Mechanical Properties and Testing Strategies for Two‐Photon Lithography: A Review of Current Practices and Emerging Challenges

Two‐photon lithography (2PL) is a high‐resolution additive manufacturing technique achieving complex three‐dimensional (3D) microstructures with sub‐micrometer precision. This capability has driven applications across optics, microfluidics, bioelectronics, metamaterials, and biomedical engineering. Beyond geometry, the functionality of 2PL‐fabricated structures critically depends on their mechanical properties, which are influenced by resin chemistry, printing parameters, and post‐processing treatments. Understanding the mechanical behavior of 2PL‐fabricated structures at both macro‐ and micro‐scales is essential for the rational design and development of advanced devices and systems. Accordingly, this review provides the reader with a concise yet comprehensive overview of the current knowledge on the mechanical properties of materials usually employed in 2PL. Common photoresist classes (e.g., hydrogel‐like, elastomeric polymer networks, rigid glassy polymers, and hybrid organic–inorganic networks) offer distinct trade‐offs in stiffness, with Young's modulus spanning several orders of magnitude. Mechanical performance can be further tuned via laser settings, environmental conditions, or post‐processing approaches such as UV curing, pyrolysis, or incorporation of responsive chemistries for dynamic “4D” behavior. We then examine the methodologies applied—or specifically developed—to characterize 2PL materials and microstructures in terms of stiffness, toughness, and viscoelastic response at the micro‐ and nanoscale. Finally, we discuss the applications where mechanical properties are critical to the functionality of 2PL structures, such as tissue engineering, microfluidics, and tunable metamaterials. Looking ahead, advances in material design, adaptive characterization, and predictive modeling will enable rational, data‐driven workflows. Treating mechanical properties as fundamental design parameters will be key for developing reliable microdevices for next‐generation technologies.