<p>Encapsulating individual inorganic colloidal particles with a conformal hydrogel shell remains challenging in aqueous media due to unfavorable interfacial wetting between hydrophilic solid surfaces and hydrogel precursors. Here, we report a simple and scalable batch-type strategy for the complete encapsulation of inorganic colloids within a crosslinked poly(ethylene glycol) (cPEG) hydrogel shell, enabled by interfacial wetting control. Using commercially available α-alumina (Al₂O₃) particles as a model system, we show that direct encapsulation with a PEG diacrylate (PEGDA) precursor in water is ineffective owing to complete non-wetting on hydrated oxide surfaces. This limitation is overcome by introducing a facile oleic acid (OA) surface pre-coating, which fundamentally alters the wetting configuration among three immiscible phases—OA, PEGDA, and water—leading to complete spreading and engulfment of the OA-coated particle surface by PEGDA, followed by UV-induced crosslinking. The resulting Al₂O₃@OA@cPEG particles are systematically characterized by SEM, TEM/EDS, and depth-resolved XPS, confirming the formation of a continuous, hydrated hydrogel shell surrounding the inorganic core. Spreading coefficient analysis quantitatively rationalizes the observed encapsulation behavior and highlights the decisive role of interfacial energetics in hydrogel-based particle encapsulation. This work provides a general and experimentally accessible framework for designing hydrogel-coated inorganic particles and is expected to be broadly applicable to hydrogel composites, biomedical and cosmetic formulations, and emerging soft-material technologies.</p> Graphical abstract <p></p>