Metal Cation Triggered Peptide Hydrogels and Their Application in Food Freshness Monitoring and Dye Adsorption

Disassembly of self-assembling peptide hydrogels as a versatile method for cell extraction and manipulation

Self-assembling peptide hydrogels (SAPHs) are increasingly being used as two-dimensional (2D) cell culture substrates and three-dimensional (3D) matrices due to their tunable properties and biomimicry of native tissues. Despite these advantages, SAPHs often represent an end-point in cell culture, as isolating cells from them leads to low yields and disruption of cells, limiting their use and post-culture analyses. Here, we report on a protocol designed to easily and effectively disassemble peptide amphiphile (PA) SAPHs to retrieve 3D encapsulated cells with high viability and minimal disruption. Due to the pivotal role played by salt ions in SAPH gelation, tetrasodium ethylenediaminetetraacetic acid (Na4EDTA) was used as metal chelator to sequester ions participating in PA self-assembly and induce a rapid, efficient, clean, and gentle gel-to-sol transition. We characterise PA disassembly from the nano- to the macro-scale, provide mechanistic and practical insights into the PA disassembly mechanism, and assess the potential use of the process. As proof-of-concept, we isolated different cell types from cell-laden PA hydrogels and demonstrated the possibility to perform downstream biological analyses including cell re-plating, gene analysis, and flow cytometry with high reproducibility and no material interference. Our work offers new opportunities for the use of SAPHs in cell culture and the potential use of cells cultured on SAPHs, in applications such as cell expansion, analysis of in vitro models, cell therapies, and regenerative medicine.

Self-assembly of heterochiral, aliphatic dipeptides with Leu

This work describes the self-assembly behavior of heterochiral, aliphatic dipeptides, l-Leu-d-Xaa (Xaa = Ala, Val, Ile, Leu), in green solvents such as acetonitrile (MeCN) and buffered water at neutral pH. Interestingly, water plays a structuring role because at 1% v/v, it enables dipeptide self-assembly in MeCN to yield organogels, which then undergo transition towards crystals. Other organic solvents and oils were tested for gelation, and metastable gels were formed in tetrahydrofuran, although at high peptide concentration (80 mM). Single-crystal X-ray diffraction revealed the dipeptides' supramolecular packing modes in amphipathic layers, as opposed to water channels reported for the homochiral Leu-Leu, or hydrophobic columns reported for homochiral Leu-Val and Leu-Ile.

Screening, separation and identification of metal-chelating peptides for nutritional, cosmetics and pharmaceutical applications

Metal-chelating peptides, which form metal-peptide coordination complexes with various metal ions, can be used as biofunctional ingredients notably to enhance human health and prevent diseases. This review aims to discuss recent insights into food-derived metal-chelating peptides, the strategies set up for their discovery, their study, and identification. After understanding the overall properties of metal-chelating peptides, their production from food-derived protein sources and their potential applications will be discussed, particularly in nutritional, cosmetics and pharmaceutical fields. In addition, the review provides an overview of the last decades of progress in discovering food-derived metal-chelating peptides, addressing several screening, separation and identification methodologies. Furthermore, it emphasizes the methods used to assess peptide-metal interaction, allowing for better understanding of chemical and thermodynamic parameters associated with the formation of peptide-metal coordination complexes, as well as the specific amino acid residues that play important roles in the metal ion coordination.

Peptide Supramolecular Self-Assembly: Regulatory Mechanism, Functional Properties, and Its Application in Foods

Peptide self-assembly, due to its diverse supramolecular nanostructures, excellent biocompatibility, and bright application prospects, has received wide interest from researchers in the fields of biomedicine and green life technology and the food industry. Driven by thermodynamics and regulated by dynamics, peptides spontaneously assemble into supramolecular structures with different functional properties. According to the functional properties derived from peptide self-assembly, applications and development directions in foods can be found and explored. Therefore, in this review, the regulatory mechanism is elucidated from the perspective of self-assembly thermodynamics and dynamics, and the functional properties and application progress of peptide self-assembly in foods are summarized, with a view to more adaptive application scenarios of peptide self-assembly in the food industry.

Divalent metal ion modulation of a simple peptide-based hydrogel: self-assembly and viscoelastic properties

Peptide self-assembly has been highly studied to understand the pathways in forming higher order structures along with the development and application of resulting hydrogel materials. Driven by noncovalent interactions, peptide hydrogels are stimuli-responsive to any addition to its gelling conditions. Here, a Phe-His based peptide, C14-FH(Trt)-OH, was synthesized and characterized with 1H NMR, FT-IR, MS, UV-vis spectroscopies and elemental analysis. Based on SEM imaging, the dipeptide conjugate was capable of forming a nanofibrous, interconnected network encapsulating buffer to produce a supramolecular hydrogel. Through the addition of Zn2+ and Cu2+, there is a clear change in the self-assembled nanostructures characterized through SEM. With this effect on self-assembly follows a change in the viscoelastic properties of the material, as determined through rheological frequency sweeps, with 2 and 3 orders of magnitude decreases in the elastic modulus G' in the presence of Zn2+ and Cu2+ respectively. This highlights the tunability of soft material properties with peptide design and self-assembly, through metal ions and Nδ-directed coordination.

Water-Based Synthesis of β-Sheet-Like Supramolecular Metallohydrogel Organized by Using a Native Ultrashort Peptide Sequence

Designing supramolecular hydrogels using short peptides is challenging. To control self-assembly, a certain amount of organic solvent is typically added to the system, or the short peptide is modified with a functional group that is hydrophobic, hydrophilic, or highly coordinative. We discovered that l-His-l-Ile-l-Thr (HIT), a very short unmodified "native" tripeptide, selectively responds to Cu2+ ions in pure water to form a transparent supramolecular metallohydrogel. Circular dichroism analysis revealed that Cu2+ ions, but no other metal species, caused HIT to change from a random-coil-like to a β-sheet-like structure. Other spectroscopic methods were used to characterize the properties of the supramolecular metallohydrogel. These results are expected to facilitate the development of native short peptides as advanced functional biomaterials.

Mechanisms and influencing factors of peptide hydrogel formation and biomedicine applications of hydrogels

Self-assembled peptide-based hydrogels have shown great potential in bio-related applications due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization. Herein, the structure and characteristics of hydrogels and the mechanism of action of several regular secondary structures during gelation are investigated. The factors influencing the formation of peptide hydrogels, especially the pH responsiveness and salt ion induction are analyzed and summarized. Finally, the biomedical applications of peptide hydrogels, such as bone tissue engineering, cell culture, antigen presentation, antibacterial materials, and drug delivery are reviewed.

Advanced review on type II collagen and peptide: preparation, functional activities and food industry application

Type II collagen is a homologous super-helical structure consisting of three identical α1(II) chains. It is a major component of animal cartilage, and is widely used in the food industry. Type II collagen can be extracted by acids, salts, enzymes, and via auxiliary methods and can be further hydrolyzed chemically and enzymatically to produce collagen peptides. Recent studies have shown that type II collagen and its polypeptides have good self-assembly properties and important biological activities, such as maintaining cartilage tissue integrity, inducing immune tolerance, stimulating chondrocyte growth and redifferentiation, and providing antioxidant benefits. This review focuses specifically on type II collagen and describes its structure, extraction, and purification, as well as the preparation of type II collagen peptides. In particular, the self-assembly properties and functional activities of type II collagen and collagen peptides are reviewed. In addition, recent research advances in the application of type II collagen and collagen peptides in functional foods, food additives, food coating materials, edible films, and carriers for the food industry are presented. This paper provides more detailed and comprehensive information on type II collagen and peptide for their application.

Peptide hydrogels: Synthesis, properties, and applications in food science

Due to the unique and excellent biological, physical, and chemical properties of peptide hydrogels, their application in the biomedical field is extremely wide. The applications of peptide hydrogels are closely related to their unique responsiveness and excellent properties. However, its defects in mechanical properties, stability, and toxicity limit its application in the food field. In this review, we focus on the fabrication methods of peptide hydrogels through the physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by the incorporation with materials is discussed. Meanwhile, the excellent properties of peptide hydrogels such as the stimulus responsiveness, biocompatibility, antimicrobial properties, rheology, and stability are reviewed. Finally, the application of peptide hydrogel in the food field is summarized and prospected.

pH-Responsive Viscoelastic Fluids of a C22-Tailed Surfactant Induced by Trivalent Metal Ions

pH-responsive viscoelastic fluids are often achieved by adding hydrotropes into surfactant solutions. However, the use of metal salts to prepare pH-responsive viscoelastic fluids has been less documented. Herein, a pH-responsive viscoelastic fluid was developed by blending an ultra-long-chain tertiary amine, N-erucamidopropyl-N, N-dimethylamine (UC₂₂AMPM), with metal salts (i.e., AlCl₃, CrCl₃, and FeCl₃). The effects of the surfactant/metal salt mixing ratio and the type of metal ions on the viscoelasticity and phase behavior of fluids were systematically examined by appearance observation and rheometry. To elucidate the role of metal ions, the rheological properties between AlCl₃- and HCl-UC₂₂AMPM systems were compared. Results showed the above metal salt evoked the low-viscosity UC₂₂AMPM dispersions to form viscoelastic solutions. Similar to HCl, AlCl₃ could also protonate the UC₂₂AMPM into a cationic surfactant, forming wormlike micelles (WLMs). Notably, much stronger viscoelastic behavior was evidenced in the UC₂₂AMPM-AlCl₃ systems because the Al³⁺ as metal chelators coordinated with WLMs, promoting the increment of viscosity. By tuning the pH, the macroscopic appearance of the UC₂₂AMPM-AlCl₃ system switched between transparent solutions and milky dispersion, concomitant with a viscosity variation of one order of magnitude. Importantly, the UC₂₂AMPM-AlCl₃ systems showed a constant viscosity of 40 mPa·s at 80 °C and 170 s^-1 for 120 min, indicative of good heat and shear resistances. The metal-containing viscoelastic fluids are expected to be good candidates for high-temperature reservoir hydraulic fracturing.

Modulation of hydrogel networks by metal ions

Self-assembling hydrogels are receiving great attention for both biomedical and technological applications. Self-assembly of protein/peptides as well as organic molecules is commonly induced in response to external triggers such as changes of temperature, concentration, or pH. An interesting strategy to modulate the morphology and mechanical properties of the gels implies the use of metal ions, where coordination bonds regulate the dynamic cross-linking in the construction of hydrogels, and coordination geometries, catalytic, and redox properties of metal ions play crucial roles. This review aims to discuss recent insights into the supramolecular assembly of hydrogels involving metal ions, with a focus on self-assembling peptides, as well as applications of metallogels in biomedical fields including tissue engineering, sensing, wound healing, and drug delivery.

Peptide-Based Materials That Exploit Metal Coordination

Metal-ion coordination has been widely exploited to control the supramolecular behavior of a variety of building blocks into functional materials. In particular, peptides offer great chemical diversity for metal-binding modes, combined with inherent biocompatibility and biodegradability that make them attractive especially for medicine, sensing, and environmental remediation. The focus of this review is the last 5 years' progress in this exciting field to conclude with an overview of the future directions that this research area is currently undertaking.

A Peptide-Based Hydrogel for Adsorption of Dyes and Pharmaceuticals in Water Remediation

The removal of dyes and pharmaceuticals from water has become a major issue in recent years due to the shortage of freshwater resources. The adsorption of these pollutants through nontoxic, easy-to-make, and environmentally friendly adsorbents has become a popular topic. In this work, a tetrapeptide-pyrene conjugate was rationally designed to form hydrogels under controlled acidic conditions. The hydrogels were thoroughly characterized, and their performance in the adsorption of various dyes and pharmaceuticals from water was investigated. The supramolecular hydrogel efficiently adsorbed methylene blue (MB) and diclofenac (DCF) from water. The effect of concentration in the adsorption efficiency was studied, and results indicated that while the adsorption of MB is governed by the availability of adsorption sites, in the case of DCF, concentration is the driving force of the process. In the case of MB, the nature of the dye-hydrogel interactions and the mechanism of the adsorption process were investigated through UV-Vis absorption spectroscopy. The studies proved how this dye is first adsorbed as a monomer, probably through electrostatic interactions; successively, at increasing concentrations as the electrostatic adsorption sites are depleted, dimerization on the hydrogel surface occurs.

A Supramolecular Hydrogel Enabled by the Synergy of Hydrophobic Interaction and Quadruple Hydrogen Bonding

The increasing preference for minimally invasive surgery requires novel soft materials that are injectable, with rapid self-healing abilities, and biocompatible. Here, by utilizing the synergetic effect of hydrophobic interaction and quadruple hydrogen bonding, an injectable supramolecular hydrogel with excellent self-healing ability was synthesized. A unique ABA triblock copolymer was designed containing a central poly(ethylene oxide) block and terminal poly(methylmethacrylate) (PMMA) block, with ureido pyrimidinone (UPy) moieties randomly incorporated (termed MA-UPy-PEO-UPy-MA). The PMMA block could offer a hydrophobic microenvironment for UPy moieties in water and thus boost the corresponding quadruple hydrogen bonding interaction of Upy-Upy dimers. Owing to the synergetic effect of hydrophobicity and quadruple hydrogen bonding interaction, the obtained MA-UPy-PEO-UPy-MA hydrogel exhibited excellent self-healing properties, and injectable capability, as well as superior mechanical strength, and therefore, it holds great promise in tissue engineering applications, including in cell support and drug release.

Cooperative Metal Ion Coordination to the Short Self-Assembling Peptide Promotes Hydrogelation and Cellular Proliferation

Non-covalent interactions among short peptides and proteins led to their molecular self-assembly into supramolecular packaging, which provides the fundamental basis of life. These biomolecular assemblies are highly susceptible to the environmental conditions, including temperature, light, pH, and ionic concentration, thus inspiring the fabrication of a new class of stimuli-responsive biomaterials. Here, we report for the first time the cooperative effect of the divalent metal ions to promote hydrogelation in the short collagen inspired self-assembling peptide for developing advanced biomaterials. Introduction of the biologically relevant metal ions (Ca²⁺ /Mg²⁺ ) to the peptide surpasses its limitation to self-assemble into a multi-scale structure at physiological pH. In particular, in presence of metal ions, the negatively charged peptide showed a distinct shift in its equilibrium point of gelation and demonstrated conversion from sol to gel and thus enabling the scope of fabricating an advanced biomaterial for controlling cellular behaviour. Interestingly, tunable mechanical strength and improved cellular response were observed within ion-coordinated peptide hydrogels compared to the peptide gelator. Microscopic analyses, rheological assessment, and biological studies established the importance of utilizing a novel strategy by simply using metal ions to modulate the physical and biological attributes of CIPs to construct next-generation biomaterials. This article is protected by copyright. All rights reserved.