Fmoc-FF and hexapeptide-based multicomponent hydrogels as scaffold materials

Conductive Peptide-Based MXene Hydrogel as a Piezoresistive Sensor

Wearable pressure sensors have become increasingly popular for personal healthcare and motion detection applications due to recent advances in materials science and functional nanomaterials. In this study, a novel composite hydrogel is presented as a sensitive piezoresistive sensor that can be utilized for various biomedical applications, such as wearable skin patches and integrated artificial skin that can measure pulse and blood pressure, as well as monitor sound as a self-powered microphone. The hydrogel is composed of self-assembled short peptides containing aromatic, positively- or negatively charged amino acids combined with 2D Ti3C2Tz MXene nanosheets. This material is low-cost, facile, reliable, and scalable for large areas while maintaining high sensitivity, a wide detection range, durability, oxidation stability, and biocompatibility. The bioinspired nanostructure, strong mechanical stability, and ease of functionalization make the assembled peptide-based composite MXene-hydrogel a promising and widely applicable material for use in bio-related wearable electronics.

Synergistic Coassembly of Folic Acid-Based Supramolecular Polymer with a Covalent Polymer Toward Fabricating Functional Antibacterial Biomaterials

Supramolecular biomaterials can recapitulate the structural and functional facets of the native extracellular matrix and react to biochemical cues, leveraging the unique attributes of noncovalent interactions, including reversibility and tunability. However, the low mechanical properties of supramolecular biomaterials can restrict their utilization in specific applications. Combining the advantages of supramolecular polymers with covalent polymers can lead to the fabrication of tailor-made biomaterials with enhanced mechanical properties/degradability. Herein, we demonstrate a synergistic coassembled self-healing gel as a multifunctional supramolecular material. As the supramolecular polymer component, we chose folic acid (vitamin B9), an important biomolecule that forms a gel comprising one-dimensional (1D) supramolecular polymers. Integrating polyvinyl alcohol (PVA) into this supramolecular gel alters its ultrastructure and augments its mechanical properties. A drastic improvement of complex modulus (G*) (∼3674 times) was observed in the folic acid-PVA gel with 15% w/v PVA (33215 Pa) compared with the folic acid gel (9.04 Pa). The coassembled hydrogels possessed self-healing and injectable/thixotropic attributes and could be printed into specific three-dimensional (3D) shapes. Synergistically, the supramolecular polymers of folic acid also improve the toughness, durability, and ductility of the PVA films. A nanocomposite of the gels with silver nanoparticles exhibited excellent catalytic efficiency and antibacterial activity. The folic acid-PVA coassembled gels and films also possessed high cytocompatibility, substantiated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and live-dead assays. Taken together, the antibacterial and cell-adhesive attributes suggest potential applications of these coassembled biomaterials for tissue engineering and wound healing.

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.

Fmoc-FF hydrogels and nanogels for improved and selective delivery of dexamethasone in leukemic cells and diagnostic applications

Dexamethasone (DEX) is a synthetic analogue of cortisol commonly used for the treatment of different pathological conditions, comprising cancer, ocular disorders, and COVID-19 infection. Its clinical use is hampered by the low solubility and severe side effects due to its systemic administration. The capability of peptide-based nanosystems, like hydrogels (HGs) and nanogels (NGs), to serve as vehicles for the passive targeting of active pharmaceutical ingredients and the selective internalization into leukemic cells has here been demonstrated. Peptide based HGs loaded with DEX were formulated via the "solvent-switch" method, using Fmoc-FF homopeptide as building block. Due to the tight interaction of the drug with the peptidic matrix, a significant stiffening of the gel (G' = 67.9 kPa) was observed. The corresponding injectable NGs, obtained from the sub-micronization of the HG, in the presence of two stabilizing agents (SPAN®60 and TWEEN®60, 48/52 w/w), were found to be stable up to 90 days, with a mean diameter of 105 nm. NGs do not exhibit hemolytic effects on human serum, moreover they are selectively internalized by RS4;11 leukemic cells over healthy PBMCs, paving the way for the generation of new diagnostic strategies targeting onco-hematological diseases.

Mesenchymal stem cells aligned and stretched in self-assembling peptide hydrogels

The presented research highlights a novel approach using fmoc-protected peptide hydrogels for the encapsulation and stretching of mesenchymal stem cells (MSCs). This study utilized a custom mechanical stretching device with a PDMS chamber to stretch human MSCs encapsulated in Fmoc hydrogels. The study assessed the influence of various solvents on the self-assembly and mechanical properties of the hydrogels, and MSC viability and alignment. Particularly we focused on fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF) prepared in dimethyl sulfoxide (DMSO), hexafluoro-2-propanol (HFP), and deionized water (DiH2O). Through molecular self-assembly of the peptide sequence into β-sheets connected by π-π aromatic stacking of F-F groups, the peptide hydrogel was found to form a stiff, hydrated gel with nanofiber morphology and a compressive modulus ranging from 174 to 277 Pa. Therefore, this hydrogel can mimic certain critical features of the extracellular matrix and collagen. Evaluations of MSCs cultured on the peptide hydrogels, including viability, morphology, and alignment assessments using various staining techniques, demonstrated that 3D-cultured MSCs in Fmoc-FF/HFP and Fmoc-FF/DMSO, followed by mechanical stretching, exhibited elongated morphology with distinct microfilament fibers compared to the control cells, which maintained a round and spherical F-actin shape. Notably, peptide gels with a concentration of 5 mM maintained 100 % MSC viability. The findings indicate the potential and specific conditions for successful cell encapsulation and alignment within peptide hydrogels, highlighting a promising tissue engineering platform through the encapsulation of MSCs in peptide nanofibers followed by a stretching process. By enhancing our understanding of MSC-peptide hydrogel interactions, this research contributes to the development of biomaterials tailored for regenerative medicine.

Ultrashort Cationic Peptide Fmoc-FFK as Hydrogel Building Block for Potential Biomedical Applications

Fmoc-diphenylalanine (Fmoc-FF) is a low-molecular-weight peptide hydrogelator. This simple all-aromatic peptide can generate self-supporting hydrogel materials, which have been proposed as novel materials for diagnostic and pharmaceutical applications. Our knowledge of the molecular determinants of Fmoc-FF aggregation is used as a guide to design new peptide-based gelators, with features for the development of improved tools. Here, we enlarge the plethora of Fmoc-FF-based hydrogelated matrices by studying the properties of the Fmoc-FFK tripeptide, alone or in combination with Fmoc-FF. For multicomponent matrices, the relative weight ratios between Fmoc-FFK and Fmoc-FF (specifically, 1/1, 1/5, 1/10, and 1/20 w/w) are evaluated. All the systems and their multiscale organization are studied using different experimental techniques, including rheology, circular dichroism, Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM). Preliminary profiles of biocompatibility for the studied systems are also described by testing them in vitro on HaCaT and 3T3-L1 cell lines. Additionally, the lysine (K) residue at the C-terminus of the Fmoc-FF moiety introduces into the supramolecular material chemical functions (amino groups) which may be useful for modification/derivatization with bioactive molecules of interest, including diagnostic probes, chelating agents, active pharmaceutical ingredients, or peptide nucleic acids.

Multicomponent Peptide-Based Hydrogels Containing Chemical Functional Groups as Innovative Platforms for Biotechnological Applications

Multicomponent hydrogels (HGs) based on ultrashort aromatic peptides have been exploited as biocompatible matrices for tissue engineering applications, the delivery of therapeutic and diagnostic agents, and the development of biosensors. Due to its capability to gel under physiological conditions of pH and ionic strength, the low molecular-weight Fmoc-FF (Nα-fluorenylmethoxycarbonyl-diphenylalanine) homodimer is one of the most studied hydrogelators. The introduction into the Fmoc-FF hydrogel of additional molecules like protein, organic compounds, or other peptide sequences often allows the generation of novel hydrogels with improved mechanical and functional properties. In this perspective, here we studied a library of novel multicomponent Fmoc-FF based hydrogels doped with different amounts of the tripeptide Fmoc-FFX (in which X= Cys, Ser, or Thr). The insertion of these tripeptides allows to obtain hydrogels functionalized with thiol or alcohol groups that can be used for their chemical post-derivatization with bioactive molecules of interest like diagnostic or biosensing agents. These novel multicomponent hydrogels share a similar peptide organization in their supramolecular matrix. The hydrogels' biocompatibility, and their propensity to support adhesion, proliferation, and even cell differentiation, assessed in vitro on fibroblast cell lines, allows us to conclude that the hybrid hydrogels are not toxic and can potentially act as a scaffold and support for cell culture growth.

Self-assembling tripeptide forming water-bound channels and hydrogels

D-Ser(tBu)-L-Phe-L-Trp is described as a self-assembling tripeptide that yields nanofibrillar hydrogels at physiological conditions (phosphate buffer at pH 7.4). The peptide is characterized by several spectroscopic methods, such as circular dichroism and fluorescence, oscillatory rheometry, and transmission electron microscopy. Single-crystal X-ray diffraction reveals supramolecular packing into water-bound channels and allows the visualization of the intermolecular interactions holding together peptide stacks.

Development of cationic peptide-based hydrogels loaded with iopamidol for CEST-MRI detection

Peptide-based hydrogels have been recently investigated as materials for biomedical applications like tissue engineering and delivery of drugs and imaging agents. Among the synthetic peptide hydrogelators, the cationic hexapeptides Ac-K1 and Ac-K2 were proposed as scaffolds for bioprinting applications. Here, we report the formulation of Ac-K1 and Ac-K2 hydrogels loaded with iopamidol, an iodinated contrast agent clinically approved for X-ray computed tomography, and more recently identified as an efficient CEST-MRI probe. Iopamidol-loaded hydrogels were soft, injectable and non-toxic both in vitro (on three tumor cell lines: GL261, TS/A and 3T3-NIH) and in vivo (in Balb/c mice inoculated with TS/A breast cancer cells). The in vitro CEST-MRI study evidenced the typical features of the CEST pattern of iopamidol, with a CEST contrast higher than 50%. Due to their injectability and good ability to retain the contrast agent, the herein investigated systems can be considered as promising candidates for the development of smart MRI detectable hydrogels.

Fmoc-diphenylalanine gelating nanoarchitectonics: A simplistic peptide self-assembly to meet complex applications

9-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF), has been has been extensively explored due to its ultrafast self-assembly kinetics, inherent biocompatibility, tunable physicochemical properties, and especially, the capability of forming self-sustained gels under physiological conditions. Consequently, various methodologies to develop Fmoc-FF gels and their corresponding applications in biomedical and industrial fields have been extensively studied. Herein, we systemically summarize the mechanisms underlying Fmoc-FF self-assembly, discuss the preparation methodologies of Fmoc-FF hydrogels, and then deliberate the properties as well as the diverse applications of Fmoc-FF self-assemblies. Finally, the contemporary shortcomings which limit the development of Fmoc-FF self-assembly are raised and the alternative solutions are proposed, along with future research perspectives.

Process Dependent Complexity in Multicomponent Gels

Mixing low molecular weight gelators (LMWGs) can be used to combine favorable properties of the individual components within a multifunctional gel. Such multicomponent systems are complex enough in themselves but the method of combining components is not commonly considered something to influence self-assembly. Herein, two multicomponent systems comprising of a naphthalene-based dipeptide hydrogelator and one of two modified naphthalene diimides (NDIs), one of which forms gels, and the other does not, are investigated. These systems are probed, examining the structures formed and their gel properties (when preparing a solution from either a mixed powder of both components or by mixing pre-formed solutions of each component) using rheology, small angle neutron scattering (SANS), and absorbance spectroscopy. It is found that by altering the method of preparation, it is can either induce self-sorting or co-assembly within the fibers formed that underpin the gel network.

Sensing Cells-Peptide Hydrogel Interaction In Situ via Scanning Ion Conductance Microscopy

Peptide-based hydrogels were shown to serve as good matrices for 3D cell culture and to be applied in the field of regenerative medicine. The study of the cell-matrix interaction is important for the understanding of cell attachment, proliferation, and migration, as well as for the improvement of the matrix. Here, we used scanning ion conductance microscopy (SICM) to study the growth of cells on self-assembled peptide-based hydrogels. The hydrogel surface topography, which changes during its formation in an aqueous solution, were studied at nanoscale resolution and compared with fluorescence lifetime imaging microscopy (FLIM). Moreover, SICM demonstrated the ability to map living cells inside the hydrogel. A zwitterionic label-free pH nanoprobe with a sensitivity > 0.01 units was applied for the investigation of pH mapping in the hydrogel to estimate the hydrogel applicability for cell growth. The SICM technique that was applied here to evaluate the cell growth on the peptide-based hydrogel can be used as a tool to study functional living cells.

Incorporation of PEG Diacrylates (PEGDA) Generates Hybrid Fmoc-FF Hydrogel Matrices

Generated by a hierarchical and multiscale self-assembling phenomenon, peptide-based hydrogels (HGs) are soft materials useful for a variety of applications. Short and ultra-short peptides are intriguing building blocks for hydrogel fabrication. These matrices can also be obtained by mixing low-molecular-weight peptides with other chemical entities (e.g., polymers, other peptides). The combination of two or more constituents opens the door to the development of hybrid systems with tunable mechanical properties and unexpected biofunctionalities or morphologies. For this scope, the formulation, the multiscale analysis, and the supramolecular characterization of novel hybrid peptide-polymer hydrogels are herein described. The proposed matrices contain the Fmoc-FF (N^α-fluorenylmethyloxycarbonyl diphenylalanine) hydrogelator at a concentration of 0.5 wt% (5.0 mg/mL) and a diacrylate α-/ω-substituted polyethylene-glycol derivative (PEGDA). Two PEGDA derivatives, PEGDA 1 and PEGDA2 (mean molecular weights of 575 and 250 Da, respectively), are mixed with Fmoc-FF at different ratios (Fmoc-FF/PEGDA at 1/1, 1/2, 1/5, 1/10 mol/mol). All the multicomponent hybrid peptide-polymer hydrogels are scrutinized with a large panel of analytical techniques (including proton relaxometry, FTIR, WAXS, rheometry, and scanning electronic microscopy). The matrices were found to be able to generate mechanical responses in the 2-8 kPa range, producing a panel of tunable materials with the same chemical composition. The release of a model drug (Naphthol Yellow S) is reported too. The tunable features, the different topologies, and the versatility of the proposed materials open the door to the development of tools for different applicative areas, including diagnostics, liquid biopsies and responsive materials. The incorporation of a diacrylate function also suggests the possible development of interpenetrating networks upon cross-linking reactions. All the collected data allow a mutual comparison between the different matrices, thus confirming the significance of the hybrid peptide/polymer-based methodology as a strategy for the design of innovative materials.

Injectable Peptide Hydrogel Encapsulation of Mesenchymal Stem Cells Improved Viability, Stemness, Anti-Inflammatory Effects, and Early Stage Wound Healing

Human-adipose-derived mesenchymal stem cells (hADMSCs) are adult stem cells and are relatively easy to access compared to other sources of mesenchymal stem cells (MSCs). They have shown immunomodulation properties as well as effects in improving tissue regeneration. To better stimulate and preserve the therapeutic properties of hADMSCs, biomaterials for cell delivery have been studied extensively. To date, hyaluronic acid (HA)-based materials have been most widely adopted by researchers around the world. PGmatrix is a new peptide-based hydrogel that has shown superior functional properties in 3D cell cultures. Here, we reported the in vitro and in vivo functional effects of PGmatrix on hADMSCs in comparison with HA and HA-based Hystem hydrogels. Our results showed that PGmatrix was far superior in maintaining hADMSC viability during prolonged incubation and stimulated expression of SSEA4 (stage-specific embryonic antigen-4) in hADMSCs. hADMSCs encapsulated in PGmatrix secreted more immune-responsive proteins than those in HA or Hystem, though similar VEGF-A and TGFβ1 release levels were observed in all three hydrogels. In vivo studies revealed that hADMSCs encapsulated with PGmatrix showed improved skin wound healing in diabetic-induced mice at an early stage, suggesting possible anti-inflammatory effects, though similar re-epithelialization and collagen density were observed among PGmatrix and HA or Hystem hydrogels by day 21.

Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators

Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive “smart” materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined.

Fmoc-Diphenylalanine Hydrogels: Optimization of Preparation Methods and Structural Insights

Hydrogels (HGs) are tri-dimensional materials with a non-Newtonian flow behaviour formed by networks able to encapsulate high amounts of water or other biological fluids. They can be prepared using both synthetic or natural polymers and their mechanical and functional properties may change according to the preparation method, the solvent, the pH, and to others experimental parameters. Recently, many short and ultra-short peptides have been investigated as building blocks for the formulation of biocompatible hydrogels suitable for different biomedical applications. Due to its simplicity and capability to gel in physiological conditions, Fmoc-FF dipeptide is one of the most studied peptide hydrogelators. Although its identification dates to 15 ago, its behaviour is currently studied because of the observation that the final material obtained is deeply dependent on the preparation method. To collect information about their formulation, here are reported some different strategies adopted until now for the Fmoc-FF HG preparation, noting the changes in the structural arrangement and behaviour in terms of stiffness, matrix porosity, and stability induced by the different formulation strategy on the final material.

Designer peptides as versatile building blocks for functional materials

Peptides and pseudopeptides show distinct self-assembled nanostructures such as fibers, nanotubes, vesicles, micelles, toroids, helices and rods. The formation of such molecular communities through the collective behavior of molecules is not fully understood at a molecular level. All these self-assembled nanostructured materials have a wide range of applications such as drug delivery, gene delivery, biosensing, bioimaging, catalysis, tissue engineering, nano-electronics and sensing. Self-assembly is one of the most efficient and a simple strategy to generate complex functional materials. Owing to its significance, the last few decades witnessed a remarkable advancement in the field of self-assembling peptides with a plethora of new designer synthetic systems being discovered. These systems range from amphiphilic, cyclic, linear and polymeric peptides. This article presents only selected examples of such self-assembling peptides and pseudopeptides.

Stabilizing gelatin-based bioinks under physiological conditions by incorporation of ethylene-glycol-conjugated Fmoc-FF peptides

Over the last decade, three-dimensional (3D) printing technologies have attracted the interest of researchers due to the possibility of fabricating tissue- and organ-like structures with similarities to the organ of interest. One of the most widely used materials for the fabrication of bioinks is gelatin (Gel) due to its excellent biocompatibility properties. However, in order to fabricate stable scaffolds under physiological conditions, the most common approach is to use gelatin methacrylate (GelMA) that allows the crosslinking and therefore the stabilization of the hydrogel through UV crosslinking. The crosslinking process can be harmful to cells thus decreasing total cell viability. To overcome the need for post-printing crosslinking, a new approach of bioink formulation was studied, incorporating the Fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) peptide into the Gel bioink. However, although Fmoc-FF possesses excellent mechanical properties, the lack of elasticity and viscosity makes it unsuitable for 3D-printing. Here, we demonstrate that covalent conjugation of two different ethylene glycol (EG) motifs to the Fmoc-FF peptide increases the hydrophilicity and elasticity properties, which are essential for 3D-printing. This new approach for bioink formulation avoids the need for any post-printing manufacturing processes, such as chemical or UV crosslinking.

Aromatic interactions directing peptide nano-assembly

Self-assembly is a process of spontaneous organization of molecules as a result of non-covalent interactions. Organized self-assembly at the nano level is emerging as a powerful tool in the bottom-up fabrication of functional nanostructures for targeted applications. Aromatic π-π stacking plays a significant role by facilitating the persistent supramolecular association of individual subunits to the self-assembled structures of high stability. Understanding, the supramolecular chemistry of the materials interacting through aromatic interactions, is of tremendous interest in not only constructing functional materials but also in revealing the mechanism of molecular assembly in living organisms. This chapter aims to focus on understanding the potential role of π-π interactions in directing and regulating the self-assembly of peptide nanostructures. The scope of the chapter starts with an outline of the history and mechanism of the aromatic π-π interactions. It progresses through the design strategy for the assembly of peptides containing aromatic rings, the conditions affecting the aromatic stacking interactions, their resulting nanoassemblies, properties, and applications. The properties and applications of the supramolecular materials formed through the aromatic stacking interactions are highlighted to provide an increased understanding of the role of weak interactions in the design and construction of novel functional materials.

Aromatic Dipeptide Homologue-Based Hydrogels for Photocontrolled Drug Release

Peptide-based hydrogels are considered of special importance due to their biocompatibility and biodegradability. They have a wide range of applications in the biomedical field, such as drug delivery, tissue engineering, wound healing, cell culture media, and biosensing. Nevertheless, peptide-based hydrogels composed of natural α-amino acids are limited for in vivo applications because of the possible degradation by proteolytic enzymes. To circumvent this issue, the incorporation of extra methylene groups within the peptide sequence and the protection of the terminal amino group can increase the enzymatic stability. In this context, we investigated the self-assembly capacity of aromatic dipeptides (Boc-α-diphenylalanine and Boc-α-dityrosine) and their β- and γ-homologues and developed stable hydrogels. Surprisingly, only the Boc-diphenylalanine analogues were able to self-assemble and form hydrogels. A model drug, l-ascorbic acid, and oxidized carbon nanotubes (CNTs) or graphene oxide were then incorporated into the hydrogels. Under near-infrared light irradiation, the photothermal effect of the carbon nanomaterials induced the destabilization of the gel structure, which caused the release of a high amount of drug, thus providing opportunities for photocontrolled on-demand drug release.

Multicomponent Hydrogel Matrices of Fmoc-FF and Cationic Peptides for Application in Tissue Engineering

In the last years, peptide based hydrogels are being increasingly used as suitable matrices for biomedical and pharmaceutical applications, including drug delivery and tissue engineering. Recently, we decrived the synthesis and the gelation properties of a small library of cationic peptides, containing a Lys residue at the C-teminus and derivatized with a Fmoc group or with the Fmoc-diphenylalanine (FmocFF) at the N-terminus. Here, we demonstrate that the combination of these peptides with the well known hydrogelator FmocFF, in different weight/weight ratios, allows the achievement of seven novel self-sorted hydrogels, which share similar peptide organization of their supramolecular matrix. Rheological and relaxometric characterization highlighted a different mechanical rigidity and water mobility in the gels as demostrated by the storage modulus values (200 Pa<G'<35000 Pa) and by relaxometry, respectively. In vitro studied demonstrated that most of the tested mixed hydrogels do not disturb significantly the cell viability (>95%) over 72h of treatment. Moreover, in virtue to its capability to strongly favour adhesion, spreading and duplication of 3T3-L1 cells, one of the tested hydrogel may be eligible as sinthetic extracellular matrix. This article is protected by copyright. All rights reserved.

A Self-Assembled Fmoc-Diphenylalanine Hydrogel-Encapsulated Pt Nanozyme as Oxidase- and Peroxidase-Like Breaking pH Limitation for Potential Antimicrobial Application

Nanomaterials with oxidase- and peroxidase-like activities have potential in antibacterial therapy. The optimal activity of most nanozymes occurred in acidic pH (3.0-5.0), while the pH in biological systems is mostly near neutral. Herein, a general system using 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc-FF) hydrogel for enhancing oxidase- and peroxidase-like activities of Pt NPs and other typical enzyme-like nanomaterials at neutral or even alkaline pH is proposed. In this system, Fmoc-FF hydrogel provides an acidic microenvironment for Pt NPs due to hydrogen protons (H⁺ ) produced by the dissociation of F at neutral pH. As a result, Pt NPs exhibits 6-fold enhanced oxidase-like and 26-fold peroxidase-like activity after being encapsulated into Fmoc-FF hydrogel at pH 7.0. Based on outstanding enzymatic activities and the antibacterial activity of Fmoc-FF hydrogel itself, Pt-Fmoc-FF hydrogel realizes excellent antibacterial effect. This design provides a universal strategy to break pH limitation of nanozymes and promotes the biological applications of nanozymes.

Peptide Coassembly to Enhance Piezoelectricity for Energy Harvesting

The discovery of piezoelectricity in self-assembled peptide nanostructures opens an avenue to a new regime of piezoelectric materials and enables the fundamental investigation of electromechanical coupling in biomaterials. However, strategies for fabricating peptides with desired properties are still lacking. We find that a peptide-based coassembly process effectively controls the properties of peptide nanomaterials and demonstrates their application potential in nanogenerators. The composing peptides and their concentration influence the morphology, molecular property, and physical property of coassembled crystals. Compared with self-assembled diphenylalanine peptides, the coassembled peptides of diphenylalanine and phenylalanine-tryptophan show a 38% increase in piezoelectric coefficient, and the resulting harvesting device shows nearly a 3-fold increase in open-circuit voltage outputs.

Molecular Co-assembly of Two Building Blocks Harnesses Both Their Attributes into a Functional Supramolecular Hydrogel

Engineering ordered nanostructures through molecular self-assembly of simple building blocks constitutes the essence of modern nanotechnology to develop functional supramolecular biomaterials. However, the lack of adequate chemical and functional diversity often hinders the utilization of unimolecular self-assemblies for practical applications. Co-assembly of two different building blocks could essentially harness both of their attributes and produce nanostructured macro-scale objects with improved physical properties and desired functional complexity. Herein, we report the co-operative co-assembly of a modified amino acid, fluorenylmethoxycarbonyl-pentafluoro-Phenylalanine (Fmoc-F₅ -Phe), and a peptide, Fmoc-Lys(Fmoc)-Arg-Gly-Asp [Fmoc-K(Fmoc)-RGD] into a functional supramolecular hydrogel. A change in the morphology and fluorescence emission, as well as improvement of the mechanical properties in the mixed hydrogels compared to the pristine hydrogels, demonstrate the signature of co-operative co-assembly mechanism. Intriguingly, this approach harnesses the advantages of both components in a synergistic way, resulting in a single homogeneous biomaterial possessing the antimicrobial property of Fmoc-F₅ -Phe and the biocompatibility and cell adhesive characteristics of Fmoc-K(Fmoc)-RGD. This work exemplifies the importance of the co-assembly process in nanotechnology and lays the foundation for future developments in supramolecular chemistry by harnessing the advantages of diverse functional building blocks into a mechanically stable functional biomaterial. This article is protected by copyright. All rights reserved.

Self-assembled di- and tripeptide gels for the passive entrapment and pH-responsive, sustained release of an antidiabetic drug, glimepiride

Diabetes is a global epidemic that poses a severe challenge to public health. The characteristic features of this disease are hyperglycemia and deterioration of the function of pancreatic β-cells, which...

Mechanical Enhancement and Kinetics Regulation of Fmoc-Diphenylalanine Hydrogels by Thioflavin T

The self-assembly of peptides is a key direction for fabrication of advanced materials. Novel approaches for fine tuning of macroscopic and microscopic properties of peptide self-assemblies are of a high demand for constructing biomaterials with desired properties. In this work, while studying the kinetics of the Fmoc-Diphenylalanine (Fmoc-FF) dipeptide self-assembly using the Thioflavin T (ThT) dye, we observed that the presence of ThT strongly modifies structural and mechanical properties of the Fmoc-FF hydrogel. Notably, the presence of ThT resulted in a tenfold increase of the gelation time and in the formation of short and dense fibers in the hydrogel. As a result of these morphological alteration higher thermal stability, and most important, tenfold increase of the hydrogel rigidity was achieved. Hence, ThT not only slowed the kinetics of the Fmoc-FF hydrogel formation, but also strongly enhanced its mechanical properties. In this study, we provide a detailed description of the ThT effect on the hydrogel properties and suggest the mechanisms for this phenomenon, paving the way for the novel approach to the control of the peptide hydrogels' micro- and macroscale properties.

Fluorescence Emission of Self-assembling Amyloid-like Peptides: Solution versus Solid State

Analysis of the intrinsic UV-visible fluorescence exhibited by self-assembling amyloid-like peptides in solution and in solid the state highlights that their physical state has a profound impact on the optical properties. In the solid state, a linear dependence of the fluorescence emission peaks as a function of excitation wavelength is detected. On the contrary, an excitation-independent emission is observed in solution. The present findings constitute a valuable benchmark for current and future explanations of the fluorescence emission by amyloids.

The Effects of a Short Self-Assembling Peptide on the Physical and Biological Properties of Biopolymer Hydrogels

Hydrogel scaffolds have attracted much interest in the last few years for applications in the field of bone and cartilage tissue engineering. These scaffolds serve as a convenient three-dimensional structure on which cells can grow while sensing the native environment. Natural polymer-based hydrogels are an interesting choice for such purposes, but they lack the required mechanical properties. In contrast, composite hydrogels formed by biopolymers and short peptide hydrogelators possess mechanical characteristics suitable for osteogenesis. Here, we describe how combining the short peptide hydrogelator, Pyrene-Lysine-Cysteine (PyKC), with other biopolymers, can produce materials that are suitable for tissue engineering purposes. The presence of PyKC considerably enhances the strength and water content of the composite hydrogels, and confers thixotropic behavior. The hyaluronic acid-PyKC composite hydrogels were shown to be biocompatible, with the ability to support osteogenesis, since MC3 T3-E1 osteoblast progenitor cells grown on the materials displayed matrix calcification and osteogenic differentiation. The osteogenesis results and the injectability of these composite hydrogels hold promise for their future utilization in tissue engineering.

Self-Assembly Dipeptide Hydrogel: The Structures and Properties

Self-assembly peptide-based hydrogels are well known and popular in biomedical applications due to the fact that they are readily controllable and have biocompatibility properties. A dipeptide is the shortest self-assembling motif of peptides. Due to its small size and simple synthesis method, dipeptide can provide a simple and easy-to-use method to study the mechanism of peptides' self-assembly. This review describes the design and structures of self-assembly linear dipeptide hydrogels. The strategies for preparing the new generation of linear dipeptide hydrogels can be divided into three categories based on the modification site of dipeptide: 1) COOH-terminal and N-terminal modified dipeptide, 2) C-terminal modified dipeptide, and 3) uncapped dipeptide. With a deeper understanding of the relationship between the structures and properties of dipeptides, we believe that dipeptide hydrogels have great potential application in preparing minimal biocompatible materials.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH₂ - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

Cationic self-assembled peptide-based molecular hydrogels for extended ocular drug delivery

The physiological barriers and clearance mechanism of the eye challenge the therapeutic delivery for treating various ocular disorders effectively. Here, we show the use of a cationic peptide (i.e., Nap-FFKK) as the molecular hydrogelator for generating supramolecular hydrogels spontaneously in a pH value of 5-7 which allows it to function as a promising ocular drug vehicle. The cationic peptide-based hydrogel hardly exhibited the cytotoxicity against human corneal epithelial cell (i.e., HCEC) from the in vitro cytotoxicity assay. Moreover, the single topical instillation of the hydrogel resulted in high ocular tolerance and biocompatibility. In vivo corneal distribution of the cationic peptide-based hydrogel showed that it dramatically increased the retention and the adhesion on the surface of cornea, compared to the anionic peptide-based analogue, owing to the ionic interactions with mucin on the ocular surface. In addition, we also synthesized environment-sensitive fluorophore-conjugated analogues (i.e., NBD-FFKK and NBD-FFD) to visualize the uptake of hydrogels in HCEC cells, revealing that the cationic peptide-based hydrogel displayed the better in vitro cellular uptake than the anionic peptide-based hydrogel. More importantly, the resulting cationic Nap-FFKK supramolecular hydrogel displayed a superior ocular bioavailability over that of anionic Nap-FFD supramolecular hydrogel, as indicated by in vivo pharmacokinetics study. This work, as a systematic investigation of ionic peptide-based molecular hydrogels in the ocular application, illustrates a new and powerful supramolecular approach for antagonizing clinically difficult ocular drug delivery. STATEMENT OF SIGNIFICANCE: Here we show the use of a cationic peptide as the molecular hydrogelator for generating supramolecular hydrogels, which allows it to function as a promising ocular drug vehicle for antagonizing the therapeutic delivery difficulties associated with the physiological barriers and clearance mechanism of the eye. The in vitro and in vivo studies of the hydrogel both show high ocular tolerance and biocompatibility. Moreover, the in vivo corneal distribution of the hydrogel exhibits the increased retention and adhesion on the surface of cornea. This work, as an investigation of cationic peptide-based molecular hydrogels in the ocular application, illustrates a powerful supramolecular approach for overcoming clinically difficult ocular drug delivery.

Constructing a Facile Biocomputing Platform Based on Smart Supramolecular Hydrogel Film Electrodes with Immobilized Enzymes and Gold Nanoclusters

Herein, fluorescent gold nanoclusters (AuNCs) and horseradish peroxidase (HRP) were simultaneously embedded into self-assembled dipeptide supramolecular films of N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) on the surface of ITO electrodes (Fmoc-FF/AuNCs/HRP) by using a simple single-step process. In the films, both the fluorescence property of AuNCs and the bioelectrocatalytic property of HRP were well maintained and could be reversibly regulated by pH-sensitive structural changes in the Fmoc-FF hydrogel films. Cu(II)/EDTA in the solution could lead to the aggregation/disaggregation of AuNCs and further quenching/dequenching the fluorescence signal from the films. Meanwhile, the blue complexes formed by Cu(II) and EDTA could produce a UV-vis signal in the solution. In addition, the coordinated Cu(II) in the films enhanced the electrocatalytic capacity toward the reduction of H₂O₂ and could switch the current signal. A biomolecular logic circuit was built based on the smart film electrode system by using pH, the concentrations of EDTA, Cu(II) and H₂O₂ as inputs, while the fluorescence intensity (FL), current (I) and UV-vis extinction (E) of the solution as outputs. Various logic devices were fabricated using the uniform platform, consisting of an encoder/decoder, demultiplexer, dual-transfer gate, keypad lock, digital comparator, half adder, and controlled NOT (CNOT) gate. Specifically, an electronic three-value logic gate, gullibility (ANY) gate, was first mimicked in this biocomputing system. This work not only demonstrated the construction of a new type of multivalued logic gate by using a dipeptide micromolecular matrix but also provided a new approach for designing sophisticated biologic functions, establishing smart multianalyte biosensing or fabricating biology information processing through the use of a simple film system.

Co-assembly and multicomponent hydrogel formation upon mixing nucleobase-containing peptides

Peptide-based hydrogels are physical gels formed through specific supramolecular self-assembling processes, leading to ordered nanostructures which constitute the water entrapping scaffold of the soft material. Thanks to the inherent properties of peptides, these hydrogels are highly considered in the biomedical domain and open new horizons in terms of application in advanced therapies and biotechnologies. The use of one, and only one, native peptide to formulate a gel is by far the most reported approach to design such materials, but suffers from several limitations, including in terms of mechanical properties. To improve peptide-based hydrogels interest and give rise to innovative properties, several strategies have been proposed in the recent years, and the development of multicomponent peptide-based hydrogels appears as a promising and relevant strategy. Indeed, mixing two or more compounds to develop new materials is a much-used approach that has proven its effectiveness in a wide variety of domains, including polymers, composites and alloys. While still limited to a handful of examples, we would like to report herein on the formulation and the comprehensive study of multicomponent hybrid DNA-nucleobase/peptide-based hydrogels using a multiscale approach based on a large panel of analytical techniques (i.e., rheometry, proton relaxometry, SAXS, electronic microscopy, infrared, circular dichroism, fluorescence, Thioflavin T assays). Among the six multicomponent systems studied, the results highlight the synergistic role of the presence of the two complementary DNA-nucleobases (i.e., adenine/thymine and guanine/cytosine) on the co-assembling process from structural (e.g., morphology of the nanoobjects) to physicochemical (e.g., kinetics of formation, fluorescence properties) and mechanical (e.g., stiffness, resistance to external stress) properties. All the data confirm the relevance of the multicomponent peptide-based approach in the design of innovative hydrogels and bring another brick in the wall of the understanding of these complex and promising systems.

Self-Supporting Hydrogels Based on Fmoc-Derivatized Cationic Hexapeptides for Potential Biomedical Applications

Peptide-based hydrogels (PHGs) are biocompatible materials suitable for biological, biomedical, and biotechnological applications, such as drug delivery and diagnostic tools for imaging. Recently, a novel class of synthetic hydrogel-forming amphiphilic cationic peptides (referred to as series K), containing an aliphatic region and a Lys residue, was proposed as a scaffold for bioprinting applications. Here, we report the synthesis of six analogues of the series K, in which the acetyl group at the N-terminus is replaced by aromatic portions, such as the Fmoc protecting group or the Fmoc-FF hydrogelator. The tendency of all peptides to self-assemble and to gel in aqueous solution was investigated using a set of biophysical techniques. The structural characterization pointed out that only the Fmoc-derivatives of series K keep their capability to gel. Among them, Fmoc-K3 hydrogel, which is the more rigid one (G’ = 2526 Pa), acts as potential material for tissue engineering, fully supporting cell adhesion, survival, and duplication. These results describe a gelification process, allowed only by the correct balancing among aggregation forces within the peptide sequences (e.g., van der Waals, hydrogen bonding, and π–π stacking).

Advances in 3D peptide hydrogel models in cancer research

In vitro cell culture models on monolayer surfaces (2D) have been widely adapted for identification of chemopreventive food compounds and food safety evaluation. However, the low correlation between 2D models and in vivo animal models has always been a concern; this gap is mainly caused by the lack of a three-dimensional (3D) extracellular microenvironment. In 2D models, cell behaviors and functionalities are altered, resulting in varied responses to external conditions (i.e., antioxidants) and hence leading to low predictability. Peptide hydrogel 3D scaffolding technologies, such as PGmatrix for cell culture, have been recently reported to grow organoid-like spheroids physiologically mimicking the 3D microenvironment that can be used as an in vitro 3D model for investigating cell activities, which is anticipated to improve the prediction rate. Thus, this review focuses on advances in 3D peptide hydrogels aiming to introduce 3D cell culture tools as in vitro 3D models for cancer-related research regarding food safety and nutraceuticals.

Recent Progress in the Design and Medical Application of In Situ Self-Assembled Polypeptide Materials

Inspired by molecular self-assembly, which is ubiquitous in natural environments and biological systems, self-assembled peptides have become a research hotspot in the biomedical field due to their inherent biocompatibility and biodegradability, properties that are afforded by the amide linkages forming the peptide backbone. This review summarizes the biological advantages, principles, and design strategies of self-assembled polypeptide systems. We then focus on the latest advances in in situ self-assembly of polypeptides in medical applications, such as oncotherapy, materials science, regenerative medicine, and drug delivery, and then briefly discuss their potential challenges in clinical treatment.

Amyloid-Like Aggregation in Diseases and Biomaterials: Osmosis of Structural Information

The discovery that the polypeptide chain has a remarkable and intrinsic propensity to form amyloid-like aggregates endowed with an extraordinary stability is one of the most relevant breakthroughs of the last decades in both protein/peptide chemistry and structural biology. This observation has fundamental implications, as the formation of these assemblies is systematically associated with the insurgence of severe neurodegenerative diseases. Although the ability of proteins to form aggregates rich in cross-β structure has been highlighted by recent studies of structural biology, the determination of the underlying atomic models has required immense efforts and inventiveness. Interestingly, the progressive molecular and structural characterization of these assemblies has opened new perspectives in apparently unrelated fields. Indeed, the self-assembling through the cross-β structure has been exploited to generate innovative biomaterials endowed with promising mechanical and spectroscopic properties. Therefore, this structural motif has become the fil rouge connecting these diversified research areas. In the present review, we report a chronological recapitulation, also performing a survey of the structural content of the Protein Data Bank, of the milestones achieved over the years in the characterization of cross-β assemblies involved in the insurgence of neurodegenerative diseases. A particular emphasis is given to the very recent successful elucidation of amyloid-like aggregates characterized by remarkable molecular and structural complexities. We also review the state of the art of the structural characterization of cross-β based biomaterials by highlighting the benefits of the osmosis of information between these two research areas. Finally, we underline the new promising perspectives that recent successful characterizations of disease-related amyloid-like assemblies can open in the biomaterial field.

Peptide-Based Hydrogels and Nanogels for Delivery of Doxorubicin

INTRODUCTION

The clinical use of the antitumoral drug doxorubicin (Dox) is reduced by its dose-limiting toxicity, related to cardiotoxic side effects and myelosuppression. In order to overcome these drawbacks, here we describe the synthesis, the structural characterization and the in vitro cytotoxicity assays of hydrogels (HGs) and nanogels (NGs) based on short peptide sequences loaded with Dox or with its liposomal formulation, Doxil.

METHODS

Fmoc-FF alone or in combination with (FY)3 or PEG8-(FY)3 peptides, at two different ratios (1/1 and 2/1 v/v), were used for HGs and NGs formulations. HGs were prepared according to the "solvent-switch" method, whereas NGs were obtained through HG submicronition by the top-down methodology in presence of TWEEN®60 and SPAN®60 as stabilizing agents. HGs gelation kinetics were assessed by Circular Dichroism (CD). Stability and size of NGs were studied using Dynamic Light Scattering (DLS) measurements. Cell viability of empty and filled Dox HGs and NGs was evaluated on MDA-MB-231 breast cancer cells. Moreover, cell internalization of the drug was evaluated using immunofluorescence assays.

RESULTS

Dox filled hydrogels exhibit a high drug loading content (DLC=0.440), without syneresis after 10 days. Gelation kinetics (20-40 min) and the drug release (16-28%) over time of HGs were found dependent on relative peptide composition. Dox filled NGs exhibit a DLC of 0.137 and a low drug release (20-40%) after 72 h. Empty HGs and NGs show a high cell viability (>95%), whereas Dox loaded ones significantly reduce cell viability after 24 h (49-57%) and 72 h (7-25%) of incubation, respectively. Immunofluorescence assays evidenced a different cell localization for Dox delivered through HGs and NGs with respect to the free drug.

DISCUSSION

A modulation of the Dox release can be obtained by changing the ratios of the peptide components. The different cellular localization of the drug loaded into HGs and NGs suggests an alternative internalization mechanism. The high DLC, the low drug release and preliminary in vitro results suggest a potential employment of peptide-based HGs and NGs as drug delivery tools.

Peptide-based hydrogels as delivery systems for doxorubicin

Hydrogels (HGs) and nanogels (NGs) have been recently identified as innovative supramolecular materials for many applications in biomedical field such as in tissue engineering, optoelectronic, and local delivery of active pharmaceutical ingredients (APIs). Due to their in vivo biocompatibility, synthetic accessibility, low cost, and tunability, peptides have been used as suitable building blocks for preparation of HGs and NGs formulations. Peptide HGs have shown an outstanding potential to deliver small drugs, protein therapeutics, or diagnostic probes, maintaining the efficacy of their loaded molecules, preventing degradation phenomena, and responding to external physicochemical stimuli. In this review, we discuss the possible use of peptide-based HGs and NGs as vehicles for the delivery of the anticancer drug doxorubicin (Dox). This anthracycline is clinically used for leukemia, stomach, lung, ovarian, breast, and bladder cancer therapy. The loading of Dox into supramolecular systems (liposomes, micelles, hydrogels, and nanogels) allows reducing its cardiotoxicity. According to a primary sequence classification of the constituent peptide, doxorubicin-loaded systems are here classified in short and ultra-short peptide-based HGs, RGD, or RADA-peptide-based HGs and peptide-based NGs.

Hydrogels to engineer tumor microenvironments in vitro

Illustration of engineered hydrogel to recapitulate aspects of the tumor microenvironment.

Recent advances in the fabrication, functionalization, and bioapplications of peptide hydrogels

Self-assembled peptide-based nanomaterials have exhibited wide application potential in the fields of materials science, nanodevices, biomedicine, tissue engineering, biosensors, energy storage, environmental science, and others. Due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization, three-dimensional self-assembled peptide hydrogels revealed promising potential in bio-related applications. To present the advances in this interesting topic, we present a review on the synthesis and functionalization of peptide hydrogels, as well as their applications in drug delivery, antibacterial materials, cell culture, biomineralization, bone tissue engineering, and biosensors. Specifically, we focus on the fabrication methods of peptide hydrogels through physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by incorporation with polymers, DNA, protein, nanoparticles, and carbon materials is introduced and discussed in detail. It is expected that this work will be helpful not only for the design and synthesis of various peptide-based nanostructures and nanomaterials, but also for the structural and functional tailoring of peptide-based nanomaterials to meet specific demands.

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.

Surface Modification by Nano-Structures Reduces Viable Bacterial Biofilm in Aerobic and Anaerobic Environments

Bacterial biofilm formation on wet surfaces represents a significant problem in medicine and environmental sciences. One of the strategies to prevent or eliminate surface adhesion of organisms is surface modification and coating. However, the current coating technologies possess several drawbacks, including limited durability, low biocompatibility and high cost. Here, we present a simple antibacterial modification of titanium, mica and glass surfaces using self-assembling nano-structures. We have designed two different nano-structure coatings composed of fluorinated phenylalanine via the drop-cast coating technique. We investigated and characterized the modified surfaces by scanning electron microscopy, X-ray diffraction and wettability analyses. Exploiting the antimicrobial property of the nano-structures, we successfully hindered the viability of Streptococcus mutans and Enterococcus faecalis on the coated surfaces in both aerobic and anaerobic conditions. Notably, we found lower bacteria adherence to the coated surfaces and a reduction of 86–99% in the total metabolic activity of the bacteria. Our results emphasize the interplay between self-assembly and antimicrobial activity of small self-assembling molecules, thus highlighting a new approach of biofilm control for implementation in biomedicine and other fields.

Design of Bio-Conjugated Hydrogels for Regenerative Medicine Applications: From Polymer Scaffold to Biomolecule Choice

Bio-conjugated hydrogels merge the functionality of a synthetic network with the activity of a biomolecule, becoming thus an interesting class of materials for a variety of biomedical applications. This combination allows the fine tuning of their functionality and activity, whilst retaining biocompatibility, responsivity and displaying tunable chemical and mechanical properties. A complex scenario of molecular factors and conditions have to be taken into account to ensure the correct functionality of the bio-hydrogel as a scaffold or a delivery system, including the polymer backbone and biomolecule choice, polymerization conditions, architecture and biocompatibility. In this review, we present these key factors and conditions that have to match together to ensure the correct functionality of the bio-conjugated hydrogel. We then present recent examples of bio-conjugated hydrogel systems paving the way for regenerative medicine applications.

Collagen-Inspired Helical Peptide Coassembly Forms a Rigid Hydrogel with Twisted Polyproline II Architecture

Collagen, the most abundant protein in mammals, possesses notable cohesion and elasticity properties and efficiently induces tissue regeneration. The Gly-Pro-Hyp canonical tripeptide repeating unit of the collagen superhelix has been well-characterized. However, to date, the shortest tripeptide repeat demonstrated to attain a helical conformation contained 3-10 peptide repeats. Here, taking a minimalistic approach, we studied a single repeating unit of collagen in its protected form, Fmoc-Gly-Pro-Hyp. The peptide formed single crystals displaying left-handed polyproline II superhelical packing, as in the native collagen single strand. The crystalline assemblies also display head-to-tail H-bond interactions and an "aromatic zipper" arrangement at the molecular interface. The coassembly of this tripeptide, with Fmoc-Phe-Phe, a well-studied dipeptide hydrogelator, produced twisted helical fibrils with a polyproline II conformation and improved hydrogel mechanical rigidity. The design of these peptides illustrates the possibility to assemble superhelical nanostructures from minimal collagen-inspired peptides with their potential use as functional motifs to introduce a polyproline II conformation into hybrid hydrogel assemblies.

Fluorescence Phenomena in Amyloid and Amyloidogenic Bionanostructures

Nanoscale optical labeling is an advanced bioimaging tool. It is mostly based on fluorescence (FL) phenomena and enables the visualization of single biocells, bacteria, viruses, and biological tissues, providing monitoring of functional biosystems in vitro and in vivo, and the imaging-guided transportation of drug molecules. There is a variety of FL biolabels such as organic molecular dyes, genetically encoded fluorescent proteins (green fluorescent protein and homologs), semiconductor quantum dots, carbon dots, plasmonic metal gold-based nanostructures and more. In this review, a new generation of FL biolabels based on the recently found biophotonic effects of visible FL are described. This intrinsic FL phenomenon is observed in any peptide/protein materials folded into β-sheet secondary structures, irrespective of their composition, complexity, and origin. The FL effect has been observed both in natural amyloid fibrils, associated with neurodegenerative diseases (Alzheimer’s, Parkinson’s, and more), and diverse synthetic peptide/protein structures subjected to thermally induced biological refolding helix-like→β-sheet. This approach allowed us to develop a new generation of FL peptide/protein bionanodots radiating multicolor, tunable, visible FL, covering the entire visible spectrum in the range of 400–700 nm. Newly developed biocompatible nanoscale biomarkers are considered as a promising tool for emerging precise biomedicine and advanced medical nanotechnologies (high-resolution bioimaging, light diagnostics, therapy, optogenetics, and health monitoring).

Stable Formulations of Peptide-Based Nanogels

Recently, nanogels have been identified as innovative formulations for enlarging the application of hydrogels (HGs) in the area of drug delivery or in diagnostic imaging. Nanogels are HGs-based aggregates with sizes in the range of nanometers and formulated in order to obtain injectable preparations. Regardless of the advantages offered by peptides in a hydrogel preparation, until now, only a few examples of peptide-based nanogels (PBNs) have been developed. Here, we describe the preparation of stable PBNs based on Fmoc-Phe-Phe-OH using three different methods, namely water/oil emulsion (W/O), top-down, and nanogelling in water. The effect of the hydrophilic-lipophilic balance (HLB) in the formulation was also evaluated in terms of size and stability. The resulting nanogels were found to encapsulate the anticancer drug doxorubicin, chosen as the model drug, with a drug loading comparable with those of the liposomes.

Coassembly-Induced Transformation of Dipeptide Amyloid-Like Structures into Stimuli-Responsive Supramolecular Materials

Conformational transition of proteins and peptides into highly stable, β-sheet-rich structures is observed in many amyloid-associated neurodegenerative disorders, yet the precise mechanism of amyloid formation at the molecular level remains poorly understood due to the complex molecular structures. Short peptides provide simplified models for studying the molecular basis of the assembly mechanism that governs β-sheet fibrillation processes underlying the formation and inhibition of amyloid-like structures. Herein, we report a supramolecular coassembly strategy for the inhibition and transformation of stable β-sheet-rich amyloid-derived dipeptide self-assemblies into adaptable secondary structural fibrillar assemblies by mixing with bipyridine derivatives. The interplay between the type and mixing ratio of bipyridine derivatives allowed the variable coassembly process with stimuli-responsive functional properties, studied by various experimental characterizations and computational methods. Furthermore, the resulting coassemblies showed functional redox- and photoresponsive properties, making them promising candidates for controllable drug release and fluorescent imprint. This work presents a coassembly strategy not only to explore the mechanism of amyloid-like structure formation and inhibition at the molecular level but also to manipulate amyloid-like structures into responsive supramolecular coassemblies for material science and biotechnology applications.

SIRT1 regulates O-GlcNAcylation of tau through OGT

Tau is modified with O-GlcNAcylation extensively in human brain. The O-GlcNAcylation levels of tau are decreased in Alzheimer's disease (AD) brain. Sirtuin type 1 (SIRT1) is an enzyme that deacetylates proteins including transcriptional factors and associates with neurodegenerative diseases, such as AD. Aberrant SIRT1 expression levels in AD brain is in parallel with the accumulation of tau. cAMP response element binding protein (CREB), a cellular transcription factor, plays a critical role in learning and memory. In this present study, we found SIRT1 deacetylates CREB and inhibits phosphorylation of CREB at Ser133. The inactivated CREB suppresses OGT expression and therefore decreases the O-GlcNAcylation of tau and thus increases the phosphorylation of tau at specific sites. These findings suggest that SIRT1 may be a potential therapeutic target for treating tauopathies.