[1] Washington State Univ, Sch Engn & Comp Sci, Vancouver, WA 98686 USA
[2] Georgia Inst Technol, George W Woodruff Sch Mech Engn, Coll Engn, Atlanta, GA 30313 USA
[3] Georgia Inst Technol, Bioengn Program, Petit Inst Bioengn & Biosci,Neural Engn Ctr, Ctr Flexible Elect,Inst Engn & Nanotechnol,Inst B, Atlanta, GA 30332 USA