Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators

Mechanism of Peptide Self-assembly and Its Study in Biomedicine

The development of peptide-based materials is one of the most challenging aspects of biomaterials research in recent years. The assembly of peptides is mainly controlled by forces such as hydrogen bonding, hydrophobic interaction, electrostatic interaction, and π-π accumulation. Peptides have unique advantages such as simple structure, easy synthesis, good biocompatibility, non-toxicity, easy modification, etc. These factors make peptides turn into ideal biomedical materials, and they have a broad application prospect in biomedical materials, and thus have received wide attention. In this review, the mechanism and classification of peptide self-assembly and its applications in biomedicine and hydrogels were introduced.

Stereochemical Behavior of Pyrrolo-Pyrazole Peptidomimetics Promoting Phase-Selective Supramolecular Organogels

Supramolecular gels were developed by taking advantage of an assembly of small dipeptides containing pyrrolo-pyrazole scaffolds. The dipeptides were prepared through a robust and ecofriendly synthetic approach from the commercially available starting materials of diazoalkanes and maleimides. By playing with the functionalization of the scaffold, the choice of the natural amino acid, and the stereochemistry, we were able to obtain phase-selective gels. In particular, one peptidomimetic showed gelation ability and thermoreversibility in aromatic solvents at very low concentrations. Rheology tests showed a typical viscoelastic solid profile, indicating the formation of strong gels that were stable under high mechanical deformation. NMR studies were performed, allowing us to determine the conformational and stereochemical features at the base of the supramolecular interactions.

Light-modulation of gel stiffness: a glyconucleoside based bolaamphiphile as a photo-cleavable low molecular weight gelator

Photo-cleavable glyconucleoside bolaamphiphiles containing a nitrophenyl unit feature gelation abilities in aqueous media. The stiffness of the resulting gels can be modulated upon light irradiation thanks to the photocleavage reaction of nitrophenyl moieties.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Manipulating supramolecular gels with surfactants: Interfacial and non-interfacial mechanisms

Gel is a class of self-supporting soft materials with applications in many fields. Fast, controllable gelation, micro/nano structure and suitable rheological properties are essential considerations for the design of gels for specific applications. Many methods can be used to control these parameters, among which the additive approach is convenient as it is a simple physical mixing process with significant advantages, such as avoidance of pH change and external energy fields (ultrasound, UV light and others). Although surfactants are widely used to control the formation of many materials, particularly nanomaterials, their effects on gelation are less known. This review summarizes the studies that utilized different surfactants to control the formation, structure, and properties of molecular and silk fibroin gels. The mechanisms of surfactants, which are interfacial and non-interfacial effects, are classified and discussed. Knowledge and technical gaps are identified, and perspectives for further research are outlined. This review is expected to inspire increasing research interest in using surfactants for designing/fabricating gels with desirable formation kinetics, structure, properties and functionalities.

Food Peptides for the Nutricosmetic Industry

In recent years, numerous reports have described bioactive peptides (biopeptides)/hydrolysates produced from various food sources. Biopeptides are considered interesting for industrial application since they show numerous functional properties (e.g., anti-aging, antioxidant, anti-inflammatory, and antimicrobial properties) and technological properties (e.g., solubility, emulsifying, and foaming). Moreover, they have fewer side effects than synthetic drugs. Nevertheless, some challenges must be overcome before their administration via the oral route. The gastric, pancreatic, and small intestinal enzymes and acidic stomach conditions can affect their bioavailability and the levels that can reach the site of action. Some delivery systems have been studied to avoid these problems (e.g., microemulsions, liposomes, solid lipid particles). This paper summarizes the results of studies conducted on biopeptides isolated from plants, marine organisms, animals, and biowaste by-products, discusses their potential application in the nutricosmetic industry, and considers potential delivery systems that could maintain their bioactivity. Our results show that food peptides are environmentally sustainable products that can be used as antioxidant, antimicrobial, anti-aging, and anti-inflammatory agents in nutricosmetic formulations. Biopeptide production from biowaste requires expertise in analytical procedures and good manufacturing practice. It is hoped that new analytical procedures can be developed to simplify large-scale production and that the authorities adopt and regulate use of appropriate testing standards to guarantee the population's safety.

Delivery of Active Peptides by Self-Healing, Biocompatible and Supramolecular Hydrogels

Supramolecular and biocompatible hydrogels with a tunable pH ranging from 5.5 to 7.6 lead to a wide variety of formulations useful for many different topical applications compatible with the skin pH. An in vitro viability/cytotoxicity test of the gel components demonstrated that they are non-toxic, as the cells continue to proliferate after 48 h. An analysis of the mechanical properties demonstrates that the hydrogels have moderate strength and an excellent linear viscoelastic range with the absence of a proper breaking point, confirmed with thixotropy experiments. Two cosmetic active peptides (Trifluoroacetyl tripeptide-2 and Palmitoyl tripeptide-5) were successfully added to the hydrogels and their transdermal permeation was analysed with Franz diffusion cells. The liquid chromatography-mass spectrometry (HPLC-MS) analyses of the withdrawn samples from the receiving solutions showed that Trifluoroacetyl tripeptide-2 permeated in a considerable amount while almost no transdermal permeation of Palmitoyl tripeptide-5 was observed.

Spectroscopic Characterization of the Binding and Release of Hydrophilic, Hydrophobic and Amphiphilic Molecules from Ovalbumin Supramolecular Hydrogels

Protein-based hydrogels have attracted growing attention for pharmaceutical and biomedical applications. Ovalbumin (OVA), the hen egg white albumin, possessing good foaming and gelling properties and being widely used in the food industry, has recently been indicated as a potential pharmaceutical vehicle. In this study, the binding and release properties of pure OVA hydrogels were investigated by electron paramagnetic resonance (EPR) spin labeling. The comparative analysis between OVA and serum albumin (SA) hydrogels revealed the same release kinetics of hydrophilic 3-carbamoyl-proxyl and 3-carboxy-proxyl, suggesting the diffusion-dominated release of small probes from both hydrogel types. The results obtained with the amphiphilic 16-doxylstearate (16-DS) indicate that OVA, unlike SAs, does not possess a specific fatty acid binding site. However, the OVA hydrogels were able to accommodate a two-fold excess of 16-DS, resulting from protein thermally induced conformational changes, as confirmed by Raman spectroscopy. Similarly, the hydrophobic modified paullone ligand HL, which was initially free in the OVA solution, was bound in the hydrogel. The hydrogels were found to retain a significant amount of 16-DS and HL after 7-day dialysis in physiological saline. The observed facilitated binding of amphiphilic/hydrophobic molecules in OVA hydrogels compared to the solution, and their sustained release, demonstrate the applicability of OVA hydrogels in pharmaceutics.

Hydrogelation tunability of bioinspired short peptides

Supramolecular assemblies of short peptides are experiencing a stimulating flowering. Herein, we report a novel class of bioinspired pentapeptides, not bearing Phe, that form hydrogels with fibrillar structures. The inherent sequence comes from the fragment 269-273 of nucleophosmin 1 protein, that is normally involved in liquid-liquid phase separation processes into the nucleolus. By means of rheology, spectroscopy, and scanning microscopy the crucial roles of the extremities in the modulation of the mechanical properties of hydrogels were elucidated. Three of four peptide showed a typical shear-thinning profile and a self-assembly into hierarchical nanostructures fibers and two of them resulted biocompatible in MCF7 cells. The presence of an amide group at C-terminal extremity caused the fastest aggregation and the major content of structured intermediates during gelling process. The tunable mechanical and structural features of this class of hydrogels render derived supramolecular systems versatile and suitable for future biomedical applications.

Self-assembly and Hydrogelation Properties of Peptides Derived from Peptic Cleavage of Aggregation-prone Regions of Ovalbumin

Egg white protein hydrolysate generated with pepsin was investigated for the presence of peptides with self-assembly and hydrogelation properties. Incubation of the hydrolysates for 16 h resulted in aggregates with significantly (p < 0.05) lower free amino nitrogen and sulfhydryl contents, and higher particle diameter and surface hydrophobicity compared to the hydrolysates. LC-MS/MS analysis of the aggregates resulted in identification of 429 ovalbumin-derived peptides, among which the top-six aggregation-prone peptides IFYCPIAIM, NIFYCPIAIM, VLVNAIVFKGL, YCPIAIMSA, MMYQIGLF, and VYSFSLASRL were predicted using AGGRESCAN by analysis of the aggregation “Hot Spots”. NIFYCPIAIM had the highest thioflavin T fluorescence intensity, particle diameter (5611.3 nm), and polydispersity index (1.0) after 24 h, suggesting the formation of β-sheet structures with heterogeneous particle size distribution. Transmission electron microscopy of MMYQIGLF, and VYSFSLASRL demonstrated the most favorable peptide self-assembly, based on the formation of densely packed, intertwined fibrils. Rheological studies confirmed the viscoelastic and mechanical properties of the hydrogels, with IFYCPIAIM, NIFYCPIAIM, VLVNAIVFKGL, and VYSFSLASRL forming elastic solid hydrogels (tan δ < 1), while YCPIAIMSA and MMYQIGLF formed viscous liquid-like hydrogels (tan δ > 1). The results provide valuable insight into the influence of peptide sequence on hydrogelation and self-assembly progression, and prospects of food peptides in biomaterial applications.

Hydrotropic Hydrogels Prepared from Polyglycerol Dendrimers: Enhanced Solubilization and Release of Paclitaxel

Polyglycerol dendrimers (PGD) exhibit unique properties such as drug delivery, drug solubilization, bioimaging, and diagnostics. In this study, PGD hydrogels were prepared and evaluated as devices for controlled drug release with good solubilization properties. The PGD hydrogels were prepared by crosslinking using ethylene glycol diglycidylether (EGDGE). The concentrations of EGDGE and PGDs were varied. The hydrogels were swellable in ethanol for loading paclitaxel (PTX). The amount of PTX in the hydrogels increased with the swelling ratio, which is proportional to EGDGE/OH ratio, meaning that heterogeneous crosslinking of PGD made high dense region of PGD molecules in the matrix. The hydrogels remained transparent after loading PTX and standing in water for one day, indicating that PTX was dispersed in the hydrogels without any crystallization in water. The results of FTIR imaging of the PTX-loaded PGD hydrogels revealed good dispersion of PTX in the hydrogel matrix. Sixty percent of the loaded PTX was released in a sink condition within 90 min, suggesting that the solubilized PTX would be useful for controlled release without any precipitation. Polyglycerol dendrimer hydrogels are expected to be applicable for rapid release of poorly water-soluble drugs, e.g., for oral administration.

External Stimuli-Responsive Characteristics of Poly(N,N′-diethylacrylamide) Hydrogels: Effect of Double Network Structure

Swelling experiments and NMR spectroscopy were combined to study effect of various stimuli on the behavior of hydrogels with a single- and double-network (DN) structure composed of poly(N,N′-diethylacrylamide) and polyacrylamide (PAAm). The sensitivity to stimuli in the DN hydrogel was found to be significantly affected by the introduction of the second component and the formation of the double network. The interpenetrating structure in the DN hydrogel causes the units of the component, which is insensitive to the given stimulus in the form of the single network (SN) hydrogel, to be partially formed as globular structures in DN hydrogel. Due to the hydrophilic PAAm groups, temperature- and salt-induced changes in the deswelling of the DN hydrogel are less intensive and gradual compared to those of the SN hydrogel. The swelling ratio of the DN hydrogel shows a significant decrease in the dependence on the acetone content in acetone–water mixtures. A certain portion of the solvent molecules bound in the globular structures was established from the measurements of the ¹H NMR spin–spin relaxation times T₂ for the studied DN hydrogel. The time-dependent deswelling and reswelling kinetics showed a two-step profile, corresponding to the solvent molecules being released and absorbed during two processes with different characteristic times.

Short Peptide-Based Smart Thixotropic Hydrogels †

Thixotropy is a fascinating feature present in many gel systems that has garnered a lot of attention in the medical field in recent decades. When shear stress is applied, the gel transforms into sol and immediately returns to its original state when resting. The thixotropic nature of the hydrogel has inspired scientists to entrap and release enzymes, therapeutics, and other substances inside the human body, where the gel acts as a drug reservoir and can sustainably release therapeutics. Furthermore, thixotropic hydrogels have been widely used in various therapeutic applications, including drug delivery, cornea regeneration and osteogenesis, to name a few. Because of their inherent biocompatibility and structural diversity, peptides are at the forefront of cutting-edge research in this context. This review will discuss the rational design and self-assembly of peptide-based thixotropic hydrogels with some representative examples, followed by their biomedical applications.