Suppressing the Step Effect of 3D Printing for Constructing Contact Lenses.

3D printing has been considered as a sustainable method to construct complicated 3D structures. However, the step effect induced by the traditional point-by-point or layer-by-layer additive manufacturing mode inevitably occurs and remains an obstacle to realizing the smoothness and uniformity of 3D samples. Here, a continuous liquid film confined 3D printing strategy is proposed to fabricate high-precision 3D structures based on the Digital Light Processing (DLP) technology. With the control of the confinement of the liquid-solid interface and the continuous printing mode, liquid film adhering to the cured structure is sucked into the cured layer structures with excess resin adhering to the cured structure scraping off, where the step effect is eliminated and post-washing is avoided. The morphology and dimension of the confined liquid film can be well regulated by ink properties and printing parameters to optimize the surface smoothness and printing fidelity. In addition, heat accumulation and thermal diffusion are also suppressed, ensuring the long-term printing stability. A centimeter-scale contact lens structure with central thickness of ≈135 µm comparable to commercial ones can be printed, which possesses extreme smoothness (sub 1.3 nm), homogeneous mechanical characteristic, biocompatibility, and high optical properties with imaging resolution of up to 228.1 lp mm-1 .