Porous biomorphic silicon carbide ceramics coated with hydroxyapatite as prospective materials for bone implants

Porous and cytocompatible silicon carbide (SiC) ceramics derived from wood precursors and coated with bioactive hydroxyapatite (HA) and HA-zirconium dioxide (HA/ZrO2) composite are materials with promising application in engineering of bone implants due to their excellent mechanical and structural properties. Biomorphic SiC ceramics have been synthesized from wood (Hornbeam, Sapele, Tilia and Pear) using a forced impregnation method. The SiC ceramics have been coated with bioactive HA and HA/ZrO2 using effective gas detonation deposition approach (GDD). The surface morphology and cytotoxicity of SiC ceramics as well as phase composition and crystallinity of deposited coatings were analyzed. It has been shown that the porosity and pore size of SiC ceramics depend on initial wood source. The XRD and FTIR studies revealed the preservation of crystal structure and phase composition of in the HA coating, while addition of ZrO2 to the initial HA powder resulted in significant decomposition of the final HA/ZrO2 coating and formation of other calcium phosphate phases. In turn, NIH 3T3 cells cultured in medium exposed to coated and uncoated SiC ceramics showed high re-cultivation efficiency as well as metabolic activity. The recultivation efficiency of cells was the highest for HA-coated ceramics, whereas HA/ZrO2 coating improved the recultivation efficiency of cells as compared to uncoated SiC ceramics. The GDD method allowed generating homogeneous HA coatings with no change in calcium to phosphorus ratio. In summary, porous and cytocompatible bio-SiC ceramics with bioactive coatings show a great promise in construction of light, robust, inexpensive and patient-specific bone implants for clinical application.

Tribological characterization of zirconia coatings deposited on Ti6Al4V components for orthopedic applications

One of the most important issues leading to the failure of total joint arthroplasty is related to the wear of the plastic components, which are generally made of ultra high molecular weight polyethylene (UHMWPE). Therefore, the reduction of joint wear represents one of the main challenges the research in orthopedics is called to address nowadays. Surface treatments and coatings have been recognized as innovative methods to improve tribological properties, also in the orthopedic field. This work investigated the possibility to realize hard ceramic coatings on the metal component of a prosthesis, by means of Pulsed Plasma Deposition, in order to reduce friction and wear in the standard coupling against UHMWPE. Ti6Al4V substrates were coated with a 2 μm thick yttria-stabilized zirconia (YSZ) layer. The mechanical properties of the YSZ coatings were assessed by nanoindentation tests performed on flat Ti6Al4V substrates. Tribological performance was evaluated using a ball-on-disk tribometer in dry and lubricated (i.e. with fetal bovine serum) highly-stressing conditions, up to an overall distance of 10 km. Tribology was characterized in terms of coefficient of friction (CoF) and wear rate of the UHMWPE disk. After testing, specimens were analyzed through optical microscopy and SEM images, in order to check the wear degradation mechanisms. Progressive loading scratch tests were also performed in dry and wet conditions to determine the effects of the environment on the adhesion of the coating. Our results supported the beneficial effect of YSZ coating on metal components. In particular, the proposed solution significantly reduced UHMWPE wear rate and friction. At 10 km of sliding distance, a wear rate reduction of about 18% in dry configuration and of 4% in presence of serum, was obtained by the coated group compared to the uncoated group. As far as friction in dry condition is concerned, the coating allowed to maintain low CoF values until the end of the tests, with an overall difference of about 40% compared to the uncoated balls. In wet conditions, the friction values were found to be comparable between coated and uncoated materials, mainly due to a premature delamination of the coating. Scratch tests in wet showed in fact a reduction of the critical load required to a complete delamination due to a formation of blister, although no change or damage occurred at the coating during the soaking period. Although conditions of high values of contact pressure were considered, further analyses are however required to fully understand the behavior of YSZ coatings in wet environment and additional research on the deposition process will be mandatory in order to improve the coating tribological performance at long distances addressing orthopedic applications.

Preparation of immobilized coating Fenton-like catalyst for high efficient degradation of phenol

In this study, solid acid amorphous Fe₃O₄/SiO₂ ceramic coating decorated with sulfur on Q235 carbon steel as Fenton-like catalyst for phenol degradation was successfully prepared by plasma electrolytic oxidation (PEO) in silicate electrolyte containing Na₂S₂O₈ as sulfur source. The surface morphology and phase composition were characterized by SEM, EDS, XRD and XPS analyses. NH₃-TPD was used to evaluate surface acidity of PEO coating. The results indicated that sulfur decorated amorphous Fe₃O₄/SiO₂ ceramic coatings with porous structure and higher acid strength had the similar pore size and the surface became more and more uneven with the increase of Na₂S₂O₈ in the silicate electrolyte. The Fenton-like catalytic activity of sulfur decorated PEO coatings was also evaluated. In contrast to negligible catalytic activity of sulfur undecorated PEO coating, catalytic activity of sulfur decorated PEO coating was excellent and PEO coating prepared with 3.0 g Na₂S₂O₈ had the highest catalytic activity which could degrade 99% of phenol within 8 min under circumneutral pH. The outstanding performance of sulfur decorated PEO coating was attributed to strong acidic microenvironment and more Fe²⁺ on the surface. The strong acid sites played a key factor in determining catalytic activity of catalyst. In conclusion, rapid phenol removal under circumneutral pH and easier separation endowed it potential application in wastewater treatment. In addition, this strategy of preparing immobilized solid acid coating could provide guidance for designing Fenton-like catalyst with excellent catalytic activity and easier separation.

Boosting the Detection Potential of Liquid Chromatography-Electron Ionization Mass Spectrometry Using a Ceramic Coated Ion Source

Detection of target and non-target substances and their characterization in complex samples is a challenging task. Here we demonstrate that coating the electron ionization (EI) ion source of an LC-MS system with a sol-gel ceramic film can drastically improve the detection of high-molecular weight and high-boiling analytes. A new ion source coated with a ceramic material was developed and tested with a mixture of polycyclic aromatic hydrocarbons (PAH) with an increasing number of rings. Comparison of the results obtained with those for an uncoated stainless steel (SS) ion source shows a dramatic improvement in the MS signals, with a nearly 40-fold increase of the signal-to-noise ratio. We also demonstrate the ability of the new system to produce excellent chromatographic profiles for hard-to-detect hormones.

A new methodology to prepare ceramic-organic composite coatings with good cavitation erosion resistance

A simple, scalable and economical method was proposed to obtain ceramic-organic composite coating with excellent comprehensive properties include hardness, toughness, elastic recovery, lamellar interfacial bonding and anti-cavitation erosion: introducing epoxy resin into the pores and micro-cracks of plasma sprayed ceramic coating. The results indicate that the epoxy resin was successfully penetrated into the whole ceramic coating and filled almost all defects by vacuum impregnation, which greatly enhanced its compactness and mechanical properties. The bonding strength between top coating and metal interlayer significantly increased from 17.3 MPa to 53.0 MPa, and the hardness (H) of top coating greatly increased from 11.07 GPa to 23.57 GPa. Besides, the value of H³/E² also increased from 0.06 GPa to 0.15 GPa, meaning the toughness of ceramic coating had been obviously improved. The pure ceramic coating had been punctured only after 4 h of cavitation test. However, the resin with high elasticity and toughness can effectively absorb impact energy, prevent cracks propagation and delay splats spallation during the cavitation erosion process. The novel composite coating displayed far better cavitation erosion resistance than pure ceramic coating, and it was still intact after 10 h of test.

Effects of working gas pressure on zirconium dioxide thin film prepared by pulsed plasma deposition: roughness, wettability, friction and wear characteristics

In joint arthroplasty one of the main issues related to the failure of prosthetic implants is due to the wear of the ultra-high molecular weight polyethylene (UHMWPE) component. Surface treatments and coatings have been recognized as enhancing methods, able to improve the tribological properties of the implants. Therefore, the main objective of this work was to investigate the possibility to fabricate yttria-stabilized zirconia (YSZ) coatings on a metal (AISI 316-L) substrate by means of Pulsed Electron Deposition, in order to improve the tribological behavior of the polymer-metal coupling, by reducing the initial wear of the UHMWPE component. In order to optimize the coating characteristics, the effects of working gas pressure on both its morphological and tribological properties were analyzed. Morphological characterization of the films was evaluated by Atomic Force Microscopy (AFM). Coating wettability was also estimated by contact angle (CA) measurement. Tribological performance (coupling friction and wear of UHMWPE) was evaluated by using a ball-on-disc tribometer during highly-stressing tests in dry and lubricated (i.e. NaCl and serum) conditions; friction and wear were specifically evaluated at the initial sliding distances - to highlight the main effect of coating morphology - and after 100m - where the influence of the intrinsic materials properties prevails. AFM analysis highlighted that the working pressure heavily affected the morphological characteristics of the realized films. The wettability of the coating at the highest and lowest deposition pressures (CA ~ 60°, closed to substrate value) decreased for intermediate pressures, reaching a maximum CA of ~ 90°. Regarding tribological tests, a strong correlation was found in the initial steps between friction coefficient and wettability, which decreased as the distance increased. Concerning UHMWPE wear associated to coated counterpart, at 100m a reduction rate of about 7% in dry, 12% in NaCl and 5% in presence of serum was obtained compared to the uncoated counterpart. Differently from what highlighted for friction, no correlation was found between wear rate and morphological parameters. These findings, in agreement with literature, underlined the effect of the deposition pressure on the morphological properties, but suggested that physical characteristics are influenced too. Further research on the deposition process will be required in order to improve the tribological performance of the coating at long distances, addressing - above all - orthopedic applications.

Tribological and corrosion performance of the plasma-sprayed conformal ceramic coating on selective laser melted CoCrMo alloy

Ceramic implants have superior performance due to the excellent wear resistance and biocompatibility. However, the poor machinability limits their applications. Plasma sprayed ceramic coating on the additively manufactured metal substrate not only provides a 3-dimensional conformal implant coating and but also forms a highly wear-resistant surface layer. In this paper, three types of ceramic coatings of Al₂O_3, ZrO₂, and Al₂O₃-ZrO₂ composite have been fabricated by atmosphere plasma spray on the CoCrMo alloy substrate prepared by selective laser melting (SLM). It has been found that the Al₂O₃-ZrO₂ composite coating has better corrosion and wear resistance compared with the ceramic coating (Al₂O_3, ZrO₂) and the CoCrMo substrate. The adhesion strength between the Al₂O₃-ZrO₂ composite coating and the substrate reaches 238 MPa. In addition, the wear and corrosion resistance increase with wear progression for all the fabricated ceramic coatings. The highly dense microstructure, fewer microcracks, and the amorphous phases are deterministic factors responsible for the superior tribological and corrosion performance of the Al₂O₃-ZrO₂ composite coating. The fabrication route has been proved very promising to manufacture high-performance implants with ceramic coating.

S-incorporated TiO2 coatings grown by plasma electrolytic oxidation for reduction of Cr(VI)-EDTA with sunlight

The plasma electrolytic oxidation (PEO) technique was used to prepare photocatalytic S-TiO₂ coatings on Ti sheets; the incorporation of the S ions was possible from the electrolyte for modifying the structural and optics characteristics of the material. In this work, substrates of Ti (ASME SB-265 of 20 × 20 × 1 mm) were used in a PEO process in 10 min, using constant voltage pulses of 340 V with frequency of 1 kHz and duty cycles of 10% and of 30%. Solutions with H₂SO₄ (0.1 M) and CH₄N₂S (52 and 79 mM) were used as electrolytes. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (EDS) were utilized to analyze the surface morphology, crystalline phase, and chemical composition of the samples. According to the results, the catalyst coatings had microporous structure and contained anatase-rutile TiO₂ nanocrystalline mixture, until 73.2% rutile and 26.8% anatase in the samples grown with 30% duty cycle and the lowest concentration of CH₄N₂S. From the EDS measurements, the incorporation of sulfur ions to the coatings was 0.08 wt%. 99.5% reduction efficiency of Cr(VI)-EDTA with sunlight was observed after 2 h; it was determined by diphenyl carbazide spectrophotometric method. These coatings have potential for effective sunlight heterogeneous photoreduction of this toxic, cumulative, and non-biodegradable heavy metal that contaminates the soil and water and is a serious risk to sustainability, ecosystems, and human health.

Influence of heating temperature and time on mechanical-degradation, microstructures and corrosion performances of Teflon/granite coated aluminum alloys used for non-stick cookware

This study explores the functional characteristics (erosion, corrosion, mechanical damage, and microstructural features) of non-stick cookware made from aluminum alloys. Typically coated with polytetrafluoroethylene (PTFE-Teflon) or ceramic for non-stick properties, we conducted a systematic investigation using corrosion, abrasion, and mechanical tests on six types of cookware from different manufacturers (Manuf-1-6). The cookware was heated at various temperatures [Room temperature (RT), 100, 175, 250, & 350 °C] and times (45 & 120 min). Tests included Taber wear, Adhesive Pull-off, hot & RT corrosion, and surface roughness measurements. Characterization involved optical microscopy, scanning electron microscope (SEM) with electron backscattered diffraction (EBSD), and x-ray diffraction (XRD). Ceramic-coated cookware from Manuf-4 demonstrated superior mechanical strength, wear, and corrosion resistance due to refined microstructures. Manuf-1's PTFE-coated cookware also performed well. Optimal results were observed when heating below 250 °C for up to 45 min. Prolonged heating and temperatures beyond 250 °C adversely affected internal structures of all cookware. Thus, it is advisable to use Al-based non-stick cookware below 250 °C for a maximum of 45 min.

A novel two-step conversion from DCPD-coated β-TCP to low crystallinity β-TCP porous scaffolds via combination between dry heating and hydrothermal methods: Effects on pre-osteoblast cell responses

This study presents a novel two-step process to fabricate low crystallinity (LC) β-tricalcium phosphate (β-TCP) porous scaffolds and evaluates their implications for pre-osteoblast cell responses. The novelty of this study lies in the two-step conversion of dicalcium phosphate dihydrate (DCPD) -coated β-TCP porous scaffold into LC β-TCP porous scaffolds through a combination of dry heating and hydrothermal conditions at 200°C. The obtained LC β-TCP porous scaffolds were characterised using a Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier-Transform Infrared (FTIR), porosity, and compressive strength analysis confirmed the successful fabrication of LC β-TCP scaffolds. Besides, in vitro tests using pre-osteoblast MC3T3-E1 cells were conducted to investigate the cell responses toward LC β-TCP porous scaffolds. The results revealed that the LC β-TCP porous scaffolds were successfully fabricated by converting the DCPD-coated β-TCP into the dicalcium phosphate anhydrous (DCPA) coated β-TCP, followed by a hydrothermal process in a 0.1 mol/L calcium chloride (CaCl2) aqueous solution at 200°C for 24 hours to obtain LC of pure β-TCP scaffold. Moreover, in vitro cell study indicated that the cell density and proliferation surrounding the surface of the LC β-TCP porous scaffold were greater than DCPD-coated β-TCP porous scaffolds. The findings from this study are expected to significantly impact bioceramic technology by enhancing cell responses.

Ultrasonic-assisted MoS2/GO/TiO2 ceramic coatings: Enhancing anti-friction performance through dual-interface optimization

Ceramic coatings containing two-dimensional materials (2D materials) provide effective protection for light alloys during wear, significantly improving their anti-friction performance. MoS2 has proven highly effective in enhancing the anti-friction performance of ceramic coatings, particularly when synthesized via plasma electrolytic oxidation (PEO). However, dislocation pinning due to the incoherent interfaces in MoS2/TiO2 coatings tends to cause localized stress concentrations and brittle fracture, requiring effectively improve nanomechanical properties by optimizing interface design. To address these issues, this study used ultrasonic-assisted PEO to disperse graphene oxide (GO), which provided more possibility for in-situ synthesis MoS2, ultimately resulting in MoS2 with modified interlayer spacing. The change in interlayer spacing induced dislocation evolution at incoherent interface, leading to dual interface formation. At MoS2 (0.534 nm)/TiO2 interface: dislocation dipoles evolve to create considerable distortion, facilitating releasing shear stresses and inhibiting crack propagations. This process is followed by dislocation annihilation, keeping to stable interfacial bonding. Additionally, the others form strong dislocation pinning to obstruct dislocation slip and enhancing deformation resistance at MoS2 (0.227 nm)/TiO2 interface. The combined effects of dual interfacial enhancements resulted in a 90.0 % reduction in friction coefficients of the MoS2/GO/TiO2 coating compared to the traditional ceramic coating. This facile technique provides a new strategy to fabricate self-lubricating ceramic coatings on light alloys, while the introduction of ultrasound during PEO offers valuable guidance for applying ultrasound in the synthesis of 2D materials.