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.

In Vivo Evaluation of Bioabsorbable Fe-35Mn-1Ag: First Reports on In Vivo Hydrogen Gas Evolution in Fe-Based Implants.

This work investigates the influence of Ag (1 wt%) on the mechanical properties, in vitro and in vivo corrosion, and biocompatibility of Fe-35Mn. The microstructure of Fe-35Mn-1Ag possesses a uniform dispersion of discrete silver particles. Slight improvements in compressive properties are attributed to enhanced density and low porosity volume. Fe-35Mn-1Ag exhibits good in vitro and in vivo corrosion rate of Fe-35Mn due to an increase in microgalvanic corrosion. Gas pockets, which originate from an inflammatory response to the implants, are observed in the rats after 4 weeks implantation but are undetectable after 12 weeks. No chronic toxicity is observed with the Fe-35Mn-1Ag, suggesting acceptable in vivo biocompatibility. The high corrosion rate of the alloy triggers an increased level of nonadverse tissue inflammatory responses 4 weeks after implantation, which subsequently subsides at 12 weeks. The Fe-35Mn-1Ag displays properties that are suitable for orthopedic 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.

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.

A biocompatible thermoset polymer binder for Direct Ink Writing of porous titanium scaffolds for bone tissue engineering.

There is increasing demand for synthetic bone scaffolds for bone tissue engineering as they can counter issues such as potential harvesting morbidity and restrictions in donor sites which hamper autologous bone grafts and address the potential for disease transmission in the case of allografts. Due to their excellent biocompatibility, titanium scaffolds have great potential as bone graft substitutes as they mimic the structure and properties of human cancellous bone. Here we report on a new thermoset bio-polymer which can act as a binder for Direct Ink Writing (DIW) of titanium artificial bone scaffolds. We demonstrate the use of the binder to manufacture porous titanium scaffolds with evenly distributed and highly interconnected porosity ideal for orthopaedic applications. Due to their porous structure, the scaffolds exhibit an effective Young's modulus similar to human cortical bone, alleviating undesirable stress-shielding effects, and possess superior strength. The biocompatibility of the scaffolds was investigated in vitro by cell viability and proliferation assays using human bone-marrow-derived Mesenchymal stem cells (hMSCs). The hMSCs displayed well-spread morphologies, well-organized F-actin and large vinculin complexes confirming their excellent biocompatibility. The vinculin regions had significantly larger Focal Adhesion (FA) area and equivalent FA numbers compared to that of tissue culture plate controls, showing that the scaffolds support cell viability and promote attachment. In conclusion, we have demonstrated the excellent potential of the thermoset bio-polymer as a Direct Ink Writing ready binder for manufacture of porous titanium scaffolds for hard tissue engineering.

Porous Titanium Scaffolds Fabricated by Metal Injection Moulding for Biomedical Applications.

Biocompatible titanium scaffolds with up to 40% interconnected porosity were manufactured through the metal injection moulding process and the space holder technique. The mechanical properties of the manufactured scaffold showed a high level of compatibility with those of the cortical human bone. Sintering at 1250 °C produced scaffolds with 36% porosity and more than 90% interconnected pores, a compressive yield stress of 220 MPa and a Young's modulus of 7.80 GPa, all suitable for bone tissue engineering. Increasing the sintering temperature to 1300 °C increased the Young's modulus to 22.0 GPa due to reduced porosity, while reducing the sintering temperature to 1150 °C lowered the yield stress to 120 MPa, indicative of insufficient sintering. Electrochemical studies revealed that samples sintered at 1150 °C have a higher corrosion rate compared with those at a sintering temperature of 1250 °C. Overall, it was concluded that sintering at 1250 °C yielded the most desirable results.

Biocompatible porous titanium scaffolds produced using a novel space holder technique.

We describe a new fabrication strategy for production of porous titanium scaffolds for skeletal implants which provides a promising new approach to repair and remodel damaged bone tissue. The new strategy involves powder sintering of titanium powder, employing pharmaceutical sugar pellets as temporary space holders, to facilitate production of porous scaffolds with structures optimized for mechanical performance and osseointegration of implants. The spherical sugar pellets, with controlled size fractions and excellent biocompatibility, are easily removed by dissolution prior to sintering providing an ideal space holder material for controlled synthesis of titanium scaffolds with desired porosities and pore sizes. The scaffolds contain pores with high degrees of sphericity and interconnectivity which impart excellent mechanical properties and superior biocompatibility to the structures. Scaffolds with 40% porosity and a pore size range of 300-425 µm exhibited an effective Young's modulus of 16.4 ± 3.5 GPa and strength of 176 ± 6 MPa, which closely mimics the properties of human bone, and were also able to support cell adhesion, viability and spreading in cell culture tests. Porous titanium scaffolds manufactured by this approach have excellent potential for hard tissue engineering applications. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2796-2806, 2018.

Mechanical properties and biocompatibility of porous titanium scaffolds for bone tissue engineering.

Synthetic scaffolds are a highly promising new approach to replace both autografts and allografts to repair and remodel damaged bone tissue. Biocompatible porous titanium scaffold was manufactured through a powder metallurgy approach. Magnesium powder was used as space holder material which was compacted with titanium powder and removed during sintering. Evaluation of the porosity and mechanical properties showed a high level of compatibility with human cortical bone. Interconnectivity between pores is higher than 95% for porosity as low as 30%. The elastic moduli are 44.2GPa, 24.7GPa and 15.4GPa for 30%, 40% and 50% porosity samples which match well to that of natural bone (4-30GPa). The yield strengths for 30% and 40% porosity samples of 221.7MPa and 117MPa are superior to that of human cortical bone (130-180MPa). In-vitro cell culture tests on the scaffold samples using Human Mesenchymal Stem Cells (hMSCs) demonstrated their biocompatibility and indicated osseointegration potential. The scaffolds allowed cells to adhere and spread both on the surface and inside the pore structures. With increasing levels of porosity/interconnectivity, improved cell proliferation is obtained within the pores. It is concluded that samples with 30% porosity exhibit the best biocompatibility. The results suggest that porous titanium scaffolds generated using this manufacturing route have excellent potential for hard tissue engineering applications.

Manufacturing of graded titanium scaffolds using a novel space holder technique.

To optimize both the mechanical and biological properties of titanium for biomedical implants, a highly flexible powder metallurgy approach is proposed to generate porous scaffolds with graded porosities and pore sizes. Sugar pellets acting as space holders were compacted with titanium powder and then removed by dissolution in water before sintering. The morphology, pore structure, porosity and pore interconnectivity were observed by optical microscopy and SEM. The results show that the porous titanium has porosity levels and pore size gradients consistent with their design with gradual and smooth transitions at the interfaces between regions of differing porosities and/or pore sizes. Meanwhile, the porous titanium has high interconnectivity between pores and highly spherical pore shapes. In this article we show that this powder metallurgy processing technique, employing the novel sugar pellets as space-holders, can generate porous titanium foams with well-controlled graded porosities and pore sizes. This method has excellent potential for producing porous titanium structures for hard tissue engineering applications.