that the corresponding exclusion zones overlap (i.e. polymers cannot fit between the colloids anymore), colloids become attractive due to an osmotic pressure imbalance. The size, orientation and hydrophilicity of the depletants can be controlled by external factors, such as pH, temperature and ionic interactions for reversible regulation of depletion interactions. In the current work, however, we aim to control colloidal interactions with a polymeric depletant that is integrated in a fuel-driven CRN. The fuel cycle integration provides autonomous control over the time domain and does not require any external temperature or pH changes. Previously, we developed a fuel-driven transient polymer acetylation CRN with acetic anhydride as chemical fuel to regulate product yield and lifetime. We were able to control polymer conformation and aggregation with two organocatalysts (pyridine and imidazole) and by varying fuel levels. The polymer we developed consisted of a poly(acrylic acid) (PAA) backbone with 25% coverage of 3-nitro-L-tyrosine (NY), which could undergo transient acetylation causing a temporal coil to globule transition. Now, we exploit this fuel-driven polymer coil-globule transition to dynamically control its depletion ability, leading to transient colloidal assembly (Figure ). PAANY with negatively charged NY groups has a random coil conformation (diameter 8.6 nm). Upon addition of the chemical fuel (acetic anhydride) the NY moieties get acetylated, generating PAANY-acyl, which adopts a compact globule conformation (diameter ~5.9 nm) due to a decreased charged density and increased hydrophobic surface. We hypothesize that native PAANY in the random coil conformation is a polymeric depletant for silica colloids (diameter = 1 µm), making the colloids assemble. PAANY-acyl, as a smaller compact globule, loses the depletion capacity, leading to disassembly of the colloids. Over time, PAANY-acyl will revert back to native PAANY through hydrolysis, leading to a conformational change and a concomitant increase in depletion ability. Hence, a full fuel cycle initiated by the addition of chemical fuel on the molecular scale causes a transient colloidal assembly-disassembly-assembly cycle on the microscopic level.