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Andreu I.,University of Zaragoza | Natividad E.,University of Zaragoza | Ravagli C.,Centro Ricerche Colorobbia | Castro M.,University of Zaragoza | Baldi G.,Centro Ricerche Colorobbia
RSC Advances | Year: 2014

The heating ability of magnetic nanoparticles (MNPs) intended for magnetic hyperthermia is quantified by means of the specific absorption rate (SAR), also referred to as specific loss power. This quantification is mainly performed on ferrofluids, even though the SAR values so obtained are often not representative of the nanoparticle performance inside tissues (solid matrices). In this study, the SAR of cobalt ferrite MNPs with mean crystallite diameters of 5.5 nm and 7.4 nm, functionalized or not, and dispersed in liquid or solid media, was determined in the 180-300 K temperature range. Higher SAR values were systematically obtained for samples in liquid media. On the one hand, heat capacity data together with zero-field-cooled and field-cooled magnetization curves allowed correlation of these results with ferrofluid dynamics originating from viscosity changes in samples dispersed in diethylene glycol. On the other hand, the higher degree of agglomeration attained by the functionalized MNPs after immobilization in paraffin wax seemed responsible for the decrease in SAR values and the shift in blocking temperature. In sum, MNP's spatial arrangements acquired after ferrofluid injection in magnetic hyperthermia should be taken into account to predict SAR values during therapies. © 2014 The Royal Society of Chemistry.

Martins N.C.T.,University of Aveiro | Freire C.S.R.,University of Aveiro | Neto C.P.,University of Aveiro | Silvestre A.J.D.,University of Aveiro | And 4 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2013

New composites of nanofibrillated cellulose (NFC) and ZnO nanoparticles (NP) have been prepared by electrostatic assembly in aqueous medium and using polyelectrolytes as macromolecular linkers. Selected NFC/ZnO systems were employed as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. Using this method, antibacterial paper with low content of ZnO (<0.03%) and slight improvements in air permeability and mechanical properties were obtained. The antibacterial activity of the ZnO/NFC coatings was investigated namely by submitting paper samples to solar light exposure and dark conditions. In both conditions, the paper samples have shown bacteriostatic and/or bactericidal activity against Gram positive (Staphylococcus aureus and Bacillus cereus) and Gram negative (Klebsiella pneumoniae) bacteria. These results seem to support that the mechanism for ZnO antimicrobial activity is not mediated only by the photoactivity of the semiconductor but also by oxidizing species formed at the particles surfaces. © 2012 Elsevier B.V.

Martins N.C.T.,University of Aveiro | Freire C.S.R.,University of Aveiro | Pinto R.J.B.,University of Aveiro | Fernandes S.C.M.,University of Aveiro | And 6 more authors.
Cellulose | Year: 2012

Nanofibrillated cellulose offers new technological solutions for the development of paper products. Here, composites of nanofibrillated cellulose (NFC) and Ag nanoparticles (NP) were prepared for the first time via the electrostatic assembly of Ag NP (aqueous colloids) onto NFC. Distinct polyelectrolytes have been investigated as macromolecular linkers in order to evaluate their effects on the building-up of Ag modified NFC and also on the final properties of the NFC/Ag composite materials. The NFC/Ag nanocomposites were first investigated for their antibacterial properties towards S. aureus and K. pneumoniae microorganisms as compared to NFC modified by polyelectrolytes linkers without Ag. Subsequently, the antibacterial NFC/Ag nanocomposites were used as fillers in starch based coating formulations for Eucalyptus globulus-based paper sheets. The potential of this approach to produce antimicrobial paper products will be discussed on the basis of complementary optical, air barrier and mechanical data. © 2012 Springer Science+Business Media B.V.

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