[1] Imperial Coll London, Dept Mat, Exhibit Rd, London SW7 2AZ, England
[2] Imperial Coll London, Dept Bioengn, Exhibit Rd, London SW7 2AZ, England
[3] Imperial Coll London, Inst Biomed Engn, Exhibit Rd, London SW7 2AZ, England
[4] Karolinska Inst, Dept Med Biochem & Biophys, Scheeles Vag 2, S-17177 Stockholm, Sweden