Rheology of Dispersions of High-Aspect-Ratio Nanofibers Assembled from Elastin-Like Double-Hydrophobic Polypeptides

Abstract

Elastin-like polypeptides (ELPs) are promising candidates for fabricating tissue-engineering scaffolds that mimic the extracellular environment of elastic tissues. We have developed a “double-hydrophobic” block ELP, GPG, inspired by non-uniform distribution of two different hydrophobic domains in natural elastin. GPG has a block sequence of (VGGVG)5-(VPGXG)25-(VGGVG)5 that self-assembles to form nanofibers in water. Functional derivatives of GPG with appended amino acid motifs can also form nanofibers, a display of the block sequence’s robust self-assembling properties. However, how the block length affects fiber formation has never been clarified. This study focuses on the synthesis and characterization of a novel ELP, GPPG, in which the central sequence (VPGVG)25 is repeated twice by a short linker sequence. The self-assembly behavior and the resultant nanostructures of GPG and GPPG were when compared through circular dichroism spectroscopy, atomic force microscopy, and transmission electron microscopy. Dynamic rheology measurements revealed that the nanofiber dispersions of both GPG and GPPG at an extremely low concentration (0.034 wt%) exhibited solid-like behavior with storage modulus G′ > loss modulus G” over wide range of angular frequencies, which was most probably due to the high aspect ratio of the nanofibers that leads to the flocculation of nanofibers in the dispersion.

Fibrous Scaffolds From Elastin-Based Materials

“…Subsequent studies revealed the dependence of self-assembly on the VGGVG content per molecule. As reported (Sugawara-Narutaki et al, 2019), an increase in the proportion of VGGVG favors the formation of β-sheet structures, thus leading to the morphogenic alignment and coalescence of nanoparticles into branched nanofibers, which laterally assemble to form bundles over time.…”

Thixotropic Hydrogels Composed of Self-Assembled Nanofibers of Double-Hydrophobic Elastin-Like Block Polypeptides

“…The mechanisms of nanofiber formation of GPGs have been proposed as follows [ 29 , 30 , 33 ]. They consist of a two-step pathway: (1) GPGs hydrophobically assemble to form nanoparticles rich in β-turn structures through dehydration of the (VPGXG) 25 block, and (2) the nanoparticles connect into nanofibers along with the formation of β-sheet structures between the nanoparticles via (VGGVG) 5 blocks ( Figure 1 b) [ 29 , 30 , 33 ].…”

“…We have reported that double-hydrophobic ELP block copolymers with (VGGVG) 5 –(VPGXG) n –(VGGVG) 5 ( n = 25 or 50) sequences self-assembled to form well-defined nanofibers in aqueous solution [ 29 , 30 ]. Dynamic rheology measurements revealed that nanofiber dispersion, even at extremely low nanofiber concentration (0.034 wt%), exhibited solid-like behavior with storage modulus G′ greater than the loss modulus G″ over a wide range of angular frequencies [ 30 ]. This gel-like behavior is attributed to the formation of high-aspect-ratio (>500) nanofibers, through which percolated networks are formed in the solution.…”

Biological properties of self-assembled nanofibers of elastin-like block polypeptides for tissue-engineered vascular grafts: platelet inhibition, endothelial cell activation and smooth muscle cell maintenance

“…At temperatures above 37°C, GPG assembles into nanoparticles by the hydrophobic collapse of (VPGXG) 25 followed by polymerization into nanofibers through the formation of hydrogen bonds between (VGGVG) 5 domains. As the nanofibers of GPG are more than 20 μm in length and can form network-like structures to create stable hydrogels [ 45 , 46 ], GPG may have utility as components of TEVGs that mimic arterial elastin nanostructures. Furthermore, various peptide motifs, including KAAK [ 47 ], GRGDS [ 48 ] and silver-binding sequence [ 49 ], can be bound to the C-terminus of GPG to modify its physicochemical and biological characteristics without impairing its fiber-forming abilities.…”