Parameter optimization for accurate and repeatable strut width in the 3D printing of composite bone scaffolds

Critically sized bone defects present a significant challenge to orthopedic surgeons due to the limited availability of autograft bone tissue, which is the current gold-standard treatment. As an alternative, 3D printed porous scaffolds can be designed to mimic bone's mechanical and biochemical properties to support tissue regeneration. However, 3D scaffold printing with high geometric accuracy and repeatability can be challenging, especially when printing new composite materials and geometries. Therefore, the objective of this study was to optimize the extrusion-based 3D bioprinting process parameters for composite polymer-ceramic scaffolds. Bone scaffolds composed of a polylactic-co-glycolic acid (PLGA) and 5 % nano-hydroxyapatite (nHA) composite were printed and analyzed to evaluate their geometric accuracy, which is primarily determined by process parameters. This empirical study investigated the effects of different process parameters, particularly, nozzle temperature, pressure, and printing speed, on the geometric accuracy (i.e., strut width) of the printed scaffolds. Starting with a full factorial design of experiments, in-situ layer-wise optical images were captured, which were analyzed using image processing for strut width characterization. Subsequently, a new iterative process optimization method was proposed that involves regression modeling and bound constraint-based minimization. A case study on printing a two-layer scaffold was used to demonstrate the effectiveness of the proposed method. Overall, the geometric accuracy of the printed scaffolds improved significantly, maintaining a range of +/- 5 % from the nominal strut width as iterative experiments were conducted, which demonstrates the significant potential of the proposed method in bioprinting process parameter optimization.