1. School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, Scotland, United Kingdom
2. European Synchrotron Radiation Facility, BP220, 38043 Grenoble, Grenoble Cedex 9, France
3. Biomaterials Centre, School of Optometry and Vision Sciences, University of Cardiff, King Edward VII Avenue, Cardiff CB10 3NB, Wales, United Kingdom