Addition of Sn to TiNb alloys to improve mechanical performance and surface properties conducive to enhanced cell activity

Titanium (Ti) alloys with Niobium (Nb) and Tin (Sn) were prepared in order to conduct a systematic study on the bulk and surface properties of as-cast c.p.Ti, binary Ti40Nb and Ti10Sn, and ternary Ti-10Nb-5Sn (at.%) to ascertain whether Sn content can be used as an enhancer for cell activity. From a metallurgy viewpoint, a range of binary and ternary alloys displaying distinctive Ti phases (i.e. β, α’, α”) were achieved at room temperature. Their surface (oxide thickness and composition, roughness, contact angle) and bulk (compressive stiffness, strength, elongation, microhardness, electrical resistance) features were characterised. The same surface roughness was imparted on all the alloys, therefore substrate-cell interactions were evaluated independently from this variable. The physico-mechanical properties of the ternary alloy presented the highest strength to stiffness ratio and thereby proved the most suitable for load-bearing orthopaedic applications. From a cellular response viewpoint, their cytotoxicity, ability to adsorb proteins, to support cell growth and to promote proliferation were studied. Metabolic activity using a mouse model was monitored for a period of 12 days to elucidate the mechanism behind an enhanced proliferation rate observed in the Sn-containing alloys. It was hypothesised that the complex passivating surface oxide layer and the bulk inhomogeneity with two dominant Ti phases were responsible for this phenomenon

Biomechanical characterisation of soft tissue for transtibial prosthetics

Biomechanical characterisation of soft tissue for transtibial prosthetic

Comparison of elastic properties of low-density polymeric foams determined by ultrasonic wave propagation and quasi-static mechanical testing

The ability to predict the mechanical performance of materials without sample extraction is of great interest to manufacturers and end-users. The aim of this work was to examine the relationship between the quasi-static measurements (i.e. the typically reported elastic property) and the non-destructive in-line in-situ ultrasonic wave propagation-derived elastic moduli of porous polyurethane foams over a range of densities. It was found that the ratio of moduli was direction-dependent: a factor of 2 when the testing was perpendicular to the pore orientation and a factor of 1.7 when parallel to the pore rising direction. The deviation was explained by ruling mechanisms such as strain rate and amplitude, deviation from orthotropic theory and anisotropy, and degree of density which affected shear wave propagation. The correlations were in agreement with those reported for other porous materials. The quantification of this correlation is a practical tool for estimating elastic properties on heterogeneous, irregularly shaped samples not suitable for bulk testing, or for in-line rapid quality control of parts in production lines

Modelling indentation of human lower-limb soft tissue: simulation parameters and their effects

Abstract Modern developments of biomedical applications demand a better understanding of mechanical behaviour of soft biological tissues. As human soft tissues demonstrate a significant structural and functional diversity, characterisation of their mechanical behaviour still remains a challenge. Limitations related with implementation of mechanical experiments on human participants lead to a use of finite-element models for analysis of mechanical responses of soft tissues to different loads. This study focuses on parameters of numerical simulation considered for modelling of indentation of a human lower limb. Assessment of the effect of boundary conditions on the model size shows that at a ratio of its length to the tissue’s thickness of 1.7 for the 3D model this effect vanishes. The numerical results obtained with models employing various sets of mechanical parameters of the first-order Ogden scheme were compared with original experimental data. Furthermore, high sensitivity of the resulting reaction forces to the indenting direction is demonstrated for cases of both linear and angular misalignments of the indenter. Finally, the effect of changes in material parameters and their domain on their contribution to the reaction forces is discussed with the aim to improve our understanding of mechanical behaviour of soft tissues based on numerical methods. The undertaken research with its results on minimal requirements for finite-element models of indentation of soft tissues can support inverse analysis of their mechanical properties and underpin orthopaedic and medical procedures

Template-free, microscale dimple patterning of pure titanium surface through anodic dissolution using non-aqueous ethylene glycol-TiCl₄ electrolytes

We report a single-step anodic dissolution route for the template-free patterning of pure titanium (Ti) surfaces into a microscale, dimpled topography using non-aqueous ethylene glycol-TiCl4 electrolytes. Anodic dissolution of Ti metal (i.e. 0.04 M Ti4+) into a 40 EG: 1 TiCl4 electrolyte was found to induce a predominant change in the anodic dissolution reaction of Ti metal, converting its surface morphology from a slightly-pitted, bright finish into a dimple-patterned surface. The dimple pattern, ca. 4.5 µm in size and 1 µm in cusp height, was found self-organised with no apparent relation to underlying metal grain structure and independent of the applied potential within the anodic current plateau. The origin of the dimple patterning is surmised to arise from a dynamic self-organisation of the double layer, templated via tracery anodic reaction products – Ti-glycolate-derived, stacked-nanolayers (SNLs)

The effect of energy density and Nb content on the microstructure and mechanical properties of selective laser melted Ti-(10-30 wt.%) Nb

In this study, Ti-(0-30 wt.%)Nb alloys developed from elemental powders were fabricated by the Selective Laser Melting (SLM) process. Compositional homogeneity, microstructure and mechanical performance were investigated as a function of energy density. The proportion of un-melted Nb particles and isolated pore count reduced with increasing energy density, while Ti allotropic content (i.e. α’, α” and β) varied with energy density due to in-situ alloying. Increasing the Nb content led to the stabilisation of the α” and β phases. The mechanical properties were similar to those compositions manufactured using casting methods, without further post processing. The addition of 20Nb (wt.%) and using an energy density of 230 J/mm3 resulted in a Young’s Modulus of 65.2 ± 1.8 GPa, a yield strength of 769 ± 36 MPa and a microstructure of predominantly α” martensite. This strength to stiffness ratio (33% higher than Ti-10Nb and 22% higher than Ti-30Nb), is attributed to in-situ alloying that promotes solid solution strengthening and homogenisation. These alloys are strong contenders as materials suitable for implantable load-bearing orthopaedic applications

Use of mechanical alloying to develop novel titanium alloy powders suitable for the selective laser melting process

Over recent years there has been a push to develop Titanium (Ti) implants with a customised compressive modulus that would mimic that of load bearing bones (i.e. 10-30 GPa). One of the approaches suggested to achieve the desired properties is by alloying Ti with biocompatible alloying elements, such as Niobium (Nb), at bespoke quantities. These alloys can then be used in Selective Laser Melting (SLM) and other AM processes, provided they have suitable particle size distributions, chemical homogeneity, and flowability. Commercial powders for AM are typically produced by atomisation routes, but this process is not financially viable unless large quantities of powdered material are produced, and therefore not suitable for small scale production such as a one-off patientspecific implant. This study assesses the feasibility of using low-volume, mechanically alloyed powders, of target Ti-Nb compositions for use in a SLM process.It investigates the particle distribution and flowability of the produced powders as well as the densification and microstructural properties of parts fabricated with them, using an array of physical and chemical tools and techniques

Physico-chemical characterisation of Ti-Nb-Sn alloys surfaces and their osteogenic properties

Implanted tissue engineering devices interact with the host tissue through their surface in the first instance. Surface chemistry triggers cell activities that stimulate bone tissue-formation mechanisms for osteoblast maturation. In this work, the bioactivity of binary Ti-40Nb and Ti-10Sn and ternary Ti-10Nb-5Sn alloys, candidates for bioengineering applications, has been studied on their surface with a view to establish their osteogenic potential compared to that of c.p. Ti. Cellular population growth was used to assess proliferative and differentiative phenotypes (via protein and Alkaline Phosphatase markers), coupled with gene expression (i.e. Runx2 and OCN) to confirm maturation. The results show that Sn-containing alloys support cell bioactivity, increase metabolic activity (i.e. metabolites content) that indicate their preferred glycolytic pathway, promote cell attachment, differentiation and osteoblast maturation. Ti-40Nb, although also non-cytotoxic, retards osteoblastic differentiation and maturation. To elucidate the features that underpin this difference, their physical (i.e. wettability, electrical state near the surface) and chemical properties (i.e. oxide layer thickness and composition) were analysed independently from topology and roughness. It was concluded that composition (esp. TiO2 % content) is a more important factor than wettability and oxide layer thickness, and that although a negatively-charged surface (represented by the surface ζ potential) was preferential for cell bioactivity given its protein-adsorption readiness, its magnitude was not a defining cause

Supplementary information files for Physico-chemical characterisation of Ti-Nb-Sn alloys surfaces and their osteogenic properties

Supplementary information files for Physico-chemical characterisation of Ti-Nb-Sn alloys surfaces and their osteogenic propertiesmplanted tissue engineering devices interact with the host tissue through their surface in the first instance. Surface chemistry triggers cell activities that stimulate bone tissue-formation mechanisms for osteoblast maturation. In this work, the bioactivity of binary Ti-40Nb and Ti-10Sn and ternary Ti-10Nb-5Sn alloys, candidates for bioengineering applications, has been studied on their surface with a view to establish their osteogenic potential compared to that of c.p. Ti. Cellular population growth was used to assess proliferative and differentiative phenotypes (via protein and Alkaline Phosphatase markers), coupled with gene expression (i.e. Runx2 and OCN) to confirm maturation. The results show that Sn-containing alloys support cell bioactivity, increase metabolic activity (i.e. metabolites content) that indicate their preferred glycolytic pathway, promote cell attachment, differentiation and osteoblast maturation. Ti-40Nb, although also non-cytotoxic, retards osteoblastic differentiation and maturation. To elucidate the features that underpin this difference, their physical (i.e. wettability, electrical state near the surface) and chemical properties (i.e. oxide layer thickness and composition) were analysed independently from topology and roughness. It was concluded that composition (esp. TiO2 % content) is a more important factor than wettability and oxide layer thickness, and that although a negatively-charged surface (represented by the surface ζ potential) was preferential for cell bioactivity given its protein-adsorption readiness, its magnitude was not a defining cause.<br

Hybrid-hybrid machining of SiC-reinforced aluminium metal matrix composite

A hybrid-hybrid (ultrasonic-assisted + laser-assisted) turning study of silicon carbide reinforced aluminium metal matrix composite is presented. The results show a significant reduction of average cutting force with an improved surface finish of machined components compared to conventional machining, implying that this new and novel paradigm is a viable machining process.</p