Effect of Elastic Modulus on Biomechanical Properties of Lumbar Interbody Fusion Cage

This work focuses on the influence of elastic modulus on biomechanical properties of lumbar interbody fusion cages by selecting two titanium alloys with different elastic modulus. They were made by a new β type alloy with chemical composition of Ti-24Nb-4Zr-7.6Sn having low Young＇s modulus -50 GPa and by a conventional biomedical alloy Ti-6Al-4V having Young＇s modulus -110 GPa. The results showed that the designed cages with low modulus （LMC） and high modulus （HMC） can keep identical compression load -9.8 kN and endure fatigue cycles higher than 5× 10^6 without functional or mechanical failure under 2.0 kN axial compression. The anti-subsidence ability of both group cages were examined by axial compression of thoracic spine specimens （T9-T10） dissected freshly from the calf with averaged age of 6 months. The results showed that the LMC has better anti-subsidence ability than the HMC （p〈0.05）. The above results suggest that the cage with low elastic modulus has great potential for clinical applications.

Influence of Component Size on the Corrosion Behavior of Ti6Al4V Alloy Fabricated by Electron Beam Powder Bed Fusion

The electrochemical behavior of Ti-6Al-4V with 1 mm and 16 mm thickness prepared by electron beam powder bed fusion(EB-PBF)was investigated in phosphate buffered saline.Electrochemical results showed that EB-PBF Ti-6Al-4V with a larger component size was more resistant to corrosion compared to the smaller component,because of less acicularαʹphase content and moreβphase content.As a non-equilibrium phase in the“high-energy state”,αʹphase has a greater susceptibility to corrode and reduces the corrosion resistance of the material,whileβphase improves corrosion resistance of titanium alloys.The results show that the phase composition has a more significant effect on the corrosion performance than the grain size.

Fatigue behavior of Ti-6Al-4V cellular structures fabricated by additive manufacturing technique

Porous titanium and its alloys have been considered as promising replacement for dense implants, as they possess low elastic modulus comparable to that of compact human bones and are capable of providing space for in-growth of bony tissues to achieve a better fixation. Recently, the additive manufacturing(AM) method has been successfully applied to the fabrication of Ti-6 Al-4 V cellular meshes and foams.Comparing to traditional fabrication methods, the AM method offers advantages of accurate control of complex cell shapes and internal pore architectures, thus attracting extensive attention. Considering the long-term safety in the human body, the metallic cellular structures should possess high fatigue strength.In this paper, the recent progress on the fatigue properties of Ti-6 Al-4 V cellular structures fabricated by the AM technique is reviewed. The various design factors including cell shapes, surface properties, post treatments and graded porosity distribution affecting the fatigue properties of additive manufactured Ti-6 Al-4 V cellular structures were introduced and future development trends were also discussed.

Biofunctional magnesium coated Ti6Al4V scaffold enhances osteogenesis and angiogenesis in vitro and in vivo for orthopedic application

The insufficient osteogenesis and osseointegration of porous titanium based scaffold limit its further application.Early angiogenesis is important for scaffold survival.It is necessary to develop a multifunctional surface on titanium scaffold with both osteogenic and angiogenic properties.In this study,a biofunctional magnesium coating is deposited on porous Ti6Al4V scaffold.For osseointegration and osteogenesis analysis,in vitro studies reveal that magnesium-coated Ti6Al4V co-culture with MC3T3-E1 cells can improve cell proliferation,adhesion,extracellular matrix(ECM)mineralization and ALP activity compared with bare Ti6Al4V cocultivation.Additionally,MC3T3-E1 cells cultured with magnesium-coated Ti6Al4V show significantly higher osteogenesisrelated genes expression.In vivo studies including fluorochrome labeling,micro-computerized tomography and histological examination of magnesium-coated Ti6Al4V scaffold reveal that new bone regeneration is significantly increased in rabbits after implantation.For angiogenesis studies,magnesium-coated Ti6Al4V improve HUVECs proliferation,adhesion,tube formation,wound-healing and Transwell abilities.HUVECs cultured with magnesium-coated Ti6Al4V display significantly higher angiogenesis-related genes(HIF-1αand VEGF)expression.Microangiography analysis reveal that magnesium-coated Ti6Al4V scaffold can significantly enhance the blood vessel formation.This study enlarges the application scope of magnesium and provides an optional choice to the conventional porous Ti6Al4V scaffold with enhanced osteogenesis and angiogenesis for further orthopedic applications.

Heat treatment enhancing the compressive fatigue properties of open-cellular Ti-6Al-4V alloy prototypes fabricated by electron beam melting

In this work, we report the effect of annealing in α＋β phase field on the fatigue properties of Ti-6A1-4V alloy meshes fabricated by electron beam melting. The results show that annealing at high temperature near the phase boundary enhances the ductility of the brittle mesh struts due to the formation of coarse α lamellas with a large thickness/length ratio. Accordingly, the fatigue endurance ratio of the studied meshes increases to up to -0.6, which is much superior to that of the as-fabricated counterparts and comparable to those of dense materials.2018 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

Improved activity of MC3T3-E1 cells by the exciting piezoelectric BaTiO_(3)/TC4 using low-intensity pulsed ultrasound

Developing bioactive materials for bone implants to enhance bone healing and bone growth has for years been the focus of clinical research.Barium titanate(BT)is an electroactive material that can generate electrical signals in response to applied mechanical forces.In this study,a BT piezoelectric ceramic coating was synthesized on the surface of a TC4 titanium alloy,forming a BT/TC4 material,and low-intensity pulsed ultrasound(LIPUS)was then applied as a mechanical stimulus.The combined effects on the biological responses of MC3T3-E1 cells were investigated.Results of scanning electron microscopy,energy-dispersive X-ray spectroscopy,and X-ray diffraction showed that an uniform nanospheres-shaped BT coating was formed on TC4 substrate.Piezoelectric behaviors were observed using piezoelectric force microscopy with the piezoelectric coefficient d_(33)of 0.42 pC/N.Electrochemical measures indicated that LIPUS-stimulated BT/TC4 materials could produce a microcurrent of approximately 10μA/cm^(2).In vitro,the greatest osteogenesis(cell adhesion,proliferation,and osteogenic differentiation)was found in MC3T3-E1 cells when BT/TC4 was stimulated using LIPUS.Furthermore,the intracellular calcium ion concentration increased in these cells,possibly because opening of the L-type calcium ion channels was promoted and expression of the Ca_(V)1.2 protein was increased.Therefore,the piezoelectric BT/TC4 material with LIPUS loading synergistically promoted osteogenesis,rending it a potential treatment for early stage formation of reliable bone-implant contact.

Fabrication of open-cellular(porous) titanium alloy implants: osseointegration, vascularization and preliminary human trials

In this study we describe the fabrication of a variety of open-cellular titanium alloy（Ti-6 Al-4 V） implants,both reticular mesh and foam structures, using electron beam melting（EBM）. These structures allow for the elimination of stress shielding by adjusting the porosity（or density） to produce an elastic modulus（or stiffness） to match that of both soft（trabecular） and hard（cortical） bone, as well as allowing for bone cell ingrowth, increased cell density, and all-matrix interactions; the latter involving the interplay between bone morphogenetic protein（BMP-2） and osteoblast functions. The early formation and characterization of elementary vascular structures in an aqueous hydrogel matrix are illustrated.Preliminary results for both animal（sheep） and human trials for a number of EBM-fabricated, and often patient-specific Tialloy implants are also presented and summarized. The results, while preliminary, support the concept and development of successful, porous, engineered ＂living＂ implants.

Effect of fluoride on the corrosion behavior of nanostructured Ti-24Nb-4Zr-8Sn alloy in acidulated artificial saliva

The surface of titanium dental implants is highly susceptible to aggressive fluoride ions in the oral environment. Nanotechnology has proven an effective approach to improve the stability and corrosion resistance of titanium by applying a passive film. In this study, we investigated the effects of fluoride on the corrosion behavior of nanostructured（NS） Ti-24 Nb-4 Zr-8 Sn（Ti2448） alloy in acidulated artificial saliva（AAS）at 37 ℃, and then conducted comparisons with its coarse grained（CG） counterpart. Electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）, as well as surface analysis including X-ray photoelectron spectroscopy（XPS） with argon ion sputtering, and scanning electronic microscopy（SEM） were employed to evaluate the effects of fluoride on sensitivity to pitting and the tolerance of Ti2448 to fluoride in AAS solution. The results demonstrate that corrosion current density increased with F-concentration. In all respects, the NS Ti2448 alloy presented corrosion resistance superior to that of its coarse grained（CG） counterpart at low F-concentrations（0.1%）.Furthermore, a high content of F-（1%） was shown to promote the active dissolution of both alloys by increasing the rate of corrosion. Following immersion in the fluoridated AAS solution for 60 days, a tissuefriendly compound, Ca3（PO4）2, was detected on the surface of the NS when F-= 0.01% and Na2 TiF6 was identified as the main component in the corrosion products of the CG as well as NS Ti2448 alloys when F-= 1%. High concentrations of F-produced pitting corrosion on the CG alloy, whereas NS Ti2448 alloy presented general corrosion in the form of lamellar separation under the same conditions. These findings demonstrate the superior corrosion resistance of the NS Ti2448 alloy as well as lower pitting sensitivity and higher tolerance to fluoride due mainly to grain refinement.

Electron Beam Melted Beta-type Ti–24Nb–4Zr–8Sn Porous Structures With High Strength-to-Modulus Ratio

Electron beam melting （EBM） has been used to manufacture β-type Ti-24Nb-4Zr-8Sn porous compo- nents with 70% porosity, EBM-produced components have favorable structural features （i.e. smooth strut surfaces, fewer defects） and an （α ＋ β）-type microstructure, similar to that subjected to aging treat- ment. EBM-produced components exhibit more than twice the strength-to-modulus ratio of porous Ti- 6A1-4V components having the same porosity. The processing-microstructure-property relationship and deformation behavior of EBM-produced components are discussed in detail. Such porous titanium com- ponents composed of non-toxic elements and having high strength-to-modulus ratio are highly attractive for biomedical applications.

Weak fatigue notch sensitivity in a biomedical titanium alloy exhibiting nonlinear elasticity

It is well known that metallic materials exhibit worse fatigue damage tolerance as they behave stronger in strength and softer in modulus. This raises concern on the long term safety of the recently developed biomechanical compatible titanium alloys with high strength and low modulus. Here we demonstrate via a model alloy, Ti-24 Nb-4 Zr-8 Sn in weight percent, that this group of multifunctional titanium alloys possessing nonlinear elastic deformation behavior is tolerant in fatigue notch damage. The results reveal that the alloy has a high strength-to-modulus（σ/E） ratio reaching2% but its fatigue notch sensitivity（q） is low, which decreases linearly from 0.45 to 0.25 as stress concentration factor increases from 2 to 4. This exceeds significantly the typical relationship between σ/E and q of other metallic materials exhibiting linear elasticity. Furthermore, fatigue damage is characterized by an extremely deflected mountain-shape fracture surface, resulting in much longer and more tortuous crack growth path as compared to these linear elastic materials. The above phenomena can be explained by the nonlinear elasticity and its induced stress relief at the notch root in an adaptive manner of higher stress stronger relief. This finding provides a new strategy to balance high strength and good damage tolerance property of metallic materials.

Electrochemical behavior of open-cellular structured Ti-6Al-4V alloy fabricated by electron beam melting in simulated physiological fluid:the significance of pore characteristics

The cellular structured titanium alloys have attracted significant attention for implants because of their lower Young’s modulus,which is comparable to human bone and has the capability of providing space for bone tissue in-growth.However,there is a gap in the knowledge in regard to the relationship between the pore characteristics and the electrochemical performance of open-cellular structured titanium alloys.In this study,we elucidate the influence of pore characteristics on the electrochemical performance of open-cellular structured Ti-6Al-4V alloys produced by electron beam melting(EBM).Intriguingly,the passive film formed on cellular structured Ti-6Al-4V alloy with a larger pore size was more stable and protective,and the corrosion performance was superior compared to the samples with a smaller pore size in phosphate buffered saline(PBS),mainly because of relatively smaller exposed surface area and unlimited flow of electrolyte.However,in acidic PBS containing fluoride ions,the pore characteristics did not play an important role in the corrosion resistance.It was considered that the protective film breaks down such that the corrosion performance of cellular structured alloys was comparable to each other in this harsh environment.

Mixture of Oxides with Different Valence States in Nanotubes

Oxide nanotubes with different diameters and lengths were fabricated on the biomedical Ti2448 alloy by anodic oxidation in neutral electrolyte. Similar to oxide nanotubes fabricated on pure titanium and its alloys, the as-grown nanotubes on Ti2448 also exhibit gradually changing chemical distribution along the direction of tube growth. Furthermore, several kinds of oxides with different valence states （MxOy） are formed simultaneously for each alloying element M, while their volume fractions vary gradually along the tube-growth direction. The findings of this study would provide insight into the effect of valence states on the desired nanotube properties and help develop ways to enhance the properties of the preferred oxide.