Controlled release of TGF-beta 1 from RADA self-assembling peptide hydrogel scaffolds

Scaffold loaded LPS-hUCMSC-sEVs promote Osteo/odontogenic differentiation and angiogenic potential of hDPSCs

OBJECTIVE

The formation of dentin-pulp complex determines the success of vital pulp therapy. Human umbilical cord mesenchymal stem cell-derived small extracellular vesicles (hUCMSC-sEVs) appeared to have stronger effect in anti-inflammatory and promoting the proliferation and migration of human dental pulp stem cells (hDPSCs). Moreover, Lipopolysaccharides (LPS) pretreatment can enhance the rapeutic potency of extracellular vesicles. LPS pretreatment hUCMSC-sEVs have the potential to regenerate the dentin-pulp complex by recruiting hDPSCs. This paper aims to develop collagen sponge/self-assembling peptide nanofiber scaffold (CS/SAPNS) composite scaffold loaded with LPS pretreatment hUCMSC-sEVs (CS/SAPNS-sEVs), and assess the release characteristics of hUCMSC-sEVs and the effect of this composite scaffold on osteo/odontogenic differentiation and angiogenic potential in hDPSCs.

METHODS

LPS pretreatment hUCMSC-sEVs (LPS-hUCMSC-sEVs) were mixed with self-assembling peptide hydrogel and loaded onto collagen sponge to obtain the CS/SAPNS-sEVs. BCA assay, nanoparticle analysis, transmission electron microscopy and laser confocal microscopy were used to investigate the characteristics of LPS-hUCMSC-sEVs loaded on CS/SAPNS. Osteo/odontogenic differentiation ability of hDPSCs were analyzed by ALP stainning, alizarin red staining. RT-PCR and Western blot analysis were performed to confirm the levels of osteo/odontogenic factors and angiogenic factors, and the involvement of NF-κB pathway was verified by immunocytochemical staining and Western blot analysis.

RESULTS

CS/SAPNS could control LPS-hUCMSC-sEVs release for 7 days and keep their structural integrity. CS/SAPNS-sEVs promoted deposition of calcified nodules and expression of osteogenic/odontogenic and angiogenic factors in hDPSCs. On the contrary, inhibition of the NF-κB pathway down-regulated the expression of CS/SAPNS-sEVs-regulated osteo/odontogenic and angiogenic factors.

CONCLUSION

CS/SNAPS could be used as scaffold for LPS-hUCMSC-sEVs, and CS/SAPNS-sEVs may promote osteo/odontogenic differentiation and enhance the angiogenic potential of hDPSCs through activating the NF-κB pathway.

Transforming growth factor-β1-loaded RADA-16 hydrogel scaffold for effective cartilage regeneration

Cartilage repair remains a major challenge in clinical trials. These current cartilage repair materials can not effectively promote chondrocyte generation, limiting their practical application in cartilage repair. In this work, we develop an implantable scaffold of RADA-16 peptide hydrogel incorporated with TGF-β1 to provide a microenvironment for stem cell-directed differentiation and chondrocyte adhesion growth. The longest release of growth factor TGF-β1 release can reach up to 600 h under physiological conditions. TGF-β1/RADA-16 hydrogel was demonstrated to be a lamellar porous structure. Based on the cell culture with hBMSCs, TGF-β1/RADA-16 hydrogel showed excellent ability to promote cell proliferation, directed differentiation into chondrocytes, and functional protein secretion. Within 14 days, 80% of hBMSCs were observed to be directed to differentiate into vigorous chondrocytes in the co-culture of TGF-β1/RADA-16 hydrogels with hBMSCs. Specifically, these newly generated chondrocytes can secrete and accumulate large amounts of collagen II within 28 days, which can effectively promote the formation of cartilage tissue. Finally, the exploration of RADA-16 hydrogel-based scaffolds incorporated with TGF-β1 bioactive species would further greatly promote the practical clinical trials of cartilage remediation, which might have excellent potential to promote cartilage regeneration in areas of cartilage damage.

Evaluation of a Peptide Hydrogel as a Chondro-Instructive Three-Dimensional Microenvironment

Articular cartilage injuries are inherently irreversible, even with the advancement in current therapeutic options. Alternative approaches, such as the use of mesenchymal stem/stromal cells (MSCs) and tissue engineering techniques, have gained prominence. MSCs represent an ideal source of cells due to their low immunogenicity, paracrine activity, and ability to differentiate. Among biomaterials, self-assembling peptide hydrogels (SAPH) are interesting given their characteristics such as good biocompatibility and tunable properties. Herein we associate human adipose-derived stem cells (hASCs) with a commercial SAPH, Puramatrix™, to evaluate how this three-dimensional microenvironment affects cell behavior and its ability to undergo chondrogenic differentiation. We demonstrate that the Puramatrix™ hydrogel comprises a highly porous matrix permissible for hASC adhesion and in vitro expansion. The morphology and cell growth dynamics of hASCs were affected when cultured on the hydrogel but had minimal alteration in their immunophenotype. Interestingly, hASCs spontaneously formed cell aggregates throughout culturing. Analysis of glycosaminoglycan production and gene expression revealed a noteworthy and donor-dependent trend suggesting that Puramatrix™ hydrogel may have a natural capacity to support the chondrogenic differentiation of hASCs. Altogether, the results provide a more comprehensive understanding of the potential applications and limitations of the Puramatrix™ hydrogel in developing functional cartilage tissue constructs.

Immunomodulatory nano-preparations for rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease (AD) caused by the aberrant attack of the immune system on its own joint tissues. Genetic and environmental factors are the main reasons of immune system impairment and high incidence of RA. Although there are medications on the market that lessen disease activity, there is no known cure for RA, and patients are at risk in varying degrees of systemic immunosuppression. By transporting (encapsulating or surface binding) RA-related self-antigens, nucleic acids, immunomodulators, or cytokines, tolerogenic nanoparticles-also known as immunomodulatory nano-preparations-have the potential to gently regulate local immune responses and ultimately induce antigen-specific immune tolerance. We review the recent advances in immunomodulatory nano-preparations for delivering self-antigen or self-antigen plus immunomodulator, simulating apoptotic cell avatars in vivo, acting as artificial antigen-presenting cells, and based on scaffolds and gels, to provide a reference for developing new immunotherapies for RA.

Self-assembling peptide RADA16: a promising scaffold for tissue engineering and regenerative medicine

RADA16 is a peptide-based biomaterial whose acidic aqueous solution spontaneously forms an extracellular matrix-like 3D structure within seconds upon contact with physiological pH body fluids. Meanwhile, its good biocompatibility, low immunogenicity, nontoxic degradation products and ease of modification make it an ideal scaffold for tissue engineering. RADA16 is a good delivery vehicle for cells, drugs and factors. Its shear thinning and thixotropic properties allow it to fill tissue voids by injection and not to swell. However, the weaker mechanical properties and poor hydrophilicity are troubling limitations of RADA16. To compensate for this limitation, various functional groups and polymers have been designed to modify RADA16, thus contributing to its scope and progress in the field of tissue engineering.

Self-Assembling Peptide RADA16 Nanofiber Scaffold Hydrogel-Wrapped Concentrated Growth Factors in Osteogenesis of MC3T3

Concentrated growth factors (CGFs) are widely used in surgery with bone grafting, but the release of growth factors from CGFs is rapid. RADA16, a self-assembling peptide, can form a scaffold that is similar to the extracellular matrix. Based on the properties of RADA16 and CGF, we hypothesized that the RADA16 nanofiber scaffold hydrogel could enhance the function of CGFs and that the RADA16 nanofiber scaffold hydrogel-wrapped CGFs (RADA16-CGFs) would perform a good osteoinductive function. This study aimed to investigate the osteoinductive function of RADA16-CGFs. Scanning electron microscopy, rheometry, and ELISA were performed, and MC3T3-E1 cells were used to test cell adhesion, cytotoxicity, and mineralization after administration with RADA16-CGFs. We found that RADA16 endowed with the sustained release of growth factors from CGFs, which can help maximize the function of CGFs in osteoinduction. The application of the atoxic RADA16 nanofiber scaffold hydrogel with CGFs can be a new therapeutic strategy for the treatment of alveolar bone loss and other problems that require bone regeneration.

Peptide-Based Hydrogels: Template Materials for Tissue Engineering

Tissue and organ regeneration are challenging issues, yet they represent the frontier of current research in the biomedical field. Currently, a major problem is the lack of ideal scaffold materials' definition. As well known, peptide hydrogels have attracted increasing attention in recent years thanks to significant properties such as biocompatibility, biodegradability, good mechanical stability, and tissue-like elasticity. Such properties make them excellent candidates for 3D scaffold materials. In this review, the first aim is to describe the main features of a peptide hydrogel in order to be considered as a 3D scaffold, focusing in particular on mechanical properties, as well as on biodegradability and bioactivity. Then, some recent applications of peptide hydrogels in tissue engineering, including soft and hard tissues, will be discussed to analyze the most relevant research trends in this field.

Release systems based on self-assembling RADA16-I hydrogels with a signal sequence which improves wound healing processes

Self-assembling peptides can be used for the regeneration of severely damaged skin. They can act as scaffolds for skin cells and as a reservoir of active compounds, to accelerate scarless wound healing. To overcome repeated administration of peptides which accelerate healing, we report development of three new peptide biomaterials based on the RADA16-I hydrogel functionalized with a sequence (AAPV) cleaved by human neutrophil elastase and short biologically active peptide motifs, namely GHK, KGHK and RDKVYR. The peptide hybrids were investigated for their structural aspects using circular dichroism, thioflavin T assay, transmission electron microscopy, and atomic force microscopy, as well as their rheological properties and stability in different fluids such as water or plasma, and their susceptibility to digestion by enzymes present in the wound environment. In addition, the morphology of the RADA-peptide hydrogels was examined with a unique technique called scanning electron cryomicroscopy. These experiments enabled us to verify if the designed peptides increased the bioactivity of the gel without disturbing its gelling processes. We demonstrate that the physicochemical properties of the designed hybrids were similar to those of the original RADA16-I. The materials behaved as expected, leaving the active motif free when treated with elastase. XTT and LDH tests on fibroblasts and keratinocytes were performed to assess the cytotoxicity of the RADA16-I hybrids, while the viability of cells treated with RADA16-I hybrids was evaluated in a model of human dermal fibroblasts. The hybrid peptides revealed no cytotoxicity; the cells grew and proliferated better than after treatment with RADA16-I alone. Improved wound healing following topical delivery of RADA-GHK and RADA-KGHK was demonstrated using a model of dorsal skin injury in mice and histological analyses. The presented results indicate further research is warranted into the engineered peptides as scaffolds for wound healing and tissue engineering.

An injectable hydrogel scaffold with IL-1β-activated MSC-derived exosomes for the treatment of endometritis

Chronic endometritis is a common gynecological disease resulting from various long-term recurrent infections, and is closely related to myositis, miscarriage, and even infertility. There is still no satisfactory treatment method currently in clinical therapy. Mesenchymal stem cell (MSC)-derived exosomes, an important kind of paracrine product, have been used to treat inflammatory diseases due to their promising immunomodulatory function and tissue repair ability similar to MSCs. Considering that the exosome contents and functions are regulated by the MSC status and the MSC status is significantly influenced by its surrounding microenvironment, we propose a hypothesis that exosomes derived from inflammation-simulated MSCs will possess stronger inhibition ability for inflammation. Herein, we used IL-1β to activate rat bone MSCs for obtaining β-exo and constructed an injectable polypeptide hydrogel scaffold by loading β-exo (β-exo@pep) for an in situ slow release of β-exo. The results showed that the polypeptide hydrogel can provide a sustained release of exosomes in 14 days. The β-exo@pep composite hydrogel can more effectively inhibit the production of inflammatory factors such as TNF-α, IL-1β, and IFN-γ, while it can promote the production of anti-inflammatory factors such as Arg-1, IL-6, and IL-10. The β-exo@pep composite hydrogel significantly promoted cell migration, invasion, and vessel tube formation in vitro. The experiments in a rat model of endometritis proved that the β-exo@pep composite scaffold possessed excellent ability towards anti-inflammation and endometrial regeneration. The research studies on the molecular mechanism revealed that the protein expressions of HMGB1 and phosphorylated IKB-α and p65 are down-regulated in the cells treated with β-exo@pep, indicating the involvement of the NF-κB signaling pathway. This study provides an effective method for the treatment of chronic endometritis, which is promising for clinical use.

Advances in Self-Assembled Peptides as Drug Carriers

In recent years, self-assembled peptide nanotechnology has attracted a great deal of attention for its ability to form various regular and ordered structures with diverse and practical functions. Self-assembled peptides can exist in different environments and are a kind of medical bio-regenerative material with unique structures. These materials have good biocompatibility and controllability and can form nanoparticles, nanofibers and hydrogels to perform specific morphological functions, which are widely used in biomedical and material science fields. In this paper, the properties of self-assembled peptides, their influencing factors and the nanostructures that they form are reviewed, and the applications of self-assembled peptides as drug carriers are highlighted. Finally, the prospects and challenges for developing self-assembled peptide nanomaterials are briefly discussed.

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.

Chirality-induced bionic scaffolds in bone defects repair-a review

Due to lack of amino sugar with aging, people will suffer from various epidemic bone diseases called "undead cancer" by the World Health Organization. The key problem in bone tissue engineering that has not been completely resolved is the repair of critical large-scale bone and cartilage defects. The chirality of the extracellular matrix plays a decisive role in the physiological activity of bone cells and the occurrence of bone tissue, but the mechanism of chirality in regulating cell adhesion and growth is still in the early stage of exploration. This paper reviews the application progress of chirality-induced bionic scaffolds in bone defects repair based on "soft" and "hard" scaffolds. The aim is to summarize the effects of different chiral structures (L-shaped and D-shaped) in the process of inducing bionic scaffolds in bone defects repair. In addition, many technologies and methods as well as issues worthy of special consideration for preparing chirality-induced bionic scaffolds are also introduced. We expect that this work can provide inspiring ideas for designing new chirality-induced bionic scaffolds and promote the development of chirality in bone tissue engineering. This article is protected by copyright. All rights reserved.

Scaffolding Biomaterials for 3D Cultivated Meat: Prospects and Challenges

Cultivating meat from stem cells rather than by raising animals is a promising solution to concerns about the negative externalities of meat production. For cultivated meat to fully mimic conventional meat's organoleptic and nutritional properties, innovations in scaffolding technology are required. Many scaffolding technologies are already developed for use in biomedical tissue engineering. However, cultivated meat production comes with a unique set of constraints related to the scale and cost of production as well as the necessary attributes of the final product, such as texture and food safety. This review discusses the properties of vertebrate skeletal muscle that will need to be replicated in a successful product and the current state of scaffolding innovation within the cultivated meat industry, highlighting promising scaffold materials and techniques that can be applied to cultivated meat development. Recommendations are provided for future research into scaffolds capable of supporting the growth of high-quality meat while minimizing production costs. Although the development of appropriate scaffolds for cultivated meat is challenging, it is also tractable and provides novel opportunities to customize meat properties.

Enhanced efficacy of transforming growth factor-β1 loaded an injectable cross-linked thiolated chitosan and carboxymethyl cellulose-based hydrogels for cartilage tissue engineering

Growth factors (GFs) are soluble proteins extracellular that control a wide range of cellular processes as well as tissue regeneration. While transforming growth factor beta-1 (TGF-β1) promotes chondrogenesis, its medical use is restricted by its potential protein instability, which necessitates high doses of the protein, which can result in adverse side effects such as inefficient cartilage formation. In this work, we have developed a novel hydrogel composite based on the polymer, cross-linked thiolated chitosan; TCS and carboxymethyl cellulose; CMC (TCS/CMC) hydrogel system was utilized as injectable TGF-β1 carriers for cartilage tissue engineering applications. Rheological measurements showed that the elastic modulus of TCS/CMC hydrogels with an optimized CMC concentration could reach around 2.5 kPa or higher than their respective viscous modulus, indicating that they behaved like strong hydrogels. Crosslinking significantly alters the overall network distribution, surface morphology, pore size, porosity, gelation time, swelling ratio, water content, and in vitro degradation of the TCS/CMC hydrogels. TCS/CMC hydrogels maintain more than 90% of their weight and retain their original form after 21 days. TGF-β1 released marginally from TCS/CMC hydrogels as incubation time increased, up to 21 days, with around 18.6 ± 0.9% of the drug stored inside the TCS/CMC hydrogels. On day 21, BMSC treated with TGF-β1 in medium or TGF-β1-loaded TCS/CMC hydrogels grew faster than the other groups. For in vivo cartilage repair, full-thickness cartilage defects were induced on rat knees for 8 weeks. The optimal ability of this novel TGF-β1-loaded TCS/CMC hydrogel system was further demonstrated by histological analysis, resulting in a novel therapeutic strategy for repairing articular cartilage defects.Research HighlightsAn in situ forming and injectable thiolated chitosan and carboxymethyl cellulose hydrogel was fabricated for cartilage tissue engineering.TCS/CMC displays suitable gelation time with high swelling ratio, tunable mechanical properties and highly porous.TGF-β1-loaded-TCS/CMC hydrogels showed maximum drug release activity.TGF-β1-loaded-TCS/CMC hydrogels had good biocompatibility to articular chondrocytes.An injectable TCS/CMC/TGF-β1 hydrogel is a promising material system for cartilage tissue engineering.

Recent advances in design and applications of biomimetic self-assembled peptide hydrogels for hard tissue regeneration

Abstract

The development of natural biomaterials applied for hard tissue repair and regeneration is of great importance, especially in societies with a large elderly population. Self-assembled peptide hydrogels are a new generation of biomaterials that provide excellent biocompatibility, tunable mechanical stability, injectability, trigger capability, lack of immunogenic reactions, and the ability to load cells and active pharmaceutical agents for tissue regeneration. Peptide-based hydrogels are ideal templates for the deposition of hydroxyapatite crystals, which can mimic the extracellular matrix. Thus, peptide-based hydrogels enhance hard tissue repair and regeneration compared to conventional methods. This review presents three major self-assembled peptide hydrogels with potential application for bone and dental tissue regeneration, including ionic self-complementary peptides, amphiphilic (surfactant-like) peptides, and triple-helix (collagen-like) peptides. Special attention is given to the main bioactive peptides, the role and importance of self-assembled peptide hydrogels, and a brief overview on molecular simulation of self-assembled peptide hydrogels applied for bone and dental tissue engineering and regeneration.

Graphic abstract

Self-Assembled Nanomaterials for Chronic Skin Wound Healing

Significance: Chronic wounds are one of the major burdens of the U.S. health care system with an annual cost of $31.7 billion and affecting an estimated 2.4-4.5 million people. Several underlying molecular and cellular pathophysiological mechanisms, including poor vascularization, excessive extracellular matrix (ECM) degradation by proteases, decreased growth factor activity, and bacterial infection can lead to chronic wounds. More effective wound therapies need to address one or more of these mechanisms to significantly advance wound care. Recent Advances: Self-assembled nanomaterials may provide new therapeutic options for chronic wound healing applications as those materials generally exhibit excellent biocompatibility and can bear multiple functionalities, such as ECM-mimicking properties, drug delivery capabilities, and tunable mechanics. Furthermore, self-assembled nanomaterials can be produced at low cost, and owing to their ability to self-organize, generate complex multifunctional structures that can be tailored to the varying sizes and shapes of chronic wounds. Self-assembled nanomaterials have been engineered to serve as wound dressings, growth factor delivery systems, and antimicrobials. Critical Issues: As there are many different types of self-assembled nanomaterials, which in turn have different mechanisms of self-assembly and physiochemical properties, one type of self-assembled nanomaterials may not be sufficient to address all underlying mechanisms of chronic wounds. However, self-assembled nanomaterials can be easily tailored, and developing multifunctional self-assembled nanomaterials that can address various targets in chronic wounds will be needed. Future Directions: Future studies should investigate combinations of various self-assembled nanomaterials to take full advantage of their multifunctional properties.

Functionalized Peptide Fibrils as a Scaffold for Active Substances in Wound Healing

Technological developments in the field of biologically active peptide applications in medicine have increased the need for new methods for peptide delivery. The disadvantage of peptides as drugs is their low biological stability. Recently, great attention has been paid to self-assembling peptides that can form fibrils. Such a formulation makes bioactive peptides more resistant to enzymatic degradation and druggable. Peptide fibrils can be carriers for peptides with interesting biological activities. These features open up prospects for using the peptide fibrils as long-acting drugs and are a valid alternative to conventional peptidic therapies. In our study, we designed new peptide scaffolds that are a hybrid of three interconnected amino acid sequences and are: pro-regenerative, cleavable by neutrophilic elastase, and fibril-forming. We intended to obtain peptides that are stable in the wound environment and that, when applied, would release a biologically active sequence. Our studies showed that the designed hybrid peptides show a high tendency toward regular fibril formation and are able to release the pro-regenerative sequence. Cytotoxicity studies showed that all the designed peptides were safe, did not cause cytotoxic effects and revealed a pro-regenerative potential in human fibroblast and keratinocyte cell lines. In vivo experiments in a dorsal skin injury model in mice indicated that two tested peptides moderately promote tissue repair in their free form. Our research proves that peptide fibrils can be a druggable form and a scaffold for active peptides.

Self-assembled peptide hydrogel scaffolds with VEGF and BMP-2 enhanced in vitro angiogenesis and osteogenesis

OBJECTIVES

The reconstruction of bone defects remains a major clinical issue. Our study aims to investigate the ability of RATEA16 (RA, [CH3CONH] RADARADARADARADA-[CONH2]) for the sustained delivering VEGF and BMP-2 to promote angiogenesis and osteogenesis in bone reconstruction.

MATERIALS AND METHODS

We prepared and investigated the characterization of RATEA16. The survival of human umbilical vein endothelial cells (HUVECs) and human stem cells of the apical papilla (SCAPs) encapsulated in RATEA16 hydrogel was detected. Then, we established RA-VEGF/BMP-2 drug delivery systems and measured their drug release pattern. The effects of RA-VEGF scaffolds on HUVECs angiogenesis were investigated in vitro. Then, osteoblastic differentiation capacity of SCAPs with RA-BMP-2 scaffolds was analyzed by ALP activity and expression of osteoblast-related genes.

RESULTS

A porous nanofiber microstructure endowed this scaffold with the ability to maintain the survival of HUVECs and SCAPs. The RA-VEGF/BMP-2 drug delivery systems exhibited several advantagesin vitro: injectability, biodegradability, good biocompatibility, and noncytotoxicity. Released rhVEGF₁₆₅ /BMP-2 were proved to promote angiogenesis of HUVECs as well as osteogenesis of SCAPs abilities.

CONCLUSION

RATEA16 loading with VEGF and BMP-2 might be a potential clinical strategy for tissue engineering, especially in bone reconstruction, due to its ability of delivering growth factors effectively and efficiently.

Injectable Hydrogels for Improving Cardiac Cell Therapy-In Vivo Evidence and Translational Challenges

Cell therapy has the potential to regenerate cardiac tissue and treat a variety of cardiac diseases which are currently without effective treatment. This novel approach to treatment has demonstrated clinical efficiency, despite low retention of the cell products in the heart. It has been shown that improving retention often leads to improved functional outcome. A feasible method of improving cell graft retention is administration of injectable hydrogels. Over the last decade, a variety of injectable hydrogels have been investigated preclinically for their potential to improve the effects of cardiac cell therapy. These hydrogels are created with different polymers, properties, and additional functional motifs and differ in their approaches for encapsulating different cell types. Only one combinational therapy has been tested in a clinical randomized controlled trial. In this review, the latest research on the potential of injectable hydrogels for delivery of cell therapy is discussed, together with potential roadblocks for clinical translation and recommendations for future explorations to facilitate future translation.

Recent advances in the fabrication and bio-medical applications of self-assembled dipeptide nanostructures

Molecular self-assembly is a widespread natural phenomenon and has inspired several researchers to synthesize a compendium of nano/microstructures with widespread applications. Biomolecules like proteins, peptides and lipids are used as building blocks to fabricate various nanomaterials. Supramolecular peptide self-assembly continue to play a significant role in forming diverse nanostructures with numerous biomedical applications; however, dipeptides offer distinctive supremacy in their ability to self-assemble and produce a variety of nanostructures. Though several reviews have articulated the progress in the field of longer peptides or polymers and their self-assembling behavior, there is a paucity of reviews or literature covering the emerging field of dipeptide-based nanostructures. In this review, our goal is to present the recent advancements in dipeptide-based nanostructures with their potential applications.

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.

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.

An Update on Antimicrobial Peptides (AMPs) and Their Delivery Strategies for Wound Infections

Bacterial infections occur when wound healing fails to reach the final stage of healing, which is usually hindered by the presence of different pathogens. Different topical antimicrobial agents are used to inhibit bacterial growth due to antibiotic failure in reaching the infected site, which is accompanied very often by increased drug resistance and other side effects. In this review, we focus on antimicrobial peptides (AMPs), especially those with a high potential of efficacy against multidrug-resistant and biofilm-forming bacteria and fungi present in wound infections. Currently, different AMPs undergo preclinical and clinical phase to combat infection-related diseases. AMP dendrimers (AMPDs) have been mentioned as potent microbial agents. Various AMP delivery strategies that are used to combat infection and modulate the healing rate-such as polymers, scaffolds, films and wound dressings, and organic and inorganic nanoparticles-have been discussed as well. New technologies such as Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)-associated protein (CRISPR-Cas) are taken into consideration as potential future tools for AMP delivery in skin therapy.

Self-Assembling Peptide Scaffold Carrying Neural-Cell Adhesion Molecule-Derived Mimetic-Peptide Transplantation Promotes Proliferation and Stimulates Neurite Extension by Modulating Tau Phosphorylation and Calpain/Glycogen Synthase Kinase 3 beta (GSK-3β) in Neurons

BACKGROUND Self-assembling peptide scaffolds have been extensively applied in tissue engineering. Many investigations have modified self-assembling peptide scaffolds by integrating functional motifs, with promising applications. This study aimed to generate a novel RADA16 self-assembling peptide scaffold integrating a neural-cell adhesion molecule-derived mimetic-peptide (SIDRVEPYSSTAQ) and evaluated the effects on neuron proliferation. MATERIAL AND METHODS A 37-amino-acids peptide of RADA16-activation motif containing neural-cell adhesion molecule-derived mimetic-peptide (SIDRVEPYSSTAQ) was synthesized and self-assembled into a scaffold. Dorsal root ganglion (DRG) and spinal cord motor neurons (SCMN) were primarily isolated and identified. Neurons (DRG and SCMN) were divided into FRM, FRM-MP, and FRM-MP-LiCl groups. The adherence ability of neurons was evaluated using toluidine blue staining. Proliferation and apoptosis of neurons were assessed using CCK-8 and flow cytometry assay, respectively. Immunofluorescence assay was used to measure neurite extension. Western blot assay was used to assess GSK-3ß/p-GSK-3ß, Tau/p-Tau, and calpain expression in neurons. RESULTS FRM-MP-LiCl released multiple-peptide with higher efficiency. FRM-MP-LiCl significantly enhanced proliferation and inhibited apoptosis compared to FRM and FRM-MP groups (p.

Ocular co-Delivery of Timolol and Brimonidine from a Self-Assembling Peptide Hydrogel for the Treatment of Glaucoma: In Vitro and Ex Vivo Evaluation

Effective pharmacotherapy during glaucoma treatment depends on interventions that reduce intraocular pressure (IOP) and retain the IOP lowering effect for sufficient time so as to reduce dosing frequency and enhance patient adherence. Combination anti-glaucoma therapy and dosage forms that increase precorneal residence time could therefore constitute a promising therapeutic intervention. The in-situ gel forming self-assembling peptide ac-(RADA)4-CONH2 was evaluated as carrier for the ocular co-delivery of timolol maleate (TM) and brimonidine tartrate (BR). The hydrogel's microstructure and mechanical properties were assessed with atomic force microscopy and rheology, respectively. Drug diffusion from the hydrogel was evaluated in vitro in simulated tear fluid and ex vivo across porcine corneas and its effect on the treated corneas was assessed through physicochemical characterization and histological analysis. Results indicated that TM and BR co-delivery affected hydrogel's microstructure resulting in shorter nanofibers and a less rigid hydrogel matrix. Rapid and complete release of both drugs was achieved within 8 h, while a 2.8-fold and 5.4-fold higher corneal permeability was achieved for TM and BR, respectively. No significant alterations were induced in the structural integrity of the corneas treated with the hydrogel formulation, suggesting that self-assembling peptide hydrogels might serve as promising systems for combination anti-glaucoma therapy.

Peptide gels for controlled release of proteins

Treatment strategies in clinics have been shifting from small molecules to protein drugs due to the promising results of a highly specific mechanism of action and reduced toxicity. Despite their prominent roles in disease treatment, delivery of the protein therapeutics is challenging due to chemical instability, immunogenicity and biological barriers. Peptide hydrogels with spatiotemporally tunable properties have shown an outstanding potential to deliver complex protein therapeutics, maintain drug efficacy and stability over time, mimicking the extracellular matrix, and responding to external stimuli. In this review, we present recent advances in peptide hydrogel design strategies, protein release kinetics and mechanisms for protein drug delivery in cellular engineering, tissue engineering, immunotherapy and disease treatments.

Controlled release of basic fibroblast growth factor from a peptide biomaterial for bone regeneration

Self-assembled peptide scaffolds based on D-RADA16 are an important matrix for controlled drug release and three-dimensional cell culture. In this work, D-RADA16 peptide hydrogels were coated on artificial bone composed of nano-hydroxyapatite/polyamide 66 (nHA/PA66) to obtain a porous drug-releasing structure for treating bone defects. The developed materials were characterized via transmission electron microscopy and scanning electron microscopy. The proliferation and adhesion of bone mesenchymal stem cells (BMSCs) were examined by confocal laser microscopy and CCK-8 experiments. The osteogenic ability of the porous materials towards bone BMSCs was examined in vitro by staining with Alizarin Red S and alkaline phosphatase, and bioactivity was evaluated in vivo. The results revealed that nHA/PA66/D-RADA16/bFGF reduces the degradation rate of D-RADA16 hydrogels and prolongs sustained release of bFGF, which would promote BMSCs proliferation, adhesion and osteogenesis in vitro and bone repair in vivo. Thus, it deserves more attention and is worthy of further research.

Self-assemble peptide biomaterials and their biomedical applications

Inspired by self-assembling peptides found in native proteins, deliberately designed engineered peptides have shown outstanding biocompatibility, biodegradability, and extracellular matrix-mimicking microenvironments. Assembly of the peptides can be triggered by external stimuli, such as electrolytes, temperature, and pH. The formation of nanostructures and subsequent nanocomposite materials often occur under physiological conditions. The respective properties of side chains in each amino acids provide numerous sites for chemical modification and conjugation choices of the peptides, enabling various resulting supramolecular nanostructures and hydrogels with adjustable mechanical and physicochemical properties. Moreover, additional functionalities can be easily induced into the hydrogels, including shear-thinning, bioactivity, self-healing, and shape memory. It further broaden the scope of application of self-assemble peptide materials. This review outlines designs of self-assembly peptide (β-sheet, α-helix, collagen-like peptides, elastin-like polypeptides, and peptide amphiphiles) with potential additional functionalities and their biomedical applications in bioprinting, tissue engineering, and drug delivery.

Injectable PNIPAM/Hyaluronic acid hydrogels containing multipurpose modified particles for cartilage tissue engineering: Synthesis, characterization, drug release and cell culture study

Novel injectable thermosensitive PNIPAM/hyaluronic acid hydrogels containing various amounts of chitosan-g-acrylic acid coated PLGA (ACH-PLGA) micro/nanoparticles were synthesized and designed to facilitate the regeneration of cartilage tissue. The ACH-PLGA particles were used in the hydrogels to play a triple role: first, the allyl groups on the chitosan-g-acrylic acid shell act as crosslinkers for PNIPAM and improved the mechanical properties of the hydrogel to mimic the natural cartilage tissue. Second, PLGA core acts as a carrier for the controlled release of chondrogenic small molecule melatonin. Third, they could reduce the syneresis of the thermosensitive hydrogel during gelation. The optimum hydrogel with the minimum syneresis and the maximum compression modulus was chosen for further evaluations. This hydrogel showed a great integration with the natural cartilage during the adhesion test, and also, presented an interconnected porous structure in scanning electron microscopy images. Eventually, to evaluate the cytotoxicity, mesenchymal stem cells were encapsulated inside the hydrogel. MTT and Live/Dead assay showed that the hydrogel improved the cells growth and proliferation as compared to the tissue culture polystyrene. Histological study of glycosaminoglycan (GAG) showed that melatonin treatment has the ability to increase the GAG synthesis. Overall, due to the improved mechanical properties, low syneresis, the ability of sustained drug release and also high bioactivity, this injectable hydrogel is a promising material system for cartilage tissue engineering.

Crafting Polymeric and Peptidic Hydrogels for Improved Wound Healing

Wound healing is a multifaceted biological process involving the replacement of damaged tissues and cellular structures, restoring the skin barrier's function, and maintaining internal homeostasis. Over the past two decades, numerous approaches are undertaken to improve the quality and healing rate of complex acute and chronic wounds, including synthetic and natural polymeric scaffolds, skin grafts, and supramolecular hydrogels. In this context, this review assesses the advantages and drawbacks of various types of supramolecular hydrogels including both polymeric and peptide-based hydrogels for wound healing applications. The molecular design features of natural and synthetic polymers are examined, as well as therapeutic-based and drug-free peptide hydrogels, and the strategies for each system are analyzed to integrate key elements such as biocompatibility, bioactivity, stimuli-responsiveness, site specificity, biodegradability, and clearance.

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

Self-assembling peptides (SAPs) are synthetic bioinspired biomaterials that can be feasibly multi-functionalized for applications in surgery, drug delivery, optics and tissue engineering (TE). Despite their promising biocompatibility and biomimetic properties, they have never been considered real competitors of polymers and/or cross-linked extracellular matrix (ECM) natural proteins. Indeed, synthetic SAP-made hydrogels usually feature modest mechanical properties, limiting their potential applications, due to the transient non-covalent interactions involved in the self-assembling phenomenon. Cross-linked SAP-hydrogels have been recently introduced to bridge this gap, but several questions remain open. New strategies leading to stiffer gels of SAPs may allow for a full exploitation of the SAP technology in TE and beyond. We have developed and characterized a genipin cross-linking strategy significantly increasing the stiffness and resiliency of FAQ(LDLK)3, a functionalized SAP already used for nervous cell cultures. We characterized different protocols of cross-linking, analyzing their dose and time-dependent efficiency, influencing stiffness, bioabsorption time and molecular arrangements. We choose the best developed protocol to electrospin into nanofibers, for the first time, self-standing, water-stable and flexible fibrous mats and micro-channels entirely made of SAPs. This work may open the door to the development and tailoring of bioprostheses entirely made of SAPs for different TE applications.

D-RADA16-RGD-Reinforced Nano-Hydroxyapatite/Polyamide 66 Ternary Biomaterial for Bone Formation

BACKGROUND

Nano-hydroxyapatite/polyamide 66 (nHA/PA66) is a composite used widely in the repair of bone defects. However, this material is insufficient bioactivity. In contrast, D-RADA16-RGD self-assembling peptide (D-RADA16-RGD sequence containing all D-amino acids is Ac-RADARADARADARADARGDS-CONH₂) shows admirable bioactivity for both cell culture and bone regeneration. Here, we describe the fabrication of a favorable biomaterial material (nHA/PA66/D-RADA16-RGD).

METHODS

Proteinase K and circular dichroism spectroscopy were employed to test the stability and secondary structural properties of peptide D-RADA16-RGD respectively. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the surface of these materials. Confocal laser scanning (CLS), cell counting kit-8 tests (CCK-8), alizarin red S staining, cell immunofluorescence analysis and Western blotting were involved in vitro. Also biosafety and bioactivity of them have been evaluated in vivo.

RESULTS

Proteinase K and circular dichroism spectroscopy demonstrated that D-RADA16-RGD in nHA/PA66 was able to form stable-sheet secondary structure. SEM and TEM showed that the D-RADA16-RGD material was 7-33 nm in width and 130-600 nm in length, and the interwoven pore size ranged from 40 to 200 nm. CLS suggests that cells in nHA/PA66/D-RADA16-RGD group were linked to adjacent cells with more actin filaments. CCK-8 analysis showed that nHA/PA66/D-RADA16-RGD revealed good biocompatibility. The results of Alizarin-red S staining and Western blotting as well as vivo osteogenesis suggest nHA/PA66/D-RADA16-RGD exhibits better bioactivity.

CONCLUSION

This study demonstrates that our nHA/PA66/D-RADA16-RGD composite exhibits reasonable mechanical properties, biocompatibility and bioactivity with promotion of bone formation.

Sustained Release of Antimicrobial Peptide from Self-Assembling Hydrogel Enhanced Osteogenesis

Biomaterials have been widely used in bone infection and osteomyelitis resulting from their versatile functionalities. As far as we know, the appearance of osteomyelitis was mainly caused by bacteria. Therefore, a biomaterial that can cure bone infection and promote osteogenesis may become an ideal candidate for the treatment of osteomyelitis. Cationic antimicrobial peptides (AMPs) have been proved to have an excellent ability to kill bacteria, fungi, viruses, and parasites. However, the application of AMPs in bone infection and osteomyelitis is quite limited. Here, we designed a new hydrogel that has an inhibitory effect on the proliferation of S. aureus and enhances osteogenesis. RADA16 self-assembling peptide has been applied for AMPs delivery. In this study, we demonstrated that RADA16 could form a stable structure and afford the sustained release of AMPs. The interwoven nanofiber morphology was detected by field emission scanning electron microscopy. The sustained release study revealed that the release of AMPs could be obtained until 28 days. In vitro research showed this new self-assembling hydrogel could promote the proliferation of bone mesenchymal stem cells (BMSCs) and inhibited the growth of S. aureus. More importantly, the results in vivo also proved that RADA16-AMP self-assembling peptide had an excellent effect on bone formation. Our findings implied that we successfully combined RADA16 and AMPs together and laid the foundation for the application of this new hydrogel and open new avenues for biomaterials.

Biofunctionalized peptide nanofiber-based composite scaffolds for bone regeneration

Bone tissue had moderate self-healing capabilities, but biomaterial scaffolds were required for the repair of some defects such as large bone defects. Peptide nanofiber scaffolds demonstrated important potential in regenerative medicine. Functional modification and controlled release of signal molecules were two significant approaches to increase the bioactivity of biofunctionalized peptide nanofiber scaffolds, but peptide scaffolds were limited by insufficient mechanical strength. Thus, it was necessary to combine peptide scaffolds with other materials including polymers, hydroxyapatite, demineralized bone matrix (DBM) and metal materials based on the requirement of different bone defects. As the development of peptide-based composite scaffolds continued to evolve, ultimate translation to the clinical environment may allow for improved therapeutic outcomes for bone repair.

Balancing hydrophobicity and sequence pattern to influence self-assembly of amphipathic peptides

Amphipathic peptides with alternating polar and nonpolar amino acid sequences efficiently self-assemble into functional β-sheet fibrils as long as the nonpolar residues have sufficient hydrophobicity. For example, the Ac-(FKFE)2 -NH2 peptide rapidly self-assembles into β-sheet bilayer nanoribbons, while Ac-(AKAE)2 -NH2 fails to self-assemble under similar conditions due to the significantly reduced hydrophobicity and β-sheet propensity of Ala relative to Phe. Herein, we systematically explore the effect of substituting only two of the four Ala residues at various positions in the Ac-(AKAE)2 -NH2 peptide with amino acids of increasing hydrophobicity, β-sheet potential, and surface area (including Phe, 1-naphthylalanine (1-Nal), 2-naphthylalanine (2-Nal), cyclohexylalanine (Cha), and pentafluorophenylalanine (F5 -Phe)) on the self-assembly propensity of the resulting sequences. It was found that double Phe variants, regardless of the position of substitution, failed to self-assemble under the conditions used in this study. In contrast, all double 1-Nal and 2-Nal variants readily self-assembled, albeit at differing rates depending on the substitution patterns. To determine whether this was due to hydrophobicity or side chain surface area, we also prepared double Cha and F5 -Phe variant peptides (both side chain groups are more hydrophobic than Phe). Each of these variants also underwent effective self-assembly, with the aromatic F5 -Phe peptides doing so with greater efficiency. These findings provide insight into the role of amino acid hydrophobicity and sequence pattern on self-assembly proclivity of amphipathic peptides and on how targeted substitutions of nonpolar residues in these sequences can be exploited to tune the characteristics of the resulting self-assembled materials.

Effects of an injectable functionalized self-assembling nanopeptide hydrogel on angiogenesis and neurogenesis for regeneration of the central nervous system

Brain injury is a devastating medical condition and represents a major health problem. Tissue and organ reconstruction have been regarded as promising therapeutic strategies. Here, we propose a regenerative methodology focusing on the provision of functionalized nanopeptide scaffolds to facilitate angiogenesis and neurogenesis at the brain injury site. The peptide RADA16-SVVYGLR undergoes self-assembly to construct an interconnected network with intertwining nanofibers, and can be controlled to display various physicochemical properties by the adjustment of microenvironmental factors such as pH and ion concentration. Such scaffolds can support endothelial cells to form tube-like structures and neural stem cells to survive and proliferate. In an in vivo zebrafish brain injury model, sprouting angiogenesis and developmental neurogenesis were achieved, and functional recovery of the severed optic tectum was enhanced in RADA16-SVVYGLR hydrogel-implanted zebrafish. This nanopeptide hydrogel was non-toxic to zebrafish embryos during early developmental stages. This angiogenic self-assembling peptide hydrogel had programmable physical properties, good biocompatibility, and regenerative ability for functional recovery in the injured brain. We suggest that functionalized self-assembling peptides encapsulated with neural stem cells or used alone could be an attractive and effective therapeutic modality for brain injury and diseases (e.g., trauma, stroke, tumor, degenerative neurological disorders, etc.).

Designer bFGF-incorporated d-form self-assembly peptide nanofiber scaffolds to promote bone repair

d-Form and l-form peptide nanofiber scaffolds can spontaneously form stable β-sheet secondary structures and nanofiber hydrogel scaffolds, and hold some promise in hemostasis and wound healing. We report here on the synthetic self-assembling peptide d-RADA16 and l-RADA16 are both found to produce stable β-sheet secondary structure and nanofiber hydrogel scaffolds based on circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM) and rheology analysis etc. d-RADA16 hydrogel and l-RADA16 hydrogel can enhance obvious bone repair in femoral condyle defects of the Sprague-Dawley (SD) rat model compared to PBS treatment. Based on micro-computed tomography (CT), it was revealed that d-RADA16 hydrogel and l-RADA16 hydrogel were capable to obtain the extensive bone healing. Histological evaluation also found that these two hydrogels facilitate the presence of more mature bone tissue within the femoral condyle defects. Additionally, d-RADA16 hydrogel showed some potential in storing and releasing basic-fibroblast growth factor (bFGF) which was able to further promote bone regeneration based on micro-CT analysis. These results indicate that d-form peptide nanofiber hydrogel have some special capacity for bone repair.