The enhancement of cell adherence and inducement of neurite outgrowth of dorsal root ganglia co-cultured with hyaluronic acid hydrogels modified with Nogo-66 receptor antagonist in vitro

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.

Innovations in 3-Dimensional Tissue Models of Human Brain Physiology and Diseases

3-dimensional (3D) laboratory tissue cultures have emerged as an alternative to traditional 2-dimensional (2D) culture systems that do not recapitulate native cell behavior. The discrepancy between in vivo and in vitro tissue-cell-molecular responses impedes understanding of human physiology in general and creates roadblocks for the discovery of therapeutic solutions. Two parallel approaches have emerged for the design of 3D culture systems. The first is biomedical engineering methodology, including bioengineered materials, bioprinting, microfluidics and bioreactors, used alone or in combination, to mimic the microenvironments of native tissues. The second approach is organoid technology, in which stem cells are exposed to chemical and/or biological cues to activate differentiation programs that are reminiscent of human (prenatal) development. This review article describes recent technological advances in engineering 3D cultures that more closely resemble the human brain. The contributions of in vitro 3D tissue culture systems to new insights in neurophysiology, neurological diseases and regenerative medicine are highlighted. Perspectives on designing improved tissue models of the human brain are offered, focusing on an integrative approach merging biomedical engineering tools with organoid biology.

CD44 expression in stem cells and niche microglia/macrophages following ischemic stroke

Background

CD44, an adhesion molecule in the hyaluronate receptor family, plays diverse and important roles in multiple cell types and organs. Increasing evidence is mounting for CD44 expression in various types of stem cells and niche cells surrounding stem cells. However, the precise phenotypes of CD44⁺ cells in the brain under pathologic conditions, such as after ischemic stroke, remain unclear.

Methods

In the present study, using a mouse model for cerebral infarction by middle cerebral artery (MCA) occlusion, we examined the localization and traits of CD44⁺ cells.

Results

In sham-mice operations, CD44 was rarely observed in the cortex of MCA regions. Following ischemic stroke, CD44⁺ cells emerged in ischemic areas of the MCA cortex during the acute phase. Although CD44 at ischemic areas was, in part, expressed in stem cells, it was also expressed in hematopoietic lineages, including activated microglia/macrophages, surrounding the stem cells. CD44 expression in microglia/macrophages persisted through the chronic phase following ischemic stroke.

Conclusions

These data demonstrate that CD44 is expressed in stem cells and cells in the niches surrounding them, including inflammatory cells, suggesting that CD44 may play an important role in reparative processes within ischemic areas under neuroinflammatory conditions; in particular, strokes.

Transplantation of Adipose Stromal Cell Sheet Producing Hepatocyte Growth Factor Induces Pleiotropic Effect in Ischemic Skeletal Muscle

Cell therapy remains a promising approach for the treatment of cardiovascular diseases. In this regard, the contemporary trend is the development of methods to overcome low cell viability and enhance their regenerative potential. In the present study, we evaluated the therapeutic potential of gene-modified adipose-derived stromal cells (ADSC) that overexpress hepatocyte growth factor (HGF) in a mice hind limb ischemia model. Angiogenic and neuroprotective effects were assessed following ADSC transplantation in suspension or in the form of cell sheet. We found superior blood flow restoration, tissue vascularization and innervation, and fibrosis reduction after transplantation of HGF-producing ADSC sheet compared to other groups. We suggest that the observed effects are determined by pleiotropic effects of HGF, along with the multifactorial paracrine action of ADSC which remain viable and functionally active within the engineered cell construct. Thus, we demonstrated the high therapeutic potential of the utilized approach for skeletal muscle recovery after ischemic damage associated with complex tissue degenerative effects.

Intracerebral Delivery of Brain-Derived Neurotrophic Factor Using HyStem®-C Hydrogel Implants Improves Functional Recovery and Reduces Neuroinflammation in a Rat Model of Ischemic Stroke

Ischemic stroke is a leading cause of death and disability worldwide. Potential therapeutics aimed at neural repair and functional recovery are limited in their blood-brain barrier permeability and may exert systemic or off-target effects. We examined the effects of brain-derived neurotrophic factor (BDNF), delivered via an extended release HyStem^®-C hydrogel implant or vehicle, on sensorimotor function, infarct volume, and neuroinflammation, following permanent distal middle cerebral artery occlusion (dMCAo) in rats. Eight days following dMCAo or sham surgery, treatments were implanted directly into the infarction site. Rats received either vehicle, BDNF-only (0.167 µg/µL), hydrogel-only, hydrogel impregnated with 0.057 µg/µL of BDNF (hydrogel + BDNF_LOW), or hydrogel impregnated with 0.167 µg/µL of BDNF (hydrogel + BDNF_HIGH). The adhesive removal test (ART) and 28-point Neuroscore (28-PN) were used to evaluate sensorimotor function up to two months post-ischemia. The hydrogel + BDNF_HIGH group showed significant improvements on the ART six to eight weeks following treatment and their behavioral performance was consistently greater on the 28-PN. Infarct volume was reduced in rats treated with hydrogel + BDNF_HIGH as were levels of microglial, phagocyte, and astrocyte marker immunoexpression in the corpus striatum. These data suggest that targeted intracerebral delivery of BDNF using hydrogels may mitigate ischemic brain injury and restore functional deficits by reducing neuroinflammation.

Assessment of degradation and biocompatibility of electrodeposited chitosan and chitosan-carbon nanotube tubular implants

Designing three-dimensional tubular materials made of chitosan is still a challenging task. Availability of such forms is highly desired by tissue engineering, especially peripheral nerve tissue engineering. Aiming at this problem, we use an electrodeposition phenomenon in order to obtain chitosan and chitosan-carbon nanotube hydrogel tubular implants. The in vitro biocompatibility of the fabricated structures is assessed using a mouse hippocampal cell line (mHippoE-18). As both implants do not induce significant cytotoxicity, they are next subjected to in vitro degradation studies in the environment simulating in vivo conditions for specified periods of time: 7, 14, and 28 days. The mass loss of implants indicates their stability at the tested time period; therefore, the materials are subcutaneously implanted in Sprague Dawley rats. The explants are collected after 7, 14, and 28 days. The assessment of composition and changes in tissues surrounding the implanted materials is made in respect to surrounding tissue thickness as well as the number of blood vessels, macrophages, lymphocytes, and neutrophils. No symptoms of acute inflammation are noticed at any point in time. The observed regular healing process allows concluding that both chitosan and chitosan-carbon hydrogel tubular implants are biocompatible with high application potential in tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2701-2711, 2016.

Self-assembling peptides for stem cell and tissue engineering

Regenerative medicine holds great potential to address many shortcomings in current medical therapies. An emerging avenue of regenerative medicine is the use of self-assembling peptides (SAP) in conjunction with stem cells to improve the repair of damaged tissues. The specific peptide sequence, mechanical properties, and nanotopographical cues vary widely between different SAPs, many of which have been used for the regeneration of similar tissues. To evaluate the potential of SAPs to guide stem cell fate, we extensively reviewed the literature for reports of SAPs and stem cell differentiation. To portray the most accurate summary of these studies, we deliberately discuss both the successes and pitfalls, allowing us to make conclusions that span the breadth of this exciting field. We also expand on these conclusions by relating these findings to the fields of nanotopography, mechanotransduction, and the native composition of the extracellular matrix in specific tissues to identify potential directions for future research.

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.

Improvements in biomaterial matrices for neural precursor cell transplantation

Progress is being made in developing neuroprotective strategies for traumatic brain injuries; however, there will never be a therapy that will fully preserve neurons that are injured from moderate to severe head injuries. Therefore, to restore neurological function, regenerative strategies will be required. Given the limited regenerative capacity of the resident neural precursors of the CNS, many investigators have evaluated the regenerative potential of transplanted precursors. Unfortunately, these precursors do not thrive when engrafted without a biomaterial scaffold. In this article we review the types of natural and synthetic materials that are being used in brain tissue engineering applications for traumatic brain injury and stroke. We also analyze modifications of the scaffolds including immobilizing drugs, growth factors and extracellular matrix molecules to improve CNS regeneration and functional recovery. We conclude with a discussion of some of the challenges that remain to be solved towards repairing and regenerating the brain.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

The Experimental Therapy on Brain Ischemia by Improvement of Local Angiogenesis with Tissue Engineering in the Mouse

Neural restoration has proven to be difficult after brain stroke, especially in its chronic stage. This is mainly due to the generation of an unpropitious niche in the injured area, including loss of vascular support but production of numerous inhibitors against neuronal regeneration. Reconstruction of a proper niche for promoting local angiogenesis, therefore, should be a key approach for neural restoration after stroke. In the present study, a new biomaterial composite that could be implanted in the injured area of the brain was created for experimental therapy of brain ischemia in the mouse. This composite was made using a hyaluronic acid (HA)-based biodegradable hydrogel scaffold, mixed with poly(lactic- co-glycolic acid) (PLGA) microspheres containing vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1), two factors that stimulate angiogenesis. In addition, the antibody of Nogo receptor (NgR-Ab), which can bind to multiple inhibitory myelin proteins and promote neural regeneration, was covalently attached to the hydrogel, making the hydrogel more bioactive and suitable for neural survival. This composite (HA–PLGA) was implanted into the mouse model with middle cerebral artery occlusion (MCAO) to explore a new approach for restoration of brain function after ischemia. A good survival and proliferation of human umbilical artery endothelial cells (HUAECs) and neural stem cells (NSCs) were seen on the HA hydrogel with PLGA microspheres in vitro. This new material was shown to have good compatibility with the brain tissue and inhibition to gliosis and inflammation after its implantation in the normal or ischemic brain of mice. Particularly, good angiogenesis was found around the implanted HA–PLGA hydrogel, and the mouse models clearly showed a behavioral improvement. The results in this present study indicate, therefore, that the HA–PLGA hydrogel is a promising material, which is able to induce angiogenesis in the ischemic region by releasing VEGF and Ang1, thus creating a suitable niche for neural restoration in later stages of stroke. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.

Scaffolds to promote spinal cord regeneration

Substantial research effort in the spinal cord injury (SCI) field is directed towards reduction of secondary injury changes and enhancement of tissue sparing. However, pathway repair after complete transections, large lesions, or after chronic injury may require the implantation of some form of oriented bridging structure to restore tissue continuity across a trauma zone. These matrices or scaffolds should be biocompatible and create an environment that facilitates tissue growth and vascularization, and allow axons to regenerate through and beyond the implant in order to reconnect with "normal" tissue distal to the injury. The myelination of regrown axons is another important requirement. In this chapter, we describe recent advances in biomaterial technology designed to provide a terrain for regenerating axons to grow across the site of injury and/or create an environment for endogenous repair. Many different types of scaffold are under investigation; they can be biodegradable or nondegradable, natural or synthetic. Scaffolds can be designed to incorporate immobilized signaling molecules and/or used as devices for controlled release of therapeutic agents, including growth factors. These bridging structures can also be infiltrated with specific cell types deemed suitable for spinal cord repair.

Hyaluronan, neural stem cells and tissue reconstruction after acute ischemic stroke

Focal stroke is a disabling disease with lifelong sensory, motor and cognitive impairments. Given the paucity of effective clinical treatments, basic scientists are developing novel options for protection of the affected brain and regeneration of lost tissue. Tissue bioengineering and stem/progenitor cell treatments have both been individually pursued for stroke neural repair therapies, with some benefit in tissue recovery. Emerging directions in stroke neural repair approaches combine these two therapies to use biopolymers with stem/progenitor transplants to promote greater cell survival in the transplant and directed delivery of bioactive molecules to the transplanted cells and the adjacent injured tissue. In this review the background literature on a combined use of neural stem/progenitor cells encapsulated in hyaluronan gels is discussed and the way this therapeutic approach can affect the important processes involved in brain tissue reconstruction, such as angiogenesis, axon regeneration, neural differentiation and inflammation is clarified. The glycosaminoglycan hyaluronan can optimize those processes and be employed in a successful neural tissue engineering approach.

Building biocompatible hydrogels for tissue engineering of the brain and spinal cord

Tissue engineering strategies employing biomaterials have made great progress in the last few decades. However, the tissues of the brain and spinal cord pose unique challenges due to a separate immune system and their nature as soft tissue. Because of this, neural tissue engineering for the brain and spinal cord may require re-establishing biocompatibility and functionality of biomaterials that have previously been successful for tissue engineering in the body. The goal of this review is to briefly describe the distinctive properties of the central nervous system, specifically the neuroimmune response, and to describe the factors which contribute to building polymer hydrogels compatible with this tissue. These factors include polymer chemistry, polymerization and degradation, and the physical and mechanical properties of the hydrogel. By understanding the necessities in making hydrogels biocompatible with tissue of the brain and spinal cord, tissue engineers can then functionalize these materials for repairing and replacing tissue in the central nervous system.

Hyaluronic acid-based scaffold for central neural tissue engineering

Central nervous system (CNS) regeneration with central neuronal connections and restoration of synaptic connections has been a long-standing worldwide problem and, to date, no effective clinical therapies are widely accepted for CNS injuries. The limited regenerative capacity of the CNS results from the growth-inhibitory environment that impedes the regrowth of axons. Central neural tissue engineering has attracted extensive attention from multi-disciplinary scientists in recent years, and many studies have been carried out to develop cell- and regeneration-activating biomaterial scaffolds that create an artificial micro-environment suitable for axonal regeneration. Among all the biomaterials, hyaluronic acid (HA) is a promising candidate for central neural tissue engineering because of its unique physico-chemical and biological properties. This review attempts to outline current biomaterials-based strategies for CNS regeneration from a tissue engineering point of view and discusses the main progresses in research of HA-based scaffolds for central neural tissue engineering in detail.

The role and mechanism of action of activin A in neurite outgrowth of chicken embryonic dorsal root ganglia

Activin A, a member of the transforming growth factor β (TGFβ) superfamily, plays an essential role in neuron survival as a neurotrophic and neuroprotective factor in the central nervous system. However, the effects and mechanisms of action of activin A on the neurite outgrowth of dorsal root ganglia (DRG) remain unclear. In the present study, we found that activin A is expressed in DRG collected from chicken embryos on embryonic day 8 (E8). Moreover, activin A induced neurite outgrowth of the primary cultured DRG and maintained the survival of monolayer-cultured DRG neurons throughout the observation period of ten days. Follistatin (FS), an activin-binding protein, significantly inhibited activin A-induced neurite outgrowth of DRG, but failed to influence the effect of nerve growth factor (NGF) on DRG neurite outgrowth. Furthermore, the results showed that activin A significantly upregulated mRNA expression of activin receptor type IIA (ActRIIA) and calcitonin gene-related peptide (CGRP) in DRG, and stimulated serotonin (5-HT) production from DRG, indicating that activin A might induce DRG neurite outgrowth by promoting CGRP expression and stimulating 5-HT release. These data suggest that activin A plays an important role in the development of DRG in an autocrine or paracrine manner.

Hydrogels in spinal cord injury repair strategies

Nowadays there are at present no efficient therapies for spinal cord injury (SCI), and new approaches have to be proposed. Recently, a new regenerative medicine strategy has been suggested using smart biomaterials able to carry and deliver cells and/or drugs in the damaged spinal cord. Among the wide field of emerging materials, research has been focused on hydrogels, three-dimensional polymeric networks able to swell and absorb a large amount of water. The present paper intends to give an overview of a wide range of natural, synthetic, and composite hydrogels with particular efforts for the ones studied in the last five years. Here, different hydrogel applications are underlined, together with their different nature, in order to have a clearer view of what is happening in one of the most sparkling fields of regenerative medicine.

Combination of hyaluronic acid hydrogel scaffold and PLGA microspheres for supporting survival of neural stem cells

PURPOSE

To develop a biomaterial composite for promoting proliferation and migration of neural stem cells (NSCs), as well as angiogenesis on the materials, to rescue central nervous system (CNS) injuries.

METHODS

A delivery system was constructed based on cross-linked hyaluronic acid (HA) hydrogels, containing embedded BDNF and VEGF-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres for controlled delivery and support for NSCs in the CNS. The surface morphologies were evaluated by SEM and AFM, mechanical property was investigated by rheological tests, and release kinetics were performed by ELISA. Bioactivity of released BDNF and VEGF was assessed by neuron and endothelial cell culture, respectively. Compatibility with NSCs was studied by immunofluorescent staining.

RESULTS

Release kinetics showed the delivery of BDNF and VEGF from PLGA microspheres and HA hydrogel composite were sustainable and stable, releasing ~20-30% within 150 h. The bioactivities preserved well to promote survival and growth of the cells. Evaluation of structure and mechanical properties showed the hydrogel composite possessed an elastic scaffold structure. Biocompatibility assay showed NSCs adhered and proliferated well on the hydrogel.

CONCLUSIONS

Our created HA hydrogel/PLGA microsphere systems have a good potential for controlled delivery of varied biofactors and supporting NSCs for brain repair and implantation.

The promotion of neural regeneration in an extreme rat spinal cord injury model using a collagen scaffold containing a collagen binding neuroprotective protein and an EGFR neutralizing antibody

In the treatment of spinal cord injury, implantation of scaffolding biomaterials and the addition of neuroprotective factors will promote neural regeneration. It has been demonstrated in our previous work that linear ordered collagen scaffold (LOCS) will bridge neural regeneration after the injury of spinal cord hemisection, and BDNF fused with a collagen binding domain (CBD-BDNF) can bind to collagen specifically to exert the neuroprotective effect. Besides neuroprotective factors, the lack of axon regeneration of the injured spinal cord has been attributed partially to regeneration inhibitors such as myelin associated proteins and chondroitin sulfate proteoglycans (CSPGs). Epidermal growth factor receptor (EGFR) activation is downstream of the signaling pathways of these inhibitors. Here, the monoclonal antibody, 151IgG that inhibits signaling of EGFR was used to neutralize EGFR. 151IgG was cross-linked to LOCS and CBD-BDNF bound to LOCS to make a triple-functional biomaterial for neural regeneration (bridging, prompting growth and neutralizing growth inhibitors). This triple-functional device was tested in a 6 mm transected SCI model. Results showed that this collagen scaffold with the addition of 151IgG and CBD-BDNF provided effective bridging and stimulation effects for neural regeneration, recovery of electrical transmission of synapses and preventing the formation of glial scars in the extreme transected rat SCI model.

Biomaterial design strategies for the treatment of spinal cord injuries

The highly debilitating nature of spinal cord injuries has provided much inspiration for the design of novel biomaterials that can stimulate cellular regeneration and functional recovery. Many experts agree that the greatest hope for treatment of spinal cord injuries will involve a combinatorial approach that integrates biomaterial scaffolds, cell transplantation, and molecule delivery. This manuscript presents a comprehensive review of biomaterial-scaffold design strategies currently being applied to the development of nerve guidance channels and hydrogels that more effectively stimulate spinal cord tissue regeneration. To enhance the regenerative capacity of these two scaffold types, researchers are focusing on optimizing the mechanical properties, cell-adhesivity, biodegradability, electrical activity, and topography of synthetic and natural materials, and are developing mechanisms to use these scaffolds to deliver cells and biomolecules. Developing scaffolds that address several of these key design parameters will lead to more successful therapies for the regeneration of spinal cord tissue.

Hydrogel matrix to support stem cell survival after brain transplantation in stroke

Stroke is a leading cause of adult disability. Stem/progenitor cell transplantation improves recovery after stroke in rodent models. These studies have 2 main limitations to clinical translation. First, most of the cells in stem/progenitor transplants die after brain transplantation. Second, intraparenchymal approaches target transplants to normal brain adjacent to the stroke, which is the site of the most extensive natural recovery in humans. Transplantation may damage this tissue. The stroke cavity provides an ideal target for transplantation because it is a compartmentalized region of necrosis, can accept a high volume transplant without tissue damage, and lies directly adjacent to the most plastic brain area in stroke. However, direct transplantation into the stroke cavity has caused massive death in the transplant. To overcome these limitations, the authors tested stem/progenitor transplants within a specific biopolymer hydrogel matrix to create a favorable environment for transplantation into the infarct cavity after stroke, and they tested this in comparison to stem cell injection without hydrogel support. A biopolymer hydrogel composed of cross-linked hyaluronan and heparin sulfate significantly promoted the survival of 2 different neural progenitor cell lines in vitro in conditions of stress and in vivo into the infarct cavity. Quantitative analysis of the transplant and surrounding tissue indicates diminished inflammatory infiltration of the graft with the hydrogel transplant. This result indicates that altering the local environment in stem cell transplantation enhances survival and diminishes cell stress. Stem cell transplantation into the infarct cavity within a pro-survival hydrogel matrix may provide a translational therapy for stroke recovery.

TAT-NEP1-40 as a novel therapeutic candidate for axonal regeneration and functional recovery after stroke

Currently available therapeutics has been less effective in promoting functional recovery from stroke or other injuries in the central nervous system (CNS). Axonal damage is a characteristic pathology seen in CNS injuries. Previously, it was reported that Nogo-A extracellular peptide residues 1-40 (NEP1-40), a competitive antagonist of Nogo-66 receptor (NgR1), has the ability to promote axonal regrowth and functional recovery after CNS injury. However, delivery of the therapeutic proteins into the brain parenchyma is limited due to its inability to cross the blood-brain barrier (BBB). We first generated a biologically active NEP1-40 fusion protein containing the protein transduction domain (PTD) of the transactivator of transcription (TAT), TAT-NEP1-40, which crosses the BBB in vivo after systemic delivery. The TAT-NEP1-40 can protect PC12 cells against oxygen and glucose deprivation (OGD) and promote neurite outgrowth when added exogenously to culture medium. The TAT-NEP1-40 protein transduced into the brain continued to sustain biological activities and protected the brain against ischemia/reperfusion injury through inhibition of neuronal apoptosis. Collectively, our data suggest that TAT-NEP1-40 may be a novel therapeutic candidate for axonal regeneration and functional recovery from CNS injuries such as cerebral hypoxia-ischemia, cerebral hemorrhage, brain trauma, and also for spinal cord injury.

Viability and differentiation of neural precursors on hyaluronic acid hydrogel scaffold

The traditional notion that injured neurons are unable to regenerate in the adult mammalian brain and spinal cord has long been a concern. This view has led to methodology designed to overcome this problem, most recently by advancements in tissue engineering. Here, neural precursor cells (NPCs) and the Nogo receptor antibody (NgR-Ab) or poly-L-lysine (PLL) were tested in concert with hyaluronic acid hydrogel scaffolds (HA). In particular, we wished to optimize viability and differentiation of NPCs within HA hydrogel scaffolds. Our results show that HA hydrogels can be modified physically or chemically to improve NPCs attachment on the scaffolding doped with NgR-Ab or PLL. Both the HA hydrogels and their modifications support the viability of NPCs. NPCs were also able to differentiate into neurons and glial cells on HA hydrogels, although this was affected by the different modifications. Immunofluorescence showed that fewer beta-III-tubulin antibody and antineurofilament antibody-positive cells were found on HA-PLL hydrogel compared with HA or HA NgR-Ab hydrogels. This indicates that the PLL-modified HA hydrogels may inhibit differentiation of NPCs, whereas modification by NgR-Ab had no such effect. Finally, the NgR-Ab-modified HA scaffold can be used as not only a NPC delivery system but also a bioactive factor transportation system for CNS repair.

Forever Young: How to Control the Elongation, Differentiation, and Proliferation of Cells Using Nanotechnology

Within the emerging field of stem cells there is a need for an environment that can regulate cell activity, to slow down differentiation or proliferation, in vitro or in vivo while remaining invisible to the immune system. By creating a nanoenvironment surrounding PC12 cells, Schwann cells, and neural precursor cells (NPCs), we were able to control the proliferation, elongation, differentiation, and maturation in vitro. We extended the method, using self-assembling nanofiber scaffold (SAPNS), to living animals with implants in the brain and spinal cord. Here we show that when cells are placed in a defined system we can delay their proliferation, differentiation, and maturation depending on the density of the cell population, density of the matrix, and the local environment. A combination of SAPNS and young cells can be implanted into the central nervous system (CNS), eliminating the need for immunosuppressants.

Hyaluronic Acid Hydrogel Modified with Nogo-66 Receptor Antibody and Poly(L-Lysine) Enhancement of Adherence and Survival of Primary Hippocampal Neurons

Hyaluronic acid (HA) hydrogel was modified with poly(L-lysine) (PLL) and Nogo-66 Receptor antibody (antiNgR) to enhance the repair of central nervous system (CNS) injuries. The immobilization of PLL was characterized by X-ray photoelectron spectroscopy (XPS) and the immobilization of antiNgR was studied by immunofluorescence. The cytocompatibility of this modified hydrogel was analyzed by culturing primary hippocampal neurons. The quantity and morphology of the neurons were influenced by different modifications; the primary hippocampal neurons cultured with modified HA hydrogel exhibited multipolar and bipolar morphology were compared with unmodified hydrogel cultures. The number of neurons obtained by culturing with HA hydrogel modified with both PLL and antiNgR was almost twice the number of neurons cultured with HA modified with only PLL or antiNgR. This phenomenon was attributed to the collaborative effect of PLL and antiNgR on the neurons. The characteristics of this new hydrogel system, including pore structure, water absorption, hydrolysis degradation did not change much when compared with the hydrogel modified with PLL or antiNgR, respectively. It is expected that this modified HA hydrogel has potential as a CNS tissue engineering material.

Implantation of neural stem cells embedded in hyaluronic acid and collagen composite conduit promotes regeneration in a rabbit facial nerve injury model

The implantation of neural stem cells (NSCs) in artificial scaffolds for peripheral nerve injuries draws much attention. NSCs were ex-vivo expanded in hyaluronic acid (HA)-collagen composite with neurotrophin-3, and BrdU-labeled NSCs conduit was implanted onto the ends of the transected facial nerve of rabbits. Electromyography demonstrated a progressive decrease of current threshold and increase of voltage amplitude in de-innervated rabbits after implantation for one, four, eight and 12 weeks compared to readouts derived from animals prior to nerve transection. The most remarkable improvement, observed using Electrophysiology, was of de-innervated rabbits implanted with NSCs conduit as opposed to de-innervated counterparts with and without the implantation of HA-collagen, NSCs and HA-collagen, and HA-collagen and neurotrophin-3. Histological examination displayed no nerve fiber in tissue sections of de-innervated rabbits. The arrangement and S-100 immunoreactivity of nerve fibers in the tissue sections of normal rabbits and injured rabbits after implantation of NSCs scaffold for 12 weeks were similar, whereas disorderly arranged minifascicles of various sizes were noted in the other three arms. BrdU+ cells were detected at 12 weeks post-implantation. Data suggested that NSCs embedded in HA-collagen biomaterial could facilitate re-innervations of damaged facial nerve and the artificial conduit of NSCs might offer a potential treatment modality to peripheral nerve injuries.

Enhanced neuronal differentiation in a three-dimensional collagen-hyaluronan matrix

Efficient 3D cell systems for neuronal induction are needed for future use in tissue regeneration. In this study, we have characterized the ability of neural stem/progenitor cells (NS/PC) to survive, proliferate, and differentiate in a collagen type I-hyaluronan scaffold. Embryonic, postnatal, and adult NS/PC were seeded in the present 3D scaffold and cultured in medium containing epidermal growth factor and fibroblast growth factor-2, a condition that stimulates NS/PC proliferation. Progenitor cells from the embryonic brain had the highest proliferation rate, and adult cells the lowest, indicating a difference in mitogenic responsiveness. NS/PC from postnatal stages down-regulated nestin expression more rapidly than both embryonic and adult NS/PC, indicating a faster differentiation process. After 6 days of differentiation in the 3D scaffold, NS/PC from the postnatal brain had generated up to 70% neurons, compared with 14% in 2D. NS/PC from other ages gave rise to approximately the same proportion of neurons in 3D as in 2D (9-26% depending on the source for NS/PC). In the postnatal NS/PC cultures, the majority of betaIII-tubulin-positive cells expressed glutamate, gamma-aminobutyric acid, and synapsin I after 11 days of differentiation, indicating differentiation to mature neurons. Here we report that postnatal NS/PC survive, proliferate, and efficiently form synapsin I-positive neurons in a biocompatible hydrogel.

Approaches to neural tissue engineering using scaffolds for drug delivery

This review seeks to give an overview of the current approaches to drug delivery from scaffolds for neural tissue engineering applications. The challenges presented by attempting to replicate the three types of nervous tissue (brain, spinal cord, and peripheral nerve) are summarized. Potential scaffold materials (both synthetic and natural) and target drugs are discussed with the benefits and drawbacks given. Finally, common methods of drug delivery, including degradable/diffusion-based delivery systems, affinity-based delivery systems, immobilized drug delivery systems, and electrically controlled drug delivery systems, are examined and critiqued. Based on the current body of work, suggestions for future directions of research in the field of neural tissue engineering are presented.

Polysaccharide hydrogels for modified release formulations

Hydrogels are three-dimensional, hydrophilic, polymeric networks, with chemical or physical cross-links, capable of imbibing large amounts of water or biological fluids. Among the numerous macromolecules that can be used for hydrogel formation, polysaccharides are extremely advantageous compared to synthetic polymers being widely present in living organisms and often being produced by recombinant DNA techniques. Coming from renewable sources, polysaccharides also have frequently economical advantages over synthetic polymers. Polysaccharides are usually non-toxic, biocompatible and show a number of peculiar physico-chemical properties that make them suitable for different applications in drug delivery systems. We review here a selection of the most important polysaccharides that have been studied and exploited in several fields related to pharmaceutics. Particular attention has been focused on the techniques used for the hydrogel network preparation, on the drug delivery results, on clinical applications as well as on the possible use of such systems as scaffolds for tissue engineering.

Potential of stem cell based therapy and tissue engineering in the regeneration of the central nervous system

The insufficiency of self-repair and regeneration of the central nervous system (CNS) leads to difficulty of rehabilitation of the injured brain. In the past few decades, the significant progress in cell therapy and tissue engineering has contributed to the functional recovery of the CNS to a great extent. The present review focuses on the potential role of stem cell based therapy and tissue engineering in the regeneration of the CNS.