3 research outputs found
Comparative toxicity of three differently shaped carbon nanomaterials on <i>Daphnia magna</i>: does a shape effect exist?
<p>The acute toxicity of three differently shaped carbon nanomaterials (CNMs) was studied on <i>Daphnia magna</i>, comparing the induced effects and looking for the toxic mechanisms. We used carbon nano-powder (CNP), with almost spherical primary particle morphology, multi-walled carbon nanotubes (CNTs), tubes of multi-graphitic sheets, and cubic-shaped carbon nanoparticles (CNCs), for which no ecotoxicological data are available so far. Daphnids were exposed to six suspensions (1, 2, 5, 10, 20 and 50āmg L<sup>ā1</sup>) of each CNM, and then microscopically analyzed. Ultrastructural analyses evidenced cellular uptake of nanoparticle in CNP and CNT exposed groups, but not in samples exposed to CNCs. Despite this difference, very similar effects were observed in tissues exposed to the three used CNMs: empty spaces between cells, cell detachment from the basal lamina, many lamellar bodies and autophagy vacuoles. These pathological figures were qualitatively similar among the three groups, but they differed in frequency and severity. CNCs caused the most severe effects, such as partial or complete dissolution of the brush border and thinning of the digestive epithelium. Being the cubic shape not allowed to be internalized into cells, but more effective than others in determining physical damages, we can conclude that shape is an important factor for driving nanoparticle uptake by cells and for determining the acute toxicological endpoints. Shape also plays a key role in determining the kind and the severity of pathologies, which are linked to the physical interactions of CNMs with the exposed tissues.</p
Self-Assembled PullulanāSilica Oxygen Barrier Hybrid Coatings for Food Packaging Applications
The scope of this study encompassed the evaluation of
pullulan
as a suitable biopolymer for the development of oxygen barrier coatings
to be applied on polyĀ(ethylene terephthalate) (PET), especially for
food packaging applications. To enhance the oxygen barrier properties
of the organic phase (pullulan) even at high relative humidity values,
an inorganic phase (silica), obtained through in situ polymerization,
was also utilized to obtain hybrid coatings via the solāgel
technique. Transmission electron microscopy (TEM) images and Fourier
transform infrared (FT-IR) spectra showed that mixing the two phases
yielded a three-dimensional hybrid network formed by self-assembly
and mediated by the occurrence of new hydrogen-bond interactions at
the intermolecular level, although the formation of new covalent bonds
could not be excluded. The deposition of the hybrid coatings decreased
the oxygen transmission rate (OTR) of the plastic substrate by up
to 2 orders of magnitude under dry conditions. The best performance
throughout the scanned humidity range (0%ā80% relative humidity)
was obtained for the formulation with the lowest amount of silica
(that is, an organic/inorganic ratio equal to 3)
Ultrasound-Assisted Pullulan/Montmorillonite Bionanocomposite Coating with High Oxygen Barrier Properties
In this paper, the preparation and characterization of
oxygen barrier
pullulan sodium montmorillonite (Na<sup>+</sup>-MMT) nanocomposite
coatings are presented for the first time. Full exfoliation of platelets
during preparation of the coating water dispersions was mediated by
ultrasonic treatment, which turned out to be a pivotal factor in the
oxygen barrier performance of the final material even at high relative
humidity (RH) conditions [oxygen permeability coefficients ā¼1.43
Ā± 0.39 and 258.05 Ā± 13.78 mLĀ·Ī¼mĀ·m<sup>ā2</sup>Ā·(24 h)<sup>ā1</sup>Ā·atm<sup>ā1</sup> at
23 Ā°C and 0% RH and 70% RH, respectively]. At the micro- and
nanoscale, the reasons are discussed. The final morphology of the
coatings revealed that clay lamellae were stacked on top of one another,
probably due to the forced confinement of the platelets within the
coating thickness after solvent evaporation. This was also confirmed
by modeling the experimental oxygen permeability data with the well-known
Nielsen and Cussler permeation theoretical models, which suggested
a reasonable aspect ratio (Ī±) of ā¼100. Electron microscopic
analyses also disclosed a peculiar cell-like arrangement of the platelets.
The stacking of the clay lamellae and the cell-like arrangement create
the excellent oxygen barrier properties. Finally, we demonstrated
that the slight haze increase in the bionanocomposite coating materials
arising from the addition of the clays depends on the clay concentration
but not so much on the sonication time, due to the balance of opposite
effects after sonication (an increase in the number of scattering
centers but a reduction in their size)