1. Center for Bioengineering 56-341, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA. Tel.: ; Fax: ; E-mail: Shuguang@mit.edu
2. Wallenberg Laboratory Plan 2 UMAS, Malmö, S-20502, Sweden. Tel.: ; Fax: ; E-mail: sabina.janciauskiene@medforsk.mas.lu.se