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Selective Laser Sintering of Bioceramic Materials for Implants

Selective Laser Sintering (SLS) process is employed for fabrication of biocerarnics for orthopedic implants. Hydroxyapatite and Calcium Phosphate ceramics are coated with polymer as a intermediate binder by using a spray drier. Polymer coated materials are SLS processed to make green parts, which are infiltrated and fired to remove the polymer. SLS processed green parts of hydroxyapatite have low density due to the small particle size with large specific surface area. This paper discusses the possibilities and problems in free-form fabrication of bioceramic. INTRODUCTION Many attempts have been made to find material that will assist in the regeneration of bone defects and injuries. Calcium phosphate ceramics, particularly hydroxyapatite(HA), Cas(OH)(P04h, has received special attention as potential bone implant material because of its biocompatibility with the tissue and its compositional similarities to human bone and tooth. Many studies and methods, from powder compaction sintering to hot isostactic pressing, have been reported for the fabrication of HA. However, sintered HA materials by conventional techniques are as weak as sea coral even at high compacting pressure, because HA decomposes at temperatures lower than the required temperature for sintering. Selective Laser Sintering (SLS) processes for preparing ceramic green parts with polymer as intermediate binder and post processing with the aid of ceramic cement have been discussed in detail in literature [1]. One advantage of SLS process for fabrication of bioceramic is the accurate construction of a complete facsimile bone structure from the geometric information obtained from either patient computed tomographic (CT) data or a computer Aided Design (CAD) software package[2]. Another advantage is the ability to controlling pore structure for biogenesis through control of polymer content. MATERIALS and METHODS HA, obtained from Monsanto Inc. as Tricalcium Phosphate, TCP, was used as starting material. HA powders are very cohesive and consist of very porous agglomerates with mean particle size of 1 to 2 /lm and bulk density of less than 0.4 g/cm3 [3]. The surface area determined by Mercury intrusion analysis is about 60 m2/g, suggesting very small particles. Stoichiometric HA contains constitutional water in the form of OHions. This water can be driven off at 1200 oc. Figure 1 shows the microstructure of finely divided HA powders.