NANOMETRIC CELLULOSIC LAYERS FOR SPECIFIC ADSORPTION OF POLYSACCHARIDES AND IMMOBILIZATION OF BIOACTIVE MOLECULESTamilselvan Mohan
, 2012, doktorska disertacija
Opis: The aim of the thesis is to investigate the applicability of nanometric amorphous cellulose model films for the immobilization of functional DNA molecules and to apply this knowledge in the field of DNA microarray preparation. To achieve this aim, the whole thesis work is divided into three major parts, namely part I (partly and fully regenerated cellulose film preparation and its characterization), part II (functional polysaccharide conjugates preparation) and part III (DNA microarray preparation from polysaccharide functional conjugates).
The first part of the work mainly focuses on the preparation of cellulose model films from spin coated trimethylsilyl cellulose (TMSC) using an in-situ and ex-situ regeneration methods and its characterization. In the in-situ method, the conversion of TMSC to pure cellulose via acid vapor hydrolysis is investigated at the gas-solid interface in real time and at ambient conditions employing quartz crystal microbalance with dissipation (QCM-D). For this purpose, a permanent flow of gaseous HCl is employed which reacts with TMSC coated surface to form pure cellulose. The kinetics behind this reaction is elucidated and reveals first order. Moreover, the influence of the acid concentration on the kinetics and on changes in mass and film thickness of TMSC is studied.
In the case of an ex-situ method, partly and fully regenerated cellulose model films are prepared from spin coated TMSC films through acid vapor phase hydrolysis. This is done by exposing the TMSC films placed in a closed container to vapors of HCl. The regeneration is carried out on one hand by exposing the films to different time intervals and on the other hand to different volume of HCl. The changes in surface morphology, structure, surface composition and film thickness in the course of regeneration (i.e. desilylation) is studied by using various surface analytical techniques like atomic force microscopy (AFM), attenuated total reflectance infrared spectroscopy, X-ray photoelectron spectroscopy (XPS) and ‘Sarfus’-technique. In order to gain detailed insight into the desilylation reaction of the films the results from ATR-IR, XPS and thickness measurements are compared with data from static contact angle (SCA) and surface free energy (SFE) determination.
Besides, to verify the completion of regeneration of cellulose from TMSC the partly and fully regenerated films prepared using ex-situ method are interacted with cellulase enzymes from Trichoderma viride using QCM-D technique. The changes in mass and energy dissipation due to the interaction of the enzymes with the substrates are correlated with the surface wettability and elemental composition of the regenerated films. The enzymatic degradation rate correlated well to the rate of regeneration. It is demonstrated that capillary zone electrophoresis (CZE) can be used to support QCM-D data via the detection of enzyme hydrolysis products in the eluates of the QCM-D cells. It is also shown that a combination of QCM-D together with enzymatic digestion is a reliable method to monitor the time dependent regeneration of TMSC to pure cellulose.
Furthermore, the effect of heat treatment on partly and fully regenerated cellulose films prepared using ex-situ method is investigated by exposing the films to elevated temperature (105 °C) for a prolonged time (6 hours). Upon heating, a structural rearrangement in the films from a featureless to a fibrillar-like structure is observed as evidenced by AFM. Several analytical methods, namely GIXRD, ATR-IR, Sarfus, XPS and SCA data are employed to analyze the alteration in the structure, surface composition, film thickness, wettability and SFE of the time dependent regenerated films before and after heat treatment. Results from solvent (D2O/H2O) exchange studies proved that water content and water uptake capacity of heat treated cellulose films are significantly reduced compared to non heated films.Additionally, a new method is developed to structure nanometric cellulose films via vapor phase acid hydrolysis and enzymat
Ključne besede: Cellulose model films, carboxymethyl cellulose, trimethylsilyl cellulose, microarrays, quartz crystal microbalance, carbodiimide coupling, aminofluorescein, DNA
Objavljeno: 28.11.2012; Ogledov: 1586; Prenosov: 95
Celotno besedilo (6,46 MB)
STRUCTURING OF SOL-GEL FUNCTIONALIZED CELLULOSE HYBRID MATERIALS AND THEIR CHARACTERIZATIONHeike M. A. Ehmann
, 2012, doktorska disertacija
Opis: The goal of this thesis is the structuring of cellulose nanocrystals using different organofunctional silane compounds and different cationic species to prepare highly functional materials with tailored properties. In addition different new aspects and approaches for the structural characterization of functionalised cellulose nanocrystals (CNC) functionalised with different organofunctionalalkoxysilanes as well as cationic species have been introduced.
Cellulose nanocrystals (CNC) are prepared using three different acidic conditions to hydrolyse microcrystalline cellulose (MCC). The sulphuric acid hydrolysis introduces highly negative charged sulphate groups on the CNC. The aqueous nanocrystalline cellulose suspensions (aNCS) are analysed in terms of ζ-potential related to the pH and concentration to investigate the stability while dynamic light scattering (DLS) is used to investigate the size distribution. The hydrochloric acid hydrolysis in contrast only removes the amorphous regions but the so obtained CNC are less stabilized (decreased ζ-potential) and tend to agglomerate very fast. The use of the mixture of both acids (HCl and H2SO4) during the hydrolysis of MCC introduces less sulphate groups compared with the sulphuric acid hydrolysis. AFM investigations show that the shapes of the CNC are highly influenced by the hydrolysis conditions. While the shape of the H2SO4 hydrolysed CNC is rod like, while the shape of the other two CNC samples is more spherical in nature. One of the major topic in this work is the analysis of aNCS in aqueous solutions by small angle x-ray scattering (SAXS). The use of the generalized indirect Fourier transformation (GIFT) method allows the analysis of these systems and structural properties such as shape, size and surface charge of aNCS can be assessed. Using this kind of characterisation it can be seen that the shape of the H2SO4 hydrolysed CNC is definitely rod like while the other CNC sample can be described with spheres. In addition to the aNCS characterisation different substrates (Si-wafer, glass slides, polystyrene, etc.) are equipped with aNCS using a variety of different deposition methods (e.g. spin coating, solution casting, dip coating). The resulting films are studied in terms of morphology AFM, SARFUS and SEM. Sophisticated scattering techniques are employed for surface structural characterisation as grazing incidence small angel x-ray scattering. The determination of surface free energies allows conclusions about the hydrophilicity and hydrophobicity as well as the interaction capacity with different liquids. It can be seen that besides the hydrophilic nature of the CNC also hydrophobic interactions are present. The highly negative charged CNC sample which was prepared using sulphuric acid hydrolysis is found to be best suitable for the further hybridization with different organofunctional silanes and for the layer by layer approach (LBL) with different cationic species.
The organofunctionalalkoxysilanes which were used in this study can be divided into three groups (e.g filler, surface functionalisation silanes, cross linking silanes). Depending on the nature of the organic residue the silanes are capable to introduce functionalities with enhanced hydrophobic and olephobic properties. The surface energies are investigated using contact angle method, while the surface energies are calculated using three different model approaches (OWRK, Wu, Acid-Base). The most increased hydrophobic and oleophobic properties were measured for trimethylfluorophenylsilantriol (PFTEOS). The morphology of the coated silanes is investigated using SAFRUS technique. It can be seen that nearly all silanes can be coated as homogeneous films onto different substrates (Si-wafer, SURFs, glass slides) with different methods (spin coating, solution casting). The macroscopic appearance of solution casted silanes is investigated using optical microscopy. The differences of the structural nature of the so obtained coatings and detaching films were investigated...
Ključne besede: Cellulose nanocrystals, sol-gel chemistry, organofunctionalalkoxysilanes, hybrid materials, small angle x-ray scattering, generalized indirect Fourier Transformation, quartz crystal microbalance dissipation, surface free energy, surface functionalisation, layer by layer
Objavljeno: 28.11.2012; Ogledov: 1539; Prenosov: 95
Celotno besedilo (8,59 MB)
Antimicrobial medical textiles based on chitosan nanoparticles for gynaecological treatmentTijana Ristić
, 2014, doktorska disertacija
Opis: The aim of this dissertation was to develop a novel medical tampon for alternative gynaecological treatment using chitosan nanoparticles as an antimicrobial agent or as a drug delivery system. For this purpose viscose tampon band was used and functionalized with chitosan and trimethyl chitosan nanoparticles. A comprehensive of interactions between chitosan and cellulose as well as characterization of prepared materials were done. At the beginning, chitosan (CS) and trimethyl chitosan (TMC) solutions, as well as nanoparticles synthesised by ionic gelation were studied. Their characterization was focused on determining the charge and antimicrobial properties against common pathogenic microorganism. The influence of cationic charge on the inhibition of microbial growth was confirmed. Since CS and TMC solutions and nanoparticles dispersions exhibited antibacterial activity against Lactobacillus, a detailed investigation in chitosan’s antimicrobial mode of action was performed using a novel diffusion nuclear magnetic resonance (D-NMR). D-NMR allowed the monitoring of intra- and extracellular water exchange from the cells indicating the membrane alteration and leakage of intracellular constituencies. Further, in order to study the adsorption phenomena and molecular interactions between CS/TMC (solution or nanoparticles) and cellulose material, model cellulose surfaces were used, and adsorption was studied by quartz crystal microbalance with dissipation. CS and TMC were favourably deposited onto cellulose model surface at higher ionic strength, higher pH values, i.e. factors causing lower solubility, where the presence of electrostatic interactions was negligible and non-electrostatic interactions were dominant. The knowledge gained from the model surfaces was extremely helpful in characterization of real systems, i.e. functionalized cellulose fibres and for understanding the obtained results. Immobilization of CS and TMC (in the form of solution and/or nanoparticles) onto cellulose viscose fibres was confirmed with several analytical methods. The attachment of chitosan onto fibres was reversible, as endorsed with desorption studies mimicking the conditions of vaginal usage. Evaluation of antimicrobial properties was performed using two different techniques, both revealing a high inhibition of the tested microorganism. In addition, Lactobacillus susceptibility testing has shown that chitosan-coated fibres do not have any negative influence on the resident microbiota. Assessment of in-vitro cytotoxicity demonstrated that samples do not cause a cytotoxic effect in direct contact. Additionally, model drug was incorporated into chitosan nanoparticles and subsequently attached onto fibres in order to create modern, vaginal drug delivery systems. Antimicrobial medical textiles investigated in the scope of this dissertation show the potential for their exploitation in gynaecological field as preventive or curative treatment without triggering any adverse effects for the user.
Ključne besede: chitosan, N, N, N-trimethyl chitosan, nanoparticles, antimicrobial activity, cellulose model films, regenerated cellulose fibres, diffusion nuclear magnetic resonance, quartz crystal microbalance, vaginal infections, drug delivery systems, cytotoxicity
Objavljeno: 13.02.2014; Ogledov: 1941; Prenosov: 75
Povezava na celotno besedilo
Hemicelluloses application for synthetic polymer surfaces functionalisationNena Dimitrušev
, 2016, doktorska disertacija
Opis: The main aim of this thesis was development of thin functional layers from hemicelluloses xylans on the polyethylene terephthalate (PET) surfaces. Hemicelluloses, xylans, as renewable polymers, were chemically modified in order to introduce anionic and cationic functional groups. Two types of chemical modifications were performed: carboxymethylation in order to increase anionic nature of xylans and improve their hydrophilic character and cationization for introducing of amino groups and antimicrobial characteristics. Both types of modifications were successful, which was proved by ATR FTIR and raman techniques, elemental analysis, total bound nitrogen determination, size exclusion chromatography and polyelectrolyte titrations. Polyelectrolyte titration results showed increased amounts of deprotonated carboxyl groups in carboxymethylated xylans as well as increased amounts of protonated groups in cationized xylans. Antimicrobial activity of xylans was investigated by the determination of minimal inhibitory concentration (MIC) against S. aureus, E. coli, and C. albicans and it was found out that the samples with higher amounts of active amino groups showed lower MIC. Cationised glucuronoxylan showed significantly higher antimicrobial activities against S. aureus in comparison to cationised arabinoxylan and nonmodified xylan samples. However, none of xylan samples was active against fungi. In order to analyze surface properties of solid surfaces, films from xylan (nonmodified and modified) water solution was formed by casting method. The surface chemical composition of films were investigated by x-ray photoelectron spectroscopy (XPS), and the results showed that films made from carboxymethylated xylans had significantly higher amounts of carbon fraction involved in O=C-O bonds, compared to nonmodified xylans. Such surface chemical structure caused higher surface free energy with higher electron-donor contribution and thus high hydrophilicity of these films. Films made by cationized xylans had higher amount of carbon involved in C-C and C-H bonds compared to nonmodified and lower surface free energy with increase of dispersive Lifshitz Van der Waals contribution. In order to thoroughly investigate the adsorption of xylans onto synthetic surfaces Quartz crystal microbalance with dissipation unit (QCM-D) was used. For these measurements model films were prepared from PET by spin coating technique. Adsorption studies were performed at different conditions, such as pH, concentration and ionic strength of xylan solutions. For all the chemically modified xylans the adsorption was improved at pH 5 and with increased ionic strength with divalent ions. The adsorption increased as well with increasing of xylan solution concentration. In order to improve binding of adsorbed xylans so-called anchoring polymers were applied. When anchoring polymers were applied, better adsorption and fixation of adsorbed layer was confirmed, thus the adsorbed masses of xylans after rinsing with water were significantly higher in comparison to the adsorption without immediate anchoring layer. On the basis of these results, real PET fabric surfaces were treated using chemically modified xylans. The xylan solutions were applied onto PET fabric samples using spray coating technique, which is the best approximate to the large-scale procedures. In the first step, PET fabric was activated by alkaline hydrolysis and after that, anchoring agents and carboxymethylated and/or cationized xylans were adsorbed. The success of these treatments was evaluated by the determination of negative and positive charge of the treated PET fabric samples by titration techniques, methylene blue and acid orange 7 adsorption methods, water contact angles and wettability determination. From the potentiometric titrations results it was clearly seen that each new adsorbed layer onto PET fabric totally screened the charge of the former one. FESEM images showed rather thick layers covering the
Ključne besede: hemicellulose, polyethylene terephthalate, glucuronoxylan, arabinoxylan, carboxymethylation, cationization, PET model films, quartz crystal microbalance, PET fabric, surface free energy, wettability, antimicrobial properties
Objavljeno: 11.03.2016; Ogledov: 852; Prenosov: 62
Celotno besedilo (4,53 MB)
Protein adsorption on various plasma-treated polyethylene-terephthalate substratesNina Recek
, Morana Jaganjac
, Metod Kolar
, Lidija Milković
, Miran Mozetič
, Karin Stana-Kleinschek
, Alenka Vesel
, 2013, izvirni znanstveni članek
Opis: Protein adhesion and cell response to plasma-treated polymer surfaces were studied. The polymer polyethylene terephthalate (PET) was treated in either an oxygen plasma to make the surface hydrophilic, or a tetrafluoromethane CF4 plasma to make the surface hydrophobic. The plasma source was radiofrequency (RF) discharge. The adsorption of albumin and other proteins from a cell-culture medium onto these surfaces was studied using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The cellular response to plasma-treated surfaces was studied as well using an MTT assay and scanning electron microscopy (SEM). The fastest adsorption rate was found on the hydrophilic oxygen plasma-treated sample, and the lowest was found on the pristine untreated sample. Additionally, the amount of adsorbed proteins was higher for the oxygen-plasma-treated surface, and the adsorbed layer was more viscoelastic. In addition, cell adhesion studies support this finding because the best cell adhesion was observed on oxygen-plasma-treated substrates.
Ključne besede: oxygen and fluorine plasma treatment, polymer surface modification, protein adsorption, cell adhesion, quartz crystal microbalance, QCM
Objavljeno: 22.06.2017; Ogledov: 258; Prenosov: 190
Celotno besedilo (2,39 MB)
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