The use of combustibles in micro-actuator technologies enables powerful impulsive actuation capabilities comparable to those of natural organisms. However, the exogenous dependence of fuel limits the development of combustion-based actuators. We present a closed-cycle reactant regeneration strategy wherein the bi-directional inter-conversion between hydrogen and water achieves real-time fuel replenishment for reactant-regenerative electrolysis and combustion reactions. Based on this, we develop a 1.5 centimeters actuator that generates forces above 20 newtons and operates continuously for >7,200 cycles without refueling (a two-orders-of-magnitude improvement over existing combustion-based actuators). Experiments confirm its strength and cross-environment versatility for removing obstacles, jetting, and striking via underwater cavitation. These features enable the actuator to be integrated into small robotic platforms, allowing them to reconfigure local surroundings in an active manner.