Synthesis and use of organic biodegradable aerogels as drug carriersAnja Veronovski
, Zoran Novak
, Željko Knez
, 2012, izvirni znanstveni članek
Opis: Aerogels of natural polysaccharides possess both biocharacteristics of polysaccharides, such as good biological compatibility and cell or enzyme-controlled degradability, and aerogel characteristics, such as very high porosity and specific surface areas that makes them highly attractive in drug delivery. Biodegradable alginate aerogels were synthesized via a sol-gel process. In the present work two methods of ionic cross-linking were used to prepare alginate hydrogels as monoliths and spheres, which can be further easily converted to high surface area aerogels. The aerogels obtained were further used as drug carriers. We investigated the effect of process parameters, such as starting concentration and viscosity of alginate solution, on synthesis products and on model drug (nicotinic acid) release. The results indicate that by using the internal setting cross-linking method for obtaining monolithic aerogels nicotinic acid was released in a more controlled manner. The aerogels thus obtained also exhibited smaller volume shrinkage than the ones described in other publications. However, with increasing alginate concentration in both types of synthesis more compact and cross-linked aerogels were formed.
Ključne besede: organic biodegradable gels, natural polysaccharides, aerogels, drug cariers
Objavljeno: 01.06.2012; Ogledov: 998; Prenosov: 36
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Rheological studies of concentrated guar gumMarija Oblonšek
, Sonja Šostar-Turk
, Romano Lapasin
, 2003, izvirni znanstveni članek
Opis: Polymers and surfactants are essential ingredients of the printing paste. Polysaccharides are used commercially to thicken, suspend or stabilise aqueoussystems. Also they are used to produce gels and to act as flocculates, binders, lubricants, to serve as modifiers of film properties, and have a function as adjusters of rheological parameters. Surfactants, on the other hand, perform numerous functions acting as dispersants, wetting agents, emulsifiers and antifoaming agents. The rheological properties of polysaccharide thickeners (guar gums with different substitution levels and different producers) at different concentrations and temperatures and, second,the effects produced by the addition of nonionic surfactants (polyoxyethylene stearyl alcohols with different numbers of EO groups) have been studied under linear and nonlinear shear conditions. Experimental data have been correlated with the different modelsČ flow curves with the Cross, Carreau and Meter-Bird model, and mechanical spectra with the generalized Maxwell model and Friedrich-Braun model. The surface tensions of aqueous systems containing polysaccharide andžor surfactants have been determined overextended concentration ranges in order to detect the CMC conditions and toprovide a better understanding about the polysaccharide-surfactant interactions.
Ključne besede: textile printing, printing pastes, polysaccharides, thickeners, rheology, viscoelasticity, surfactants, guar gum
Objavljeno: 01.06.2012; Ogledov: 1125; Prenosov: 6
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Surface modification of silicone with polysaccharides for the development of antimicrobial urethral cathetersMatej Bračič
, 2016, doktorska disertacija
Opis: In this work, alternative polysaccharide-based coatings were used to improve the antimicrobial and antifouling properties of silicone surfaces used for urethral catheters. The introduction of a catheter in the urethra is commonly connected with a high risk of microbial infections which often result in long-term health damage. Polysaccharide-based coatings like chitosan, carboxymethyl chitosan, and a synergistic formulation between hyaluronic acid and a natural lysine-based surfactant, were used to treat silicone surfaces to overcome the infection problems as an alternative to conventional approaches, which include the administration of antibiotics or coatings with metal ions. The polysaccharide-based macromolecular solutions and dispersions were firstly characterised by means of pH-titrations, dynamic light scattering and scanning electron microscopy in order to determine the size of particles in dispersions and their pH dependant charging behaviour. The knowledge gained from this was used to thoroughly study the interactions of the polysaccharide-based solutions and dispersions with the model silicone surfaces. The model surfaces were ultra-thin films prepared by dissolution of silicone in toluene and subsequent spin-coating on quartz crystals. The influence of pH, salt concentration, and various surface activation processes on the adsorption behaviour was evaluated by means of a very precise quartz crystal microbalance with dissipation. This knowledge was transferred to the application of the coatings on real systems i.e. casted silicone sheets and silicone tubes. The surface morphology, surface chemistry, as well as the mechanical and chemical stability of the coatings were further characterised on both model and real systems. For this purpose different microscopy and spectroscopy methods, pH-potentiometric titrations and methods for evaluation of mechanical properties were used. Finally the antimicrobial and antifouling properties were evaluated. The antimicrobial properties were tested against gram-positive and gram-negative bacteria as well as fungi, which are commonly found in infected urine, while the antifouling properties were tested by measuring the adhesion of bovine serum albumin, fibrinogen, and lysozyme biomolecules onto functionalised model films using the quartz crystal microbalance. The results showed that homogeneous and stable coatings can be achieved by adsorption from dispersions of the polysaccharide-based nanoparticles of 200-300 nm in size, which are formed by precipitation; i.e. careful pH adjustments of chitosan to pH = 6.5, carboxymethyl chitosan to pH = 7, and by mixing the hyaluronic acid and natural lysine-based surfactant solutions at concentrations of 2.5 x 10-4 mol/L and 1.25 x 10- 3 mol/L for the hyaluronic acid and 5.0 x 10-4 mol/L and 1.2 x 10-3 mol/L for the surfactant, respectively . The mass of the coatings on model silicone films can be increased by a 3-step adsorption, which directly influences the antimicrobial properties of the coatings that are improved with increasing coating mass, reaching values of up to 90 % in reduction of microorganism growth. It was also shown that the hyaluronic acid-natural surfactant formulation is superior to the chitosan coatings. The same conclusions were drawn from the antifouling evaluation where the zwitterionic nature of the formulation between natural based lysine surfactant and HA successfully suppressed the adhesion of biomolecules on silicone surfaces, while the chitosan coatings only moderately prevented the adhesion of proteins. One can conclude that the polysaccharide-based coatings can be successfully introduced to silicone surfaces from dispersion and as such successfully prevent biomolecule adhesion and reduce the growth of pathogen microorganisms which can be found in the urine during urethral infections.
Ključne besede: Urethral catheters, Antimicrobial coatings, Silicone, Polysaccharides, Natural surfactants
Objavljeno: 24.10.2016; Ogledov: 573; Prenosov: 72
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Formation, characterization and application of polysaccharide aerogelsGabrijela Horvat
, 2018, doktorska disertacija
Opis: The aim of this PhD dissertation was to describe and analyze the preparation and characterization of polysaccharide aerogels and their future pharmaceutical and medical application. For the research, we used four types of polysaccharides: pectin, alginate, xanthan and guar. We used two types of pectin, high-methoxyl and low-methoxyl pectin, because of their different gelation mechanisms. The first part of the dissertation describes the preparation and characterization of pure polysaccharide aerogels. First, we prepared pectin spherical aerogels, cross-linked with three different ions, and we investigated their final properties. Later, we developed a new method for the preparation of alginate, pectin, xanthan and guar aerogels. We used only ethanol and no other cross-linkers. Ethanol was removed in the later processes of supercritical drying, and the remaining final material was thus only porous polysaccharide. By this method, we were able to prepare pure xanthan and guar aerogels. Prior to this study, xanthan and guar aerogels were prepared only as composites. Pectin aerogels prepared by the new method have amazing properties. On the other hand, alginate aerogels show poor characteristics, and thus the methods need to be optimised. We tried different alginate viscosities, different alcohols (methanol, ethanol, 1-propanol and 1-butanol), and we investigated longer (24h) and shorter (1h) gel setting times.
The second part of this dissertation describes the pharmaceutical and medical applications of prepared aerogels. The release of diclofenac sodium from spherical pectin aerogels was investigated in vitro. Calcium cross-linked aerogels were not able to retain the drug, and its release was immediate. In order to achieve controlled release of diclofenac sodium, zinc ions had to be used as cross-linkers. Later, a low water-soluble drug, nifedipine, was used as a model drug for the monolithic aerogels prepared by the new method. The release of nifedipine from pectin and alginate aerogels was highly increased, compared to the crystalline drug. This result is promising for future evaluation of these materials for increasing the bioavailability of poorly water-soluble drugs. Nifedipine release from xanthan and guar aerogels was prolonged up to two weeks. This result reveals a new perspective on such materials for their potential use in medicine as implants and local drug delivery. According to these results, we then developed a new coating material for medical-grade stainless steel from xanthan and pectin. An aerogel coating was loaded with diclofenac sodium and indomethacin, and their release profiles were investigated in vitro. Electrochemical analysis and cell tests proved the safety of such materials for use in medicine. Using aerogel coatings, the drug can be introduced locally into the body; therefore, the need for intravenous, post-operational treatment is greatly reduced.
Ključne besede: polysaccharides, aerogels, supercritical drying, drug carriers
Objavljeno: 09.04.2018; Ogledov: 99; Prenosov: 21
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