Bio-Inspired Micro- and Nano-Scale Surface Features Produced by Femtosecond Laser-Texturing Enhance TiZr-Implant Osseointegration.

Surface design plays a critical role in determining the integration of dental implants with bone tissue. Femtosecond laser-texturing has emerged as a breakthrough technology offering excellent uniformity and reproducibility in implant surface features. However, when compared to state-of-the-art sandblasted and acid-etched surfaces, laser-textured surface designs typically underperform in terms of osseointegration. This study investigates the capacity of a bio-inspired femtosecond laser-textured surface design to enhance osseointegration compared to state-of-the-art sandblasted & acid-etched surfaces. Laser-texturing facilitates the production of an organized trabeculae-like microarchitecture with superimposed nano-scale laser-induced periodic surface structures on both 2D and 3D samples of titanium-zirconium-alloy. Following a boiling treatment to modify the surface chemistry, improving wettability to a contact angle of 10°, laser-textured surfaces enhance fibrin network formation when in contact with human whole blood, comparable to state-of-the-art surfaces. In vitro experiments demonstrate that laser-textured surfaces significantly outperform state-of-the-art surfaces with a 2.5-fold higher level of mineralization by bone progenitor cells after 28 days of culture. Furthermore, in vivo evaluations reveal superior biomechanical integration of laser-textured surfaces after 28 days of implantation. Notably, during abiological pull-out tests, laser-textured surfaces exhibit comparable performance, suggesting that the observed enhanced osseointegration is primarily driven by the biological response to the surface.

Two Steady-State Adsorption Modes of Phosphonic Acids on Aluminum Surfaces.

The phosphonic acid (PA) surface treatment on various metal substrates is of high industrial relevance, and the PA molecular structure significantly affects its quality. In this work, systematic variation of the PA molecular steric and electron environment helps discern two steady-state adsorption modes on an aluminum surface. The PA molecular structure was varied systematically, which included inorganic phosphorus acid, alkyl phosphonic acids, and phenyl phosphonic acids. To explore their in situ dynamics of adsorption/desorption on the electrochemically unstable aluminum, techniques such as electrochemical impedance spectroscopy and inductively coupled plasma optical emission spectrometry were employed. A range of different types of interfacial layers are formed on the aluminum surface, namely, from the dissolution-limiting physisorbed layer to a quasi-inhibiting chemisorbed layer on the aluminum surface in acidic (pH ≈ 2.2) solution. Presented findings establish the dynamic steady-state nature of this type of interface. They reveal fundamental relationships among adsorbent steric or electronic effects, the steady-state interface morphology, and the steady-state aluminum dissolution rate. The study brings also a more differentiated molecular structure-related description of the aluminum dissolution inhibition of PAs and relates it to molecular density functional theory calculations.

Elucidating the Rate-Limiting Processes in High-Temperature Sodium-Metal Chloride Batteries.

Sodium-metal chloride batteries are considered a sustainable and safe alternative to lithium-ion batteries for large-scale stationary electricity storage, but exhibit disadvantages in rate capability. Several studies identify metal-ion migration through the metal chloride conversion layer on the positive electrode as the rate-limiting step, limiting charge and discharge rates in sodium-metal chloride batteries. Here the authors present electrochemical nickel and iron chlorination with planar model electrodes in molten sodium tetrachloroaluminate electrolyte at 300 °C. It is discovered that, instead of metal-ion migration through the metal chloride conversion layer, it is metal-ion diffusion in sodium tetrachloroaluminate which limits chlorination of both the nickel and iron electrodes. Upon charge, chlorination of the nickel electrode proceeds via uniform oxidation of nickel and the formation of NiCl2 platelets on the surface of the electrode. In contrast, the oxidation of the iron electrodes proceeds via localized corrosion attacks, resulting in nonuniform iron oxidation and pulverization of the iron electrode. The transition from planar model electrodes to porous high-capacity electrodes, where sodium-ion migration along the tortuous path in the porous electrode can become rate limiting, is further discussed. These mechanistic insights are important for the design of competitive next-generation sodium-metal chloride batteries with improved rate performance.

Electrophoretic Deposition of Nanoporous Oxide Coatings from Concentrated CuO Nanoparticle Dispersions.

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.

Biocorrosion Zoomed In: Evidence for Dealloying of Nanometric Intermetallic Particles in Magnesium Alloys.

Biodegradable magnesium alloys generally contain intermetallic phases on the micro- or nanoscale, which can initiate and control local corrosion processes via microgalvanic coupling. However, the experimental difficulties in characterizing active degradation on the nanoscale have so far limited the understanding of how these materials degrade in complex physiological environments. Here a quasi-in situ experiment based on transmission electron microscopy (TEM) is designed, which enables the initial corrosion attack at nanometric particles to be accessed within the first seconds of immersion. Combined with high-resolution ex situ cross-sectional TEM analysis of a well-developed corrosion-product layer, mechanistic insights into Mg-alloys' degradation on the nanoscale are provided over a large range of immersion times. Applying this methodology to lean Mg-Zn-Ca alloys and following in detail the dissolution of their nanometric Zn- and Ca-rich particles the in statu nascendi observation of intermetallic-particle dealloying is documented for magnesium alloys, where electrochemically active Ca and Mg preferentially dissolve and electropositive Zn enriches, inducing the particles' gradual ennoblement. Based on electrochemical theory, here, the concept of cathodic-polarization-induced dealloying, which controls the dynamic microstructural changes, is presented. The general prerequisites for this new dealloying mechanism to occur in multicomponent alloys and its distinction to other dealloying modes are also discussed.

Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area.

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100-140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20-40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.

Anodizing of Self-Passivating W xTi1- x Precursors for W xTi1- xO n Oxide Alloys with Tailored Stability.

TiO2 and WO3 are two of the most important, industrially relevant earth-abundant oxides. Although both materials show complementary functionality and are promising candidates for similar types of applications such as catalysis, sensor technology, and energy conversion, their chemical stability in reactive environments differs remarkably. In this study, anodic barrier oxides are grown on solid-solution W xTi1- x alloy precursors covering a wide compositional range (0 ≤ x ≤ 1) with the goal of creating functional oxides with tailored stability. A strong Ti-cation enrichment in the surface region of the grown W xTi1- xO n layer is observed, which can be controlled by both the anodizing conditions and precursor composition. For Ti concentrations above 50 at. %, a continuous nanometer-thick TiO2 protective coating is achieved on top of a homogeneous W xTi1- xO n film as evidenced by X-ray photoelectron spectroscopy and transmission electron microscopy analyses. A comprehensive electrochemical assessment demonstrates a very stable passivation of the surface in both acidic and alkaline environments. This increase in chemical stability correlates directly with the presence of this protective TiO2 film. The results of this work provide insights into the oxidation behavior of W1- xTi x alloys, but more importantly demonstrate how controlled oxidation of self-passivating alloys can lead to oxide alloys with thin, protective surface layers that otherwise would require more sophisticated deposition methods.

Differential apoptotic response of MC3T3-E1 pre-osteoblasts to biodegradable magnesium alloys in an in vitro direct culture model.

The biodegradable magnesium-based implants have been widely utilized in medical orthopedic applications in recent years. We have recently shown that direct culture on Pure Mg and Mg2Ag alloys lead to a progressive differentiation impairment of MC3T3-E1 pre-osteoblasts. In this study, we aimed to analyze the apoptotic reaction of MC3T3-E1 cells in response to the direct culture on Pure Mg, Mg2Ag and Extreme High Pure Mg (XHP Mg) alloy samples. Our results demonstrated that long-term culturing of MC3T3-E1 cells on Pure Mg and Mg2Ag alloys induce time-dependent expression of active caspase-3 (active casp-3) and cleaved PARP-1 (cl. PARP-1), the hallmark of apoptosis reactions concomitant with a significant increase in the number of dead cells. However, direct culture on XHP Mg material results in a lower number of dead cells in comparison to Pure Mg and Mg2Ag alloys. Furthermore, XHP Mg materials influence expression of apoptotic markers in a process resembles that of observed in osteogenic condition apparently indicative of MC3T3-E1 osteodifferentiation. This study indicates that Mg alloy samples mediated differential apoptotic reactions of MC3T3-E1 cells can be ascribed to factors such as distinct topography and hydrophobicity features of Mg material surfaces, contrasting nature/composition of corrosion products as well as different impurities of these materials. Therefore, initial Mg alloys surface preparation, controlling the growth and composition of corrosion products and Mg alloys purity enhancement are necessary steps towards optimizing the Mg alloys usage in medical orthopedic applications.

The influence of heat treatment and plastic deformation on the bio-degradation of a Mg-Y-RE alloy.

In this study the bio-degradation behavior of a Mg-Y-RE alloy in different heat treatment states with respect to the alloy's potential application as biodegradable implant material was investigated by electrochemical impedance spectroscopy in two body-similar fluids. The heat treatments increase the degradation resistance of the alloy and lead to the formation of a thermal oxide layer on the sample surface and to a change in microstructure such as the distribution of yttrium. The varying Y distribution in the alloy does not significantly influence the degradation behavior, and all samples show a similar low polarization resistance. However, samples with a thermal oxide layer, which consists mainly of Y(2)O(3), degrade much more slowly and feature remarkably high polarization resistance. Nevertheless, in some cases localized corrosion attack occurs and drastically impairs performance. Cracks in the oxide layer, intentionally induced by straining of the samples and which in practice could originate from the implantation process, reduce the corrosion resistance. However, these samples perform still better than polished specimens and show a macroscopically homogeneous degradation behavior without localized corrosion. Microscopically, corrosion attacks start at the cracks and undermining of the oxide layer occurs with time. For all the material conditions a remarkable dependence of the degradation rate on the electrolyte is noted.

Impedance characterization and modeling of electrodes for biomedical applications.

A low electrode-electrolyte impedance interface is critical in the design of electrodes for biomedical applications. To design low-impedance interfaces a complete understanding of the physical processes contributing to the impedance is required. In this work a model describing these physical processes is validated and extended to quantify the effect of organic coatings and incubation time. Electrochemical impedance spectroscopy has been used to electrically characterize the interface for various electrode materials: platinum, platinum black, and titanium nitride; and varying electrode sizes: 1 cm2, and 900 microm2. An equivalent circuit model comprising an interface capacitance, shunted by a charge transfer resistance, in series with the solution resistance has been fitted to the experimental results. Theoretical equations have been used to calculate the interface capacitance impedance and the solution resistance, yielding results that correspond well with the fitted parameter values, thereby confirming the validity of the equations. The effect of incubation time, and two organic cell-adhesion promoting coatings, poly-L-lysine and laminin, on the interface impedance has been quantified using the model. This demonstrates the benefits of using this model in developing better understanding of the physical processes occurring at the interface in more complex, biomedically relevant situations.