Revealing bactericidal events on graphene oxide nano films deposited on metal implant surfaces.

At the time when pathogens are developing robust resistance to antibiotics, the demand for implant surfaces with microbe-killing capabilities has significantly risen. To achieve this goal, profound understanding of the underlying mechanisms is crucial. Our study demonstrates that graphene oxide (GO) nano films deposited on stainless steel (SS316L) exhibit superior antibacterial features. The physicochemical properties of GO itself play a pivotal role in influencing biological events and their diversity may account for the contradictory results reported elsewhere. However, essential properties of GO coatings, such as oxygen content and the resulting electrical conductivity, have been overlooked so far. We hypothesize that the surface potential and electrical resistance of the oxygen content in the GO-nano films may induce bacteria-killing events on conductive metallic substrates. In our study, the GO applied contains 52 wt% of oxygen, and thus exhibits insulating properties. When deposited as a nano film on an electrically conducting steel substrate, GO flakes generate a Schottky barrier at the interface. This barrier, consequently, impedes the transfer of electrons to the underlying conductive substrate. As a result, this creates reactive oxygen species (ROS), leading to bacterial death. We confirmed the presence of GO coatings and their hydrolytic stability by using X-ray photoelectron spectroscopy (XPS), µRaman spectroscopy, scanning electron microscopy (SEM), and Kelvin probe force microscopy (KPFM) measurements. The biological evaluation was performed on the MG63 osteoblast-like cell line and two selected bacteria species: S. aureus and P. aeruginosa, demonstrating both the cytocompatibility and antibacterial behavior of GO-coated SS316L substrates. We propose a two-step bactericidal mechanism: electron transfer from the bacteria membrane to the substrate, followed by ROS generation. This mechanism finds support in changes observed in contact angle, surface potential, and work function, identified as decisive factors. By addressing overlooked factors and effectively bridging the gap between understanding and practicality, we present a transformative approach for implant surfaces, combating microbial resistance, and offering new application possibilitie.

Porous Zirconia Scaffolds Functionalized with Calcium Phosphate Layers and PLGA Nanoparticles Loaded with Hydrophobic Gentamicin.

Implant-related infections are a worldwide issue that is considered very challenging. Conventional therapies commonly end up failing; thus, new solutions are being investigated to overcome this problem. The in situ delivery of the drug at the implant site appears to be more sufficient compared to systemic antibiotic therapy. In this study, we manufactured porous zirconia scaffolds using the foam replication method. To improve their overall bioactivity, they were coated with a calcium phosphate (CaP) layer containing antibiotic-loaded degradable polymer nanoparticles (NPs) obtained by the double emulsion method to achieve the antibacterial effect additionally. Encapsulation efficiency (EE) and drug loading (DL) were superior and were equal to 99.9 ± 0.1% and 9.1 ± 0.1%, respectively. Scaffolds were analyzed with scanning electron microscopy, and their porosity was evaluated. The porosity of investigated samples was over 90% and resembled the microstructure of spongy bone. Furthermore, we investigated the cytocompatibility with osteoblast-like MG-63 cells and antimicrobial properties with Staphylococcus aureus. Scaffolds coated with a CaP layer were found non-toxic for MG-63 cells. Moreover, the presence of antibiotic-loaded nanoparticles had no significant influence on cell viability, and the obtained scaffolds inhibited bacteria growth. Provided processes of fabrication of highly porous zirconia scaffolds and surface functionalization allow minimizing the risk of implant-related infection.

Surface Multifunctionalization of Inert Ceramic Implants by Calcium Phosphate Biomimetic Coating Doped with Nanoparticles Encapsulating Antibiotics.

Aseptic loosening and periprosthetic infections are complications that can occur at the interface between inert ceramic implants and natural body tissues. Therefore, the need for novel materials with antibacterial properties to prevent implant-related infection is evident. This study proposes multifunctionalizing the inert ceramic implant surface by biomimetic calcium phosphate (CaP) coating decorated with antibiotic-loaded nanoparticles for bioactivity enhancement and antibacterial effect. This study aimed to coat zirconium dioxide (ZrO2) substrates with a bioactive CaP-layer containing drug-loaded degradable polymer nanoparticles (NPs). The NPs were loaded with two antibiotics, gentamicin or bacitracin. The immobilization of NPs happened by two deposition methods: coprecipitation and drop-casting. X-ray diffraction (XRD), scanning electron microscopy (SEM), and cross-section analyses were used to characterize the coatings. MG-63 osteoblast-like cells and human mesenchymal stem cells (hMSC) were chosen for in vitro tests. Antibacterial activity was assessed with S. aureus and E. coli. The coprecipitation method allowed for a favorable homogeneous distribution of the NPs within the CaP coating. The CaP coating was constituted of hydroxyapatite and octacalcium phosphate; its thickness was 3.8 ± 1 µm with cavities of around 1 µm suitable for hosting NPs with a size of 200 nm. Antibiotics were released from the coatings in a controlled manner for 1 month. The cell culture study has confirmed the excellent behavior of the coprecipitated coating, showing cytocompatibility and a homogeneous distribution of the cells on the coated surfaces. The increase in alkaline phosphatase activity showed osteogenic differentiation. The materials were found to inhibit the growth of bacteria. Newly developed coatings with antibacterial and bioactive properties are promising candidates to prevent peri-implant infectious bone diseases.

Unveiling the main factors triggering the coagulation at the SiC-blood interface.

Hemocompatibility is the most significant criterion for blood-contacting materials in successful in vivo applications. Prior to the clinical tests, in vitro analyses must be performed on the biomaterial surfaces in accordance with the ISO 10993-4 standards. Designing a bio-functional material requires engineering the surface structure and chemistry, which significantly influence the blood cell activity according to earlier studies. In this study, we elucidate the role of surface terminations and polymorphs of SiC single crystals in the initial stage of the contact coagulation. We present a detailed analysis of phase, roughness, surface potential, wettability, consequently, reveal their effect on cytotoxicity and hemocompatibility by employing live/dead stainings, live cell imaging, ELISA and Micro BCA protein assay. Our results showed that the surface potential and the wettability strongly depend on the crystallographic polymorph as well as the surface termination. We show, for the first time, the key role of SiC surface termination on platelet activation. This dependency is in good agreement with the results of our in vitro analysis and points out the prominence of cellular anisotropy. We anticipate that our experimental findings bridge the surface properties to the cellular activities, and therefore, pave the way for tailoring advanced hemocompatible surfaces.

Ti3C2 MXene Membranes for Gas Separation: Influence of Heat Treatment Conditions on D-Spacing and Surface Functionalization.

Two-dimensional (2D) MXene materials have recently been the focus of membrane research due to their unique properties, such as their single-atomic-layer thickness, flexibility, molecular filtration abilities and microstructural similarities with graphene, which is currently the most efficient precursor material for gas separation applications. In addition, the potential to process nanoscale channels has motivated investigations of parameters which can improve membrane permeability and selectivity. Interlayer spacing and defects, which are still challenging to control, are among the most crucial parameters for membrane performance. Herein, the effect of heat treatment on the d-spacing of MXene nanosheets and the surface functionalization of nanolayers was shown regarding its impact on the gas diffusion mechanism. The distance of the layers was reduced by a factor of over 10 from 0.345 nm to 0.024 nm, the defects were reduced, and the surface functionalization was maintained upon treatment of the Ti3C2 membrane at 500 °C under an Ar/H2 atmosphere as compared to 80 °C under vacuum. This led to a change from Knudsen diffusion to molecular sieving, as demonstrated by single-gas permeation tests at room temperature. Overall, this work shows a simple and promising way to improve H2/CO2 selectivity via temperature treatment under a controlled atmosphere.

Solvent Co-Intercalation-Induced Activation and Capacity Fade Mechanism of Few-/Multi-Layered MXenes in Lithium Ion Batteries.

MXenes attract tremendous research efforts since their discovery in 2011 due to their unique physical and chemical properties, allowing for application in various fields. One of them is electrochemical energy storage due to their pseudocapacitive (=redox) behavior, high electronic conductivity, and charge storage versatility regarding the cationic species (e.g., Li+ ). MXenes typically display stable charge/discharge cycling behavior over hundreds of cycles in numerous electrolytes, however, a drastic loss of reversible capacity is detectable during the initial cycles. Furthermore, an electrochemical "activation" is also reported in the literature, especially for free-standing electrodes. Here, these electrochemical phenomena are investigated by electrochemical and analytical means to decipher the responsible mechanism by comparing few-layered and multi-layered Ti3 C2 Tx . A change in the pseudocapacitive behavior of MXenes during cycling can be explained by in situ X-ray diffraction studies, revealing solvent co-intercalation in the first cycle for the morphologically different MXenes. This co-intercalation is responsible for the capacity decay detected in the first cycles and is also responsible for the ongoing "activation" occurring in later cycles.

Injection Molding and Near-Complete Densification of Monolithic and Al2O3 Fiber-Reinforced Ti2AlC MAX Phase Composites.

Near-net shape components composed of monolithic Ti2AlC and composites thereof, containing up to 20 vol.% Al2O3 fibers, were fabricated by powder injection molding. Fibers were homogeneously dispersed and preferentially oriented, due to flow constriction and shear-induced velocity gradients. After a two-stage debinding procedure, the injection-molded parts were sintered by pressureless sintering at 1250 °C and 1400 °C under argon, leading to relative densities of up to 70% and 92%, respectively. In order to achieve near-complete densification, field assisted sintering technology/spark plasma sintering in a graphite powder bed was used, yielding final relative densities of up to 98.6% and 97.2% for monolithic and composite parts, respectively. While the monolithic parts shrank isotropically, composite assemblies underwent anisotropic densification due to constrained sintering, on account of the ceramic fibers and their specific orientation. No significant increase, either in hardness or in toughness, upon the incorporation of Al2O3 fibers was observed. The 20 vol.% Al2O3 fiber-reinforced specimen accommodated deformation by producing neat and well-defined pyramidal indents at every load up to a 30 kgf (~294 N).

Scalable Synthesis of MAX Phase Precursors toward Titanium-Based MXenes for Lithium-Ion Batteries.

MXenes have emerged as one of the most interesting material classes, owing to their outstanding physical and chemical properties enabling the application in vastly different fields such as electrochemical energy storage (EES). MXenes are commonly synthesized by the use of their parent phase, i.e., MAX phases, where "M" corresponds to a transition metal, "A" to a group IV element, and "X" to carbon and/or nitrogen. As MXenes display characteristic pseudocapacitive behaviors in EES technologies, their use as a high-power material can be useful for many battery-like applications. Here, a comprehensive study on the synthesis and characterization of morphologically different titanium-based MXenes, i.e., Ti3C2 and Ti2C, and their use for lithium-ion batteries is presented. First, the successful synthesis of large batches (≈1 kg) of the MAX phases Ti3AlC2 and Ti2AlC is shown, and the underlying materials are characterized mainly by focusing on their structural properties and phase purity. Second, multi- and few-layered MXenes are successfully synthesized and characterized, especially toward their ever-present surface groups, influencing the electrochemical behavior to a large extent. Especially multi- and few-layered Ti3C2 are achieved, exhibiting almost no oxidation and similar content of surface groups. These attributes enable the precise comparison of the electrochemical behavior between morphologically different MXenes. Since the preparation method for few-layered MXenes is adapted to process both active materials in a "classical" electrode paste processing method, a better comparison between both materials is possible by avoiding macroscopic differences. Therefore, in a final step, the aforementioned electrochemical performance is evaluated to decipher the impact of the morphology difference of the titanium-based MXenes. Most importantly, the delamination leads to an increased non-diffusion-limited contribution to the overall pseudocapacity by enhancing the electrolyte access to the redox-active sites.

Solvent Co-intercalation into Few-layered Ti3C2Tx MXenes in Lithium Ion Batteries Induced by Acidic or Basic Post-treatment.

MXenes, as an emerging class of 2D materials, display distinctive physical and chemical properties, which are highly suitable for high-power battery applications, such as lithium ion batteries (LIBs). Ti3C2Tx (Tx = O, OH, F, Cl) is one of the most investigated MXenes to this day; however, most scientific research studies only focus on the design of multilayered or monolayer MXenes. Here, we present a comprehensive study on the synthesis of few-layered Ti3C2Tx materials and their use in LIB cells, in particular for high-rate applications. The synthesized Ti3C2Tx MXenes are characterized via complementary XRD, Raman spectroscopy, XPS, EDX, SEM, TGA, and nitrogen adsorption techniques to clarify the structural and chemical changes, especially regarding the surface groups and intercalated cations/water molecules. The structural changes are correlated with respect to the acidic and basic post-treatment of Ti3C2Tx. Furthermore, the detected alterations are put into an electrochemical perspective via galvanostatic and potentiostatic investigations to study the pseudocapacitive behavior of few-layered Ti3C2Tx, exhibiting a stable capacity of 155 mAh g-1 for 1000 cycles at 5 A g-1. The acidic treatment of Ti3C2Tx synthesized via the in situ formation of HF through LiF/HCl is able to increase the initial capacity in comparison to the pristine or basic treatment. To gain further insights into the structural changes occurring during (de)lithiation, in situ XRD is applied for LIB cells in a voltage range from 0.01 to 3 V to give fundamental mechanistic insights into the structural changes occurring during the first cycles. Thereby, the increased initial capacity observed for acidic-treated MXenes can be explained by the reduced co-intercalation of solvent molecules.

MXene Titanium Carbide-based Biosensor: Strong Dependence of Exfoliation Method on Performance.

Transition metal carbides, known as MXenes, are generated via the selective etching of "A" layers from their layered, ternary parent compounds, MAX phases, where M corresponds to early d-transition metal, A being a main group sp-element from either Group 13 or 14 and carbon or nitrogen being denoted by X. MXenes are being recognized as a new and uprising class of 2D materials with extraordinary physical and electrochemical properties. The huge specific surface area and outstanding electrical conductivity of MXenes, make them ideal candidates for sensing and energy applications. Herein, we demonstrated the successful incorporation of pristine MXene, Ti3C2 produced via HF etching and subsequent delamination with TBAOH, as a transducer platform toward the development of a second generation electrochemical glucose biosensor. Chronoamperometric studies demonstrate that the proposed biosensing system exhibits high selectivity and excellent electrocatalytic activity toward the detection of glucose, spanning over wide linear ranges of 50-27 750 µM and possess a low limit of detection of 23.0 µM. The findings reported in this study conceptually proves the probable applications of pristine MXenes toward the field of biosensors and pave ways for the future developments of highly selective and sensitive electrochemical biosensors for biomedical and food sampling applications.

Molten salt shielded synthesis of oxidation prone materials in air.

To prevent spontaneous oxidation during the high-temperature synthesis of non-oxide ceramics, an inert atmosphere is conventionally required1,2. This, however, results in high energy demand and high production costs. Here, we present a process for the synthesis and consolidation of oxidation-prone materials, the 'molten salt shielded synthesis/sintering' process (MS3), which uses molten salts as a reaction medium and also to protect the ceramic powders from oxidation during high-temperature processing in air. Synthesis temperatures are also reduced, and the final product is a highly pure, fine and loose powder that does not require additional milling steps. MS3 has been used for the synthesis of different ternary transition metal compounds (MAX phases, such as Ti3SiC23, Ti2AlN4, MoAlB5), binary carbides (TiC) and for the sintering of titanium. The availability of high-quality powders, combined with energy and cost savings, may remove one of the bottlenecks for the industrial application of these materials.

Improved compaction of ZnO nano-powder triggered by the presence of acetate and its effect on sintering.

The retention of nanocrystallinity in dense ceramic materials is still a challenge, even with the application of external pressure during sintering. The compaction behavior of high purity and acetate enriched zinc oxide (ZnO) nano-powders was investigated. It was found that acetate in combination with water plays a key role during the compaction into green bodies at moderate temperatures. Application of constant pressure resulted in a homogeneous green body with superior packing density (86% of theoretical value) at moderate temperature (85 °C) in the presence of water. In contrast, no improvement in density could be achieved if pure ZnO powder was used. This compaction behavior offers superior packing of the particles, resulting in a high relative density of the consolidated compact with negligible coarsening. Dissolution accompanying creep diffusion based matter transport is suggested to strongly support reorientation of ZnO particles towards densities beyond the theoretical limit for packing of ideal monosized spheres. Finally, the sintering trajectory reveals that grain growth is retarded compared to conventional processing up to 90% of theoretical density. Moreover, nearly no radial shrinkage was observed after sinter-forging for bodies performed with this advanced processing method.