Abstract
The present study investigated the structure, morphology, thermal behavior, and bacterial growth analysis of novel three-component hybrid materials synthesized by the sol-gel method. The inorganic silica matrix was weakly bonded to the network of two organic components: a well-known polymer such as polyethylene glycol (PEG, average molar mass of about 4000 g/mol), and an antioxidant constituted by chlorogenic acid (CGA). In particular, a first series was made by a 50 wt% PEG-based (CGA-free) silica hybrid along with two 50 wt% PEG-based hybrids containing 10 and 20 wt% of CGA (denoted as SP50, SP50C10 and SP50C20, respectively). A second series contained a fixed amount of CGA (20 wt%) in silica-based hybrids: one was the PEG-free material (SC20) and the other two contained 12 and 50 wt% of PEG, respectively (SP12C20 and SP50C20, respectively), being the latter already included in the first series. The X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images of freshly prepared materials confirmed that all the materials were amorphous and homogeneous regardless of the content of PEG or CGA. The thermogravimetric (TG) analysis revealed a higher water content was adsorbed into the two component hybrids (SP50 and SC20) because of the availability of a larger number of H-bonds to be formed with water with respect to those of silica/PEG/CGA (SPC), where silica matrix was involved in these bonds with both organic components. Conversely, the PEG-rich materials (SP50C10 and SP50C20, both with 50 wt% of the polymer) retained a lower content of water. Decomposition of PEG and CGA occurred in almost the same temperature interval regardless of the content of each organic component. The antibacterial properties of the SiO2/PEG/CGA hybrid materials were studied in pellets using either Escherichia coli and Enterococcus faecalis, respectively. Excellent antibacterial activity was found against both bacteria regardless of the amount of polymer in the hybrids.
Highlights
All the results obtained in this study are discussed in four distinct sections: the structural and morphological characterization, the thermal behavior study (Section 3.2), the Fourier transform infrared (FTIR) study (Section 3.3) and the analysis of antibacterial properties in pellets by treating the materials with Escherichia coli and Enterococcus faecalis (Section 3.4)
Organic–inorganic three-component hybrid materials with a well-defined composition have been prepared by the sol-gel method
The inorganic silica matrix reacted with two organic components, a polymer that increases the hydrophilicity of the resulted hybrids and a non-flavonoid polyphenolic compound, chlorogenic acid (CGA), because of its good antibacterial, anti-inflammatory, and antioxidant properties
Summary
When pro-oxidant species are overproduced and/or the biological repairing mechanisms are not so effective, the homeostatic processes may fail, compromising the usual prooxidative/antioxidative cellular balance. Under this severe condition, namely “oxidative stress”, reactive oxygen and nitrogen species (denoted as ROS and RNS, respectively), and lipid peroxidation (LPO) products commonly promote tissue damage and cellular injury [1,2]. The study of the thermo-oxidative behavior of ultra-high molecular weight polyethylene (UHMWPE)-based nanocomposites recently revealed that sonication of carbon nanotubes has a detrimental effect on the thermo-oxidative stability of nanocomposites, especially for long exposure times [3]
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