No abstract

In order to obtain an antimicrobial gel, a starch-based hydrogel reinforced with silica-coated copper nanoparticles (Cu NPs) was developed. Cu NPs were synthesized by use of a copper salt and hydrazine as a reducing agent. In order to enhance Cu NP stability over time, they were synthesized in a starch medium followed by a silica coating. The starch hydrogel was prepared by use of urea and water as plasticizers and it was treated with different concentrations of silica-coated copper nanoparticles (Si-Cu NPs). The obtained materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, scanning electron microscopy (SEM), and rheometry. FT-IR and EPR spectra were used for characterization of Cu NPs and Si-Cu NPs, confirming that a starch cap was formed around the Cu NP and demonstrating the stability of the copper nanoparticle after the silica coating step. SEM images showed Cu NP, Si-Cu NP, and hydrogel morphology. The particle size was polydisperse and the structure of the gels changed along with particle concentration. Increased NP content led to larger pores in starch structure. These results were in accordance with the rheological behavior, where reinforcement by the Si-Cu NP was seen. Antimicrobial activity was evaluated against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacterial species. The hydrogels were demonstrated to maintain antimicrobial activity for at least four cycles of use. A dermal acute toxicity test showed that the material could be scored as slightly irritant, proving its biocompatibility. With these advantages, it is believed that the designed Si-Cu NP loaded hydrogel may show high potential for applications in various clinical fields, such as wound dressings and fillers.

Superparamagnetic nanocomposites were obtained by dispersion of oleic acid (OA)-coated magnetite NPs in an epoxy system based on diglycidylether of bisphenol A (DGEBA) modified with OA. Dispersion of conventional oleic acidstabilized magnetite NPs in a typical epoxy matrix is not possible due to the dissimilar chemical structures of the organic coating and the reactive solvent. However, by modification of a DGEBA-based epoxy with 20 wt % OA, we obtained a suitable reactive solvent to disperse up to at least 8 wt % of OA-stabilized magnetite NPs. A tertiary amine was used to catalyze the epoxy−acid reaction and initiate the homopolymerization of the epoxy excess. Both reactions occurred practically in series, first the epoxy−acid and then the epoxy homopolymerization. It was necessary to complete the first reaction to attain a very good dispersion of magnetite NPs in the reactive solvent previous to the occurrence of the final reaction. Magnetization curves and TEM images revealed a uniform dispersion of individual nanoparticles in the cross-linked epoxy. A sample containing 8 wt % OA-coated magnetite NPs exhibited a temperature increase of 25 °C at its surface when exposed to an alternating magnetic field. The temperature increase was enough to induce the shape memory effect of the nanocomposite.