Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.|Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.|Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.|Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.|Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.|Mechanical and Instruments Division, Bioengineering Group, Cambridge, MA 02139, USA.