Strengthen additively manufactured micro-springs with ultraviolet post-curing treatment

As an emerging micro-nano additive manufacturing technology , two-photon polymerization (TPP) technology suffers from modelling failure due to the collapse or entanglement of printed structures caused by a capillary force raised in a develop step. Here, ultraviolet (UV) curing is applied to strengthen the TPP-printed micro-springs and reliable 3D printing of robust micro-springs with high aspect ratios is demonstrated. The influence of laser power and scanning speed on the structure quality is explored to optimize the TPP printing process. With UV curing introduced in the TPP process, it is found that collapse and entanglement of micro-springs are greatly improved as prolonging the UV curing time. To theoretically understand the phenomenon, numerical simulation of the mechanical response of micro-springs to a capillary force generated as developer solution evaporates is performed. The results show that the displacement of micro-springs is shortened as elevating Young’s modulus of the micro-spring material or decreasing micro-spring height. This suggests that Young’s modulus enhanced by UV curing makes micro-springs robust and well-resist the influence from capillary force. The positive role of UV curing in strengthening TPP-printed 3D structures would facilitate the development of TPP in practical micro-manufacturing.