Scavenging Capacity Is Not a Dose: Toward Redox Dosimetry for Antioxidant Hydrogels in Bone Regeneration

Hydrogels that remove reactive oxygen species (ROS) are now a standard design response to the oxidative environment of a bone defect, and the supporting literature has grown quickly across polyphenols, metal–phenolic networks, inorganic nanozymes, ROS-cleavable polymers, and oxygen-generating composites. The evidence offered for these systems almost always takes one form: a percentage of a synthetic radical scavenged in a cuvette, a reduction in intracellular probe fluorescence, and an increase in bone volume in a rodent defect. We argue that this chain has a missing link. The first measurement is a capacity-an equilibrium property of a material sample-while the quantity that determines a biological effect is a dose: an amount of oxidant removed, per unit volume of tissue, over a defined interval, at a defined position. Capacity and dose are different physical quantities with different units, and no published transformation connects them. The problem is sharpened by the fact that ROS in bone are not purely pathological: osteoclast differentiation, hypoxia-driven angiogenic signalling and macrophage transition all depend on them, so the therapeutic target is a moving setpoint rather than zero. We review the redox biology of the healing defect as a design specification, reclassify the available chemistries by turnover mode and localization rather than by chemical family, and show by unit analysis why percentage scavenging cannot specify a design. We propose two reportable quantities-scavenging flux density and redox residence time-identify the integrated oxidant burden of a healing defect as the field’s central unmeasured denominator, and close with a reporting checklist.