Responsive soft-nanoarchitectures with unexpected induced changes

JUAN M. GIUSSI ; CATALINA VON BILDERLING; M LORENA CORTEZ; GABRIEL S. LONGO; ELIANA MAZA; CARMEN MIJANGOS; MARTA MARTINEZ; SERGIO MOYA; OMAR AZZARONI

Estocolmo

Congreso; European Advanced Materials Congress; 2018

The surface properties of soft nanostructured hydrogels are crucial in the design of responsive materials.1 By selecting the chemical nature and the type of nanoarchitecure one can produce platforms displaying adaptive properties. Part of the appeal of nanostructured hydrogel surfaces relies on the fact that they can incorporate different functional units and depending on the characteristics of these functional entities, the hydrogel can undergo well-defined physicochemical changes in the presence of specific stimuli, such as temperature, pH, salt concentration, solvent nature and more. The most studied thermosensitive polymer is poly (N-isopropylacrylamide) (PNIPAm).2 At 32°C PNIPAm-based hydrogels architectures in aqueous solution experiment a drastic deswelling due to their lower critical solution temperature (LCST). Below 32°C, the Gibbs free energy is dominates by hydrogen bonding effects and the hydrogel absorbs water. Above 32°C, the entropy term dominates and the system expels water.We have designed and synthesized two kinds of thermosensitive nanoarchitectures based on PNIPAm, ?spheres and pillars?. On one hand, nanospheres/nanogels containing a pH sensitive monomer, methacrylic acid, were layer-by-layer assembled with polyallylamine hydrochloride (PAH). As expected, the film exhibited an increase in hydrophobicity, stiffness and adhesion properties upon increasing temperature above LCST, but unexpectly, the permeability of redox probes through the film remained unchanged.3 On the other hand, PNIPAm-based nanopillars show abrupt changes in wettability as well as in topological and mechanical properties due to introduction of hydrophilic entity, acrylamide.4 Our molecular dynamics simulations proposed a local molecular rearrangement in the nanosystems during LCST. Further, PNIPAm nanopillars showed amplified surface properties through the incorporation of Fe3O4 nanoparticles.5 The incorporation of magnetic nanoparticles into the nanopillars, sharply increased their stiffness and hydrophobicity when increasing the temperature above LCST. The possibility of designing responsive surfaces with tuneable stiffness, adhesion, wettability and redox properties opens new avenues in the application of these substrates as "smart" scaffolds for cell culture, biosensing, drug delivery, human hyperthermia, and more.