Manuel Elices is a Foreign Member of the National Academy of Engineering, USA, Member of the Royal Spanish Academy of Sciences, Member of the Royal Spanish Academy of Engineering, and Emeritus Professor of Materials Science at the Polytechnical University of Madrid, Spain. Gustavo Guinea is a Corresponding Member of the Royal Spanish Academy of Sciences, Professor of Materials Science, former Director of the Centre for Biomedical Technology at the Polytechnic University of Madrid, Spain, and Head of the Laboratory for Biomaterials and Regenerative Engineering at this Centre. John Morton is a Fellow in Engineering Science at University College Oxford, UK.