Bioactive Co-Cr alloy for biomedical applications prepared by surface modification using self-assembled monolayers and poly-γ-glutamic acid

Solid-State Processing of CoCrMoNbTi High-Entropy Alloy for Biomedical Applications

High-entropy alloys (HEAs) gained interest in the field of biomedical applications due to their unique effects and to the combination of the properties of the constituent elements. In addition to the required property of biocompatibility, other requirements include properties such as mechanical resistance, bioactivity, sterility, stability, cost effectiveness, etc. For this paper, a biocompatible high-entropy alloy, defined as bio-HEA by the literature, can be considered as an alternative to the market-available materials due to their superior properties. According to the calculation of the valence electron concentration, a majority of body-centered cubic (BCC) phases were expected, resulting in properties such as high strength and plasticity for the studied alloy, confirmed by the XRD analysis. The tetragonal (TVC) phase was also identified, indicating that the presence of face-centered cubic (FCC) phases in the alloyed materials resulted in high ductility. Microstructural and compositional analyses revealed refined and uniform metallic powder particles, with a homogeneous distribution of the elemental particles observed from the mapping analyses, indicating that alloying had occurred. The technological characterization of the high-entropy alloy-elaborated powder revealed the particle dimension reduction due to the welding and fracturing process that occurs during mechanical alloying, with a calculated average particle size of 45.12 µm.

Nanoscale self-assembly: concepts, applications and challenges

Self-assembly offers unique possibilities for fabricating nanostructures, with different morphologies and properties, typically from vapour or liquid phase precursors. Molecular units, nanoparticles, biological molecules and other discrete elements can spontaneously organise or form via interactions at the nanoscale. Currently, nanoscale self-assembly finds applications in a wide variety of areas including carbon nanomaterials and semiconductor nanowires, semiconductor heterojunctions and superlattices, the deposition of quantum dots, drug delivery, such as mRNA-based vaccines, and modern integrated circuits and nanoelectronics, to name a few. Recent advancements in drug delivery, silicon nanoelectronics, lasers and nanotechnology in general, owing to nanoscale self-assembly, coupled with its versatility, simplicity and scalability, have highlighted its importance and potential for fabricating more complex nanostructures with advanced functionalities in the future. This review aims to provide readers with concise information about the basic concepts of nanoscale self-assembly, its applications to date, and future outlook. First, an overview of various self-assembly techniques such as vapour deposition, colloidal growth, molecular self-assembly and directed self-assembly/hybrid approaches are discussed. Applications in diverse fields involving specific examples of nanoscale self-assembly then highlight the state of the art and finally, the future outlook for nanoscale self-assembly and potential for more complex nanomaterial assemblies in the future as technological functionality increases.

Colorimetric detection of Cr3+ ions in aqueous solution using poly(γ-glutamic acid)-stabilized gold nanoparticles

Detection of heavy metal ions in water is of paramount significance for environmental pollution control. Here, we report the use of γ-polyglutamic acid (γ-PGA)-stabilized gold nanoparticles (γ-PGA-Au NPs) as a probe to sense trivalent chromium (Cr3+) in aqueous solution. In our study, γ-PGA-Au NPs were first formed through one-step sodium borohydride reduction of Au salt in the presence of γ-PGA. The formed γ-PGA-Au NPs with a mean particle size of 4.6 nm show desirable colloidal stability and a significant color change from wine red to gray after exposure to Cr3+ ions, which is visible to the naked eye and easily detected by colorimetric assay using UV-vis spectrometry. The limit of detection of Cr3+ ions is 100 ppb by the naked eye and 0.2 ppb by UV-vis spectroscopy, respectively. We further show that the detection of Cr3+ using γ-PGA-Au NPs has excellent selectivity, and the recovery percentage is higher than 82% for different water samples such as lake water, river water, tap water or mineral water. Our study demonstrates that γ-PGA-Au NPs can be utilized as an efficient probe for colorimetric sensing of Cr3+ ions in a water environment.

Co–Cr–Mo alloy binding peptide as molecular glue for constructing biomedical surfaces

The mechanical properties of Co–Cr–Mo (CCM) alloys are advantageous in various biomedical applications. However, because of their bioinert surface, CCM alloys exhibit poor endothelial cell attachment properties; thus, problems of biocompatibility remain. In this study, we aimed to improve the biocompatibility of the CCM alloy surface using solid-binding peptides. We selected peptides with high binding affinity for cast CCM alloy surfaces through in vitro evolution by the phage display method. The peptides were functionalized on the CCM alloy surfaces by simple immersion in the peptide solution. The peptide bound to both cast and 3D-printed CCMs with the same affinity. The peptides linked to the amino acid motif that promotes cell adhesion, and improved the attachment of endothelial cells on the 3D-printed CCM in serum and serum-free conditions. Hence, CCM-binding peptides are attractive tools for constructing a biofunctional surface on CCM-based biodevices.

Interface Engineering of Fully Metallic Stents Enabling Controllable H2O2 Generation for Antirestenosis

Despite significant advances in the design of metallic materials for bare metal stents (BMSs), restenosis induced by the accumulation of smooth muscle cells (SMCs) has been a major constraint on improving the clinical efficacy of stent implantation. Here, a new strategy for avoiding this issue by utilizing hydrogen peroxide (H₂O₂) generated by the galvanic coupling of nitinol (NiTi) stents and biodegradable magnesium-zinc (Mg-Zn) alloys is reported. The amount of H₂O₂ released is carefully optimized via the biodegradability engineering of the alloys and by controlling the immersion time to selectively inhibit the proliferation and function of SMCs without harming vascular endothelial cells. Based on demonstrations of its unique capabilities, a fully metallic stent with antirestenotic functionality was successfully fabricated by depositing Mg layers onto commercialized NiTi stents. The introduction of surface engineering to yield a patterned Mg coating ensured the maintenance of a stable interface between Mg and NiTi during the process of NiTi stent expansion, showing high feasibility for clinical application. This new concept of an inert metal/degradable metal hybrid system based on galvanic metal coupling, biodegradability engineering, and surface patterning can serve as a novel way to construct functional and stable BMSs for preventing restenosis.