What If…? Pandemic policy-decision-support to guide a cost-benefit-optimised, country-specific response.

Background: After 18 months of responding to the COVID-19 pandemic, there is still no agreement on the optimal combination of mitigation strategies. The efficacy and collateral damage of pandemic policies are dependent on constantly evolving viral epidemiology as well as the volatile distribution of socioeconomic and cultural factors. This study proposes a data-driven approach to quantify the efficacy of the type, duration, and stringency of COVID-19 mitigation policies in terms of transmission control and economic loss, personalised to individual countries.

Cold-swappable DNA gels.

We report an experimental investigation of an all-DNA gel composed by tetra-functional DNA nanoparticles acting as network nodes and bi-functional ones acting as links. The DNA binding sequence is designed to generate at room and lower temperatures a persistent long-lived network. Exploiting ideas from DNA-nanotechnology, we implement in the binding base sequences an appropriate exchange reaction which allows links to swap, constantly retaining the total number of network links.

All-DNA System Close to the Percolation Threshold.

We characterize via small-angle neutron scattering the structural properties of a mixture of all-DNA particles with functionalities 4 (A) and 2 (B) constrained by design to reside close to the percolation threshold. DNA base sequences are selected such that A particles can only bind with B ones and that at the studied temperature (10 °C) all AB bonds are formed and long-lived, originating highly polydisperse persistent equilibrium clusters. The concentration dependence of the scattered intensity and its wavevector dependence is exploited to determine the fractal dimension and the size distribution of the clusters, which are found to be consistent with the critical exponents of the 3-D percolation universality class.

Microrheology of DNA hydrogel gelling and melting on cooling.

We present systematic characterisation by means of dynamic light scattering and particle tracking techniques of the viscosity and of the linear viscoelastic moduli, G'(ω) and G''(ω), for two different DNA hydrogels. These thermoreversible systems are composed of tetravalent DNA-made nanostars whose sticky sequence is designed to provide controlled interparticle bonding. While the first system forms a gel on cooling, the second one has been programmed to behave as a re-entrant gel, turning again to a fluid solution at low temperature.

Binding branched and linear DNA structures: From isolated clusters to fully bonded gels.

The proper design of DNA sequences allows for the formation of well-defined supramolecular units with controlled interactions via a consecution of self-assembling processes. Here, we benefit from the controlled DNA self-assembly to experimentally realize particles with well-defined valence, namely, tetravalent nanostars (A) and bivalent chains (B). We specifically focus on the case in which A particles can only bind to B particles, via appropriately designed sticky-end sequences.

Re-entrant DNA gels.

DNA is acquiring a primary role in material development, self-assembling by design into complex supramolecular aggregates, the building block of a new-materials world. Using DNA nanoconstructs to translate sophisticated theoretical intuitions into experimental realizations by closely matching idealized models of colloidal particles is a much less explored avenue. Here we experimentally show that an appropriate selection of competing interactions enciphered in multiple DNA sequences results into the successful design of a one-pot DNA hydrogel that melts both on heating and on cooling.

Small-angle neutron scattering and molecular dynamics structural study of gelling DNA nanostars.

DNA oligomers with properly designed sequences self-assemble into well defined constructs. Here, we exploit this methodology to produce bulk quantities of tetravalent DNA nanostars (each one composed of 196 nucleotides) and to explore the structural signatures of their aggregation process. We report small-angle neutron scattering experiments focused on the evaluation of both the form factor and the temperature evolution of the scattered intensity at a nanostar concentration where the system forms a tetravalent equilibrium gel.