Using a kinase/phosphatase switch to regulate a supramolecular hydrogel and forming the supramolecular hydrogel in vivo

Crosslinker-Induced Effects on the Gelation Pathway of a Low Molecular Weight Hydrogel

The use of polymeric crosslinkers is an attractive method to modify the mechanical properties of supramolecular materials, but their effects on the self-assembly of the underlying supramolecular polymer networks are poorly understood. Modulation of the gelation pathway of a reaction-coupled low molecular weight hydrogelator is demonstrated using (bio)polymeric crosslinkers of disparate physicochemical identities, providing a handle for control over materials properties.

Inhibition of peptide aggregation by means of enzymatic phosphorylation

As is the case in numerous natural processes, enzymatic phosphorylation can be used in the laboratory to influence the conformational populations of proteins. In nature, this information is used for signal transduction or energy transfer, but has also been shown to play an important role in many diseases like tauopathies or diabetes. With the goal of determining the effect of phosphorylation on amyloid fibril formation, we designed a model peptide which combines structural characteristics of α-helical coiled-coils and β-sheets in one sequence. This peptide undergoes a conformational transition from soluble structures into insoluble amyloid fibrils over time and under physiological conditions and contains a recognition motif for PKA (cAMP-dependent protein kinase) that enables enzymatic phosphorylation. We have analyzed the pathway of amyloid formation and the influence of enzymatic phosphorylation on the different states along the conformational transition from random-coil to β-sheet-rich oligomers to protofilaments and on to insoluble amyloid fibrils, and we found a remarkable directing effect from β-sheet-rich structures to unfolded structures in the initial growth phase, in which small oligomers and protofilaments prevail if the peptide is phosphorylated.

Ultrashort self-assembling Fmoc-peptide gelators for anti-infective biomaterial applications

Biomaterial-related infections have a significant impact on society and are a major contributor to the growing threat of antimicrobial resistance. Current licensed antibiotic classes struggle to breakdown or penetrate the exopolysaccharide biofilm barrier, resulting in sub-therapeutic concentrations of antibiotic at the surface of the biomaterial, treatment failure and increased spread of resistant isolates. This paper focuses for the first time on the ability of ultrashort Fmoc-peptide gelators to eradicate established bacterial biofilms implicated in a variety of medical device infections (Gram-positive: Staphylococcus aureus, Staphylococcus epidermidis and Gram-negative Escherichia coli, Pseudomonas aeruginosa). The effect of increasing the cationicity of FmocFF via addition of di-lysine and di-orntithine was also studied with regard to antibacterial activity. Our studies demonstrated that Fmoc-peptides (FmocFF, FmocFFKK, FmocFFFKK, FmocFFOO) formed surfactant-like soft gels at concentrations of 1% w/v and above using a method of glucono-δ-Lactone pH induction. The majority of Fmoc-peptides (0.5-2% w/v) demonstrated selective action against established (grown for 24 h) biofilms of Gram-positive and Gram-negative pathogens. These results are likely to increase the clinical translation of short-peptide gelator platforms within the area of anti-infective biomaterials including as wound dressings and coatings for prostheses, catheters, heart valves and surgical tubes. In the long term, this will lead to wider treatment choices for clinicians and patients involved in the management of medical device infections and reduce the burden of antimicrobial resistance. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Drug delivery by supramolecular design

Principles rooted in supramolecular chemistry have empowered new and highly functional therapeutics and drug delivery devices. This general approach offers elegant tools rooted in molecular and materials engineered to address the many challenges faced in treating disease.

An ionic coordination hybrid hydrogel for bioseparation

An ionic coordination hybrid hydrogel is formed with ionic and covalent crosslinked networks via one-step copolymation.

Ligand-Receptor Interaction Modulates the Energy Landscape of Enzyme-Instructed Self-Assembly of Small Molecules

The concurrence of enzymatic reaction and ligand-receptor interactions is common for proteins, but rare for small molecules and has yet to be explored. Here we show that ligand-receptor interaction modulates the morphology of molecular assemblies formed by enzyme-instructed assembly of small molecules. While the absence of ligand-receptor interaction allows enzymatic dephosphorylation of a precursor to generate the hydrogelator that self-assembles to form long nanofibers, the presence of the ligand-receptor interaction biases the pathway to form precipitous aggregates containing short nanofibers. While the hydrogelators self-assemble to form nanofibers or nanoribbons that are unable to bind with the ligand (i.e., vancomycin), the addition of surfactant breaks up the assemblies to restore the ligand-receptor interaction. In addition, an excess amount of the ligands can disrupt the nanofibers and result in the precipitates. As the first example of the use of ligand-receptor interaction to modulate the kinetics of enzymatic self-assembly, this work not only provides a solution to evaluate the interaction between aggregates and target molecules but also offers new insight for understanding the emergent behavior of sophisticated molecular systems having multiple and parallel processes.

HEAT repeats - versatile arrays of amphiphilic helices working in crowded environments?

Cellular proteins do not work in isolation. Instead, they often function as part of large macromolecular complexes, which are transported and concentrated into specific cellular compartments and function in a highly crowded environment. A central theme of modern cell biology is to understand how such macromolecular complexes are assembled efficiently and find their destinations faithfully. In this Opinion article, we will focus on HEAT repeats, flexible arrays of amphiphilic helices found in many eukaryotic proteins, such as karyopherins and condensins, and discuss how these uniquely designed helical repeats might underlie dynamic protein-protein interactions and support cellular functions in crowded environments. We will make bold speculations on functional similarities between the action of HEAT repeats and intrinsically disordered regions (IDRs) in macromolecular phase separation. Potential contributions of HEAT-HEAT interactions, as well as cooperation between HEATs and IDRs, to mesoscale organelle assembly will be discussed.

In Situ Construction and Characterization of Chlorin-Based Supramolecular Aggregates in Tumor Cells

We demonstrate in situ construction and characterization of supramolecular aggregates from chlorin p6 (Cp6) molecules in tumor cells. Fully deprotonated Cp6 molecules in neutral condition were partially protonated inside the acidic lysosomes of cells and significantly increased the hydrophobicity of them that resulted in simultaneous formation of J-type aggregates. Importantly, the formation of J-aggregates was fully characterized in artificial tissues by UV-vis, circular dichroism (CD) and transmission electron microscope (TEM) techniques. Compared to the monomers, the J-aggregates exhibited 55-fold enhanced thermal conversion efficiency (η) at the optimal excitation wavelength (690 nm). The remarkably increased heat effect contributed to the stronger photoacoustic (PA) signals, leading to at least 2 orders of magnitude increase of the tumor-to-normal tissue ratio (T/N), which was defined as the PA signal ratio between tumor site and surrounding normal tissue. We envision that this proof-of-concept study will open a new way to develop tumor environment-induced self-assembly for variable biomedical applications.

Engineering responsive supramolecular biomaterials: Toward smart therapeutics

Engineering materials using supramolecular principles enables generalizable and modular platforms that have tunable chemical, mechanical, and biological properties. Applying this bottom-up, molecular engineering-based approach to therapeutic design affords unmatched control of emergent properties and functionalities. In preparing responsive materials for biomedical applications, the dynamic character of typical supramolecular interactions facilitates systems that can more rapidly sense and respond to specific stimuli through a fundamental change in material properties or characteristics, as compared to cases where covalent bonds must be overcome. Several supramolecular motifs have been evaluated toward the preparation of "smart" materials capable of sensing and responding to stimuli. Triggers of interest in designing materials for therapeutic use include applied external fields, environmental changes, biological actuators, applied mechanical loading, and modulation of relative binding affinities. In addition, multistimuli-responsive routes can be realized that capture combinations of triggers for increased functionality. In sum, supramolecular engineering offers a highly functional strategy to prepare responsive materials. Future development and refinement of these approaches will improve precision in material formation and responsiveness, seek dynamic reciprocity in interactions with living biological systems, and improve spatiotemporal sensing of disease for better therapeutic deployment.

Modulating the Nucleated Self-Assembly of Tri-β(3) -Peptides Using Cucurbit[n]urils

The modulation of the hierarchical nucleated self-assembly of tri-β(3) -peptides has been studied. β(3) -Tyrosine provided a handle to control the assembly process through host-guest interactions with CB[7] and CB[8]. By varying the cavity size from CB[7] to CB[8] distinct phases of assembling tri-β(3) -peptides were arrested. Given the limited size of the CB[7] cavity, only one aromatic β(3) -tyrosine can be simultaneously hosted and, hence, CB[7] was primarily acting as an inhibitor of self-assembly. In strong contrast, the larger CB[8] can form a ternary complex with two aromatic amino acids and hence CB[8] was acting primarily as cross-linker of multiple fibers and promoting the formation of larger aggregates. General insights on modulating supramolecular assembly can lead to new ways to introduce functionality in supramolecular polymers.

Using L-STM to directly visualize enzymatic self-assembly/disassembly of nanofibers

Self-assembly/disassembly is ubiquitous in nature and plays an important role in many biological events. But noninvasive characterization of this process in real time at molecular resolution remains challenging. Herein, using homebuilt liquid-phase scanning tunneling microscopy (L-STM) with ultrahigh stability, we directly visualized enzymatic self-assembly/disassembly of oligopeptide nanofibers in real time for the first time. Static high-resolution L-STM images clearly showed the molecular packing details in the supramolecular nanofiber and the diameter of the nanofiber was consistent with that of cryo transmission electron microscopy (cryo-TEM) observations. Moreover, the self-repairing behavior of the supramolecular nanofibers was also directly observed at high resolution for the first time. This work unprecedentedly revealed new insights into Nature-mimic self-assembly and disassembly at the molecular level. It also illustrates the potential of our homebuilt L-STM in studying delicate biological processes in physiological solution with high resolution.

Hydrogelation of the Short Self-Assembling Peptide I3QGK Regulated by Transglutaminase and Use for Rapid Hemostasis

The self-assembly of short peptides is a promising route to the creation of smart biomaterials. To combine peptide self-assembly with enzymatic catalysis, we design an amphiphilic short peptide I3QGK that can self-assemble into long nanoribbons in aqueous solution. Upon addition of transglutaminase (TGase), the peptide solution undergoes a distinct sol-gel transition to form a rigid hydrogel, which shows strong shear-thinning and immediate recovery properties. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements indicate the occurrence of considerable nanofibers in addition to the original nanoribbons. Liquid chromatography and mass spectrometry analyses reveal the enzymatic formation of peptide dimers from monomers through intermolecular ε-(γ-glutamyl)lysine isopeptide bonding. The dimers rapidly self-assemble into flexible and entangled nanofibers, and the coexistence of the original nanoribbons and the newly created nanofibers is responsible for hydrogelation. Factor XIII in blood is converted by thrombin to an active TGase (Factor XIIIa) during bleeding, so the peptide solution shows a more rapid and effective hemostasis via a combination of gelling blood and promoting platelet adhesion, relative to other hemostasis methods or materials. These features of I3QGK, together with its low cytotoxicity against normal mammalian cells and noninduction of nonspecific immunogenic responses, endow it with great potential for future clinical hemostasis applications.

The Multiple Faces of Disordered Nucleoporins

An evolutionary advantage of intrinsically disordered proteins (IDPs) is their ability to bind a variety of folded proteins-a paradigm that is central to the nucleocytoplasmic transport mechanism, in which nuclear transport receptors mediate the translocation of various cargo through the nuclear pore complex by binding disordered phenylalanine-glycine-rich nucleoporins (FG-Nups). FG-Nups are highly dynamic, which poses a substantial problem when trying to determine precisely their function using common experimental approaches. FG-Nups have been studied under a variety of conditions, ranging from those that constitute single-molecule measurements to physiological concentrations at which they can form supramolecular structures. In this review, I describe the physicochemical properties of FG-Nups and compare them to those of other disordered systems, including well-studied IDPs. From this comparison, it is apparent that FG-Nups not only share some properties with IDPs in general but also possess unique characteristics that might be key to their central role in the nucleocytoplasmic transport machinery.

Self-assembling bisphosphonates into nanofibers to enhance their inhibitory capacity on bone resorption

Osteoporosis (OP) is an important aging-related disease and the effective prevention/treatment of this disease remains challenging. Considering the acidic microenvironment of bone resorption lacunae, herein, we rationally designed two pamidronate (Pami)-derivative and alendronate (Alen)-derivative hydrogelators and which self-assemble into nanofibers to form supramolecular hydrogels under acidic conditions. Cell viability assay, osteoclastogenesis, osteoclastic gene expression, and in vitro bone resorption results indicated that both and have better inhibitory effects on osteoclastic formation and bone resorption than Pami and Alen, respectively. We anticipate that our new drugs and could "smartly" self-assemble and locally concentrate the drugs at bone resorption lacunae in vivo and subsequently prevent/treat osteoporosis more efficiently.

Nanonets Collect Cancer Secretome from Pericellular Space

Identifying novel cancer biomarkers is important for early cancer detection as it can reduce mortality rates. The cancer secretome, the collection of all macromolecules secreted by a tumor cell, alters its composition compared to normal tissue, and this change plays an important role in the observation of cancer progression. The collection and accurate analysis of cancer secretomes could lead to the discovery of novel biomarkers, thus improving outcomes of cancer treatment. We unexpectedly discovered that enzyme-instructed self-assembly (EISA) of a D-peptide hydrogelator results in nanonets/hydrogel around cancer cells that overexpress ectophosphatases. Here we show that these nanonets are able to rapidly collect proteins in the pericellular space (i.e., near the surface) of cancer cells. Because the secretory substances are at their highest concentration near the cell surface, the use of pericellular nanonets to collect the cancer secretome maximizes the yield and quality of samples, reduces pre-analytical variations, and allows the dynamic profiling of secretome samples. Thus, this new approach has great potential in identifying the heterotypic signaling in tumor microenvironments thereby improving the understanding of tumor microenvironments and accelerating the discovery of potential biomarkers in cancer biology. Data are available via ProteomeXchange with identifier PXD003924.

Reaction-diffusion processes at the nano- and microscales

The bottom-up fabrication of nano- and microscale structures from primary building blocks (molecules, colloidal particles) has made remarkable progress over the past two decades, but most research has focused on structural aspects, leaving our understanding of the dynamic and spatiotemporal aspects at a relatively primitive stage. In this Review, we draw inspiration from living cells to argue that it is now time to move beyond the generation of structures and explore dynamic processes at the nanoscale. We first introduce nanoscale self-assembly, self-organization and reaction-diffusion processes as essential features of cells. Then, we highlight recent progress towards designing and controlling these fundamental features of life in abiological systems. Specifically, we discuss examples of reaction-diffusion processes that lead to such outcomes as self-assembly, self-organization, unique nanostructures, chemical waves and dynamic order to illustrate their ubiquity within a unifying context of dynamic oscillations and energy dissipation. Finally, we suggest future directions for research on reaction-diffusion processes at the nano- and microscales that we find hold particular promise for a new understanding of science at the nanoscale and the development of new kinds of nanotechnologies for chemical transport, chemical communication and integration with living systems.

Controlling Cell Functions and Fate with Surfaces and Hydrogels: The Role of Material Features in Cell Adhesion and Signal Transduction

In their natural environment, cells are constantly exposed to a cohort of biochemical and biophysical signals that govern their functions and fate. Therefore, materials for biomedical applications, either in vivo or in vitro, should provide a replica of the complex patterns of biological signals. Thus, the development of a novel class of biomaterials requires, on the one side, the understanding of the dynamic interactions occurring at the interface of cells and materials; on the other, it requires the development of technologies able to integrate multiple signals precisely organized in time and space. A large body of studies aimed at investigating the mechanisms underpinning cell-material interactions is mostly based on 2D systems. While these have been instrumental in shaping our understanding of the recognition of and reaction to material stimuli, they lack the ability to capture central features of the natural cellular environment, such as dimensionality, remodelling and degradability. In this work, we review the fundamental traits of material signal sensing and cell response. We then present relevant technologies and materials that enable fabricating systems able to control various aspects of cell behavior, and we highlight potential differences that arise from 2D and 3D settings.

Using "On/Off" (19)F NMR/Magnetic Resonance Imaging Signals to Sense Tyrosine Kinase/Phosphatase Activity in Vitro and in Cell Lysates

Tyrosine kinase and phosphatase are two important, antagonistic enzymes in organisms. Development of noninvasive approach for sensing their activity with high spatial and temporal resolution remains challenging. Herein, we rationally designed a hydrogelator Nap-Phe-Phe(CF3)-Glu-Tyr-Ile-OH (1a) whose supramolecular hydrogel (i.e., Gel 1a) can be subjected to tyrosine kinase-directed disassembly, and its phosphate precursor Nap-Phe-Phe(CF3)-Glu-Tyr(H2PO3)-Ile-OH (1b), which can be subjected to alkaline phosphatase (ALP)-instructed self-assembly to form supramolecular hydrogel Gel 1b, respectively. Mechanic properties and internal fibrous networks of the hydrogels were characterized with rheology and cryo transmission electron microscopy (cryo-TEM). Disassembly/self-assembly of their corresponding supramolecular hydrogels conferring respective "On/Off" (19)F NMR/MRI signals were employed to sense the activity of these two important enzymes in vitro and in cell lysates for the first time. We anticipate that our new (19)F NMR/magnetic resonance imaging (MRI) method would facilitate pharmaceutical researchers to screen new inhibitors for these two enzymes without steric hindrance.

Facile synthesis of a peptidic Au(I)-metalloamphiphile and its self-assembly into luminescent micelles in water

We report a short synthetic route for the preparation of a peptidic Au(I)-metalloamphiphile which, in buffered environments of physiological ionic strength, self-assembles into luminescent micellar nanostructures of 14 nm in diameter.

In situ clicking methylglyoxal for hierarchical self-assembly of nanotubes in supramolecular hydrogel

Methylglyoxal (MGO) is a toxic, dicarbonyl metabolite in all living cells and its detoxification is regulated by glyoxalase I (GLOI). Herein, we rationally designed a precursor o-phenylenediamine-Phe-Phe-OH (1) which “click” reacts with MGO to yield amphiphilic methylquinoxaline-Phe-Phe-OH (2) to self-assemble into supramolecular hydrogel II (Gel II). Cryo-TEM images of Gel II suggested that there existed two orders of self-assembly to form the 32.8 nm width-nanotubes in the hydrogel. The hypothesis was validated with the analyses of the fluorescence, transmittance, and circular dichroism data of the serial dilutions of Gel II. Interference tests indicated that hydrogelation of 1 with MGO would not be affected by nitric oxide (NO). Our results suggest that 1 could be applied for specific hydrogelation with MGO, and potentially the removal of MGO in vitro.

Photo/chemo dual-controlled reversible morphological conversion and chiral modulation of supramolecular nanohelixes with nanosquares and nanofibers

A photo/chemo dually interconvertible system was constructed with switchable morphologies among a nanohelix, nanofiber and nanosquare.

Supramolecular biomaterials

Polymers, ceramics and metals have historically dominated the application of materials in medicine. Yet rationally designed materials that exploit specific, directional, tunable and reversible non-covalent interactions offer unprecedented advantages: they enable modular and generalizable platforms with tunable mechanical, chemical and biological properties. Indeed, the reversible nature of supramolecular interactions gives rise to biomaterials that can sense and respond to physiological cues, or that mimic the structural and functional aspects of biological signalling. In this Review, we discuss the properties of several supramolecular biomaterials, as well as their applications in drug delivery, tissue engineering, regenerative medicine and immunology. We envision that supramolecular biomaterials will contribute to the development of new therapies that combine highly functional materials with unmatched patient- and application-specific tailoring of both material and biological properties.

Tuning of gel morphology with supramolecular chirality amplification using a solvent strategy based on an Fmoc-amino acid building block

The self-assembly of an aromatic amino acid affords diverse aggregates from flat nanofibers to twist nanofibers with tunable supramolecular chirality.

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.

Fabrication of hydrogels with elasticity changed by alkaline phosphatase for stem cell culture

The objective of this study is to design hydrogels whose elasticity can be changed by alkaline phosphatase (ALP) in cell culture and evaluate the effect of hydrogel elasticity on an osteogenic gene expression of cells. Hydrogels were prepared by the radical polymerization of acrylamide (AAm), N,N'-methylenebisacrylamide (BIS), and Phosmer™M containing phosphate groups (PE-PAAm hydrogels). The storage modulus of PE-PAAm hydrogels prepared was changed by the preparation conditions. When human mesenchymal stem cells (hMSC) were cultured on the ALP-responsive PE-PAAm hydrogels in the presence or absence of ALP, the morphology of hMSC was observed and one of the osteogenic differentiation markers, Runx2, was evaluated. By ALP addition into the culture medium, the morphology of hMSC was changed into an elongated shape without cell damage. ALP addition modified the level of Runx2 gene expression, which was influenced by the modulus of PE-PAAm hydrogels. It is concluded that the elasticity change of hydrogel substrates in cell culture had an influence on the Runx2 gene expression of hMSC.

STATEMENT OF SIGNIFICANCE

Stem cells sense the surface elasticity of culture substrates, and their differentiation fate is biologically modified by substrate properties. Most of experiments have been performed in static conditions during cell culture, while the in vivo microenvironment is dynamically changed. In this study, we established to design an enzyme-responsive hydrogel whose elasticity can be changed by alkaline phosphatase (ALP) in cell culture to mimic in vivo conditions. As a result, the cells were deformed and the gene expression level of an osteogenic maker, Runx2, was modified by ALP treatment. This is the novel report describing to demonstrate that the dynamic alteration of hydrogel substrate elasticity could modulate the osteoblastic gene expression of human MSC in vitro.

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.

New Synthesis Route of Hydrogel through A Bioinspired Supramolecular Approach: Gelation, Binding Interaction, and in Vitro Dressing

Peptide-based supramolecular hydrogels have been comprehensively investigated in biomaterial applications because of their unique bioactivity, biofunctionality, and biocompatible features. However, the presence of organic building blocks in peptide-based hydrogels often results in low mechanical stability. To expand their practical use and range of applications, it is necessary to develop the tool kit available to prepare bioinspired, peptide-based supramolecular hydrogels with improved mechanical stability. In this paper, we present an innovative electrostatic and cross-linking approach in which naphthyl-Phe-Phe-Cys (NapFFC) oligopeptides are combined with gold nanoparticles (AuNPs) and calcium ions (Ca(2+)) to produce peptide-based supramolecular hydrogels. We further investigate the interactions among NapFFC, AuNPs and Ca(2+) by microscopy. The morphology of the nanofibrous network constructions and the binding forces exhibited from the hydrogel demonstrated that the combination of two mechanisms successfully enhanced the mechanical stability through the formation of a densely entangled fibrous network of peptide multimers that is attributed to the AuNP linkage and Ca(2+)-induced agglomeration. UV-vis spectrophotometry and fluorescence analysis were also used to demonstrate the enhanced stability of the hydrogel under various conditions such as thermal, solvent erosion, pH value and sonication. All results indicate that the presence of AuNPs and Ca(2+) can strengthen the prepared hydrogel by more than doubling the diameter of NapFFC nanofibers, enabling the formation of stronger frameworks and slowing the release of components. Further experiments confirmed that HeLa cells can grow on the bioinspired NapFFC-AuNP hydrogel and exhibit high cell viability and that these cells were killed on contact with a hydrogel containing a drug. Our peptide-based supramolecular hydrogels prepared from the observed electrostatic and cross-linking mechanisn exhibited a significantly improved mechanical stability, making them well suited to use as a drug carrier in hydrogel dressings and as extracellular materials (ECMs) for tissue engineering.

Self-healing metal-coordinated hydrogels using nucleotide ligands

A supramolecular gel formed by coordination of Zn(2+) with adenosine monophosphate (AMP) is reported. The adenine base, the monophosphate, and Zn(2+) are all important for gel formation. Mechanically disrupted gels can re-form upon centrifugation; applications of this gel for guest-molecule entrapment are explored.

Supramolecular Assemblies Responsive to Biomolecules toward Biological Applications

Stimuli-responsive supramolecular assemblies consisting of small molecules are attractive functional materials for biological applications such as drug delivery, medical diagnosis, enzyme immobilization, and tissue engineering. By use of their dynamic and reversible properties, many supramolecular assemblies responsive to a variety of biomolecules have been designed and synthesized. This review focuses on promising strategies for the construction of such dynamic supramolecular assemblies and their functions. While studies of biomolecule-responsive supramolecular assemblies have mainly been performed in vitro, it has recently been demonstrated that some of them can work in live cells. Supramolecular assemblies now open up new avenues in chemical biology and biofunctional materials.

Enzyme-instructed self-assembly: a multistep process for potential cancer therapy

The central dogma of the action of current anticancer drugs is that the drug tightly binds to its molecular target for inhibition. The reliance on tight ligand-receptor binding, however, is also the major root of drug resistance in cancer therapy. In this article, we highlight enzyme-instructed self-assembly (EISA)-the integration of enzymatic transformation and molecular self-assembly-as a multistep process for the development of cancer therapy. Using apoptosis as an example, we illustrate that the combination of enzymatic transformation and self-assembly, in fact, is an inherent feature of apoptosis. After the introduction of EISA of small molecules in the context of supramolecular hydrogelation, we describe several key studies to underscore the promises of EISA for developing cancer therapy. Particularly, we will highlight that EISA allows one to develop approaches to target "undruggable" targets or "untargetable" features of cancer cells and provides the opportunity for simultaneously interacting with multiple targets. We envision that EISA, used separately or in combination with current anticancer therapeutics, will ultimately lead to a paradigm shift for developing anticancer medicine that inhibit multiple hallmark capabilities of cancer.

Rational Design of Chiral Nanostructures from Self-Assembly of a Ferrocene-Modified Dipeptide

We report a new paradigm for the rational design of chiral nanostructures that is based on the hierarchical self-assembly of a ferrocene (Fc)-modified dipeptide, ferrocene-L-Phe-L-Phe-OH (Fc-FF). Compared to other chiral self-assembling systems, Fc-FF is unique because of its smaller size, biocompatibility, multiple functions (a redox center), and environmental responsiveness. X-ray and spectroscopic analyses showed that the incorporation of counterions during the hierarchical self-assembly of Fc-FF changed the conformations of the secondary structures from flat β sheets into twisted β sheets. This approach enables chiral self-assembly and the formation of well-defined chiral nanostructures composed of helical twisted β sheets. We identified two elementary forms for the helical twist of the β sheets, which allowed us to create a rich variety of rigid chiral nanostructures over a wide range of scales. Furthermore, through subtle modulations in the counterions, temperature, and solvent, we are able to precisely control the helical pitch, diameter, and handedness of the self-assembled chiral nanostructures. This unprecedented level of control not only offers insights into how rationally designed chiral nanostructures can be formed from simple molecular building blocks but also is of significant practical value for the use in chiroptics, templates, chiral sensing, and separations.

Photo-induced reversible structural transition of cationic diphenylalanine peptide self-assembly

The photo-induced self-assembly of a cationic diphenylalanine peptide (CDP) is investigated using a photoswitchable sulfonic azobenzene as the manipulating unit. A reversible structural transition between a branched structure and a vesicle-like structure is observed by alternating between UV and visible light irradiation.

Spontaneous structural transition in phospholipid-inspired aromatic phosphopeptide nanostructures

Phospholipid membranes could be considered a prime example of the ability of nature to produce complex yet ordered structures, by spontaneous and efficient self-assembly. Inspired by the unique properties and architecture of phospholipids, we designed simple amphiphilic decapeptides, intended to fold in the center of the peptide sequence, with a phosphorylated serine "head" located within a central turn segment, and two hydrophobic "tails". The molecular design also included the integration of the diphenylalanine motif, previously shown to facilitate self-assembly and increase nanostructure stability. Secondary structure analysis of the peptides indeed indicated the presence of stabilized conformations in solution, with a central turn connecting two hydrophobic "tails", and interactions between the hydrophobic strands. The mechanisms of assembly into supramolecular structures involved structural transitions between different morphologies, which occurred over several hours, leading to the formation of distinctive nanostructures, including half-elliptical nanosheets and curved tapes. The phosphopeptide building blocks appear to self-assemble via a particular combination of aromatic, hydrophobic and ionic interactions, as well as hydrogen bonding, as demonstrated by proposed constructed simulated models of the peptides and self-assembled nanostructures. Molecular dynamics simulations also gave insight into mechanisms of structural transitions of the nanostructures at a molecular level. Because of the biocompatibility of peptides, the phosphopeptide assemblies allow for expansion of the library of biomolecular nanostructures available for future design and application of biomedical devices.

Mechanics of single peptide hydrogelator fibrils

The rigidity of peptide fibers is essential for their chemical and biological functions, despite that it remains largely unexplored. Here, we present the first direct measurement of the mechanics of individual fibers in peptide hydrogels by AFM imaging and statistical analysis and find that the intermolecular interactions play a considerable role.

pH responsiveness of fibrous assemblies of repeat-sequence amphipathic α-helix polypeptides

We reported previously that our designed polypeptide α3 (21 residues), which has three repeats of a seven-amino-acid sequence (LETLAKA)3, forms not only an amphipathic α-helix structure but also long fibrous assemblies in aqueous solution. To address the relationship between the electrical states of the polypeptide and its α-helix and fibrous assembly formation, we characterized mutated polypeptides in which charged amino acid residues of α3 were replaced with Ser. We prepared the following polypeptides: 2Sα3 (LSTLAKA)3, in which all Glu residues were replaced with Ser residues; 6Sα3 (LETLASA)3, in which all Lys residues were replaced with Ser; and 2S6Sα3 (LSTLASA)3; in which all Glu and Lys residues were replaced with Ser. In 0.1M KCl, 2Sα3 formed an α-helix under basic conditions and 6Sα3 formed an α-helix under acid conditions. In 1M KCl, they both formed α-helices under a wide pH range. In addition, 2Sα3 and 6Sα3 formed fibrous assemblies under the same buffer conditions in which they formed α-helices. α-Helix and fibrous assembly formation by these polypeptides was reversible in a pH-dependent manner. In contrast, 2S6Sα3 formed an α-helix under basic conditions in 1M KCl. Taken together, these findings reveal that the charge states of the charged amino acid residues and the charge state of the Leu residue located at the terminus play an important role in α-helix formation.

Supramolecular hydrogels: synthesis, properties and their biomedical applications

As a novel class of three-dimensional (3D) hydrophilic cross-linked polymers, supramolecular hydrogels not only display unique physicochemical properties (e.g., water-retention ability, drug loading capacity, biodegradability and biocompatibility, biostability) as well as specific functionalities (e.g., optoelectronic properties, bioactivity, self-healing ability, shape memory ability), but also have the capability to undergo reversible gel-sol transition in response to various environmental stimuli inherent to the noncovalent cross-linkages, thereby showing great potential as promising biomaterial scaffolds for diagnosis and therapy. In this Review, we summarized the recent progress in the design and synthesis of supramolecular hydrogels through specific, directional noncovalent interactions, with particular emphasis on the structure-property relationship, as well as their wide-ranging applications in disease diagnosis and therapy including bioimaging, biodetection, therapeutic delivery, and tissue engineering. We believe that these current achievements in supramolecular hydrogels will greatly stimulate new ideas and inspire persistent efforts in this hot topic area in future.

Monoglyceride-based organogelator for broad-range oil uptake with high capacity

Oil/water separation has been a worldwide subject because of increasing release of oil-containing wastewater as well as several marine oil spills. The phase-selective organogelators (PSOGs) are thought to offer a potential and effective implement for addressing this issue. An ideal PSOG for oil adsorption must fulfill some requirements involving effective gelation, easy synthesis, low cost, and recyclable for reuse. However, beyond those, the ability of gelation for a broad-range oil phase without selectivity is also important. However, most of the reported PSOGs have limitation in this respect thus far. In this paper, a new class of saturated 1-monoglyceride-derived organogelators can efficiently uptake almost all of the common fuel oils from water and gelate organic solvents with extremely low minimum gelation concentration (MGC). In addition, the oils in the gel and gelator molecules can be recovered quantitatively through simple vacuum distillation.

Dual-tuning multidimensional superstructures based on a T-shaped molecule: vesicle, helix, membrane and nanofiber-constructed gel

Dual-tuning self-assembly of Fmoc–Gly (a T-shape molecule) supramolecular self assembly was firstly reported here.

Using a peptide segment to covalently conjugate doxorubicin and taxol for the study of drug combination effect

Doxorubicin (Dox) and Taxol can be covalently bonded to the same peptide segment via proper structural modification.

Real time quantification of the chemical cross-link density of a hydrogel by in situ UV-vis spectroscopy

A UV-vis spectroscopy-based method has been proposed to determine the cross-link density of the samples.

Exploring thermodynamically downhill nanostructured peptide libraries: from structural to morphological insight

Biocatalytic evolution of thermodynamically downhill nanostructured peptide libraries in hydrogel states are envisaged.

Tapping a bacterial enzymatic pathway for the preparation and manipulation of synthetic nanomaterials

We present a spherical micelle generated in a three-step sequence in which a farnesyl-pantetheine conjugate is phosphorylated, adenylated, and phosphorylated once more to generate a farnesyl-CoA amphiphile that self-assembles into spherical micelles. A sphere-to-fibril morphological switch is achieved by enzymatically transferring the farnesyl group of the farnesyl-CoA micelle onto a peptide via phosphopantetheinyl transferase to generate a peptide amphiphile. Each step in the sequence is followed with characterization by HPLC, MS, TEM, and DLS. This system offers an entry into cofactor-mediated peptide decoration by extending the principles of bioresponsive polymeric materials to sequential enzyme cascades.