Skip to main content

Polyelectrolyte nanocomplexes

Final Report Summary - PE-NANOCOMPLEXES (Polyelectrolyte nanocomplexes)

Project context and objectives

Electrostatic self-assembly is of increasing interest in recent years since charged polymer molecules (polyelectrolytes) have become the key component in various industrial, biotechnological and medical applications such as surface coatings, drug encapsulation and gene delivery. The project is related to two fields of polyelectrolyte complex formation, namely optimising DNA/polyelectrolyte complex uptake by cells through controlling the interfacial structure of the complexes (work package one, WP1) and the effect of multivalent ions on the interaction of polyelectrolytes and oppositely charged surfactants (work package two, WP2). WP1 aimed at developing a nanoprobe technique that could be used to determine the optimal interfacial structure of nanocomplexes in cellular uptake. WP2 addresses the effect of multivalent ions on the interaction of a flexible polyelectrolyte and an oppositely charged surfactant both in the bulk phase and at interfaces. Altogether, the two WPs have defined four scientific objectives:

O1: To develop a nanoprobe technique that can be used to determine the optimal interfacial structure of nanocomplexes in cellular uptake.

O2: To characterise the effect of multivalent counterions on the surfactant binding to oppositely charged polyelectrolytes in the bulk phase.

O3: To probe the equilibrium/non-equilibrium nature of the interaction of the polyelectrolyte/surfactant interaction.

O4: To correlate the bulk results with the interfacial behaviour the polyelectrolyte/surfactant systems.

Project results

The project was executed at the host institution (Eötvös Loránd University, Hungary) with the active participation of three PhD students and several international collaborating partners. The main results are summarised below:

-Synthetic methods to produce both hard (silica) and soft, responsive poly-N-ispropylacrylamide-based nanoparticles with controlled core/shell structure and controlled interfacial properties have been developed. Methods to control the structure of adsorbed polyelectrolyte layers have been established and were used to investigate the effect of polyelectrolyte adsorption layer structure on the cell/nanoparticle interaction.

-The effect of electrolytes on the polyelectrolyte/surfactant interaction was investigated using the poly(sodium styrene)/dodecyltrimethylammonium bromide (PSS/DTAB) system. It was shown that monovalent inert electrolytes (e.g. NaCl and NaBr) have only a minor effect on the PSS/DTAB interaction. At the same time they destabilise the electrostatically stabilised PSS/DTAB aggregates, which leads to enhanced precipitation in the system at intermediated electrolyte concentration. However, with increasing ionic strength the formation of non-equilibrium aggregates and precipitation are completely suppressed. This could be understood in terms of the decreasing critical micelle concentration (cmc) of the surfactant with increasing ionic strength.

-In terms of the slow non-equilibrium processes taking place in the bulk phase we were able to fully interpret the air/liquid interfacial behaviour of the polyelectrolyte/surfactant systems. We have shown that the two main types of interfacial behaviours described in the literature can be transformed into each other by manipulating the bulk aggregation. We have also demonstrated that Bragg peaks in neutron reflectivity curves can be the result of bulk aggregates transported to the interface e.g. due to density differences, thus Bragg peaks are not a clear evidence of interfacial self-assembly. These results initiated new research directions to control the delivery of biomacromolecules to interfaces.

Potential impact

The long-term reintegration of the researcher required not only the successful execution of the research project but his participation in the teaching activities of the host institution, his successful habilitation and his successful applications for further funding. To meet these requirements the researcher has offered four serious lectures for BSc and MSc students. Furthermore, he has supervised laboratory practices for undergraduate students, and supervised the diploma work of BSc, MSc and PhD students. He has also successfully defended his habilitation thesis. Finally, based on his scientific results the researcher was able to organise a Marie Curie Initial Training Network (NanoS3) with the participation of ten full partners (eight academic and two industrial) and two associated partners (a research institute and a biotech small and medium enterprise). The application was favourably evaluated, funded and started its activities in April 2012.