Design of Highly Porous Hydroxyapatite Scaffolds by Conversion of 3D Printed Gypsum Structures – A Comparison Study

Hydroxyapatite (HA) is a bioceramic material with excellent biological properties. However, these properties are strongly dependent of its crystallinity degree, with high values of crystallinity associated to poor resorption rates and bioactivity. This work evaluates the properties of HA samples produced by two different free-forming conformation methods, CNC machining and 3D printing. In both cases, porous gypsum samples were produced and subsequently converted into HA in a reaction with di-ammonium hydrogen phosphate at 100 °C and pH 8. A total conversion of the samples was achieved after 36 h independently of the conformation method used. The microstructure, however, before and after the conversion is showed to be dependent on the method used. After conversion the machined samples achieved a maximum compressive strength of 3.5 MPaforporosities of circa 80%, while 3D printed samples achieved a tensile strength of 2.0 MPa by porosities of 61%.