Jasna Ivanovic

Application of cellulose acetate for controlled release of thymol

Cellulose acetate (CA) was investigated as a carrier towards development of material with controlled release of thymol as a natural substance with strong antibacterial properties using high pressure techniques. Effect of thymol content on CA was confirmed by SEM, FTIR and DSC methods. Kinetic of thymol release from CA was tested using simulated gastric and intestinal fluids (hydrochloric acid and phosphate buffer saline). Results were correlated with Korsmeyer-Peppas and Weibull model. Depending on the thymol content and chemical nature of the release medium, the time of thymol release varied from one to three days indicating CA as a promising carrier of thymol with potential uses from medicine to agriculture. The impregnated CA showed antibacterial activity against 23 tested bacterial strains including methicillin-resistant Staphylococcus aureus (MRSA) which is particularly important bearing in mind that this strain causes fatal infections in humans and animals.

Functionalization of polycaprolactone/hydroxyapatite scaffolds with Usnea lethariiformis extract by using supercritical CO2.

Investigation of an integrated supercritical fluid extraction and supercritical solvent impregnation process for fabrication of microporous polycaprolactone-hydroxyapatite (PCL-HA) scaffolds with antibacterial activity is presented. The HA content and particle size as well as the operating conditions of the integrated process is optimized regarding the amount of impregnated antibacterial agent (Usnea lethariiformis extract) in the PCL-HA matrix, scaffold morphology and antibacterial activity against methicillin resistant Staphylococcus aureus (MRSA) strains. High pressure differential scanning calorimetry (HP-DSC) assay reveals that an increasing amount of HA results in decreasing melting temperature as well as crystallinity at an operating pressure of 17 MPa. The PCL-HA composites with micrometric sizes of the HA particles are convenient for being processed by the integrated process due to the simple preparation, a good interaction between the PCL matrix and filler and the advantageous impact on sorption. The scaffold obtained from PCL-HA with 20% of the HA shows the highest impregnation yield at 17 MPa and 35 °C (5.9%) and subsequently also the best bactericidal effect on the tested MRSA strains at an initial bacterial inoculum of 2 × 10(-4)CFU/mL.

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%.

The analysis of different processes of extraction: yield of extracts obtained from Aloe vera (Aloe barbadensis Miller) and sweet bay (Laurus nobilis L.) and the exergy analysis of applied processes

The present study was aimed to investigate and compare the efficiency of different methods for the isolation extract from a plant material. Extracts from dried leaves of Aloe vera (A. barbadensis Mill.) and Sweet Bay (Laurus nobilis L.) were obtained applying the following techniques: supercritical carbon dioxide (SC CO2) extraction at 30 MPa and 100°C, a combined ultrasonic extraction and pre-treatment using SC CO2 (US-SCCO2), and a conventional ultrasonic extraction (US) with 96% ethanol. US-SCCO2 resulted in much higher yields of extracts of aloe and bay compared to SC CO2 extraction. Determined extracts yield was used for calculating the maximum useful work and exergy loss as a measure of irreversibility of the extraction process. Calculated maximum useful work per 1 kg of the extract was ranged from 0.7 to 226 kJ while estimated values of the exergy loss were from 48 to 416 kJ per 1 kg of the extract. The maximum useful work and exergy loss have the largest value for SCE much more than for other processes of extraction (US and US-SCCO2). The pre-treatment of the plant material with SC CO2 before an ultrasound-assisted extraction or the decrease of a particle size used for ultrasound-assisted extraction of Aloe vera has led to the decrease of maximum useful work and exergy loss. Unlike, pre-treatment with SC CO2 followed by ultrasound-assisted extraction increased the exergy loss when bay was used as the plant material.

Investigation of antibacterial activity of supercritical extracts of plants, as well as of extracts obtained by other technological processes on some bacteria isolated from animals

The multiresistance of bacteria to antibiotics, as well as the lack of new antibiotics on the market encouraged the research of antibacterial activity of non-antibiotic substances including plant extracts. During the previous decades, it has been proven that extracts of certain plants have a strong antibacterial activity, but their clinical use was limited due to the presence of organic solvents. However, plant extracts obtained by the process of supercritical fluid extraction contain no traces of solvents, and the latest researches have established that they do have antibacterial effects on some gram-positive bacteria. This comparative study included extracts of Common Mullein, Angelica and Echinacea obtained by means of supercritical fluid extraction, Soxlet extraction and ultrasound-assisted extraction. The study of their antibacterial activity was performed on some strains of Staphylococcus, Enterobacter cloacae and E. coli isolated from clinical material of human and animal origin. A referential strain of S. aureus ATCC 25923 was included in the research. In the study broth macrodilution method was applied by which the MIC values of extracts were determined. The Angelica extract obtained by ultrasound-assisted extraction had the strongest antibacterial activity, i.e. the lowest MIC value of 40 μg/mL for S. epidermidis strain. The Angelica extract obtained by supercritical fluid extraction also showed substantial antibacterial activity to all Staphylococcus strains included in this study, with the MIC values of 320 to 640 μg/mL. The extracts of Echinacea and Common Mullein obtained by supercritical fluid extraction, as well as of Echinacea extract obtained by Soxlet extraction showed no antibacterial activity since the MIC values of these extracts were 2560 μg/mL or >2560 μg/mL for all bacterial strains icluded in the study.

Cellulose Acetate Based Material with Antibacterial Properties Created by Supercritical Solvent Impregnation

Supercritical CO2 was used as a green solvent and impregnation medium for loading cellulose acetate beads with carvacrol in order to obtain a biomaterial with antibacterial properties. Supercritical solvent impregnation was performed in a high-pressure view cell at temperature of 50°C and pressures of 10, 21, and 30 MPa with the processing time ranging from 2 to 18 h. The rate of impregnation increased with the pressure increase. However, maximum impregnation yield (round 60%) was not affected by the pressure applied. Selected samples of the impregnated cellulose acetate containing 6–60% of carvacrol were proven to have considerable antibacterial effect against Gram-positive and Gram-negative bacterial strains including methicillin-resistant Staphylococcus aureus which causes severe infections in humans and animals. In addition, cellulose acetate beads containing 6.0–33.6% of carvacrol were shown to have a porous structure with submicron pores which is of interest for the controlled delivery applications.

Antibacterial effects of mixtures of extracts of usnea, thyme and angelica obtained using different technological processes against certain types of bacteria of importance in veterinary medicine

Antibacterial effects of plant extracts were examined using mixtures of extracts obtained using different technological processes: usnea extract was obtained using the process of supercritical extraction (NKE), angelica extract was obtained through supercritical extraction processes (NKE) and ultrasound extraction using ethanol (UZ), and thyme extract was obtained using the process of hydrodistillation (HD). Mixtures of the listed extracts were examined in various ratios: U (NKE) and T (HD) in a ratio of 1:1, U (NKE) and T (HD) in a ratio of 7:3, U (NKE), T (HD) and A (NKE) in a ratio of 2:2:1, and U (NKE), T (HD) and A (UZ) in a ratio of 2:2:1. The investigations covered 15 strains of bacteria of the genus Staphylococcus, Streptococcus and Enterococus, including the strains MRSA, VRE as well as reference strains of S. pyogenes ATCC 19615, S. agalactiae ATCC 27959 and S. aureus ATCC 11632. The antibacterial action of mixes of plant extracts was examined using the microdilution method in bouillon, and the examined mix concentrations were from 1.25 g/mL to 1280 g/mL. The strongest antibacterial effect was exhibited by mixes of usnea (NKE) and thyme (HD) in ratios of 1:1 and 7:3 with obtained MIC values from 5 g/mL to 160 g/mL, but the MIC value of the listed mixtures for the biggest number of strains amounted to 40 g/mL. A somewhat weaker effect was exhibited by the other examined extract mixtures with obtained MIC values of 10 g/mL to 320 g/mL. Based on the obtained MIC values and the results of previous investigations, it can be concluded that the examined mixtures of plant extracts exhibited a very strong antibacterial effect on the examined bacteria strains. .