Exploring the gelation and AIE properties of a tripodal acylhydrazone-based probe: turn-on Zn(II) sensing in HEPES buffer

Two C3-symmetric acylhydrazone-based AIE active probes, TRI-QUI and TRI-NAP, were synthesized with different peripheral substituents. The probe containing a quinoline moiety in the periphery displayed a selective turn-on response towards Zn2+ in HEPES buffer, with a calculated detection limit of 6.45 μM. The probe TRI-QUI was also identified as a supergelator as it formed a gel in DMSO-H2O (2 : 3, v/v) with a minimum gelation concentration of 0.5 mg mL-1. The gelator could interact with various metal ions or anions in the gel phase. Furthermore, the gelator could encapsulate small molecules like methyl orange and bromophenol blue, making the probe a multifunctional smart material.

Clustering of the Membrane Protein by Molecular Self-Assembly Downregulates the Signaling Pathway for Cancer Cell Inhibition

This work reports a cyclic peptide appended self-assembled scaffold that recognizes the membrane protein EGFR and arrests the EGFR signaling through multivalent interactions by assembly-induced aggregation. When incubated with cells, the oligomers of PAD-1 first recognize the overexpressed EGFR on cancer cell membranes for arresting EGFR, which then initiates cellular uptake through endocytosis. The accumulation of PAD-1 and EGFR in the lysosome results in the formation of nanofibers, leading to the lysosomal membrane permeabilization (LMP). These processes disrupt the homeostasis of EGFR and inhibit the downstream signaling transduction of EGFR for cancer cell survival. Moreover, LMP induced the release of protein aggregates that could generate endoplasmic reticulum (ER) stress, resulting in cancer cell death selectively. In vivo studies indicate the efficient antitumor efficiency of PAD-1 in tumor-bearing mice. As a first example, this work provides an alternative strategy for controlling protein behavior for tuning cellular events in living cells.

Smart Molecular Imaging and Theranostic Probes by Enzymatic Molecular In Situ Self-Assembly

Enzymatic molecular in situ self-assembly (E-MISA) that enables the synthesis of high-order nanostructures from synthetic small molecules inside a living subject has emerged as a promising strategy for molecular imaging and theranostics. This strategy leverages the catalytic activity of an enzyme to trigger probe substrate conversion and assembly in situ, permitting prolonging retention and congregating many molecules of probes in the targeted cells or tissues. Enhanced imaging signals or therapeutic functions can be achieved by responding to a specific enzyme. This E-MISA strategy has been successfully applied for the development of enzyme-activated smart molecular imaging or theranostic probes for in vivo applications. In this Perspective, we discuss the general principle of controlling in situ self-assembly of synthetic small molecules by an enzyme and then discuss the applications for the construction of "smart" imaging and theranostic probes against cancers and bacteria. Finally, we discuss the current challenges and perspectives in utilizing the E-MISA strategy for disease diagnoses and therapies, particularly for clinical translation.

A bio-inspired silkworm 3D cocoon-like hierarchical self-assembled structure from π-conjugated natural aromatic amino acids

The formation of spontaneous 3D self-assembled hierarchical structures from 1D nanofibers is a significant breakthrough in materials science. Overcoming the major challenges associated with developing these 3D structures, such as uncontrolled self-assembly, complex procedures, and machinery, has been a formidable task. However, the current discovery reveals that simple π-system (fluorenyl)-functionalized natural aromatic amino acids, phenylalanine (Fmoc-F) and tyrosine (Fmoc-Y), can form bio-inspired 3D cocoon-like structures. These structures are composed of entangled 1D nanofibers created through supramolecular self-assembly using a straightforward one-step process of solvent casting. The self-assembly process relies on π-π stacking of the fluorenyl (π-system) moieties and intermolecular hydrogen bonding between urethane amide groups. The cocoon-like structures are versatile and independent of concentration, temperature, and humidity, making them suitable for various applications. This discovery has profound implications for materials science and the developed advanced biomaterials, such as Fmoc-F and Fmoc-Y, can serve as flexible foundational components for constructing 3D fiber-based structures.

Orderly Self-Assembly of Organic Fluorophores for Sensing and Imaging

Fluorescence imaging utilizing traditional organic fluorophores is extensively applied in both cellular and in vivo studies. However, it faces significant obstacles, such as low signal-to-background ratio (SBR) and spurious positive/negative signals, primarily due to the facile diffusion of these fluorophores. To cope with this challenge, orderly self-assembled functionalized organic fluorophores have gained significant attention in the past decades. These fluorophores can create nanoaggregates via a well-ordered self-assembly process, thus prolonging their residency time within cells and in vivo settings. The development of self-assembled-based fluorophores is an emerging field, and as such, in this review, we present a summary of the progress and challenges of self-assembly fluorophores, focusing on their development history, self-assembly mechanisms, and biomedical applications. We hope that the insights provided herein will assist scientists in further developing functionalized organic fluorophores for in situ imaging, sensing, and therapy.

Thermoreversible and tunable supramolecular hydrogels based on chitosan and metal cations

A new thermoreversible and tunable hydrogel CS-M with high water content prepared by metal cation (M = Cu²⁺, Zn²⁺, Cd²⁺ and Ni²⁺) and chitosan (CS) was reported. The influence of metal cations on the thermosensitive gelation of CS-M systems were studied. All prepared CS-M systems were in the transparent and stable sol state and could become the gel state at gelation temperature (T_g). These systems after gelation could recover to its original sol state at low temperature. CS-Cu hydrogel was mainly investigated and characterized due to its large T_g scale (32-80 °C), appropriate pH range (4.0-4.6) and low Cu²⁺ concentration. The result showed that the T_g range was influenced and could be tuned by adjusting Cu²⁺ concentration and system pH within an appropriate range. The influence of anions (Cl^-, NO3^- and Ac^-) in cupric salts in the CS-Cu system was also investigated. Scale application as heat insulation window was investigated outdoors. The different supramolecular interactions of the -NH₂ group in chitosan at different temperatures were proposed to dominate the thermoreversible process of CS-Cu hydrogel.

Self-assembling NBD-tripeptide as a dual-mode colorimetric platform for naked eye and smartphone joint detection of micro to nanomolar Copper(II) ions

Compared to conventionally synthesized organic compounds, peptides with amphiphiles have unique advantages, especially in self-assembly. Herein, we reported a peptide-based molecule rationally designed for the visual detection of copper ions (Cu²⁺) in multiple modes. The peptide exhibited excellent stability, high luminescence efficiency, and environmentally responsive molecular self-assembly in water. In the presence of Cu²⁺, the peptide undergoes an ionic coordination interaction and a coordination-driven self-assembly process that leads to the quenching of fluorescence and the formation of aggregates. Therefore, the concentration of Cu²⁺ can be determined by the residual fluorescence intensity and the color difference between peptide and competing chromogenic agents before and after Cu²⁺ incorporation. More importantly, this variation in fluorescence and color can be presented visually, thus allowing qualitative and quantitative analysis of Cu²⁺ based on the naked eye and smartphones. Overall, our study not only extends the application of self-assembling peptides but also provides a universal method for dual-mode visual detection of Cu²⁺, which would significantly promote point-of-care testing (POCT) of metal ions in pharmaceuticals, food, and drinking water.

Zero-Background Small-Molecule Sensors for Near-IR Fluorescent Imaging of Biomacromolecular Targets in Cells

In this study, we report a general approach to the design of a new generation of small-molecule sensors that produce a zero background but are brightly fluorescent in the near-IR spectral range upon selective interaction with a biomolecular target. We developed a fluorescence turn-on/-off mechanism based on the aggregation/deaggregation of phthalocyanine chromophores. As a proof of concept, we designed, prepared, and characterized sensors for in-cell visualization of epidermal growth factor receptor (EGFR) tyrosine kinase. We established a structure/bioavailability correlation, determined conditions for the optimal sensor uptake and imaging, and demonstrated binding specificity and applications over a wide range of treatment options involving live and fixed cells. The new approach enables high-contrast imaging and requires no in-cell chemical assembly or postexposure manipulations (i.e., washes). The general design principles demonstrated in this work can be extended toward sensors and imaging agents for other biomolecular targets.

Self-Assembly of the Tetraphenylethylene-Capped Diserine through a Hierarchical Assembly Process

We report a new peptide-based urchin-shaped structure prepared through two-step self-assembly of tetraphenylethylene-diserine (TPE-SS). Hydrogelation generated nanobelts through the first stage of self-assembly of TPE-SS; these nanobelts further transformed on silicon wafers into urchin-like microstructures featuring nanosized spines. The presence of the TPE moiety in the hydrogelator resulted in aggregation-induced emission characteristics both in the solution and in the gel phases. TPE-SS has the lowest molecular weight of any TPE-capped hydrogelator with β-sheet-like structures under physiological pH. This new design strategy appears to be useful for generating three-dimensional self-assembled microstructures and multifunctional biomaterials. We found that TPE-SS is biocompatible with human mesenchymal stem cells and breast cancer cells, making them potential applications in tissue engineering and biomedical research.

A tumor-targetable NIR probe with photoaffinity crosslinking characteristics for enhanced imaging-guided cancer phototherapy

Spatiotemporally manipulating the in situ immobilization of theranostic agents within cancer cells to improve their bioavailability is highly significant yet challenging in tumor diagnosis and treatment. Herein, as a proof-of concept, we for the first time report a tumor-targetable near-infrared (NIR) probe DACF with photoaffinity crosslinking characteristics for enhanced tumor imaging and therapeutic applications. This probe possesses great tumor-targeting capability, intensive NIR/photoacoustic (PA) signals, and a predominant photothermal effect, allowing for sensitive imaging and effective photothermal therapy (PTT) of tumors. Most notably, upon 405 nm laser illumination, DACF could be covalently immobilized within tumor cells through a photocrosslinking reaction between photolabile diazirine groups and surrounding biomolecules resulting in enhanced tumor accumulation and prolonged retention simultaneously, which significantly facilitates the imaging and PTT efficacy of tumor in vivo. We therefore believe that our current approach would provide a new insight for achieving precise cancer theranostics.

Self-Assembly and Disassembly of Membrane Curvature-Sensing Peptide-Based Deep-Red Fluorescent Probe for Highly Sensitive Sensing of Exosomes

With increasing knowledge of the diverse roles of exosomes in biological processes, much attention has been paid to the development of analytical methods for exosome analysis. Here, we developed a new class of amphipathic helical (AH) peptide-based fluorescent probes for highly sensitive detection of exosomes in a mix and read manner. Membrane curvature-sensing AH peptide (ApoC) was coupled with lipophilic tail (C12)-carrying thiazole red (TR) for construction of a self-assembly/disassembly based fluorescence "off-on" sensing system for target exosomes. ApoC-TR_C12 has extremely weak emission due to the formation of the aggregates, whereas it becomes emissive in response to the target exosomes through the binding-induced disassembly of ApoC-TR_C12. We demonstrated that the C12 unit attached to the TR unit had a favorable effect on both fluorescence response (signal-to-background: S/B) and binding affinity. ApoC-TR_C12 was applicable to rapid and simple detection of exosomes with high detection sensitivity (limit of detection ≈ 10³ particles/μL).

Supramolecular Host-Guest Hydrogel Based on γ-Cyclodextrin and Carboxybenzyl Viologen Showing Reversible Photochromism and Photomodulable Fluorescence

Much effort has been devoted to the development of supramolecular hydrogels due to their broad applications and conveniently controllable properties. Here, we demonstrate a novel supramolecular host-guest hydrogel, which is constructed by the host γ-CD complexed with the guest 1-(4-carboxybenzyl)-4,4'-bipyridinium chloride (1⁺·Cl^-) through the π···π interaction, hydrogen bonding, and host-guest interactions. The supramolecular hydrogel [1⁺@γ-CD]_n exhibits reversible electron transfer photochromic behavior and photomodulable fluorescence. The excellent photochromic and fluorescence properties support the practical utility of the supramolecular hydrogel as a visual display and anti-counterfeiting material.

Supermolecules as a quality markers of herbal medicinal products

Herbal medicines have greatly contributed to human health worldwide for thousands of years. In particular, traditional Chinese medicine plays an essential role in the prevention and treatment of COVID-19. With the exponentially increasing use and global attention to herbal medicinal products (HMPs), efficacy and safety have become major public concerns in many countries. In general, the quantification and qualification of quality markers (Q-markers) is the most common way to solve this issue. In the last few decades, small molecules, including flavonoids, terpenes, phenylpropanoids, alkaloids, phenols, and glycosides have been extensively investigated as Q-markers for HMP quality control. With the development of biotechnology in the last decade, scientists have begun to explore HMPs macromolecules, including polysaccharides and DNA, for their establishment as Q-markers. In recent years, supermolecules with stronger biological activities have been found in HMPs. In this review, we summarize and discuss the current Q-markers for HMP quality control; in particular, the possibility of using supermolecules as Q-markers based on structure and activity was discussed.

Serum Albumin Inspired Self-Assembly/Disassembly of a Fluorogenic Nanoprobe for Real-Time Monitoring and Quantification of Urinary Albumin with Live Cell Imaging Application

Abnormal levels (high/low) of urinary human serum albumin (HSA) are associated with a number of diseases and thus act as an essential biomarker for quick therapeutic monitoring and biomedical diagnosis, entailing the urgent development of an effective chemosensor to quantify the albumin levels. Herein, we have rationally designed and developed a small fluorogenic molecular probe, (Z)-2-(5-((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl) methylene)-4-oxo-2-thioxothiazolidin-3-yl) acetic acid (HJRA) with a twisted intramolecular charge transfer (TICT) property, which can easily self-assemble into nonfluorescent nanoaggregates in aqueous solution. However, HJRA nanoaggregates can selectively bind with serum albumin proteins (HSA/BSA) in ∼100% PBS medium, thereby facilitating the disassembly of nanoaggregates into monomers, exhibiting a clear turn-on red fluorescent response toward HSA and BSA. Analysis of the specific binding mechanism between HJRA and HSA using a site-selective fluorescence displacement assay and molecular docking simulations indicates that a variety of noncovalent interactions are responsible for the disassembly of nanoaggregates with the concomitant trapping of the HJRA monomer at site I in HSA, yielding a substantial red emission caused by the inhibition of intramolecular rotation of HJRA probe inside the hydrophobic cavity of HSA. The limit of detection (LOD) determined by the 3σ/slope method was found to be 1.13 nM, which is substantially below the normal HSA concentration level in healthy urine, signifying the very high sensitivity of the probe toward HSA. The comparable results and quick response toward quantification of HSA in urine by HJRA with respect to the Bradford method clearly point toward the superiority of this method compared to the existing ones and may lead to biomedical applications for HSA quantification in urine. It may also find potential application in live-cell imaging of HSA.

An Insight into Skeletal Networks Analysis for Smart Hydrogels

Hydrogels are 3D cross‐linked polymer networks. Benefiting from the flexible designs and reasonable constructions of these networks, a large number of smart hydrogels with response characteristics to specific stimuli have received widespread attention and developed rapidly. The skeletal networks composed of the skeletal polymer chains and effectual cross‐links are the soul of such soft materials, and the response behaviors fundamentally depend on the dynamic characteristics of skeletal networks. Herein, the novel concepts of skeletal networks analysis to describe, understand, and guide the advanced designs and applications of smart hydrogels are proposed. Representative glucose‐sensitive hydrogels and DNA‐based smart hydrogels are reviewed to demonstrate the principle of skeletal networks analysis and clarify its practical guidance. Summarizing and classifying the characterizations and conversions of skeletal networks dynamics based on different response mechanisms provides a realistic solution. On this basis, advanced applications of smart hydrogels guided by skeletal networks dynamics including biochemical detection, cell mechanics sensing, drug delivery systems, and dynamic complex soft materials are typically reviewed. The skeletal networks analysis for smart hydrogels is of great significance for understanding the microstructures of hydrogels and guiding the designs of soft materials and their smart applications in the fields of analytical science and advanced materials.

Self-assembly driven chiral transfer from a dipeptide to the twist and stacking handedness of cyanobiphenylyl groups

The chiral transfer phenomenon was studied on four Ala–Ala lipodipeptides with a cyanobiphenylyl group at the terminal alkyl chain.

"Indanonalkene" Photoluminescence Platform: Application in Real-Time Tracking the Synthesis, Remodeling, and Degradation of Soft Materials

In this Article, we present a strategy to visually track chemically triggered covalent bonding processes in gelation, remodeling, and degradation of soft materials, i.e., hydrogels, based on a new photoluminescence platform. Initially in the development of photoluminophors named "indanonalkenes", turn-on emission can be tracked and quantified in the optical reaction between a conjugate acceptor and amine derivatives. On this basis, fluorescence enhancement and mechanical changes were recorded during the gelation process through amine-thiol exchanges under organic and aqueous conditions. Next in macromolecular remodeling, we realized a stimulus-induced transformation of one architecture into another one, exploiting the orthogonality of chemical covalent bonding that could be visualized using luminescence. Furthermore, the hydrogel network can be degraded to release the coupling partner induced by ethylene diamine, and the process can be monitored using fluorescence changes and quantified through gel permeation chromatography, while the released components can be utilized again to regenerate a new hydrogel. In addition, the photographic images provide alternatives to fluorescence spectra and can be digitally processed to quantify the macroscopic changes, resulting in a photographic imaging approach. The real-time observation and quantification of chemically triggered polymeric formation, morphology, and degradation through luminescence in spatial and time scales herald a new generation of "smart" materials.

An activated excretion-retarded tumor imaging strategy towards metabolic organs

Intraoperative fluorescence-based tumor imaging plays a crucial role in performing the oncological safe tumor resection with the advantage of differentiating tumor from normal tissues. However, the application of these fluorescence contrast agents in renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC) was dramatically hammered as a result of lacking active targeting and poor retention time in tumor, which limited the Signal to Noise Ratio (SNR) and narrowed the imaging window for complicated surgery. Herein, we reported an activated excretion-retarded tumor imaging (AERTI) strategy, which could be in situ activated with MMP-2 and self-assembled on the surface of tumor cells, thereby resulting in a promoted excretion-retarded effect with an extended tumor retention time and enhanced SNR. Briefly, the AERTI strategy could selectively recognize the Integrin α_vβ₃. Afterwards, the AERTI strategy would be activated and in situ assembled into nanofibrillar structure after specifically cleaved by MMP-2 upregulated in a variety of human tumors. We demonstrated that the AERTI strategy was successfully accumulated at the tumor sites in the 786-O and HepG2 xenograft models. More importantly, the modified modular design strategy obviously enhanced the SNR of AERTI strategy in the imaging of orthotopic RCC and HCC. Taken together, the results presented here undoubtedly confirmed the design and advantage of this AERTI strategy for the imaging of tumors in metabolic organs.

•

Fluorescence-based tumor imaging plays a crucial role in performing the oncological safe tumor resection.

•

Self-assembled peptide possesses the advantage of active targeting and long-term retention time in tumor.

•

The activated excretion-retarded tumor imaging strategy extended the tumor retention time and enhanced SNR.

•

Assembly-mediated peptide probe successfully achieved the accurate identification of tumor boundaries and detection of minimal tumors (<2 mm).

Fine-Tuning of Molecular Structures to Generate Carbohydrate Based Super Gelators and Their Applications for Drug Delivery and Dye Absorption

Carbohydrate-based low molecular weight gelators (LMWGs) exhibit many desirable properties making them useful in various fields including applications as drug delivery carriers. In order to further understand the structural connection to gelation properties, especially the influence of halide substitutions, we have designed and synthesized a series of para-chlorobenzylidene acetal protected D-glucosamine amide derivatives. Fifteen different amides were synthesized, and their self-assembling properties were assessed in multiple organic solvents, as well as mixtures of organic solvents with water. All derivatives were found to be gelators for at least one solvent and majority formed gels in multiple solvents at concentrations lower than 2 wt%. A few derivatives rendered remarkably stable gels in aqueous solutions at concentrations below 0.1 wt%. The benzamide 13 formed gels in water and in EtOH/H2O (v/v 1:2) at 0.36 mg/mL. The gels were characterized using optical microscopy and atomic force microscopy, and the self-assembly mechanism was probed using variable temperature 1H-NMR spectroscopy. Gel extrusion studies using H2O/DMSO gels successfully printed lines of gels on glass slides, which retained viscoelasticity based on rheology. Gels formed by the benzamide 13 were used for encapsulation and the controlled release of chloramphenicol and naproxen, as well as for dye removal for toluidine blue aqueous solutions.

Self-Assembled Hybrid Nanogel as a Multifunctional Theranostic Probe for Enzyme-Regulated Ultrasound Imaging and Tumor Therapy

Multifunctional theranostic nanoprobes integrated with stimuli-responsive imaging and therapeutic capabilities have shown great potential to enhance the early cancer diagnostic efficacy and therapeutic efficiency. Elevated levels of lactate and hydrogen peroxide have been considered as the characteristic feature of the tumor microenvironment and can thus be exploited for developing promising theranostic strategies. We demonstrate here that the biocompatible and responsive enzyme-based nanogel probe has been designed as a promising theranostic tool to target high lactate and hydrogen peroxide for ultrasound imaging (US) and cancer treatment. We encapsulate the dual enzyme lactate oxidase (LOD) and catalase (CAT) into the self-assembled nanogels to fabricate responsive nanoprobe LOD/CAT-loaded nanogels (LCNGs). The nanoprobes can respond to the lactate and H₂O₂ rich tumor microenvironment to generate abundant oxygen, which further accumulates into microbubbles for enhanced US imaging. Besides, LCNGs@DOX has been further created by integrating the nanoprobes with doxorubicin (DOX) for cancer therapy. Both in vitro and in vivo results demonstrate enhanced US imaging and effective cell proliferation inhibition of LCNGs@DOX, allowing the preparation of safe and efficient theranostic nanoprobes capable of responsive US imaging and treating tumors.

Scratching the Surface of Unventured Possibilities with In Situ Self-Assembly: Protease-Activated Developments for Imaging and Therapy

In situ self-assembly has attracted increasing research interest for applications in imaging and therapy in recent years. Particularly for protease-activated developments, inspiration is drawn from the innate specificity of their catalytic activities, rapid discovery of the various roles they play in the proliferation of certain diseases, and inherent susceptibility of small molecule peptide conjugates to proteolytic digestion in vivo. The overexpression of a disease-related protease of interest can be exploited as an endogenous stimulus for site-specific self-assembly to largely amplify a molecular event happening at the cellular level. This holds great potential for applications in early stage disease detection, long-term disease monitoring, and sustained therapeutic effects. This review summarizes the recent developments in protease-activated self-assemblies for imaging and therapeutic applications toward the manifestation of tumors, bacterial infections, neurodegenerative disorders, and wound recovery.

Fluorescence Response and Self-Assembly of a Tweezer-Type Synthetic Receptor Triggered by Complexation with Heme and Its Catabolites

There is increasing interest in the development and applications of synthetic receptors that recognize target biomolecules in aqueous media. We have developed a new tweezer-type synthetic receptor that gives a significant fluorescence response upon complexation with heme in aqueous solution at pH 7.4. The synthetic receptor consists of a tweezer-type heme recognition site and sulfo-Cy5 as a hydrophilic fluorophore. The receptor-heme complex exhibits a supramolecular amphiphilic character that facilitates the formation of self-assembled aggregates, and both the tweezer moiety and the sulfo-Cy5 moiety are important for this property. The synthetic receptor also exhibits significant fluorescence responses to biliverdin and bilirubin, but shows very weak fluorescence responses to flavin mononucleotide, folic acid, and nicotinamide adenine dinucleotide, which contain smaller π-scaffolds.

Self-assembled Camptothecin derivatives - Curcuminoids conjugate for combinatorial chemo-photodynamic therapy to enhance anti-tumor efficacy

Camptothecin (CPT), an alkaloid, was first discovered from plants and has potent anti-tumor activity. Since then, CPT analogs (namely Irinotecan and Topotecan) have been approved by the FDA for cancer treatments. Curcumin, on the other hand, is a widely used photosensitizer in photodynamic therapy (PDT) treatment. In our previous work, we have reported a straightforward strategy to construct a drug self-delivery system in which two-molecular species Irinotecan and Curcumin can self-assembly into a complex of ion pairs, namely ICN, through intermolecular non-covalent interactions. We found that ICN has slightly better chemotherapy efficacy than its individual components with much fewer side effects. In this paper, we aim to combine the chemotherapy and the PDT of ICN to further improve its anti-tumor performance. The efficient cellular uptake of ICNs was observed by confocal microscopy. Dichloro-dihydro-fluorescein diacetate (DCFH-DA) assay was used to detect the generation of singlet oxygen species. We found that the cell viability was 9% with both chemotherapy and PDT, and 31% with chemotherapy alone for the case with an ICN concentration of 10 μM, which demonstrated that the anti-tumor efficacy against the HT-29 cancer cell line was enhanced substantially with the combination therapy strategy. The study with an in vivo mouse model has further verified that the chemo-PDT dual therapy can inhibit tumor growth by 84% and 18.8% comparing with the control group and the chemotherapy group, respectively. Our results demonstrated that the new strategy using self-assembly and carrier-free nanoparticles with their chemo-PDT dual therapy may provide new opportunities to develop future combinatorial therapy methods in treating cancer.

Receptor tyrosine kinases-instructed release of its inhibitor from hydrogel to delay ovarian aging

Premature ovarian failure (POF) is the most frequently occurred disease in ovary. Direct inhibition of mammalian target of rapamycin (mTOR) activity can treat woman POF but brings adverse effects to women. Herein, by rational design of a hydrogelator Nap-Phe-Phe-Asp-Arg-Leu-Tyr-OH (Y) and co-assembling Y with an inhibitor of receptor tyrosine kinase (RTK, an upstream kinase of mTOR), Ala-Glu-Ala-Ala-Leu-Tyr-Lys-Asn-Leu-Leu-His-Ser-OH (Inh), to form hydrogel Gel Y + Inh, we develop a "smart" strategy of RTK-responsive disassembly of the hydrogel to release Inh. Release of Inh moderately inhibits the activity of mTOR and therefore delays ovarian aging. Oocyte and zygote experiments show that Gel Y + Inh improves both meiotic maturation of the oocytes and early embryonic development of the zygotes. In vivo animal experiments indicate that Gel Y + Inh effectively delays ovarian aging in aged mice by down regulation of mTOR activity, stimulation of ovaries to secrete estrogen and progesterone, and development of more antral follicles for reproduction. We expect that our new hydrogel Gel Y + Inh could be applied to treat woman POF, as well as delay ovarian aging, in clinic in the near future.

Bifunctional supramolecular nanofiber inhibits atherosclerosis by enhancing plaque stability and anti-inflammation in apoE-/- mice

Background and Purpose: Atherosclerosis is vascular disease of chronic inflammation and lipid disorder, which is a major cause of coronary heart disease. Foam cell formation is key progress during the atherosclerosis development. Insulin-like growth factor (IGF)-1 is a growth hormone that plays a crucial role in growth, metabolism, and homeostasis. Previous studies have demonstrated that increase in circulating IGF-1 can reduce atherosclerotic burden. However, active IGF-1 is characterized with poor tissue retention and is at a very low level in circulation system. Therefore, supplementation of exogenous IGF-1 to restore the physiological level is a promising approach to inhibit atherosclerosis. In this study, we develop a self-assembling, anti-inflammatory drug-modified peptide derived from IGF-1 to mimic IGF-1 bioactivity and simultaneously with an anti-inflammatory property for the treatment of atherosclerosis.

Methods: ApoE^-/- mice were subcutaneously (s.c.) injected with the different hydrogels or natural IGF-1 protein solution per week and simultaneously fed a high-fat diet for 16 weeks. Atherosclerotic lesion formation and stability were assessed after treatment. Moreover, peritoneal macrophage and serum samples were collected to determine lipid profile and inflammatory cytokines. Concurrently, we determined the effect of bifunctional supramolecular nanofibers/hydrogel on cholesterol efflux, foam cell formation, phenotypic transformation of VSMC to macrophage-like cells, and macrophage polarization in vitro or in vivo.

Results: Bifunctional supramolecular nanofibers/hydrogel for the treatment of atherosclerosis was formed by a short peptide consisting of a tetrapeptide SSSR from C-region of growth factor IGF-1, an anti-inflammatory drug naproxen (Npx), and a powerful self-assembling D-peptide ^DF^DF. The resulting hydrogel of Npx-^DF^DFGSSSR (Hydrogel 1, H1) possessed both the anti-inflammatory and IGF-1 mimicking properties, and it efficiently promoted the expression of ABCA1 and ABCG1, thereby significantly reducing cholesterol accumulation in macrophages and preventing foam cell formation. Moreover, H1 markedly inhibited the transformation of vascular smooth muscle cells (VSMCs) into macrophage-like cells which also contributed to foam cell formation. In addition, H1 significantly reduced the inflammatory response in vitro and in vivo. Most importantly, the IGF-1 mimetic peptide showed comparable performance to IGF-1 in vivo and inhibited atherosclerosis by markedly reducing lesion area and enhancing plaque stability.

Conclusions: Our study provides a novel supramolecular nanomaterial to inhibit pathological progress of atherosclerosis through regulating cholesterol efflux and inflammation, which may contribute to the development of a promising nanomedicine for the treatment of atherosclerosis in the clinic.

An Ultrashort Peptide-Based Supramolecular Hydrogel Mimicking IGF-1 to Alleviate Glucocorticoid-Induced Sarcopenia

Sarcopenia is a common disease in older people due to aging, and it can also occur in midlife because of diseases including cancer. Sarcopenia, characterized by rapid loss of muscle mass and accelerated loss of function, can lead to adverse outcomes such as frailty, falls, and even mortality. The development of pharmacological and therapeutic approaches to treat sarcopenia remains challenging. The growth status and quantity of myoblasts are the key factors directly affecting muscle formation. Therefore, enhancing the function of myoblasts is crucial for the treatment of sarcopenia. In our study, we introduced an insulin-like growth factor-I (IGF-1) mimicking supramolecular nanofibers/hydrogel formed by Nap-FFGSSSR that effectively promoted proliferation and significantly reduced dexamethasone-induced apoptosis of myoblasts, assisted myoblasts to differentiate into myotubes, and prevented the fibrosis of muscle tissue and the deposition of collagen, ultimately achieving outstanding effects in the treatment of sarcopenia. The RNA-sequencing results revealed that our nanofibers possessed similar bioactivity to the growth factor IGF-1, which increased the phosphorylation of Akt by activating the insulin signaling pathway. We prepared novel supramolecular nanomaterials to reverse glucocorticoid-induced myoblast dysfunction, which was promising for the treatment of muscular atrophy. In addition, we envisioned the generation of biofunctional nanomaterials by molecular self-assembly for the treatment of chronic diseases in middle-aged and older people.

Recent advances in stimuli-responsive in situ self-assembly of small molecule probes for in vivo imaging of enzymatic activity

Stimuli-responsive in situ self-assembly of small molecule probes into nanostructures has been promising for the construction of molecular probes for in vivo imaging. In the past few years, a number of intelligent molecular imaging probes with fluorescence, magnetic resonance imaging (MRI), positron electron tomography (PET) or photoacoustic imaging (PA) modality have been developed based on the in situ self-assembly strategy. In this minireview, we summarize the recent advances in the development of different modality imaging probes through controlling in situ self-assembly for in vivo imaging of enzymatic activity. This review starts from the brief introduction of two different chemical approaches amenable for in situ self-assembly, including (1) stimuli-mediated proteolysis and (2) stimuli-triggered biocompatible reaction. We then discuss their applications in the design of fluorescence, MRI, PET, PA, and bimodality imaging probes for in vivo imaging of different enzymes, such as caspase-3, furin, gelatinase and phosphatase. Finally, we discuss the current and prospective challenges in the stimuli-responsive in situ self-assembly strategy for in vivo imaging.

100th Anniversary of Macromolecular Science Viewpoint: Synthetic Protein Hydrogels

Our bodies are composed of soft tissues made of various proteins. In contrast, most hydrogels designed for biological applications are made of synthetic polymers. Recently, it is increasingly recognized that genetically synthesized proteins can be tailored as building blocks of hydrogels with biological, chemical, and mechanical properties similar to native soft tissues. In this Viewpoint, we summarize recent progress in synthetic protein hydrogels. We compare the structural and mechanical properties of different protein building blocks. We discuss various biocompatible cross-linking strategies based on covalent chemical reactions and noncovalent physical interactions. We introduce how stimulus-responsive conformational changes or intermolecular interactions at the molecular level can be used to engineer responsive hydrogels. We highlight that hydrogel network structures are as important as the protein sequences for the properties and functions of protein hydrogels and should be carefully designed. Despite great progress and potentials of synthetic protein hydrogels, there are still quite a few unsettled challenges and unexploited opportunities, providing abundant room for future investigation and development, particularly as this field is quickly expanding beyond its initial stage. We discuss a number of possible directions, including optimizing protein production and reducing cost, engineering anisotropic hydrogels to better mimic native tissues, rationally designing hydrogel mechanical properties, investigating interplays of hydrogels and residing cells for 3D cell culture and organoid construction, and evaluating long-term cytotoxicity and immune response.

In situ construction of a self-assembled AIE probe for tumor hypoxia imaging

This communication reported a hypoxia-responsive fluorescent probe based on the in situ concept, which combines a water-soluble azobenzene containing copolymer with a carbamate linkage and an anionic water-soluble aggregation-induced emission fluorogen (AIEgen) tetraphenylethene (TPE). The water-soluble copolymer can be transformed into a protonated primary amine containing polymer by the reduction of the azo bond and through a 1,6-self elimination cascade reaction under hypoxic conditions. The transition of anionic TPE from the molecular dispersed state to the aggregation state induced by self-assembly with the cationic polymer would lead to an obvious increase in fluorescence according to the AIE characteristics.

Metal ions modulation of the self-assembly of short peptide conjugated nonsteroidal anti-inflammatory drugs (NSAIDs)

Metal ions are essential components that help maintain the processes of normal life, and they can be used to fabricate self-assembled building blocks for peptide derivatives, proteins and nucleic acids. Here, we have developed a novel strategy to construct supramolecular hydrogels modulated using metal cations. Upon introducing a variety of metal ions into aqueous solutions of a gelator (naproxen-FF), including a nonsteroidal anti-inflammatory drug (NSAID) and dipeptide, we obtain stable hydrogels under neutral or alkaline conditions. It is found that these hydrogels with three-dimensional nanofiber networks exhibit excellent mechanical properties and thixotropy, as well as superb responsivity to multiple metal ions. Due to the significance of potassium ions in biological processes, the K-triggered hydrogel has been chosen as a model, and its self-assembly mechanism has been explored via various spectral analysis processes. In addition, the self-assembly performances of peptides are significantly affected by the chemical structures of the gelator molecules. This work provides deep insight into the aggregation mechanism of dipeptide-conjugating drug molecules through introducing a variety of metal ions, laying the foundation for further biological applications.

Novel "Carrier-Free" Nanofiber Codelivery Systems with the Synergistic Antitumor Effect of Paclitaxel and Tetrandrine through the Enhancement of Mitochondrial Apoptosis

Paclitaxel (Ptx), a type of microtubule depolymerization inhibitor, is one of the main components in gastric cancer chemotherapy. Some studies have demonstrated that tetrandrine (Tet), a bisbenzylisoquinoline alkaloid, has potential antitumor effects in several cancers. Aside from the direct anticancer effect, Tet is proved to synergistically enhance the antitumor effect of Ptx in gastric cancer. However, the application of the combinational strategy is limited by the poor solubility of both drugs. Nanodrug delivery systems including polymeric nanoparticles, self-assembled nanofibers, hydrogels, etc., hold the potential to meet the need. Here, a novel supramolecular nanomaterial, based on the concept of "carrier-free nanodrugs", is reported as a feasible platform for synergistic drug delivery. Ptx-SA-RGD is obtained through the conjugation of Ptx and the tumor-specific peptide RGD (arginine-glycine-aspartic acid) with succinic acid (SA) as a linker. Ptx-SA-RGD could self-assemble into Ptx nanofibers (P-NFs) with high drug-loading efficiency. Tet was then encapsulated into P-NFs to acquire novel Ptx and Tet coloaded self-assembled nanofibers (P/T-NFs). The uptake study shows the dynamic internalization of P/T-NFs by the gastric cancer cell line MGC-803. P/T-NFs significantly triggered the accumulation of reactive oxygen species (ROS) in gastric cancer cells MGC803 and further decreased the mitochondrial membrane potential, which led to the induction of mitochondrial apoptosis with superior cytotoxicity against free drugs. Moreover, P/T-NFs suppressed the expressions of p-STAT3 and p-JAK, initiated cytochrome-C release, and promoted caspase protein expression. Furthermore, P/T-NFs demonstrated the strongest tumor-delaying effect as well as the lowest toxicity. Therefore, self-assembled nanofibers of P/T-NFs demonstrated an increase of the mitochondrial apoptosis level and a stronger antitumor effect both in vitro and in vivo, which could be a potential way to enhance the clinical efficacy and reduce the side-effects of Ptx in gastric cancer.

Synthesis of new fluorescent pyrylium dyes and study of their interaction with N-protected amino acids

Six new fluorescent styrylpyrylium dyes have been synthesized and the collisional quenching taking place upon their interaction with Z-protected amino acids has been studied.

The effect of vicinal di-halo substituents on the organogelling properties of aromatic supramolecular gelators and their application as soft templates

Vicinal di-halo substituents have a determinant effect on the supramolecular self-assembly and properties of aromatic physical gelators with application as soft templates.

A supramolecular protein chaperone for vaccine delivery

Rationale: Nanomaterials capable of specifically interacting with proteins are very important for protein storage and vaccine delivery. Supramolecular hydrogels based on peptides have emerged as promising vaccine adjuvants because of their good compatibility, ease of antigen incorporation and display, and efficiency in activating immune responses. Methods: We synthesized a self-assembling peptide (Fbp-GDFDFDYDK(γE)2-NH2, Comp. 1 ) serving as a supramolecular protein chaperone for protein antigen delivery. The gelation was triggered by simply mixing Comp. 1 and proteins. The vaccine adjuvant potential of Comp. 1 was demonstrated by using two protein antigens, ovalbumin (OVA) and hepatitis B surface antigen (HBsAg). Results: The peptide derivative Comp. 1 exhibited high protein binding capacity. Upon contacting proteins, Comp. 1 rapidly formed coassembled nanofibers/hydrogels with the proteins, which greatly delayed the release of protein antigens. Our supramolecular protein chaperone significantly stimulated specific antibody titers by assisting protein delivery to antigen-presenting cells, promoting dendritic cell (DC) maturation, prolonging antigen accumulation and retention in the lymph nodes, and eliciting the secretion of cytokines. Most importantly, our supramolecular protein chaperone strongly stimulated the cellular immune response and significantly retarded tumor growth. Conclusion: Our study demonstrated the great potential of the supramolecular protein chaperone in protein storage and delivery, vaccine production and tumor immunotherapy.

Photoresponsive Zn2+-specific metallohydrogels coassembled from imidazole containing phenylalanine and arylazopyrazole derivatives

Stimuli-responsive supramolecular gels and metallogels have been widely explored in the past decade, but the fabrication of metallogels with reversible photoresponsive properties remains largely unexplored.

Directional molecular sliding movement in peptide hydrogels accelerates cell proliferation

Adjusting the mechanical cues generated in cellular microenvironments is important for manipulating cell behaviour. Here we report on mechanically dynamic hydrogels undergoing directional domain sliding motion and investigate the effect of the well-defined mechanical motion on accelerating cell proliferation. The mechanically dynamic hydrogels were prepared via self-assembly of an amphiphilic peptide consisting of two alternating polar and nonpolar domains cross-linked by disulfide bonds at a nonsymmetrical position. The cross-linked peptide assembled into entangled nanofibers driven by the hydrophobic collapse involving a partial-length sequence due to the covalent constraint. Reduction of the disulfide bonds led to formation of non-equilibrated peptide bilayers, which underwent directional domain sliding motion along each promoted by the thermodynamically favourable transition from the partial to full hydrophobic collapse. The mechanical cues resulting from the directional domain sliding motion within the mechanically dynamic hydrogels accelerated cell proliferation when incubating cells on the hydrogel, compared to the thermodynamically static counterparts, via a mechanotransduction mechanism as supported by the facilitated translocation of yes-associated proteins into the nucleus of the cells. Our finding demonstrates the great potential of mechanically dynamic hydrogels as new-generation biomimetic extracellular matrices in tissue engineering and regeneration.

Dynamic peptide hydrogels undergoing directional domain sliding movement upon release of covalent constraint accelerate cell proliferation through a mechanotransduction pathway.

Self-assembled injectable biomolecular hydrogels towards phototherapy

Biomolecular hydrogels assembled from biomolecules, such as proteins, peptides, and polysaccharides, are promising candidates for facilitating biomedical applications due to their advantages of high biocompatibility, adjustable mechanical properties, functional diversity, and good degradability. This review focuses on current progress in the field of supramolecular injectable biomolecular hydrogels and their applications in antitumor photodynamic therapy (PDT), photothermal therapy (PTT), combined PDT and PTT, and antibacterial phototherapy with emphasis on biomolecular hydrogelators, injectable behaviors, phototherapeutic functions, and the remaining challenges. We hope that this review can provide useful inspiration for the construction and biological applications of novel photo-functional hydrogels as well as phototherapies.