Additive manufacturing of silica aerogels.

Owing to their ultralow thermal conductivity and open pore structure1-3, silica aerogels are widely used in thermal insulation4,5, catalysis6, physics7,8, environmental remediation6,9, optical devices10 and hypervelocity particle capture11. Thermal insulation is by far the largest market for silica aerogels, which are ideal materials when space is limited. One drawback of silica aerogels is their brittleness. Fibre reinforcement and binders can be used to overcome this for large-volume applications in building and industrial insulation5,12, but their poor machinability, combined with the difficulty of precisely casting small objects, limits the miniaturization potential of silica aerogels. Additive manufacturing provides an alternative route to miniaturization, but was "considered not feasible for silica aerogel"13. Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol.

Liquid flow and control without solid walls.

When miniaturizing fluidic circuitry, the solid walls of the fluid channels become increasingly important1 because they limit the flow rates achievable for a given pressure drop, and they are prone to fouling2. Approaches for reducing the wall interactions include hydrophobic coatings3, liquid-infused porous surfaces4-6, nanoparticle surfactant jamming7, changes to surface electronic structure8, electrowetting9,10, surface tension pinning11,12 and use of atomically flat channels13. A better solution may be to avoid the solid walls altogether. Droplet microfluidics and sheath flow achieve this but require continuous flow of the central liquid and the surrounding liquid1,14. Here we demonstrate an approach in which aqueous liquid channels are surrounded by an immiscible magnetic liquid, both of which are stabilized by a quadrupolar magnetic field. This creates self-healing, non-clogging, anti-fouling and near-frictionless liquid-in-liquid fluidic channels. Manipulation of the field provides flow control, such as valving, splitting, merging and pumping. The latter is achieved by moving permanent magnets that have no physical contact with the liquid channel. We show that this magnetostaltic pumping method can be used to transport whole human blood with very little damage due to shear forces. Haemolysis (rupture of blood cells) is reduced by an order of magnitude compared with traditional peristaltic pumping, in which blood is mechanically squeezed through a plastic tube. Our liquid-in-liquid approach provides new ways to transport delicate liquids, particularly when scaling channels down to the micrometre scale, with no need for high pressures, and could also be used for microfluidic circuitry.

Feasibility and safety of synchrotron-based X-ray phase contrast imaging as a technique complementary to histopathology analysis.

X-ray phase contrast imaging (X-PCI) is a powerful technique for high-resolution, three-dimensional imaging of soft tissue samples in a non-destructive manner. In this technical report, we assess the quality of standard histopathological techniques performed on formalin-fixed, paraffin-embedded (FFPE) human tissue samples that have been irradiated with different doses of X-rays in the context of an X-PCI experiment. The data from this study demonstrate that routine histochemical and immunohistochemical staining quality as well as DNA and RNA analyses are not affected by previous X-PCI on human FFPE samples. From these data we conclude it is feasible and acceptable to perform X-PCI on FFPE human biopsies.

Refractive axicon for X-ray microscopy applications: design, optimization, and experiment.

In a full-field transmission X-ray microscopy (TXM) setup, a condenser X-ray optical element is used to illuminate the sample by condensing the X-ray beam delivered by the synchrotron storage ring. On-going and future upgrades of synchrotron facilities to diffraction-limited storage rings will pose new challenges to these TXM setups, such as much smaller X-ray beams on the condenser. Here, we demonstrate that a refractive axicon can be used as an X-ray beam shaper to match the ring-shaped aperture of the condenser. Aiming at more efficient use of the incoming X-ray intensity, we explore several axicon designs both analytically and with numerical simulations. The axicons were produced by two-photon polymerization 3D printing on thin silicon nitride membrane substrates. The first characterization of the axicon was carried out at the TOMCAT beamline of the Swiss Light Source (Switzerland).

A Novel Three-Dimensional Approach Towards Evaluating Endomyocardial Biopsies for Follow-Up After Heart Transplantation: X-Ray Phase Contrast Imaging and Its Agreement With Classical Histopathology.

Endomyocardial biopsies are the gold standard for surveillance of graft rejection following heart transplantation, and are assessed by classical histopathology using a limited number of previously stained slices from several biopsies. Synchrotron propagation-based X-ray phase contrast imaging is a non-destructive method to image biological samples without tissue preparation, enabling virtual 2D and 3D histopathology. We aimed to show the feasibility of this method to assess acute cellular rejection and its agreement to classical histopathology. Right ventricular biopsies were sampled from 23 heart transplantation recipients (20 males, mean age 54±14 years) as part of standard follow-up. The clinical diagnosis of potential rejection was made using classical histopathology. One additional study sample was harvested and imaged by X-ray phase contrast imaging, producing 3D datasets with 0.65 µm pixel size, and up to 4,320 images per sample. An experienced pathologist graded both histopathological and X-ray phase contrast images in a blinded fashion. The agreement between methods was assessed by weighted kappa, showing substantial agreement (kappa up to 0.80, p < 0.01) between X-ray phase contrast imaging and classical histopathology. X-ray phase contrast imaging does not require tissue processing, allows thorough analysis of a full myocardial sample and allows identification of acute cellular rejection.

Visualizing plating-induced cracking in lithium-anode solid-electrolyte cells.

Lithium dendrite (filament) propagation through ceramic electrolytes, leading to short circuits at high rates of charge, is one of the greatest barriers to realizing high-energy-density all-solid-state lithium-anode batteries. Utilizing in situ X-ray computed tomography coupled with spatially mapped X-ray diffraction, the propagation of cracks and the propagation of lithium dendrites through the solid electrolyte have been tracked in a Li/Li6PS5Cl/Li cell as a function of the charge passed. On plating, cracking initiates with spallation, conical 'pothole'-like cracks that form in the ceramic electrolyte near the surface with the plated electrode. The spallations form predominantly at the lithium electrode edges where local fields are high. Transverse cracks then propagate from the spallations across the electrolyte from the plated to the stripped electrode. Lithium ingress drives the propagation of the spallation and transverse cracks by widening the crack from the rear; that is, the crack front propagates ahead of the Li. As a result, cracks traverse the entire electrolyte before the Li arrives at the other electrode, and therefore before a short circuit occurs.

High sensitivity X-ray phase contrast imaging by laboratory grating-based interferometry at high Talbot order geometry.

X-ray phase contrast imaging is a powerful analysis technique for materials science and biomedicine. Here, we report on laboratory grating-based X-ray interferometry employing a microfocus X-ray source and a high Talbot order (35th) asymmetric geometry to achieve high angular sensitivity and high spatial resolution X-ray phase contrast imaging in a compact system (total length <1 m). The detection of very small refractive angles (∼50 nrad) at an interferometer design energy of 19 keV was enabled by combining small period X-ray gratings (1.0, 1.5 and 3.0 µm) and a single-photon counting X-ray detector (75 µm pixel size). The performance of the X-ray interferometer was fully characterized in terms of angular sensitivity and spatial resolution. Finally, the potential of laboratory X-ray phase contrast for biomedical imaging is demonstrated by obtaining high resolution X-ray phase tomographies of a mouse embryo embedded in solid paraffin and a formalin-fixed full-thickness sample of human left ventricle in water with a spatial resolution of 21.5 µm.

NRStitcher: non-rigid stitching of terapixel-scale volumetric images.

SUMMARY: In modern microscopy, the field of view is often increased by obtaining an image mosaic, where multiple sub-images are taken side-by-side and combined post-acquisition. Mosaic imaging often leads to long imaging times that can increase the probability of sample deformation during the acquisition due to, e.g. changes in the environment, damage caused by the radiation used to probe the sample or biologically induced deterioration. Here we propose a technique, based on local phase correlation, to detect the deformations and construct an artifact-free image mosaic from deformed sub-images. The implementation of the method supports distributed computing and can be used to generate teravoxel-size mosaics. We demonstrate its capabilities by assembling a 5.6 teravoxel tomographic image mosaic of microvasculature in whole mouse brain. The method is compared to existing rigid stitching implementations designed for very large datasets, and observed to create artifact-free image mosaics in comparable runtime with the same hardware resources. AVAILABILITY AND IMPLEMENTATION: The stitching software and C++/Python source code are available at GitHub (https://github.com/arttumiettinen/pi2) along with an example dataset and user instructions.

Sleep problems and dissociation in preschool victims of sexual abuse.

OBJECTIVE: Child sexual abuse (CSA) is associated with a host of deleterious impacts, yet little is known about the short-term correlates in children. This study aimed to investigate the association between dissociation and sleep problems in a sample of preschool-age sexual abuse victims while controlling for potentially confounding variables, including gender, age, polytrauma, CSA characteristics, and parental distress. METHOD: The sample consisted of 179 children (ages 3-6 years) and their non-offending parents. Parents completed questionnaires assessing their child's dissociative symptoms and sleep problems as well as their own level of psychological distress. RESULTS: Regression analyses revealed that sleep problems were significantly associated with dissociative symptoms over and above all other control variables (children's gender and age, polytrauma, and parental distress). A longer duration of sexual abuse also predicted greater dissociative symptoms in preschool children. CONCLUSION: Findings highlight the association between sleep problems and dissociation in preschool-age victims of CSA. Further research is needed to understand their impact on children's development to design appropriate treatment and prevention initiatives aimed at fostering resilience in young vulnerable children.

Sleep problems over a year in sexually abused preschoolers.

OBJECTIVES: The aim of the present study was to explore sleep problems in sexually abused preschoolers over a year. METHODS: The sample consisted of 224 abused children and 83 nonabused children aged 3 to 6 years old at enrolment into the study (T1), and 85 abused children and 73 nonabused children at the second evaluation, approximately 1 year later (T2). Sleep problems were assessed using parental reports on the Child Behavior Checklist - Preschool Version. RESULTS: Multivariate analysis of covariance revealed that sexually abused preschoolers presented higher scores of sleep problems than nonabused children on all items related to sleep problems at T1. Results from a regression analysis revealed that sexual abuse remained associated with higher levels of sleep problems after controlling for sociodemographical variables. At T2, abused preschoolers still presented more sleep problems than nonabused children on all but one of the sleep items. Results from a repeated measure one-way analysis of covariance revealed that abused preschoolers presented higher total sleep scores at both measurement times. Time was not associated with levels of sleep problems and sleep problems did not evolve differently for abused and nonabused children. CONCLUSIONS: Sexually abused preschoolers are at risk of presenting with sleep problems. These results are worrisome given the negative impacts of sleep problems on child development. Research and clinical implications are discussed.

Emotion Regulation in Sexually Abused Preschoolers: The Contribution of Parental Factors.

Child sexual abuse (CSA) is associated with emotion regulation deficits in childhood. Parents play a crucial role in the development of emotion regulation in their children, especially at younger ages. Close to 50% of mothers of sexually abused children report having been sexually victimized themselves as children. They are consequently at risk of experiencing significant distress following the disclosure of sexual abuse of their child. Parents' distress could interfere with their ability to provide support and to foster development of emotion regulation in their children. The aim of the present study was to explore the relationship of parental factors (history of sexual victimization in childhood and the current level of distress) to sexually abused preschoolers' emotion regulation competencies. Emotion regulation was assessed in 153 preschoolers by their parents with the Emotion Regulation Checklist; 75 of these children were abused (14 boys); 78 were not abused (21 boys) and were part of a comparison group. Parents reported their level of distress using the Psychiatric Symptom Index. Results indicated that parental factors contributed to some dimensions of preschoolers' emotion regulation (namely displays of underregulation of emotion) above and beyond children's victimization status and gender (Cohen's ƒ(2) = .15). Identifying parental distress and history of sexual victimization as positively associated with emotional dysregulation in preschool children victims of CSA has important research and clinical implications.

LiOH Decomposition by NiO/ZrO2 in Li-Air Battery: Chemical Imaging with Operando Synchrotron Diffraction and Correlative Neutron/X-Ray Computed-Tomography Analysis.

Li-air batteries attract significant attention due to their highest theoretical energy density among all existing energy storage technologies. Currently, challenges related to extending lifetime and long-term stability limit their practical application. To overcome these issues and enhance the total capacity of Li-air batteries, this study introduces an innovative approach with NiO/ZrO2 catalysts. Operando advanced chemical imaging with micrometer spatial resolution unveils that NiO/ZrO2 catalysts substantially change the kinetics of crystalline lithium hydroxide (LiOH) formation and facilitate its rapid decomposition with heterogeneous distribution. Moreover, ex situ combined neutron and X-ray computed tomography (CT) analysis, provide evidence of distinct lithium phases homogeneously distributed in the presence of NiO/ZrO2 . These findings underscore the material's superior physico-chemical and electronic properties, with more efficient oxygen diffusion and indications of lower obstruction to its active sites, avoiding clogging in the active electrode, a common cause of capacity loss. Electrochemical tests conducted at high current density demonstrated a significant kinetic enhancement of the oxygen reduction and evolution reactions, resulting in improved charge and discharge processes with low overpotential. This pioneering approach using NiO/ZrO2 catalysts represents a step toward on developing the full potential of Li-air batteries as high-energy-density energy storage systems.

The human middle ear in motion: 3D visualization and quantification using dynamic synchrotron-based X-ray imaging.

The characterization of the vibrations of the middle ear ossicles during sound transmission is a focal point in clinical research. However, the small size of the structures, their micrometer-scale movement, and the deep-seated position of the middle ear within the temporal bone make these types of measurements extremely challenging. In this work, dynamic synchrotron-based X-ray phase-contrast microtomography is used on acoustically stimulated intact human ears, allowing for the three-dimensional visualization of entire human eardrums and ossicular chains in motion. A post-gating algorithm is used to temporally resolve the fast micromotions at 128 Hz, coupled with a high-throughput pipeline to process the large tomographic datasets. Seven ex-vivo fresh-frozen human temporal bones in healthy conditions are studied, and the rigid body motions of the ossicles are quantitatively delineated. Clinically relevant regions of the ossicular chain are tracked in 3D, and the amplitudes of their displacement are computed for two acoustic stimuli.

From Corrosion Casting to Virtual Dissection: Contrast-Enhanced Vascular Imaging using Hafnium Oxide Nanocrystals.

Vascular corrosion casting is a method used to visualize the three dimensional (3D) anatomy and branching pattern of blood vessels. A polymer resin is injected in the vascular system and, after curing, the surrounding tissue is removed. The latter often deforms or even fractures the fragile cast. Here, a method is proposed that does not require corrosion, and is based on in situ micro computed tomography (micro-CT) scans. To overcome the lack of CT contrast between the polymer cast and the animals' surrounding soft tissue, hafnium oxide nanocrystals (HfO2 NCs) are introduced as CT contrast agents into the resin. The NCs dramatically improve the overall CT contrast of the cast and allow for straightforward segmentation in the CT scans. Careful design of the NC surface chemistry ensures the colloidal stability of the NCs in the casting resin. Using only 5 m% of HfO2 NCs, high-quality cardiovascular casts of both zebrafish and mice can be automatically segmented using CT imaging software. This allows to differentiate even µ $\umu$ m-scale details without having to alter the current resin injection methods. This new method of virtual dissection by visualizing casts in situ using contrast-enhanced CT imaging greatly expands the application potential of the technique.

Sample Preparation and Warping Accuracy for Correlative Multimodal Imaging in the Mouse Olfactory Bulb Using 2-Photon, Synchrotron X-Ray and Volume Electron Microscopy.

Integrating physiology with structural insights of the same neuronal circuit provides a unique approach to understanding how the mammalian brain computes information. However, combining the techniques that provide both streams of data represents an experimental challenge. When studying glomerular column circuits in the mouse olfactory bulb, this approach involves e.g., recording the neuronal activity with in vivo 2-photon (2P) calcium imaging, retrieving the circuit structure with synchrotron X-ray computed tomography with propagation-based phase contrast (SXRT) and/or serial block-face scanning electron microscopy (SBEM) and correlating these datasets. Sample preparation and dataset correlation are two key bottlenecks in this correlative workflow. Here, we first quantify the occurrence of different artefacts when staining tissue slices with heavy metals to generate X-ray or electron contrast. We report improvements in the staining procedure, ultimately achieving perfect staining in ∼67% of the 0.6 mm thick olfactory bulb slices that were previously imaged in vivo with 2P. Secondly, we characterise the accuracy of the spatial correlation between functional and structural datasets. We demonstrate that direct, single-cell precise correlation between in vivo 2P and SXRT tissue volumes is possible and as reliable as correlating between 2P and SBEM. Altogether, these results pave the way for experiments that require retrieving physiology, circuit structure and synaptic signatures in targeted regions. These correlative function-structure studies will bring a more complete understanding of mammalian olfactory processing across spatial scales and time.

Sub-micrometer morphology of human atherosclerotic plaque revealed by synchrotron radiation-based µCT-A comparison with histology.

Histology is a long standing and well-established gold standard for pathological characterizations. In recent years however, synchrotron radiation-based micro-computed tomography (SRµCT) has become a tool for extending the imaging of two-dimensional thin sections into three-dimensional imaging of tissue blocks, enabling so-called virtual histology with arbitrary clipping planes, volumetric rendering and automatic segmentation. In this study, we present a thorough characterization of human carotid plaques after endarterectomy of patients with stroke or transient ischemic attack (TIA), investigating several different pathologic structures using both SRµCT and histology. Phase-contrast SRµCT was performed with two different magnifications (voxel sizes 6.5 µm and 0.65 µm, respectively), and histology was performed with multiple different stainings (Alpha-actin, Glycophorin A, von Kossa, Movat, CD68). The 0.65 µm high-resolution SRµCT was performed on selected areas with plaque typical relevant morphology, identified on the 6.5 µm low-resolution SRµCT. The tomography datasets were reconstructed with additional 3D volume rendering and compared to histology. In total, nine different regions with typical pathologic structures were identified and imaged with high-resolution SRµCT. The results show many characteristics typical for advanced atherosclerotic plaques, clinically relevant, namely ruptures with thrombosis, neo-vascularization, inflammatory infiltrates in shoulder regions, lipid rich necrotic cores (LRNC), thin fibrous cap, calcifications, lumen irregularities, and changes in vessel wall structures such as the internal elastic membrane. This method's non-destructive nature renders details of micro-structures with an excellent visual likeness to histology, with the additional strength of multiplanar and 3D visualization and the possibility of multiple re-scans.

A tomographic microscopy-compatible Langendorff system for the dynamic structural characterization of the cardiac cycle.

Introduction: Cardiac architecture has been extensively investigated ex vivo using a broad spectrum of imaging techniques. Nevertheless, the heart is a dynamic system and the structural mechanisms governing the cardiac cycle can only be unveiled when investigating it as such. Methods: This work presents the customization of an isolated, perfused heart system compatible with synchrotron-based X-ray phase contrast imaging (X-PCI). Results: Thanks to the capabilities of the developed setup, it was possible to visualize a beating isolated, perfused rat heart for the very first time in 4D at an unprecedented 2.75 µm pixel size (10.6 µm spatial resolution), and 1 ms temporal resolution. Discussion: The customized setup allows high-spatial resolution studies of heart architecture along the cardiac cycle and has thus the potential to serve as a tool for the characterization of the structural dynamics of the heart, including the effects of drugs and other substances able to modify the cardiac cycle.

Functional and multiscale 3D structural investigation of brain tissue through correlative in vivo physiology, synchrotron microtomography and volume electron microscopy.

Understanding the function of biological tissues requires a coordinated study of physiology and structure, exploring volumes that contain complete functional units at a detail that resolves the relevant features. Here, we introduce an approach to address this challenge: Mouse brain tissue sections containing a region where function was recorded using in vivo 2-photon calcium imaging were stained, dehydrated, resin-embedded and imaged with synchrotron X-ray computed tomography with propagation-based phase contrast (SXRT). SXRT provided context at subcellular detail, and could be followed by targeted acquisition of multiple volumes using serial block-face electron microscopy (SBEM). In the olfactory bulb, combining SXRT and SBEM enabled disambiguation of in vivo-assigned regions of interest. In the hippocampus, we found that superficial pyramidal neurons in CA1a displayed a larger density of spine apparati than deeper ones. Altogether, this approach can enable a functional and structural investigation of subcellular features in the context of cells and tissues.

Biomimetic Light-Driven Aerogel Passive Pump for Volatile Organic Pollutant Removal.

Inspired by the solar-light-driven oxygen transportation in aquatic plants, a biomimetic sustainable light-driven aerogel pump with a surface layer containing black manganese oxide (MnO2 ) as an optical absorber is developed. The flow intensity of the pumped air is controlled by the pore structure of nanofilbrillated cellulose, urea-modified chitosan, or polymethylsilsesquioxane (PMSQ) aerogels. The MnO2 -induced photothermal conversion drives both the passive gas flow and the catalytic degradation of volatile organic pollutants. All investigated aerogels demonstrate superior pumping compared to benchmarked Knudsen pump systems, but the inorganic PMSQ aerogels provide the highest flexibility in terms of the input power and photothermal degradation activity. Aerogel light-driven multifunctional gas pumps offer a broad future application potential for gas-sensing devices, air-quality mapping, and air quality control systems.

Micro- and Nano-Scales Three-Dimensional Characterisation of Softwood.

Understanding the mechanical response of cellular biological materials to environmental stimuli is of fundamental importance from an engineering perspective in composites. To provide a deep understanding of their behaviour, an exhaustive analytical and experimental protocol is required. Attention is focused on softwood but the approach can be applied to a range of cellular materials. This work presents a new non-invasive multi-scale approach for the investigation of the hygro-mechanical behaviour of softwood. At the TOMCAT beamline of the Paul Scherrer Institute, in Switzerland, the swelling behaviour of softwood was probed at the cellular and sub-cellular scales by means of 3D high-resolution phase-contrast X-ray imaging. At the cellular scale, new findings in the anisotropic and reversible swelling behaviour of softwood and in the origin of swelling hysteresis of porous materials are explained from a mechanical perspective. However, the mechanical and moisture properties of wood highly depend on sub-cellular features of the wood cell wall, such as bordered pits, yielding local deformations during a full hygroscopic loading protocol.