  The encapsulation of fragile biomacromolecules is crucial for many
biotechnological applications but remains challenging. Interfacial complexation
(IC) in water-in-oil emulsions turned out to be an efficient process for the
formation of protective polymer layers at the surface of capsule-precursor
water droplets. We propose to further enhance this IC process by introducing
thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) strands in the
interfacial polymer layer. In this work, we implement surfactant-polymer IC in
water-in-fluorocarbon oil emulsions between a water-soluble
poly(L-lysine)-g-poly(N-isopropylacrylamide) cationic copolymer (PLL-g-PNIPAM)
and an oil-soluble anionic surfactant. We demonstrate that the thermal collapse
transition of PNIPAM strands triggers an enrichment of the polymer layer
initially formed by IC. This process is leveraged to irreversibly segregate
water-soluble nanoparticles in the interfacial polymer layer, resulting in
gel-like mixed shells. We demonstrate that this thermo-enhancement of
conventional IC is a promising approach for the formation, strengthening and
functionalization of capsule shells. As implemented in mild conditions,
thermo-enhanced IC is additionally compatible with the encapsulation of
proteins, paving the way for new delivery systems of biomacromolecules.
