Benjamin J. Wiley

The ultimate goal of this work is to create an engineered aerosol that acts as one‐way smoke, i.e. it creates an asymmetric vision environment in which the ability to image objects depends on the viewing direction. To this end, a rapid, one‐pot synthesis of copper‐based microclubs is developed that consists of a Cu₂O octahedron attached to a Cu₂O@Cu shaft. Millions of synthesized particles are analyzed in minutes with a FlowCam to provide a robust statistical analysis of their geometry, and rapidly elucidate the roles of the reaction constituents on the particle shape and yield. The combination of asymmetry in both shape and composition introduces a 30% difference in scattering of light propagating parallel to the microclub axis from opposing directions. This work represents a first step toward the creation of an asymmetric imaging environment with an aerosol consisting of acoustically aligned microclubs.

We use synthesis, electrochemistry, and DFT calculations to show the presence or absence of Cl ⁻ modulates binding of PVP to (100) facets, leading to the formation of nanocubes with Cl ⁻ , or truncated octahedra without it.

High surface area nanocatalysts combined with conductive carbon-based gas-diffusion layers (GDL) enable high CO₂ flux and conversion, but can suffer from ineffective catalyst utilization and flooding of the GDL ultimately limiting the lifetime of electrolyzer operation. Herein we explore an alternative gas-diffusion electrode that incorporates a self-conducting network of Ag nanowires on a non-conductive PTFE GDL (Figure 1 a-b) as a gas-diffusion electrode (GDE) for CO₂ conversion (Figure 1 c-d). Properties influenced by Ag nanowire mat thickness and durability of the Ag nanowires are explored. Furthermore a 1-D model of the electrode morphology and microstructure quantitatively captures the steady-state compositional gradients (Figure 1d) within the catalyst layer giving insight into the observed empirical differences in catalyst layer thickness. The self-conductive nanowire network and robust hydrophobic porous support structure provide an effective platform to further understanding of meso-scale properties and microenvironment present during CO₂ electroreduction. Figure Caption: (a) Top-down and (b) Cross-section electron micrographs of a Ag nanowire covered PTFE GDL. (c) Schematic depicting the utilization of the Ag NW covered PTFE GDL as an electrode for electrochemical CO₂ reduction and (d) resulting relationships between catalyst layer thickness, mass activity and simulated local pH. Figure 1

Key hurdles for replacing damaged cartilage with an equivalent synthetic construct are the development of a hydrogel with a strength that exceeds that of cartilage and fixation of this hydrogel onto the surface of an articulating joint. This article describes the first hydrogel with a tensile and compressive strength (51 and 98 MPa) that exceeds those of cartilage (40 and 59 MPa), and the first attachment of a hydrogel to a metal backing with a shear strength (2.0 MPa) that exceeds that of cartilage on bone (1.2 MPa). The hydrogel strength is achieved through reinforcement of crystallized polyvinyl alcohol with bacterial cellulose. The high attachment strength is achieved by securing freeze‐dried bacterial cellulose to a metal backing with an adhesive and a shape memory alloy clamp prior to infiltration and crystallization of the polyvinyl alcohol. The bacterial cellulose‐reinforced polyvinyl alcohol is three times more wear resistant than cartilage over one million cycles and exhibits the same coefficient of friction. These advances in hydrogel strength and attachment enable the creation of a hydrogel‐based implant for durable resurfacing of damaged articulating joints.

Shape-controlled synthesis of metal nanocrystals is usually achieved by the addition of capping agents and serves an important approach to endowing metal nanomaterials with desired properties.¹ A widely accepted hypothesis in the role of capping agents is they suppress the atomic deposition on the facets they selectively adsorb to, which leads to anisotropic growth.² However, the roles of capping agents are often qualitatively deduced from the shape of metal nanocrystals formed, making it difficult to rationally design a synthetic condition for a certain shape or aspect ratio. Single-crystal electrochemical measurements have been used to uncover the facet-selective roles of a wide range of capping agents, such as chloride in the synthesis of Cu nanowires, bromide in the synthesis of Au nanorods, and iodide in the synthesis of Cu microplates.^3-6 However, the anisotropic growth revealed by the growth of these nanocrystals is 10 times higher than that predicted by the single-crystal electrochemical measurements, indicating planar defects, such as twin planes and stacking faults, can also cause anisotropic growth. To elucidate the effects surface capping and defects in the anisotropic growth of metal nanocrystals, the work presented here combines synthetic methods and electrochemical measurements to reveal the roles of citrate in the growth of seeds with different structures.⁷ The single-crystal Ag seeds (Figure 1A) grow into cuboctahedra in the absence of citrate (Figure 1B) and octahedra in the presence of citrate (Figure 1C), which closely matches the shape prediction from the electrochemical measurements. Linear sweep voltammetry (LSV) measurements under the synthetic conditions demonstrate the anisotropic growth with citrate is a result of citrate selectively suppressing the oxidation of a reducing agent, ascorbic acid, and citrate does not affect silver ion reduction. The Ag nanoplate seeds with planar defects (Figure 1D) undergo isotropic growth in the absence of citrate (Figure 1E), but exhibit 30~100 times more anisotropic growth in the presence of citrate than the single-crystal seeds and electrochemical prediction (Figure 1F). Further investigation suggests planar defects can catalyze silver atom deposition to the nanoplate side planes and citrate suppresses surface diffusion to the nanoplate basal planes. (1) Yang, T.-H.; Shi, Y.; Janssen, A.; Xia, Y., Surface Capping Agents and Their Roles in Shape-Controlled Synthesis of Colloidal Metal Nanocrystals. Angew. Chem., Int. Ed. 2020, 59, 15378-15401. (2) Xia, Y.; Xiong, Y.; Lim, B.; Skrabalak, S. E., Shape-Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics? Angew. Chem., Int. Ed. 2009, 48, 60-103. (3) Kim, M. J.; Brown, M.; Wiley, B. J., Electrochemical investigations of metal nanostructure growth with single crystals. Nanoscale 2019, 11, 21709-21723. (4) Kim, M. J.; Alvarez, S.; Chen, Z.; Fichthorn, K. A.; Wiley, B. J., Single-Crystal Electrochemistry Reveals Why Metal Nanowires Grow. J. Am. Chem. Soc. 2018, 140, 14740-14746. (5) Brown, M.; Wiley, B. J., Bromide Causes Facet-Selective Atomic Addition in Gold Nanorod Syntheses. Chem. Mater. 2020, 32, 6410-6415. (6) Kim, M. J.; Cruz, M. A.; Chen, Z.; Xu, H.; Brown, M.; Fichthorn, K. A.; Wiley, B. J., Isotropic Iodide Adsorption Causes Anisotropic Growth of Copper Microplates. Chem. Mater. 2021, 33, 881-891. (7) Xu, H.; Wiley, B. J., The Roles of Citrate and Defects in the Anisotropic Growth of Ag Nanostructures. Chem. Mater. 2021, 33, 8301-8311. Figure 1

Purpose: The purpose of this work was to characterize and improve the ability of fused filament fabrication to create anthropomorphic physical phantoms for CT research. Specifically, we sought to develop the ability to create multiple levels of X‐ray attenuation with a single material.Methods: CT images of 3D printed cylinders with different infill angles and printing patterns were assessed by comparing their 2D noise power spectra to determine the conditions that produced minimal and uniform noise. A backfilling approach in which additional polymer was extruded into an existing 3D printed background layer was developed to create multiple levels of image contrast.Results: A print with nine infill angles and a rectilinear infill pattern was found to have the best uniformity, but the printed objects were not as uniform as a commercial phantom. An HU dynamic range of 600 was achieved by changing the infill percentage from 40% to 100%. The backfilling technique enabled control of up to eight levels of contrast within one object across a range of 200 HU, similar to the range of soft tissue. A contrast detail phantom with six levels of contrast and an anthropomorphic liver phantom with four levels of contrast were printed with a single material.Conclusion: This work improves the uniformity and levels of contrast that can be achieved with fused filament fabrication, thereby enabling researchers to easily create more detailed physical phantoms, including realistic, anthropomorphic textures.