Echeverria, C, Aguirre LE, Merino EG, Almeida PL, Godinho MH.
2015.
Carbon Nanotubes as Reinforcement of Cellulose Liquid Crystalline Responsive Networks. ACS Appl Mater Interfaces. 7:21005-9., Number 38
AbstractThe incorporation of small amount of highly anisotropic nanoparticles into liquid crystalline hydroxypropylcellulose (LC-HPC) matrix improves its response when is exposed to humidity gradients due to an anisotropic increment of order in the structure. Dispersed nanoparticles give rise to faster order/disorder transitions when exposed to moisture as it is qualitatively observed and quantified by stress-time measurements. The presence of carbon nanotubes derives in a improvement of the mechanical properties of LC-HPC thin films.
Echeverria, C, Almeida PL, Feio G, Figueirinhas JL, Godinho MH.
2015.
A cellulosic liquid crystal pool for cellulose nanocrystals: Structure and molecular dynamics at high shear rates. European Polymer Journal. 72:72-81.
AbstractCellulose and its derivatives, such as hydroxypropylcellulose (HPC) have been studied for a long time but they are still not well understood particularly in liquid crystalline solutions. These systems can be at the origin of networks with properties similar to liquid crystalline (LC) elastomers. The films produced from LC solutions can be manipulated by the action of moisture allowing for instance the development of a soft motor (Geng et al., 2013) driven by humidity. Cellulose nanocrystals (CNC), which combine cellulose properties with the specific characteristics of nanoscale materials, have been mainly studied for their potential as a reinforcing agent. Suspensions of CNC can also self-order originating a liquid-crystalline chiral nematic phases. Considering the liquid crystalline features that both LC-HPC and CNC can acquire, we prepared LC-HPC/CNC solutions with different CNC contents (1,2 and 5 wt.%). The effect of the CNC into the LC-HPC matrix was determined by coupling rheology and NMR spectroscopy - Rheo-NMR a technique tailored to analyse orientational order in sheared systems. (C) 2015 Elsevier Ltd. All rights reserved.
Carvalho, A, Domingues I, Goncalves MC.
2015.
Core-shell superparamagnetic nanoparticles with interesting properties as contrast agents for MRI. Materials Chemistry and Physics. 168:42-49.
AbstractCore shell nanoparticles (NPs) formed by superparamagnetic iron oxide NPs (SPIONs) coated with inorganic or organically modified (ORMOSIL) sol gel silica exhibited promising properties as negative contrast agents (CA) for MRI applications. The potentiality of these new core shell NPs as negative CA for MRI is demonstrated and quantified. The longitudinal and transverse relaxivities of NPs with three different coating compositions were studied at a 7 T magnetic field: silica (TEOS), (3-aminopropyl) triethoxysilane (APTES) and (3-glycidoxypropyl) methyldiethoxysilane (GPTMS). Clearly, it was found that the core shell NPs efficiency as CA was strongly depend on the SPIONs coating. All the three core shell NPs studied presented a very small effect on the longitudinal relaxation time but a pronounced one on the transverse relaxation time, leading to a very high transverse longitudinal relaxivities ratio, decisive for their efficiency as negative CA for MRI The effect of the core shell NPs on the MRI contrast enhancement is obtained and quantified in a set of MRI of agar phantoms obtained at 7 T magnetic field and with a imaging gradient field of 1.6 T/m. The core shell NPs were tested in Zebra-fish (Danio rerio) animal model. Zebra-fish MRI were obtained with animals injected with the three core shell NPs and the contrast enhancement validated. (C) 2015 Elsevier B.V. All rights reserved.
Palma, SI, Carvalho A, Silva J, Martins P, Marciello M, Fernandes AR, Del Puerto Morales M, Roque AC.
2015.
Covalent coupling of gum arabic onto superparamagnetic iron oxide nanoparticles for MRI cell labeling: physicochemical and in vitro characterization. Contrast Media Mol Imaging. 10:320-8., Number 4
AbstractGum arabic (GA) is a hydrophilic composite polysaccharide derived from exudates of Acacia senegal and Acacia seyal trees. It is biocompatible, possesses emulsifying and stabilizing properties and has been explored as coating agent of nanomaterials for biomedical applications, namely magnetic nanoparticles (MNPs). Previous studies focused on the adsorption of GA onto MNPs produced by co-precipitation methods. In this work, MNPs produced by a thermal decomposition method, known to produce uniform particles with better crystalline properties, were used for the covalent coupling of GA through its free amine groups, which increases the stability of the coating layer. The MNPs were produced by thermal decomposition of Fe(acac)3 in organic solvent and, after ligand-exchange with meso-2,3-dimercaptosuccinic acid (DMSA), GA coating was achieved by the establishment of a covalent bond between DMSA and GA moieties. Clusters of several magnetic cores entrapped in a shell of GA were obtained, with good colloidal stability and promising magnetic relaxation properties (r2 /r1 ratio of 350). HCT116 colorectal carcinoma cell line was used for in vitro cytotoxicity evaluation and cell-labeling efficiency studies. We show that, upon administration at the respective IC50 , GA coating enhances MNP cellular uptake by 19 times compared to particles bearing only DMSA moieties. Accordingly, in vitro MR images of cells incubated with increasing concentrations of GA-coated MNP present dose-dependent contrast enhancement. The obtained results suggest that the GA magnetic nanosystem could be used as a MRI contrast agent for cell-labeling applications.