Customizable and highly sensitive 3D micro-springs produced by two-photon polymerizations with improved post-treatment processes

Springs are ubiquitous in a variety of scientific and engineering fields. However, the comprehensive study on mechanical properties of micro-spring has not been fully conducted yet due to a lack of reliable productions of varied-shaped micro-springs. Here, we report the design and manufacturing of triple-helix-shaped springs employing two-photon polymerization (TPP) technologies and present a systemic study on the mechanical properties of micro-springs particularly involving spring constants of k. To construct high-quality hollow microstructures, we optimize the TPP process by combining violet light post-treatment with a proper selection of cleaning liquid. Consequently, we demonstrate that the sensitives k can be actively tuned over a range of two orders of magnitude, from ∼1.5 to ∼108.2 μN/μm while maintaining a high resolution of ∼1 μN/μm. Furthermore, compression tests showcase an excellent agreement among all force-vs-displacement lineshapes, resulting in a small k fluctuation of <1%. On the whole, we expected that the modified TPP technique along with proposed helical springs opens an alternative avenue toward micro-scale force detection, leading to potential applications in the field of bio-sensing, where typical forces to be measured exist within a broad range from several piconewtons to several micronewtons.