Tribological aspects of some biodegradable magnesium alloys

In recent years, biodegradable alloys have made their presence felt in a wide variety of fields, such as aeronautics, automotive and medical fields. Biodegradable alloys are considered to be the 3rd generation of biocompatible alloys, replacing classic alloys such as stainless steels and Co-Cr alloys. The paper aims to study the structural aspect and identify some mechanical characteristics of magnesium-calcium alloys used as biodegradable materials in the medical field. It has been observed the formation of a eutectic compound at the limit of magnesium grains and the relative constant value of the apparent coefficient of friction with increasing Ca concentration.

Composition Dependence of the β Phase Stability and Mechanical Properties of Ti–Nb Thin Films

Shape memory alloys (SMAs) are commonly used for various applications, e.g., in the aerospace and automotive industries, robotics, and biomedical sciences. Although Ti–Ni SMAs are commercially available, the low biocompatibility of Ni has stimulated research into the development of Ti–Nb based SMAs as potential replacements of Ti–Ni alloys in biomedical applications. Ti–Nb alloys have attracted attention because of their low stiffness and superelasticity. Superelastic thin films can be used in medical applications, including the fabrication of stents for neurovascular blood vessels, which relies on a thin film and on the use of a Ti–Nb alloy coating for less biocompatible alloys. In this study, Ti–Nb thin films were prepared using magnetron sputtering. A Nb content in the range 12.2–35.9 at.% was used in the films, which was determined using energy-dispersive X-ray spectroscopy. X-ray diffraction measurement was used to analyze the crystal structure of the thin films, and their mechanical properties were investigated using nanoindentation.

Elaboration of Ti-based Biocompatible Alloys Using Nb, Fe and Zr as Alloying Elements

Increasing biocompatibility of implant materials is an important factor in developing better and long-lasting implants that function in a very close way to real tissue and bone. Various alloys have been chosen due to their biocompatibility, such as: stainless steels, titanium alloys and nickel or cobalt alloys. According to the alloying elements it is possible to change the material properties to fit into various application niches such as pacemaker devices, stents, biosensors, dental or bone implants and others. Some alloying elements confer higher biocompatibility than others and the commonly used alloys include elements that can be detrimental to human health such as Nickel, Vanadium and Cobalt. Choosing alloying elements such as Nb, Fe and Zr in order to replace the commonly used metals reduces the risks of accumulation of various substances that can damage the human tissues and lead to health complications. The proposed alloys are elaborated in a Five Celes melting furnace under argon atmosphere in order to create a more homogeneous material with lesser defects and inclusions. The cast alloys are then analyzed through modern methods such as SEM, XRD, EDS and their mechanical properties such as hardness and strength and these properties are compared to that of the bone in order to assess mechanical reliability.

Exploring a wider range of Mg–Ca–Zn metallic glass as biocompatible alloys using combinatorial sputtering

Using combinatorial thin film processing and characterization techniques, we demonstrate a new capability of exploring a wider composition range of Mg–Ca–Zn metallic glass for biocompatible applications.

Evaluating a NiTi Implant Under Realistic Loads: A Simulation Study

Additive manufacturing (i.e. 3D printing) has only recently be shown as a well-established technology to create complex shapes and porous structures from different biocompatible metal powder such as titanium, nitinol, and stainless steel alloys. This allows for manufacturing bone fixation hardware with patient-specific geometry and properties (e.g. density and mechanical properties) directly from CAD files. Superelastic NiTi is one of the most biocompatible alloys with high shock absorption and biomimetic hysteresis behavior. More importantly, NiTi has the lowest stiffness (36–68 GPa) among all biocompatible alloys [1]. The stiffness of NiTi can further be reduced, to the level of the cortical bone (10–31.2 GPa), by introducing engineered porosity using additive manufacturing [2–4]. The low level of fixation stiffness allows for bone to receive a stress profile close to that of healthy bone during the healing period. This enhances the bone remodeling process (Wolf’s Law) which primarily driven by the pattern of stress. Also, this match in the stiffness of bone and fixation mitigates the problem of stress shielding and detrimental stress concentrations. Stress shielding is a known problem for the currently in-use Ti-6Al-4V fixation hardware. The high stiffness of Ti-6Al-4V (112 GPa) compared to bone results in the absence of mechanical loading on the adjacent bone that causes loss of bone mass and density and subsequently bone/implant failure. We have proposed additively manufactured porous NiTi fixation hardware with a patient-specific stiffness to be used for the mandibular reconstructive surgery (MRS). In MRS, the use of metallic fixation hardware and double barrel fibula graft is the standard methodology to restore the mandible functionality and aesthetic. A validated finite element model was developed from a dried cadaveric mandible using CT scan data. The model simulated a patient’s mandible after mandibular reconstructive surgery to compare the performance of the conventional Ti-6Al-4V fixation hardware with the proposed one (porous superelastic NiTi fixation plates). An optimized level of porosity was determined to match the NiTi equivalent stiffness to that of a resected bone, then it was imposed to the simulated fixation plates. Moreover, the material property of superelastic NiTi was simulated by using a validated customized code. The code was calibrated by using DSC analysis and mechanical tests on several prepared bulk samples of Ni-rich NiTi. The model was run under common activities such as chewing by considering different levels of the applied fastening torques on screws. The results show a higher level of stress distribution on mandible cortical bone in the case of using NiTi fixation plates. Based on wolf’s law it can lead to a lower level of stress shielding on the grafted bone and over time bone can remodel itself. Moreover, the results suggest an optimum fastening torque for fastening the screws for the superelastic fixations causes more normal distribution of stress on the bone similar to that for the healthy mandible. Finally, we successfully fabricated the stiffness-matched porous NiTi fixation plates using selective laser melting technique, and they were mounted on the dried cadaveric mandible used to create the finite element model.

Structural Analysis of CoCrMoSi6 Alloy Used in Medical Applications

Increase the life exploitation of implants has been the motor factor in the elaboration of the new biocompatible alloys based on cobalt. The paper aims the complete structural characterizations for CoCrMoSi6 alloy, based on modern investigation methods, like compositional analysis by EDX method, optical and electronic microscopy analysis, X-ray diffractrometric analysis, fracture analysis. The experiments aimed to establish all the structural aspects for CoCrMoSi6 alloy and his recommendation for using to manufacture the components for medical applications. The results obtained from the SEM microstructural analysis, for the original version allied with silicon in percentage of 6%, certify a dendritic structure specific to the cobalt base alloys. This paper established the structural aspects for a new variant of CoCrMoSi6 alloy and recommends their use successfully in the production of components for medical applications.