Oral: pH-Responsive swelling of poly(methacrylic acid) multilayer hydrogels through controlling polyacid chain conformations*

Stimuli-sensitive nanostructured multilayer hydrogels obtained from layer-by-layer (LbL) polymer films have shown precise control over network composition, thickness, crosslink density, and fast and reversible stimuli-triggered hydrogel volume changes. These properties are crucial for biomedical applications, including drug and gene delivery, tissue engineering, and cell interactions. We showed that for chemically crosslinked PMAA multilayer hydrogels obtained from hydrogen-bonded multilayer templates, the internal hydrogel structure ranges from well-stratified to highly intermixed depending on the LbL assembly method. Herein, we explored the effect of the polymer architecture and the chain conformation on the properties of PMAA multilayer hydrogels. We synthesized PMAA-based polyampholytes with different content of amino group (PMAA-NH₂ from 2.1 to 6.2 mol.%) from well-defined precursors (M_w of ∼45 kDa and 80 kDa, Đ < 1.35). The distribution of amino groups in the copolymer was found as a gradient according to ¹H NMR analysis. The effects of chain conformation in pH-sensitive polyelectrolyte complexes were studied for PMAA hydrogel fabrication via spin-assisted LbL approach. The effects of crosslink density and deposition conditions on the properties of the hydrogels were studied through in-situ ellipsometry and AFM techniques. This work opens opportunities for developing thin hydrogels with precisely tuned morphology, pH-triggered swelling, and hydration.