Peptide hydrogels as mucoadhesives for local drug delivery

Vaccine delivery systems and administration routes: Advanced biotechnological techniques to improve the immunization efficacy

Since the first use of vaccine tell the last COVID-19 pandemic caused by spread of SARS-CoV-2 worldwide, the use of advanced biotechnological techniques has accelerated the development of different types and methods for immunization. The last pandemic showed that the nucleic acid-based vaccine, especially mRNA, has an advantage in terms of development time; however, it showed a very critical drawback namely, the higher costs when compared to other strategies, and its inability to protect against new variants. This showed the need of more improvement to reach a better delivery and efficacy. In this review we will describe different vaccine delivery systems including, the most used viral vector, and also variable strategies for delivering of nucleic acid-based vaccines especially lipid-based nanoparticles formulation, polymersomes, electroporation and also the new powerful tools for the delivery of mRNA, which is based on the use of cell-penetrating peptides (CPPs). Additionally, we will also discuss the main challenges associated with each system. Finlay, the efficacy and safety of the vaccines depends not only on the formulations and delivery systems, but also the dosage and route of administration are also important players, therefore we will see the different routes for the vaccine administration including traditionally routes (intramuscular, Transdermal, subcutaneous), oral inhalation or via nasal mucosa, and will describe the advantages and disadvantage of each administration route.

Using Chemistry To Recreate the Complexity of the Extracellular Matrix: Guidelines for Supramolecular Hydrogel-Cell Interactions

Hydrogels have emerged as a promising class of extracellular matrix (ECM)-mimicking materials in regenerative medicine. Here, we briefly describe current state-of-the-art of ECM-mimicking hydrogels, ranging from natural to hybrid to completely synthetic versions, giving the prelude to the importance of supramolecular interactions to make true ECM mimics. The potential of supramolecular interactions to create ECM mimics for cell culture is illustrated through a focus on two different supramolecular hydrogel systems, both developed in our laboratories. We use some recent, significant findings to present important design principles underlying the cell-material interaction. To achieve cell spreading, we propose that slow molecular dynamics (monomer exchange within fibers) is crucial to ensure the robust incorporation of cell adhesion ligands within supramolecular fibers. Slow bulk dynamics (stress-relaxation─fiber rearrangements, τ1/2 ≈ 1000 s) is required to achieve cell spreading in soft gels (<1 kPa), while gel stiffness overrules dynamics in stiffer gels. Importantly, this resonates with the findings of others which specialize in different material types: cell spreading is impaired in case substrate relaxation occurs faster than clutch binding and focal adhesion lifetime. We conclude with discussing considerations and limitations of the supramolecular approach as well as provide a forward thinking perspective to further understand supramolecular hydrogel-cell interactions. Future work may utilize the presented guidelines underlying cell-material interactions to not only arrive at the next generation of ECM-mimicking hydrogels but also advance other fields, such as bioelectronics, opening up new opportunities for innovative applications.

Advancements in self-assembling peptides: Bridging gaps in 3D cell culture and electronic device fabrication

Self-assembling peptides (SAPs) show promise in creating synthetic microenvironments that regulate cellular function and tissue repair. Also, the precise π-π interactions and hydrogen bonding within self-assembled peptide structures enable the creation of quantum confined structures, leading to reduced band gaps and the emergence of semiconductor properties within the superstructures. This review emphasizes the need for standardized 3D cell culture methods and electronic devices based on SAPs for monitoring cell communication and controlling cell surface morphology. Additionally, the gap in understanding the relationship between SAP peptide sequences and nanostructures is highlighted, underscoring the importance of optimizing peptide deposition parameters, which affect charge transport and bioactivity due to varying morphologies. The potential of peptide nanofibers as extracellular matrix mimics and the introduction of the zone casting method for improved film deposition are discussed within this review, aiming to bridge knowledge gaps and offer insights into fields like tissue engineering and materials science, with the potential for groundbreaking applications at the interface of biology and materials engineering.

Fmoc-diphenylalanine gelating nanoarchitectonics: A simplistic peptide self-assembly to meet complex applications

9-fluorenylmethoxycarbonyl-diphenylalanine (Fmoc-FF), has been has been extensively explored due to its ultrafast self-assembly kinetics, inherent biocompatibility, tunable physicochemical properties, and especially, the capability of forming self-sustained gels under physiological conditions. Consequently, various methodologies to develop Fmoc-FF gels and their corresponding applications in biomedical and industrial fields have been extensively studied. Herein, we systemically summarize the mechanisms underlying Fmoc-FF self-assembly, discuss the preparation methodologies of Fmoc-FF hydrogels, and then deliberate the properties as well as the diverse applications of Fmoc-FF self-assemblies. Finally, the contemporary shortcomings which limit the development of Fmoc-FF self-assembly are raised and the alternative solutions are proposed, along with future research perspectives.

Preparation and applications of artificial mucins in biomedicine

Mucus is an essential barrier material that separates organisms from the outside world. This slippery material regulates the transport of nutrients, drugs, gases, and pathogens toward the cell surface. The surface of the cell itself is coated in a mucus-like barrier of glycoproteins and glycolipids. Mucin glycoproteins are the primary component of mucus and the epithelial glycocalyx. Aberrant mucin production is implicated in diverse disease states from cancer and inflammation to pre-term birth and infection. Biological mucins are inherently heterogenous in structure, which has challenged understanding their molecular functions as a barrier and as biochemically active proteins. Therefore, many synthetic materials have been developed as artificial mucins with precisely tunable structures. This review highlights advances in design and synthesis of artificial mucins and their application in biomedical studies of mucin chemistry, biology, and physics.

Synthesis and biomedical applications of mucin mimic materials

Mucin glycoproteins are the major component of mucus and coat epithelial cell surfaces forming the glycocalyx. The glycocalyx and mucus are involved in the transport of nutrients, drugs, gases, and pathogens toward the cell surface. Mucins are also involved in diverse diseases such as cystic fibrosis and cancer. Due to inherent heterogeneity in native mucin structure, many synthetic materials have been designed to probe mucin chemistry, biology, and physics. Such materials include various glycopolymers, low molecular weight glycopeptides, glycopolypeptides, polysaccharides, and polysaccharide-protein conjugates. This review highlights advances in the area of design and synthesis of mucin mimic materials, and their biomedical applications in glycan binding, epithelial models of infection, therapeutic delivery, vaccine formulation, and beyond.

Peptide-Based Supramolecular Hydrogels as Drug Delivery Agents: Recent Advances

Supramolecular peptide hydrogels have many important applications in biomedicine, including drug delivery applications for the sustained release of therapeutic molecules. Targeted and selective drug administration is often preferential to systemic drug delivery, as it can allow reduced doses and can avoid the toxicity and side-effects caused by off-target binding. New discoveries are continually being reported in this rapidly developing field. In this review, we report the latest developments in supramolecular peptide-based hydrogels for drug delivery, focusing primarily on discoveries that have been reported in the last four years (2018-present). We address clinical points, such as peptide self-assembly and drug release, mechanical properties in drug delivery, peptide functionalization, bioadhesive properties and drug delivery enhancement strategies, drug release profiles, and different hydrogel matrices for anticancer drug loading and 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.

Targeting Multidrug Resistance With Antimicrobial Peptide-Decorated Nanoparticles and Polymers

As a category of small peptides frequently found in nature, antimicrobial peptides (AMPs) constitute a major part of the innate immune system of various organisms. Antimicrobial peptides feature various inhibitory effects against fungi, bacteria, viruses, and parasites. Due to the increasing concerns of antibiotic resistance among microorganisms, development of antimicrobial peptides is an emerging tool as a favorable applicability prospect in food, medicine, aquaculture, animal husbandry, and agriculture. This review presents the latest research progress made in the field of antimicrobial peptides, such as their mechanism of action, classification, application status, design techniques, and a review on decoration of nanoparticles and polymers with AMPs that are used in treating multidrug resistance. Lastly, we will highlight recent progress in antiviral peptides to treat emerging viral diseases (e.g., anti-coronavirus peptides) and discuss the outlook of AMP applications.

Nanovaccine Delivery Approaches and Advanced Delivery Systems for the Prevention of Viral Infections: From Development to Clinical Application

Viral infections causing pandemics and chronic diseases are the main culprits implicated in devastating global clinical and socioeconomic impacts, as clearly manifested during the current COVID-19 pandemic. Immunoprophylaxis via mass immunisation with vaccines has been shown to be an efficient strategy to control such viral infections, with the successful and recently accelerated development of different types of vaccines, thanks to the advanced biotechnological techniques involved in the upstream and downstream processing of these products. However, there is still much work to be done for the improvement of efficacy and safety when it comes to the choice of delivery systems, formulations, dosage form and route of administration, which are not only crucial for immunisation effectiveness, but also for vaccine stability, dose frequency, patient convenience and logistics for mass immunisation. In this review, we discuss the main vaccine delivery systems and associated challenges, as well as the recent success in developing nanomaterials-based and advanced delivery systems to tackle these challenges. Manufacturing and regulatory requirements for the development of these systems for successful clinical and marketing authorisation were also considered. Here, we comprehensively review nanovaccines from development to clinical application, which will be relevant to vaccine developers, regulators, and clinicians.

Recent Advances and Challenges in Nanodelivery Systems for Antimicrobial Peptides (AMPs)

Antimicrobial peptides (AMPs) can be used as alternative therapeutic agents to traditional antibiotics. These peptides have abundant natural template sources and can be isolated from animals, plants, and microorganisms. They are amphiphilic and mostly net positively charged, and they have a broad-spectrum inhibitory effect on bacteria, fungi, and viruses. AMPs possess significant rapid killing effects and do not interact with specific receptors on bacterial surfaces. As a result, drug resistance is rarely observed with treatments. AMPs, however, have some operational problems, such as a susceptibility to enzymatic (protease) degradation, toxicity in vivo, and unclear pharmacokinetics. However, nanodelivery systems loaded with AMPs provide a safe mechanism of packaging such peptides before they exert their antimicrobial actions, facilitate targeted delivery to the sites of infection, and control the release rate of peptides and reduce their toxic side effects. However, nanodelivery systems using AMPs are at an early stage of development and are still in the laboratory phase of development. There are also some challenges in incorporating AMPs into nanodelivery systems. Herein, an insight into the nanotechnology challenges in delivering AMPs, current advances, and remaining technological challenges are discussed in depth.

Self-assembling peptides as vectors for local drug delivery and tissue engineering applications

Molecular self-assembly has forged a new era in the development of advanced biomaterials for local drug delivery and tissue engineering applications. Given their innate biocompatibility and biodegradability, self-assembling peptides (SAPs) have come in the spotlight of such applications. Short and water-soluble SAP biomaterials associated with enhanced pharmacokinetic (PK) and pharmacodynamic (PD) responses after the topical administration of the therapeutic systems, or improved regenerative potential in tissue engineering applications will be the focus of the current review. SAPs are capable of generating supramolecular structures using a boundless array of building blocks, while peptide engineering is an approach commonly pursued to encompass the desired traits to the end composite biomaterials. These two elements combined, expand the spectrum of SAPs multi-functionality, constituting them potent biomaterials for use in various biomedical applications.

Respiratory delivery of favipiravir-tocilizumab combination through mucoadhesive protein-lipidic nanovesicles: prospective therapeutics against COVID-19

Coronavirus disease 19 (COVID-19) is the prime global health concern of the year 2020. Infecting more than 112 million individuals so far, this pandemic has already reported more than 2.4 million deaths around the world. With such high infectivity and mortality, effective treatment intervention is the need of the hour. The integration of medical science with nanotechnology may solve the current problem by exploring collective benefits. In this manuscript, we theoretically proposed the duo-combination of an approved antiviral i.e. favipiravir along with an immunomodulator i.e. tocilizumab loaded in protein-lipid nanovesicles as an effective anti-COVID-19 therapeutic. This proposed nanomedicine delivered through the respiratory mode may enhance the effectiveness of the antiviral and help in restricting the virus and associated complications, utilizing both anti-viral activity and immunomodulation in COVID-19 patients. This proposed nanomedicine could be an effective treatment modality for the severe acute respiratory syndrome- coronavirus-2 (SARS-CoV-2) infected patients.

Engineering a cell-hydrogel-fibre composite to mimic the structure and function of the tendon synovial sheath

The repair of tendon injuries is often compromised by post-operative peritendinous adhesions. Placing a physical barrier at the interface between the tendon and the surrounding tissue could potentially solve this problem by reducing adhesion formation. At present, no such system is available for routine use in clinical practice. Here, we propose the development of a bilayer membrane combining a nanofibrous poly(ε-caprolactone) (PCL) electrospun mesh with a layer of self-assembling peptide hydrogel (SAPH) laden with type-B synoviocytes. This bilayer membrane would act as an anti-adhesion system capable of restoring tendon lubrication, while assisting with synovial sheath regeneration. The PCL mesh showed adequate mechanical properties (Young's modulus=19±4 MPa, ultimate tensile stress=9.6±1.7 MPa, failure load=0.5±0.1 N), indicating that the membrane is easy to handle and capable to withstand the frictional forces generated on the tendon's surface during movement (~0.3 N). Morphological analysis confirmed the generation of a mesh with nanosized PCL fibres and small pores (< 3 μm), which prevented fibroblast infiltration to impede extrinsic healing but still allowing diffusion of nutrients and waste. Rheological tests showed that incorporation of SAPH layer allows good lubrication properties when the membrane is articulated against porcine tendon or hypodermis, suggesting that restoration of tendon gliding is possible upon implantation. Moreover, viability and metabolic activity tests indicated that the SAPH was conducive to rabbit synoviocyte growth and proliferation over 28 days of 3D culture, sustaining cell production of specific matrix components, particularly hyaluronic acid. Synoviocyte-laden peptide hydrogel promoted a sustained endogenous production of hyaluronic acid, providing an anti-friction layer that potentially restores the tendon gliding environment.

Hydrogels as Drug Delivery Systems: A Review of Current Characterization and Evaluation Techniques

Owing to their tunable properties, controllable degradation, and ability to protect labile drugs, hydrogels are increasingly investigated as local drug delivery systems. However, a lack of standardized methodologies used to characterize and evaluate drug release poses significant difficulties when comparing findings from different investigations, preventing an accurate assessment of systems. Here, we review the commonly used analytical techniques for drug detection and quantification from hydrogel delivery systems. The experimental conditions of drug release in saline solutions and their impact are discussed, along with the main mathematical and statistical approaches to characterize drug release profiles. We also review methods to determine drug diffusion coefficients and in vitro and in vivo models used to assess drug release and efficacy with the goal to provide guidelines and harmonized practices when investigating novel hydrogel drug delivery systems.

Recent advances in the fabrication, functionalization, and bioapplications of peptide hydrogels

Self-assembled peptide-based nanomaterials have exhibited wide application potential in the fields of materials science, nanodevices, biomedicine, tissue engineering, biosensors, energy storage, environmental science, and others. Due to their porous structure, strong mechanical stability, high biocompatibility, and easy functionalization, three-dimensional self-assembled peptide hydrogels revealed promising potential in bio-related applications. To present the advances in this interesting topic, we present a review on the synthesis and functionalization of peptide hydrogels, as well as their applications in drug delivery, antibacterial materials, cell culture, biomineralization, bone tissue engineering, and biosensors. Specifically, we focus on the fabrication methods of peptide hydrogels through physical, chemical, and biological stimulations. In addition, the functional design of peptide hydrogels by incorporation with polymers, DNA, protein, nanoparticles, and carbon materials is introduced and discussed in detail. It is expected that this work will be helpful not only for the design and synthesis of various peptide-based nanostructures and nanomaterials, but also for the structural and functional tailoring of peptide-based nanomaterials to meet specific demands.

Block copolymer [(L-GluA-5-BE)-b-(L-AspA-4-BE)]-based nanoflower capsules with thermosensitive morphology and pH-responsive drug release for cancer therapy

Herein, the synthesis of an amino-acid-based di-block copolymer (di-BCP) in-between an l-glutamic acid-5-benzyl ester and l-aspartic acid-4-benzyl ester [(l-GluA-5-BE)-b-(l-AspA-4-BE)] has been reported. However, the synthesis of di-BCP of [(l-GluA-5-BE)-b-(l-AspA-4-BE)] was carried out through the facile modified ring-opening polymerization (ROP) without using any surfactants and harmful chemicals. Interestingly, the synthesized [(l-GluA-5-BE)-b-(l-AspA-4-BE)] has been used to design nanoflower capsules (NFCs) with surface-functionalized nanoflakes and petals. Notably, the simple solvent propanol has been used as a dispersing medium for the di-BCP-based powder to observe morphology of NFCs. Moreover, these amino-acid-based NFCs are biocompatible, biodegradable, and bio-safe for mankind usage. Consequently, di-BCP-based NFCs show changes in morphology with different temperature conditions, i.e., at ∼10 °C, ∼25 °C (RT), and ∼37 °C (body temperature). Furthermore, the average thickness of the surface-functionalized nanopetals has been calculated as ∼324 nm (in diameter). Similarly, the average distance between petals is calculated as 3.6 μm and the pore depth is ∼21 nm. Additionally, the porosity throughout the surface of capsules in-between nanopetals is an advantageous characteristic feature to improve the drug/paclitaxel (PTX) loading capacity. It is a unique and novel approach to design NFCs, which are a potential payload for nanomedicine and cancer therapy. Furthermore, NFCs were used to evaluate the loading efficacy of drugs and showed ∼78% (wt/wt%) of the PTX loading. Moreover, NFCs showed ∼74% drug release at physiological body temperature. Thus, NFCs showed remarkable release at acidic pH medium. However, PTX released from NFCs showed greater cell inhibition (i.e., ∼79%) with an increase of the PTX concentration after 24 h incubation over HeLa (human epithelial cervical cancer) cells. Besides, PTX released from NFC showed significant (∼34%) cell killing capacity. Such promising NFCs are recommended for breast, liver, and lung cancer therapeutics.

Improving and fine-tuning the properties of peptide-based hydrogels via incorporation of peptide nucleic acids

Peptide self-assemblies have attracted intense research interest over the last few decades thanks to their implications in key biological processes (e.g., amyloid formation) and their use in biotechnological and (bio)material fields. In particular, peptide-based hydrogels have been highly considered as high potential supramolecular materials in the biomedical domain and open new horizons in terms of applications. To further understand their self-assembly mechanisms and to optimize their properties, several strategies have been proposed with the modification of the constituting amino acid chains via, per se, the introduction of d-amino acids, halogenated amino acids, pseudopeptide bonds, or other chemical moieties. In this context, we report herein on the incorporation of DNA-nucleobases into their peptide nucleic acid (PNA) forms to develop a new series of hybrid nucleopeptides. Thus, depending on the nature of the nucleobase (i.e., thymine, cytosine, adenine or guanine), the physicochemical and mechanical properties of the resulting hydrogels can be significantly improved and fine-tuned with, for instance, drastic enhancements of both the gel stiffness (up to 70-fold) and the gel resistance to external stress (up to 40-fold), and the generation of both thermo-reversible and uncommon red-edge excitation shift (REES) properties. To decipher the actual role of each PNA moiety in the self-assembly processes, the induced modifications from the molecular to the macroscopic scales are studied thanks to the multiscale approach based on a large panel of analytical techniques (i.e., rheology, NMR relaxometry, TEM, thioflavin T assays, FTIR, CD, fluorescence, NMR chemical shift index). Thus, such a strategy provides new opportunities to adapt and fit hydrogel properties to the intended ones and pushes back the limits of supramolecular materials.

Self-assembling Peptides in Current Nanomedicine: Versatile Nanomaterials for Drug Delivery

BACKGROUND

The development of modern nanomedicine greatly depends on the involvement of novel materials as drug delivery system. In order to maximize the therapeutic effects of drugs and minimize their side effects, a number of natural or synthetic materials have been widely investigated for drug delivery. Among these materials, biomimetic self-assembling peptides (SAPs) have received more attention in recent years. Considering the rapidly growing number of SAPs designed for drug delivery, a summary of how SAPs-based drug delivery systems were designed, would be beneficial.

METHOD

We outlined research works on different SAPs that have been investigated as carriers for different drugs, focusing on the design of SAPs nanomaterials and how they were used for drug delivery in different strategies.

RESULTS

Based on the principle rules of chemical complementarity and structural compatibility, SAPs such as ionic self-complementary peptide, peptide amphiphile and surfactant-like peptide could be designed. Determined by the features of peptide materials and the drugs to be delivered, different strategies such as hydrogel embedding, hydrophobic interaction, electrostatic interaction, covalent conjugation or the combination of them could be employed to fabricate SAPs-drug complex, which could achieve slow release, targeted or environment-responsive delivery of drugs. Furthermore, some SAPs could also be combined with other types of materials for drug delivery, or even act as drug by themselves.

CONCLUSION

Various types of SAPs have been designed and used for drug delivery following various strategies, suggesting that SAPs as a category of versatile nanomaterials have promising potential in the field of nanomedicine.

Self-assembling peptide-based nanodrug delivery systems

Self-assembling peptide-based nanodrug delivery systems (NDDs), consisting of naturally occurring amino acids, not only share the advantages of traditional nanomedicine but also possess the unique properties of excellent biocompatibility, biodegradability, flexible responsiveness, specific biological function, and synthetic feasibility. Physical methods, enzymatic reaction, chemical reaction, and biosurface induction can yield versatile peptide-based NDDs; flexible responsiveness is their main advantage. Different functional peptides and abundant covalent modifications endow such systems with precise controllability and multifunctionality. Inspired by the above merits, researchers have taken advantage of the self-assembling peptide-based NDDs and achieved the accurate delivery of drugs to the lesion site. The present review outlines the methods for designing self-assembling peptide-based NDDs for small-molecule drugs, with an emphasis on the different drug delivery strategies and their applications in using peptides and peptide conjugates.

Molecular Sponge: pH-Driven Reversible Squeezing of Stimuli-Sensitive Peptide Monolayers

The cyclic change of structure, thickness, and density, with pH switching from acidic (pH = 3) to basic (pH = 11) condition, has been revealed for chemisorbed monolayers of the peptide Lipo-Aib-Lys-Leu-Aib-Lys-Lys-Leu-Aib-Lys-Ile-Lol, a trichogin GA IV-analogue carrying Lys residues instead of Gly ones at positions 2, 5, 6, and 9, while a homologous peptide not containing Lys residues does not show any response to pH changes. Experimental and theoretical results, obtained by means of quartz crystal microbalance with dissipation monitoring, surface plasmon resonance, nanoplasmonic sensing technique, Fourier transform infrared-reflection attenuated spectroscopy and dynamic force spectroscopy, and molecular dynamics simulations provide detailed information on the overall monolayer structure changes with pH, including the analysis of the intra- and interchain peptide dynamics, the structure of the peptide layer/water/solid interface, as well as the position and role of solvation and nonsolvation water. The observed stimuli-responsive behavior of L1 peptide monolayers is accounted in terms of the occurrence of a pH-induced wetting/dewetting process, due to the pH-induced switching of the hydrophilic character of charged lysine groups to hydrophobic one of the same uncharged groups, along the peptide chain. This behavior in turn promotes the collective change of the aggregation state of the peptide chains. The present results may pave the way to critically reexamine the mechanism of stimuli-responsive systems.

Mechanics of composite hydrogels approaching phase separation

For polymer-particle composites, limited thermodynamic compatibility of polymers and particles often leads to poor dispersal and agglomeration of the particles in the matrix, which negatively impacts the mechanics of composites. To study the impact of particle compatibility in polymer matrices on the mechanical properties of composites, we here study composite silica- protein based hydrogels. The polymer used is a previously studied telechelic protein-based polymer with end groups that form triple helices, and the particles are silica nanoparticles that only weakly associate with the polymer matrix. At 1mM protein polymer, up to 7% of silica nanoparticles can be embedded in the hydrogel. At higher concentrations the system phase separates. Oscillatory rheology shows that at high frequencies the particles strengthen the gels by acting as short-lived multivalent cross-links, while at low frequencies, the particles reduce the gel strength, presumably by sequestering part of the protein polymers in such a way that they can no longer contribute to the network strength. As is generally observed for polymer/particle composites, shear-induced polymer desorption from the particles leads to a viscous dissipation that strongly increases with increasing particle concentration. While linear rheological properties as function of particle concentration provide no signals for an approaching phase separation, this is very different for the non-linear rheology, especially fracture. Strain-at-break decreases rapidly with increasing particle concentration and vanishes as the phase boundary is approached, suggesting that the interfaces between regions of high and low particle densities in composites close to phase separation provide easy fracture planes.

RNA extraction from self-assembling peptide hydrogels to allow qPCR analysis of encapsulated cells

Self-assembling peptide hydrogels offer a novel 3-dimensional platform for many applications in cell culture and tissue engineering but are not compatible with current methods of RNA isolation; owing to interactions between RNA and the biomaterial. This study investigates the use of two techniques based on two different basic extraction principles: solution-based extraction and direct solid-state binding of RNA respectively, to extract RNA from cells encapsulated in four β-sheet forming self-assembling peptide hydrogels with varying net positive charge. RNA-peptide fibril interactions, rather than RNA-peptide molecular complexing, were found to interfere with the extraction process resulting in low yields. A column-based approach relying on RNA-specific binding was shown to be more suited to extracting RNA with higher purity from these peptide hydrogels owing to its reliance on strong specific RNA binding interactions which compete directly with RNA-peptide fibril interactions. In order to reduce the amount of fibrils present and improve RNA yields a broad spectrum enzyme solution-pronase-was used to partially digest the hydrogels before RNA extraction. This pre-treatment was shown to significantly increase the yield of RNA extracted, allowing downstream RT-qPCR to be performed.

Antimicrobial Peptides and Nanotechnology, Recent Advances and Challenges

Antimicrobial peptides are sequences of amino acids, which present activity against microorganisms. These peptides were discovered over 70 years ago, and are abundant in nature from soil bacteria, insects, amphibians to mammals and plants. They vary in amino acids number, the distance between amino acids within individual peptide structure, net charge, solubility and other physical chemical properties as well as differ in mechanism of action. These peptides may provide an alternative treatment to conventional antibiotics, which encounter resistance such as the peptide nisin applied in treating methicillin resistant Staphylococcus aureus (MRSA) or may behave synergistically with known antibiotics against parasites for instance, nisin Z when used in synergy with ampicillin reported better activity against Pseudomonas fluorescens than when the antibiotic was alone. AMPs are known to be active against viruses, bacteria, fungi and protozoans. Nanotechnology is an arena which explores the synthesis, characterization and application of an array of delivery systems at a one billionth of meter scale. Such systems are implemented to deliver drugs, proteins, vaccines, and peptides. The role of nanotechnology in delivering AMPs is still at its early development stage. There are challenges of incorporating AMPs into drug delivery system. This review intends to explore in depth, the role of nanotechnology in delivering AMPs as well as presenting the current advances and accompanying challenges of the technology.

In vivo characterisation of a therapeutically relevant self-assembling 18 F-labelled β-sheet forming peptide and its hydrogel using positron emission tomography

Positron emission tomography (PET) and fluorescence labelling have been used to assess the pharmacokinetics, biodistribution and eventual fate of a hydrogel‐forming nonapeptide, FEFKFEFKK (F9), in healthy mice, using ¹⁸F‐labelled and fluorescein isothiocyanate (FITC)‐labelled F9 analogues. F9 was site‐specifically radiolabelled with 2‐[¹⁸F]fluoro‐3‐pyridinecarboxaldehyde ([¹⁸F]FPCA) via oxime bond formation. [¹⁸F]FPCA‐F9 in vivo fate was evaluated both as a solution, following intravenous administration, and as a hydrogel when subcutaneously injected. The behaviour of FITC‐F9 hydrogel was assessed following subcutaneous injection. [¹⁸F]FPCA‐F9 demonstrated high plasma stability and primarily renal excretion; [¹⁸F]FPCA‐F9 when in solution and injected into the bloodstream displayed prompt bladder uptake (53.4 ± 16.6 SUV at 20 minutes postinjection) and rapid renal excretion, whereas [¹⁸F]FPCA‐F9 hydrogel, formed by co‐assembly of [¹⁸F]FPCA‐F9 monomer with unfunctionalised F9 peptide and injected subcutaneously, showed gradual bladder accumulation of hydrogel fragments (3.8 ± 0.4 SUV at 20 minutes postinjection), resulting in slower renal excretion. Gradual disaggregation of the F9 hydrogel from the site of injection was monitored using FITC‐F9 hydrogel in healthy mice (60 ± 3 over 96 hours), indicating a biological half‐life between 1 and 4 days. The in vivo characterisation of F9, both as a gel and a solution, highlights its potential as a biomaterial.

Cross-linking of a biopolymer-peptide co-assembling system

The ability to guide molecular self-assembly at the nanoscale into complex macroscopic structures could enable the development of functional synthetic materials that exhibit properties of natural tissues such as hierarchy, adaptability, and self-healing. However, the stability and structural integrity of these kinds of materials remains a challenge for many practical applications. We have recently developed a dynamic biopolymer-peptide co-assembly system with the capacity to grow and undergo morphogenesis into complex shapes. Here we explored the potential of different synthetic (succinimidyl carboxymethyl ester, poly (ethylene glycol) ether tetrasuccinimidyl glutarate and glutaraldehyde) and natural (genipin) cross-linking agents to stabilize membranes made from these biopolymer-peptide co-assemblies. We investigated the cross-linking efficiency, resistance to enzymatic degradation, and mechanical properties of the different cross-linked membranes. We also compared their biocompatibility by assessing the metabolic activity and morphology of adipose-derived stem cells (ADSC) cultured on the different membranes. While all cross-linkers successfully stabilized the system under physiological conditions, membranes cross-linked with genipin exhibited better resistance in physiological environments, improved stability under enzymatic degradation, and a higher degree of in vitro cytocompatibility compared to the other cross-linking agents. The results demonstrated that genipin is an attractive candidate to provide functional structural stability to complex self-assembling structures for potential tissue engineering or in vitro model applications.

STATEMENT OF SIGNIFICANCE

Molecular self-assembly is widely used for the fabrication of complex functional biomaterials to replace and/or repair any tissue or organ in the body. However, maintaining the stability and corresponding functionality of these kinds of materials in physiological conditions remains a challenge. Chemical cross-linking strategies (natural or synthetic) have been used in an effort to improve their structural integrity. Here we investigate key performance parameters of different cross-linking strategies for stabilising self-assembled materials with potential biomedical applications using a novel protein-peptide co-assembling membrane as proof-of-concept. From the different cross-linkers tested, the natural cross-linker genipin exhibited the best performance. This cross-linker successfully enhanced the mechanical properties of the system enabling the maintenance of the structure in physiological conditions without compromising its bioactivity and biocompatibility. Altogether, we provide a systematic characterization of cross-linking alternatives for self-assembling materials focused on biocompatibility and stability and demonstrate that genipin is a promising alternative for the cross-linking of such materials with a wide variety of potential applications such as in tissue engineering and drug delivery.

Engineering β-sheet peptide assemblies for biomedical applications

Hydrogels have been widely studied in various biomedical applications, such as tissue engineering, cell culture, immunotherapy and vaccines, and drug delivery. Peptide-based nanofibers represent a promising new strategy for current drug delivery approaches and cell carriers for tissue engineering. This review focuses on the recent advances in the use of self-assembling engineered β-sheet peptide assemblies for biomedical applications. The applications of peptide nanofibers in biomedical fields, such as drug delivery, tissue engineering, immunotherapy, and vaccines, are highlighted. The current challenges and future perspectives for self-assembling peptide nanofibers in biomedical applications are discussed.

Peptide hydrogel in vitro non-inflammatory potential

Peptide‐based hydrogels have attracted significant interest in recent years as these soft, highly hydrated materials can be engineered to mimic the cell niche with significant potential applications in the biomedical field. Their potential use in vivo in particular is dependent on their biocompatibility, including their potential to cause an inflammatory response. In this work, we investigated in vitro the inflammatory potential of a β‐sheet forming peptide (FEFEFKFK; F: phenylalanine, E: glutamic acid; K: lysine) hydrogel by encapsulating murine monocytes within it (3D culture) and using the production of cytokines, IL‐β, IL‐6 and TNFα, as markers of inflammatory response. No statistically significant release of cytokines in our test sample (media + gel + cells) was observed after 48 or 72 h of culture showing that our hydrogels do not incite a pro‐inflammatory response in vitro. These results show the potential biocompatibility of these hydrogels and therefore their potential for in vivo use. The work also highlighted the difference in monocyte behaviour, proliferation and morphology changes when cultured in 2D vs. 3D. © 2016 The Authors Journal of Peptide Science published by European Peptide Society and John Wiley & Sons Ltd.

Self-assembling peptide hydrogel for intervertebral disc tissue engineering

Cell-based therapies for regeneration of intervertebral discs are regarded to hold promise for degenerative disc disease treatment, a condition that is strongly linked to lower back pain. A de novo self-assembling peptide hydrogel (SAPH), chosen for its biocompatibility, tailorable properties and nanofibrous architecture, was investigated as a cell carrier and scaffold for nucleus pulposus (NP) tissue engineering. Oscillatory rheology determined that the system would likely be deliverable via minimally invasive procedure and mechanical properties could be optimised to match the stiffness of the native human NP. After three-dimensional culture of NP cells (NPCs) in the SAPH, upregulation of NP-specific genes (KRT8, KRT18, FOXF1) confirmed that the system could restore the NP phenotype following de-differentiation during monolayer culture. Cell viability was high throughout culture whilst, similarly to NPCs in vivo, the viable cell population remained stable. Finally, the SAPH stimulated time-dependent increases in aggrecan and type II collagen deposition, two important NP extracellular matrix components. Results supported the hypothesis that the SAPH could be used as a cell delivery system and scaffold for the treatment of degenerative disc disease.

STATEMENT OF SIGNIFICANCE

Lower back pain (LBP) prevalence is widespread due to an aging population and the limited efficacy of current treatments. As LBP is strongly associated with intervertebral disc (IVD) degeneration, it is thought that cell-based therapies could alleviate LBP by repairing IVD tissue. Various natural and synthetic biomaterials have been investigated as potential IVD tissue engineering scaffolds. Self-assembling peptide hydrogels (SAPHs) combine advantages of both natural and synthetic biomaterials; for example they are biocompatible and have easily modifiable properties. The present study demonstrated that a de novo SAPH had comparable strength to the native tissue, was injectable, restored the IVD cell phenotype and stimulated deposition of appropriate matrix components. Results illustrated the promise of SAPHs as scaffolds for IVD tissue engineering.

Modification of β-Sheet Forming Peptide Hydrophobic Face: Effect on Self-Assembly and Gelation

β-Sheet forming peptides have attracted significant interest for the design of hydrogels for biomedical applications. One of the main challenges is the control and understanding of the correlations between peptide molecular structure, the morphology, and topology of the fiber and network formed as well as the macroscopic properties of the hydrogel obtained. In this work, we have investigated the effect that functionalizing these peptides through their hydrophobic face has on their self-assembly and gelation. Our results show that the modification of the hydrophobic face results in a partial loss of the extended β-sheet conformation of the peptide and a significant change in fiber morphology from straight to kinked. As a consequence, the ability of these fibers to associate along their length and form large bundles is reduced. These structural changes (fiber structure and network topology) significantly affect the mechanical properties of the hydrogels (shear modulus and elasticity).

Supramolecular Hydrogelators and Hydrogels: From Soft Matter to Molecular Biomaterials

In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping address fundamental questions about the mechanisms or the consequences of the self-assembly of molecules, including low molecular weight ones. Finally, we provide a perspective on supramolecular hydrogelators. We hope that this review will serve as an updated introduction and reference for researchers who are interested in exploring supramolecular hydrogelators as molecular biomaterials for addressing the societal needs at various frontiers.

Novel glycopolymer hydrogels as mucosa-mimetic materials to reduce animal testing

Glycopolymer hydrogels capable of mimicking mucosal tissue in mucoadhesion testing have been designed.

Self-assembling peptide/thermoresponsive polymer composite hydrogels: effect of peptide-polymer interactions on hydrogel properties

We have investigated the effect of doping the self-assembling octapeptide FEFEFKFK (F, phenylalanine; E, glutamic acid; K, lysine) hydrogels with various amounts of thermoresponsive conjugate of FEFEFKFK and poly(N-isopropylacrylamide) (PNIPAAm) in order to create novel hydrogels. The samples were characterized using a range of techniques including microdifferential scanning calorimetry (μDSC), oscillatory rheology, transmission electron microscopy (TEM), atomic force microscopy (AFM), and small angle neutron scattering (SANS). The peptide from the conjugate was shown to be incorporated into the peptide fiber, resulting in the polymer being anchored to the peptide fiber. The conjugation of the polymer to the peptide and its anchoring to the peptide fibers did not affect its lower critical solution temperature (LCST). On the other hand, it did result in a decrease in the LCST enthalpy and a significant increase in the G' of the hydrogels, suggesting the presence of hydrogen bond interactions between the peptide and the polymer. As a result, the polymer was found to adopt a fibrillar arrangement tightly covering the peptide fiber. The polymer was still found to go through a conformational change at the LCST, suggesting that it collapses onto the peptide fiber. On the other hand, the fibrillar network was found to be mainly unaffected by the polymer LCST. These changes at the LCST were also found to be fully reversible. The nature of the interaction between the polymer and the peptide was shown to have a significant effect on the conformation adopted by the polymer around the fibers and the mechanical properties of the hydrogels.