Bacterial biofilms are interface-associated colonies of bacteria embedded in an extracellular matrix that is composed primarily of polymers and proteins. They can be viewed in the context of soft matter physics: the rigid bacteria are analogous to colloids, and the extracellular matrix is a cross-linked polymer gel. This perspective is beneficial for understanding the structure, mechanics, and dynamics of the biofilm. Bacteria regulate the water content of the biofilm by controlling the composition of the extracellular matrix, and thereby controlling the mechanical properties. The mechanics of well-defined soft materials can provide insight into the mechanics of biofilms and, in particular, the viscoelasticity. Furthermore, spatial heterogeneities in gene expression create heterogeneities in polymer and surfactant production. The resulting concentration gradients generate forces within the biofilm that are relevant for biofilm spreading and survival.

Bacteria often live in the form of surface-associated communities of cells termed biofilms. Within biofilms, there is a division of labor in which genetically identical cells differentiate to serve distinct functions. This cellular differentiation results from a response to extracellular signals that occur due to changes in the local environment of a cell or in response to signaling molecules that the cells themselves produce. In this review, we discuss differentiation in biofilms, focusing on the molecular mechanisms that regulate differentiation in the bacterium Bacillus subtilis. In this organism, there is a subpopulation of cells within a biofilm that produces a signal, while a different subpopulation of cells responds to it. Studying what signals cells use to communicate with each other within a biofilm will allow for better design of strategies to prevent and disrupt biofilms.

Despite modern advancements in sterilization and aseptic procedures, bacterial infections remain a major and significant impediment to the long-term success of medical implants and devices, including catheters, artificial prosthetics, and subcutaneous sensors. It has been estimated that upward of 60% of nosocomial, or hospital-acquired, infections are associated with implants, with an estimated one million cases per year in the United States alone. Current treatment regimens primarily rely on the systemic administration of antibiotics or local administration through irrigation of the surgical site. However, after decades of prophylactic antibiotic use, high infection rates continue to persist, particularly with the emergence of drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA). Consequently, recent research efforts have focused on the use of non-antibiotic-based coatings to inhibit bacteria colonization and subsequent biofilm formation on implant surfaces. In particular, advancements in surface treatment strategies and ongoing development of new antimicrobial agents have led to encouraging progress in the design of better coatings. Here, we present and discuss representative examples of novel surface engineering approaches to address device-associated infections, focusing in particular on coatings that can be easily administered onto implant material surfaces.

Bacterial biofilms are integrated, multi-species communities of cells that adhere to almost any surface and are fundamental to the ecology and biology of bacteria. Not only do biofilms contribute to human health and disease, they also play important roles in the context of energy and the environment. The formation of biofilms requires interactions between bacteria and the surfaces they colonize, and both microbe and surface can impact the structure, function, and composition of these communities. Bacteria in biofilms exhibit surprisingly sophisticated social behavior, both cooperative and competitive, made possible by their cell biology. However, they are also hierarchically organized systems governed by complex physical and chemical interactions. Because of this, the study of bacterial biofilms has recently attracted the attention of materials scientists, physicists, chemists, and nanotechnology experts who import not only new tools, but also new concepts and perspectives. This issue reviews recent progress in multidisciplinary studies of biofilms.

B2O3-SiO2 is shown to act as a transient liquid phase sintering aid that reduces the sintering temperature of Nd:YAG ceramics to 1600 °C. 1 at.% Nd3xY3-3xAl5O12 (Nd:YAG) ceramics were doped with 0.34–1.35 mol% B2O3-SiO2 and sintered between 1100 and 1700 °C. Dilatometric measurements show that B2O3-SiO2 doping increases the densification rate during intermediate-stage sintering relative to SiO2-doped samples. B3+ content is reduced to <5 ppm in samples heated to 1500 °C, as determined by mass spectrometry. For B2O3-SiO2-doped samples, final stage densification and grain growth follow a more densifying sintering trajectory than SiO2-doped 1 at.% Nd:YAG ceramics because there is less SiO2 during final-stage densification. The increased densification kinetics during intermediate-stage sintering lead to highly transparent Nd:YAG ceramics when sintered at 1600 °C in either vacuum or oxygen. Thus, transparent Nd:YAG ceramics can be sintered without the need for expensive refractory metal vacuum furnaces or pressure-assisted densification.

The local structures about Cu, In, and Se atoms in a series of Cu2Se–In2Se3 pseudobinary compounds have been investigated by x-ray absorption fine structure (XAFS). In K-edge XAFS and L3-edge x-ray absorption near-edge structure (XANES) suggest that CuInSe2, Cu0.9InSe1.95, Cu0.82InSe1.91, and Cu2In3Se5.5 have a nominally four-coordinated InSe4 structure, whereas CuIn3Se5 and CuIn5Se8 possess two different InSe4 structures. Cu K-edge XAFS also showed that CuIn3Se5 and CuIn5Se8 possess two different CuSe4 structures, whereas others have a CuSe4 structure. Se K-edge XANES and curve fitting analysis reveal that the Cu vacancy (VCu) gradually forms with decreasing Cu/In ratio. Moreover, the substitution of In for VCu (InCu) is observed in CuIn3Se5 and CuIn5Se8. These results were compared to the previously proposed Cu–In–Se models. We conclude that Cu0.9InSe1.95 and Cu0.82InSe1.91 have a chalcopyrite structure with VCu and that the structure of CuIn3Se5 and CuIn5Se8 is a stannite-like structure with VCu and InCu defects.

As a narrow gap, strongly correlated electron semiconductor, FeSb2 single crystals can exhibit a colossal thermopower1 (on the order of −40,000 μV/K or greater) and a relatively high lattice thermal conductivity2 (over 300 W/m-K) at temperatures around 10 K. In this work, a series of FeSb2 polycrystalline samples with different amounts of additional Indium were prepared by a quench-and-anneal method followed by a spark plasma sintering procedure. The x-ray diffraction, scanning electron microscopy, and elemental analysis verified that the Sb/InSb nanoinclusions were formed in situ on the boundaries of coarse FeSb2 grains. The presence of such nanoinclusions and other as-formed multiscale microstructures can scatter phonons and thus dramatically reduce the corresponding lattice thermal conductivity. Furthermore, the electrical properties can be also improved because of the addition of high mobility carriers from the InSb nanoinclusions. Overall, FeSb2-based materials have shown some promising potential for possible thermoelectric cooling applications at cryogenic temperatures.

We have measured at room temperature polarized visible and near-infrared and unpolarized mid-infrared (2.7 μm) emission spectra of Er3+ in LiNbO3 (LN) crystals grown from congruent melts doped with 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol% In2O3/Er2O3. From the measured emission spectra, the emission and absorption cross section spectral distributions were analyzed based on McCumber theory and discussed in comparison with those spectra of only Er-doped LN bulk material and/or Ti: Er: LN waveguide structure and with the results from the unpolarized absorption measurements. For the 530 and 1530 nm transitions, the cross section value, polarization dependence, and spectral shape all change from the only Er-doped material to the In–Er-codoped crystal and show definite In2O3 doping level effect. The 559, 673, 996, and 1530 nm emission lifetimes were also measured and used to evaluate nonradiative multiphonon relaxation rate. The calculated radiative, measured lifetimes, and multiphonon relaxation rate also show In-codoping effects.