Laminated object manufacturing of bioactive ceramic implants
Final Report Abstract
Multilayer hydroxyapatite (HAP) and tricalcium phosphate (TCP) ceramics were developed using a water-based tape casting and lamination process. The tape casting slurries were optimized concerning high solid loading at low viscosity. Monolithic HAP laminates sintered at 1250 °C attained a fractional sintering density of >99%. Multilayer laminates with a sandwich HAP-TCP-HAP structure were produced by pressureless sintering at 1150 °C. Differential sintering due to differences in sintering rates between HAP and TCP layers was recorded and correlated with critical conditions for achieving delaminaion free multilayer composites and a residual porosity of < 5%. Multilayer sandwich TCP-HAP-TCP and TCP-TCP-TCP laminates were produced with different TCP raw materials varying in the thermal expansion coefficient. Strengthening of the multilayer composites by forming residual compressive stresses on the outer surface layers was investigated. In TCP-HAP-TCP and TCP-TCP-TCP sandwich laminates residual compressive stresses in the outer surface layers of approximately 15 and 10 MPa, respectively, were measured by surface strain relaxation method. The residual compressive stresses gives rise for an increase of compound bending strength by about 15 % compared to stress free laminates. In conclusion, formation of residual stresses in calciumphosphate based bioceramics was successfully demonstrated. Though the increment of residual stress strengthening is still rather small, optimization of processing and composition is expected to yield improved mechanical properties. Enhancement of biomechanical performance offers a high potential to extend application of bioactive as well as bioresorbable calciumphposphate based ceramic systems to (moderate) load bearing applications in bone regeneration.
Publications
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Influence of aggregated powder structures on sintering behaviour of multilayer hydroxyapatite laminates, J.Ceram. Sci.Techn. 2 (2011) 61-68
E. Hahn, J. Hum, J. Will, K. Zuo, D. Jiang, P. Greil
