Multi-step exposure method for improving structure flatness in digital light processing-based printing

Abstract

Digital light processing (DLP)-based printing system equipped with ultraviolet (UV) source has been used to fabricate user-defined complex structures for biomedical applications. For printing large-scale structure, improving the structural consistency remains a challenge owing to the non-uniformly distributed UV light. Here, we present a multi-step exposure (MSE) method that takes advantage of a series of gradient digital masks to compensate the under-cured regions with additional UV exposure and eventually improve the surface flatness. First, for the established DLP-based printing system, the distribution of the UV power density is me asured and the relationship between the UV power density, exposure time and printing thickness are studied. The structure thickness can be calculated by the distribution of UV power density and exposure time. Then, the MSE method is proposed and an algorithm is customized to automatically modify the original mask into a series of gradient masks for MSE printing. Experimental validation was carried out by evaluating the morphologies of stripes printed without and with MSE. Printing of helix microfluidic chips revealed that the consistency of the channel thickness can be ensured by employing the MSE method. Thus, this MSE method for DLP-based printing is promising for printing large-scale structures with a consistent thickness and high resolution.