Development of a novel aqueous hydroxyapatite suspension for stereolithography applied to bone tissue engineering

Stereolithography (SLA) has a good ability to form complex bodies, while hydroxyapatite (HA) ceramic has good mechanical and biological properties because of its similarity in composition with natural bone. Some researchers tried combining SLA technology with HA bioceramic for bone tissue engineering. However, the ceramic suspension used in SLA generally has a relatively higher viscosity and are not environmentally friendly. In this paper, a novel aqueous HA suspension for SLA applied to bone tissue engineering was developed. The effect of surfactant concentration, solid loading and particle size on the rheological property of the HA suspension was investigated to preliminarily determine the formulation of the suspension. By a viscosity test and a sedimentation experiment, a conclusion was drawn that the surfactant PAA-NH4 had an optimum concentration of about 0.3 mg/m2. In addition, the maximum value of viscosity reached up to 7.3 Pa s, when the solid loading was 56 vol%. Taking account of viscosity of suspension and the strength of sintered parts, the particle size of 1 µm was relatively reasonable to be used in the HA suspension. According to the study of curing behaviour, the suspension had a critical exposure of 20.3 mJ/cm2 and a penetration depth of 50.7 µm. The final sintered HA parts provided a strength of 37 MPa meeting the requirement of cancellous bone, and was similar to original HA powders in chemical composition implying an ideal biological performance. Therefore, this kind of HA suspension has a broad prospect in bone tissue engineering applied to the treatment of bone disease for thousands of people.