High-entropy alloys (HEAs) have been around since 2004. The breakthroughs in this field led to several potential applications of these alloys as refractory, structural, functional, and biomedical materials. In this work, a short overview on the concept of high-entropy alloys is provided, as well as the theoretical design approach. The special focus of this review concerns one novel class of these alloys: biomedical high-entropy alloys. Here, a literature review on the potential high-entropy alloys for biomedical applications is presented. The characteristics that are required for these alloys to be used in biomedical-oriented applications, namely their mechanical and biocompatibility properties, are discussed and compared to commercially available Ti6Al4V. Different processing routes are also discussed.

The aim of the present study is to investigate the effect of the hydrolysis process on the properties of nanocrystalline cellulose (NCC) isolated from different precursors and the subsequent use of the extracted NCC for the reduction of graphene oxide (GO). The raw materials (almond and peanut shells) chosen for the isolation of cellulose were selected on the basis of their abundance and their poorly investigation in the production of NCC. Microcrystalline cellulose (MCC) was firstly extracted by alkali and bleaching treatments, then hydrolyzed under different processes to produce NCC polymorphs with structure I (NCC-I) and NCC structure II (NCC-II). The Fourier transform infrared spectroscopy, the X-ray diffraction (XRD) and the 13C NMR studies of the alkali and bleached products confirmed the formation of cellulose type I with high purity and good crystallinity, while scanning electron microscopy (SEM) showed micrometric fibers with lengths reaching 80 µm. Sulfuric acid treatment of these microfibers results in NCC type I or II, depending on the hydrolysis process. SEM of the NCC samples exhibited nanorods with diameter and aspect ratio in the range of 20–40 and 20–25 nm, respectively. Thermogravimetric analysis (TGA) of the MCC and NCC products indicated stable materials with a degradation temperature reaching 240 and 200 °C for MCC and NCC, respectively. The other part of our work concerns the use of the obtained cellulose nanocrystals (type II) for the preparation of reduced graphene oxide composite (NCC/RGO), to demonstrate the reducing properties of the isolated NCCII.

Nanometric and sub-micrometric monodispersed hydroxyapatite (HAp) particles with different morphologies (spheres and rods) were synthesized via a simple solvothermal method using Ca(NO3)2·4H2O and P2O5 as starting materials without any requirement to use organic templates. The growth, evolution and purity of the nanoparticles were investigated by controlling the synthesis conditions, including the alkalinity and the temperature of the solvothermal treatment. The increasing of the alkaline ratio results in a great change of the elaborated particles’ morphology that evolved from anisotropic forms (nanorods, sub-micrometric rod) at pH 9, short rod particles at pH 9.5 to spherical ones at higher pH (pH≥10).
Powder X-Ray diffractometry (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and Nitrogen adsorption and desorption studies (BET) were used to characterize the structure and composition of the as-prepared samples.
The thermal analysis of the synthesized particles conducted by differential scanning calorimetry (DSC) shows a good stability for all morphologies with a degradation temperature reaching 1300 °C.

Sub-micrometric Co fibers were prepared via a modified polyol process at 90 °C under an external magnetic field of about 550 Oe, using ethelyne glycol as solvent and hydrazine as reducing agent. The structure, the size and the morphology of the as-elaborated products were highly controlled through properly monitoring the synthesis parameters (amount of NaOH added, the amount of the reducing agent, precursor’ concentration and precursors mixing protocol). The XRD characterization confirmed the formation of pure cobalt powders with either hexagonal compact (hcp) or face-centered-cubic (fcc) structure depending on the concentration of the metal precursor and sodium hydroxide. The scanning electron microscopy observations of the powders shows sub-micrometric fibers with about 0.4–0.6 µm in diameter and a length that could reach 15 µm. Fibers prepared at high reducing ratio were constituted of flower-like spheres that coalesce in the direction of the applied magnetic field. For their high contact surface, these fibers offer new opportunities for catalysis applications. The hysteresis loop measurements show an enhancement of the Hc of the as-obtained fibers compared to their bulk counterparts and permit to confirm the relationship between the structure and the magnetic properties of the materials.