Rheological and Biophysical Properties of Living Fluids Under Shear: Active Suspensions of Synechocystis sp. CPCC 534

In this study, we focus on the response of biological, rheological, and physical properties of dilute suspensions of cyanobacterium Synechocystis sp. CPCC534 to shear induced by stirring. Experiments were carried out at three different stirring rates in well-controlled conditions and the results are compared with stationary conditions where only molecular diffusion and cell motility govern the transport phenomena and cell growth. Our results show that the growth, biomass, total chlorophyll, and carotenoid production of Synechocystis sp. under various shear conditions were improved significantly, and the yield was nearly doubled. The viscosity of Synechocystis suspensions, subjected to different shear rates, was also measured. The data showed Newtonian behavior for suspensions at different cell concentrations. Cell concentration showed a noticeable increase in the viscosity of suspensions. However, we observed that this increase was smaller than the one predicted for a suspension of hard spheres. Addition of shear to the cyanobacterium Synechocystis sp. culture demonstrated a positive impact on the production of value-added products from the microorganism. The obtained results can be used to improve the bioreactor design for better productivity.

Velocity measurements of dilute suspensions over and through various porous media models

This study is focused on the motion of a dilute suspension containing rigid, spherical, non-Brownian, noncolloidal particles flowing over and through porous media models. The flow is confined to very low Reynolds numbers. To examine the velocity distribution particle image velocimetry (PIV) was applied in conjunction with refractive index matching (RIM) techniques. This study is the first of its kind analyzing the interaction between two common engineering systems: suspension fluid and porous media.

The Influence of Irreversibly Electroporated Cells on Post Pulse Drug Delivery to Reversibly Electroporated Cells

Electroporation can result in cell death in some proportion of a population of cells and, because the nature of the membrane disruption can vary significantly in irreversibly electroporated cells, there is uncertainty in the magnitude of and the transient behaviour of the associated permeability increases. This study numerically investigates the drug uptake by a population of cells that includes both reversibly and irreversibly electroporated cells. A theoretical continuum model is developed and simulations are conducted in conditions of low porosity (cells in tissues) and of high porosity (cells in suspension). This model estimates the permeability increases of electroporated cells using empirically based predictions of the dependence of long-lived electropore density on the local electric field magnitude. A parametric investigation investigates how the transmembrane transport characteristics of irreversibly electroporated cells (permeability and resealing rate) affect the drug uptake of the surviving cells. The results show that the magnitude and duration of the permeability increases of irreversibly electroporated cells is much more influential in low porosity tissues than in high porosity dilute suspensions. In applications of electroporation of cells in tissues, the uncertainty of irreversibly electroporated cells should be considered in regions of tissue experiencing field strengths for which the fraction of the total cells that are irreversibly electroporated exceeds about 0.1.

Inverse Rheological Methods for the Determination of Polymer Structures, Diffusion of Small Molecules and Nanofiber Lengths

This paper presents so-called inverse rheology methods to determine various parameters that are essential to go further in terms of modelling and/or simulation in the field of polymer processing. The following systems from our previous works are presented: i) Determination of the molecular structure of a poly(e-caprolactone) polymerized in-situ by ring-opening; ii) Measurement of the mutual diffusion coefficient: two cases are considered, namely the diffusion of a plasticizer and the diffusion of an organic peroxide in a polymer melt and iii) Determination of the average length of polymer nanofibers in suspension and study of the universal behavior of nanofibers of different natures in dilute and semi-dilute suspensions. The application of these different studies in the field of reactive extrusion, blending and multi-scale structuring are presented and discussed.

A thin line between plankton and biofilm

<p>Planktonic bacterial cells are by definition not aggregated. However, our previous work, where we have demonstrated the invisible mechanical connections between bacterial cells in dilute planktonic suspensions, challenged this assumption. Here we provide an experimental evidence using autocorrelation analysis of micrographs that in planktonic suspensions of <em>B. subtilis</em> a size continuum of aggregated structures is formed. In the microbial aggregates viable cells were embedded in the nucleic acid network. The eDNA was released during regular cell lysis events. To determine the size distribution of planktonic bacterial aggregates a pair-wise spatial correlations of bacterial cells in microscopic images were calculated. The monotonously decreasing shape of the autocorrelation function indicated a continuous distribution of bacterial aggregate sizes from monomer to multimers. Soft bacterial aggregates in dilute suspensions provide a missing link in a continuum of organic matter in aqueous environments and can significantly improve our understanding how non-attached biofilms form during planktonic growth.</p>