Long-term stability of aerophilic metallic surfaces underwater.

Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater. Long-term stability is achieved by the formation of highly rough hierarchically structured surfaces via electrochemical anodization combined with a low-surface-energy coating produced by a fluorinated surfactant. Aerophilic Ti surfaces drastically reduce blood adhesion and, when submerged in water, prevent adhesion of bacteria and marine organisms such as barnacles and mussels. Overall, we demonstrate a general strategy to achieve the long-term stability of plastrons on aerophilic surfaces for previously unattainable underwater applications.

Iron oxide nanoparticle-based nanocomposites in biomedical application.

Iron-oxide-based biomagnetic nanocomposites, recognized for their significant properties, have been utilized in MRI and cancer treatment for several decades. The expansion of clinical applications is limited by the occurrence of adverse effects. These limitations are largely attributed to suboptimal material design, resulting in agglomeration, reduced magnetic relaxivity, and inadequate functionality. To address these challenges, various synthesis methods and modification strategies have been used to tailor the size, shape, and properties of iron oxide nanoparticle (FeONP)-based nanocomposites. The resulting modified nanocomposites exhibit significant potential for application in diagnostic, therapeutic, and theranostic contexts, including MRI, drug delivery, and anticancer and antimicrobial activity. Yet, their biosafety profile must be rigorously evaluated. Such efforts will facilitate the broader clinical translation of FeONP-based nanocomposites in biomedical applications.

Silicone-Based Lubricant-Infused Slippery Coating Covalently Bound to Aluminum Substrates for Underwater Applications.

Wetting of solid surfaces is crucial for biological and industrial processes but is also associated with several harmful phenomena such as biofouling and corrosion that limit the effectiveness of various technologies in aquatic environments. Despite extensive research, these challenges remain critical today. Recently, we have developed a facile UV-grafting technique to covalently attach silicone-based coatings to solid substrates. In this study, the grafting process was evaluated as a function of UV exposure time on aluminum substrates. While short-time exposure to UV light results in the formation of lubricant-infused slippery surfaces (LISS), a flat, nonporous variant of slippery liquid-infused porous surfaces, longer exposure leads to the formation of semi-rigid cross-linked polydimethylsiloxane (PDMS) coatings, both covalently bound to the substrate. These coatings were exposed to aquatic media to evaluate their resistance to corrosion and biofouling. While the UV-grafted cross-linked PDMS coating effectively inhibits aluminum corrosion in aquatic environments and allows organisms to grow on the surface, the LISS coating demonstrates improved corrosion resistance but inhibits biofilm adhesion. The synergy between facile and low-cost fabrication, rapid binding kinetics, eco-friendliness, and nontoxicity of the applied materials to aquatic life combined with excellent wetting-repellent characteristics make this technology applicable for implementation in aquatic environments.

Radiolysis-Driven Evolution of Gold Nanostructures - Model Verification by Scale Bridging In Situ Liquid-Phase Transmission Electron Microscopy and X-Ray Diffraction.

Utilizing ionizing radiation for in situ studies in liquid media enables unique insights into nanostructure formation dynamics. As radiolysis interferes with observations, kinetic simulations are employed to understand and exploit beam-liquid interactions. By introducing an intuitive tool to simulate arbitrary kinetic models for radiation chemistry, it is demonstrated that these models provide a holistic understanding of reaction mechanisms. This is shown for irradiated HAuCl4 solutions allowing for quantitative prediction and tailoring of redox processes in liquid-phase transmission electron microscopy (LP-TEM). Moreover, it is demonstrated that kinetic modeling of radiation chemistry is applicable to investigations utilizing X-rays such as X-ray diffraction (XRD). This emphasizes that beam-sample interactions must be considered during XRD in liquid media and shows that reaction kinetics do not provide a threshold dose rate for gold nucleation relevant to LP-TEM and XRD. Furthermore, it is unveiled that oxidative etching of gold nanoparticles depends on both, precursor concentration, and dose rate. This dependency is exploited to probe the electron beam-induced shift in Gibbs free energy landscape by analyzing critical radii of gold nanoparticles.

Nontoxic Liquid-Infused Slippery Coating Prepared on Steel Substrates Inhibits Corrosion and Biofouling Adhesion.

Wetting of surfaces plays a vital role in many biological and industrial processes. There are several phenomena closely related to wetting such as biofouling and corrosion that cause the deterioration of materials, while the efforts to prevent the degradation of surface functionality have spread over several millennia. Antifouling coatings have been developed to prevent/delay both corrosion and biofouling, but the problems remain unsolved, influencing the everyday life of the modern society in terms of safety and expenses. In this study, liquid-infused slippery surfaces (LISSs), a recently developed nontoxic repellent technology, that is, a flat variation of omniphobic slippery liquid-infused porous surfaces (SLIPSs), were studied for their anti-corrosion and marine anti-biofouling characteristics on metallic substrates under damaged and plain undamaged conditions. Austenitic stainless steel was chosen as a model due to its wide application in aquatic environments. Our LISS coating effectively prevents biofouling adhesion and decays corrosion of metallic surfaces even if they are severely damaged. The mechanically robust LISS reported in this study significantly extends the SLIPS technology, prompting their application in the marine environment due to the synergy between the facile fabrication process, rapid binding kinetics, nontoxic, ecofriendly, and low-cost applied materials together with excellent repellent characteristics.

Influence of bovine serum albumin on biodegradation behavior of pure Zn.

Zinc is emerging as a promising biodegradable metal for temporary implant applications. In this work, we investigate the influence of bovine serum albumin (BSA)-the most abundant blood protein in simulated body fluid (SBF) on degradation of pure Zn via electrochemical measurements and long-term immersion. Electrochemical experiments indicate a decrease of the corrosion rate of bare Zn with increasing BSA concentration in solution for short-term exposures. Samples were characterized with scanning electron microscope (SEM) (including energy dispersive spectroscopy [EDS], X-ray photoelectron spectroscopy [XPS], Fourier transform infrared spectroscopy [FTIR], and time-of-flight secondary ion mass spectrometry [TOF-SIMS]) after immersion up to 21 days. Presence of BSA in the electrolyte, decrease the amount of Ca-phosphate precipitation on Zn surface. However, a more compact surface layer formed in the presence of BSA in solution. Most noteworthy, in long-term exposures, BSA enhances localized corrosion of Zn-such detrimental localized attack was not observed in BSA-free solution. We suggest that a sealed space forming between the Zn substrate and a protein adsorption layer restricts mass transport, thus triggering localized corrosion of Zn.

Tuning of the Mg Alloy AZ31 Anodizing Process for Biodegradable Implants.

Coatings were grown on the AZ31 Mg alloy by a hard anodizing process in the hot glycerol phosphate-containing electrolyte. Anodizing conditions were optimized, maximizing corrosion resistance estimated by impedance measurements carried out in Hank's solution at 37 °C. A post anodizing annealing treatment (350 °C for 24 h) allowed us to further enhance the corrosion resistance of the coatings mainly containing magnesium phosphate according to energy-dispersive X-ray spectroscopy and Raman analyses. Gravimetric measurements revealed a hydrogen evolution rate within the limits acceptable for application of AZ31 in biomedical devices. In vitro tests demonstrated that the coatings are biocompatible with a preosteoblast cell line.

Static Wettability of Differently Mechanically Treated and Amphiphobic-Coated Aluminium Surfaces.

Wettability, roughness and surface treatment methods are essential for the majority of practical applications, where liquid-solid surface interactions take place. The present study experimentally investigated the influence of different mechanical surface treatment methods on the static wettability of uncoated and amphiphobic-coated aluminium alloy (AlMg3) samples, specially focusing on the interaction between surface finishing and coating. Five different surfaces were prepared: as-received substrate, polished, sandpapered, fleece-abraded and sandblasted. After characterisation, the samples were spray-coated using an amphiphobic coating. The characterisation of the uncoated and coated samples involved measurements of the roughness parameters and the apparent contact angles of demineralized water and rapeseed oil. The coating was initially characterised regarding its adhesion to the sample and elevated temperature stability. The applied surface treatments resulted in the scattered sample roughness in the range of Sa = 0.3-15.8 µm, water contact angles of θ a p , w = 78°-106° and extremely low oil contact angles. Coating the samples more than doubled the surface roughness to Sa = 13.3-29 µm, whereas the initial surface treatment properties (structure, anisotropy, etc.) were entirely repressed by the coating properties. Coating led the water contact angles to increase to θ a p , w _ c o a t e d = 162°-173° and even more pronounced oil contact angles to increase to θ a p , o _ c o a t e d = 139°-150°, classifying the surfaces as superhydrophobic and oleophobic.

In Vitro Osteocompatibility and Enhanced Biocorrosion Resistance of Diammonium Hydrogen Phosphate-Pretreated/Poly(ether imide) Coatings on Magnesium for Orthopedic Application.

Magnesium, as a biodegradable metal, is a promising candidate for biomedical applications. To modify the degradation behavior of magnesium and improve its osteocompatibility, chemical conversion and spin coating methods were combined to develop a diammonium hydrogen phosphate-pretreated/poly(ether imide) (DAHP/PEI) co-coating system. The diammonium hydrogen phosphate pretreatment was employed to enhance the attachment between PEI coatings and the magnesium substrate; meanwhile, it could serve as another bioactive and anticorrosion layer when PEI coatings break down. Surface characterization, electrochemical tests, and short-term immersion tests in DMEM were performed to evaluate DAHP/PEI coatings. Electrochemical measurements showed that DAHP/PEI coatings significantly improved the corrosion resistance of pure magnesium. No obvious changes of the chemical compositions of DAHP/PEI coatings occurred after 72 h of immersion in DMEM. An in vitro cytocompatibility study confirmed that viability and LDH activity of human osteoblast-like cells on DAHP/PEI coatings showed higher values than those on the DAHP-pretreated layer and pure magnesium. The DAHP-pretreated layer could still enhance the ALP activity of MG-63 cells after the degradation of PEI in DAHP/PEI coatings. Besides that, the in vitro cellular response to the treated magnesium was investigated to gain knowledge on the differentiation and proliferation of human adipose-derived stem cells (hADSCs). Cell distribution and morphology were observed by fluorescence and SEM images, which demonstrated that DAHP/PEI coatings facilitated cell differentiation and proliferation. The high level of C-terminals of collagen type I production of hADSCs on DAHP/PEI coatings indicated the potential of the coating for promoting osteogenic differentiation. Positive results from long-term cytocompatibility and proliferation tests indicate that DAHP/PEI coatings can offer an excellent surface for hADSCs.

Influence of proteins on the corrosion behavior of a chitosan-bioactive glass coated magnesium alloy.

The current study explored the degradation behavior of a WE43 Mg alloy during immersion tests in Dulbecco's Modified Eagle's Medium (DMEM) for 3d and 7d, for a bare alloy surface as well as for samples with surface pre-treatment, and finally for samples coated with chitosan-bioactive glass. The immersion tests were conducted with and without addition of serum, to study the influence of proteins on the degradation process. Mass-loss was measured to determine the corrosion rate after 3d and 7d of immersion. The samples were analyzed by SEM with respect to their surface morphology and the chemical composition was screened by high-resolution XPS. The results demonstrate not only a significant, time-dependent influence of serum addition on the corrosion behavior of the materials studied, but noteworthy is that depending on the sample type, proteins in solution were observed to either accelerate or inhibit corrosion. These results are discussed in correlation to observed changes in surface chemistry taking place upon immersion in the absence and presence of proteins.

Electrophoretic Deposition of Bioadaptive Drug Delivery Coatings on Magnesium Alloy for Bone Repair.

Biodegradable polymer coatings on magnesium alloys are attractive, as they can provide corrosion resistance as well as additional functions for biomedical applications, e.g., drug delivery. A gelatin nanospheres/chitosan (GNs/CTS) composite coating on WE43 substrate was fabricated by electrophoretic deposition with simvastatin (SIM) loaded into the GNs. Apart from a sustained drug release over 28 days, an anticorrosion behavior of the coated WE43 substrates was confirmed by electrochemical tests. Both the degradation and corrosion rates of the coated substrate were significantly minimized in contrast to bare WE43. The cytocompatibility of the coated samples was analyzed  both quantitatively and qualitatively. Additionally, the osteogenic differentiation of MC3T3-E1 cells on SIM-containing coatings was assessed by measuring the expression of osteogenic genes and related proteins, alkaline phosphatase (ALP) activity, and extracellular matrix mineralization, showing that the SIM-loaded composite coating could upregulate the expression of osteogenic genes and related proteins, promote ALP activity, and enhance extracellular matrix mineralization. In summary, the SIM-loaded GNs/CTS composite coatings were able to enhance the corrosion resistance of the WE43 substrate and promote osteogenic activity, thus demonstrating a promising coating system for modifying the surface of magnesium alloys targeted for orthopedic applications.

Modification of in vitro degradation behavior of pure iron with ultrasonication treatment: Comparison of two different pseudo-physiological solutions.

An ultrasonication treatment is developed as an external method to control the degradation behavior of pure iron. Immersion tests (weight loss measurements) and electrochemical measurements were conducted in two different pseudo-physiological solutions, simulated body fluid (SBF) and Dulbecco's modified Eagle medium (DMEM) solution. By the comparison study in these two different solutions, more information and the mechanism of the degradation process can be revealed. Degradation morphologies (with and without ultrasonication treatment) were observed by scanning electron microscope (SEM), and degradation products on the surface were characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Moreover, the biocompatibility of iron surfaces after being ultrasonicated was evaluated. Ultrasonication was found to accelerate the degradation rate in DMEM, while it makes no difference in SBF solution; the origin of this different behavior is investigated and discussed. The parameters of the ultrasonication treatment, intensity and frequency, show an influence on the degradation rate. No adverse effects on the proliferation and adhesion of human osteoblast-like cells (MG-63) are observed on surfaces after ultrasonication treatment, as compared to bare iron. Based on these results, ultrasonication treatment is considered to have high potential to control the biodegradation behavior of iron-based materials in an external and flexible manner.

Combinatorial Study on Phase Formation and Oxidation in the Thin Film Superalloy Subsystems Co-Al-Cr and Co-Al-Cr-W.

Two Co-based superalloy subsystems, the ternary system Co-Al-Cr and the quasi-ternary system Co-Al-Cr-W with a constant amount of 10 at. % W, were deposited as thin-film materials libraries and analyzed in terms of phase formation and oxidation behavior at 500 °C in air. By combining energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy high-throughput composition measurements, a detailed evaluation of the dependence between the initial multinary metal composition and the oxide scale composition which is forming upon oxidation on the surface of the thin film is established. Phase maps for both materials libraries are provided by high-throughput X-ray diffraction. In addition, the oxidation of a Co-Al-Cr-W bulk sample was analyzed and compared to a corresponding film in the library.

Electrophoretic deposition of lawsone loaded bioactive glass (BG)/chitosan composite on polyetheretherketone (PEEK)/BG layers as antibacterial and bioactive coating.

In this study, chitosan/bioactive glass (BG)/lawsone coatings were deposited by electrophoretic deposition (EPD) on polyetheretherketone (PEEK)/BG layers (previously deposited by EPD on 316-L stainless steel) to produce bioactive and antibacterial coatings. First, the EPD of chitosan/BG/lawsone was optimized on stainless steel in terms of suspension stability, homogeneity and thickness of coatings. Subsequently, the optimized EPD parameters were used to produce bioresorbable chitosan/bioactive glass (BG)/lawsone coatings on PEEK/BG layers. The produced layered coatings were characterized in terms of composition, microstructure, corrosion resistance, in vitro bioactivity, drug release kinetics and antibacterial activity. Ultraviolet/Visible (UV/VIS) spectroscopic analyses confirmed the release of lawsone from the coatings. Moreover, the deposition of chitosan/BG coatings was confirmed by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared spectroscopy (FTIR). The coated specimens presented higher corrosion resistance (10 times) in comparison to that of bare 316-L stainless steel and showed convenient wettability for initial protein attachment. The presence of lawsone in the top layer provided antibacterial effects against Staphylococcus carnosus. Moreover, the developed coatings formed apatite-like crystals upon immersion in simulated body fluid, indicating the possibility of achieving close interaction between the coating surface and bone. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3111-3122, 2018.

A novel local drug delivery system: Superhydrophobic titanium oxide nanotube arrays serve as the drug reservoir and ultrasonication functions as the drug release trigger.

A local drug delivery system consisting of superhydrophobic titanium oxide nanotube (S-TNTs) arrays and ultrasonic-controlled release trigger was developed in this work. Hydrophilic TNTs arrays are converted into superhydrophobic after being treated by 1H,1H,2H,2H- perfluorooctyl-triethoxysilane (POTS). S-TNTs arrays serving as a drug-carrying vehicle require no extra sealing treatment due to the excellent isolation effect from the trapped air layer on the surface. Different amounts of drugs could be loaded into S-TNTs arrays by control of the structure of arrays (including length and diameter of tubes) and the original amount of drug in the drug-loading solution. The relation between surface morphology of TNTs arrays and superhydrophobicity (isolation effect) was thoroughly investigated. To achieve a stimulus-responsive drug delivery system, ultrasonication was employed as an efficient drug release trigger. Trapped air layer could be selectively removed by ultrasonication, and therefore the loaded drug could be released in a multiple and controlled manner. Any drugs that can dissolve in nonpolar solutions are expected to be suitable for this local drug delivery system.

Cu-releasing bioactive glass/polycaprolactone coating on Mg with antibacterial and anticorrosive properties for bone tissue engineering.

Bioactive glass nanoparticles containing copper (Cu-BGNs) were introduced into polycaprolactone (PCL) coating systems to improve the bioactivity, antibacterial properties, and corrosion resistance of vulnerable magnesium matrices under physiological conditions. The influence of different amounts of Cu-BGNs in PCL coatings was thoroughly investigated in determining the wettability, electrochemical properties, and antibacterial effects against Staphylococcus carnosus and Escherichia coli, as well as their cyto-compatibility. Cu-BGNs were observed randomly scattered in PCL coatings. Increasing the concentration of Cu-BGNs resulted in a slight decrease of the water contact angle, and a reduction in anticorrosion properties of the Cu-BGN composite coatings. Yet higher Cu-BGN content in coatings led to more calcium phosphate formation on the surface after 7 days of immersion in Dulbecco's modified Eagle's medium, which was confirmed by Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy. The growth of S. carnosus and E. coli was inhibited by Cu2+ ions released from the Cu-BGN coatings. In addition, both direct and indirect cyto-compatibility experiments showed that the viability and proliferation of MG-63 cells on Cu-BGN coatings were highly increased compared to pure magnesium; however, an additional increase of Cu-BGN concentration showed a slight decrease of cell proliferation and cell activity. In summary, Cu-BGN/PCL composite coatings impart magnesium-based biomaterials with antibacterial and anticorrosive properties for clinical applications.

Electrophoretic deposition of organic/inorganic composite coatings containing ZnO nanoparticles exhibiting antibacterial properties.

To address one of the serious problems associated with permanent implants, namely bacterial infections, novel organic/inorganic coatings containing zinc oxide nanoparticles (nZnO) are proposed. Coatings were obtained by electrophoretic deposition (EPD) on stainless steel 316L. Different deposition conditions namely: deposition times in the range 60-300s and applied voltage in the range 5-30V as well as developing a layered coating approach were studied. Antibacterial tests against gram-positive Staphylococcus aureus and gram-negative Salmonella enteric bacteria confirmed the activity of nZnO to prevent bacterial growth. Coatings composition and morphology were analyzed by thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Moreover, the corrosion resistance was analyzed by evaluation of the polarization curves in DMEM at 37°C, and it was found that coatings containing nZnO increased the corrosion resistance compared to the bare substrate. Considering all results, the newly developed coatings represent a suitable alternative for the surface modification of metallic implants.

Alternating Current Electrophoretic Deposition for the Immobilization of Antimicrobial Agents on Titanium Implant Surfaces.

One prominent cause of implant failure is infection; therefore, research is focusing on developing surface coatings that render the surface resistant to colonization by micro-organisms. Permanently attached coatings of antimicrobial molecules are of particular interest because of the reduced cytoxicity and lower risk of developing resistance compared to controlled release coatings. In this study, we focus on the chemical grafting of bioactive molecules on titanium. To concentrate the molecules at the metallic implant surface, we propose electrophoretic deposition (EPD) applying alternating current (AC) signals with an asymmetrical wave shape. We show that for the model molecule bovine serum albumin (BSA), as well as for the clinically relevant antifungal lipopeptide caspofungin (CASP), the deposition yield is drastically improved by superimposing a DC offset in the direction of the high-amplitude peak of the AC signal. Additionally, in order to produce immobilized CASP coatings, this experimental AC/DC-EPD method is combined with an established surface activation protocol. Principle component analysis (PCA) of time-of-flight secondary ion mass spectrometry (ToF-SIMS) data confirm the immobilization of CASP with higher yield as compared to a diffusion-controlled process, and higher purity than the clinical CASP starting suspensions. Scratch testing data indicate good coating adhesion. Importantly, the coatings remain active against the fungal pathogen C. albicans as shown by in vitro biofilm experiments. In summary, this paper delivers a proof-of-concept for the application of AC-EPD as a fast grafting tool for antimicrobial molecules without compromising their activities.

Albumin coatings by alternating current electrophoretic deposition for improving corrosion resistance and bioactivity of titanium implants.

Although Ti alloys are generally regarded to be highly corrosion resistant, inflammatory conditions following surgery can instigate breakdown of the TiO2 passivation layer leading to an increased metal ion release. Furthermore proteins present in the surrounding tissue will readily adsorb on a titanium surface after implantation. In this paper alternating current electrophoretic deposition (AC-EPD) of bovine serum albumin (BSA) on Ti6Al4V was investigated in order to increase the corrosion resistance and control the protein adsorption capability of the implant surface. The Ti6Al4V surface was characterized with SEM, XPS and ToF-SIMS after long-term immersion tests under physiological conditions and simulated inflammatory conditions either in Dulbecco's Modified Eagle Medium (DMEM) or DMEM supplemented with fetal calf serum (FCS). The analysis showed an increased adsorption of amino acids and proteins from the different immersion solutions. The BSA coating was shown to prevent selective dissolution of the vanadium (V) rich ß-phase, thus effectively limiting metal ion release to the environment. Electrochemical impedance spectroscopy measurements confirmed an increase of the corrosion resistance for BSA coated surfaces as a function of immersion time due to the time-dependent adsorption of the different amino acids (from DMEM) and proteins (from FCS) as observed by ToF-SIMS analysis.