Understanding factors affecting alignment of self-assembling nanofibers patterned by sonication-assisted solution embossing

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 the persistence length λ from atomic force microscopy (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.