Functional Self-Assembling Peptide Nanofiber Hydrogels Designed for Nerve Degeneration

Abstract

Self-assembling peptide (SAP) RADA16-I (Ac-(RADA)4-CONH2) has been suffering from a main drawback associated with low pH, which damages cells and host tissues upon direct exposure. In this study, we presented a strategy to prepare nanofiber hydrogels from two designer SAPs at neutral pH. RADA16-I was appended with functional motifs containing cell adhesion peptide RGD and neurite outgrowth peptide IKVAV. The two SAPs were specially designed to have opposite net charges at neutral pH, the combination of which created a nanofiber hydrogel (-IKVAV/-RGD) characterized by significantly higher G' than G″ in a viscoelasticity examination. Circular dichroism, Fourier transform infrared spectroscopy, and Raman measurements were performed to investigate the secondary structure of the designer SAPs, indicating that both the hydrophobic/hydrophilic properties and electrostatic interactions of the functional motifs play an important role in the self-assembling behavior of the designer SAPs. The neural progenitor cells (NPCs)/stem cells (NSCs) fully embedded in the 3D-IKVAV/-RGD nanofiber hydrogel survived, whereas those embedded within the RADA 16-I hydrogel hardly survived. Moreover, the -IKVAV/-RGD nanofiber hydrogel supported NPC/NSC neuron and astrocyte differentiation in a 3D environment without adding extra growth factors. Studies of three nerve injury models, including sciatic nerve defect, intracerebral hemorrhage, and spinal cord transection, indicated that the designer -IKVAV/-RGD nanofiber hydrogel provided a more permissive environment for nerve regeneration than the RADA 16-I hydrogel. Therefore, we reported a new mechanism that might be beneficial for the synthesis of SAPs for in vitro 3D cell culture and nerve regeneration.

Ile‐Lys‐Val‐ala‐Val (IKVAV) peptide for neuronal tissue engineering

“…When conjugated with cell adhesion peptide RGD and neurite outgrowth peptide IKVAV, the widely investigated self‐assembling peptide RADA16‐1 (comprised of repetitive segments of arginine [R], alanine [A], and aspartic acid [D]) creates a 3D hydrogel with a permissive environment to assist with neuron and glial differentiation from neural progenitor cells and NSCs without any exogenous growth factors. In addition, the hydrogel supported the regrowth of the axon at the lesion site after nerve injury compared with unconjugated RADA16‐1 . In another study, self‐assembling peptide RADA16 and conjugated RADA16‐IKVAV hydrogel were utilized to enhance encapsulated NSC reconstruction of the injured brain.…”

“…In addition, the hydrogel supported the regrowth of the axon at the lesion site after nerve injury compared with unconjugated RADA16-1. 34 In another study, self-assembling peptide RADA16 and conjugated RADA16-IKVAV hydrogel were utilized to enhance encapsulated NSC reconstruction of the injured brain. Cell viability of NSCs increased 30 times in both RADA16 and RADA16-IKVAV hydrogels compared with the initial density after 14 days.…”

Building an Artificial Stem Cell Niche: Prerequisites for Future 3D‐Formation of Inner Ear Structures—Toward 3D Inner Ear Biotechnology

“…The study showed that the hydrogel modified with IKVAV can increase cell viability and neuronal differentiation when compared with cells encapsulated with silk fibroin hydrogel alone (Sun et al, ). Recently, studies with synthetic PuraMatrix™ covalently combined with the IKVAV motif showed promising results by differentiating NSCs toward neurons and astrocytes without the addition of growth factors (Sun et al, ).…”

Nanofiber‐Based Hydrogels: Controllable Synthesis and Multifunctional Applications

“…As one of the ionic self‐complementary peptides, Ac‐(RADA) 4 ‐CONH 2 (RADA 16 ) can self‐assemble into nanofibers and eventually form 3D networks, thus it has been widely used to prepare self‐assembled peptide NFHGs . By synthesizing and combining the oppositely charged cell adhesion peptide arginine‐glycine‐aspartic acid (RGD)‐grafted RADA 16 as well as neurite outgrowth peptide isoleucine‐lysine‐valine‐alanine‐valine (IKVAV)‐grafted RADA 16 , Wu and co‐workers created a novel nanofiber‐based hydrogel (−IKVAV/−RGD) . The −IKVAV/−RGD provided a mimic ECM for promoting 3D cell culture and axon regrowth across damaged nerve sites, which was expected to be a next generation nerve regeneration material.…”