Responsive microgels as hosts of some model macromolecules

JUAN M GIUSSI; MARTA MARTÍNEZ MORO; NÉSTOR A. PÉREZ-CHÁVEZ; DESIRÉ DI SILVIO; M. LORENA CORTEZ; GABRIEL S. LONGO; IRANTZU LLARENA CONDE; OMAR AZZARONI; SERGIO MOYA

San Sebastian

Workshop; Workshop on Self-assembly and Hierarchical Materials in biomedicine: Drug Delivery, Tissue Engineering, Sensing and Safety Issues; 2018

CIC BIOMAGUNE

Microgels are materials widely used as hosts for active molecules in many applications, especially in the biomedical field. The encapsulation of small molecules in stimulus-responsive microgels has been well described in the literature. On the contrary, there are few studies of the encapsulation of macromolecules, such as polyelectrolytes, proteins, carbohydrates. In this work, we present an exhaustive study of the interaction between pH and temperature-responsive microgels, based on N-isopropylacrylamide and methacrylic acid, P(NIPAm-co-MAA) hydrogels, and a model positively charged polyelectrolyte, poly allylamine hydrochloride (PAH). P(NIPAm-co-MAA) microgels are negatively charged and will interact electrostatically with PAH. At temperatures over 30-32°C the hydrogel particle collapses resulting in a surface segregation of MAA segments and a reduction in the size of hydrogel pores. Studies were conducted at temperatures below and above the phase transition and for PAH of 15 kDa and 50 kDa of molecular weight, in order to rule out the impact of pore size and charge distribution on the interaction of PAH with the P(NIPAm-co-MAA) microgels. Dynamic light scattering measurements showed a clear effect in the size of the hydrogel particle due to the presence of the polyelectrolyte. Such is it so, PAH of 15 kDa revealed a particle contraction below NIPAm phase transition, on the contrary, PAH of 50 kDa did not produce size change below this temperature. Above 32°C, the systems collapsed and the shrinkage of the particle occurred largely for the microgel without PAH, then the microgel with the PAH of 15 kDa and the system that showed the least collapse was the microgel with the PAH of 50 kDa. Z potential values below NIPAm phase transition suggested that in one case, the interaction between the microgel and the polymer occurs mostly on the particle surface and in the other case, the incorporation of the polymer inside the particle occurs. By means of confocal microscopy, flow cytometry and energy transfer we could quantify the PAH molecular weight effects in their incorporation into the particle. Isothermal titration calorimetry results showed a meticulous competition between electrostatic interactios between the polyelectrolyte with MAA entities of the microgels (enthalpy) vs. the endothermic contribution associated to MAA dehydration. Finally, through molecular modelling, we were able to understand and postulated clear arguments to describe the subtle difference in molecular weights of PAH in their interaction with microgels based on NIPAm and MAA.