Skin burns and ulcers are considered hard-to-heal wounds due to their high infection risk. For this reason, designing new options for wound dressings is a growing need. The objective of this work is to investigate the properties of poly (ε-caprolactone)/poly (vinyl-pyrrolidone) (PCL/PVP) microfibers produced via electrospinning along with sorbents loaded with Argovit™ silver nanoparticles (Ag-Si/Al2O3) as constituent components for composite wound dressings. The physicochemical properties of the fibers and sorbents were characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The mechanical properties of the fibers were also evaluated. The results of this work showed that the tested fibrous scaffolds have melting temperatures suitable for wound dressings design (58–60 °C). In addition, they demonstrated to be stable even after seven days in physiological solution, showing no macroscopic damage due to PVP release at the microscopic scale. Pelletized sorbents with the higher particle size demonstrated to have the best water uptake capabilities. Both, fibers and sorbents showed antimicrobial activity against Gram-negative bacteria Pseudomona aeruginosa and Escherichia coli, Gram-positive Staphylococcus aureus and the fungus Candida albicans. The best physicochemical properties were obtained with a scaffold produced with a PCL/PVP ratio of 85:15, this polymeric scaffold demonstrated the most antimicrobial activity without affecting the cell viability of human fibroblast. Pelletized Ag/Si-Al2O3-3 sorbent possessed the best water uptake capability and the higher antimicrobial activity, over time between all the sorbents tested. The combination of PCL/PVP 85:15 microfibers with the chosen Ag/Si-Al2O3-3 sorbent will be used in the following work for creation of wound dressings possessing exudate retention, biocompatibility and antimicrobial activity.
Recently, we developed methods of synthesis of an original group of 2-imidazoline nitroxides containing imidazol-4-yl substituents in the side chain and a series of their heterospin metal complexes [1,2]. A specific feature inherent in Fur-135 and Fur-176 is their abnormally high solubility and kinetic stability in aqueous solutions. These facts prompted us to study the in-principle possibility of using these nitroxides as contrast agents for magnetic resonance imaging (MRI). Our study revealed the high efficiency of these compounds as contrast agents for generation of magnetic resonance (MR) images. MRI visualization, which makes possible the rapid and noninvasive study of living tissues and the efficient visualization of pathological processes [3], is based on the difference in the spin-lattice ( T 1) and spin-spin ( T 2) relaxation rates of protons in biological tissues. Different pulse sequences used in MRI allow one to obtain images whose contrast is dominated by the T 1 or T 2 relaxation times [4]. At the same time, even the state-of-the-art technology does not always provide a sufficient level of visualization of the tissue to be studied. Special compounds are used for enhancing the signal from pathological foci. These compounds can be taken up into lesions and are able to enhance the con- Fur-135Fur-176trast of T 1-or T 2-weighted images ( T 1-WIs and T 2-WIs) [5,6]. Basically, these are Gd 3+ salts with polydentate ligands, such as deprotonated diethylenetriaminepentaacetic acid (the preparations Magnevist and Omniscan) [6]. Manganese and iron compounds (Teslascan, Abdoscan) are sometimes used. However, despite the high contrast of the images obtained with the use of these preparations, their application is associated with some risk. Cases of the development of anaphylactic reactions of the immune system and of kidney disorder have been documented [7]. For this reason, a paramagnetic metal ion that enhances the spin relaxation is, as a rule, introduced as a coordination compound with a high-denticity organic ligand. Such ligands should not only neutralize the charge on the metal ion but also firmly hold it in a complex since the human body has a very low tolerance for free transition metal ions [8].The thermodynamic stability of complexes can be enhanced only due to the chelate effect of polydentate ligands since, for rare-earth ions and highspin Mn 2+ and Fe 3+ ions with the d 5 electronic configuration, the crystal field stabilization energy upon complex formation is zero [9]. However, the natural limitation on the number of coordination sites (no more than 6-9) puts a limit on the thermodynamic stability of these complexes. In addition, specially synthesized polydentate ligands, such as diethylenetriaminepentaacetic acid ( H 5 DTPA ), are not metabolites and are foreign substances in living organisms. An alternative approach to the solution of the problem of safe application of contrast agents can be the use of purely organic paramagnets based on nontoxic stable nitroxide radicals. An additional adva...
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