Browsing by Author "Miguel, M. G."
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- Cyclodextrin-grafted cellulose: physico-chemical characterizationPublication . Medronho, B.; Andrade, R.; Vivod, V.; Ostlund, A.; Miguel, M. G.; Lindman, B.; Voncina, B.; Valente, A. J. M.Cyclodextrins (CDs) can form inclusion complexes with a wide variety of molecules making them very attractive in different areas, such as pharmaceutics, biochemistry, food chemistry and textile. In this communication we will report on the physico-chemical characterization of cellulose modified with CDs by means of infra-red spectroscopy (FTIR), cross polarization magic angle spinning solid state nuclear magnetic resonance (CP-MAS NMR), polarized optical microscopy (POM) and thermal gravimetric analysis (TGA). Both CP-MAS NMR and FTIR indicate that CDs are chemically attached to cellulose backbone through the formation of ester bonds. Furthermore, the CD-grafted cellulose was dissolved in a "superphosphoric" acid solution but, despite the increase of hydrophilicity due to the modification, POM revealed that grafted cellulose was less soluble when compared to the unmodified polymer. The formation of a complex CD-cellulose network is suggested. (C) 2012 Elsevier Ltd. All rights reserved.
- Development of carboxymethyl cellulose-chitosan hybrid micro- and macroparticles for encapsulation of probiotic bacteriaPublication . Singh, P.; Medronho, B.; Alves, L.; da Silva, G. J.; Miguel, M. G.; Lindman, B.Novel carboxymethyl cellulose-chitosan (CMC-Cht) hybrid micro- and macroparticles were successfully prepared in aqueous media either by drop-wise addition or via nozzle-spray methods. The systems were either physically or chemically crosslinked using genipin as the reticulation agent. The macroparticles (ca. 2 mm) formed are found to be essentially of the core-shell type, while the microparticles (ca. 5 tim) are apparently homogeneous. The crosslinked particles are robust, thermally resistant and less sensitive to pH changes. On the other hand, the physical systems are pH sensitive presenting a remarkable swelling at pH 7.4, while little swelling is observed at pH 2.4. Furthermore, model probiotic bacteria (Lactobacillus rhamnosus GG) was for the first time successfully encapsulated in the CMC-Cht based particles with acceptable viability count. Overall, the systems developed are highly promising for probiotic encapsulation and potential delivery in the intestinal tract with the purpose of modulating gut microbiota and improving human health. (C) 2017 Elsevier Ltd. All rights reserved.
- Gelled polymerizable microemulsions. Part 3 RheologyPublication . Magno, M.; Tessendorf, R.; Medronho, B.; Miguel, M. G.; Stubenrauch, C.is the first report on the rheological properties of oil-gelled polymerizable bicontinuous microemulsions. The polymerizable base system consists of H2O/NIPAm/BisAm - n-dodecane-C13/15E5 (a technical grade n-alkyl polyglycol ether), where NIPAm denotes the monomer N-isopropylacrylamide and BisAm the cross-linker N, N'-methylene bisacrylamide. For the planned polymerization of the aqueous phase a scaffold is needed to preserve the structure of the templating microemulsion during the polymerization. This scaffold is supposed to be a gel, which was formed by adding the gelator 12-hydroxyoctadecanoic acid (12-HOA) to the oil phase of the microemulsion. The influence of the water-to-oil ratio alpha, of the gelator concentration beta, and of the monomer concentration psi on the rheological behavior of gelled microemulsions has been studied in detail. The most important result of the study at hand is the observation of a transition from a high viscous solution to a gel, i.e. from a transient to a permanent network, with increasing gelator concentration and increasing amount of the oil phase. In other words, it is only under well-defined conditions that an oil-gelled microemulsion is formed.
- Gels of catanionic vesicles and hydrophobically modified poly(ethylene glycol)Publication . Medronho, B.; Antunes, F. E.; Lindman, B.; Miguel, M. G.The association between hydrophobically modified polyethylene glycol (HM-PEG) and sodium dodecyl sulphate/didodecyldimethylammonium bromide (SDS/DDAB) catanionic vesicles is studied by rheology, (1)H-NMR, and cryo-TEM techniques. Phase behavior studies were performed as a function of polymer weight fraction and vesicle volume fraction. At sufficiently high polymer weight fraction and/or vesicle volume fraction, a gel phase is detected, indicating the presence of a three-dimensional network. Phase separation was also identified, with a dilute solution coexisting with a bluish precipitate ( gel fraction). Vesicle-polymer binding is expected to occur via the insertion of the polymer hydrophobes into the vesicle bilayer. Each vesicle can act as a cross-linking point in the network structure. The size of the vesicles is found to be important in terms of the storage modulus and viscosity of the polymer-vesicle mixed solutions. On the other hand, changes in the vesicle total net charge do not influence the association and the rheological properties. We also address the question of how the length of the hydrophobic modification can influence the rheology of the system and, as expected, larger hydrophobic groups increase the cross-linking and the relaxation time.
- Honey as a complementary medicinePublication . Miguel, M. G.; Antunes, Maria Dulce; Faleiro, Maria LeonorThe beneficial effects of honey on human health have long been recognized. Today, many of those positive effects have been studied to elucidate its mode of action. This review briefly summarizes the best studied features of honey, highlighting it as an appealing alternative medicine. In these reports, the health benefits of honey range from antioxidant, immunomodulatory, and anti-inflammatory activity to anticancer action, metabolic and cardiovascular benefits, prebiotic properties, human pathogen control, and antiviral activity. These studies also support that the honey's biological activity is mainly dependent on its floral or geographic origin. In addition, some promising synergies between honey and antibiotics have been found, as well as some antiviral properties that require further investigation. Altogether, these studies show that honey is effectively a nutraceutical foodstuff.
- How does a non-ionic hydrophobically modified telechelic polymer interact with a non-ionic vesicle? Rheological aspectsPublication . dos Santos, T.; Medronho, B.; Antunes, F. E.; Lindman, B.; Miguel, M. G.The association between hydrophobically modified polyethylene glycol, HM-PEG, and non-ionic vesicles of tetraethylene glycol monododecyl ether, C12E4, was investigated. HM-PEG is in a triblock form, with an alkyl chain attached to each hydrophilic polymer-end. Such polymer structure is denoted as telechelic. The vesicle average radius was measured by self-diffusion measurements. The system exhibits both a monophasic gel and biphasic regions. The monophasic region was characterized from a theological point of view. We argue that the gel formation is due to the presence. of polymer crosslinks between different surfactant aggregates, once the polymer's hydrophobic moieties may adsorb into the vesicle bilayer. This association is strongly concentration dependent which is reflected in the monotonic increase of the storage modulus, relaxation time and shear viscosity with the addition of surfactant and/or polymer. (C) 2007 Elsevier B.V. All rights reserved.
- Metastability of multi-lamellar vesicles in a nonionic systemPublication . Filippelli, L.; Medronho, B.; Rossi, C. O.; Miguel, M. G.; Olsson, U.Nuclear magnetic resonance spectroscopy and rheological analysis have been used to investigate the stability of mechanically induced tri-ethylene-glycol-mono-n-decyl-ether (C(10)E(3))/deuterium oxide (D(2)O) multi-lamellar vesicles (MLVs) and the transition from MLVs to planar lamellae. It was found that MLVs prepared by vortex stirring, relax back to the lamellar phase in a few hours while the relaxation of the shear induced MLVs takes days. Pulsed gradient spin echo and water self-diffusion coefficient experiments, revealed that the MLVs texture, obtained by vortex stirring, is composed of large size structures. These data indicate that the kinetics of lamellar re-formation depend on the MLVs number density.
- Phase behavior and rheological properties of DNA-cationic polysaccharide mixturesPublication . dos Santos, S.; Piculell, L.; Medronho, B.; Miguel, M. G.; Lindman, B.Associative aqueous mixtures over a range of concentrations of double- (ds) or single- (ss) stranded DNA with dilute or semidilute solutions of two cationic derivatives of hydroxyethyl cellulose (cat-HEC and cat-HMHEC,(1) the latter carrying grafted hydrophobic groups), were studied. The phase behavior showed an interesting asymmetry: Phase separation occurred immediately when small (sub-stoichiometric) amounts of cationic polyelectrolyte were added to the DNA solution, but redissolution into a single cat-(HM)HEC/DNA/H2O phase occurred already with a modest charge excess of the cationic polyelectrolyte, at a charge ratio approximately independent of the overall polyelectrolyte concentration. Cat-HEC/dsDNA/H2O and cat-HEC/ssDNA/H2O systems presented a considerable difference in the extension of the phase separation region. The one-phase samples with excess cationic polyelectrolyte were studied by rheology. The presence of DNA strengthened the viscoelastic behavior of the solutions of the cationic polyelectrolytes, reflected in an increase in storage modulus and viscosity. Differences in phase behavior and rheology were observed, particularly between systems containing cat-HEC or cat-HMHEC, but also between dsDNA and ssDNA. Thus, these systems allow for the preparation of DNA formulations with widely variable rheology and water uptake. (C) 2012 Elsevier Inc. All rights reserved.
- Planar lamellae and onions: a spatially resolved rheo-NMR approach to the shear-induced structural transformations in a surfactant model systemPublication . Medronho, B.; Brown, J.; Miguel, M. G.; Schmidt, C.; Olsson, U.; Galvosas, P.The shear-induced transformations between oriented planar lamellae and a state of closely packed multilamellar vesicles (MLVs) in a lyotropic nonionic surfactant model system were studied by the combination of nuclear magnetic resonance (NMR) spectroscopy and diffusometry with magnetic resonance imaging (MRI). (2)H NMR imaging confirmed the discontinuous nature of the transition from onions to planar lamellae, revealing the spatial coexistence of both states within the gap of the cylindrical Couette geometry. On the other hand, NMR diffusion measurements in three principal directions and at various values of strain strongly suggest that a multi-lamellar cylindrical or undulated intermediate structure exists during the continuous and spatially homogeneous transition from planar lamellae to MLVs.
- Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactionsPublication . Medronho, B.; Romano, Anabela; Miguel, M. G.; Stigsson, L.; Lindman, B.Despite being the world's most abundant natural polymer and one of the most studied, cellulose is still challenging researchers. Cellulose is known to be insoluble in water and in many organic solvents, but can be dissolved in a number of solvents of intermediate properties, like N-methylmorpholine N-oxide and ionic liquids which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen bonding between cellulose molecules. Revisiting some fundamental polymer physicochemical aspects (i.e. intermolecular interactions) a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to understand its solubility pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based on a critical analysis of the intermolecular interactions involved and mechanisms of dissolution.