Abstract: BACKGROUND: The repair of large-scale bone defects is still facing serious challenges. It is of great significance to develop personalized, low-cost, and osteogenic-inducing tissue engineering scaffolds for bone repair.
OBJECTIVE: To explore the process of 3D printing bone tissue engineering scaffold containing pearl composite material by low-temperature condensation deposition method, and further test the physicochemical properties and in vitro biological functions of the composite scaffold. 
METHODS: Pearl powder was prepared by grinding and sieving. The pearl powder of different qualities was added into the poly-L-lactic acid ink, so that the mass ratio of pearl powder to poly-L-lactic acid was 0, 0.1, 0.2, 0.3, and 0.5, respectively. The 3D-printed poly-L-lactic acid/pearl powder scaffolds were prepared using the low-temperature condensation deposition method. The microstructure, compressive properties, water contact angle, cytocompatibility, and in vitro bone differentiation ability of the printed poly-L-lactic acid/pearl powder composite scaffolds were detected. 
RESULTS AND CONCLUSION: (1) Scanning electron microscopy showed that the five groups of scaffolds all had micropores with a diameter of 2 μm or even smaller, irregular shapes and interconnectivity. (2) All the five groups had good compressive properties. The compressive strength of the pearl powder 0.5 group was higher than that of the other four groups (P < 0.05). The water contact angle of the pearl powder 0.2 group and the pearl powder 0.5 group was smaller than that of the pearl powder 0 group (P < 0.01, P < 0.001). (3) Bone marrow mesenchymal stem cells were co-cultured with five groups of scaffolds for 1, 3, and 5 days, respectively. The cell proliferation in pearl powder 0.1, 0.2, 0.3, and 0.5 groups cultured for 3 and 5 days was faster than that in pearl powder 0 group (P < 0.05). After 1 day of culture, live-dead staining exhibited that the number of cells on the scaffold was small, but all of them were living cells. (4) Bone marrow mesenchymal stem cells were inoculated on the scaffold surface of the pearl powder 0 group and pearl powder 0.1 group respectively for osteogenic differentiation. The alkaline phosphatase activity induced for 4 and 6 days in the pearl powder 0.1 group was higher than that in the pearl powder 0 group (P < 0.05). (5) The results showed that the poly-L-lactic acid/pearl powder composite scaffold had good compressive strength, hydrophilicity, cytocompatibility, and osteogenic properties.

Key words: low-temperature condensation deposition method, 3D printing, poly-L-lactic acid, pearl powder, composite scaffold, bone tissue repair, cytocompatibility, osteogenic differentiation