Closing the Loop: High-Precision 3D Photofabrication in Living Tissues.

Multiphoton absorption enables three-dimensional fabrication of photoresists ranging from ceramics to hydrogels and has recently been extended to the writing of microstructures within the dermis, muscle, and brain of living animals. However, an intrinsic difficulty prevents its widespread application in vivo. Absorption, cure kinetics, heat accumulation, and matrix stiffness each vary steeply across neighboring micro-environments and across intervals spanning a single pulse to several minutes. Therefore, any pre-selected exposure drifts out of the safe and effective window as fabrication proceeds. Rigorous feedback control should ideally act simultaneously at three scales: between pulses to bound heating (microseconds), within each voxel to confirm cure and stiffness (milliseconds), and across the finished volume to verify geometry (seconds). Phase-resolved optical coherence tomography and luminescent thermometry already satisfy these demands, with photoacoustic, Brillouin, and diamond-defect techniques reaching further into depth, contrast, and sensitivity. We analyze critically how this technology supports predictive controllers at the three scales that learn tissue behavior on the fly, turning these readings into adaptive feedforward with supervisory feedback. We synthesize this toolkit into a single perspective toward adaptive intravital light interventions.