Tuning the stiffness of two-photon polymerized elastomer by controlling the sparsity and helicity of printing paths

Two-photon polymerization (TPP) is one of the emerging technologies for manufacturing high-precision micro-nano 3D structures. Common resin materials used in TPP are limited to, for example, acrylates or epoxy oligomers. The mechanical properties of these resins are difficult to tune after exposure, limiting their applications in advanced fields such as biomedicine, soft robotics, and microelectronics. In this work, an elastomer photoresist based on polyurethane acrylate (PUA) is designed, which combines the flexibility of polyurethane with the rapid curing characteristics of acrylates. Microstructures with good self-supporting properties are prepared by TPP-3D printing, and the mechanical properties of the elastomer photoresist are tuned by controlling the line spacing and rotation angle. Through in-situ compression tests, it is found that the modulus of the elastomer photoresist could be tuned from 284 MPa to 665 MPa, the yield strength from 43 MPa to 59 MPa, and the initial cycle energy absorption from 18 MJ/m³ to 27 MJ/m³, showcasing an effective strategy of tuning mechanical properties through printing parameters. Finally, three types of recoverable structures are designed and printed, validating the potential of this elastomer photoresist for applications in flexible electronics and microelectronic device protection. This study provides an effective approach for the design of elastomer photoresist and the tunable mechanical properties of TPP-3D printed structure.