atomic force microscopy to characterize the fiber morphology of ecf-5 peptide hydrogels for tissue engineering

<meta charset="utf8"></head><body> 肽水凝胶：ECF-5 的环境响应性凝胶化方法

Through the design of peptide sequences, non-covalent interactions between peptides induce self-assembly, leading to the formation of ordered micro- and nanometer structures, including nanotubes, nanoribbons, nanofibers, and spherical structures1. When self-assembled into micro- and nanometer fibers/ribbons, these structures macroscopically exhibit hydrogel properties. Peptide self-assembling hydrogels differ from polymer hydrogels in that they self-assemble through non-covalent interactions, their gel form is reversible, and they readily respond to specific conditions to transition between solution and gel phases2. For instance, aromatic amino acid peptides can be induced to gelatinize based on solvent switching3,4,5, RADA16 peptides form gels through cationic and anionic electrostatic interactions6, and E1Y9 peptide is induced to form a hydrogel via Ca2+ ions7. Natural amino acids can be metabolized by the human body and offer excellent biocompatibility, a feature that polymer hydrogels cannot achieve8. Proteins are the molecules that execute biological functions, and differences in peptide sequences create their specific biological functions. Therefore, embedding specific biofunctional peptide sequences and endowing them with self-assembling properties can design peptide self-assembling hydrogels with unique biological functions and morphologies9,10,11. This article introduces three methods for preparing peptide hydrogels, where the gelation process is triggered by environmental responsiveness. It also briefly discusses methods for characterizing the mechanical properties and morphology of peptide hydrogels.
The pH regulates the charge of amino acids, triggering the gelation of some peptides. For instance, positively charged amino acids (e.g., arginine, lysine, histidine) are regulated by pH to attain positive or neutral states. Negatively charged amino acids are regulated by pH to achieve negative or neutral states, moving away from their isoelectric point and thereby altering their hydrophilicity in aqueous solutions. Therefore, controlling electrostatic and hydrophobic interactions between peptides facilitates their ordered self-assembly. Zhang et al. designed an amphiphilic pH-responsive self-assembling peptide, methotrexate-coupled KKFKFEFEF, which responds to slightly acidic environments both in vitro and in vivo, enabling a sol-to-gel phase transition. This leads to efficient cellular uptake and endocytosis, thereby delivering anti-cancer drugs and improving chemotherapy effectiveness12. Shen et al.13 designed the FF8 (KRRFFRRK) peptide, which easily self-assembles into fibers at a pH greater than 9.4. Under neutral conditions, microorganisms neutralize their positive charges due to electrostatic interactions with their negatively charged phospholipid membranes, coordinating with phospholipid molecules to self-assemble, causing membrane rupture and enhancing bactericidal effects13.
Triggering peptide supramolecular self-assembly into hydrogels using coordination metals is a relatively rare method14. When metal ions interact electrostatically with peptides, they form salt bridges that connect peptide molecules, leading to non-covalent interactions and self-assembly, which results in gelation properties. For example, Abul-Haija et al.15 designed the tripeptide FFD, which transitions from a liquid to a hydrogel upon the addition of copper ions. Tao et al.16 developed the glutamic acid and phenylalanine-rich peptide E3F3, which self-assembles into fibrous hydrogels in the presence of zinc ions, and is used for prostate drug delivery.
Solvent exchange formation of peptide hydrogels is the most common supramolecular self-assembly triggering condition. After hydrophobic peptides dissolve in organic solvents, their hydrophobic groups are fully exposed. When transferred to an aqueous phase, the hydrophobic groups approach each other, and water molecules facilitate the formation of peptide hydrogen bonds, leading to rapid self-assembly and easy formation of hydrogels. For instance, Zhang et al.17 designed a peptide that could dissolve stably at high concentrations in polar organic solvents and, upon dilution with water, self-assembled into &#946;-sheet structures to form peptide fiber hydrogels. Shen et al.13 designed a reductive peptide ECF-5 (ECAFF), pre-dissolved in dimethyl sulfoxide (DMSO) and then injected into an aqueous phase to form a reductive hydrogel, used for the targeted removal of reactive oxygen species produced by ischemia-reperfusion, which subsequently degraded into a solution after scavenging.
This study selected three simple, rapid, and highly generalizable peptide hydrogel preparation strategies based on previous experiences: (1) pH response method: peptides are dissolved in a solution with a pH far from their isoelectric point, and then the pH is adjusted to near the isoelectric point. This change allows certain self-assembling peptides to form fibers and create peptide hydrogels; (2) Metal ion addition method: coordination cations are added to water-soluble, negatively charged self-assembling peptides. The metal coordination chelation between peptides leads to their self-assembly into hydrogels; (3) Solvent exchange method: high-concentration peptides are dissolved in organic solvents and then diluted into an aqueous phase, inducing gelation behavior.

<meta charset="utf8"></head><body>作者聚焦：改进自组装纤维和肽水凝胶的生产以获得卓越的生物相容性

机械稳定的自组装肽水凝胶的制备

原子力显微镜表征组织工程用 ECF-5 肽水凝胶的纤维形态

atomic-force-microscopy-to-characterize-fiber-morphology-ecf-5

Research

JoVE Journal

Biochemistry

Atomic Force Microscopy to Characterize the Fiber Morphology of ECF-5 Peptide Hydrogels for Tissue Engineering

93 次观看. 首先，使用合适的方法制备肽水凝胶。涂上双面胶以去除一层云母，然后使用 APTES 溶液粘附云母表面，静置 5 分钟。使用前用纯水彻底冲洗云母表面。稀释水凝胶并充分混合，然后将其滴到改性云母表面进行静态吸收。五分钟后，用纯净水冲洗表面并擦干。原子力显微镜显示，凝胶表面有许多肽纤维，具有密集的孔隙，可捕获水，单个纤维形?...

视频: 原子力显微镜表征组织工程用 ECF-5 肽水凝胶的纤维形态

Preparation of Mechanically Stable Self-Assembled Peptides Hydrogels

Peptide hydrogels are highly hydrophilic, three-dimensional network gels formed by the self-assembly of nanofibers or polymers, creating water-locking networks. Their morphology closely resembles that of the extracellular matrix, allowing them to exhibit both the biological functions of peptides and responsive gelation properties. These unique characteristics have led to their extensive application in tissue engineering, three-dimensional cell culture, cancer therapy, regenerative medicine, and other biomedical fields. This article describes three methods for preparing ECF-5 peptide hydrogels using self-assembling peptides with environmentally responsive gelation processes: (1) pH-responsive gelation: varying pH levels induce the protonation or deprotonation of amino acid residues, altering electrostatic interactions between peptide molecules and promoting their self-assembly into hydrogels; (2) Metal ion addition: polyvalent metal ions chelate with negatively charged amino acid residues, acting as bridges between peptides to form a network hydrogel; (3) Solvent exchange: hydrophobic peptides are initially dissolved in non-polar organic solvents and subsequently induce self-assembly into hydrogels upon transitioning to a polar aqueous environment. These methods utilize conventional experimental procedures to facilitate peptide self-assembly into hydrogels. By designing peptide sequences to align with specific gelation-inducing conditions, it is possible to achieve finely tuned micro/nanostructures and biological functions, highlighting the significant potential of peptide hydrogels in the biomedical domain.

This protocol presents three fast and simple preparation methods that use environmental conditions to trigger the self-assembly of peptides into hydrogels. Additionally, the characterization of peptide hydrogels is described, demonstrating that mechanically stable peptide hydrogels can be formed under these straightforward conditions.

Peptide hydrogels are highly hydrophilic, three-dimensional network gels formed by the self-assembly of nanofibers or polymers, creating water-locking ...