Geometry‐Dependent Fidelity Limits in Projection Photopolymerization of Millimeter‐Scale PEG‐Based Hydrogels

ABSTRACT Projection photopolymerization enables rapid fabrication of hydrogel architectures with micrometer‐scale lateral resolution, yet its applicability to biologically relevant millimeter‐scale constructs remains constrained by poorly understood three‐dimensional fidelity limits. Here, a quantitative framework that defines geometry‐dependent fabrication limits governing structural continuity and permeability in thick hydrogel scaffolds is established. Using a custom projection photolithography platform, the effects of hydrogel thickness, feature size, and optical boundary conditions in PEG‐based systems are systematically investigated. Feature distortion follows exponential scaling with thickness, arising from the coupled effects of optical attenuation and beam divergence, motivating the introduction of a dimensionless scaling parameter (). A critical threshold, beyond which void features fail to propagate through the material, is identified at . Furthermore, optically induced crosslink gradients impose secondary constraints on scaffold functionality, affecting diffusion and post‐curing swelling behavior. These results define a fabrication window that links process parameters to final architecture and function. As a proof of concept, the engineered channel architecture was associated with cell migration and spatial cell distribution within the scaffold. This work introduces a scaling framework for projection photopolymerization of hydrogels and provides preliminary evidence for its applicability across two PEG‐based formulations, supporting more predictable fabrication of thick, millimeter‐scale hydrogel scaffolds.