Fluorocarbon Plasma-Polymerized Layer Increases the Release Time of Silver Ions and the Antibacterial Activity of Silver-Based Coatings.

Silver-based antibacterial coatings limit the spread of hospital-acquired infections. Indeed, the use of silver and silver oxide nanoparticles (Ag and AgO NPs) incorporated in amorphous hydrogenated carbon (a-C:H) as a matrix demonstrates a promising approach to reduce microbial contamination on environmental surfaces. However, its success as an antibacterial coating hinges on the control of Ag+ release. In this sense, if a continuous release is required, an additional barrier is needed to extend the release time of Ag+. Thus, this research investigated the use of a plasma fluoropolymer (CFx) as an additional top layer to elongate Ag+ release and increase the antibacterial activity due to its high hydrophobic nature. Herein, a porous CFx film was deposited on a-C:H containing Ag and AgO NPs using pulsed afterglow low pressure plasma polymerization. The chemical composition, surface wettability and morphology, release profile, and antibacterial activity were analyzed. Overall, the combination of a-C:H:Ag (12.1 at. % of Ag) and CFx film (120.0°, F/C = 0.8) successfully inactivated 88% of E. coli and delayed biofilm formation after 12 h. Thus, using a hybrid approach composed of Ag NPs and a hydrophobic polymeric layer, it was possible to increase the overall antibacterial activity of the coating.

Silver-based antibacterial strategies for healthcare-associated infections: Processes, challenges, and regulations. An integrated review.

Healthcare-associated infections (HCAIs) are a major cause of morbidity and mortality worldwide. One of the main routes of transmission is by contact with contaminated surfaces, where nosocomial pathogens form sessile communities called biofilms. When forming biofilms, these pathogens are extremely resistant to antibiotics and standard cleaning procedures. In this regard, in order to eliminate the extent of biofilm formation on these surfaces, intensive efforts have been deployed, particularly in recent years, to develop new antibacterial surfaces containing silver or silver compounds, which can be used to prevent the formation of biofilm. In this review, recent developments in the design and manufacturing of silver-based antibacterial surfaces are described in detail. Up-to-date toxicity and governmental regulations are then extensively presented. Finally, based on current research in this promising field, the main challenges and perspectives for their effective implementation are discussed.

A Complementary Metal Oxide Semiconductor Process-Compatible Ferroelectric Tunnel Junction.

In recent years, experimental demonstration of ferroelectric tunnel junctions (FTJ) based on perovskite tunnel barriers has been reported. However, integrating these perovskite materials into conventional silicon memory technology remains challenging due to their lack of compatibility with the complementary metal oxide semiconductor process (CMOS). This communication reports the fabrication of an FTJ based on a CMOS-compatible tunnel barrier Hf0.5Zr0.5O2 (6 unit cells thick) on an equally CMOS-compatible TiN electrode. Analysis of the FTJ by grazing angle incidence X-ray diffraction confirmed the formation of the noncentrosymmetric orthorhombic phase (Pbc21, ferroelectric phase). The FTJ characterization is followed by the reconstruction of the electrostatic potential profile in the as-grown TiN/Hf0.5Zr0.5O2/Pt heterostructure. A direct tunneling current model across a trapezoidal barrier was used to correlate the electronic and electrical properties of our FTJ devices. The good agreement between the experimental and theoretical model attests to the tunneling electroresistance effect (TER) in our FTJ device. A TER ratio of ∼15 was calculated for the present FTJ device at low read voltage (+0.2 V). This study suggests that Hf0.5Zr0.5O2 is a promising candidate for integration into conventional Si memory technology.

Novel Concept of Gas Sensitivity Characterization of Materials Suited for Implementation in FET-Based Gas Sensors.

We propose a novel technique to investigate the gas sensitivity of materials for implementation in field-effect transistor-based gas sensors. Our technique is based on the measurement of the surface charge induced by gas species adsorption, using an electrometer. Platinum sensitivity to hydrogen diluted in synthetic air has been evaluated with the proposed charge measurement technique in the operation temperature range from 80 to 190 °C at constant H2 concentration of 4 % and for different concentrations ranging from 0.5 to 4 % at 130 °C.

Influence of Ni Catalyst Layer and TiN Diffusion Barrier on Carbon Nanotube Growth Rate.

Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700 degrees C. This behavior is likely related to a transition in the growth mode from a predominantly "base growth" to that of a "tip growth." For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO(2) layer.

Improving biocompatibility of implantable metals by nanoscale modification of surfaces: an overview of strategies, fabrication methods, and challenges.

The human body is an intricate biochemical-mechanical system, with an exceedingly precise hierarchical organization in which all components work together in harmony across a wide range of dimensions. Many fundamental biological processes take place at surfaces and interfaces (e.g., cell-matrix interactions), and these occur on the nanoscale. For this reason, current health-related research is actively following a biomimetic approach in learning how to create new biocompatible materials with nanostructured features. The ultimate aim is to reproduce and enhance the natural nanoscale elements present in the human body and to thereby develop new materials with improved biological activities. Progress in this area requires a multidisciplinary effort at the interface of biology, physics, and chemistry. In this Review, the major techniques that have been adopted to yield novel nanostructured versions of familiar biomaterials, focusing particularly on metals, are presented and the way in which nanometric surface cues can beneficially guide biological processes, exerting influence on cellular behavior, is illustrated.

Nanoscale oxidative patterning of metallic surfaces to modulate cell activity and fate.

In the field of regenerative medicine, nanoscale physical cuing is clearly becoming a compelling determinant of cell behavior. Developing effective methods for making nanostructured surfaces with well-defined physicochemical properties is thus mandatory for the rational design of functional biomaterials. Here, we demonstrate the versatility of simple chemical oxidative patterning to create unique nanotopographical surfaces that influence the behavior of various cell types, modulate the expression of key determinants of cell activity, and offer the potential of harnessing the power of stem cells. These findings promise to lead to a new generation of improved metal implants with intelligent surfaces that can control biological response at the site of healing.