Injectable uncrosslinked biomimetic hydrogels as candidate scaffolds for neural stem cell delivery

Expansion and differentiation of human neural stem cells on synthesized integrin binding peptide surfaces

The extracellular matrix plays a crucial role in the growth of human neural stem cells (hNSCs) by forming a stem cell niche, bothin vitroandin vivo. The demand for defined synthetic substrates has been increasing recently in stem cell research, reflecting the requirements for precise functions and safety concerns in potential clinical approaches. In this study, we tested the adhesion and expansion of one of the most representative hNSC lines, the ReNcell VM Human Neural Progenitor Cell Line, in a pure-synthesized short peptide-basedin vitroniche using a previously established integrin-binding peptide array. Spontaneous cell differentiation was then induced using two differentin vitroapproaches to further confirm the multipotent features of cells treated with the peptides. Twelve different integrin-binding peptides were capable of supporting hNSC adhesion and expansion at varied proliferation rates. In the ReNcell medium-based differentiation approach, cells detached in almost all peptide-based groups, except integrinα5β1 binding peptide. In an altered differentiation process induced by retinoic acid containing neural differentiation medium, cell adhesion was retained in all 12 peptide groups. These peptides also appeared to have varied effects on the differentiation potential of hNSCs towards neurons and astrocytes. Our findings provide abundant options for the development ofin vitroneural stem cell niches and will help develop promising tools for disease modeling and future stem cell therapies for neurological diseases.

Injectable Hydrogels for Nervous Tissue Repair-A Brief Review

The repair of nervous tissue is a critical research field in tissue engineering because of the degenerative process in the injured nervous system. In this review, we summarize the progress of injectable hydrogels using in vitro and in vivo studies for the regeneration and repair of nervous tissue. Traditional treatments have not been favorable for patients, as they are invasive and inefficient; therefore, injectable hydrogels are promising for the treatment of damaged tissue. This review will contribute to a better understanding of injectable hydrogels as potential scaffolds and drug delivery system for neural tissue engineering applications.

Strengthening the Key Features of Volumizing Fillers: Projection Capacity and Long-Term Persistence

Volumizing fillers aim to create or restore facial volume in fat layers. To provide strong tissue lifting and long-term persistence, gels are generally designed with stiff properties, characterized by a high storage modulus (G'). However, clinical evidence shows a discrepancy between high G' and good lifting capacities, especially after skin tension has been exerted on the gel. To better explore the in vivo behavior of a gel, we first evaluated the elastic moduli of five commercial volumizers (RHA4, JUVVOL, RESVOL, RESLYFT, and BELVOL) in dynamic compression mode, E'. We further developed a Projection Index score based on the rheological assessment of creep in compression to mimic skin tension-induced stress relaxation (flattening). Finally, the ability of a gel to resist enzymatic degradation was analyzed with a multidose approach. Despite similar clinical indications, volumizers exhibited distinct behaviors. RHA4 and BELVOL showed the highest E' values (resistance to strain), RHA4, JUVVOL, and RESVOL exhibited the greatest projection capacities, while JUVVOL and RHA4 offered the largest persistence to enzymatic degradation. In this article, we introduce the use of the Projection Index to efficiently assess the ability of a gel to lift tissues, thus increasing preclinical models' efficiency and reducing the need for animal studies.

Injectable pH Thermo-Responsive Hydrogel Scaffold for Tumoricidal Neural Stem Cell Therapy for Glioblastoma Multiforme

Glioblastoma multiforme (GBM) is the most common malignant brain tumor in adults and despite recent advances in treatment modalities, GBM remains incurable. Injectable hydrogel scaffolds are a versatile delivery system that can improve delivery of drug and cell therapeutics for GBM. In this report, we investigated an injectable nanocellulose/chitosan-based hydrogel scaffold for neural stem cell encapsulation and delivery. Hydrogels were prepared using thermogelling beta-glycerophosphate (BGP) and hydroxyethyl cellulose (HEC), chitosan (CS), and cellulose nanocrystals (CNCs). We evaluated the impact of neural stem cells on hydrogel gelation kinetics, microstructures, and degradation. Furthermore, we investigated the biomaterial effects on cell viability and functionality. We demonstrated that the incorporation of cells at densities of 1, 5 and 10 million does not significantly impact rheological and physical properties CS scaffolds. However, addition of CNCs significantly prolonged hydrogel degradation when cells were seeded at 5 and 10 million per 1 mL hydrogel. In vitro cell studies demonstrated high cell viability, release of TRAIL at therapeutic concentrations, and effective tumor cell killing within 72 h. The ability of these hydrogel scaffolds to support stem cell encapsulation and viability and maintain stem cell functionality makes them an attractive cell delivery system for local treatment of post-surgical cancers.

Advanced injectable hydrogels for cartilage tissue engineering

The rapid development of tissue engineering makes it an effective strategy for repairing cartilage defects. The significant advantages of injectable hydrogels for cartilage injury include the properties of natural extracellular matrix (ECM), good biocompatibility, and strong plasticity to adapt to irregular cartilage defect surfaces. These inherent properties make injectable hydrogels a promising tool for cartilage tissue engineering. This paper reviews the research progress on advanced injectable hydrogels. The cross-linking method and structure of injectable hydrogels are thoroughly discussed. Furthermore, polymers, cells, and stimulators commonly used in the preparation of injectable hydrogels are thoroughly reviewed. Finally, we summarize the research progress of the latest advanced hydrogels for cartilage repair and the future challenges for injectable hydrogels.

Fractone Stem Cell Niche Components Provide Intuitive Clues in the Design of New Therapeutic Procedures/Biomatrices for Neural Repair

The aim of this study was to illustrate recent developments in neural repair utilizing hyaluronan as a carrier of olfactory bulb stem cells and in new bioscaffolds to promote neural repair. Hyaluronan interacts with brain hyalectan proteoglycans in protective structures around neurons in perineuronal nets, which also have roles in the synaptic plasticity and development of neuronal cognitive properties. Specialist stem cell niches termed fractones located in the sub-ventricular and sub-granular regions of the dentate gyrus of the hippocampus migrate to the olfactory bulb, which acts as a reserve of neuroprogenitor cells in the adult brain. The extracellular matrix associated with the fractone stem cell niche contains hyaluronan, perlecan and laminin α5, which regulate the quiescent recycling of stem cells and also provide a means of escaping to undergo the proliferation and differentiation to a pluripotent migratory progenitor cell type that can participate in repair processes in neural tissues. Significant improvement in the repair of spinal cord injury and brain trauma has been reported using this approach. FGF-2 sequestered by perlecan in the neuroprogenitor niche environment aids in these processes. Therapeutic procedures have been developed using olfactory ensheathing stem cells and hyaluronan as a carrier to promote neural repair processes. Now that recombinant perlecan domain I and domain V are available, strategies may also be expected in the near future using these to further promote neural repair strategies.

Increased connectivity of hiPSC-derived neural networks in multiphase granular hydrogel scaffolds

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 μm) after seven days compared to bulk hydrogels (22.90 ± 4.70 μm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures.

Relationship between Structure and Rheology of Hydrogels for Various Applications

Hydrogels have gained a lot of attention with their widespread use in different industrial applications. The versatility in the synthesis and the nature of the precursor reactants allow for a varying range of hydrogels with different mechanical and rheological properties. Understanding of the rheological behavior and the relationship between the chemical structure and the resulting properties is crucial, and is the focus of this review. Specifically, we include detailed discussion on the correlation between the rheological characteristics of hydrogels and their possible applications. Different rheological tests such as time, temperature and frequency sweep, among others, are described and the results of those tests are reported. The most prevalent applications of hydrogels are also discussed.

Evaluation of the Effect of Hyaluronic Acid-Based Biomaterial Enriched With Tenascin-C on the Behavior of the Neural Stem Cells

One of the most important natural extracellular constituents is hyaluronic acid (HA) with the potential to develop a highly organized microenvironment. In the present study, we enriched HA hydrogel with tenascin-C (TN-C) and examined the viability and survival of mouse neural stem cells (NSCs) using different biological assays. Following NSCs isolation and expansion, their phenotype was identified using flow cytometry analysis. Cell survival was measured using MTT assay and DAPI staining after exposure to various concentrations of 50, 100, 200, and 400 nM TN-C. Using acridine orange/ethidium bromide staining, we measured the number of live and necrotic cells after exposure to the combination of HA and TN-C. MTT assay revealed the highest NSCs viability rate in the group exposed to 100 nM TN-C compared to other groups, and a combination of 1% HA + 100 nM TN-C increased the viability of NSCs compared to the HA group after 24 hours. Electron scanning microscopy revealed the higher attachment of these cells to the HA + 100 nM TN-C substrate relative to the HA substrate. Epifluorescence imaging and DAPI staining of loaded cells on HA + 100 nM TN-C substrate significantly increased the number of NSCs per field over 72 hours compared to the HA group (P < 0.05). Live and dead assay revealed that the number of live NSCs significantly increased in the HA + 100 TN-C group compared to HA and control groups. The enrichment of HA substrate with TN-C promoted viability and survival of NSCs and could be applied in neural tissue engineering approaches and regenerative medicine.

Composition and Mechanism of Three-Dimensional Hydrogel System in Regulating Stem Cell Fate

Three-dimensional (3D) hydrogel systems integrating different types of stem cells and scaffolding biomaterials have an important application in tissue engineering. The biomimetic hydrogels that pattern cell suspensions within 3D configurations of biomaterial networks allow for the transport of bioactive factors and mimic the stem cell niche in vivo, thereby supporting the proliferation and differentiation of stem cells. The composition of a 3D hydrogel system determines the physical and chemical characteristics that regulate stem cell function through a biological mechanism. Here, we discuss the natural and synthetic hydrogel compositions that have been employed in 3D scaffolding, focusing on their characteristics, fabrication, biocompatibility, and regulatory effects on stem cell proliferation and differentiation. We also discuss the regulatory mechanisms of cell-matrix interaction and cell-cell interaction in stem cell activities in various types of 3D hydrogel systems. Understanding hydrogel compositions and their cellular mechanisms can yield insights into how scaffolding biomaterials and stem cells interact and can lead to the development of novel hydrogel systems of stem cells in tissue engineering and stem cell-based regenerative medicine. Impact statement Three-dimensional hydrogel system of stem cell mimicking the stemcell niche holds significant promise in tissue engineering and regenerative medicine. Exactly how hydrogel composition regulates stem cell fate is not well understood. This review focuses on the composition of hydrogel, and how the hydrogel composition and its properties regulate the stem cell adhesion, growth, and differentiation. We propose that cell-matrix interaction and cell-cell interaction are important regulatory mechanisms in stem cell activities. Our review provides key insights into how the hydrogel composition regulates the stem cell fate, untangling the engineering of three-dimensional hydrogel systems for stem cells.

Biomimetic Nanomembranes: An Overview

Nanomembranes are the principal building block of basically all living organisms, and without them life as we know it would not be possible. Yet in spite of their ubiquity, for a long time their artificial counterparts have mostly been overlooked in mainstream microsystem and nanosystem technologies, being a niche topic at best, instead of holding their rightful position as one of the basic structures in such systems. Synthetic biomimetic nanomembranes are essential in a vast number of seemingly disparate fields, including separation science and technology, sensing technology, environmental protection, renewable energy, process industry, life sciences and biomedicine. In this study, we review the possibilities for the synthesis of inorganic, organic and hybrid nanomembranes mimicking and in some way surpassing living structures, consider their main properties of interest, give a short overview of possible pathways for their enhancement through multifunctionalization, and summarize some of their numerous applications reported to date, with a focus on recent findings. It is our aim to stress the role of functionalized synthetic biomimetic nanomembranes within the context of modern nanoscience and nanotechnologies. We hope to highlight the importance of the topic, as well as to stress its great applicability potentials in many facets of human life.

Impact of composite scaffold degradation rate on neural stem cell persistence in the glioblastoma surgical resection cavity

Tumoricidal neural stem cells (NSCs) are an emerging therapy to combat glioblastoma (GBM). This therapy employs genetically engineered NSCs that secrete tumoricidal agents to seek out and kill tumor foci remaining after GBM surgical resection. Biomaterial scaffolds have previously been utilized to deliver NSCs to the resection cavity. Here, we investigated the impact of scaffold degradation rate on NSC persistence in the brain resection cavity. Composite acetalated dextran (Ace-DEX) gelatin electrospun scaffolds were fabricated with two distinct degradation profiles created by changing the ratio of cyclic to acyclic acetal coverage of Ace-DEX. In vitro, fast degrading scaffolds were fully degraded by one week, whereas slow degrading scaffolds had a half-life of >56 days. The scaffolds also retained distinct degradation profiles in vivo. Two different NSC lines readily adhered to and remained viable on Ace-DEX gelatin scaffolds, in vitro. Therapeutic NSCs secreting tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) had the same TRAIL output as tissue culture treated polystyrene (TCPS) when seeded on both scaffolds. Furthermore, secreted TRAIL was found to be highly potent against the human derived GBM cell line, GBM8, in vitro. Firefly luciferase expressing NSCs were seeded on scaffolds, implanted in a surgical resection cavity and their persistence in the brain was monitored by bioluminescent imaging (BLI). NSC loaded scaffolds were compared to a direct injection (DI) of NSCs in suspension, which is the current clinical approach to NSC therapy for GBM. Fast and slow degrading scaffolds enhanced NSC implantation efficiency 2.87 and 3.08-fold over DI, respectively. Interestingly, scaffold degradation profile did not significantly impact NSC persistence. However, persistence and long-term survival of NSCs was significantly greater for both scaffolds compared to DI, with scaffold implanted NSCs still detected by BLI at day 120 in most mice. Overall, these results highlight the benefit of utilizing a scaffold for application of tumoricidal NSC therapy for GBM.

Effects of Collagenase Type II on Vitreous Humor—An In Situ Rheological Study

The purpose of this study is to quantify the impact of enzyme activity on the vitreous humor structure over time to understand the mechanical characteristics of the vitreous humor gel. Changes in the mechanical behavior of the vitreous occur due to many reasons including aging, which may lead to many vitreoretinal diseases. The degeneration process of the vitreous has been studied; however, in situ experimental procedures to validate the existing hypotheses are limited. We examined thirty-eight porcine eyes using in situ rheological creep tests to measure the mechanical properties of the vitreous humor of the eyes prior to, 1 h and 24 h after the intravitreal injection. Eyes in one group were injected with collagenase type II solution and eyes in the control group were injected with phosphate buffered saline solution (PBS) with calcium and magnesium chloride. Prior to the injection, viscosity and creep compliance intercept values between both groups were not statistically different. At 1 h and 24 h after the injection, vitreous properties in the eyes from the first group showed a statistically significant increase in the J intercept values (representing the inverse of elasticity) compared to the control group. In addition, 1 h and 24 h after the injection, vitreous viscosity was lower in the eyes from the first group than in the eyes from the control group. These findings are a foundation for future studies on the effectiveness of intravitreal drugs that modify the mechanical properties of the vitreous humor.

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.

Enhancement of neural stem cell survival, proliferation and differentiation by IGF-1 delivery in graphene oxide-incorporated PLGA electrospun nanofibrous mats

The mammalian central nervous system has a limited ability for self-repair under injury conditions.

Simple Synthetic Molecular Hydrogels from Self-Assembling Alkylgalactonamides as Scaffold for 3D Neuronal Cell Growth

In this work, we demonstrated that the hydrogel obtained from a very simple and single synthetic molecule, N-heptyl-galactonamide was a suitable scaffold for the growth of neuronal cells in 3D. We evidenced by confocal microscopy the presence of the cells into the gel up to a depth of around 200 μm, demonstrating that the latter was permissive to cell growth and enabled a true 3D colonization and organization. It also supported successfully the differentiation of adult human neuronal stem cells (hNSCs) into both glial and neuronal cells and the development of a really dense neurofilament network. So the gel appears to be a good candidate for neural tissue regeneration. In contrast with other molecular gels described for cell culture, the molecule can be obtained at the gram scale by a one-step reaction. The resulting gel is very soft, a quality in accordance with the aim of growing neuronal cells, that requires low modulus substrates similar to the brain. But because of its fragility, specific procedures had to be implemented for its preparation and for cell labeling and confocal microscopy observations. Notably, the implementation of a controlled slow cooling of the gel solution was needed to get a very soft but nevertheless cohesive gel. In these conditions, very wide straight and long micrometric fibers were formed, held together by a second network of flexible narrower nanometric fibers. The two kinds of fibers guided the neurite and glial cell growth in a different way. We also underlined the importance of a tiny difference in the molecular structure on the gel performances: parent molecules, differing by a one-carbon increment in the alkyl chain length, N-hexyl-galactonamide and N-octyl-galactonamide, were not as good as N-heptyl-galactonamide. Their differences were analyzed in terms of gel fibers morphology, mechanical properties, solubility, chain parity, and cell growth.

Novel biomaterials to study neural stem cell mechanobiology and improve cell-replacement therapies

Neural stem cells (NSCs) are a valuable cell source for tissue engineering, regenerative medicine, disease modeling, and drug screening applications. Analogous to other stem cells, NSCs are tightly regulated by their microenvironmental niche, and prior work utilizing NSCs as a model system with engineered biomaterials has offered valuable insights into how biophysical inputs can regulate stem cell proliferation, differentiation, and maturation. In this review, we highlight recent exciting studies with innovative material platforms that enable narrow stiffness gradients, mechanical stretching, temporal stiffness switching, and three-dimensional culture to study NSCs. These studies have significantly advanced our knowledge of how stem cells respond to an array of different biophysical inputs and the underlying mechanosensitive mechanisms. In addition, we discuss efforts to utilize engineered material scaffolds to improve NSC-based translational efforts and the importance of mechanobiology in tissue engineering applications.

The role of nanomaterials in cell delivery systems

In more than one decade, cell transplantation has created an important strategy to treat a wide variety of diseases characterized by tissue and cell dysfunctions. In this course of action, cell delivery to target site has been always one of the most important constraints and complications, as only a small proportion of the cells are housed in the target sites. Nanotechnology and nanoscale biomaterials have been helpful for cell transplantation in various fields of regenerative medicine including diagnosis, delivery systems for the cell, drug or gene, and cells protection system. In this study, the basic concepts and recently studied aspects of cell delivery systems based on nanoscale biomaterials for transplantation and clinical applications are highlighted. Nanomaterials may be used in combination with cell therapy to control the release of drugs or special factors of engineered cells after transplantation.

PTMAc-PEG-PTMAc hydrogel modified by RGDC and hyaluronic acid promotes neural stem cells' survival and differentiation in vitro

The enhancement of the biological properties of hydrogels by surface modifying with bioactive molecules is of great significance, especially for the treatment of central nervous system injury by combining engrafted cells.