Characterization of Ti-HA composite fabricated by mechanical alloying

Synthesis and characterization of TiNbZrMo medium-entropy bio-composites: Microstructure, mechanical properties, and in vitro degradation

This study reports the synthesis and characterization of hydroxyapatite (HA)-based bio-composites reinforced with varying amounts (by weight, 1-15 wt.%) of bio-medium entropy alloy (BioMEA) for load-bearing implant applications. BioMEA powders consisting of Ti, Nb, Zr, and Mo were mechanically alloyed for 100 h and subsequently added to HA using powder metallurgy techniques. To show the effect of BioMEA, the microstructure, density, and mechanical tests have been conducted and the synthesized BioMEA was characterized by scanning electron microscope (SEM), x-ray diffractometer (XRD), and Fourier-transform infrared spectroscopy (FTIR) analysis. In addition, in vitro degradation behavior and bioactivity analyses of bio-composites have been conducted. XRD analysis revealed the formation of BioMEA after 20 h of mechanical alloying. The highest density value of 2.47 g/cm3 was found in 15 wt.% BioMEA-reinforced bio-composite. The addition of BioMEA reinforcement led to a significant increase in hardness and tensile strength values, with the highest values observed at 15 wt.% reinforcement. Compression tests demonstrated a significant increase in compressive strength and deformation capability of the bio-composites with the highest values observed at 15 wt.% BioMEA addition. The highest toughness of 7.68 kJ/m2 was measured in 10 wt.% MEA-reinforced bio-composites. The produced bio-composite materials have an elastic modulus between 3.5-5.5 GPa, which may provide a solution to the stress shielding problems caused by the high elastic modulus of metallic implant materials. The most severe degradation occurred in 15 wt.% MEA-reinforced bio-composites, and the effect of degradation caused a decrease in Ca and an increase in Ti-Ni-Zr-Mo in all bio-composites. These findings suggest that HA/BioMEA bio-composites have the potential to be developed as advanced biomaterials with moderate mechanical and biological properties for load-bearing implant applications.

Effect of HA Content on Microstructure and Properties of Ti-27Nb-17Ta-8Zr/HA Composite

In this paper, Ti-27Nb-17Ta-8Zr/HA series composite materials were prepared by spark plasma sintering (SPS) technology. The medical titanium alloy (Ti-27Nb-17Ta-8Zr) with good mechanical properties, wear resistance, and corrosion resistance was combined with the hydroxyapatite (HA) bioactive ceramic with high biological activity and bone-binding ability. Moreover, the density, microstructure evolution, metal/ceramic reaction, mechanical behavior, in vitro bioactivity, and influencing mechanisms of composite materials with different HA contents were studied. The research results indicate that all biological composite materials are composed of β-Ti solution, α-Ti, and ceramic phases (T_i2O, CaTiO₃, CaO, Ti_xP_y). With the increase of HA content, the compressive strength and yield strength of the composite material show a trend of first increasing, then decreasing, and then slowly increasing. After soaking in SBF artificial simulated body fluid for 5 days, the deposition of elements such as Ca and P on the surface significantly increased, while elements such as Ti, Nb, Ta, and Zr were evenly distributed in the matrix, demonstrating good in vitro mineralization ability and facilitating the attachment and growth of osteoblasts.

Micro-hydroxyapatite reinforced Ti-based composite with tailored characteristics to minimize stress-shielding impact in bio-implant applications

Biomaterials having higher strength and increased bioactivity are widely researched topics in the area of scaffold and implant fabrication. Metal-based biomaterials are favorably suitable for load-bearing implants due to their outstanding mechanical and structural properties. The issue with pure metallic material used for bio-implant is the mismatch between the mechanical properties of the human body parts and the implant. The mismatch in modulus and hardness values causes damage to muscles and other body parts due to the phenomena of 'stress-shielding'. As per the rule of mixture, combining a biocompatible ceramic with metals will not only lower the overall mechanical strength, but will also enhance the composite's bioactivity. In the present work, a Metal-Ceramic composite of Ti and μ-HAp is processed through high-energy mechanical alloying. The μ-HAp powders (in a weight fraction of 1%, 2%, and 3%) were alloyed with Pure Ti powder sintered using microwave hybrid heating (MHH). The homogeneously alloyed materials were inspected for chemical and elemental characteristics using XRD, SEM-EDX, and FTIR analyses. Nano-mechanical and micro-hardness properties were inspected for the fabricated Ti- μ-HAp composites and it shows a decreasing trend. Elastic modulus declined from 130.8 GPa to 50.11 GPa for 3 wt% μ-HAp compared to pure-Ti sample. The mechanical behaviour of developed composites confirms that it can minimize the stress-shielding impact due to comparatively lesser strength and hardness than pure metallic samples.

The correlation between osseointegration and bonding strength at the bone-implant interface: In-vivo & ex-vivo investigations on hydroxyapatite and hydroxyapatite/titanium coatings

This study investigated the effects of hydroxyapatite (HA) and hydroxyapatite/titanium (HA/Ti) coatings on osseointegration and bonding strength at the bone-implant interface. The coatings were made using air plasma spray (APS), and three study groups were examined: 1) Uncoated commercial pure titanium (CP-Ti) rods; 2) HA-coated CP-Ti rods, and 3) Composite of 50 %wt HA + 50 %wt Ti coated CP-Ti rods. The rods were implanted into the distal femurs and proximal tibias of fifteen New Zealand white rabbits, and 8 weeks after the implantation, the samples were harvested. The results of pull-out tests showed that the ultimate strength of HA and HA/Ti coatings were significantly greater than the uncoated samples (P < 0.05). Moreover, even though the histological evaluations showed significantly greater osseointegration of HA/Ti composite coatings compared with HA coatings (P < 0.05), nonetheless, the composite of HA/Ti offers no significant increase in the ultimate strength, stiffness, and bonding strength at the bone-implant interface, compared with the HA group (P > 0.05). Thus, in an eight-week study, there was no linear correlation between the osseointegration and the bonding strength at the bone-implant interface. The results of this work may imply that the extent of osseointegration at the bone-implant interface does not necessarily determine the value of the bonding strength at the bone-implant interface. It is speculated that, in a longer-term study, a greater quality of bone formation may occur during osseointegration, between the implant and its adjacent bone, which can lead to a more enhanced bonding strength, compared with the 8-weeks post-surgery follow up.

Physicochemical Characterization and Antibacterial Activity of Titanium/Shellac-Coated Hydroxyapatite Composites

Titanium and hydroxyapatite are widely used as materials for implants. Titanium has good mechanical properties, good corrosion resistance, and a high modulus of elasticity. Hydroxyapatite has good biocompatibility, bioactivity, and significant osteoinductivity. In this study, powder metallurgy was used as a method to combine titanium and hydroxyapatite for use in implants. Shellac was used as a binder between ceramic and metal due to its lower melting point. The surface morphology and chemical properties were evaluated by scanning electron microscopy–energy dispersive X-ray (SEM-EDX), whereby the SEM revealed the appearance of micropores in the Ti-HA composites during the sintering process, and the EDX showed that the final product had high amounts of Ti and Ca and low P. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses were used to achieve the chemical characterization of composites, whereby a weak diffraction peak was observed in the XRD spectrum of Ti-HA composites, and the FTIR analysis confirmed that the composites had carbonate (CO3)2−, phosphate (PO4)3−, and hydroxyl (OH)− groups. Oxygen was sufficient due to the sintering process being conducted in an air environment. The antibacterial activities were characterized using the disc diffusion method with Escherichia coli and Staphylococcus aureus bacteria, whereby the prepared Ti-HA composites had a greater antibacterial effect on E. coli than on S. aureus. Finally, pH changes were observed during the 24 h incubation. The result showed that the Ti-HA composite did not contain chemical compounds that could cause harmful effects for humans and had good antibacterial activity against E. coli.

Microstructure and Mechanical Properties of Titanium–Equine Bone Biocomposites

Microstructure and mechanical properties of Ti-6Al-4V/equine bone (EB) composites fabricated by ball milling and spark plasma sintering (SPS) have been investigated. Ti-6Al-4V/EB composites were successfully fabricated by a planetary ball-milling of spherical Ti6Al4V powder and natural EB powder and SPS at 1000 °C within 15 min under 50 MPa. EB was uniformly dispersed in the Ti6Al4V matrix owing to ball-milling, and beta phase transformation temperature of 1000 °C provided phase stability. The composites containing 0.5 wt.% EB exhibit Vickers hardness and elastic modulus of 540.6 HV and 130.5 GPa, respectively. The microstructures and mechanical properties of the composites were observed using scanning electron micrograph and nanoindentation.

Microstructure and Mechanical Properties of Nano-Carbon Reinforced Titanium Matrix/Hydroxyapatite Biocomposites Prepared by Spark Plasma Sintering

Nano-carbon reinforced titanium matrix/hydroxyapatite (HA) biocomposites were successfully prepared by spark plasma sintering (SPS). The microstructure, mechanical properties, biocompatibility, and the relationship between microstructure and properties of biocomposites were systematically investigated. Results showed there are some new phases in sintered composites, such as β-Ti, TiO₃, ZrO₂, etc. Moreover, a small amount of Ti₁₇P₁₀, CaTiO₃, Ca₃(PO₄)₂ were also detected. The reaction that may occur during the preparation process is suppressed to some extent, which is because that the addition of second phases can prevent the direct contact of titanium with HA and reduce the contact areas. Transmission electron microscope (TEM) analysis proved the existence of elemental diffusion and chemical reactions in sintered composites. Compared with results of composites prepared by hot-pressed sintering before, mechanical properties (microhardness, compressive strength, and shear strength) of 0.5-GNFs composites prepared by SPS were increased by about 2.8, 4.8, and 4.1 times, respectively. The better mechanical properties of 0.5-GNFs composite in nano-carbon reinforced composites are mainly due to the lower degree of agglomeration of tubular carbon nanotubes (CNTs) compared to lamellar graphene nanoflakes (GNFs). Moreover, the strengthening and toughening mechanisms of nano-carbon reinforced titanium alloy/HA biocomposite prepared by spark plasma sintering (SPS) mainly included second phase strengthening, grain refinement strengthening, solution strengthening, graphene extraction, carbon nanotubes bridging, crack tail stripping, etc. In addition, in vitro bioactivity test revealed that the addition of nano-carbon was beneficial to promote the adhesion and proliferation of cells on the surface of titanium alloy/HA composite, because nano-carbon can enhance the formation of mineralized necks in the composites after transplantation, stimulate biomineralization and promote bone regeneration.

Research Progress Regarding Interfacial Characteristics and the Strengthening Mechanisms of Titanium Alloy/Hydroxyapatite Composites

Titanium alloy/Hydroxyapatite (HA) composites have become a hot research topic in biomedical materials, while there are some challenges concerning bioactivity and mechanical properties such as low interface adhesion at the interface between metal and ceramic, complex interfacial reactions, and so on. Nevertheless, composites with reinforced phases can reach special properties that meet the requirements of biomedical materials due to the strong interfacial interactions between reinforcing phases (nano-carbon, partial oxides, and so on) and Titanium alloys or HA. This review summarizes the interface properties and mechanisms of Titanium alloy/HA composites, including interfacial bonding methods, strengthening and toughening mechanisms, and performance evaluation. On this basis, the interface characteristics and mechanisms of the Titaniumalloy/HA composites with enhanced phase are prospected. The results show that the interfacial bonding methods in the Titanium alloy/HA composites include chemical reactions and mechanical effects. The strengthening and toughening mechanisms contain grain refinement strengthening, second phase strengthening, solution strengthening, cracks and pulling out mechanisms, etc. This review provides a guidline for the fabrication of biocomposites with both mechanical properties and bioactivity.

Microstructure and Mechanical Properties of Graphene-Reinforced Titanium Matrix/Nano-Hydroxyapatite Nanocomposites

Biomaterial composites made of titanium and hydroxyapatite (HA) powder are among the most important biomedicalmaterials due to their good mechanical properties and biocompatibility. In this work, graphene-reinforced titanium matrix/nano-hydroxyapatite nanocomposites were prepared by vacuum hot-pressing sintering. The microstructure and mechanical properties of graphene-reinforced titanium matrix/nano-hydroxyapatite nanocomposites with different graphene content were systematically investigated. Microstructures of the nanocomposites were examined by X-ray diffraction (XRD), back scattered electron imaging (BSE), scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS), electron probe microanalyzer (EPMA), and transmission electron microscope (TEM). The mechanical properties were determined from microhardness, shear strength, and compressive strength. Results showed that during the high-temperature sintering process, complex chemical reactions occurred, resulting in new phases of nucleation such as Ca₃(PO₄)₂, Ti_xP_y, and Ti₃O.The new phases, which easily dropped off under the action of external force, could hinder the densification of sintering and increase the brittleness of the nanocomposites. Results demonstrated that graphene had an impact on the microstructure and mechanical properties of the nanocomposites. Based on the mechanical properties and microstructure of the nanocomposites, the strengthening and fracture mechanisms of the graphene-reinforced titanium matrix/nano-hydroxyapatite nanocomposites with different graphene content were analyzed.

Powder metallurgical low-modulus Ti-Mg alloys for biomedical applications

In this work, powder metallurgical (PM) Ti-Mg alloys were prepared using combined techniques of mechanical alloying and spark plasma sintering. The alloys mainly consist of super saturations of Mg in Ti matrix, and some laminar structured Ti- and Mg-rich phases. The PM Ti-Mg alloys contain a homogeneous mixtures of nanocrystalline Mg and Ti phases. The novel microstructures result in unconventional mechanical and biological properties. It has been shown that the PM Ti-Mg alloys have a much lower compression modulus (36-50GPa) compared to other Ti alloys, but still remain a very high compressive strength (1500-1800MPa). In addition, the PM Ti-Mg alloys show good biocompatibility and bioactivity. Mg can dissolve in the simulated body fluids, and induce the formation of the calcium phosphate layer. The compression modulus of PM Ti-Mg alloys decreases with the amount of Mg, while the bioactivity increases. Although the corrosion resistance of Ti-Mg alloys decreases with the content of Mg, the alloys still show good stability in simulated body fluid under electrochemical conditions. The indirect and direct cytotoxicity results show that PM Ti-Mg alloys have a good biocompatibility to NIH-3T3 cells. Therefore, the PM Ti-Mg alloys are promising candidates in biomedical applications.