Controlled release of heparin-binding growth factors using heparin-containing particulate systems for tissue regeneration

Control and interplay of scaffold-biomolecule interactions applied to cartilage tissue engineering

Cartilage tissue engineering based on the combination of biomaterials, adult or stem cells and bioactive factors is a challenging approach for regenerative medicine with the aim of achieving the formation of a functional neotissue stable in the long term. Various 3D scaffolds have been developed to mimic the extracellular matrix environment and promote cartilage repair. In addition, bioactive factors have been extensively employed to induce and maintain the cartilage phenotype. However, the spatiotemporal control of bioactive factor release remains critical for maximizing the regenerative potential of multipotent cells, such as mesenchymal stromal cells (MSCs), and achieving efficient chondrogenesis and sustained tissue homeostasis, which are essential for the repair of hyaline cartilage. Despite advances, the effective delivery of bioactive factors is limited by challenges such as insufficient retention at the site of injury and the loss of therapeutic efficacy due to uncontrolled drug release. These limitations have prompted research on biomolecule-scaffold interactions to develop advanced delivery systems that provide sustained release and controlled bioavailability of biological factors, thereby improving therapeutic outcomes. This review focuses specifically on biomaterials (natural, hybrid and synthetic) and biomolecules (molecules, proteins, nucleic acids) of interest for cartilage engineering. Herein, we review in detail the approaches developed to maintain the biomolecules in scaffolds and control their release, based on their chemical nature and structure, through steric, non-covalent and/or covalent interactions, with a view to their application in cartilage repair.

Heparin-Functionalized Bioactive Glass to Harvest Endogenous Growth Factors for Pulp Regeneration

Pulp and periapical diseases can lead to the cessation of tooth development, resulting in compromised tooth structure and functions. Despite numerous efforts to induce pulp regeneration, effective strategies are still lacking. Growth factors (GFs) hold considerable promise in pulp regeneration due to their diverse cellular regulatory properties. However, the limited half-lives and susceptibility to degradation of exogenous GFs necessitate the administration of supra-physiological doses, leading to undesirable side effects. In this research, a heparin-functionalized bioactive glass (CaO-P2O5-SiO2-Heparin, abbreviated as PSC-Heparin) with strong bioactivity and a stable neutral pH is developed as a promising candidate to addressing challenges in pulp regeneration. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis reveal the successful synthesis of PSC-Heparin. Scanning electron microscopy and X-ray diffraction show the hydroxyapatite formation can be observed on the surface of PSC-Heparin after soaking in simulated body fluid for 12 h. PSC-Heparin is capable of harvesting various endogenous GFs and sustainably releasing them over an extended duration by the enzyme-linked immunosorbent assay. Cytological experiments show that developed PSC-Heparin can facilitate the adhesion, migration, proliferation, and odontogenic differentiation of stem cells from apical papillae. Notably, the histological analysis of subcutaneous implantation in nude mice demonstrates PSC-Heparin is capable of promoting the odontoblast-like layers and pulp-dentin complex formation without the addition of exogenous GFs, which is vital for clinical applications. This work highlights an effective strategy of harvesting endogenous GFs and avoiding the involvement of exogenous GFs to achieve pulp-dentin complex regeneration, which may open a new horizon for regenerative endodontic therapy.

Evaluation of GHK peptide-heparin interactions in multifunctional liposomal covering

Small biospecific peptides with defined chemical structure and cellular responses are promising alternatives to full-length therapeutic proteins. Identification of these peptides solely or in combination with other bioactive factors and determination of their targets are of substantial interest in current drug delivery research. This study is aimed at the development of new liposomal formulations of ECM-derived GHK peptide known for its multiple regeneration-related activities but poorly recognized cellular targets. In situ association of membranotropic GHK derivative with unilamellar liposomes was performed to prepare GHK-modified liposomes with defined properties. According to DLS, the GHK component on the liposomal surface interacted with heparin in a specific manner compared to other polysaccharides and RGD counterpart, whereas ITC analysis of such interactions was complicated. The results provide a useful tool for screening of bio-interactions of synthetic peptide-presenting liposomes by the DLS technique. They were also employed to produce a multi-functional nanosized GHK-heparin covering for liposomes. The resulting composite liposomes possessed low size dispersity, increased anionic charge, and mechanical rigidity. The heparin component significantly promoted the accumulation of GHK-modified liposomes in 3T3 fibroblasts so that the composite liposomes exhibited the highest cell-penetrating activity. Furthermore, the latter formulation stimulated cell proliferation and strongly inhibited ROS production and GSH depletion under oxidative stress conditions. Together, the results support that cell-surface glycosaminoglycans can be involved in GHK-mediated liposomal delivery, which can be further greatly enhanced by association with heparin. The composite liposomes with GHK-heparin covering can be considered as an advanced GHK-based formulation for therapeutic and cosmeceutical applications.

Macro, Micro, and Nano-Inspired Bioactive Polymeric Biomaterials in Therapeutic, and Regenerative Orofacial Applications

Introducing dental polymers has accelerated biotechnological research, advancing tissue engineering, biomaterials development, and drug delivery. Polymers have been utilized effectively in dentistry to build dentures and orthodontic equipment and are key components in the composition of numerous restorative materials. Furthermore, dental polymers have the potential to be employed for medication administration and tissue regeneration. To analyze the influence of polymer-based investigations on practical medical trials, it is required to evaluate the research undertaken in this sector. The present review aims to gather evidence on polymer applications in dental, oral, and maxillofacial reconstruction.

Biocompatibility and Antimicrobial Activity of Electrospun Fibrous Materials Based on PHB and Modified with Hemin

The effect of the hemin (Hmi) on the structure and properties of nanocomposite electrospun materials based on poly-3-hydroxybutyrate (PHB) is discussed in the article. The additive significantly affected the morphology of fibers allowed to produce more elastic material and provided high antimicrobial activity. The article considers also the impact of the hemin on the biocompatibility of the nonwoven material based on PHB and the prospects for wound healing.

Regeneration of Osteochondral Defects by Combined Delivery of Synovium-Derived Mesenchymal Stem Cells, TGF-β1 and BMP-4 in Heparin-Conjugated Fibrin Hydrogel

The regeneration of cartilage and osteochondral defects remains one of the most challenging clinical problems in orthopedic surgery. Currently, tissue-engineering techniques based on the delivery of appropriate growth factors and mesenchymal stem cells (MSCs) in hydrogel scaffolds are considered as the most promising therapeutic strategy for osteochondral defects regeneration. In this study, we fabricated a heparin-conjugated fibrin (HCF) hydrogel with synovium-derived mesenchymal stem cells (SDMSCs), transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein-4 (BMP-4) to repair osteochondral defects in a rabbit model. An in vitro study showed that HCF hydrogel exhibited good biocompatibility, a slow degradation rate and sustained release of TGF-β1 and BMP-4 over 4 weeks. Macroscopic and histological evaluations revealed that implantation of HCF hydrogel with SDMSCs, TGF-β1 and BMP-4 significantly enhanced the regeneration of hyaline cartilage and the subchondral bone plate in osteochondral defects within 12 weeks compared to hydrogels with SDMSCs or growth factors alone. Thus, these data suggest that combined delivery of SDMSCs with TGF-β1 and BMP-4 in HCF hydrogel may synergistically enhance the therapeutic efficacy of osteochondral defect repair of the knee joints.

Characterizing the extracellular matrix transcriptome of cervical, endometrial, and uterine cancers

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The matrisome plays a critical role in the progression of cancer, but the matrisomes of gynecological cancers have not been well characterized.

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We built an in silico analysis pipeline to analyze publicly available bulk RNA-seq datasets of cervical, endometrial, and uterine cancers.

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Using a machine learning approach, we identified genes and gene networks that held inferential significance for cancer stage and patient survival.

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Cervical, endometrial, and uterine cancers are highly distinct from one another and should be analyzed separately.

Increasingly, the matrisome, a set of proteins that form the core of the extracellular matrix (ECM) or are closely associated with it, has been demonstrated to play a key role in tumor progression. However, in the context of gynecological cancers, the matrisome has not been well characterized. A holistic, yet targeted, exploration of the tumor microenvironment is critical for better understanding the progression of gynecological cancers, identifying key biomarkers for cancer progression, establishing the role of gene expression in patient survival, and for assisting in the development of new targeted therapies. In this work, we explored the matrisome gene expression profiles of cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), uterine corpus endometrial carcinoma (UCEC), and uterine carcinosarcoma (UCS) using publicly available RNA-seq data from The Cancer Genome Atlas (TCGA) and The Genotype-Tissue Expression (GTEx) portal. We hypothesized that the matrisomal expression patterns of CESC, UCEC, and UCS would be highly distinct with respect to genes which are differentially expressed and hold inferential significance with respect to tumor progression, patient survival, or both. Through a combination of statistical and machine learning analysis techniques, we identified sets of genes and gene networks which characterized each of the gynecological cancer cohorts. Our findings demonstrate that the matrisome is critical for characterizing gynecological cancers and transcriptomic mechanisms of cancer progression and outcome. Furthermore, while the goal of pan-cancer transcriptional analyses is often to highlight the shared attributes of these cancer types, we demonstrate that they are highly distinct diseases which require separate analysis, modeling, and treatment approaches. In future studies, matrisome genes and gene ontology terms that were identified as holding inferential significance for cancer stage and patient survival can be evaluated as potential drug targets and incorporated into in vitro models of disease.

The Comparison of Advanced Electrospun Materials Based on Poly(-3-hydroxybutyrate) with Natural and Synthetic Additives

The comparison of the effect of porphyrins of natural and synthetic origin containing the same metal atom on the structure and properties of the semi-crystalline polymer matrix is of current concern. A large number of modifying additives and biodegradable polymers for biomedical purposes, composed of poly(-3-hydroxybutyrate)-porphyrin, are of particular interest because of the combination of their unique properties. The objective of this work are electrospun fibrous material based on poly(-3-hydroxybutyrate) (PHB), hemin (Hmi), and tetraphenylporphyrin with iron (Fe(TPP)Cl). The structure of these new materials was investigated by methods such as optical and scanning electron microscopy, X-ray diffraction analysis, Electron paramagnetic resonance method, and Differential scanning calorimetry. The properties of the electrospun materials were analyzed by mechanical and biological tests, and the wetting contact angle was measured. In this work, it was found that even small concentrations of porphyrin can increase the antimicrobial properties by 12 times, improve the physical and mechanical properties by at least 3.5 times, and vary hydrophobicity by at least 5%. At the same time, additives similar in the structure had an oppositely directed effect on the supramolecular structure, the composition of the crystalline, and the amorphous phases. The article considers assumptions about the nature of such differences due to the influence of Hmi and Fe(TPP)Cl) on the macromolecular and fibrous structure of PHB.

Acellular Vascular Scaffolds Preloaded With Heparin and Hepatocyte Growth Factor for Small-Diameter Vascular Grafts Might Inhibit Intimal Hyperplasia

To develop small-diameter (<6 mm) scaffolds capable of accelerating rapid endothelialization and improving long-term patency rate, we created acellular vascular scaffolds preloaded with heparin and hepatocyte growth factor (HGF). Heparin was conjugated to suppress thrombogenic responses, and HGF was immobilized to induce endothelial cells (ECs) proliferation and migration. The scaffolds immobilized with heparin exhibited highly effective localization and sustained release of HGF for 30 days in vitro. We implanted this modified scaffold into the carotid artery of a rabbit model to investigate the efficacy in vivo. The acellular vascular scaffold with heparin only was used as control. After transplantation, the patency of this modified scaffold was 91.67% at 1, 3, 6, and 12 months, while the patency rate in the group with grafted heparin only was 83.33% at 1, 3, 6, and 12 months. This modified scaffold significantly stimulated ECs proliferation and the endothelium aligned in the direction of flow after 12 months. In addition, intimal hyperplasia was significantly reduced in the grafts coated with HGF compared with the control grafts. The small-diameter vascular grafts with an inner diameter of 2.5 mm preloaded with heparin and HGF may be a substitute for autologous blood vessels in clinic.

Effect of the Hemin Molecular Complexes on the Structure and Properties of the Composite Electrospun Materials Based on Poly(3-hydroxybutyrate)

The creation of innovative fibrous materials based on biodegradable semicrystalline polymers and modifying additives is an urgent scientific problem. In particular, the development of biomedical materials based on molecular complexes and biopolymers with controlled properties is of great interest. The paper suggests an approach to modifying the structure and properties of the composite materials based on poly(3-hydroxybutyrate) (PHB) obtained by the electrospinning method using molecular complexes of hemin. The introduction of 1-5 wt. % of hemin has a significant effect on the supramolecular structure, morphology and properties of PHB-based fibers. Changes in the supramolecular structure intensified with the increasing hemin concentration. On the one hand, a decrease in the fraction of the crystalline phase by 8-10% was observed. At the same time, there is a decrease in the density of the amorphous phase by 15-70%. Moreover, the addition of hemin leads to an improvement in the strength characteristics of the material: the elongation at break increased by 1.5 times, and in the tensile strength, it increased by 3 times. The antimicrobial activity of the hemin-containing composite materials against Escherichia coli and Staphylococcus aureus was confirmed. The obtained materials are proposed to be used in the creation of composite systems for regenerative medicine.

Strategies for inclusion of growth factors into 3D printed bone grafts

There remains a critical need to develop new technologies and materials that can meet the demands of treating large bone defects. The advancement of 3-dimensional (3D) printing technologies has allowed the creation of personalized and customized bone grafts, with specific control in both macro- and micro-architecture, and desired mechanical properties. Nevertheless, the biomaterials used for the production of these bone grafts often possess poor biological properties. The incorporation of growth factors (GFs), which are the natural orchestrators of the physiological healing process, into 3D printed bone grafts, represents a promising strategy to achieve the bioactivity required to enhance bone regeneration. In this review, the possible strategies used to incorporate GFs to 3D printed constructs are presented with a specific focus on bone regeneration. In particular, the strengths and limitations of different methods, such as physical and chemical cross-linking, which are currently used to incorporate GFs to the engineered constructs are critically reviewed. Different strategies used to present one or more GFs to achieve simultaneous angiogenesis and vasculogenesis for enhanced bone regeneration are also covered in this review. In addition, the possibility of combining several manufacturing approaches to fabricate hybrid constructs, which better mimic the complexity of biological niches, is presented. Finally, the clinical relevance of these approaches and the future steps that should be taken are discussed.

ECM-mimicking nanofibrous scaffold enriched with dual growth factor carrying nanoparticles for diabetic wound healing

Polymeric nanofibrous scaffolds provide fine-tuned structures with inter-connecting pores resembling the natural extracellular matrix (ECM) in tissues, and show good potential in assisting the creation of artificial functional tissue. Additional application of growth factors helps to regulate the cellular behaviors and tissue assembly in the scaffolds, which eases the healing process. In this study, we synthesized an electrospun polymer scaffold system enriched with nanoparticles containing growth factors for accelerated healing of diabetic wounds. BSA nanoparticles were synthesized by cross-linking with PEG aldehyde. To free the amino group of BSA, heparin was conjugated by EDC/NHS chemistry. The angiogenic growth factors bFGF and VEGF were bound to heparin by electrostatic interaction. These nanoparticles were adsorbed on to electrospun collagen/PLGA/chitosan nanofibers. The synthesized nanofiber system was evaluated in vitro for its cell viability and proliferation. In vivo experiments conducted in a streptozotocin-induced diabetic mice model showed accelerated wound healing. The excellent healing efficiency of this ECM-mimicking nanofiber scaffold makes it a great candidate for therapeutic application in diabetic wounds.

Immobilization of Growth Factors for Cell Therapy Manufacturing

Cell therapy products exhibit great therapeutic potential but come with a deterring price tag partly caused by their costly manufacturing processes. The development of strategies that lead to cost-effective cell production is key to expand the reach of cell therapies. Growth factors are critical culture media components required for the maintenance and differentiation of cells in culture and are widely employed in cell therapy manufacturing. However, they are expensive, and their common use in soluble form is often associated with decreased stability and bioactivity. Immobilization has emerged as a possible strategy to optimize growth factor use in cell culture. To date, several immobilization techniques have been reported for attaching growth factors onto a variety of biomaterials, but these have been focused on tissue engineering. This review briefly summarizes the current landscape of cell therapy manufacturing, before describing the types of chemistry that can be used to immobilize growth factors for cell culture. Emphasis is placed to identify strategies that could reduce growth factor usage and enhance bioactivity. Finally, we describe a case study for stem cell factor.

Evaluation of top-down mass spectrometry and ion-mobility spectroscopy as a means of mapping protein-binding motifs within heparin chains

Identifying structural elements within heparin (as well as other glycosaminoglycan) chains that enable their interaction with a specific client protein remains a challenging task due to the high degree of both intra- and inter-chain heterogeneity exhibited by this polysaccharide. The new experimental approach explored in this work is based on the assumption that the heparin chain segments bound to the protein surface will be less prone to collision-induced dissociation (CID) in the gas phase compared to the chain regions that are not involved in binding. Facile removal of the unbound chain segments from the protein/heparin complex should allow the length and the number of sulfate groups within the protein-binding segment of the heparin chain to be determined by measuring the mass of the truncated heparin chain that remains bound to the protein. Conformational integrity of the heparin-binding interface on the protein surface in the course of CID is ensured by monitoring the evolution of collisional cross-section (CCS) of the protein/heparin complexes as a function of collisional energy. A dramatic increase in CCS signals the occurrence of large-scale conformational changes within the protein and identifies the energy threshold, beyond which relevant information on the protein-binding segments of heparin chains is unlikely to be obtained. Testing this approach using a 1 : 1 complex formed by a recombinant form of an acidic fibroblast growth factor (FGF-1) and a synthetic pentasaccharide GlcNS,6S-GlcA-GlcNS,3S,6S-IdoA2S-GlcNS,6S-Me as a model system indicated that a tri-saccharide fragment is the minimal-length FGF-binding segment. Extension of this approach to a decameric heparin chain (dp10) allowed meaningful binding data to be obtained for a 1 : 1 protein/dp10 complex, while the ions representing the higher stoichiometry complex (2 : 1) underwent dissociation via asymmetric charge partitioning without generating truncated heparin chains that remain bound to the protein.

An injectable heparin-conjugated hyaluronan scaffold for local delivery of transforming growth factor β1 promotes successful chondrogenesis

Cartilage lacks basic repair mechanisms and thus surgical interventions are necessary to treat lesions. Minimally-invasive arthroscopic procedures require the development of injectable biomaterials to support chondrogenesis of implanted cells. However, most cartilage tissue engineering approaches rely on pre-culture of scaffolds in media containing growth factors (GFs) such as transforming growth factor (TGF)-β1, which are crucial for cartilage formation and homeostasis. GFs media-supplementation is incompatible with injectable approaches and has led to a knowledge gap about optimal dose of GFs and release profiles needed to achieve chondrogenesis. This study aims to determine the optimal loading and release kinetics of TGF-β1 bound to an engineered GAG hydrogel to promote optimal cartilaginous matrix production in absence of TGF-β1 media-supplementation. We show that heparin, a GAG known to bind a wide range of GFs, covalently conjugated to a hyaluronan hydrogel, leads to a sustained release of TGF-β1. Using this heparin-conjugated hyaluronan hydrogel, 0.25 to 50 ng TGF-β1 per scaffold was loaded and cell viability, proliferation and cartilaginous matrix deposition of the encapsulated chondroprogenitor cells were measured. Excellent chondrogenesis was found when 5 ng TGF-β1 per scaffold and higher were used. We also demonstrate the necessity of a sustained release of TGF-β1, as no matrix deposition is observed upon a burst release. In conclusion, our biomaterial loaded with an optimal initial dose of 5 ng/scaffold TGF-β1 is a promising injectable material for cartilage repair, with potentially increased safety due to the low, locally administered GF dose. STATEMENT OF SIGNIFICANCE: Cartilage cell-based products are dependent on exogenous growth factor supplementation in order for proper tissue maturation. However, for a one-step repair of defects without need for expensive tissue maturation, an injectable, growth factor loaded formulation is required. Here we show development of an injectable hyaluronan hydrogel, which achieves a sustained release of TGF-β1 due to covalent conjugation of heparin. These grafts matured into cartilaginous tissue in the absence of growth factor supplementation. Additionally, this system allowed us to screen TGF-β1 concentrations to determine the mimimum amount of growth factor required for chondrogenesis. This study represents a critical step towards development of a minimally-invasive, arthroscopic treatment for cartilage lesions.

Fully Synthetic Heparan Sulfate-Based Neural Tissue Construct That Maintains the Undifferentiated State of Neural Stem Cells

Heparin and heparan sulfate (HS) are attractive components for constructing biomaterials due to their ability to recruit and regulate the activity of growth factors. The structural and functional heterogeneity of naturally derived heparin and HS is, however, an impediment for the preparation of biomaterials for regenerative medicine. To address this problem, we have prepared hydrogels modified by well-defined synthetic HS-derived disaccharides. Human induced pluripotent cell-derived neural stem cells (HIP-NSCs) encapsulated in a polyethylene glycol-based hydrogel modified by a pendent HS disaccharide that is a known ligand for fibroblast growth factor-2 (FGF-2) exhibited a significant increase in proliferation and self-renewal. This observation is important because evidence is emerging that undifferentiated stems cells can yield significant therapeutic benefits via their paracrine signaling mechanisms. Our data indicate that the HS disaccharide protects FGF-2, which has a very short biological half-live, from degradation. It is anticipated that, by careful selection of a synthetic HS oligosaccharide, it will be possible to control retention and release of specific growth factor, which in turn will provide control over cell fate.

Multiple cargo deliveries of growth factors and antimicrobial peptide using biodegradable nanopolymer as a potential wound healing system

Background

Treatment of wounds with the help of nanoparticles (NPs) is more effective and superior in comparison to traditional wound healing methods as it protects and sustains active drug release at the wound site thus enhancing the safety of the drug and reducing the possibility of side effects. The advantages of this method are the possibility of allowing a reduction in administered dose, limiting toxicity levels to the minimum, and increasing safety of topical delivery of the drug.

Materials and methods

We report the synthesis of a novel poly (lactic-co-glycolic acid) (PLGA) NP-based multicargo delivery system for growth factors and antimicrobial peptide. Growth factors vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were entrapped in PLGA NPs by solvent diffusion method and an antimicrobial peptide (K4) was conjugated to the NP by carbodiimide chemistry. The developed multiple cargo delivery systems with growth factors (VEGF and bFGF) and an antimicrobial peptide (K4) were investigated and optimized for potential wound healing.

Results

The system showed a sustained release of growth factors and was evaluated for cytotoxicity by MTT and live/dead assay, which revealed that the bioactivity of the growth factor-entrapped NPs was higher than that of free growth factors, and it also induced enhanced cell proliferation in vitro.

Conclusion

The development of a system for the codelivery of growth factors (VEGF and bFGF) and an antimicrobial peptide (K4) was investigated for potential wound healing application. The entrapment of growth factors with very high efficiency is an advantage in this method along with its sustained release from the nanoparticulate system, which will enhance the angiogenesis. Our system also displayed broad-spectrum antimicrobial activity against both gram-positive and gram-negative bacteria.

Bioinspired Heparin Nanosponge Prepared by Photo-crosslinking for Controlled Release of Growth Factors

Growth factors have great therapeutic potential for various disease therapy and tissue engineering applications. However, their clinical efficacy is hampered by low bioavailability, rapid degradation in vivo and non-specific biodistribution. Nanoparticle based delivery systems are being evaluated to overcome these limitations. Herein, we have developed a thermosensitive heparin nanosponge (Hep-NS) by a one step photopolymerization reaction between diacrylated pluronic and thiolated heparin molecules. The amount of heparin in Hep-NS was precisely controlled by varying the heparin amount in the reaction feed. Hep-NS with varying amounts of heparin showed similar size and shape properties, though surface charge decreased with an increase in the amount of heparin conjugation. The anticoagulant activity of the Hep-NS decreased by 65% compared to free heparin, however the Hep-NS retained their growth factor binding ability. Four different growth factors, bFGF, VEGF, BMP-2, and HGF were successfully encapsulated into Hep-NS. In vitro studies showed sustained release of all the growth factors for almost 60 days and the rate of release was directly dependent on the amount of heparin in Hep-NS. The released growth factors retained their bioactivity as assessed by a cell proliferation assay. This heparin nanosponge is therefore a promising nanocarrier for the loading and controlled release of growth factors.

Stimulation of vascularization of a subcutaneous scaffold applicable for pancreatic islet-transplantation enhances immediate post-transplant islet graft function but not long-term normoglycemia

The liver as transplantation site for pancreatic islets is associated with significant loss of islets, which can be prevented by grafting in a prevascularized, subcutaneous scaffold. Supporting vascularization of a scaffold to limit the period of ischemia is challenging and was developed here by applying liposomes for controlled release of angiogenic factors. The angiogenic capacity of platelet-derived growth factor, vascular endothelial growth factor, acidic fibroblast growth factor (aFGF), and basic FGF were compared in a tube formation assay. Furthermore, the release kinetics of different liposome compositions were tested. aFGF and L-α-phosphatidylcholine/cholesterol liposomes were selected to support vascularization. Two dosages of aFGF-liposomes (0.5 and 1.0 μg aFGF per injection) were administered weekly for a month after which islets were transplanted. We observed enhanced efficacy in the immediate post-transplant period compared to the untreated scaffolds. However, on the long-term, glucose levels of the aFGF treated animals started to increase to diabetic levels. These results suggest that injections with aFGF liposomes do improve vascularization and the immediate restoration of blood glucose levels but does not facilitate the long-term survival of islets. Our data emphasize the need for long-term studies to evaluate potential beneficial and adverse effects of vascularization protocols of scaffolds. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2533-2542, 2017.

Multifunctional Nanocomposite Films for Synergistic Delivery of bFGF and BMP-2

The development of novel materials capable of delivering multiple growth factors is urgent and essential for rapid and effective tissue regeneration. In this study, a kind of composite film composed of poly-l-lysine (PLL), heparin (Hep), and Au nanoparitcles (Au nps) has been fabricated to deliver the basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) simultaneously. The films have been found to show enhanced mechanical property due to the incorporation of Au nps. They have also shown good anticoagulation activity with long activated partial thromboplastin time because of the contribution of Hep molecules. Moreover, the osteogenesis studies reveal that the loaded bFGF and BMP-2 in the composite films have a synergistic differentiation effect on mesenchymal stem cells, as indicated by alkaline phosphatase (ALP) activity assay and collagen type I (Col-I) gene expression. In contrast to the (PLL/Hep)6/BMP-2/(PLL/Au nps)6/(PLL/Hep)6 and (PLL/Hep)6/(PLL/Au nps)6/(PLL/Hep)6/bFGF films, the (PLL/Hep)6/BMP-2/(PLL/Au nps)6/(PLL/Hep)6/bFGF films have shown higher ALP activity and higher Col-I expression level. Therefore, the developed multifunctional films could be potentially used as osteoinductive coatings of biomaterials. Particularly, this simple and convenient strategy provides an effective approach for the immobilization of multiple growth factors, which may be extended to other bioactive systems for the development of novel multifunctional bioactive surfaces.

The use of heparin chemistry to improve dental osteogenesis associated with implants

In this study, we designed a hybrid Ti by heparin modifying the Ti surface followed by Growth/differentiation factor-5 (GDF-5) loading. After that, products were characterized by physicochemical analysis. Quantitative analysis of functionalized groups was also confirmed. The release behavior of GDF-5 grafted samples was confirmed for up to 21days. The surface modification process was found to be successful and to effectively immobilize GDF-5 and provide for its sustained release behavior. As an in vitro test, GDF-5 loaded Ti showed significantly enhanced osteogenic differentiation with increased calcium deposition under nontoxic conditions against periodontal ligament stem cells (PDLSc). Furthermore, an in vivo result showed that GDF-5 loaded Ti had a significant influence on new bone formation in a rabbit model. These results clearly confirmed that our strategy may suggest a useful paradigm by inducing osseo-integration as a means to remodeling and healing of bone defects for restorative procedures in dentistry.

Poly(3,4-ethylenedioxythiophene):GlycosAminoGlycan Aqueous Dispersions: Toward Electrically Conductive Bioactive Materials for Neural Interfaces

There is an actual need of advanced materials for the emerging field of bioelectronics. One commonly used material is the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (

PEDOT

PSS) due to its general use in organic electronics. However, depending on the application in bioelectronics,

PEDOT

PSS is not fully biocompatible due to the high acidity of the residual sulfonate protons of PSS. In this paper, the synthesis and biocompatibility properties of new poly(3,4-ethylenedioxythiophene):GlycosAminoGlycan (

PEDOT

GAG) aqueous dispersions and its resulting films are shown. Thus, negatively charged GAGs as an alternative to PSS are presented. Three different commercially available GAGs, hyaluronic acid, heparin, and chondroitin sulfate are used. Indeed,

PEDOT

GAGs dispersions are prepared through an oxidative chemical polymerization in water. Biocompatibility assays of the

PEDOT

GAGs coatings are performed using SH-SY5Y and CCF-STTG1 cell lines and with ATP and Ca(2+) . Results show full biocompatibility and a pronounced anti-inflammatory effect. This last characteristic becomes crucial if implanted in the body. These materials can be used for in vivo applications, as transistor or electrode for electrical recording and for all the possible situations when there is contact between electronic circuits and living tissues.

Tissue engineering advances in spine surgery

Autograft, while currently the gold standard for bone grafting, has several significant disadvantages including limited supply, donor site pain, hematoma formation, nerve and vascular injury, and fracture. Bone allografts have their own disadvantages including reduced osteoinductive capability, lack of osteoprogenitor cells, immunogenicity and risk of disease transmission. Thus demand exists for tissue-engineered constructs that can produce viable bone while avoiding the complications associated with human tissue grafts. This review will focus on recent advancements in tissue-engineered bone graft substitutes utilizing nanoscale technology in spine surgery applications. An evaluation will be performed of bone graft substitutes, biomimetic 3D scaffolds, bone morphogenetic protein, mesenchymal stem cells and intervertebral disc regeneration strategies.

Control of growth factor binding and release in bisphosphonate functionalized hydrogels guides rapid differentiation of precursor cells in vitro

Sequestration and active release of BMP-2 in HA-BP hydrogels to precursor cells aid rapid differentiation to osteoblasts.

Spatial regulation of controlled bioactive factor delivery for bone tissue engineering

Limitations of current treatment options for critical size bone defects create a significant clinical need for tissue engineered bone strategies. This review describes how control over the spatiotemporal delivery of growth factors, nucleic acids, and drugs and small molecules may aid in recapitulating signals present in bone development and healing, regenerating interfaces of bone with other connective tissues, and enhancing vascularization of tissue engineered bone. State-of-the-art technologies used to create spatially controlled patterns of bioactive factors on the surfaces of materials, to build up 3D materials with patterns of signal presentation within their bulk, and to pattern bioactive factor delivery after scaffold fabrication are presented, highlighting their applications in bone tissue engineering. As these techniques improve in areas such as spatial resolution and speed of patterning, they will continue to grow in value as model systems for understanding cell responses to spatially regulated bioactive factor signal presentation in vitro, and as strategies to investigate the capacity of the defined spatial arrangement of these signals to drive bone regeneration in vivo.

Extracellular matrix-inspired BMP-2-delivering biodegradable fibrous particles for bone tissue engineering

A heparin conjugated fibrous particle resembling the structure of an extracellular matrix was developed. The BMP-2 loaded particles promoted osteogenic differentiation and healing of a bone defect, in vitro and in vivo.

An overview of the suitability of hydrogel-forming polymers for extrusion-based 3D-printing

In this review hydrogel-forming polymers that are suitable for extrusion-based 3D printing are evaluated.

Recent advances in nerve tissue engineering

Nerve injury secondary to trauma, neurological disease or tumor excision presents a challenge for surgical reconstruction. Current practice for nerve repair involves autologous nerve transplantation, which is associated with significant donor-site morbidity and other complications. Previously artificial nerve conduits made from polycaprolactone, polyglycolic acid and collagen were approved by the FDA (USA) for nerve repair. More recently, there have been significant advances in nerve conduit design that better address the requirements of nerve regrowth. Innovations in materials science, nanotechnology, and biology open the way for the synthesis of new generation nerve repair conduits that address issues currently faced in nerve repair and regeneration. This review discusses recent innovations in this area, including the use of nanotechnology to improve the design of nerve conduits and to enhance nerve regeneration.

Signaling pathways regulating dose-dependent dual effects of TNF-α on primary cultured Schwann cells

After peripheral nerve injury, Schwann cells are rapidly activated to participate in the regenerative process and modulate local immune reactions. Tumor necrosis factor-α (TNF-α), one of the major initiators of the inflammatory cascade, has been known to exert pleiotropic functions during peripheral nerve injury and regeneration. In this study, we aimed to investigate the in vitro effects of TNF-α on peripheral neural cells. First, gene-microarray analysis was applied to the RNA samples extracted from injured peripheral nerves, providing the information of gene interactions post nerve injury. Then, after primary cultured Schwann cells were treated with increasing dosages (0-40 ng/ml) of TNF-α, cell proliferation and migration were examined by EdU incorporation and a transwell-based assay, and cell apoptosis was observed and quantified by electron microscopy and Annexin V-FITC assay, respectively. The results showed that lower dosages of TNF-α increased cell proliferation and migration, whereas higher dosages of TNF-α decreased cell proliferation and migration and enhanced cell apoptosis. The tests using a chemical inhibitor of TNF-α further confirmed the above effects of TNF-α. To understand how TNF-α produced the dose-dependent dual effects on primary cultured Schwann cells, we performed co-immunoprecipitation, Western blot analysis, and immunocytochemistry to decipher the complex network of biochemical pathways involving many signaling molecules, i.e., TNF receptor-associated death domain, Fas-associated death domain, receptor interacting protein, JNK, NF-κB p65, and caspases, thus assuming the mechanisms by which TNF-α activated the death and survival pathways and achieved a balance between the two opposite actions in primary cultured Schwann cells.

Systematic engineering of 3D pluripotent stem cell niches to guide blood development

Pluripotent stem cells (PSC) provide insight into development and may underpin new cell therapies, yet controlling PSC differentiation to generate functional cells remains a significant challenge. In this study we explored the concept that mimicking the local in vivo microenvironment during mesoderm specification could promote the emergence of hematopoietic progenitor cells from embryonic stem cells (ESCs). First, we assessed the expression of early phenotypic markers of mesoderm differentiation (E-cadherin, brachyury (T-GFP), PDGFRα, and Flk1: +/-ETPF) to reveal that E-T+P+F+ cells have the highest capacity for hematopoiesis. Second, we determined how initial aggregate size influences the emergence of mesodermal phenotypes (E-T+P+F+, E-T-P+/-F+, and E-T-P+F-) and discovered that colony forming cell (CFC) output was maximal with ~100 cells per PSC aggregate. Finally, we introduced these 100-cell PSC aggregates into a low oxygen environment (5%; to upregulate endogenous VEGF secretion) and delivered two potent blood-inductive molecules, BMP4 and TPO (bone morphogenetic protein-4 and thrombopoietin), locally from microparticles to obtain a more robust differentiation response than soluble delivery methods alone. Approximately 1.7-fold more CFCs were generated with localized delivery in comparison to exogenous delivery, while combined growth factor use was reduced ~14.2-fold. By systematically engineering the complex and dynamic environmental signals associated with the in vivo blood developmental niche we demonstrate a significant role for inductive endogenous signaling and introduce a tunable platform for enhancing PSC differentiation efficiency to specific lineages.

Glycosaminoglycan and chemokine/growth factor interactions

Heparin and glycosaminoglycans (GAGs) related structurally to heparin, notably heparan sulphate, bind to most, if not all, chemokines and many growth factors. The chemokine and growth factor interactions with GAGs localise the peptide mediators to specific sites in tissues and influence their stability and function. This chapter discusses the nature of these interactions and the effect on the function of a number of chemokines (PF-4, interleukin-8, RANTES and SDF-1) and growth factors (FGF, HGF, VEGF) in normal physiology and the disease setting. Novel therapeutic interventions that target chemokine and growth factor interactions with GAGs are also discussed.

Hydrogels in acellular and cellular strategies for intervertebral disc regeneration

Low back pain is an extremely common illness syndrome that causes patient suffering and disability and requires urgent solutions to improve the quality of life of these patients. Treatment options aimed to regenerate the intervertebral disc (IVD) are still under development. The cellular complexity of IVD, and consequently its fine regulatory system, makes it a challenge to the scientific community. Biomaterials-based therapies are the most interesting solutions to date, whereby tissue engineering and regenerative medicine (TE&RM) strategies are included. By using such strategies, i.e., combining biomaterials, cells, and biomolecules, the ultimate goal of reaching a complete integration between native and neo-tissue can be achieved. Hydrogels are promising materials for restoring IVD, mainly nucleus pulposus (NP). This study presents an overview of the use of hydrogels in acellular and cellular strategies for intervertebral disc regeneration. To better understand IVD and its functioning, this study will focus on several aspects: anatomy, pathophysiology, cellular and biomolecular performance, intrinsic healing processes, and current therapies. In addition, the application of hydrogels as NP substitutes will be addressed due to their similarities to NP mechanical properties and extracellular matrix. These hydrogels can be used in cellular strategies when combined with cells from different sources, or in acellular strategies by performing the functionalization of the hydrogels with biomolecules. In addition, a brief summary of therapies based on simple injection for primary biological repair will be examined. Finally, special emphasis will focus on reviewing original studies reporting on the use of autologous cells and biomolecules such as platelet-rich plasma and their potential clinical applications.

The effect of vascular endothelial growth factor (VEGF) presentation within fibrin matrices on endothelial cell branching

Vascular endothelial growth factor (VEGF) has been extensively investigated to promote vascularization at damaged or diseased sites and in tissue implants. Here we are interested in determining if the manner in which VEGF is presented from a scaffold to endothelial cells influences the architecture of the blood vessels formed. We bound VEGF to nanoparticles and placed these nanoparticles inside fibrin hydrogels, which contained human umbilical vein endothelial cells (HUVECs) bound to cytodex beads. Fibroblast cells are plated on top of the fibrin gel to further mimic a physiologic environment. In addition, we used a chorioallantoic membrane (CAM) assay to determine the role of VEGF presentation on angiogenesis in vivo. We tested VEGF bound in high density and low density to study differences between growth factor presentation in heterogeneous nanodomains and homogenous distribution. VEGF covalently bound to nanoparticles at high density led to an increase in HUVEC tube branching, thickness, and total vessel network length compared to soluble VEGF. While VEGF bound electrostatically exhibited no significant difference with covalently bound VEGF in the tube formation assay, this method failed to promote host vessel infiltration into the fibrin implant on the CAM. Together our data suggest that the mode of VEGF presentation to endothelial cells influences the vessel architecture and vascularization of implants in vivo.

Affinity-based growth factor delivery using biodegradable, photocrosslinked heparin-alginate hydrogels

Photocrosslinkable biomaterials are promising for tissue engineering applications due to their capacity to be injected and form hydrogels in situ in a minimally invasive manner. Our group recently reported on the development of photocrosslinked alginate hydrogels with controlled biodegradation rates, mechanical properties, and cell adhesive properties. In this study, we present an affinity-based growth factor delivery system by incorporating heparin into photocrosslinkable alginate hydrogels (HP-ALG), which allows for controlled, prolonged release of therapeutic proteins. Heparin modification had minimal effect on the biodegradation profiles, swelling ratios, and elastic moduli of the hydrogels in media. The release profiles of growth factors from this affinity-based platform were sustained for 3weeks with no initial burst release, and the released growth factors retained their biological activity. Implantation of bone morphogenetic protein-2 (BMP-2)-loaded photocrosslinked alginate hydrogels induced moderate bone formation around the implant periphery. Importantly, BMP-2-loaded photocrosslinked HP-ALG hydrogels induced significantly more osteogenesis than BMP-2-loaded photocrosslinked unmodified alginate hydrogels, with 1.9-fold greater peripheral bone formation and 1.3-fold greater calcium content in the BMP-2-loaded photocrosslinked HP-ALG hydrogels compared to the BMP-2-loaded photocrosslinked unmodified alginate hydrogels after 8weeks implantation. This sustained and controllable growth factor delivery system, with independently controllable physical and cell adhesive properties, may provide a powerful modality for a variety of therapeutic applications.