Understanding the self-assembly of Fmoc-phenylalanine to hydrogel formation

A co-assembly process for high strength and injectable dual network gels with sustained doxorubicin release performance

Adopting a non-covalent co-assembly strategy shows great potential in loading drugs efficiently and safely in drug delivery systems. However, finding an efficient method for developing high strength gels with thixotropic characteristics is still challenging. In this work, by hybridizing the low molecular weight gelator fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-F) (first single network, 1st SN) and alginate (second single network, 2nd SN) into a dual network (DN) gel, gels with high strength as well as thixotropy were prepared efficiently. The DN gels showed high strength (103 Pa in SN gels and 105 Pa in DN gels) and thixotropic characteristics (yield strain <25%; recovery ratio >85% within 100 seconds). The application performance was verified by loading doxorubicin (DOX), showing better encapsulation capacity (77.06% in 1st SN, 59.11% in 2nd SN and 96.71% in DN) and sustained release performance (lasting one week under physiological conditions) than single network gels. Experimental and DFT results allowed the elaboration of the specific non-covalent co-assembly mechanism for DN gel formation and DOX loading. The DN gels were formed by co-assembly driven by H-bond and π-π stacking interactions and then strengthened by Ca2+-coupling. Most DOX molecules co-assembled with Fmoc-F and alginate through π-π stacking and H-bond interactions (DOX-I), with a few free DOX molecules (DOX-II) left. Proven by the release dynamics test, DOX was released through a diffusion-erosion process, in an order of DOX-I first and then DOX-II. This work suggests that non-covalent co-assembly is a useful technique for effective material strengthening and drug delivery.

Low-molecular-weight gels from amino acid and peptide derivatives for controlled release and delivery

Low-molecular-weight (LMW) gelators are a versatile class of compounds able to self-assemble and to form supramolecular materials, such as gels. The use of LMW peptides to produce these gels shows many advantages, because of their wide structure tunability, the low-cost and effective synthesis, and the in vivo biocompatibility and biodegradability, which makes them optimal candidates for release and delivery applications. In addition, in these materials, the binding of the hosts may occur through a variety of noncovalent interactions, which are also the main factors responsible for the self-assembly of the gelators, and through specific interactions with the fibers or the pores of the gel matrix. This review aims to report LMW gels based on amino acid and peptide derivatives used for the release of many different species (drugs, fragrances, dyes, proteins, and cells) with a focus on the possible strategies to incorporate the cargo in these materials, and to demonstrate how versatile these self-assembled materials are in several applications.

Engineering Amino Acid and Peptide Supramolecular Architectures through Fluorination

Fluorinated non-natural amino acids are attracting considerable research interest, especially in the biomedical field and in materials science, thanks to their ability to self-assemble into peculiar supramolecular structures. The conformational changes induced by the presence of fluorine atoms obviously affect their functions, as well as the biological activity of the deriving peptides and proteins. Here, we will briefly describe the main effects of fluorination on the aggregation behavior of such building blocks, focusing in particular on their improved tendency to form fibrils, and gels therefrom. Our aim is to underline the promising potential of fluorination as a tool to affect the self-assembly features of amino acids, both when used alone and when inserted into polypeptide sequences. The ability of fluorine to influence physical, chemical, and structural properties of these substrates offers the possibility to engineer bioinspired materials with specific and tunable functions.

Comparison of the self-assembly and cytocompatibility of conjugates of Fmoc (9-fluorenylmethoxycarbonyl) with hydrophobic, aromatic, or charged amino acids

The self-assembly in aqueous solution of three Fmoc-amino acids with hydrophobic (aliphatic or aromatic, alanine or phenylalanine) or hydrophilic cationic residues (arginine) is compared. The critical aggregation concentrations were obtained using intrinsic fluorescence or fluorescence probe measurements, and conformation was probed using circular dichroism spectroscopy. Self-assembled nanostructures were imaged using cryo-transmission electron microscopy and small-angle X-ray scattering (SAXS). Fmoc-Ala is found to form remarkable structures comprising extended fibril-like objects nucleating from spherical cores. In contrast, Fmoc-Arg self-assembles into plate-like crystals. Fmoc-Phe forms extended structures, in a mixture of straight and twisted fibrils coexisting with nanotapes. Spontaneous flow alignment of solutions of Fmoc-Phe assemblies is observed by SAXS. The cytocompatibility of the three Fmoc-amino acids was also compared via MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] mitochondrial activity assays. All three Fmoc-amino acids are cytocompatible with L929 fibroblasts at low concentration, and Fmoc-Arg shows cell viability up to comparatively high concentration (0.63 mM).

Salt-induced Fmoc-tripeptide supramolecular hydrogels: a combined experimental and computational study of the self-assembly

Delving into the mechanism behind the molecular interactions at the atomic level of short-sequence peptides plays a key role in the development of nanomaterials with specific structure-property-function relationships from a bottom-up perspective. Due to their poor water solubility, the self-assembly of Fmoc-bearing peptides is usually induced by dissolution in an organic solvent, followed by a dilution step in water, pH changes, and/or a heating-cooling process. Herein, we report a straightforward methodology for the gelation of Fmoc-FFpY (F: phenylalanine; Y: tyrosine; and p: PO42-), a negatively charged tripeptide, in NaCl solution. The electrostatic interactions between Fmoc-FFpY and Na+ ions give rise to different nanofibrillar hydrogels with rheological properties and nanofiber sizes modulated by the NaCl concentration in pure aqueous media. Initiated by the electrostatic interactions between the peptide phosphate groups and the Na+ ions, the peptide self-assembly is stabilized thanks to hydrogen bonds between the peptide backbones and the π-π stacking of aromatic Fmoc and phenyl units. The hydrogels showed self-healing and thermo-responsive properties for potential biomedical applications. Molecular dynamics simulations from systems devoid of prior training not only confirm the aggregation of peptides at a critical salt concentration and the different interactions involved, but also corroborate the secondary structure of the hydrogels at the microsecond timescale. It is worth highlighting the remarkable achievement of reproducing the morphological behavior of the hydrogels using atomistic simulations. To our knowledge, this study is the first to report such a correspondence.

A Unique Temperature-Induced Reverse Supramolecular Chirality-Assisted Gel-to-Gel Transition

Supramolecular hydrogels typically undergo a gel-to-sol transition with heat, as intermolecular interactions within the gel weaken. Although gel-to-gel transitions during heating are rare, they may occur due to minor rearrangements caused by thermal forces in the supramolecular self-assembled structure. Here, an unprecedented temperature-induced gel-to-gel transition assisted by supramolecular chiral inversion in a hydrogel system is presented. The transition results from a left-handed M-type helix to a right-handed P-type helix, attributed to the π-system-conjugated amino acid, l-Tyrosine (Fm- l-Tyr). Upon solvent dilution, Fm-l-Tyr induces translucent hydrogel formed by entangled fibers with a kinetically stable left-handed M-type supramolecular helix. At 70 °C, hydrogel transforms into an opaque gel with a reverse supramolecular chirality yielding a thermodynamically stable right-handed P-type helix. Supramolecular chiral inversion is substantiated by two chiroptical methods. This unique gel-to-gel transition, accompanied by chiral inversion, is anticipated to attract attention, especially for applications sensitive to chirality.

Evaluation of Pharmacokinetic and Pharmacodynamic (PK/PD) of Novel Fluorenylmethoxycarbonyl- Phenylalanine Antimicrobial Agent

OBJECTIVE

To assess the pharmacokinetic profile, in-vivo toxicity, and efficacy of 9-Fluorenylmethoxycarbonyl-L-phenylalanine (Fmoc-F) as a potential antibacterial agent, with a focus on its suitability for clinical translation.

METHODS

An RP-HPLC-based bio-analytical method was developed and qualified to quantify Fmoc-F levels in mouse plasma for pharmacokinetic analysis. Oral bioavailability was determined, and in-vivo toxicity was evaluated following intra-peritoneal administration. Efficacy was assessed by measuring the reduction in Staphylococcus aureus burden and survival rates in BALB/c mice.

RESULTS

The RP-HPLC method is highly sensitive, detecting as low as 0.8 µg mL-1 (~ 2 µM) of Fmoc-F in blood plasma. This study revealed that Fmoc-F has an oral bioavailability of 65 ± 18% and suitable pharmacokinetic profile. Further, we showed that intra-peritoneal administration of Fmoc-F is well tolerated by BALB/c mice and Fmoc-F treatment (100 mg/kg, i.p.) significantly reduces Staphylococcus aureus burden from visceral organs in BALB/c mice but falls short in enhancing survival rates at higher bacterial loads.

CONCLUSIONS

The study provides crucial insights into the pharmacokinetic and pharmacodynamic properties of Fmoc-F. The compound displayed favourable oral bioavailability and in-vivo tolerance. Its significant reduction of bacterial burden underscores its potential as a treatment for systemic infections. However, limited effectiveness for severe infections, short half-life, and inflammatory response at higher doses need to be addressed for its clinical application.

Peptide Supramolecular Self-Assembly: Regulatory Mechanism, Functional Properties, and Its Application in Foods

Peptide self-assembly, due to its diverse supramolecular nanostructures, excellent biocompatibility, and bright application prospects, has received wide interest from researchers in the fields of biomedicine and green life technology and the food industry. Driven by thermodynamics and regulated by dynamics, peptides spontaneously assemble into supramolecular structures with different functional properties. According to the functional properties derived from peptide self-assembly, applications and development directions in foods can be found and explored. Therefore, in this review, the regulatory mechanism is elucidated from the perspective of self-assembly thermodynamics and dynamics, and the functional properties and application progress of peptide self-assembly in foods are summarized, with a view to more adaptive application scenarios of peptide self-assembly in the food industry.

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.

Phenylalanine-based fibrillar systems

Phenylketonuria (PKU) is an inborn metabolic disorder characterized by excess accumulation of phenylalanine (Phe) and its fibril formation, resulting in progressive intellectual disability. Several research groups have approached from various directions to understand the formation of toxic amyloid fibrils from the essential amino acid Phe. Different parameters like the nature of the solvent, pH, Phe concentration, temperature, etc. influence the fibril formation kinetics. In this article, we have summarized all major findings regarding the formation of Phe-based fibrils in aqueous and organic media and discussed how non-covalent interactions are involved in the self-assembly process using spectroscopic and microscopic techniques. The toxicity of Phe-based fibrils is compared with other neurodegenerative peptides. It is noted that the Phe-based fibrils can also induce various globular proteins into toxic fibrils. Later, we discuss the different approaches to inhibit fibril formation and reduce its toxicity. The presence of polyphenolic compounds, drugs, amino acids, nanoparticles, metal ions, crown ethers, and others showed a remarkable inhibitory effect on fibril formation. To the best of our knowledge, this is the first-ever etymological analysis of the Phe-fibrillar system and its inhibition to create a strong database against PKU.

Self-Assembly and Cytocompatibility of Amino Acid Conjugates Containing a Novel Water-Soluble Aromatic Protecting Group

There has been considerable interest in peptides in which the Fmoc (9-fluorenylmethoxycarbonyl) protecting group is retained at the N-terminus, since this bulky aromatic group can drive self-assembly, and Fmoc-peptides are biocompatible and have applications in cell culture biomaterials. Recently, analogues of new amino acids with 2,7-disulfo-9-fluorenylmethoxycarbonyl (Smoc) protecting groups have been developed for water-based peptide synthesis. Here, we report on the self-assembly and biocompatibility of Smoc-Ala, Smoc-Phe and Smoc-Arg as examples of Smoc conjugates to aliphatic, aromatic, and charged amino acids, respectively. Self-assembly occurs at concentrations above the critical aggregation concentration (CAC). Cryo-TEM imaging and SAXS reveal the presence of nanosheet, nanoribbon or nanotube structures, and spectroscopic methods (ThT fluorescence circular dichroism and FTIR) show the presence of β-sheet secondary structure, although Smoc-Ala solutions contain significant unaggregated monomer content. Smoc shows self-fluorescence, which was used to determine CAC values of the Smoc-amino acids from fluorescence assays. Smoc fluorescence was also exploited in confocal microscopy imaging with fibroblast cells, which revealed its uptake into the cytoplasm. The biocompatibility of these Smoc-amino acids was found to be excellent with zero cytotoxicity (in fact increased metabolism) to fibroblasts at low concentration.

Acid⋅⋅⋅Amide Supramolecular Synthon for Tuning Amino Acid-Based Hydrogels' Properties

Supramolecular hydrogels formed by the self-assembly of N-Fmoc-l-phenylalanine derivatives are gaining relevance for several applications in the materials and biomedical fields. In the challenging attempt to predict or tune their properties, we selected Fmoc-pentafluorophenylalanine (1) as a model efficient gelator, and studied its self-assembly in the presence of benzamide (2), a non-gelator able to form strong hydrogen bonds with the amino acid carboxylic group. Equimolar mixtures of 1 and 2 in organic solvents afforded a 1 : 1 co-crystal thanks to the formation of an acid⋅⋅⋅amide heterodimeric supramolecular synthon. The same synthon occurred in the transparent gels formed by mixing the two components in 1 : 1 ratio in aqueous media, as revealed by structural, spectroscopic, and thermal characterizations performed on both the co-crystal powder and the lyophilized hydrogel. These findings revealed the possibility of modulating the properties of amino acid-based hydrogels by involving the gelator in the formation of a co-crystal. Such a crystal engineering-based approach is shown also to be useful for the time-delayed release of suitable bioactive molecules, when involved as hydrogel coformers.

Diversity at the nanoscale: laser-oxidation of single-layer graphene affects Fmoc-phenylalanine surface-mediated self-assembly

We report the effects of a laser-oxidized single layer graphene (SLG) surface on the self-assembly of amphiphilic gelator N-fluorenylmethoxycarbonyl-L-phenylalanine (Fmoc-Phe) towards an gel-SLG interface. Laser oxidation modulates the levels of hydrophobicity/hydrophilicity on the SLG surface. Atomic force, scanning electron, helium ion and scattering scanning nearfield optical microscopies (AFM, SEM, HIM, s-SNOM) were employed to assess the effects of surface properties on the secondary and tertiary organization of the formed Fmoc-Phe fibres at the SLG-gel interface. S-SNOM shows sheet-like secondary structures on both hydrophobic/hydrophilic areas of SLG and helical or disordered structures mainly on the hydrophilic oxidized surface. The gel network heterogeneity on pristine graphene was observed at the scale of single fibres by s-SNOM, demonstrating its power as a unique tool to study supramolecular assemblies and interfaces at nanoscale. Our findings underline the sensitivity of assembled structures to surface properties, while our characterization approach is a step forward in assessing surface-gel interfaces for the development of bionic devices.

Probing the Gelation Synergies and Anti-Escherichia coli Activity of Fmoc-Phenylalanine/Graphene Oxide Hybrid Hydrogel

The N-fluorenyl-9-methyloxycarbonyl (Fmoc)-protected amino acids have shown high antimicrobial application potential, among which the phenylalanine derivative (Fmoc-F) is the most well-known representative. However, the activity spectrum of Fmoc-F is restricted to Gram-positive bacteria only. The demand for efficient antimicrobial materials expanded research into graphene and its derivatives, although the reported results are somewhat controversial. Herein, we combined graphene oxide (GO) flakes with Fmoc-F amino acid to form Fmoc-F/GO hybrid hydrogel for the first time. We studied the synergistic effect of each component on gelation and assessed the material's bactericidal activity on Gram-negative Escherichia coli (E. coli). GO flakes do not affect Fmoc-F self-assembly per se but modulate the elasticity of the gel and speed up its formation. The hybrid hydrogel affects E. coli survival, initially causing abrupt bacterial death followed by the recovery of the surviving ones due to the inoculum effect (IE). The combination of graphene with amino acids is a step forward in developing antimicrobial gels due to their easy preparation, chemical modification, graphene functionalization, cost-effectiveness, and physicochemical/biological synergy of each component.

Hemostatic effects of FmocF-ADP hydrogel consisted of Fmoc-Phenylalanine and ADP

During trauma and surgery, bleeding is a major concern. One of the crucial strategies for hemostasis is the use of biological hemostatic material. Herein, we reported an amino acid-based hydrogel FmocF-ADP hydrogel, which consisted of N-[(9H-fluoren-9-ylmethoxy) carbonyl]-3-phenyl-L-alanine (FmocF) and adenosine diphosphate (ADP) sodium solution. The hydrogel was created by FmocF self-assembling to nanofiber in ADP sodium solution and then cross-linking to hydrogel. FmocF-ADP hydrogel showed good in vitro coagulation activity as measured by whole blood clotting assays, platelet clotting assays, platelet activation assays, and platelet adhesion assays. Further, it was noted to reveal an exceptional in vivo hemostatic effect in a mouse liver bleeding model. Together with the previous report of the good biocompatibility and antimicrobial activity of FmocF hydrogel, our study would extend the biomedical application of FmocF hydrogel. In conclusion, the present study would provide a constructive strategy for the development of new antimicrobial and hemostatic materials or develop a potential hemostatic material.

Supramolecular Phenylalanine-Derived Hydrogels for the Sustained Release of Functional Proteins

Protein-based therapeutics have emerged as next-generation pharmaceutical agents for oncology, bone regeneration, autoimmune disorders, viral infections, and other diseases. The clinical application of protein therapeutics has been impeded by pharmacokinetic and pharmacodynamic challenges including off-target toxicity, rapid clearance, and drug stability. Strategies for the localized and sustained delivery of protein therapeutics have shown promise in addressing these challenges. Hydrogels are critical materials that enable these delivery strategies. Supramolecular hydrogels composed of self-assembled materials have demonstrated biocompatibility advantages over polymer hydrogels, with peptide and protein-based gels showing strong potential. However, cost is a significant drawback of peptide-based supramolecular hydrogels. Supramolecular hydrogels composed of inexpensive low-molecular-weight (LMW) gelators, including modified amino acid derivatives, have been reported as viable alternatives to peptide-based materials. Herein, we report the encapsulation and release of proteins from supramolecular hydrogels composed of perfluorinated fluorenylmethyloxcarbonyl-modified phenylalanine (Fmoc-F₅-Phe-DAP). Specifically, we demonstrate release of four model proteins (ribonuclease A (RNase A), trypsin inhibitor (TI), bovine serum albumin (BSA), and human immunoglobulin G (IgG)) from these hydrogels. The emergent viscoelastic properties of these materials are characterized, and the functional and time-dependent release of proteins from the hydrogels is demonstrated. In addition, it is shown that the properties of the aqueous solution used for hydrogel formulation have a significant influence on the in vitro release profiles, as a function of the isoelectric point and molecular weight of the protein payloads. These studies collectively validate that this class of supramolecular LMW hydrogel possesses the requisite properties for the sustained and localized release of protein therapeutics.

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.

Anion Effects on the Supramolecular Self-Assembly of Cationic Phenylalanine Derivatives

Supramolecular hydrogels have emerged as a class of promising biomaterials for applications such as drug delivery and tissue engineering. Self-assembling peptides have been well studied for such applications, but low molecular weight (LMW) amino acid-derived gelators have attracted interest as low-cost alternatives with similar emergent properties. Fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-Phe) is one such privileged motif often chosen due to its inherent self-assembly potential. Previously, we developed cationic Fmoc-Phe-DAP gelators that assemble into hydrogel networks in aqueous NaCl solutions of sufficient ionic strength. The chloride anions in these solutions screen the cationic charge of the gelators to enable self-assembly to occur. Herein, we report the effects of varying the anions of sodium salts on the gelation potential, nanoscale morphology, and hydrogel viscoelastic properties of Fmoc-Phe-DAP and two of its fluorinated derivatives, Fmoc-3F-Phe-DAP and Fmoc-F₅-Phe-DAP. It was observed that both the anion identity and gelator structure had a significant impact on the self-assembly and gelation properties of these derivatives. Changing the anion identity resulted in significant polymorphism of the nanoscale morphology of the assembled states that was dependent on the chemical structure of the gelator. The emergent viscoelastic character of the hydrogel networks was also found to be reliant on the anion identity and gelator structure. These results demonstrate the complex interplay between the gelator and environment that have a profound and often unpredictable impact on both self-assembly properties and emergent viscoelasticity in supramolecular hydrogels formed by LMW compounds. This work also illustrates the current lack of understanding that limits the rational design of potential biomaterials that will be in contact with complex biological fluids and provides motivation for additional research to correlate the chemical structure of LMW gelators with the structure and emergent properties of the resulting supramolecular assemblies as a function of environment.

Impact of aromatic residues on the intrinsic disorder and transitional behaviour of model IDPs

Understanding the interplay between order and disorder in intrinsically disorder proteins (IDPs), and its impact on the properties and features of materials manufactured from them, is a major challenge in the design of protein-based synthetic polymers intended for advanced functions. In this paper an elastin-like diblock co-recombinamer amphiphile (Phe-ELR) based on a hydrophobic block containing five phenylalanine (Phe) residues proximal to the carboxyl function of a glutamic acid (Glu) residue upon folding, and with Glu as the guest residue in the hydrophilic part, was engineered and its assembly behaviour compared with another amphiphilic ELR used as control. Phe-ELR was tailored in order to clarify the impact of the presence of aromatic residues in the amino acid sequence, which even in early studies by Urry's group already demonstrated a certain out-of-trend behaviour compared with other apolar amino acids, especially non-aromatic ones, on ELR behaviour. The combination of several experimental techniques indicates strong molecular interactions associated with the Phe residue, thus resulting in limited reversible character of the temperature-induced transitions during sequential thermal cycles, a lower than expected transition enthalpy, and clear differences in its supramolecular assembly with respect to the control ELR. A distinctive pre-aggregated state for the Phe-ELR under any condition of pH and temperature is found. Eventually, this state gives rise to Phe-core micelles or a solid jelly-like material, depending on the concentration, pH and presence of salts. In conclusion, it appears that the presence of aromatic residues and their ability to promote strong inter- and intramolecular interactions at any temperature and pH causes a complete modification of the order-disorder interplay present in other, non-aromatic ELRs. These molecular events have a profound impact on the physical properties of the resulting polymer when compared with other ELRs. This work helps to shed light on the limits that govern intrinsic disorder in ELRs beyond its inverse temperature transition.

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.

Side-chain halogen effects on self-assembly and hydrogelation of cationic phenylalanine derivatives

Low molecular weight (LMW) supramolecular hydrogels have great potential as next-generation biomaterials for drug delivery, tissue engineering, and regenerative medicine. The design of LMW gelators is complicated by the lack of understanding regarding how the chemical structure of the gelator correlates to self-assembly potential and emergent hydrogel material properties. The fluorenylmethyloxycarbonyl-phenylalanine (Fmoc-Phe) motif is a privileged scaffold that is prone to undergo self-assembly into self-supporting hydrogel networks. Cationic Fmoc-Phe-DAP derivatives modified with diaminopropane (DAP) at the C-terminus have been developed that self-assemble into hydrogel networks in aqueous solutions of sufficient ionic strength. We report herein the impact of side-chain halogenation on the self-assembly and hydrogelation properties of Fmoc-Phe-DAP derivatives. A systematic study of the self-assembly and hydrogelation of monohalogenated Fmoc-Phe-DAP derivatives with F, Cl, or Br atoms in the ortho, meta, or para positions of the phenyl side chain reveal significant differences in self-assembly and gelation potential, nanoscale assembly morphology, and hydrogel viscoelastic properties as a function of halogen identity and substitution position. These results demonstrate the profound impact that subtle changes to the chemical scaffold can have on the behavior of LMW supramolecular gelators and illustrate the ongoing difficulty of predicting the emergent self-assembly and hydrogelation behavior of LMW gelators that differ even modestly in chemical structure.

Controlled aggregation properties of single amino acids modified with protecting groups

The self-assembling properties of single amino acids modified with protecting groups under controlled conditions of temperature and concentration are illustrated.

Diffusion-controlled release of the theranostic protein-photosensitizer Azulitox from composite of Fmoc-Phenylalanine Fibrils encapsulated with BSA hydrogels

Hydrogels offer a promising potential for the encapsulation and regulated release of drugs due to their biocompatibility and their tunable properties as materials. Only a limited number of systems and procedures enable the encapsulation of sensitive proteins. N-terminally fmoc-protected phenylalanine has been shown to self-assemble into a transparent, stable hydrogel It can be considered a supergelator due to the low amount of monomers necessary for hydrogelation (0.1% w/v), making it a good candidate for the encapsulation and stabilization of sensitive proteins. However, application options for this hydrogel are rather limited to those of many other fibril-based materials due to its intrinsic lack of mechanical strength and high susceptibility to changes in environmental conditions. Here, we demonstrate that the stability of a fibrillary system and the resulting release of the protein-photosensitizer Azulitox can be increased by combining the hydrogel with a tightly cross-linked BSA hydrogel. Azulitox is known to display cell-penetrating properties, anti-proliferative activity and has a distinctive fluorescence. Confocal microscopy and fluorescence measurements verified the maintenance of all essential functions of the encapsulated protein. In contrast, the combination of fibrillary and protein hydrogel resulted in a significant stabilization of the matrix and an adjustable release pattern for encapsulated protein.

Photochromic and photothermal hydrogels derived from natural amino acids and heteropoly acids

A new class of supramolecular hydrogels have been designed and synthesized via the co-assembly of basic amino acids (AAs) and heteropoly acids (HPAs) under acidic conditions. The formation of gel-like samples is identified using an inverted tube method, rheology, and scanning and transmission electron microscopy. Fourier transform infrared spectroscopy reveals that the structural integrity of the HPAs is maintained during the gelation process. X-ray photoelectron spectroscopy (XPS) and proton nuclear magnetic resonance spectroscopy demonstrate that the anionic HPAs interact with both the protonated α-NH₂ and the protonated side groups of the basic amino acids, initiating the preferential growth of one-dimensional nanofibers. These nanofibers bundle and entangle with each other to form extended three-dimensional network structures. The resulting AA/HPA supramolecular hydrogels show clear stereoselectivity of the basic amino acids. With the decreasing enantiomeric excess of the basic amino acids, the gelation propensity of the AA/HPA complexes is found to be depressed. The co-assembled hydrogels show the UV-responsive photochromic behaviour because of the presence of HPAs. The corresponding XPS data confirm that the photochromism of the hydrogels is attributed to the intervalence charge-transfer transition resulting from the reduction of HPAs. Interestingly, the reduced HPAs within the hydrogel matrix can absorb the near-infrared (NIR) light and exhibit photo-thermal conversion properties, which elevates the bulk temperature of the AA/HPA hydrogels and induces the gel-to-sol transition. This study unveils that HPAs have unique capacity to promote the gelation of basic amino acids for the construction of supramolecular soft materials with functional features.

New Physical Hydrogels Based on Co-Assembling of FMOC-Amino Acids

In the last years, physical hydrogels have been widely studied due to the characteristics of these structures, respectively the non-covalent interactions and the absence of other necessary components for the cross-linking processes. Low molecular weight gelators are a class of small molecules which form higher ordered structures through hydrogen bonding and π-π interactions. In this context it is known that the formation of hydrogels based on FMOC-amino acids is determined by the primary structures of amino acids and the secondary structure arrangement (alpha-helix or beta-sheet motifs). The present study aimed to obtain supramolecular gels through co-assembly phenomenon using FMOC-amino acids as low molecular weight gelators. The stability of the new structures was evaluated by the vial inversion test, while FTIR spectra put into evidence the interaction between the compounds. The gel-like structure is evidenced by viscoelastic parameters in oscillatory shear conditions. SEM microscopy was used to obtain the visual insight into the morphology of the physical hydrogel network while DLS measurements highlighted the sol-gel transition. The molecular arrangement of gels was determined by circular dichroism, fluorescence and UV-Vis spectroscopy.

Stimuli-Responsive Nucleotide-Amino Acid Hybrid Supramolecular Hydrogels

The ability to assemble chemically different gelator molecules into complex supramolecular hydrogels provides excellent opportunities to construct functional soft materials. Herein, we demonstrate the formation of hybrid nucleotide–amino acid supramolecular hydrogels. These are generated by the silver ion (Ag⁺)-triggered formation of silver–guanosine monophosphate (GMP) dimers, which undergo self-assembly through non-covalent interactions to produce nanofilaments. This process results in a concomitant pH reduction due to the abstraction of a proton from the guanine residue, which triggers the in situ gelation of a pH-sensitive amino acid, N-fluorenylmethyloxycarbonyl tyrosine (FY), to form nucleotide–amino acid hybrid hydrogels. Alterations in the supramolecular structures due to changes in the assembly process are observed, with the molar ratio of Ag:GMP:FY affecting the assembly kinetics, and the resulting supramolecular organisation and mechanical properties of the hydrogels. Higher Ag:GMP stoichiometries result in almost instantaneous gelation with non-orthogonal assembly of the gelators, while at lower molar ratios, orthogonal assembly is observed. Significantly, by increasing the pH as an external stimulus, nanofilaments comprising FY can be selectively disassembled from the hybrid hydrogels. Our results demonstrate a simple approach for the construction of multicomponent stimuli-responsive supramolecular hydrogels with adaptable network and mechanical properties.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH₂ - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

From Supramolecular Hydrogels to Multifunctional Carriers for Biologically Active Substances

Supramolecular hydrogels are 3D, elastic, water-swelled materials that are held together by reversible, non-covalent interactions, such as hydrogen bonds, hydrophobic, ionic, host-guest interactions, and metal-ligand coordination. These interactions determine the hydrogels' unique properties: mechanical strength; stretchability; injectability; ability to self-heal; shear-thinning; and sensitivity to stimuli, e.g., pH, temperature, the presence of ions, and other chemical substances. For this reason, supramolecular hydrogels have attracted considerable attention as carriers for active substance delivery systems. In this paper, we focused on the various types of non-covalent interactions. The hydrogen bonds, hydrophobic, ionic, coordination, and host-guest interactions between hydrogel components have been described. We also provided an overview of the recent studies on supramolecular hydrogel applications, such as cancer therapy, anti-inflammatory gels, antimicrobial activity, controlled gene drug delivery, and tissue engineering.

From Folding to Assembly: Functional Supramolecular Architectures of Peptides Comprised of Non-Canonical Amino Acids

The engineering of biological molecules is the fundamental concept behind the design of complex materials with desirable functions. Over the last few decades, peptides and proteins have emerged as useful building blocks for well-defined nanostructures with controlled size and dimensions. Short peptides in particular have received much attention due to their inherent biocompatibility, lower synthetic cost, and ease of tunability. In addition to the diverse self-assembling properties of short peptides comprising coded amino acids and their emerging applications in nanotechnology, there is now growing interest in the properties of peptides composed of non-canonical amino acids. Such non-natural oligomers have been shown in recent years to form well-defined secondary structures similar to natural proteins, with the ability to self-assemble to generate a wide variety of nanostructures with excellent biostability. This review describes recent events in the development of supramolecular assemblies of peptides composed completely of non-coded amino acids and their hybrid analogues. Special attention is paid to understanding the supramolecular assemblies at the atomic level and to considering their potential applications in nanotechnology.

Mimosine functionalized gold nanoparticles (Mimo-AuNPs) suppress β-amyloid aggregation and neuronal toxicity

Evidence suggests that increased level/aggregation of beta-amyloid (Aβ) peptides initiate neurodegeneration and subsequent development of Alzheimer's disease (AD). At present, there is no effective treatment for AD. In this study, we reported the effects of gold nanoparticles surface-functionalized with a plant-based amino acid mimosine (Mimo-AuNPs), which is found to cross the blood-brain barrier, on the Aβ fibrillization process and toxicity. Thioflavin T kinetic assays, fluorescence imaging and electron microscopy data showed that Mimo-AuNPs were able to suppress the spontaneous and seed-induced Aβ_1-42 aggregation. Spectroscopic studies, molecular docking and biochemical analyses further revealed that Mimo-AuNPs stabilize Aβ_1-42 to remain in its monomeric state by interacting with the hydrophobic domain of Aβ_1-42 (i.e., Lys₁₆ to Ala₂₁) there by preventing a conformational shift towards the β-sheet structure. Additionally, Mimo-AuNPs were found to trigger the disassembly of matured Aβ_1-42 fibers and increased neuronal viability by reducing phosphorylation of tau protein and the production of oxyradicals. Collectively, these results reveal that the surface-functionalization of gold nanoparticles with mimosine can attenuate Aβ fibrillization and neuronal toxicity. Thus, we propose Mimo-AuNPs may be used as a potential treatment strategy towards AD-related pathologies.

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Mimosine functionalized with gold nanoparticles (Mimo-AuNPs) can cross blood-brain barrier.

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Mimo-AuNPs inhibit aggregation of Aβ peptides by interacting with its hydrophobic domain.

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Mimo-AuNPs can trigger disassembly of pre-aggregated Aβ fibers.

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Mimo-AuNPs can protect neurons against Aβ toxicity by attenuating intracellular signaling.

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Luminescence sensitization of terbium-loaded supramolecular gels by hydroxybenzoic acids and used for salicylates sensing

The luminescent terbium (Tb³⁺)-loaded supramolecular gels were facilely prepared through the self-assembly of Fmoc-diphenylalanine (FmocPhePhe) at room temperature. Hydroxybenzoic acid (HA, the isomers are denoted as 2-HA, 3-HA, and 4-HA depending upon the positions of hydroxyl groups) was used as a sensitizer to Tb³⁺. The luminescence sensitization of Tb³⁺ in the gels was realized by the coordination with hydroxybenzoic acids. The spectra of luminescence, UV-vis, FT-IR, and ¹H NMR verified that this sensitization was attributed to the energy transfer from hydroxybenzoic acids to Tb³⁺. The results of XRD, SEM, and phase transfer temperature further indicated that the initial molecule arrangement of the gels was significantly changed by 2-HA, resulting in more ordered and more compact morphology of the gels. 2-HA exhibited more effective sensitization to Tb³⁺ in the gels than 3-HA and 4-HA. It was also found that 2-HA did not affect the self-assembly of FmocPhePhe. Due to the effective fluorescence sensitization by 2-HA, the as-prepared gels can be used for salicylic acid sensing with 6.8 μM of the detection limit. This strategy has been successfully used for the detection of salicylates in pharmaceuticals and cosmetics.

Amyloid-Like Aggregation in Diseases and Biomaterials: Osmosis of Structural Information

The discovery that the polypeptide chain has a remarkable and intrinsic propensity to form amyloid-like aggregates endowed with an extraordinary stability is one of the most relevant breakthroughs of the last decades in both protein/peptide chemistry and structural biology. This observation has fundamental implications, as the formation of these assemblies is systematically associated with the insurgence of severe neurodegenerative diseases. Although the ability of proteins to form aggregates rich in cross-β structure has been highlighted by recent studies of structural biology, the determination of the underlying atomic models has required immense efforts and inventiveness. Interestingly, the progressive molecular and structural characterization of these assemblies has opened new perspectives in apparently unrelated fields. Indeed, the self-assembling through the cross-β structure has been exploited to generate innovative biomaterials endowed with promising mechanical and spectroscopic properties. Therefore, this structural motif has become the fil rouge connecting these diversified research areas. In the present review, we report a chronological recapitulation, also performing a survey of the structural content of the Protein Data Bank, of the milestones achieved over the years in the characterization of cross-β assemblies involved in the insurgence of neurodegenerative diseases. A particular emphasis is given to the very recent successful elucidation of amyloid-like aggregates characterized by remarkable molecular and structural complexities. We also review the state of the art of the structural characterization of cross-β based biomaterials by highlighting the benefits of the osmosis of information between these two research areas. Finally, we underline the new promising perspectives that recent successful characterizations of disease-related amyloid-like assemblies can open in the biomaterial field.

Antibiofilm activity of Fmoc-phenylalanine against Gram-positive and Gram-negative bacterial biofilms

Biofilm associated infections are the major contributor of mortality, morbidity and financial burden in patients with a bacterial infection. About 65% of all bacterial infections are associated with the information of bacterial biofilms. Bacterial biofilms not only reduce the efficacy of antibacterial treatment but also increases the threat of developing antibacterial resistance. Recently, our group has discovered the antibacterial activity of Fmoc-phenylalanine (Fmoc-F) and other Fmoc-amino acids (Fmoc-AA). Fmoc-F and other Fmoc-AA showed antibacterial activity due to their surfactant properties. Surfactants are known to eradicate biofilm and enhance antimicrobial activity in biofilm. Thus, in the present study, we evaluated the anti-biofilm activity of Fmoc-F against clinically relevant bacteria. We found that Fmoc-F not only inhibits the biofilm formation in Staphylococcus aureus and Pseudomonas aeruginosa, but also eradicates the already formed biofilms over the surface. Further, Fmoc-F coated glass surface resists S. aureus and P. aeruginosa biofilm formation and attachment, when biofilm is grown over the surface. The mechanistic investigation suggests that Fmoc-F reduces the extracellular matrix (ECM) components such as proteins, carbohydrates and eDNA in the biofilm and affect its stability via direct interactions with ECM components and/ or indirectly through reducing bacterial cell population. Finally, we showed that Fmoc-F treatment in combination with vancomycin and ampicillin synergistically inhibit biofilm formation. Overall, the study demonstrates the potential application of Fmoc-F and other Fmoc-AA molecules individually as well as in combination as anti-biofilm coating material for treating biofilm associated infections.

Impact of C-Terminal Chemistry on Self-Assembled Morphology of Guanosine Containing Nucleopeptides

Herein, we report the design and characterization of guanosine-containing self-assembling nucleopeptides that form nanosheets and nanofibers. Through spectroscopy and microscopy analysis, we propose that the peptide component of the nucleopeptide drives the assembly into β-sheet structures with hydrogen-bonded guanosine forming additional secondary structures cooperatively within the peptide framework. Interestingly, the distinct supramolecular morphologies are driven not by metal cation responsiveness common to guanine-based materials, but by the C-terminal peptide chemistry. This work highlights the structural diversity of self-assembling nucleopeptides and will help advance the development of applications for these supramolecular guanosine-containing nucleopeptides.

Development of mechanism-based antibacterial synergy between Fmoc-phenylalanine hydrogel and aztreonam

Recently, fluorenylmethyloxycarbonyl (Fmoc) conjugated amino acids (Fmoc-AA), especially Fmoc-phenylalanine (Fmoc-F), have been discovered to have antimicrobial properties specific to Gram-positive bacteria including MRSA. Their weak antibacterial activity against Gram-negative bacteria is due to their inability to cross the bacterial membrane. Here in order to increase the antibacterial spectrum of Fmoc-F, we prepared a formulation of Fmoc-F with the Gram-negative specific antibiotic aztreonam (AZT). This formulation displayed antibacterial activity against both Gram-positive and Gram-negative bacteria and significantly reduced the bacterial load in a mouse wound infection model. The combination produced a synergistic effect and higher efficacy against P. aeruginosa due to the increased Fmoc-F permeability by AZT through the bacterial membrane. This combinatorial approach could be an effective strategy for other Fmoc-AA having a Gram-positive specific antibacterial effect for the better management of bacterial wound infections.

Impact of gelation method on thixotropic properties of phenylalanine-derived supramolecular hydrogels

Supramolecular hydrogels formed by noncovalent self-assembly of low molecular weight (LMW) agents are promising next-generation biomaterials. Thixotropic shear response and mechanical stability are two emergent properties of hydrogels that are critical for biomedical applications including drug delivery and tissue engineering in which injection of the hydrogel will be necessary. Herein, we demonstrate that the emergent thixotropic properties of supramolecular phenylalanine-derived hydrogels are dependent on the conditions in which they are formulated. Specifically, hydrogels formed from fluorenylmethoxycarbonyl (Fmoc) modified phenylalanine derivatives, 3-fluorophenylalanine (Fmoc-3F-Phe) and pentafluorophenylalanine (Fmoc-F5-Phe), were characterized as a function of gelation conditions to examine how shear response and mechanical stability properties correlate to mode of gelation. Two distinct methods of gelation were compared. First, spontaneous self-assembly and gelation was triggered by a solvent exchange method in which a concentrated solution of the gelator in dimethylsulfoxide was diluted in water. Second, gelation was promoted by dissolution of the gelator in water at basic pH followed by gradual pH adjustment from basic to mildly acidic by the hydrolysis of glucono-delta-lactone. Hydrogels formed under solvent exchange conditions were mechanically unstable and poorly shear-responsive whereas hydrogels formed by gradual acidification were temporally stable and had highly shear-responsive viscoelastic character. These studies confirm that gelation environment and mechanism have a significant influence on the emergent properties of supramolecular hydrogels and offer insight into how gelation conditions can be used to tune hydrogel properties for specific applications.

Surface Modification by Nano-Structures Reduces Viable Bacterial Biofilm in Aerobic and Anaerobic Environments

Bacterial biofilm formation on wet surfaces represents a significant problem in medicine and environmental sciences. One of the strategies to prevent or eliminate surface adhesion of organisms is surface modification and coating. However, the current coating technologies possess several drawbacks, including limited durability, low biocompatibility and high cost. Here, we present a simple antibacterial modification of titanium, mica and glass surfaces using self-assembling nano-structures. We have designed two different nano-structure coatings composed of fluorinated phenylalanine via the drop-cast coating technique. We investigated and characterized the modified surfaces by scanning electron microscopy, X-ray diffraction and wettability analyses. Exploiting the antimicrobial property of the nano-structures, we successfully hindered the viability of Streptococcus mutans and Enterococcus faecalis on the coated surfaces in both aerobic and anaerobic conditions. Notably, we found lower bacteria adherence to the coated surfaces and a reduction of 86–99% in the total metabolic activity of the bacteria. Our results emphasize the interplay between self-assembly and antimicrobial activity of small self-assembling molecules, thus highlighting a new approach of biofilm control for implementation in biomedicine and other fields.

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.

N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite hybrid supramolecular hydrogels as drug delivery vehicles with antibacterial property and cytocompatibility

The intrinsic fragility of hydroxyapatite (HAP) restricts its wider applications for local delivery of antibiotics. The composites formed by integrating HAP with hydrogels can improve the properties of HAP. However, these reported composites not only require tedious preparation and employ organic solvent and toxic reagents, but also hardly have inherent antimicrobial property. In this study, N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite (Fmoc-L-Phe/nHAP) hybrid supramolecular hydrogels with antibacterial property and cytocompatibility was prepared by integrating nHAP as reinforcement with Fmoc-L-Phe supramolecular hydrogels. The results showed that nHAP bounds in the chamber of the gel network and adheres to the fiber of Fmoc-L-Phe due to intermolecular interaction, remarkably improving the mechanical strength of Fmoc-L-Phe supramolecular hydrogels. The results of inhibition zone experiment and MTT experiment showed that the Fmoc-L-Phe/nHAP hybrid supramolecular hydrogels possess antimicrobial property and cytocompatibility. In vitro release experiment of chlorogenic acid (CGA) from the hybrid supramolecular hydrogels was performed. The study of the release kinetics indicated that the release behavior of CGA from the hybrid supramolecular hydrogels is following Weibull model and release mechanism involved Fickian diffusion and erosion of the surface of hydrogel matrix. The release of CGA shows a good inhibition effect on S. aureus. The results show that the Fmoc-L-Phe/nHAP hybrid hydrogels with antibacterial property and cytocompatibility have promising applications as drug delivery carrier. Due to the intrinsic fragility of hydroxyapatite (HAP), the properties of HAP could be improved by incorporation into hydrogels. However, these reported composites not only require tedious preparation and employ organic solvent and toxic reagents, but also hardly have inherent antimicrobial property. We prepared N-(9-Fluorenylmethoxycarbonyl)-L-Phenylalanine/nano-hydroxyapatite (Fmoc-L-Phe/nHAP) hybrid supramolecular hydrogels by integrating nHAP as reinforcement with Fmoc-L-Phe supramolecular hydrogels. The results showed that nHAP bounds in the chamber of the gel network and adheres to the fiber of Fmoc-L-Phe due to intermolecular interaction, remarkably improving the mechanical strength of Fmoc-L-Phe supramolecular hydrogels. The results of inhibition zone experiment and MTT experiment showed that the Fmoc-L-Phe/nHAP hybrid supramolecular hydrogels possess antibacterial property and cytocompatibility. In vitro release experiment of chlorogenic acid (CGA) from the hybrid supramolecular hydrogels was performed. The study of the release kinetics indicated that the release behavior of CGA from the hybrid supramolecular hydrogels is following Weibull model and release mechanism involved Fickian diffusion and erosion of the surface of hydrogel matrix. The release of CGA shows a good inhibition effect on S. aureus. The results show that the Fmoc-L-Phe/nHAP hybrid hydrogels with antibacterial property and cytocompatibility have promising applications as drug delivery carrier.

Self-assembly of novel Fmoc-cardanol compounds into hydrogels - analysis based on rheological, structural and thermal properties

Hydrogels of low molecular weight molecules are particularly appealing for various biomedical applications such as drug delivery, tissue engineering, and antitumor therapy due to their excellent biocompatibility, biodegradability, and easy availability. Fmoc-peptide hydrogels form an essential category of these hydrogels. Herein we report a new class of Fmoc hydrogels in which cardanol (3-pentadecyl phenol (PDP)) is covalently linked with fluorenylmethyloxycarbonyl group. Cardanol is a plant-based renewable raw material, readily obtained from Cashew Nut Shell Liquid (CNSL). The long aliphatic chain of pentadecyl phenol helps in bringing a structural incompatibility and generates different nanostructures such as nanospheres, nanotapes, and nanofibers depending on Fmoc substitution and the solvents used. Stable hydrogels were formed from Fmoc-PDP in DMSO/H2O, and the critical aggregation concentration (CAC) and critical gelation concentration (CGC) were determined. The role of non-covalent forces such as hydrogen-bonding, hydrophobicity, and π-π stacking interactions in governing self-assembly to hydrogel formation was studied for Fmoc, DiFmoc and Boc groups attached to PDP. The thermal properties were analyzed, and smectic and nematic phases were identified for the molecules depending on the substitutions involved. Overall the study supports the mechanisms of aggregation and gelation in novel Fmoc-cardanol derivatives.