Jonathan Hardy

Hydroxyapatite coatings containing graphene oxide and palladium were hydrothermally deposited on a β-type Ti30Zr5Mo alloy in order to establish how the organization of graphene oxide and the incorporation of palladium influence the structural, electrochemical, and biological performance of the coating system. Six compositions—hydroxyapatite, hydroxyapatite with 1 wt% palladium, hydroxyapatite with 2 wt% palladium, hydroxyapatite/graphene oxide, and the corresponding graphene oxide composites containing 1 and 2 wt% palladium—were compared using X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, potentiodynamic polarization, cell-density analysis with A7R5 cells, and bioluminescence imaging of Staphylococcus aureus Xen36. The apatite framework was retained in every composition, and Raman spectroscopy confirmed that the carbon phase derived from graphene oxide survived hydrothermal processing. X-ray photoelectron spectroscopy of the graphene oxide coating containing 2 wt% palladium revealed oxygenated carbon environments and predominantly oxidized, oxygen-coordinated palladium species rather than metallic palladium. Electrochemical behavior depended strongly on composition. The hydroxyapatite coating containing 2 wt% palladium showed the lowest corrosion current density, 1.46 ± 0.02 µA cm⁻² (0.0127 ± 0.0002 mm year⁻¹), and a mean total resistance of 15.73 ± 0.13 kΩ cm², close to that of the unmodified hydroxyapatite coating (1.95 ± 0.04 µA cm⁻²; 16.52 ± 0.40 kΩ cm²). The hydroxyapatite/graphene oxide coating showed the weakest barrier behavior, with a corrosion current density of 4.21 ± 0.07 µA cm⁻² (0.0366 ± 0.0006 mm year⁻¹) and a mean total resistance of only 8.50 ± 0.15 kΩ cm². Microscopic and electrochemical evidence indicated that the expected barrier effect of graphene oxide was lost because the graphene oxide-containing layer was structurally heterogeneous. This layer contained folded, sheet-like domains and pathways that remained accessible to the electrolyte, and restacking or aggregation of the sheets induced by calcium ions is proposed as a plausible origin of this morphology. Adding 1 wt% palladium partially restored coating coverage and raised the mean total resistance to 14.97 ± 0.20 kΩ cm² (2.15 ± 0.04 µA cm⁻²), whereas 2 wt% palladium lowered the interfacial charge-transfer resistance and reduced the mean total resistance to 11.73 ± 0.30 kΩ cm² (2.91 ± 0.06 µA cm⁻²), even though the outer part of the coating remained intact. All coatings supported higher short-term A7R5 cell densities than the uncoated substrate, and the highest value, 330.2% of the control, was obtained for the graphene oxide coating containing 2 wt% palladium. The same graphene-oxide/palladium coatings, however, produced considerably stronger bioluminescent responses from Staphylococcus aureus than the remaining compositions. Overall, the hydroxyapatite coating containing 2 wt% palladium offered the most balanced combination of electrochemical and biological performance. The results show that the behavior of these coatings is governed by the organization of graphene oxide, by the interfacial chemistry associated with palladium, by the pathways available to the electrolyte, and by buried charge-transfer processes, rather than by nominal additive content alone. Their architecture is characterized by folded sheet-like domains and accessible electrolyte pathways, with Ca²⁺-mediated restacking/aggregation proposed as a plausible origin. Incorporation of 1 wt% Pd partially restored coating coverage and increased the mean total resistance to 14.97 ± 0.20 kΩ cm², whereas increasing Pd to 2 wt% reduced the interfacial charge-transfer resistance and decreased the mean total resistance to 11.73 ± 0.30 kΩ cm² despite retention of the outer-coating barrier. All coatings supported higher short-term A7R5 cell densities than the uncoated substrate, with HA/GO-2Pd reaching 330.2% of the control. However, the GO/Pd coatings produced substantially higher Xen36 bioluminescent responses than the remaining compositions. Overall, HA-2Pd provided the most balanced electrochemical and biological performance, while the results demonstrate that the behavior of HA/GO/Pd coatings is governed by GO organization, Pd-associated interfacial chemistry, electrolyte-access pathways, and buried interfacial charge-transfer processes rather than nominal additive content alone.

Advanced biomaterials are required for bone reconstruction to overcome the mechanical and biological limitations of conventional titanium alloys. In this study, hydroxyapatite–chitosan–palladium (HA-Cs-Pd) composite coatings were successfully synthesized on metastable β-Ti12Cr alloy surfaces using a hydrothermal method. The coatings were characterized using XRD, Raman, FT-IR, XPS, and FE-SEM/EDS analyses, while their electrochemical, wettability, antibacterial, and cellular response properties were systematically evaluated. The results showed that chitosan incorporation improved coating compactness and corrosion resistance by enhancing barrier properties, whereas Pd addition influenced crystal growth behavior and enhanced antibacterial activity against Pseudomonas aeruginosa. In vitro biological analyses demonstrated favorable cell viability and surface adhesion behavior on the coated samples. Among the investigated systems, the HA–Cs–wt.%2Pd coating exhibited the most balanced overall performance. The findings suggest that HA–Cs–Pd composite coatings may provide an effective surface modification strategy for orthopedic and dental implant applications.

Listeria monocytogenes is a facultative intracellular bacterial pathogen that is a potent inducer of cell-mediated immunity, which has led to the development of attenuated, Listeria -based cancer vaccines. L. monocytogenes strains, such as live-attenuated double-deleted Listeria (LADD), lacking two key virulence factors, Δ actA and Δ inlB , have been used safely in clinical trials and showed promising anti-tumor activity. Despite early clinical success, improving potency and safety by preventing extracellular bacterial growth is paramount for the development of further clinical applications. We describe a quadruple attenuated intracellular Listeria (QUAIL) strain that, in addition to Δ actA Δ inlB, lacks ribC and ribF , which encode enzymes required for generating the essential flavin cofactors flavin mononucleotide (FMN) and flavin adenine nucleotide (FAD). QUAIL imported FMN and FAD during intracellular growth but was unable to grow extracellularly in blood or on vascular catheters in mice, which reduced its lethality. Despite its lack of extracellular growth, QUAIL maintained its immunoprotective properties, which were comparable to LADD. Furthermore, we showed that QUAIL can be engineered to synthesize riboflavin, leading to expansion and activation of mucosal-associated invariant T cells. Together, our data support the use of QUAIL as a promising therapeutic platform with an improved safety profile that is amenable to further modifications to expand its immune-activating potential. IMPORTANCE: Listeria -based live-attenuated cancer vaccines represent a promising therapy in many different pre-clinical tumor models and in clinical trials. Enhancing its anti-cancer immunity and increasing its safety profile will advance the clinical applications of Listeria vaccines. By manipulating Listeria monocytogenes flavin metabolism, we engineered a quadruple attenuated intracellular Listeria (QUAIL) vaccine candidate strain that has limited toxicity associated with extracellular growth in major extracellular niches in vivo, including blood and implanted catheter ports. Furthermore, we showed that QUAIL can be effectively programmed to engage innate-like T cells known as mucosal-associated invariant T cells, which could be harnessed for future cancer immunotherapies. The results presented here lay the foundation for further analysis of QUAIL as a safer, yet immunopotent L. monocytogenes vaccine or therapeutic vector.

Placental immunity is critical for fetal health during pregnancy, as invading pathogens spread from the parental blood to the fetus through this organ. However, inflammatory responses in the placenta can adversely affect both the fetus and the pregnant person, and the balance between protective placental immune response and detrimental inflammation is poorly understood.

Background Epidemiological data indicate that prenatal infection is associated with an increased risk of several neurodevelopmental disorders in the progeny. These disorders display sex differences in presentation. The role of the placenta in the sex-specificity of infection-induced neurodevelopmental abnormalities is not well-defined. We used an imaging-based animal model of the bacterial pathogen Listeria monocytogenes to identify sex-specific effects of placental infection on neurodevelopment of the fetus. Methods Pregnant CD1 mice were infected with a bioluminescent strain of Listeria on embryonic day 14.5 (E14.5). Excised fetuses were imaged on E18.5 to identify the infected placentas. The associated fetal brains were analyzed for gene expression and altered brain structure due to infection. The behavior of adult offspring affected by prenatal Listeria infection was analyzed. Results Placental infection induced sex-specific alteration of gene expression patterns in the fetal brain and resulted in abnormal cortical development correlated with placental infection levels. Furthermore, male offspring exhibited abnormal social interaction, whereas females exhibited elevated anxiety. Conclusion Placental infection by Listeria induced sex-specific abnormalities in neurodevelopment of the fetus. Prenatal infection also affected the behavior of the offspring in a sex-specific manner. Impact Placental infection with Listeria monocytogenes induces sexually dichotomous gene expression patterns in the fetal brains of mice. Abnormal cortical lamination is correlated with placental infection levels. Placental infection results in autism-related behavior in male offspring and heightened anxiety levels in female offspring.