Lossless Immunocytochemistry Based on Large-Scale Porous Hydrogel Pellicle for Accurate Rare Cell Analysis

Rare cells, such as circulating tumor cells or circulating fetal cells, provide important information for the diagnosis and prognosis of cancer and prenatal diagnosis. Since undercounting only a few cells can lead to significant misdiagnosis and incorrect decisions in subsequent treatment, it is crucial to minimize cell loss, particularly for rare cells. Moreover, the morphological and genetic information on cells should be preserved as intact as possible for downstream analysis. The conventional immunocytochemistry (ICC), however, fails to meet these requirements, causing unexpected cell loss and deformation of the cell organelles which may mislead the classification of benign and malignant cells. In this study, a novel ICC technique for preparing lossless cellular specimens was developed to improve the diagnostic accuracy of rare cell analysis and analyze intact cellular morphology. To this end, a robust and reproducible porous hydrogel pellicle was developed. This hydrogel encapsulates cells to minimize cell loss from the repeated exchange of reagents and prevent cell deformation. The soft hydrogel pellicle allows stable and intact cell picking for further downstream analysis, which is difficult with conventional ICC methods that permanently immobilize cells. The lossless ICC platform will pave the way for robust and precise rare cell analysis toward clinical practice.

Enzymatic one-pot preparation of carboxylmethyl chitosan-based hydrogel with inherent antioxidant and antibacterial properties for accelerating wound healing

Facile preparation of multifunctional hydrogel wound dressings with inherent versatile properties is highly desirable in practical healthcare. Here, a biocompatible hydrogel was designed and fabricated via mild enzymatic crosslinking and polymerization. We first designed an enzymatic system containing horseradish peroxidase (HRP), H₂O₂, and the macromolecular initiator-acetoacetyl polyvinyl alcohol (PVA-ACAC), which can generate active PVA-ACAC carbon radicals via HRP-mediated oxidation by H₂O₂. Trimethylammonium chloride (Q), methacryloyl (MA) and phenol (Ph)-grafted carboxymethyl chitosan (Ph-QCMCS-MA) was then synthesized. HRP catalyzes the oxidation of phenol groups to achieve the fast phenol crosslinking, and PVA-ACAC carbon radicals initiate the polymerization of MA groups simultaneously, finally obtaining the target PPQM gel. The quaternary ammonium and phenol groups endow the PPQM gel with excellent antibacterial and antioxidant properties, respectively. This multifunctional hydrogel, which has additional adhesive and hemostatic properties, could promote wound healing processes in an in vivo full-thickness skin defect experiment by reducing the generation of pro-inflammatory cytokines (IL-6) and upregulating anti-inflammatory factors (IL-10) and angiogenesis-related cytokines (VEGF and α-SMA). As a result, it could be used as competitive wound dressings.

Biosensor-Integrated Drug Delivery Systems as New Materials for Biomedical Applications

Biosensor-integrated drug delivery systems are innovative devices in the health area, enabling continuous monitoring and drug administration. The use of smart polymer, bioMEMS, and electrochemical sensors have been extensively studied for these systems, especially for chronic diseases such as diabetes mellitus, cancer and cardiovascular diseases as well as advances in regenerative medicine. Basically, the technology involves sensors designed for the continuous analysis of biological molecules followed by drug release in response to specific signals. The advantages include high sensitivity and fast drug release. In this work, the main advances of biosensor-integrated drug delivery systems as new biomedical materials to improve the patients’ quality of life with chronic diseases are discussed.

Recent Advances in Polymer Additive Engineering for Diagnostic and Therapeutic Hydrogels

Hydrogels are hydrophilic polymer materials that provide a wide range of physicochemical properties as well as are highly biocompatible. Biomedical researchers are adapting these materials for the ever-increasing range of design options and potential applications in diagnostics and therapeutics. Along with innovative hydrogel polymer backbone developments, designing polymer additives for these backbones has been a major contributor to the field, especially for expanding the functionality spectrum of hydrogels. For the past decade, researchers invented numerous hydrogel functionalities that emerge from the rational incorporation of additives such as nucleic acids, proteins, cells, and inorganic nanomaterials. Cases of successful commercialization of such functional hydrogels are being reported, thus driving more translational research with hydrogels. Among the many hydrogels, here we reviewed recently reported functional hydrogels incorporated with polymer additives. We focused on those that have potential in translational medicine applications which range from diagnostic sensors as well as assay and drug screening to therapeutic actuators as well as drug delivery and implant. We discussed the growing trend of facile point-of-care diagnostics and integrated smart platforms. Additionally, special emphasis was given to emerging bioinformatics functionalities stemming from the information technology field, such as DNA data storage and anti-counterfeiting strategies. We anticipate that these translational purpose-driven polymer additive research studies will continue to advance the field of functional hydrogel engineering.

A biocompatible hydrogel as a template for oxidative decomposition reactions: a chemodosimetric analysis and in vitro imaging of hypochlorite

The self-assembly properties of new biocompatible, thermoreversible fluorescent hydrogels, composed of amino acid residues have been reported. A unique gel-to-sol transition is triggered by chemodosimetric interaction in the presence of hypochlorite.

Enzyme-Laden Bioactive Hydrogel for Biocatalytic Monitoring and Regulation

Enzymes, a class of highly efficient and specific catalysts in Nature, dictate a myriad of reactions that constitute various cascades in biological systems. There is growing evidence that many cellular reactions within metabolic pathways are catalyzed by matrix-associated multienzyme complexes, not via the free enzymes, verifying the vital effects of microenvironmental organization, which would reveal implications for the high efficiency, specificity, and regulation of metabolic pathways. The extracellular matrix (ECM), as the noncellular component, is composed of various proteins such as collagens, laminins, proteoglycans, and remodeling enzymes, playing the key role in tissue architecture and homeostasis. Hydrogels are defined as highly hydrated polymer materials and maintain structural integrity by physical and chemical force, which are thought of as the most suitable materials for matching the chemical, physical, and mechanical properties with natural ECM. As one specific type of soft and wet materials, hydrogels are suitable three-dimensional carriers to locally confine bioactive guests, such as enzymes, for molecular-level biological interactions. The efficient cascade catalysis can be realized by enzyme-laden hydrogels, which can potentially interact with cells and tissues by material-to-biology communication. In this Account, we present recent progress on the preparation of enzymatic bioactive hydrogels, including in situ coassembly, in situ cross-linking strategy, and in situ enzymatic radical polymerization technology, further promoting their applications on biomedical tissue engineering, biocatalytic health monitoring, and therapeutic research. First, we provide a brief introduction of the basic concept related to an enzymatic strategy in living systems and the importance of bioinspired enzyme-laden bioactive hydrogel systems. We discuss the difficulties of the fabrication of a bioactive hydrogel with a high catalytic efficiency, thereby providing the novel molecular design and regulation based on a noncovalent coassembly and in situ self-immobilization strategy to obtain the compartmentalized enzyme-laden structure. Then the applications of an enzyme-laden bioactive hydrogel for biocatalytic applications are discussed in detail. The enzyme-laden bioactive hydrogel can maintain the favorable perception and regulation behavior of enzymes with optimal enzymatic efficacy between this confined hydrogel network and a surrounding environment. A highlight to the advances in the responsively biocatalytic monitoring and regulation of bioactive hydrogel, including the enzymatic biomedical tissue engineering and health monitoring, enzymatic regulation of tumor reactive oxygen species and therapeutic research are given. Finally, the outlook of open challenges and future developments of this rapidly evolving field is provided. This Account with highlights of diverse enzyme-laden bioactive hydrogel systems not only provides interesting insights to understand the cascade enzymatic strategy of life but also inspires to broaden and enhance the molecular-level material design and bioapplications of existing enzymatic materials in chemistry, materials science, and biology.

Interfacial Coating Method for Amine-Rich Surfaces using Poly(ethylene glycol) Diacrylate Applied to Bioprosthetic Valve Tissue Models

Bioprosthetic heart valve implants are beset by calcification and failure due to the interactions between the body and the transplant. Hydrogels can be used as biological blank slates that may help to shield implants from these interactions; however, traditional light-based hydrogel polymerization is impeded by tissue opacity and topography. Therefore, new methods must be created to bind hydrogel to implant tissues. To address these complications, a two-step surface-coating method for bioprosthetic valves was developed. A previously developed bioprosthetic valve model (VM) was used to investigate and optimize the coating method. Generally, this coating is achieved by first reacting surface amine groups with an NHS-PEG-acrylate while also allowing glucose to absorb into the bulk. Then, glucose oxidase, poly(ethylene glycol) diacrylate (PEGDA), and iron ions are added to the system to initiate free-radical polymerization that bonds the PEGDA hydrogel to the acrylates sites on the surface. Results showed a thin (∼8 μm), continuous coating on VM samples that is capable of repelling protein adhesion (2% surface fouling versus 20% on uncoated samples) and does not significantly affect the surface mechanical properties. Based on this success, the coating method was translated to glutaraldehyde-fixed valve tissue samples. Results showed noncontinuous but evident coating on the surface, which was further improved by adjusting the coating solution. These results demonstrate the feasibility of the proposed two-step surface coating method for modifying the surface of bioprosthetic valve replacements.

Radical polymerization reactions for amplified biodetection signals

This review summarizes various radical polymerization chemistries for amplifying biodetection signals and compares them from the practical point of view.

Strength-tunable printing of xanthan gum hydrogel via enzymatic polymerization and amide bioconjugation

Amide bioconjugation and interfacial enzyme polymerization for improving the mechanical strength of hydrogel bio-ink.

Triggering Sequential Catalytic Fenton Reaction on 2D MXenes for Hyperthermia-Augmented Synergistic Nanocatalytic Cancer Therapy

The unique characteristics of a tumor microenvironment (TME) enable the development of new tumor-therapeutic modalities with high efficiency, biosafety, and tumor specificity. In this work, we report on the construction of photothermal-enhanced and nanocatalyst-enabled sequential catalytic reaction for TME-specific cancer therapy. This conceptual advance is achieved by engineering the surface of two-dimensional Ti₃C₂ MXene with two separate catalysts, including natural glucose oxidase (GOD) as glucose catalysts and superparamagnetic iron oxide nanoparticles (IONPs) as Fenton-reaction nanocatalysts. A sequential catalytic reaction is triggered by using GOD for catalyzing the tumor-overtaken glucose to generate large amounts of hydrogen peroxide molecules. Subsequently IONPs can catalyze the transformation of pregenerated hydrogen peroxide into large amounts of highly toxic hydroxyl radicals to kill the cancer cells subsequently in TME-enabled acidity condition. The two-dimensional (2D) Ti₃C₂ MXene matrix efficiently converts the near-infrared light into thermal energy to synergistically enhance the catalytic efficiency of this sequential catalytic reaction and therefore achieve the high synergistic cancer-therapeutic outcome, accompanied with the high biocompatibility of the constructed composite nanocatalysts. Both in vitro cancer-cell evaluation and in vivo tumor xenograft on nude mice with complete tumor eradication demonstrate the high synergistic efficiency of photothermal-enhanced sequential nanocatalytic cancer therapy. Therefore, this work substantially broadens the biomedical applications of 2D MXenes to nanocatalytic cancer therapy by enhancing the Fenton reaction-based nanocatalytic therapy via converting the near-infrared light into thermal energy and subsequently elevating the local Fenton-reaction temperature.

Improved antibacterial performance using hydrogel-immobilized lysozyme as a catalyst in water

Silver nanoparticle-based catalysts are used extensively to kill bacteria in drinking water treatment. However secondary contamination and their high cost require scientists to seek alternatives with non-toxicity, high activity and low cost. In this article, we develop a new hydrogel-immobilized lysozyme (h-lysozyme) that shows excellent antibacterial performance, including high activity duration of up to 55 days, inhibition efficiency as high as 99.4%, good recycling capability of up to 11 cycles, a wide temperature window and extremely low concentration. The immobilized lysozyme displayed greatly improved bacterial inhibition with both Gram-negative E. coli and Gram-positive B. subtilis, which enables broad antibacterial applications in various water systems. In parallel, the non-toxic structure and high stability of the h-lysozyme without additional contamination make it a promising alternative to nanoparticle catalysts fur use in drinking water purification.

Hydrogel-immobilized lysozyme for antibacterial membrane modification.

Development of improved dual-diazonium reagents for faster crosslinking of tobacco mosaic virus to form hydrogels

New bench-stable reagents with two diazonium sites were designed and synthesized for protein crosslinking. Because of the faster diazonium-tyrosine coupling reaction, hydrogels from the crosslinking of tobacco mosaic virus and the reagent DDA-3 could be prepared within 1 min at room temperature. Furthermore, hydrogels with the introduction of disulfide bonds viaDDA-4 could be chemically degraded by dithiothreitol. Our results provided a facile approach for the direct construction of virus-based hydrogels.

Improved dual-diazonium reagents were developed for more efficient crosslinking of tobacco mosaic virus to form hydrogels.

Oxidoreductase-Initiated Radical Polymerizations to Design Hydrogels and Micro/Nanogels: Mechanism, Molding, and Applications

Due to their 3D cross-linked networks and tunable physicochemical properties, polymer hydrogels with different sizes are applied widely in tissue engineering, drug-delivery systems, pollution regulation, ionic conducting electrolytes, agricultural drought-resistance, cosmetics, and the food industry. Novel, environmentally friendly, and efficient oxidoreductase-initiated radical polymerizations to design hydrogels and micro/nanogels have gained increasing attention. Herein, the recent advances on the use of novel enzyme-initiated systems for hydrogel polymerization, including the mechanisms, and molding of polymeric and hybrid-polymeric networks are reviewed. Preliminary progress related to interfacial enzymatic polymerization for the generation of hybrid micro/nanogels is introduced as an emerging initiating approach. In addition, certain biological applications in tissue engineering, bioimaging, and therapy are demonstrated step by step. Finally, some perspectives on the safety profile of enzymatic formed hydrogels, new enzymatic systems, and potential theranostic applications are discussed.

Catalytic chemistry of glucose oxidase in cancer diagnosis and treatment

This tutorial review focuses on the state-of-the-art progress in GOx-based cancer diagnosis and treatment, including the general principles for the design and construction of GOx-based biosensors and cancer therapeutic approaches, and their biological applications in detail. Moreover, the current trends and key problems, as well as the challenges and future prospects of GOx-based catalytic systems in biomedicine are also discussed in the end.

Fluorine substitution enhances the self-assembling ability of hydrogelators

When supramolecular hydrogels are applied as tissue culture scaffolds, their mechanical strength and biocompatibility are the two most important factors that must be considered. However, systematic studies on the structure-mechanical property (or structure-cytotoxicity) relationship of hydrogels are rare. Herein, we rationally designed three hydrogelators and their corresponding phosphate precursors, and systematically studied their self-assembling ability and cytotoxicity. The results indicated that fluorine substitution, but not trifluoromethyl substitution with more fluorine atoms, to the phenylalanine motif enhanced the self-assembling ability and cytotoxicity of the hydrogelators (or precursors). We envision that our preliminary study of hydrogelator fluorination would provide a strategy for the development of supramolecular hydrogels for wider biomedical applications.

Aptamer-functionalized hydrogel for self-programmed protein release via sequential photoreaction and hybridization

A dynamic hydrogel that sequentially responds to two independent but interrelated physical and biomolecular signals was reported in this work. Once hit by an external light signal, an immobilized internal molecular signal is activated and freed via photoreaction; and subsequently the freed molecular signal works as a self-programming factor of the hydrogel to induce the dissociation of a biomolecular complex to release protein via hybridization reaction. Notably, pulsatile external light input can be converted to periodical protein output from the hydrogel to regulate cell migration. Thus, this hydrogel holds potential as a self-programming platform for biological and biomedical applications such as controlled release of bioactive substances.

Supramolecular biofunctional materials

This review discusses supramolecular biofunctional materials, a novel class of biomaterials formed by small molecules that are held together via noncovalent interactions. The complexity of biology and relevant biomedical problems not only inspire, but also demand effective molecular design for functional materials. Supramolecular biofunctional materials offer (almost) unlimited possibilities and opportunities to address challenging biomedical problems. Rational molecular design of supramolecular biofunctional materials exploit powerful and versatile noncovalent interactions, which offer many advantages, such as responsiveness, reversibility, tunability, biomimicry, modularity, predictability, and, most importantly, adaptiveness. In this review, besides elaborating on the merits of supramolecular biofunctional materials (mainly in the form of hydrogels and/or nanoscale assemblies) resulting from noncovalent interactions, we also discuss the advantages of small peptides as a prevalent molecular platform to generate a wide range of supramolecular biofunctional materials for the applications in drug delivery, tissue engineering, immunology, cancer therapy, fluorescent imaging, and stem cell regulation. This review aims to provide a brief synopsis of recent achievements at the intersection of supramolecular chemistry and biomedical science in hope of contributing to the multidisciplinary research on supramolecular biofunctional materials for a wide range of applications. We envision that supramolecular biofunctional materials will contribute to the development of new therapies that will ultimately lead to a paradigm shift for developing next generation biomaterials for medicine.

Oxygen-tuned nanozyme polymerization for the preparation of hydrogels with printable and antibacterial properties

Nanozymes merge nanotechnology with biology and provide a lower cost and higher stability options, compared to that of natural enzymes. However, nanozyme catalyzed polymerization under physiological conditions is still a big challenge due to heavy oxygen inhibition. In this study, the simple glucose oxidase system can effectively adjust oxygen concentration and generate hydrogen peroxide, which assists in the realization of nanozyme-catalyzed polymerization. The nanozyme based hydrogel is printable due to its mild preparation with gradually increased viscosity. The antibacterial performance is ascribed to the in situ generated hydroxyl radical via the reaction of the bound nanozyme and glucose.

A novel H2O2responsive supramolecular hydrogel for controllable drug release

We reported a peptide-based supramolecular hydrogel possessing a gel–sol phase transition triggered by H₂O₂.

d-Serine enzymatic metabolism induced formation of a powder-remoldable PAAM–CS hydrogel

The metabolism of d-serine by d-amino acid oxidase was developed to induce radical polymerization and formation of a powder-remoldable PAAM–CS hydrogel.

Laccase-mediated formation of mesoporous silica nanoparticle based redox stimuli-responsive hybrid nanogels as a multifunctional nanotheranostic agent

In this work, we designed a new hybrid nanogel with redox responsive polymer gel shells and mesoporous silica nanoparticles (MSNs) cores via laccase-mediated radical polymerization. The successful coating of the responsive gel shells on the MSNs was confirmed by the morphology and increased diameters of the particles as determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). As observed by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS), the presence of the element S around the MSNs further confirmed the formation of the gel shell. When loaded with doxorubicin (DOX), these hybrid nanogels had a significantly higher cumulative DOX release in a reductive environment than that found under physiological conditions. The MSNs with mesoporous channels were loaded with perfluorohexane (PFH) for ultrasound imaging, which was enhanced by the presence of the elastic gel shells.

Redox/pH dual stimuli-responsive degradable Salecan-g-SS-poly(IA-co-HEMA) hydrogel for release of doxorubicin

Salecan is a novel water-soluble extracellular β-glucan and possesses excellent physicochemical and biological properties. Here, redox/pH dual stimuli-responsive hydrogel based on Salecan grafted with itaconic acid (IA) and 2-hydroxyethyl methacrylate (HEMA) were prepared using disulfide-functionalized crosslinker N,N-bis(acryloyl)cystamine (BAC) for controlled drug delivery. The introduction of carboxylic groups endows the system with pH-sensitive character, swelling behavior of the hydrogel was conducted by changing the pH and Salecan content. It was demonstrated that DOX was efficiently loaded into the hydrogels and released in a controlled fashion via pH-control and swelling-shrinking mechanism. More importantly, DOX-loaded hydrogels showed dose dependent cytotoxicity toward A549 cell, and efficient cell killing was observed. Furthermore, a key point of this study was that the presence of disulfide linkage in system favored the degradation of hydrogels in the reductive environment. These results highlight the potential of Salecan-g-SS-poly(IA-co-HEMA) hydrogel as a novel system for the controlled release of anti-cancer drugs.

Hierarchical design of a polymeric nanovehicle for efficient tumor regression and imaging

Effective delivery of therapeutics to disease sites significantly contributes to drug efficacy, toxicity and clearance. Here we designed a hierarchical polymeric nanoparticle structure for anti-cancer chemotherapy delivery by utilizing state-of-the-art polymer chemistry and co-assembly techniques. This novel structural design combines the most desired merits for drug delivery in a single particle, including a long in vivo circulation time, inhibited non-specific cell uptake, enhanced tumor cell internalization, pH-controlled drug release and simultaneous imaging. This co-assembled nanoparticle showed exceptional stability in complex biological media. Benefiting from the synergistic effects of zwitterionic and multivalent galactose polymers, drug-loaded nanoparticles were selectively internalized by cancer cells rather than normal tissue cells. In addition, the pH-responsive core retained their cargo within their polymeric coating through hydrophobic interaction and released it under slightly acidic conditions. In vivo pharmacokinetic studies in mice showed minimal uptake of nanoparticles by the mononuclear phagocyte system and excellent blood circulation half-lives of 14.4 h. As a result, tumor growth was completely inhibited and no damage was observed for normal organ tissues. This newly developed drug nanovehicle has great potential in cancer therapy, and the hierarchical design principle should provide valuable information for the development of the next generation of drug delivery systems.

Controllable Heparin-Based Comb Copolymers and Their Self-assembled Nanoparticles for Gene Delivery

Polysaccharide-based copolymers have attracted much attention due to their effective performances. Heparin, as a kind of polysaccharide with high negative charge densities, has attracted much attention in biomedical fields. In this work, we report a flexible way to adjust the solubility of heparin from water to oil via the introduction of tetrabutylammonium groups for further functionalization. A range of heparin-based comb copolymers with poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMEMA), poly(dimethylaminoethyl methacrylate) (PDMAEMA), or PPEGMEMA-b-PDMAEMA side chains were readily synthesized in a MeOH/dimethylsulfoxide mixture via atom-transfer radical polymerization. The heparin-based polymer nanoparticles involving cationic PDMAEMA were produced due to the electrostatic interaction between the negatively charged heparin backbone and PDMAEMA grafts. Then the pDNA condensation ability, cytotoxicity, and gene transfection efficiency of the nanoparticles were characterized in comparison with the reported gene vectors. The nanoparticles were proved to be effective gene vectors with low cytotoxicity and high transfection efficiency. This study demonstrates that by adjusting the solubility of heparin, polymer graft functionalization of heparin can be readily realized for wider applications.

Radical-Mediated Enzymatic Polymerizations

Polymerization reactions are commonly effected by exposing monomer formulations to some initiation stimulus such as elevated temperature, light, or a chemical reactant. Increasingly, these polymerization reactions are mediated by enzymes--catalytic proteins--owing to their reaction efficiency under mild conditions as well as their environmental friendliness. The utilization of enzymes, particularly oxidases and peroxidases, for generating radicals via reduction-oxidation mechanisms is especially common for initiating radical-mediated polymerization reactions, including vinyl chain-growth polymerization, atom transfer radical polymerization, thiol-ene step-growth polymerization, and polymerization via oxidative coupling. While enzyme-mediated polymerization is useful for the production of materials intended for subsequent use, it is especially well-suited for in situ polymerizations, where the polymer is formed in the place where it will be utilized. Such polymerizations are especially useful for biomedical adhesives and for sensing applications.

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.

Fe3O4@nanogel via UOx/HRP initiated surface polymerization for pH sensitive drug delivery

This study describes a new strategy to fabricate core–shell nanogels by surface free-radical polymerization initiated by the cascade reaction of UOx and HRP, which showed excellent biocompatible, high loading capacity and pH-responsive drug release.

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.

Microgel coating of magnetic nanoparticles via bienzyme-mediated free-radical polymerization for colorimetric detection of glucose

This study describes a new strategy for the fabrication of magnetic core-shell microgels by free-radical polymerization triggered by the cascade reaction of glucose oxidase (GOx) and horseradish peroxidase (HRP). The mild polymerization around the interface of the magnetic nanoparticles permits the mild coating of the microgel layer with excellent characteristics for various applications in biocatalysis and medical diagnostics, as well as in clinical fields. The immobilized bienzyme within the microgel has a largely retained activity relative to the non-immobilized one. The confining effect of the microgel and the well designed distance between the two enzymes can benefit the diffusion of intermediates to the HRP active site. The final microgels can be incontestably employed as sensitive biosensors for colorimetric glucose detection.

Enzyme-instructed self-assembly of taxol promotes axonal branching

Axonal branching is important for vertebrate neuron signaling. Taxol has a biphasic effect on axonal branching (i.e., high concentration inhibits axonal growth but low concentration restores it). To the best of our knowledge, low concentration of taxol to promote axonal branching has not been reported yet. Herein, we rationally designed a taxol derivative Fmoc-Phe-Phe-Lys(taxol)-Tyr(H2PO4)-OH (1) which could be subjected to alkaline phosphatase (ALP)-catalyzed self-assembly to form taxol nanofibers. We found that, at 10 μM, 1 has a microtubule (MT) condensation effect similar to that of taxol on mammalian cells but with more chronic toxicity than taxol on the cells. At a low concentration of 10 nM, 1 not only promoted neurite elongation as taxol did but also promoted axonal branching which was not achieved by using taxol. We propose that self-assembly of 1 along the MTs prohibited their lateral contacts and thus promoted axonal branching. Our strategy of enzyme-instructed self-assembly (EISA) of a taxol derivative provides a new tool for scientists to study the morphology of neurons, as well as their behaviours.

Bioinorganic nanocomposite hydrogels formed by HRP-GOx-cascade-catalyzed polymerization and exfoliation of the layered composites

The mild preparation of multifunctional nanocomposite hydrogels is of great importance for practical applications. We report that bioinorganic nanocomposite hydrogels, with calcium niobate nanosheets as cross-linkers, can be prepared by dual-enzyme-triggered polymerization and exfoliation of the layered composite. The layered HRP/calcium niobate composites (HRP=horseradish peroxidase) are formed by the assembly of the calcium niobate nanosheets with HRP. The dual-enzyme-triggered polymerization can induce the subsequent exfoliation of the layered composite and final gelation through the interaction between polymer chains and inorganic nanosheets. The self-immobilized HRP-GOx enzymes (GOx=glucose oxidase) within the nanocomposite hydrogel retain most of enzymatic activity. Evidently, their thermal stability and reusability can be improved. Notably, our strategy could be easily extended to other inorganic layered materials for the fabrication of other functional nanocomposite hydrogels.

Dual-Enzyme-Loaded Multifunctional Hybrid Nanogel System for Pathological Responsive Ultrasound Imaging and T2-Weighted Magnetic Resonance Imaging

A dual-enzyme-loaded multifunctional hybrid nanogel probe (SPIO@GCS/acryl/biotin-CAT/SOD-gel, or SGC) has been developed for dual-modality pathological responsive ultrasound (US) imaging and enhanced T2-weighted magnetic resonance (MR) imaging. This probe is composed of functionalized superparamagnetic iron oxide particles, a dual enzyme species (catalase and superoxide dismutase), and a polysaccharide cationic polymer glycol chitosan gel. The dual-modality US/MR imaging capabilities of the hybrid nanogel for responsive US imaging and enhanced T2-weighted MR imaging have been evaluated both in vitro and in vivo. These results show that the hybrid nanogel SGC can exhibit efficient dual-enzyme biocatalysis with pathological species for responsive US imaging. SGC also demonstrates increased accumulation in acidic environments for enhanced T2-weighted MR imaging. Further research on these nanogel systems may lead to the development of more efficient US/MR contrast agents.

Bipyridine hydrogel for selective and visible detection and absorption of Cd(2+)

Herein, we report for the first time the use of bipyridine-based hydrogel for selective and visible detection and absorption of Cd(2+). At low concentrations, hydrogelator 1 was applied for selective detection of Cd(2+) in vitro and in living cells with high sensitivity. In the absence of metal ions, 1 is nonfluorescent at 470 nm. Upon addition of metal ions, 1 selectively coordinates to Cd(2+), causing an 86-fold increase of fluorescence intensity at 470 nm via the chelation enhanced fluorescence (CHEF) effect, as revealed by first-principles simulations. At 1.5 wt% and pH 5.5, 1 self-assembles into nanofibers to form hydrogel Gel I. Since Cd(2+) could actively participate in the hydrogelation and promote the self-assembly, we also successfully applied Gel I for visible detection and absorption of Cd(2+). With these excellent properties, Gel I is expected to be explored as one type of versatile biomaterial for not only environmental monitoring but also for pollution treatment in the near future.

Supramolecular nanofibers of self-assembling peptides and proteins for protein delivery

Supramolecular nanofibers of proteins and peptides could be used for intracellular protein delivery.

The formation of biodegradable micelles from a therapeutic initiator for enzyme-mediated drug delivery

The direct grafting of amphiphilic macromolecules by sequentialn-carboxyanhydride ring-opening polymerisation (NCA ROP) from a therapeutic initiator enables the formation of monodisperse drug-containing micelles.

Hydrogel-coated enzyme electrodes formed by GOx-mediated polymerization for glucose detecting

This communication reports the mild fabrication of a hydrogel-coated enzyme electrode for glucose detecting with high sensitivity (35.19 μA mM⁻¹ cm⁻²) and robust stability.