Ti6Al4V Cylinders Research Articles

Microstructural effects on the rotating bending fatigue behavior of Ti–6Al–4V produced via laser powder bed fusion with novel heat treatments

The rotating bending fatigue (RBF) behavior (fully reversed, R = −1) of additively manufactured (AM) Ti–6Al–4V alloy produced via laser powder bed fusion (PBF-L) was investigated with respect to different microstructures achieved through novel heat treatments. The investigation herein seeks to elucidate the effect of microstructure by controlling variables that can affect fatigue behavior in Ti–6Al–4V, such as chemistry, porosity, and surface roughness. In order to control these variables, different hot isostatic pressing (HIP) treatments at 800 °C, 920 °C, and 1050 °C with a 920 °C temper were applied to three sets of Ti–6Al–4V cylinders that originated from the same PBF-L build, such that there were 30 tests per condition. After HIP treatment, the specimens were machined and tested. The highest runout stress was achieved after sub-β transus HIP at 800 °C for 2 h at 200 MPa of pressure. A significant drop in fatigue strength was attributed to large prior-β grains and grain boundary α resulting from super-β transus HIP treated specimens. For the sub-β transus HIP specimens, differences in fatigue strength were attributed to α lath thickness, relative dislocation density, and dislocation boundary strengthening.

Topography rules the ultra-mild wear regime under boundary lubricated gross-slip fretting corrosion

Fretting corrosion of biomedical taper junctions has raised concerns about adverse local tissue reactions. A low release of ions and other reaction products into the body is desirable, and this can be achieved by, e.g., optimizing the topography. Retrieval analysis has revealed that circumferential machining marks with high ridges and low valleys reduce the release of wear products. Thus, we hypothesized that a rougher titanium surface decreases metal release under gross-slip fretting because of a change in wear mechanisms. Fretting tests (polished CoCr29Mo6 alloy pins (Ra ≈ 0.006 μm) against fluted Ti6Al4V cylinders (Ra ≈ 5.6 μm)) were carried out. The worn surfaces were analyzed using SEM and LRS (Laser-Raman Spectroscopy) while ICP-MS of the lubricant (BCS) rendered the wear loss. Results were compared with the wear loss of identically polished CoCr29Mo6 pins rubbing against fine-machined Ti6Al4V cylinders (Ra ≈ 0.245 μm) reported earlier. The fluted topography led to microploughing and microcutting on both CoCr29Mo6 and Ti6Al4V surfaces, triggering tribocorrosion and mechanical mixing of tribomaterial containing Cr-, Mo-, and Ti-oxides and denatured/cleaved proteins. While friction was controlled by mechanical-dominated microploughing and microcutting the steady-state wear was characterized by chemical-dominated tribocorrosion. The total wear loss of the fluted system was half of the fine machined system, albeit the Co-side lost more. Despite the rougher topography the tribomaterial still acted as boundary lubricant and protected the surfaces.

Wear Behavior of Ti6Al4V Surfaces Functionalized through Ultrasonic Vibration Turning

Even if titanium alloys are widely used for biomedical applications, the tendency they show to wear is a matter of concern for their durability. In this research work, Ultrasonic Vibration Turning (UVT) was used to generate texturized surfaces on Ti6Al4V cylinders for improving their wear performances. To prove that, in vitro wear tests were performed, during which the UVT-ed Ti6Al4V cylinders were made to slide against polyethylene disks to replicate a currently used biomedical pair. It was shown that the UVT-ed Ti6Al4V cylinders were characterized by enhanced performances in terms of coefficient of friction and wear rate, which were reduced to 52 and 25%, respectively, compared to polished Ti6Al4V surfaces.

In-vivo performance of plasma-sprayed CaO–MgO–SiO2-based bioactive glass-ceramic coating on Ti–6Al–4V alloy for bone regeneration

The CaO–MgO–SiO2-based bioactive glass-ceramic coating (named M2) on Ti–6Al–4V alloy has been proven to behave well in vitro. But how to make full sense of its performances in terms of osteogenesis and osseointegration in vivo matters very much. For this, the M2-coated Ti–6Al–4V cylinders were prepared by atmospheric plasma spraying (APS) and implanted into New Zealand rabbit for 1, 2 and 3 months, respectively, by setting commercial HA-coated Ti–6Al–4V as the control. It is encouraging that, the two groups bonded with the surrounding tissues stably and newly formed bone grew towards or around the implants after 3-month implantation according to radiographic images. From the histological sections, it is obvious that, compared to the control, the M2-coated implant was more favorable for the osteogenesis and neo-vascularisation in the whole experimental process and demonstrated a better osseointegration with the host bone, indicating the former possessed better osteoconductivity, osteoinductivity and osteogenic ability. The study indicated that the M2-coated Ti–6Al–4V implant exerted a great potential to substitute the commercial HA-coated Ti–6Al–4V implant in repairing load-bearing bone defects.

On the increase of the chemical reactivity of cp titanium and Ti6Al4V at low electrical current in a protein-rich medium

The aim of this study was to evaluate the effect of two electrical current intensities on titanium surface changes in a simulated physiological environment. Commercially pure titanium (cp Ti) grade IV and Ti6Al4V cylinders were coupled to a potentiostat and immersed in DMEM medium enriched with fetal bovine serum (FBS). Samples were divided into four groups: free of electrical stimulation at (C1) room environment or (C2) immersed in DMEM/FBS; and on 5 μA or 10 μA electrical stimulation in DMEM/FBS. After electrical stimulation, the protein adsorption was evaluated by Lowry method and FTIR. Additionally, titanium surfaces were studied by open circuit potencial (OCP), electrochemical impedance spectroscopy (EIS), optical profilometry, and scanning electron microscopy (SEM). FTIR analysis revealed energy bands indicating the presence of amide groups from proteins on all samples immersed in DMEM enriched with FBS. The highest amount of adsorbed total protein was noted on the control groups (p < 0.05). Regarding surface topography, the profilometric analyses showed higher Ra roughness values for cp Ti samples submitted to 10 μA (p < 0.05). Ti6Al4V surfaces had the highest Ra roughness values on 5 μA although no statistical difference within 10 μA group was noticed (p > 0.05). After electrochemical assays, test samples showed higher corrosion resistance than that recorded on control groups. The electrical stimulation increased the chemical reactivity between titanium-based surfaces resulting in a significant increase in roughness as well as on the thickness of the titanium oxide layer.

Effects of interfacial micromotions on vitality and differentiation of human osteoblasts.

ObjectivesEnhanced micromotions between the implant and surrounding bone can impair osseointegration, resulting in fibrous encapsulation and aseptic loosening of the implant. Since the effect of micromotions on human bone cells is sparsely investigated, an in vitro system, which allows application of micromotions on bone cells and subsequent investigation of bone cell activity, was developed.MethodsMicromotions ranging from 25 µm to 100 µm were applied as sine or triangle signal with 1 Hz frequency to human osteoblasts seeded on collagen scaffolds. Micromotions were applied for six hours per day over three days. During the micromotions, a static pressure of 527 Pa was exerted on the cells by Ti6Al4V cylinders. Osteoblasts loaded with Ti6Al4V cylinders and unloaded osteoblasts without micromotions served as controls. Subsequently, cell viability, expression of the osteogenic markers collagen type I, alkaline phosphatase, and osteocalcin, as well as gene expression of osteoprotegerin, receptor activator of NF-κB ligand, matrix metalloproteinase-1, and tissue inhibitor of metalloproteinase-1, were investigated.ResultsLive and dead cell numbers were higher after 25 µm sine and 50 µm triangle micromotions compared with loaded controls. Collagen type I synthesis was downregulated in respective samples. The metabolic activity and osteocalcin expression level were higher in samples treated with 25 µm micromotions compared with the loaded controls. Furthermore, static loading and micromotions decreased the osteoprotegerin/receptor activator of NF-κB ligand ratio.ConclusionOur system enables investigation of the behaviour of bone cells at the bone-implant interface under shear stress induced by micromotions. We could demonstrate that micromotions applied under static pressure conditions have a significant impact on the activity of osteoblasts seeded on collagen scaffolds. In future studies, higher mechanical stress will be applied and different implant surface structures will be considered.Cite this article: J. Ziebart, S. Fan, C. Schulze, P. W. Kämmerer, R. Bader, A. Jonitz-Heincke. Effects of interfacial micromotions on vitality and differentiation of human osteoblasts. Bone Joint Res 2018;7:187–195. DOI: 10.1302/2046-3758.72.BJR-2017-0228.R1.

Bone tissue response induced by bioactive polymer functionalized Ti6Al4V surfaces: In vitro and in vivo study

Ti6Al4V is commonly used for orthopedic applications. This study was designed to test the potentially added benefit of Ti6Al4V functionalized with a bioactive polymer poly(sodium styrene sulfonate) both in vitro and in vivo. Cell-based assays with MC3T3-E1 osteoblast-like cells were used to measure the cell adhesion strength, cell spreading, focal contact formation, cell differentiation and the mineralization of extracellular matrix on grafted and ungrafted Ti6Al4V discs in combination with FBS and collagen type I. Bone morphogenetic protein-2 (BMP-2) was also included in the cell differentiation assay. Results showed that the grafted surface combined with collagen I gave superior levels in every parameter tested with cell-based assays and was almost equivalent to BMP-2 for cell differentiation. In vivo testing was conducted in rabbits (n=42) with cylinders of grafted and ungrafted Ti6Al4V implanted in defects made to the femoral and lateral condyles and animals that were maintained to 1, 3 and 12months. Hydroxyapatite coated Ti6Al4V cylinders were included as a clinical reference control. Osseointegration was assessed post-mortem using histomorphometric analysis conducted on resin sections of explanted undecalcified bone. Two histomorphometric parameters, that of bone-to-implant contact and the bone area, were analyzed by a trained observer blinded to sample identity. Results showed osseointegration on grafted Ti6Al4V was marginally better than both ungrafted and hydroxyapatite coated Ti6Al4V. Overall, the study found that the grafted Ti6Al4V significantly promoted all aspects of osteogenesis tested in vitro and, although in vivo outcomes were less compelling, histomorphometry showed osseointegration of grafted Ti6Al4V implants was equivalent or better than controls.

Tribocorrosion behavior of veneering biomedical PEEK to Ti6Al4V structures

In dentistry, prosthetic structures must be able to support masticatory loads combined with a high biocompatibility and wear resistance in the presence of a corrosive environment. In order to improve the simultaneous wear and corrosion response of highly biocompatible prosthetic structures, a veneering poly-ether-ether-ketone (PEEK) to Ti6Al4V substrate was assessed by tribocorrosion analyses under conditions mimicking the oral environment. Samples were synthesized by hot pressing the PEEK veneer onto Ti6Al4V cylinders. The tribocorrosion tests on Ti6Al4V or PEEK/Ti6Al4V samples were performed on a reciprocating ball-on-plate tribometer at 30N normal load, 1Hz and stroke length of 3mm. The tests were carried out in artificial saliva at 37°C. Open circuit potential (OCP) was measured before, during and after reciprocating sliding tests. The worn surfaces were characterized by scanning electron microscopy. The results revealed a lower wear rate on PEEK combined with a lower coefficient of friction (COF), when compared to Ti6Al4V. In fact, PEEK protected Ti6Al4V substrate against the corrosive environment and wear avoiding the release of metallic ions to the surrounding environment.

Electron Beam Melting Fabrication of Porous Ti6Al4V Scaffolds: Cytocompatibility and Osteogenesis

Titanium‐based implants possessing adequately low elasticity modulus and custom­designed structures are urgently demanded in recent years for orthopedic applications. Electron beam melting (EBM) provides an opportunity to fabricated porous titanium scaffolds that meet the as‐mentioned requirements, and it further allows for improved bone regeneration and increased contact area at implant–tissue interface. As a novel additive manufacturing (AM) technique, EBM could conveniently produce scaffolds with tunable porosity and shapes and complex structures based on the popular “bottom‐up” concept. In the present work, EBM‐produced Ti6Al4V cylinders designed with either a small pore size (EBMS, 640 μm) or a large one (EBML, 1200 μm) were characterized in respect of microstructure, permeability and specific surface area, and their cytocompatibility and osteogenic ability were evaluated subsequently in vitro. Both samples EBMS and EBML could support the attachment and proliferation of hMSCs with minimal inflammatory cytokines secretion. The EBMS scaffolds were relatively more compatible with hMSCs than the EBML and they better sustained osteogenesis probably for their larger specific surface area.

Controlled‐release of bone morphogenetic protein‐2 from a microsphere coating applied to acid‐etched Ti6AL4V implants increases biological bone growth in vivo

A central clinical challenge regarding the surgical treatment of bone and joint conditions is the eventual loosening of an orthopedic implant as a result of insufficient bone ingrowth at the bone-implant interface. We investigated the in vivo effectiveness of a coating containing recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded microspheres applied to acid-etched Ti6Al4V cylinders for implantation. Three groups of rabbits (24 per group) were used for implantation: (1) acid-etched Ti6Al4V implants coated with a mixture of rhBMP-2-loaded microspheres (125 ng rhBMP-2/mg microspheres) and α-butyl cyanoacrylate; (2) acid-etched, uncoated implants; and (3) bare, smooth uncoated implants. After implantation, 12 rabbits from each group were used for bone ingrowth determination at 4, 5, 6, 7, 8, and 12 weeks (2 rabbits per time point), while the remainder were used for histological analysis and push-out testing at 12 weeks. Scanning electron microscopy showed significant improvement in bone growth of the rhBMP-2 microspheres/α-butyl cyanoacrylate group compared with the other groups (p<0.01). Histological analysis and push-out testing also demonstrated enhanced bone growth of the rhBMP-2 group over that in the other two groups (p<0.01). The rhBMP-2 group showed the most significant bone growth, suggesting that coating acid-etched implants with a mixture of rhBMP-2-loaded microspheres and α-butyl cyanoacrylate may be an effective method to improve the osseointegration of orthopedic implants.

Influence of the processing route of porcelain/Ti–6Al–4V interfaces on shear bond strength

This study aims at evaluating the two-fold effect of initial surface conditions and dental porcelain-to-Ti–6Al–4V alloy joining processing route on the shear bond strength. Porcelain-to-Ti–6Al–4V samples were processed by conventional furnace firing (porcelain-fused-to-metal) and hot pressing. Prior to the processing, Ti–6Al–4V cylinders were prepared by three different surface treatments: polishing, alumina or silica blasting. Within the firing process, polished and alumina blasted samples were subjected to two different cooling rates: air cooling and a slower cooling rate (65°C/min). Metal/porcelain bond strength was evaluated by shear bond test. The data were analyzed using one-way ANOVA followed by Tuckey's test (p<0.05). Before and after shear bond tests, metallic surfaces and metal/ceramic interfaces were examined by Field Emission Gun Scanning Electron Microscope (FEG-SEM) equipped with Energy Dispersive X-Ray Spectroscopy (EDS). Shear bond strength values of the porcelain-to-Ti–6Al–4V alloy interfaces ranged from 27.1±8.9MPa for porcelain fused to polished samples up to 134.0±43.4MPa for porcelain fused to alumina blasted samples. According to the statistical analysis, no significant difference were found on the shear bond strength values for different cooling rates. Processing method was statistically significant only for the polished samples, and airborne particle abrasion was statistically significant only for the fired samples. The type of the blasting material did not cause a statistically significant difference on the shear bond strength values. Shear bond strength of dental porcelain to Ti–6Al–4V alloys can be significantly improved from controlled conditions of surface treatments and processing methods.

Properties of Titanium Foams for Biomedical Applications

AbstractTitanium foams are presently used in various load bearing orthopedic applications. Such foams are characterized by an open network of porosity with high surface area. This paper presents the structure, microstructure, and properties of titanium foams produced with a powder metallurgy process. Fully porous CpTi and Ti6Al4V cylinders and CpTi foam coating on CpTi and Ti6Al4V substrates were produced and characterized. The microstructure of the foam cell walls is representative of annealed CpTi and Ti6Al4V. Alloying elements and oxygen in solution increase the mechanical strength of the foams but lower their ductility. Ductility affects the fatigue life of the material. When CpTi foam is bonded to Ti6Al4V substrates, migration of alloying elements in the foam cell walls is observed. Good metallurgical bonding is created between the coatings and the dense substrate and shear strength above the requirements of the FDA guidelines are obtained.

Effect of Biomimetic Nanocrystalline Apatite Surface on Bone Ingrowth

The Success of Hydroxyapatite-Coated Acetabular Components Has Not Been Consistent. Plasma-Sprayed Hydroxyapatite Coatings Work Well on Nonporous Substrates but Do Not Coat the Inner Surfaces of Open-Porous Substrates. Solution Deposition Can Generate Consistent Bioceramic Coats on Porous Surfaces that More Closely Mimic the Trabecular Pattern and Biochemistry at the Bone Interface. we Compared Bone Response to the Following Implants: Porous-Coated Ti6al4v Cylinders with 1 of 3 Treatments: Plasma Sprayed with Hydroxyapatite (HA), Coated with a Solution-Deposited Biomimetic Apatite Coating (BA), and Untreated (Control). Bilateral Femurs in 36 Rabbits Were Implanted with One of the above Implants. Bone Ingrowth for HA and BA Surfaces Was Significantly Higher than that for Control Surfaces. No Fragmentation or Debris Production Was Evident in the Apatite Coat of the BA Group. A Biomimetic Coat of Solution-Deposited Apatite May Be Resistant to Coating Delamination and Particle Generation.

The influence of residual stress on the shear strength between the bone and plasma-sprayed hydroxyapatite coating

Plasma-sprayed HA coating (HAC) 50 and 200 microm thick on Ti6Al4V cylinders was transcortically implanted in the femora of canines. Push-out testing of implant-bone interfaces showed that the HAC coating exhibited higher shear strength at 50 microm coating than 200 microm one. The plasma-sprayed HACs were exhibited compressive residual stresses and the thicker HAC exhibited higher residual stress than that of the thinner HAC. Due to the structure for 50 and 200 microm implants were the same, meaning similar cohesive strength of the lamellar splats. And, there was no difference in the physiological environment; hence the difference of the shear strength for the 50 and 200 microm-HAC implants could best be attributed to the compressive residual stress existed in the HA coating.

Increased Bone Ingrowth on a Biomimetic Nanocrystalline Apatite Surface

Typical plasma-sprayed hydroxyapatite coatings work well on non-porous substrates but do not coat the inner surfaces of open-porous substrates. Solution deposition can produce consistent bioceramic coats of precise thickness on porous surfaces. The resultant “biomimetic” surface more closely mimics the trabecular pattern and biochemistry at the bone interface. This report compares bone response to porous surfaces with biomimetic hydroxyapatite coatings. Implants were manufactured as Ti6Al4V cylinders (5-mm diameter, 41-mm long) coated with c.p-Ti PorocoatÒ porous layer with a thickness of 750 (± 250 µm). Implants were divided into three groups based on surface treatments. The porous surfaces of control group implants did not receive any treatment. The porous surfaces of HA group implants were plasma sprayed with hydroxyapatite. The porous surfaces of BAp group implants were coated with a biomimetic apatite (BAp) coating using a lowtemperature solution-based process that mimics bone mineralization. BAp coating is pure apatite coating of uniform structure and composition, with a thickness of approximately 15 µm on the outer beads. Because of the reduced thickness, the BAp coating does not block the pores or alter the porous structure. Bilateral femurs in thirty-six rabbits were implanted with one of the above groups. Twelve rabbits each were euthanized at 2, 4, and 12 weeks. Osseointegration was measured by automated computerized histomorphometry of scanning electron microscopy images of sections taken through the implant. Bone ingrowth on the Control surface was 45 % at 2 weeks and 47% at 12 weeks. Bone ingrowth on the PS surface increased from 51% at 2 weeks to 67% at 12 weeks. Bone ingrowth on the BAp surface increased from 45 % at 2 weeks to 71% at 12 weeks. At both time points mean bone ingrowth on PS and BAp coated implants was significantly higher than the control uncoated implants (p &lt; 0.01). By 12 weeks the PS hydroxyapatite coat began showing evidence of fragmentation and debris production on SEM. This was not evident in the BAp coat. This study supports the hypothesis that apatite coating benefits osseointegration. A biomimetic coat of solution deposited apatite may not show the disadvantages of coating delamination and particle generation. Biomimetic apatite coatings may be attractive alternatives for noncemented total hip arthroplasty.

Growth and dissolution of apatite precipitates formed in vivoon the surface of a bioactive glass coating film and its relevance tobioactivity

Development of bioactive glasses for use as a coating on Ti6Al4Vprostheses requires a better understanding of reactions at thebone/bioactive glass interface. Indeed, the bioactive glasses bond to bonethrough physico-chemical reactions. In vivo, an apatite rich layeris built up on top of a pure silica rich layer at the bioactive glassperiphery. In this paper, we have studied Ti6Al4V cylinders coated with abioactive glass and implanted in sheep femora for two, three and sixmonths. At each time period, the samples were analysed with scanningtransmission electron microscopy coupled with energy dispersive x-rayspectroscopy. In vivo, the bioactive glass dissolution led to theformation on its surface of spherical particles with different sizes. Thedistributions of Si, Al, Ca, P and Mg concentrations across the particlesreveal precipitation of apatite with the incorporation of magnesium.Apatite precipitation is governed by diffusion through an Si layer andoccurs under specific supersaturation conditions. Measurements ofsupersaturation for Ca and P demonstrate that the largest precipitatesgrow and the smallest dissolve. These results allow us to study the growthand dissolution rate of the apatite precipitates and their relevance tobioactivity. Particles with a radius twice the average radius (⟨R⟩) grow the fastest and, if the radius increases, the rate ofgrowth decreases. Before three months, the growth of apatite precipitates(⟨R⟩≈1 µm) leads to the growth of a Ca-Pinterfacial layer. After three months, ⟨R⟩ is of the orderof 0.5 µm, and the majority of the apatite layer dissolves. Theeffects of aluminium and magnesium on apatite generation are alsostudied.

Carcinogenicity of CoCrMo (F-75) implants in the rat.

A long-term study was conducted in rats to assess the contribution of the surface area of CoCrMo devices to carcinogenesis. Groups consisting of 104 rats each (52 male, 52 female) were either implanted with metal cylinders fixed on the left, lateral femur (groups 1-3) or injected with a suspension of metal microspheres in the dorsal subcutis (group 4). Group 1 (control) received solid Ti6Al4V cylinders [surface area to body weight (SA/BW) ratio measuring 1.35 times that of human total hip prosthesis (HTHP)]. Group 2 was implanted with solid CoCrMo (SA/BW ratio: identical to implants of group 1). Group 3 received sintered-porous CoCrMo devices (SA/BW ratio: 30 x HTHP). Group 4 was injected with a suspension of CoCrMO microspheres (SA/BW ratio: 135 x HTHP). Implant-associated tumors (IATs) were observed in 23, 14, 3, and 15 rats of groups 1, 2, 3, and 4, respectively. Within groups 1 and 2, 34 IATs were associated with loose implants, three with undetermined implant fixation status, and none with fixed implants. A significantly increased accumulation of chronic inflammatory tissues around loose rather than fixed implants suggested a foreign-body reaction as the primary mechanism of carcinogenesis. A secondary role in carcinogenesis was ascribed to the increased CoCrMo implant SA/BW ratios as indicated by a 14.6% IAT incidence in group 4 versus 3% in group 3. These results support the notion that early intervention in the removal of loose metal devices is warranted to mitigate against foreign body-induced carcinogenesis, at least in this animal model.