Ultrauniform, strong, and ductile 3D-printed titanium alloy through bifunctional alloy design.

Coarse columnar grains and heterogeneously distributed phases commonly form in metallic alloys produced by three-dimensional (3D) printing and are often considered undesirable because they can impart nonuniform and inferior mechanical properties. We demonstrate a design strategy to unlock consistent and enhanced properties directly from 3D printing. Using Ti-5Al-5Mo-5V-3Cr as a model alloy, we show that adding molybdenum (Mo) nanoparticles promotes grain refinement during solidification and suppresses the formation of phase heterogeneities during solid-state thermal cycling. The microstructural change because of the bifunctional additive results in uniform mechanical properties and simultaneous enhancement of both strength and ductility. We demonstrate how this alloy can be modified by a single component to address unfavorable microstructures, providing a pathway to achieve desirable mechanical characteristics directly from 3D printing.

Fabrication and Properties of Biodegradable Akermanite-Reinforced Fe35Mn Alloys for Temporary Orthopedic Implant Applications.

As a representative of the biodegradable iron (Fe)-manganese (Mn) alloys, Fe35Mn has been investigated as a promising biodegradable metal biomaterial for orthopedic applications. However, its slow degradation rate, though better than pure Fe, and poor bioactivity are concerns that retard its clinical applications. Akermanite (Ca2MgSi2O7, Ake) is a silicate-based bioceramic, showing desirable degradability and bioactivity for bone repair. In the present work, Fe35Mn/Ake composites were prepared via a powder metallurgy route. The effect of different contents of Ake (0, 10, 30, 50 vol %) on the microstructure, mechanical properties, degradation, and biocompatibility of the composites was investigated. The ceramic phases were found to be evenly distributed in the metal matrix. The Ake reacted with Fe35Mn and generated CaFeSiO4 during sintering. The addition of Ake increased the relative density of pure Fe35Mn from ∼90 to ∼94-97%. The compressive yield strength (CYS) and elastic modulus (Ec) increased with increasing Ake, with Fe35Mn/50Ake exhibiting the highest CYS of ∼403 MPa and Ec of ∼18 GPa. However, the ductility decreased at higher Ake concentrations (30 and 50%). Microhardness also showed an increasing trend with the addition of Ake. Electrochemical measurements indicated that higher concentrations of Ake (30 and 50%) could potentially increase the corrosion rate of Fe35Mn from ∼0.25 to ∼0.39 mm/year. However, all of the compositions tested did not show measurable weight loss after immersion in simulated body fluid (SBF) for 4 weeks, attributed to the use of prealloyed raw material, high sintered density of the fabricated composites, and the formation of a dense Ca-, P-, and O-rich layer on the surface. Human osteoblasts on Fe35Mn/Ake composites showed increasing viability with increasing Ake content, indicating improved in vitro biocompatibility. These preliminary results suggest that Fe35Mn/Ake can be a potential material for biodegradable bone implant applications, particularly Fe35Mn/30Ake, if the slow corrosion of the composite can be addressed.

Diamond-like carbon films prepared by a low temperature periodic process for application in ventricular assist devices.

Due to the poor tribological properties of titanium (Ti) and its alloy Ti6Al4V (commonly used for ventricular assist devices manufacturing), diamond-like carbon (DLC) films with excellent anti-wear properties are pursued to improve the wear resistance of Ti and its alloys. Considering the effect of temperature on magnets inside pump impellers and workpiece deformation, DLC films are preferred to be prepared under low temperature. In this study, DLC films were prepared on Ti6Al4V alloys by periodic and continuous processes, and the corresponding maximum deposition temperature was 85 and 154°C, respectively. The periodic DLC films exhibited the feature of columnar structure, and the surface hillocks were less uniform than that of continuous DLC films. The periodic DLC films possessed more sp3 -bonded structures, and the accessorial sp3 -bonding mainly existed in the form of CH. Compared to continuous DLC films, the periodic DLC films had lower residual stress and better adhesion with Ti6Al4V substrates. Both DLC films could effectively reduce the friction coefficient and wear rate of Ti6Al4V alloys both in air and fetal bovine serum (FBS), and the periodic DLC films exhibited superior anti-wear properties to that of continuous DLC films in FBS. Haemocompatibility evaluation revealed that both DLC films presented similar levels of more human platelet adhesion and activation as compared with that of bare Ti6Al4V. However, both DLC films significantly prolonged plasma clotting time in comparison to bare Ti6Al4V. This study demonstrates the potential of low-temperature DLC films as wear-resistant surface modification for VADs.

Design, mechanical and degradation requirements of biodegradable metal mesh for pelvic floor reconstruction.

Pelvic organ prolapse is the herniation of surrounding tissue and organs into the vagina and/or rectum and is a result of the weakening of pelvic floor muscles, connective tissue, and fascia. It is widely accepted that 50% of women will develop prolapse, with the prevalence increasing with age, and up to 10-20% of those seek evaluation for their condition. Suture repairs of pelvic floor defects are associated with a high failure rate, and permanent meshes were introduced to reduce the recurrence rate. The meshes were successful in reducing the rate of recurrence but were also associated with a higher rate of complications (pain or erosion into surrounding organs) and as such have been banned in many countries. New materials that are able to provide tissue support without complications are urgently required. A promising new material may be a biodegradable metal, which provides support during healing and subsequently completely degrades. We summarise pelvic mesh usage, and evaluate the use of a biodegradable metal, which has advantages of biocompatibility, antibacterial properties, and mechanical properties. The remaining challenges are discussed as follows: (1) degradation rate, (2) stiffness, (3) corrosion fatigue, (4) zinc aging, and (5) MRI artifacts.

Surface Modification of Biomedical Ti and Ti Alloys: A Review on Current Advances.

Ti is widely used as a material for orthopedic implants. As rapid and effective osseointegration is a key factor for the successful application of implants, biologically inert Ti materials start to show inherent limitations, such as poor surface cell adhesion, bioactivity, and bone-growth-inducing capabilities. Surface modification can be an efficient and effective approach to addressing the biocompatibility, mechanical, and functionality issues of the various Ti implant materials. In this study, we have overviewed more than 140 papers to summarize the recent progress in the surface modification of Ti implants by physical and/or chemical modification approaches, aiming at optimizing their wear resistance, biocompatibility, and antimicrobial properties. As an advanced manufacturing technology for Ti and Ti alloys, additive manufacturing was particularly addressed in this review. We also provide an outlook for future research directions in this field as a contribution to the development of advanced Ti implants for biomedical applications.

In vivo performance of a rare earth free Mg-Zn-Ca alloy manufactured using twin roll casting for potential applications in the cranial and maxillofacial fixation devices.

A magnesium alloy containing essential, non-toxic, biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process (TRC). Microstructure, mechanical properties, in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth (RE) element containing WE43 alloy. TRC Mg-0.5 wt% Zn- 0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150 µm. Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%. The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51 ± 0.07 mm/y similar to that of the WE43 alloy (0.47 ± 0.09 mm/y) in the rat model after 1 week of implantation. By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant. The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation. The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

Surface Coatings for Rotary Ventricular Assist Devices: A Systematic Review.

Rotary ventricular assist devices (VADs) are frequently used to provide mechanical circulatory support to patients suffering from end-stage heart failure. Therefore, these devices and especially their pump impeller and housing components have stringent requirements on wear resistance and hemocompatibility. Various surface coatings have been investigated to improve the wear resistance or hemocompatibility of these devices. The aim of the present systematic review was to build a comprehensive understanding of these coatings and provide potential future research directions. A Boolean search for peer-reviewed studies was conducted in online databases (Web of Science, Scopus, PubMed, and ScienceDirect), and a preferred reporting items for systematic reviews and meta-analyses (PRISMA) process was followed for selecting relevant papers for analysis. A total of 45 of 527 publications were included for analysis. Eighteen coatings were reported to improve wear resistance or hemocompatibility of rotary VADs with the most common coatings being diamond-like carbon (DLC), 2-methacryloyloxyethyl phosphorylcholine (MPC), and heparin. Ninety-three percent of studies focused on hemocompatibility, whereas only 4% of studies focused on wear properties. Thirteen percent of studies investigated durability. This review provides readers with a systematic catalogue and critical review of surface coatings for rotary VADs. The review has identified that more comprehensive studies especially investigations on wear properties and durability are needed in future work.

Anti-thrombogenic Surface Coatings for Extracorporeal Membrane Oxygenation: A Narrative Review.

Extracorporeal membrane oxygenation (ECMO) is used in critical care to manage patients with severe respiratory and cardiac failure. ECMO brings blood from a critically ill patient into contact with a non-endothelialized circuit which can cause clotting and bleeding simultaneously in this population. Continuous systemic anticoagulation is needed during ECMO. The membrane oxygenator, which is a critical component of the extracorporeal circuit, is prone to significant thrombus formation due to its large surface area and areas of low, turbulent, and stagnant flow. Various surface coatings, including but not limited to heparin, albumin, poly(ethylene glycol), phosphorylcholine, and poly(2-methoxyethyl acrylate), have been developed to reduce thrombus formation during ECMO. The present work provides an up-to-date overview of anti-thrombogenic surface coatings for ECMO, including both commercial coatings and those under development. The focus is placed on the coatings being developed for oxygenators. Overall, zwitterionic polymer coatings, nitric oxide (NO)-releasing coatings, and lubricant-infused coatings have attracted more attention than other coatings and showed some improvement in in vitro and in vivo anti-thrombogenic effects. However, most studies lacked standard hemocompatibility assessment and comparison studies with current clinically used coatings, either heparin coatings or nonheparin coatings. Moreover, this review identifies that further investigation on the thrombo-resistance, stability and durability of coatings under rated flow conditions and the effects of coatings on the function of oxygenators (pressure drop and gas transfer) are needed. Therefore, extensive further development is required before these new coatings can be used in the clinic.

TiB Nanowhisker Reinforced Titanium Matrix Composite with Improved Hardness for Biomedical Applications.

Titanium and its alloys have been employed in the biomedical industry as implants and show promise for more broad applications because of their excellent mechanical properties and low density. However, high cost, poor wear properties, low hardness and associated side effects caused by leaching of alloy elements in some titanium alloys has been the bottleneck to their wide application. TiB reinforcement has shown promise as both a surface coating for Ti implants and also as a composite reinforcement phase. In this study, a low-cost TiB-reinforced alpha titanium matrix composite (TMC) is developed. The composite microstructure includes ultrahigh aspect ratio TiB nanowhiskers with a length up to 23 µm and aspect ratio of 400 and a low average Ti grain size. TiB nanowhiskers are formed in situ by the reaction between Ti and BN nanopowder. The TMC exhibited hardness of above 10.4 GPa, elastic modulus above 165 GPa and hardness to Young's modulus ratio of 0.062 representing 304%, 170% and 180% increases in hardness, modulus and hardness to modulus ratio, respectively, when compared to commercially pure titanium. The TiB nanowhisker-reinforced TMC has good biocompatibility and shows excellent mechanical properties for biomedical implant applications.

Sintering and biocompatibility of blended elemental Ti-xNb alloys.

Titanium-niobium (Ti-Nb) alloys have great potential for biomedical applications due to their superior biocompatibility and mechanical properties that match closely to human bone. Powder metallurgy is an ideal technology for efficient manufacture of titanium alloys to generate net-shape, intricately featured and porous components. This work reports on the effects of Nb concentrations on sintered Ti-xNb alloys with the aim to establish an optimal composition in respect to mechanical and biological performances. Ti-xNb alloys with 33, 40, 56 and 66 wt% Nb were fabricated from elemental powders and the sintering response, mechanical properties, microstructures and biocompatibility assessed and compared to conventional commercial purity titanium (CPTi). The sintered densities for all Ti-xNb compositions were around 95%, reducing slightly with increasing Nb due to increasing open porosity. Higher Nb levels retarded sintering leading to more inhomogeneous phase and pore distributions. The compressive strength decreased with increasing Nb, while all Ti-xNb alloys displayed higher strengths than CPTi except the Ti-66Nb alloy. The Young's moduli of the Ti-xNb alloys with ≥40 wt% Nb were substantially lower (30-50%) than CPTi. In-vitro cell culture testing revealed excellent biocompatibility for all Ti-xNb alloys comparable or better than tissue culture plate and CPTi controls, with the Ti-40Nb alloy exhibiting superior cell-material interactions. In view of its mechanical and biological performance, the Ti-40Nb composition is most promising for hard tissue engineering applications.

Effect of Fe addition on properties of Ti-6Al-xFe manufactured by blended elemental process.

The mechanical properties of titanium alloys produced by powder metallurgy (PM) are dependent on the amount of porosity within the fabricated component. The space between powder particles and the behaviour of alloying elements during sintering contribute to the formation of pores. Iron (Fe) is well known to be a cost-effective alloying element for titanium alloys which acts to stabilise the ß-phase. This study aims to investigate the effects of Fe addition on the sintering response of titanium alloys containing aluminium. Ti-6Al-xFe(x = 1, 3, and 5 wt %) alloy systems were manufactured by press and sinter PM from blended-elemental powders. The density, mechanical properties, microstructures and pore distribution in the sintered parts were evaluated. The compressive strength of the alloys was positively correlated to the levels of Fe. Grain boundary and solid solution strengthening accounted for the strength improvements. Furthermore, Ti-6Al-3Fe exhibited the highest strength/modulus ratio. Evaluation of the pore distributions revealed that the number of fine pores was reduced significantly as the amount of Fe was increased, though concomitantly the number of larger pores increased. It is argued that the increasing number of larger pores with higher levels of Fe is due to coalescence of fine Kirkendall porosity during the latter stages of sintering. With excessive iron additions, large pores counteract any beneficial impacts on the sintering response. It is suggested to limit the amount of Fe additions to around 3 wt% to reduce adverse effects from large pores and to maximise the strength/modulus ratio.

Absorbable Mg surgical tack: Proof of concept &in situ fixation strength.

A prototype magnesium (Mg) surgical tack is tested comparatively against commercially available tacks made of titanium (ProTacktm, Medtronic) and PLGA (AbsorbaTacktm, Medtronic). The pull-out force is measured in situ in a lap-shear pull-out test, using porcine abdominal muscle tissue as a model. The Mg tack had a pull-out force comparable to those of the commercially available tacks. The majority of the Mg tacks also had a more ductile failure mode (i.e. the tacks deformed prior to failure), compared to the commercial tacks which pulled directly from the tissue with no deformation. The Mg tacks deformed as they were removed from the tissue, causing less damage to the tissue in the process. This is the first reported use of a Mg alloy in this application, and the proof of concept indicates that this is an area that deserves further interest and study.

Flexible Thermoelectric Materials and Generators: Challenges and Innovations.

The urgent need for ecofriendly, stable, long-lifetime power sources is driving the booming market for miniaturized and integrated electronics, including wearable and medical implantable devices. Flexible thermoelectric materials and devices are receiving increasing attention, due to their capability to convert heat into electricity directly by conformably attaching them onto heat sources. Polymer-based flexible thermoelectric materials are particularly fascinating because of their intrinsic flexibility, affordability, and low toxicity. There are other promising alternatives including inorganic-based flexible thermoelectrics that have high energy-conversion efficiency, large power output, and stability at relatively high temperature. Herein, the state-of-the-art in the development of flexible thermoelectric materials and devices is summarized, including exploring the fundamentals behind the performance of flexible thermoelectric materials and devices by relating materials chemistry and physics to properties. By taking insights from carrier and phonon transport, the limitations of high-performance flexible thermoelectric materials and the underlying mechanisms associated with each optimization strategy are highlighted. Finally, the remaining challenges in flexible thermoelectric materials are discussed in conclusion, and suggestions and a framework to guide future development are provided, which may pave the way for a bright future for flexible thermoelectric devices in the energy market.

Evaluation of the mechanical compatibility of additively manufactured porous Ti-25Ta alloy for load-bearing implant applications.

Integrating porous networks in load-bearing implants is essential in order to improve mechanical compatibility with the host tissue. Additive manufacturing has enabled the optimisation of the mechanical properties of metallic biomaterials, notably with the use of novel periodic regular geometries as porous structures. In this work, we successfully produced solid and lattice structures made of Ti-25Ta alloy with selective laser melting (SLM) using a Schwartz primitive unit-cell for the first time. The manufacturability and repeatability of the process was assessed through macrostructural and microstructural observations along with compressive testing. The mechanical properties are found to be suitable for bone replacement applications, showing significantly reduced elastic moduli, ranging from 14 to 36 GPa depending on the level of porosity. Compared to the conventionally used biomedical Ti-6Al-4V alloy, the Ti-Ta alloy offers superior mechanical compatibility for the targeted applications with lower elastic modulus, similar strength and higher ductility, making the Ti-25Ta alloy a promising candidate for a new generation of load-bearing implants.

Exploring the Role of Manganese on the Microstructure, Mechanical Properties, Biodegradability, and Biocompatibility of Porous Iron-Based Scaffolds.

In this work, the role that manganese plays in determining the structure and performance of sintered biodegradable porous Fe-Mn alloys is described. Powder metallurgy processing was employed to produce a series of biodegradable porous Fe-xMn (x = 20, 30, and 35 wt %) alloys suitable for bone scaffold applications. Increasing manganese content increased the porosity volume in the sintered alloys and influenced the ensuing properties of the metal. The Fe-35Mn alloy possessed optimum properties for orthopedic application. X-ray diffraction analysis and magnetic characterization confirmed the predominance of the antiferromagnetic austenitic phase and ensured the magnetic resonance imaging (MRI) compatibility of this alloy. The porous Fe-35Mn alloy possessed mechanical properties (tensile strength of 144 MPa, elastic modulus of 53.3 GPa) comparable to human cortical bone. The alloy exhibited high degradation rates (0.306 mm year-1) in simulated physiological fluid, likely due to its considerable Mn content and the high surface area inherent to its porous structures, while cytotoxicity and morphometry tests using mammalian preosteoblast cells (MC3T3-E1) indicated good cell viability in the Fe-35Mn alloy.

Comparison of the Microstructure and Biocorrosion Properties of Additively Manufactured and Conventionally Fabricated near ß Ti-25Nb-3Zr-3Mo-2Sn Alloy.

The microstructure and biodegradability of a near ß Ti-25Nb-3Zr-3Mo-2Sn alloy produced by laser engineered net shaping have been compared to those of alloys produced via casting and cold rolling in order to identify the key effects of processing pathways on the development of microstructure and biocorrosion properties. Results confirm the significant influence of processing technique on microstructure and concomitant biocompatibility of the alloy. Tests using mesenchymal stem cells confirm the ability of the additively manufactured alloy to support cell adhesion and spreading.

Dual Ag/ZnO-Decorated Micro-/Nanoporous Sulfonated Polyetheretherketone with Superior Antibacterial Capability and Biocompatibility via Layer-by-Layer Self-Assembly Strategy.

Polyetheretherketone is attractive for dental and orthopedic applications due to its mechanical attributes close to that of human bone; however, the lack of antibacterial capability and bioactivity of polyetheretherketone has substantially impeded its clinical applications. Here, a dual therapy implant coating is developed on the 3D micro-/nanoporous sulfonated polyetheretherketone via layer-by-layer self-assembly of Ag ions and Zn ions. Material characterization studies have indicated that nanoparticles consisting of elemental Ag and ZnO are uniformly incorporated on the porous sulfonated polyetheretherketone surface. The antibacterial assays demonstrate that Ag-decorated sulfonated polyetheretherketone and Ag/ZnO-codecorated sulfonated polyetheretherketone effectively inhibit the reproduction of Gram-negative and Gram-positive bacteria. Owing to the coordination of micro-/nanoscale topological cues and Zn induction, the Ag/ZnO-codecorated sulfonated polyetheretherketone substrates are found to enhance biocompatibility (cell viability, spreading, and proliferation), and hasten osteodifferentiation and -maturation (alkaline phosphate activity (ALP) production, and osteogenesis-related genetic expression), compared with the Ag-decorated sulfonated polyetheretherketone and the ZnO-decorated sulfonated polyetheretherketone counterparts. The dual therapy Ag/ZnO-codecorated sulfonated polyetheretherketone has an appealing bacteriostatic performance and osteogenic differentiation potential, showing great potential for dental and orthopedic implants.

Realizing zT of 2.3 in Ge1-x-y Sbx Iny Te via Reducing the Phase-Transition Temperature and Introducing Resonant Energy Doping.

GeTe with rhombohedral-to-cubic phase transition is a promising lead-free thermoelectric candidate. Herein, theoretical studies reveal that cubic GeTe has superior thermoelectric behavior, which is linked to (1) the two valence bands to enhance the electronic transport coefficients and (2) stronger enharmonic phonon-phonon interactions to ensure a lower intrinsic thermal conductivity. Experimentally, based on Ge1-x Sbx Te with optimized carrier concentration, a record-high figure-of-merit of 2.3 is achieved via further doping with In, which induces the distortion of the density of states near the Fermi level. Moreover, Sb and In codoping reduces the phase-transition temperature to extend the better thermoelectric behavior of cubic GeTe to low temperature. Additionally, electronic microscopy characterization demonstrates grain boundaries, a high-density of stacking faults, and nanoscale precipitates, which together with the inevitable point defects result in a dramatically decreased thermal conductivity. The fundamental investigation and experimental demonstration provide an important direction for the development of high-performance Pb-free thermoelectric materials.

The influence of two common sterilization techniques on the corrosion of Mg and its alloys for biomedical applications.

This paper studied the influence of two common sterilization techniques, ethylene oxide (EO) and gamma irradiation (GI), on the corrosion rate of four Mg-based materials in CO2 -bicarbonate buffered Hanks' solution. The four materials were: high-purity (HP)-Mg, ZE41, ultra-high purity (XHP)-Mg, and XHP-ZX00. The corrosion rate was measured through mass loss (Pm ) and hydrogen evolution (PH ). Two-way analysis of variance (ANOVA) was conducted to assess the effect of the sterilization techniques on the corrosion rates across the four materials. The ANOVA analyzed the variables of (1) material, (2) sterilization condition (EO, GI, and an unsterilized control group), and (3) the interaction between these two independent variables. Neither sterilization technique (EO and GI) significantly influenced the corrosion rate as measured by Pm (p < 0.84) nor PH (p < 0.08). This result was consistent across the four materials tested, as there was no interaction between the test variables of material and sterilization condition for Pm (p < 0.49) or PH (p < 0.27). As neither EO nor GI influenced the corrosion rates, either of these techniques warrants consideration for use on Mg-based medical implants and devices. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1907-1917, 2018.

Granular Nanostructure: A Facile Biomimetic Strategy for the Design of Supertough Polymeric Materials with High Ductility and Strength.

The realization of high strength, large ductility, and great toughness for polymeric materials is a vital factor for practical applications in industry. Unfortunately, until now this remains a huge challenge due to the common opposing trends that exist when promoting improvements in these properties using materials design strategies. In the natural world, the cuticle of mussel byssus exhibits a breaking strain as high as 100%, which is revealed to arise from an architectural granular microphase-separated structure within the protein matrix. Herein, a facile biomimetic designed granular nanostructured polymer film is reported. Such biomimetic nanostructured polymer films show a world-record toughness of 122 (± 6.1) J g-1 as compared with other polyvinyl alcohol films, with a breaking strain as high as 205% and a high tensile strength of 91.2 MPa, which is much superior to those of most engineering plastics. This portfolio of outstanding properties can be attributed to the unique nanoscale granular phase-separated structure of this material. These biomimetic designed polymer films are expected to find promising applications in tissue engineering and biomaterials fields, such as artificial skin and tendon, which opens up an innovative methodology for the design of robust polymer materials for a range of innovative future applications.