Hydroxyapatite implants with designed internal architecture

Porous hydroxyapatite (HA) has been used as a bone graft material in the cl inics for decades. Traditionally, the pores in these HAs are either obtaine d from the coralline exoskeletal patterns or from the embedded organic part icles in the starting HA powder. Both processes offer very limited control on the pore structure. A new method for manufacturing porous HA with design ed pore channels has been developed. This method is essentially a lost-mold technique with negative molds made with Stereolithography and a highly loa ded curable HA suspension as the ceramic carrier. Implants with designed ch annels and connection patterns were first generated from a Computer-Aided-D esign (CAD) software and Computer Tomography (CT) data. The negative images of the designs were used to build the molds on a stereolithography apparat us with epoxy resins. A 40 vol% HA suspension in propoxylated neopentyl gly col diacrylate (PNPGDA) and iso-bornyl acrylate (IBA) was formulated. HA su spension was cast into the epoxy molds and cured into solid at 85 degreesC. The molds and acrylate binders were removed by pyrolysis, followed by HA g reen body sintering. With this method, implants with six different channel designs were built successfully and the designed channels were reproduced i n the sintered HA implants. The channels created in the sintered HA implant s were between 366 mum and 968 mum in diameter with standard deviations of 50 mum or less. The porosity created by the channels were between 26% and 5 2%. The results show that HA implants with designed connection pattern and well controled channel size can be built with the technique developed in th is study. (C) 2001 Kluwer Academic Publishers.