Printer Changeover, Cleaning Validation and Cross-Contamination Control

Changing a vat-photopolymerisation system from one resin to another is not merely a housekeeping operation. Residual liquid resin, pigments, fillers, photoinitiator-containing material, cleaner, or particulate can be transferred into the next build and alter the state of the incoming formulation. The resulting defect may be visible, such as colour carryover, or effectively invisible until cure response, dimensional stability, surface quality, mechanics, optics, or biological-contact risk is affected. The engineering question is therefore not whether equipment appears clean, but whether the changeover process has reduced relevant carryover below a scientifically justified and analytically demonstrable acceptance limit for the next material and use case. This review develops a qualification architecture for printer, vat, build-platform, tooling and accessory changeover. It separates cleaning action from cleaning validation, links residue limits to credible next-product failure modes, and treats sampling location and analytical capability as part of the decision. Direct vat-photopolymerisation evidence is used to establish relevance, while general cleaning-validation guidance is used only for verification principles and not for importing pharmaceutical residue limits into photoresin processing.