RESUMEN
Copolymerizations of ethylene and alfa-olefins, using Ziegler-Natta or metallocene catalysts, testing two methods of co-monomer addition, through batch or dossing mode during the reactions, are reported in this work. Copolymerizations are monitored by in line Raman spectroscopy, comparing the effect of the kind of catalyst and the co-monomer addition modes on the chemical composition of the copolymers produced. The global co-monomer composition is determined by 13C NMR spectroscopy, compared with the monitoring by Raman spectroscopy along the reactions, where it is possible to define homogeneous or heterogeneous co-monomer distributions. Batch addition achieves higher incorporations of co-monomers, compared to dosed addition, where it is possible to determine the maximal co-monomer addition without affecting activities by transfer reactions. The incorporation mode of alfa-olefins in this type of reaction has been little reported, and until it is known, there is no rapid technique available to determine the uniformity of the co-monomer incorporations in real time. Copolymerization kinetics are also reported here and correlated to the addition method of the comonomers in both kinds of reactions. Homogeneous and heterogeneous co-monomer incorporations promoted by a single site catalyst (metallocene) or multisite system (Ziegler-Natta) is related to the homogeneous or heterogeneous co-monomer distributions detected by Raman spectroscopy, using each kind of catalytic system.
RESUMEN
The purpose of this study was to generate novel chitosan hydrogels (CHs) loaded with silver nanoparticles (AgNPs) and ampicillin (AMP) to prevent early formation of biofilms. AgNPs and CHs were characterized by UV-Vis, DLS, TEM, rheology, FT-IR, Raman, and SEM. The antibiofilm effect of the formulations was investigated against four multidrug-resistant and extensively drug-resistant pathogens using a colony biofilm, a high cell density and gradients model. Also, their hemostatic properties and cytotoxic effect were evaluated. Rheology results showed that CHs with AgNPs and AMP are typical non-Newtonian pseudoplastic fluids. The CH with 25 ppm of AgNPs and 50 ppm AMP inhibited the formation of biofilms of Acinetobacter baumannii, Enterococcus faecium and Staphylococcus epidermidis, while a ten-fold increase of the antimicrobial's concentration was needed to inhibit the biofilm of the ß-lactamase positive Enterobacter cloacae. Further, CH with 250 ppm of AgNPs and 500 ppm AMP showed anticoagulant effect, and it was shown that all formulations were biocompatible. Besides to previous reports that described the bioadhesion properties of chitosan, these results suggest that AgNPs and AMP CHs loaded could be used as prophylactic treatment in patients with central venous catheter (CVC), inhibiting the formation of biofilms in their early stages, in addition to their anticoagulant effect and biocompatibility, those properties could keep the functionality of CVC helping to prevent complications such as sepsis and thrombosis.
