Spatially-extended nucleation-aggregation-fragmentation models for the dynamics of prion-like neurodegenerative protein-spreading in the brain and its connectome

The prion-like hypothesis of neurodegenerative diseases states that the accumulation of misfolded proteins in the form of aggregates is responsible for tissue death and its associated neurodegenerative pathology and cognitive decline. Some disease-specific misfolded proteins can interact with healthy proteins to form long chains that are transported through the brain along axonal pathways. Since aggregates of different sizes have different transport properties and toxicity, it is important to follow independently their evolution in space and time. Here, we model the spreading and propagation of aggregates of misfolded proteins in the brain using the general Smoluchowski theory of nucleation, aggregation, and fragmentation. The transport processes considered here are either anisotropic diffusion along axonal bundles or discrete Laplacian transport along a network. In particular, we model the spreading and aggregation of both amyloid-β and τ molecules in the brain connectome. We show that these two models lead to different size distributions and different propagation along the network. A detailed analysis of these two models reveals the existence of four different stages with different dynamics and invasive properties.

Effect of LPS Removal on Electrophoretic Softness of Acidithiobacillus ferrooxidans Cells

Applicability of Ohshima’s soft-particle model to evaluate the surface potential of Acidithiobacillus ferrooxidans cells is discussed here. The electrokinetic properties were examined by electrophoretic mobility measurements and analyzed using the soft particle electrophoresis theory. As the ionic concentration increased, the mobility of the bacterial cells converged to nonzero values suggesting that the particles exhibited typical soft-particle characteristics. Also, cell surface potentials based on soft-particle theory were lower than those estimated using the conventional Smoluchowski theory. Effect of removal of LPS from the cell surface on surface softness and charge density are investigated and discussed.

Dynamics of Dipole Chains in a Ferrofluid Emulsion

Structure formation and chain dynamics in a dilute, monodisperse ferrofluid emulsion under the influence of an external magnetic field have been studied using dynamic light scattering. Chain formation is found to be a diffusion-limited process that is well described by the Smoluchowski theory of irreversible aggregation. The characteristic time on which chain formation occurs depends strongly on volume fraction and on magnetic field strength. Rescaling the time leads to a universal behavior. Internal chain dynamics i.e.chain fluctuations are revealed by measurements of the apparent short-time diffusion coefficient as a function of the scattering angle. They show a strong dependence on the strength of the applied magnetic field.