Dipeptide Hydrogel Research Articles

A Well-Coupled Supramolecular System Accelerates Photophosphorylation.

Supramolecular assembly allows multiple chemical/bio-components integrated as one system for cascade biochemical reactions. Herein the graphitic carbon nitrides (g-C3N4) as photocatalyst trapped in a dipeptide hydrogel covering adenosine triphosphate (ATP) synthase accelerates the photophosphorylation through ATP synthesis. Self-assembled N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) as nanofibrils to allow g-C3N4 nanosheets are embedded as a complex Fmoc-FF/g-C3N4 hydrogel. Fmoc-FF gel exhibits good electronic coupling with g-C3N4, which enables a photo-induced proton generation. The transmembrane proton gradient can be established by ATP synthase-lipid reconstituted on the surface of the Fmoc-FF/g-C3N4 hydrogel to enhance the ATP synthesis. It indicates that the Fmoc-FF/g-C3N4/ATP synthase-lipid film can possess a longer-term ATP production capability and allow repeated immersion for sustained ATP production. Such a hydrogel-supported ATP synthesis platform is achieved by a procedure at a larger scale.

Antimicrobial Potency of Fmoc-Phe-Phe Dipeptide Hydrogels with Encapsulated Porphyrin Chromophores Is a Promising Alternative in Antimicrobial Resistance.

Antimicrobial resistance (AMR) poses a significant global health risk as a consequence of misuse of antibiotics. Owing to the increasing antimicrobial resistance, it became imperative to develop novel molecules and materials with antimicrobial properties. Porphyrins and metalloporphyrins are compounds which present antimicrobial properties especially after irradiation. As a consequence, porphyrinoids have recently been utilized as antimicrobial agents in antimicrobial photodynamic inactivation in bacteria and other microorganisms. Herein, we report the encapsulation of porphyrins into peptide hydrogels which serve as delivery vehicles. We selected the self-assembling Fmoc-Phe-Phe dipeptide, a potent gelator, as a scaffold due to its previously reported biocompatibility and three different water-soluble porphyrins as photosensitizers. We evaluated the structural, mechanical and in vitro degradation properties of these hydrogels, their interaction with NIH3T3 mouse skin fibroblasts, and we assessed their antimicrobial efficacy against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) bacteria. We found out that the hydrogels are cytocompatible and display antimicrobial efficiency against both strains with the zinc porphyrins being more efficient. Therefore, these hydrogels present a promising alternative for combating bacterial infections in the face of growing AMR concerns.

Lysine-based non-cytotoxic ultrashort self-assembling peptides with antimicrobial activity.

Peptide-based molecules and their hydrogels are useful materials for biomedical applications due to the reversible nature of their self-assembly as well as the diversity of nanostructures that can be created starting from low-molecular weight compounds. In this study, we have focused on comprehending the characteristics of fibrillar networks of l-lysine-based self-assembled dipeptide hydrogels with a focus on their antibacterial properties. For that purpose, l-lysine has been complemented with hydrophobic aromatic moieties coming from l-phenylalanine and benzyloxyxarbonyl N-capping. In addition, the peptide C-terminus is blocked with alkylamides of different chain lengths which introduces additional dispersive interactions and hydrophobicity. These materials were well characterized by transmission electron microscopy, scanning electron microscopy, wide-angle powder X-ray diffraction and oscillatory rheology. Finally, biocompatibility and antimicrobial tests were performed showing that these hydrogels are compatible with HEK 293 cells and present a remarkable antibacterial activity against both Gram positive (S. aureus) and Gram negative (E. coli) bacteria.

Dipeptide-polysaccharides hydrogels through co-assembly.

Self-assembling dipeptide hydrogels are attracting attention in food, materials, and biomedicine. However, there are still limitations such as weak hydrogel properties. Herein, we introduced two types of polysaccharides (Arabic gum and citrus pectin) into an alkyl-chain modified dipeptide (C13-tryptophan-tyrosine (C13-WY)) to generate co-assembled C13-WY-arabic gum and C13-WY-pectin hydrogels. The co-assembled hydrogels exhibited enhanced mechanical properties and stability. The G' value of C13-WY-arabic gum and C13-WY-pectin hydrogels was 3 and 10 times larger than that of C13-WY hydrogel, respectively. The addition of Arabic gum and citrus pectin led to the co-assembly and molecular rearrangement. Moreover, co-assembled hydrogels showed more β-sheet structure and hydrogen bonds. Importantly, the self-/co-assembled hydrogels showed low cytotoxicity. We utilized these hydrogels for the encapsulation of docetaxel and they showed a high embedding rate and slow-release. Our findings provide a novel strategy for the development of stable supramolecular peptide hydrogels with good biocompatibility through simple co-assembly.

Titanium dioxide nanoparticles embedded in assembled dipeptide hydrogels for microfluidic photodegradation

Dipeptides can be self-assembled via non-covalent bonds towards functional nanostructures for diverse applications in nanotechnology. Here, we introduce a convenient microfluidics-guided dipeptide design as a platform for photodegradation of contaminants in water. Titanium dioxide (TiO2) nanoparticles (NPs) are chosen as photocatalysts due to their vastly studied properties. By using a well-defined microchannel architecture, the dipeptide N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF) and TiO2 NPs are efficiently mixed leading to a self-assembled Fmoc-FF hydrogel with embedded TiO2. Owing to shear-thinning and rapid self-healing of Fmoc-FF hydrogels, we can transfer and inject Fmoc-FF/TiO2 hydrogels into any other microdevice for specific applications, where these low-molecular-weight-gelator- (LMWG-)based Fmoc-FF hydrogels fill out the microchannel volume. Different morphologies of Fmoc-FF/TiO2 hydrogels are obtained by simple concentration screening of TiO2 NPs and Fmoc-FF. Owing to the density of the three-dimensionally twined Fmoc-FF nanofibers, solutions swelling the dipeptide hydrogel can be exchanged without leaching out TiO2 NPs. By further analysis, our hydrogel-filled flow cell can be employed for continuous-flow photodegradation in water under light irradiation. Especially, compared to the TiO2 NPs suspension, Fmoc-FF/TiO2 hydrogels with relatively low concentrations of TiO2 exhibit enhanced photodegradation capabilities due to better dispersion of nanoparticles. Such strategy provides a versatile platform for embedment of small inorganic catalysts or enzymes for (bio-)chemical conversion of solutes passing through the hydrogel network.

Ultralong hydroxyapatite nanowires-incorporated dipeptide hydrogel with enhanced mechanical strength and superior in vivo osteogenesis activity

Self-assembling peptide hydrogels have attracted considerable interest in tissue engineering for their biocompatibility, biodegradability, low immunogenicity, facile modification, and similarity to the native extracellular matrix. However, they still suffer from weak mechanical strength and lack of specific bioactivity. Ultralong hydroxyapatite nanowires (UHANWs) are synthesized to work as a reinforcement agent similar to the steel bars in the reinforced concrete to co-assemble with dipeptide nanofibers, endowing the hybrid hydrogel with enhancing and controllable mechanical properties. Furthermore, additional factors BMP-2 can be introduced into the hydrogel to improve its bioactivity. The experimental results show that the incorporation of UHANWs into the hydrogel matrix leads to an obvious increase in the storage modulus of scaffolds, exhibiting good biocompatibility and bioactivity. The hybrid hydrogels can facilitate the proliferation and osteogenetic differentiation of cells on their surface. The in vivo evaluation reveals that bone defects implanted with the as-designed hydrogel scaffolds show enhanced bone regeneration activity, implying their great potential in biomedical fields.

Three-dimensional (3D) bioprinting of medium toughened dipeptide hydrogel scaffolds with Hofmeister effect

Short peptide self-assembled hydrogels as 3D bioprinting inks show excellent biocompatibility and diverse functional expansion, and have broad application prospects in cell culture and tissue engineering. However, the preparation of biological hydrogel inks with adjustable mechanical strength and controllable degradation for 3D bioprinting still faces big challenges. Herein, we develop dipeptide bio-inks that can be gelled in-situ based on Hofmeister sequence, and prepare hydrogel scaffold by using a layer-by-layer 3D printing strategy. Excitingly, after the introduction of Dulbecco's Modified Eagle's medium (DMEM), which is necessary for cell culture, the hydrogel scaffolds show an excellent toughening effect, which matches the needs of cell culture. It’s notable that in the whole process of preparation and 3D printing of hydrogel scaffolds, no cross-linking agent, ultraviolet (UV), heating or other exogenous factors are involved, ensuring high biosafety and biocompatibility. After two weeks of 3D culture, millimeter-sized cell spheres are obtained. This work provides an opportunity for the development of short peptide hydrogel bioinks without exogenous factors in 3D printing, tissue engineering, tumor simulant reconstruction and other biomedical fields.

Synthesis and Investigation of Backbone Modified Squaramide Dipeptide Self-Assembly.

Dipeptides are minimalistic peptide building blocks that form well ordered structures through molecular self-assembly. The driving forces involved are cooperative noncovalent interactions such as π-π stacking, hydrogen bonding, and ionic as well as hydrophobic interactions. One of the most intriguing self-assembled motifs that has been extensively explored as a low molecular weight hydrogel for drug delivery, tissue engineering, imaging and techtonics, etc. is Phe-Phe (FF). The backbone of the dipeptide is very crucial for extending secondary structures in self-assembly, and any subtle change in the backbone drastically affect the molecular recognitions. The squaramide (SQ) motif has the unique advantage of hydrogen bonding which can promote the self-assembly process. In this work we have integrated the SQ unit into the dipeptide FF backbone to achieve molecular self-assembly. The resulting carbamate protected backbone modified dipeptide (BocFSAF-OH, 10) has exhibited molecular self-assembly with a fibrilar network. It formed a stable hydrogel (with CAC of 0.024 ± 0.0098 wt %) via the solvent switch method and was found to possess excellent enzymatic stability. The dipeptide and the resulting hydrogel were found to be cytocompatible. When integrated with a polysaccharide based biopolymer, e.g. sodium alginate, the resulting matrix exhibited strong hydrogel character. Therefore, the dipeptide hydrogel of 10 may find its applications in a variety of fields including drug delivery and tissue engineering.

Emerging Role of Injectable Dipeptide Hydrogels in Biomedical Applications.

Owing to their properties such as biocompatibility, tunable mechanical properties, permeability toward oxygen, nutrients, and the ability to hold a significant amount of water, hydrogels have wide applications in biomedical research. They have been engaged in drug delivery systems, 3D cell culture, imaging, and extracellular matrix (ECM) mimetics. Injectable hydrogels represent a major subset of hydrogels possessing advantages of site-specific conformation with minimal invasive techniques. It preserves the inherent properties of drug/biomolecules and is devoid of any side effects associated with surgery. Various polymeric materials utilized in developing injectable hydrogels are associated with the limitations of toxicity, immunogenicity, tedious manufacturing processes, and lack of easy synthetic tunability. Peptides are an important class of biomaterials that have interesting properties such as biocompatibility, stimuli responsiveness, shear thinning, self-healing, and biosignaling. They lack immunogenicity and toxicity. Therefore, numerous peptide-based injectable hydrogels have been explored in the past, and a few of them have reached the market. In recent years, minimalistic dipeptides have shown their ability to form stable hydrogels through cooperative noncovalent interactions. In addition to inherent properties of lengthy peptide-based injectable hydrogels, dipeptides have the unique advantages of low production cost, high synthetic accessibility, and higher stability. Given the instances of expanding significance of injectable peptide hydrogels in biomedical research and an emerging recent trend of dipeptide-based injectable hydrogels, a timely review on dipeptide-based injectable hydrogels shall highlight various aspects of this interesting class of biomaterials. This concise review that focuses on the dipeptide injectable hydrogel may stimulate the current trends of research on this class of biomaterial to translate its significance as interesting products for biomedical applications.

Non-linear dilational rheology of liquid-liquid interfaces stabilized by dipeptide hydrogels

We investigate the effects of salt concentration on the rheological properties of dipeptide hydrogel fibres at liquid-liquid interfaces. The interfaces were subjected to large amplitude oscillatory dilation (LAOD) experiments across a range of oscillation strains and frequencies. Lissajous plots of pressure-strain were used for characterizing the viscoelastic properties and for identifying apparent yielding. We show that key aspects of the rheological response of the interfaces vary significantly with salt concentration. At low strain, independent of salt concentration, Lissajous curves show an almost elliptical shape. As the strain is increased, asymmetry in Lissajous curves evidences a non-linear response. The departure from an ellipse is most obvious at negative strain (at moderate to high salt concentrations) and is suggestive of strain-hardening on compression. The Lissajous curves tilt towards the diagonal at elevated salt concentration demonstrating that the interfaces are becoming increasingly elastic. However, increasing the frequency of the oscillation has little systematic effect. We infer that the addition of salt leads to the development of structure on the interfaces from our observations strain-hardening and of the increasingly elastic response. To fully capture the range of behaviour, we suggest a modification of the analysis to calculate the strain-hardening ratio S used to quantify the degree of non-linearities from Lissajous figures, so as to better reveal the presence of instant strain-softening and strain-hardening responses.

Process Dependent Complexity in Multicomponent Gels.

Mixing low molecular weight gelators (LMWGs) can be used to combine favorable properties of the individual components within a multifunctional gel. Such multicomponent systems are complex enough in themselves but the method of combining components is not commonly considered something to influence self-assembly. Herein, two multicomponent systems comprising of a naphthalene-based dipeptide hydrogelator and one of two modified naphthalene diimides (NDIs), one of which forms gels, and the other does not,are investigated. These systems are probed, examining the structures formed and their gel properties (when preparing a solution from either a mixed powder of both components or by mixing pre-formed solutions of each component) using rheology, small angle neutron scattering (SANS), and absorbance spectroscopy. It is found that by altering the method of preparation, it is can either induce self-sorting or co-assembly within the fibers formed that underpin the gel network.

Chemically Modified Dipeptide Based Hydrogel Supports Three-Dimensional Growth and Functions of Primary Hepatocytes.

A huge shortage of organ donors, particularly in the case of liver, has necessitated the development of alternative therapeutic strategies. Primary hepatocytes (pHCs) transplantation has made a considerable transition from bench to bedside, but the short-term viability and functionality of pHCs in in vitro limit their use for clinical applications. Different cell culture strategies are required to maintain the proliferation of pHCs for extended periods. Here, we described the formation of a hybrid scaffold based on a modified dipeptide for the culture of pHCs. First, the dipeptide (Dp), isoleucine-α,β-dehydrophenylalanine (IΔF) was synthesized, purified, and fully characterized. IΔF readily formed a highly stable hydrogel, which was also characterized by CD, TEM, and thioflavin T assay. The addition of soluble liver extracellular matrix (sLEM) to the dipeptide readily formed a hybrid scaffold that was characterized by TEM, and its mechanical strength was determined by rheology experiments. The hybrid scaffold was translucent, biocompatible, and proteolytically stable and, with its mechanical strength, closely mimicked that of the native liver. LEM1-Dp matrix exhibited high biocompatibility in the readily available adherent liver cell line Huh7 and primary rat hepatocyte cells (pHCs). pHCs cultured on LEM1-Dp matrix also maintained significantly higher cell viability and an escalated expression of markers related to the hepatocytes such as albumin as compared to that observed in cells cultured on collagen type I (Col I)-coated substrate plate (col-TCTP). Z-stacking of confocal laser microscopy's volume view clearly indicated pHCs seeded on top of the hydrogel matrix migrated toward the Z direction showing 3D growth. Our results indicated that low molecular weight dipeptide hydrogel along with sLEM can resemble biomimetic 3D-like microenvironments for improved pHCs proliferation, differentiation, and function. This hybrid scaffold is also easy to scale up, which makes it suitable for several downstream applications of hepatocytes, including drug development, pHCs transplantation, and liver regeneration.

Probing the self-assembly and anti-glioblastoma efficacy of a cinnamoyl-capped dipeptide hydrogelator.

Herein, we introduce the first diphenylalanine dipeptide hydrogelator capped with the cinnamoyl functional group (Cin-L-F-L-F). We evaluate the effects of the cinnamoyl moiety on molecular self-assembly events and resultant physical properties of the hydrogel formed. In addition, we report our preliminary results of this dipeptide's cytotoxicity against glioblastoma (GBM) cancer cells.

Electrofabrication of large volume di- and tripeptide hydrogels via hydroquinone oxidation

The fabrication of protected peptide-based hydrogels on electrode surfaces can be achieved by employing the electrochemical oxidation of hydroquinone to benzoquinone, liberating protons at the electrode-solution interface. The localised reduction in pH below the dipeptide gelator molecules pKa initiates the neutralisation, self-assembly and formation of self-supporting hydrogels exclusively at the electrode surface. Previous examples have been on a nanometre to millimetre scale, using deposition times ranging from seconds to minutes. However, the maximum size to which these materials can grow and their subsequent mechanical properties have not yet been investigated. Here, we report the fabrication of the largest reported di- and tri-peptide based hydrogels using this electrochemical method, employing deposition times of two to five hours. To overcome the oxidation of hydroquinone in air, the fabrication process was performed under an inert nitrogen atmosphere. We show that this approach can be used to form multilayer gels, with the mechanical properties of each layer determined by gelator composition. We also describe examples where gel-to-crystal transitions and syneresis occur within the material.

Multi-layer 3D printed dipeptide-based low molecular weight gels.

We describe the direct 3D printing of dipeptide hydrogels, forming layers from gels prepared from different dipeptides. The dipeptides self-assemble into fibres that lead to very different microstructures letting us differentiate between the gels. We show how the mechanical properties of the overall 3D printed structures are affected by the composition of each of the layers, allowing us to build up structures with different microstructure and stiffness. We also discuss the interface between layers formed from different gelators, showing that the gels remain independent from neighbouring printed material, even when prepared in very close proximity.

Engineered Biocompatible and Stable Dipeptide Hydrogel with Tunable Mechanical and Cell Growth Properties to Embolden Neuroglial Cell Growth

Engineered Biocompatible and Stable Dipeptide Hydrogel with Tunable Mechanical and Cell Growth Properties to Embolden Neuroglial Cell Growth

Self-Assembly Dipeptide Hydrogel: The Structures and Properties.

Self-assembly peptide-based hydrogels are well known and popular in biomedical applications due to the fact that they are readily controllable and have biocompatibility properties. A dipeptide is the shortest self-assembling motif of peptides. Due to its small size and simple synthesis method, dipeptide can provide a simple and easy-to-use method to study the mechanism of peptides’ self-assembly. This review describes the design and structures of self-assembly linear dipeptide hydrogels. The strategies for preparing the new generation of linear dipeptide hydrogels can be divided into three categories based on the modification site of dipeptide: 1) COOH-terminal and N-terminal modified dipeptide, 2) C-terminal modified dipeptide, and 3) uncapped dipeptide. With a deeper understanding of the relationship between the structures and properties of dipeptides, we believe that dipeptide hydrogels have great potential application in preparing minimal biocompatible materials.

Chitosan–dipeptide hydrogels as potential anticancer drug delivery systems

A novel chitosan–dipeptide hydrogel was fabricated through a combination of self-assembly of 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc–FF) and its electrostatic interaction with glycol chitosan (GCS). Hydrogel strength and stability depended on its composition. The highest gel strength was observed at a Fmoc–FF mass fraction (ϕFF) of 0.85, whereby the highest combined strength of the two interactions was achieved. As the ϕFF increased above 0.6, gel stability decreased in buffered solution at pH 7.46. The incorporation of doxorubicin (DOX) as a cationic model drug significantly increased the stability of the complex hydrogels. DOX-loaded hydrogels exhibited slow DOX release, probably due to the drug's strong binding to Fmoc–FF via electrostatic attraction and the high gel stability. These hydrogels also exhibited excellent thixotropic features that facilitated the development of injectable self-healing drug delivery systems. Notably, DOX release was significantly accelerated as the pH of the medium decreased from 7.46 to 5.5 and 4.0, possibly due to hydrogel components' protonation. The DOX-loaded hydrogel exhibited notable cytotoxicity against A549 human lung cancer cells, which suggests the newly developed hydrogel to be a promising candidate vehicle for the localized and controlled drug delivery in cancer therapy.

Production and Immunogenicity of a Tag-Free Recombinant Chimera Based on PfMSP-1 and PfMSP-3 Using Alhydrogel and Dipeptide-Based Hydrogels.

A fusion chimeric vaccine comprising multiple protective domains of different blood-stage Plasmodium falciparum antigens is perhaps necessary for widening the protective immune responses and reducing the morbidity caused by the disease. Here we continue to build upon the prior work of developing a recombinant fusion chimera protein, His-tagged PfMSP-Fu24, by producing it as a tag-free recombinant protein. In this study, tag-free recombinant PfMSPFu24 (rFu24) was expressed in Escherichia coli, and the soluble protein was purified using a three-step purification involving ammonium sulphate precipitation followed by 2-step ion exchange chromatography procedures and shown that it was highly immunogenic with the human-compatible adjuvant Alhydrogel. We further investigated two dipeptides, phenylalanine-α, β-dehydrophenylalanine (FΔF) and Leucine-α, β-dehydrophenylalanine (LΔF) based hydrogels as effective delivery platforms for rFu24. These dipeptides self-assembled spontaneously to form a highly stable hydrogel under physiological conditions. rFu24 was efficiently entrapped in both the F∆F and L∆F hydrogels, and the three-dimensional (3D) mesh-like structures of the hydrogels remained intact after the entrapment of the antigen. The two hydrogels significantly stimulated rFu24-specific antibody titers, and the sera from the immunized mice showed an invasion inhibitory activity comparable to that of Alhydrogel. Easily synthesized dipeptide hydrogels can be used as an effective antigen delivery platform to induce immune responses.

Preparation of conductive and transparent dipeptide hydrogels for wearable biosensor

Preparation of conductive and transparent dipeptide hydrogels for wearable biosensor