From microlattices to 3d microprinting of multiphase micro-components: Resolution limits and mechanical properties under extreme conditions

Two-photon lithography (TPL) enables the fabrication of metamaterials such as polymer micro-lattices. They are designed to achieve their envisioned mechanical properties through stretching and bending of individual trusses. Several novel approaches are developed here to a) directly print metal microlattices, b) fabricate multiphase composite microlattices and c) shrink the truss diameter below the diffraction limit of light, all with the ultimate goal to enable fabrication of a full dense material with microprinted 3D architecture of different phases. Copper microlattices and micropillars with truss diameters in the few micron range were printed directly via fluid AFM based local electroplating [1]. It was identified that microcrystalline copper micropillars deform in a singleshear like manner exhibiting a weak strain rate dependence at all strain rates. Ultrafine grained (UFG) copper micropillars, however, deform homogenously via barreling and show strong rate-dependence and small activation volumes at strain rates up to ∼ 0.1 s−1, suggesting dislocation nucleation as the deformation mechanism. At higher strain rates, yield stress saturates remarkably, resulting in a decrease of strain rate sensitivity implying a transition in deformation mechanism to collective dislocation nucleation. Finally, the copper microlattices are shown to increase in strength if conformally coated with Nickel with thicknesses in the several 100nm range. Please click Download on the upper right corner to see the full abstract

On deconvolution problems: numerical aspects

An optimal algorithm is described for solving the deconvolution problem of the form ${\bf k}u:=\int_0^tk(t-s)u(s)ds=f(t)$ given the noisy data $f_\delta$, $||f-f_\delta||\leq \delta.$ The idea of the method consists of the representation ${\bf k}=A(I+S)$, where $S$ is a compact operator, $I+S$ is injective, $I$ is the identity operator, $A$ is not boundedly invertible, and an optimal regularizer is constructed for $A$. The optimal regularizer is constructed using the results of the paper MR 40#5130.Comment: 7 figure

Temperature-dependent dynamic plasticity of micro-scale fused silica

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Assessing minipig compact jawbone quality at the microscale

Preclinical studies often require animal models for in vivo experiments. Particularly in dental research, pig species are extensively used due to their anatomical similarity to humans. However, there is a considerable knowledge gap on the multiscale morphological and mechanical properties of the miniature pigs’ jawbones, which is crucial for implant studies and a direct comparison to human tissue. In the present work, we demonstrate a multimodal framework to assess the jawbone quantity and quality for a minipig animal model that could be further extended to humans. Three minipig genotypes, commonly used in dental research, were examined: Yucatan, G ̈ottingen, and Sinclair. Three animals per genotype were tested. Cortical bone samples were extracted from the premolar region of the mandible, opposite to the teeth growth. Global morphological, compositional, and mechanical properties were assessed using micro-computed tomography (micro-CT) together with Raman spectroscopy and nano- indentation measurements, averaged over the sample area. Local mineral-mechanical relationships were investigated with the site-matched Raman spectroscopy and micropillar compression tests. For this, a novel femtosecond laser ablation protocol was developed, allowing high-throughput micropillar fabrication and testing without exposure to high vacuum. At the global averaged sample level, bone relative mineralization demonstrated a significant difference between the genotypes, which was not observed from the complementary micro-CT measurements. Moreover, bone hardness measured by nanoindentation showed a positive trend with the relative mineralization. For all genotypes, significant differences between the relative mineralization and elastic properties were more pronounced within the osteonal regions of cortical bone. Site-matched micropillar compression and Raman spectroscopy highlighted the differences between the genotypes’ yield stress and mineral to matrix ratios. The methods used at the global level (averaged over sample area) could be potentially correlated to the medical tools used to assess jawbone toughness and morphology in clinics. On the other hand, the local analysis methods can be applied to quantify compressive bone mechanical properties and their relationship to bone mineralization

Composition and micromechanical properties of the femoral neck compact bone in relation to patient age, sex and hip fracture occurrence

Current clinical methods of bone health assessment depend to a great extent on bone mineral density (BMD) measurements. However, these methods only act as a proxy for bone strength and are often only carried out after the fracture occurs. Besides BMD, composition and tissue-level mechanical properties are expected to affect the whole bone's strength and toughness. While the elastic properties of the bone extracellular matrix (ECM) have been extensively investigated over the past two decades, there is still limited knowledge of the yield properties and their relationship to composition and architecture. In the present study, morphological, compositional and micropillar compression bone data was collected from patients who underwent hip arthroplasty. Femoral neck samples from 42 patients were collected together with anonymous clinical information about age, sex and primary diagnosis (coxarthrosis or hip fracture). The femoral neck cortex from the inferomedial region was analyzed in a site-matched manner using a combination of micromechanical testing (nanoindentation, micropillar compression) together with micro-CT and quantitative polarized Raman spectroscopy for both morphological and compositional characterization. Mechanical properties, as well as the sample-level mineral density, were constant over age. Only compositional properties demonstrate weak dependence on patient age: decreasing mineral to matrix ratio (p = 0.02, R2 = 0.13, 2.6 % per decade) and increasing amide I sub-peak ratio I~1660/I~1683 (p = 0.04, R2 = 0.11, 1.5 % per decade). The patient's sex and diagnosis did not seem to influence investigated bone properties. A clear zonal dependence between interstitial and osteonal cortical zones was observed for compositional and elastic bone properties (p  200). The proposed classification algorithm together with the output database of bone tissue properties can be used for the future comparison of existing methods to evaluate bone quality as well as to form a better understanding of the mechanisms through which bone tissue is affected by aging or disease

Crumbling Reefs and Cold-Water Coral Habitat Loss in a Future Ocean: Evidence of “Coralporosis” as an Indicator of Habitat Integrity

Ocean acidification is a threat to the net growth of tropical and deep-sea coral reefs, due to gradual changes in the balance between reef growth and loss processes. Here we go beyond identification of coral dissolution induced by ocean acidification and identify a mechanism that will lead to a loss of habitat in cold-water coral reef habitats on an ecosystem-scale. To quantify this, we present in situ and year-long laboratory evidence detailing the type of habitat shift that can be expected (in situ evidence), the mechanisms underlying this (in situ and laboratory evidence), and the timescale within which the process begins (laboratory evidence). Through application of engineering principals, we detail how increased porosity in structurally critical sections of coral framework will lead to crumbling of load-bearing material, and a potential collapse and loss of complexity of the larger habitat. Importantly, in situ evidence highlights that cold-water corals can survive beneath the aragonite saturation horizon, but in a fundamentally different way to what is currently considered a biogenic cold-water coral reef, with a loss of the majority of reef habitat. The shift from a habitat with high 3-dimensional complexity provided by both live and dead coral framework, to a habitat restricted primarily to live coral colonies with lower 3-dimensional complexity represents the main threat to cold-water coral reefs of the future and the biodiversity they support. Ocean acidification can cause ecosystem-scale habitat loss for the majority of cold-water coral reefs.BN/Marie-Eve Aubin-Tam La

Regularized energy-dependent solar flare hard x-ray spectral index

The deduction from solar flare X-ray photon spectroscopic data of the energy dependent model-independent spectral index is considered as an inverse problem. Using the well developed regularization approach we analyze the energy dependency of spectral index for a high resolution energy spectrum provided by Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The regularization technique produces much smoother derivatives while avoiding additional errors typical of finite differences. It is shown that observations imply a spectral index varying significantly with energy, in a way that also varies with time as the flare progresses. The implications of these findings are discussed in the solar flare context.Comment: 13 pages; 5 figures, Solar Physics in pres

Micro- and nanomechanics of mineralised collagen fibre elasto-plasticity

Musculoskeletal diseases such as osteoporosis, osteoarthritis and bone cancer pose a significant social and economic challenge in ageing societies worldwide. In digital healthcare, computational models could be a cornerstone in mitigating these challenges by facilitating, for example, personalised bone strength analyses or manufacturing of bespoke implants. Such models, however, critically depend on understanding the complex characteristics of bone as a material. Currently, there is limited knowledge on the elasto-plastic behaviour of bone’s fundamental mechanical building block, the mineralised collagen fibre. Especially the load transfer between mineralised collagen fibrils and mineral particles, its main mechanical components, is unclear. Therefore, we aimed at (i) simultaneously quantifying the fibre, fibril and mineral deformation using a micro- and nanomechanical testing protocol, (ii) formulating a statistical constitutive model to explain the fibre behaviour and the load transfer between its constituents as well as (iii) using (i) and (ii) to test under quasi-physiologic conditions. Laser manufacturing and focused ion beam milling were used to extract micrometre sized samples from individual mineralised collagen fibres of mineralised turkey leg tendon, a model system for bone. These micropillars were tested in an experimental set-up that combined micropillar compression and X-ray scattering or diffraction under dry and rehydrated conditions. An elasto-plastic statistical constitutive model was developed in which two shear lag models simulate the stress transfer between fibre, fibril and mineral. Ultrastructural features were included based on nanoscale imaging data. Experimental data show small fibril and mineral strains compared to the fibre strain. This was related to localised strains and heterogeneous fibril deformations due to a gradual nonlinear fibril recruitment. By incorporating this recruitment, the model can explain the elasto-plastic fibre behaviour as seen in dry and rehydrated experiments including the load transfer between fibre, fibrils and mineral particles with an accuracy of 95% for dry and 89% for rehydrated conditions. The model provides distributions for the micro- and nanomechanical responses and, thus, directly simulates strain ratios determined experimentally by in-situ mechanical testing and X-ray scattering/diffraction measurements. Experiment and model allowed it to identify the micro- and nanome-chanical behaviour of the fibril array. Rehydration decreased fibre stiffness by 60%, yield and compressive strength by 75%, and fibril stiffness by 25%. The new insights into the micro- and nanoscale elasto-plastic behaviour of bone’s fundamental mechanical building block help to understand bone’s hierarchical material mechanics. Results may be used to inform computational models for nonlinear bone strength analyses as well as the design of tissue engineered bio-inspired implants.Engineering and Physical Sciences Research Council (EPSRC