574 research outputs found
Density-dependent interactions and structure of charged colloidal dispersions in the weak screening regime
We determine the structure of charge-stabilized colloidal suspensions at low
ionic strength over an extended range of particle volume fractions using a
combination of light and small angle neutron scattering experiments. The
variation of the structure factor with concentration is analyzed within a
one-component model of a colloidal suspension. We show that the observed
structural behavior corresponds to a non-monotonic density dependence of the
colloid effective charge and the mean interparticle interaction energy. Our
findings are corroborated by similar observations from primitive model computer
simulations of salt-free colloidal suspensions.Comment: Revised version, accepted to Phys. Rev. Let
Structure and Dynamics of Viscoelastic Surfactant Solutions - An Application of Concepts from Polymer Science
This article shows how additional information on the structure, phase behavior, and dynamics of polymer-like surfactant solutions can be obtained through concepts borrowed from polymer physics. Particular emphasis is given to the interpretation of static and dynamic light scattering
and small-angle neutron scattering experiments
A colloid approach to self-assembling antibodies
Concentrated solutions of monoclonal antibodies have attracted considerable attention due to their importance in pharmaceutical formulations, yet their tendency to aggregate and the resulting high viscosity pose considerable problems. Here we tackle this problem by a soft condensed matter physics approach which combines a variety of experimental measurements with a patchy colloid model, amenable of analytical solution. We thus report results of antibodies structural and dynamic properties obtained through scattering methods and microrheological experiments. 1 We model the data using a colloid-inspired approach, explicitly taking into account both the anisotropic shape of the molecule and their charge distribution. Our simple patchy model is able to disentangle self-assembly and intermolecular interactions, and to quantitatively describe the concentration dependence of the osmotic compressibility, collective diffusion coefficient and zero shear viscosity. Our results offer new insights on the key problem of antibody formulations providing a theoretical and experimental framework for a quantitative assessment of the effects of additional excipients or chemical modifications and a prediction of the resulting viscosity.
1) Nicholas Skar-Gislinge, Michela Ronti, Tommy Garting, Christian Rischel, Peter Schurtenberger, Emanuela Zaccarelli, and Anna Stradner, Molecular Pharm. (2019, submitted
Modeling Equilibrium Clusters in Lysozyme Solutions
We present a combined experimental and numerical study of the equilibrium
cluster formation in globular protein solutions under no-added salt conditions.
We show that a cluster phase emerges as a result of a competition between a
long-range screened Coulomb repulsion and a short-range attraction. A simple
effective potential, in which only depth and width of the attractive part of
the potential are optimized, accounts in a remarkable way for the wavevector
dependence of the X-ray scattering structure factor.Comment: 4 pages, 4 figure
Interplay between Spinodal Decomposition and Glass Formation in Proteins Exhibiting Short-Range Attractions
We investigate the competition between spinodal decomposition and dynamical
arrest using aqueous solutions of the globular protein lysozyme as a model
system for colloids with short-range attractions. We show that quenches below a
temperature Ta lead to gel formation as a result of a local arrest of the
proteindense phase during spinodal decomposition. The rheological properties of
these gels allow us to use centrifugation experiments to determine the local
densities of both phases and to precisely locate the gel boundary and the
attractive glass line close to and within the unstable region of the phase
diagram
Contrasting the dynamics of elastic and non-elastic deformations across an experimental colloidal Martensitic transition
We present a framework to segregate the roles of elastic and non-elastic
deformations in the examination of real-space experiments of solid-solid
Martensitic transitions. The Martensitic transformation of a
body-centred-tetragonal(BCT) to a body-centred-orthorhombic(BCO) crystal
structure has been studied in a model system of micron-scale ionic microgel
colloids. Non-affine fluctuations, i.e., displacement fluctuations that do not
arise from purely elastic(affine) deformations, are detected in particle
configurations acquired from the experiment. Tracking these fluctuations serves
as a highly sensitive tool in signaling the onset of the Martensitic transition
and precisely locating particle rearrangements occurring at length scales of a
few particle diameters. Particle rearrangements associated with non-affine
displacement modes become increasingly favorable during the transformation
process. The nature of the displacement fluctuation modes that govern the
transformation are shown to be different from those predominant in an
equilibrium crystal. We show that BCO crystallites formed through shear may,
remarkably, co-exist with those resulting from local rearrangements within the
same sample
Superresolution Microscopy of the Volume Phase Transition of pNIPAM Microgels
Hierarchical polymer structures such as pNIPAM microgels have been
extensively studied for their ability to undergo significant structural and
physical transformations that can be controlled by external stimuli such as
temperature, pH or solvent composition. However, direct three-dimensional
visualization of individual particles in situ have so far been hindered by
insufficient resolution, with optical microscopy, or contrast, with electron
microscopy. In recent years superresolution microscopy techniques have emerged
that in principle can provide nanoscopic optical resolution. Here we report on
the in-situ superresolution microscopy of dye-labeled submicron sized pNIPAM
microgels revealing the internal microstructure during swelling and collapse of
individual particles. Using direct STochastic Optical Reconstruction Microscopy
(dSTORM) we demonstrate a lateral optical resolution of 30nm and an axial
resolution of 60nm.Comment: 7 pages, 5 figure
A colloid approach to self-assembling antibodies
Concentrated solutions of monoclonal antibodies have attracted considerable
attention due to their importance in pharmaceutical formulations, yet their
tendency to aggregate and the resulting high solution viscosity has posed
considerable problems. It remains a very difficult task to understand and
predict the phase behavior and stability of such solutions. Here we present a
systematic study of the concentration dependence of the structural and dynamic
properties of monoclonal antibodies using a combination of different scattering
methods and microrheological experiments. To interpret these data, we use a
colloid-inspired approach based on a simple patchy model, which explicitly
takes into account the anisotropic shape and the charge distribution of the
molecules. Combining theory, simulations and experiments, we are able to
disentangle self-assembly and intermolecular interactions and to quantitatively
describe the concentration dependence of structural and dynamic quantities such
as the osmotic compressibility, the collective diffusion coefficient and the
zero shear viscosity over the entire range of investigated concentrations. This
simple patchy model not only allows us to consistently describe the
thermodynamic and dynamic behavior of mAb solutions, but also provides a robust
estimate of the attraction between their binding sites. It will thus be an
ideal starting point for future work on antibody formulations, as it provides a
quantitative assessment of the effects of additional excipients or chemical
modifications on antibody interactions, and a prediction of their effect on
solution viscosity
Modelling microgels with controlled structure across the volume phase transition
Thermoresponsive microgels are soft colloids that find widespread use as
model systems for soft matter physics. Their complex internal architecture,
made of a disordered and heterogeneous polymer network, has been so far a major
challenge for computer simulations. In this work we put forward a
coarse-grained model of microgels whose structural properties are in
quantitative agreement with results obtained with small-angle X-ray scattering
experiments across a wide range of temperatures, encompassing the volume phase
transition. These results bridge the gap between experiments and simulations of
individual microgel particles, paving the way to theoretically address open
questions about their bulk properties with unprecedented nano and microscale
resolution
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