Dissertation Defense Schedule
Sharing original dissertation research is a principle to which the University of Delaware is deeply committed. It is the single most important assignment our graduate students undertake and upon completion is met with great pride.
We invite you to celebrate this milestone by attending their dissertation defense. Please review the upcoming dissertation defense schedule below and join us!
PROGRAM | Materials Science & Engineering
PROGRAMMABLE HIERARCHICAL CONSTRUCTION OF ONE DIMENSIONAL NANOSTRUCTURED MATERIALS FROM COMPUTATIONALLY DESIGNED HELICAL PEPTIDE BUNDLES
Naturally occurring protein materials exhibit a significant structural hierarchy that is highly related to their multifunctional properties. Mimicking the hierarchical assembly of natural fiber materials is an important design challenge in the manufacturing of nanostructured materials with biomolecules such as peptides. Peptides are desirable candidates for material building blocks due to their sequence-structure relationship as well as ease of chemical modification. In this dissertation, we have examined hierarchically assembled nanostructures constructed from computationally designed, helical peptide bundles and their properties including mechanical properties and solution behavior.
Firstly, hierarchically organized nanofiber materials were produced with control of structure over multiple length scales, ranging from peptide molecule assembly into supramolecular coiled coil ‘bundlemer’ building blocks, to rigid rod formation through covalent connection of the bundlemer building blocks, and, ultimately, to uniaxially-oriented fibers made with the rigid rod polymers. The basic peptide building blocks were designed to physically assemble into tetrameric coiled coil bundles, or bundlemers, and to covalently interact with each other in an end-to-end fashion via a thiol-Michael click reaction to produce rigid rod-like polymers. The rigid rod chains were used to produce solid fiber materials via electrospinning processing, all the while preserving their unique rod-like structural characteristics. Morphological and structural investigations of the nanofibers through scanning electron microscopy, transmission electron microscopy, and x-ray scattering, as well as molecular characterization via FTIR and Raman spectroscopy, reveal the continuous nanofibers are composed of oriented rigid rod chains constituted by alpha-helical peptides within bundle building blocks. Additionally, mechanical property measurements show the stiffness and strength of the electrospun nanofibers are comparable with other protein fiber materials. The establishment of multiscale hierarchy by producing fiber materials from the oriented rigid-rod polymer reveals bundlemer rod chains as a viable tool for the development of new fiber materials with targeted structure and properties.
Moreover, we have explored microstructure and viscoelastic properties of concentrated rod suspensions. Due to structural stability, rigidity, and unique rod-like structure, the rod polymers are expected to exhibit rheological properties characteristic of rigid rods and liquid crystals in suspension. Additionally, adjusting inter-rod interactions can affect the microstructure and rheological behavior of rod suspensions since rods can possess polyelectrolyte behavior due to the constituent peptide-based bundlemers and their exterior amino acid side chains. The importance of changes in the interactions between rods under different surface charge density based on sequence, pH, and ionic strength conditions are illustrated through comparisons of the microstructure and rheological behavior of rod suspensions. The combined observations by microscopy, x-ray scattering, and rheology help to elucidate the possible interactions and consequent microstructures responsible for the resulting structural information and solution behavior as well as to expand our understanding of the bundlemer-based rods in solution state.
Our findings in this dissertation provide a fascinating opportunity to build new materials with desired structure and properties. The hierarchically constructed materials, through molecular design combined with solution processing, are promising candidates for use in a wide range of applications including biomedical and nanotechnology applications.