Fig. 1. Core-shell nanoparticles assemble into noncomplex coacervate to adapt to the harsh gastrointestinal (GI) tract environment.

a Schematic illustration of harsh environmental conditions in the peristaltic GI tract. b Our noncomplex nanoparticle-assembled (NPA) coacervate compared with the conventional pH- and salt-dependent complex coacervate stabilized by electrostatic interactions between polyanions and polycations. c Driven by the gastrointestinal peristalsis, fluid NPA coacervate can effectively spread to coat and adhere on the large intestinal surface area via catechol-mediated wet bioadhesion. d The structure of as-prepared core-shell nanoparticles for fabricating NPA coacervates contains a hydrophobic core, hydrophilic PEG chains as the shell, and end groups of the PEG chains that provide physical interactions to induce nanoparticle assembly. The capacities of different nanoparticles (NP₁, NP₂, and NP₃) to form coacervates via nanoparticle assembly were examined. e The formation of NPA₂ coacervate (stained by Fast Green FCF) via NP₂ nanoparticle assembly can be visualized by fluid–fluid phase separation and further observed by TEM. f The liquid-like (G′ < G″) NPA₂ coacervate (stained by Fast Green FCF) can be injected through a 21 G needle and remained stable in buffers with a wide range of pH after 2 days. g Noncomplex NPA₂ coacervate showed a salting-out effect, confirming that the formation of NPA coacervates should be attributed to hydrogen bonding-induced nanoparticle assembly rather than electrostatic interactions. Source data are provided as a Source Data file for Fig. 1g.