Nanofiber structures of some peptides and proteins as biological materials have been studied extensively, but their molecular mechanism of self-assembly and reassembly still remains unclear. We report here the reassembly of an ionic self-complementary peptide RADARADARADARADA (RADA16-I) that forms a well defined nanofiber scaffold. The 16-residue peptide forms stable ␤-sheet structure and undergoes molecular self-assembly into nanofibers and eventually a scaffold hydrogel consisting of >99.5% water. In this study, the nanofiber scaffold was sonicated into smaller fragments. Circular dichroism, atomic force microscopy, and rheology were used to follow the kinetics of the reassembly. These sonicated fragments not only quickly reassemble into nanofibers that were indistinguishable from the original material, but their reassembly also correlated with the rheological analyses showing an increase of scaffold rigidity as a function of nanofiber length. The disassembly and reassembly processes were repeated four times and, each time, the reassembly reached the original length. We proposed a plausible sliding diffusion model to interpret the reassembly involving complementary nanofiber cohesive ends. This reassembly process is important for fabrication of new scaffolds for 3D cell culture, tissue repair, and regenerative medicine.atomic force microscopy ͉ circular dichroism ͉ dynamic behaviors ͉ ionic self-complementary peptides ͉ nanofiber hydrogels M olecular design, development, and fabrication of biological materials are a prerequisite for the advancement of medical technologies. These include scaffolds for fostering tissue regeneration, tissue engineering in regenerative medicine, and controlled drug release (1-7). Synthetic polymers and biodegradable biomaterials have had a significant impact in medicine over the last two decades (8-10). However, the continuous discovery and design of materials of biological origins are of great interest to multiple and diverse scientific and medical communities. The fabrication of materials at the molecular scale from ''the bottom up,'' one molecule at a time through synthesis and one unit at a time through self-assembly, has many advantages (11,12). This approach is not only flexible and simple, but these materials can be tailor-made, thus facilitating the incorporation of many biochemically and medically desired features.We previously reported the discovery and development of a class of self-assembling peptide scaffold materials to culture cells in three dimensions (13-17). These short, 8-to 16-residue (Ϸ2.5-5 nm in length) peptides are chemically synthesized and form extremely stable ␤-sheet structures in water (13, 14). They not only self-assemble to form stable nanofibers, but also form higher-order nanofiber scaffolds, namely, hydrogels with extremely high water content [Ͼ99.5 (wt͞vol)% water] (15-17). The gelation process is accelerated either by changing to neutral pH or adding physiological concentrations of salt solutions (13-15, 18-21). However, although it has high wat...

Peptide RATEA16 spontaneously self-assembled into higher-order nanofiber hydrogels with extremely high water content (>99.5% (wt/vol)) under physiological condition. The hydrogels could undergo pH-reversible transitions from viscous solution to elastic hydrogel and to precipitate. The supramolecular self-assembly and the three phase transitions are driven by hydrophobic interactions, intermolecular hydrogen bonds, and a combination of attractive or repulsive electrostatic interactions. These hydrogels are rich in beta-sheet nanofibers, as demonstrated by CD and FTIR data. Rheological measurements reveal that the viscoelasticity of the material can be tuned by environmental pH and peptide concentration. The storage modulus of the hydrogels increases with increasing peptide concentration, and the self-assembled hydrogels are able to recover from mechanical breakdowns. AFM images show that the elasticity is attributed to a network nanostructure consisting of fibrous self-assemblies. The hydrogels are promising for a variety of possible biomedical applications, including drug delivery.

The aim of this present study was to provide a scaffold as a tool for the investigation of the effect of mechanical stimulation on three-dimensionally cultured cells. For this purpose, we developed an artificial self-assembling peptide (SPG-178) hydrogel scaffold. The structural properties of the SPG-178 peptide were confirmed by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and transmission electron microscopy (TEM). The mechanical properties of the SPG-178 hydrogel were studied using rheology measurements. The SPG-178 peptide was able to form a stable, transparent hydrogel in a neutral pH environment. In the SPG-178 hydrogel, mouse skeletal muscle cells proliferated successfully (increased by 12.4 ± 1.5 times during 8 days of incubation; mean ± SEM). When the scaffold was statically stretched, a rapid phosphorylation of ERK was observed (increased by 2.8 ± 0.2 times; mean ± SEM). These results demonstrated that the developed self-assembling peptide gel is non-cytotoxic and is a suitable tool for the investigation of the effect of mechanical stimulation on three-dimensional cell culture.