Liquid Marbles in Liquid

Abstract Traditional liquid marbles (LMs), liquid droplets encapsulated by hydrophobic particles at the liquid–gas interface, are restricted by their short lifetime and low heat transfer efficiency. Herein, a new paradigm for LMs immersed in various liquid mediums with massive enhanced heat transfer and spatial recognition is designed; without compromising the structural integrity, the lifetime of the liquid marbles in liquid (LMIL) is extended by ≈1000 times compared to classical LMs in air or naked droplets in organic reagents. The LMIL shows promising reverse structural re‐configurability while under external stimuli and maintaining their functionality for a very long period of time (≈weeks). These superior behaviors are further exploited as a miniature reactor with prolonged lifetimes and excellent temperature control, combined with its feasible operation, new opportunities will open up in the advanced chemical and biomedical engineering fields. It is also shown that LMIL can be applied in methylene blue degradation and 3D in‐vitro yeast cell cultures. These findings have important implications for real‐world use of LMs, with a number of applications in cell culture technology, lab‐in‐a‐drop, polymerization, encapsulation, formulation, and drug delivery.