Continuous printing of bone-inspired hierarchical porous objects using video projection-based stereolithography

Abstract

Bone-inspired porous structures have attracted intense attention in biomedical and mechanical applications due to their unique combination of strength, toughness, and low weight. Although layer-by-layer-based additive manufacturing techniques can build structures with high geometric complexity, it remains challenging to fabricate porous objects with gradient porosity and pore size ranging from nano- to micro-scale. This research investigates the video projection-based stereolithography (VP-SL) process, which is a continuous 3D printing process, also known as Continuous Liquid Interface Production (CLIP), for fabricating hierarchical porous structures with nano-, micro- and macro-scale pores and surface features. This work tested the hypothesis that tuning the printing speed during the VP-SL process can generate an imbalance between curing and resin recoating, resulting in pores in cured polymer. First, the VP-SL process, setup, and the mechanisms of forming micropores and nanowrinkles were introduced. Then, the printing range of the VP-SL process was characterized using curing depth experiments. To validate the efficiency and feasibility of the proposed approach, various three-dimensional hierarchical structures were fabricated with homogeneous and gradient porosity, and the effect of porosity distribution on mechanical properties was studied. Test cases were printed and characterized to validate the feasibility and efficiency of the proposed approach. The results demonstrated the capability of the VP-SL process and its potential in the production of gradient porous objects for various applications, such as scaffolds for custom bone implants.