Veljko Djokic

Novel modified nanocellulose applicable as reinforcement in high-performance nanocomposites

The influence of modification and vacuum/supercritical CO2 (scCO2) drying methods on the surface properties, morphology and thermal stability of cellulose nanocrystals (NC) was presented in this study. Introduction of reactive vinyl groups on NC surface was performed by either direct esterification with oleic acid, linseed or sunflower oil fatty acids; or by amidation of maleic acid/ethylene diamine with methyl ester of fatty acid. Obtained modified NC (m-NC) were characterized using FTIR and Raman spectroscopy; and by determination of acid, iodine and ester values. Structural analysis of m-NC showed varieties of forms, from spongy to nanostructural non-uniform layered morphology with observable agglomeration, which confirmed morphology dependence on modification/processing methods Thermogravimetry-MS spectrometry showed different thermal stability and degradation pathways of NC/m-NC. Incorporation of 1 wt% of reactive m-NC in unsaturated polyester lead to high performance nanocomposites and contributed to increase of stress at break in the range from 76 to 93%.

Enhanced absorption of TiO2 nanotubes by N-doping and CdS quantum dots sensitization: insight into the structure

Anodization of titanium film sputtered on fluorine doped tin oxide (FTO) glass was performed to obtain highly ordered ∼2 μm long and ∼60 nm wide TiO2 nanotubes. The titania films were annealed in ammonia atmosphere to enable the doping with N. The annealing did not affect the nanotubular morphology and the porosity remained open which is a very important requirement for further deposition of CdS quantum dots. The analysis done by transmission electron microscopy (TEM) has shown that the N-doped nanotubes have a smaller interplanar distance as compared to the undoped ones, whose interplanar distance corresponded to anatase phase. This difference was attributed to the N doping and the Sn migration from the substrate, as demonstrated by energy dispersive spectroscopy (EDS) combined with electron energy loss spectroscopy (EELS). The near edge X-ray absorption fine structure (NEXAFS) analysis clearly demonstrated that also the doped TiO2 film has anatase phase. Regarding the chemical composition of the studied samples, the X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoelectron spectroscopy (SRPES) analyses have shown that N is incorporated both interstitially and substitutionally in the TiO2 lattice, with a decreased contribution of the interstitial after ionic sputtering. The shift of the valence band maximum (VBM) position for the doped TiO2 vs. the undoped TiO2 proved the narrowing of the band gap. The CdS/TiO2 films show bigger VBM shifting that can be attributed to CdS deposit. Comparing the absorption spectra of the bare undoped and doped TiO2 samples, it was noticed that the doping causes a red shift from 397 to 465 nm. Furthermore, the CdS deposition additionally enhances the absorption in the visible range (575 nm for undoped TiO2/CdS and 560 nm for doped TiO2/CdS films).

Cefazolin-loaded polycaprolactone fibers produced via different electrospinning methods: Characterization, drug release and antibacterial effect

ABSTRACT Antibiotic containing polycaprolactone (PCL) fibers were produced by using three electrospinning methods: blend, emulsion and co‐axial electrospinning (labeled as S1, S2 and S3, respectively). The profiles of drug release from three different systems were studied and antimicrobial properties of produced materials were evaluated. Morphology of the produced fibers was characterized and revealed that cefazolin‐loaded PCL fibers had smaller diameter compared to neat PCL fibers, while the chemical interaction between the antibiotic and PCL showed that cefazolin neither had reacted with PCL phase, nor had degraded during the electrospinning process. The crystallinity and thermal characterization of fabricated fibers showed that the addition of cefazolin decreased the crystallinity of PCL. The results of the drug release behavior of the blend and co‐axial electrospun fibers was on a higher level (˜68% and ˜43%, respectively) compared to the emulsion electrospun fibers (˜5%), after a period of 30days. The obtained data had the best fitting with the first order model and the Higuchi model, while the Korsmeyer‐Peppas model showed a Pseudo‐Fickian diffusion of the drug. Antibacterial evaluations showed that cefazolin‐loaded PCL fibers had better effects on Staphylococcus aureus compared to Escherichia coli during the treatment period and that the effect of the emulsion fibers was notably weaker than the other two studied systems. The aim of the study was to test different systems for control drug release of different dynamics, which will be applied for prevent bacterial accumulation when indwelling urinary catheters, applied for different periods of time.