Solid-state NMR study of structure, size and dynamics of domains in hybrid siloxane networks

Resveratrol-Loaded Polydimethylsiloxane-Silica Hybrid Materials: Synthesis, Characterization, and Antitumoral Activity

In this work, hybrid materials within the polydimethylsiloxane-silica (PDMS-SiO2) system, synthesized via the sol-gel method, were developed and characterized for their potential to incorporate and release the bioactive compound resveratrol (RES). RES was incorporated into the materials with a high loading efficiency (>75%) using the rotary evaporator technique. This incorporation induced the amorphization of RES, resulting in enhanced solubility and in vitro release when compared to the free polyphenolic compound. The release profiles displayed pH dependence, exhibiting notably faster release at pH 5.2 compared to pH 7.4. The gradual release of RES over time demonstrated an initial time lag of approximately 4 h, being well described by the Weibull model. In vitro cytotoxicity studies were conducted on human osteosarcoma cells (MG-63), revealing a concentration-dependent decrease in cell viability for RES-loaded samples (for concentrations >50 µg mL-1).

Cellular Response to Sol-Gel Hybrid Materials Releasing Boron and Calcium Ions

Poly(dimethylsiloxane) (PDMS)-SiO₂-CaO-based hybrid materials prepared by sol-gel have proved to be very promising materials for tissue engineering applications and drug-delivery systems. These hybrids are biocompatible and present osteogenic and bioactive properties supporting osteoblast attachment and bone growth. The incorporation of therapeutic elements in these materials, such as boron (B) and calcium (Ca), was considered in this study as an approach to develop biomaterials capable of stimulating bone regeneration. The main purpose of this work was thus to produce, by sol-gel, bioactive and biocompatible hybrid materials of the PDMS-SiO₂-B₂O₃-CaO system, capable of a controlled Ca and B release. Different compositions with different boron amounts were prepared using the same precursors resulting in different monolithic materials, with distinct structures and microstructures. Structural features were assessed by Fourier transform infrared (FT-IR) spectrometry and solid-state nuclear magnetic resonance (NMR) techniques, which confirmed the presence of hybrid bonds (Si-O-Si) between organic (PDMS) and inorganic phase (tetraethyl orthosilicate (TEOS)), as well as borosiloxane bonds (B-O-Si). From the ¹¹B NMR results, it was found that Ca changes the boron coordination, from trigonal (BO₃) to tetrahedral (BO₄). Scanning electron microscopy (SEM) micrographs and N₂ isotherms showed that the incorporation of boron modifies the material's microstructure by increasing the macroporosity and decreasing the specific surface area (SSA). In vitro tests in simulated body fluid (SBF) showed the precipitation of a calcium phosphate layer on the material surface and the controlled release of therapeutic ions. The cytocompatibility of the prepared hybrids was studied with bone marrow stromal cells (ST-2 cell line) by analyzing the cell viability and cell density. The results demonstrated that increasing the dilution rate of extraction medium from the hybrids leads to improved cell behavior. The relationship between the in vitro response and the structural and microstructural features of the materials was explored. It was shown that the release of calcium and boron ions, determined by the hybrid structure was crucial for the observed cells behavior. Although not completely understood, the encouraging results obtained constitute an incentive for further studies on this topic.

Sensitivity enhancement via multiple contacts in the {1H–29Si}–1H cross polarization experiment: a case study of modified silica nanoparticle surfaces

{¹H–²⁹Si}–¹H double cross polarization inverse detection (DCPi) solid-state NMR, has recently been shown to be a powerful tool for studying molecules adsorbed on the silica surface. In this contribution, we develop an improved version (MCPi) which incorporates a block of multiple contact pulses, and quantitatively compare the sensitivities of MCPi and DCPi over a typical range of experimental parameters. The MCPi pulse sequence aims at higher sensitivity and robustness for studying samples with various relaxation characteristics. In the case of dimethyl sulfoxide (DMSO) molecules adsorbed on the silica surface, MCPi performs equally well or up to 2.5 times better than DCPi over a wide range of parameters. The applicability to and performance of MCPi on composite materials was demonstrated using a sample of polymer–silica composite, where significantly higher sensitivity could be achieved at very long total mixing times. The results also showed that both techniques are surface specific in the sense that only the groups close to the surface can be detected.

In this paper we demonstrate {¹H–²⁹Si}–¹H multiple cross polarization inverse detection (MCPi) solid state NMR as a robust technique for studying modified silica nanoparticle surfaces.

Chemical and physicochemical investigation of an aminoalkylalkoxysilane as strengthening agent for cellulosic materials

AMDES (aminopropylmethyldiethoxysilane) was used to investigate the physicochemical and chemical events related to the introduction of aminoalkylalkoxysilanes in cellulosic materials. Using (29)Si CP-MAS and (1)H NMR to study the reactivity and structural modification of AMDES in the paper it was shown that polymerization occurs in situ. The distribution of the active compound on the surface of the fibers and throughout the fibers' thickness was visualized by SEM-EDS. A relation between moisture content, fiber swelling, and uptake of AMDES was found. To better represent old and brittle documents, the paper was predegraded by oxidation with sodium hypochlorite. XRD confirmed the advanced destruction of the amorphous areas of cellulose. Adding AMDES in the oxidized paper resulted in improved mechanical properties, a roughly unmodified degree of polymerization of cellulose, but a slight increase in the yellowing, probably due to several possible reaction products such as imines, amine, amides, and Maillard reactions products. The deacidification efficacy was established and the strengthening effect was shown to arise from the interaction of AMDES with the cellulose fibers.

Deformable hollow hybrid silica/siloxane colloids by emulsion templating

A procedure to obtain hollow colloidal particles has been developed using an emulsion templating technique. Monodisperse silicone oil droplets were prepared by hydrolysis and polymerization of dimethyldiethoxysilane monomer and incorporated in a solid shell using tetraethoxysilane. Hollow shells were obtained by exchange of the core. The formation of the oil droplets was investigated using static light scattering and 29Si solution NMR, and the hollow shells were characterized by electron microscopy and static light scattering. Details on the composition of the shell material were obtained from energy-dispersive X-ray analysis and 29Si solid state NMR, revealing that the shells consist of a hybrid cross-linked network of silica and siloxane units. Confocal microscopy was used to show that the shells are permeable to small dye molecules. The thickness of the coating can be easily varied from a few nanometers upward. Depending on the ratio of shell thickness to particle radius, three types of hollow shells can be distinguished depending on the way in which they buckle upon drying. We designate them as microspheres, microcapsules, and microballoons. As a result of their monodispersity, these particles can be used for making 3D-ordered materials.