High-fidelity and high-efficiency additive manufacturing using tunable pre-curing digital light processing

Abstract

To improve printing fidelity, reducing the slice thickness to eliminate the staircase effect is of great importance for digital light processing (DLP) technology. However, using a thinner slice printing model leads to a longer total printing time in the conventional DLP approach, which significantly reduces printing efficiency. In this work, a tunable pre-curing DLP approach was developed where the relationship between the forming layer thickness and ultraviolet (UV) exposure time is theoretically analyzed, and the curing process of photo-curable solutions is divided into two sub-processes: pre-curing and further curing. In the pre-curing process, the photo-curable solution is initially pre-cured and kept at the pre-gelled state due to continuous UV exposure during subsequent DLP printing. Then, the pre-cured photo-curable solution is quickly cured to form a designed thickness in each printing cycle. Also, the UV absorbing agent is added to the photo-curable hydrogel solutions to regulate the pre-curing process. Using a 10 μm slice for DLP printing, the total printing time of the tunable pre-curing DLP is approximately 5.6% of the conventional DLP, and the staircase effect on the surface is significantly eliminated using 10 μm slice tunable pre-curing DLP approach, which leads to a better printing fidelity. Thus, both printing fidelity and efficiency are significantly and simultaneously improved by the tunable pre-curing DLP approach. Moreover, the reduction of UV exposure time and slice thickness is beneficial for cell viability during DLP bioprinting of thick bulk structures, which is demonstrated by the printing of PC12 cell-laden gelatin methacrylate (GelMA) bioinks. Using the tunable pre-curing DLP approach, the PC12 cells achieved higher cell viability (90.2 ± 6.1%) and better cell morphology than the conventional DLP approach (54.5 ± 4.8%). The tunable pre-curing DLP approach provides a promising alternative to extend the application of DLP printing greatly.