To: 07/10/2020 14:00
My research revolves around soft, room temperature materials with a particular interest in the way microscopic interactions, especially non-covalent ones, dictate macroscopic properties. I shall focus on two bio-inspired examples of projects in which physics may provide an in-depth understanding of use to biology and materials science.
Typically, materials exhibit a trade-off between stiffness and extensibility, ultimately limiting the energy density that can be absorbed before fracture. For example, in polymer networks, an increase in cross-link density leads to enhanced stiffness, but compromised extensibility. Dynamic reformable bonds and complex network topologies, such as interpenetrating networks, have been used to circumnavigate this issue in dry and hydrated environments. Inspired by and transferring the chemistry of marine mussels, we present a dry, thermoset, single network that circumvents this inherent trade-off of stiffness and extensibility by incorporating sacrificial, reversible, iron-catecholate cross-links into a loosely covalently linked network.1,2 We attribute the enhancement of mechanical properties to the cooperative effects of the increased cross-link density and the chain-restricting ionomeric nanodomains the iron-catecholate complexes form. We will discuss the effects of moisture, oxidation, and future chemistry variations in order to understand the physics of the system.
Healthy cells, as well as cells under stress and disease, are known to form membrane-less organelles. Many of the participating biomacromolecules are intrinsically-disordered, low-complexity proteins that highly resemble polymers. One of the current hypotheses is that such organelles are formed due to proteins undergoing liquid-liquid phase separation to a dense phase and a dilute phase under certain conditions of temperature, pH, salt and protein concentrations. By focusing on low-complexity intrinsically-disordered protein and their corresponding peptides and peptoids that we plan to design, we aim to study quantitatively the effect of their zwitterionic nature, hydrogen bonding, inclusion of hydrophobic side chains and pi-cation interactions on liquid-liquid phase separation by measuring complete phase diagrams in vitro. By using techniques and theory from polymer physics to examine the heteropolymer phase separation and choosing amino acids and post-translational modifications of biological interest, we hope to provide a physical basis of understanding of interest to biology.
 Filippidi, E. et al, Science, 358, 6362, 502-505 (2017)
 Cristiani, T. R. et al, Macromolecules, 53, 10, 4099-4109 (2020)