No abstract

Successful bone formation which leads to functional osseointegration is determined by the local mechanical environment around boneinterfacing implants. In this work, a novel porous titanium material is developed and tested and then impact of porosity on mechanical properties as a function of bone ingrowth is studied numerically. A superplastic foaming technique is used to produce CP-Ti material with rounded, interconnected pores of 50% porosity; the pore size and morphology is particularly suitable for bone ingrowth. In order to understand the structure-property relations for this new material, a numerical simulation is performed to study the effect of the porous microstructure and bone ingrowth on the mechanical properties. Using ABAQUS, we create two-dimensional representative microstructures for fully porous samples, as well as samples with partial and full bone ingrowth. We then use the finite element method to predict the macroscopic mechanical properties of the foam, e.g., overall Young's modulus and yield stress, as well as the local stress and strain pattern of both the titanium foam and bone inclusions. The strain-stress curve, stress concentrations and stress shielding caused by the bone-implant modulus mismatch are examined for different microstructures in both elastic and plastic region. The results are compared with experimental data from the porous titanium samples. Based on the finite element predictions, bone ingrowth is predicted to dramatically reduce stress concentrations around the pores. It is shown that the morphology of the implants will influence both macroscopic properties (such as modulus) and localized behavior (such as stress concentrations). Therefore, these studies provide a methodology for the optimal design of porous titanium as an implant material.

Porous titanium with elongated and aligned pores, mimicking the anisotropic structure of bone, was created by solid-state expansion of argon trapped in elongated pores between titanium wires. Both elastic moduli and yield strengths are larger in the longitudinal direction (E = 51 GPa, sigma y = 338 MPa) than in the transverse direction (E = 41 GPa, sigma y = 267 MPa). Finite-element analysis of simplified anisotropic structures provides insight into the local micromechanical behavior of these porous materials, evaluating elastic modulus, resistance to plastic deformation, and localized stress concentrations which may be experienced under biological loading. Preliminary in vitro cell culture studies further demonstrate the influence of the elongated porous microstructure on osteoblast colonization behavior. These studies suggest that as an optimized material, titanium with aligned, elongated pores is promising for applications in orthopedic tissue engineering, as it combines high strength, toughness, and biocompatibility of titanium with the reduced stiffness and open porosity suitable for mechanical integration with bone tissue produced by aligned pores.

What is already known about this topic? A considerable percentage of the population has received both primary and booster vaccinations, which could potentially provide protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron infections and related symptoms. What is added by this report? The self-reported infection rate, as determined from an online survey, reached its peak (15.5%) between December 19 and 21, 2022, with an estimated 82.4% of individuals in China being infected as of February 7, 2023. During the epidemic, the effectiveness of booster vaccinations against SARS-CoV-2 Omicron infection was found to be 49.0% within three months of vaccination and 37.9% between 3 and 6 months following vaccination. Furthermore, the vaccine effectiveness of the booster vaccination in relation to symptom prevention varied from 48.7% to 83.2% within three months and from 25.9% to 69.0% between 3 and 6 months post-booster vaccination. What are the implications for public health practice? The development and production of efficacious vaccines, together with prompt vaccinations or emergency vaccinations, have the potential to mitigate the epidemic’s impact and safeguard public health.

Grassland ecosystems cover c. 40% of global land area and contain c. 40% of soil organic carbon. Understanding the effects of adding nutrients to grasslands is essential because they provide much of our food, support diverse ecosystem services and harbor rich biodiversity.Using the meadow steppe (grassland) study site of Inner Mongolia, we manipulated seven key nutrients and a cocktail of micronutrients to examine their effects on grassland biomass productivity and diversity.The results, explained in structural equation models, link two previously disparate hypotheses in grassland ecology: (1) the light asymmetry competition hypothesis and (2) the genome size-nutrient interaction hypothesis. We show that aboveground net primary productivity increases predominantly from species with large genome sizes with the addition of nitrogen, and nitrogen plus phosphorus. This drives an asymmetric competition for light, causing a decline in species richness mainly in species with small genome sizes.This dynamic is likely to be caused by the nutrient demands of the nucleus and/or the scaling effects of nuclear size on cell size which impact water use efficiency. The model will help inform the best management approaches to reverse the rapid and unprecedented degradation of grasslands globally.