Characterisation and modelling of a periodically distributed porosity gradient in functionally graded materials

New trends in the design and manufacture of orthopaedic implants and scaffolds are moving towards the fabrication of functionally designed specimens that not only offer a network for the cells to grow and proliferate on, but also an environment in which this process can be accelerated (e.g. using tailored chemistry for the cavities’ walls, and a porosity gradation to alleviate clogging and isolation of the cells that are situated at the very centre of the scaffold). This new strategy for the generation of geometries and chemical environments is aligned with the biomimetic approach of manufacturing, in which the final specimen is made to both look like and behave like natural materials (muscle, cartilage, and bone tissues etc.). The work presented here is an example of this emerging research field: a sonication technique is used to manufacture a porosity graded materials to match the requirements of biological substrates for bioengineering applications. The characterisation of the density distribution in these solid foams is of vital importance because this data can be used to inform the manufacture process and further improve their properties and functionalities. However, the manufacture of functionally tailored materials (e.g. density engineered foams) has developed at a faster pace than methods for their effective representation and analysis. Consequently, a standard methodology for the 3d characterisation and quantification of density gradient materials is still missing. The intention of bringing this problem to the attention of mathematicians and modellers was to generate ideas and workable solutions for the quantification and representation of porosity tailored structures. Once this is achieved, there is an opportunity to fully exploit the manufacturing of these artifacts for use in orthopaedic applications.