Active Nematodynamics on Curved Surfaces–The Influence of Geometric Forces on Motion Patterns of Topological Defects

We derive and numerically solve a surface active nematodynamics model.We validate the numerical approach on a sphere and analyse the influence of hydro-dynamics on the oscillatory motion of topological defects.For ellipsoidal surfaces the influence of geometric forces on these motion patterns is addressed by taking into ac-count the effects of intrinsic as well as extrinsic curvature contributions.The numerical experiments demonstrate the stronger coupling with geometric properties if extrinsic curvature contributions are present and provide a possibility to tuneflow and defect motion by surface properties.

Compressive holographic sensing simplifies quantitative phase imaging

Quantitative phase imaging (QPI) has emerged as method for investigating biological specimen and technical objects. However, conventional methods often suffer from shortcomings in image quality, such as the twin image artifact. A novel computational framework for QPI is presented with high quality inline holographic imaging from a single intensity image. This paradigm shift is promising for advanced QPI of cells and tissues.

Quantitative phase imaging through an ultra-thin lensless fiber endoscope

Quantitative phase imaging(QPI)is a label-free technique providing both morphology and quantitative biophysical information in biomedicine.However,applying such a powerful technique to in vivo pathological diagnosis remains challenging.Multi-core fiber bundles(MCFs)enable ultra-thin probes for in vivo imaging,but current MCF imaging techniques are limited to amplitude imaging modalities.We demonstrate a computational lensless microendoscope that uses an ultra-thin bare MCF to perform quantitative phase imaging with microscale lateral resolution and nanoscale axial sensitivity of the optical path length.The incident complex light field at the measurement side is precisely reconstructed from the far-field speckle pattern at the detection side,enabling digital refocusing in a multi-layer sample without any mechanical movement.The accuracy of the quantitative phase reconstruction is validated by imaging the phase target and hydrogel beads through the MCF.With the proposed imaging modality,three-dimensional imaging of human cancer cells is achieved through the ultra-thin fiber endoscope,promising widespread clinical applications.

Highly sensitive force measurements in an optically generated, harmonic hydrodynamic trap

The use of optical tweezers to measure forces acting upon microscopic particles has revolutionised fields from material science to cell biology.However,despite optical control capabilities,this technology is highly constrained by the material properties of the probe,and its use may be limited due to concerns about the effect on biological processes.Here we present a novel,optically controlled trapping method based on light-induced hydrodynamic flows.Specifically,we leverage optical control capabilities to convert a translationally invariant topological defect of a flow field into an attractor for colloids in an effectively one-dimensional harmonic,yet freely rotatable system.Circumventing the need to stabilise particle dynamics along an unstable axis,this novel trap closely resembles the isotropic dynamics of optical tweezers.Using magnetic beads,we explicitly show the existence of a linear force-extension relationship that can be used to detect femtoNewton-range forces with sensitivity close to the thermal limit.Our force measurements remove the need for laser-particle contact,while also lifting material constraints,which renders them a particu-larly interesting tool for the life sciences and engineering.