Recent Advances in Polyurethane/POSS Hybrids for Biomedical Applications

Advanced organic-inorganic materials-composites, nanocomposites, and hybrids with various compositions offer unique properties required for biomedical applications. One of the most promising inorganic (nano)additives are polyhedral oligomeric silsesquioxanes (POSS); their biocompatibility, non-toxicity, and phase separation ability that modifies the material porosity are fundamental properties required in modern biomedical applications. When incorporated, chemically or physically, into polyurethane matrices, they substantially change polymer properties, including mechanical properties, surface characteristics, and bioactivity. Hence, this review is dedicated to POSS-PU composites that have recently been developed for applications in the biomedical field. First, different modes of POSS incorporation into PU structure have been presented, then recent developments of PU/POSS hybrids as bio-active composites for scaffolds, cardiovascular stents, valves, and membranes, as well as in bio-imaging and cancer treatment, have been described. Finally, characterization and methods of modification routes of polyurethane-based materials with silsesquioxanes were presented.

Modification of Glass/Polyester Laminates with Flame Retardants

This paper presents a review of flame retardants used for glass/polyester laminates. It concerns flame retardants withdrawn from use such as compounds containing halogen atoms and flame retardants currently used in the industry, such as inorganic hydroxides, phosphorus and nitrogen-containing compounds, antimony, and boron compounds, as well as tin–zinc compounds. Attention is also drawn to the use of nanoclays and the production of nanocomposites, intumescent flame retardant systems, and mats, as well as polyhedral oligomeric silsesquioxanes. The paper discusses the action mechanism of particular flame retardants and presents their advantages and disadvantages.

Cationic Phenosafranin Photosensitizers Based on Polyhedral Oligomeric Silsesquioxanes for Inactivation of Gram-Positive and Gram-Negative Bacteria

The high photodynamic effect of the Newman strain of the S. aureus and of clinical strains of S. aureus MRSA 12673 and E. coli 12519 are observed for new cationic light-activated phenosafranin polyhedral oligomeric silsesquioxane (POSS) conjugates in vitro. Killing of bacteria was achieved at low concentrations of silsesquioxanes (0.38 µM) after light irradiation (λem. max = 522 nm, 10.6 mW/cm2) for 5 min. Water-soluble POSS-photosensitizers are synthesized by chemically coupling a phenosafranin dye (PSF) (3,7-diamino-5-phenylphenazine chloride) to an inorganic silsesquioxane cage activated by attachment of succinic anhydride rings. The chemical structure of conjugates is confirmed by 1H, 13C NMR, HRMS, IR, fluorescence spectroscopy and UV-VIS analyzes. The APDI and daunorubicin (DAU) synergy is investigated for POSSPSFDAU conjugates. Confocal microscopy experiments indicate a site of intracellular accumulation of the POSSPSF, whereas iBuPOSSPSF and POSSPSFDAU accumulate in the cell wall or cell membrane. Results from the TEM study show ruptured S. aureus cells with leaking cytosolic mass and distorted cells of E. coli. Bacterial cells are eradicated by ROS produced upon irradiation of the covalent conjugates that can kill the bacteria by destruction of cellular membranes, intracellular proteins and DNA through the oxidative damage of bacteria.

EFFECTS OF OV-POSS NANOPARTICLES ON THE VULCANIZATION KINETICS OF NATURAL RUBBER COMPOUNDS

Polyhedral oligomeric silsesquioxanes (POSSs) are new-generation additives, which can provide improved properties in polymer matrices by physical and/or chemical interactions between the polymer molecules and their reactive sites. In the case of rubber-based polymeric systems, POSSs are also able to accompany with the vulcanization reaction. In this study, it was aimed to investigate the effect of octavinyl functionalized POSS (OV-POSS) on sulphur vulcanization of a model natural rubber (NR) based compound. The reaction kinetics was studied by using various kinetic approaches based on Moving Die Rheometry and Differential Scanning Calorimetry. Rheometric data was evaluated by using a common non-linear cure kinetic model, which is called Isayev and Deng Model. Kissinger, Flynn-Wall-Ozawa, and Crane Models were used to process thermal data for curing reactions. All the models were found to be able to analyze vulcanization kinetics of OV-POSS containing NR-based rubber compounds as well as the effect of OV-POSS incorporation.

The effect of polyhedral oligomeric silsesquioxanes (POSSs) incorporation in ethylene-propylene-diene-terpolymer (EPDM): a thermal study

A series of ethylene-propylene-diene-terpolymer (EPDM)/polyhedral oligomeric silsesquioxane (POSS) composites at different percentage of POSS were prepared and subjected to γ-irradiation. Both irradiated and non-irradiated EPDM and composites were investigated by the means of thermal analysis to verify if the presence of POSS molecules is able to reduce the oxidation level of free radicals generated during the degradation and to evaluate the effects of the irradiation. EPDM composites at 1, 3 and 5 mass% of POSS were thus degraded in a thermogravimetric (TG) balance in dynamic heating conditions (25–700 °C), in both inert and oxidative atmosphere by flowing nitrogen and air respectively. Thermal characterization was then completed by carrying out Differential Scanning Calorimetry (DSC) analysis from sub-ambient to better highlight the melting of the polymer and polymer composites occurring just above the room temperature. FTIR spectroscopy was also performed for the prepared samples to check the presence of the molecular filler in the composites and for the TG’s residue at 700 °C, in order to evaluate its nature. DSC and TGA parameters were detected and discussed to have information about the effect of the degradation’s environment, the effect of irradiation on polymer stabilization and the effect of POSS content in the polymer matrix.