Hierarchical Structure of the Fibrillar Hydrogel Network of a Self‐Assembled Synthetic Peptide Revealed by X‐ray Scattering and Atmospheric Scanning Electron Microscopy

Abstract

Summary:We herein developed a self-assembling peptide with the ability to form a gel in water at pH $7 (SPG-178 (a self-assembling peptide gel with the amino acid sequence #178; [CH 3 CO]-RLDLRLALRLDLR-[NH 2 ]; R ¼ arginine, L ¼ leucine, D ¼ aspartic acid, and A ¼ alanine). Leucine residues were employed to increase the hydrophobic interaction of SPG-178 in water, which was one of the important driving forces of selfassembly, and stabilize fibrillar hydrogel formation. The hierarchical structure of the fibrillar hydrogel of the peptide was analyzed using small/wide angle X-ray scattering measurements (SAXS and WAXS), atomic force microscopy (AFM), transmission electron microscopy (TEM), and atmospheric scanning electron microscopy (ASEM). SAXS, AFM, and TEM measurements revealed the fibril nano-structure of the selfassembled peptide; the width of the fibril was $5 nm, which coincided with the length of one molecule in the b-sheet structure revealed by FT-IR and WAXS in water. ASEM permitted in situ observations, even in water, without freezing. The fibrillar network structure of the gel (micrometer scale) was directly visualized using ASEM measurements.

Mechanical Characteristics of SPG-178 Hydrogels: Optimizing Viscoelastic Properties through Microrheology and Response Surface Methodology

“…Leucine has a large hydrophobic side chain [41] . Thus, with a slight NaCl induction, hydrophobic forces become dominant over repulsive forces and the peptides rapidly converge to cylindrical β-sheet structures, in which the hydrophobic sides are inserted into the interior of the fiber [11] .…”

“…RADA16 is the most investigated SApeptides and is well known for its application in hemostasis and tissue regeneration [8][9][10] . SPG-178 is the most recently introduced SApeptides with the amino acid sequence of [CH 3 CONH]-RLDLRLALRLDLR-[CONH 2 ] (R, L, D, and A indicate arginine, leucine, aspartic acid, and alanine, respectively), forming a fibrillar hydrogel structure via the self-assembling process, similar to RADA16 [11] . SPG-178 hydrogel has potential applications in tissue engineering, including vitreous substitute for eyes [12] , bone regeneration [13,14] , neurite outgrowth of the spinal motor neurons [15] , and rapid hemostasis [16] .…”

Heterotypic supramolecular hydrogels

“…Because of their many useful properties, such as forming hierarchical structures, 77 shear thinning, 78, 79 self-healing, 79–82 and exhibiting phase transition upon external stimuli, 83, 84 supramolecular hydrogels have found numerous applications in a wide range of fields, such food processing, 85 bioanalysis, 86, 87 drug delivery, 81, 88 tissue engineering, 89 and biomedicine. 78 The applications of heterotypic hydrogels, however, are rather limited.…”