1. 1Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA; email: prl@andrew.cmu.edu
2. 2Current affiliation: Department of Neuroscience, Scripps Research, San Diego, California, USA
3. 3Current affiliation: Department of NanoEngineering, University of California San Diego, La Jolla, California, USA
4. 4Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA; email: minden@andrew.cmu.edu
5. 7Department of Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
6. 5Department of Computational Biology, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA
7. 6Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA