The Complex, Unique, and Powerful Imaging Instrument for Dynamics (CUPI2D) at the Spallation Neutron Source (invited).

The Oak Ridge National Laboratory is planning to build the Second Target Station (STS) at the Spallation Neutron Source (SNS). STS will host a suite of novel instruments that complement the First Target Station's beamline capabilities by offering an increased flux for cold neutrons and a broader wavelength bandwidth. A novel neutron imaging beamline, named the Complex, Unique, and Powerful Imaging Instrument for Dynamics (CUPI2D), is among the first eight instruments that will be commissioned at STS as part of the construction project. CUPI2D is designed for a broad range of neutron imaging scientific applications, such as energy storage and conversion (batteries and fuel cells), materials science and engineering (additive manufacturing, superalloys, and archaeometry), nuclear materials (novel cladding materials, nuclear fuel, and moderators), cementitious materials, biology/medical/dental applications (regenerative medicine and cancer), and life sciences (plant-soil interactions and nutrient dynamics). The innovation of this instrument lies in the utilization of a high flux of wavelength-separated cold neutrons to perform real time in situ neutron grating interferometry and Bragg edge imaging-with a wavelength resolution of δλ/λ ≈ 0.3%-simultaneously when required, across a broad range of length and time scales. This manuscript briefly describes the science enabled at CUPI2D based on its unique capabilities. The preliminary beamline performance, a design concept, and future development requirements are also presented.

Engineering living building materials for enhanced bacterial viability and mechanical properties.

Living building materials (LBMs) utilize microorganisms to produce construction materials that exhibit mechanical and biological properties. A hydrogel-based LBM containing bacteria capable of microbially induced calcium carbonate precipitation (MICP) was recently developed. Here, LBM design factors, i.e., gel/sand ratio, inclusion of trehalose, and MICP pathways, are evaluated. The results show that non-saturated LBM (gel/sand = 0.13) and gel-saturated LBM (gel/sand = 0.30) underwent distinct failure modes. The inclusion of trehalose maintains bacterial viability under ambient conditions with low relative humidity, without affecting mechanical properties of the LBM. Comparison of biotic and abiotic LBM shows that MICP efficiency in this material is subject to the pathway selected: the LBM with heterotrophic ureolytic Escherichia coli demonstrated the most mechanical enhancement from the abiotic controls, compared with either ureolytic or CO2-concentrating mechanisms from Synechococcus. The study shows that tailoring of LBM properties can be accomplished in a manner that considers both LBM microstructure and MICP pathways.

Engineered Ureolytic Microorganisms Can Tailor the Morphology and Nanomechanical Properties of Microbial-Precipitated Calcium Carbonate.

We demonstrate for the first time that the morphology and nanomechanical properties of calcium carbonate (CaCO3) can be tailored by modulating the precipitation kinetics of ureolytic microorganisms through genetic engineering. Many engineering applications employ microorganisms to produce CaCO3. However, control over bacterial calcite morphology and material properties has not been demonstrated. We hypothesized that microorganisms genetically engineered for low urease activity would achieve larger calcite crystals with higher moduli. We compared precipitation kinetics, morphology, and nanomechanical properties for biogenic CaCO3 produced by two Escherichia coli (E. coli) strains that were engineered to display either high or low urease activity and the native producer Sporosarcina pasteurii. While all three microorganisms produced calcite, lower urease activity was associated with both slower initial calcium depletion rate and increased average calcite crystal size. Both calcite crystal size and nanoindentation moduli were also significantly higher for the low-urease activity E. coli compared with the high-urease activity E. coli. The relative resistance to inelastic deformation, measured via the ratio of nanoindentation hardness to modulus, was similar across microorganisms. These findings may enable design of novel advanced engineering materials where modulus is tailored to the application while resistance to irreversible deformation is not compromised.

PM2.5 generated during rapid failure of fiber-reinforced concrete induces TNF-alpha response in macrophages.

Failure of large, concrete structures can lead to the generation of very small fragments, including aerosols in the fine fraction, which have aerodynamic diameters of ≤2.5 µm (PM2.5). These aerosols can persist in the environment, pose exposure risks, and potentially cause negative health effects. New trends in construction favor the use of concrete reinforced with steel fibers, but little is known about the nature of the fragments generated during its failure. This study investigated the fragmentation of several steel-fiber reinforced concrete formulations using dynamic compression testing. The release of tumor necrosis factor alpha (TNF-α), an inflammatory marker widely used in both human and animal studies, was then analyzed to determine the effects of the fragments in the aerosol fine fraction on mouse macrophages (RAW 264.7). All concrete formulations studied showed statistically increased TNF-α release, which was inversely correlated with fiber length and fiber content (% weight). In addition, results from a select set of concrete formulations also showed a clear dose-response relationship. This paper postulates the fracture mechanisms by which concrete parameters (i.e., fiber length and content) lead to the generation of PM2.5, producing the observed TNF-α release.