135 research outputs found
A molecular dynamics study of chemical gelation in a patchy particle model
We report event-driven molecular dynamics simulations of the irreversible
gelation of hard ellipsoids of revolution containing several associating
groups, characterizing how the cluster size distribution evolves as a function
of the extent of reaction, both below and above the gel point. We find that in
a very large interval of values of the extent of reaction, parameter-free
mean-field predictions are extremely accurate, providing evidence that in this
model the Ginzburg zone near the gel point, where non-mean field effects are
important, is very limited. We also find that the Flory's hypothesis for the
post-gelation regime properly describes the connectivity of the clusters even
if the long-time limit of the extent of reaction does not reach the fully
reacted state. This study shows that irreversibly aggregating asymmetric
hard-core patchy particles may provide a close realization of the mean-field
model, for which available theoretical predictions may help control the
structure and the connectivity of the gel state. Besides chemical gels, the
model is relevant to network-forming soft materials like systems with
bioselective interactions, functionalized molecules and patchy colloids.Comment: 6 pages, 4 figures, to be published in Soft Matte
Brillouin scattering of phonons in complex materials
Initially, the theory of propagation of long-wavelength
acoustic phonons and Brillouin scattering of laser light
in condensed matter is concisely summarized. Then, the
case of two relevant classes of complex materials in which
Brillouin scattering can be measured is reviewed. First, in lowdensity,
low-dimensional, disordered materials, the crossover
between confinement and propagation is discussed on the
basis of experimental findings. Moreover, the possibility of
measuring the local mechanical properties of these materials
at the mesoscale by Brillouin scattering is critically discussed.
Second the application of Brillouin scattering to biological
materials, a rather hot topic, is presented
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Hyperspectral analysis applied to micro-Brillouin maps of amyloid-beta plaques in Alzheimer’s disease brains
A recent investigation on the architecture and chemical composition of amyloid-β (Aβ) plaques in ex vivo
histological sections of an Aβ-overexpressing transgenic mouse hippocampus has shed light on the infrared
light signature of cell-activation related biomarkers of Alzheimer’s disease. A correlation was highlighted
between the biomechanical properties detected by Brillouin microscopy and the molecular make-up of Aβ
plaques provided by FTIR spectroscopic imaging and Raman microscopy (with correlative immunofluorescence
imaging) in this animal model of the disease. In the Brillouin spectra of heterogeneous materials such
as biomedical samples, peaks are likely the result of multiple contributions, more or less overlaid on a spatial
and spectral scale. The ability to disentangle these contributions is very important as it may give access to
discrete components that would otherwise be buried within the Brillouin peak envelope. Here, we applied
an unsupervised non-negative matrix factorization method to analyse the spontaneous Brillouin microscopy
maps of Aβ plaques in transgenic mouse hippocampal sections. The method has already been proven successful
in decomposing chemical images and is applied here for the first time to acoustic maps acquired
with a Fabry–Perot Brillouin microscope. We extracted and visualised a decrease in tissue rigidity from the
core through to the periphery of the plaque, with spatially distinct components that we assigned to specific
entities. This work demonstrates that it is possible to reveal the structure and mechanical properties of Aβ
plaques, with details visualized by the projection of the mechanical contrast into a few relevant channels
Scleroderma-like Impairment in the Network of Telocytes/CD34+ Stromal Cells in the Experimental Mouse Model of Bleomycin-Induced Dermal Fibrosis
Considerable evidence accumulated over the past decade supports that telocytes (TCs)/CD34+ stromal cells represent an exclusive type of interstitial cells identifiable by transmission electron microscopy (TEM) or immunohistochemistry in various organs of the human body, including the skin. By means of their characteristic cellular extensions (telopodes), dermal TCs are arranged in networks intermingled with a multitude of neighboring cells and, hence, they are thought to contribute to skin homeostasis through both intercellular contacts and releasing extracellular vesicles. In this context, fibrotic skin lesions from patients with systemic sclerosis (SSc, scleroderma) appear to be characterized by a disruption of the dermal network of TCs, which has been ascribed to either cell degenerative processes or possible transformation into profibrotic myofibroblasts. In the present study, we utilized the well-established mouse model of bleomycin-induced scleroderma to gain further insights into the TC alterations found in cutaneous fibrosis. CD34 immunofluorescence revealed a severe impairment in the dermal network of TCs/CD34+ stromal cells in bleomycin-treated mice. CD31/CD34 double immunofluorescence confirmed that CD31−/CD34+ TC counts were greatly reduced in the skin of bleomycin-treated mice compared with control mice. Ultrastructural signs of TC injury were detected in the skin of bleomycin-treated mice by TEM. The analyses of skin samples from mice treated with bleomycin for different times by either TEM or double immunostaining and immunoblotting for the CD34/α-SMA antigens collectively suggested that, although a few TCs may transition to α-SMA+ myofibroblasts in the early disease stage, most of these cells rather undergo degeneration, and then are lost. Taken together, our data demonstrate that TC changes in the skin of bleomycin-treated mice mimic very closely those observed in human SSc skin, which makes this experimental model a suitable tool to (i) unravel the pathological mechanisms underlying TC damage and (ii) clarify the possible contribution of the TC loss to the development/progression of dermal fibrosis. In perspective, these findings may have important implications in the field of skin regenerative medicine
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