Prevalence of hepatitis B virus infection and its associated factors among students in N'Djamena, Chad.

INTRODUCTION: Infection by hepatitis B virus (HBV) is a major issue in public health. The prevalence of HBV in Chad is 12.4%, all age groups considered. Here, we aimed to determine the prevalence of HBV and its associated factors among university students in N'Djamena, the country's capital. METHODS: A cross-sectional survey of students at either the University of N'djamena or Emi Koussi University was conducted from 3 to 23 July 2021. All participating students provided signed, informed consent and were included in the study consecutively. Blood samples were collected, and serum tested for hepatitis B surface antigen (HBsAg) using the Determine HBsAg rapid test kit, with confirmation of positive tests on an Abbott Architect i1000SR analyzer. Descriptive analysis and logistic regression were used to determine associations between the outcome variable and independent/covariate variables. RESULTS: A total of 457 students with a median age of 24 years were included across different faculties. The prevalence of HBV infection was 14.87% (68/457). Most students (75%) were aged 25 years or less. Unprotected sex was reported by 64.9% of the students and multiple sexual partners by 53.6%. Furthermore, 45.7% of them reported having no knowledge of hepatitis B. Having an HBsAg-positive mother (AOR: 2.11), having a history of transcutaneous medical procedures (AOR: 2.97) and living with a family (AOR: 4.63) were significantly associated with HBV status. Age ≥26 years appeared as a protective factor (AOR = 0.41). CONCLUSION: Our study detected a high, 14.87% prevalence of HBV infection among students in N'djamena, Chad, and shed light on its associated factors. HBV prevention strategies should include raising awareness among students, making full hepatitis vaccination mandatory before children begin school, promoting mass screening to identify and treat chronic HBV carriers and reduce transmission, and reducing the cost of vaccination.

Nanomechanical testing in drug delivery: Theory, applications, and emerging trends.

Mechanical properties play a central role in drug formulation development and manufacturing. Traditional characterization of mechanical properties of pharmaceutical solids relied mainly on large compacts, instead of individual particles. Modern nanomechanical testing instruments enable quantification of mechanical properties from the single crystal/particle level to the finished tablet. Although widely used in characterizing inorganic materials for decades, nanomechanical testing has been relatively less employed to characterize pharmaceutical materials. This review focuses on the applications of existing and emerging nanomechanical testing methods in characterizing mechanical properties of pharmaceutical solids to facilitate fast and cost-effective development of high quality drug products. Testing of pharmaceutical materials using nanomechanical techniques holds potential to develop fundamental knowledge in the structure-property relationships of molecular solids, with implications for solid form selection, milling, formulation design, and manufacturing. We also systematically discuss pitfalls and useful tips during sample preparation and testing for reliable measurements from nanomechanical testing.

Simultaneous High-Strength and Deformable Nanolaminates With Thick Biphase Interfaces.

Two-phase nanolaminates are known for their high strength, yet they suffer from loss of ductility. Here, we show that broadening heterophase interfaces into "3D interfaces" as thick as the individual layers breaks this strength-ductility trade-off. In this work, we use micropillar compression and transmission electron microscopy to examine the processes underlying this breakthrough mechanical performance. The analysis shows that the 3D interfaces stifle flow instability via shear band formation through their interaction with dislocation pileups. To explain this observation, we use phase field dislocation dynamics (PFDD) simulations to study the interaction between a pileup and a 3D interface. Results show that when dislocation pileups fall below a characteristic size relative to the 3D interface thickness, transmission across interfaces becomes significantly frustrated. Our work demonstrates that 3D interfaces attenuate pileup-induced stress concentrations, preventing shear localization and offering an alternative way to enhanced mechanical performance.

3D Periodic and Interpenetrating Tungsten-Silicon Oxycarbide Nanocomposites Designed for Mechanical Robustness.

Metal-ceramic nanocomposites exhibit exceptional mechanical properties with a combination of high strength, toughness, and hardness that are not achievable in monolithic metals or ceramics, which make them valuable for applications in fields such as the aerospace and automotive industries. In this study, interpenetrating nanocomposites of three-dimensionally ordered macroporous (3DOM) tungsten-silicon oxycarbide (W-SiOC) were prepared, and their mechanical properties were investigated. In these nanocomposites, the crystalline tungsten and amorphous silicon oxycarbide phases both form continuous and interpenetrating networks, with some discrete free carbon nanodomains. The W-SiOC material inherits the periodic structure from its 3DOM W matrix, and this periodic structure can be maintained up to 1000 °C. In situ SEM micropillar compression tests demonstrated that the 3DOM W-SiOC material could sustain a maximum average stress of 1.1 GPa, a factor of 22 greater than that of the 3DOM W matrix, resulting in a specific strength of 640 MPa/(Mg/m3) at 30 °C. Deformation behavior of the developed 3DOM nanocomposite in a wide temperature range (30-575 °C) was investigated. The deformation mode of 3DOM W-SiOC exhibited a transition from fracture-dominated deformation at low temperatures to plastic deformation above 425 °C.

Effects of Phase Purity and Pore Reinforcement on Mechanical Behavior of NU-1000 and Silica-Infiltrated NU-1000 Metal-Organic Frameworks.

Metal-organic framework (MOF) materials have shown promise in many applications, ranging from gas storage to absorption and catalysis. Because of the high porosity and low density of many MOFs, densification methods such as pelletization and extrusion are needed for practical use and for commercialization of MOF materials. Therefore, it is important to elucidate the mechanical properties of MOFs and to develop methods of further enhancing their mechanical strength. Here, we demonstrate the influence of phase purity and the presence of a pore-reinforcing component on elastic modulus and yield stress of NU-1000 MOFs through nanoindentation methods and finite element simulation. Three types of NU-1000 single crystals were compared: phase-pure NU-1000 prepared with biphenyl-4-carboxylic acid as a modulator (NU-1000-bip), NU-1000 prepared with benzoic acid as a modulator (NU-1000-ben), which results in an additional, denser impurity phase of NU-901, and NU-1000-bip whose mesopores were infiltrated with silica (SiOx(OH)y@NU-1000) by nanocasting methods. By maintaining phase purity and minimizing defects, the elastic modulus could be enhanced by nearly an order of magnitude: phase-pure NU-1000-bip crystals exhibited an elastic modulus of 21 GPa, whereas the value for NU-1000-ben crystals was only 3 GPa. The introduction of silica into the mesopores of NU-1000-bip did not strongly affect the measured elastic modulus (19 GPa) but significantly increased the load at failure from 2000 µN to 3000-4000 µN.

Probing nanoscale damage gradients in ion-irradiated metals using spherical nanoindentation.

We discuss and demonstrate the application of recently developed spherical nanoindentation stress-strain protocols in characterizing the mechanical behavior of tungsten polycrystalline samples with ion-irradiated surfaces. It is demonstrated that a simple variation of the indenter size (radius) can provide valuable insights into heterogeneous characteristics of the radiation-induced-damage zone. We have also studied the effect of irradiation for the different grain orientations in the same sample.

Strong, Ductile, and Thermally Stable bcc-Mg Nanolaminates.

Magnesium has attracted attention worldwide because it is the lightest structural metal. However, a high strength-to-weight ratio remains its only attribute, since an intrinsic lack of strength, ductility and low melting temperature severely restricts practical applications of Mg. Through interface strains, the crystal structure of Mg can be transformed and stabilized from a simple hexagonal (hexagonal close packed hcp) to body center cubic (bcc) crystal structure at ambient pressures. We demonstrate that when introduced into a nanocomposite bcc Mg is far more ductile, 50% stronger, and retains its strength after extended exposure to 200 C, which is 0.5 times its homologous temperature. These findings reveal an alternative solution to obtaining lightweight metals critically needed for future energy efficiency and fuel savings.

Adhesion of voids to bimetal interfaces with non-uniform energies.

Interface engineering has become an important strategy for designing radiation-resistant materials. Critical to its success is fundamental understanding of the interactions between interfaces and radiation-induced defects, such as voids. Using transmission electron microscopy, here we report an interesting phenomenon in their interaction, wherein voids adhere to only one side of the bimetal interfaces rather than overlapping them. We show that this asymmetrical void-interface interaction is a consequence of differing surface energies of the two metals and non-uniformity in their interface formation energy. Specifically, voids grow within the phase of lower surface energy and wet only the high-interface energy regions. Furthermore, because this outcome cannot be accounted for by wetting of interfaces with uniform internal energy, our report provides experimental evidence that bimetal interfaces contain non-uniform internal energy distributions. This work also indicates that to design irradiation-resistant materials, we can avoid void-interface overlap via tuning the configurations of interfaces.

Spray-Dried Multiscale Nano-biocomposites Containing Living Cells.

Three-dimensional encapsulation of cells within nanostructured silica gels or matrices enables applications as diverse as biosensors, microbial fuel cells, artificial organs, and vaccines; it also allows the study of individual cell behaviors. Recent progress has improved the performance and flexibility of cellular encapsulation, yet there remains a need for robust scalable processes. Here, we report a spray-drying process enabling the large-scale production of functional nano-biocomposites (NBCs) containing living cells within ordered 3D lipid-silica nanostructures. The spray-drying process is demonstrated to work with multiple cell types and results in dry powders exhibiting a unique combination of properties including highly ordered 3D nanostructure, extended lipid fluidity, tunable macromorphologies and aerodynamic diameters, and unexpectedly high physical strength. Nanoindentation of the encasing nanostructure revealed a Young's modulus and hardness of 13 and 1.4 GPa, respectively. We hypothesized this high strength would prevent cell growth and force bacteria into viable but not culturable (VBNC) states. In concordance with the VBNC state, cellular ATP levels remained elevated even over eight months. However, their ability to undergo resuscitation and enter growth phase greatly decreased with time in the VBNC state. A quantitative method of determining resuscitation frequencies was developed and showed that, after 36 weeks in a NBC-induced VBNC, less than 1 in 10,000 cells underwent resuscitation. The NBC platform production of large quantities of VBNC cells is of interest for research in bacterial persistence and screening of drugs targeting such cells. NBCs may also enable long-term preservation of living cells for applications in cell-based sensing and the packaging and delivery of live-cell vaccines.

Effects of helium implantation on the tensile properties and microstructure of Ni73P27 metallic glass nanostructures.

We report fabrication and nanomechanical tension experiments on as-fabricated and helium-implanted ∼130 nm diameter Ni73P27 metallic glass nanocylinders. The nanocylinders were fabricated by a templated electroplating process and implanted with He(+) at energies of 50, 100, 150, and 200 keV to create a uniform helium concentration of ∼3 atom % throughout the nanocylinders. Transmission electron microscopy imaging and through-focus analysis reveal that the specimens contained ∼2 nm helium bubbles distributed uniformly throughout the nanocylinder volume. In situ tensile experiments indicate that helium-implanted specimens exhibit enhanced ductility as evidenced by a 2-fold increase in plastic strain over as-fabricated specimens with no sacrifice in yield and ultimate tensile strengths. This improvement in mechanical properties suggests that metallic glasses may actually exhibit a favorable response to high levels of helium implantation.

The critical role of grain orientation and applied stress in nanoscale twinning.

Numerous recent studies have focused on the effects of grain size on deformation twinning in nanocrystalline fcc metals. However, grain size alone cannot explain many observed twinning characteristics. Here we show that the propensity for twinning is dependent on the applied stress, grain orientation and stacking fault energy. The lone factor for twinning dependent on grain size is the stress necessary to nucleate partial dislocations from a boundary. We use bulk processing of controlled nanostructures coupled with unique orientation mapping at the nanoscale to show the profound effect of crystal orientation on deformation twinning. Our theoretical model reveals an orientation-dependent critical threshold stress for twinning, which is presented in the form of a generalized twinnability map. Our findings provide a newfound orientation-based explanation for the grain size effect: as grain size decreases the applied stress needed for further deformation increases, thereby allowing more orientations to reach the threshold stress for twinning.

Emergence of stable interfaces under extreme plastic deformation.

Atomically ordered bimetal interfaces typically develop in near-equilibrium epitaxial growth (bottom-up processing) of nanolayered composite films and have been considered responsible for a number of intriguing material properties. Here, we discover that interfaces of such atomic level order can also emerge ubiquitously in large-scale layered nanocomposites fabricated by extreme strain (top down) processing. This is a counterintuitive result, which we propose occurs because extreme plastic straining creates new interfaces separated by single crystal layers of nanometer thickness. On this basis, with atomic-scale modeling and crystal plasticity theory, we prove that the preferred bimetal interface arising from extreme strains corresponds to a unique stable state, which can be predicted by two controlling stability conditions. As another testament to its stability, we provide experimental evidence showing that this interface maintains its integrity in further straining (strains > 12), elevated temperatures (> 0.45 Tm of a constituent), and irradiation (light ion). These results open a new frontier in the fabrication of stable nanomaterials with severe plastic deformation techniques.

Engineering interface structures and thermal stabilities via SPD processing in bulk nanostructured metals.

Nanostructured metals achieve extraordinary strength but suffer from low thermal stability, both a consequence of a high fraction of interfaces. Overcoming this tradeoff relies on making the interfaces themselves thermally stable. Here we show that the atomic structures of bi-metal interfaces in macroscale nanomaterials suitable for engineering structures can be significantly altered via changing the severe plastic deformation (SPD) processing pathway. Two types of interfaces are formed, both exhibiting a regular atomic structure and providing for excellent thermal stability, up to more than half the melting temperature of one of the constituents. Most importantly, the thermal stability of one is found to be significantly better than the other, indicating the exciting potential to control and optimize macroscale robustness via atomic-scale bimetal interface tuning. Taken together, these results demonstrate an innovative way to engineer pristine bimetal interfaces for a new class of simultaneously strong and thermally stable materials.

Design of radiation tolerant materials via interface engineering.

A novel interface engineering strategy is proposed to simultaneously achieve superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered composites of a model face-centered-cubic (Cu)/body-centered-cubic (Nb) system. By synthesizing bulk nanolayered Cu-Nb composites containing interfaces with controlled sink efficiencies, a novel material is designed in which nearly all irradiation-induced defects are annihilated.

High-strength and thermally stable bulk nanolayered composites due to twin-induced interfaces.

Bulk nanostructured metals can attribute both exceptional strength and poor thermal stability to high interfacial content, making it a challenge to utilize them in high-temperature environments. Here we report that a bulk two-phase bimetal nanocomposite synthesised via severe plastic deformation uniquely possesses simultaneous high-strength and high thermal stability. For a bimetal spacing of 10 nm, this composite achieves an order of magnitude increase in hardness of 4.13 GPa over its constituents and maintains it (4.07 GPa), even after annealing at 500 °C for 1 h. It owes this extraordinary property to an atomically well-ordered bimaterial interface that results from twin-induced crystal reorientation, persists after extreme strains and prevails over the entire bulk. This discovery proves that interfaces can be designed within bulk nanostructured composites to radically outperform previously prepared bulk nanocrystalline materials, with respect to both mechanical and thermal stability.

Aligned carbon nanotubes sandwiched in epitaxial NbC film for enhanced superconductivity.

Highly aligned carbon nanotube (CNT) ribbons were sandwiched in epitaxial superconducting NbC films by a chemical solution deposition method. The incorporation of aligned long CNTs into NbC film enhances the normal-state conductivity and improves the superconducting properties of the assembly.

Epitaxial superconducting δ-MoN films grown by a chemical solution method.

The synthesis of pure δ-MoN with desired superconducting properties usually requires extreme conditions, such as high temperature and high pressure, which hinders its fundamental studies and applications. Herein, by using a chemical solution method, epitaxial δ-MoN thin films have been grown on c-cut Al(2)O(3) substrates at a temperature lower than 900 °C and an ambient pressure. The films are phase pure and show a T(c) of 13.0 K with a sharp transition. In addition, the films show a high critical field and excellent current carrying capabilities, which further prove the superior quality of these chemically prepared epitaxial thin films.