Hydrogel formulation determines cell fate of fetal and adult neural progenitor cells

Minimally Invasive Syringe-Injectable Hydrogel with Angiogenic Factors for Ischemic Stroke Treatment

Ischemic stroke (IS) accounts for most stroke incidents and causes intractable damage to brain tissue. This condition manifests as diverse aftereffects, such as motor impairment, emotional disturbances, and dementia. However, a fundamental approach to curing IS remains unclear. This study proposes a novel approach for treating IS by employing minimally invasive and injectable jammed gelatin-norbornene nanofibrous hydrogels (GNF) infused with growth factors (GFs). The developed GNF/GF hydrogels are administered to the motor cortex of a rat IS model to evaluate their therapeutic effects on IS-induced motor dysfunction. GNFs mimic a natural fibrous extracellular matrix architecture and can be precisely injected into a targeted brain area. The syringe-injectable jammed nanofibrous hydrogel system increased angiogenesis, inflammation, and sensorimotor function in the IS-affected brain. For clinical applications, the biocompatible GNF hydrogel has the potential to efficiently load disease-specific drugs, enabling targeted therapy for treating a wide range of neurological diseases.

Advances in current in vitro models on neurodegenerative diseases

Many neurodegenerative diseases are identified but their causes and cure are far from being well-known. The problem resides in the complexity of the neural tissue and its location which hinders its easy evaluation. Although necessary in the drug discovery process, in vivo animal models need to be reduced and show relevant differences with the human tissues that guide scientists to inquire about other possible options which lead to in vitro models being explored. From organoids to organ-on-a-chips, 3D models are considered the cutting-edge technology in cell culture. Cell choice is a big parameter to take into consideration when planning an in vitro model and cells capable of mimicking both healthy and diseased tissue, such as induced pluripotent stem cells (iPSC), are recognized as good candidates. Hence, we present a critical review of the latest models used to study neurodegenerative disease, how these models have evolved introducing microfluidics platforms, 3D cell cultures, and the use of induced pluripotent cells to better mimic the neural tissue environment in pathological conditions.

A review on 3D printing functional brain model

Modern neuroscience increasingly relies on 3D models to study neural circuitry, nerve regeneration, and neural disease. Several different biofabrication approaches have been explored to create 3D neural tissue model structures. Among them, 3D bioprinting has shown to have great potential to emerge as a high-throughput/high precision biofabrication strategy that can address the growing need for 3D neural models. Here, we have reviewed the design principles for neural tissue engineering. The main challenge to adapt printing technologies for biofabrication of neural tissue models is the development of neural bioink, i.e., a biomaterial with printability and gelation properties and also suitable for neural tissue culture. This review shines light on a vast range of biomaterials as well as the fundamentals of 3D neural tissue printing. Also, advances in 3D bioprinting technologies are reviewed especially for bioprinted neural models. Finally, the techniques used to evaluate the fabricated 2D and 3D neural models are discussed and compared in terms of feasibility and functionality.

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.

The Effect of Physical Cues of Biomaterial Scaffolds on Stem Cell Behavior

Stem cells have been sought as a promising cell source in the tissue engineering field due to their proliferative capacity as well as differentiation potential. Biomaterials have been utilized to facilitate the delivery of stem cells in order to improve their engraftment and long-term viability upon implantation. Biomaterials also have been developed as scaffolds to promote stem cell induced tissue regeneration. This review focuses on the latter where the biomaterial scaffold is designed to provide physical cues to stem cells in order to promote their behavior for tissue formation. Recent work that explores the effect of scaffold physical properties, topography, mechanical properties and electrical properties, is discussed. Although still being elucidated, the biological mechanisms, including cell shape, focal adhesion distribution, and nuclear shape, are presented. This review also discusses emerging areas and challenges in clinical translation.

The potential of biomaterials for central nervous system cellular repair

The central nervous system (CNS) can be injured or damaged through a variety of insults including traumatic injury, stroke, and neurodegenerative or demyelinating diseases, including Alzheimer's disease, Parkinson's disease and multiple sclerosis. Existing pharmacological and other therapeutics strategies are limited in their ability to repair or regenerate damaged CNS tissue meaning there are significant unmet clinical needs facing patients suffering CNS damage and/or degeneration. Through a variety of mechanisms including neuronal replacement, secretion of therapeutic factors, and stimulation of host brain plasticity, cell-based repair offers a potential mechanism to repair and heal the damaged CNS. However, over the decades of its evolution as a therapeutic strategy, cell-based CNS repair has faced significant hurdles that have prevented its translation to widespread clinical practice. In recent years, advances in cell technologies combined with advances in biomaterial-based regenerative medicine and tissue engineering have meant there is very real potential for many of these hurdles to be overcome. This review will provide an overview of the main CNS conditions that lend themselves to cellular repair and will then outline the potential of biomaterial-based approaches for improving the outcome of cellular repair in these conditions.

3D brain tissue physiological model with co-cultured primary neurons and glial cells in hydrogels

Recently, researchers have focused on the role of gut microbiota on human health and reported the existence of a bidirectional relationship between intestinal microbiota and the brain, referred to as microbiota-gut-brain axis (MGBA). In this context, the development of an organ-on-a-chip platform recapitulating the main players of the MGBA would help in the investigations of the biochemical mechanisms involved. In this work, we focused on the development of a new, hydrogel-based, 3D brain-like tissue model to be hosted in the brain compartment of the aforementioned platform. We previously cultured primary mouse microglial cells, cortical neurons and astrocytes independently, once embedded or covered by a millimeter layer of two selected collagen-based hydrogels. We evaluated cell metabolic activity up to 21 days, cell morphology, spatial distribution and synapse formation. Then, we exploited the best performing culturing condition and developed a more complex brain-like tissue model based on the co-culture of cortical neurons and glial cells in physiological conditions. The obtained results indicate that our 3D hydrogel-based brain tissue model is suitable to recapitulate in vitro the key biochemical parameters of brain tissue.

Foetal neural progenitors contribute to postnatal circuits formation ex vivo: an electrophysiological investigation

Neuronal progenitor cells (NPC) play an essential role in homeostasis of the central nervous system (CNS). Considering their ability to differentiate into specific lineages, their manipulation and control could have a major therapeutic impact for those CNS injuries or degenerative diseases characterized by neuronal cell loss. In this work, we established an in vitro co-culture and tested the ability of foetal NPC (fNPC) to integrate among post-mitotic hippocampal neurons and contribute to the electrical activity of the resulting networks. We performed extracellular electrophysiological recordings of the activity of neuronal networks and compared the properties of spontaneous spiking in hippocampal control cultures (HCC), fNPC, and mixed circuitries ex vivo. We further employed patch-clamp intracellular recordings to examine single-cell excitability. We report of the capability of fNPC to mature when combined to hippocampal neurons, shaping the profile of network activity, a result suggestive of newly formed connectivity ex vivo.

Hydrogel systems and their role in neural tissue engineering

Neural tissue engineering (NTE) is a rapidly progressing field that promises to address several serious neurological conditions that are currently difficult to treat. Selecting the right scaffolding material to promote neural and non-neural cell differentiation as well as axonal growth is essential for the overall design strategy for NTE. Among the varieties of scaffolds, hydrogels have proved to be excellent candidates for culturing and differentiating cells of neural origin. Considering the intrinsic resistance of the nervous system against regeneration, hydrogels have been abundantly used in applications that involve the release of neurotrophic factors, antagonists of neural growth inhibitors and other neural growth-promoting agents. Recent developments in the field include the utilization of encapsulating hydrogels in neural cell therapy for providing localized trophic support and shielding neural cells from immune activity. In this review, we categorize and discuss the various hydrogel-based strategies that have been examined for neural-specific applications and also highlight their strengths and weaknesses. We also discuss future prospects and challenges ahead for the utilization of hydrogels in NTE.

Development of an Anisotropically Organized Brain dECM Hydrogel-Based 3D Neuronal Culture Platform for Recapitulating the Brain Microenvironment in Vivo

To mimic the brain tissue microenvironment in vitro, the biological and structural properties of the utilized system must be similar to those of the native brain in the microenvironment in vivo. To promote the bioactive (biological) properties of matrix hydrogels, we used the decellularized extracellular matrix (dECM) of porcine brain, which was found to enhance neuronal differentiation/outgrowth and neuron-to-brain dECM interactions. To implement the desired structural properties, we aligned microfibrils within a composite hydrogel mixed with the brain dECM and collagen I, with or without encapsulated neurons, by the stretching and releasing of a hydrogel-based chip. We then tested the ability of the aligned brain dECM hydrogel-based three-dimensional (3D) culture platform to mimic the in vivo brain microenvironment. We found that dECM-containing gels harbored brain-derived ECM proteins, including collagen I, collagen IV, laminin, and various cytokines, and that neurons incubated in these gels exhibited enhanced neurite outgrowth and development compared to those incubated in collagen gel (dECM 0 mg/mL). We evaluated the surface morphology and mechanical properties of the hydrogel with and without the brain dECM and found that their encapsulated neurons showed similar levels of cell viability. We then used a mechanical process to align the composite dECM hydrogel, conferring the desired structural properties to our system. Together, our results suggest that our newly developed brain dECM-based 3D culture platform could potentially be further developed for use in drug screening.

A roadmap for promoting endogenous in situ tissue restoration using inductive bioscaffolds after acute brain injury

The regeneration of brain tissue remains one of the greatest unsolved challenges in medicine and by many is considered unfeasible. Indeed, the adult mammalian brain does not regenerate tissue, but there is ongoing endogenous neurogenesis, which is upregulated after injury and contributes to tissue repair. This endogenous repair response is a conditio sine que non for tissue regeneration. However, scarring around the lesion core and cavitation provide unfavorable conditions for tissue regeneration in the brain. Based on the success of using extracellular matrix (ECM)-based bioscaffolds in peripheral soft tissue regeneration, it is plausible that the provision of an inductive ECM-based hydrogel inside the volumetric tissue loss can attract neural cells and create a de novo viable tissue. Following perturbation theory of these successes in peripheral tissues, we here propose 9 perturbation parts (i.e. requirements) that can be solved independently to create an integrated series to build a functional and integrated de novo neural tissue. Necessities for tissue formation, anatomical and functional connectivity are further discussed to provide a new substrate to support the improvement of behavioral impairments after acute brain injury. We also consider potential parallel developments of this tissue engineering effort that can support therapeutic benefits in the absence of de novo tissue formation (e.g. structural support to veterate brain tissue). It is envisaged that eventually top-down inductive "natural" bioscaffolds composed of decellularized tissues (i.e. ECM) will be replaced by bottom-up synthetic designer hydrogels that will provide very defined structural and signaling properties, potentially even opening up opportunities we currently do not envisage using natural materials.

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.

Encapsulation of Biological Agents in Hydrogels for Therapeutic Applications

Hydrogels are materials specially suited for encapsulation of biological elements. Their large water content provides an environment compatible with most biological molecules. Their crosslinked nature also provides an ideal material for the protection of encapsulated biological elements against degradation and/or immune recognition. This makes them attractive not only for controlled drug delivery of proteins, but they can also be used to encapsulate cells that can have therapeutic applications. Thus, hydrogels can be used to create systems that will deliver required therapies in a controlled manner by either encapsulation of proteins or even cells that produce molecules that will be released from these systems. Here, an overview of hydrogel encapsulation strategies of biological elements ranging from molecules to cells is discussed, with special emphasis on therapeutic applications.

Ex vivo biomechanical characterization of syringe-needle ejections for intracerebral cell delivery

Intracerebral implantation of cell suspensions is finding its clinical translation with encouraging results in patients with stroke. However, the survival of cells in the brain remains poor. Although the biological potential of neural stem cells (NSCs) is widely documented, the biomechanical effects of delivering cells through a syringe-needle remain poorly understood. We here detailed the biomechanical forces (pressure, shear stress) that cells are exposed to during ejection through different sized needles (20G, 26G, 32G) and syringes (10, 50, 250 µL) at relevant flow rates (1, 5, 10 µL/min). A comparison of 3 vehicles, Phosphate Buffered Saline (PBS), Hypothermosol (HTS), and Pluronic, indicated that less viscous vehicles are favorable for suspension with a high cell volume fraction to minimize sedimentation. Higher suspension viscosity was associated with greater shear stress. Higher flow rates with viscous vehicle, such as HTS reduced viability by ~10% and also produced more apoptotic cells (28%). At 5 µL/min ejection using a 26G needle increased neuronal differentiation for PBS and HTS suspensions. These results reveal the biological impact of biomechanical forces in the cell delivery process. Appropriate engineering strategies can be considered to mitigate these effects to ensure the efficacious translation of this promising therapy.

Engineering Hydrogel Microenvironments to Recapitulate the Stem Cell Niche

Stem cells are a powerful resource for many applications including regenerative medicine, patient-specific disease modeling, and toxicology screening. However, eliciting the desired behavior from stem cells, such as expansion in a naïve state or differentiation into a particular mature lineage, remains challenging. Drawing inspiration from the native stem cell niche, hydrogel platforms have been developed to regulate stem cell fate by controlling microenvironmental parameters including matrix mechanics, degradability, cell-adhesive ligand presentation, local microstructure, and cell-cell interactions. We survey techniques for modulating hydrogel properties and review the effects of microenvironmental parameters on maintaining stemness and controlling differentiation for a variety of stem cell types. Looking forward, we envision future hydrogel designs spanning a spectrum of complexity, ranging from simple, fully defined materials for industrial expansion of stem cells to complex, biomimetic systems for organotypic cell culture models.

Exploiting natural polysaccharides to enhance in vitro bio-constructs of primary neurons and progenitor cells

Current strategies in Central Nervous System (CNS) repair focus on the engineering of artificial scaffolds for guiding and promoting neuronal tissue regrowth. Ideally, one should combine such synthetic structures with stem cell therapies, encapsulating progenitor cells and instructing their differentiation and growth. We used developments in the design, synthesis, and characterization of polysaccharide-based bioactive polymeric materials for testing the ideal composite supporting neuronal network growth, synapse formation and stem cell differentiation into neurons and motor neurons. Moreover, we investigated the feasibility of combining these approaches with engineered mesenchymal stem cells able to release neurotrophic factors. We show here that composite bio-constructs made of Chitlac, a Chitosan derivative, favor hippocampal neuronal growth, synapse formation and the differentiation of progenitors into the proper neuronal lineage, that can be improved by local and continuous delivery of neurotrophins.

STATEMENT OF SIGNIFICANCE

In our work, we characterized polysaccharide-based bioactive platforms as biocompatible materials for nerve tissue engineering. We show that Chitlac-thick substrates are able to promote neuronal growth, differentiation, maturation and formation of active synapses. These observations support this new material as a promising candidate for the development of complex bio-constructs promoting central nervous system regeneration. Our novel findings sustain the exploitation of polysaccharide-based scaffolds able to favour neuronal network reconstruction. Our study shows that Chitlac-thick may be an ideal candidate for the design of biomaterial scaffolds enriched with stem cell therapies as an innovative approach for central nervous system repair.

Hydrogels-Assisted Cell Engraftment for Repairing the Stroke-Damaged Brain: Chimera or Reality

The use of advanced biomaterials as a structural and functional support for stem cells-based therapeutic implants has boosted the development of tissue engineering applications in multiple clinical fields. In relation to neurological disorders, we are still far from the clinical reality of restoring normal brain function in neurodegenerative diseases and cerebrovascular disorders. Hydrogel polymers show unique mechanical stiffness properties in the range of living soft tissues such as nervous tissue. Furthermore, the use of these polymers drastically enhances the engraftment of stem cells as well as their capacity to produce and deliver neuroprotective and neuroregenerative factors in the host tissue. Along this article, we review past and current trends in experimental and translational research to understand the opportunities, benefits, and types of tentative hydrogel-based applications for the treatment of cerebral disorders. Although the use of hydrogels for brain disorders has been restricted to the experimental area, the current level of knowledge anticipates an intense development of this field to reach clinics in forthcoming years.

ECM hydrogel for the treatment of stroke: Characterization of the host cell infiltrate

Brain tissue loss following stroke is irreversible with current treatment modalities. The use of an acellular extracellular matrix (ECM), formulated to produce a hydrogel in situ within the cavity formed by a stroke, was investigated as a method to replace necrotic debris and promote the infiltration of host brain cells. Based on magnetic resonance imaging measurements of lesion location and volume, different concentrations of ECM (0, 1, 2, 3, 4, 8 mg/mL) were injected at a volume equal to that of the cavity (14 days post-stroke). Retention of ECM within the cavity occurred at concentrations >3 mg/mL. A significant cell infiltration into the ECM material in the lesion cavity occurred with an average of ∼36,000 cells in the 8 mg/mL concentration within 24 h. An infiltration of cells with distances of >1500 μm into the ECM hydrogel was observed, but the majority of cells were at the tissue/hydrogel boundary. Cells were typically of a microglia, macrophage, or neural and oligodendrocyte progenitor phenotype. At the 8 mg/mL concentration, ∼60% of infiltrating cells were brain-derived phenotypes and 30% being infiltrating peripheral macrophages, polarizing toward an M2-like anti-inflammatory phenotype. These results suggest that an 8 mg/mL ECM concentration promotes a significant acute endogenous repair response that could potentially be exploited to treat stroke.

Engineered 3D Silk-collagen-based Model of Polarized Neural Tissue

Despite huge efforts to decipher the anatomy, composition and function of the brain, it remains the least understood organ of the human body. To gain a deeper comprehension of the neural system scientists aim to simplistically reconstruct the tissue by assembling it in vitro from basic building blocks using a tissue engineering approach. Our group developed a tissue-engineered silk and collagen-based 3D brain-like model resembling the white and gray matter of the cortex. The model consists of silk porous sponge, which is pre-seeded with rat brain-derived neurons, immersed in soft collagen matrix. Polarized neuronal outgrowth and network formation is observed with separate axonal and cell body localization. This compartmental architecture allows for the unique development of niches mimicking native neural tissue, thus enabling research on neuronal network assembly, axonal guidance, cell-cell and cell-matrix interactions and electrical functions.

In vitro bioengineered model of cortical brain tissue

A bioengineered model of 3D brain-like tissue was developed using silk-collagen protein scaffolds seeded with primary cortical neurons. The scaffold design provides compartmentalized control for spatial separation of neuronal cell bodies and neural projections, which resembles the layered structure of the brain (cerebral cortex). Neurons seeded in a donut-shaped porous silk sponge grow robust neuronal projections within a collagen-filled central region, generating 3D neural networks with structural and functional connectivity. The silk scaffold preserves the mechanical stability of the engineered tissues, allowing for ease of handling, long-term culture in vitro and anchoring of the central collagen gel to avoid shrinkage, and enabling neural network maturation. This protocol describes the preparation and manipulation of silk-collagen constructs, including the isolation and seeding of primary rat cortical neurons. This 3D technique is useful for mechanical injury studies and as a drug screening tool, and it could serve as a foundation for brain-related disease models. The protocol of construct assembly takes 2 d, and the resulting tissues can be maintained in culture for several weeks.

Profile analysis of hepatic porcine and murine brain tissue slices obtained with a vibratome

This study is aimed at characterizing soft tissue slices using a vibratome. In particular, the effect of two sectioning parameters (i.e., step size and sectioning speed) on resultant slice thickness was investigated for fresh porcine liver as well as for paraformaldehyde-fixed (PFA-fixed) and fresh murine brain. A simple framework for embedding, sectioning and imaging the slices was established to derive their thickness, which was evaluated through a purposely developed graphical user interface. Sectioning speed and step size had little effect on the thickness of fresh liver slices. Conversely, the thickness of PFA-fixed murine brain slices was found to be dependent on the step size, but not on the sectioning speed. In view of these results, fresh brain tissue was sliced varying the step size only, which was found to have a significant effect on resultant slice thickness. Although precision-cut slices (i.e., with regular thickness) were obtained for all the tissues, slice accuracy (defined as the match between the nominal step size chosen and the actual slice thickness obtained) was found to increase with tissue stiffness from fresh liver to PFA-fixed brain. This quantitative investigation can be very helpful for establishing the most suitable slicing setup for a given tissue.

Hydrogel design of experiments methodology to optimize hydrogel for iPSC-NPC culture

Bioactive signals can be incorporated in hydrogels to direct encapsulated cell behavior. Design of experiments methodology methodically varies the signals systematically to determine the individual and combinatorial effects of each factor on cell activity. Using this approach enables the optimization of three ligands concentrations (RGD, YIGSR, IKVAV) for the survival and differentiation of neural progenitor cells.

3D in vitro modeling of the central nervous system

There are currently more than 600 diseases characterized as affecting the central nervous system (CNS) which inflict neural damage. Unfortunately, few of these conditions have effective treatments available. Although significant efforts have been put into developing new therapeutics, drugs which were promising in the developmental phase have high attrition rates in late stage clinical trials. These failures could be circumvented if current 2D in vitro and in vivo models were improved. 3D, tissue-engineered in vitro systems can address this need and enhance clinical translation through two approaches: (1) bottom-up, and (2) top-down (developmental/regenerative) strategies to reproduce the structure and function of human tissues. Critical challenges remain including biomaterials capable of matching the mechanical properties and extracellular matrix (ECM) composition of neural tissues, compartmentalized scaffolds that support heterogeneous tissue architectures reflective of brain organization and structure, and robust functional assays for in vitro tissue validation. The unique design parameters defined by the complex physiology of the CNS for construction and validation of 3D in vitro neural systems are reviewed here.

Hyaluronic acid and neural stem cells: implications for biomaterial design

While in the past hyaluronic acid (HA) was considered a passive structural component, research over the past few decades has revealed its diverse and complex biological functions resulting in a major ideological shift. This review describes recent advances in biological interactions of HA with neural stem cells, with a focus on leveraging these interactions to develop advanced biomaterials that aid regeneration of the central nervous system.

Biomimetic niche for neural stem cell differentiation using poly-L-lysine/hyaluronic acid multilayer films

Polyelectrolyte multilayer films have been suggested as tunable substrates with flexible surface properties that can modulate cell behavior. However, these films’ biological effects on neural stem/progenitor cells have rarely been studied. Herein, biomimetic multilayer films composed of hyaluronic acid and poly-L-lysine were chosen to mimic the native extracellular matrix niche of brain tissue and were evaluated for their inductive effects, without the addition of chemical factors. Because neural stem/progenitor cells are sensitive to substrate properties, it is important that this system provides control over the surface charge, and slight stiffness variations are also possible. Both of these factors affect neural stem/progenitor cell differentiation. The results showed that neural stem/progenitor cells were induced to differentiate on the poly-L-lysine/hyaluronic acid multilayer films with 0.5–4 alternating layers. In addition, the neurite outgrowth length was regulated by the surface charge of the terminal layer but did not increase with the layer number. In contrast, the quantity of differentiated neurons was enhanced slightly as the number of layers increased but was not affected by the surface charge of the terminal layer. In sum, material pairs in the form of native poly-L-lysine/hyaluronic acid films achieved important targets for neural regenerative medicine, including enhancement of the neurite outgrowth length, regulation of neuron differentiation, and the formation of a network. These extracellular matrix–mimetic poly-L-lysine/hyaluronic acid multilayer films may provide a versatile platform that could be useful for surface modification for applications in neural engineering.