Microstructure, mechanical properties, castability and in vitro biocompatibility of Ti-Bi alloys developed for dental applications

Shape memory effect and aging behavior of Bi-added Ti–Cr alloys for biomedical applications

For the further development of biocompatible metastable β (bcc) Ti alloys, the purpose of this study is to evaluate the potential of bismuth (Bi) addition in terms of shape memory properties and phase stability. It was found that the shape memory effect appeared in Ti-5Cr-1.6Bi (mol%) alloy. However, permanent (unrecoverable) deformation due to dislocations or twinning was also introduced simultaneously from the early stage of deformation. Regarding the formation of isothermal ω phase and the resulting hardness change by aging, it was found that the hardness change was large and that the isothermal ω phase formed in Ti-5Cr-1.6Bi alloy, while age hardening was small and no isothermal ω phase formed in Ti-5Cr-6.1Bi alloy. These results indicate the suppression of not only athermal ω but also isothermal ω phase by Bi addition. However, considering the fact that the alloy becomes brittle when Bi addition is over 3 mol%, it can be concluded that 1-3 mol% Bi addition is worth for the improvement of shape memory effect, suppression of ω phase, X-ray imaging, magnetic resonance imaging, and biocompatibility in metastable β Ti alloys.

Enhanced Mechanical and Corrosion Properties via Annealing Treatment on the Hot-Rolled Ti-Zr-Mo Alloy

In this work, the Ti-20Zr-15Mo alloy in its hot-rolled state was annealed in different phase zones, and the effects of the annealing treatment on the phase composition, organization, mechanical and corrosion resistance properties of the alloy were systematically investigated. The results showed that the original β grains of the alloy had all recrystallized to form the β equiaxial grains when annealed at 800 °C, and the grains had been significantly refined. This allowed the alloy to reach a tensile strength of 1000 MPa, a maximum of 28% after stretching, and a significant increase in plasticity. Also, due to the single beta phase, there was no galvanic corrosion, making the alloy annealed at 800 °C have the best corrosion resistance.

Fabrication of multilevel porous structure networks on Nb-Ta-Ti alloy scaffolds and the effects of surface characteristics on behaviors of MC3T3-E1 cells

Porous Nb-25Ta-25Ti alloys (60% porosity and 100-600 μm pore size) for bone implant applications were manufactured combining impregnation and sintering methods. Surfaces with porous micro-nanostructured networks on Nb-Ta-Ti alloys were successfully modified by various surface pre-treatments (acid etching, alkali-heat treatment and annealing treatment). Surface characteristics and Ca-P layer deposition behaviors of the multilevel structured porous Nb-Ta-Ti alloys were investigated by conducting various tests, including x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray, atomic force microscopy and optical contact angle measurement. In particular, bulk Nb-Ta-Ti alloys were also used as mutual control. The results demonstrated that the porous alloy exhibited a unique multilevel porous structure with macro-networks and micro-pits after pre-treatments. The surface passive TiO₂/Nb₂O₅/Ta₂O₅layers on Nb-Ta-Ti alloys were partially dissolved by the corrosive attack of hydroxyl ions during alkali heat treatment. In addition, subsequent annealing treatment increased the density of the gel layers formed during alkali heat treatment. After immersion in SBF for 14 d, a continuous relatively uniform apatite layer was formed on the multilevel structured surfaces. Moreover, the mechanism of surface mineralization can be construed as electrostatic interactions between substrates and ions. Furthermore,in vitrocell culture showed that Nb-Ta-Ti alloys had a good biocompatibility and the multilevel porous structure could enhance the cellular behaviors including: cell adhesion and spreading.

Effects of Different Titanium Surface Treatments on Adhesion, Proliferation and Differentiation of Bone Cells: An In Vitro Study

The objective of this study was to evaluate the impacts of different sandblasting procedures in acid etching of Ti6Al4V surfaces on osteoblast cell behavior, regarding various physicochemical and topographical parameters. Furthermore, differences in osteoblast cell behavior between cpTi and Ti6Al4V SA surfaces were evaluated. Sandblasting and subsequent acid etching of cpTi and Ti6Al4V discs was performed with Al2O3 grains of different sizes and with varying blasting pressures. The micro- and nano-roughness of the experimental SA surfaces were analyzed via confocal, atomic force and scanning electron microscopy. Surface free energy and friction coefficients were determined. hFOB 1.19 cells were seeded to evaluate adhesion, proliferation and osteoblastic differentiation for up to 12 d via crystal violet assays, MTT assays, ALP activity assays and Alizarin Red staining assays. Differences in blasting procedures had significant impacts on surface macro- and micro-topography. The crystal violet assay revealed a significant inverse relationship between blasting grain size and hFOB cell growth after 7 days. This trend was also visible in the Alizarin Red assays staining after 12 d: there was significantly higher biomineralization visible in the group that was sandblasted with smaller grains (F180) when compared to standard-grain-size groups (F70). SA samples treated with reduced blasting pressure exhibited lower hFOB adhesion and growth capabilities at initial (2 h) and later time points for up to 7 days, when compared to the standard SA surface, even though micro-roughness and other relevant surface parameters were similar. Overall, etched-only surfaces consistently exhibited equivalent or higher adhesion, proliferation and differentiation capabilities when compared to all other sandblasted and etched surfaces. No differences were found between cpTi and Ti6Al4V SA surfaces. Subtle modifications in the blasting protocol for Ti6Al4V SA surfaces significantly affect the proliferative and differentiation behavior of human osteoblasts. Surface roughness parameters are not sufficient to predict osteoblast behavior on etched Ti6Al4V surfaces.

Wear Resistance and Biocompatibility of Co-Cr Dental Alloys Fabricated with CAST and SLM Techniques

Cobalt–chromium (Co-Cr) alloys have been widely used as dental-restoration materials for many years. This study sought to investigate whether selective laser melting (SLM) is a more appropriate process than traditional casting (CAST) for fabricating dental Co-Cr alloys. Metallurgical microscopy, X-ray photoelectron spectroscopy (XPS), Vickers hardness and nanoindentation tests, and friction and wear tests were used to evaluate the microstructure, surface compositions, mechanical properties, and wear resistance, respectively. Additionally, the biocompatibilities and cell adhesion of the alloys were evaluated with L-929 fibroblasts via CCK-8 assay, Live/Dead staining, flow cytometric analysis, scanning electron microscopy (SEM) observation and real-time PCR (RT-PCR) assay. The XPS results showed that the two alloys were all mainly comprised of Co, Cr, and O. The hardness in the CAST group equaled 7.15 ± 0.48 GPa, while in the SLM group, it equaled 9.06 ± 0.49 GPa. The friction coefficient of SLM alloys remained at approximately 0.46, but the CAST specimens fluctuated significantly. SLM alloys exhibited shallower wear scars and less wear debris compared with CAST alloys, simultaneously. Additionally, there were higher survival and expression of cell-adhesion-related genes on SLM alloys of L-929 cells, which meant that the deleterious effect on L-929 cells was significantly reduced compared with that for the CAST alloys. Overall, the wear resistances and biocompatibilities of the Co-Cr dental alloys were dramatically affected by the fabrication technique. The SLM technique is advantageous over the CAST technique for fabricating Co-Cr dental alloys.

Insight Into Corrosion of Dental Implants: From Biochemical Mechanisms to Designing Corrosion-Resistant Materials

Purpose of Review

Despite advanced technologies to avoid corrosion of dental implants, the mechanisms toward the release of metals and their role in the onset of peri-implant diseases are still under-investigated. Effective knowledge on the etiopathogenesis of corrosive products and preventive strategies mitigating the risks for surface degradation are thus in dire need. This review aimed to summarize evidence toward biocorrosion in the oral environment and discuss the current strategies targeting the improvement of dental implants and focusing on the methodological and electrochemical aspects of surface treatments and titanium-based alloys.

Recent Findings

Recent studies suggest the existence of wear/corrosion products may correlate with peri-implantitis progress by triggering microbial dysbiosis, the release of pro-inflammatory cytokines, and animal bone resorption. Furthermore, current clinical evidence demonstrating the presence of metal-like particles in diseased tissues supports their possible role as a risk factor for peri-implantitis. For instance, to overcome the drawback of titanium corrosion, researchers are primarily focusing on developing corrosion-resistant alloys and coatings for dental implants by changing their physicochemical features.

Summary

The current state-of-art discussed in this review found corrosion products effective in affecting biofilm virulence and inflammatory factors in vitro. Controversial and unstandardized data are limitations, making the premise of corrosion products being essential for peri-implantitis onset. On the other hand, when it comes to the strategies toward reducing implant corrosion rate, it is evident that the chemical and physical properties are crucial for the in vitro electrochemical behavior of the implant material. For instance, it is foreseeable that the formation of films/coatings and the incorporation of some functional compounds into the substrate may enhance the material’s corrosion resistance and biological response. Nevertheless, the utmost challenge of research in this field is to achieve adequate stimulation of the biological tissues without weakening its protective behavior against corrosion. In addition, the translatability from in vitro findings to clinical studies is still in its infancy. Therefore, further accumulation of high-level evidence on the role of corrosion products on peri-implant tissues is expected to confirm the findings of the present review besides the development of better methods to improve the corrosion resistance of dental implants. Furthermore, such knowledge could further develop safe and long-term implant rehabilitation therapy.

Impact of Engineering Surface Treatment on Surface Properties of Biomedical TC4 Alloys under a Simulated Human Environment

The impact of sandblasting, anodic oxidation, and anodic oxidation after sandblasting on the surface structure and properties of titanium alloys was investigated. It was found that the surface treatments had a significant influence on the surface roughness values, contact angle values, Vickers hardness, wear resistance, and corrosion resistance of titanium alloys. The surface roughness of titanium alloys with sandblasting treatment was increased by 67% compared to untreated specimen. The Vickers hardness of titanium alloys treated with anodic oxidation after sandblasting was found to increase from 380.8 HV to 408.5 HV, which was increased by 7.3%. The surface treatments in this work improved the wear resistance of the titanium alloys to some extent, and it can be found that the wear scar width is reduced by up to 18.6%. The corrosion resistance of the titanium alloys was found to improve on anodic oxidation. Sandblasting was found to increase surface roughness and promote the formation of a porous layer during the anodization process, resulting in a slight decrease in corrosion resistance. The corrosion current density was increased by 21% compared to the untreated specimen. The corrosion current density of the titanium alloy treated with anodic oxidation decreased to 7.01 × 10−8 A/cm2. The corrosion current density was decreased by 24% compared to the untreated specimen. The corrosion current density of the titanium alloys treated with anodic oxidation after sandblasting decreased to 7.63 × 10−8 A/cm2. The corrosion current density was decreased by 8.8% compared to the specimen with anodic oxidation. The anodic oxidation provided a hydrophilic property for the surface of Ti alloys, which could show a better osseointegration characteristic than that of sandblasting. The impact of the surface treatments on surface structure and properties of titanium alloys was studied.

Prediction of tribocorrosion processes in titanium-based dental implants using acoustic emission technique: Initial outcome

The use of dental implants is growing rapidly for the last few decades and Ti-based dental implants are a commonly used prosthetic structure in dentistry. Recently, the combined effect of corrosion and wear, called tribocorrosion, is considered as a major driving process in the early failure of dental implants. However, no previous study has reported the prediction of tribocorrosion processes in advance. Therefore, this study is a novel investigation on how the acoustic emission (AE) technique can predict tribocorrosion processes in commercially-pure titanium (cpTi) and titanium-zirconium (TiZr) alloys. In this study, tribocorrosion tests were performed under potentiostatic conditions and AE detection system associated with it captures AE data. Current evolution and friction coefficient data obtained from the potentiostatic evaluations were compared with AE absolute energy showcased the same data interpretation of tribocorrosion characteristics. Other AE data such as duration, count, and amplitude, matched more closely with other potentiostatic corrosion evaluations and delivered more promising results in the detection of tribocorrosion. Hence, AE can be consider as a tool for predicting tribocorrosion in dental implants. Experimental results also reveal Ti5Zr as one of the most appropriate dental implant materials while exposing Ti10Zr's lower effectiveness to withstand in the simulated oral environment.

Development and properties of dental Ti-Zr binary alloys

In this study, two medium Zr-containing Ti-based alloys with commercially pure titanium as control were systematically investigated to assess their potential biomedical application. After samples subjected to TMP and CR, it was found that the Zr addition significantly affected the microstructure, phase constitutions, mechanical properties and cytocompatibility. The microstructural results showed that increasing Zr concentrations resulted in more refined grains. Furthermore, Zr changed the phase constitution: CR Ti-20Zr was formed by the single α-phase while CR Ti-30Zr alloy was formed by the coexistence of α and deformation-induced FCC phases. The P-type FCC phase was dominant and more prone to occur than the B-type one. The mechanical tests demonstrated that the increasing Zr content led to a simultaneous increase in micro-hardness, strength and plasticity of CR samples due to the combined effects of solution strengthening, work hardening and the FCC phase. The SEM fractography indicated that the brittle fracture of CR Ti-20Zr due to deformation twins and ductile fracture of CR Ti-30Zr because of FCC phase. Furthermore, Ti-Zr alloys presented comparable cytocompatibility to the CP-Ti control based on cell viability, proliferation and intracellular O^2- content of MSCs. Specifically, alkaline phosphatase activity in BMSCs were significantly higher for grain refined CR Ti-30Zr. Considering all these results, CR Ti-30Zr alloy exhibited the optimal comprehensive performance to be potential dental materials.

Physiochemical and biological evaluation of SLM-manufactured Ti-10Ta-2Nb-2Zr alloy for biomedical implant applications

Titanium alloys, such as Ti-10Ta-2Nb-2Zr (TTNZ), are promising biomaterials due to their excellent biocompatibility and low Young's modulus. The TTNZ samples herein were manufactured by selective laser melting and the novel material was evaluated as a dental implant in vitro and in vivo. The microstructure, mechanical properties, electrochemical behaviour, cytotoxicity, haemocompatibility and osteogenic differentiation were systematically investigated. Based on the tensile test results, the as-printed TTNZ samples had an elongation of 20.23% ± 1.95%, an ultimate tensile strength of 646.61 ± 24.96 MPa and a Young's modulus of 23.72 ± 1.18 GPa. According to the biocompatible value, the as-printed TTNZ sample exhibited no cell cytotoxicity and it showed even better cell adhesion ability than that of the as-printed Ti-6Al-4 V and wrought Ti-6Al-4 V samples. The haemolysis percentage of the as-printed TTNZ sample was 0.629% ± 0.363%. Moreover, the as-printed TTNZ sample facilitated protein adsorption and osteogenic differentiation of human osteoblast-like (MG-63) cells in vitro. The in vivo data also demonstrated the histocompatibility of the as-printed TTNZ. In summary, the as-printed TTNZ developed in this study demonstrated good biocompatibility, low stress shielding, excellent ductility and great osteogenic differentiation. These results indicated that as-printed TTNZ alloys can be promising for end-use human biomedical applications.

Influence of chemical composition on cell viability on titanium surfaces: A systematic review

STATEMENT OF PROBLEM

A consensus on which dental implant alloy and surface treatment provide the best cell viability is unclear.

PURPOSE

The purpose of this systematic review was to provide information on the influence of surface and intrinsic titanium alloy chemical components on cell viability.

MATERIAL AND METHODS

The PubMed, LILACS, COCHRANE library, and Science Direct databases were electronically searched for the terms dental implants AND titanium AND cytotoxicity. Inclusion criteria were research articles that studied titanium or its alloys for chemical composition and cell viability and were published in English between 1999 and 2019. Articles that did not study titanium and its alloys, articles with nondental or biomedical implants, and articles that were not found in their entirety were excluded.

RESULTS

A total of 1226 articles selected by title or abstract according to the inclusion and exclusion criteria resulted in 51 articles that were reduced to 27 after reading in full. The treatments analyzed were arc fusion, electron beam physical deposition, plasma electrolytic oxidation, coating addition, micro arc oxidation, anodization, thermochemical process, BMP-2 immobilization, pressure-assisted sintering, and alkali heat treatment.

CONCLUSIONS

The evaluated literature did not allow a determination of the best surface treatment for cell viability because of the heterogeneity of the studies regarding the type of alloy, cell used in the MTT assay, study, and implant purpose (biomedical or dental). The cytotoxic effect of chemical components was dependent on dose, time, size, temperature, and cell type. The niobium, tantalum, zirconium, and molybdenum elements have been most often added in the development of less toxic Ti alloys with lower modulus of elasticity and increased strength.

Biological and Mechanical Effects of Micro-Nanostructured Titanium Surface on an Osteoblastic Cell Line In vitro and Osteointegration In vivo

Hybrid micro-nanostructure implant surface was produced on titanium (Ti) surface by acid etching and anodic oxidation to improve the biological and mechanical properties. The biological properties of the micro-nanostructure were investigated by simulated body fluid (SBF) soaking test and MC3T3-E1 cell co-culture experiment. The cell proliferation, spreading, and bone sialoprotein (BSP) gene expression were examined by MTT, SEM, and reverse transcription-polymerase chain reaction (RT-PCR), respectively. In addition, the mechanical properties were evaluated by instrumented nanoindentation test and friction-wear test. Furthermore, the effect of the micro-nanostructure surface on implant osteointegration was examined by in vivo experiment. The results showed that the formation of bone-like apatite was accelerated on the micro-nanostructured Ti surface after immersion in simulated body fluid, and the proliferation, spreading, and BSP gene expression of the MC3T3-E1 cells were also upregulated on the modified surface. The micro-nanostructured Ti surface displayed decreased friction coefficient, stiffness value, and Young's modulus which were much closer to those of the cortical bone, compared to the polished Ti surface. This suggested much better mechanical match to the surrounding bone tissue of the micro-nanostructured Ti surface. Furthermore, the in vivo animal experiment showed that after implantation in the rat femora, the micro-nanostructure surface displayed higher bonding strength between bone tissues and implant; hematoxylin and eosin (H&E) staining suggested that much compact osteoid tissue was observed at the interface of Micro-nano-Ti-bone than polished Ti-bone interface after implantation. Based on these results mentioned above, it was concluded that the improved biological and mechanical properties of the micro-nanostructure endowed Ti surface with good biocompatibility and better osteointegration, implying the enlarged application of the micro-nanostructure surface Ti implants in future.

Screening on binary Ti alloy with excellent mechanical property and castability for dental prosthesis application

In the present study, the microstructure, mechanical property, castability, corrosion behavior and in vitro cytocompatibility of binary Ti–2X alloys with various alloying elements, including Ag, Bi, Ga, Ge, Hf, In, Mo, Nb, Sn and Zr, were systematically investigated, in order to assess their potential applications in dental field. The experimental results showed that all binary Ti‒2X alloys consisted entirely α–Ti phase. The tensile strength and microhardness of Ti were improved by adding alloying elements. The castability of Ti was significantly improved by separately adding 2 wt.% Bi, Ga, Hf, Mo, Nb, Sn and Zr. The corrosion resistance of Ti in both normal artificial saliva solution (AS) and extreme artificial saliva solution (ASFL, AS with 0.2 wt.% NaF and 0.3 wt.% lactic acid) has been improved by separately adding alloying elements. In addition, the extracts of studied Ti‒2X alloys produced no significant deleterious effect to both fibroblasts L929 cells and osteoblast-like MG63 cells, indicating a good in vitro cytocompatibility, at the same level as pure Ti. The combination of enhanced mechanical properties, castability, corrosion behavior, and in vitro cytocompatibility make the developed Ti‒2X alloys have great potential for future stomatological applications.

Characterization, corrosion behavior, cellular response and in vivo bone tissue compatibility of titanium-niobium alloy with low Young's modulus

β-Type titanium alloys with a low elastic modulus are a potential strategy to enhance bone remodeling and to mitigate the concern over the risks of osteanabrosis and bone resorption caused by stress shielding, when used to substitute irreversibly impaired hard tissue. Hence, in this study, a Ti-45Nb alloy with low Young's modulus and high strength was developed, and microstructure, mechanical properties, corrosion behaviors, cytocompatibility and in vivo osteo-compatibility of the alloy were systematically investigated for the first time. The results of mechanical tests showed that Young's modulus of the Ti-Nb alloy was reduced to about 64.3GPa (close to human cortical bone) accompanied with higher tensile strength and hardness compared with those of pure Ti. Importantly, the Ti-Nb alloy exhibited superior corrosion resistance to Ti in different solutions including SBF, MAS and FAAS (MAS containing NaF) media. In addition, the Ti-Nb alloy produced no deleterious effect to L929 and MG-63 cells, and cells performed excellent cell attachment onto Ti-Nb surface, indicating a good in vitro cytocompatibility. In vivo evaluations indicated that Ti-Nb had comparable bone tissue compatibility to Ti determined from micro-CT and histological evaluations. The Ti-Nb alloy with an elasticity close to human bone, thus, could be suitable for orthopedic/dental applications.