Microstructural Patterns Research Articles

Optimization of Microstructure Patterning for Flexible Bioelectronics Application

Recent advancements in flexible electronics and wearable sensors have given biomedical technology a new edge overcoming the limitations of traditional rigid silicon-based electronics. Furthermore, high flexibility of these wearable sensors enables it to conformally sit over any uneven surface helping in accurate determination of any physical, chemical, or physiological parameter associate with the surface. Conventionally expensive micro/nano photolithography techniques under strict clean room conditions are used for the development of these flexible and wearable biomedical sensors with high degree of accuracy and sensitivity. However, the developed wearable sensors need not only be extremely sensitive, but also cost effective for its successful usage. To address this, the present work discusses the use of a photo-patternable UV sheet for realization of micro patterns over flexible copper cladded surface eliminating the need of costly clean room facilities. It demonstrates the standardization of various design geometries using the photo-patternable UV sheet over the flexible surface similar to photolithography process and involves optimization of the exposure timing of the UV sheets and their development time towards various design patterns over different thick film metal surfaces. Finally, patterned micro devices like micro-electrodes were successfully realized using the above process to ascertain its efficacy.

Novel Fabrication of 3-D Cell Laden Micro-Patterned Porous Structure on Cell Growth and Proliferation by Layered Manufacturing.

This study focuses on developing and characterizing a novel 3-dimensional cell-laden micro-patterned porous structure from a mechanical engineering perspective. Tissue engineering holds great promise for repairing damaged organs but faces challenges related to cell viability, biocompatibility, and mechanical strength. This research aims to overcome these limitations by utilizing gelatin methacrylate hydrogel as a scaffold material and employing a photolithography technique for precise patterned fabrication. The mechanical properties of the structure are of particular interest in this study. We evaluate its ability to withstand external forces through compression tests, which provide insights into its strength and stability. Additionally, structural integrity is assessed over time to determine its performance in in vitro and potential in vivo environments. We investigate cell viability and proliferation within the micro-patterned porous structure to evaluate the biological aspects. MTT assays and immunofluorescence staining are employed to analyze the metabolic activity and distribution pattern of cells, respectively. These assessments help us understand the effectiveness of the structure in supporting cell growth and tissue regeneration. The findings of this research contribute to the field of tissue engineering and provide valuable insights for mechanical engineers working on developing scaffolds and structures for regenerative medicine. By addressing challenges related to cell viability, biocompatibility, and mechanical strength, we move closer to realizing clinically viable tissue engineering solutions. The novel micro-patterned porous structure holds promise for applications in artificial organ development and lays the foundation for future advancements in large soft tissue construction.

Microemulsions supported by octyl monoglucoside and geraniol. 3. Microstructure & general pattern

This paper completes previous studies on the phase behaviour and microstructure of the quaternary microemulsion water – cyclohexane – n-octyl-β-D-glucoside (β-C8G1) – geraniol. The properties of this system are almost insensitive to temperature, while they can be tuned easily by adding an alcohol as co-surfactant. The addition of the alcohol changes the composition of the interfacial film, which, in turn, is the tuning parameter for the quaternary system. Studies of the phase behaviour together with SANS and NMR measurements allow drawing a quantitative picture of how the domain size ξ, the curvature H, and the interfacial tension σab depend on the composition of the interfacial film. The SANS data of both oil-in-water and water-in-oil droplet microemulsions recorded near the emulsification failure boundary were evaluated with the Generalised Indirect Fourier Transformation (GIFT), revealing a growth towards cylindrical structures when approaching the respective critical end point. We will show that the general behaviour of ternary and quaternary systems is equal if the appropriate tuning parameters are chosen. In addition, we will show that it is possible to apply the scaling description derived for temperature-dependent ternary systems to composition-dependent quaternary systems: plotting the reduced domain size, the reduced curvature and the reduced interfacial tension against the proper reduced tuning parameter, i.e., either the reduced temperature or the reduced interfacial composition, leads to one master curve for all systems.

Acoustic resonance effects and cavitation in SAW aerosol generation

The interaction of surface acoustic waves (SAWs) with liquids enables the production of aerosols with adjustable droplet sizes in the micrometer range expelled from a very compact source. Understanding the nonlinear acousto-hydrodynamics of SAWs with a regulated micro-scale liquid film is essential for acousto-microfluidics platforms, particularly aerosol generators. In this study, we demonstrate the presence of micro-cavitation in a MHz-frequency SAW aerosol generation platform, which is touted as a leap in aerosol technology with versatile application fields including biomolecule inhalation therapy, micro-chromatography and spectroscopy, olfactory displays, and material deposition. Using analysis methods with high temporal and spatial resolution, we demonstrate that SAWs stabilize spatially arranged liquid micro-domes atop the generator's surface. Our experiments show that these liquid domes become acoustic resonators with highly fluctuating pressure amplitudes that can even nucleate cavitation bubbles, as supported by analytical modeling. The observed fragmentation of liquid domes indicates the participation of three droplet generation mechanisms, including cavitation and capillary-wave instabilities. During aerosol generation, the cavitation bubbles contribute to the ejection of droplets from the liquid domes and also explain observed microstructural damage patterns on the chip surface eventually caused by cavitation-based erosion.

Strain-induced collagen denaturation is rate dependent in failure of cerebral arteries.

While soft tissues are commonly damaged by mechanical loading, the manifestation of this damage at the microstructural level is not fully understood. Specifically, while rate-induced stiffening has been previously observed in cerebral arteries, associated changes in microstructural damage patterns following high-rate loading are largely undefined. In this study, we stretched porcine middle cerebral arteries to failure at 0.01 and >150 s-1, both axially and circumferentially, followed by probing for denatured tropocollagen using collagen hybridizing peptide (CHP). We found that collagen fibrils aligned with the loading direction experienced less denaturation following failure tests at high than low rates. Others have demonstrated similar rate dependence in tropocollagen denaturation during soft tissue failure, but this is the first study to quantify this behavior using CHP and to report it for cerebral arteries. These findings may have significant implications for traumatic brain injury and intracranial balloon angioplasty. We additionally observed possible tropocollagen denaturation in vessel layers primarily composed of fibrils transversely aligned to the loading axis. To our knowledge, this is the first observation of collagen denaturation due to transverse loading, but further research is needed to confirm this finding. STATEMENT OF SIGNIFICANCE: Previous work shows that collagen hybridizing peptide (CHP) can be used to identify collagen molecule unfolding and denaturation in mechanically overloaded soft tissues, including the cerebral arteries. But experiments have not explored collagen damage at rates relevant to traumatic brain injury. In this work, we quantified collagen damage in cerebral arteries stretched to failure at both high and low rates. We found that the collagen molecule is less damaged at high than at low rates, suggesting that damage mechanisms of either the collagen molecule or other elements of the collagen superstructure are rate dependent. This work implies that arteries failed at high rates, such as in traumatic brain injury, will have different molecular-level damage patterns than arteries failed at low rates. Consequently, improved understanding of damage characteristics may be expanded in the future to better inform clinically relevant cases of collagen damage such as angioplasty and injury healing.

Physical properties and structural characteristics of particulate matter emitted from a diesel engine fueled with biodiesel blends

This research explores the influence of renewable fuels, including three kinds of biodiesel along with ethanol on the physical properties and structural characteristics of particulate matter (PM) emitted from a diesel engine in comparison with pure diesel. After adding 10 vol% of grape seed biodiesel, coffee biodiesel and eucalyptus oil into diesel, three biodiesel blended fuels (10% grape seed biodiesel (DGs10), 10% spent coffee ground biodiesel (DC10) and eucalyptus oil biodiesel (DEu10)) were produced and tested in this study. Besides, one ethanol blend containing 9 vol% of ethanol and 1 vol% of biodiesel (blend stabilizer) was also tested to do the comparison. In the present study, scanning transmission electron microscope (STEM) and scanning electron microscope (SEM) were employed for analyzing the microstructure, nanostructure and electron diffraction pattern of PM. Raman spectrometer (RS) was also used for the analysis of structural characterization of PM. In addition, several experimental instruments like microbalance, measuring cup, viscometer, oxygen bomb calorimeter and Gas Chromatography-Mass Spectrometer (GC-MS) were employed to detect the fuel properties, including density, heating value, viscosity, composition and cetane number. A conclusion can be drawn that both biodiesel blends and ethanol blend have a changing effect on the PM properties compared to pure diesel, where biodiesel blends have a slightly weaker influence than ethanol blend. Regarding the biodiesel blends, DGs10 has more impact than DC10 and DEu10 in changes of PM properties, particularly in the reduction of PM mass, making it a good candidate for renewable fuel for diesel engines.

Investigating the Relationship between Growth Rate, Shell Morphology, and Trace Element Composition of the Pacific Littleneck Clam (Leukoma staminea): Implications for Paleoclimate Reconstructions

Due to their robust preservation and widespread nature, marine bivalve shells are increasingly used as informative, high-resolution records of past environmental conditions. Unfortunately, few studies have investigated variability amongst individuals in a genetic cohort and throughout their ontogeny. We measured several morphological properties and the element patterning of 200-day-old juvenile Leukoma staminea (Conrad, 1837) grown in identical conditions from the same reproductive cohort. We hypothesized that slower shell growth would correspond to the reduced incorporation of trace/minor elements (Sr, Mg, and S) in the aragonite lattice, as has been documented in other biomineralizing marine invertebrates. Microprobe analyses of adult shells revealed higher levels of S, Sr, and Mg in the dark, slower-growing growth lines compared to the light, faster-growing increments, particularly in the inner shell layer, thus refuting our hypothesis. Moreover, elemental count variation within single adult shells generally tracked changes in shell microstructure (i.e., higher counts in prismatic microstructures) and growth line patterns, and these differences are detectable on a micrometer scale. Juvenile shells of different sizes showed variation in S, Sr, and Mg counts as well, but it was unclear whether the variability closely tracked changes in microstructure, body size, and/or growth line patterns. In all individuals, regardless of life stage, the outermost shell layer showed higher Sr and S count values, and these elements closely mirrored each other within individual shells. The results presented herein represent the first in-depth description of the shell mineralogy, microstructure, body size variability, and geochemical properties of modern L. staminea, a common eastern Pacific, shallow, infaunal bivalve, allowing for the rigorous evaluation of L. staminea shells as recorders of past environmental and biological change. Significant intraspecific variation in the young body size, growth band patterning, and elemental composition of individuals of the same age and genetic stock complicates the use of size alone as a proxy for age in historical studies. Additionally, elemental composition shifted from high to low values (for example, Sr ranging from ~190 to 100 counts) at a very fine (micrometer) scale within single shells, as evidenced by visible correlations between microstructure and elemental composition. While young L. staminea shells are likely not useful as archives of (paleo)environmental conditions, adult L. staminea shells are likely suitable if micrometer-scale variability in shell structure and chemistry is accounted for.

Suberic Acid-Based Supramolecular Metallogels of Ni(II), Zn(II), and Cd(II) for Anti-Pathogenic Activity and Semiconducting Diode Fabrication

The importance of three synthesized metallogels of suberic acid distinctly with nickel, zinc, and cadmium acetate salts has been uncovered. For the creation of these soft materials, N,N'-dimethyl formamide was utilized as a source of the trapped solvent. The synthesized metallogels display intriguing viscoelasticity, and the interpretation of experimental parameters obtained from rheological results advocates the gel behavior. Microstructural analysis combined with energy-dispersive X-ray confirms the occurrence of individual gel-developing constituents as observed in different hierarchical microstructural patterns. Significant variations in microstructural arrangements with diverse extent of supramolecular non-covalent patterns inside gel networks were perceived through field emission scanning electron microscopy, atomic force microscopy, and transmission electron microscopy analyses. Fourier transform infrared and electrospray ionization-mass spectral analyses and powder X-ray diffraction analysis of metallogel samples of different gel-establishing ingredients help to investigate the possible supramolecular interactions dictating the metallogel scaffolds. Thermogravimetric analysis of xerogel samples was collected from the synthesized metallogels to understand the thermal stability. These gel materials were characterized by their potential antibacterial efficiency. The potency of metallogels against selective Gram-positive and Gram-negative bacteria was visualized via a spectrophotometer. Human pathogens like Klebsiella pneumoniae (MTCC 109), Salmonella typhi (MTCC 733), Vibrio parahaemolyticus, Bacillus cereus (MTCC 1272), Lactobacillus fermentum (NCDO 955), and Staphylococcus aureus (MTCC 96) are employed in this study. Apart from the biological significance, our metallogels demonstrate as incredible diode performance of fabricated semiconducting systems, which exhibit a considerable amount of non-linearity demonstrating a non-ohmic conduction mechanism at room temperature in dark conditions. Device fabrication was achieved from these metallogels employing the sandwich model with indium tin oxide-coated glass substrates/metallogel/Al structure.

Comparative Study of Iron-Tailings-Based Cementitious Mortars with Incorporated Graphite Ore and Graphite Tailings: Strength Properties and Microstructure.

Graphite ore and graphite tailings were blended into iron-tailings-based cementitious mortars, and their mechanical properties and microstructure were experimentally investigated. The flexural and compressive strengths of the resulting material were tested to compare the effects of graphite ore and graphite tailings as supplementary cementitious materials and fine aggregates on the mechanical properties of iron-tailings-based cementitious mortars. Additionally, their microstructure and hydration products were mainly analyzed using scanning electronic microscope and X-ray powder diffraction techniques. The experimental results showed that the mechanical properties of the mortar material incorporating graphite ore were reduced due to the lubricating properties of graphite ore. As a result, the unhydrated particles and aggregates were not tightly bound to the gel phase, making the direct application of graphite ore in construction materials unfeasible. In the iron-tailings-based cementitious mortars prepared in this work, the optimal incorporation rate of graphite ore as a supplementary cementitious material was 4 wt%. The compressive strength of the optimal mortar test block after 28 days of hydration was 23.21 MPa, and the flexural strength was 7.76 MPa. The mechanical properties of the mortar block were found to be optimal with a graphite-tailings content of 40 wt% and an iron-tailings content of 10 wt%, resulting in a 28-day compressive strength of 48.8 MPa and a flexural strength of 11.7 MPa. By observing the microstructure and XRD pattern of the 28-day hydrated mortar block, it was determined that the hydration products of the mortar with graphite tailings as an aggregate included ettringite, Ca(OH)2, and C-A-S-H gel.

Multiscale modelling of the thermoelastic properties of alumina-zirconia ceramics for 3D printing

Additive manufacturing appears to facilitate the accurate manufacturing of alumina-zirconia technical ceramics. Nevertheless, the fine tuning of the manufacturing of these components by 3D printing requires an analysis of the parameters that influence their final thermoelastic properties. In this context, this work presents the application of (finite element-based) numerical procedures that aim at the prediction of the effective thermoelastic properties of 3D-printed alumina-zirconia ceramics. The numerical modelling considers three different scales: micro-, meso- and macroscale. The microscale corresponds to the microstructural level of, sintered at 1500 °C, slip-casted samples with different compositions of alumina-zirconia. On the other hand, the macroscale corresponds to the macrostructural level of porous lattice of 3D-printed ceramics, being defined at the mesoscale level by a periodic unit cell. Thus, an initial microstructural analysis (at microscale level) provides the influence of the alumina/zirconia ratio on the (macroscopically homogeneous and isotropic) material thermoelastic properties, which together with the definition of the geometry of a periodic unit cell (at mesoscale level), provides, by a second analysis (at both the meso- and macroscale levels), the coupled influence of material and geometry of the macrostructural lattice on the structural (macroscopically heterogeneous and anisotropic) thermoelastic properties. Moreover, experimental thermoelastic properties of the sintered slip-casted specimens were obtained for several alumina/zirconia ratios and analysed together with microstructure patterns. Prediction of the microstructural effective thermoelastic properties was also made using micromechanics and composite theory (analytical) models. All the numerical, experimental and analytical results for the microstructural level are presented and compared. Numerical results for the meso- and macrostructural levels are also presented.

Influence of 3D Microstructure Pattern and Infill Density on the Mechanical and Thermal Properties of PET-G Filaments.

This study aims to evaluate the thermal and mechanical performances of PET-G thermoplastics with different 3D microstructure patterns and infill densities. The production costs were also estimated to identify the most cost-effective solution. A total of 12 infill patterns were analysed, including Gyroid, Grid, Hilbert curve, Line, Rectilinear, Stars, Triangles, 3D Honeycomb, Honeycomb, Concentric, Cubic, and Octagram spiral with a fixed infill density of 25%. Different infill densities ranging from 5% to 20% were also tested to determine the best geometries. Thermal tests were conducted in a hotbox test chamber and mechanical properties were evaluated using a series of three-point bending tests. The study used printing parameters to meet the construction sector's specific needs, including a larger nozzle diameter and printing speed. The internal microstructures led to variations of up to 70% in thermal performance and up to 300% in mechanical performance. For each geometry, the mechanical and thermal performance was highly correlated with the infill pattern, where higher infill improved thermal and mechanical performances. The economic performance showed that, in most cases, except for the Honeycomb and 3D Honeycomb, there were no significant cost differences between infill geometries. These findings can provide valuable insights for selecting the optimal 3D printing parameters in the construction industry.

Effects of surface topography through laser texturing on the surface characteristics of zirconia-based dental materials: surface hydrophobicity, antibacterial behavior, and cellular response

The continuous need for high-performance implants that provide significant biological properties has led to extensive research into the topographic patterns of bioceramics in recent years. Their excellent aesthetics, biocompatibility, low plaque affinity, and ability to reproduce a natural-looking appearance have contributed to their success in dentistry. 3 mol% Yttria-stabilized zirconia (3YSZ) is gaining popularity as a material for dental implants due to its excellent mechanical properties and minimal degradation when exposed to body temperature. However, such materials show limited biological and antibacterial performance for dental applications. The purpose of this work was to develop microtopographies on the surface of 3YSZ ceramic by laser ablation technique, in order to improve its biological response and antibacterial behaviors. Two types of microtextures, including micro-grooves and micro-channels geometries were fabricated onto the zirconia ceramics using the laser ablation technique. The effects of different microtextures on the wettability, biological and antibacterial behaviors of 3YSZ ceramics were studied. The results indicate that all of the microstructure patterns are capable of improving the performance of 3YSZ. Wettability is a decisive factor that determines the antibacterial performance of textured zirconia ceramics. The microtextured surfaces all display hydrophobic behavior, thus yielding an effective improvement of antibacterial performance for 3YSZ ceramics. Cell-surface interactions were assessed for 7 days on both zirconia textured surfaces and a nontextured control with pre-osteoblast MC3T3-E1 cells. The obtained results showed the positive influence of textured zirconia surfaces on cell biological response.

Patterns of risk-Using machine learning and structural neuroimaging to identify pedophilic offenders.

Child sexual abuse (CSA) has become a focal point for lawmakers, law enforcement, and mental health professionals. With high prevalence rates around the world and far-reaching, often chronic, individual, and societal implications, CSA and its leading risk factor, pedophilia, have been well investigated. This has led to a wide range of clinical tools and actuarial instruments for diagnosis and risk assessment regarding CSA. However, the neurobiological underpinnings of pedosexual behavior, specifically regarding hands-on pedophilic offenders (PO), remain elusive. Such biomarkers for PO individuals could potentially improve the early detection of high-risk PO individuals and enhance efforts to prevent future CSA. To use machine learning and MRI data to identify PO individuals. From a single-center male cohort of 14 PO individuals and 15 matched healthy control (HC) individuals, we acquired diffusion tensor imaging data (anisotropy, diffusivity, and fiber tracking) in literature-based regions of interest (prefrontal cortex, anterior cingulate cortex, amygdala, and corpus callosum). We trained a linear support vector machine to discriminate between PO and HC individuals using these WM microstructure data. Post hoc, we investigated the PO model decision scores with respect to sociodemographic (age, education, and IQ) and forensic characteristics (psychopathy, sexual deviance, and future risk of sexual violence) in the PO subpopulation. We assessed model specificity in an external cohort of 53 HC individuals. The classifier discriminated PO from HC individuals with a balanced accuracy of 75.5% (sensitivity = 64.3%, specificity = 86.7%, P 5000 = 0.018) and an out-of-sample specificity to correctly identify HC individuals of 94.3%. The predictive brain pattern contained bilateral fractional anisotropy in the anterior cingulate cortex, diffusivity in the left amygdala, and structural prefrontal cortex-amygdala connectivity in both hemispheres. This brain pattern was associated with the number of previous child victims, the current stance on sexuality, and the professionally assessed risk of future sexual violent reoffending. Aberrant white matter microstructure in the prefronto-temporo-limbic circuit could be a potential neurobiological correlate for PO individuals at high-risk of reoffending with CSA. Although preliminary and exploratory at this point, our findings highlight the general potential of MRI-based biomarkers and particularly WM microstructure patterns for future CSA risk assessment and preventive efforts.

Micromechanical, corrosion and wet sliding wear behaviours of Co-28Cr-6Mo alloy: Wrought vs. LPBF

The work is dedicated to the comparative study of a Co-28Cr-6Mo alloy fabricated by two methods (forging and laser bed fusion (LPBF)), in terms of micro-mechanical, corrosion, and tribological properties. The wrought alloy had an ε-HCP (60.4 vol%)+ γ-FCC structure with a grain size of 43.9 ± 7.1 µm and a cast-based dendritic pattern. The LPBF alloy presented a γ-FCC (72.8 vol%)+ ε-HCP structure featuring three main microstructural patterns: (1) melt pools and columnar grains, (2) a solidification cellular network, and (3) dislocations walls and strain-aged elemental segregations. The solidification of the alloys was accompanied by preferential segregations of Mo and Cr in the interdendritic areas (wrought specimen) and along the cell boundaries (LPBF specimen) with an increased (by 1.7–1.8 wt%) content of each element. The hierarchical cellular structure of the LPBF alloy with a cell size of 0.60 ± 0.05 µm ensured increased properties as compared to the wrought alloy, specifically: elastic modulus - by 6 GPa, hardness - by 0.93 GPa, wear resistance under sliding in simulated body fluid (SBF) - by 25%. Both alloys exhibited similar electrochemical behaviour, featuring true passivation, low corrosion current densities (of the order of 10–4 mA/cm2) and very high resistance to localized corrosion. Despite a more complicated and finer microstructure, the LPBF alloy presented (moderately) lower corrosion current density and passive current density as compared to the wrought alloy attributed to a lower level of residual stresses and a lower amount of martensite.

Influence of Ti elements on the evolution of microstructure, mechanical properties and thermal stability of Al-Cu alloy

This paper compares the evolution patterns of microstructure, mechanical properties and heat exposure response behavior of alloys with low (0.15 wt%) and high Ti (0.75 wt%) content prepared by conventional casting processes. The results show that the alloy with high Ti content has slightly finer grains and no improvement in the thermal stability of the θ' precipitates compared to the low Ti content alloy. Moreover, after exposing the as-aged alloy to 300 ℃ for 100 h, the high Ti content alloy exhibits higher tensile strength at room temperature, attributing to the reinforcement effect of Al3Ti nanoparticles. The results of geometric phase analysis and transmission electron microscope images reveal that the compressive strain field occurring on the Al3Ti/matrix interface can validly block the movement of dislocations, thus hardening the alloy. Finally, the classical nucleation theory was referred to explain the difference on the thermal exposure response behavior of two alloys with various Ti contents at 300 ℃. With increasing thermal exposure time, the stiffening role of the Al3Ti nanoparticles gradually overcomes the softening behavior caused by the destabilization of coarsened θ' and becomes the dominant factor governing the mechanical properties of the alloy. The theoretical analysis is consistent with the microstructure and the thermal exposure hardness response behavior.

Maskless lithography for large area patterning of three-dimensional microstructures with application on a light guiding plate.

This paper presents a maskless lithography system that can perform three-dimensional (3D) ultraviolet (UV) patterning on a photoresist (PR) layer. After PR developing processes, patterned 3D PR microstructures over a large area are obtained. This maskless lithography system utilizes an UV light source, a digital micromirror device (DMD), and an image projection lens to project a digital UV image on the PR layer. The projected UV image is then mechanically scanned over the PR layer. An UV patterning scheme based on the idea of obliquely scanning and step strobe lighting (OS3L) is developed to precisely control the spatial distribution of projected UV dose, such that desired 3D PR microstructures can be obtained after PR development. Two types of concave microstructures with truncated conical and nuzzle-shaped cross-sectional profiles are experimentally obtained over a patterning area of 160 ×115 mm2. These patterned microstructures are then used for replicating nickel molds and for mass-production of light-guiding plates used in back-lighting and display industry. Potential improvements and advancements of the proposed 3D maskless lithography technique for future applications will be addressed.

Substrate‐Independent Electrohydrodynamic Jet Printing with Dual‐Ring Electrostatic Focusing Structure

AbstractElectrohydrodynamic jet (E‐Jet) printing is one of the most effective methods for fabricating micro/nanostructures due to its high‐resolution, broad material adaptability, and simple process. However, printing high‐resolution patterns on curved or insulated substrates still is of a great challenge because it is quite difficult to keep the electric field distribution stable between the nozzle and the substrate during the printing process. To address these issues, a dual‐ring electrostatic focused electrohydrodynamic jet (DEFEJ) printing method is proposed. In this technique, a microtip with a radius of curvature (ROC) of several micrometers is placed in a conductive dual‐ring structure to form the built‐in electrostatic focusing and drive the Taylor cone. The high‐speed jets then fall on the substrate due to their own motion inertia, eliminating the influence of the substrate curvature and its conductivity on the electric field distribution. Submicrometer droplets with an average diameter of about 0.83 µm are obtained using a 10‐µm‐ROC microtip. In addition, high‐resolution microstructure patterns are also printed on substrates with different conductivity and curvature. This DEFEJ printing method not only has the same printing accuracy as conventional E‐Jet printing, but also can significantly increase the adaptability of E‐Jet printing to different substrates.

A pore-level multiscale method for the elastic deformation of fractured porous media

Pore-scale models are useful for understanding and upscaling the mechanical deformation of fractured porous media. The highest fidelity solutions are obtained by direct numerical simulation (DNS), in which the governing equations are discretized and solved with a fine-grid solver (e.g., finite elements) over a 3D image (e.g., X-ray) of a porous sample. However, the downside of DNS is its high computational cost. We present a pore-level multiscale method (PLMM) that approximates DNS efficiently and with controllable accuracy in modeling the linear elastic response of porous solids with arbitrary microstructure and crack pattern. PLMM decomposes the solid into subdomains, over which local basis and correction functions are built. These functions are then coupled with a global problem to yield an approximate solution, whose errors can be iteratively corrected. A key feature of PLMM is that the decomposition need not conform to the cracks, unlike a previous formulation by the authors. This paves the way towards solving crack nucleation and growth problems in the future without the need to dynamically update the decomposition. We represent cracks diffusely using a phase-field variable and explore three strategies for capturing them through either the basis or correction functions. The implications of each strategy on the convergence rate and computational cost are analyzed.

A micromechanical constitutive model of high-temperature shape memory alloys

In this work, a new micromechanical constitutive model is constructed for high-temperature shape memory alloys. Different from the classical constitutive models, the microstructural patterns, heterogeneities of stress and strain fields at the microscopic scale are addressed. In the proposed model, three different inelastic deformation mechanisms, i.e., reversible martensitic transformation, irreversible transformation-induced plasticity, viscoplasticity, as well as their complex interactions, are considered. In addition to the well-known austenite and martensite phases, a new austenite-martensite interface phase is introduced to address the high local stress induced by the martensitic transformation. The modified Mori-Tanaka's homogenization scheme and Hill's interfacial operator are employed to determine the non-uniform stress fields of the three phases. To satisfy the thermodynamic compatibility of the proposed model, the driving forces and evolution equations of the three inelastic deformation mechanisms are derived based on the constructed Helmholtz free energy and the fundamental laws of irreversible thermodynamics. Inheritances of the plastic deformation induced by moving austenite-martensite (A-M) interface during repeated martensitic transformation and its reverse are incorporated. Temperature evolution caused by internal heat production and heat exchange with the ambient medium is also addressed. To validate the capability of the new constructed model, the predicted results of creep behavior and stress-assisted two-way shape memory effect of NiTiPd high-temperature shape memory alloys are compared with the experimental ones. The proposed model provides a theoretical tool for simultaneously analyzing the deformation behaviors at the macroscopic scale and underlying mechanisms at the microscopic scale.

Rapid growth in Late Cretaceous sea turtles reveals life history strategies similar to extant leatherbacks.

Modern sea turtle long bone osteohistology has been surprisingly well-studied, as it is used to understand sea turtle growth and the timing of life history events, thus informing conservation decisions. Previous histologic studies reveal two distinct bone growth patterns in extant sea turtle taxa, with Dermochelys (leatherbacks) growing faster than the cheloniids (all other living sea turtles). Dermochelys also has a unique life history compared to other sea turtles (large size, elevated metabolism, broad biogeographic distribution, etc.) that is likely linked to bone growth strategies. Despite the abundance of data on modern sea turtle bone growth, extinct sea turtle osteohistology is virtually unstudied. Here, long bone microstructure of the large, Cretaceous sea turtle Protostega gigas is examined to better understand its life history. Humeral and femoral analysis reveals bone microstructure patterns similar to Dermochelys with variable but sustained rapid growth through early ontogeny. Similarities between Progostegea and Dermochelys osteohistology suggest similar life history strategies like elevated metabolic rates with rapid growth to large body size and sexual maturity. Comparison to the more basal protostegid Desmatochelys indicates elevated growth rates are not present throughout the entire Protostegidae, but evolved in larger and more derived taxa, possibly in response to Late Cretaceous ecological changes. Given the uncertainties in the phylogenetic placement of the Protostegidae, these results either support convergent evolution towards rapid growth and elevated metabolism in both derived protostegids and dermochelyids, or a close evolutionary relationship between the two taxa. Better understanding the evolution and diversity of sea turtle life history strategies during the Late Cretaceous greenhouse climate can also impact current sea turtle conservation decisions.