Ni-free Ti-based Bulk Metallic Glasses Research Articles

Hierarchical Surface Pattern on Ni-Free Ti-Based Bulk Metallic Glass to Control Cell Interactions.

Ni-free Ti-based bulk metallic glasses (BMGs) are exciting materials for biomedical applications because of their outstanding biocompatibility and advantageous mechanical properties. The glassy nature of BMGs allows them to be shaped and patterned via thermoplastic forming (TPF). This work demonstrates the versatility of the TPF technique to create micro- and nano-patterns and hierarchical structures on Ti40Zr10Cu34Pd14Sn2 BMG. Particularly, a hierarchical structure fabricated by a two-step TPF process integrates 400nm hexagonal close-packed protrusions on 2.5µm square protuberances while preserving the advantageous mechanical properties from the as-cast material state. The correlations between thermal history, structure, and mechanical properties are explored. Regarding biocompatibility, Ti40Zr10Cu34Pd14Sn2 BMGs with four surface topographies (flat, micro-patterned, nano-patterned, and hierarchical-structured surfaces) are investigated using Saos-2 cell lines. Alamar Blue assay and live/dead analysis show that all tested surfaces have good cell proliferation and viability. Patterned surfaces are observed to promote the formation of longer filopodia on the edge of the cytoskeleton, leading to star-shaped and dendritic cell morphologies compared with the flat surface. In addition to potential implant applications, TPF-patterned Ti-BMGs enable a high level of order and design flexibility on the surface topography, expanding the available toolbox for studying cell behavior on rigid and ordered surfaces.

Surmounting the thermal processing limits: Patterning TiZrCuPdSn bulk metallic glass even with nanocrystallization

Ni-free Ti-based bulk metallic glasses (BMGs) are promising for biomedical applications, thanks to their excellent biocompatibility and high corrosion resistance. BMGs can be shaped and patterned by viscous flow deformation using thermoplastic net-shaping. This work presents a novel strategy for thermoplastic net-shaping of Ti40Zr10Cu34Pd14Sn2 BMG. Instead of operating for a short time slightly above the glass transition temperature to avoid crystallization, the proposed method accepts the formation of nanocrystals and makes use of the lower viscosity of the supercooled liquid when processing above the glass transition temperature. Following this approach, Ti40Zr10Cu34Pd14Sn2 BMG is deformed from a rod to a thin disk, and patterns scaling from 5 μm to 300 μm are successfully created on the Ti-BMG surfaces, demonstrating the potential to create complex features for functional materials. Furthermore, after the thermoplastic net-shaping treatment, the Vickers hardness increases by 6% while the corrosion and passivation current density decrease by an order of magnitude. This work reveals that the BMGs can still be deformed and patterned via the thermoplastic net-shaping technique if the first crystallization event of the BMG systems is the formation of nanocrystals. Most importantly, this work reveals the possibility of processing a broad family of mediocre glass-forming systems and semi-crystalline composites via thermoplastic net-shaping.

Formation and properties of biocompatible Ti-based bulk metallic glasses in the Ti–Cu–Zr–Fe–Sn–Si–Ag system

The Ni-free Ti-based bulk metallic glasses (BMGs) with high glass-forming ability (GFA) can be synthesized in the (Ti, Cu, Zr)92.5Fe2.5Sn2Si1Ag2 alloy system over a wide composition range by copper-mold casting. Especially, the Ti48Cu37Zr7.5Fe2.5Sn2Si1Ag2 glassy alloy can form the BMG rod with a diameter up to 6 mm and showed a high compressive strength of ~ 2.05 GPa, elastic modulus of ~ 100 GPa, and microhardness of ~ 571 Hv. The Ti-based BMGs presented good bio-corrosion resistance in a simulated physiological environment attributed to the formation of Ti-, Zr-, Si-, and Fe-enriched passive films. The biocompatibility of the Ti-based glassy alloys was systematically investigated by both indirect cytotoxicity test and direct cell-culture experiments. The Ti-based BMG extracts had no cytotoxic effects on the proliferation of the cells. The good cell adhesion, proliferation, differentiation, and mineralization of bone-forming MC3T3-E1 pre-osteoblasts on the BMGs were parallel to those on the Ti–6Al–4V alloy. These results manifested that the present Ti-based BMGs are promising candidates as biomaterials.

Development and characterization of titanium-based bulk metallic glasses

The amorphous structure of bulk metallic glasses results in outstanding properties, which are able to outshine the properties of common metallic biomaterials. In particular, Ti-based bulk metallic glasses are interesting candidates for the use as biomaterial or as structural material in lightweight applications. However, the usage of known Ti-based bulk metallic glasses with casting thicknesses of several millimeters is strongly limited due to the large content of rare, expensive and harmful elements. In this work, we design Ni-free Ti-based bulk metallic glasses with a low Cu-content, being suitable for the application as biomaterial. On the basis of the binary Ti-Ni system, novel glass forming alloys are developed by the addition of sulfur. In order to increase the glass forming ability and to reduce the Ni-content, Ti was substituted with Zr and Ni with Cu. Finally, it is possible to produce synchrotron X-ray amorphous samples with a diameter of 3 mm for the Ni-free alloy Ti40Zr35Cu17S8. Furthermore, it is shown that industrial grade raw materials can be used for the synthesis of amorphous samples of this alloy without diminishing the glass forming ability or the mechanical properties. Characterization by mechanical and electrochemical tests proves the superiority of the novel alloys over commercial amorphous and crystalline alloys. All in all, a new class of Ni-free Ti-based bulk metallic glasses with unprecedented properties is developed, being highly attractive for a widespread use.

Tribological behaviors of a Ni-free Ti-based bulk metallic glass in air and a simulated physiological environment

Ni-free Ti-based bulk metallic glasses (BMGs) with good mechanical properties, high corrosion resistance, and good biocompatibility are potential biomaterials. For the applications as load-bearing orthopedic implant materials, excellent wear resistance is required. In the present study, tribological behaviors of the Ni-free Ti47Cu38Zr7.5Fe2.5Sn2Si1Ag2 BMG in air and a phosphate buffer saline (PBS) solution were investigated and compared with Ti−6Al−4V and Co−28Cr−6Mo alloys. It was found that the wear resistance of the Ti-based BMG in air was superior to that of the Ti−6Al−4V alloy and paralleled with that of the Co−28Cr−6Mo alloy, mainly attributing to the high hardness of the Ti-based BMG. Under the dry-sliding condition, the predominant wear mechanism of the Ti-based BMG was characterized as the oxidation and abrasive wear. Under the PBS-solution condition, although the Ti-based BMG suffered from tribocorrosion that is controlled by the combined effects of abrasive and corrosive wear, the wear resistance of the Ti-based BMG was three times lower than that of the Ti−6Al−4V alloy and slightly inferior to that of the Co−28Cr−6Mo alloy. The effect of corrosion behavior on wear resistance of the Ti-based BMG in the PBS solution is discussed.

Biocompatibility study on Ni-free Ti-based and Zr-based bulk metallic glasses

Safety and reliability are crucial issues for medical instruments and implants. In the past few decays, bulk metallic glasses (BMGs) have drawn attentions due to their superior mechanical properties, good corrosion resistance, antibacterial and good biocompatibility. However, most Zr-based and Ti-based BMGs contain Ni as an important element which is prone to human allergy problem. In this study, the Ni-free Ti-based and Zr-based BMGs, Ti40Zr10Cu36Pd14, and Zr48Cu36Al8Ag8, were selected for systematical evaluation of their biocompatibility. Several biocompatibility tests, co-cultural with L929 murine fibroblast cell line, were carried out on these two BMGs, as well as the comparison samples of Ti6Al4V and pure Cu. The results in terms of cellular adhesion, cytotoxicity, and metallic ion release affection reveal that the Ti40Zr10Cu36Pd14 BMG and Ti6Al4V exhibit the optimum biocompatibility; cells still being attached on the petri dish with good adhesion and exhibiting the spindle shape after direct contact test. Furthermore, the Ti40Zr10Cu36Pd14 BMG showed very low Cu ion release level, in agreement with the MTT results. Based on the current findings, it is believed that Ni-free Ti-based BMG can act as an ideal candidate for medical implant.

Micro-patterning by thermoplastic forming of Ni-free Ti-based bulk metallic glasses

The development of bulk metallic glasses for biomedical applications has become the focus of intense research interest. In this work, we report on the unique thermoplastic behavior of two Ni-free Ti-based bulk metallic glasses by utilizing the dramatic softening of the amorphous structure in the super cooled liquid region. Ti40Zr10Cu34Pd14Ga2 and Ti40Zr10Cu34Pd14Sn2 bulk glassy alloys were produced by copper mold casting. Ga and Sn micro-alloying (2at%) improve the glass-forming ability and mechanical properties of Ti40Zr10Cu36Pd14 alloy effectively. The cast rods were thermo-mechanically characterized to determine the most suitable processing temperature and time, and the load that has to be applied for thermoplastic net-shaping of the BMGs into anisotropically etched cavities of silicon chips. Periodic features with high surface smoothness and uniform height (24μm high circular bumps with sub-μm roughness) were created on the surface of the BMGs. The surface patterning with controllable roughness of Ti-based BMGs can be useful in biomedical studies by mediating material - cell interactions.

Corrosion behaviour of porous Ni-free Ti-based bulk metallic glass produced by spark plasma sintering in Hanks' solution

Porous bulk metallic glasses (BMGs) are promising biomedical materials to be used for surgical implants. Here we report on successful formation of porous Ni-free Ti-based BMGs with a diameter exceeding 15 mm by spark plasma sintering the mixture of the gas-atomized Ti-based (Ti45Zr10Cu31Pd10Sn4) glassy alloy powder and solid salt powder, followed by leaching treatment into water to eliminate the salt phase. Corrosion behaviour of the produced porous Ti-based BMGs was investigated in Hanks' solution. The potentiodynamic polarization curves showed that the anodic current density in the porous Ti-based BMGs slowly increased during anodic polarization, suggesting the crevice corrosion.

Ni-free Ti-based bulk metallic glass with potential for biomedical applications produced by spark plasma sintering

We produced large size Ni-free Ti-based bulk metallic glasses (BMGs) by a spark plasma sintering (SPS) process using gas-atomized Ti45Zr10Cu31Pd10Sn4 glassy alloy powders. The effects of sintering temperature on densification, structure, mechanical properties and corrosion behavior in Hanks' solution of the sintered samples were investigated. The high strength sintered samples with high densification and no crystallization were obtained by the SPS process at a sintering temperature of 643 K with a loading pressure of 600 MPa. The BMGs produced by the SPS process can offer excellent properties and satisfying large sample-size requirements. The Ti-based BMGs without toxic elements open possibilities of application as biomedical materials.

Characterization of Surface Properties, Osteoblast Cell Culture in Vitro and Processing with Flow-Viscosity of Ni-Free Ti-Based Bulk Metallic Glass for Biomaterials

Ni-free type Ti-based metallic glass evaluated in this study has imposing performances for biomaterials that is based on high bulk forming ability (BFA) for implantable materials, superior specific strength, low Young's modulus as hard tissue replacements and excellent workability. Especially, surface characteristics of Ti-based bulk metallic glass for corrosion resistance exhibit a high potential for application to be used as dental implants in the oral cavity. We also made an examination of chemical stability for human cell test with osteoblasts (SaOS2) in vitro. Results of the good biocompatibility and high glass forming ability evaluated in this study are expected to increase utility value for biomedical application

Distinct plastic strain of Ni-free Ti–Zr–Cu–Pd–Nb bulk metallic glasses with potential for biomedical applications

(Ti 40Zr 10Cu 36Pd 14) 100− x Nb x ( x = 1, 3, 5 at.%) bulk metallic glasses containing nano-particles exhibited ultrahigh strength and distinct plastic strain. The yield strength exceeding 2050 MPa, Young's modulus of about 80 GPa and the plastic strain of over 6.5% were obtained for 1% and 3% Nb-added alloys due to the suppression of the propagation of shear bands by nano-particles in situ formed in the glassy matrix. The developed Ni-free Ti-based bulk metallic glasses with low Young's modulus and good mechanical properties are promising candidates for application as artificial dental root materials and other biomaterials.

Effects of Additional Elements on Structure, Mechanical Strength and Chemical Properties of Ni-Free Ti-Based Bulk Metallic Glasses for Biomaterials

We started investigation of new Ti-based bulk metallic glass (BMG) alloys with higher glass forming ability (GFA) for dental implants for medical market. These Ti-based BMG alloys do not contain Ni, Al and Be elements which are well known to be harmful for human body. In particular, cylindrical rod specimens of newly designed Ti-based BMG alloys with produced by copper mold casting exhibit compressive strength of above 1800 MPa. Ti-based BMG alloys also have high corrosion resistance that is passivated at the lower passive current densities of approximately 10-2Am-2 in 1 mass% lactic acid, 10-2~10-3Am-2 in PBS (-) at 310K which are lower than those of pure Titanium and Ti-6Al-4V alloy. These BMG alloys have high potentials to be applied as biomaterials in various forms, such as melt spun ribbons and cylindrical rods.

Synthetic relationship between titanium and alloying elements in designing Ni-free Ti-based bulk metallic glass alloys

Ni-free Ti-based bulk metallic glass (BMG) alloys were reported to have a high enough glass forming ability (GFA). In this study, the glass forming ability of Ti-based BMG alloys without Ni and Be additions is analyzed using Inoue’s empirical rules, bonding order (Bo), and molecular d-orbital energy values (Md). The developed Ti-based BMG alloys revealed a separable location on the Bo¯-Md¯ diagram which presents the direction for design of Ti-based BMG alloys with high GFA.

XPS study on the surface films of a newly designed Ni-free Ti-based bulk metallic glass

The electrochemical and corrosion behavior of a newly designed Ni-free Ti-based bulk metallic glass (BMG) was investigated. The Ti 45Zr 10Pd 10Cu 31Sn 4 BMG exhibits excellent corrosion resistance after immersion in 3 mass% NaCl, 1 N H 2SO 4 and 1 N H 2SO 4 + 0.01 N NaCl solutions. X-ray photoelectron spectroscopy measurements were used to analyze the changes of the elements on the alloy surface before and after immersion in various solutions. The formation of Ti- and Zr-enriched highly protective thin surface films is responsible for the high corrosion resistance of this alloy in corrosive solutions.