Laser sintering of hydroxyapatite by layer-wise slurry deposition (LSD) Dissertation

Layer-wise slurry deposition (LSD) is an approach in solid freeform fabrication (SFF), that can be used for fabrication of hydroxyapatite (HA) bone implants. In view of biocompatibility, HA is a suitable ceramic material for hard tissue replacement implants. SFF technique is the prototyping of objects directly from computer models without part-specific tooling or human intervention. A slurry is processed by a LSD device designed by the Clausthal University of Technology. The general purpose of this method of rapid prototyping (RP) is to reduce the time for product development by shortening the period between design and testing without using of any mould. Another useful feature of the technology is to provide a relatively simple interface to the sliced geometry from computer aided design (CAD) solids models of sources such as computed tomography (CT) and magnetic resonance imaging (MRI) images. LSD process is sequentially layering of slurry and then laser sintering of these layers. The aim of the present work is to analyze the influence of laser parameters on the LSD fabrication process of HA implant. The rheological properties of the hydroxyapatite slurries play an important role in facilitating the layering operation. The most influential process parameters on microstructure and composition of the samples are laser power and laser beam speed. The current work focuses on the preparation of stable-dispersed HA ceramic slurries for LSD and investigation on the effects of laser parameters on the LSD process and penetration depth. Xray diffraction (XRD), fourier transformation infrared spectroscopy (FTIR) and scaning electron microscopy (SEM) were used to investigate the influence of laser parameters on the formation of the phases. After laser sintering the presence of α-tricalcium phosphate (TCP) and amorphous calcium phosphate (ACP) was detected. TCP and ACP are beneficial for accelerated fixation and remodeling of the prothesis. The laser sintered samples have a high porosity that the pore size of samples expressed as a function of laser parameters and green density of layer. Also, this current work includes comparing of the direct laser sintering process with conventional sintering of layers. Also, in this study, the fabrication of the porous and dense glass-reinforced HA composite by laser sintering and conventional sintering has been investigated. The final microstructure consisted of a triphasic bioceramic after sintering.