Surface characterisation of Ti–15Mo alloy modified by a PEO process in various suspensions

Analysis of the Calcium Phosphate-Based Hybrid Layer Formed on a Ti-6Al-7Nb Alloy to Enhance the Ossseointegration Process

This paper reports on hybrid, bioactive ceramic Ca-P-based coating formation on a Ti-6Al-7Nb alloy substrate to enhance the osseointegration process. The Ti alloy was anodized in a Ca₃(PO₄)₂ suspension and then the additional layer was formed by the sol-gel technique to obtain a mixture of the calcium phosphate compounds. The oxide layer was porous and additional ceramic particles were formed after sol-gel treatment (scanning electron microscopy analysis coupled with energy-dispersive x-ray spectroscopy). The ceramic particles were formed on some parts of the oxide layer and did not completely fill the pores. The layer thickness of the anodized Ti alloy was comprised between 3.01 and 5.03 µm and increased to 7.52–12.30 µm after the formation of an additional layer. Post-treatment of the anodized Ti alloys caused a decrease in surface roughness, and the layer became strongly hydrophilic. Crystalline phase analysis (X-ray diffraction, XRD) showed that the hybrid layer was composed of TiO₂ (anatase), Ca₃(PO₄)₂, Ca₁₀(PO₄)₆(OH)₂ and a partially amorphous phase; thus, the layer was also analyzed by Raman spectroscopy. The hybrid layer showed worse adhesion to the substrate than the anodized layer only; however, the coating was not brittle, and the first delamination of the layer was determined at 1.84 ± 0.11 N during scratch-test measurement. The hybrid coating was favorable for collagen type I and lactoferrin adsorption, strongly influencing the proliferation of osteoblast-like MG-63 cells. The coatings were cytocompatible and may find applications in formation of the functional layers on long-term implants’ surface after.

Effect of V2O5 Additive on Micro-Arc Oxidation Coatings Fabricated on Magnesium Alloys with Different Loading Voltages

Effect of V2O5 additive in silicate-containing electrolyte on AZ91D magnesium alloys treated by micro-arc oxidation (MAO) technology under different loading voltages was investigated. The results showed that vanadium was well up-taken into the coating chemically. Moreover, a new phase of MgV2O4 with spinel structure was obtained in MAO coatings due to V2O5 added into the electrolyte. The MgV2O4 phase was responsible for the coatings exhibiting brown color and also was beneficial to improving the anti-corrosion property. In spotting tests, the corrosion resistances of coatings prepared under the high voltage are about 6–9 times higher than those of the low voltage because of the thicker coatings of the former. In potentiodynamic polarization tests, the coatings’ corrosion resistances were improved with the addition of V2O5, which was more significant under the low voltage than that under the high voltage. When the concentration of V2O5 was 0.2 g/L, the corrosion current density of the coating was the lowest, which means that the coating’s corrosion resistance under the low voltage is the best. Hence, it is necessary to carry out targeted design of the coating’s microstructure according to the different applications.

Synthesis of bioactive glass-based coating by plasma electrolytic oxidation: Untangling a new deposition pathway toward titanium implant surfaces

HYPOTHESIS

Although bioactive glass (BG) particle coatings were previously developed by different methods, poor particle adhesion to surfaces and reduced biological effects because of glass crystallization have limited their biomedical applications. To overcome this problem, we have untangled, for the first time, plasma electrolytic oxidation (PEO) as a new pathway for the synthesis of bioactive glass-based coating (PEO-BG) on titanium (Ti) materials.

EXPERIMENTS

Electrolyte solution with bioactive elements (Na₂SiO₃-5H₂O, C₄H₆O₄Ca, NaNO₃, and C₃H₇Na₂O₆P) was used as a precursor source to obtain a 45S5 bioglass-like composition on a Ti surface by PEO. Subsequently, the PEO-BG coating was investigated with respect to its surface, mechanical, tribological, electrochemical, microbiological, and biological properties, compared with those of machined and sandblasted/acid-etched control surfaces.

FINDINGS

PEO treatment produced a coating with complex surface topography, Ti crystalline phases, superhydrophilic status, chemical composition, and oxide layer similar to that of 45S5-BG (~45.0Si, 24.5 Ca, 24.5Na, 6.0P w/v%). PEO-BG enhanced Ti mechanical and tribological properties with higher corrosion resistance. Furthermore, PEO-BG had a positive influence in polymicrobial biofilms, by reducing pathogenic bacterial associated with biofilm-related infections. PEO-BG also showed higher adsorption of blood plasma proteins without cytotoxic effects on human cells, and thus may be considered a promising biocompatible approach for biomedical implants.

Physico-chemical and biological evaluation of doxycycline loaded into hybrid oxide-polymer layer on Ti-Mo alloy

Oxide-polymer coatings were formed on the surface of the vanadium-free Ti–15Mo titanium alloy. The Ti alloy surface was modified by the plasma electrolytic oxidation process, and then, the polymer layer of a poly (D, l-lactide-co-glycolide) with doxycycline was formed. The polymer evenly covered the porous oxide layer and filled some of the pores. However, the microstructure of the polymer surface was completely different from that of the PEO layer. The surface morphology, roughness and microstructure of the polymer layer were examined by scanning electron microscopy (SEM) and a confocal microscope. The results confirmed the effectiveness of polymer and doxycycline deposition in their stable chemical forms. The drug analysis was performed by high-performance liquid chromatography. The ¹H NMR technique was used to monitor the course of hydrolytic degradation of PLGA. It was shown that the PLGA layer is hydrolysed within a few weeks, and the polyglycolidyl part of the copolymer is hydrolysed to glycolic acid as first and much faster than the polylactide one to lactic acid. This paper presents influence of different microstructures on the biological properties of modified titanium alloys. Cytocompatibility and bacterial adhesion tests were evaluated using osteoblast-like MG-63 cells and using the reference S. aureus and S. epidermidis strains. The results showed that the optimum concentration of doxycycline was found to inhibit the growth of the bacteria and that the layer is still cytocompatible.

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Formation of the oxide-polymer layer containing doxycycline is presented.

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Changes in the doxycycline structure and the evaluation of their stability was analyzed using the HPLC.

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Thickness of the polymer layer was determined using the confocal microscopy.

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The coatings showed the antibacterial properties and were cytocompatible with osteoblast-ike MG-63 cells.

Functionalization of PEO layer formed on Ti-15Mo for biomedical application

In the present work, deposition of poly(sebacic anhydride) PSBA loaded by amoxicillin, cefazolin, or vancomycin on a previously anodized Ti-15Mo surface is presented. PSBA loaded by the drug was deposited so as not to lose the functionality of the porous oxide layer microstructure. The morphology was evaluated using scanning electron microscopy, surface roughness, and wettability. The drug concentration was evaluated using high-performance liquid chromatography. It was determined that the drugs were loaded into coatings in the range of 35.2-122.87 μg/cm² of Ti sample. The drugs released more than 16% after 0.5 hr of the hybrid coating immersion in artificial saliva. After 3 days, the PSBA coatings were degraded by 51.3 mol %, and after 7 days by 77.8 mol %, which makes it possible to load the material by different, biologically active substances. An antimicrobial investigation of Staphylococcus aureus (DSM 24167) and Staphylococcus epidermidis (ATCC 700296) confirmed the activity of the hybrid layers against the pathogens. Hybrid layer with vancomycin best inhibits the adhesion of the bacteria, whereas coatings with amoxicillin and cefazolin showed a much better bactericidal activity. In this article, the difference in the obtained results is discussed, as well as the possibility of the application of this functional material in biomedicine.

Influence of the Processing Method on the Properties of Ti-23 at.% Mo Alloy

In this paper, binary β type Ti-23 at.% Mo alloys were obtained by arc melting as well as by mechanical alloying and powder metallurgical process with cold powder compaction and sintering or, interchangeably, hot pressing. The influence of the synthesis method on the microstructure and properties of bulk alloys were studied. The produced materials were characterized by an X-ray diffraction technique, scanning electron microscopy and chemical composition determination. Young’s modulus was evaluated with nanoindentation testing method based on the Oliver and Pharr approach. The mechanically alloyed Ti-23 at.% Mo powders, after inductively hot-pressed at 800 °C for 5 min, allowed the formation of single Ti(β) phase alloy. In this case, Young’s modulus and Vickers hardness were 127 GPa and 454 HV0.3, respectively. Among the examined materials, the porous (55%) single-phase scaffold showed the lowest indentation modulus (69.5 GPa). Analytical approach performed in this work focuses also on the surface properties. The estimation includes the corrosion resistance analyzed in the potentiodynamic test, and also some wettability properties as a contact angle, and surface free energy values measured in glycerol and diiodomethane testing fluids. Additionally, surface modification of processed material by micro-arc oxidation and electrophoretic deposition on the chosen samples was investigated. Proposed procedures led to the formation of apatite and fluorapatite layers, which influence both the corrosion resistance and surface wetting properties in comparison to unmodified samples. The realized research shows that a single-phase ultrafine-grained Ti-23 at.% Mo alloy for medical implant applications can be synthesized at a temperature lower than the transition point by the application of hot pressing of mechanically alloyed powders. The material processing, that includes starting powder preparation, bulk alloy transformation, and additional surface treatment functionalization, affect final properties by the obtained phase composition and internal structure.

Visible-Light-Induced Photocatalytic and Antibacterial Activity of TiO2 Codoped with Nitrogen and Bismuth: New Perspectives to Control Implant-Biofilm-Related Diseases

Biofilm-associated diseases are one of the main causes of implant failure. Currently, the development of implant surface treatment goes beyond the osseointegration process and focuses on the creation of surfaces with antimicrobial action and with the possibility to be re-activated (i.e., light source activation). Titanium dioxide (TiO₂), an excellent photocatalyst used for photocatalytic antibacterial applications, could be a great alternative, but its efficiency is limited to the ultraviolet (UV) range of the electromagnetic spectrum. Since UV radiation has carcinogenic potential, we created a functional TiO₂ coating codoped with nitrogen and bismuth via the plasma electrolytic oxidation (PEO) of titanium to achieve an antibacterial effect under visible light with re-activation potential. A complex surface topography was demonstrated by scanning electron microscopy and three-dimensional confocal laser scanning microscopy. Additionally, PEO-treated surfaces showed greater hydrophilicity and albumin adsorption compared to control, untreated titanium. Bismuth incorporation shifted the band gap of TiO₂ to the visible region and facilitated higher degradation of methyl orange (MO) in the dark, with a greater reduction in the concentration of MO after visible-light irradiation even after 72 h of aging. These results were consistent with the in vitro antibacterial effect, where samples with nitrogen and bismuth in their composition showed the greatest bacterial reduction after 24 h of dual-species biofilm formation ( Streptococcus sanguinis and Actinomyces naeslundii) in darkness with a superior effect at 30 min of visible-light irradiation. In addition, such a coating presents reusable photocatalytic potential and good biocompatibility by presenting a noncytotoxicity effect on human gingival fibroblast cells. Therefore, nitrogen and bismuth incorporation into TiO₂ via PEO can be considered a promising alternative for dental implant application with antibacterial properties in darkness, with a stronger effect after visible-light application.

PLGA-amoxicillin-loaded layer formed on anodized Ti alloy as a hybrid material for dental implant applications

In this paper, the preparation of a functional hybrid coating loaded with a drug (amoxicillin) on a promising titanium alloy - Ti-15Mo alloy is presented. The titanium alloy surface was anodized in solution with bioactive compounds to obtain a porous oxide layer favorable for MG-63 osteoblast-like cell adhesion. Then, a poly(lactide-co-glycolide) (PLGA) loaded with amoxicillin layer was formed using a dip-coating technique to cover the oxide layer, without filling in all of the pores. The morphology of the surface was evaluated using scanning electron microscopy supported by 3D Roughness Reconstruction software. The surface treatment of the Ti-15Mo alloy surface caused the surface roughness to increase up to 1.71 μm. The anodization process caused the Ti-15Mo alloy surface to become slightly more hydrophilic; however, the formation of the PLGA layer loaded with drug increased the contact angle to 96.5° ± 2.2°, respectively. After 4 weeks of polymer layer degradation, the registered signals on the ¹H NMR spectrum were identical to the signals registered for lactic acid (LAc), which confirms that the polymer layer was degraded within a short period of time. The concentration of drug released into the artificial saliva was investigated using high-performance liquid chromatography (HPLC) up to 12 h of coatings immersion. During the first hour of coating degradation in artificial saliva, and the concentration of the drug (13 μg/ml) was enough to inhibit bacterial growth of S. aureus and S. epidermidis. These results were confirmed by agar plate diffusion method and evaluation of the minimal inhibitory concentration (MIC). The cytocompatibility of the materials was determined using the osteoblast-like cells MG-63, and the viability and cell morphology (live/dead staining) were also evaluated. The results showed that amoxicillin influences the osteoblast-like MG-63 cells' behavior during cell culture, especially for the first few hours. The influence on the type of surface treatment on MG-63 cell behavior during 7 days of culture is discussed in this paper. To the best of our knowledge, this is the first time that a fast-degrading layer with amoxicillin has been deposited on previously anodized Ti surface. The formation of functional coating may find application as a cytocompatible coating to prevent bacterial adhesion on long-term implant surfaces.

Effect of phosphate additives on the microstructure, bioactivity, and degradability of microarc oxidation coatings on Mg-Zn-Ca-Mn alloy

Calcium phosphate coatings were prepared on the surface of self-designed Mg-Zn-Ca-Mn alloy using microarc oxidization technology. To characterize the microstructures, cross-section morphologies, and compositions of the coatings, the authors used scanning electron microscopy equipped with an energy-disperse spectrometer, x-ray diffraction, and Fourier transform infrared spectroscopy. Potentiodynamic polarization in the simulated body fluid (SBF) was used to evaluate the corrosion behaviors of the samples. An SBF immersion test was used to evaluate the coating bioactivity and degradability. After the immersion tests, some bonelike apatite formed on the coating surfaces indicate that bioactivity of the coatings is excellent. The coating prepared in electrolyte containing (NaPO3)6 had slower degradation rate after immersion test for 21 days.

Characteristics and in vitro response of thin hydroxyapatite-titania films produced by plasma electrolytic oxidation of Ti alloys in electrolytes with particle additions

Enhanced incorporation of hydroxyapatite nanoparticles in porous titania coating formed by plasma electrolytic oxidation significantly increases surface osteogenic activity.

The enhancement of the biological properties of Ti by surface doping with hydroxyapatite (HA) is of great significance, especially for orthodontic applications. This study addressed the effects of HA particle size in the electrolyte suspension on the characteristics and biological properties of thin titania-based coatings produced on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO). Detailed morphological investigation of the coatings formed by a single-stage PEO process with two-step control of the electrical parameters was performed using the Minkowski functionals approach. The surface chemistry was studied by glow discharge optical emission spectroscopy and Fourier transform infrared spectroscopy, whereas mechanical properties were evaluated using scratch tests. The biological assessment included in vitro evaluation of the coating bioactivity in simulated body fluid (SBF) as well as studies of spreading, proliferation and osteoblastic differentiation of MC3T3-E1 cells. The results demonstrated that both HA micro- and nanoparticles were successfully incorporated in the coatings but had different effects on their surface morphology and elemental distributions. The micro-particles formed an irregular surface morphology featuring interpenetrated networks of fine pores and coating material, whereas the nanoparticles penetrated deeper into the coating matrix which retained major morphological features of the porous TiO₂ coating. All coatings suffered cohesive failure in scratch tests, but no adhesive failure was observed; moreover doping with HA increased the coating scratch resistance. In vitro tests in SBF revealed enhanced bioactivity of both HA-doped PEO coatings; furthermore, the cell proliferation/morphometric tests showed their good biocompatibility. Fluorescence microscopy revealed a well-organised actin cytoskeleton and focal adhesions in MC3T3-E1 cells cultivated on these substrates. The cell alkaline phosphatase activity in the presence of ascorbic acid and β-glycerophosphate was significantly increased, especially in HA nanoparticle-doped coatings.

Formation mechanism and cytocompatibility of nano-shaped calcium silicate hydrate/calcium titanium silicate/TiO2 composite coatings on titanium

Compared with as-MAOed TiO₂, the triple-layered coating (HT2h) comprised of an outer layer of nanoleaf Ca₃Si₆O₁₅(H₂O)₇, a middle layer of nanograined Ca(Si_1.9Ti_0.1)O₅ and an inner layer of microporous TiO₂ can significantly improve the behaviors of osteoblasts.