Growth factor binding on heparin mimetic peptide nanofibers

Self-Assembly of Sulfate-Containing Peptides Sequesters VEGF for Inhibiting Cancer Cell Invasion

Heparan sulfate proteoglycans (HSPGs) play a crucial role in regulating cancer growth and migration by mediating interactions with growth factors. In this study, we developed a self-assembling peptide (S1) containing a sulfate group to simulate the contiguous sulfated regions (S-domains) in heparan sulfate for growth factor binding, aiming to sequester growth factors like VEGF. Spectral and structural studies as well as simulation studies suggested that S1 self-assembled into nanostructures similar to the heparan sulfate chains and effectively bound to VEGF. On cancer cell surfaces, S1 self-assemblies sequestered VEGF, leading to a reduction in VEGF levels in the medium, consequently inhibiting cancer cell growth, invasion, and angiogenesis. This study highlights the potential of self-assembling peptides to emulate extracellular matrix functions, offering insights for future cancer therapeutic strategies.

A review of advanced hydrogels for cartilage tissue engineering

With the increase in weight and age of the population, the consumption of tobacco, inappropriate foods, and the reduction of sports activities in recent years, bone and joint diseases such as osteoarthritis (OA) have become more common in the world. From the past until now, various treatment strategies (e.g., microfracture treatment, Autologous Chondrocyte Implantation (ACI), and Mosaicplasty) have been investigated and studied for the prevention and treatment of this disease. However, these methods face problems such as being invasive, not fully repairing the tissue, and damaging the surrounding tissues. Tissue engineering, including cartilage tissue engineering, is one of the minimally invasive, innovative, and effective methods for the treatment and regeneration of damaged cartilage, which has attracted the attention of scientists in the fields of medicine and biomaterials engineering in the past several years. Hydrogels of different types with diverse properties have become desirable candidates for engineering and treating cartilage tissue. They can cover most of the shortcomings of other treatment methods and cause the least secondary damage to the patient. Besides using hydrogels as an ideal strategy, new drug delivery and treatment methods, such as targeted drug delivery and treatment through mechanical signaling, have been studied as interesting strategies. In this study, we review and discuss various types of hydrogels, biomaterials used for hydrogel manufacturing, cartilage-targeting drug delivery, and mechanosignaling as modern strategies for cartilage treatment.

Designing Cardin-Motif Peptide and Heparin-Based Multicomponent Advanced Bioactive Hydrogel Scaffolds to Control Cellular Behavior

Recently, peptide and sugar-based multicomponent systems have gained much interest in attaining the sophisticated structure and biofunctional complexity of the extracellular matrix (ECM). To this direction, we have designed for the first time a biologically relevant minimalist Cardin-motif peptide capable of binding ECM-derived glycosaminoglycans. Herein, we explored Cardin-motif peptide and heparin-based biomolecular matrix by employing simple noncovalent interactions at the molecular level. Interestingly, this peptide was inadequate to induce hydrogelation at ambient pH due to the presence of basic amino acids. However, addition of heparin successfully triggered its gelation at physiological pH following favorable electrostatic interactions with heparin. Importantly, the newly developed scaffolds displayed tunable nanofibrous morphology and superior mechanical properties as controlled simply by the differential mixing ratio of both biomolecular entities. Additionally, these composite scaffolds could closely mimic the complexity of ECM as they demonstrated superior biocompatibility and enhanced growth and proliferation of neural cells as compared to the peptide scaffold.

Peptide Hydrogels and Nanostructures Controlling Biological Machinery

Peptides are versatile building blocks for the fabrication of various nanostructures that result in the formation of hydrogels and nanoparticles. Precise chemical functionalization promotes discrete structure formation, causing controlled bioactivity and physical properties for functional materials development. The conjugation of small molecules on amino acid side chains determines their intermolecular interactions in addition to their intrinsic peptide characteristics. Molecular information affects the peptide structure, formation, and activity. In this Perspective, peptide building blocks, nanostructure formation mechanisms, and the properties of these peptide materials are discussed with the results of recent publications. Bioinstructive and stimuli-responsive peptide materials have immense impacts on the nanomedicine field including drug delivery, cellular engineering, regenerative medicine, and biomedicine.

Optimizing Delivery of Therapeutic Growth Factors for Bone and Cartilage Regeneration

Bone- and cartilage-related diseases, such as osteoporosis and osteoarthritis, affect millions of people worldwide, impairing their quality of life and increasing mortality. Osteoporosis significantly increases the bone fracture risk of the spine, hip, and wrist. For successful fracture treatment and to facilitate proper healing in the most complicated cases, one of the most promising methods is to deliver a therapeutic protein to accelerate bone regeneration. Similarly, in the setting of osteoarthritis, where degraded cartilage does not regenerate, therapeutic proteins hold great promise to promote new cartilage formation. For both osteoporosis and osteoarthritis treatments, targeted delivery of therapeutic growth factors, with the aid of hydrogels, to bone and cartilage is a key to advance the field of regenerative medicine. In this review article, we propose five important aspects of therapeutic growth factor delivery for bone and cartilage regeneration: (1) protection of protein growth factors from physical and enzymatic degradation, (2) targeted growth factor delivery, (3) controlling GF release kinetics, (4) long-term stability of regenerated tissues, and (5) osteoimmunomodulatory effects of therapeutic growth factors and carriers/scaffolds.

Synthetic extracellular matrices with function-encoding peptides

The communication of cells with their surroundings is mostly encoded in the epitopes of structural and signalling proteins present in the extracellular matrix (ECM). These peptide epitopes can be incorporated in biomaterials to serve as function-encoding molecules to modulate cell-cell and cell-ECM interactions. In this Review, we discuss natural and synthetic peptide epitopes as molecular tools to bioengineer bioactive hydrogel materials. We present a library of functional peptide sequences that selectively communicate with cells and the ECM to coordinate biological processes, including epitopes that directly signal to cells, that bind ECM components that subsequently signal to cells, and that regulate ECM turnover. We highlight how these epitopes can be incorporated in different biomaterials as individual or multiple signals, working synergistically or additively. This molecular toolbox can be applied in the design of biomaterials aimed at regulating or controlling cellular and tissue function, repair and regeneration.

Engineered organoids in oral and maxillofacial regeneration

Oral and maxillofacial organoids, as three-dimensional study models of organs, have attracted increasing attention in tissue regeneration and disease modeling. However, traditional strategies for organoid construction still fail to precisely recapitulate the key characteristics of real organs, due to the difficulty in controlling the self-organization of cells in vitro. This review aims to summarize the recent progress of novel approaches to engineering oral and maxillofacial organoids. First, we introduced the necessary components and their roles in forming oral and maxillofacial organoids. Besides, we discussed cutting-edge technology in advancing the architecture and function of organoids, especially focusing on oral and maxillofacial tissue regeneration via novel strategy with designed cell-signal scaffold compounds. Finally, current limitations and future prospects of oral and maxillofacial organoids were represented to provide guidance for further disciplinary progression and clinical application to achieve organ regeneration.

Sulfated GAG mimetic peptide nanofibers enhance chondrogenic differentiation of mesenchymal stem cells in 3D in vitro models

Articular cartilage, which is exposed to continuous repetitive compressive stress, has limited self-healing capacity in the case of trauma. Thus, it is crucial to develop new treatment options for the effective regeneration of the cartilage tissue. Current cellular therapy treatment options are microfracture and autologous chondrocyte implantation; however, these treatments induce the formation of fibrous cartilage, which degenerates over time, rather than functional hyaline cartilage tissue. Tissue engineering studies using biodegradable scaffolds and autologous cells are vital for developing an effective long-term treatment option. 3D scaffolds composed of glycosaminoglycan-like peptide nanofibers are synthetic, bioactive, biocompatible, and biodegradable and trigger cell-cell interactions that enhance chondrogenic differentiation of cells without using any growth factors. We showed differentiation of mesenchymal stem cells into chondrocytes in both 2D and 3D culture, which produce a functional cartilage extracellular matrix, employing bioactive cues integrated into the peptide nanofiber scaffold without adding exogenous growth factors.

Photoactuating Artificial Muscles of Motor Amphiphiles as an Extracellular Matrix Mimetic Scaffold for Mesenchymal Stem Cells

Mimicking the native extracellular matrix (ECM) as a cell culture scaffold has long attracted scientists from the perspective of supramolecular chemistry for potential application in regenerative medicine. However, the development of the next-generation synthetic materials that mimic key aspects of ECM, with hierarchically oriented supramolecular structures, which are simultaneously highly dynamic and responsive to external stimuli, remains a major challenge. Herein, we present supramolecular assemblies formed by motor amphiphiles (MAs), which mimic the structural features of the hydrogel nature of the ECM and additionally show intrinsic dynamic behavior that allow amplifying molecular motions to macroscopic muscle-like actuating functions induced by light. The supramolecular assembly (named artificial muscle) provides an attractive approach for developing responsive ECM mimetic scaffolds for human bone marrow-derived mesenchymal stem cells (hBM-MSCs). Detailed investigations on the photoisomerization by nuclear magnetic resonance and UV–vis absorption spectroscopy, assembled structures by electron microscopy, the photoactuation process, structural order by X-ray diffraction, and cytotoxicity are presented. Artificial muscles of MAs provide fast photoactuation in water based on the hierarchically anisotropic supramolecular structures and show no cytotoxicity. Particularly important, artificial muscles of MAs with adhered hBM-MSCs still can be actuated by external light stimulation, showing their ability to convert light energy into mechanical signals in biocompatible systems. As a proof-of-concept demonstration, these results provide the potential for building photoactuating ECM mimetic scaffolds by artificial muscle-like supramolecular assemblies based on MAs and offer opportunities for signal transduction in future biohybrid systems of cells and MAs.

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

The Potential of FGF-2 in Craniofacial Bone Tissue Engineering: A Review

Bone is a hard-vascularized tissue, which renews itself continuously to adapt to the mechanical and metabolic demands of the body. The craniofacial area is prone to trauma and pathologies that often result in large bone damage, these leading to both aesthetic and functional complications for patients. The "gold standard" for treating these large defects is autologous bone grafting, which has some drawbacks including the requirement for a second surgical site with quantity of bone limitations, pain and other surgical complications. Indeed, tissue engineering combining a biomaterial with the appropriate cells and molecules of interest would allow a new therapeutic approach to treat large bone defects while avoiding complications associated with a second surgical site. This review first outlines the current knowledge of bone remodeling and the different signaling pathways involved seeking to improve our understanding of the roles of each to be able to stimulate or inhibit them. Secondly, it highlights the interesting characteristics of one growth factor in particular, FGF-2, and its role in bone homeostasis, before then analyzing its potential usefulness in craniofacial bone tissue engineering because of its proliferative, pro-angiogenic and pro-osteogenic effects depending on its spatial-temporal use, dose and mode of administration.

Affinity Hydrogels for Protein Delivery

Proteins have been studied as therapeutic agents for treatment of various human diseases. However, the delivery of protein drugs into the body is challenging. In this review, we summarize and highlight progress in developing affinity hydrogels (i.e., hydrogels functionalized with protein-bound ligands) for controlled protein release. Contrary to traditional hydrogels, which release proteins mainly through diffusion, affinity hydrogels stably retain and sustainably release proteins based mainly on diffusion coupled with a binding reaction. These hydrogels can also be modulated to release proteins in response to defined molecules in a triggered manner. Future research efforts may focus on the development of intelligent affinity hydrogels to mimic the properties of human tissues in sensing different environmental stimuli for on-demand release of single or multiple proteins (i.e., biomimetic intelligence for protein delivery).

Biomaterial-based cell delivery strategies to promote liver regeneration

Chronic liver disease and cirrhosis is a widespread and untreatable condition that leads to lifelong impairment and eventual death. The scarcity of liver transplantation options requires the development of new strategies to attenuate disease progression and reestablish liver function by promoting regeneration. Biomaterials are becoming an increasingly promising option to both culture and deliver cells to support in vivo viability and long-term function. There is a wide variety of both natural and synthetic biomaterials that are becoming established as delivery vehicles with their own unique advantages and disadvantages for liver regeneration. We review the latest developments in cell transplantation strategies to promote liver regeneration, with a focus on the use of both natural and synthetic biomaterials for cell culture and delivery. We conclude that future work will need to refine the use of these biomaterials and combine them with novel strategies that recapitulate liver organization and function in order to translate this strategy to clinical use.

Heparin-conjugated collagen as a potent growth factor-localizing and stabilizing scaffold for regenerative medicine

Introduction

Growth factors are crucial bioactive molecules in vitro and in vivo. Among them, basic fibroblast growth factor (bFGF) has been used widely for various applications such as cell culture and regenerative medicine. However, bFGF has extremely poor stability in aqueous solution; thus, it is difficult to maintain its high local concentration. Heparin-conjugated materials have been studied recently as promising scaffold-immobilizing growth factors for biological and medical applications. The previous studies have focused on the local concentration maintenance and sustained release of the growth factors from the scaffold.

Methods

In this paper, we focused on the biological stability of bFGF immobilized on the heparin-conjugated collagen (hep-col) scaffold. The stability of the immobilized bFGF was quantitatively evaluated at physiological temperature (37 °C) using cell culture and ELISA.

Results

The immobilized bFGF had twice higher stability than the bFGF solution. Furthermore, the hep-col scaffold was able to immobilize not only bFGF but also other growth factors (i.e., vascular endothelial growth factor and hepatocyte growth factor) at high efficiency.

Conclusions

The hep-col scaffold can localize several kinds of growth factors as well as stabilize bFGF under physiological temperature and is a promising potent scaffold for regenerative medicine.

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Heparin-conjugated collagen scaffold immobilized bFGF, VEGF, and HGF with a high efficiency of 80–90% even at 100 ng/mL.

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Cell proliferation of HUVECs was promoted depending on the bFGF amount on the scaffold, and slowed by pre-incubation at 37 °C.

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Growth factor-immobilization on the scaffold stabilized bFGF and maintained its bioactivity longer than bFGF solution.

Hyaluronic Acid Biomaterials for Central Nervous System Regenerative Medicine

Hyaluronic acid (HA) is a primary component of the brain extracellular matrix and functions through cellular receptors to regulate cell behavior within the central nervous system (CNS). These behaviors, such as migration, proliferation, differentiation, and inflammation contribute to maintenance and homeostasis of the CNS. However, such equilibrium is disrupted following injury or disease leading to significantly altered extracellular matrix milieu and cell functions. This imbalance thereby inhibits inherent homeostatic processes that support critical tissue health and functionality in the CNS. To mitigate the damage sustained by injury/disease, HA-based tissue engineering constructs have been investigated for CNS regenerative medicine applications. HA's effectiveness in tissue healing and regeneration is primarily attributed to its impact on cell signaling and the ease of customizing chemical and mechanical properties. This review focuses on recent findings to highlight the applications of HA-based materials in CNS regenerative medicine.

Electrospun Nanofibers for Improved Angiogenesis: Promises for Tissue Engineering Applications

Angiogenesis (or the development of new blood vessels) is a key event in tissue engineering and regenerative medicine; thus, a number of biomaterials have been developed and combined with stem cells and/or bioactive molecules to produce three-dimensional (3D) pro-angiogenic constructs. Among the various biomaterials, electrospun nanofibrous scaffolds offer great opportunities for pro-angiogenic approaches in tissue repair and regeneration. Nanofibers made of natural and synthetic polymers are often used to incorporate bioactive components (e.g., bioactive glasses (BGs)) and load biomolecules (e.g., vascular endothelial growth factor (VEGF)) that exert pro-angiogenic activity. Furthermore, seeding of specific types of stem cells (e.g., endothelial progenitor cells) onto nanofibrous scaffolds is considered as a valuable alternative for inducing angiogenesis. The effectiveness of these strategies has been extensively examined both in vitro and in vivo and the outcomes have shown promise in the reconstruction of hard and soft tissues (mainly bone and skin, respectively). However, the translational of electrospun scaffolds with pro-angiogenic molecules or cells is only at its beginning, requiring more research to prove their usefulness in the repair and regeneration of other highly-vascularized vital tissues and organs. This review will cover the latest progress in designing and developing pro-angiogenic electrospun nanofibers and evaluate their usefulness in a tissue engineering and regenerative medicine setting.

Fibroblast Growth Factor 2-A Review of Stabilisation Approaches for Clinical Applications

Basic fibroblast growth factor (FGF)-2 has been shown to regulate many cellular functions including cell proliferation, migration, and differentiation, as well as angiogenesis in a variety of tissues, including skin, blood vessel, muscle, adipose, tendon/ligament, cartilage, bone, tooth, and nerve. These multiple functions make FGF-2 an attractive component for wound healing and tissue engineering constructs; however, the stability of FGF-2 is widely accepted to be a major concern for the development of useful medicinal products. Many approaches have been reported in the literature for preserving the biological activity of FGF-2 in aqueous solutions. Most of these efforts were directed at sustaining FGF-2 activity for cell culture research, with a smaller number of studies seeking to develop sustained release formulations of FGF-2 for tissue engineering applications. The stabilisation approaches may be classified into the broad classes of ionic interaction modification with excipients, chemical modification, and physical adsorption and encapsulation with carrier materials. This review discusses the underlying causes of FGF-2 instability and provides an overview of the approaches reported in the literature for stabilising FGF-2 that may be relevant for clinical applications. Although efforts have been made to stabilise FGF-2 for both in vitro and in vivo applications with varying degrees of success, the lack of comprehensive published stability data for the final FGF-2 products represents a substantial gap in the current knowledge, which has to be addressed before viable products for wider tissue engineering applications can be developed to meet regulatory authorisation.

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.

Advanced Biomaterials and Processing Methods for Liver Regeneration: State-of-the-Art and Future Trends

Liver diseases contribute markedly to the global burden of mortality and disease. The limited organ disposal for orthotopic liver transplantation results in a continuing need for alternative strategies. Over the past years, important progress has been made in the field of tissue engineering (TE). Many of the early trials to improve the development of an engineered tissue construct are based on seeding cells onto biomaterial scaffolds. Nowadays, several TE approaches have been developed and are applied to one vital organ: the liver. Essential elements must be considered in liver TE-cells and culturing systems, bioactive agents or growth factors (GF), and biomaterials and processing methods. The potential of hepatocytes, mesenchymal stem cells, and others as cell sources is demonstrated. They need engineered biomaterial-based scaffolds with perfect biocompatibility and bioactivity to support cell proliferation and hepatic differentiation as well as allowing extracellular matrix deposition and vascularization. Moreover, they require a microenvironment provided using conventional or advanced processing technologies in order to supply oxygen, nutrients, and GF. Herein the biomaterials and the conventional and advanced processing technologies, including cell-sheets process, 3D bioprinting, and microfluidic systems, as well as the future trends in these major fields are discussed.

Development of heparin-conjugated nanofibers and a novel biological signal by immobilized growth factors for peripheral nerve regeneration

Aligned fibers have been used as a scaffold of nerve guidance conduit owing to their guiding function of neural cells for peripheral nerve regeneration. However, the recovery performance of nerve guidance conduits using aligned fibrous scaffold is insufficient, and further improvements in scaffold function is required for promoting regeneration. In this study, we developed aligned heparin-conjugated fibers and supplied a biological signal to neural cells by the growth factors immobilized through heparin. Results indicated that neural model cells (PC12 cells) were cultured well on the scaffold without inhibiting cell adhesion by heparin conjugation and exhibited more vigorous cell proliferation than in a heparin-free condition. The cells extended their neurites along the fiber direction. Furthermore, PC12 cells on the heparin-conjugated fibrous scaffold pre-exposed to a nerve growth factor solution sprouted more neurites compared to those of heparin-free condition. These results verified that our scaffold exhibited high biocompatibility to neural cells and could maintain an effective local concentration of growth factors on the scaffold surface. Therefore, aligned heparin-conjugated fibers are promising scaffolds of nerve guidance conduits for promoting peripheral nerve regeneration by the combinatorial effect of topological and biological signals.

Bioinspired Self-assembling Peptide Hydrogel with Proteoglycan-assisted Growth Factor Delivery for Therapeutic Angiogenesis

Critical challenges still exist in surgical theaters and emergency rooms to stop bleeding effectively and facilitate wound healing efficiently. In circumstances of tissue ischemia, it is essential to induce proper angiogenesis to provide adequate vascular supply to the injury site. Methods: In view of these clinical unmet needs, we propose an applicable approach by designing functionalized self-assembling peptide (SAP) hydrogel with two sequences of RADA16-GGQQLK (QLK) and RADA16-GGLRKKLGKA (LRK) in this study. The SAP hydrogel conjugated with QLK functional motif could be crosslinked by endogenous transglutaminase, one of the intrinsic factors secreted during the coagulation process, the mechanical property of the hydrogel can then be enhanced without the need of external support. On the other hand, the LRK sequence exhibited a good binding affinity with the proteoglycan heparan sulfate and could act as a cofactor by sustaining the release of embedded growth factors. Results: The results showed that this SAP solution underwent self-assembling process in a physiological environment, formed hydrogel in situ, and possessed good shear thinning property with injectability. After pH adjustment, the SAP developed densely-compacted fiber entanglement that closely mimicked the three-dimensional fibrous framework of natural extracellular matrix. Such scaffold could not only support the survival of encapsulating cells but also promote the capillary-like tubular structure formation by dual angiogenic growth factors. The ex ovo chicken chorioallantoic membrane assay demonstrated that the growth factor-loaded hydrogel promoted the sprout of surrounding vessels in a spoke-wheel pattern compared to growth factor-free counterparts. Conclusion: The designer bioinspired SAP hydrogel may be an attractive and promising therapeutic modality for minimally-invasive surgery, ischemic tissue disorders and chronic wound healing.

Supramolecular Nanofibrous Peptide/Polymer Hydrogels for the Multiplexing of Bioactive Signals

The ability to provide multiple functions within a single scaffold biomaterial is a major goal in tissue engineering. Self-assembling peptide-based hydrogels are gaining significant attention as three-dimensional biomaterials because they provide a network of nanofibers similar to the native extracellular matrix while allowing the presentation of multiple biochemical cues for cell signaling. Herein, we combine a positively charged peptide amphiphile (PA) and the negatively charged synthetic polymer poly(sodium 4-styrenesulfonate) (PSS) to fabricate hybrid hydrogels through supramolecular self-assembly. PSS/PA hydrogels show rather high mechanical stiffness while being stable in buffered environment. The sulfonate functionality in PSS promotes hydrogel mineralization which can be controlled if undertaken in standard osteogenic medium. Loading proteins with different charges in the hydrogels reveals their ability to retain and sustain their release and indicates their potential for the controlled delivery of growth factors. Human mesenchymal stem cells encapsulated in PSS/PA hydrogels remain viable. The biomimetic nanofibrous structure of the hydrogels, together with multiplexing of bioactive signals, can provide a suitable environment for stem cell differentiation.

Engineered delivery strategies for enhanced control of growth factor activities in wound healing

Growth factors (GFs) are versatile signalling molecules that orchestrate the dynamic, multi-stage process of wound healing. Delivery of exogenous GFs to the wound milieu to mediate healing in an active, physiologically-relevant manner has shown great promise in laboratories; however, the inherent instability of GFs, accompanied with numerous safety, efficacy and cost concerns, has hindered the clinical success of GF delivery. In this article, we highlight that the key to overcoming these challenges is to enhance the control of the activities of GFs throughout the delivering process. We summarise the recent strategies based on biomaterials matrices and molecular engineering, which aim to improve the conditions of GFs for delivery (at the 'supply' end of the delivery), increase the stability and functions of GFs in extracellular matrix (in transportation to target cells), as well as enhance the GFs/receptor interaction on the cell membrane (at the 'destination' end of the delivery). Many of these investigations have led to encouraging outcomes in various in vitro and in vivo regenerative models with considerable translational potential.

Soybean-modified polyamide-6 mats as a long-term cutaneous wound covering

Engineered skin coverings have been adopted clinically to support extensive and deep wounds that result in fewer healthy skin remaining and therefore take longer to heal. Nonetheless, these biomaterials demand intensive labor and an expensive final cost. In comparison to conventional bandages, which do not meet all the requirements of wound care, electrospun fiber mats could potentially provide an excellent environment for healing. In this work, we developed two nanostructured scaffolds based on polyamide-6 (PA-6) to be tested as a wound covering in a rat model of full-thickness incisional wound healing. The central idea was to create a bioconstruct that is simple to implement and biologically safe, with a high survival rate, which provides physical support and biological recognition for new functional tissues. An unmodified PA-6 and a soybean-modified PA-6 were employed as nanofibrillar matrices in this study. The biomaterials showed a dimensional homology to natural extracellular matrix components and neither in vitro toxicity nor in vivo side effects. Both polymeric scaffolds were resistant to the sterilization process and could promote the attachment of 3T3 fibroblast cells, besides successfully incorporating the growth factor PDGF-BB, which had its bioactivity extended for up to 12 h under simulated conditions. The modification of PA-6 chains with a fatty acid derivative increased the scaffold's surface free energy, favoring cell proliferation, collagen formation, and ECM secretion. These results confirm the potential of these materials as a topical dermal covering for skin regeneration.

Cardiac Extracellular Matrix Modification as a Therapeutic Approach

The cardiac extracellular matrix (cECM) is comprised of proteins and polysaccharides secreted by cardiac cell types, which provide structural and biochemical support to cardiovascular tissue. The roles of cECM proteins and the associated family of cell surface receptor, integrins, have been explored in vivo via the generation of knockout experimental animal models. However, the complexity of tissues makes it difficult to isolate the effects of individual cECM proteins on a particular cell process or disease state. The desire to further dissect the role of cECM has led to the development of a variety of in vitro model systems, which are now being used not only for basic studies but also for testing drug efficacy and toxicity and for generating therapeutic scaffolds. These systems began with 2D coatings of cECM derived from tissue and have developed to include recombinant ECM proteins, ECM fragments, and ECM mimics. Most recently 3D model systems have emerged, made possible by several developing technologies including, and most notably, 3D bioprinting. This chapter will attempt to track the evolution of our understanding of the relationship between cECM and cell behavior from in vivo model to in vitro control systems. We end the chapter with a summary of how basic studies such as these have informed the use of cECM as a direct therapy.

Vascular Remodeling Process of Heparin-Conjugated Poly(ε-Caprolactone) Scaffold in a Rat Abdominal Aorta Replacement Model

In the field of vascular graft research, poly-ε-caprolactone (PCL) is used owing to its good mechanical strength and biocompatibility. In this study, PCL scaffold was prepared by electrospinning and surface modification with heparin via hexamethylenediamine. Then the scaffolds were implanted into the infrarenal abdominal aorta of Wistar rats and contrast-enhanced micro-ultrasound was used to monitor the patency of grafts after implantation. These grafts were extracted from the rats at 1, 3, and 6 months for histological analysis, immunofluorescence staining, and scanning electron microscopy observation. Although some grafts experienced aneurysmal change, results showed that all implanted grafts were patent during the course of 6 months and these grafts demonstrated well-organized neotissue with endothelium formation, smooth muscle regeneration, and extracellular matrix formation. Such findings confirm feasibility to create heparin-conjugated scaffolds of next-generation vascular grafts.

Peptide supramolecular materials for therapeutics

Supramolecular assembly of peptide-based monomers into nanostructures offers many promising applications in advanced therapies. In this Tutorial Review, we introduce molecular designs to control the structure and potential biological function of supramolecular assemblies. An emphasis is placed on peptide-based supramolecular nanostructures that are intentionally designed to signal cells, either directly through the incorporation of amino acid sequences that activate receptors or indirectly by recruiting native signals such as growth factors. Additionally, we describe the use and future potential of hierarchical structures, such as single molecules that assemble into nanoscale fibers which then align to form macroscopic strings; the strings can then serve as scaffolds for cell growth, proliferation, and differentiation.

Hydrolytically Labile Linkers Regulate Release and Activity of Human Bone Morphogenetic Protein-6

Release of growth factors while simultaneously maintaining their full biological activity over a period of days to weeks is an important issue in controlled drug delivery and in tissue engineering. In addition, the selected strategy to immobilize growth factors largely determines their biological activity. Silica surfaces derivatized with glycidyloxy propyl trimethoxysilane and poly(glycidyl methacrylate) brushes yielded epoxide-functionalized surfaces onto which human bone morphogenetic protein-6 (hBMP-6) was immobilized giving stable secondary amine bonds. The biological activity of hBMP-6 was unleashed by hydrolysis of the surface siloxane and ester bonds. We demonstrate that this type of labile bonding strategy can be applied to biomaterial surfaces with relatively simple and biocompatible chemistry, such as siloxane, ester, and imine bonds. Our data indicates that the use of differential hydrolytically labile linkers is a versatile method for functionalization of biomaterials with a variety of growth factors providing control over their biological activity.

Supramolecular Platform Stabilizing Growth Factors

High concentrations of supplemented growth factors can cause oversaturation and adverse effects in in vitro and in vivo studies, though these supraphysiological concentrations are often required due to the low stability of growth factors. Here we demonstrate the stabilization of TGF-β1 and BMP4 using supramolecular polymers. Inspired by heparan sulfate, sulfonated peptides were presented on a supramolecular polymer to allow for noncovalent binding to growth factors in solution. After mixing with excipient molecules, both TGF-β1 and BMP4 were shown to have a prolonged half-life compared to the growth factors free in solution. Moreover, high cellular response was measured by a luciferase assay, indicating that TGF-β1 remained highly active upon binding to the supramolecular assembly. The results demonstrate that significant lower concentrations of growth factors can be used when supramolecular polymers bearing growth factor binding moieties are implemented. This approach can also be exploited in hydrogel systems to control growth factor release.

Unidirectional BMP2-loaded collagen scaffolds induce chondrogenic differentiation

Microfracture surgery may be improved by the implantation of unidirectional collagen scaffolds that provide a template for mesenchymal stem cells to regenerate cartilage. Incorporation of growth factors in unidirectional scaffolds may further enhance cartilage regeneration. In scaffolds, immobilization of growth factors is required to prolong in vivo activity, to limit diffusion and to reduce the amount of growth factor needed for safe clinical application. We investigated the immobilization of bone morphogenetic protein 2 (BMP2) to unidirectional collagen scaffolds and the effect on in vitro chondrogenesis. C3H10T1/2 cells were seeded on unidirectional collagen scaffolds with and without covalently attached heparin, and with and without incubation with BMP2 (1 and 10 μg), or with BMP2 present in the culture medium (10-200 ng ml^-1). Culturing was for 2 weeks and readout parameters included histology, immunohistochemistry, biochemical analysis and molecular biological analysis. The unidirectional pores facilitated the distribution of C3H10T1/2 cells and matrix formation throughout scaffolds. The effective dose of medium supplementation with BMP2 was 100 ng ml^-1 (total exposure 1 μg BMP2), and similar production of cartilage-specific molecules chondroitin sulfate (CS) and type II collagen was found for scaffolds pre-incubated with 10 μg BMP2. Pre-incubation with 1 μg BMP2 resulted in less cartilage matrix formation. The conjugation of heparin to the scaffolds resulted in more CS and less type II collagen deposition compared to scaffolds without heparin. In conclusion, unidirectional collagen scaffolds pre-incubated with 10 μg BMP2 supported chondrogenesis in vitro and may be suitable for prolonged cartilage matrix synthesis in vivo.

Supramolecular Peptide Nanofiber Morphology Affects Mechanotransduction of Stem Cells

Chirality and morphology are essential factors for protein function and interactions with other biomacromolecules. Extracellular matrix (ECM) proteins are also similar to other proteins in this sense; however, the complexity of the natural ECM makes it difficult to study these factors at the cellular level. The synthetic peptide nanomaterials harbor great promise in mimicking specific ECM molecules as model systems. In this work, we demonstrate that mechanosensory responses of stem cells are directly regulated by the chirality and morphology of ECM-mimetic peptide nanofibers with strictly controlled characteristics. Structural signals presented on l-amino acid containing cylindrical nanofibers (l-VV) favored the formation of integrin β1-based focal adhesion complexes, which increased the osteogenic potential of stem cells through the activation of nuclear YAP. On the other hand, twisted ribbon-like nanofibers (l-FF and d-FF) guided the cells into round shapes and decreased the formation of focal adhesion complexes, which resulted in the confinement of YAP proteins in the cytosol and a corresponding decrease in osteogenic potential. Interestingly, the d-form of twisted-ribbon like nanofibers (d-FF) increased the chondrogenic potential of stem cells more than their l-form (l-FF). Our results provide new insights into the importance and relevance of morphology and chirality of nanomaterials in their interactions with cells and reveal that precise control over the chemical and physical properties of nanostructures can affect stem cell fate even without the incorporation of specific epitopes.

Angiogenic peptide nanofibers repair cardiac tissue defect after myocardial infarction

Myocardial infarction remains one of the top leading causes of death in the world and the damage sustained in the heart eventually develops into heart failure. Limited conventional treatment options due to the inability of the myocardium to regenerate after injury and shortage of organ donors require the development of alternative therapies to repair the damaged myocardium. Current efforts in repairing damage after myocardial infarction concentrates on using biologically derived molecules such as growth factors or stem cells, which carry risks of serious side effects including the formation of teratomas. Here, we demonstrate that synthetic glycosaminoglycan (GAG) mimetic peptide nanofiber scaffolds induce neovascularization in cardiovascular tissue after myocardial infarction, without the addition of any biologically derived factors or stem cells. When the GAG mimetic nanofiber gels were injected in the infarct site of rodent myocardial infarct model, increased VEGF-A expression and recruitment of vascular cells was observed. This was accompanied with significant degree of neovascularization and better cardiac performance when compared to the control saline group. The results demonstrate the potential of future clinical applications of these bioactive peptide nanofibers as a promising strategy for cardiovascular repair.

STATEMENT OF SIGNIFICANCE

We present a synthetic bioactive peptide nanofiber system can enhance cardiac function and enhance cardiovascular regeneration after myocardial infarction (MI) without the addition of growth factors, stem cells or other biologically derived molecules. Current state of the art in cardiac repair after MI utilize at least one of the above mentioned biologically derived molecules, thus our approach is ground-breaking for cardiovascular therapy after MI. In this work, we showed that synthetic glycosaminoglycan (GAG) mimetic peptide nanofiber scaffolds induce neovascularization and cardiomyocyte differentiation for the regeneration of cardiovascular tissue after myocardial infarction in a rat infarct model. When the peptide nanofiber gels were injected in infarct site at rodent myocardial infarct model, recruitment of vascular cells was observed, neovascularization was significantly induced and cardiac performance was improved. These results demonstrate the potential of future clinical applications of these bioactive peptide nanofibers as a promising strategy for cardiovascular repair.

Polysaccharide matrices used in 3D in vitro cell culture systems

Polysaccharides comprise a diverse class of polymeric materials with a history of proven biocompatibility and continual use as biomaterials. Recent focus on new matrices appropriate for three-dimensional (3D) cell culture offers new opportunities to apply polysaccharides as extracellular matrix mimics. However, chemical and structural bases for specific cell-polysaccharide interactions essential for their utility as 3-D cell matrices are not well defined. This review describes how these naturally sourced biomaterials satisfy several key properties for current 3D cell culture needs and can also be synthetically modified or blended with additional components to tailor their cell engagement properties. Beyond their benign interactions with many cell types in cultures, their economical and high quality sourcing, optical clarity for ex situ analytical interrogation and in situ gelation represent important properties of these polymers for 3D cell culture applications. Continued diversification of their versatile glycan chemistry, new bio-synthetic sourcing strategies and elucidation of new cell-specific properties are attractive to expand the polysaccharide polymer utility for cell culture needs. Many 3D cell culture priorities are addressed with the portfolio of polysaccharide materials available and under development. This review provides a critical analysis of their properties, capabilities and challenges in 3D cell culture applications.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Injectable hydrogels for cartilage and bone tissue engineering

Tissue engineering has become a promising strategy for repairing damaged cartilage and bone tissue. Among the scaffolds for tissue-engineering applications, injectable hydrogels have demonstrated great potential for use as three-dimensional cell culture scaffolds in cartilage and bone tissue engineering, owing to their high water content, similarity to the natural extracellular matrix (ECM), porous framework for cell transplantation and proliferation, minimal invasive properties, and ability to match irregular defects. In this review, we describe the selection of appropriate biomaterials and fabrication methods to prepare novel injectable hydrogels for cartilage and bone tissue engineering. In addition, the biology of cartilage and the bony ECM is also summarized. Finally, future perspectives for injectable hydrogels in cartilage and bone tissue engineering are discussed.

Direct catechol conjugation of mussel-inspired biomacromolecule coatings to polymeric membranes with antifouling properties, anticoagulant activity and cytocompatibility

TheO-sulfated chitosan andN,O-sulfated chitosan coatings were prepared by direct catechol conjugation to enrich the biological applications of polymeric membranes.

Drug delivery by supramolecular design

Principles rooted in supramolecular chemistry have empowered new and highly functional therapeutics and drug delivery devices. This general approach offers elegant tools rooted in molecular and materials engineered to address the many challenges faced in treating disease.

Diabetic wound regeneration using heparin-mimetic peptide amphiphile gel in db/db mice

There is an urgent need for more efficient treatment of chronic wounds in diabetic patients especially with a high risk of leg amputation.

Biomaterials and Culture Technologies for Regenerative Therapy of Liver Tissue

Regenerative approach has emerged to substitute the current extracorporeal technologies for the treatment of diseased and damaged liver tissue. This is based on the use of biomaterials that modulate the responses of hepatic cells through the unique matrix properties tuned to recapitulate regenerative functions. Cells in liver preserve their phenotype or differentiate through the interactions with extracellular matrix molecules. Therefore, the intrinsic properties of the engineered biomaterials, such as stiffness and surface topography, need to be tailored to induce appropriate cellular functions. The matrix physical stimuli can be combined with biochemical cues, such as immobilized functional groups or the delivered actions of signaling molecules. Furthermore, the external modulation of cells, through cocultures with nonparenchymal cells (e.g., endothelial cells) that can signal bioactive molecules, is another promising avenue to regenerate liver tissue. This review disseminates the recent approaches of regenerating liver tissue, with a focus on the development of biomaterials and the related culture technologies.

Heparin-Mimicking Polymers: Synthesis and Biological Applications

Heparin is a naturally occurring, highly sulfated polysaccharide that plays a critical role in a range of different biological processes. Therapeutically, it is mostly commonly used as an injectable solution as an anticoagulant for a variety of indications, although it has also been employed in other forms such as coatings on various biomedical devices. Due to the diverse functions of this polysaccharide in the body, including anticoagulation, tissue regeneration, anti-inflammation, and protein stabilization, and drawbacks of its use, analogous heparin-mimicking materials are also widely studied for therapeutic applications. This review focuses on one type of these materials, namely, synthetic heparin-mimicking polymers. Utilization of these polymers provides significant benefits compared to heparin, including enhancing therapeutic efficacy and reducing side effects as a result of fine-tuning heparin-binding motifs and other molecular characteristics. The major types of the various polymers are summarized, as well as their applications. Because development of a broader range of heparin-mimicking materials would further expand the impact of these polymers in the treatment of various diseases, future directions are also discussed.

A Heparin-Mimicking Block Copolymer Both Stabilizes and Increases the Activity of Fibroblast Growth Factor 2 (FGF2)

Fibroblast growth factor 2 (FGF2) is a protein involved in cellular functions in applications such as wound healing and tissue regeneration. Stabilization of this protein is important for its use as a therapeutic since the native protein is unstable during storage and delivery. Additionally, the ability to increase the activity of FGF2 is important for its application, particularly in chronic wound healing and the treatment of various ischemic conditions. Here we report a heparin mimicking block copolymer, poly(styrenesulfonate-co-poly(ethylene glycol) methyl ether methacrylate)-b-vinyl sulfonate) (p(SS-co-PEGMA)-b-VS, that contains a segment that enhances the stability of FGF2 and one that binds to the FGF2 receptor. The FGF2 conjugate retained activity after exposure to refrigeration (4 °C) and room temperature (23 °C) for 7 days, while unmodified FGF2 was inactive after these standard storage conditions. A cell study performed with a cell line lacking native heparan sulfate proteoglycans indicated that the conjugated block copolymer facilitated binding of FGF2 to its receptor similar to the addition of heparin to FGF2. A receptor-based enzyme-linked immunosorbant assay (ELISA) confirmed the results. The conjugate also increased the migration of endothelial cells by 80% compared to FGF2 alone. Additionally, the FGF2-p(SS-co-PEGMA)-b-VS stimulated endothelial cell sprouting 250% better than FGF2 at low concentration. These data verify that this rationally designed protein-block copolymer conjugate enhances receptor binding, cellular processes such as migration and tube-like formation, and stability, and suggest that it may be useful for applications in biomaterials, tissue regeneration, and wound healing.