Abstract: BACKGROUND: Polyetheretherketone materials have the advantages of stable physical, chemical and mechanical properties, radiation transparency and elastic modulus similar to human bones, but there is a biological inertia problem, which limits its clinical application.
OBJECTIVE: To evaluate the biocompatibility of polyetheretherketone/hydroxyapatite composites prepared by fused deposition molding 3D printing. 
METHODS: Polyetheretherketone and polyetheretherketone/hydroxyapatite composite materials (hydroxyapatite mass fraction 10%) were prepared by fused deposition molding 3D printing technology, which were denoted as polyetheretherketone group (control group) and polyetheretherketone/hydroxyapatite group (experimental group). Passage 3 mouse preosteoblasts (MC3T3-E1) were co-cultured with the extracts of the two groups of materials, separately.  Cells cultured alone were used as positive controls. The survival and proliferation of MC3T3-E1 were detected by Live/Dead fluorescence staining and CCK-8 assay. The adhesion growth and proliferation of MC3T3-E1 on the surface of the materials were observed by scanning electron microscopy. 
RESULTS AND CONCLUSION: (1) Live/Dead fluorescence staining exhibited that the MC3T3-E1 cells in two kinds of extracts grew well and presented good viability. The cell survival rate was higher than 90%. The two materials had no obvious cytotoxicity. The cells proliferated well with the extension of culture time. (2) The results of CCK-8 assay showed that the cytotoxicity of the two kinds of materials was qualified. The proliferation absorbance value of cells in the experimental group was higher than that of positive control group and control group at 3, 5 and 7 days of culture (P < 0.05). (3) Scanning electron microscope observation showed the good adhesion and cell spreading. Matrix secretion of MC3T3-E1 cells was numerous in the experimental group at 1 day of inoculation. The number of cells adhering to the surface of the two groups of materials increased, and more matrixes were secreted at the same time, among which the number of cells adhering to the surface of the experimental group and the secretion of matrix were more at 3 days of inoculation. The overlapping growth of cells appeared on the surface of the two groups of materials, and the cells in the experimental group were more efficient in spreading growth and secreting matrix at 7 days of inoculation. (4) These findings verify that the polyetheretherketone/hydroxyapatite composite prepared by 3D printing has good biocompatibility. 

Key words: 3D printing, fused deposition molding, polyetheretherketone, hydroxyapatite, composite, biocompatibility, cage, mouse preosteoblast