Correlating Molar Mass, π-Conjugation, and Optical Properties of Narrowly Distributed Anionic Polythiophenes in Aqueous Solutions

Polythiophene-based conjugated polyelectrolytes (CPE) are attracting increasing attention as sensor or interface materials in chemistry and biology. While cationic polythiophenes are better understood, limited structural information is available on their anionic counterparts. Limited access to well-defined polymers has made the study of structure-property relationships difficult and clear correlations have remained elusive. By combining controlled Kumada catalyst transfer polymerization with a polymer-analog substitution, regioregular and narrowly distributed poly(6-(thiophen-3-yl)hexane-1-sulfonate)s (PTHS) with tailored chain length are prepared. Analysis of their aqueous solution structures by small-angle neutron scattering (SANS) revealed a cylindrical conformation for all polymers tested, with a length close to the contour length of the polymer chains, while the estimated radii remain too small (<1.5 nm) for extensive π-stacking of the chains. The latter is particularly interesting as the longest polymer exhibits a concentration-independent structured absorption typical of crystalline polythiophenes. Increasing the ionic strength of the solution diminishes these features as the Coulomb repulsion between the charged repeat units is shielded, allowing the polymer to adopt a more coiled conformation. The extended π-conjugation, therefore, appears to be a key parameter for these unique optical features, which are not present in the corresponding cationic polythiophenes.

Synthetic cell-based materials extract positional information from morphogen gradients

Biomaterials composed of synthetic cells have the potential to adapt and differentiate guided by physicochemical environmental cues. Inspired by biological systems in development, which extract positional information (PI) from morphogen gradients in the presence of uncertainties, we here investigate how well synthetic cells can determine their position within a multicellular structure. To calculate PI, we created and analyzed a large number of synthetic cellular assemblies composed of emulsion droplets connected via lipid bilayer membranes. These droplets contained cell-free feedback gene circuits that responded to gradients of a genetic inducer acting as a morphogen. PI is found to be limited by gene expression noise and affected by the temporal evolution of the morphogen gradient and the cell-free expression system itself. The generation of PI can be rationalized by computational modeling of the system. We scale our approach using three-dimensional printing and demonstrate morphogen-based differentiation in larger tissue-like assemblies.

Comparison of the Development of SARS-Coronavirus-2-Specific Cellular Immunity, and Central Memory CD4+ T-Cell Responses Following Infection versus Vaccination

Memory T-cell responses following infection with coronaviruses are reportedly long-lived and provide long-term protection against severe disease. Whether vaccination induces similar long-lived responses is not yet clear since, to date, there are limited data comparing memory CD4+ T-cell responses induced after SARS-CoV-2 infection versus following vaccination with BioNTech/Pfizer BNT162b2. We compared T-cell immune responses over time after infection or vaccination using ELISpot, and memory CD4+ T-cell responses three months after infection/vaccination using activation-induced marker flow cytometric assays. Levels of cytokine-producing T-cells were remarkably stable between three and twelve months after infection, and were comparable to IFNγ+ and IFNγ+IL-2+ T-cell responses but lower than IL-2+ T-cell responses at three months after vaccination. Consistent with this finding, vaccination and infection elicited comparable levels of SARS-CoV-2 specific CD4+ T-cells after three months in addition to comparable proportions of specific central memory CD4+ T-cells. By contrast, the proportions of specific effector memory CD4+ T-cells were significantly lower, whereas specific effector CD4+ T-cells were higher after infection than after vaccination. Our results suggest that T-cell responses-as measured by cytokine expression-and the frequencies of SARS-CoV-2-specific central memory CD4+T-cells-indicative of the formation of the long-lived memory T-cell compartment-are comparably induced after infection and vaccination.