Niacinamide (NIA) is a widely used skincare ingredient with established benefits for skin barrier support, inflammation reduction, and dermal health. However, the mechanisms governing its transdermal delivery remain insufficiently understood, particularly regarding how formulation pH influences its permeation through the stratum corneum (SC). This study investigates how donor phase pH (5.0 vs. 7.4) modulates NIA skin permeation and how these effects relate to pH induced changes in SC electrical properties. Franz cell diffusion experiments were combined with electrical impedance spectroscopy (EIS) using full‑thickness human skin and 3D reconstructed epidermal tissue models. Permeation was quantified over 24 h and in pH switch experiments, while EIS characterized pH dependent changes in membrane resistance (Rmem) and effective capacitance (Ceff). Additional analyses assessed microbial conversion of NIA to nicotinic acid during prolonged exposure. Neutral donor pH (7.4) increased NIA permeation by roughly twofold compared with acidic pH (5.0) in both membrane types. Correspondingly, pH 7.4 decreased Rmem and increased Ceff, indicating pH driven changes in SC lipid organization and dielectric behavior. These effects were reversible and likely stem from alterations in SC lipid domains, including pH dependent partial deprotonation of free fatty acids that modifies the continuous lipid regions and introduce localized structural microdefects. Such changes enhance NIA and ion permeability and increase SC dielectric properties at neutral pH. Although microbial conversion of NIA to nicotinic acid was negligible within the first 24 h, it became clearly detectable upon prolonged experiments. In conclusion, donor phase pH is a critical determinant of NIA skin permeation, primarily through reversible modulation of SC lipid structure and transport pathways. These findings highlight the importance of pH control in topical formulations and underscore the need to consider microbiota‑mediated transformations when evaluating the efficacy and safety of skin care products containing NIA.

Niacinamide (NIA) is widely used in skincare for its favorable safety profile, anti-aging effects, and proven clinical efficacy in treating various skin conditions. However, its direct impact on the hydration and molecular organization of the stratum corneum (SC), the primary skin barrier, remains unclear. This study examines how NIA influences the SC's lipid matrix organization, soft keratin structure, and water sorption behavior across varying relative humidity (RH) levels. Using small- and wide-angle X-ray diffraction and dynamic vapor sorption measurements, we compared NIA-treated SC samples to untreated controls under different RHs. The main findings show that while NIA is non-hygroscopic, it enhances water uptake of the SC at high humidity (95% RH). At low humidity (60% RH), NIA swells the keratin monomer spacing, although the SC water content remains low, suggesting a plasticizing effect that could increase SC flexibility in dry conditions. NIA also modifies the diffraction intensities from the lipid matrix differently at 60% and 95% RH, implying that it interacts with the SC lipid matrix and influences the water distribution within the SC lipid and protein domains. These effects appear independent of the investigated dose regime, indicating a specific concentration threshold. Overall, NIA shows distinct interaction with keratin, swelling the spacing between keratin monomers in dry conditions, without acting as a traditional keratolytic agent.

The prevailing form of bacterial infection is within the urinary tract, encompassing a wide array of bacteria that harness the urinary metabolome for their growth. Through their metabolic actions, the chemical composition of the growth medium undergoes modifications as the bacteria metabolize urine compounds, leading to the subsequent release of metabolites. These changes can indirectly indicate the existence and proliferation of bacterial organisms. Here, we investigate the use of an electronic tongue, a powerful analytical instrument based on a combination of non-selective chemical sensors with a partial specificity for data gathering combined with principal component analysis, to distinguish between infected and non-infected artificial urine samples. Three prevalent bacteria found in urinary tract infections were investigated, Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis. Furthermore, the electronic tongue analysis was supplemented with 1H NMR spectroscopy and flow cytometry. Bacteria-specific changes in compound consumption allowed for a qualitative differentiation between artificial urine medium and bacterial growth.

In vitro cultured 3D models of CRC have been demonstrated to hold considerable worth in drug discovery, drug resistance analysis, and in studying cell-cell and cell-matrix interactions that occur in the tumor microenvironment. The 3D models resemble the in vivo physiological microenvironment by replicating the cell type composition and tissue architecture. Molecularly imprinted polymers (MIPs) have been investigated for use instead of antibodies against small non-immunogenic structures, such as sialic acid (SA). Glyco-conjugates including SA are present on all cells, and often deregulated on cancer cells. Here, we present a novel approach for targeting and detecting colorectal cancer cells (CRC) by using in vitro cultured HT29 3D spheroids co-cultured in vitro with either fluorescent MIPs targeting SA, SA-MIPs, or the two lectins targeting SA, MAL I, and SNA. Both formaldehyde-fixed and viable HT29 3D spheroids with or without SA-MIPs were imaged in 3D by confocal microscopy. The results revealed a preserved cell morphology and viability of the HT29 3D spheroids co-cultured in vitro with SA-MIPs. However, the lectins MAL I and SNA targeting the a-2,3 or a-2,6 SA glycosidic linkages, respectively, affected the cell viability when co-cultured with the viable HT29 3D spheroids, and no living cells could be detected. Here, we have shown that the SA-MIPs could be used as a safe and low-cost diagnostic tool for targeting and detecting cancer cells in a physiologically relevant 3D cancer model in vitro.