Modification of structured bio­carbon derived from spongin-based scaffolds with nickel compounds to produce a functional catalyst for reduction and oxidation reactions: Potential for use in environmental protection.

Three different 3D fibrous-like NiO/Ni(OH)2/Ni­carbonized spongin-based materials were prepared via a simple sorption-reduction method. Depending on the support used, the catalysts were composed of carbon, nickel oxide, nickel hydroxide and zero-valent nickel, with the surface content of the nickel-containing phase in the range 15.2-26.0 wt%. Catalytic studies showed promising activity in the oxidation of phenolic compounds in water and in the reduction of 4-nitrophenol. The oxidation efficiency depends on the substrate used and ranges from 80% for phenol at pH 2 to 99% for 4-chlorophenoxyacetic acid (4-CPA) and methylchlorophenoxypropionic acid (MCPP). In the reduction reaction, all catalysts exhibited superior activity, with rate constants in the range 0.648-1.022 min-1. The work also includes a detailed investigation of reusability and kinetic studies.

Cytotoxic effect of galvanically coupled magnesium-titanium particles.

Recent work has shown that reduction reactions at metallic biomaterial surfaces can induce significant killing of cells in proximity to the surface. To exploit this phenomenon for therapeutic purposes, for example, for cancer tumor killing or antibacterial effects (amongst other applications), magnesium metal particles, galvanically coupled to titanium by sputtering, have been evaluated for their cell-killing capability (i.e. cytotoxicity). Magnesium (Mg) particles large enough to prevent particle phagocytosis were investigated, so that only electrochemical reactions, and not particle toxicity per se, caused cytotoxic effects. Titanium (Ti) coated magnesium particles, as well as magnesium-only particles were introduced into MC3T3-E1 mouse pre-osteoblast cell cultures over a range of particle concentrations, and cells were observed to die in a dosage-dependent manner. Ti-coated magnesium particles killed more cells at lower particle concentration than magnesium alone (P<0.05), although the pH measured for magnesium and magnesium-titanium had no significant difference at similar particle concentrations. Complete cell killing occurred at 750µg/ml and 1500µg/ml for Mg-Ti and Mg, respectively. Thus, this work demonstrates that galvanically coupled Mg-Ti particles have a significant cell killing capability greater than Mg alone. In addition, when the pH associated with complete killing with particles was created using NaOH only (no particles), then the percentage of cells killed was significantly less (P<0.05). Together, these findings show that pH is not the sole factor associated with cell killing and that the electrochemical reactions, including the reduction reactions, play an important role. Reduction reactions on galvanically coupled Mg-Ti and Mg particles may generate reactive oxygen intermediates that are able to kill cells in close proximity to the particles and this approach may lead to potential therapies for infection and cancer. STATEMENT OF SIGNIFICANCE: This paper demonstrates that during active corrosion of both Mg and Mg-Ti particles cells cultured with the particles are killed in a dose-dependent particle concentration fashion. Additionally, galvanically-coupled magnesium-titanium microparticles kill cells more effectively than magnesium particles alone. The killing effect was shown to not be due to pH shifts since no differences were seen for different particle types and pH adjusted medium without particles did not exhibit the same level of killing. The significance of this work is the recognition of this killing effect with Mg particles and the potential therapeutic applications in infection control and cancer treatment that this process may provide.