An anionic shell shields a cationic core allowing for uptake and release of polyelectrolytes within core–shell responsive microgels

Abstract

To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows the cationic core to be shielded while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights to investigate the influence of their chain length on the uptake and release process. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core-shell microgels depending on their size. By combining these scattering results with UV-vis spectroscopy, electrophoretic mobility and potentiometric titrations we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core-shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare the experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake of guest molecules into the cationic core. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel-polyelectrolyte complexes with respect to the cationic precursor microgel alone.

Contrast variation SANS measurement of shell monomer density profiles of smart core–shell microgels

“…28,58 We have therefore studied the evolution of the shell density profile, applying the same contrast condition highlighting the shell, and analysing our data using the multi-shell reverse Monte Carlo approach. In Figure 3a the scattering curves of SANS measurements of the D7-pNNPAM shell with the matched H-pNIPMAM core are shown for five different temperatures (15,30,35,40,55 °C, black symbols). The green lines are the best-fitting scattering curves calculated with the multi-shell RMC model.…”

Determination of Internal Density Profiles of Smart Acrylamide-Based Microgels by Small-Angle Neutron Scattering: A Multishell Reverse Monte Carlo Approach

“…Similarly, the model was used to examine shell interpenetration, and in particular the effect of shell inversion, by Brugnoni et al 48 The incorporation of guest molecules in anand cat-ionically modified core-shell microgel particles was also followed by SANS (among other techniques), using the fuzzy core-shell model. 49 A different model based on a Flory-Rehner approach was recently proposed by Boon and Schurtenberger, allowing them to investigate non-homogeneous crosslinker distributions in PNIPAM microgels. 51 Together with the Gaussian fuzzy-sphere model, it was used to describe density distributions obtained by super resolution microscopy.…”

Recent advances in stimuli-responsive core-shell microgel particles: synthesis, characterisation, and applications

“…Naturally, nanorod structures as studied by Dong et al [114], the groups of Dietsch and Schurtenberger [42,43], and the ones of Ballauff and Müller [70] can also be apprehended in detail by scattering due to the high degree of symmetry. Computer simulations have certainly not been treated here at the level they deserve, as they now allow to follow the formation of complex topologies in detail [115][116][117][118]. Finally, self-assembly of microgels, as well as their interfacial activity and their possible application as switchable cell culture substrates for vertebrate cells have also been omitted [119].…”