Gallium-doped zinc oxide spin-coated thin films have been prepared by the sol–gel method. The influence of two solvents, isopropanol and 2-methoxyethanol (2-ME), and two chelating agents, monoethanolamine (MEA) and diethanolamine (DEA), was investigated. X-ray diffraction shows preferential (002) c-axis orientation of the crystallites influenced by the doping content and starting solution composition. Better orientation was obtained with 2-ME as a solvent because of a slower evaporation rate during the spin coating. Better orientation was also obtained using MEA as a stabilizer due to the weaker bonds formed with the Zn2+ ions. Typical film thickness was 550 nm. The transparency of the films was greater than 85% in the entire visible range. A sheet resistance of 68 Ω/□ was obtained for the ZnO film doped with 2 at.% of Ga using 2-ME and MEA as a solvent and stabilizer, respectively. The results show that the denser packing created using a high boiling temperature solvent and a low organic content stabilizer improved the layer’s electrical and optical properties.

Single-crystalline p-type silicon nanowire (SiNW) arrays have been formed by electroless metal deposition on a silicon wafer piece in an ionic Ag/fluorhydric acid (HF) solution through selective etching. They display mechanical properties that are different from those of both bulk silicon and single SiNWs. As any practical application of these materials is likely to involve a large number of nanowires in close proximity to each other, it is necessary to understand the mechanical properties of SiNW arrays. In this work, as a first step to characterize their mechanical properties, the buckling instabilities of the surfaces formed by vertically aligned SiNWs have been studied by nanoindentation tests.

Nickel-titanium (NiTi) alloys combine several remarkable characteristics, among them are shape-memory, superelasticity, great strain recovery, good biocompatibility, and corrosion resistance. These render them well suited to a wide range of medical applications, such as cardiovascular stents, laparoscopy, and dental applications such as NiTi endodontic files (EFs) used for root canal treatment, which are the focus of this work. Unfortunately, fatigue-induced and incidental failure of NiTi EFs is not uncommon, which may lead to severe medical consequences. Here we examine the effects of cobalt coatings with impregnated fullerene-like WS2 nanoparticles on file fatigue and failure. Dynamic x-ray diffraction, nanoindentation and torque measurements all indicate a significant improvement in the fatigue resistance and time to breakage of the coated files, stemming from reduced friction between the file and the surrounding tissue. These methods are possibly applicable to a variety of NiTi-based medical devices where fatigue and consequent failure are of relevance.

Bacteria living in surface-attached biofilm communities must maintain electrochemical gradients to support basic cellular functions, including chemo-osmotic transport and adenosine triphosphate synthesis. Central to this is the maintenance of electron flow to terminal electron acceptors. These acceptors can be soluble inorganic and organic molecules, such as oxygen, nitrate, sulfate, dimethyl sulfoxide, or fumarate, or solid metal oxides, such as Fe(III) and Mn(IV) oxides. When electrons are transferred to a solid substrate, they may be (1) carried directly to the acceptor via outer membrane cytochromes, (2) carried by electron shuttle molecules, (3) transferred along conductive protein nanowires, or (4) conducted through other extracellular matrices. No matter what the electron acceptor is, in the laboratory, bacterial biofilms are frequently studied while growing on inert surfaces, incapable of electron transfer. However, in natural environments, as well as many industrial and biotechnology settings, biofilms grow on electrically active surfaces. In this review, we propose that the study of bacterial biofilms on redox-active surfaces is important both for the development of industrial processes, such as microbial fuel cells and wastewater treatment systems, as well as for our understanding of how these communities of microbes affect global nutrient cycling, other geobiological processes, and even human disease.

This article reviews the physical and chemical constraints of environments on biofilm formation. We provide a perspective on how materials science and engineering can address fundamental questions and unmet technological challenges in this area of microbiology, such as biofilm prevention. Specifically, we discuss three factors that impact the development and organization of bacterial communities. (1) Physical properties of surfaces regulate cell attachment and physiology and affect early stages of biofilm formation. (2) Chemical properties influence the adhesion of cells to surfaces and their development into biofilms and communities. (3) Chemical communication between cells attenuates growth and influences the organization of communities. Mechanisms of spatial and temporal confinement control the dimensions of communities and the diffusion path length for chemical communication between biofilms, which, in turn, influences biofilm phenotypes. Armed with a detailed understanding of biofilm formation, researchers are applying the tools and techniques of materials science and engineering to revolutionize the study and control of bacterial communities growing at interfaces.

Many bacteria grow attached to a surface as biofilms. Several factors dictate biofilm formation, including responses by the colonizing bacteria to their environment. Here we review how bacteria use cell-cell signaling (also called quorum sensing) and motility during biofilm formation. Specifically, we describe quorum sensing and surface motility exhibited by the bacterium Pseudomonas aeruginosa, a ubiquitous environmental organism that acts as an opportunistic human pathogen in immunocompromised individuals. P. aeruginosa uses acyl-homoserine lactone signals during quorum sensing to synchronize gene expression important to the production of polysaccharides, rhamnolipid, and other virulence factors. Surface motility affects the assembly and architecture of biofilms, and some aspects of motility are also influenced by quorum sensing. While some genes and their function are specific to P. aeruginosa, many aspects of biofilm development can be used as a model system to understand how bacteria differentially colonize surfaces.

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.