Alberto Martín-Molina

Nanogels (as well as other polymer networks) can absorb nanoparticles that give them new properties and expand their application possibilities. The resulting hybrid entities constitute a kind of polymer nanocomposites, which have become an emerging area of research. In this work, coarse-grained simulations have been used to study how certain properties of these nanocomposites (size, number of nanoparticles inside, net charge, and surface potential) change with temperature. Four nanocomposites with different values of charge anchored to the polymer network (known as bare charge) were simulated. The degree to which nanocomposites shrink and expel the particles they contain depends strongly on the bare charge, which, in turn, could be related to the pH in pH-sensitive micro- and nanogels. Our results also reveal that nanoparticles are responsible for nanocomposites exhibiting much richer and more complex behavior than nanogels. Furthermore, the strong correlations that nanoparticles experience when the polymer network shrinks should not be ignored in mean-field theories that try to predict how nanocomposites behave.

Polymer nanocomposites (PNCs) are cutting-edge materials that enhance polymer matrices with nanoparticles to achieve superior performance. The properties of these composites are significantly influenced by interactions at the nanoparticle–polymer interface. This study explores how inorganic nanorods (NRs) and various organic nanodimers (NDs)—differentiated by their interaction with the polymer and including Janus types—impact the structure, dynamics, and viscosity of PNCs. Through molecular simulations, we reveal how these nanoparticles interact within block copolymer and homopolymer matrices. Our findings show that ND–monomer interactions notably affect ND organization and improve barrier properties, while the structuring of NRs contributes to increased mechanical resistance. Furthermore, different PNCs provide a wide range of thickening behavior depending on the polymer matrix and the embedded nanoparticles. We observe increments of up to six times the melt’s viscosity when both nanoparticles are introduced into copolymers. The viscosity of the systems is evaluated using a non-equilibrium method, the SLLOD algorithm, and the Green–Kubo relation to obtain both the shear-thinning curve and the zero-shear viscosity value. These results underscore the importance of nanoparticle interactions and configurations in determining PNC behavior, providing critical insights for advancing material design and functionality.

In this work, we study how electrostatic forces slow down the diffusion of solute in flexible gels through coarse-grained simulations. The model used explicitly considers the movement of solute particles and polyelectrolyte chains. These movements are performed by following a Brownian dynamics algorithm. The effect of three electrostatic parameters characterizing the system (solute charge, polyelectrolyte chain charge, and ionic strength) is analyzed. Our results show that the behavior of both the diffusion coefficient and the anomalous diffusion exponent changes upon the reversal of the electric charge of one of the species. In addition, the diffusion coefficient in flexible gels differs significantly from that in rigid gels if the ionic strength is low enough. However, the effect of chain flexibility on the exponent of anomalous diffusion is significant even at high ionic strength (100 mM). Our simulations also prove that varying the polyelectrolyte chain charge does not have exactly the same effect as varying the solute particle charge.

The diffusion-controlled release of drugs housed in flexible nanogels has been simulated with the help of a coarse-grained model that explicitly considers polymer chains. In these in silico experiments, the effect of its flexibility is assessed by comparing it with data obtained for a rigid nanogel with the same volume fraction and topology. Our results show that the initial distribution of the drug can exert a great influence on the release kinetics. This work also reveals that certain surface phenomena driven by steric interactions can lead to apparently counterintuitive behaviors. Such phenomena are not usually included in many theoretical treatments used for the analysis of experimental release kinetics. Therefore, one should be very careful in drawing conclusions from these formalisms. In fact, our results suggest that the interpretation of drug release curves in terms of kinetic exponents (obtained from the Ritger–Peppas Equation) is a tricky question. However, such curves can provide a first estimate of the drug diffusion coefficient.

Micro- and nanogels are being increasingly used to encapsulate bioactive compounds. Their soft structure allows large loading capacity while their stimuli responsiveness makes them extremely versatile. In this work, the complexation of DNA with thermoresponsive microgels is presented. To this end, PEGylated charged microgels based on poly-N-isopropylacrylamide have been synthesized, allowing one to explore the electrostatics of the complexation. Cationic microgels complexate spontaneously by electrostatic attraction to oppositely charged DNA as demonstrated by electrophoretic mobility of the complexes. Then, Langmuir monolayers reveal an increased interaction of DNA with swollen microgels (20 °C). Anionic microgels require the presence of multivalent cations (Ca²⁺) to promote the complexation, overcoming the electrostatic repulsion with negatively charged DNA. Then again, Langmuir monolayers evidence their complexation at the surface. However, the presence of Ca²⁺ seems to induce profound changes in the interaction and surface conformation of anionic microgels. These alterations are further explored by measuring adsorbed films with the pendant drop technique. Conformational changes induced by Ca²⁺ on the structure of the microgel can ultimately affect the complexation with DNA and should be considered in the design. The combination of microstructural and surface properties for microgels offers a new perspective into complexation of DNA with soft particles with biomedical applications.

Steric effects on solute diffusion in flexible polymer gels can be described by a very simple mathematical rule.

Coarse-grained model of nanogel–polyelectrolyte complex.