Preparation and characterization of biomimetically and electrochemically deposited hydroxyapatite coatings on micro-arc oxidized Ti-13Nb-13Zr

Enhanced in vitro immersion behavior and antibacterial activity of NiTi orthopedic biomaterial by HAp-Nb2O5 composite deposits

NiTi is a class of metallic biomaterials, benefit from superelastic behavior, high biocompatibility, and favorable mechanical properties close to that of bone. However, the Ni ion leaching, poor bioactivity, and antibacterial activity limit its clinical applications. In this study, HAp-Nb2O5 composite layers were PC electrodeposited from aqueous electrolytes containing different concentrations of the Nb2O5 particles, i.e., 0-1 g/L, to evaluate the influence of the applied surface engineering strategy on in vitro immersion behavior, Ni2+ ion leaching level, and antibacterial activity of the bare NiTi. Surface characteristics of the electrodeposited layers were analyzed using SEM, TEM, XPS, and AFM. The immersion behavior of the samples was comprehensively investigated through SBF and long-term PBS soaking. Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) infective reference bacteria were employed to address the antibacterial activity of the samples. The results illustrated that the included particles led to more compact and smoother layers. Unlike bare NiTi, composite layers stimulated apatite formation upon immersion in both SBF and PBS media. The concentration of the released Ni2+ ion from the composite layer, containing 0.50 g/L Nb2O5 was ≈ 60% less than that of bare NiTi within 30 days of immersion in the corrosive PBS solution. The Nb2O5-reinforced layers exhibited high anti-adhesive activity against both types of pathogenic bacteria. The hybrid metallic-ceramic system comprising HAp-Nb2O5-coated NiTi offers the prospect of a potential solution for clinical challenges facing the orthopedic application of NiTi.

Effect of hydroxyapatite/alumina composite coatings using HVOF on immersion behavior of NiTi alloys

Hydroxyapatite (HA) coatings have been widely used to improve biocompatibility of metal alloys. This paper discusses the effect of hydroxyapatite (HA) and HA/alumina coated NiTi on their corrosion and dissolution behavior in Phosphate Buffer Saline (PBS) and Ringer's lactate solutions. The HA was synthesized from biogenic method and used as initial powder in High-Velocity Oxygen Fuel (HVOF) spray technique for the deposition of two coating types, fully HA and HA + 15 wt.% alumina composite coating. The as-synthesized HA had irregular porous structure with relatively low Ca/P ratio of 1.52. Tafel polarization curves obtained from electrochemical test had showed that both coatings increased the corrosion resistance of the NiTi substrates significantly. The ICP-MS analysis results that indicated a low nickel dissolved in both solutions after immersion in 21 days had supported these findings. The nickel levels in the solutions from all samples, either bared substrate or coated samples, in fact below the maximum limit for allergies of the human body. Immersion testing showed the stability of HA and HA/alumina layers as a barrier which maintains its morphology in PBS solution but slightly changed in Ringers.

Native Osseous CaP Biomineral Coating on a Biomimetic Multi-Spiked Connecting Scaffold Prototype for Cementless Resurfacing Arthroplasty Achieved by Combined Electrochemical Deposition

The multi-spiked connecting scaffold (MSC-Scaffold) prototype with spikes mimicking the interdigitations of articular subchondral bone is an essential innovation in surgically initiated fixation of resurfacing arthroplasty (RA) endoprosthesis components. This paper aimed to present a determination of the suitable range of conditions for the calcium phosphate (CaP) potentiostatic electrochemical deposition (ECD_V=const) on the MSC-Scaffold prototype spikes to achieve a biomineral coating with a native Ca/P ratio. The CaP ECD_V=const process on the MSC-Scaffold Ti4Al6V pre-prototypes was investigated for potential V_ECDfrom −9 to −3 V, and followed by 48 h immersion in a simulated body fluid. An acid–alkaline pretreatment (AAT) was applied for a portion of the pre-prototypes. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) studies of deposited coatings together with coatings weight measurements were performed. Themost suitable V_ECD range, from −5.25 to −4.75 V, was determined as the native biomineral Ca/P ratio of coatings was achieved. AAT increases the weight of deposited coatings (44% for V_ECD = −5.25 V, 9% for V_ECD = −5.00 V and 15% for V_ECD = −4.75 V) and the coverage degree of the lateral spike surfaces (40% for V_ECD = −5.25 V, 14% for V_ECD = −5.00 V and 100% for V_ECD = −4.75 V). XRD confirmed that the multiphasic CaP coating containing crystalline octacalcium phosphate is produced on the lateral surface of the spikes of the MSC-Scaffold. ECD_V=const preceded by AAT prevents micro-cracks on the bone-contacting surfaces of the MSC-Scaffold prototype, increases its spikes’ lateral surface coverage, and results in the best modification effect at V_ECD = −5.00 V. To conclude, the biomimetic MSC-Scaffold prototype with desired biomineral coating of native Ca/P ratio was obtained for cementless RA endoprostheses.

Anticorrosion Performance of the Electrochemically Grown Mixed Porous Oxide Films on Titanium Alloy in Biological Solution

A thin porous mixed layer of TiO₂-ZrO₂ was grown on titanium-zirconium alloy surface by electrochemical oxidation. Further comparison of the corrosion behavior in Fusayama-Meyer biological solution was performed. Scanning electron microscopy surface morphology investigations confirm the presence of porous oxide film, while energy-dispersive X-ray spectroscopy analyses provide a high amount of oxygen element in the porous film and a higher amount of Zr element, concluding the mixed nature of oxide film formed, TiO₂-ZrO₂. For corrosion investigations, electrochemical techniques such as open-circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization were applied. The corrosion investigations reveal better behavior of the thin porous mixed oxide layer on titanium alloy compared to the untreated alloy having on their surface the native oxide formed in contact with the air, confirming the possibility to improve the properties of such implant application in saliva solution.

Research Progress Regarding Interfacial Characteristics and the Strengthening Mechanisms of Titanium Alloy/Hydroxyapatite Composites

Titanium alloy/Hydroxyapatite (HA) composites have become a hot research topic in biomedical materials, while there are some challenges concerning bioactivity and mechanical properties such as low interface adhesion at the interface between metal and ceramic, complex interfacial reactions, and so on. Nevertheless, composites with reinforced phases can reach special properties that meet the requirements of biomedical materials due to the strong interfacial interactions between reinforcing phases (nano-carbon, partial oxides, and so on) and Titanium alloys or HA. This review summarizes the interface properties and mechanisms of Titanium alloy/HA composites, including interfacial bonding methods, strengthening and toughening mechanisms, and performance evaluation. On this basis, the interface characteristics and mechanisms of the Titaniumalloy/HA composites with enhanced phase are prospected. The results show that the interfacial bonding methods in the Titanium alloy/HA composites include chemical reactions and mechanical effects. The strengthening and toughening mechanisms contain grain refinement strengthening, second phase strengthening, solution strengthening, cracks and pulling out mechanisms, etc. This review provides a guidline for the fabrication of biocomposites with both mechanical properties and bioactivity.

Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation

Tantalum has recently become an actively researched biomaterial for the bone reconstruction applications because of its excellent corrosion resistance and successful clinical records. However, a bare Ta surface is not capable of directly bonding to the bone upon implantation and requires some method of bioactivation. In this study, this was realized by direct current (DC) plasma electrolytic oxidation (PEO). Susceptibility to corrosion is a major factor determining the service-life of an implant. Therefore, herein, the corrosion resistance of the PEO coatings on Ta was investigated in Ringer’s solution. The coatings were formed by galvanostatic anodization up to 200, 300 and 400 V, after which the treatment was conducted potentiostatically until the total process time amounted to 5 min. Three solutions containing Ca(H₂PO₂)₂, Ca(HCOO)₂ and Mg(CH₃COO)₂ were used in the treatment. For the corrosion characterization, electrochemical impedance spectroscopy and potentiodynamic polarization techniques were chosen. The coatings showed the best corrosion resistance at voltages low enough so that the intensive sparking was absent, which resulted in the formation of thin films. The impedance data were fitted to the equivalent electrical circuits with two time constants, namely R(Q[R(QR)]) and R(Q[R(Q[RW])]). The inclusion of W in the circuit helped to fit the low-frequency part of the samples PEO-ed at 400 V, hinting at the important role of diffusion in the corrosion resistance of the PEO coatings described in the research.