Understanding Factors Affecting Alignment of Self-Assembling Nanofibers Patterned by Sonication-Assisted Solution Embossing

Abstract

We recently reported simultaneous self-assembly, alignment, and patterning of peptide amphiphile (PA) nanofibers over large areas by a soft lithographic technique termed sonication-assisted solution embossing (SASE). The present work examines the effect of ultrasonication, channel width, and nanofiber persistence length λ on the degree of alignment of nanofibers patterned by SASE. Polarized transmission and reflection infrared spectroscopy are used to establish a figure of merit for comparing nanofiber alignment based on a model of the supramolecular structures being composed of oriented β-sheets. The aligned nanostructures show orientation parameters of up to 0.4, and estimates of λ the persistence length from AFM images range from 2.0 to 11 μm depending on the chemical structure of molecules used. The data suggest that stiffer nanofibers, defined as those with longer persistence lengths, may actually align less well due to increased difficulty in cleaving them during the alignment process. Alignment can be enhanced with the addition of ultrasonic agitation and confinement of the self-assembled structures within channels around 400 nm in width.

Effect of the Peptide Secondary Structure on the Peptide Amphiphile Supramolecular Structure and Interactions

“…This fibrillar structure is similar to those reported by analogous peptide amphiphiles rich in alanines immediately after the acyl chain (C 16 A x -peptide) reported in literature. 16,21,22 Hydrogen bonding occurs between adjacent PAs and runs axially along the micelles. It is not clear at this point whether there is a twist in the beta-sheets or they run parallel to the central axis.…”

Tuning Supramolecular Rigidity of Peptide Fibers through Molecular Structure

“…Previous FTIR studies of peptide amphiphiles have shown that the hydrogen bonding of β-sheets tends to be aligned along the long axis of fibers but with some amount of twisting or disruptions in the β-sheets 32,33,43. These studies were carried out on PA nanofiber monolayers using polarization modulation-infrared reflection absorption spectroscopy (PM-IRRAS), an FTIR method in which electric waves normal to a conductive surface are enhanced while the electromagnetic field parallel to the surface is eliminated.…”

Peptide conjugate hydrogelators

“…147 In all cases, lowering the pH past the second apparent pK a results in precipitation, with TEM showing large flat ribbons at lower pH where a gel is no longer present. IR spectroscopy demonstrates that the β-sheets were broken up with evidence of random coils appearing at low pH.…”