Three Distinct Read-Out Modes for Enzyme Activity Can Operate in a Semi-Wet Supramolecular Hydrogel

A Review on Recent Advances in Stabilizing Peptides/Proteins upon Fabrication in Hydrogels from Biodegradable Polymers

Hydrogels evolved as an outstanding carrier material for local and controlled drug delivery that tend to overcome the shortcomings of old conventional dosage forms for small drugs (NSAIDS) and large peptides and proteins. The aqueous swellable and crosslinked polymeric network structure of hydrogels is composed of various natural, synthetic and semisynthetic biodegradable polymers. Hydrogels have remarkable properties of functionality, reversibility, sterilizability, and biocompatibility. All these dynamic properties of hydrogels have increased the interest in their use as a carrier for peptides and proteins to be released slowly in a sustained manner. Peptide and proteins are remarkable therapeutic agents in today's world that allow the treatment of severe, chronic and life-threatening diseases, such as diabetes, rheumatoid arthritis, hepatitis. Despite few limitations, hydrogels provide fine tuning of proteins and peptides delivery with enormous impact in clinical medicine. Novels drug delivery systems composed of smart peptides and molecules have the ability to drive self-assembly and form hydrogels at physiological pH. These hydrogels are significantly important for biological and medical fields. The primary objective of this article is to review current issues concerned with the therapeutic peptides and proteins and impact of remarkable properties of hydrogels on these therapeutic agents. Different routes for pharmaceutical peptides and proteins and superiority over other drugs candidates are presented. Recent advances based on various approaches like self-assembly of peptides and small molecules to form novel hydrogels are also discussed. The article will also review the literature concerning the classification of hydrogels on a different basis, polymers used, "release mechanisms" their physical and chemical characteristics and diverse applications.

Design Strategies of Stimuli-Responsive Supramolecular Hydrogels Relying on Structural Analyses and Cell-Mimicking Approaches

Stimuli-responsive hydrogels are intriguing biomaterials useful for spatiotemporal controlled release of drugs, cells, and biological cues, cell engineering for various applications, and medical diagnosis. To date, many physical and chemical stimuli-responsive polymer hydrogels have been developed by chemical modification of polymer chains and cross-linking points. In particular, conjugation with biomolecules to polymers produced promising biomolecule-responsive hydrogels. These examples clearly indicate high potentials of stimuli-responsive hydrogels as promising biomaterials. In addition to polymer hydrogels, supramolecular hydrogels formed by the assembly of small molecules (hydrogelators) via noncovalent interactions have also been regarded as unique and promising soft materials due to their flexible programmability in rendering them stimuli-responsive with the larger macroscopic change (i.e., gel-sol transition). This Account describes our strategies for the rational design of stimuli-responsive supramolecular hydrogels and their biological applications. Following the detailed structural analysis of a lead hydrogelator that clearly indicates the appropriate sites for incorporation of stimuli-responsive modules, we designed supramolecular hydrogels capable of responding to simple physical (thermal and light) and chemical (pH and metal ions) stimuli. More importantly, biomolecule-responsive hydrogels were successfully developed by supramolecularly mimicking the complex yet well-ordered structures and functions of live cells containing multiple components (a cell-mimicking approach). Development of biomolecule-responsive supramolecular hydrogels has been difficult as the conventional strategy relies on the chemical incorporation of stimuli-responsive modules, owing to the lack of modules that can effectively respond to structurally diverse and complicated biomolecules. Inspired by natural systems where functional compartments (e.g., cell organelles) sophisticatedly interact with each other, we sought to integrate the two distinct microenvironments of supramolecular hydrogels (the aqueous cavity surrounded by fibers and the fluidic hydrophobic fiber domain) with other functional materials (e.g., enzymes, peptides or proteins, fluorescent chemosensors, or inorganic porous or layered nanomaterials) for biomolecule responses. In situ fluorescence microscopy imaging clearly demonstrated that chemical isolation and crosstalk are highly successful between the integrated microenvironments in supramolecular hydrogels, similar to organelles in living cells, which allow for the construction of unique optical response and sensing systems for biomolecules. Furthermore, programmed hybridization of our chemically reactive hydrogels with appropriate enzymes can provide an unprecedented universal platform for biomolecule-degradable supramolecular hydrogels. Such biomolecule-responsive hydrogels are a potentially promising tool for user-friendly early diagnostics and on-demand drug-releasing soft materials. We expect that our rational design strategies for stimuli-responsive supramolecular hydrogels by modification of chemical structures and hybridization with functional materials will inspire scientists in various fields and lead to development of novel soft materials for biological applications.

Printable hybrid hydrogel by dual enzymatic polymerization with superactivity

Hybrid hydrogels were fabricated via a new approach employing a dual enzyme-mediated redox initiation reaction and their applications for 3D printing and biocatalysis.

A new approach has been developed to fabricate tough hybrid hydrogels by employing dual enzyme-mediated redox initiation to achieve post-self-assembly cross-linking polymerization. The resulting hydrogel combines the merits of supramolecular hydrogels with polymeric hydrogels to achieve higher mechanical strength and porous networks. Designed 3D constructs were fabricated via in situ 3D printing. The in situ immobilized GOx/HRP in Gel II exhibited superactivity compared to free enzymes, which might be attributed to the synergistic effect of co-localized GOx and HRP minimizing the distances for mass transport between the gel and the bulk solution. This mechanically strong hybrid hydrogel maintained high reusability and thermal stability as well. In addition, in situ 3D cell culture was demonstrated, thus indicating that this biodegradable hybrid hydrogel is biocompatible with cells. The subsequent 3D cell printing further indicates that the hybrid hydrogel is a promising scaffold for bio-related applications such as biocatalysis and tissue engineering.

Molecular nanofibers of paclitaxel form supramolecular hydrogel for preventing tumor growth in vivo

A conjugate of tripeptide RGD and paclitaxel can form a nanofibrous hydrogel with a high payload of 66.7%, which can serve as both carrier and cargo for delaying tumor growth in vivo.

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.

Recent advances in the development of synthetic chemical probes for glycosidase enzymes

The emergence of synthetic glycoconjugates as chemical probes for the detection of glycosidase enzymes has resulted in the development of a range of useful chemical tools with applications in glycobiology, biotechnology, medical and industrial research. Critical to the function of these probes is the preparation of substrates containing a glycosidic linkage that when activated by a specific enzyme or group of enzymes, irreversibly releases a reporter molecule that can be detected. Starting from the earliest examples of colourimetric probes, increasingly sensitive and sophisticated substrates have been reported. In this review we present an overview of the recent advances in this field, covering an array of strategies including chromogenic and fluorogenic substrates, lanthanide complexes, gels and nanoparticles. The applications of these substrates for the detection of various glycosidases and the scope and limitations for each approach are discussed.

Metallogels self-assembled from linear rod-like platinum complexes: influence of the linkage

Two linear rod-like platinum complexes, which only differed in the linkage, were prepared. They both self-assemble into metallogels in nonpolar solvents; however, a very big contrast was observed. Unexpectedly, a much weaker gel was acquired upon replacing the ester linkage by an amide group. The intermolecular hydrogen bonding offered by the amide motif leads to a different stacking fashion and mechanism. The results demonstrated herein contribute to the rational design of metallogels as well as other functional supramolecular materials.

Supramolecular hydrogels made of basic biological building blocks

As a consequence of the self-assembly of small organic molecules in water, supramolecular hydrogels are evolving from serendipitous events during organic synthesis to become a new type of materials that hold promise for applications in biomedicine. In this Focus Review, we describe recent advances in the use of basic biological building blocks for creating molecules that act as hydrogelators and the potential applications of the corresponding hydrogels. After introducing the concept of supramolecular hydrogels and defining the scope of this review, we briefly describe the methods for making and characterizing supramolecular hydrogels. We then discuss representative hydrogelators according to the categories of their building blocks, such as amino acids, nucleobases, and saccharides, and highlight the applications of the hydrogels when necessary. Finally, we offer our perspective and outlook on this fast-growing field at the interface of organic chemistry, materials, biology, and medicine. By providing a snapshot for chemists, engineers, and medical scientists, we hope that this Focus Review will contribute to the development of multidisciplinary research on supramolecular hydrogels for a wide range of applications in different fields.

Supramolecular hydrogels based on bola-amphiphilic glycolipids showing color change in response to glycosidases

We developed supramolecular hydrogels exhibiting reversible thermochromism concurrently with gel-to-sol transition from four glycolipids. In addition, these gels showed the similar color change in response to glycosidases, which can be employed to construct a colorimetric sensor array chip for sensing glycosidases with the naked eye.

Synthesis and characterization of maltose-based amphiphiles as supramolecular hydrogelators

Low molecular mass amphiphilic glycolipids have been prepared by linking a maltose polar head and a hydrophobic linear chain either by amidation or copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition. The liquid crystalline properties of these amphiphilic materials have been characterized. The influence of the chemical structure of these glycolipids on the gelation properties in water has also been studied. Glycolipids obtained by the click coupling of the two components give rise to stable hydrogels at room temperature. The fibrillar structure of supramolecular hydrogels obtained by the self-assembly of these gelators have been characterized by electron microscopy. Fibers showed some torsion, which could be related with a chiral supramolecular arrangement of amphiphiles, as confirmed by circular dichroism (CD). The sol-gel transition temperature was also determined by differential scanning calorimetry (DSC) and NMR.

Supramolecular hydrogel-based protein and chemosensor array

The development of protein and sensor arrays is crucial for rapid and high-throughput assays of biological events, markers, environmental pollutants, and others. We describe supramolecular hydrogel as a unique material for use as a matrix for immobilizing proteins, peptides, substrates, chemosensors, and mesoporous silica particles, and thereby array them on solid supports. The semi-wet conditions provided by the gel, which consists of 3D supramolecular nanofiber network structure, are suitable for entrapping such substances whilst retaining their activity and function. Moreover, the hydrophobic interior of the nanofibers of the supramolecular hydrogel can reversibly entrap hydrophobic molecules, which allows the development of various read-out systems, such as fluorescence enhancement and fluorescence resonance energy transfer (FRET), by which one can monitor the signal changes associated with, for instance, molecular recognition and enzyme activity.

High-tech applications of self-assembling supramolecular nanostructured gel-phase materials: from regenerative medicine to electronic devices

It is likely that nanofabrication will underpin many technologies in the 21st century. Synthetic chemistry is a powerful approach to generate molecular structures that are capable of assembling into functional nanoscale architectures. There has been intense interest in self-assembling low-molecular-weight gelators, which has led to a general understanding of gelation based on the self-assembly of molecular-scale building blocks in terms of non-covalent interactions and packing parameters. The gelator molecules generate hierarchical, supramolecular structures that are macroscopically expressed in gel formation. Molecular modification can therefore control nanoscale assembly, a process that ultimately endows specific material function. The combination of supramolecular chemistry, materials science, and biomedicine allows application-based materials to be developed. Regenerative medicine and tissue engineering using molecular gels as nanostructured scaffolds for the regrowth of nerve cells has been demonstrated in vivo, and the prospect of using self-assembled fibers as one-dimensional conductors in gel materials has captured much interest in the field of nanoelectronics.

Stimuli-responsive polyguanidino-oxanorbornene membrane transporters as multicomponent sensors in complex matrices

We introduce guanidinium-containing synthetic polymers based on polyguanidino-oxanorbornenes (PGONs) as anion transporters in lipid bilayers that can be activated and inactivated by chemical stimulation. According to fluorogenic anion export experiments with vesicles, PGON transporters are most active in neutral bilayers near their phase transition, with EC50's in the nanomolar range. Six times higher effective transporter concentrations were measured with aminonaphthalene-1,3,6-trisulfonate than with 5(6)-carboxyfluorescein, demonstrating the importance of anion binding for transport and excluding nonspecific efflux. Negative surface potentials efficiently annihilate transport activity, while inside-negative membrane potentials slightly increase it. These trends demonstrate the functional importance of counterions to hinder the binding of hydrophilic counterions and to minimize the global positive charge of the transporter-counterion complexes. Strong, nonlinear increases in activity with polymer length reveal a significant polymer effect. Overall, the characteristics of PGONs do not match those of similar systems (for example, polyarginine) and hint toward an interesting mode of action, clearly different from nonspecific leakage caused by detergents. The activity of PGONs increases in the presence of amphiphilic anions such as pyrenebutyrate (EC50 = 70 microM), while several other amphiphilic anions tested were inactive. PGONs are efficiently inactivated by numerous hydrophilic anions including ATP (IC 50 = 150 microM), ADP (IC50 = 460 microM), heparin (IC50 = 1.0 microM), phytate (IC50 = 0.4 microM), and CB hydrazide (IC50 = 26 microM). The compatibility of this broad responsiveness with multicomponent sensing in complex matrices is discussed and illustrated with lactate sensing in sour milk. The PGON lactate sensor operates together with lactate oxidase as a specific signal generator and CB hydrazide as an amplifier for covalent capture of the pyruvate product as CB hydrazone (IC50 = 1.5 microM).

High catalytic activities of artificial peroxidases based on supramolecular hydrogels that contain heme models

Composed of a supramolecular hydrogel and a heme model compound, a new type of artificial peroxidase shows high catalytic activity in organic media. The activity of this new type of artificial enzyme is significantly higher than that of the heme model compounds alone. Changes in the distal substituents above the coordinated-metal centers of the model compounds directly modulate catalytic activity. This supramolecular-hydrogel-based artificial enzyme is most active in toluene, reaching about 90% of the nascent activity of horseradish peroxidase. Moreover, this study confirms that the incorporation of the heme models into the nanofibers of gelators accounts for most of the enhancement of catalytic activity.

Synthetic pores with reactive signal amplifiers as artificial tongues

The sensation of taste is mediated by activation or deactivation of transmembrane pores. Artificial stimulus-responsive pores are enormously appealing as sensor components because changes in their activity are readily detectable in many different ways. However, the detection of multiple components in complex matrices (such as foods) with one pore sensor has so far remained elusive because the specificity necessary for sensing a target compound in complex mixtures is incompatible with the broad applicability needed for the detection of multiple components. Here, we present synthetic pores that, like our tongues, can sense flavours in food and in addition make them visibly detectable. Differential sensing and pattern recognition are solutions based on empirical and biomimetic approaches. They have been explored with synthetic receptor arrays and electronic tongues. In contrast, our approach is non-empirical as it exploits reactive amplifiers that covalently capture elusive analytes after enzymatic signal generation and drag them into synthetic pores for blockage. Reactive amplification proved to be highly sensitive and adaptable to various analytes and pores. Moreover, it can be combined with reactive filtration for minimizing interference. The system was tested on real food samples for detection of sucrose, lactose, lactate, acetate, citrate and glutamate to demonstrate the feasibility of these synthetic pores as universal sensors.

Construction of superhydrophobic surfaces by fibrous aggregation of perfluoroalkyl chain-containing organogelators

Superhydrophobic surfaces, characterized by water contact angles greater than 150 degrees, can be produced by means of intermediate organogels, which were formed by perfluoroalkyl chain-containing organogelators with volatile organic solvents.