Development of calcium phosphate suspensions suitable for the stereolithography process

With the median age of the population steadily rising, the rate of bone disorders increases as well, making the need of bone implants more and more urgent in our society. However, manufacturing of synthetic bioimplants requires high flexibility of the process and materials with sufficient mechanical strength and biocompatible properties. This paper is devoted to the printing of 8-tricalcium phosphate (8-TCP) by stereolithography. The suspensions or pastes containing the photosensitive-resin mixed with 8-TCP powder were assessed for the following parameters: rheological behaviour, thermal degradation of photo-cured samples, quality of green and sintered parts. It appeared that the composition of the photo-sensitive resin influences the viscosity of the paste. However, no direct correlation could be drawn between the viscosity of the photo-sensitive resins and the viscosity of the whole paste. A hypothesis is that the chemical structure of the monomers composing the photosensitive resin also impacts the viscosity of the paste. A thermal debinding cycle was built from the thermogravimetric analysis of the photo-cured samples. The structure of the post printed (green) parts and final parts (parts after debinding and sintering) was evaluated. It appeared that the pastes with the lowest viscosity were the easiest to process, and that the green parts made with these pastes were the easiest to clean, reducing the number of defects in the sintered parts. Process optimisation was also assessed. Different light parameters were evaluated, and it appeared that reducing the light power during the printing improved the resolution as well as the quality of the sintered parts.