Birefringence Imaging Research Articles

Unexpected Fracture Behavior of Ultrasoft Associative Hydrogels Due to Strain-Induced Crystallization.

Strain-induced crystallization (SIC) is a well-known toughening strategy in elastomers, but is rarely observed in hydrogels due to their high-water content and limited deformability. Here we report a phenomenon of SIC in highly swollen and associative hydrogels by introducing an extremely large deformation by indentation with a needle. Using in situ birefringence imaging, we discovered that SIC occurs close to the needle tip upon large strain, displacing the nucleation of a crack from the needle tip to a position further away from the tip. The morphology of the fracture as well as the force to induce the gel fracture with the needle can be controlled by playing with temperature and cross-linking and hence triggering or not the SIC. Our discovery points to a future direction in creating SIC in highly swollen hydrogels, with potential implications for many biological material designs, and surgical injury prediction or prevention in associative tissues.

Non-destructive identification of edge-component burgers vector of threading dislocations in SiC wafers by birefringence imaging

Non-destructive characterization of crystalline defects in SiC wafers is important for manufacturing high-performance SiC power devices with high productivity. The present study shows that the edge component of the Burgers vector can be identified by birefringence imaging under conditions deviating slightly from the crossed-Nicols condition and by calculation of the in-plane shear stress distribution. It is also found that the combination of birefringence observation and X-ray topography allows the discrimination of the family of threading screw dislocations. The present results will further the understanding of the relationship between defect structure and the properties of SiC power devices.

Smartphone-based hand-held polarized light microscope for on-site pharmaceutical crystallinity characterization.

Polarized light microscopy (PLM) is a common but critical method for pharmaceutical crystallinity characterization, which has been widely introduced for research purposes or drug testing and is recommended by many pharmacopeias around the world. To date, crystallinity characterization of pharmaceutical solids is restricted to laboratories due to the relatively bulky design of the conventional PLM system, while little attention has been paid to on-site, portable, and low-cost applications. Herein, we developed a smartphone-based polarized microscope with an ultra-miniaturization design ("hand-held" scale) for these purposes. The compact system consists of an optical lens, two polarizers, and a tailor-made platform to hold the smartphone. Analytical performance parameters including resolution, imaging quality of interference color, and imaging reproducibility were measured. In a first approach, we illustrated the suitability of the device for pharmaceutical crystallinity characterization and obtained high-quality birefringence images comparable to a conventional PLM system, and we also showed the great promise of the device for on-site characterization with high flexibility. In a second approach, we employed the device as a proof of concept for a wider application ranging from liquid crystal to environmental pollutants or tissues from plants. As such, this smartphone-based hand-held polarized light microscope shows great potential in helping pharmacists both for research purposes and on-site drug testing, not to mention its broad application prospects in many other fields.

Direct laser writing in YAG single crystal: Evolution from amorphization to nanograting formation and phase transformation

Femtosecond laser writing is a versatile and effective technique for high-precision 3D micromachining of crystals for applications in photonics. Here, we demonstrate the femtosecond laser-assisted control over the structure and phase composition in yttrium aluminum garnet (YAG) single crystal. Increasing the energy of the laser pulse enables achieving extremely high temperature and pressure in the laser beam waist region, which leads to pronounced plastic deformation of the crystal structure and even to its complete amorphization inside forming nanogratings or a phase transition from the garnet phase to the perovskite phase. The main types of laser-induced modifications in YAG single crystal are described using quantitative phase microscopy, quantitative birefringence imaging and transmission high-resolution electron microscopy. For the first time, the mechanism of plastic deformation responsible for the formation of dislocations and amorphous phase is experimentally confirmed. The results obtained contribute to the deeper understanding of fundamentals of the direct laser writing in crystals which are essential for the optimization of selective etching processes and fabrication of photonic crystal waveguides.

Flow-induced alignment of protein nanofibril dispersions

HypothesisProtein nanofibrils (PNF) resulting from the self-assembly of proteins or peptides can present structural ordering triggered by numerous factors, including the shear flow. We hypothesize that i) depending on the contour length of the PNF and the magnitude of the shear rate applied to the PNF dispersion, they exhibit specific orientation, and ii) it is possible to predict the alignment of PNF by establishing a flow-alignment relationship. Understanding such a relationship is pivotal to improving the fundamental knowledge and application of fibril systems. ExperimentsWe use β-lactoglobulin PNF aqueous dispersions with different average contour lengths but equal persistence lengths. We employ simple shear-dominated microfluidic devices with state-of-the-art imaging techniques: flow-induced birefringence (FIB) and micro-particle image velocimetry (μ-PIV), to probe the effect of shear flow on PNF alignment. FindingsWe provide an empirical relationship connecting the birefringence Δn (quantifying the extent of PNF alignment), and the Péclet number Pe (correlating the shear rate of the flow relative to the rotational diffusion of PNF) to understand the flow-alignment behavior of PNF under shear-dominated flows. Furthermore, we assess the alignment and flow profile of PNF at both high and low flow rates. The length of PNF emerges as a controlling parameter capable of modulating PNF alignment at specific shear rates. Our results shed new insights into the hydrodynamic behavior of PNF, which is highly relevant to various industrial processes involving the fibril systems.

Observation of in-plane shear stress fields in off-axis SiC wafers by birefringence imaging.

For the nondestructive characterization of SiC wafers for power device application, birefringence imaging is one of the promising methods. In the present study, it is demonstrated that birefringence image contrast variation in off-axis SiC wafers corresponds to the in-plane shear stress under conditions slightly deviating from crossed Nicols according to both theoretical consideration and experimental observation. The current results indicate that the characterization of defects in SiC wafers is possible to achieve by birefringence imaging.

DXM-TransFuse U-net: Dual cross-modal transformer fusion U-net for automated nerve identification.

Accurate nerve identification is critical during surgical procedures to prevent damage to nerve tissues. Nerve injury can cause long-term adverse effects for patients, as well as financial overburden. Birefringence imaging is a noninvasive technique derived from polarized images that have successfully identified nerves that can assist during intraoperative surgery. Furthermore, birefringence images can be processed under 20ms with a GPGPU implementation, making it a viable image modality option for real-time processing. In this study, we first comprehensively investigate the usage of birefringence images combined with deep learning, which can automatically detect nerves with gains upwards of 14% over its color image-based (RGB) counterparts on the F2 score. Additionally, we develop a deep learning network framework using the U-Net architecture with a Transformer based fusion module at the bottleneck that leverages both birefringence and RGB modalities. The dual-modality framework achieves 76.12 on the F2 score, a gain of 19.6 % over single-modality networks using only RGB images. By leveraging and extracting the feature maps of each modality independently and using each modality's information for cross-modal interactions, we aim to provide a solution that would further increase the effectiveness of imaging systems for enabling noninvasive intraoperative nerve identification.

160-LB: Age-Related Adipose Tissue Fibrosis and Neuropathy in the Genetically Diverse HET3 Mouse

Changes in adipose tissue's extracellular matrix, as with fibrosis, inhibits the tissue's ability to shrink and expand as needed, resulting in sheer stress on adipocytes and chronic inflammation, as well as decreased insulin sensitivity. With aging, a state of metabolic dysregulation and increased incidence of insulin resistance, we have observed a reduction in adipose innervation. This ‘adipose neuropathy' likely poses a physiological challenge for tissue metabolic function and glucose homeostasis, as has been observed in adipose denervation studies. Using second-harmonic generation label-free imaging of adipose collagen and advanced image co-localization techniques, we found that obese adipose tissue exhibits higher co-localization of nerves with collagen fibers, indicating that changes in tissue fibrosis may tie mechanistically with tissue neuropathy. We compared C57BL/6J mice with the more genetically diverse HET3 mouse model that is used by the NIA's intervention testing program, to investigate age-related neuropathy and adipose fibrosis. We found that HET3 mice displayed mitigated neuropathy phenotypes in skin, muscle and adipose, compared to inbred C56BL/6J mice. Tissue fibrosis was significantly increased with age in subcutaneous and visceral white adipose depots of both strains of mice. Using birefringence imaging, we found that the relative distribution of type I / thick filament collagen increased with age while type III / thin filament collagen decreased. Gene expression by qPCR revealed significant increases in collagen genes Col1a1, Col3a1, and Col5a1 in adipose with age. Despite its success as a longevity treatment, the mTOR inhibitor rapamycin had little to no effect on reducing or preventing the onset of neuropathy in HET3 aged mice, and importantly it worsened the fibrotic phenotype with increased type 1 collagen in adipose. Together, we found that rapamycin's longevity effects are uncoupled from healthspan producing effects, with detrimental impacts on adipose fibrosis that may impact age-related insulin resistance. Disclosure J. Willows: None. G. Mishra: None. M. Blaszkiewicz: None. K. L. Townsend: Other Relationship; Neuright, Inc. Funding American Heart Association (AHA) Collaborative Sciences Award (18CSA34090028)

Using birefringent elements and imaging Michelsons for the calibration of high-precision planet-finding spectrographs

Context. One of the main methods used for finding extrasolar planets is the radial velocity technique, in which the Doppler shift of a star due to an orbiting planet is measured. These measurements are typically performed using cross-dispersed echelle spectrographs. Unfortunately, such spectrographs are large and expensive, and their accurate calibration continues to be challenging. Aims. The aim is to develop a different way to provide a calibration signal. Methods. A commonly used way to introduce a calibration signal is to insert an iodine cell in the beam. Disadvantages of this include that the lines are narrow, do not cover the entire spectrum, and light is absorbed. Here I show that inserting a birefringent element or an imaging Michelson, combined with Wollaston prisms, eliminates these three shortcomings while maintaining most of the benefits of the iodine approach. Results. The proposed designs can be made very compact, thereby providing a convenient way of calibrating a spectrograph. Similar to the iodine cell approach, the calibration signal travels with the stellar signal, thereby reducing the sensitivity to spectrograph stability. The imposed signal covers the entire visible range, and any temperature drifts will be consistent and describable by a single number. Based on experience with similar devices that were used in a different configuration by the Helioseismic and Magnetic Imager, it is shown that the calibration device can be made stable at the 0.1 m/s level over a significant wavelength range on short to medium timescales. Conclusions. While the design is promising, many details still need to be worked out. In particular, a number of laboratory measurements are required in order to finalize a design and estimate actual performance, and it would be desirable to make a proof of concept.

Non-Newtonian flows and instabilities in 3D glass microfluidic devices

<h2>Abstract</h2> In this virtual seminar we will discuss the use of selective laser-induced etching (SLE) for the fabrication of glass microfluidic devices, in particular for the study of non-Newtonian fluid dynamics problems [1]. SLE enables the precise monolithic fabrication of three-dimensional (3D) channels and structures embedded in a rigid and transparent fused-silica substrate, and thus provides opportunities for a wealth of novel microscale flow experiments. We will highlight various recent and ongoing microfluidic projects from our laboratory that have been made possible by SLE fabrication. Our focus will be on flows of viscoelastic wormlike micellar and polymer solutions in microscale geometries featuring, for instance, slender rigid or cantilevered posts [2,3]. 3D intersections [4,5], and axisymmetric contraction/expansions [6]. We make use of state-of-the-art quantitative techniques such as high-speed flow-induced birefringence imaging and volumetric 3-component micro-particle image velocimetry to characterize and understand purely-elastic and inertioelastic flow instabilities arising in these complex systems.

Optical Polarization-Based Measurement Methods for Characterization of Self-Assembled Peptides' and Amino Acids' Micro- and Nanostructures.

In recent years, self-assembled peptides’ and amino acids’ (SAPA) micro- and nanostructures have gained much research interest. Here, description of how SAPA architectures can be characterized using polarization-based optical measurement methods is provided. The measurement methods discussed include: polarized Raman spectroscopy, polarized imaging microscopy, birefringence imaging, and fluorescence polarization. An example of linear polarized waveguiding in an amino acid Histidine microstructure is discussed. The implementation of a polarization-based measurement method for monitoring peptide self-assembly processes and for deriving molecular orientation of peptides is also described.

Birefringent tissue-mimicking phantom for polarization-sensitive optical coherence tomography imaging.

.Significance: Tissue birefringence is an important parameter to consider when designing realistic, tissue-mimicking phantoms. Options for suitable birefringent materials that can be used to accurately represent tissue scattering are limited.Aim: To introduce a method of fabricating birefringent tissue phantoms with a commonly used material—polydimethylsiloxane (PDMS)—for imaging with polarization-sensitive optical coherence tomography (PS-OCT).Approach: Stretch-induced birefringence was characterized in PDMS phantoms made with varying curing ratios, and the resulting phantom birefringence values were compared with those of biological tissues.Results: We showed that, with induced birefringence levels up to , PDMS can be used to resemble the birefringence levels in weakly birefringent tissues. We demonstrated the use of PDMS in the development of phantoms to mimic the normal and diseased bladder wall layers, which can be differentiated by their birefringence levels.Conclusions: PDMS allows accurate control of tissue scattering and thickness, and it exhibits controllable birefringent properties. The use of PDMS as a birefringent phantom material can be extended to other birefringence imaging systems beyond PS-OCT and to mimic other organs.

Polarization Sensitive Digital Holographic Imaging in Biology

A new, simple digital holography-based polarization microscope for quantitative birefringence imaging of biological cells is presented. As a proof of concept, two different class of cells have been characterized by polarization sensitive digital holographic imaging (PSDHI). These two cases study reported are: differentiation of leukaemia cells and identification of reacted sperm cells. Although further experimentation is necessary, the suggested approach could represent a prospective label-free diagnostic tool for use in biological and medical research and diagnosis.

Birefringence Imaging-Based Investigation of Stress-Induced Phase Transitions in SrTiO3

The spatial distributions of ferroelectric and structural phase transitions in quantum paraelectric SrTiO3 under uniaxial stress were microscopically observed using birefringence imaging techniques.

Polarization sensitive optical coherence tomography with single input for imaging depth-resolved collagen organizations

Collagen organization plays an important role in maintaining structural integrity and determining tissue function. Polarization-sensitive optical coherence tomography (PSOCT) is a promising noninvasive three-dimensional imaging tool for mapping collagen organization in vivo. While PSOCT systems with multiple polarization inputs have demonstrated the ability to visualize depth-resolved collagen organization, systems, which use a single input polarization state have not yet demonstrated sufficient reconstruction quality. Herein we describe a PSOCT based polarization state transmission model that reveals the depth-dependent polarization state evolution of light backscattered within a birefringent sample. Based on this model, we propose a polarization state tracing method that relies on a discrete differential geometric analysis of the evolution of the polarization state in depth along the Poincare sphere for depth-resolved birefringent imaging using only one single input polarization state. We demonstrate the ability of this method to visualize depth-resolved myocardial architecture in both healthy and infarcted rodent hearts (ex vivo) and collagen structures responsible for skin tension lines at various anatomical locations on the face of a healthy human volunteer (in vivo).

Nanostructure and anisotropy of 3D printed lyotropic liquid crystals studied by scattering and birefringence imaging

Extrusion-based 3D printing of hexagonal and lamellar lyotropic liquid crystals is a powerful technique to produce hierarchical materials with well-defined anisotropic structure. Tailoring the properties of 3D printed objects requires a precise control of the nanostructure; however, a sufficiently high degree of anisotropy is often not achieved. In this study, scanning small angle X-ray scattering was performed in situ at the exit of the needle during 3D printing. We study the induced anisotropy and nanostructure in hexagonal and lamellar lyotropic liquid crystals. Mapping of extruded filaments during printing revealed that narrower nozzle diameters (370 µm) resulted in less anisotropic structures with a wider distribution of orientation angles across the cross section, while larger nozzle diameters (550 µm) resulted in more anisotropic structures with an overall higher degree of orientation. The apparent wall shear rate is higher for the narrower nozzle, which produces wall slip, resulting in a highly anisotropic shell, and a less aligned filament core. Further examination of the filaments revealed phase transitions due to solvent evaporation. The time scales were of 10–20 min of exposure to atmospheric conditions. Simultaneously, a loss in the macroscopic anisotropy of the hexagonal self-assembled structure was observed. These processes occur during and after extrusion-based 3D printing of liquid crystals and limit the fine control of the final structure. The variability of structures achieved for our different systems highlights the importance of structural characterization during and after extrusion to guarantee high anisotropy and well-defined structures.

Laser-induced dynamic alignment and nonlinear-like optical transmission in liquid suspensions of 2D atomically thin nanomaterials.

Nonlinear optical property of atomically thin materials suspended in liquid has attracted a lot of attention recently due to the rapid development of liquid exfoliation methods. Here we report laser-induced dynamic orientational alignment and nonlinear-like optical response of the suspensions as a result of their intrinsic anisotropic properties and thermal convection of solvents. Graphene and graphene oxide suspensions are used as examples, and the transition to ordered states from initial optically isotropic suspensions is revealed by birefringence imaging. Computational fluid dynamics is performed to simulate the velocity evolution of convection flow and understand alignment-induced birefringence patterns. The optical transmission of these suspensions exhibits nonlinear-like saturable or reverse saturable absorptions in Z-scan measurements with both nanosecond and continuous-wave lasers. Our findings not only demonstrate a non-contact controlling of macroscopic orientation and collective optical properties of nanomaterial suspensions by laser but also pave the way for further explorations of optical properties and novel device applications of low-dimensional nanomaterials.

Mueller matrix imaging with a polarization camera: application to microscopy.

In this work, we describe the design and implementation of a Mueller matrix imaging polarimeter that uses a polarization camera as a detector. This camera simultaneously measures the first three Stokes components, allowing for the top three rows of the Mueller matrix to be determined after only N = 4 measurements using a single rotating compensator, which is sufficient to fully characterize nondepolarizing samples. This setup provides the polarimetric analysis with micrometric resolution in about 3 seconds and can also perform live birefringence imaging at the camera frame rate by fixing the compensator at a static 45° angle. To further improve the conditioning of the setup, we also give the first experimental demonstration of an optimal elliptical retarder design.

Label-free assessment of myelin status using birefringence microscopy

BackgroundLabel-free methods for quantifying myelination can reduce expense, time, and variability in results when examining tissue white matter pathology. New methodWe sought to determine whether the optical birefringent properties of myelin could be exploited to determine myelination status of white matter in tissue sections. Sections of forebrains of mice (normal, and treated with cuprizone to cause demyelination) were examined by birefringence using a birefringence imaging system (Thorlabs LCC7201), and results compared with sections stained using Luxol Fast Blue. ResultsQuantitative birefringence analysis of myelin was not only reliable in detecting demyelination, but also showed abnormalities that preceded myelin loss in cuprizone-treated mice. Comparison with existing methodsSubtle myelin pathology visible with electron microscopy but not with conventional histopathological staining was readily detected with birefringence microscopy. ConclusionsBirefringence imaging provides a rapid, label-free method of analyzing the myelin content and nanostructural status in longitudinal white matter structures, being sensitive to subtle myelin changes that precede overt pathological damage.

Forensic medical differential diagnosis of brain infarctions and hemorrhasis of traumatic genesis by mueller-matrix microscopy

Abstract. The aim of the work is to develop forensic criteria for differential diagnosis of traumatic hemorrhages (HTG), ischemic stroke (IS), and hemorrhages of nontraumatic genesis (HNG) formation by 3D Mueller-matrix microscopy of layers of azimuthal-invariant Mueller-matrix images of circular birefringence of histological sections of the brain. Material and methods. Native sections of brain taken from 110 corpses were used for the study in the case of: death from coronary heart disease - 20 (18.1%) native sections (group 1 - control); HTG - 30 (27.3%) sections (group 2), IIB - 30 (27.3%) sections (group 3), HNG - 30 (27.3%) sections (group 4). Measurement of the values of the distribution of coordinate parameters of polarization at the points of microscopic images was performed at the location of the standard Stokes polarimeter. Results. It is found that for each of the phase cross-sections of the field, the volume of distributions of complex amplitudes of sensitivity, specificity and balanced accuracy of statistical analysis of coordinate distributions of Mueller-matrix invariants of circular dichroism have maximum values for small phase shifts corresponding to their level. The maximum level of balanced accuracy of intergroup differentiation was revealed by calculating statistical moments of the 3rd and 4th order, which characterize the asymmetry and excess distributions of the Mueller-matrix invariants values of circular dichroism of histological sections of brain substance. Conclusions. Excellent balanced accuracy (95% - 96%) of differential diagnosis was achieved between the control group and all study groups, good accuracy (92% - 93%) between ischemic stroke and traumatic hemorrhage and satisfactory accuracy (85% - 86%) between traumatic and hemorrhagic strokes genesis.