Indirect selective laser sintering of an apatite-mullite glass-ceramic
The main objective of this work was to determine the feasibility of using indirect selective laser sintering (SLS) to produce parts for bone replacement applications from glass-ceramic materials. A castable glass based on the system SiO2-Al2O3"P2O5-CaO-CaFth2a t crystallises to a glass-ceramic with apatite and mullite phases was produced, ground to a powder and blended with an acrylic binder at various ratios by mass. An experimental sinterstation with a 250W CO2 laser was used to determine the viability of indirectly sintering the glass ceramic across a range of processing parameters. Green parts with good structural integrity were produced using a wide range of processing conditions, allowing both monolayer and multilayer components to be constructed. The effect of powder properties, such as glass particle size and binder content, on the surface qualities and structural integrity of the parts was also examined. Following SLS the parts were post-processed to remove the binder which may otherwise have rendered them unsuitable for biological use, and fully crystallise the material, evolving the apatite and mullite phases to improve both biological and mechanical properties. The parts were heated to 1200°C using a number of different time-temperature profiles, following which the processed material was analysed by DTA, XRD, SEM, gCT, and tested for its flexural strength. An increase in strength was achieved by infiltrating the brown parts with PMMA and a resorbable phosphate glass, although the latter altered the crystal phases present in the material. In vitro cytotoxicity and bioactivity tests were carried out to assess the biological properties of the produced parts. The laser sintered material was found to be non-toxic by both contact and extract methods. There was no evidence of an apatite layer forming on the surface of the material when soaked in a simulated body fluid suggesting that the material was unlikely to exhibit bioactive behaviour in vivo. However, following implantation in rabbit tibiae for 4 weeks, bone was seen to have grown into the porous structure of the laser sintered parts, and appeared to form a close bond with the material surface.