[1] UCL, Dept Chem, 20 Gordon St, London WC1H 0AJ, England
[2] Imperial Coll London, Inst Biomed Engn, Dept Mat, Dept Bioengn, London SW7 2AZ, England
[3] Univ Strasbourg, Inst Med Strasbourg, Biofunct Chem, UMR 7199, 74 Route Rhin, F-67400 Illkirch Graffenstaden, France