High performance hydroxyapatite (HA) ceramics with excellent densification and mechanical properties were successfully fabricated by digital light processing (DLP) three-dimensional (3D) printing technology. It was found that the sintering atmosphere of wet CO2 can dramatically improve the densification process and thus lead to better mechanical properties. HA ceramics with a relative density of 97.12% and a three-point bending strength of 92.4 MPa can be achieved at a sintering temperature of 1300 , which makes a solid foundation for application ℃ in bone engineering. Furthermore, a relatively high compressive strength of 4.09 MPa can be also achieved for a DLP-printed p-cell triply periodic minimum surface (TPMS) structure with a porosity of 74%, which meets the requirement of cancellous bone substitutes. A further cell proliferation test demonstrated that the sintering atmosphere of wet CO2 led to improve cell vitality after 7 days of cell culture Moreover, with the possible benefit from the bio-inspired structure, the 3D-printed TPMS structure significantly improved the cell vitality, which is crucial for early osteogenesis and osteointegration.

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Due to the lack of commercially available high-quality hydroxyapatite (HA) powder, it is still rarely reported by the literature concerning the development of UV resin for digital light processing 3D printing. The previous studies still had the problem of delamination and also poor sintering performance led by low solid-load slurry. Here low viscosity and high solid-load hydroxyapatite (HA) UV resin suspensions were developed for digital light processing 3D printing. In this study, the effect of the type of dispersant, the dose levels of dispersant and the solid load of HA powder on the rheology properties were thoroughly investigated to obtain a flowable highly-concentrated HA UV resin suspension. Finally, a 40vol% slurry with viscosity of 3.7Pa·s at a shear rate of 10 s-1 was successfully developed. After 3D printing and sintering, a dense ceramic with relative density of 95.85% can be obtained at a sintering temperature of 1300°C.