title: Structural, nanomechanical, and computational characterization of D,L-cyclic peptide assemblies.
abstract: The rigid geometry and tunable chemistry of D,L-cyclic peptides makes them an intriguing building-block for the rational design of nano- and microscale hierarchically structured materials. Herein, we utilize a combination of electron microscopy, nanomechanical characterization including depth sensing-based bending experiments, and molecular modeling methods to obtain the structural and mechanical characteristics of cyclo-[(Gln-D-Leu)4] (QL4) assemblies. QL4 monomers assemble to form large, rod-like structures with diameters up to 2 μm and lengths of tens to hundreds of micrometers. Image analysis suggests that large assemblies are hierarchically organized from individual tubes that undergo bundling to form larger structures. With an elastic modulus of 11.3 ± 3.3 GPa, hardness of 387 ± 136 MPa and strength (bending) of 98 ± 19 MPa the peptide crystals are among the most robust known proteinaceous micro- and nanofibers. The measured bending modulus of micron-scale fibrils (10.5 ± 0.9 GPa) is in the same range as the Young's modulus measured by nanoindentation indicating that the robust nanoscale network from which the assembly derives its properties is preserved at larger length-scales. Materials selection charts are used to demonstrate the particularly robust properties of QL4 including its specific flexural modulus in which it outperforms a number of biological proteinaceous and nonproteinaceous materials including collagen and enamel. The facile synthesis, high modulus, and low density of QL4 fibers indicate that they may find utility as a filler material in a variety of high efficiency, biocompatible composite materials.
authors.affiliation: †Harvard University, School of Engineering and Applied Sciences, Cambridge, Massachusetts 02138, United States.|‡Wyss Institute for Biologically Inspired Engineering, Cambridge, Massachusetts 02138, United States.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Rubin
authors.affiliation: §School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.|∥Center for Biomimetic Sensor Science, Nanyang Technological University, Singapore 637553, Singapore.
authors.forename: Shahrouz
authors.initials: S
authors.lastname: Amini
authors.affiliation: §School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
authors.forename: Feng
authors.initials: F
authors.lastname: Zhou
authors.affiliation: §School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.
authors.forename: Haibin
authors.initials: H
authors.lastname: Su
authors.affiliation: §School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore.|∥Center for Biomimetic Sensor Science, Nanyang Technological University, Singapore 637553, Singapore.|⊥School of Biological Sciences, Nanyang Technological University, Singapore 637551, Singapore.
authors.forename: Ali
authors.initials: A
authors.lastname: Miserez
authors.affiliation: †Harvard University, School of Engineering and Applied Sciences, Cambridge, Massachusetts 02138, United States.|‡Wyss Institute for Biologically Inspired Engineering, Cambridge, Massachusetts 02138, United States.
authors.forename: Neel S
authors.initials: NS
authors.lastname: Joshi
mesh_terms: D055119:Elastic Modulus; D008422:Materials Testing; D056004:Molecular Dynamics Simulation; D057139:Nanofibers / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D010456:Peptides, Cyclic
keywords: amyloid; cyclic peptides; elastic modulus; molecular dynamics; nanoindentation; supramolecular