Segmental bone defects are a severe challenge in orthopaedic surgery. Besides inherent material properties like biocompatibility and mechanical performance, the irregular shape and individual size of such defects shows the need for innovative fabrication techniques. Additive manufacturing (AM) is the key to patient-specific implants with accurate fitting and bone ingrowth. The aim of this study was to fabricate segmental bone implants by combining 3D powder printing (3DP) as AM technique with centrifugally casting of mineral bone cements. To match mechanical requirements hydroxyapatite (HA) and poly-HEMA were used as a model for a dual-setting system.
Materials & Methods
Pure HA was prepared by α-TCP and a Na2HPO4 solution. For the dual-setting system, powder phase composed of α-TCP and 0.5 % APS was mixed with the liquid phase HEMA, TEMED and Na2HPO4 solution. Centrifugally casting was performed with an IKA RW16 basic stirrer in micro tubes. HEMA was added with concentrations up to 50 % and compared to pure HA. Prior to wet testing, samples were stored for 7 days at 37 °C. A universal testing machine was used for the brittle ring test at a test speed of 1 mm/min. Toughness was calculated by integration of the strength-elongation curve.
Results & Discussion
We were able to fabricate replica of a long bone segment by centrifugally casting technique. For the systematic investigation of the materials properties, rotationally symmetric tubes were produced. However, it was also possible to generate a replica of a long bone segment by an irregular shaped silicone mould prepared from a 3D printed defect model. In addition to the shape adaption, the material properties were tuned. Calcium phosphate cements like HA are very brittle and therefore not suitable for load-bearing defects. By the addition of poly-HEMA the toughness could be increased enormously due to a higher ductility.
By the combination of 3DP and centrifugally casting, we fabricated patient-specific long-bone replacements. Furthermore, the mechanical performance of the brittle HA could be improved to a rather damage tolerant, ductile compound. The ductility can be adjusted by applying a dual-setting cement paste with the simultaneous polymerisation of an organic phase.