Peptide-Based Hydrogels: New Materials for Biosensing and Biomedical Applications

Peptide-based hydrogels have attracted increasing attention for biological applications and diagnostic research due to their impressive features including biocompatibility and biodegradability, injectability, mechanical stability, high water absorption capacity, and tissue-like elasticity. The aim of this review will be to present an updated report on the advancement of peptide-based hydrogels research activity in recent years in the field of anticancer drug delivery, antimicrobial and wound healing materials, 3D bioprinting and tissue engineering, and vaccines. Additionally, the biosensing applications of this key group of hydrogels will be discussed mainly focusing the attention on cancer detection.

Intramitochondrial Disulfide Polymerization Controls Cancer Cell Fate

Recent advances in supramolecular chemistry research have led to the development of artificial chemical systems that can form self-assembled structures that imitate proteins involved in the regulation of cellular function. However, intracellular polymerization systems that operate inside living cells have been seldom reported. In this study, we developed an intramitochondrial polymerization-induced self-assembly system for regulating the cellular fate of cancer cells. It showed that polymeric disulfide formation inside cells occurred due to the high reactive oxygen species (ROS) concentration of cancer mitochondria. This polymerization barely occurs elsewhere in the cell owing to the reductive intracellular environment. The polymerization of the thiol-containing monomers further increases the ROS level inside the mitochondria, thereby autocatalyzing the polymerization process and creating fibrous polymeric structures. This process induces dysfunction of the mitochondria, which in turn activates cell necroptosis. Thus, this in situ polymerization system shows great potential for cancer treatment, including that of drug-resistant cancers.

Amphiphilic self-assembly peptides: Rational strategies to design and delivery for drugs in biomedical applications

Amphiphilic self-assembling peptides are widely used in tissue and cell engineering, antimicrobials, drug-delivery systems and other biomedical fields due to their good biocompatibility, functionality, flexibility of design and synthesis, and tremendous potential as delivery carriers for drugs. Currently, the design and study of amphipathic peptides by a bottom-up method to develop new biomedical materials have become a hot topic. However, defined rules have not been established for the design and development of self-assembled peptides. Therefore, the focus of this review is to summarize and provide several rational strategies for the design and study of amphiphilic self-assembly peptides. In addition, this paper also describes the types and general self-assembling mechanism of amphipathic peptides, and outlines their applications in the delivery of hydrophobic drugs, nucleic acid drugs, peptide drugs and vaccines. Amphiphilic self-assembled peptides are expected to exploit new functional materials for drug delivery and other applications.

NBD-based synthetic probes for sensing small molecules and proteins: design, sensing mechanisms and biological applications

Compounds with a nitrobenzoxadiazole (NBD) skeleton exhibit prominent useful properties including environmental sensitivity, high reactivity toward amines and biothiols (including H2S) accompanied by distinct colorimetric and fluorescent changes, fluorescence-quenching ability, and small size, all of which facilitate biomolecular sensing and self-assembly. Amines are important biological nucleophiles, and the unique activity of NBD ethers with amines has allowed for site-specific protein labelling and for the detection of enzyme activities. Both H2S and biothiols are involved in a wide range of physiological processes in mammals, and misregulation of these small molecules is associated with numerous diseases including cancers. In this review, we focus on NBD-based synthetic probes as advanced chemical tools for biomolecular sensing. Specifically, we discuss the sensing mechanisms and selectivity of the probes, the design strategies for multi-reactable multi-quenching probes, and the associated biological applications of these important constructs. We also highlight self-assembled NBD-based probes and outline future directions for NBD-based chemosensors. We hope that this comprehensive review will facilitate the development of future probes for investigating and understanding different biological processes and aid the development of potential theranostic agents.

The bright fluorescence of non-aromatic molecules in aqueous solution originates from pH-induced CTE behavior

Non-aromatic fluorescent materials with inherent visible light emission have received widespread attention. In this work, a biomimetic fluorescent molecule CA-AEP with a dipeptide structure is introduced. CA-AEP will emit bright biomimetic fluorescence in aqueous solutions by adjusting the pH, which has never been reported. This unique luminescent characteristic can be rationalized by the clustering-triggered emission (CTE) mechanism. In addition, CA-AEP can be used to monitor the maximum dynamic pH in the alkaline range of aqueous systems. Finally, the cytotoxicity assay to A549 cells showed that CA-AEP was non-toxic. Therefore, this work provides a new type of luminogen, which has potential application prospects in the field of environmental monitoring and cell biology.

Supramolecular Self-Assembled Nanofibers Efficiently Activate the Precursor of Hepatocyte Growth Factor for Angiogenesis in Myocardial Infarction Therapy

The reconstruction of blood perfusion is a crucial therapeutic method to save and protect cardiac function after acute myocardial infarction (AMI). The activation of the hepatocyte growth factor precursor (pro-HGF) has a significant effect on promoting angiogenesis and antiapoptosis. The oxygen/glucose deprivation (OGD) caused by AMI could induce vascular adventitia fibroblasts to differentiate into myofibroblasts and secrete the pro-HGF. Meanwhile, the specific Met receptor of the hepatocyte growth factor (HGF) is upregulated in endothelial cells during AMI. However, the poor prognosis of AMI suggests that the pro-HGF is not effectively activated. Improving the activation efficiency of the pro-HGF may play a positive role in the treatment of AMI. Herein, we designed supramolecular nanofibers self-assembled by compound 1 (Comp.1, Nap-FFEG-IVGGYPWWMDV), which can strongly activate the pro-HGF and initiate HGF-Met signaling. Studies have proven that Comp.1 possesses a better ability to activate the pro-HGF to perform antiapoptosis and pro-angiogenesis. In vivo results have confirmed that the retention time of Comp.1 and its accumulation in the infarct area of the heart are promoted. Moreover, Comp.1 plays an effective role in promoting angiogenesis in the marginal area of AMI, reducing myocardial fibrosis, and protecting cardiac function. Herein, we will optimize the structure of bioactive peptides through supramolecular self-assembly and amplify their therapeutic effect by improving their efficiency, providing a new strategy for the therapy of AMI.

Microenvironment pH-Induced Selective Cell Death for Potential Cancer Therapy Using Nanofibrous Self-Assembly of a Peptide Amphiphile

Self-assembly of synthetic molecules has been drawing broad attention as a novel emerging approach in drug discovery. Here, we report selective cell death induced by a novel peptide amphiphile that self-assembles to form entangled nanofibers (hydrogel) based on intracellular pH (pH_i). We found that a palmitoylated hexapeptide (C₁₆-VVAEEE) formed a hydrogel below pH 7. The formation of the nanofibrous self-assembly was responsive to a small pH change around pH 7. The cytotoxicity of C₁₆-VVAEEE was correlated with pH_i of cells. Microscope observation demonstrated the self-assembly of C₁₆-VVAEEE inside HEK293 cells. In vivo experiments revealed that the transcutaneous administration of C₁₆-VVAEEE showed remarkable anti-tumor activity. This study proposes that distinct microenvironment inside living cells can be used as a trigger for the intracellular self-assembly of a peptide amphiphile, which provide a new clue to drug discovery.

pH response of a hydroxyl-functionalized luminescent metal–organic framework based phosphor

The ligand sensitized Tb³⁺ centered emission of Tb-doped Y-based hydroxyl functionalized MOFs has been utilized for pH sensing in the visible range.

A review on recent advances in polymer and peptide hydrogels

In this review, we focus on the very recent developments on the use of the stimuli responsive properties of polymer hydrogels for targeted drug delivery, tissue engineering, and biosensing utilizing their different optoelectronic properties. Besides, the stimuli-responsive hydrogels, the conducting polymer hydrogels are discussed, with specific attention to the energy generation and storage behavior of the xerogel derived from the hydrogel. The electronic and ionic conducting gels have been discussed that have applications in various electronic devices, e.g., organic field effect transistors, soft robotics, ionic skins, and sensors. The properties of polymer hybrid gels containing carbon nanomaterials have been exemplified here giving attention to applications in supercapacitors, dye sensitized solar cells, photocurrent switching, etc. Recent trends in the properties and applications of some natural polymer gels to produce thermal and acoustic insulating materials, drug delivery vehicles, self-healing material, tissue engineering, etc., are discussed. Besides the polymer gels, peptide gels of different dipeptides, tripeptides, oligopeptides, polypeptides, cyclic peptides, etc., are discussed, giving attention mainly to biosensing, bioimaging, and drug delivery applications. The properties of peptide-based hybrid hydrogels with polymers, nanoparticles, nucleotides, fullerene, etc., are discussed, giving specific attention to drug delivery, cell culture, bio-sensing, and bioimaging properties. Thus, the present review delineates, in short, the preparation, properties, and applications of different polymer and peptide hydrogels prepared in the past few years.