The Role of Functional Groups in Tuning the Self-Assembly Modes and Physical Properties of Multicomponent Gels

We have analyzed the nature and role of functional groups on the self-assembly modes and the physical properties of multicomponent gels with structurally similar individual components. The gelation properties of individual and mixed enantiomeric compounds of biphenyl bis-(amides) of alanine (BPA) or phenylalanine (BPP) methyl ester were analyzed in various solvent/solvent mixtures. Multicomponent gels were formed by mixing the enantiomeric BPP compounds at a lower concentration, but a higher concentration was required for mixed alanine-based BPA gels. The comparison of the mechanical strength of the individual and mixed BPP compounds indicated that the mixed BPP gels displayed enhanced mechanical strength (∼2-fold increase) in p-xylene, but a weaker gel was observed in DMSO/water. However, a reverse trend was observed for BPA gels, indicating the role of functional groups in the gel network formation. X-ray diffraction analysis of the gelator and the xerogels in the solid state confirmed the formation of co-assembled networks in mixed enantiomeric gels. The stability of the gels towards anions was evaluated by analyzing the anion induced stimuli-responsive properties. These results indicate the effective modeling of the functional groups of the individual components could lead to multicomponent gels with tunable properties.

Antioxidative, cytotoxic, and antibacterial properties of self-assembled glycine-histidine-based dipeptides with or without silver nanoparticles in bio-inspired film

Recent years have seen much attention being given to self-assembly of dipeptide-based structures, especially to self-regulation of dipeptide structures with different amino acid sequences. In this study we investigated the effects of varying solvent environments on the self-assembly of glycine-histidine (Gly-His) dipeptide structures. First we determined the morphological properties of Gly-His films formed in different solvent environments with scanning electron microscopy and then structural properties with Fourier-transform infrared (FTIR) spectroscopy. In addition, we studied the effects of Gly-His films on silver nanoparticle (AgNP) formation and the antioxidant and cytotoxic properties of AgNPs obtained in this way. We also, assessed antibacterial activities of Gly-His films against Gram-negative Escherichia coli and Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Silver nanoparticle-decorated Gly-His films were not significantly cytotoxic at concentrations below 2 mg/mL but had antibacterial activity. We therefore believe that AgNP-decorated Gly-His films at concentrations below 2 mg/mL can be used safely against bacteria.

Study on the self-assembly of aromatic antimicrobial peptides based on different PAF26 peptide sequences

Antimicrobial peptide (AMP) self-assembly is an effective way to synthesis antimicrobial biomaterials. In previous studies, we found PAF26 AMP (Ac-RKKWFW-NH2) and its derivative K2–F2 peptide (Ac-KKRKKWFWFF-NH2) could both self-assemble into hydrogels, but they had distinct microscopic structures. Therefore, in this work five PAF26 peptide derivatives with different numbers of aromatic amino acids are designed to better understand the self-assembly mechanism of aromatic AMP. The transmission electron microscopy, infrared spectroscopy, circular dichroism, and fluorescence spectroscopy characterizations are carried out to study the microscope structure, secondary conformation, and molecular interactions. It is found that the five peptide derivatives have different microscopic structures, and the number of aromatic amino acids will affect the peptide hydrogen bonding and aromatic stacking interactions, causing significant differences in the secondary conformation and microscopic structure. This work will enhance the comprehension of aromatic AMP self-assembly.

Synthesis, Characterization and Evaluation of Peptide Nanostructures for Biomedical Applications

There is a challenging need for the development of new alternative nanostructures that can allow the coupling and/or encapsulation of therapeutic/diagnostic molecules while reducing their toxicity and improving their circulation and in-vivo targeting. Among the new materials using natural building blocks, peptides have attracted significant interest because of their simple structure, relative chemical and physical stability, diversity of sequences and forms, their easy functionalization with (bio)molecules and the possibility of synthesizing them in large quantities. A number of them have the ability to self-assemble into nanotubes, -spheres, -vesicles or -rods under mild conditions, which opens up new applications in biology and nanomedicine due to their intrinsic biocompatibility and biodegradability as well as their surface chemical reactivity via amino- and carboxyl groups. In order to obtain nanostructures suitable for biomedical applications, the structure, size, shape and surface chemistry of these nanoplatforms must be optimized. These properties depend directly on the nature and sequence of the amino acids that constitute them. It is therefore essential to control the order in which the amino acids are introduced during the synthesis of short peptide chains and to evaluate their in-vitro and in-vivo physico-chemical properties before testing them for biomedical applications. This review therefore focuses on the synthesis, functionalization and characterization of peptide sequences that can self-assemble to form nanostructures. The synthesis in batch or with new continuous flow and microflow techniques will be described and compared in terms of amino acids sequence, purification processes, functionalization or encapsulation of targeting ligands, imaging probes as well as therapeutic molecules. Their chemical and biological characterization will be presented to evaluate their purity, toxicity, biocompatibility and biodistribution, and some therapeutic properties in vitro and in vivo. Finally, their main applications in the biomedical field will be presented so as to highlight their importance and advantages over classical nanostructures.

A Self-Assembled Nanoindicator from Alizarin Red S-Borono-Peptide for Potential Imaging of Cellular Copper(II) Ions

Recently, smart nanomaterials from peptide self-assembly have received extensive attention in the field of biological and medical applications. Through rationally designing the molecular structure, we constructed a borono-peptide that self-assembled into well-defined nanofibers. Relying on the specific recognition between the vicinal diol compound and boronic acid, a novel alizarin red S (ARS)-borono-peptide (BP) spherical nanoindicator was fabricated, accompanying with the emission of strong fluorescent signal. The fluorescent nanoindicator displayed an intense response to copper(II) ions and underwent the fluorescent "turn-off" due to the strong binding-induced displacement. Originating from the high selectivity toward copper(II) ions, good biocompatibility and cancer cell targeting, the nanoindicator offered the opportunity to image copper(II) ions in cancer cells via fluorescent change.

Dual-ligand supramolecular nanofibers inspired by the renin-angiotensin system for the targeting and synergistic therapy of myocardial infarction

Rationale: The compensatory activation of the renin-angiotensin system (RAS) after myocardial infarction (MI) plays a crucial role in the pathogenesis of heart failure. Most existing studies on this subject focus on mono- or dual-therapy of blocking the RAS, which exhibit limited efficacy and often causes serious adverse reactions. Few studies have been conducted on targeted therapy based on the activated RAS post-MI. Thus, the development of multiple-functional nanomedicine with concurrent targeting ability and synergistic therapeutic effect against RAS may show great promise in improving cardiac function post-MI.

Methods: We utilized a cooperative self-assembly strategy constructing supramolecular nanofibers— telmisartan-doped co-assembly nanofibers (TDCNfs) to counter-regulate RAS through targeted delivery and combined therapy. TDCNfs were prepared through serial steps of solvent exchange, heating incubation, gelation, centrifugation, and lyophilization, in which the telmisartan was doped in the self-assembly process of Ang1-7 to obtain the co-assembly nanofibers wherein they act as both therapeutic agents and target-guide agents.

Results: TDCNfs exhibited the desired binding affinity to the two different receptors, AT1R and MasR. Through the dual ligand-receptor interactions to mediate the coincident downstream pathways, TDCNfs not only displayed favorably targeted properties to hypoxic cardiomyocytes, but also exerted synergistic therapeutic effects in apoptosis reduction, inflammatory response alleviation, and fibrosis inhibition in vitro and in vivo, significantly protecting cardiac function and mitigating post-MI adverse outcomes.

Conclusion: A dual-ligand nanoplatform was successfully developed to achieve targeted and synergistic therapy against cardiac deterioration post-MI. We envision that the integration of multiple therapeutic agents through supramolecular self-assembly would offer new insight for the systematic and targeted treatment of cardiovascular diseases.

Stimuli-Responsive, Pentapeptide, Nanofiber Hydrogel for Tissue Engineering

Short peptides are uniquely versatile building blocks for self-assembly. Supramolecular peptide assemblies can be used to construct functional hydrogel biomaterials-an attractive approach for neural tissue engineering. Here, we report a new class of short, five-residue peptides that form hydrogels with nanofiber structures. Using rheology and spectroscopy, we describe how sequence variations, pH, and peptide concentration alter the mechanical properties of our pentapeptide hydrogels. We find that this class of seven unmodified peptides forms robust hydrogels from 0.2-20 kPa at low weight percent (less than 3 wt %) in cell culture media and undergoes shear-thinning and rapid self-healing. The peptides self-assemble into long fibrils with sequence-dependent fibrillar morphologies. These fibrils exhibit a unique twisted ribbon shape, as visualized by transmission electron microscopy (TEM) and Cryo-EM imaging, with diameters in the low tens of nanometers and periodicities similar to amyloid fibrils. Experimental gelation behavior corroborates our molecular dynamics simulations, which demonstrate peptide assembly behavior, an increase in β-sheet content, and patterns of variation in solvent accessibility. Our rapidly assembling pentapeptides for injectable delivery (RAPID) hydrogels are syringe-injectable and support cytocompatible encapsulation of oligodendrocyte progenitor cells (OPCs), as well as their proliferation and three-dimensional process extension. Furthermore, RAPID gels protect OPCs from mechanical membrane disruption and acute loss of viability when ejected from a syringe needle, highlighting the protective capability of the hydrogel as potential cell carriers for transplantation therapies. The tunable mechanical and structural properties of these supramolecular assemblies are shown to be permissive to cell expansion and remodeling, making this hydrogel system suitable as an injectable material for cell delivery and tissue engineering applications.

Multicomponent peptide assemblies

Self-assembled peptide nanostructures have been increasingly exploited as functional materials for applications in biomedicine and energy. The emergent properties of these nanomaterials determine the applications for which they can be exploited. It has recently been appreciated that nanomaterials composed of multicomponent coassembled peptides often display unique emergent properties that have the potential to dramatically expand the functional utility of peptide-based materials. This review presents recent efforts in the development of multicomponent peptide assemblies. The discussion includes multicomponent assemblies derived from short low molecular weight peptides, peptide amphiphiles, coiled coil peptides, collagen, and β-sheet peptides. The design, structure, emergent properties, and applications for these multicomponent assemblies are presented in order to illustrate the potential of these formulations as sophisticated next-generation bio-inspired materials.

Novel oligopeptide nanoprobe for targeted cancer cell imaging

Co-assembly of WFFW tetrapeptide and RGDWFFW heptapeptide generated the photostable and fluorescence-tunable nanoprobe, which could selectively image the cancer cells.

Photocontrolled protein assembly for constructing programmed two-dimensional nanomaterials

A rapid and efficient strategy was developed to construct photocontrolled 2D protein nanosheets with an orderly arrangement.

Self-assembling peptide and protein amyloids: from structure to tailored function in nanotechnology

Self-assembled peptide and protein amyloid nanostructures have traditionally been considered only as pathological aggregates implicated in human neurodegenerative diseases. In more recent times, these nanostructures have found interesting applications as advanced materials in biomedicine, tissue engineering, renewable energy, environmental science, nanotechnology and material science, to name only a few fields. In all these applications, the final function depends on: (i) the specific mechanisms of protein aggregation, (ii) the hierarchical structure of the protein and peptide amyloids from the atomistic to mesoscopic length scales and (iii) the physical properties of the amyloids in the context of their surrounding environment (biological or artificial). In this review, we will discuss recent progress made in the field of functional and artificial amyloids and highlight connections between protein/peptide folding, unfolding and aggregation mechanisms, with the resulting amyloid structure and functionality. We also highlight current advances in the design and synthesis of amyloid-based biological and functional materials and identify new potential fields in which amyloid-based structures promise new breakthroughs.

Design, synthesis, and characterisation of glyoxylamide-based short peptides as self-assembled gels

First example of glyoxylamide-based short peptides which can encapsulate organic solvents and water at relatively low concentrations.

Construction of poly(dopamine) doped oligopeptide hydrogel

Incorporation of poly(dopamine) (PDA) into the native oligopeptide hydrogel not only improve the rigidity but also endow the hydrogel with efficient free radical scavenging ability.

Semiconducting polymer–dipeptide nanostructures by ultrasonically-assisted self-assembling

The preparation of bio-organic nanostructures containing dipeptides and conjugated polymers like P3HT–diphenylalanine is trigged by ultrasound energy owing the study of such hybrid materials in solution processed OFETs and beyond.

Fmoc–RGDS based fibrils: atomistic details of their hierarchical assembly

We describe the 3D supramolecular structure of Fmoc–RGDS fibrils, where Fmoc and RGDS refer to the hydrophobic N-(fluorenyl-9-methoxycarbonyl) group and the hydrophilic Arg-Gly-Asp-Ser peptide sequence, respectively.

Enzyme–substrate interactions promote the self-assembly of amino acid derivatives into supramolecular hydrogels

The first example of enzyme-substrate interaction-promoted self-assembly was reported for the synthesis of supramolecular hydrogels from Fmoc-amino acids and amino acid esters in the presence of α-chymotrypsin.

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Electrostatic and aromatic interaction-directed supramolecular self-assembly of a designed Fmoc-tripeptide into helical nanoribbons

Supramolecular self-assembly offers an efficient pathway for creating macroscopically chiral structures in biology and materials science. Here, a new peptide consisting of an N-(9-fluorenylmethoxycarbonyl) headgroup connected to an aromatic phenylalanine-tryptophan dipeptide and terminated with zwitterionic lysine (Fmoc-FWK) and its cationic form (Fmoc-FWK-NH2) were designed for self-assembly into chiral structures. It was found that the Fmoc-FWK peptide self-assembled into left-handed helical nanoribbons at pH 11.2-11.8, whereas it formed nanofibers at pH 5 and 12 and large flat ribbons composed of many nanofibers in the pH range of 6-11. However, only nanofibers were observed in the cases of Fmoc-FWK-NH2 at different values. A series of structural characterizations based on CD, FTIR, UV-vis and fluorescence spectroscopy reveal that the electrostatic and aromatic interactions and the associated hydrogen bonding direct the self-assembly into various structures. The enhanced π-π stacking and hydrogen bonding were found in the helical nanoribbons. This difference in intermolecular interactions should be derived from the ionization of carboxyl and amino groups from lysine residues at different pH values. Furthermore, we performed molecular dynamics simulations to gain insight into the assembly mechanisms. The results imply that a relatively rigid molecular conformation and the strong intramolecular aromatic interaction between Trp and Fmoc groups favor chiral self-assembly. This study is the first attempt to design a Fmoc-tripeptide for the fabrication of helical structures with macroscopic chirality, which provides a successful example and allows us to create new peptide-based chiral assembly systems.

Adjustable nanofibers self-assembled from an irregular conformational peptide amphiphile

A peptide amphiphile adopting an irregular conformation self-assembled into dendritic nanofibers, peacock-feather-like nanofibers, and even parallel nanofibers.

Polypeptide thermogels as a three dimensional culture scaffold for hepatogenic differentiation of human tonsil-derived mesenchymal stem cells

Tonsil-derived mesenchymal stem cells (TMSCs) were investigated for hepatogenic differentiation in the 3D matrixes of poly(ethylene glycol)-b-poly(l-alanine) (PEG-L-PA) thermogel. The diblock polymer formed β-sheet based fibrous nanoassemblies in water, and the aqueous polymer solution undergoes sol-to-gel transition as the temperature increases in a concentration range of 5.0-8.0 wt %. The cell-encapsulated 3D matrix was prepared by increasing the temperature of the cell-suspended PEG-L-PA aqueous solution (6.0 wt %) to 37 °C. The gel modulus at 37 °C was about 1000 Pa, which was similar to that of decellularized liver tissue. Cell proliferation, changes in cell morphology, hepatogenic biomarker expressions, and hepatocyte-specific biofunctions were compared for the following 3D culture systems: TMSC-encapsulated thermogels in the absence of hepatogenic growth factors (protocol M), TMSC-encapsulated thermogels where hepatogenic growth factors were supplied from the medium (protocol MGF), and TMSC-encapsulated thermogels where hepatogenic growth factors were coencapsulated with TMSCs during the sol-to-gel transition (protocol GGF). The spherical morphology and size of the encapsulated cells were maintained in the M system during the 3D culture period of 28 days, whereas the cells changed their morphology and significant aggregation of cells was observed in the MGF and GGF systems. The hepatocyte-specific biomarker expressions and metabolic functions were negligible for the M system. However, hepatogenic genes of albumin, cytokeratin 18 (CK-18), and hepatocyte nuclear factor 4α (HNF 4α) were significantly expressed in both MGF and GGF systems. In addition, production of albumin and α-fetoprotein was also significantly observed in both MGF and GGF systems. The uptake of cardiogreen and low-density lipoprotein, typical metabolic functions of hepatocytes, was apparent for MGF and GGF. The above data indicate that the 3D culture system of PEG-L-PA thermogels provides cytocompatible microenvironments for hepatogenic differentiation of TMSCs. In particular, the successful results of the GGF system suggest that the PEG-L-PA thermogel can be a promising injectable tissue engineering system for liver tissue regeneration after optimizing the aqueous formulation of TMSCs, hepatogenic growth factors, and other biochemicals.

β sheets not required: combined experimental and computational studies of self-assembly and gelation of the ester-containing analogue of an Fmoc-dipeptide hydrogelator

In our work toward developing ester-containing self-assembling peptides as soft biomaterials, we have found that a fluorenylmethoxycarbonyl (Fmoc)-conjugated alanine-lactic acid (Ala-Lac) sequence self-assembles into nanostructures that gel in water. This process occurs despite Fmoc-Ala-Lac's inability to interact with other Fmoc-Ala-Lac molecules via β-sheet-like amide-amide hydrogen bonding, a condition previously thought to be crucial to the self-assembly of Fmoc-conjugated peptides. Experimental comparisons of Fmoc-Ala-Lac to its self-assembling peptide sequence analogue Fmoc-Ala-Ala using a variety of microscopic, spectroscopic, and bulk characterization techniques demonstrate distinct features of the two systems and show that while angstrom-scale self-assembled structures are similar, their nanometer-scale size and morphological properties diverge and give rise to different bulk mechanical properties. Molecular dynamics simulations were performed to gain more insight into the differences between the two systems. An analysis of the hydrogen-bonding and solvent-surface interface properties of the simulated fibrils revealed that Fmoc-Ala-Lac fibrils are stronger and less hydrophilic than Fmoc-Ala-Ala fibrils. We propose that this difference in fibril amphiphilicity gives rise to differences in the higher-order assembly of fibrils into nanostructures seen in TEM. Importantly, we confirm experimentally that β-sheet-type hydrogen bonding is not crucial to the self-assembly of short, conjugated peptides, and we demonstrate computationally that the amide bond in such systems may act mainly to mediate the solvation of the self-assembled single fibrils and therefore regulate a more extensive higher-order aggregation of fibrils. This work provides a basic understanding for future research in designing highly degradable self-assembling materials with peptide-like bioactivity for biomedical applications.

High length-diameter ratio nanotubes self-assembled from a facial cyclopeptide

A six-residue facial cyclopeptide was designed with the following sequence: c-[D-Leu-L-Lys-D-Ala-L-Lys-D-Leu-L-Gln] (CP). Extensive hydrogen bonding between the cyclopeptide backbones mainly regulated CP to self-assemble into single-walled nanotubes. Simultaneously, the hydrophobic interaction among facial hydrophobic side chains of CP was introduced to stabilize the hydrogen bonding, resulting in the formation of the thick-walled nanotubes with high length–diameter ratios.

Theranostic GO-based nanohybrid for tumor induced imaging and potential combinational tumor therapy

Graphene oxide (GO)-based theranostic nanohybrid is designed for tumor induced imaging and potential combinational tumor therapy. The anti-tumor drug, Doxorubicin (DOX) is chemically conjugated to the poly(ethylenimine)-co-poly(ethylene glycol) (PEI-PEG) grafted GO via a MMP2-cleavable PLGLAG peptide linkage. The therapeutic efficacy of DOX is chemically locked and its intrinsic fluorescence is quenched by GO under normal physiological condition. Once stimulated by the MMP2 enzyme over-expressed in tumor tissues, the resulting peptide cleavage permits the unloading of DOX for tumor therapy and concurrent fluorescence recovery of DOX for in situ tumor cell imaging. Attractively, this PEI-bearing nanohybrid can mediate efficient DNA transfection and shows great potential for combinational drug/gene therapy. This tumor induced imaging and potential combinational therapy will open a window for tumor treatment by offering a unique theranostic approach through merging the diagnostic capability and pathology-responsive therapeutic function.