Publications

Despite advances in bone graft design and surgical techniques, bacterial infection remains a major cause of graft failure, exacerbated by the global rise in antimicrobial resistance. This has intensified the pursuit of antibioticfree strategies to prevent bacterial colonization. Among these, antibacterial surface nanotopographies have emerged as promising tools, leveraging nanoscale geometries to physically disrupt bacteria upon contact. In this study, we engineered the surface of a calcium phosphate bone graft to confer antimicrobial functionality through a dual approach: the creation of high-aspect-ratio nanotopographies and ionic doping with fluoride. Through controlled hydrolysis of alpha-tricalcium phosphate by biomimetic and hydrothermal treatments, we generated calcium deficient hydroxyapatite nanoneedle structures whose morphology and biofunctionality were tuned via fluoride incorporation. XRD and Raman spectroscopy confirmed the formation of hydroxy-fluorapatite, with phase composition and surface morphology dependent on fluoride concentration and processing parameters. Fluoride doping significantly altered nanoneedle dimensions and spacing and enhanced bactericidal activity, particularly against P. aeruginosa, and to a lesser extent S. aureus. Notably, fluoride-doping alone showed no antibacterial effects; however, when combined with nanotopography, a synergistic increase in efficacy was observed. Importantly, the antimicrobial surfaces supported the proliferation and osteogenic differentiation of SaOS-2 cells. Co-culture assays modeling pre- and post-implantation infection scenarios demonstrated robust cell adhesion and markedly reduced bacterial colonization. In conclusion, our findings present a multifunctional, synthetic bone graft with both physical and chemical antibacterial properties, offering a promising strategy to mitigate infection risks while supporting osteointegration.

JTD Keywords: Antibacterial nanotopography, Bactericidal surfaces, Biomaterials, Bone regeneration, Calcium phosphate, Cements, Coatings, Cytokines, Fluoride, Hydroxyapatite, Infections, Magnesium, Pseudomonas-aeruginosa, Setting reaction

Since the discovery that nanostructured surfaces were able to kill bacteria, many works have been published focusing on the design of nanopatterned surfaces with antimicrobial properties. Synthetic bone grafts, based on calcium phosphate (CaP) formulations, can greatly benefit from this discovery if adequate nanotopographies can be developed. However, CaP are reactive materials and experience ionic exchanges when placed into aqueous solutions which may in turn affect cell behaviour and complicate the interpretation of the bactericidal results. The present study explores the bactericidal potential of two nanopillared CaP prepared by hydrolysis of two different sizes of alpha-tricalcium phosphate (alpha-TCP) powders under biomimetic or hydrothermal conditions. A more lethal bactericidal response toward Pseudomonas aeruginosa (similar to 75% killing efficiency of adhered bacteria) was obtained from the hydrothermally treated CaP which consisted in a more irregular topography in terms of pillar size (radius: 20-60 nm), interpillar distances (100-1500 nm) and pillar distribution (pillar groups forming bouquets) than the biomimetically treated one (radius: 20-40 nm and interpillar distances: 50-200 nm with a homogeneous pillar distribution). The material reactivity was greatly influenced by the type of medium (nutrient-rich versus nutrient-free) and the presence or not of bacteria. A lower reactivity and superior bacterial attachment were observed in the nutrient-free medium while a lower attachment was observed for the nutrient rich medium which was explained by a superior reactivity of the material paired with the lower tendency of planktonic bacteria to adhere on surfaces in the presence of nutrients. Importantly, the ionic exchanges produced by the presence of materials were not toxic to planktonic cells. Thus, we can conclude that topography was the main contributor to mortality in the bacterial adhesion tests.

JTD Keywords: bactericidal, calcium deficient hydroxyapatite, calcium phosphates, nanopillars, pseudomonas aeruginosa, reactivity, Adhesion, Anti-bacterial agents, Antibacterial, Bacterial adhesion, Bactericidal, Biomaterials, Biomimetics, Calcium deficient hydroxyapatite, Calcium phosphates, Hydroxyapatite, In-vitro, Infections, Nanopillars, Nanostructures, Pseudomonas aeruginosa, Pseudomonas-aeruginosa, Reactivity, Recent progress, Silver, Topography, Transmission

Water contamination is one of the most persistent problems of public health. Resistance of some pathogens to conventional disinfectants can require the combination of multiple disinfectants or increased disinfectant doses, which may produce harmful byproducts. Here, we describe an efficient method for disinfecting Escherichia coli and removing the bacteria from contaminated water using water self-propelled Janus microbots decorated with silver nanoparticles (AgNPs). The structure of a spherical Janus microbot consists of a magnesium (Mg) microparticle as a template that also functions as propulsion source by producing hydrogen bubbles when in contact with water, an inner iron (Fe) magnetic layer for their remote guidance and collection, and an outer AgNP-coated gold (Au) layer for bacterial adhesion and improving bactericidal properties. The active motion of microbots increases the chances of the contact of AgNPs on the microbot surface with bacteria, which provokes the selective Ag+ release in their cytoplasm, and the microbot self-propulsion increases the diffusion of the released Ag+ ions. In addition, the AgNP-coated Au cap of the microbots has a dual capability of capturing bacteria and then killing them. Thus, we have demonstrated that AgNP-coated Janus microbots are capable of efficiently killing more than 80% of E. coli compared with colloidal AgNPs that killed only less than 35% of E. coli in contaminated water solutions in 15 min. After capture and extermination of bacteria, magnetic properties of the cap allow collection of microbots from water along with the captured dead bacteria, leaving water with no biological contaminants. The presented biocompatible Janus microbots offer an encouraging method for rapid disinfection of water.

JTD Keywords: Bactericidal, Magnetic control, Micromotors, Microswimmers, Self-propulsion, Silver nanoparticles