1. Department of Materials; Imperial College London; London SW7 2AZ UK
2. Division of Cell and Molecular Biology; Imperial College London; London SW7 2AZ UK
3. National Physical Laboratory; Teddington Middlesex TW11 0LW UK
4. The Institute of Biomedical Engineering; Imperial College London; London SW7 2AZ UK
5. Department of Bioengineering; Imperial College London; London SW7 2AZ UK
6. Department of Physics; Imperial College London; London SW7 2AZ UK