of samples such as zebra-fish larvae and tumor spheroids in a controlled and reproducible manner. We further developed a model-based compressive algorithm, which is able to exploit the diverse multi-angle OCT volumes for a 3D-reconstruction with isotropic resolution and estimation of refractive index values. We demonstrate and validate our approach on zebrafish larvae. We believe that our approach represents a powerful enabling tool for developmental biology and for organoid and cancer spheroid research.
Combining optical tweezers with acoustic trapping in one platform allows us to trap and manipulate sub-millimeter sized biological samples in suspension in a contact-less and flexible manner. The acoustic radiation forces levitate and trap the sample and steerable holographic optical tweezers give us an additional means of manipulation. We have implemented 3D acoustic trapping on a microfluidic chip, with three independent MHz transducers in three orthogonal directions; two side-transducers and one transparent top-transducer facilitating optical access for optical trapping and imaging. We can reorient the samples, or induce sustained rotations to gain access to multiple viewing angles of the object.
As cells and tissues are highly dependent on their specific microenvironment, in-vitro models need to incorporate this 3D structure to yield reliable results in biomedical research. Cancer cell spheroids and organoids have become valuable tools in oncology and development studies as they are more representative of in-vivo tissues than the traditional 2D cell culture models and have the potential to improve throughput in drug-screening compared to animal-models and also to go towards personalized medicine. Platforms for both assembly and non-invasive long-term monitoring of such models and also for layered bio-engineered tissues are of great interest. We have developed a sono-optical microfluidic device with 3D acoustic trapping and optical tweezers for non-contact manipulation and imaging of biological samples in liquid suspension. 3D acoustic trapping is achieved with two orthogonal side-transducers and an optically transparent top-transducer that enables optical access for imaging and tweezers to the sample volume. We have demonstrated trapping of biological samples and cancer cell spheroids of several 100µm in size. With acoustics alone or combined with optical tweezers, we can trap samples, change their location and orientation or induce sustained rotation of them, without the sample being in contact with confining structures or embedded in gels. With 3D independent control of the transducers we can adjust the relative strength of the acoustic radiation and viscous torques which will determine whether transient reorientation or continuous rotation of a given sample takes place, and along with numerical simulations and experimental insight we can optimize our strategy to achieve a desired manipulation, within limitations depending on sample size and shape asymmetry. Our technique offers access to optical tomographic information, by rotation of samples around one chosen axis or two axes, and mechanical probing or it can be used for 3D patterning of cells and cell structures in gel precursors for tissue-engineering.
We combine acoustic and optical trapping in a versatile, low-cost micro-fluidic chip for contact-free manipulation and imaging of sub-millimeter sized live biological samples in liquids. Our fully reconfigurable hybrid ‘sono-optical’ device opens up for 3D patterning where ultrasound in three orthogonal directions provide confinement and alignment of the sample suspended in the resonator, and tunable holographic optical tweezers enable us to modify and refine the acoustic trapping landscape on a finer spatial scale. We can induce sustained rotations of samples, as spheroids, embryos etc., providing access to the image data required for volumetric reconstruction of the sample by diffuse optical tomography. Our approach paves the way for long-term biological studies of micro-organism, developing embryos or larvae, or of cancer spheroids and organoids, in terms of local or global mechanical probing or in terms of non-invasive 3D visual inspection.
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