Modification of a Ti–Mo alloy surface via plasma electrolytic oxidation in a solution containing calcium and phosphorus

Electrophoretically deposited titanium and its alloys in biomedical engineering: Recent progress and remaining challenges

Over the past decade, titanium implants have gained popularity as the number of performed implantation operations has significantly increased. There are a number of methods for modifying the surface of biomaterials, which are aimed at extending the life of titanium implants. The developments in this field in recent years have required a comprehensive discussion of all the properties of electrophoretically deposited coatings on titanium and its alloys, taking into account their bioactivity. The development that took place in this field in recent years required a comprehensive discussion of all the properties of coatings electrophoretically deposited on titanium and its alloys, with particular emphasis on their bioactivity. Herein, we attempt to assess the influence of the electrophoretic deposition (EPD) process parameters on these coatings' biological and mechanical properties. Particular attention has been addressed to the in-vitro and in-vivo studies conducted hitherto. We have seen an increased interest in using titanium alloys without the addition of toxic compounds and gaps in the EPD field such as the uncommon endeavors to develop a "Design of experiments" approach as well as the lack of assessment of the surface free energy and detailed topography of electrophoretically deposited coatings. The exact correlation of coating properties with EPD process parameters still seems explicitly not understood, necessitating more future investigations. Ipso facto, the exact mechanism of particle agglomeration and Hamaker's law need to be fathomable.

A Two-Step Approach to Tune the Micro and Nanoscale Morphology of Porous Niobium Oxide to Promote Osteointegration

We present a two-step surface modification process to tailor the micro and nano morphology of niobium oxide layers. Niobium was firstly anodized in spark regime in a Ca- and P-containing solution and subsequently treated by acid etching. The effects of anodizing time and applied potential on the surface morphology is investigated with SEM and AFM, complemented by XPS compositional analysis. Anodizing with a limiting potential of 250 V results in the fast growth of oxide layers with a homogeneous distribution of micro-sized pores. Cracks are, however, observed on 250 V grown layers. Limiting the anodizing potential to 200 V slows down the oxide growth, increasing the anodizing time needed to achieve a uniform pore coverage but produces fracture-free oxide layers. The surface nano morphology is further tuned by a subsequent acid etching process that leads to the formation of nano-sized pits on the anodically grown oxide surface. In vitro tests show that the etching-induced nanostructure effectively promotes cell adhesion and spreading onto the niobium oxide surface.

Electrochemical Oxidation of Ti15Mo Alloy-The Impact of Anodization Parameters on Surface Morphology of Nanostructured Oxide Layers

It is well-known that the structure and composition of the material plays an important role in the processes occurring at the surface. In this paper, a surface morphology of nanostructured oxide layers electrochemically grown on Ti15Mo, tuned by applying different anodization parameters, was investigated in detail. The one-step anodization of Ti15Mo alloy was performed at room temperature in an ethylene glycol-based electrolyte containing 0.11 M NH4F and 1.11 M H2O. Different anodization times (ranging from 5 to 60 min) and applied potentials (40-100 V) were tested, and the surface morphology, elemental content, and crystalline structure were monitored by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), and X-ray diffractometry (XRD), respectively. The results showed that contrary to the multistep anodization of titanium foil, the surface morphology of anodic oxide obtained via the one-step process contains the nanoporous outer layer covering the nanotubular structure. What is more, the pore diameter (Dp) and interpore distance (Dint) of such layers exhibit different trends than those observed for anodization of pure titanium. In particular, at a certain potential range, a decrease in both Dp and Dint with increasing potential was observed. However, independently on the used anodization conditions, the elemental content of oxide layers remained similar, showing the amount of molybdenum at c.a. 15 wt.%. Finally, the amorphous nature of as-anodized layers was confirmed, and their optical band-gap was determined from the diffuse reflectance UV-Vis spectra. It was found that Eg is tunable to some extent by changing the anodizing potential. However, further thermal treatment in air at 400 °C resulted in the anatase phase formation that was accompanied by a significant Eg reduction. Therefore, we believe that the presented results will greatly contribute to the understanding of anodic formation of nanostructured functional oxide layers with tunable properties that can be applied in various fields.

Metal Ions Supported Porous Coatings by Using AC Plasma Electrolytic Oxidation Processing

Coatings enriched with zinc and copper as well as calcium or magnesium, fabricated on titanium substrate by Plasma Electrolytic Oxidation (PEO) under AC conditions (two cathodic voltages, i.e., -35 or -135 V, and anodic voltage of +400 V), were investigated. In all experiments, the electrolytes were based on concentrated orthophosphoric acid (85 wt%) and zinc, copper, calcium and/or magnesium nitrates. It was found that the introduced calcium and magnesium were in the ranges 5.0-5.4 at% and 5.6-6.5 at%, respectively, while the zinc and copper amounts were in the range of 0.3-0.6 at%. Additionally, it was noted that the metals of the block S (Ca and Mg) could be incorporated into the structure about 13 times more than metals of the transition group (Zn and Cu). The incorporated metals (from the electrolyte) into the top-layer of PEO phosphate coatings were on their first (Cu⁺) or second (Cu²⁺, Ca²⁺ and Mg²⁺) oxidation states. The crystalline phases (TiO and Ti₃O) were detected only in coatings fabricated at cathodic voltage of -135 V. It has also been pointed that fabricated porous calcium-phosphate coatings enriched with biocompatible magnesium as well as with antibacterial zinc and copper are dedicated mainly to medical applications. However, their use for other applications (e.g., catalysis and photocatalysis) after additional functionalizations is not excluded.

Electrochemical modification of the Ti-15Mo alloy surface in solutions containing ZnO and Zn3(PO4)2 particles

This paper reports on the plasma electrolytic oxidation (PEO) of titanium alloy Ti-15Mo in baths containing zinc to obtain biomaterials with bacteriostatic and antibacterial properties. The Ti-15Mo surface was oxidised in a 0.1 M Ca(H₂PO₂)₂ bath containing zinc compound particles: ZnO or Zn₃(PO₄)₂. During the PEO process, the applied voltage was 300 V, and the current density was 150 mA∙cm^-2. The surface morphology, roughness and wettability were determined. It has been noted that both roughness and wettability of Ti-15Mo alloy surface increased after PEO. EDX and XPS chemical composition analysis was carried out, and Raman spectroscopy was also performed indicating that Zn has been successfully incorporated into oxide layer. To investigate the antibacterial properties of the PEO oxide coatings, microbial tests were carried out. The bacterial adhesion test was performed using four different bacterial strains: reference Staphylococcus aureus (ATCC 25923), clinical Staphylococcus aureus (MRSA 1030), reference Staphylococcus epidermidis (ATCC 700296) and clinical Staphylococcus epidermidis (15560). Performed zinc-containing oxide coatings did not indicate the bacteria growth inducing effect. Additionally, the cytocompatibility of the formed oxide layers was characterised by MG-63 osteoblast-like live/dead tests. The surface bioactivity and cytocompatibility increased after the PEO process. The zinc was successfully incorporated into the titanium oxide layer. Based on the obtained results of the studies, it can be claimed that zinc-containing PEO layers can be an interesting course of bacteriostatic titanium biomaterials development.