Schematic 1.

By orchestrating energy metabolism and osteogenesis, the bioenergetic-driven microgel composite hydrogel with Mg²⁺ as an energy propellant constructed herein was shown to improve low-dose BMP-2-driven bone regeneration. A) Using microfluidic devices and a water-in-oil strategy, methacrylated alginate (AlMA) microgels containing Mg²⁺ and BMP-2 were fabricated. The microgels were then embedded in GelMA for the subsequent 3D printing of a microgel composite hydrogel scaffold. B) "Propelled" by BMP-2 and Mg²⁺, the hydrogel functioned as a "cell shuttle" to drive the osteogenic differentiation of host stem cells. C) Mg²⁺, as the "energy propellant" of the "shuttle", significantly improved the osteoinductivity of BMP-2 by activating the main metabolic pathways to thereby fuel the bioenergetic demand related to osteogenesis.