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A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 8 2 1 TACKLING THE CHALLENGE OF BIOMATERIALS SELECTION Coming from an educational perspective, this article explores two case studies regarding biocompatibility specifically related to implantable medical devices and identifies some important issues to consider and how to address them. Claes Fredriksson and Phillipa Newby Granta Design, Cambridge, U.K. H owdowemake the right materials choices for bioengineering appli- cations? Here we draw on our ex- perience in creating and applying tools to address this question, both for teaching bioengineering students and for making materials selection choices in industry. CASE STUDY I: GLASS- CERAMIC SCAFFOLDS In the field of bone tissue engineer- ing, bioactive glass-ceramic scaffolds have generated significant interest, as they can provide a 3D template that promotes new bone formation. Such scaffolds have proven that they can mimic trabecular bone structure as well as exhibiting bioactivity to support the growth of new bone tissue [1] . Research is aiming to further improve the me- chanical properties of these highly po- rous scaffolds. These scaffolds were investigated here as part of an educa- tional project to help students under- stand the potential of these materials and the factors that limit them. For ma- terials that come into contact with the human body, biocompatibility is an essential requirement. Ensuring that thematerial will elic- it an appropriate biological response to a specific application, biocompat- ibility also addresses the importance of suitable structural and mechanical properties. This is particularly the case for implants that are part of the skele- tal system, where it is critical to avoid the stresses that might otherwise re- sult. The materials used must also be approved by regulators for use in the human body. Further, they must have appropriate porosity to be assimilat- ed by the body. The porosity of the im- plant material is linked to its average (effective) density in a linear fashion; the more porous, the lower the implant density. It is also linked to other proper- ties such as strength or stiffness. How do we find materials that meet these interrelated criteria? A sys- tematic approach is enabled by the CES EduPack educational software from Granta Design, which combines a comprehensive database of materi- als properties (including bioengineer- ing properties) with tools and methods that enable students to filter, identify, and compare candidate materials for an application. CES EduPack includes a synthesizer tool, with which it is pos- sible to investigate the influence of porosity on the biomechanical proper- ties of a scaffold material modeled as a foam. One can then compare these properties with other relevant biomate- rials and biological materials. The start- ing point for comparison in this study will be bone-like materials, such as calcium phosphate and bioglass vari- ants that fulfill typical biomedical con- straints. The main mechanical property to consider is compressive strength. The man-made scaffolds consid- ered have a porous structure that mim- ics trabecular bone porosity. They can induce formation of hydroxyapatite (HA) on their surfaces in physiological conditions that naturally encourage bone attachment and promote bone regeneration. However, these scaffolds exhibit certain drawbacks in terms of mechanical performance, as they do not have the required compressive strength for safe load-bearing applica- tions. Moreover, these materials have not yet been fully tailored to enhance their bone-regeneration capabilities. Nor has the structural integrity of the scaffolds been optimized, including their resistance to crack propagation. EXPLORING LIMITATIONS These limitations were demon- strated by comparing existing biolog- ical and biomedical materials with a range of hypothetical candidate mate- rials, with properties estimated by the synthesizer tool. This tool can mod- el properties, starting with typical me- chanical properties—yield strength and Young’s modulus—for hypothetical HA foams with relative densities ranging from 5% to 50%. The relative density for SEM image shows the typical porous structure of a bioglass-based glass- ceramic scaffold [2] .