145 research outputs found
Soft self-assembled nanoparticles with temperature-dependent properties
The fabrication of versatile building blocks that are reliably self-assemble
into desired ordered and disordered phases is amongst the hottest topics in
contemporary material science. To this end, microscopic units of varying
complexity, aimed at assembling the target phases, have been thought, designed,
investigated and built. Such a path usually requires laborious fabrication
techniques, especially when a specific funcionalisation of the building blocks
is required. Telechelic star polymers, i.e., star polymers made of a number
of di-block copolymers consisting of solvophobic and solvophilic monomers
grafted on a central anchoring point, spontaneously self-assemble into soft
patchy particles featuring attractive spots (patches) on the surface. Here we
show that the tunability of such a system can be widely extended by controlling
the physical and chemical parameters of the solution. Indeed, at fixed external
conditions the self-assembly behaviour depends only on the number of arms
and/or on the ratio of solvophobic to solvophilic monomers. However, changes in
temperature and/or solvent quality makes it possible to reliably change the
number and size of the attractive patches. This allows to steer the mesoscopic
self-assembly behaviour without modifying the microscopic constituents.
Interestingly, we also demonstrate that diverse combinations of the parameters
can generate stars with the same number of patches but different radial and
angular stiffness. This mechanism could provide a neat way of further
fine-tuning the elastic properties of the supramolecular network without
changing its topology.Comment: 8 pages, 7 figures. Submitted to Nanoscal
Multiblob coarse-graining for mixtures of long polymers and soft colloids
Soft nanocomposites represent both a theoretical and an experimental
challenge due to the high number of the microscopic constituents that strongly
influence the behaviour of the systems. An effective theoretical description of
such systems invokes a reduction of the degrees of freedom to be analysed,
hence requiring the introduction of an efficient, quantitative, coarse-grained
description. We here report on a novel coarse graining approach based on a set
of transferable potentials that quantitatively reproduces properties of
mixtures of linear and star-shaped homopolymeric nanocomposites. By
renormalizing groups of monomers into a single effective potential between a
-functional star polymer and an homopolymer of length , and through a
scaling argument, it will be shown how a substantial reduction of the to
degrees of freedom allows for a full quantitative description of the system.
Our methodology is tested upon full monomer simulations for systems of
different molecular weight, proving its full predictive potential
Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules
Limited bonding valence, usually accompanied by well-defined directional
interactions and selective bonding mechanisms, is nowadays considered among the
key ingredients to create complex structures with tailored properties: even
though isotropically interacting units already guarantee access to a vast range
of functional materials, anisotropic interactions can provide extra
instructions to steer the assembly of specific architectures. The anisotropy of
effective interactions gives rise to a wealth of self-assembled structures both
in the realm of suitably synthesized nano- and micro-sized building blocks and
in nature, where the isotropy of interactions is often a zero-th order
description of the complicated reality. In this review, we span a vast range of
systems characterized by limited bonding valence, from patchy colloids of new
generation to polymer-based functionalized nanoparticles, DNA-based systems and
proteins, and describe how the interaction patterns of the single building
blocks can be designed to tailor the properties of the target final structures
Off-equilibrium confined dynamics in a glassy system with level-crossing states
We study analytically the dynamics of a generalized p-spin model, starting
with a thermalized initial condition. The model presents birth and death of
states, hence the dynamics (even starting at equilibrium) may go out of
equilibrium when the temperature is varied. We give a full description of this
constrained out of equilibrium behavior and we clarify the connection to the
thermodynamics by computing (sub-dominant) TAP states, constrained to the
starting equilibrium configuration.Comment: 10 pages, 3 figures; longer version with appendi
Multi-blob coarse graining for ring polymer solutions
We present a multi-scale molecular modeling of concentrated solutions of unknotted and non-concatenated ring polymers under good solvent conditions. The approach is based on a multi-blob representation of each ring polymer, which is capable of overcoming the shortcomings of single-blob approaches that lose their validity at concentrations exceeding the overlap density of the solution [A. Narros, A. J. Moreno, and C. N. Likos, Soft Matter, 2010, 6, 2435]. By means of a first principles coarse-graining strategy based on analytically determined effective pair potentials between the blobs, computed at zero density, we quantitatively reproduce the single molecule and solution properties of a system with well-defined topological constraints. Detailed comparisons with the underlying, monomer-resolved model demonstrate the validity of our approach, which employs fully transferable pair potentials between connected and unconnected blobs. We demonstrate that the pair structure between the centers of mass of the rings is accurately reproduced by the multi-blob approach, thus opening the way for simulation of arbitrarily long polymers. Finally, we show the importance of the topological constraint of non-concatenation on the structure of the concentrated solution and in particular on the size of the correlation hole and the shrinkage of the rings as melt concentrations are approached.This work has been supported by the Austrian Science Fund (FWF), Grant 23400-N16.Peer Reviewe
A multi-blob representation of semi-dilute polymer solutions
A coarse-grained multi-blob description of polymer solutions is presented,
based on soft, transferable effective interactions between bonded and
non-bonded blobs. The number of blobs is chosen such that the blob density does
not exceed their overlap threshold, allowing polymer concentrations to be
explored deep into the semi-dilute regime. This quantitative multi-blob
description is shown to preserve known scaling laws of polymer solutions and
provides accurate estimates of amplitudes, while leading to orders of magnitude
increase of simulation efficiency and allowing analytic calculations of
structural and thermodynamic properties.Comment: 4 pages, 4 figure
Genetic diversity in the env V1-V2 region of proviral quasispecies from long-term controller MHC-typed cynomolgus macaques infected with SHIVSF162P4cy
Intra-host evolution of human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) has been shown by viral RNA analysis in subjects who naturally suppress plasma viremia to low levels, known as controllers. However, little is known about the variability of proviral DNA and the inter-relationships among contained systemic viremia, rate of reservoir reseeding and specific major histocompatibility complex (MHC) genotypes, in controllers. Here, we analysed the proviral DNA quasispecies of the env V1-V2 region, in PBMCs and in anatomical compartments of 13 long-term controller monkeys after 3.2 years of infection with simian/human immunodeficiency virus (SHIV)SF162P4cy. A considerable variation in the genetic diversity of proviral quasispecies was present among animals. Seven monkeys exhibited env V1-V2 proviral populations composed of both clusters of identical ancestral sequences and new variants, whereas the other six monkeys displayed relatively high env V1-V2 genetic diversity with a large proportion of diverse novel sequences. Our results demonstrate that in SHIVSF162P4cy-infected monkeys there exists a disparate pattern of intra-host viral diversity and that reseeding of the proviral reservoir occurs in some animals. Moreover, even though no particular association has been observed between MHC haplotypes and the long-term control of infection, a remarkably similar pattern of intra-host viral diversity and divergence was found within animals carrying the M3 haplotype. This suggests that in animals bearing the same MHC haplotype and infected with the same virus, viral diversity follows a similar pattern with similar outcomes and control of infection
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ErbB3 Phosphorylation as Central Event in Adaptive Resistance to Targeted Therapy in Metastatic Melanoma. Early Detection in CTCs during Therapy and Insights into Regulation by Autocrine Neuregulin
In recent years the introduction of target therapies with BRAF and MEK inhibitors (MAPKi) and of immunotherapy with anti-CTLA-4 and anti-PD-1 monoclonal antibodies have dramatically improved survival of metastatic melanoma patients. Despite these changes drug resistance remains a major hurdle. Several mechanisms are at the basis of drug resistance. Particular attention has been devoted over the last years to unravel mechanisms at the basis of adaptive/non genetic resistance occurring in BRAF mutated melanomas upon treatment with to MAPKi. In this paper we focus on the involvement of activation of ErbB3 receptor following early exposure of melanoma cells to BRAF or MEK inhibitors, and the following induction of PI3K/AKT pathway. Although different mechanisms have been invoked in the past at the basis of this activation we show here with a combination of approaches that autocrine production of neuregulin by melanoma cells is a major factor responsible for ErbB3 phosphorylation and downstream AKT activation. Interestingly the kinetic of neuregulin production and of the ensuing ErbB3 phosphorylation is different in different melanoma cell lines which underscores the high degree of tumor heterogeneity. Moreover, heterogeneity is further highlighted by the evidence that in different cell lines neuregulin upregulation can occur at the transcriptional or at the post-transcritpional level. Finally we complement our study by showing with a liquid biopsy assay that circulating tumor cells (CTCs) from melanoma patients undergo upregulation of ErbB3 phosphorylation in vivo shortly after initiation of therapy
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