Hydrostatic support-free fabrication of three-dimensional soft structures

This paper presents a support-free fabrication method for three-dimensional soft structures by creating a hydrostatic condition. The hydrostatic force inside the polymer resin can, theoretically, keep a soft structure in position and shape. The key technology behind this method is the low one-photon polymerization (LOPP), which can initiate polymerization at the focusing spot under the resin surface, as opposed to the surface one-photon polymerization in stereolithography (SLA). To prove the concept of LOPP, an optics setup for a wide beam gradient along with a low-absorption wavelength was built for this study. An ultraviolet (UV) curable silicone was adopted as the soft material. The experiments consisted of a qualitative observation for LOPP phenomenon and a quantitative study on the cured geometry and volume under various UV exposure conditions. Results have demonstrated the “in-liquid” polymerization using LOPP and also unveiled the challenges of geometrical resolution and accuracy as a function of UV beam gradient, intensity, and exposure time. Further investigation is required for better control over this method.