Peptide-modified alginate surfaces as a growth permissive substrate for neurite outgrowth

Alginate as a Sustainable and Biodegradable Material for Medical and Environmental Applications-The Case Studies

Alginates are salts of alginic acid derived mainly from sea algae of the genus brown algae. They are also synthesized by some bacteria. They belong to negatively charged polysaccharides exhibiting some rheological properties. High plasticity and the ability to modify the structure are the reasons for their application in numerous industries. Moreover, when in contact with the living tissue, they do not trigger an immune response, and for this reason they are the most often tested materials for medical applications. The paper discusses the latest applications, including 3D bioprinting, drug delivery systems, and sorptive properties. Recognizing alginates as biomaterials, it emphasizes the necessity for precise processing and modification to industrialize them for specific uses. This review aims to provide a thorough understanding of the advancements in alginate research, underscoring their potential for innovative applications.

Non-integrin laminin receptor (LamR) plays a role in axonal outgrowth from chicken DRG via modulating the Akt and Erk signaling

37/67 kDa laminin receptor (LamR)/ribosomal protein SA exhibits dual function as both a ribosomal protein and cell surface receptor for laminin. LamR influences critical cellular processes such as invasion, adhesion, and migration when acting as a receptor. Despite the acknowledged importance of LamR/67LR in various cellular processes, its contribution to the peripheral nervous system development is obscure. Thus, this study investigated the biological activity of LamR in peripheral axonal outgrowth in the presence of laminin-1 or Ile-Lys-Val-Ala-Val (IKVAV) peptide, whose important role in dorsal root ganglia (DRG) axonal outgrowth we recently showed. Unexpectedly, we did not observe LamR on the surface of DRG cells or in a conditioned medium, suggesting its intracellular action in the negative regulation of DRG axonal outgrowth. Using C-terminus LamR-targeting IgG, we demonstrated the role of LamR in that process, which is independent of the presence of Schwann cell precursors (SCPs) and is mediated by extracellular signal-regulated kinase (Erk) and Protein kinase B (Akt1/2/3) signaling pathways. Additionally, we show that the action of LamR towards laminin-1-dependent axonal outgrowth is unmasked only when the activity of integrin β1 is perturbed. We believe that modulation of LamR activity provides the basis for its use for inhibiting axon growth as a potential therapeutic agent for regulating abnormal or excessive neurite growth during neurodevelopmental diseases or pathological nerve regeneration.

A Library of Elastin-like Proteins with Tunable Matrix Ligands for In Vitro 3D Neural Cell Culture

Hydrogels with encapsulated cells have widespread biomedical applications, both as tissue-mimetic 3D cultures in vitro and as tissue-engineered therapies in vivo. Within these hydrogels, the presentation of cell-instructive extracellular matrix (ECM)-derived ligands and matrix stiffness are critical factors known to influence numerous cell behaviors. While individual ECM biopolymers can be blended together to alter the presentation of cell-instructive ligands, this typically results in hydrogels with a range of mechanical properties. Synthetic systems that allow for the facile incorporation and modulation of multiple ligands without modification of matrix mechanics are highly desirable. In the present work, we leverage protein engineering to design a family of xeno-free hydrogels (i.e., devoid of animal-derived components) consisting of recombinant hyaluronan and recombinant elastin-like proteins (ELPs), cross-linked together with dynamic covalent bonds. The ELP components incorporate cell-instructive peptide ligands derived from ECM proteins, including fibronectin (RGD), laminin (IKVAV and YIGSR), collagen (DGEA), and tenascin-C (PLAEIDGIELTY and VFDNFVL). By carefully designing the protein primary sequence, we form 3D hydrogels with defined and tunable concentrations of cell-instructive ligands that have similar matrix mechanics. Utilizing this system, we demonstrate that neurite outgrowth from encapsulated embryonic dorsal root ganglion (DRG) cultures is significantly modified by cell-instructive ligand content. Thus, this library of protein-engineered hydrogels is a cell-compatible system to systematically study cell responses to matrix-derived ligands.

Collagen-alginate 3D microscaffolds for studying cellular migration

Metastasis is one of the major causes for cancer mortality. Its early steps comprise of invasion of basement membrane and migration. Thus, it is hypothesized that a platform, that allows quantification and grading of migration capability of cells can potentially be used for predicting metastatic potential. Two-dimensional (2D) models have been rendered inadequate for modelling in-vivo microenvironment due to various reasons. To attenuate homogeneity observed in 2D, three-dimensional (3D) platforms supplemented with bioinspired components have been designed. Unfortunately, till date there are no simple models to capture the migration of cells in 3D along with quantification of the process. In this study, we report an alginate-collagen based 3D model system, which can predict the migratory property of the cells within 72 h. The micron size of the scaffold enabled faster readout and the optimum pore-size provided conducive cellular growth environment. The platform's ability to allow observation of cellular migration was validated by encapsulating cells with transiently upregulated matrix metalloprotease 9 (MMP9), which has been reported to play a significant role in migration of cells during metastasis. The readout for migration was clustering of cells in the microscaffolds detected in a short span of 48 h. The observed clustering in MMP9 upregulated cells was validated by observing changes in the epithelial-mesenchymal transition (EMT) markers. Thus, this simple 3D platform can be used to study migration and predict the metastatic potential of cells.

State of Innovation in Alginate-Based Materials

This review article presents past and current alginate-based materials in each application, showing the widest range of alginate's usage and development in the past and in recent years. The first segment emphasizes the unique characteristics of alginates and their origin. The second segment sets alginates according to their application based on their features and limitations. Alginate is a polysaccharide and generally occurs as water-soluble sodium alginate. It constitutes hydrophilic and anionic polysaccharides originally extracted from natural brown algae and bacteria. Due to its promising properties, such as gelling, moisture retention, and film-forming, it can be used in environmental protection, cosmetics, medicine, tissue engineering, and the food industry. The comparison of publications with alginate-based products in the field of environmental protection, medicine, food, and cosmetics in scientific articles showed that the greatest number was assigned to the environmental field (30,767) and medicine (24,279), whereas fewer publications were available in cosmetic (5692) and food industries (24,334). Data are provided from the Google Scholar database (including abstract, title, and keywords), accessed in May 2023. In this review, various materials based on alginate are described, showing detailed information on modified composites and their possible usage. Alginate's application in water remediation and its significant value are highlighted. In this study, existing knowledge is compared, and this paper concludes with its future prospects.

Alginate hydrogels: A potential tissue engineering intervention for intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a major cause of low back pain and disability, affecting millions of people worldwide. Current treatments for IVD degeneration are limited to invasive surgery or pain management. Recently, there has been increasing interest in the use of biomaterials, such as alginate hydrogels, for the treatment of IVD degeneration. Alginate hydrogels are an example of such a biomaterial that is biocompatible and can be tailored to mimic the native extracellular matrix of the IVD. Derived from alginate, a naturally derived polysaccharide from brown seaweed that can be transformed into a gelatinous solution, alginate hydrogels are emerging in the field of tissue engineering. They can be used to deliver therapeutic agents, such as growth factors or cells, to the site of injury, providing a localized and sustained release that may enhance treatment outcomes. This paper provides an overview on the use of alginate hydrogels for the treatment of IVD degeneration. We discuss the properties of alginate hydrogels and their potential applications for IVD regeneration, including the mechanism against IVD degeneration. We also highlight the research outcomes to date along with the challenges and limitations of using alginate hydrogels for IVD regeneration, including their mechanical properties, biocompatibility, and surgical compatibility. Overall, this review paper aims to provide a comprehensive overview of the current research on alginate hydrogels for IVD degeneration and to identify future directions for research in this area.

The Impact of the Cellular Environment and Aging on Modeling Alzheimer's Disease in 3D Cell Culture Models

Creating a cellular model of Alzheimer's disease (AD) that accurately recapitulates disease pathology has been a longstanding challenge. Recent studies showed that human AD neural cells, integrated into three-dimensional (3D) hydrogel matrix, display key features of AD neuropathology. Like in the human brain, the extracellular matrix (ECM) plays a critical role in determining the rate of neuropathogenesis in hydrogel-based 3D cellular models. Aging, the greatest risk factor for AD, significantly alters brain ECM properties. Therefore, it is important to understand how age-associated changes in ECM affect accumulation of pathogenic molecules, neuroinflammation, and neurodegeneration in AD patients and in vitro models. In this review, mechanistic hypotheses is presented to address the impact of the ECM properties and their changes with aging on AD and AD-related dementias. Altered ECM characteristics in aged brains, including matrix stiffness, pore size, and composition, will contribute to disease pathogenesis by modulating the accumulation, propagation, and spreading of pathogenic molecules of AD. Emerging hydrogel-based disease models with differing ECM properties provide an exciting opportunity to study the impact of brain ECM aging on AD pathogenesis, providing novel mechanistic insights. Understanding the role of ECM aging in AD pathogenesis should also improve modeling AD in 3D hydrogel systems.

Comparative Study of Physicochemical Properties of Alginate Composite Hydrogels Prepared by the Physical Blending and Electrostatic Assembly Methods

Alginate hydrogel commonly suffers from defects, such as weak mechanical properties, the shortage of long-term stability in physiological medium and the lack of mammalian cell adhesivity due to its strong hydrophilicity in biomedical application. For this reason, the homogeneous alginate hydrogels (Alg Gel) were successfully prepared by the D-glucono-δ-lactone/hydroxyapatite (HAP/GDL) cross-linking system, and then, the physical blending and alternating electrostatic assembly technology were proposed to fabricate alginate composite hydrogels (Alg-GT, Alg-CS-GT and ALG/GT-CS). The feasibility of the design methods was verified through the comparative analysis of their physicochemical properties and biological activity. In particular, the effects of physical blending and alternating electrostatic assembly technology on the pore structure, mechanical properties, swelling, degradation, cell adhesion and proliferation of composite hydrogels were also investigated. Experimental results showed that the formation of polyelectrolyte complexes by electrostatic assembly between biological macromolecules and the covalent cross-linking of EDC/NHS to GT improved the vulnerability of ion cross-linking, enhanced the mechanical properties and swelling stability of the composite hydrogels, and regulated their pore structure and in vitro biodegradability properties. Furthermore, MC3T3-E1 cells could exhibit good cell adhesion, cell viability and cell proliferation on the alginate composite hydrogels. Among them, Alg-CS-GT showed the best cell proliferation ability and differentiation effect due to its good cell adhesion. In view of the excellent physicochemical properties and biological activity of Alg-CS-GT, it exhibited great potential in biomedical application for tissue engineering.

Application of biomimetic surfaces and 3D culture technology to study the role of extracellular matrix interactions in neurite outgrowth and inhibition

The microenvironment that cells experience during in vitro culture can often be far removed from the native environment they are exposed to in vivo. To recreate the physiological environment that developing neurites experience in vivo, we combine a well-established model of human neurite development with, functionalisation of both 2D and 3D growth substrates with specific extracellular matrix (ECM) derived motifs displayed on engineered scaffold proteins. Functionalisation of growth substrates provides biochemical signals more reminiscent of the in vivo environment and the combination of this technology with 3D cell culture techniques, further recapitulates the native cellular environment by providing a more physiologically relevant geometry for neurites to develop. This biomaterials approach was used to study interactions between the ECM and developing neurites, along with the identification of specific motifs able to enhance neuritogenesis within this model. Furthermore, this technology was employed to study the process of neurite inhibition that has a detrimental effect on neuronal connectivity following injury to the central nervous system (CNS). Growth substrates were functionalised with inhibitory peptides released from damaged myelin within the injured spinal cord (Nogo & OMgp). This model was then utilised to study the underlying molecular mechanisms that govern neurite inhibition in addition to potential mechanisms of recovery.

Reinforced Hyaluronic Acid-Based Matrices Promote 3D Neuronal Network Formation

3D neuronal cultures attempt to better replicate the in vivo environment to study neurological/neurodegenerative diseases compared to 2D models. A challenge to establish 3D neuron culture models is the low elastic modulus (30-500 Pa) of the native brain. Here, an ultra-soft matrix based on thiolated hyaluronic acid (HA-SH) reinforced with a microfiber frame is formulated and used. Hyaluronic acid represents an essential component of the brain extracellular matrix (ECM). Box-shaped frames with a microfiber spacing of 200 µm composed of 10-layers of poly(ɛ-caprolactone) (PCL) microfibers (9.7 ± 0.2 µm) made via melt electrowriting (MEW) are used to reinforce the HA-SH matrix which has an elastic modulus of 95 Pa. The neuronal viability is low in pure HA-SH matrix, however, when astrocytes are pre-seeded below this reinforced construct, they significantly support neuronal survival, network formation quantified by neurite length, and neuronal firing shown by Ca²⁺ imaging. The astrocyte-seeded HA-SH matrix is able to match the neuronal viability to the level of Matrigel, a gold standard matrix for neuronal culture for over two decades. Thus, this 3D MEW frame reinforced HA-SH composite with neurons and astrocytes constitutes a reliable and reproducible system to further study brain diseases.

Tyramine-Functionalized Alginate-Collagen Hybrid Hydrogel Inks for 3D-Bioprinting

Extrusion-based 3D-bioprinting using hydrogels has exhibited potential in precision medicine; however, researchers are beset with several challenges. A major challenge of this technique is the production of constructs with sufficient height and fidelity to support cellular behavior in vivo. In this study, we present the 3D-bioprinting of cylindrical constructs with tunable gelation kinetics by controlling the covalent crosslinking density and gelation time of a tyramine-functionalized alginate hydrogel (ALG-TYR) via enzymatic reaction by horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The extruded filament was crosslinked for a second time on a support bath containing H₂O₂ to increase fidelity after printing. The resulting tubular construct, with a height of 6 mm and a wall thickness of 2 mm, retained its mechanical properties and had a maximum 2-fold swelling after 2 d. Furthermore, collagen (COL) was introduced into the ALG-TYR hydrogel network to increase the mechanical modulus and cell cytocompatibility, as the encapsulated fibroblast cells exhibited a higher cell viability in the ALG-TYR/COL construct (92.13 ± 0.70%) than in ALG-TYR alone (68.18 ± 3.73%). In summary, a vascular ECM-mimicking scaffold was 3D-bioprinted with the ALG-TYR/COL hybrid hydrogel, and this scaffold can support tissue growth for clinical translation in regenerative and personalized medicine.

The Role of Alginate Hydrogels as a Potential Treatment Modality for Spinal Cord Injury: A Comprehensive Review of the Literature

Objective

To comprehensively characterize the utilization of alginate hydrogels as an alternative treatment modality for spinal cord injury (SCI).

Methods

An extensive review of the published literature on studies using alginate hydrogels to treat SCI was performed. The review of the literature was performed using electronic databases such as PubMed, EMBASE, and OVID MEDLINE electronic databases. The keywords used were “alginate,” “spinal cord injury,” “biomaterial,” and “hydrogel.”

Results

In the literature, we identified a total of 555 rat models that were treated with alginate scaffolds for regenerative biomarkers. Alginate hydrogels were found to be efficient and promising substrates for tissue engineering, drug delivery, neural regeneration, and cellbased therapies for SCI repair. With its ability to act as a pro-regenerative and antidegenerative agent, the alginate hydrogel has the potential to improve clinical outcomes.

Conclusion

The emerging developments of alginate hydrogels as treatment modalities may support current and future tissue regenerative strategies for SCI.

Biocompatibility of hydroxyethyl cellulose/glycine/RuO2 composite scaffolds for neural-like cells

Fabrication of scaffolds for nerve regeneration is one of the most challenging topics in regenerative medicine at the moment, which is also interlinked with the development of biocompatible substrates for cells growth. This work is targeted towards the development of green biomaterial composite scaffolds for nerve cell culture applications. Hybrid scaffolds of hydroxyethyl cellulose/glycine (HEC/Gly) composite doped with different concentrations of green ruthenium oxide (RuO₂) were synthesized and characterized via a combination of different techniques. X-rays diffraction (XRD) and differential scanning calorimetry (DSC) analyses showed a crystalline nature for all the samples with noticeable decrease in the peak intensity of the fabricated scaffolds as compared to that for pure glycine. Fourier transform infrared spectroscopy (FTIR) tests revealed an increase in the vibrational bands of the synthesized RuO₂ containing scaffolds which are related to the functional groups of the natural plant extract (Aspalathuslinearis) used for RuO₂ nanoparticles (NPs) synthesis. Scanning electron microscopy (SEM) results revealed a 3D porous structure of the scaffolds with variant features attributed to the concentration of RuO₂ NPs in the scaffold. The compressive test results recorded an enhancement in mechanical properties of the fabricated scaffolds (up to 8.55 MPa), proportionally correlated to increasing the RuO₂ NPs concentration in HEC/Gly composite scaffold. Our biocompatibility tests revealed that the composite scaffolds doped with 1 and 2 ml of RuO₂ demonstrated the highest proliferation percentages (152.2 and 135.6%) compared to control. Finally, the SEM analyses confirmed the impressive cells attachments and differentiation onto the scaffold surfaces as evidenced by the presence of many neuron-like cells with apparent cell bodies and possessing few short neurite-like processes. The presence of RuO₂ and glycine was due to their extraordinary biocompatibility due to their cytoprotective and regenerative effects. Therefore, we conclude that these scaffolds are promising for accommodation and growth of neural-like cells.

Design of experiments approach to developing a robust ink for bioprinting

Despite advancements in tissue engineering, the methods used to generate three-dimensional (3D)in vitromodels for rapid screening and characterization studies remain time and labor intensive. Bioprinting offers an opportunity to offset these limitations by providing a scalable, high-throughput method with precise control over biomaterial scaffold and cellular deposition. However, the process of formulating bioinks can be complex in terms of balancing the mechanical integrity of a bioscaffold and viability of cells. One key factor, especially in alginate-based bioinks, is the rate of bioscaffold dissolution. It must allow cells to replace the bioscaffold with extracellular matrix (ECM), yet remain durable during extended tissue culture. This study uses a Design of Experiments (DoE) approach to understand the dependencies of multiple variables involved in the formulation and processing of an alginate-based bioink. The focus of the DoE was to understand the effects of hydrogel composition on bioink durability while maintaining cell viability. Three ingredients were varied in all: alginate, nanocellulose, and fibrinogen. Their effects on the bioink were then measured with respect to extrudability, strength, and stiffness as determined by dynamic mechanical analysis (DMA). The DoE demonstrated that mechanical integrity increased with increasing alginate concentration. In contrast, fibrinogen and nanofibril concentration had no statistically significant effect. The optimized ink containing fibroblasts was printable using multiple nozzle sizes while also supporting fibroblast cell viability. DMA characterization further showed that the composition of the cell culture medium did not modulate the degradation rate of the hydrogel. Ultimately, the study outlines a methodology for formulating a bioink that will result in robust bioscaffolds forin vitromodel development.

Polysaccharide peptide conjugates: Chemistry, properties and applications

The intention of this publication is to give an overview on research related to conjugates of polysaccharides and peptides. Dextran, chitosan, and alginate were selected, to cover four of the most often encountered functional groups known to be present in polysaccharides. These groups are the hydroxyl, the amine, the carboxyl, and the acetal functionality. A collection of the commonly used chemical reactions for conjugation is provided. Conjugation results into distinct properties compared to the parent polysaccharide, and a number of these characteristics are highlighted. This review aims at demonstrating the applicability of said conjugates with a strong emphasis on biomedical applications, drug delivery, biosensing, and tissue engineering. Some suggestions are made for more rigorous chemistries and analytics that could be investigated. Finally, an outlook is given into which direction the field could be developed further. We hope that this survey provides the reader with a comprehensive summary and contributes to the progress of works that aim at synthetically combining two of the main building blocks of life into supramolecular structures with unprecedented biological response.

An alginate-based encapsulation system for delivery of therapeutic cells to the CNS

Treatment options for neurodegenerative conditions such as Parkinson's disease have included the delivery of cells which release dopamine or neurotrophic factors to the brain. Here, we report the development of a novel approach for protecting cells after implantation into the central nervous system (CNS), by developing dual-layer alginate beads that encapsulate therapeutic cells and release an immunomodulatory compound in a sustained manner. An optimal alginate formulation was selected with a view to providing a sustained physical barrier between engrafted cells and host tissue, enabling exchange of small molecules while blocking components of the host immune response. In addition, a potent immunosuppressant, FK506, was incorporated into the outer layer of alginate beads using electrosprayed poly-ε-caprolactone core–shell nanoparticles with prolonged release profiles. The stiffness, porosity, stability and ability of the alginate beads to support and protect encapsulated SH-SY5Y cells was demonstrated, and the release profile of FK506 and its effect on T-cell proliferation in vitro was characterized. Collectively, our results indicate this multi-layer encapsulation technology has the potential to be suitable for use in CNS cell delivery, to protect implanted cells from host immune responses whilst providing permeability to nutrients and released therapeutic molecules.

Novel composite cell encapsulation system: dual-layer, micro-scale beads maintain cell survival while releasing immunomodulatory FK506 in a sustained manner. This biotechnology platform could be applicable for treatment of CNS and other disorders.

Microsphere incorporation as a strategy to tune the biological performance of bioinks

Although alginate is widely used as a matrix in the formulation of cell-laden inks, this polymer often requires laborious processing strategies due to its lack of cell adhesion moieties. The main objective of the present work was to explore the incorporation of microspheres into alginate-based bioinks as a simple and tuneable way to solve the cell adhesion problems, while adding extra biological functionality and improving their mechanical properties. To this end, three types of microspheres with different mineral contents (i.e. gelatine with 0% of hydroxyapatite, gelatine with 25 wt% of hydroxyapatite nanoparticles and 100 wt% of calcium -deficient hydroxyapatite) were synthesised and incorporated into the formulation of cell-laden inks. The results showed that the addition of microspheres generally improved the rheological properties of the ink, favoured cell proliferation and positively affected osteogenic cell differentiation. Furthermore, this differentiation was found to be influenced by the type of microsphere and the ability of the cells to migrate towards them, which was highly dependent on the stiffness of the bioink. In this regard, Ca²⁺ supplementation in the cell culture medium had a pronounced effect on the relaxation of the stiffness of these cell-loaded inks, influencing the overall cell performance. In conclusion, we have developed a powerful and tuneable strategy for the fabrication of alginate-based bioinks with enhanced biological characteristics by incorporating microspheres into the initial ink formulation.

Oxidation and RGD Modification Affect the Early Neural Differentiation of Murine Embryonic Stem Cells Cultured in Core-Shell Alginate Hydrogel Microcapsules

Directed neural differentiation of embryonic stem cells (ESCs) has been studied extensively to improve the treatment of neurodegenerative disorders. This can be done through stromal-cell derived inducing activity (SDIA), by culturing ESCs directly on top of a layer of feeder stromal cells. However, the stem cells usually become mixed with the feeder cells during the differentiation process, making it difficult to obtain a pure population of the differentiated cells for further use. To address this issue, a non-planar microfluidic device is used here to encapsulate murine ESCs (mESCs) in the 3D liquid core of microcapsules with an alginate hydrogel shell of different sizes for early neural differentiation through SDIA, by culturing mESC-laden microcapsules over a feeder layer of PA6 cells. Furthermore, the alginate hydrogel shell of the microcapsules is modified via oxidation or RGD peptide conjugation to examine the mechanical and chemical effects on neural differentiation of the encapsulated mESC aggregates. A higher expression of Nestin is observed in the aggregates encapsulated in small (∼300 μm) microcapsules and cultured over the PA6 cell feeder layer. Furthermore, the modification of the alginate with RGD facilitates early neurite extension within the microcapsules. This study demonstrates that the presence of the RGD peptide, the SDIA effect of the PA6 cells, and the absence of leukemia inhibition factor from the medium can lead to the early differentiation of mESCs with extensive neurites within the 3D microenvironment of the small microcapsules. This is the first study to investigate the effects of cell adhesion and degradation of the encapsulation materials for directed neural differentiation of mESCs. The simple modifications (i.e., oxidation and RGD incorporation) of the miniaturized 3D environment for improved early neural differentiation of mESCs may potentially enhance further downstream differentiation of the mESCs into more specialized neurons for therapeutic use and drug screening.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

Modification of Alginates to Modulate Their Physic-Chemical Properties and Obtain Biomaterials with Different Functional Properties

Modified alginates have a wide range of applications, including in the manufacture of dressings and scaffolds used for regenerative medicine, in systems for selective drug delivery, and as hydrogel materials. This literature review discusses the methods used to modify alginates and obtain materials with new or improved functional properties. It discusses the diverse biological and functional activity of alginates. It presents methods of modification that utilize both natural and synthetic peptides, and describes their influence on the biological properties of the alginates. The success of functionalization depends on the reaction conditions being sufficient to guarantee the desired transformations and provide modified alginates with new desirable properties, but mild enough to prevent degradation of the alginates. This review is a literature description of efficient methods of alginate functionalization using biologically active ligands. Particular attention was paid to methods of alginate functionalization with peptides, because the combination of the properties of alginates and peptides leads to the obtaining of conjugates with properties resulting from both components as well as a completely new, different functionality.

Hydrogel, Electrospun and Composite Materials for Bone/Cartilage and Neural Tissue Engineering

Injuries of the bone/cartilage and central nervous system are still a serious socio-economic problem. They are an effect of diversified, difficult-to-access tissue structures as well as complex regeneration mechanisms. Currently, commercially available materials partially solve this problem, but they do not fulfill all of the bone/cartilage and neural tissue engineering requirements such as mechanical properties, biochemical cues or adequate biodegradation. There are still many things to do to provide complete restoration of injured tissues. Recent reports in bone/cartilage and neural tissue engineering give high hopes in designing scaffolds for complete tissue regeneration. This review thoroughly discusses the advantages and disadvantages of currently available commercial scaffolds and sheds new light on the designing of novel polymeric scaffolds composed of hydrogels, electrospun nanofibers, or hydrogels loaded with nano-additives.

Integrin-Linked Kinase (ILK) Plays an Important Role in the Laminin-Dependent Development of Dorsal Root Ganglia during Chicken Embryogenesis

Integrin-linked kinase (ILK) is mainly localized in focal adhesions where it interacts and modulates the downstream signaling of integrins affecting cell migration, adhesion, and survival. The interaction of dorsal root ganglia (DRG) cells, being part of the peripheral nervous system (PNS), with the extracellular matrix (ECM) via integrins is crucial for proper PNS development. A few studies have focused on ILK’s role in PNS development, but none of these have focused on chicken. Therefore, we decided to investigate ILK’s role in the development of Gallus gallus domesticus’s DRG. First, using RT-PCR, Western blotting, and in situ hybridization, we show that ILK is expressed in DRG. Next, by immunocytochemistry, we show ILK’s localization both intracellularly and on the cell membrane of DRG neurons and Schwann cell precursors (SCPs). Finally, we describe ILK’s involvement in multiple aspects of DRG development by performing functional experiments in vitro. IgG-mediated interruption of ILK’s action improved DRG neurite outgrowth, modulated their directionality, stimulated SCPs migration, and impacted growth cone morphology in the presence of laminin-1 or laminin-1 mimicking peptide IKVAV. Taken together, our results show that ILK is important for chicken PNS development, probably via its exposure to the ECM.

The efficacy of lapine preconditioned or genetically modified IL4 over-expressing bone marrow-derived mesenchymal stromal cells in corticosteroid-associated osteonecrosis of the femoral head in rabbits

Cell-based therapy for augmentation of core decompression (CD) using mesenchymal stromal cells (MSCs) is a promising treatment for early stage osteonecrosis of the femoral head (ONFH). Recently, the therapeutic potential for immunomodulation of osteogenesis using preconditioned (with pro-inflammatory cytokines) MSCs (pMSCs), or by the timely resolution of inflammation using MSCs that over-express anti-inflammatory cytokines has been described. Here, pMSCs exposed to tumor necrosis factor-alpha and lipopolysaccharide for 3 days accelerated osteogenic differentiation in vitro. Furthermore, injection of pMSCs encapsulated with injectable hydrogels into the bone tunnel facilitated angiogenesis and osteogenesis in the femoral head in vivo, using rabbit bone marrow-derived MSCs and a model of corticosteroid-associated ONFH in rabbits. In contrast, in vitro and in vivo studies demonstrated that genetically-modified MSCs that over-express IL4 (IL4-MSCs), established by using a lentiviral vector carrying the rabbit IL4 gene under the cytomegalovirus promoter, accelerated proliferation of MSCs and decreased the percentage of empty lacunae in the femoral head. Therefore, adjunctive cell-based therapy of CD using pMSCs and IL4-MSCs may hold promise to heal osteonecrotic lesions in the early stage ONFH. These interventions must be applied in a temporally sensitive fashion, without interfering with the mandatory acute inflammatory phase of bone healing.

Mechanotransduction assays for neural regeneration strategies: A focus on glial cells

Glial cells are mechanosensitive, and thus, engineered systems have taken a step forward to design mechanotransduction platforms in order to impart diverse mechanical stresses to cells. Mechanical strain encountered in the central nervous system can arise from diverse mechanisms, such as tissue reorganization, fluid flow, and axon growth, as well as pathological events including axon swelling or mechanical trauma. Biomechanical relevance of the in vitro mechanical testing requires to be placed in line with the physiological and mechanical changes in central nervous tissues that occur during the progression of neurodegenerative diseases. Mechanotransduction signaling utilized by glial cells and the recent approaches intended to model altered microenvironment adapted to pathological context are discussed in this review. New insights in systems merging substrate's stiffness and topography should be considered for further glial mechanotransduction studies, while testing platforms for drug discoveries promise great advancements in pharmacotherapy. Potential leads and strategies for clinical outcomes are expected to be developed following the exploration of these glial mechanosensitive signaling pathways.

Phenolated alginate-collagen hydrogel induced chondrogenic capacity of human amniotic mesenchymal stem cells

Horseradish peroxidase (HRP)-catalyzed hydrogels are considered to be an important platform for tissue engineering applications. In this study, we investigated the chondrogenic capacity of phenolated (1.2%) alginate-(0.5%) collagen hydrogel on human amniotic mesenchymal stem cells after 21 days. Using NMR, FTIR analyses, and SEM imaging, we studied the phenolation and structure of alginate-collagen hydrogel. For physicochemical evaluations, gelation time, mechanical properties, swelling, and degradation rate were assessed. The survival rate was monitored using the MTT assay and DAPI staining. Western blotting was performed to measure the chondrogenic differentiation of cells. NMR showed successful phenolation of the alginate-collagen hydrogel. FTIR exhibited the interaction between the functional groups of collagen with phenolated alginate. SEM showed the existence of collagen microfibrils in the alginate-collagen hydrogel. Compared to phenolated alginate, the addition of collagen increased hydrogel elasticity by 10%. Both swelling rate and biodegradability were reduced in the presence of collagen. We noted an increased survival rate in phenolated alginate-collagen compared to the control cells (p < 0.05). Western blotting revealed the increase of chondrocyte-associated proteins such as SOX9 and COL2A1 in phenolated-alginate-collagen hydrogels after 21 days. These data showed that phenolated alginate-collagen hydrogel is an appropriate 3 D substrate to induce chondrogenic capacity of human mesenchymal stem cells.

Chemical Conjugation Strategies for the Development of Protein-Based Subunit Nanovaccines

The production of subunit nanovaccines relies heavily on the development of a vaccine delivery system that is safe and efficient at delivering antigens to the target site. Nanoparticles have been extensively investigated for vaccine delivery over the years, as they often possess self-adjuvanting properties. The conjugation of antigens to nanoparticles by covalent bonds ensures co-delivery of these components to the same subset of immune cells in order to trigger the desired immune responses. Herein, we review covalent conjugation strategies for grafting protein or peptide antigens onto other molecules or nanoparticles to obtain subunit nanovaccines. We also discuss the advantages of chemical conjugation in developing these vaccines.

Direct and Indirect Biomimetic Peptide Modification of Alginate: Efficiency, Side Reactions, and Cell Response

In the fast-developing field of tissue engineering there is a constant demand for new materials as scaffolds for cell seeding, which can better mimic a natural extracellular matrix as well as control cell behavior. Among other materials, polysaccharides are widely used for this purpose. One of the main candidates for scaffold fabrication is alginate. However, it lacks sites for cell adhesion. That is why one of the steps toward the development of suitable scaffolds for cells is the introduction of the biofunctionality to the alginate structure. In this work we focused on bone-sialoprotein derived peptide (TYRAY) conjugation to the molecule of alginate. Here the comparison study on four different approaches of peptide conjugation was performed including traditional and novel modification methods, based on 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxy succinimide (EDC/NHS), 4-(4,6-dimethoxy-1,3,5-triazine-2-yl)-4-methylmorpholinium chloride (DMTMM), thiol-Michael addition and Cu-catalyzed azide-alkyne cycloaddition reactions. It was shown that the combination of the alginate amidation with the use of and subsequent Cu-catalyzed azide-alkyne cycloaddition led to efficient peptide conjugation, which was proven with both NMR and XPS methods. Moreover, the cell culture experiment proved the positive effect of peptide presence on the adhesion of human embryonic stem cells.

Soft matter polysaccharide-based hydrogels as versatile bioengineered platforms for brain tissue repair and regeneration

Acute or chronic brain injuries promote deaths and the life-long debilitating neurological status where, despite advances in therapeutic strategies, clinical outcome hardly achieves total patient recovery. In recent decades, brain tissue engineering emerged as an encouraging area of research for helping in damaged central nervous system (CNS) recovery. Polysaccharides are abundant naturally occurring biomacromolecules with a great potential enhancement of advanced technologies in brain tissue repair and regeneration (BTRR). Besides carrying rich biological information, polysaccharides can interact and communicate with biomolecules, including glycosaminoglycans present in cell membranes and many signaling moieties, growth factors, chemokines, and axon guidance molecules. This review includes a comprehensive investigation of the current progress on designing and developing polysaccharide-based soft matter biomaterials for BTRR. Although few interesting reviews concerning BTRR have been reported, this is the first report specifically focusing on covering multiple polysaccharides and polysaccharide-based functionalized biomacromolecules in this emerging and intriguing field of multidisciplinary knowledge. This review aims to cover the state of art challenges and prospects of this fascinating field while presenting the richness of possibilities of using these natural biomacromolecules for advanced biomaterials in prospective neural tissue engineering applications.

Recent Development of Alginate-Based Materials and Their Versatile Functions in Biomedicine, Flexible Electronics, and Environmental Uses

Alginate is a natural polysaccharide that is easily chemically modified or compounded with other components for various types of functionalities. The alginate derivatives are appealing not only because they are biocompatible so that they can be used in biomedicine or tissue engineering but also because of the prospering bioelectronics that require various biomaterials to interface between human tissues and electronics or to serve as electronic components themselves. The study of alginate-based materials, especially hydrogels, have repeatedly found new frontiers over recent years. In this Review, we document the basic properties of alginate, their chemical modification strategies, and the recent development of alginate-based functional composite materials. The newly thrived functions such as ionically conductive hydrogel or 3D or 4D cell culturing matrix are emphasized among other appealing potential applications. We expect that the documentation of relevant information will stimulate scientific efforts to further develop biocompatible electronics or smart materials and to help the research domain better address the medicine, energy, and environmental challenges faced by human societies.

In-situ stable injectable collagen-based hydrogels for cell and growth factor delivery

Here we report development of in-situ stable injectable hydrogels for delivery of cells and growth factors based on two precursors, alginate, and collagen/calcium sulfate (CaSO4). The alg/col hydrogels were shear-thinning, injectable through commercially available needles and stable right after injection. Rheological measurements revealed that pre-crosslinked alg/col hydrogels fully crosslinked at 37°C and that the storage modulus of alg/col hydrogels increased with increasing the collagen content or the concentration of CaSO4. The viscoelastic characteristics and injectability of the alg/col hydrogels were not significantly impacted by the storage of precursor solutions for 28 days. An osteoinductive bone morphogenic protein-2 (BMP-2) loaded into alg/col hydrogels was released in 14 days. Human mesenchymal stem cells (hMSCs) encapsulated in alg/col hydrogels had over 90% viability over 7 days after injection. The DNA content of hMSC-laden alg/col hydrogels increased by 6-37 folds for 28 days, depending on the initial cell density. In addition, hMSCs encapsulated in alg/col hydrogels and incubated in osteogenic medium were osteogenically differentiated and formed a mineralized matrix. Finally, a BMP-2 loaded alg/col hydrogel was used to heal a critical size calvarial bone defect in rats after 8 weeks of injection. The alg/col hydrogel holds great promise in tissue engineering and bioprinting applications.

A Review on the Adaption of Alginate-Gelatin Hydrogels for 3D Cultures and Bioprinting

Sustaining the vital functions of cells outside the organism requires strictly defined parameters. In order to ensure their optimal growth and development, it is necessary to provide a range of nutrients and regulators. Hydrogels are excellent materials for 3D in vitro cell cultures. Their ability to retain large amounts of liquid, as well as their biocompatibility, soft structures, and mechanical properties similar to these of living tissues, provide appropriate microenvironments that mimic extracellular matrix functions. The wide range of natural and synthetic polymeric materials, as well as the simplicity of their physico-chemical modification, allow the mechanical properties to be adjusted for different requirements. Sodium alginate-based hydrogel is a frequently used material for cell culture. The lack of cell-interactive properties makes this polysaccharide the most often applied in combination with other materials, including gelatin. The combination of both materials increases their biological activity and improves their material properties, making this combination a frequently used material in 3D printing technology. The use of hydrogels as inks in 3D printing allows the accurate manufacturing of scaffolds with complex shapes and geometries. The aim of this paper is to provide an overview of the materials used for 3D cell cultures, which are mainly alginate-gelatin hydrogels, including their properties and potential applications.

Alginate Hydrogels with Tuneable Properties

Alginate is a material that has many biomedical applications due to its low toxicity and a variety of favourable physical properties. In particular, the ease in which hydrogels are formed from alginate and the variety of mechanical behaviours that can be imparted on the hydrogels, by understanding alginate chemistry and intuitive design, has made alginate the most widely investigated polysaccharide used for tissue engineering. This chapter provides an overview of alginate, from how the source and natural variations in composition can influence mechanical properties of alginate hydrogels, through to some innovative techniques used to modify and functionalise the hydrogels designed specifically for cell-based therapies. The main focus is on how these strategies of understanding and controlling the chemistry of alginates have resulted in the development of hydrogels that can be tuned to deliver the physical behaviours required for successful application. This will also highlight how research on the physicochemical properties has helped alginate evolve from a structural polysaccharide in brown seaweed into a highly tuneable, multifunctional, smart biomaterial, which is likely to find further biomedical applications in the future.

Recent trends in the development of peptide and protein-based hydrogel therapeutics for the healing of CNS injury

Traumatic brain injury (TBI) and spinal cord injury (SCI) cause millions of deaths and permanent or prolonged physical disabilities around the globe every year. It generally happens due to various incidents, such as accidents during sports, war, physical assault, and strokes which result in severe damage to brain and spinal cord. If this remains untreated, traumatic CNS injuries may lead to early development of several neurodegenerative diseases like Alzheimer's, Parkinson, multiple sclerosis, and other mental illnesses. The initial physical reaction, which is also termed as the primary phase, includes swelling, followed by inflammation as a result of internal haemorrhage causing damage to indigenous tissue, i.e., axonal shear injury, rupture of blood vessels, and partial impaired supply of oxygen and essential nutrients in the neurons, thereby initiating a cascade of events causing secondary injuries such as hypoxia, hypotension, cognitive impairment, seizures, imbalanced calcium homeostasis and glutamate-induced excitotoxicity resulting in concomitant neuronal cell death and cumulative permanent tissue damage. In the modern era of advanced biomedical technology, we are still living with scarcity of the clinically applicable comparative non-invasive therapeutic strategies for regeneration or functional recovery of neurons or neural networks after a massive CNS injury. One of the key reasons for this scarcity is the limited regenerative ability of neurons in CNS. Growth-impermissive glial scar and the lack of a synthetic biocompatible platform for proper neural tissue engineering and controlled supply of drugs further retard the healing process. Injectable or implantable hydrogel materials, consisting majorly of water in its porous three-dimensional (3D) structure, can serve as an excellent drug delivery platform as well as a transplanted cell-supporting scaffold medium. Among the various neuro-compatible bioinspired materials, we are limiting our discussion to the recent advancement of engineered biomaterials comprising mainly of peptides and proteins due to their growing demand, low immunogenicity and versatility in the fabrication of neuro regenerative medicine. In this article, we try to explore all the recent scientific avenues that are developing gradually to make peptide and peptide-conjugated biomaterial hydrogels as a therapeutic and supporting scaffold for treating CNS injuries.

Polymer microcapsules and microbeads as cell carriers for in vivo biomedical applications

Polymer microcarriers are being extensively explored as cell delivery vehicles in cell-based therapies and hybrid tissue and organ engineering. Spherical microcarriers are of particular interest due to easy fabrication and injectability. They include microbeads, composed of a porous matrix, and microcapsules, where matrix core is additionally covered with a semipermeable membrane. Microcarriers provide cell containment at implantation site and protect the cells from host immunoresponse, degradation and shear stress. Immobilized cells may be genetically altered to release a specific therapeutic product directly at the target site, eliminating side effects of systemic therapies. Cell microcarriers need to fulfil a number of extremely high standards regarding their biocompatibility, cytocompatibility, immunoisolating capacity, transport, mechanical and chemical properties. To obtain cell microcarriers of specified parameters, a wide variety of polymers, both natural and synthetic, and immobilization methods can be applied. Yet so far, only a few approaches based on cell-laden microcarriers have reached clinical trials. The main issue that still impedes progress of these systems towards clinical application is limited cell survival in vivo. Herein, we review polymer biomaterials and methods used for fabrication of cell microcarriers for in vivo biomedical applications. We describe their key limitations and modifications aiming at improvement of microcarrier in vivo performance. We also present the main applications of polymer cell microcarriers in regenerative medicine, pancreatic islet and hepatocyte transplantation and in the treatment of cancer. Lastly, we outline the main challenges in cell microimmobilization for biomedical purposes, the strategies to overcome these issues and potential future improvements in this area.

Hydrogels based on modified pectins capable of modulating neural cell behavior as prospective biomaterials in glioblastoma treatment

Glioblastoma is the most common malignant tumor of the brain, but its treatment outcomes can be improved by new therapeutic techniques using biocompatible materials. Utilizing controllable alkaline de-esterification we obtained pectin preparation with 27.4% esterification degree and used it for bio-artificial matrix production. We discovered optimal gelation conditions in the presence of Ca²⁺ by the analysis of visco-elastic properties of the gels and produced a series of biomaterials in hydrogel forms. Hydrogels based on low-esterified pectin significantly slow down the metabolism of C6 glioma cells and neural stem cells (NSCs) and slightly decrease the viability of the C6 glioma, but not of NSCs. This happens due to a decrease in cell proliferation rate, while apoptosis degrees remain stable or negligibly decrease. We created a set of pectin hydrogels supplemented with different ratios of two ECM proteins-collagens I and IV. We have shown that the formation of cell processes in glioma C6 can be regulated by varying the ratio of two ECM proteins in gels used for 3D cell cultivation. Thus, composite matrix materials obtained can be used for modeling brain tumor invasion. The results presented suggest that modified pectins supplemented with two collagen types may serve as prospective biomaterials for glioblastoma treatment due to their ability to regulate glioma cell dynamics.

Conjugates of Copper Alginate with Arginine-Glycine-Aspartic Acid (RGD) for Potential Use in Regenerative Medicine

Current restrictions on the use of antibiotics, associated with increases in bacterial resistance, require new solutions, including materials with antibacterial properties. In this study, copper alginate fibers obtained using the classic wet method were used to make nonwovens which were modified with arginine-glycine-aspartic acid (RGD) derivatives. Stable polysaccharide-peptide conjugates formed by coupling with 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate (DMT/NMM/TosO-), and materials with physically embedded RGD derivatives, were obtained. The materials were found to be characterized by very high antibacterial activity against S. aureus and K. pneumoniae. Cytotoxicity studies confirmed that the materials are not cytotoxic. Copper alginate conjugates with RGD peptides have strong potential for use in regenerative medicine, due to their biocompatibility and innate antibacterial activity.

Bio-conjugation of platelet-rich plasma and alginate through carbodiimide chemistry for injectable hydrogel therapies

Alginate is a highly tailorable, biocompatible polymer whose properties can be tuned to mimic the properties of native nucleus pulposus (NP) tissue. Platelet-rich plasma (PRP) is a highly accessible, inexpensive, and readily available mix of pro-regenerative factors. By functionalizing alginate with PRP, a mechanically optimized, bioactive alginate NP analogue may stimulate NP cells to proliferate and accumulate matrix over a longer period of time than if the PRP were solely encapsulated within the hydrogel. In this study, PRP was chemically bound to alginate using carbodiimide chemistry and mechanically, physically, and cytologically compared to plain alginate as well as alginate containing free-floating lyophilized PRP. The alginates were mechanically and physically characterized; PRP-conjugated alginate had similar mechanical properties to controls and had the benefit of retained PRP proteins within the hydrogel. Human nucleus pulposus cells (hNPCs) were seeded within the modified alginates and cultured for 14 days. Quantification data of glycosaminoglycans suggests that PRP-incorporated alginate has the potential to increase ECM production within the characterized alginate constructs, and that PRP-functionalized alginate can retain protein within the hydrogel over time. This is the first study to functionalize the milieu of PRP proteins onto alginate and characterize the mechanical and physical properties of the modified alginates. This study also incorporates hNPCs into the characterized PRP-modified alginates to observe phenotypic maintenance when encapsulated within the in situ gelling constructs.

Silk fibroin-alginate based beads for human mesenchymal stem cell differentiation in 3D

Lately silk fibroin has gained a lot of popularity as a tissue engineering scaffold due to its exceptional mechanical properties, negligible inflammatory reactions, remarkable biocompatibility, and tunable biodegradability. Nonetheless, 3 dimensional (3D) silk fibroin based scaffolds, which allow simultaneous formation of scaffolds and cell encapsulation with minimal damage to the cells, are unavailable, as most of the methods involve the use of some cell destructive techniques. Thus, cells have to be loaded after the scaffold formation and the study has to rely upon the ability of the cells to penetrate the scaffold to obtain a 3D microenvironment. Hence, these platforms do not allow for a true 3D system replicating the in vivo environment. Here silk fibroin-alginate based beads have been developed, and retain silk fibroin for a longer period of time and allow for simultaneous cell encapsulation as the crosslinking method is cell-compatible. It is demonstrated for the first time that these silk fibroin-alginate beads can be used to encapsulate the cells at varying cell densities depending on the desired application. These beads were further used to study the effect of functional groups on human mesenchymal stem cell (hMSC) differentiation in 3D, by utilizing carboxylic groups naturally present in alginate as well as introducing phosphate groups. The results showed that these beads were able to support the growth and proliferation of hMSCs and induced differentiation solely due to functional groups within 14 days. These beads were better in directing hMSC differentiation into osteogenic and chondrogenic lineages compared to 2D surfaces and differentiation media.

Rapid and efficient in vivo angiogenesis directed by electro-assisted bioprinting of alginate/collagen microspheres with human umbilical vein endothelial cell coating layer

Rapid reconstruction of functional microvasculature is the urgent challenge of regenerative medicine and ischemia therapy development. The purpose of this study was to provide an alternative solution for obtaining functional blood vessel networks in vivo, through assessing whether hydrogel-based microspheres coated by human umbilical vein endothelial cells (HUVECs) can direct rapid and efficient in vivo angiogenesis without the addition of exogenous growth factors or other supporting cells. Uniform alginate microspheres with adjustable diameter were biofabricated by electro-assisted bioprinting technology. Collagen fibrils were evenly coated on the surface of alginate microspheres through simple self-assembly procedure, and collagen concentration is optimized to achieve the highest HUVECs adhesion and proliferation. Immunofluorescence staining and gene analysis confirmed the formation of the prevascularized tubular structure and significantly enhanced endothelial gene expression. HUVECs-coated hydrogel microspheres with different diameters were subcutaneously injected in immune-deficient mice, which demonstrated rapid blood vessel regeneration and functional anastomosis with host blood vessels within 1 week. Besides, microsphere diameter demonstrated influence on blood vessel density with statistical differences but showed no obvious influence on the area occupied by blood vessels. This study provided a powerful tool for rapid and minimal-invasion angiogenesis of bioprinting constructs and a potential method for vascularized tissue regeneration and ischemia treatment with clinically relevant dimensions.

Peptide-modified, hyaluronic acid-based hydrogels as a 3D culture platform for neural stem/progenitor cell engineering

Neural stem/progenitor cell (NS/PC)-based therapies have shown exciting potential for regeneration of the central nervous system (CNS) and NS/PC cultures represent an important resource for disease modeling and drug screening. However, significant challenges limiting clinical translation remain, such as generating large numbers of cells required for model cultures or transplantation, maintaining physiologically representative phenotypes ex vivo and directing NS/PC differentiation into specific fates. Here, we report that culture of human NS/PCs in 3D, hyaluronic acid (HA)-rich biomaterial microenvironments increased differentiation toward oligodendrocytes and neurons over 2D cultures on laminin-coated glass. Moreover, NS/PCs in 3D culture exhibited a significant reduction in differentiation into reactive astrocytes. Many NS/PC-derived neurons in 3D, HA-based hydrogels expressed synaptophysin, indicating synapse formation, and displayed electrophysiological characteristics of immature neurons. While inclusion of integrin-binding, RGD peptides into hydrogels resulted in a modest increase in numbers of viable NS/PCs, no combination of laminin-derived, adhesive peptides affected differentiation outcomes. Notably, 3D cultures of differentiating NS/PCs were maintained for at least 70 days in medium with minimal growth factor supplementation. In sum, results demonstrate the use of 3D, HA-based biomaterials for long-term expansion and differentiation of NS/PCs toward oligodendroglial and neuronal fates, while inhibiting astroglial fates. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 704-718, 2019.

Neural tissue engineering with structured hydrogels in CNS models and therapies

The development of techniques to create and use multiphase microstructured hydrogels (granular hydrogels or microgels) has enabled the generation of cultures with more biologically relevant architecture and use of structured hydrogels is especially pertinent to the development of new types of central nervous system (CNS) culture models and therapies. We review material choice and the customisation of hydrogel structure, as well as the use of hydrogels in developmental models. Combining the use of structured hydrogel techniques with developmentally relevant tissue culture approaches will enable the generation of more relevant models and treatments to repair damaged CNS tissue architecture.

Alginate Nanoparticles for Drug Delivery and Targeting

Nanotechnology refers to the control, manipulation, study and manufacture of structures and devices at the nanometer size range. The small size, customized surface, improved solubility and multi-functionality of nanoparticles will continue to create new biomedical applications, as nanoparticles allow to dominate stability, solubility and bioavailability, as well controlled release of drugs. The type of a nanoparticle, and its related chemical, physical and morphological properties influence its interaction with living cells, as well as determine the route of clearance and possible toxic effects. This field requires cross-disciplinary research and gives opportunities to design and develop multifunctional devices, which allow the diagnosis and treatment of devastating diseases. Over the past few decades, biodegradable polymers have been studied for the fabrication of drug delivery systems. There was extensive development of biodegradable polymeric nanoparticles for drug delivery and tissue engineering, in view of their applications in controlling the release of drugs, stabilizing labile molecules from degradation and site-specific drug targeting. The primary aim is to reduce dosing frequency and prolong the therapeutic outcomes. For this purpose, inert excipients should be selected, being biopolymers, e.g. sodium alginate, commonly used in controlled drug delivery. Nanoparticles composed of alginate (known as anionic polysaccharide widely distributed in the cell walls of brown algae which, when in contact with water, forms a viscous gum) have emerged as one of the most extensively characterized biomaterials used for drug delivery and targeting a set of administration routes. Their advantages include not only the versatile physicochemical properties, which allow chemical modifications for site-specific targeting but also their biocompatibility and biodegradation profiles, as well as mucoadhesiveness. Furthermore, mechanical strength, gelation, and cell affinity can be modulated by combining alginate nanoparticles with other polymers, surface tailoring using specific targeting moieties and by chemical or physical cross-linking. However, for every physicochemical modification in the macromolecule/ nanoparticles, a new toxicological profile may be obtained. In this paper, the different aspects related to the use of alginate nanoparticles for drug delivery and targeting have been revised, as well as how their toxicological profile will determine the therapeutic outcome of the drug delivery system.

Tyramine-conjugated alginate hydrogels as a platform for bioactive scaffolds

Alginate‐based hydrogels represent promising microenvironments for cell culture and tissue engineering, as their mechanical and porous characteristics are adjustable toward in vivo conditions. However, alginate scaffolds are bioinert and thus inhibit cellular interactions. To overcome this disadvantage, bioactive alginate surfaces were produced by conjugating tyramine molecules to high‐molecular‐weight alginates using the carbodiimide chemistry. Structural elucidation using nuclear magnetic resonance spectroscopy and contact angle measurements revealed a surface chemistry and wettability of tyramine‐alginate hydrogels similar to standard cell culture treated polystyrene. In contrast to stiff cell culture plastic, tyramine‐alginate scaffolds were found to be soft (60–80 kPa), meeting the elastic moduli of human tissues such as liver and heart. We further demonstrated an enhanced protein adsorption with increasing tyramine conjugation, stable for several weeks. Cell culture studies with human mesenchymal stem cells and human pluripotent stem cell‐derived cardiomyocytes qualified tyramine‐alginate hydrogels as bioactive platforms enabling cell adhesion and contraction on (structured) 2‐D layer and spherical matrices. Due to the alginate functionalization with tyramines, stable cell–matrix interactions were observed beneficial for an implementation in biology, biotechnology, and medicine toward efficient cell culture and tissue substitutes. © 2018 The Authors. Journal of Biomedical Materials Research Part A published by Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 114–121, 2019.

Tuning the mechanical properties of alginate-peptide hydrogels

Alginate, a polysaccharide that gels in the presence of divalent ions, has been used in the field of regenerative medicine to facilitate cell growth in impaired tissues by providing an artificial bio-surrounding similar to the natural extra cellular matrix (ECM). Here, we present a systematic investigation of the effect of three arginine-glycine-aspartic acid (RGD)-containing peptides, G6KRGDY, A6KRGDY and V6KRGDY, on the physical properties of alginate-peptide hydrogels. Rheology measurements showed that the storage modulus of the alginate-A6KRGDY and alginate-V6KRGDY gels is an order of magnitude higher than that of the alginate-G6KRGDY gel. Small angle X-ray scattering (SAXS) measurements suggest that the difference in the mechanical properties of the gels is due to the formation of larger peptide junction zones in addition to the ones formed by calcium ions. These findings indicate that the peptides' ability to self-assemble in aqueous solution is a significant factor in tuning the stiffness of the alginate/peptide hybrid hydrogels.