Biocompatible Elements Research Articles

Formation of self-ordered oxide nanotubes layer on the equiatomic TiNbZrHfTa high entropy alloy and bioactivation procedure

The TiNbZrHfTa high entropy alloy was studied for its use as a base material for orthopedic implants. The alloy produced by arc melting contains only biocompatible elements and has an attractive combination of mechanical properties with a tensile strength of 1050 MPa and Young's modulus of 66 GPa. Surface modification techniques were carried out to bioactivate the alloy surface, ensuring better interaction between the implanted material and the human body. The first technique was the anodization in an organic electrolyte, containing F- ions in different potentials and time, obtaining the best condition at 10 V potential for 2 h at 20 °C, producing an ordered and adherent nanotubular morphology to the substrate. The second technique was precalcification. Using the alternation immersion method (AIM), the saturation and nucleation of Ca-P deposits were guaranteed, providing high deposition rates of hydroxyapatite (HAP) when immersed in simulated body fluid (SBF) solution. Structural characterizations were performed by XRD and XPS. Morphological analyses were performed by SEM and chemical semi-quantitative analyses by EDX. Corrosion resistance properties were performed through polarization and impedance curves. The TiNbZrHfTa high entropy alloy proved to be a competitive and attractive candidate in the research for new compositions to replace conventional alloys, having biocompatibility, high strength, and low Young's modulus, reducing stress shielding effects and showing good bioactivity characteristics through the surface modification techniques presented here.

Investigation of the superelastic behavior of a Ti-16Zr-13Nb-2Sn sputtered film by nanoindentation

A new Ti-16Zr-13Nb-2Sn superelastic film incorporating β-stabilizing and highly biocompatible elements was elaborated by magnetron sputtering. The morphological, crystallographic and microstructural characteristics of the obtained films were studied by scanning electron microscopy, atomic force microscopy, X-ray diffraction, and transmission electron microscopy. Superelastic response of the film was investigated at local scale by nanoindentation using both spherical and Berkovich indenters. The sputter-deposited film revealed nanograined β microstructure with preferential growth orientation along [110] direction and excellent superelastic recovery at room temperature. Special attention was paid to the indenter geometry influencing reliable evaluation of the superelastic nature of the film. Evolution of the deformation mechanisms during nanoindentation at increasing depths was rationalized by the calculated representative strain beneath the indenting tips and is discussed in this work.

Biocompatible High Entropy Alloys with Excellent Degradation Resistance in a Simulated Physiological Environment.

Bioimplants are susceptible to simultaneous wear and corrosion degradation in the aggressive physiological environment. High entropy alloys with equimolar proportion of constituent elements represent a unique alloy design strategy for developing bioimplants due to their attractive mechanical properties, superior wear, and corrosion resistance. In this study, the tribo-corrosion behavior of an equiatomic MoNbTaTiZr high entropy alloy consisting of all biocompatible elements was evaluated and compared with 304 stainless steel as a benchmark. The high entropy alloy showed a low wear rate and a friction coefficient as well as quick and stable passivation in simulated body fluid. An increase from room temperature to body temperature showed excellent temperature assisted passivity and nobler surface layer of the high entropy alloy, resulting in four times better wear resistance compared to stainless steel. Stem cells and osteoblast cells displayed proliferation and migratory behavior, indicating in vitro biocompatibility. Several filopodia extensions on the cell periphery indicated early osteogenic commitment, and cell adhesion on the high entropy alloy. These results pave the way for utilizing the unique combination of tribo-corrosion resistance, excellent mechanical properties, and biocompatibility of MoNbTaTiZr high entropy alloy to develop bioimplants with improved service life and lower risk of implant induced cytotoxicity in the host body.

Development of Novel Lightweight Metastable Metal-(Metal + Ceramic) Composites Using a New Powder Metallurgy Approach.

In the current study, metal–(metal + ceramic) composites composed of biocompatible elements, magnesium (Mg), zinc (Zn), calcium (Ca) and manganese (Mn) were synthesized using a sinter-less powder metallurgy method. The composite has a composition of Mg49Zn49Ca1Mn1 (wt.%) in which the compositional ratio between Mg and Zn was chosen to be near eutectic Mg-Zn composition. The synthesis method was designed to avoid/minimize intermetallic formation by using processing temperatures lower than the Mg-Zn binary eutectic temperature (~ 340 °C). The synthesis process involved extrusion of green compacts at two different temperatures, 150 °C and 200 °C, without sintering. Extrusion was performed directly on the green compacts as well as on the compacts soaked at temperatures of 150 °C and 200 °C, respectively. Microstructure and mechanical properties of the materials synthesized under various processing conditions were investigated. Effect of extrusion temperature as well as soaking temperature on the materials’ properties were also evaluated in details and different properties showed an optimum under different conditions. All the synthesized materials showed no evidence of intermetallic formation which was confirmed by SEM/EDS, XRD, and Differential Scanning Calorimetry (DSC) techniques. The study establishes development of unconventional metal–(metal + ceramic) eco-friendly composites and provides important insight into realizing certain properties without using sintering step thus to minimize the energy consumption of the process. The study also highlights the use of magnesium turnings (recyclability) to develop advanced materials.

Electrochemical Analysis and In Vitro Assay of Mg-0.5Ca-xY Biodegradable Alloys.

In recent years, biodegradable Mg-based materials have been increasingly studied to be used in the medical industry and beyond. A way to improve biodegradability rate in sync with the healing process of the natural human bone is to alloy Mg with other biocompatible elements. The aim of this research was to improve biodegradability rate and biocompatibility of Mg-0.5Ca alloy through addition of Y in 0.5/1.0/1.5/2.0/3.0wt.%. To characterize the chemical composition and microstructure of experimental Mg alloys, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), light microscopy (LM), and X-ray diffraction (XRD) were used. The linear polarization resistance (LPR) method was used to calculate corrosion rate as a measure of biodegradability rate. The cytocompatibility was evaluated by MTT assay (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide) and fluorescence microscopy. Depending on chemical composition, the dendritic α-Mg solid solution, as well as lamellar Mg2Ca and Mg24Y5 intermetallic compounds were found. The lower biodegradability rates were found for Mg-0.5Ca-2.0Y and Mg-0.5Ca-3.0Y which have correlated with values of cell viability. The addition of 2–3 wt.%Y in the Mg-0.5Ca alloy improved both the biodegradability rate and cytocompatibility behavior.

A New Ternary Alloy Ti26Zr24Nb for Biomedical Application: Behavior in Corrosion, Wear, and Tribocorrosion

Titanium (Ti)-based alloys with only β-phase have arisen the interest of academics and industrials for bone implants due to their mechanical properties close to those of hard tissues, and for the capability of allowing with β-stabilizers, totally biocompatible elements like Nb, Ta, and Zr. However, there is no consensus about the most adequate composition and, in many cases, tribocorrosion behavior is not considered during their development. New ternary alloy Ti26Zr24Nb as biomaterial is the matter of study of this work regarding wear and corrosion resistances, and the tribocorrosion behavior of this alloy in contact with pH 7, deaerated Hanks solution at 37 °C to simulate a body fluid. All samples have had surface prepared according to the same protocol and a subtract characterization previously and after the electrochemical, dry wear, and tribocorrosion experiments. Results showed high corrosion resistance, with constant open circuit potential (~ − 200 mV) and low corrosion current density (~ 0.9 × 10−8 A/cm2) and important pitting resistance, as well as higher coefficient of friction (COF) for both wear (0.69) and tribocorrosion (0.65) tests than those reported in the literature and, additionally, less wear under tribocorrosion condition compared to dry wear test.

Bio-corrosion behavior and in vitro biocompatibility of equimolar TiZrHfNbTa high-entropy alloy

Ti20Zr20Hf20Nb20Ta20 high-entropy alloy (TiZrHfNbTa HEA) is considered to be attractive for biomedical applications due to its good mechanical properties and composition that composed of biocompatible elements. In the present study, the bio-corrosion behavior in a simulated physiological environment and in vitro biocompatibility of the TiZrHfNbTa HEA were investigated in comparison with those of the Ti-6Al-4V alloy. It was found that the TiZrHfNbTa HEA exhibited as good bio-corrosion resistance as that of the Ti-6Al-4V alloy in the Hank's solution at 310 K, as revealed by the spontaneously-passivating behavior with a low passive current density of about 10−2 A/m2, a low corrosion rate in the order of 10−4 mm/year, and high electrochemical impedance of the HEA. X-ray photoelectron spectroscopy (XPS) analysis of the alloy surface suggested that the formation of the passive film composed of TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5 is responsible for the high bio-corrosion resistance of the HEA. The good adhesion, viability and proliferation behaviors of MC3T3-E1 pre-osteoblasts on the TiZrHfNbTa HEA indicated its good in vitro biocompatibility. The combination of the good bio-corrosion resistance and in vitro biocompatibility demonstrates the potential of the TiZrHfNbTa HEA for biomedical applications.

The Effect of Hot Working on the Mechanical Properties of High Strength Biomedical Ti-Nb-Ta-Zr-O Alloy.

Beta titanium alloy Ti-35Nb-6Ta-7Zr-0.7O (wt%) was developed as a material intended for the manufacturing of a stem of a hip joint replacement. This alloy contains only biocompatible elements and possesses a very high yield strength already in the cast condition (900 MPa). However, the porosity, large grain size and chemical inhomogeneity reduce the fatigue performance below the limits required for utilization in the desired application. Two methods of hot working, die forging and hot rolling, were used for processing of this alloy. Microstructural evolution, tensile properties and fatigue performance of the hot worked material were investigated and compared to the cast material. Microstructural observations revealed that porosity is removed in all hot-worked conditions and the grain size is significantly reduced when the area reduction exceeds 70%. Static tensile properties were improved by both processing methods and ultimate tensile strength (UTS) of 1200 MPa was achieved. Fatigue results were more reproducible in the hot rolled material due to better microstructural homogeneity, but forging leads to an improved fatigue performance. Fatigue limit of 400 MPa was achieved in the die-forged condition after 70% of area reduction and in the hot rolled condition after 86% of area reduction.

Development of a robotic plasma spraying system for biocompatible coatings

The results of the development of the database of implants and plasma deposition plants in MS SQL Server 2012 are presented. The design of the infological model, the data design, the physical design, the architecture of the software and hardware complex are given. Possibilities of plasma spraying of implants with biocompatible elements are investigated. The system of classification of implants according to the type of application and manufacturing materials has been developed, implants have been classified according to the geometric-topological dimensions of the components. A scheme of plasma spraying of metal and ceramic surfaces of parts and assemblies using a robotic complex is described.

Investigation of Copper Alloying in a TNTZ-Cux Alloy.

Alloying copper into pure titanium has recently allowed the development of antibacterial alloys. The alloying of biocompatible elements (Nb, Ta and Zr) into pure titanium has also achieved higher strengths for a new alloy of Ti-1.6 wt.% Nb-10 wt.% Ta-1.7 wt.% Zr (TNTZ), where strength was closer to Ti-6Al-4V and higher than grade 4 titanium. In the present study, as a first step towards development of a novel antibacterial material with higher strength, the existing TNTZ was alloyed with copper to investigate the resultant microstructural changes and properties. The initial design and modelling of the alloy system was performed using the calculation of phase diagrams (CALPHAD) methods, to predict the phase transformations in the alloy. Following predictions, the alloys were produced using arc melting with appropriate heat treatments. The alloys were characterized using energy dispersive X-ray spectroscopy in scanning transmission electron microscopy (STEM-EDS) with transmission Kikuchi diffraction (TKD). The manufactured alloys had a three-phased crystal structure that was found in the alloys with 3 wt.% Cu and higher, in line with the modelled alloy predictions. The phases included the α-Ti (HCP-Ti) with some Ta present in the crystal, Ti2Cu, and a bright phase with Ti, Cu and Ta in the crystal. The Ti2Cu crystals tended to precipitate in the grain boundaries of the α-Ti phase and bright phase. The hardness of the alloys increased with increased Cu addition, as did the presence of the Ti2Cu phase. Further studies to optimize the alloy could result in a suitable material for dental implants.

Micro-dot-matrix induced by femtosecond laser on titanium surface for Ca-P phase deposition

A series of regular dot-matrix microstructures were constructed on titanium (Ti) surface via a femtosecond laser microfabrication in different medium, in air and in hydroxyapatite (HA) suspension, for depositing biocompatible elements Ca-P. The X-ray diffraction (XRD) results reveal that the deposition of Ca-P mainly exists in the form of Ca3(PO4)2 crystal on Ti surfaces. Compared with its counterpart prepared in air, the building block of dot-matrix microstructure fabricated in HA suspension presents a micro-hole shape with inner wall filled with mastoid-like nanostructures, which is more conducive to the deposition of Ca-P. Moreover, its composition is also more stable, supported by the atomic percentages of Ca and P on the treated Ti surfaces. Such textured Ti surfaces demonstrate good hydrophilic properties, beneficial to Ca-P deposition. The strategy for effective deposition of Ca-P on Ti surfaces shows great potential in the design of biocompatible surface of implants and medical devices and the improvement of their performance.

Microstructural, mechanical and electrochemical characterization of TiZrTaHfNb and Ti1.5ZrTa0.5Hf0.5Nb0.5 refractory high-entropy alloys for biomedical applications

The state-of-the-art metallic biomaterials are 316L, CoCrMo and Ti6Al4V but they all suffer from known issues relating to biocompatibility, wear resistance and corrosion resistance. Therefore, there is always the motivation to identify novel superior metallic biomaterials to 316L, CoCrMo and Ti6Al4V. The concept of refractory high-entropy alloys (RHEAs) provides an interesting research direction towards developing novel metallic biomaterials, initially because RHEAs consist of purely biocompatible elements, but a systematic study of the performance of RHEAs targeting biomedical applications, while comparing to that of the state-of-the-art 316L, CoCrMo and Ti6Al4V, was not existing before and constitutes the theme of the current work. Two exemplary RHEAs that are studied in detail in this work, TiZrTaHfNb and Ti1.5ZrTa0.5Hf0.5Nb0.5, show highly promising characteristics as novel superior metallic biomaterials in that they possess a desirable combination of wear resistance, wettability and pitting and general corrosion resistance, outperforming 316L, CoCrMo and Ti6Al4V almost in all these important aspects. In addition, it is also shown in this work that how appropriate alloying in RHEAs can be utilized to fine-tune their performance as better metallic biomaterials, such as the correlation between lattice strain and corrosion resistance.

Liquid Exfoliation of Atomically Thin Antimony Selenide as an Efficient Two-Dimensional Antibacterial Nanoagent.

The ever-growing global crisis of multidrug-resistant bacteria has triggered a tumult of activity in the design and development of antibacterial formulations. Here, atomically thin antimony selenide nanosheets (Sb2Se3 NSs), a minimal-toxic and low-cost semiconductor material, were explored as a high-performance two-dimensional (2D) antibacterial nanoagent via a liquid exfoliation strategy integrating cryo-pretreatment and polyvinyl pyrrolidone (PVP)-assisted exfoliation. When cultured with bacteria, the obtained PVP-capped Sb2Se3 NSs exhibited intrinsic long-term antibacterial capability, probably due to the reactive oxygen species generation and sharp edge-induced membrane cutting during physical contact between bacteria and nanosheets. Upon near-infrared laser irradiation, Sb2Se3 NSs achieved short-time hyperthermia sterilization because of strong optical absorption and high photothermal conversion efficiency. By virtue of the synergistic effects of these two broad-spectrum antibacterial mechanisms, Sb2Se3 NSs exhibited high-efficiency inhibition of conventional Gram-negative Escherichia coli, Gram-positive methicillin-resistant Staphylococcus aureus, and wild bacteria from a natural water pool. Particularly, these three categories of bacteria were completely eradicated after being treated with Sb2Se3 NSs (300 μM) plus laser irradiation for only 5 min. In vivo wound healing experiment further demonstrated the high-performance antibacterial effect. In addition, Sb2Se3 NSs depicted excellent biocompatibility due to the biocompatible element constitute and bioinert PVP modification. This work enlightened that atomically thin Sb2Se3 NSs hold great promise as a broad-spectrum 2D antibacterial nanoagent for various pathogenic bacterial infections.

Mechanical tests for Ti-based alloys as new medical materials

Medical implants of titanium alloys are frequently used in medicine being in attention for the researchers to develop alloys with properties close to the human bone. The most important thing in development of alloys for medical apllications is to be composed from biocompatible elements to avoid to affect the health of patients. The paper contains some mechanical properties of three alloys of Ti-Mo-Zr-Ta. Results revealed that it possesses very good mechanical properties for use in medical applications.

Effect of Al Addition on Corrosion Protection of Ti-39Nb-6Zr Alloy for Biological Applications.

For metals to be used as biomaterials, there must not be harmful reaction between the corrosion product of metal or eluted ion, and bio-tissue. Titanium is one of the excellent bio-compatible materials and generally it has tendency to have a small amount elution of Ti ions inside the body. Titanium alloy need to have low elastic modulus for reducing the stress shield effect. Ti-39Nb-6Zr alloy which is consist of biocompatible element such as Nb and Zr, has low elastic modulus with below 60 GPa, but it shows lower yield stress and tensile stress compared with Ti-6Al-4V alloy. In order to increase the strength of Ti-39Nb-6Zr alloy, aluminum was added in this alloy. Since aluminum elements are reported to lead to Alzheimer disease in human, high corrosion resistance is required to use Ti-39Nb-6Zr-0.45Al alloy containing a small amount of Al. In this study, corrosion behaviors were investigated under the solution of three conditions of 0.9% NaCl (pH 7), 0.1% NaF (pH 3) and 0.1% NaF (pH 5). The behaviors were stable under all the conditions. But Ti-39Nb- 6Zr-0.45Al alloy had better corrosion resistance than Ti-39Nb-6Zr alloy in all the conditions. This is because oxide mixtures such as Al₃Ti5O₂, Al₂TiO5 are formed inside the surface layer, which results in forming more stable oxide film than TiO₂ surface film. Ti-39Nb-6Zr-0.45Al alloy has high corrosion resistance and can reduce the concern about aluminum ion elution inside the body.

Preparation, characterization, and biocompatibility of different metal oxide/PEG-based hybrid coating synthesized by sol–gel dip coating method for surface modification of titanium

The aim of the study was to synthesized organic-inorganic experimental nanocomposite materials via sol–gel dip coating and to characterized its biological response. The sols consist of an inorganic–organic matrix based on ZrO2, TiO2, Li+ and polyethylene glycol (PEG). The obtained hybrid-coated titanium samples have been characterized using atomic force microscope (AFM), Scanning Electronic Microscope (SEM), Energy Dispersive X-Ray Analysis (EDX). Biocompatibility of the hybrid coatings was evaluated by cytotoxicity tests. AFM analysis detailed that the obtained materials were rough nanostructured hybrids. SEM results presented covered surfaces and the presence of particles with different sizes and formats. The EDX data allowed to know the quantitative percentage of the elements present on the surface of the hybrid-coated titanium samples compatible with the sols composition. Cytotoxicity showed that all the hybrid-coated titanium samples had non-cytotoxic effect on target cells, having the groups that included Li+ in the surface higher cellular grown. The sol gel dipcoating method represents a viable alternative to include inorganic and organic elements on titanium and form stable hybrid layers. The modified surfaces of titanium with the experimental materials were rough, presented biocompatible elements and allowed high cellular grown.

DC plasma electrolytic oxidation treatment of gum metal for dental implants

Vanadium- and aluminium-free biomedical Ti alloys are getting more and more attention because of the harmful character of these alloying elements. For this reason, it was proposed to substitute them with more biocompatible elements such as Ta, Nb and Zr. So-called gum metal alloys (Ti-Nb-Zr-Ta systems) belong to β-type Ti alloys which are characterized by excellent biocompatibility and possess the modulus of elasticity more closely related to that of a human bone. The present study aims at elucidating the process stages during DC plasma electrolytic oxidation (PEO) of gum metal (Ti-36Nb-3Zr-2Ta alloy) in calcium hypophosphite-based electrolyte system. The effect of the stages on the surface characteristics of the obtained oxide coatings was also determined. The coatings were characterized using SEM/EDS, XPS and contact angle measurements. It was found that the process comprised at least five different stages. The initiation of relatively strong B-type sparks in the third stage of the treatment was necessary to induce significant incorporation of electrolyte components into the oxide coatings. As the treatment continued beyond that point, the composition of the oxide films was getting more similar to that of hydroxyapatite as it was determined from the valence band XPS spectra. The surface morphology of the films was also closely related to the process stage at which the further growth of the oxide was halted. The composition of the electrolyte (regarding the salts used and their concentration) had a tremendous influence on the duration of the process stages and the surface characteristics of the obtained films. The process was also tested for its usefulness in coating gum metal dental implants in order to form bioactive interfaces. Keeping the voltage below a certain limit (before the onset of more powerful surface sparks) was crucial to obtaining good-quality coatings.

ZnII Complexes for Bioimaging and Correlated Applications.

Zinc is a biocompatible element that exists as the second most abundant transition metal ion and an indispensable trace element in the human body. Compared to traditional metal-organic complexes systems, d10 metal ZnII complexes not only exhibit a large Stokes shift and good photon stability but also possess strong emission and low cytotoxicity with a relatively small molecular weight. The use of ZnII complexes has emerged in the last decade as a versatile and convenient tool for numerous biological applications, including bioimaging, molecular and protein recognition, as well as photodynamic therapy. Herein, we review recent developments involving ZnII metal complexes applied as specific subcellular compartment imaging probes and their correlated utilizations.

Development and Characterisation of New Biocompatible Sn-Mg Lead-Free Solder

This work is focused on a development and research of a new lead-free Sn-Mg solder, alloy compatible with the human body. Tin and magnesium are biocompatible elements which do not cause an inflammation or allergic reactions with living tissues. We have prepared the Sn97Mg3 solder (wt. %) by a rapid solidification of its melt on a copper wheel (melt-spinning technique). This solder may find applications in electronic devices for intracorporeal utilisation. The microstructure of the prepared solder exhibits a heterogeneous distribution of the SnMg2 intermetallic particles within the β-Sn matrix. Structure of the solder was studied by an in-situ high energy X-ray diffraction experiment (energy of an X-ray photon: 60 keV) where 2D XRD patterns were collected from the sample in the temperature range from 298 K to 566 K. The experiment was performed at a high brilliance 3rd generation synchrotron source of radiation (PETRA III storage ring, DESY, Hamburg, Germany) at the P02 undulator beamline. From the measured X-ray diffraction data by applying the Rietveld refinement technique we have obtained thermal volume expansion data, mean positions of atoms as well as isotropic atomic displacement parameters of the constituent SnMg2 and the β-Sn crystalline phases. Thermal behaviour was studied by differential scanning calorimetry at heating rates of 5, 15, 30 and 60 K.min-1 and compared with the measured X-ray data. Our main goal lies in a preparation of a lead-free solder with fine grain structure made exclusively of biocompatible elements. We demonstrated that the rapid melt solidification technique leads to in an improvement and better thermal stability of this alloy.

Surface functionalization via PEO coating and RGD peptide for nanostructured titanium implants and their in vitro assessment

This research follows a biomimetic approach for implant surface design, and it concerns surface functionalization for nanostructured Ti Grade 4 with a composite coating obtained by plasma electrolytic oxidation (PEO) with organic pore filler of integrin-active RGD containing peptide (Arg-Gly-Asp-Cys). It was shown that Ti nanostructuring via ECAP-C technique almost two-fold improves its mechanical strength; also, the nanostructuring depassivates the surface, both PEO coated and uncoated. The PEO coating on nano-Ti contains 2–3% more biocompatible elements, amorphous and bio-crystalline phases. The RGD peptide was linked to the surface via phosphonate groups allowing the organic pore filler deposition by dipping method; the RGD presence in the PEO coating pores was proven by the EIS. For the in vitro tests, fibroblasts were used; it was shown that PEO coating on nano-Ti gives 43% increase in the number of cells compared to CG-Ti + PEO; the combination of PEO coating and RGD peptide on nano-Ti gives 45% increase in the number of cells compared to nano-Ti, and 66% compared to CG-Ti. Therefore, this surface functionalization contributes to the development of Ti implants having high strength and providing improved cell proliferation.