Photochromic Micro-Patterned Anti-Counterfeiting Labels via High-Resolution 3D Printing

Reversible photochromic behavior, enhanced through microstructural design, offers a robust strategy for next-generation anti-counterfeiting. In this study, high-resolution anti-counterfeiting labels were fabricated using melt electrowriting (MEW), a high-precision additive manufacturing technique. Poly( ε -caprolactone) (PCL) served as the polymer matrix and was incorporated with two photochromic dyes exhibiting distinct and reversible color transitions under UV/visible light irradiation. The chromatic contrast and fatigue resistance were quantitatively assessed by monitoring the total color difference (Δ E *), which exhibited negligible degradation even after over 500 switching cycles at high dye concentrations, confirming excellent reversibility and stability. Since stable jet formation is crucial for high-fidelity printing, the critical translation speed (CTS) and Taylor cone area variation were systematically analyzed to elucidate the influence of dye concentration on printability, and the mechanical properties of the printed scaffolds were concurrently evaluated. The results demonstrated that a 4 wt% dye loading achieved optimal jet stability and mechanical integrity. Moreover, by employing a dual-spinneret MEW system, a variety of complex, multicolor micro-patterns with both figurative and realistic features were successfully produced, significantly enhancing the difficulty of counterfeiting and broadening the applicability of MEW-based technologies in secure and intelligent labeling.