Role of Tyrosine in Native Silk Fiber Spinning and its Application to Biomaterial Development
Partlow, Benjamin.
2016
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Abstract: Native
silk fibers exhibit strength and toughness values that rival those of the best synthetic
fibers. In addition the silk worm is able to spin these fibers using only water as a
solvent with fine control of applied shear, pH and salt concentrations to efficiently
convert the spinning dope into a fiber. In contrast, synthetic polymers require harsh
solvents and extreme processing ... read moreconditions. These requirements result in the synthetic
fibers being orders of magnitude more energy intensive to produce and generating
chemical wastes that require disposal. It has been found that these fibers can be
solubilized and utilized in the field of biomedical engineering as a biomaterial for
tissue engineering and regenerative medicine applications. However, the processing of
the silk fibroin into these scaffolds and matrices results in significant protein
degradation. In order to provide material properties for the engineering of new
materials, we examine how the regeneration process impacts the rheological and material
properties of the resulting silk based biomaterials. Additionally, despite significant
research on the spinning processes of silkworms and spiders, a comprehensive
understanding of the mechanisms by which silkworms are capable of spinning such tough
fibers eludes researchers. Here we propose that π-π interactions of the
phenolic side chains on tyrosine residues provide a template to properly orient the silk
molecules such that the crystalline domains are in registration and drives the
self-assembly of the spinning dope. A combination of empirical and modeling based
approaches elucidate the role of the tyrosine residues present in the semi-crystalline
regions of the silk fibroin protein and how to exploit these interactions. The
association of the tyrosine residues and correlation to self-assembly in solution was
empirically determined by assessing the intrinsic fluorescence in combination with
circular dichroism. In situ FTIR found that enzymatic crosslinking of the tyrosine
residues initiated the immediate development of higher ordered combination. The degree
of crosslinking was similarly found to correlate with the final crystallinity when the
crosslinked samples were dehydrated. Molecular dynamic simulations were undertaken in
order to understand the atomistic association of these protein residues. The findings
are consistent with the empirical data suggesting that tyrosine is an important factor
in the self-assembly of the silk proteins. The activity of the tyrosine residues and
potential for crosslinking also provides for a facile method of generating materials
with unique and tunable properties which will be explored and characterized. Thus, a
greater understanding of the spinning process and role of the protein sequence has been
determined and provided avenues for expanding the platform of silk
biomaterials.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Biomedical Engineering.
Advisor: David Kaplan.
Committee: James Harden, Peggy Cebe, and Qiaobing Xu.
Keyword: Biomedical engineering.read less - ID:
- cz30q449h
- Component ID:
- tufts:21274
- To Cite:
- TARC Citation Guide EndNote
