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Caries is a chronic disease that causes the alteration of the structure of dental tissues by acid dissolution (in enamel, dentine and cementum) and proteolytic degradation (dentine and cementum) and generates an important cost of care. There is a need to visualise and characterise the acid dissolution process on enamel due to its hierarchical structure leading to complex structural modifications. The process starts at the enamel surface and progresses into depth, which necessitates the study of the internal enamel structure. Artificial demineralisation is usually employed to simulate the process experimentally. In the present study, the demineralisation of human enamel was studied using surface analysis carried out with atomic force microscopy as well as 3D internal analysis using synchrotron X-ray tomography during acid exposure with repeated scans to generate a time-lapse visualisation sequence. Two-dimensional analysis from projections and virtual slices and 3D analysis of the enamel mass provided details of tissue changes at the level of the rods and inter-rod substance. In addition to the visualisation of structural modifications, the rate of dissolution was determined, which demonstrated the feasibility and usefulness of these techniques. The temporal analysis of enamel demineralisation is not limited to dissolution and can be applied to other experimental conditions for the analysis of treated enamel or remineralisation.

The reported study was devoted to the investigation of viscoelastic behavior for solid and porous ultra-high molecular weight polyethylene (UHMWPE) under compression. The obtained experimental stress curves were interpreted using a two-term Prony series to represent the superposition of two coexisting activation processes corresponding to long molecular (~160 s) and short structural (~20 s) time scales, respectively, leading to good statistical correlation with the observations. In the case of porous polymer, the internal strain redistribution during relaxation was quantified using digital image correlation (DIC) analysis. The strongly inhomogeneous deformation of the porous polymer was found not to affect the relaxation times. To illustrate the possibility of generalizing the results to three dimensions, X-ray tomography was used to examine the porous structure relaxation at the macro- and micro-scale levels. DIC analysis revealed positive correlation between the applied force and relative density. The apparent stiffness variation for UHMWPE foams with mixed open and closed cells was described using a newly proposed three-term expression. Furthermore, in situ tensile loading and X-ray scattering study was applied for isotropic solid UHMWPE specimens to investigate the evolution of internal structure and orientation during drawing and stress relaxation in another loading mode.

Diatoms are single cell microalgae enclosed in silica exoskeletons (frustules) that provide inspiration for advanced hybrid nanostructure designs mimicking multi-scale porosity to achieve outstanding mechanical and optical properties. Interrogating the structure and properties of diatoms down to nanometer scale leads to breakthrough advances reported here in the nanomechanical characterization of Coscinodiscus oculus-iridis diatom pure silica frustules, as well as of air-dried and wet cells with organic content. Static and dynamic mode Atomic Force Microscopy (AFM) and in-SEM nanoindentation revealed the peculiarities of diatom response with separate contributions from material nanoscale behavior and membrane deformation of the entire valve. Significant differences in the nanomechanical properties of the different frustule layers were observed. Furthermore, the deformation response depends strongly on silica hydration and on the support from the internal organic content. The cyclic loading revealed that the average compliance of the silica frustule is 0.019 m/N and increases with increasing number of cycles. The structure–mechanical properties relationship has a direct impact on the vibrational properties of the frustule as a complex micrometer-sized mechanical system. Lessons from Nature’s nanostructuring of diatoms open up pathways to new generations of nano- and microdevices for electronic, electromechanical, photonic, liquid, energy storage, and other applications.

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 μm) after seven days compared to bulk hydrogels (22.90 ± 4.70 μm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures., Graphical abstract Image 1, Highlights • In longer-term culture, granular hydrogels supported the development of neural culture with extensive neurite outgrowth. • Granular hydrogels supported significantly higher cell viability and neurite outgrowth over 7 days of culture. • A simple 3D printed extrusion and mixing toolset is used to generate and homogenously seed cells into granular hydrogels. • The toolset designs are provided for 3D printing, enabling use and customization of the techniques described.

Siliceous diatom frustules represent an up-and-coming platform for a range of bio-assisted nanofabrication processes able to overcome the complexity and high cost of current engineering technology solutions in terms of negligibly small power consumption and environmentally friendly processing combined with unique highly porous structures and properties. Herein, the modification of diatomite - a soft, loose, and fine-grained siliceous sedimentary rock composed of the remains of fossilized diatoms - with gold nanoparticles using layer-by-layer technology in combination with a freezing-induced loading approach is demonstrated. The obtained composite structures are characterized by dynamic light scattering, extinction spectroscopy, scanning (SEM) and transmission electron microscopy (TEM), and photoacoustic imaging techniques, and tested as a platform for surface-enhanced Raman scattering (SERS) using Rhodamine 6G. SEM, TEM, and energy dispersive X-ray spectroscopy (EDX) confirmed a dense coating of gold nanoparticles with an average size of 19 nm on the surface of the diatomite and within the pores. The photoacoustic signal excited at a wavelength of 532 nm increases with increasing loading cycles of up to three polyelectrolyte-gold nanoparticle bilayers. The hybrid materials based on diatomite modified with gold nanoparticles can be used as SERS substrates, but also as biosensors, catalysts, and platforms for advanced bioimaging.

Finite element analysis of magnetic materials allows accurate prediction of losses and is crucial in the design of electromagnetic devices and products. Soft magnetic composites are an alternative to silicon steel laminations, yet the electromagnetic material properties are less well documented and include uncertainties which can lead to inaccurate iron and Joule loss computations. The microstructure of soft magnetic composites, which is based on ferromagnetic particles coated by inorganic resistive insulation, makes the process of iron loss prediction unique. Composite core materials require further attention by design engineers in terms of the effect of component size and pressing processes on core loss predictions, which for laminations uses the well-known Steinmetz law. This study accesses the existing soft magnetic composite core loss modelling trends using experimentally measured results. The challenges of estimating and using Steinmetz core loss coefficients via curve fitting approaches are discussed. The study indicates that soft magnetic composite components need to be treated differently to laminated iron cores. Modelling the composite materials in finite element software requires experimentally informed loss models to be able to accurately compute power losses under varying magnetic flux density and electrical frequency. An approach is suggested which can predict iron losses to within 7%, but is only validated for component cross sectional areas of 144 mm2 or less.

Recent years witnessed progressive broadening of the practical use of 3D-printed aluminium alloy parts, in particular for specific aerospace applications where weight saving is of great importance. Selective laser melting (SLM) is an intrinsically multi-parametric fabrication technology that offers multiple means of controlling mechanical properties (elastic moduli, yield strength, and ductility) through the control over grains size, shape, and orientation. Targeted control over mechanical properties is achieved through the tuning of 3D-printing parameters and may even obviate the need of heat treatment or mechanical post-processing. Systematic studies of grain structure for different printing orientations with the help of EBSD techniques in combination with mechanical testing at different dimensional levels are the necessary first steps to implement this agenda. Samples of 3D-printable Al-Mg-Si RS-333 alloy were fabricated in three orientations with respect to the principal build direction and the fast laser beam scanning direction. Sample structure and proper-ties were investigated using a number of techniques, including EBSD, in situ SEM tensile testing, roughness measurements, and nanoindentation. The as-printed samples were found to display strong variation in Young’s modulus values from nanoindentation (from 43 to 66 GPa) and tensile tests (from 54 to 75 GPa), yield stress and ultimate tensile strength (100–195 and 130–220 MPa) in different printing orientations, and almost constant hardness of about 0.8 GPa. A further preliminary study was conducted to assess the effect of surface finishing on the mechanical performance. Surface polishing was seen to reduce Young’s modulus and yield strength but improves ductility, whereas the influence of sandblasting was found to be more controversial. The experimental results are discussed in connection with the grain morphology and orientation.

This study reports the characterisation of human dental enamel caries using synchrotron nanoscale correlative ptychography and spectroscopic mapping in combination with scanning electron microscopy. A lamella ̴2.4 µm thick was extracted from a carious enamel region of a tooth using focused ion beam-scanning electron microscopy and transferred to two synchrotron beamlines to perform hard X-ray nano-fluorescence spectroscopy simultaneously with differential phase contrast mapping at a beam size of 55 × 45 nm. Soft X-ray ptychography data was then reconstructed with a pixel size of 8 nm. The two dimensional variation in chemistry and structure of carious enamel was revealed at the nanoscale, namely, the organisation of hydroxyapatite nano-crystals within enamel rods was imaged together with the inter-rod region. Correlative use of electron and X-ray scanning microscopies for the same sample allowed visualisation of the connection between structure and composition as presented in a compound image where colour indicates the relative calcium concentration in the sample, as indicated by the calcium Kα fluorescence intensity and grey scale shows the nanostructure. This highlights the importance of advanced correlative imaging to investigate the complex structure-composition relationships in nanomaterials of natural or artificial origin.

In the present study, pins made from the novel Mg-2Zn-2Ga alloy were installed within the femoral bones of six Wistar rats. The level of bioresorption was assessed after 1, 3, and 6 months by radiography, histology, SEM, and EDX. Significant bioresorption was evident after 3 months, and complete dissolution of the pins occurred at 6 months after the installation. No pronounced gas cavities could be found at the pin installation sites throughout the postoperative period. The animals’ blood parameters showed no signs of inflammation or toxication. These findings are sufficiently encouraging to motivate further research to broaden the experimental coverage to increase the number of observed animals and to conduct tests involving other, larger animals.

The reported study was devoted to the investigation of viscoelastic behavior for solid and porous ultra-high-molecular-weight polyethylene (UHMWPE) under compression. The obtained experimental stress curves were interpreted using a two-term Prony series to represent the superposition of two coexisting activation processes corresponding to long molecular (~160 s) and short structural (~20 s) time scales, respectively, leading to good statistical correlation with the observations. In the case of porous polymer, the internal strain redistribution during relaxation was quantified using Digital Image Correlation (DIC) analysis. The strongly inhomogeneous deformation of the porous polymer was found not to affect the relaxation times. In order to generalize the results to three dimensions, X-ray tomography was used to examine the porous structure at the macro- and micro-scale levels. DIC analysis revealed positive correlation between the applied force and relative density. The apparent stiffness variation for UHMWPE foams with mixed open and closed cells was described using a newly proposed three-term expression. Furthermore, the in situ tensile loading and X-ray scattering study was applied for isotropic solid UHMWPE specimens to investigate their parameters of internal structure during orientation and stress relaxation process at another mode.

Ptychography is a scanning coherent diffraction imaging technique that provides high-resolution imaging and complete spatial information of the complex probe and object transmission function. The wavefront error caused by aberrated optics has previously been recovered using ptychography when a highly coherent source is used, but has not been demonstrated with partial coherence due to the multi-modal probe required. Here, we demonstrate that partial coherence can be accounted for in ptychographic reconstructions using the multi-modal approach and assuming that decoherence arises from either the probe or the object. This equivalence recovers coherent (or single state) reconstructions of both the probe and the object even in the presence of partial coherence. We demonstrate this experimentally by using hard x-ray ptychography with a partially coherent source to image a Siemens star test object and to also recover the wavefront error from an aberrated beryllium compound refractive lens. The source properties and resolving capabilities are analyzed, and the wavefront error results are compared with another at-wavelength metrology technique. Our work demonstrates the capability of ptychography to provide high-resolution imaging and optics characterization even in the presence of partial coherence.

The problems of non-slipping contacts between dissimilar elastic solids are studied under the conditions of plane strain. When two dissimilar solids are incrementally pressed into contact, a relative tangential displacement along the contact interface emerges because of the material property mismatch. The spatial derivative of the relative tangential displacement is referred to as the interface mismatch eigenstrain, which is separately investigated subject to the non-adhesive and adhesive surface conditions. The explicit solutions of the interface mismatch eigenstrain for non-slipping contacts with symmetrical indenter profiles are obtained. These results provide the foundation for improved precision contact deformation modelling at different scales.

Hard dental tissues possess a complex hierarchical structure that is particularly evident in enamel, the most mineralised substance in the human body. Its complex and interlinked organisation at the Ångstrom (crystal lattice), nano-, micro-, and macro-scales is the result of evolutionary optimisation for mechanical and functional performance: hardness and stiffness, fracture toughness, thermal, and chemical resistance. Understanding the physical–chemical–structural relationships at each scale requires the application of appropriately sensitive and resolving probes. Synchrotron X-ray techniques offer the possibility to progress significantly beyond the capabilities of conventional laboratory instruments, i.e., X-ray diffractometers, and electron and atomic force microscopes. The last few decades have witnessed the accumulation of results obtained from X-ray scattering (diffraction), spectroscopy (including polarisation analysis), and imaging (including ptychography and tomography). The current article presents a multi-disciplinary review of nearly 40 years of discoveries and advancements, primarily pertaining to the study of enamel and its demineralisation (caries), but also linked to the investigations of other mineralised tissues such as dentine, bone, etc. The modelling approaches informed by these observations are also overviewed. The strategic aim of the present review was to identify and evaluate prospective avenues for analysing dental tissues and developing treatments and prophylaxis for improved dental health.

Graphical abstract, In the past years, a significant amount of effort has been directed at the observation and characterisation of caries using experimental techniques. Nevertheless, relatively little progress has been made in numerical modelling of the underlying demineralisation process. The present study is the first attempt to provide a simplified calculation framework for the numerical simulation of the demineralisation process at the length scale of enamel rods and its validation by comparing the data with statistical analysis of experimental results. FEM model was employed to simulate a time-dependent reaction-diffusion equation process in which H ions diffuse and cause demineralisation of the enamel. The local orientation of the hydroxyapatite crystals was taken into account. Experimental analysis of the demineralising front was performed using advanced high-resolution synchrotron X-ray micro-Computed Tomography. Further experimental investigations were conducted by means of SEM and STEM imaging techniques. Besides establishing and validating the new modelling framework, insights into the role of the etchant solution pH level were obtained. Additionally, some light was shed on the origin of different types of etching patterns by simulating the demineralisation process at different etching angles of attack. The implications of this study pave the way for simulations of enamel demineralisation within different complex scenarios and across the range of length scales. Indeed, the framework proposed can incorporate the presence of chemical species other than H ions and their diffusion and reaction leading to dissolution and re-precipitation of hydroxyapatite. It is the authors’ hope and aspiration that ultimately this work will help identify new ways of controlling and preventing caries.

The thermal stability of Cu/W nano-multilayers deposited on a Si substrate using ion beam deposition was analyzed in situ by GISAXS and transmission EDX—a combination of methods permitting the observation of diffusion processes within buried layers. Further supporting techniques such as XRR, TEM, WAXS, and AFM were employed to develop an extensive microstructural understanding of the multilayer before and during heating. It was found that the pronounced in-plane compressive residual stress and defect population induced by ion beam deposition result in low thermal stability driven by thermally activated self-interstitial and vacancy diffusion, ultimately leading to complete degradation of the layered structure at moderate temperatures. The formation of Cu protrusions was observed, and a model was formulated for stress-assisted Cu diffusion driven by Coble creep along W grain boundaries, along with the interaction with Si substrate, which showed excellent agreement with the observed experimental data. The model provided the explanation for the experimentally observed strong correlation between thin film deposition conditions, microstructural properties, and low thermal stability that can be applied to other multilayer systems.

To explore the possibility of customising the functional behaviour of NiTi shape memory alloy via controlling texture, binary Ni55Ti45 (wt.%) alloys were manufactured in as cast and hot swaged conditions, presenting contrasting initial texture and macroscopic performance. In situ time-of-flight neutron diffraction technique was employed to study the texture effect on the microstructural evolution during Shape Memory Effect (SME), and a range of properties were evaluated. It was found that (i) hot swaging process leads to change in grain morphology and increase in microstrain; (ii) thermal expansion coefficients of martensite and austenite variants were weakly affected by the texture and phase transformation constraint; (iii) significant texture effect on the elastic properties at both macro- and micro-scale was quantified by Elasto-Plastic Self-Consistent (EPSC) modelling approach, while the anisotropic elastic moduli lie within the range of single crystal state and twinned structure; (iv) texture evolution during SME is weakly related to the initial microstructure; (v) martensite reoriented so that the axis became aligned parallel to the loading direction, and retained this orientation upon unloading, revealing the underlying correlation between texture evolution and detwinning. Based on the experimental results, a multi-variant model was proposed to quantify the lattice strain evolution during SME. Validity of the conceptually simple and parametrically parsimonious model was confirmed by validation against experimental data.

Photosynthetic single-celled diatom algae, due to their unique structure and properties, represent promising candidates for various applications in technology and biomedicine. These nanostructured objects, enveloped within a silica cell wall called a frustule, play a significant role in Earth’s ecology. In this study, we proposed new techniques for monitoring the growth of diatoms—in situ fluorescence measurements using the IVIS imaging system and photoacoustic measurements with a raster scanning optoacoustic mesoscopy (RSOM) setup. Two different diatom cultures, Achnanthidium sibiricum and Encyonema silesiacum, were cultivated under the optimal conditions in the incubator and monitored over the period of 70 days. Our results showed that the total radiant efficiency increases with increasing incubation time for E. silesiacum. Simultaneously, for A. sibiricum it slightly decreases after 56 days, indicating that diatoms were at the end of their exponential growth phase. The photoacoustic signal from E. silesiacum was lower than from A. sibiricum, which is in good agreement with spectroscopic characterization results. The IVIS imaging system made it possible to assess the growth and viability of diatom cells without compromising cell integrity. In contrast, photoacoustic imaging has proved to be suitable for the rapid detection and thorough in situ assessment of the density of diatom colonies due to the presence of light-absorbing chromophores. These methods can be used to monitor the growth of diatoms and facilitate the harvesting of bioactive substances derived from diatoms for pharmaceutical and biomedical purposes.

To explore an effective route of customizing the superelasticity (SE) of NiTi shape memory alloys via modifying the grain structure, binary Ni55Ti45 (wt) alloys were fabricated in as-cast, hot swaged, and hot-rolled conditions, presenting contrasting grain sizes and grain boundary types. In situ synchrotron X-ray Laue microdiffraction and in situ synchrotron X-ray powder diffraction techniques were employed to unravel the underlying grain structure mechanisms that cause the diversity of SE performance among the three materials. The evolution of lattice rotation, strain field, and phase transformation has been revealed at the micro-and mesoscale, and the effect of grain structure on SE performance has been quantified. It was found that (i) the Ni4Ti3 and NiTi2 precipitates are similar among the three materials in terms of morphology, size, and orientation distribution; (ii) phase transformation happens preferentially near high-angle grain boundary (HAGB) yet randomly in low-angle grain boundary (LAGB) structures; (iii) the smaller the grain size, the higher the phase transformation nucleation kinetics, and the lower the propagation kinetics; (iv) stress concentration happens near HAGBs, while no obvious stress concentration can be observed in the LAGB grain structure during loading; (v) the statistical distribution of strain in the three materials becomes asymmetric during loading; (vi) three grain lattice rotation modes are identified and termed for the first time, namely, multi-extension rotation, rigid rotation, and nondispersive rotation; and (vii) the texture evolution of B2 austenite and B19 ' martensite is not strongly dependent on the grain structure. Web of Science

The present article overviews the current state-of-the-art and future prospects for the use of diatomaceous earth (DE) in the continuously expanding sector of energy science and technology. An eco-friendly direct source of silica and the production of silicon, diatomaceous earth possesses a desirable nano- to micro-structure that offers inherent advantages for optimum performance in existing and new applications in electrochemistry, catalysis, optoelectronics, and biomedical engineering. Silica, silicon and silicon-based materials have proven useful for energy harvesting and storage applications. However, they often encounter setbacks to their commercialization due to the limited capability for the production of materials possessing fascinating microstructures to deliver optimum performance. Despite many current research trends focusing on the means to create the required nano- to micro-structures, the high cost and complex, potentially environmentally harmful chemical synthesis techniques remain a considerable challenge. The present review examines the advances made using diatomaceous earth as a source of silica, silicon-based materials and templates for energy related applications. The main synthesis routes aimed at preserving the highly desirable naturally formed neat nanostructure of diatomaceous earth are assessed in this review that culminates with the discussion of recently developed pathways to achieving the best properties. The trend analysis establishes a clear roadmap for diatomaceous earth as a source material of choice for current and future energy applications.

Electrospinning is a well-established method for the fabrication of polymer biomaterials, including those with core-shell nanofibers. The variability of structures presents a great range of opportunities in tissue engineering and drug delivery by incorporating biologically active molecules such as drugs, proteins, and growth factors and subsequent control of their release into the target microenvironment to achieve therapeutic effect. The object of study is non-woven core-shell PVA–PEG–SiO2@PVA–GO fiber mats assembled by the technology of coaxial electrospinning. The task of the core-shell fiber development was set to regulate the degradation process under external factors. The dual structure was modified with silica nanoparticles and graphene oxide to ensure the fiber integrity and stability. The influence of the nano additives and crosslinking conditions for the composite was investigated as a function of fiber diameter, hydrolysis, and mechanical properties. Tensile mechanical tests and water degradation tests were used to reveal the fracture and dissolution behavior of the fiber mats and bundles. The obtained fibers were visualized by confocal fluorescence microscopy to confirm the continuous core-shell structure and encapsulation feasibility for biologically active components, selectively in the fiber core and shell. The results provide a firm basis to draw the conclusion that electrospun core-shell fiber mats have tremendous potential for biomedical applications as drug carriers, photocatalysts, and wound dressings.

The topic of interactions between plastic and natural communities is now more relevant than ever before. Gradual accumulation of artificial polymer products and their fragments in the natural environment has reached a level at which it is already impossible to ignore the affect of these materials on living organisms. First and foremost, microorganism colonies inhabiting different biotopes, both aquatic and terrestrial, have been affected. These species are at the front-end of interaction with plastic, including those present in marine ecosystems. Nevertheless, in order to understand these processes, it is necessary to take into account several aspects of such interactions: the impact of different types of plastic on microbial community through the release of their decomposed products into the environment, the forms of plastic usage by microorganisms themselves, including mechanisms for surface colonization, as well as possible biodegradation processes of polymers due to the actions of microorganisms. At the same time, types of plastic may differ not only in mechanical strength, but also in their resistance to biodegradation caused by microorganisms. Experiments with surface colonization of types of plastic, which are different in composition and mechanical strength, provide a wide range of results that are not just relevant for understanding modern natural processes involving plastic: these results are also important for application in certain areas of technology development (for example, when creating composite materials). In particular, researches into the forms and mechanisms of sustainable colonization of particularly strong polymers by diatoms from natural communities are of great interest. Due to the fouling of surface of particularly strong synthetic polymers by diatoms, it is possible to form a single diatom-polymeric composite with general properties being already substantially different from those of the polymer itself. For example, when a polymer is fouled with diatoms that are firmly held on its surface due to physiological mechanisms that ensure their reliable fixation, total surface area of the composite increases by 2–3 orders of magnitude compared with this of bare polymer. Such composites and their properties are formed due to mechanisms of substrate colonization used by diatoms from natural marine cenoses – during the transfer of these mechanisms to a new material being prospective for diatom settlement. The practical applications of these composites lie in the sphere of heat and sound insulation, as well as in the field of creating prosthetic tissues for bone operations. In our experiments, we tracked the sequence of development of a stable composite when diatoms colonized the surface of samples of a particularly strong synthetic polymer being resistant to corrosion. In this case, the sample population process took place on the basis of colonies formed in accumulative cultures from the natural marine environment. Samples of ultra-high molecular weight polyethylene (UHMWPE) with a smooth and porous surface structure (with an open cell, bulk porosity up to 80 %) were colonized by diatoms Karayevia amoena (Hust.) Bukht., 2006, Halamphora coffeaeformis (C. Agardh) Levkov, 2009, and Halamphora cymbifera (W. Greg.) Levkov, 2009. These laboratory experiments lasted for three weeks. Accumulative microphyte cultures, on the basis of which the experiments were conducted, were obtained from the Baltic Sea (Baltiysk area, Russia) and the Arabian Sea (Mumbai area, India). The types and stages of development of colonial settlements on various elements of the frontal surface microrelief and in the underlying caverns were studied using a scanning electron microscope on samples subjected to stepwise thermal drying. Individual cells of K. amoena, H. coffeaeformis, and H. cymbifera, their chain-like aggregates, and outstretched colonial settlements occupied varying in degree non-homogeneous microrelief surface elements, forming structures with a thickness of 1–2 layers with an average settlement height of 1–1.3 single specimen height. K. amoena cells were tightly fixed to the polymer substrate using the pore apparatus of the flap of the frustule. Observations using scanning electron microscope revealed shell imprints on the substrate, which were signs of a polymer substrate introduction into hypotheca areoles. The spread mechanisms of diatoms of three mentioned species on various elements of UHMWPE surface were explored, as well as the formation of the characteristic elements of colonial settlements, including for K. amoena – consecutively in the form of “pots” and spheres, by means of interaction with polymer surface and its extension with the increase in the number of tightly attached cells in the colonial settlement.

Digital optical microscopy (DOM) has revolutionised many aspects of industrial inspection and metrology through its ability to acquire and manipulate accurate images of samples using the power of computers. We report the application of HokusAI®, a suite of techniques for digital optical microscopy developed at the Hierarchically Structured Materials (HSM) lab at the Skolkovo Institute of Science and Technology (Skoltech), to elasto-plastic deformation and fracture mechanics analysis of samples of stainless steel AISI 304. Focus Stacking Optical Microscopy (FSOM) is combined with image stitching and Digital Image Correlation (DIC) to collect exhaustive and precise description of sample geometry, surface roughness, fracture surface morphology, and the evolution of deformation during in situ tensile testing. The implications of these advances for the analysis of deformation and fracture of advanced engineering materials are discussed.

Phantoms are widely used substitutes for various types of soft tissues with mechanically and anatomically matching properties. They can be used as advanced tools for training before the surgical manipulation on human organs such as the brain or liver as part of complex operation planning and preparation. We report 3D printing fabrication and characterization of hydrogel composites based on the combination of two biocompatible materials, namely, polyvinyl alcohol (PVA) and phytagel (PHY). The hydrogels were used for the fabrication of brain phantoms in a multistage procedure based around 3D printing. The main goal of this study is to demonstrate the simple, low cost and relatively fast procedure for the creation of hydrogel organ phantoms of high anatomical and mechanical fidelity made from commonly available materials. To this end, three different types of samples were produced to illustrate the flexibility of hydrogel-based 3D printing approach in mimicking the mechanical properties of human organs: brain, lung, and liver soft tissues. The mechanical response was studied using Deben MicroTest 1 kN mechanical testing device and Q800 Dynamic Mechanical Analyser in compression mode. The results reveal close matching of the dynamic non-linear mechanical response of the phantoms to those of the corresponding natural soft tissues.

Electrospinning fabrication of mats presents new opportunities for flexible manufacturing of hierarchically structured materials. Electrospun mats were fabricated from the solutions of 10 wt% polyvinyl alcohol (PVA) and 2 wt% of collagen gel mixed in different mass ratios (50:50, 60:40, 70:30, 80:20, 90:10). The use of 10 wt% PVA aqueous solution leads to stable fiber formation. In the present study we demonstrate that this solution provides a good base to produce collagen-PVA fiber mats by electrospinning. Beadless fibers were formed for collagen concentration not exceeding 0.6 wt% from the whole solution, that corresponds to the 70:30 mixing ratio of the PVA solution to collagen gel. All PVA-collagen solutions were measured to find out the dynamic viscosity at the corresponded shear rate.

Ni-base superalloys are used in a wide range of applications where components made from these alloys are exposed to extreme conditions of high temperature and high pressure, and dependable performance is critical for mission success, the safety of human lives, and multi-million commercial investment. To ensure robustness and reliability of highly demanding engineering solutions, it is crucial to advance the development of cutting-edge computational design tools based on artificial intelligence and fuzzy techniques, combined with the application of materials characterization and materials design. In the present study, the use of the contour method in combination with eigenstrain theory provided new insights into 3D residual stress states in Ni-base superalloy samples. As-welded and heat-treated specimens were made using bead-on-plate design to investigate the effect of complex fabrication conditions on welds process in large components. The widely used relief of residual stresses during post-weld heat treatment was simulated using eigenstrain-creep model. Furthermore, artificial intelligence (AI) based eigenstrain-contour and eigenstrain-creep models, that use fuzzy techniques, were developed by the present authors for materials used in advanced ultra-supercritical coal-powered plants, showing good match with experiments. The present study reports the combination of eigenstrain theory with artificial intelligence for the modelling of welding residual stresses and simulation of post-weld heat treatment process and highlights the benefits of AI-based eigenstrain-contour and eigenstrain-creep methods on the development of robust and reliable aeroengine components. (C) 2020 Elsevier Ltd. All rights reserved.

This paper presents a summary of recently developed experimental and computational tools to reconstruct residual stress fields and analyze creep in nickel superalloy welds used in aerospace engineering components. This approach combines experimental data with eigenstrain theory to reconstruct stress fields at the macroscopic scale and provided reliable means for numerical prediction of creep behavior of welded components under complex loading conditions. Experimental data in the form of profilometry scans was interpreted using a range of iterative eigenstrain methods that included the adaptation of the contour method and artificial intelligence models for eigenstrain-creep analysis. The integration of principles of artificial intelligence with eigenstrain models allowed highly accurate results to be obtained which were validated by comparison with experimental data obtained using independent techniques such as neutron diffraction. The use of artificial intelligence models is discussed for residual stress reconstruction and creep behavior prediction in annular aeroengine parts manufactured using inertia friction welding. To extend the range of experimental data taken into consideration, the height Digital Image Correlation (hDIC) technique was introduced that utilizes information regarding triaxial displacements obtained from profilometry, allowing deeper and more reliable analysis to be conducted. The hDIC technique was validated using operando tensile testing data.

The powder characteristics of nanostructured silicon produced via Magnesiothermic Reduction Reaction (MRR) of raw (amorphous) and calcined (crystalline) diatomite powders were studied. Magnesiothermic reduction reaction of diatomaceous earth samples was carried out in an argon-filled electric furnace at 700 °C for 2.5 h. Both X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis of calcined diatomite powders confirmed the crystallization of opal to cristobalite and the preservation of the nano-scale morphology of natural diatomite after calcination at 1200 °C for 4 h. Raw and calcined diatomite after MRR contained product nanostructured silicon, unreacted silica, and by-product MgO. Silicon with nano-scale morphology was obtained after etching the reduced powder with 1.0 M HCl and 5% HF severally. Among the different grades of nanostructured Si produced via different routes, the one obtained from the diatomite powder calcined under argon flow showed nano-scale morphology identical to that of the precursor powder. X-ray diffraction analysis and Raman spectroscopy confirmed the prevalence of nanostructured silicon. All samples showed intense Raman signals with variations in peak positions confirming a difference in crystallinity between the silicon types. This work provides insights into the effects of different calcination conditions on the final structure of product silicon.

The pursuit of new nanotechnologies is driven by the demand for miniaturization, ubiquitous computing, increasing connectivity and the Internet of Things (IoT) paradigm, the environmental agenda, and the confluence between microelectronics and biomedical fields. Of particular interest for the present overview are the capabilities of prokaryotic and eukaryotic microorganisms to fabricate numerous nanostructured self-copies from ecologically friendly and renewable raw materials offering new pathways for low energy consumption, smart nanofabrication at production rates that remain unattainable for today’s engineering technologies. The present discussion is focused on the use of stiff and strong nanostructured silica diatom frustules that is widely mooted in the literature in consideration of photonic, photovoltaic, plasmonic, and drug delivery applications. Chemical post-processing routes can be applied to synthesize and deposit nanostructures (Ag, Au, MnO2, ZnO etc.) using templates and substrates of diatomaceous earth and individual diatom frustules. In this concise overview we discuss the background knowledge, motivation and justification for the use of siliceous diatom frustules as a platform for smart nanofabrication, and attempt to anticipate future developments in this field.

Diatom algae are active and efficient photosynthesizing single cell organisms responsible for a quarter of biomass and a quarter of oxygen release on the Earth surface. Diatoms form an enormously diverse class of microorganisms possessing stiff and strong, durable exoskeletons made from hydrated amorphous silica forming neat 3D nanostructures, and displaying hierarchical organization up to the scale of tens of micrometres. In our ongoing research into the structure and properties of diatoms we observed their colonization patterns on various surfaces, including polymers (PE, PP, PC and PETF) and silicon. This process can be guided by purposeful surface patterning to introduce pits, grooves, and ledges. Guided colonization opens the prospect of assembly and harvesting diatom frustules for applications in micro- and nano-electro-mechanical systems (MEMS and NEMS). Additionally, the wide range and specificity of diatoms opens the possibility of using them as tags and markers that are below the level of visibility by naked eye, but present specific spectroscopic fingerprints in visible light and UV ranges. Diatom ‘tags’ can also be read using high magnification imaging using Scanning Electron Microscopy (SEM). As a contributory guidance to morphological diversity of diatoms we present a mini-atlas of diatom in the form of high resolution SEM images.

Electrospinning is a well-established method for the fabrication of polymer biomaterials, including those with core-shell nanofibers. The variability of structures presents a great range of opportunities in tissue engineering and drug delivery by incorporating biologically active molecules such as drugs, proteins, and growth factors and subsequent control of their release into the target microenvironment to achieve therapeutic effect. The object of study is non-woven core-shell PVA-PEG-SiO

All solid state, thin film Li-NMC batteries produced by Physical Vapour Deposition have the potential to revolutionize the internet of things by integrating ultra-fast charging and high energy densities into small portable devices. In these systems, the integrity of the cathode-solid electrolyte interface is of particular importance, as it determines the internal battery resistance and attainable charge rate. To understand and control the effect of manufacturing parameters on the performance and interface stability in these systems, as well as the mechanisms resulting in interface degradation, a novel approach was used that combined in situ battery lamella charging with electron nano-diffraction and multiphysics Finite Element modeling. Experimentally observed cathode strains and degradation were correlated with deposition parameter-controlled grain orientation, to determine ideal deposition conditions for enhanced thin film battery charging and discharging behavior. It was identified that (104) oriented cathode grains minimize anode-electrolyte interface degradation, while allowing for high charge and discharge rates, as well as significantly reducing the cathode-electrolyte interface resistance. Furthermore, the residual stress state of individual thin film battery layers, as well as the cathode grain orientation were identified as material design parameters to optimize cell performance and durability with potential capacity retention enhancements of up to 28%.

The study reveals the polymer–crosslinker interactions and functionality of hydrophilic nanofibers for antibacterial wound coatings. Coaxial electrospinning leverages a drug encapsulation protocol for a core–shell fiber composite with a core derived from polyvinyl alcohol and polyethylene glycol with amorphous silica (PVA-PEG-SiO2), and a shell originating from polyvinyl alcohol and graphene oxide (PVA-GO). Crosslinking with GO and SiO2 initiates the hydrogel transition for the fiber composite upon contact with moisture, which aims to optimize the drug release. The effect of hydrogel-inducing additives on the drug kinetics is evaluated in the case of chlorhexidine digluconate (CHX) encapsulation in the core of core–shell fiber composite PVA-PEG-SiO2-1x-CHX@PVA-GO. The release rate is assessed with the zero, first-order, Higuchi, and Korsmeyer–Peppas kinetic models, where the inclusion of crosslinking silica provides a longer degradation and release rate. CHX medicated core–shell composite provides sustainable antibacterial activity against Staphylococcus aureus.

Over the next decade, the extremely brilliant fourth generation synchrotron radiation sources are set to become a key driving force in materials characterization and technology development. In this study, we present a conceptual design of a versatile “Materia” diffraction and imaging beamline for a low-emittance synchrotron radiation facility. The beamline was optimized for operation with three main principal delivery regimes: parallel collimated beam ∼1 mm beam size, micro-focus regime with ∼10 μm beam spot size on the sample, and nano-focus regime with −2. The manuscript presents the details of the principal characteristics selected for the insertion device and beamline optics, the materials characterization techniques, including the simulations of thermal load impact on the critical beamline optics components. Significant efforts were made to design the monochromators to mitigate the very high beam power load produced by a superconducting undulator source. The manuscript will be of interest to research groups involved in the design of new synchrotron beamlines.

SLM Additive Manufacturing has demonstrated great potential for aerospace applications when structural elements of individual design and/or complex shape need to be promptly supplied. 3D-printable AlSi10Mg (RS-300) alloy is widely used for the fabrication of different structures in aerospace industry. The importance of the evaluation of residual stresses that arise as a result of complex 3D-printing process thermal history is widely discussed in literature, but systematic assessment remains lacking for their magnitude, spatial distribution, and comparative analysis of different evaluation techniques. In this study we report the results of a systematic study of residual stresses in a 3D-printed double tower shaped samples using several approaches: the contour method, blind hole drilling laser speckle interferometry, X-ray diffraction, and Xe pFIB-DIC micro-ring-core milling analysis. We show that a high level of tensile and compressive residual stresses is inherited from SLM 3D-printing and retained for longer than 6 months. The stresses vary over a significant proportion of the material yield stress. All residual stress evaluation techniques considered returned comparable values of residual stresses even regardless of dramatically different dimensional scales from millimeters for the Contour Method down, laser speckle interferometry and XRD and down to small fractions of a mm (70 μm) for Xe pFIB-DIC ring-core drilling. The use of residual stress evaluation is discussed in the context of optimizing the printing strategy to enhance the mechanical performance and long-term durability.

SLM additive manufacturing has demonstrated great potential for aerospace applications when structural elements of individual design and/or complex shape need to be promptly supplied. 3D-printable AlSi10Mg (RS-300) alloy is widely used for the fabrication of different structures in the aerospace industry. The importance of the evaluation of residual stresses that arise as a result of the 3D-printing process’ complex thermal history is widely discussed in literature, but systematic assessment remains lacking for their magnitude, spatial distribution, and comparative analysis of different evaluation techniques. In this study, we report the results of a systematic study of residual stresses in 3D-printed double tower shaped samples using several approaches: the contour method, blind hole drilling laser speckle interferometry, X-ray diffraction, and Xe pFIB-DIC micro-ring-core milling analysis. We show that a high level of tensile and compressive residual stresses is inherited from SLM 3D-printing and retained for longer than 6 months. The stresses vary (from −80 to +180 MPa) over a significant proportion of the material yield stress (from −⅓ to ¾). All residual stress evaluation techniques considered returned comparable values of residual stresses, regardless of dramatically different dimensional scales, which ranged from millimeters for the contour method, laser speckle interferometry, and XRD down to small fractions of a mm (70 μm) for Xe pFIB-DIC ring-core drilling. The use of residual stress evaluation is discussed in the context of optimizing printing strategies to enhance mechanical performance and long-term durability.

In the last decade, perovskite photovoltaics gained popularity as a potential rival for crystalline silicon solar cells, which provide comparable efficiency for lower fabrication costs. However, insufficient stability is still a bottleneck for technology commercialization. One of the key aspects for improving the stability of perovskite solar cells (PSCs) is encapsulating the photoactive material with the hole-transport layer (HTL) with low gas permeability. Recently, it was shown that the double HTL comprising organic and inorganic parts can perform the protective function. Herein, a systematic investigation and comparison of four double HTLs incorporating polytriarylamine and thermally evaporated transition metal oxides in the highest oxidation state are presented. In particular, it was shown that MoOx, WOx, and VOx-based double HTLs provided stable performance of PSCs for 1250 h, while devices with NbOx lost 30% of their initial efficiency after 1000 h. Additionally, the encapsulating properties of all four double HTLs were studied in trilayer stacks with HTL covering perovskite, and insignificant changes in the absorber composition were registered after 1000 h under illumination. Finally, it was demonstrated using ToF-SIMS that the double HTL prevented the migration of perovskite volatile components within the structure. Our findings pave the way towards improved PSC design that ensures their long-term operational stability.

It is interesting to consider just how many of us don't think about the importance of mechanical engineering when we go about our daily lives. Whether we are crossing bridges, getting into our cars, riding on trains, flying in planes or entering buildings, we are relying on mechanical engineers and researchers to have performed an enormous amount of calculations to ensure the integrity of these structures. Indeed, the main purpose of many engineering activities is to design structures against failure. By employing physics, mathematical principles, experience, technical knowledge and modelling capabilities, teams can confidently predict the safe operations of complex engineering systems. Dr Masaru Ogawa, who is based at the Department of Mechanical Systems Engineering, Kogakuin University, is working alongside Professor Alexander M Korsunsky and a number of researchers to elucidate the origins and effects of residual stresses. They are using the eigenstrain reconstruction method to estimate 3D residual stress distribution.

Shallow cracks are often observed in dental enamel, however do not normally lead to deep fractures. Previous work has highlighted the toughening mechanisms that operate in enamel during crack propagation, but very little is known about the deformation and stress fields arising around the propagating cracks during realistic loading conditions. This work aims to elucidate how the stresses are distributed within human dental enamel when a pre-existing crack is subjected to opening and surface contact with in situ indentation. We present a synchrotron-based insitu analysis coupled with a linear elastic finite element method simulation. The experimental reconstructed stress fields identified a prominent residual stress within the enamel, accompanied by a visible pattern that appeared clearly associated with its underlying microstructure. The numerical modelling of the stress field and discerning of surface contact and crack opening caused by the indentation was subsequently possible, even if in this study the influence of the anisotropy induced by the presence of features at a smaller scale was neglected. The implications of these findings and directions for future research are discussed.

We present a combined experimental and numerical study that provides the understanding of deformation mechanisms and stresses in Mg AZ31B alloy across scales, from macro-scale (Type I) to micro- (inter-granular, Type II) and nano-scale (intra-granular, Type III). The combination of in situ synchrotron X-ray diffraction (XRD), in situ electron backscattered diffraction (EBSD) and crystal plasticity finite element (CPFE) modeling of crystal slip and twinning/detwinning was employed. The crystal rotation observed directly in the XRD and EBSD experiments revealed the onset and completion of the twinning/detwinning processes during in situ cyclic compression-tension loading. It also allowed reliable calibration of the key model parameters, in particular critical resolved shear stress (CRSS) of detwinning. The validation of the model was performed at distinct different scales corresponding to all stress types. Direct comparison with the data from the loading device provided the confirmation of the model validity in terms of correct description of the macroscopic stress-strain response (Type I stresses). The calibration led to the CRSS detwinning value of 23 MPa, and twinning of 46.5 MPa. At the inter-granular micro-scale (Type II stresses), the model satisfactorily predicted the transition between different plastic deformation modes (slip, twinning and detwinning), as confirmed by the comparison with peak intensities in XRD experiments. For the intra-granular (nano-scale) Type III stresses, it was concluded that the model was also valid at the level of statistical description (rather than local behavior). Namely, it has not been possible to predict correctly the real morphology of the twins observed in EBSD experiments.

The eigenstrain theory provides a range of fruitful concepts for advanced modelling of the behaviour of materials and components obtained using sophisticated manufacturing routes, their response to thermal and mechanical loading, and deformation under fatigue and creep conditions. In recent years the method has been shown to be able to provide predictions of residual stresses for a limited range of processing and simulated service conditions for which experimental data is available. The authors recently presented advances in the use of eigenstrain-based analysis to include accurate determination of the domain and boundaries of eigenstrain fields in the weld zone. This approach allowed effective modelling of large-scale components and the determination of volumetric distributions of residual stresses through the use of additional model coefficients that need to be determined. Due to the non-linear dependence of the prediction on these parameters, the algorithm of the decision-making process has a profound influence on the cost of the simulation, and the reliability of its output. To address this challenge, the principles of Artificial Intelligence were adopted for use in the eigenstrain contour method to develop fuzzy Finite Element Model (fFEM) for the eigenstrain the reconstruction of residual stresses in large structures. The deterministic finite element eigenstrain model uses contour measurements for reconstruction process, and the developed fFEM behaves as an artificial agent to determine the coefficients of the deterministic finite element eigenstrain model. As an example application, as-welded and post-weld heat-treated specimens of non-uniform weldments of Inconel Alloy 740H were investigated using the proposed model. The results were verified using displacement measurements and residual stress calculations of the contour method. The determination of model coefficients by artificial agent allowed effective reconstruction of volumetric residual stresses in complex shaped components using limited data without the requirement of costly and destructive multi-cut experimental procedures.

OBJECTIVE: Residually strained porcelain is influential in the early onset of failure in Yttria Partially Stabilised Zirconia (YPSZ) - porcelain dental prosthesis. In order to improve current understanding it is necessary to increase the spatial resolution of residual strain analysis in these veneers. METHODS: Few techniques exist which can resolve residual stress in amorphous materials at the microscale resolution required. For this reason, recent developments in Pair Distribution Function (PDF) analysis of X-ray diffraction data of dental porcelain have been exploited. This approach has facilitated high-resolution (70μm) quantification of residual strain in a YPSZ-porcelain dental prosthesis. In order to cross-validate this technique, the sequential ring-core focused ion beam and digital image correlation approach was implemented at a step size of 50μm. This semi-destructive technique exploits microscale strain relief to provide quantitative estimates of the near-surface residual strain. RESULTS: The two techniques were found to show highly comparable results. The residual strain within the veneer was found to be primarily tensile, with the highest magnitude stresses located at the YPSZ-porcelain interface where failure is known to originate. Oscillatory tensile and compressive stresses were also found in a direction parallel to the interface, likely to be induced by the multiple layering used during fabrication. SIGNIFICANCE: This study provides the insights required to improve prosthesis modelling, to develop new processing routes that minimise residual stress and ultimately to reduce prosthesis failure rates. The PDF approach also offers a powerful new technique for microscale strain quantification in amorphous materials.