Magnesium alloy biodegradable scaffolds: Simulation of casting and manufacturing

Metallic scaffolds of magnesium alloys combine the properties of biodegradability and biocompatibility of the base material with the best of physical and mechanical properties of these structures, such as high energy absorption, controlled degradation, high permeability for gas and liquid and high strength-to-weight ratio. All these characteristics allow a wide application of these metallic structures in biomedical fields, for instance prostheses and even for the control of release, diagnosis and detection of drugs in the organism. Furthermore, once fabricated in open cells scaffolds, these structures allow the growth of new bone tissue and ease the transport of body fluids. A large number of processes are commonly used to manufacture these metallic structures, such as castings process, powder metallurgy, additive techniques, among others. The purpose of this work is the manufacturing of metallic scaffolds in magnesium alloys (AZ91D Eco) by vacuum investment casting process. Open cell models were obtained with additive manufacturing techniques which were used to produce the plaster moulds. The molten alloy was then poured, in a vacuum chamber (0-1 bar), to obtain the final scaffolds. Different experimental values of vacuum pressure and geometries were analyzed to study the filling capacity and compared with numerical casting simulation performed in NovaFlow&Solid software package. The results allowed to conclude that the increase of vacuum pressure promotes a better filling of the mould cavities and a better sanity of the final samples. In addition, the variation of the geometry had large influence in the filling behavior.