Self-assembling peptides cross-linked with genipin: resilient hydrogels and self-standing electrospun scaffolds for tissue engineering applications

Advances and applications of crosslinked electrospun biomacromolecular nanofibers

Electrospinning is a technology for fabricating ultrafine fibers from natural or synthetic polymers that have novel or enhanced functional properties. These fibers have found applications in a diverse range of fields, including the food, medicine, cosmetics, agriculture, and chemical industries. However, the tendency for electrospun nanofibers to dissociate when exposed to certain environmental conditions limits many of their practical applications. The structural integrity and functional attributes of these nanofibers can be improved using physical and/or chemical crosslinking methods. This review article discusses the formation of polymeric nanofibers using electrospinning and then describes how different crosslinking methods can be used to enhance their mechanical, thermal, and biological attributes. Methods for optimizing the crosslinking reactions are discussed, including proper selection of crosslinker type and reaction conditions. Then, food, medical, and separation applications of crosslinked electrospun fibers are assessed, including in bone and skin tissue engineering, wound healing, drug delivery, air filtration, water filtration, oil removal, food packaging, food preservation, and bioactive delivery. Finally, areas where future research are needed are highlighted, as well as possible future applications of crosslinked nanofibers.

In Situ Transglutaminase Cross-Linking Improves Mechanical Properties of Self-Assembling Peptides for Biomedical Applications

The development of three-dimensional (3D) biomaterials that mimic natural tissues is required for efficiently restoring physiological functions of injured tissues and organs. In the field of soft hydrogels, self-assembled peptides (SAPs) stand out as distinctive biomimetic scaffolds, offering tunable properties. They have garnered significant attention in nanomedicine due to their innate ability to self-assemble, resulting in the creation of fibrous nanostructures that closely mimic the microenvironment of the extracellular matrix (ECM). This unique feature ensures their biocompatibility and bioactivity, making them a compelling area of study over the past few decades. As they are soft hydrogels, approaches are necessary to enhance the stiffness and resilience of the SAP materials. This work shows an enzymatic strategy to selectively increase the stiffness and resiliency of functionalized SAPs using transglutaminase (TGase) type 2, an enzyme capable of triggering the formation of isopeptide bonds. To this aim, we synthesized a set of SAP sequences and characterized their cross-linking via rheological experiments, atomic force microscopy (AFM), thioflavin-T binding assay, and infrared spectroscopy (ATR-FTIR) tests. The results showed an improvement of the storage modulus of cross-linked SAPs at no cost of the maximum stress-at-failure. Further, in in vitro tests, we examined and validated the TGase capability to cross-link SAPs without hampering seeded neural stem cells (hNSCs) viability and differentiation, potentially leaving the door open for safe in situ cross-linking reactions in vivo.

Multiparametric in vitro and in vivo analysis of the safety profile of self-assembling peptides

Self-assembling peptides (SAPs) have gained significant attention in biomedicine because of their unique properties and ability to undergo molecular self-assembly driven by non-covalent interactions. By manipulating their composition and structure, SAPs can form well-ordered nanostructures with enhanced selectivity, stability and biocompatibility. SAPs offer advantages such as high chemical and biological diversity and the potential for functionalization. However, studies concerning its potentially toxic effects are very scarce, a limitation that compromises its potential translation to humans. This study investigates the potentially toxic effects of six different SAP formulations composed of natural amino acids designed for nervous tissue engineering and amenable to ready cross-linking boosting their biomechanical properties. All methods were performed in accordance with the relevant guidelines and regulations. A wound-healing assay was performed to evaluate how SAPs modify cell migration. The results in vitro demonstrated that SAPs did not induce genotoxicity neither skin sensitization. In vivo, SAPs were well-tolerated without any signs of acute systemic toxicity. Interestingly, SAPs were found to promote the migration of endothelial, macrophage, fibroblast, and neuronal-like cells in vitro, supporting a high potential for tissue regeneration. These findings contribute to the development and translation of SAP-based biomaterials for biomedical applications.

Recent Advances in the Development of Biomimetic Materials

In this review, we focused on recent efforts in the design and development of materials with biomimetic properties. Innovative methods promise to emulate cell microenvironments and tissue functions, but many aspects regarding cellular communication, motility, and responsiveness remain to be explained. We photographed the state-of-the-art advancements in biomimetics, and discussed the complexity of a "bottom-up" artificial construction of living systems, with particular highlights on hydrogels, collagen-based composites, surface modifications, and three-dimensional (3D) bioprinting applications. Fast-paced 3D printing and artificial intelligence, nevertheless, collide with reality: How difficult can it be to build reproducible biomimetic materials at a real scale in line with the complexity of living systems? Nowadays, science is in urgent need of bioengineering technologies for the practical use of bioinspired and biomimetics for medicine and clinics.

Low-power microwaves: a cell-compatible physical treatment to enhance the mechanical properties of self-assembling peptides

Biomaterials designed for tissue engineering applications should, among other requirements, mimic the native extracellular matrix (ECM) of the tissues to be regenerated, both in terms of biomimetic and mechanical properties. Ideally, the scaffold stiffness and stress resistance should be tuned for each specific implantation therapy. Self-assembling peptides (SAPs) are promising synthetic bionanomaterials prone to easy multi-functionalization, bestowing biomimetic properties. However, they usually yield soft and fragile hydrogels unsuited for the regeneration of medium-to-hard tissues. For this purpose, chemical cross-linking of SAPs is an option, but it often requires a moderately toxic and expensive chemical compound and/or the presence of specific residues/reactive sites, posing issues for its feasibility and translational potential. In this work, we introduced, characterized by rheology, atomic force microscopy (AFM), Thioflavin-T assay (ThT), and Fourier transform infrared (FT-IR) tests, and optimized (by tuning the power, temperature and treatment time) a novel fast, green and affordable methodology using mild microwave (MW) irradiation to increase the mechanical properties of diverse classes of SAPs. Low-power MWs increase stiffness, resilience, and β-structuration, while high-power MW treatments partially denature the tested SAPs. Our pure-physical methodology does not alter the SAP biomimetic properties (verified via in vitro tests of viability and differentiation of human neural stem cells), is compatible with already seeded cells, and is also synergic with genipin-based cross-linking of SAPs; therefore, it may become the next standard for SAP preparation in tissue engineering applications at hand of all research labs and in clinics.

Biomimetic Electrospun Self-Assembling Peptide Scaffolds for Neural Stem Cell Transplantation in Neural Tissue Engineering

Spinal cord regeneration using stem cell transplantation is a promising strategy for regenerative therapy. Stem cells transplanted onto scaffolds that can mimic natural extracellular matrix (ECM) have the potential to significantly improve outcomes. In this study, we strived to develop a cell carrier by culturing neural stem cells (NSCs) onto electrospun 2D and 3D constructs made up of specific crosslinked functionalized self-assembling peptides (SAPs) featuring enhanced biomimetic and biomechanical properties. Morphology, architecture, and secondary structures of electrospun scaffolds in the solid-state and electrospinning solution were studied step by step. Morphological studies showed the benefit of mixed peptides and surfactants as additives to form thinner, uniform, and defect-free fibers. It has been observed that β-sheet conformation as evidence of self-assembling has been predominant throughout the process except for the electrospinning solution. In vitro NSCs seeded on electrospun SAP scaffolds in 2D and 3D conditions displayed desirable proliferation, viability, and differentiation in comparison to the gold standard. In vivo biocompatibility assay confirmed the permissibility of implanted fibrous channels by foreign body reaction. The results of this study demonstrated that fibrous 2D/3D electrospun SAP scaffolds, when shaped as micro-channels, can be suitable to support NSC transplantation for regeneration following spinal cord injury.

A Light Scattering Investigation of Enzymatic Gelation in Self-Assembling Peptides

Self-assembling peptides (SAPs) have been increasingly studied as hydrogel-former gelators because they can create biocompatible environments. A common strategy to trigger gelation, is to use a pH variation, but most methods result in a change in pH that is too rapid, leading to gels with hardly reproducible properties. Here, we use the urea-urease reaction to tune gel properties, by a slow and uniform pH increase. We were able to produce very homogeneous and transparent gels at several SAP concentrations, ranging from c=1g/L to c=10g/L. In addition, by exploiting such a pH control strategy, and combining photon correlation imaging with dynamic light scattering measurements, we managed to unravel the mechanism by which gelation occurs in solutions of (LDLK)3-based SAPs. We found that, in diluted and concentrated solutions, gelation follows different pathways. This leads to gels with different microscopic dynamics and capability of trapping nanoparticles. At high concentrations, a strong gel is formed, made of relatively thick and rigid branches that firmly entrap nanoparticles. By contrast, the gel formed in dilute conditions is weaker, characterized by entanglements and crosslinks of very thin and flexible filaments. The gel is still able to entrap nanoparticles, but their motion is not completely arrested. These different gel morphologies can potentially be exploited for controlled multiple drug release.

Designed peptide amphiphiles as scaffolds for tissue engineering

Peptide amphiphiles (PAs) are peptide-based molecules that contain a peptide sequence as a head group covalently conjugated to a hydrophobic segment, such as lipid tails. They can self-assemble into well-ordered supramolecular nanostructures such as micelles, vesicles, twisted ribbons and nanofibers. In addition, the diversity of natural amino acids gives the possibility to produce PAs with different sequences. These properties along with their biocompatibility, biodegradability and a high resemblance to native extracellular matrix (ECM) have resulted in PAs being considered as ideal scaffold materials for tissue engineering (TE) applications. This review introduces the 20 natural canonical amino acids as building blocks followed by highlighting the three categories of PAs: amphiphilic peptides, lipidated peptide amphiphiles and supramolecular peptide amphiphile conjugates, as well as their design rules that dictate the peptide self-assembly process. Furthermore, 3D bio-fabrication strategies of PAs hydrogels are discussed and the recent advances of PA-based scaffolds in TE with the emphasis on bone, cartilage and neural tissue regeneration both in vitro and in vivo are considered. Finally, future prospects and challenges are discussed.

Multifunctional Dual Cross-Linked Bioadhesive Patch with Low Immunogenic Response and Wet Tissues Adhesion

The development of bioadhesives is an important, yet challenging task as seemingly mutually exclusive properties need to be combined in one material, that is, strong adhesion, water resistance, and high biocompatibility. Here, a biocompatible and biodegradable protein-based bioadhesive patch (PBP) with high adhesion strength and low immunogenic response is reported. PBP exists as a strong adhesion for biological surfaces, which is higher than some conventional bioadhesives (i.e., polyethylene glycol and fibrin). Robust adhesion and strength are realized through the removal of interfacial water and fast formation of multiple supramolecular interactions induced by metal ions. The PBP's high biocompatibility is evaluated and immunogenic response in vitro and in vivo is neglected. The strong adhesion on soft biological tissues qualifies the PBP as biomedical glue outperforming some commercial products for applications in hemostasis performance, accelerated wound healing, and sealing of defected organs, anticipating to be useful as a tissue adhesive and sealant.

Protein-engineered biomaterials for cartilage therapeutics and repair

Cartilage degeneration and injury are major causes of pain and disability that effect millions, and yet treatment options for conditions like osteoarthritis (OA) continue to be mainly palliative or involve complete replacement of injured joints. Several biomaterial strategies have been explored to address cartilage repair either by the delivery of therapeutics or as support for tissue repair, however the complex structure of cartilage tissue, its mechanical needs, and lack of regenerative capacity have hindered this goal. Recent advances in synthetic biology have opened new possibilities for engineered proteins to address these unique needs. Engineered protein and peptide-based materials benefit from inherent biocompatibility and nearly unlimited tunability as they utilize the body's natural building blocks to fabricate a variety of supramolecular structures. The pathophysiology and needs of OA cartilage are presented here, along with an overview of the current state of the art and next steps for protein-engineered repair strategies for cartilage.

Novel Approaches Guiding the Future of Spinal Biologics for Bone Regeneration

Purpose of Review

Despite the continued growth of spine fusion procedures, the ideal material for bone regeneration remains unclear. Current bone graft substitutes and extenders in use such as exogenous BMP-2 or demineralized bone matrix and hydroxyapatite either have serious complications associated with use or lead to clinically significant rates of non-union. The introduction of nanotechnology and 3D printing to regenerative medicine facilitates the development of safer and more efficacious bone regenerative scaffolds that present solutions to these problems. Many researchers in orthopedics recognize the importance of lowering the dose of recombinant growth factors like BMP-2 to avoid the complications associated with its normal required supraphysiologic dosing to achieve high rates of fusion in spine surgery.

Recent Findings

Recent iterations of bioactive scaffolds have moved towards peptide amphiphiles that bind endogenous osteoinductive growth factor sources at the site of implantation. These molecules have been shown to provide a highly fluid, natural mimetic of natural extracellular matrix to achieve 100% fusion rates at 10–100 times lower doses of BMP-2 relative to controls in pre-clinical animal posterolateral fusion models. Alternative approaches to bone regeneration include the combination of existing natural growth factor sources like human bone combined with bioactive, biocompatible components like hydroxyapatite using 3D-printing technologies. Their elastomeric, 3D-printed scaffolds demonstrate an optimal safety profile and high rates of fusion (~92%) in the rat posterolateral fusion model.

Summary

Bioactive peptide amphiphiles and developments in 3D printing offer the promising future of a recombinant growth factor- free bone graft substitute with similar efficacy but improved safety profiles compared to existing bone graft substitutes.

Supramolecular Peptide Nanofiber Hydrogels for Bone Tissue Engineering: From Multihierarchical Fabrications to Comprehensive Applications

Bone tissue engineering is becoming an ideal strategy to replace autologous bone grafts for surgical bone repair, but the multihierarchical complexity of natural bone is still difficult to emulate due to the lack of suitable biomaterials. Supramolecular peptide nanofiber hydrogels (SPNHs) are emerging biomaterials because of their inherent biocompatibility, satisfied biodegradability, high purity, facile functionalization, and tunable mechanical properties. This review initially focuses on the multihierarchical fabrications by SPNHs to emulate natural bony extracellular matrix. Structurally, supramolecular peptides based on distinctive building blocks can assemble into nanofiber hydrogels, which can be used as nanomorphology-mimetic scaffolds for tissue engineering. Biochemically, bioactive motifs and bioactive factors can be covalently tethered or physically absorbed to SPNHs to endow various functions depending on physiological and pharmacological requirements. Mechanically, four strategies are summarized to optimize the biophysical microenvironment of SPNHs for bone regeneration. Furthermore, comprehensive applications about SPNHs for bone tissue engineering are reviewed. The biomaterials can be directly used in the form of injectable hydrogels or composite nanoscaffolds, or they can be used to construct engineered bone grafts by bioprinting or bioreactors. Finally, continuing challenges and outlook are discussed.

Biomaterials via peptide assembly: Design, characterization, and application in tissue engineering

A core challenge in biomaterials, with both fundamental significance and technological relevance, concerns the rational design of bioactive microenvironments. Designed properly, peptides can undergo supramolecular assembly into dynamic, physical hydrogels that mimic the mechanical, topological, and biochemical features of native tissue microenvironments. The relatively facile, inexpensive, and automatable preparation of peptides, coupled with low batch-to-batch variability, motivates the expanded use of assembling peptide hydrogels for biomedical applications. Integral to realizing dynamic peptide assemblies as functional biomaterials for tissue engineering is an understanding of the molecular and macroscopic features that govern assembly, morphology, and biological interactions. In this review, we first discuss the design of assembling peptides, including primary structure (sequence), secondary structure (e.g., α-helix and β-sheets), and molecular interactions that facilitate assembly into multiscale materials with desired properties. Next, we describe characterization tools for elucidating molecular structure and interactions, morphology, bulk properties, and biological functionality. Understanding of these characterization methods enables researchers to access a variety of approaches in this ever-expanding field. Finally, we discuss the biological properties and applications of peptide-based biomaterials for engineering several important tissues. By connecting molecular features and mechanisms of assembling peptides to the material and biological properties, we aim to guide the design and characterization of peptide-based biomaterials for tissue engineering and regenerative medicine. STATEMENT OF SIGNIFICANCE: Engineering peptide-based biomaterials that mimic the topological and mechanical properties of natural extracellular matrices provide excellent opportunities to direct cell behavior for regenerative medicine and tissue engineering. Here we review the molecular-scale features of assembling peptides that result in biomaterials that exhibit a variety of relevant extracellular matrix-mimetic properties and promote beneficial cell-biomaterial interactions. Aiming to inspire and guide researchers approaching this challenge from both the peptide biomaterial design and tissue engineering perspectives, we also present characterization tools for understanding the connection between peptide structure and properties and highlight the use of peptide-based biomaterials in neural, orthopedic, cardiac, muscular, and immune engineering applications.

Structural and photoactive properties of self-assembled peptide-based nanostructures and their optical bioapplication in food analysis

BACKGROUND

Food processing plays an important role in the modern industry because food quality and security directly affect human health, life safety, and social and economic development. Accurate, efficient, and sensitive detection technology is the basis for ensuring food quality and security. Optosensor-based technology with the advantage of fast and visual real-time detection can be used to detect pesticides, metal ions, antibiotics, and nutrients in food. As excellent optical centres, self-assembled peptide-based nanostructures possess attractive advantages, such as simple preparation methods, controllable morphology, tunable functionality, and inherent biocompatibility.

AIM OF REVIEW

Self-assembled peptide nanostructures with good fabrication yield, stability, dispersity in a complex sample matrix, biocompatibility, and environmental friendliness are ideal development goals in the future. Owing to its flexible and unique optical properties, some short peptide self-assemblies can possibly be used to achieve the purpose of rapid and sensitive detection of composition in food, agriculture, and the environment, expanding the understanding and application of peptide-based optics in analytical chemistry.

KEY SCIENTIFIC CONCEPT OF REVIEW

The self-assembly process of peptides is driven by noncovalent interactions, including hydrogen bonding, electrostatic interactions, hydrophobic interactions, and π-π stacking, which are the key factors for obtaining stable self-assembled peptide nanostructures with peptides serving as assembly units. Controllable morphology of self-assembled peptide nanostructures can be achieved through adjustment in the type, concentration, and pH of organic solvents and peptides. The highly ordered nanostructures formed by the self-assembly of peptides have been proven to be novel biological structures and can be used for the construction of optosensing platforms in biological or other systems. Optosensing platforms make use of signal changes, including optical signals and electrical signals caused by specific reactions between analytes and active substances, to determine the content or concentration of an analyte.

Boosted Cross-Linking and Characterization of High-Performing Self-Assembling Peptides

Tissue engineering (TE) strategies require the design and characterization of novel biomaterials capable of mimicking the physiological microenvironments of the tissues to be regenerated. As such, implantable materials should be biomimetic, nanostructured and with mechanical properties approximating those of the target organ/tissue. Self-assembling peptides (SAPs) are biomimetic nanomaterials that can be readily synthesized and customized to match the requirements of some TE applications, but the weak interactions involved in the self-assembling phenomenon make them soft hydrogels unsuited for the regeneration of medium-to-hard tissues. In this work, we moved significant steps forward in the field of chemical cross-linked SAPs towards the goal of stiff peptidic materials suited for the regeneration of several tissues. Novel SAPs were designed and characterized to boost the 4-(N-Maleimidomethyl) cyclohexane-1-carboxylic acid 3-sulpho-N-hydroxysuccinimide ester (Sulfo-SMCC) mediated cross-linking reaction, where they reached G′ values of ~500 kPa. An additional orthogonal cross-linking was also effective and allowed to top remarkable G′ values of 840 kPa. We demonstrated that cross-linking fastened the pre-existing self-aggregated nanostructures, and at the same time, a strong presence of ß-structures is necessary for an effective cross-linking of (LKLK)₃-based SAPs. Combining strong SAP design and orthogonal cross-linking reactions, we brought SAP stiffness closer to the MPa threshold, and as such, we opened the door of the regeneration of skin, muscle and lung to biomimetic SAP technology.

Bioinspired photo-crosslinkable self-assembling peptides with pH-switchable "on-off" luminescence

Significant progress has been made in peptide self-assembly over the past two decades; however, the in situ cross-linking of self-assembling peptides yielding better performing nanomaterials is still in its infancy. Indeed, self-assembling peptides (SAPs), relying only on non-covalent interactions, are mechanically unstable and susceptible to solvent erosion, greatly hindering their practical application. Herein, drawing inspiration from the biological functions of tyrosine, we present a photo-cross-linking approach for the in situ cross-linking of a tyrosine-containing LDLK12 SAP. This method is based on the ruthenium-complex-catalyzed conversion of tyrosine to dityrosine upon light irradiation. We observed a stable formation of dityrosine cross-linking starting from 5 minutes, with a maximum peak after 1 hour of UV irradiation. Furthermore, the presence of a ruthenium complex among the assembled peptide bundles bestows unusual fluorescence intensity stability up to as high as 42 °C, compared to the bare ruthenium complex. Also, due to a direct deprotonation-protonation process between the ruthenium complex and SAP molecules, the fluorescence of the photo-cross-linked SAP is capable of exhibiting "off-on-off-on" luminescence switchable from acid to basic pH. Lastly, we showed that the photo-cross-linked hydrogel exhibited enhanced mechanical stability with a storage modulus of ∼26 kPa, due to the formation of a densely entangled fibrous network of SAP molecules through dityrosine linkages. As such, this ruthenium-mediated photo-cross-linked SAP hydrogel could be useful in the design of novel tyrosine containing SAP materials with intriguing potential for biomedical imaging, pH sensing, photonics, soft electronics, and bioprinting.

Preclinical Efficacy of Pro- and Anti-Angiogenic Peptide Hydrogels to Treat Age-Related Macular Degeneration

Pro-angiogenic and anti-angiogenic peptide hydrogels were evaluated against the standard of care wet age-related macular degeneration (AMD) therapy, Aflibercept (Eylea®). AMD was modeled in rats (laser-induced choroidal neovascularization (CNV) model), where the contralateral eye served as the control. After administration of therapeutics, vasculature was monitored for 14 days to evaluate leakiness. Rats were treated with either a low or high concentration of anti-angiogenic peptide hydrogel (0.02 wt% 8 rats, 0.2 wt% 6 rats), or a pro-angiogenic peptide hydrogel (1.0 wt% 7 rats). As controls, six rats were treated with commercially available Aflibercept and six with sucrose solution (vehicle control). Post lasering, efficacy was determined over 14 days via fluorescein angiography (FA) and spectral-domain optical coherence tomography (SD-OCT). Before and after treatment, the average areas of vascular leak per lesion were evaluated as well as the overall vessel leakiness. Unexpectedly, treatment with pro-angiogenic peptide hydrogel showed significant, immediate improvement in reducing vascular leak; in the short term, the pro-angiogenic peptide performed better than anti-angiogenic peptide hydrogel and was comparable to Aflibercept. After 14 days, both the pro-angiogenic and anti-angiogenic peptide hydrogels show a trend of improvement, comparable to Aflibercept. Based on our results, both anti-angiogenic and pro-angiogenic peptide hydrogels may prove good therapeutics in the future to treat wet AMD over a longer-term treatment period.

A guide-tag system controlling client enrichment into Y15 peptide-based granules for an in-cell protein recruitment assay

Self-assembling peptides (SAPs) are valuable building blocks for the fabrication of artificial supramolecules. We developed a guide-tag system that concentrates client proteins into SAP-based scaffolds in cellular environments at various enrichment levels. This system provides a tool to analyse the protein-protein interactions caused by protein clustering in cells.

Aligned fibrin/functionalized self-assembling peptide interpenetrating nanofiber hydrogel presenting multi-cues promotes peripheral nerve functional recovery

Nerve guidance conduits with hollow lumen fail to regenerate critical-sized peripheral nerve defects (15 mm in rats and 25 mm in humans), which can be improved by a beneficial intraluminal microenvironment. However, individual cues provided by intraluminal filling materials are inadequate to eliminate the functional gap between regenerated nerves and normal nerves. Herein, an aligned fibrin/functionalized self-assembling peptide (AFG/fSAP) interpenetrating nanofiber hydrogel that exerting synergistic topographical and biochemical cues for peripheral nerve regeneration is constructed via electrospinning and molecular self-assembly. The hydrogel possesses an aligned structure, high water content, appropriate mechanical properties and suitable biodegradation capabilities for nerve repair, which enhances the alignment and neurotrophin secretion of primary Schwann cells (SCs) in vitro, and successfully bridges a 15-mm sciatic nerve gap in rats in vivo. The rats transplanted with the AFG/fSAP hydrogel exhibit satisfactory morphological and functional recovery in myelinated nerve fibers and innervated muscles. The motor function recovery facilitated by the AFG/fSAP hydrogel is comparable with that of autografts. Moreover, the AFG/fSAP hydrogel upregulates the regeneration-associated gene expression and activates the PI3K/Akt and MAPK signaling pathways in the regenerated nerve. Altogether, the AFG/fSAP hydrogel represents a promising approach for peripheral nerve repair through an integration of structural guidance and biochemical stimulation.

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A novel aligned interpenetrating nanofiber hydrogel is first constructed for peripheral nerve regeneration.

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The aligned hydrogel presents synergistic topographical and biochemical cues for peripheral nerve regeneration.

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Nerve conduits filled with the aligned hydrogel can repair the long-distance sciatic nerve defects in 12 weeks.

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The function recovery facilitated by the aligned hydrogel is comparable with that of autografts.

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The aligned hydrogel upregulates regeneration-related genes and activates the PI3K/Akt and MAPK signaling pathways.

Peptide-Based Electrospun Fibers: Current Status and Emerging Developments

Electrospinning is a well-known, straightforward, and versatile technique, widely used for the preparation of fibers by electrifying a polymer solution. However, a high molecular weight is not essential for obtaining uniform electrospun fibers; in fact, the primary criterion to succeed is the presence of sufficient intermolecular interactions, which function similar to chain entanglements. Some small molecules able to self-assemble have been electrospun from solution into fibers and, among them, peptides containing both natural and non-natural amino acids are of particular relevance. Nowadays, the use of peptides for this purpose is at an early stage, but it is gaining more and more interest, and we are now witnessing the transition from basic research towards applications. Considering the novelty in the relevant processing, the aim of this review is to analyze the state of the art from the early 2000s on. Moreover, advantages and drawbacks in using peptides as the main or sole component for generating electrospun nanofibers will be discussed. Characterization techniques that are specifically targeted to the produced peptide fibers are presented.

Genipin-cross-linked hydrogels based on biomaterials for drug delivery: a review

Genipin is a naturally occurring nontoxic cross-linker, which has been widely used for drug delivery due to its excellent biocompatibility, admirable biodegradability and stable cross-linked attributes. These advantages led to its extensive application in the fabrication of hydrogels for drug delivery. This review describes the physicochemical characteristics and pharmacological activities of genipin and attempts to elucidate the detailed mechanisms of the cross-linking reaction between genipin and biomaterials. The current article entails a general review of the different biomaterials cross-linked by genipin: chitosan and its derivatives, collagen, gelatin, etc. The genipin-cross-linked hydrogels for various pharmaceutical applications, including ocular drug delivery, buccal drug delivery, oral drug delivery, anti-inflammatory drug delivery, and antibiotic and antifungal drug delivery, are reported. Finally, the future research directions and challenges of genipin-cross-linked hydrogels for pharmaceutical applications are also discussed in this review.

Self-assembling peptide scaffolds in the clinic

Well-defined scaffold hydrogels made of self-assembling peptides have found their way into clinical products. By examining the properties and applications of two self-assembling peptides-EAK16 and RADA16-we highlight the potential for translating designer biological scaffolds into commercial products.

Synthetic peptide hydrogels as 3D scaffolds for tissue engineering

The regeneration of tissues and organs poses an immense challenge due to the extreme complexity in the research work involved. Despite the tissue engineering approach being considered as a promising strategy for more than two decades, a key issue impeding its progress is the lack of ideal scaffold materials. Nature-inspired synthetic peptide hydrogels are inherently biocompatible, and its high resemblance to extracellular matrix makes peptide hydrogels suitable 3D scaffold materials. This review covers the important aspects of peptide hydrogels as 3D scaffolds, including mechanical properties, biodegradability and bioactivity, and the current approaches in creating matrices with optimized features. Many of these scaffolds contain peptide sequences that are widely reported for tissue repair and regeneration and these peptide sequences will also be discussed. Furthermore, 3D biofabrication strategies of synthetic peptide hydrogels and the recent advances of peptide hydrogels in tissue engineering will also be described to reflect the current trend in the field. In the final section, we will present the future outlook in the design and development of peptide-based hydrogels for translational tissue engineering applications.

Host macrophage response to injectable hydrogels derived from ECM and α-helical peptides

Tissue engineering materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated. Traditional natural and synthetic materials are superseded by bespoke materials that cross the boundary between these two categories. Here we present hydrogels that are derived from decellularised extracellular matrix and those that are synthesised from de novo α-helical peptides. We assess in vitro activation of murine macrophages to our hydrogels and whether these gels induce an M1-like or M2-like phenotype. This was followed by the in vivo immune macrophage response to hydrogels injected into rat partial-thickness abdominal wall defects. Over 28 days we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface without promoting a foreign body reaction and see no evidence of hydrogel encapsulation or formation of multinucleate giant cells. We also note an upregulation of myogenic differentiation markers and the expression of anti-inflammatory markers Arginase1, IL-10, and CD206, indicating pro-remodelling for all injected hydrogels. Furthermore, all hydrogels promote an anti-inflammatory environment after an initial spike in the pro-inflammatory phenotype. No difference between the injected site and the healthy tissue is observed after 28 days, indicating full integration. These materials offer great potential for future applications in regenerative medicine and towards unmet clinical needs. STATEMENT OF SIGNIFICANCE: Materials play a key role in how closely the complex architectural and functional characteristics of native healthy tissue can be replicated in tissue engineering. Here we present injectable hydrogels derived from decellularised extracellular matrix and de novo designed α-helical peptides. Over 28 days in the rat abdominal wall we observe an increase in mononuclear cell infiltration at the hydrogel-tissue interface with no foreign body reaction, no evidence of hydrogel encapsulation and no multinucleate giant cells. Our data indicate pro-remodelling and the promotion of an anti-inflammatory environment for all injected hydrogels with evidence of full integration with healthy tissue after 28 days. These unique materials offer great potential for future applications in regenerative medicine and towards designing materials for unmet clinical needs.

Cross-Linked Self-Assembling Peptides and Their Post-Assembly Functionalization via One-Pot and In Situ Gelation System

Supramolecular nanostructures formed through peptide self-assembly can have a wide range of applications in the biomedical landscape. However, they often lose biomechanical properties at low mechanical stress due to the non-covalent interactions working in the self-assembling process. Herein, we report the design of cross-linked self-assembling peptide hydrogels using a one-pot in situ gelation system, based on 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide/N-hydroxysulfosuccinimide (EDC/sulfo–NHS) coupling, to tune its biomechanics. EDC/sulfo–NHS coupling led to limited changes in storage modulus (from 0.9 to 2 kPa), but it significantly increased both the strain (from 6% to 60%) and failure stress (from 19 to 35 Pa) of peptide hydrogel without impairing the spontaneous formation of β-sheet-containing nano-filaments. Furthermore, EDC/sulfo–NHS cross-linking bestowed self-healing and thixotropic properties to the peptide hydrogel. Lastly, we demonstrated that this strategy can be used to incorporate bioactive functional motifs after self-assembly on pre-formed nanostructures by functionalizing an Ac-LDLKLDLKLDLK-CONH₂ (LDLK12) self-assembling peptide with the phage display-derived KLPGWSG peptide involved in the modulation of neural stem cell proliferation and differentiation. The incorporation of a functional motif did not alter the peptide’s secondary structure and its mechanical properties. The work reported here offers new tools to both fine tune the mechanical properties of and tailor the biomimetic properties of self-assembling peptide hydrogels while retaining their nanostructures, which is useful for tissue engineering and regenerative medicine applications.

Preparation and modeling of electrospun polyhydroxybutyrate/polyaniline composite scaffold modified by plasma and printed by an inkjet method and its cellular study

The reconstruction of the nerve tissue engineering scaffold is always of particular interest due to the inability to recover and repair neural tissues after being damaged by diseases or physical injuries. The primary purpose of this study was obtaining a model used to predict the diameter of the fibers of electrospun polyhydroxybutyrate (PHB) scaffolds. Accordingly, the range of operating parameters, namely the applied voltage, the distance between the nozzle to the collector, and solution concentration, was designed for the electrospinning process at three different levels, giving seventeen experiments. These data were modeled utilizing response surface methodology and artificial neural network method using Design Expert and Matlab software.The effect of process parameters on the diameter, as well as their interactions were investigated in detail, and the corresponding models were suggested. Both the RSM and ANN models showed an excellent agreement between the experimental and predicted response values. In the second phase of the study, PHB natural polymer was electrospun into scaffolds with high biocompatibility, resulting in a 224-360 nm diameter range .To further modify the scaffold in order to improve the compatibility of PHB, the fibrous surface of scaffolds was exposed to oxygenated plasma gas radiation under controlled conditions. Next, polyaniline (PANI) nanoparticles were then synthesized and printed on the surface of scaffolds as parallel lines. Then samples were exposed to the electric field. Fourier-transform infrared spectroscopy, water contact angle, optical and electron microscopy, tensile test, and cell viability analysis were performed to study properties of resulting scaffolds. The results indicated the fact that modification of the scaffolds by oxygen plasma and printing PANI nanoparticles in particular patterns had a favorable impact on cell adhesion and direction of cell growth, showing the potential of resulting scaffolds for nerve tissue engineering applications.

Chitosan-g-oligo(L,L-lactide) Copolymer Hydrogel Potential for Neural Stem Cell Differentiation

We evaluated the applicability of chitosan-g-oligo(L,L-lactide) copolymer (CLC) hydrogel for central nervous system tissue engineering. The biomechanical properties of the CLC hydrogel were characterized and its biocompatibility was assessed with neural progenitor cells obtained from two different sources: H9-derived neural stem cells (H9D-NSCs) and directly reprogrammed neural precursor cells (drNPCs). Our study found that the optically transparent CLC hydrogel possessed biomechanical characteristics suitable for culturing human neural stem/precursor cells and was noncytotoxic. When seeded on films prepared from CLC copolymer hydrogel, both H9D-NSC and drNPC adhered well, expanded and exhibited signs of spontaneous differentiation. While H9D-NSC mainly preserved multipotency as shown by a high proportion of Nestin+ and Sox2+ cells and a comparatively lower expression of the neuronal markers βIII-tubulin and MAP2, drNPCs, obtained by direct reprogramming, differentiated more extensively along the neuronal lineage. Our study indicates that the CLC hydrogel may be considered as a substrate for tissue-engineered constructs, applicable for therapy of neurodegenerative diseases. Impact statement We synthetized a chitosan-g-oligo(L,L-lactide) hydrogel that sustained multipotency of embryonic-derived neural stem cells (NSCs) and supported differentiation of directly reprogrammed NSC predominantly along the neuronal lineage. The hydrogel exhibited no cytotoxicity in vitro, both in extraction and contact cytotoxicity tests. When seeded on the hydrogel, both types of NSCs adhered well, expanded, and exhibited signs of spontaneous differentiation. The biomechanical properties of the hydrogel were similar to that of human spinal cord with incised pia mater. These data pave the way for further investigations of the hydrogel toward its applicability in central nervous system tissue engineering.

A new colitis therapy strategy via the target colonization of magnetic nanoparticle-internalized Roseburia intestinalis

The homeostasis process in the gut tissue of humans relies on intestinal bacteria. However, the intestine is a complex structural tissue with a huge superficial area, and thus the effective application of probiotics in the treatment of Crohn's disease (CD) is still challenging. Herein, we show the feasibility of probiotic target delivery and retention using magnetic iron oxide nanoparticle-internalized Roseburia intestinalis, which can be easily directed by a magnetic field in vitro and in vivo. Subsequently, the increased colonization of this core profitable flora not only resulted in a better therapy effect than traditional intragastric administration but also altered the bacterial composition, leading to a higher diversity in microbial taxa in rats with colitis. Our findings illustrate the exciting opportunities that nanotechnology offers for alternative strategies to modulate biological systems remotely and precisely, which represent a step towards the wireless magnetic manipulation of living biological entities in microbiology.

Probing mechanical properties and failure mechanisms of fibrils of self-assembling peptides

Self-assembling peptides (SAPs) are a promising class of biomaterials amenable to easy molecular design and functionalization. Despite their increasing usage in regenerative medicine, a detailed analysis of their biomechanics at the nanoscale level is still missing. In this work, we propose and validate, in all-atom dynamics, a coarse-grained model to elucidate strain distribution, failure mechanisms and biomechanical effects of functionalization of two SAPs when subjected to both axial stretching and bending forces. We highlight different failure mechanisms for fibril seeds and fibrils, as well as the negligible contribution of the chosen functional motif to the overall system rupture. This approach could lay the basis for the development of "more" coarse-grained models in the long pathway connecting SAP sequences and hydrogel mechanical properties.

Wound healing and antimicrobial effect of active secondary metabolites in chitosan-based wound dressings: A review

Wound healing can lead to complex clinical problems, hence finding an efficient approach to enhance the healing process is necessary. An ideal wound dressing should treat wounds at reasonable costs, with minimal inconveniences for the patient. Chitosan is one of the most investigated biopolymers for wound healing applications due to its biocompatibility, biodegradability, non-toxicity, and antimicrobial activity. Moreover, chitosan and its derivative have attracted numerous attentions because of the accelerating wound healing, and easy processability into different forms (gels, foams, membranes, and beads). All these properties make chitosan-based materials particularly versatile and promising for wound dressings. Besides, secondary natural metabolites could potentially act like the antimicrobial and anti-inflammatory agents and accelerate the healing process. This review collected almost all studies regarding natural compounds applications in wound healing by focusing on the chitosan-based bioactive wound dressing systems. An accurate analysis of different chitosan formulations and the influence of bioactive compounds on their wound healing properties are reported.

Zein/gelatin/nanohydroxyapatite nanofibrous scaffolds are biocompatible and promote osteogenic differentiation of human periodontal ligament stem cells

In bone tissue engineering, it is important for biomaterials to promote the osteogenic differentiation of stem cells to achieve tissue regeneration.