'Out-of-equilibrium self-assembly pathways: from functional architectures for gene delivery to microfluidic manipulation of soft materials'

Soft materials encompass a wide variety of nano- and meso-structured materials, and by definition are deformable by thermal stresses and fluctuations. These materials are ubiquitous in biology (e.g. in the membranes and cytoskeleton of cells) and technological applications (e.g. in drug delivery formulations and liquid crystal displays). Nevertheless, despite their equilibrium properties having been the subject of considerable attention, much remains unknown about their out-of-equilibrium behavior and dynamics. In this talk, I will show some examples of how small-angle x-ray scattering (SAXS) and microfluidics with in-situ SAXS can be used to study the rich out-of-equilibrium behavior of soft matter systems of practical relevance.

In the first part of this talk I will show that complexation of PEGylated lipid-DNA nanoparticles in brine is pathway dependent [1]. These nanoparticles are among the most promising materials for use in gene delivery therapeutic applications. I will show that knowledge of key colloidal interactions in the mechanism of lipid-DNA nanoparticle formation allows us to influence the assembly pathway and control the final structure. With SAXS we observe that PEGylated lipid-DNA nanoparticles formed under physiological ionic-strength conditions display a small number of lamellar layers (nL<5). Conversely, nanoparticles formed in water first and transferred to physiological ionic strength media later display a large number of lamellar layers (nL>20). The final nanoparticle size and number of layer distributions constitute kinetically-trapped states (hence out-of-equilibrium), but remain stable for long periods of time. This method provides a new approach to further tailor the structure of PEGylated lipid-DNA nanoparticles for enhanced future in-vivo therapeutical applications.

In the second part of this talk, I will show how microfluidic chips (devices that involve precise control and manipulation of fluids under sub-millimeter confinement), can be used to manipulate soft materials at the nano- scale [2]. This allows us to study fundamental out-of-equilibrium processes (e.g. coupling of structure and flow, dissipation), as well as control and build complex out-of-equilibrium structures of technological interest. In a first example, we use this manipulation ability to create well-defined flowing interfaces to study the interplay between shear-flow forces and the structure of liquid crystals and surfactant monolayers [3]. In a second example, I will show how microfluidics with in-situ SAXS can be used to study the kinetic evolution of phase transitions, more specifically, the lamellar-to-microemulsion transition in surfactant-oil-water systems.