Fmoc-conjugated dipeptide-based hydrogels and their pH-tuneable behaviour

In this work, we designed three dipeptide-based hydrogelators by attaching different hydrophilic amino acids (aspartic acid, glutamic acid, and glutamine) to Fmoc-conjugated phenylalanine. Self-assembly and gelation of the three dipeptides were studied in 50 mM phosphate buffer solutions. The gelation efficiency and kinetics of glutamine-based hydrogelators (FQ) were better than those of aspartic acid and glutamic acid-based hydrogelators FD and FE respectively at neutral pH. The lower gelation efficiency of FE and FD was due to the pH-responsive side chain (carboxylic acid) compared to FQ, where amide group was present as a side chain. Three hydrogelators exhibited better gelation efficiency at lower pHs as the anionic carboxylate group was protonated to the carboxylic group, facilitating better self-assembly and gelation processes. Thioflavin-T (ThT) binding study of hydrogels indicated the formation of β-sheet-like structure in the hydrogel state. The self-assembly process was inspected using molecular dynamic study, revealing that the newly developed FQ gelator possesses a higher aggregation tendency than FE and FD. Finally, these peptide-based injectable biomaterials were examined using fluorescence and FT-IR spectroscopy, scanning electron microscopy, and rheology.

Advances in ionic liquid-based antimicrobial wound healing platforms

Wound infections, marked by the proliferation of microorganisms at surgical sites, necessitate the development of innovative wound dressings with potent bactericidal properties to curb microbial growth and prevent bacterial infiltration. This study explores the recent strides in utilizing ionic liquid-based polymers as highly promising antimicrobial agents for advanced wound healing applications. Specifically, cationic polymers containing quaternary ammonium, imidazolium, guanidinium, pyridinium, triazolium, or phosphonium groups have emerged as exceptionally effective antimicrobial compounds. Their mechanism of action involves disrupting bacterial membranes, thereby preventing the development of resistance and minimizing toxicity to mammalian cells. This comprehensive review not only elucidates the intricate dynamics of the skin's immune response and the various stages of wound healing but also delves into the synthesis methodologies of ionic liquid-based polymers. By spotlighting the practical applications of antimicrobial wound dressings, particularly those incorporating ionic liquid-based materials, this review aims to lay the groundwork for future research endeavors in this burgeoning field. Through a nuanced examination of these advancements, this article seeks to contribute to the ongoing progress in developing cutting-edge wound healing platforms that can effectively address the challenges posed by microbial infections in surgical wounds.

Current status of development and biomedical applications of peptide-based antimicrobial hydrogels

Microbial contamination poses a serious threat to human life and health. Through the intersection of material science and modern medicine, advanced bionic hydrogels have shown great potential for biomedical applications due to their unique bioactivity and ability to mimic the extracellular matrix environment. In particular, as a promising antimicrobial material, the synthesis and practical biomedical applications of peptide-based antimicrobial hydrogels have drawn increasing research interest. The synergistic effect of peptides and hydrogels facilitate the controlled release of antimicrobial agents and mitigation of their biotoxicity while achieving antimicrobial effects and protecting the active agents from degradation. This review reports on the progress and trends of researches in the last five years and provides a brief outlook, aiming to provide theoretical background on peptide-based antimicrobial hydrogels and make suggestions for future related work.

Constructing ROS-Responsive Supramolecular Gel with Innate Antibacterial Properties

Bacterial infections, especially antibiotic-resistant bacterial infections, pose a significant threat to human health. Supramolecular gel with innate antibacterial properties is an advanced material for the treatment of bacterial infections, which have attracted great attention. Herein, a reactive oxygen species (ROS)-responsive innate antibacterial supramolecular gel is developed by a bottom-up approach based on phenylalanine and hydrazide with innate antibacterial properties. The structure of gelators and intermediate products was characterized by proton nuclear magnetic resonance (1H NMR) and a high-resolution mass spectrum (HRMS). The results of 1H NMR and the Fourier transform infrared spectrum (FT-IR) experiment disclosed that hydrogen bonding and the π-π stacking force are the important self-assembly driving forces of gelators. The microstructure and mechanical properties of gel were studied by Scanning electron microscope (SEM) and Rheometer, respectively. An in vitro degradation experiment proved that the gelator has ROS-responsive degradation properties. The in vitro drug release experiment further manifested that antibiotic-loaded gel has ROS-responsive drug-release performances. An in vitro cytotoxicity experiment showed that the supramolecular gel has good biocompatibility and could promote cell proliferation. The in vitro antibacterial experiment proved that the supramolecular gel has excellent inherent antibacterial properties, and the antibacterial rate against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was 98.6% and 99.1%, respectively. The ROS-responsive supramolecular gel as a novel antibacterial agent has great application prospects in treating antibiotic-resistant bacterial-infected wounds and preventing the development of bacterial resistance.

Modified Chemoselective Reduction and Consecutive Regioselective Deuteration Reaction Catalyzed by B(C6F5)3

An efficient chemoselective reduction of isatin derivatives using catalyst B(C₆F₅)₃, benzyldimethylsilane, and H₂O is described. Notably, a small amount of water is shown to be a highly effective reaction promoter that decreases the reaction time and temperature for the synthesis of indolin-3-ones. Moreover, using method, excellent deuterium incorporation is achieved via the catalytic α-deuteration of indolin-3-ones using B(C₆F₅)₃ and D₂O.

Hydrogels with intrinsic antibacterial activity prepared from naphthyl anthranilamide (NaA) capped peptide mimics

In this study, we prepared antibacterial hydrogels through the self-assembly of naphthyl anthranilamide (NaA) capped amino acid based cationic peptide mimics. These ultra-short cationic peptide mimics were rationally designed with NaA as a capping group, L-phenylalanine, a short aliphatic linker, and a cationic group. The synthesized peptide mimics efficiently formed hydrogels with minimum gel concentrations between 0.1 and 0.3%w/v. The resulting hydrogels exhibited desirable viscoelastic properties which can be tuned by varying the cationic group, electronegative substituent, or counter anion. Importantly, nanofibers from the NaA-capped cationic hydrogels were found to be the source of hydrogels' potent bacteriacidal actvity against both Gram-positive and Gram-negative bacteria while remaining non-cytotoxic. These intrinsically antibacterial hydrogels are ideal candidates for further development in applications where bacterial contamination is problematic.

Injectable thermo-sensitive and wide-crack self-healing hydrogel loaded with antibacterial anti-inflammatory dipotassium glycyrrhizate for full-thickness skin wound repair

Severe skin injuries are hard to repair and susceptible to bacterial infection. Development of a versatile antimicrobial anti-inflammatory hydrogel dressing that eliminates concern over antibiotic resistance is urgently needed but remains an elusive goal. Our research, described herein, the design and fabrication of a new family of supramolecular hydrogels based on hydroxypropyl chitosan (HPCS) and poly(N-isopropylacrylamide) (PNIPAM) may prove to be that goal. Employing the reversible cross-linking by β-cyclodextrin (β-CD) and adamantyl (AD) pre-assembly, the hydrogels can be formed in a facile one-pot method. Additionally, the structure and performance of the hydrogels can be controlled by a simple adjustment of the AD content. The obtained hydrogels exhibit an abundance of desired properties; they are injectable, thermosensitive, highly ductile, self-healable (will self-heal recurring damage to the hydrogel bandage of up to several millimeters wide), biocompatible, and have antimicrobial activity against Staphylococcus aureus when infused with dipotassium glycyrrhizinate (DG). Using a mouse full-thickness skin defect model, in vivo wound healing evaluations revealed that the DG-loaded hydrogels (HP-3/DG10) applied to the wound resulted in rapid wound closure. The hydrogels promoted efficient tissue remolding, collagen deposition, decreased inflammation and performed better than the control groups of commercial Tegaderm^TM film and 3M dressing. Given their multifunctionality and in vivo efficacy, the DG-loaded HP hydrogels hold great potential as a wound dressing for full-thickness skin repair. STATEMENT OF SIGNIFICANCE: Injectable hydrogels are receiving increasing attention as an ideal wound dressing. To the best of our knowledge, however, injectable and wide-crack self-healing hydrogel dressings have been hardly studied. A versatile antimicrobial hydrogel without drug resistance or cytotoxicity is also highly required. Therefore, in the present study, we constructed injectable thermosensitive and wide-crack self-healing hydrogels with antibacterial and anti-inflammatory properties. These hydrogels were developed through novel strategies of the wide-crack self-healing design and the loading of the bioactive antibacterial and anti-inflammatory agent dipotassium glycyrrhizinate. The simple preparation method and multifunctionality of the studied hydrogel composites may provide important insights for the development of future biomaterials for wound dressings and other biomedical applications.

Low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, wound healing, anticancer, drug delivery, bioimaging and 3D bioprinting applications

In this review, we have focused on the design and development of low molecular weight self-assembling peptide-based materials for various applications including cell proliferation, tissue engineering, antibacterial, antifungal, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting. The first part of the review describes about stimuli and various noncovalent interactions, which are the key components of various self-assembly processes for the construction of organized structures. Subsequently, the chemical functionalization of the peptides has been discussed, which is required for the designing of self-assembling peptide-based soft materials. Various low molecular weight self-assembling peptides have been discussed to explain the important structural features for the construction of defined functional nanostructures. Finally, we have discussed various examples of low molecular weight self-assembling peptide-based materials for cell culture, antimicrobial, anti-inflammatory, anticancer, wound healing, drug delivery, bioimaging and 3D bioprinting applications.

Electrostatic interactions regulate the release of small molecules from supramolecular hydrogels

Supramolecular hydrogels have great potential as biomaterials for sustained delivery of therapeutics. While peptide-based supramolecular hydrogels have been developed that show promise for drug delivery applications, the high cost of production has limited their widespread adoption. Low molecular weight (LMW) supramolecular hydrogels are emerging as attractive and inexpensive alternatives to peptide-based hydrogels. We recently reported novel cationic fluorenylmethyloxycarbonyl-modified phenylalanine (Fmoc-Phe) hydrogels for localized and sustained in vivo release of an anti-inflammatory agent for functional pain remediation. In an effort to further elucidate design principles to optimize these materials for delivery of a variety of molecular agents, we herein report a systematic examination of electrostatic effects on the release of cargo molecules from Fmoc-Phe derived hydrogels. Specifically, we interrogate the release of cationic, anionic, and neutral cargo molecules from a series of cationic and anionic Fmoc-Phe derived hydrogels. We observed that cargo was readily released from the hydrogels except when the cargo and hydrogel network had complementary charges, in which case the cargo was highly retained in the network. These results demonstrate that the electrostatic characteristics of both the hydrogel network and the specific cargo are critical design parameters in the formulation of LMW supramolecular hydrogel systems in the development of next-generation materials for drug delivery applications.

Ultrashort Peptide Self-Assembly: Front-Runners to Transport Drug and Gene Cargos

The translational therapies to promote interaction between cell and signal come with stringent eligibility criteria. The chemically defined, hierarchically organized, and simpler yet blessed with robust intermolecular association, the peptides, are privileged to make the cut-off for sensing the cell-signal for biologics delivery and tissue engineering. The signature service and insoluble network formation of the peptide self-assemblies as hydrogels have drawn a spell of research activity among the scientists all around the globe in the past decades. The therapeutic peptide market players are anticipating promising growth opportunities due to the ample technological advancements in this field. The presence of the other organic moieties, enzyme substrates and well-established protecting groups like Fmoc and Boc etc., bring the best of both worlds. Since the large sequences of peptides severely limit the purification and their isolation, this article reviews the account of last 5 years' efforts on novel approaches for formulation and development of single molecule amino acids, ultra-short peptide self-assemblies (di- and tri- peptides only) and their derivatives as drug/gene carriers and tissue-engineering systems.

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.

Anthranilamide-based Short Peptides Self-Assembled Hydrogels as Antibacterial Agents

In this study, we describe the synthesis and molecular properties of anthranilamide-based short peptides which were synthesised via ring opening of isatoic anhydride in excellent yields. These short peptides were incorporated as low molecular weight gelators (LMWG), bola amphiphile, and C3-symmetric molecules to form hydrogels in low concentrations (0.07-0.30% (w/v)). The critical gel concentration (CGC), viscoelastic properties, secondary structure, and fibre morphology of these short peptides were influenced by the aromaticity of the capping group or by the presence of electronegative substituent (namely fluoro) and hydrophobic substituent (such as methyl) in the short peptides. In addition, the hydrogels showed antibacterial activity against S. aureus 38 and moderate toxicity against HEK cells in vitro.