Nanoporous hybrid core–shell nanoparticles for sequential release

In this article, a new type of core–shell nanoparticle is introduced. In contrast to most reported core–shell systems, the particles presented here consist of a porous core as well as a porous shell using only non-metal materials. The core–shell nanoparticles were successfully synthesized using nanoporous silica nanoparticles (NPSNPs) as the starting material, which were coated with nanoporous phenylene-bridged organosilica, resulting in a total particle diameter of about 80 nm. The combination of a hydrophilic nanoporous silica core and a more hydrophobic nanoporous organosilica shell provides regions of different chemical character and slightly different pore sizes within one particle. These different properties combined in one particle enable the selective adsorption of guest molecules at different parts of the particle depending on the molecular charge and polarity. On the other hand, the core–shell make-up of the particles provides a sequential release of guest molecules adsorbed at different parts of the nanoparticles. As a proof of concept, loading and release experiments with dyes were performed using non polar fluorescein and polar and charged methylene blue as model guest molecules. Non polar fluorescein is mostly adsorbed on the hydrophobic organosilica shell and therefore quickly released whereas the polar methylene blue, accumulated in the hydrophilic silica core, is only released subsequently. This occurs in small doses for an extended time corresponding to a sustained release over at least one year, controlled by the organosilica shell which acts as a diffusion barrier. An initial experiment with two drugs — non polar ibuprofen and polar and charged procaine hydrochloride — has been carried out as well and shows that the core–shell nanoparticles presented here can also be used for the sequential release of more relevant combinations of molecules

Deformation Dynamics of Nanopores upon Water Imbibition

Capillarity-driven transport in nanoporous solids is ubiquitous in nature and is of increasing importance for the functionality of modern liquid-infused engineering materials. During imbibition, highly curved menisci are driven by negative Laplace pressures of several hundred atmospheres, exerting an enormous contractile load on an increasing portion of the porous matrix. Due to the challenge of simultaneously monitoring imbibition and deformation with high spatial resolution, the resulting coupling of solid elasticity to liquid capillarity has remained largely unexplored. Here, we study water imbibition in mesoporous silica using optical imaging, gravimetry, and high-resolution dilatometry. In contrast to an expected Laplace pressure-induced contraction, we find a square-root-of-time expansion and an additional abrupt length increase when the menisci reach the top surface. The final expansion is absent when we stop the imbibition front inside the porous medium in a dynamic imbibition-evaporation equilibrium, as is typical for water transport and transpiration in plants. These peculiar deformation behaviors are validated by single-nanopore molecular dynamics simulations and described by a continuum model that highlights the importance of expansive surface stresses at the pore walls (Bangham effect) and the buildup or release of contractile Laplace pressures as nanoscale menisci collectively advance, arrest, or disappear. Our model predicts that these observations are valid not only for water imbibition in silica, but for any imbibition process in nanopores, regardless of the liquid/solid combination. This also suggests that simple deformation measurements can be used to quantify surface stresses and Laplace pressures or transport in a wide variety of natural and artificial porous media.Comment: 11 pages, 4 figures. Supplementary information and 3 movies are stored as ancillary file

Translational and rotational diffusion coefficients in nanofluids from polarized dynamic light scattering

Nanofluids representing nanometer-sized solid particles dispersed in liquids are of interest in many fields of process and energy engineering, e.g., heat transfer, catalysis, and the design of functionalized materials [1]. The physical, chemical, optical, and electronic properties of nanofluids are strongly driven by the size, shape, surface potential, and concentration of the nanoparticles. For the analysis of diffusive processes in nanofluids allowing access to, e.g., particle size and its distribution, dynamic light scattering (DLS) is the state-of-the-art technique. It is based on the analysis of microscopic fluctuations originating from the random thermal movement of particles in the continuous liquid phase at macroscopic thermodynamic equilibrium. For anisotropic particles or particle aggregates, besides translational diffusion also rotational diffusion occurs. To obtain the sum of the orientation-averaged translational (DT) and rotational (DR) diffusivities by depolarized DLS [2], a homodyne detection scheme is usually applied which can hardly be fulfilled in the experimental realization. Furthermore, the experiments are restricted to limited ranges for temperature, particle concentration, and viscosity

Comparative Gas Sorption and Cryoporometry Study of Mesoporous Glass Structure: Application of the Serially Connected Pore Model

Nitrogen sorption and melting and freezing of water in a small pore size mesoporous glass with irregular pore structure is studied. The analysis of the experimentally obtained data is performed using the recently developed serially connected pore model (SCPM). The model intrinsically incorporates structural disorder by introducing coupling between nucleation and phase growth mechanisms in geometrically disordered mesopore spaces. It is shown that, in contrast to the independent pore models prevailing in the literature, SCPM self-consistently describes not only boundary transitions, but also the entire family of the scanning transitions. The scanning behavior is shown to be very sensitive to microscopic details of the fluid phase distribution within the porous materials, hence can be used to check the validity of the thermodynamic models and to improve the structural analysis. We show excellent quantitative agreement between the structural information evaluated from the cryoporometry and gas sorption data using SCPM

Effective Thermal Conductivity of Nanofluids: Measurement and Prediction

Abstract In the present study, the effective thermal conductivity of nanoparticle dispersions, so-called nanofluids, is investigated experimentally and theoretically. For probing the influence of the nanoparticles on the effective thermal conductivity of dispersions with water as liquid continuous phase, nearly spherical and monodisperse titanium dioxide (TiO2), silicon dioxide (SiO2), and polystyrene (PS) nanoparticles with strongly varying thermal conductivities were used as model systems. For the measurement of the effective thermal conductivity of the nanofluids with particle volume fractions up to 0.31, a steady-state guarded parallel-plate instrument was applied successfully at temperatures between (298 and 323) K. For the same systems, dynamic light scattering (DLS) was used to analyze the collective translational diffusion, which provided information on the dispersion stability and the distribution of the particle size as essential factors for the effective thermal conductivity. The measurement results for the effective thermal conductivity show no temperature dependency and only a moderate change as a function of particle volume fraction, which is positive or negative for particles with larger or smaller thermal conductivities than the base fluid. Based on these findings, our theoretical model for the effective thermal conductivity originally developed for nanofluids containing fully dispersed particles of large thermal conductivities was revisited and also applied for a reliable prediction in the case of particles of relatively low thermal conductivities

Quinine Inhibits Infection of Human Cell Lines with SARS-CoV-2

While vaccination campaigns are ongoing worldwide, there is still a tremendous medical need for efficient antivirals against SARS-CoV-2 infection. Among several drug candidates, chloroquine (CQN) and hydroxychloroquine (H-CQN) were tested intensively, and any contentious therapeutic effect of both has been discussed controversially in the light of severe side effects and missing efficacy. Originally, H-CQN descended from the natural substance quinine, a medicinal product used since the Middle Ages, which actually is regulatory approved for various indications. We hypothesized that quinine also exerts anti-SARS-CoV-2 activity. In Vero cells, quinine inhibited SARS-CoV-2 infection more effectively than CQN, and H-CQN and was less toxic. In human Caco-2 colon epithelial cells as well as the lung cell line A549 stably expressing ACE2 and TMPRSS2, quinine also showed antiviral activity. In consistence with Vero cells, quinine was less toxic in A549 as compared to CQN and H-CQN. Finally, we confirmed our findings in Calu-3 lung cells, expressing ACE2 and TMPRSS2 endogenously. In Calu-3, infections with high titers of SARS-CoV-2 were completely blocked by quinine, CQN, and H-CQN in concentrations above 50 µM. The estimated IC50s were ~25 µM in Calu-3, while overall, the inhibitors exhibit IC50 values between ~3.7 to ~50 µM, dependent on the cell line and multiplicity of infection (MOI). Conclusively, our data indicate that quinine could have the potential of a treatment option for SARS-CoV-2, as the toxicological and pharmacological profile seems more favorable when compared to its progeny drugs H-CQN or CQN