1. a Center for Biologically Inspired Materials & Material Systems, Duke University, Durham, NC 27708, USA; Mechanical Engineering and Materials Science, Pratt School of Engineering, Duke University, Durham, NC 27708, USA
2. b Center for Biologically Inspired Materials & Material Systems, Duke University, Durham, NC 27708, USA; Mechanical Engineering and Materials Science, Pratt School of Engineering, Duke University, Durham, NC 27708, USA