Department of Biomedical Engineering, Kings College London, London, SE1 7EH, UK. giovanni.montana@kcl.ac.uk.|Department of Biomedical Engineering, Kings College London, London, SE1 7EH, UK. alastair.young@imperial.ac.uk.|Department of Mathematics, Imperial College London, London, SW7 2AZ, UK. giovanni.montana@kcl.ac.uk.