Peptide-based Hydrogels Research Articles

Green In Situ Synthesis of Silver Nanoparticles-Peptide Hydrogel Composites: Investigation of Their Antibacterial Activities.

The present paper investigated the synthesis of peptide-based hydrogel composites containing photo-generated silver nanoparticles (AgNPs) obtained in the presence and absence of honey as tensile strength enhancer and hydrogel stabilizer. Fmoc-Phe and diphenylalanine (Phe2) were used as starting reagents for the hydrogelator synthesis via an enzymatic method. In particular, we developed an in situ one-pot approach for preparing AgNPs inside peptide hydrogels using a photochemical synthesis, without any toxic reducing agents, with reaction yields up to 30%. The structure and morphology of the nanohybrids were characterized with different techniques such as FESEM, UV-Vis, DLS, SAXS and XPS. Moreover, the antibacterial activity of these hybrid biomaterials was investigated on a laboratory strain and on a clinical isolate of Staphylococcus aureus. Results demonstrated that honey increased both swelling ability and also mechanical stability of the hydrogel. Finally, a higher antibacterial effect of AgNPs in the hybrid was observed in the presence of honey. In particular, AgNPs/hgel and AgNPs/hgel-honey showed an enhanced antibacterial activity (3.12 mg/L) compared to the free form of AgNPs, alone or in combination with honey (6.25 mg/L) for both S. aureus strains.

Insights into current directions of protein and peptide-based hydrogel drug delivery systems for inflammation

Insights into current directions of protein and peptide-based hydrogel drug delivery systems for inflammation

Self-Assembled Peptide Hydrogel for Accelerated Wound Healing: Impact of N-Terminal and C-Terminal Modifications.

Wound dressings are required to provide a moist environment for wounds, protect against invading infections, expedite tissue regeneration, and improve wound healing efficiency. Developing biomaterials with all aforesaid properties is still a big challenge. However, peptide-based hydrogels have the potential to overcome these challenges as they are biocompatible, biodegradable as well as have the ability to mimic the extracellular matrix and provide an appropriate moist environment which is important for wound healing. With this in mind, we report the preparation and comparison of three hexapeptide-based hydrogels, LIVAGD, with the aim to understand the importance of the N-terminal protecting group as well as the C-terminal amino acid substitution on its various biological efficacies. Fmoc and acetyl groups were used for N-terminal peptide protection, while aspartic acid was substituted with lysine at the C-terminus. The resulting peptide-based hydrogels were compared. Fmoc peptide-based hydrogels exhibited efficient anti-inflammatory action along with improved biocompatibility while lysine provided enhanced antibacterial effect to the hydrogel. Additionally, in vivo efficacy was examined using a mouse model, and Fmoc hydrogels demonstrated an improved wound healing ability with ∼40 % faster healing rate in comparison to the reported acetylated peptide hydrogels.

A Peptide-Based Hydrogel for Adsorption of Dyes and Pharmaceuticals in Water Remediation.

The removal of dyes and pharmaceuticals from water has become a major issue in recent years due to the shortage of freshwater resources. The adsorption of these pollutants through nontoxic, easy-to-make, and environmentally friendly adsorbents has become a popular topic. In this work, a tetrapeptide–pyrene conjugate was rationally designed to form hydrogels under controlled acidic conditions. The hydrogels were thoroughly characterized, and their performance in the adsorption of various dyes and pharmaceuticals from water was investigated. The supramolecular hydrogel efficiently adsorbed methylene blue (MB) and diclofenac (DCF) from water. The effect of concentration in the adsorption efficiency was studied, and results indicated that while the adsorption of MB is governed by the availability of adsorption sites, in the case of DCF, concentration is the driving force of the process. In the case of MB, the nature of the dye–hydrogel interactions and the mechanism of the adsorption process were investigated through UV–Vis absorption spectroscopy. The studies proved how this dye is first adsorbed as a monomer, probably through electrostatic interactions; successively, at increasing concentrations as the electrostatic adsorption sites are depleted, dimerization on the hydrogel surface occurs.

Fabrication of the low molecular weight peptide-based hydrogels and analysis of gelation behaviors

Peptide-based hydrogels were formed using low molecular weight peptides (LMWPs) derived from diphenylalanine as gelling agents. Sodium alginate (SA)was incorporated into the peptide skeleton to form a double-cross-linked hydrogel. The self-assembling mechanism was investigated by NMR, and the gelation behavior was studied by rheological tests. Hydrogen bonding and π-π stacking interactions play important roles in self-assembling of LMWPs. The rheological tests showed that the single-cross-linked hydrogel was formed by self-assembling AcNH-Thr-Phe-Phe-CONH 2 (AcTFFNH 2 , critical gelling concentration: 0.3 wt%), and the gelation temperature was in a range of 8–12 °C depending on the concentration of AcTFFNH2. The rigidity, stability and self-healing of the binary composite hydrogels were enhanced particularly when the content of AcTFFNH 2 and SA were 0.5 wt% and 0.3 wt%, respectively. Significant improvement of properties could be attributed to the double-cross-linking and enfolding in the assembled fibers with SA. These results indicate that peptide-based hydrogels formed by low molecular weight peptides have potential applications in the food industry. • Development of new, self-assembled low molecular weight peptide-based hydrogels. • NMR analysis of self-assembly mechanisms. • Fabrication of binary composite hydrogels with improved mechanical properties. • Analysis of gelation behaviors and rheological properties of the new hydrogels.

Impact of doubling peptide length on in vivo hydrogel stability and sustained drug release

Peptide-based hydrogels represent promising systems for the sustained release of different types of drugs, ranging from small molecules to biologicals. Aiming at subcutaneous injection, which is a desirable parenteral administration route, especially for biologicals, we herein focus on physically crosslinked systems possessing thixotropic behaviour. The purpose of this study was to evaluate the in vitro and in vivo properties of hydrogels based on the amphipathic hexapeptide H-FQFQFK-NH2, which served as the lead sequence. Upon doubling the length of this peptide, the dodecapeptide H-FQFQFKFQFQFK-NH2 gave a significant improvement in terms of in vivo stability of the hydrogel post-injection, as monitored by nuclear SPECT/CT imaging. This increased hydrogel stability also led to a more prolonged in vivo release of encapsulated peptide cargoes. Even though no direct link with the mechanical properties of the hydrogels before injection could be made, an important effect of the subcutaneous medium was noticed on the rheological properties of the hydrogels in post in vivo injection measurements. The results were validated in vivo for a therapeutically relevant analgesic peptide using the hot-plate test as an acute pain model. It was confirmed that elongation of the hydrogelator sequence induced more extended antinociceptive effects. Altogether, this simple structural modification of the hydrogelating peptide could provide a basis for reaching longer durations of action upon use of these soft biomaterials.

Application of Hydrogels as Carrier in Tumor Therapy: A Review.

Cancer is one of the most intractable diseases in the world because of its high recurrence rate, high metastasis rate and high lethality rate. Traditional chemotherapy, radiotherapy and surgery have unsatisfactory therapeutic effects and cause many severe side effects at the same time. Hydrogel is a new type of biomaterial with the advantages of good biocompatibility and easy degradation, which can be used as a carrier of functional nanomaterials for tumor therapy. Herein, we represent the progress of hydrogels with different skeletons and their application as carrier in tumor treatment. The hydrogels are listed as polyethylene glycol-based hydrogels, chitosan-based hydrogels, peptide-based hydrogels, hyaluronic acid-based hydrogels, steroid-based hydrogels and other hydrogels by skeletons, and their properties, modifications and toxicities were introduced. Some representative applications of combined hydrogels with nanomaterial for chemotherapy, photodynamic therapy, photothermal therapy, sonodynamic therapy, chemodynamic therapy and synergistic therapy are highlighted.

"Crystal memory" Affects the Properties of Peptide Hydrogels - The Case of the Cyclic Tyr-Tyr dipeptide.

In this work a relationship between the crystal form and morphology and rheological properties of peptide-based hydrogels is examined. We show, that under favorable circumstances a correlation between a starting solid material and a self-assembly processes in solution can exist, leading to different properties of a resulting soft matter. This observation, together with an in-depth analysis of the influence of stereochemistry of self-assembled (ll) and (dl) Tyr-Tyr cyclic dipeptides (cYY) on the observed relationship between gelation and crystallization allowed us to gain a deeper understanding of the peptide hydrogelation processes at a molecular level, using liquid state NMR, rheological studies and scanning electron microscopy. In the course of our studies, several crystal forms of (ll)-cYY has been discovered and described in details using single crystal X-ray diffraction, as well as advanced solid state NMR, X-ray diffraction of powders, thermal analysis, FTIR, circular dichroism and crystal structure prediction (CSP) calculations. Subsequently, we found that while (ll)-cYY easily assembles into hydrogels with different properties depending on the starting solid form, (dl)-cYY always precipitated as one crystal form in the tested conditions. Molecular-level justification for this observation is given.

Injectable Peptide Hydrogel Encapsulation of Mesenchymal Stem Cells Improved Viability, Stemness, Anti-Inflammatory Effects, and Early Stage Wound Healing.

Human-adipose-derived mesenchymal stem cells (hADMSCs) are adult stem cells and are relatively easy to access compared to other sources of mesenchymal stem cells (MSCs). They have shown immunomodulation properties as well as effects in improving tissue regeneration. To better stimulate and preserve the therapeutic properties of hADMSCs, biomaterials for cell delivery have been studied extensively. To date, hyaluronic acid (HA)-based materials have been most widely adopted by researchers around the world. PGmatrix is a new peptide-based hydrogel that has shown superior functional properties in 3D cell cultures. Here, we reported the in vitro and in vivo functional effects of PGmatrix on hADMSCs in comparison with HA and HA-based Hystem hydrogels. Our results showed that PGmatrix was far superior in maintaining hADMSC viability during prolonged incubation and stimulated expression of SSEA4 (stage-specific embryonic antigen-4) in hADMSCs. hADMSCs encapsulated in PGmatrix secreted more immune-responsive proteins than those in HA or Hystem, though similar VEGF-A and TGFβ1 release levels were observed in all three hydrogels. In vivo studies revealed that hADMSCs encapsulated with PGmatrix showed improved skin wound healing in diabetic-induced mice at an early stage, suggesting possible anti-inflammatory effects, though similar re-epithelialization and collagen density were observed among PGmatrix and HA or Hystem hydrogels by day 21.

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.

Peptide-Based Hydrogels: New Materials for Biosensing and Biomedical Applications.

Peptide-based hydrogels have attracted increasing attention for biological applications and diagnostic research due to their impressive features including biocompatibility and biodegradability, injectability, mechanical stability, high water absorption capacity, and tissue-like elasticity. The aim of this review will be to present an updated report on the advancement of peptide-based hydrogels research activity in recent years in the field of anticancer drug delivery, antimicrobial and wound healing materials, 3D bioprinting and tissue engineering, and vaccines. Additionally, the biosensing applications of this key group of hydrogels will be discussed mainly focusing the attention on cancer detection.

Growth and differentiation of human induced pluripotent stem cell (hiPSC)-derived kidney organoids using fully synthetic peptide hydrogels

Human induced pluripotent stem cell (hiPSC)-derived kidney organoids have prospective applications ranging from basic disease modelling to personalised medicine. However, there remains a necessity to refine the biophysical and biochemical parameters that govern kidney organoid formation. Differentiation within fully-controllable and physiologically relevant 3D growth environments will be critical to improving organoid reproducibility and maturation. Here, we matured hiPSC-derived kidney organoids within fully synthetic self-assembling peptide hydrogels (SAPHs) of variable stiffness (storage modulus, G′). The resulting organoids contained complex structures comparable to those differentiated within the animal-derived matrix, Matrigel. Single-cell RNA sequencing (scRNA-seq) was then used to compare organoids matured within SAPHs to those grown within Matrigel or at the air-liquid interface. A total of 13,179 cells were analysed, revealing 14 distinct clusters. Organoid compositional analysis revealed a larger proportion of nephron cell types within Transwell-derived organoids, while SAPH-derived organoids were enriched for stromal-associated cell populations. Notably, differentiation within a higher G’ SAPH generated podocytes with more mature gene expression profiles. Additionally, maturation within a 3D microenvironment significantly reduced the derivation of off-target cell types, which are a known limitation of current kidney organoid protocols. This work demonstrates the utility of synthetic peptide-based hydrogels with a defined stiffness, as a minimally complex microenvironment for the selected differentiation of kidney organoids.

Co-assembled C13-dipeptide hydrogels by Gallic Acid (CA) and epigallocatechin gallate (EGCG) with antibacterial activity

The self-assembled peptide-based hydrogels have been widely utilized in foods. However, the self-assembled hydrogels still have some shortages such as low mechanical properties and hydrogel stabilities. Herein, we designed two co-assembled C13-WS hydrogels conjugated by Gallic Acid (CA) and Epigallocatechin Gallate (EGCG). The introduction of CA and EGCG into C13-WS hydrogels can significantly improve the mechanical properties and hydrogel stabilities. The storage modulus (G’) values of co-assembled C13-WS/CA and C13-WS/EGCG were 13.33 KPa and 16 KPa, respectively. From transmission electron microscope (TEM) results, CA and EGCG contributed to the rearrangement of C13-WS molecules during co-assembly. Moreover, the self-/co-assembled C13-WS hydrogels showed antimicrobial activity against E. coli, P. aeruginosa, and S. epidermidis. The introduction of CA and EGCG significantly enhanced the antibacterial activity of C13-WS hydrogels. Our findings provide a novel strategy for the development of stable supramolecular antibacterial short peptide hydrogels through co-assembly.

Zn2+ Cross-Linked Alginate Carrying Hollow Silica Nanoparticles Loaded with RL-QN15 Peptides Provides Promising Treatment for Chronic Skin Wounds.

Chronic and non-healing wounds pose a great challenge to clinical management and patients. Many studies have explored novel interventions against skin wounds, with bioactive peptides, nanoparticles, and hydrogels arousing considerable attention regarding their therapeutic potential. In this study, the prohealing peptide RL-QN15 was loaded into hollow silica nanoparticles (HSNs), with these HSN@RL-QN15 nanocomposites then combined with zinc alginate (ZA) gels to obtain HSN@RL-QN15/ZA hydrogel. The characteristics, biological properties, and safety profiles of the hydrogel composites were then evaluated. Results showed that the hydrogel had good porosity, hemocompatibility, biocompatibility, and broad-spectrum antimicrobial activity, with the slow release of loaded RL-QN15. Further analysis indicated that the hydrogel promoted skin cell proliferation and keratinocyte scratch repair, regulated angiogenesis, reduced inflammation, and accelerated re-epithelialization and granulation tissue formation, resulting in the rapid healing of both full-thickness skin wounds and methicillin-resistant Staphylococcus aureus biofilm-infected chronic wounds in mice. This peptide-based hydrogel provides a novel intervention for the treatment of chronic skin wounds and shows promise as a wound dressing in the field of tissue regeneration.

Emergence of Elastic Properties in a Minimalist Resilin-Derived Heptapeptide upon Bromination.

Bromination is herein exploited to promote the emergence of elastic behavior in a short peptide-SDSYGAP-derived from resilin, a rubber-like protein exerting its role in the jumping and flight systems of insects. Elastic and resilient hydrogels are obtained, which also show self-healing behavior, thanks to the promoted non-covalent interactions that limit deformations and contribute to the structural recovery of the peptide-based hydrogel. In particular, halogen bonds may stabilize the β-sheet organization working as non-covalent cross-links between nearby peptide strands. Importantly, the unmodified peptide (i.e., wild type) does not show such properties. Thus, SDSY(3,5-Br)GAP is a novel minimalist peptide elastomer.

Angiogenic Hydrogels to Accelerate Early Wound Healing.

Diabetes mellitus affects an increasing proportion of the population, and is projected to double by 2060. Comorbidities contribute to an interrupted healing process which is delayed, prolonged, and associated with increased susceptibility to infection and unresolved inflammation. This leads to chronic nonhealing wounds and potential amputation. Here, the use of a bioactive angiogenic peptide-based hydrogel, SLan, is examined to improve early wound healing in diabetic rats, and its performance is compared to clinically utilized biosynthetic peptide-based materials such as Puramatrix. Streptozotocin-treated diabetic rats underwent 8mm biopsy wounding in their dorsum. Wounds are treated with either Low (1 w%) SLan, High (4 w%) SLan, phosphate buffered saline (PBS), Puramatrix, or K2 (an unfunctionalized nonbioactive control sequentially similar to SLan), covered with Tegaderm, and monitored on for a month; animals are sacrificed for histomorphic analyses and immunostaining. Pharmacokinetic analysis showing no trafficking of peptides from the wound into the circulation. SLan groups show similar wound contraction as control groups (Puramatrix, PBS, and K2), however, showing marked improvement in healing in earlier time points, including increased deposition of new mature blood vessels. Altogether the results suggest this material can be used to "jumpstart" the diabetic wound healing process.

Multicomponent Hydrogel Matrices of Fmoc-FF and Cationic Peptides for Application in Tissue Engineering.

In the last years, peptide-based hydrogels are being increasingly used as suitable matrices for biomedical and pharmaceutical applications, including drug delivery and tissue engineering. Recently, the synthesis and the gelation properties of a small library of cationic peptides, containing a Lys residue at the C-terminus and derivatized with an Fmoc group or with the fluorenyl methoxycarbonyl-diphenylalanine (FmocFF) at the N-terminus are derived. Here, it is demonstrated that the combination of these peptides with the well-known hydrogelator FmocFF, in different weight/weight ratios, allows the achievement of seven novel self-sorted hydrogels, which share similar peptide organization of their supramolecular matrix. Rheological and relaxometric characterization highlight a different mechanical rigidity and water mobility in the gels as demonstrated by the storage modulus values (200 Pa < G' < 35 000Pa) and by relaxometry, respectively. In vitro studies demonstrate that most of the tested mixed hydrogels do not disturb significantly the cell viability (>95%) over 72 h of treatment. Moreover, in virtue to its capability to strongly favor adhesion, spreading and duplication of 3T3-L1 cells, one of the tested hydrogel may be eligible as synthetic extracellular matrix.

Aromatic Dipeptide Homologue-Based Hydrogels for Photocontrolled Drug Release.

Peptide-based hydrogels are considered of special importance due to their biocompatibility and biodegradability. They have a wide range of applications in the biomedical field, such as drug delivery, tissue engineering, wound healing, cell culture media, and biosensing. Nevertheless, peptide-based hydrogels composed of natural α-amino acids are limited for in vivo applications because of the possible degradation by proteolytic enzymes. To circumvent this issue, the incorporation of extra methylene groups within the peptide sequence and the protection of the terminal amino group can increase the enzymatic stability. In this context, we investigated the self-assembly capacity of aromatic dipeptides (Boc-α-diphenylalanine and Boc-α-dityrosine) and their β- and γ-homologues and developed stable hydrogels. Surprisingly, only the Boc-diphenylalanine analogues were able to self-assemble and form hydrogels. A model drug, l-ascorbic acid, and oxidized carbon nanotubes (CNTs) or graphene oxide were then incorporated into the hydrogels. Under near-infrared light irradiation, the photothermal effect of the carbon nanomaterials induced the destabilization of the gel structure, which caused the release of a high amount of drug, thus providing opportunities for photocontrolled on-demand drug release.

Controlling Doxorubicin Release from a Peptide Hydrogel through Fine-Tuning of Drug-Peptide Fiber Interactions.

Hydrogels are versatile materials that have emerged in the last few decades as promising candidates for a range of applications in the biomedical field, from tissue engineering and regenerative medicine to controlled drug delivery. In the drug delivery field, in particular, they have been the subject of significant interest for the spatially and temporally controlled delivery of anticancer drugs and therapeutics. Self-assembling peptide-based hydrogels, in particular, have recently come to the fore as potential candidate vehicles for the delivery of a range of drugs. In order to explore how drug–peptide interactions influence doxorubicin (Dox) release, five β-sheet-forming self-assembling peptides with different physicochemical properties were used for the purpose of this study, namely: FEFKFEFK (F8), FKFEFKFK (FK), FEFEFKFE (FE), FEFKFEFKK (F8K), and KFEFKFEFKK (KF8K) (F: phenylalanine; E: glutamic acid; K: lysine). First, Dox-loaded hydrogels were characterized to ensure that the incorporation of the drug did not significantly affect the hydrogel properties. Subsequently, Dox diffusion out of the hydrogels was investigated using UV absorbance. The amount of drug retained in F8/FE composite hydrogels was found to be directly proportional to the amount of charge carried by the peptide fibers. When cation−π interactions were used, the position and number of end-lysine were found to play a key role in the retention of Dox. In this case, the amount of Dox retained in F8/KF8K composite hydrogels was linked to the amount of end-lysine introduced, and an end-lysine/Dox interaction stoichiometry of 3/1 was obtained. For pure FE and KF8K hydrogels, the maximum amount of Dox retained was also found to be related to the overall concentration of the hydrogels and, therefore, to the overall fiber surface area available for interaction with the drug. For 14 mM hydrogel, ∼170–200 μM Dox could be retained after 24 h. This set of peptides also showed a broad range of susceptibilities to enzymatic degradation opening the prospect of being able to control also the rate of degradation of these hydrogels. Finally, the Dox released from the hydrogel was shown to be active and affect 3T3 mouse fibroblasts viability in vitro. Our study clearly shows the potential of this peptide design as a platform for the formulation of injectable or sprayable hydrogels for controlled drug delivery.

Growth and differentiation of human induced pluripotent stem cell (hiPSC) derived kidney organoids using fully synthetic peptide hydrogels

Human induced pluripotent stem cell (hiPSC)‐derived kidney organoids have prospective applications ranging from basic disease modelling to personalised medicine. However, there remains a necessity to refine the biophysical and biochemical parameters that govern kidney organoid formation. Differentiation within fully‐controllable and physiologically relevant 3D growth environments will be critical to improving organoid reproducibility and maturation. Here, we matured hiPSC‐derived kidney organoids within fully synthetic self‐assembling peptide hydrogels (SAPHs) of variable stiffness (storage modulus, G′). The resulting organoids contained complex structures comparable to those differentiated within the animal‐derived matrix, Matrigel. Single‐cell RNA sequencing (scRNA‐seq) was then used to compare organoids matured within SAPHs to those grown within Matrigel or at the air‐liquid interface. A total of 13,179 cells were analysed, revealing 14 distinct clusters. Organoid compositional analysis revealed a larger proportion of nephron cell types within Transwell‐derived organoids, while SAPH derived organoids were enriched for stromal‐associated cell populations. Notably, differentiation within a higher G’ SAPH generated podocytes with more mature gene expression profiles. Additionally, maturation within a 3D microenvironment significantly reduced the derivation of offtarget cell types, which are a known limitation of current kidney organoid protocols. This work demonstrates the utility of synthetic peptide‐based hydrogels with a defined stiffness, as a minimally complex microenvironment for the selected differentiation of kidney organoids.