Thermoresponsive Injectable Hydrogel To Mimic the Heat- and Strain-Stiffening Behavior of Biopolymers toward Muscle Cell Proliferation

A hydrogel based on Fe(II)-GMP demonstrates tunable emission, self-healing mechanical strength and Fenton chemistry-mediated notable antibacterial properties

Supramolecular hydrogels serve as an excellent platform to enable in situ reactive oxygen species (ROS) generation while maintaining controlled localized conditions, thereby mitigating cytotoxicity. Herein, we demonstrate hydrogel formation using guanosine-5'-monophosphate (GMP) with tetra(4-carboxylphenyl) ethylene (1) to exhibit aggregation-induced emission (AIE) and tunable mechanical strength in the presence of divalent metal ions such as Ca2+, Mg2+, and Fe2+. The addition of divalent metal ions leads to structural transformation in the metallogels (M-1GMP). Furthermore, the incorporation of Fe2+ ions into the hydrogel (Fe-1GMP) promotes the Fenton reaction that could be upregulated upon adding ascorbic acid (AA), demonstrating antibacterial efficacy via ROS generation. In vitro studies on AA-loaded Fe-1GMP demonstrate excellent bacterial killing efficacy against E. coli, S. aureus and vancomycin-resistant enterococci (VRE) strains. Finally, in vivo studies involving topical administration of Fe-1GMP to Balb/c mice with skin infections further suggest the potential antibacterial efficacy of the hydrogel. Taken together, the hydrogel with its unique combination of mechanical tunability, ROS generation capability and antibacterial efficacy can be used for biomedical applications, particularly in wound healing and infection control.

Stimuli-Responsive Control over Self-Assembled Nanostructures in Sequence-Specific Functional Block Copolymers

The precise sequence of a protein's primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin (C) and ferrocene (F) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UVB light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F, P- b -F- b -C, and P- b -C- r -F affects the extent of the hydrophobic-hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles.

Supramolecular Assembly and Thermogelation Strategies Using Peptide-Polymer Conjugates

Peptide-polymer conjugates (PPCs) are of particular interest in the development of responsive, adaptive, and interactive materials due to the benefits offered by combining both building blocks and components. This review presents pioneering work as well as recent advances in the design of peptide-polymer conjugates, with a specific focus on their thermoresponsive behavior. This unique class of materials has shown great promise in the development of supramolecular structures with physicochemical properties that are modulated using soft and biorthogonal external stimuli. The temperature-induced self-assembly of PPCs into various supramolecular architectures, gelation processes, and tuning of accessible processing parameters to biologically relevant temperature windows are described. The discussion covers the chemical design of the conjugates, the supramolecular driving forces involved, and the mutual influence of the polymer and peptide segments. Additionally, some selected examples for potential biomedical applications of thermoresponsive PPCs in tissue engineering, delivery systems, tumor therapy, and biosensing are highlighted, as well as perspectives on future challenges.

Injectable Thermo-Responsive Peptide Hydrogels and Its Enzyme Triggered Dynamic Self-Assembly

Endogenous stimuli-responsive injectable hydrogels hold significant promise for practical applications due to their spatio-temporal controllable drug delivery. Herein, we report a facile strategy to construct a series of in situ formation polypeptide hydrogels with thermal responsiveness and enzyme-triggered dynamic self-assembly. The thermo-responsive hydrogels are from the diblock random copolymer mPEG-b-P(Glu-co-Tyr). The L-glutamic acid (Glu) segments with different γ-alkyl groups, including methyl, ethyl, and n-butyl, offer specific secondary structure, facilitating the formation of hydrogel. The L-tyrosine (Tyr) residues not only provide hydrogen-bond interactions and thus adjust the sol-gel transition temperatures, but also endow polypeptide enzyme-responsive properties. The PTyr segments could be phosphorylated, and the phosphotyrosine copolymers were amphiphilies, which could readily self-assemble into spherical aggregates and transform into sheet-like structures upon dephosphorylation by alkaline phosphatase (ALP). P(MGlu-co-Tyr/P) and P(MGlu-co-Tyr) copolymers showed good compatibility with both MC3T3-E1 and Hela cells, with cell viability above 80% at concentrations up to 1000 μg/mL. The prepared injectable polypeptide hydrogel and its enzyme-triggered self-assemblies show particular potential for biomedical applications.

pH-Responsive Co-Assembled Peptide Hydrogel to Inhibit Drug-Resistant Bacterial Infection and Promote Wound Healing

Drug-resistant bacterial infection and biofilm formation are the key inhibitors of wound healing, and new strategies are urgently needed to address these issues. In this study, we designed a pH-responsive co-assembled peptide hydrogel to inhibit Methicillin-resistant Staphylococcus aureus (MRSA) infection and promote wound healing. We synthesized a cationic short peptide (Nap-FFKKK) and a co-assembled hydrogel with curcumin at pH ∼ 7.8. The loaded curcumin was continuously released in a weak acid environment (pH ∼ 5.5). The lysine-rich cationic peptide inhibited biofilm formation in MRSA via electrostatic interaction with the negatively charged bacterial cell surface and, thus, provided a reinforcing antibacterial effect with curcumin. In vitro antibacterial experiments showed that the co-assembled system considerably reduced the minimum inhibitory concentration of curcumin against MRSA by 10-fold and promoted wound healing in a mouse model of MRSA-infected wounds. This study provides a simple and promising strategy to treat drug-resistant bacterial infections in wounds.

Metal co-factors to enhance catalytic activity of short prion-derived peptide sequences

Development of biomolecular enzyme mimics to efficiently catalyse biochemical reactions are of prime relevance for the bulk scale production of industrially relevant biocatalyst. In this regard, amyloidogenic peptides act as suitable self-assembling scaffolds, providing stable nanostructures with high surface area facilitating biocatalysis. Herein, we rationally design two positional amyloidogenic peptide isomers, "Fmoc-VYYAHH (1)" and "Fmoc-VHHAYY (2)" considering catalytic and metal binding affinity of histidine and tyrosine when placed in periphery vs. inner core of the peptide sequence. With an ultimate objective of designing metalloenzyme mimic, we choose Co2+ and Cu2+ as divalent transition metal cations for peptide complexation to aid in catalysis. After optimizing self-assembly of innate peptides, we investigate metal-peptide binding ratio and co-ordination, finally selecting 1:1 peptide metal complex suitable for biocatalysis. Metallopeptides act as better catalysts than the innate peptides as acyl esterase when tyrosines were present at the periphery. Kinetic parameters for assessing hydrolysis rate were calculated by fitting data into Michaelis-Menten and Lineweaver Burk plots. Catalytic activity is altered depending on the stability of peptide metal complexes. 2-Cu acting as the best biocatalyst with a kcat/KM = 0.08 M/s. The protocols mentioned in this chapter meticulously cover the design, synthesis, self-assembly and enzyme kinetics.

Thermo-Chemical Cues-Mediated Strategy to Control Peptide Self-Assembly and Charge Transfer Complexation

Peptide amphiphiles (PAs) are known for their remarkable ability to undergo molecular self-assembly, a process that is highly responsive to the local microenvironment. Herein, we design a pyrene tethered peptide amphiphile Py-VFFAKK, 1 that exhibits pathway-driven self-assembly from metastable nanoparticles to kinetically controlled nanofibers and thermodynamically stable twisted bundles upon modulations in pH, temperature, and chemical cues. The presence of the pyrene moiety ensures donation of the electron to an electron acceptor, namely, 7,7,8,8-tetracyanoquinodimethane (TCNQ), to form a supramolecular charge transfer complex in aqueous solution that was studied in detail with microscopic and spectroscopic techniques. Excitation of the donor species in its excimer state facilitates electron donation to the acceptor moiety, paving away a long-lived charge-separated state that persists for over a nanosecond, as ascertained through transient absorption spectroscopy. Finally, the self-assembled charge transfer complex is explored toward antimicrobial properties with Escherichia coli while maintaining biocompatibility toward L929 mice fibroblast cells.