In vitro corrosion behavior and biocompatibility of nanostructured Ti6Al4V

Comparative Study on Passive Film Formation Mechanism of Cast and PBF-LB/M-TC4 in Simulated Physiological Solution

Personalized laser powder bed fusion (PBF-LB/M) Ti-6Al-4V (TC4) has a broader application prospect than that of traditional casting. In this paper, the composition and corrosion resistance of the passive film formation mechanism of TC4 prepared by optimization of PBF-LB/M techniques and traditional casting were systematically studied in 0.9 wt.% NaCl at 37 °C by electrochemical technique and surface analysis. The rates of the passive film formation process, corrosion resistance and composition of TC4 show different characteristics for the different preparation processes. Although the rate of passive film formation of cast-TC4 was higher at the initial immersion, the open circuit potential was more positive, and the film thickness was larger after stabilization, those facts show no positive correlation with corrosion resistance. On the contrary, with no obvious defects on the optimized PBF-LB/M-TC4, the passive film resistance is 2.5 times more, the defect concentration is reduced by 30%, and the TiO2 content is higher than that of the cast-TC4, making the martensitic-based PBF-LB/M-TC4 exhibit excellent corrosion resistance. This also provides good technical support for the further clinical application of PBF-LB/M-TC4.

Fabrication of a micro/nanocomposite structure on the surface of high oxygen concentration titanium to promote bone formation

This study investigated the properties of the micro/nano composite structure on the surface of high oxygen concentration titanium (HOC-Ti) after anodic oxidation modification (HOC-NT) and evaluated its biocompatibility as a dental implant material in vitro and in vivo. HOC-Ti was produced by titanium powders and rutile powders using the powder metallurgy method. Its surface was modified by anodic oxidation. After detecting the electrochemical characteristics, the surface properties of HOC-NT were investigated. MC3T3 and MLO-Y4 cells were employed to evaluate the biocompatibility of HOC-NT and cocultured to study the effects of the changes in osteocytes induced by HOC-NT on osteoblasts. While, its possible mechanism was investigated. In addition, osseointegration around the HOC-NT implant was investigated through in vivo experiments. The results showed that a unique micronano composite structure on the HOC-Ti surface with excellent hydrophilicity and suitable surface roughness was created after anodic oxidation promoted by its electrochemical characteristics. The YAP protein may play an important role in regulating bone remodeling by β-catenin and Rankl/OPG Signaling Pathways. An in vivo study also revealed an accelerated formation rate of new bone and more stable osseointegration around the HOC-NT implant. In view of all experimental results, it could be concluded that the unique morphology of HOC-NT has enhanced physicochemical and biological properties. The promotion of bone formation around implants indicated the feasibility of HOC-NT for applications in oral implants.

Corrosion Behavior and Bio-Functions of the Ultrafine-Grained Ti6Al4V-5Cu Alloy with a Dual-Phase Honeycomb Shell Structure in Simulated Body Fluid

Titanium alloys are widely used in biomedical applications. However, cases of implant failure due to fatigue fracture and bacterial infection are common. In addition, implants are susceptible to metal ions (Al, V) released by long-term exposure to human body fluids, which causes neuropathy, mental disorders, and other diseases. Thus, development of novel materials to achieve long-term safety of implants is currently a research hotspot. Recently, our research group has developed an ultrafine-grained Ti6Al4V-5Cu alloy with a unique "dual-phase honeycomb shell" (DPHS) structure, which possesses high fatigue strength and stability. This study further affirmed its higher corrosion behavior, antibacterial properties, and cytocompatibility compared to the coarse-grained Ti6Al4V and Ti6Al4V-5Cu alloys. The ultrafine-grained structure of Ti6Al4V-5Cu having DPHS increased the proportion of phases (Cu-rich phases, β-phase, and Ti₂Cu intermetallic phase) with a lower surface potential. It was observed that the developed microstructure was conducive to a stable configuration of the oxide (passive) layer on the alloy surface. In addition, the low-phase interfacial energies of the ultrafine-grained structure with DPHS even facilitated the improvement of the denseness of the protective passive film and eventually enhanced the corrosion behavior. Besides, the fine-Cu-rich phases and the micro-galvanic couples formed between them and the matrix significantly increased the contact frequency of bacteria, thus increasing the contact sterilization efficiency of the ultrafine-grained Ti6Al4V-5Cu alloy. These results showed that the new ultrafine-grained Ti6Al4V-5Cu alloy has excellent corrosion resistance and biological functions for clinical application.

Using a two-step method of surface mechanical attrition treatment and calcium ion implantation to promote the osteogenic activity of mesenchymal stem cells as well as biomineralization on a β-titanium surface

Combination of the SMAT technique and Ca-ion implantation produced a β-titanium alloy with a bioactive surface layer, which was proved to effectively promote the osteogenic activity of MSCs and Ca–P mineral deposition in vitro.

Effect of Iron Content on Corrosion Properties of Pure Titanium as Grain Refiner

Microstructures and corrosion properties of pure titanium were characterized when iron was used as a grain refiner. The added Fe element acted as a strong grain refiner for pure titanium by forming β Ti phase at grain boundaries, and 0.15 wt% Fe was revealed to be a sufficient amount to make the grain size of pure titanium below 20 μm, which was the requirement for the desired titanium cathode. However, corrosion resistance was decreased with the Fe amount added. From the open circuit potential (OCP) results, it was obvious that the TiO₂ stability against the reducing acid environment was deteriorated with the Fe amount, which seemed to be the main reason for the decreased corrosion resistance. Electrochemical impedance spectroscopy (EIS) results showed that both the decrease in the compact oxide film’s resistance (R_b) and the appearance of the outer porous film occurred as a result of the dissolution of the TiO₂ layer, whose phenomena became more apparent as more Fe was added.

A more defective substrate leads to a less defective passive layer: Enhancing the mechanical strength, corrosion resistance and anti-inflammatory response of the low-modulus Ti-45Nb alloy by grain refinement

Orthopedic and dental implants made of β-type Ti alloys have low elastic modulus which can better relieve the stress shielding effects after surgical implantation. Nevertheless, clinical application of β-type Ti alloys is hampered by the insufficient mechanical strength and gradual release of pro-inflammatory metallic ions under physiological conditions. In this study, the β-type Ti-45Nb alloy is subjected to high-pressure torsion (HPT) processing to refine the grain size. After HPT processing, the tensile strength increases from 370 MPa to 658 MPa due to grain boundary strengthening and at the same time, the favorable elastic modulus is maintained at a low level of 61-72 GPa because the single β-phase is preserved during grain refinement. More grain boundaries decrease the work function and facilitate the formation of thicker and less defective passive films leading to better corrosion resistance. In addition, more rapid repair of the passive layer mitigates release of metallic ions from the alloy and consequently, the inflammatory response is suppressed. The results reveal a strategy to simultaneously improve the mechanical and biological properties of metallic implant materials for orthopedics and dentistry. STATEMENT OF SIGNIFICANCE: The low modulus Ti-45Nb alloy is promising in addressing the complication of stress shielding induced by biomedical Ti-based materials with too-high elastic modulus. However, its insufficient strength hampers its clinical application, and traditional strengthening via heat treatments will compromise the low elastic modulus. In the current study, we enhanced the ultimate tensile strength of Ti-45Nb from 370 MPa to 658 MPa through grain-refinement strengthening, while the elastic modulus was maintained at a low value (61-72 GPa). Moreover, substrate grain-refinement has been proved to improve the corrosion resistance of Ti-45Nb with reduced inflammatory response both in vitro and in vivo. A relationship between the substrate microstructure and the surface passive layer has been established to explain the beneficial effects of substrate grain-refinement.

Titanium and Protein Adsorption: An Overview of Mechanisms and Effects of Surface Features

Titanium and its alloys, specially Ti6Al4V, are among the most employed materials in orthopedic and dental implants. Cells response and osseointegration of implant devices are strongly dependent on the body-biomaterial interface zone. This interface is mainly defined by proteins: They adsorb immediately after implantation from blood and biological fluids, forming a layer on implant surfaces. Therefore, it is of utmost importance to understand which features of biomaterials surfaces influence formation of the protein layer and how to guide it. In this paper, relevant literature of the last 15 years about protein adsorption on titanium-based materials is reviewed. How the surface characteristics affect protein adsorption is investigated, aiming to provide an as comprehensive a picture as possible of adsorption mechanisms and type of chemical bonding with the surface, as well as of the characterization techniques effectively applied to model and real implant surfaces. Surface free energy, charge, microroughness, and hydroxylation degree have been found to be the main surface parameters to affect the amount of adsorbed proteins. On the other hand, the conformation of adsorbed proteins is mainly dictated by the protein structure, surface topography at the nano-scale, and exposed functional groups. Protein adsorption on titanium surfaces still needs further clarification, in particular concerning adsorption from complex protein solutions. In addition, characterization techniques to investigate and compare the different aspects of protein adsorption on different surfaces (in terms of roughness and chemistry) shall be developed.

[Research progress on the biological properties of the surface nanocrystals of typical medical metal materials]

Biomedical metal materials have always been a major biomedical material with a large and wide range of clinical use due to their excellent properties such as high strength and toughness, fatigue resistance, easy forming, and corrosion resistance. They are also the preferred implant material for hard tissues (bones and teeth that need to withstand higher loads) and interventional stents. And nano-medical metal materials have better corrosion resistance and biocompatibility. This article focuses on the changes and improvements in the properties of several typical medical metal materials surfaces after nanocrystallization, and discusses the current problems and development prospects of nano-medical metal materials.

Design, characterization and in vitro evaluation of thin films enriched by tannic acid complexed by Fe(III) ions

Materials based on carbohydrate polymers may be used for biomedical application. However, materials based on natural polymers have weak physicochemical properties. Thereby, there is a challenge to improve their properties without initiation of toxicity. The alternative method compared to toxic chemical agents’ addition is the use of metal complexation method. In this study, chitosan/tannic acid mixtures modified by Fe(III) complexation are proposed and tested for potential applications as wound dressings. Thereby, surface properties, blood compatibility as well as platelet adhesion was tested. In addition, the periodontal ligament stromal cells compatibility studies were carried out. The results showed that the iron(III) addition to chitosan/tannic acid mixture improves properties due to a decrease in the surface free energy and exhibited a reduction in the hemolysis rate (below 5%). Moreover, cells cultured on the surface of films with Fe(III) showed higher metabolic activity. The current findings allow for the medical application of the proposed materials as wound dressings.

Effect of Protein and Mechanical Strain on the Corrosion Resistance and Cytotoxicity of the Orthodontic Composite Arch Wire

In this study, the effects of the exposure to different types of salivary proteins (fibrinogen, IgG, and mucin) and application of an in vitro bending strain on the laser welding orthodontic composite arch wire (CAW) were investigated, and the resultant corrosion behavior and cytotoxicity were studied in vitro. The purpose was to determine the mechanisms by which protein exposure and bending loads contribute to the corrosion of the CAW either alone or in combination by mimicking the clinical application. The results showed that the application of a mechanical strain significantly decreased the corrosion resistance of the CAW and increased the release of toxic corrosion products. The addition of the proteins inhibited the corrosion of the CAW, but the mechanical loads counteracted this effect. Mucin enhanced the corrosion resistance of the CAW. The effects of the proteins or strain, either alone or in combination, should be considered in the application of medical materials of heterogenetic alloys.

The effect of laser frequency on roughness, microstructure, cell viability and attachment of Ti6Al4V alloy

Titanium alloys are commonly used in orthopedic devices due to their good corrosion resistance, high specific strength and excellent biological response. The direct contact between the implant surface and the host tissue results in notable effect of surface properties such as surface topography on the biological responses. The aim of this study is to investigate the effect of frequency of pulsed Nd-YAG laser on Ti6Al4V alloy surface topography and its influence on the improvement of biocompatibility while other laser parameters kept constant. The range of applied frequency values were selected from 1 to 20 Hz. The range of surface roughness was found between 452 nm and 3.37 μm. The untreated sample and also samples with the highest and the lowest average surface roughness parameter were subjected to the further analyses. Characterization of the samples was performed with surface roughness tester, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). The high rate of melt and solidification during the laser treatment led to the martensite formation and consequently an increase about 12-25% in hardness. Furthermore, in vitro study was carried out using MG-63 osteoblast like cells. The analyses of cell viability for 3 culture times, cell morphology and cell spreading area revealed that sample with the highest average surface roughness parameter is more biocompatible. 10 Hz frequency was found as the optimum parameter which led to the highest surface roughness and thus the biocompatibility enhancement. In conclusion, the pulsed Nd-YAG laser with an optimum value of applied frequency can be utilized as an effective technique to improve the biological characteristics.