1. Department of Materials Science and Engineering and A. J. Drexel Nanomaterials Institute, Drexel University, Philadelphia, Pennsylvania 19104, United States
2. Department of Neurology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
3. School of Applied Sciences, University of Brighton, Brighton BN2 4AT, U.K.
4. Department of Oral and Maxillofacial Surgery & Pharmacology, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania 19104, United States
5. Department of Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
6. Department of Physical Medicine and Rehabilitation, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States