Kai Kamada

A simple inclined-drying process controlled α-ZrP nanosheet orientation in PVA membranes, leading to markedly different gas barrier properties.

Antimicrobial resistance (AMR) poses a critical global health threat, particularly for immuno-compromised patients, such as those undergoing treatment for hematological malignancies. To address the limitations of conventional antibiotics, two-dimensional (2D) inorganic nanomaterials have attracted increasing attention as alternative antimicrobial platforms owing to their tunable surface chemistry and mechanical rigidity. In this study, we investigated the antibacterial mechanisms of copper‑ or silver‑doped titanate nanosheets (Cu‑TNS and Ag‑TNS), focusing on how the dopant species and their structural locations influence antibacterial activity. Fine titanate nanosheets with low aspect ratios were synthesized through a liquid-phase reaction, enabling the evaluation of the chemical contributions of trace metal dopants while minimizing nanosheet-induced mechanical killing effects, as reported previously. Comprehensive characterization, including Raman spectroscopy, DLS, and XPS, revealed that Cu⁺ ions were substitutionally incorporated into the titanate lattice, generating oxygen vacancies and modulating the electronic structure, whereas Ag⁺ ions resided in the interlayer galleries as exchangeable cations. Antibacterial assays against Staphylococcus aureus and Escherichia coli demonstrated that Cu‑TNS exerted stable, contact‑dependent antibacterial effects without ion diffusion, whereas Ag‑TNS exhibited strong but transient activity driven by Ag⁺ release, which was consistent with the inhibition‑zone formation observed in disk diffusion tests. Overall, Ag‑TNS is suited for short‑term, high‑intensity disinfection, whereas Cu‑TNS provides durable surface antibacterial properties ideal for long‑term applications, such as antimicrobial coatings. This study provides the first systematic elucidation of metal-dependent antibacterial mechanisms from a chemical perspective and highlights design principles for next-generation inorganic antimicrobial materials.

This study reports the development of electrospun poly(methyl methacrylate) (PMMA) fiber mats incorporating ibuprofen (IBU)-intercalated layered double hydroxides (LDH) for enhanced transdermal drug delivery systems (TDDS). IBU, in its anionic form, was successfully intercalated into LDH, which possesses anion exchange capabilities, and subsequently embedded into PMMA fibers via electrospinning. In vitro drug release experiments demonstrated that UPMMA–LDH–IBU fibers exhibited significantly higher IBU release than PMMA–IBU controls. This enhancement was attributed to the improved hydrophilicity and water absorption imparted by the LDH, as confirmed by contact angle and water uptake measurements. Furthermore, artificial skin permeation tests revealed that the UPMMA–LDH–IBU fibers maintained comparable release rates to those observed during buffer immersion, indicating that the rate-limiting step was the diffusion of IBU within the fiber matrix rather than the interface with the skin or buffer. These findings highlight the critical role of LDH in modulating drug release behavior and suggest that UPMMA–LDH–IBU electrospun fiber mats offer a promising and efficient platform for advanced TDDS applications.

We fabricated composite membranes containing inorganic nanosheets (NSs) and polymers and demonstrated their outstanding antibacterial performance against several opportunistic pathogens. Layered alpha-zirconium phosphate [Zr(HPO4)(2), alpha-ZrP] as a pristine compound of NS was exfoliated by ion-exchanging protons in the interlayer space of alpha-ZrP with bulky tetraalkylammonium ions (TRA(+): R = butyl, hexyl, and octyl). During the exfoliation process, TRA(+) was electrostatically adsorbed onto alpha-ZrP NS with a negative surface charge (ZrP-TRA-NS). The produced PMMA membrane including alpha-ZrP NS (PM-ZrP-TRA-NS) was optically transparent and prohibited bacterial growth, and the effect was stronger for Gram-positive Staphylococcus aureus than Gram-negative Escherichia coli. The antibacterial activity of PM-ZrP-TRA-NS was based on physical damage induced by both 2D ceramic NSs and sharp alkyl chains of TRA(+). Despite the inherent flexibility of alkyl chains, when adsorbed onto the NSs, they can act in a manner that effectively pierces the bacterial cell wall. The piercing force of TRA(+) was greater for the longer alkyl chains (TBA(+) < THA(+) < TOA(+)). Focusing on the difference in the cell wall structure between these bacteria, the growth of Gram-positive S. aureus with loose peptidoglycan layers as an outer membrane could be easily inhibited by contact with the composite film. In contrast, Gram-negative bacteria E. coli, surrounded by a relatively dense outer cell wall composed of peptidoglycan and lipopolysaccharide layers, could not be damaged easily. In this study, the antibacterial mechanism of PM-ZrP-TRA-NS membranes was elucidated, and their usefulness as antimicrobial coatings for existing solid surfaces was demonstrated.

A drug-delivery system consisting of an inorganic host—layered double hydroxide (LDH)—and an anticancer drug—methotrexate (MTX)—was prepared via the intercalation route (MTX-LDH), and its hematocompatibility was investigated. Hemolysis, a red blood cell counting assay, and optical microscopy revealed that the MTX-LDH had no harmful toxic effect on blood cells. Both scanning electron microscopy and atomic force microscopy exhibited that the MTX-LDH particles softly landed on the concave part inred blood cells without serious morphological changes of the cells. The time-dependent change in the surface charge and hydrodynamic radius of MTX-LDH in the plasma condition demonstrated that the proteins can be gently adsorbed on the MTX-LDH particles, possibly through protein corona, giving rise to good colloidal stability. The fluorescence quenching assay was carried out to monitor the interaction between MTX-LDH and plasma protein, and the result showed that the MTX-LDH had less dynamic interaction with protein compared with MTX alone, due to the capsule moiety of the LDH host. It was verified by a quartz crystal microbalance assay that the surface interaction between MTX-LDH and protein was reversible and reproducible, and the type of protein corona was a soft one, having flexibility toward the biological environment.

Porous (pr-)SnO₂-based powders were synthesized by ultrasonic spray pyrolysis employing home-made polymethylmethacrylate (PMMA) microspheres (typical particle size: 70 nm in diameter), and effects of the Cu_xO addition to the pr-SnO₂ powder on the acetone and toluene sensing properties were investigated. Well-developed spherical pores reflecting the morphology of the PMMA microsphere templates were formed in the SnO₂-based powders, which were quite effective in enhancing the acetone and toluene responses. The 0.8 wt% Cu-added pr-SnO₂ sensor showed the largest acetone response at 350 °C among all the sensors. Furthermore, we clarified that the addition of Cu_xO onto the pr-SnO₂ decreased the concentration of carrier electrons and the acetone-oxidation activity, leading to the improvement of the acetone-sensing properties of the pr-SnO₂ sensor.

Herein, the effect of immobilizing lipase onto layered α-zirconium phosphate ceramic nanosheets (α-ZrP NS) on the enzymatic transesterification of allylic alcohols was investigated in organic solvents. α-ZrP NS modified with quaternary ammonium ions show a excellent dispersion stability in n-hexane. Lipase immobilized on α-ZrP NS enables the improved synthesis of chiral allylic alcohols and esters, with significantly reduced reaction times compared to reactions performed in the absence of α-ZrP NS. The coexistence of α-ZrP NS also results in more efficient steric inversion of the resulting allyl ester, suggesting the utility of α-ZrP NS as a support for lipase-induced stereospecific reactions. The present manuscript discusses on mechanisms of high dispersion stability of α-ZrP NS and their preferable immobilizing effect for the lipase inducing the steric inversion in detail.