Effects of dispersant concentration on the properties of hydroxyapatite slurry and scaffold fabricated by digital light processing

For the UV-curable hydroxyapatite (HA) slurry used in digital light processing (DLP), the optimal dispersant concentration is always selected based on the viscosity and stability of the slurry. However, the interaction mechanism between the dispersant and HA particles and its influence on the fabrication process were overlooked. In this study, the dispersion mechanism of BYK111 and its effects on the rheology, stability, and curing behavior of the HA slurry, as well as the linear shrinkage and layer morphology of the HA scaffold, were systematically investigated. The results indicated that changes in viscosity and stability affected the penetration of UV light and the propagation rate of the polymerization reaction. Insufficient dispersion of the slurry (3 wt% BYK111) led to reduced printing precision due to high viscosity, settling, and scattering. Interestingly, the lower viscosity and enhanced stability of HA slurry with 4 wt% BYK111 did not yield both the deepest curing depth and narrowest excess curing width. The high curing accuracy of the HA slurry (4 wt% BYK111) was evidenced by the largest broadening depth. Moreover, the improved slurry performance also helped reduce printing defects and improve surface quality.