Skip to main content


Improvements in biomaterial matrices for neural precursor cell transplantation

Article metrics

  • 3407 Accesses

  • 16 Citations


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.


Tissue engineering (TE) is a relatively new and expanding field. Using principles from material engineering and molecular biology, tissue engineers develop organic substitutes to support or replace portions of malfunctioning tissues or organs [1]. These substitutes are commonly created using living cells, biomaterial scaffolding and signaling molecules [2]. Studies have shown that cell replacement and tissue repair is improved when engrafted cells are delivered on a biomaterial scaffold. This is because a scaffold can provide structural support for the cells as well as carry necessary factors that enhance their survival and function. TE has been investigated in a variety of organs and is an area of active investigation for central nervous system (CNS) repair. TE for brain injury has not been as widely explored — likely due to the complexity of central neural circuitry. TE has recently gained in popularity with the realization that transplanting stem cells with a biomaterial substrate is more effective. In this article we review progress to date employing TE to promote cell replacement using neural precursors (NPs) to restore neurological function after traumatic brain injuries and stroke. The therapeutic value in transplanting neural precursors is extremely high due to the inability of neurons to undergo mitosis and the incapacity of the brain to repair large injuries on its own.

Brain injuries

Approximately 1.7 million Americans sustain traumatic brain injuries (TBI) each year as a result of falls, motor vehicle accidents, being struck by objects or assaults. An additional 800,000 individuals are affected by stroke, of which 80% are ischemic and are of varying severity. These numbers do not include major brain injuries caused by infections, tumors or other CNS diseases that account for another large population. Brain injuries are generally classified as mild, moderate or severe depending on the damage sustained. The majority of TBIs are mild, resulting in a change in mental status or state of consciousness. Severe brain injuries may cause amnesia, long periods of unconsciousness, irreversible changes in cognitive (attention and memory), motor (coordination, balance, and limb weakness/paralysis) and sensorimotor function (vision, hearing, and touch), alteration in emotions (anxiety, depression, and personality changes) and sometimes death [3, 4].


Individuals who do not die within the first few months after sustaining a severe brain injury are often left with disabilities and a poor prognosis for the duration of their lives. The acute affects can be observed within the first hours after injury and can be amplified within the first several weeks, generally attributed to the pro-inflammatory response to the injury that can last for months or years [5]. Neuronal damage and cell loss have been extensively documented and characterized in the cerebral cortex, the hippocampus and the thalamus in the acute phase following experimental brain injury [69]. The primary damage created by mechanical forces at the moment of the impact is irreversible. In response, immune cells are recruited to the damaged site, whereupon they release cytokines and chemokines triggering a neuroinflammatory reaction that produces a wave of secondary cell death. After a delay, the astrocytes surrounding the injury begin to produce a glial scar. Once formed, this scar tissue creates an inhibitory environment eliminating the possibilities of axonal regeneration due to the formation of a complex extracellular matrix (ECM) [1012]. This prolonged and progressive pathologic cascade becomes the basis for the deficits in cognitive and motor function that begin in the first hours after TBI and may continue for years.


After a person sustains an injury, the medical team will provide resuscitation procedures, and stabilize vital functions to minimize secondary damage to the brain. Mechanical ventilation is used to support respiration and to maintain lower intracranial pressure. Sensory devices may be surgically placed into the brain cavity to monitor or control intracranial pressure. Surgery may be required to repair hemorrhaged arteries or to eliminate blood clots. Blood, fluid and bone particles can be removed while damaged tissue, blood vessels or the skull can be surgically remodeled in severe cases where there is extensive swelling. Patients are also kept sedated with medications to prevent them from causing any additional injury and to prevent seizures and spasticity. Doctors try to maximize cerebral perfusion pressure and blood flow (which includes oxygen and nutrients being supplied to the brain) while minimizing the swelling caused by pressure that may damage more cells [13, 14]. Pharmaceutical agents also may be used to limit secondary damage to the brain which include: diuretics to reduce edema thus decreasing pressure; anti-seizure drugs to avoid additional brain damage; and coma-inducing drugs because a comatosed brain requires less oxygen to function [15]. Other medications such as analgesics, anti-anxiety agents, anti-depressants, anti-psychotics, muscle relaxants, sedatives and stimulants are also commonly utilized in patients sustaining TBI [16]. To date, however, there are no therapies capable of replacing the neurons lost to brain injuries, thus making full functional recovery after severe TBI impossible.

Endogenous stem cells

The brain is arguably the most difficult organ to repair after an injury due to the complexity of network of cells that comprise the central nervous system. Its capacity to regenerate is complicated by the inability of neurons to undergo mitosis. Scientists have tried to expand the endogenous stem cells found inside the brain to repair damage after CNS injury. Despite significant work, several problems still exist with this approach. First, few neurons are generated in response to injury, as the vast majority of the new cells that are produced become glia. While infants have significantly larger numbers of neural stem cells (NSCs) than adults, and thus greater potential for repair [17, 18], the NSCs of the immature brain simply do not produce many new neurons after TBI (Goodus et al., Submitted). Another barrier to regeneration from the endogenous stem cells of the brain is that the pools of NSCs are depleted with age [19].

These observations hold for several different CNS injury models. Arvidsson et al. [20] researched the mechanisms of neuronal repair after stroke in an adult rat model and reported that less than 1% of the destroyed neurons are replaced from the endogenous neural precursors (NPs) of the subventricular zone (SVZ). Similar results were obtained in rat models of stroke in the immature animal where cell counts of immature neurons vs. mature neurons revealed that greater than 75% of the newly produced neurons failed to survive. Moreover, of those neurons that did survive, they were predominantly GABAergic interneurons [21, 22]. In a mouse model of TBI the same pattern was seen [23]. Salman et al. [23] found that SVZ cells proximal to the injured area produced a very small percentage of new neurons (not quantified), while the majority became astrocytes. Whether the newly generated neurons died at the injury site or failed to migrate from the SVZ to the damaged region is unclear. However, it is known that in the adult brain, neural progenitors have a difficult time migrating to the injured cortex due to dense white matter tracts [24].

Researchers are looking at pharmacological means to generate a more robust response from SVZ precursors, to stimulate their proliferation, increase their migration to the affected sites and to increase their production of region-appropriate neurons. Major advancements have yet to be made; therefore, alternative solutions have been sought by a number of groups.

Transplanting exogenous stem cells

Given the limitations of the endogenous NSCs, transplanting exogenous NPs into the injured brain has gained traction as a more appropriate solution to promote CNS regeneration. Yet this raises the issue of which cell type to transplant. Since brain injuries result in the demise of a range of different neuronal cell types as well as the astrocytes and oligodendrocytes that support them, the ideal cell would be one that has the capacity to produce a large repertoire of different neurons and glia. A benefit of transplanting a stem cell is that a stem cell can produce a large number of progeny that are capable of integrating into many regions as neurons and glia to replace missing or dysfunctional neural cells [2528]. To date, several types of CNS progenitors as well as several neural stem cell lines have been transplanted into the injured brain. Cells possessing the properties of neurons have been observed, however, it is important to note that a significant proportion, regardless of the starting precursor, express the biochemical and phenotypic characteristics of glia [2938]. Both progenitor and stem cell grafts have been shown to improve functional outcome following TBI [3942] and in experimental stroke [4349]. Generally speaking, studies that transplanted progenitors or more differentiated cells have been less successful than studies using neural stem cells in replacing or rebuilding a neural circuit. Although there is no study directly comparing neuron, progenitor and stem cell transplantations, the vast majority of research on CNS regeneration focuses on the use of stem cell or early progenitor therapies. Lineage progression from a stem cell to a mature neuron is a process in which proliferation, migration and multipotential capacity decreases. Bliss et al. [50], transplanted human post-mitotic neurons (from hNT cell line derived from human teratocarcinoma) into a rat model of stroke and noticed low donor cell survival [51]. Although they saw neurite extension from hNT neurons, there was no migration. Conversely, transplanted stem cells have shown excellent migration to lesions even when transplanted into the contralateral hemisphere [5153]. Poor cell survival in the cell preparation and during the transplantation process has been noted, especially when transplanting more committed cells into the unwelcoming milieu of a focal neocortical injury. Thus stem cell transplantation studies are more commonly observed in CNS therapeutics, whereas neurons and more differentiated cell types are generally avoided. Bone marrow stromal cells have been shown to improve outcome after brain injury and stroke [5463], but the evidence suggests that the functional improvements obtained are not a result of cell replacement but are due to secreted factors that are neuroprotective.

Immortalized multipotent stem cell lines, such as C17.2 (immortalized mouse neural progenitor cell line), HiB5 (rat hippocampal stem cell line) and MHP-36 (murine neural stem cell line), which display properties of stem cells, have been successfully transplanted into rodents subjected to either ischemic or contusive injuries [6466]. Upon directly transplanting these cell lines each engrafted and migrated preferentially to areas with active neurodegeneration [6770]. HiB5 is an immortalized cell line from embryonic day 16 rat hippocampus. Philips et al. [71] transplanted HiB5 cells into the brain one week following fluid percussion brain injury and reported that they reduced cell death in the CA3 region of the hippocampus. MHP-36 is an immortalized mouse hippocampal neuroepithelial stem cell line derived from embryonic day 14 heterozygous H-2Kb-tsA58 transgenic mice (a mouse line containing an inducible Class I antigen transgene). When grafted into rat brains 2–3 weeks after global ischemia or excitotoxic hippocampal injury, MHP-36 cells migrated, improved motor and sensory function and repopulated the lesioned CA1 hippocampal region [7275]. Sinden et al. and Riess et al. transplanted MHP-36 cells after hypoxia/ischemia and fluid percussion injury respectively [41]. Sinden observed a reduction in lesion size after transplantation while Riess noticed a decrease in learning deficits that correlated with the migration of MHP-36 cells to the injury site [76]. Despite these encouraging results, the MHP-36 cells cause a profound inflammatory response [74].

Studies have also shown that these cell lines, including the immortalized C-17.2 cell, can produce tumors when transplanted following TBI [77]; thus, the likelihood that immortalized stem cell lines might ever be used to treat patients is low. Therefore, many researchers have evaluated grafting primary fetal and early postnatal neural stem cells into the adult CNS to repair the brain after injury. The rationale for using primary cells is that in the future it may be possible to derive similar donor cells from human embryonic stem cells (ESC) or induced pluripotent stem cells (iPSC). Transplanting primary NPs has shown promise as many groups have demonstrated the ability to achieve engraftment and differentiation. Hoane et al. [78] and Gao et al. [79] have reported differentiation of rodent NPs into neurons, and these cells survived one year post-transplantation into the brain. Even though a significant improvement in cognitive recovery was not evident, the researchers did observe greater sensorimotor recovery in these rodents. Calcagnotto et al. [80], transplanted cells from the mouse medial ganglionic eminences (MGE), and demonstrated that these NPs migrated and differentiated into cortical GABAergic interneurons. Local pyramidal neurons were patched and electrophysiological recordings indicated functional integration of the transplanted MGE cells into the host tissue.

These experimental studies suggest that many obstacles have been overcome in the grand quest to heal TBI with exogenous cell transplants, but the extent of neuronal cell replacement has still been variable and few of transplanted cells are retained [81, 82]. Most of the transplanted cells either do not survive [8385] or differentiate into glial cells instead of neurons [52, 8688]. This is a concern that the stem cells transplanted do not differentiate into reactive astrocytes that can contribute to glial scarring. Shear et al. [87] and Boockvar et al. [52], found that NG2 positive glial cells were produced upon transplanting NPs and Sun et al. [88], observed that the majority of the precursors that they transplanted became Olig2 positive cells (presumably glia). Ma et al. [86], transplanted NPs (comprised of 4% NSCs) and reported that only 11% of the differentiated cells expressed a neuronal marker. We have generated data that parallel these findings, once again obtaining poor survival of NPs when transplanted directly into the parenchyma following TBI [89]. A new technique or paradigm for overcoming these problems associated with NP transplantation is necessary.

Brain tissue engineering

A focal traumatic brain injury results in a large number of dead cells and debris that are localized near the region of impact. Macrophages clear away the remnants of dead or dying cells, but the injury creates a harsh, non-permissive environment that lacks nutrients, survival factors and most importantly, a habitable substrate and the extracellular matrix (ECM) that they once resided within [14, 39, 40, 90]. This ECM is a scaffold that provides cells with structural and functional support. It is comprised of interconnected proteins and proteoglycans that create a framework that cells adhere to. Attachment to the individual components of this matrix transduces mechanical signals that regulate both basic and complex cellular processes. The proteins and proteoglycans that comprise the ECM bind to a number of surface receptors found on cells that can affect proliferation, migration, differentiation, survival and other functions [9194]. Although reactive astrocytes produce ECM molecules in the process of generating the glial scar, this ECM is distinctly different from the normal ECM in the brain functionally, chemically and mechanically [95].

Scaffolds are three-dimensional artificial structures that are created to recapitulate the in vivo milieu providing cells with an appropriate microenvironment. Since brain injuries vary in shape and size, scaffolds that form after injection into the wound cavity allow for a one-size-fits-all solution. Several factors must be considered when creating a scaffold for a particular biological application. In the pursuit of the ideal biomaterial design a wish list of desirable functions can be created. The wish list should include:

  • The scaffold must be nontoxic and biocompatible with transplantable cells. This means that the scaffold should not adversely affect cell function or cell survival.

  • The scaffold must be biocompatible with the brain tissue environment. The scaffold should not elicit a damaging immune response, be toxic, carcinogenic, or adversely affect the survival of the host cells. Upon degradation the scaffold should not generate toxic, corrosive or acidic byproducts.

  • The scaffold can maintain the “stemness” of the transplanted cells. Indeed, because stem cells require fewer survival factors than committed cells [96], a transplanted stem cell, as opposed to a committed cell or a differentiated precursor, might stand a better chance of surviving transplantation. Stemness can be maintained by including ligands that will promote self-renewal and proliferation while simultaneously decreasing differentiation.

  • Biodegradation of the scaffold should be controlled. This rate should be designed to mirror the proliferation and growth of the transplanted cells. In essence, as cells begin to fill the void created by an injury, the implanted support structure should degrade in such a fashion that it remains available while the engrafted cells continue to grow. Importantly, were the scaffold to remain intact it could increase in intracranial pressure, inflammation and fibrous encapsulation with adverse effects.

  • The scaffold should be injectable. Furthermore, brain injuries evolve and produce lesions of different shapes and sizes. An injectable matrix will accommodate the various types of brain defects that need to be repaired. Instead of designing biomaterial implants with varying shapes and sizes, only one type of injection material would be needed (with varying volume). Economically speaking, this would drastically reduce manufacturing and patient costs.

  • The scaffold must remain local. It is important that the injected material, whether intact or degraded, does not redistribute into unintended regions of the brain or body. The scaffold should sit in, or around, the lesion cavity until the wound has healed. Diffusion of the scaffold itself, or the transplanted cells into improper locations could have adverse affects.

  • The scaffold should be porous. Interconnected pores, in the scaffold would promote blood vessel ingrowth, nutrient flow and cellular infiltration. Without these properties the transplanted cells may not survive or integrate into the native tissue due to the lack of nutrients and waste removal.An illustration of modifications and additions made to biomaterial scaffolds for brain TE can be seen in Figure 1.

Figure 1

Modifications made to brain tissue engineered scaffolds to promote tissue repair. Biomaterial matrices can be designed to incorporate cells (e.g. stem cells and progenitors), trophic and tropic factors to support exogenous or endogenous cells, factors that induce angiogenesis, anti-inflammatory agents and synthetic adhesion molecules or extracellular matrix (ECM) derivatives.

Biomaterial scaffold structures

From this list we may narrow down the types of scaffolds and the compositions of biomaterials optimal for use. Since an injectable scaffold is desired, this significantly limits the biomaterials available. Two common designs that would apply would be hydrogel systems and micro- or nano-particle systems. Hydrogels are liquid, but undergo gelation upon injection into the brain. Often times this is achieved through the change in temperature from ambient air temperature of ~ 21°C to the body temperature of ~ 37°C. Alternatively, micro- or nano-particles could be produced varying in configuration from microscopic spheres, irregular particles or as fibers that are subsequently suspended in a liquid or gel for transplantation.


Hydrogels are water-soluble polymer chain networks. They can absorb up to 99 percent water, which makes them a strong candidate for brain scaffolding. They have excellent nutrient and oxygen permeability, allowing cell survival in the scaffold [97]. Hydrogels can also be modified with proteins, glycosaminoglycans (GAGs), cytokines, drugs and other factors that will stimulate cell adhesion and/or growth [98]. Cells are readily encapsulated into hydrogels to replace missing autologous cells. Most importantly, hydrogels form in situ. As their name suggests, they gel following injection into tissues [99]. Furthermore, hydrogels possess elastic properties that are similar to those of natural brain tissue. Hydrogels can be created with low compressive moduli that tend to direct stem cell differentiation toward neural lineages [100107].

A downside to hydrogels is that cellular migration and outgrowth is often poor due to its weak mechanical structure. In the CNS migration is essential for the initial formation of cortical architectural, for axonal growth and synaptogenesis and for white matter colonization by oligodendrocyte progenitors prior to myelination. Moreover, cells, and in particular neurons, do not extend their neurites through three-dimensional matrices efficiently [102, 108112]. Neurite outgrowth is best observed on 2-D rigid structures. This is due, in part, because neuronal growth cones require stiff substrates to pull on in order to grow or stretch. The filopodia of many cells have similar properties. Cells placed onto softer substrates are often round and maintain very short processes. Thus a hydrogel will not likely create a suitable environment for radial glial cells (RGCs) that naturally extend their processes long distances to the pial surface of the brain during embryonic development. Another disadvantage in using hydrogels is that their biodegradation is hard to control [113, 114]. Because the majority of hydrogel systems focus on gelation and cytocompatibility, degradation rates are often sacrificed or difficult to manipulate.

Microspheres and microparticle s

Microspheres and microparticles on the other hand, possess a rigid surface structure, as opposed to the soft structure of hydrogels. Due to their rigidity, the tension that neuronal growth cones require can be created and maintained more easily on microspheres than on hydrogels. Furthermore, microspheres can be transplanted by syringe, whereupon they can mold to the injury dimensions. In addition, microspheres can be fabricated to encapsulate, immobilize and deliver specific growth or trophic factors to aid engraftment and survival of the transplanted cells [115]. A downside in using microspheres is that they may be more difficult to inject than hydrogels, since hydrogels are liquid within the injection syringe and gel upon contact with the brain (usually due to temperature differences) whereas, microparticles typically need to be suspended in an additional solution. Another limitation is the weak elasticity of microparticles. Stiffness might increase neurite outgrowth, although it might also decrease differentiation. Studies have shown that materials constructed with elastic properties similar to that of natural brain tissue are more likely to favor neuronal differentiation [100, 116]. Microspheres are inferior in this regard.

Natural versus synthetic polymers

The material composition to be used for biomatrix construction must be carefully selected. Biomaterial matrices can be formed using natural or synthetic polymers, each possessing unique characteristics and gelling properties depending on fabrication. Natural polymers have many attractive features for TE. Since these polymers are extracted from biological sources, they often resemble GAGs found inside the human body. Furthermore, natural molecules possess functional side chains that allow growth promoting peptides, trophic factors and other bioactive proteins to be attached. Natural materials are often degraded safely by enzymes, whose endogenous substrates are structurally similar. For example, the utility of chitosan, a natural material derived from chitin (discussed in more detail below) has been demonstrated in studies using microcapsules containing the neurotrophic factor NT-3. Implanting neurotrophin-containing microcapsules increased regeneration of rat hippocampal neurons, supporting the safety of chitosan for in vivo applications [90]. Obstacles do exist for natural materials, including immunogenicity, degradation rates and mechanical properties. Common natural materials used in CNS TE applications include: alginate, chitosan, collagen, gelatin and hyaluronic acid.

In contrast to natural polymers, the degradation rates and mechanical properties of synthetic polymers are much easier to control. Encapsulating drugs or growth factors is also easier for synthetic material scaffolds. Unfortunately, these polymers are rarely used in their raw form, as they often require chemical modifications to make them biocompatible. For example, microspheres or rods comprised of poly(lactic-co-glycolic acid) (PLGA) have been successfully transplanted into the brain within minimal side effects. Glial infiltration was reported to be the same in animals that received PLGA scaffolds compared to controls [117119]. There is some concern that PLGA degrades into acidic by-products within the brain that may exacerbate inflammation and secondary damage after brain injuries. Polycapralactone (PCL) or other polymers might be a safer alternative [120], but these are not as commonly explored as PLGA. Common synthetic materials used in CNS TE applications include poly lactic acid (PLA), poly glycolic acid (PGA), PLGA, poly ethylene glycol (PEG), PCL and others.


Stem cell transplantation using biomaterial scaffolds

Numerous studies have been performed in vitro to compare the efficacy of scaffolds for neuronal differentiation and survival [97, 121, 122] however; studies are just now being published reporting the efficacy of stem cells transplanted together with a biomaterial matrix in TBI models. Each scientific team has chosen to use a different biomaterial matrix. To date, scaffolds using natural and synthetic materials constructed into rigid microparticles, rigid nanofibers and hydrogels have been tested. Moreover, in some cases the scaffolds were modified by the addition of growth factors and/or ECM molecules (Table 1).

Table 1 Brain tissue engineering studies

Natural biomaterials

Tate and Shear, were some of the first investigators to use stem cells for brain TE in models of TBI. They produced collagen gels that contained either fibronectin and/or laminin and showed that these scaffolds increased the survival of transplanted mouse NPs compared to NPs transplanted without the collagen matrix. The majority of cells observed weeks and months later were glia and mainly NG2+ oligodendrocyte progenitors. Tate et al. [39], obtained better long-term survival of NPs when transplanted within a supportive fibronectin and laminin matrix after TBI than transplanted directly into the brain parenchyma. Animals receiving these transplants also showed improved performance in spatial learning tasks compared to injured mice that did not receive NPs [40]. Similarly, Yu et al. [42], transplanted E14 rat NPs within a collagen type 1 hydrogel into an adult rat model of transient cerebral ischemic injury. Twenty-four hours after middle cerebral artery occlusion (MCAO) the NPs were transplanted directly into the tissue lesion with or without the scaffold. They reported that the collagen-NP scaffold promoted tissue repair better than the NPs alone. Yu et al. [42], also reported that some NPs differentiated into neurons and formed synapses, which correlated with improvements in functional recovery.

Elias et al. [123], used a similar approach repurposed for TBI. They designed a collagen scaffold to deliver adult rat hippocampal NPs in a penetrative TBI model and delivered the NPs 1 week post-injury. When examined 4 weeks later, NPs transplanted on the scaffold showed increased survival and migration compared to cells injected without the scaffold; however, neuronal engraftment was not observed as only glial and endothelial cells were observed amongst the grafted cells. They concluded that an additional growth factor or biochemical stimulus would be needed to achieve differentiated neurons in vivo.

Jin et al. [124], used Matrigel™ to deliver NPs to treat focal cerebral ischemia. Human NPs derived from the ESC line BG01, were transplanted within Matrigel™ scaffolds into rats recovering from MCAO by electrocoagulation 3 weeks prior. NPs transplanted within Matrigel™ decreased the infarct volume by 60%, which was superior to protection obtained when only cells or only scaffolds were injected. Moreover, cells provided with a scaffold showed greater survival and neuronal differentiation evidence by immunostaining and patch-clamp recordings. Four to 9 weeks post-transplantation improvements in sensorimotor and cognitive function were observed. While these results are promising, Matrigel™ is formed from the ECM secreted by mouse tumor cells. The specific composition is Matrigel™ is thus not suitable for clinical studies.

Another popular material being explored is hyaluronic acid, which is an abundant glycosaminoglycan in the brain. Liang et al. [125], incorporated C17.2 cells, human NP cells (ReNcells) and human glial restricted precursors into a hyaluronic acid: gelatin: polyethyleneglycol diacrylate (2:2:1) gel. C17.2 cells were transplanted into the brains of immune-competent rats whereas the ReNcells and the glial precursors were transplanted into the brains of immuno-competent mice. Survival rates for each type of precursor cell improved when encapsulated within the hydrogel.

In a very unique study, Wang et al. [126] cultured NPs in a bioreactive scaffold fabricated from porcine urinary bladders. The matrix was produced from a powder obtained after de-cellularizing and lyophilizing the bladder. De-cellularized organs (often bladders, livers and kidneys) are rich in ECM proteins like laminin, fibronectin and collagen. This powder was then rehydrated to form a hydrogel. Wang et al. [126] transplanted NPs into the brains of rats recovering from severe controlled cortical impact (CCI) injuries. This matrix supported NP proliferation and differentiation while also reducing inflammation. Furthermore, studies through 4 weeks showed improvements in motor memory and cognition that correlated with reduced tissue damage, neuron loss and white matter injury. Transplanting urinary bladder matrix alone generated the same motor and sensorimotor recovery as combined therapy; however, only the scaffold plus NPs attenuated memory and cognitive function.

Synthetic biomaterials

Although not as commonly employed as natural materials, synthetic materials also have been used in brain TE applications. Park et al. [127] demonstrated greater engraftment using a polymer scaffold in a stroke model. They used a fibrous poly(glycolic acid) scaffold seeded with the C17.2 cell line and showed that these cells could differentiate and reduce the extent of inflammation and glial scarring. In a more advanced study, Bible et al. [128], produced 100–200 μm PLGA microparticles that were plasma polymerized allylamine(ppAm) treated and coated with fibronectin. MHP36 NPs were transplanted on these microparticles 2 weeks after transient right MCAO. They reported that the cells integrated effectively within the host tissue and formed primitive neural tissue evidenced by Sox2, NeuN and GFAP staining. Surprisingly, Bible et al. [128] determined that transplanting MHP36 NPs into intact tissue lead to further damage.

Some groups are encapsulating NPs into self-assembling peptide hydrogels. Peptides readily self-assemble and they can form nano-fibrous networks that mimic native ECM. Moreover, like hydrogels they can be injected in soluble form and subsequently solidify to form gels in situ. Cheng et al. [129], linked the laminin adhesion motif isoleucine-lysine-valine-alanine-valine (IKVAV) to a self-assembling peptide AcN-RADARADARADARADA-CONH2 (RADA16) to form a hydrogel that possessed a mechanical stiffness similar to brain tissue. Rat NPs were encapsulated in the RADA16 –IKVAV hydrogel and transplanted into rats recovering from a 2 mm biopsy punch-induced neocortical injury. Histological analyses revealed that the RADA16 –IKVAV gel enhanced the survival of transplanted NPs (compared to NPs delivered in saline), that it reduced glial scar formation and by 6 weeks post-transplantation some of the precursors had differentiated into immature and mature neurons evidenced by βIII-tubulin, neurofilament-H, synapsin-1 and MAP2 immunostaining. Some of these cells also expressed the astrocytic marker, GFAP.

Incorporating growth factors

Many of the aforementioned studies reported that cell survival was often poor and neuronal differentiation difficult to achieve from transplanted neural stem and progenitor cells. Therefore, investigators have found that they need to increase the complexity of their scaffolds to incorporate survival and/or differentiation factors. Neurotrophic factors have been incorporated into biomaterial based drug delivery systems to promote nervous tissue repair. Nerve growth factor (NGF) [130136], glial cell line-derived neurotrophic factor (GDNF) [137142], brain derived neurotrophic factor (BDNF) [141, 143145] and neurotrophin-3 (NT-3) [90, 135, 141, 146148] have all been added to biomaterials to treat TBI as well as neurodegenerative disorders spinal cord injuries and peripheral nerve injuries. Growth factors such as fibroblast growth factor-2 (FGF-2), epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) also have been used for a range of CNS disorders [147158].

In their studies, Bible et al. [159], noted that the tissue that formed wasn’t sufficiently vascularized and hypothesized that this was likely due to deficiencies in nutrients and oxygen. Therefore, in a subsequent study they incorporated 0.1% (w/v) vascular endothelial growth factor (VEGF) into the PLGA microparticles (50–100 μm) to induce angiogenesis. When transplanted 2 weeks post-MCAO [159], Bible et al., noticed significant endothelial cell infiltration and neovasularization within the tissue formed by a conditionally immortalized human NP cell line that had been transplanted on the VEGF-PLGA microparticles into the damaged hemisphere. Microglial infiltration was also observed in these conditions. Although, the VEGF promoted neurovascularizataion, neither the survival nor the differentiation of the engrafted cells was improved.

For the past several years we have endeavored to produce a multifunctional microsphere scaffold optimized for transplanting NPs into the TBI brain. The scaffold that we have fabricated is produced by electrospraying a 3% chitosan solution into a coagulation bath to generate microspheres that range from 30-100 μm in diameter (mean: 64 μm). Similar gelation techniques have been used in other drug delivery methods because it is a simple process with few demerits [160162]. Heparin, which binds FGF-2 with high affinity while retaining its biological activity, is then covalently cross-linked to the chitosan scaffolds using genipin (Figure 2). At 1 μg/mL approximately 80% of the FGF-2 binds to the scaffold. The scaffold is then further modified by coating it with fibronectin to promote cell attachment and to increase proliferation while decreasing differentiation through integrin signaling pathways. The rationale for using FGF-2, is that this growth factor is a known mitogen and survival factor for NPs and it also maintains them in a primitive state and FGF-2 also has been shown to increase the numbers of stem/progenitor cells in the SVZ following TBI [163, 164]. Interestingly, soluble FGF-2 has been reported to have a half-life of 24 hours at 32°C [165] and less than 5 hours at 37°C [166]. On the other hand, it stability increases when affixed to heparan sulfate proteoglycans [167]. Therefore, we predicted that immobilizing the FGF-2 to the scaffold would increase its biological half-life. Indeed, we have shown that fetal rat NPs plated onto a multifunctional film comprised as described above proliferated and remained multipotent for at least 3 days without providing soluble FGF-2. Moreover, they remained less mature and more highly proliferative than cells maintained on fibronectin-coated substrates in culture medium supplemented with soluble FGF-2 [168, 169].

Figure 2

Chitosan microsphere scaffold. Schematic representation of the formation, modification and transplantation of chitosan microspheres for TBI repair. Chitosan is formed by electrospray technique. Heparin (red) is cross-linked to the microspheres using genipin (blue). FGF-2 (black) selectively binds to heparin. NP cells (expressing green fluorescent protein (GFP)) are attach to the scaffold by addition of fibronectin (purple). Spheres with cells are then transplanted subacutely into the lesion cavity following TBI.

When these multifunctional microspheres containing adherent embryonic rat radial glial cells (RGCs) that expressed green fluorescent protein were injected subacutely (7 days post injury) into the lesion cavities of adult rats that had previously sustained CCI injuries, NPs adhered to the microspheres could be observed 3 days after transplantation surrounding the microspheres and these cells were immunopositive for the primitive stem cell/progenitor markers Nestin and BLBP. Furthermore, these transplanted RGCs expressed the cell proliferation marker Ki67. At 2 weeks post-transplantation, the transplanted cells showed a reduction in stem cell/progenitor markers compared to 3 days, having acquired doublecortin (DCX), Vimentin, and Oligodendrocyte Lineage Transcription Factor 2 (Olig2), markers indicative of maturation towards neuronal, astrocytic and oligodendrocytic lineages respectively. Two weeks are still too early to expect differentiation into fully mature neurons, astrocytes, and oligodendrocytes and the continuous supply of FGF-2 from the scaffold will have delayed this process. Studies examining differentiation at 1 month post-transplantation or longer will be necessary.

We are very encouraged by these findings as they suggest that this paradigm enables balanced production of the 3 neural cell types found in the brain, whereas most groups [8, 18, 38, 39] that have transplanted primary NPs find that the majority of transplanted cells differentiate into glial cells. Furthermore, with this approach, large numbers of engrafted cells are observed that are repopulating portions of the injury and these cells are spreading across damaged neocortical regions with little clustering. This is notable, as NPs transplanted without a scaffold often remain clustered at the site of injection [89]. It is possible that the FGF-2 that is delivered on the scaffold is facilitating the migration of the NPs [40]. Several of the groups listed above also have reported greater migration of transplanted NPs when delivered using a biomaterial scaffold.

Future directions

Significant progress has been made in neural TE, yet there are further modifications that can be made to enhance regeneration by combining stem cells and biomaterials. Four major areas of concern exist: 1) achieving a high percentage of cells that survive transplantation and persist after engraftment; 2) obtaining the correct types of differentiated cells; 3) obtaining the correct balance of the different neuronal subtypes and ensuring that they are positioned appropriately; and 4) facilitating the integration of these new neurons into existing circuits. Of these, the first 3 can be addressed by improvements in neural TE.

Progress continues to be made to address the problem of poor cell survival by modifying the biomaterial support and new innovations are being implemented that include altering the engrafted cells by introducing trophic factor genes or preconditioning the cells prior to transplantation [52]. For example, investigators have transduced NPs using lentiviral vectors encoding the neurotrophic factors BDNF, CNTF, GDNF, and NT-3 prior to implanting these cells into the injured brain [170]. Genetically engineering stem cells prior to transplantation may seem promising; however, this manipulation will create hurdles that will slow translation of this therapeutic approach into the clinic. Another approach that has been used to modify the engrafted cells is to precondition the cells. Sakata et al. [171], preconditioned NPs with interlukin-6 (IL-6) before transplanting them 6–7 hours after transient MCAO. The preconditioned NPs were protected from death and they released VEGF resulting in increased angiogenesis within the target site.

As an alternative to pre-conditioning or genetically engineering cells prior to delivery, cells can be seeded onto scaffolds that contain components necessary to induce these changes. Investigators are developing biomaterials that contain immobilized plasmids that are taken up by both the transplanted cells as well as by endogenous cells to modify their gene expression [172174]. With this approach a variety of different gene products can be provided, and it is relatively simple to deliver multiple gene products simultaneously. Incorporating plasmids into biomaterial scaffolds has been applied towards liver [175], cartilage [176, 177], bone [178180], skin [181], vascular/heart [182184] and spinal cord injury [185] TE applications. Brain injuries would likely benefit from biomaterials seeded with stem cells and loaded with plasmids that would promote cell growth, neovascularization, and support donor cell survival until they can receive trophic support from their synaptic partners.

Investigators are also realizing that the developing brain is generated from a variety of different NPs; therefore, they are being more precise in matching the type of neural precursor used for engraftment. As iPSC technology becomes more refined, investigators will be able to more accurately control the type of NP that can be used for transplantation. Controlling which cell types are produced and controlling the timing of their production will require that the local environment surrounding the engrafted cells provides them with appropriate signals. Therefore, investigators will need to establish the means to deliver relevant growth and differentiation factors in a temporally defined sequence. This might require that peptides or plasmids are encapsulated for slow release from the scaffold or that they are encapsulated in a form that requires processing to become biologically active.

Another problem that needs to be overcome is to devise a strategy to regenerate a laminated brain tissue. All of the studies to date have employed basic TE strategies to enhance NP engraftment, survival and orchestrating a balanced production of neuronal and glial lineages. In order to fully repair a brain lesion, the architecture of the regenerated neural parenchyma must recapitulate the structure of the adjacent host tissue. This is especially true in the case of the neocortex, a region of the brain that is frequently damaged by trauma. The neocortex is a laminar tissue with 6 layers where the neurons located within each layer have specific neurochemical properties and they receive inputs from specific brain regions. Moreover, they send their axons to other, highly specified targets. Thus, in regenerating the neocortex, the neurons that reside in the deeper layers of the cortex (layers 5 and 6) cannot be located in more superficial regions (layers 1 through 4), and vice versa. It has been documented that NPs have the ability to sense their surroundings and reorganize to appropriately fit a cortical layer [186], though it is not likely that transplanted NPs will do the same. Therefore, new biomaterial techniques will be required to ensure the appropriate differentiation and location of NPs within the specific brain region of interest. For the neocortex, we can envision creating a multilayered scaffold, in which the different biomaterial layers govern the migration, differentiation and survival of appropriate laminar neurons. Alternatively, it might be possible to inject a biomaterial that would organize into a gradient and within this gradient, plasmids, proteins or other bioactive molecules would be organized to promote the systematic migration and differentiation of engrafted NPs [187]. Although it may be more difficult to achieve such a highly organized structure as required to repair neural circuits compared to other organ systems, utilizing TE applications to heal the injured brain remains a promising discipline for future studies.


Over the past decade, TE strategies have been designed and tested for brain injury repair. Studies have shown that engraftment is improved when the stem cells are provided functionalized biomaterial scaffolds. These biomaterial scaffolds allow essential growth factors and other beneficial molecules to be delivered resulting in improved NP survival and repair. Even though natural materials have been more commonly evaluated, there is little evidence that they are superior to synthetic materials. While great progress has been achieved, additional research is necessary to determine which material(s), growth factors and/or pharmaceutical agents produce the best outcome and to determine how to best deliver them. Additional research also is needed to match the donor cells to the region of brain damage.



Brain derived neurotrophic factor


Controlled cortical impact


Central nervous system


Ciliary neurotrophic factor


Extracellular matrix


Epidermal growth factor


Embryonic stem cell


Fibroblast growth factor 2




Glial cell line-derived neurotrophic factor


Induced pluripotent stem cell


Middle cerebral artery occlusion


Neural degenerative disorders


Nerve growth factor


Neural precursor


Neural stem cell




Platelet-derived growth factor


Poly(lactic co-glycolic acid)


Peripheral nerve injury


Radial glial cell


Spinal cord injury


Subventricular zone


Traumatic brain injury


Tissue engineering


Vascular endothelial growth factor


Ventricular zone.


  1. 1.

    Langer R, Vacanti JP: Tissue engineering. Science. 1993, 260 (5110): 920-926.

  2. 2.

    Kim IY, Seo SJ, Moon HS, Yoo MK, Park IY, Kim BC, Cho CS: Chitosan and its derivatives for tissue engineering applications. Biotechnol Adv. 2008, 26 (1): 1-21.

  3. 3.

    Centers for Disease Control and Prevention (CDC), N.C.f.I.P.a.C: Report to Congress on mild traumatic brain injury in the United States: steps to prevent a serious public health problem. 2003, Centers for Disease Control and Prevention

  4. 4.

    Faul M, Likang X, Wald MM, Coronado VG: Traumatic brain injury in the United States: emergency department visits, hospitalizations, and deaths. 2010, Centers for Disease Control and Prevention, National Center for Injury Prevention and Control

  5. 5.

    Smith DH, Chen XH, Pierce JE, Wolf JA, Trojanowski JQ, Graham DI, McIntosh TK: Progressive atrophy and neuron death for one year following brain trauma in the rat. J Neurotrauma. 1997, 14 (10): 715-727.

  6. 6.

    Cortez SC, McIntosh TK, Noble LJ: Experimental fluid percussion brain injury: vascular disruption and neuronal and glial alterations. Brain Res. 1989, 482 (2): 271-282.

  7. 7.

    Hicks R, Soares H, Smith D, McIntosh T: Temporal and spatial characterization of neuronal injury following lateral fluid-percussion brain injury in the rat. Acta Neuropathol (Berl). 1996, 91 (3): 236-246.

  8. 8.

    Colicos MA, Dixon CE, Dash PK: Delayed, selective neuronal death following experimental cortical impact injury in rats: possible role in memory deficits. Brain Res. 1996, 739 (1–2): 111-119.

  9. 9.

    Dietrich WD, Alonso O, Halley M: Early microvascular and neuronal consequences of traumatic brain injury: a light and electron microscopic study in rats. J Neurotrauma. 1994, 11 (3): 289-301.

  10. 10.

    Silver J, Miller JH: Regeneration beyond the glial scar. Nat Rev Neurosci. 2004, 5 (2): 146-156.

  11. 11.

    Morganti-Kossmann MC, Satgunaseelan L, Bye N, Kossmann T: Modulation of immune response by head injury. Injury. 2007, 38 (12): 1392-1400.

  12. 12.

    Molcanyi M, Riess P, Bentz K, Maegele M, Hescheler J, Schafke B, Trapp T, Neugebauer E, Klug N, Schafer U: Trauma-associated inflammatory response impairs embryonic stem cell survival and integration after implantation into injured rat brain. J Neurotrauma. 2007, 24 (4): 625-637.

  13. 13.

    (CDC), C.f.D.C.a.P: Injury Prevention & Control: Traumatic Brain Injury. 2014, Available from:

  14. 14.

    Crompton KE, Goud JD, Bellamkonda RV, Gengenbach TR, Finkelstein DI, Horne MK, Forsythe JS: Polylysine-functionalised thermoresponsive chitosan hydrogel for neural tissue engineering. Biomaterials. 2007, 28 (3): 441-449.

  15. 15.

    Clinic M: Traumatic Brain Injury, Treatments and Drugs. 2014,,

  16. 16.

    America, B.I.A.o: Living With Brain Injury: Treatment. 2014,,

  17. 17.

    Encinas JM, Michurina TV, Peunova N, Park JH, Tordo J, Peterson DA, Fishell G, Koulakov A, Enikolopov G: Division-coupled astrocytic differentiation and age-related depletion of neural stem cells in the adult hippocampus. Cell Stem Cell. 2011, 8 (5): 566-579.

  18. 18.

    Ahlenius H, Visan V, Kokaia M, Lindvall O, Kokaia Z: Neural stem and progenitor cells retain their potential for proliferation and differentiation into functional neurons despite lower number in aged brain. J Neurosci. 2009, 29 (14): 4408-4419.

  19. 19.

    Sanai N, Nguyen T, Ihrie RA, Mirzadeh Z, Tsai HH, Wong M, Gupta N, Berger MS, Huang E, Garcia-Verdugo JM, Rowitch DH, Alvarez-Buylla A: Corridors of migrating neurons in the human brain and their decline during infancy. Nature. 2011, 478 (7369): 382-386.

  20. 20.

    Arvidsson A, Collin T, Kirik D, Kokaia Z, Lindvall O: Neuronal replacement from endogenous precursors in the adult brain after stroke. Nat Med. 2002, 8 (9): 963-970.

  21. 21.

    Yang Z, Levison SW: Perinatal Hypoxic/Ischemic Brain Injury Induces Persistent Production of Striatal Neurons from Subventricular Zone Progenitors. Dev Neurosci. 2007, 29 (4–5): 331-340.

  22. 22.

    Yang Z, You Y, Levison SW: Neonatal hypoxic/ischemic brain injury induces production of calretinin-expressing interneurons in the striatum. J Comp Neurol. 2008, 511 (1): 19-33.

  23. 23.

    Salman H, Ghosh P, Kernie SG: Subventricular zone neural stem cells remodel the brain following traumatic injury in adult mice. J Neurotrauma. 2004, 21 (3): 283-292.

  24. 24.

    Sundholm-Peters NL, Yang HK, Goings GE, Walker AS, Szele FG: Subventricular zone neuroblasts emigrate toward cortical lesions. J Neuropathol Exp Neurol. 2005, 64 (12): 1089-1100.

  25. 25.

    Svendsen CN, Smith AG: New prospects for human stem-cell therapy in the nervous system. Trends Neurosci. 1999, 22 (8): 357-364.

  26. 26.

    Snyder EY, Park KI, Flax JD, Liu S, Rosario CM, Yandava BD, Aurora S: Potential of neural "stem-like" cells for gene therapy and repair of the degenerating central nervous system. Adv Neurol. 1997, 72: 121-132.

  27. 27.

    McKay RD: Stem cell biology and neurodegenerative disease. Philos Trans R Soc Lond B Biol Sci. 2004, 359 (1445): 851-856.

  28. 28.

    Gage FH, Coates PW, Palmer TD, Kuhn HG, Fisher LJ, Suhonen JO, Peterson DA, Suhr ST, Ray J: Survival and differentiation of adult neuronal progenitor cells transplanted to the adult brain. Proc Natl Acad Sci U S A. 1995, 92 (25): 11879-11883.

  29. 29.

    Martinez-Serrano A, Bjorklund A: Protection of the neostriatum against excitotoxic damage by neurotrophin-producing, genetically modified neural stem cells. J Neurosci. 1996, 16 (15): 4604-4616.

  30. 30.

    Martinez-Serrano A, Fischer W, Bjorklund A: Reversal of age-dependent cognitive impairments and cholinergic neuron atrophy by NGF-secreting neural progenitors grafted to the basal forebrain. Neuron. 1995, 15 (2): 473-484.

  31. 31.

    Shihabuddin LS, Brunschwig JP, Holets VR, Bunge MB, Whittemore SR: Induction of mature neuronal properties in immortalized neuronal precursor cells following grafting into the neonatal CNS. J Neurocytol. 1996, 25 (2): 101-111.

  32. 32.

    Shihabuddin LS, Hertz JA, Holets VR, Whittemore SR: The adult CNS retains the potential to direct region-specific differentiation of a transplanted neuronal precursor cell line. J Neurosci. 1995, 15 (10): 6666-6678.

  33. 33.

    Shihabuddin LS, Holets VR, Whittemore SR: Selective hippocampal lesions differentially affect the phenotypic fate of transplanted neuronal precursor cells. Exp Neurol. 1996, 139 (1): 61-72.

  34. 34.

    Snyder EY, Deitcher DL, Walsh C, Arnold-Aldea S, Hartwieg EA, Cepko CL: Multipotent neural cell lines can engraft and participate in development of mouse cerebellum. Cell. 1992, 68 (1): 33-51.

  35. 35.

    Snyder EY, Macklis JD: Multipotent neural progenitor or stem-like cells may be uniquely suited for therapy for some neurodegenerative conditions. Clin Neurosci. 1995, 3 (5): 310-316.

  36. 36.

    White LA, Eaton MJ, Castro MC, Klose KJ, Globus MY, Shaw G, Whittemore SR: Distinct regulatory pathways control neurofilament expression and neurotransmitter synthesis in immortalized serotonergic neurons. J Neurosci. 1994, 14 (11 Pt 1): 6744-6753.

  37. 37.

    Whittemore SR, Neary JT, Kleitman N, Sanon HR, Benigno A, Donahue RP, Norenberg MD: Isolation and characterization of conditionally immortalized astrocyte cell lines derived from adult human spinal cord. Glia. 1994, 10 (3): 211-226.

  38. 38.

    Whittemore SR, White LA: Target regulation of neuronal differentiation in a temperature-sensitive cell line derived from medullary raphe. Brain Res. 1993, 615 (1): 27-40.

  39. 39.

    Tate CC, Shear DA, Tate MC, Archer DR, Stein DG, LaPlaca MC: Laminin and fibronectin scaffolds enhance neural stem cell transplantation into the injured brain. J Tissue Eng Regen Med. 2009, 3 (3): 208-217.

  40. 40.

    Tate MC, Shear DA, Hoffman SW, Stein DG, Archer DR, LaPlaca MC: Fibronectin promotes survival and migration of primary neural stem cells transplanted into the traumatically injured mouse brain. Cell Transplant. 2002, 11 (3): 283-295.

  41. 41.

    Sinden JD, Rashid-Doubell F, Kershaw TR, Nelson A, Chadwick A, Jat PS, Noble MD, Hodges H, Gray JA: Recovery of spatial learning by grafts of a conditionally immortalized hippocampal neuroepithelial cell line into the ischaemia-lesioned hippocampus. Neuroscience. 1997, 81 (3): 599-608.

  42. 42.

    Yu H, Cao B, Feng M, Zhou Q, Sun X, Wu S, Jin S, Liu H, Lianhong J: Combinated transplantation of neural stem cells and collagen type I promote functional recovery after cerebral ischemia in rats. Anat Rec (Hoboken). 2010, 293 (5): 911-917.

  43. 43.

    Yasuhara T, Matsukawa N, Yu G, Xu L, Mays RW, Kovach J, Deans RJ, Hess DC, Carroll JE, Borlongan CV: Behavioral and histological characterization of intrahippocampal grafts of human bone marrow-derived multipotent progenitor cells in neonatal rats with hypoxic-ischemic injury. Cell Transplant. 2006, 15 (3): 231-238.

  44. 44.

    Xiao J, Nan Z, Motooka Y, Low WC: Transplantation of a novel cell line population of umbilical cord blood stem cells ameliorates neurological deficits associated with ischemic brain injury. Stem Cells Dev. 2005, 14 (6): 722-733.

  45. 45.

    Wieloch T, Nikolich K: Mechanisms of neural plasticity following brain injury. Curr Opin Neurobiol. 2006, 16 (3): 258-264.

  46. 46.

    Park KI, Hack MA, Ourednik J, Yandava B, Flax JD, Stieg PE, Gullans S, Jensen FE, Sidman RL, Ourednik V, Snyder EY: Acute injury directs the migration, proliferation, and differentiation of solid organ stem cells: evidence from the effect of hypoxia-ischemia in the CNS on clonal "reporter" neural stem cells. Exp Neurol. 2006, 199 (1): 156-178.

  47. 47.

    Ourednik V, Ourednik J, Flax JD, Zawada WM, Hutt C, Yang C, Park KI, Kim SU, Sidman RL, Freed CR, Snyder EY: Segregation of human neural stem cells in the developing primate forebrain. Science. 2001, 293 (5536): 1820-1824.

  48. 48.

    Ikeda R, Kurokawa MS, Chiba S, Yoshikawa H, Ide M, Tadokoro M, Nito S, Nakatsuji N, Kondoh Y, Nagata K, Hashimoto T, Suzuki N: Transplantation of neural cells derived from retinoic acid-treated cynomolgus monkey embryonic stem cells successfully improved motor function of hemiplegic mice with experimental brain injury. Neurobiol Dis. 2005, 20 (1): 38-48.

  49. 49.

    Bachoud-Levi AC, Gaura V, Brugieres P, Lefaucheur JP, Boisse MF, Maison P, Baudic S, Ribeiro MJ, Bourdet C, Remy P, Cesaro P, Hantraye P, Peschanski M: Effect of fetal neural transplants in patients with Huntington's disease 6 years after surgery: a long-term follow-up study. Lancet Neurol. 2006, 5 (4): 303-309.

  50. 50.

    Bliss TM, Kelly S, Shah AK, Foo WC, Kohli P, Stokes C, Sun GH, Ma M, Masel J, Kleppner SR, Schallert T, Palmer T, Steinberg GK: Transplantation of hNT neurons into the ischemic cortex: cell survival and effect on sensorimotor behavior. J Neurosci Res. 2006, 83 (6): 1004-1014.

  51. 51.

    Bakshi A, Shimizu S, Keck CA, Cho S, LeBold DG, Morales D, Arenas E, Snyder EY, Watson DJ, McIntosh TK: Neural progenitor cells engineered to secrete GDNF show enhanced survival, neuronal differentiation and improve cognitive function following traumatic brain injury. Eur J Neurosci. 2006, 23 (8): 2119-2134.

  52. 52.

    Boockvar JA, Schouten J, Royo N, Millard M, Spangler Z, Castelbuono D, Snyder E, O'Rourke D, McIntosh T: Experimental traumatic brain injury modulates the survival, migration, and terminal phenotype of transplanted epidermal growth factor receptor-activated neural stem cells. Neurosurgery. 2005, 56 (1): 163-171. discussion 171

  53. 53.

    Flax JD, Aurora S, Yang C, Simonin C, Wills AM, Billinghurst LL, Jendoubi M, Sidman RL, Wolfe JH, Kim SU, Snyder EY: Engraftable human neural stem cells respond to developmental cues, replace neurons, and express foreign genes. Nat Biotechnol. 1998, 16 (11): 1033-1039.

  54. 54.

    Seyfried D, Ding J, Han Y, Li Y, Chen J, Chopp M: Effects of intravenous administration of human bone marrow stromal cells after intracerebral hemorrhage in rats. J Neurosurg. 2006, 104 (2): 313-318.

  55. 55.

    Mahmood A, Lu D, Yi L, Chen JL, Chopp M: Intracranial bone marrow transplantation after traumatic brain injury improving functional outcome in adult rats. J Neurosurg. 2001, 94 (4): 589-595.

  56. 56.

    Mahmood A, Lu D, Qu C, Goussev A, Chopp M: Long-term recovery after bone marrow stromal cell treatment of traumatic brain injury in rats. J Neurosurg. 2006, 104 (2): 272-277.

  57. 57.

    Mahmood A, Lu D, Qu C, Goussev A, Chopp M: Human marrow stromal cell treatment provides long-lasting benefit after traumatic brain injury in rats. Neurosurgery. 2005, 57 (5): 1026-1031. discussion 1026–31

  58. 58.

    Mahmood A, Lu D, Chopp M: Intravenous administration of marrow stromal cells (MSCs) increases the expression of growth factors in rat brain after traumatic brain injury. J Neurotrauma. 2004, 21 (1): 33-39.

  59. 59.

    Lu J, Moochhala S, Moore XL, Ng KC, Tan MH, Lee LK, He B, Wong MC, Ling EA: Adult bone marrow cells differentiate into neural phenotypes and improve functional recovery in rats following traumatic brain injury. Neurosci Lett. 2006, 398 (1–2): 12-17.

  60. 60.

    Lu D, Li Y, Mahmood A, Wang L, Rafiq T, Chopp M: Neural and marrow-derived stromal cell sphere transplantation in a rat model of traumatic brain injury. J Neurosurg. 2002, 97 (4): 935-940.

  61. 61.

    Li Y, McIntosh K, Chen J, Zhang C, Gao Q, Borneman J, Raginski K, Mitchell J, Shen L, Zhang J, Lu D, Chopp M: Allogeneic bone marrow stromal cells promote glial-axonal remodeling without immunologic sensitization after stroke in rats. Exp Neurol. 2006, 198 (2): 313-325.

  62. 62.

    Dezawa M, Hoshino M, Ide C: Treatment of neurodegenerative diseases using adult bone marrow stromal cell-derived neurons. Expert Opin Biol Ther. 2005, 5 (4): 427-435.

  63. 63.

    Chen Q, Long Y, Yuan X, Zou L, Sun J, Chen S, Perez-Polo JR, Yang K: Protective effects of bone marrow stromal cell transplantation in injured rodent brain: synthesis of neurotrophic factors. J Neurosci Res. 2005, 80 (5): 611-619.

  64. 64.

    Hodges H, Veizovic T, Bray N, French SJ, Rashid TP, Chadwick A, Patel S, Gray JA: Conditionally immortal neuroepithelial stem cell grafts reverse age-associated memory impairments in rats. Neuroscience. 2000, 101 (4): 945-955.

  65. 65.

    Hodges H, Sowinski P, Virley D, Nelson A, Kershaw TR, Watson WP, Veizovic T, Patel S, Mora A, Rashid T, French SJ, Chadwick A, Gray JA, Sinden JD: Functional reconstruction of the hippocampus: fetal versus conditionally immortal neuroepithelial stem cell grafts. Novartis Found Symp. 2000, 231: 53-65. discussion 65–9

  66. 66.

    Hodges H, Sowinski P, Fleming P, Kershaw TR, Sinden JD, Meldrum BS, Gray JA: Contrasting effects of fetal CA1 and CA3 hippocampal grafts on deficits in spatial learning and working memory induced by global cerebral ischaemia in rats. Neuroscience. 1996, 72 (4): 959-988.

  67. 67.

    Vink R, McIntosh TK: Pharmacological and physiological effects of magnesium on experimental traumatic brain injury. Magnes Res. 1990, 3 (3): 163-169.

  68. 68.

    McIntosh TK, Vink R, Soares H, Hayes R, Simon R: Effect of noncompetitive blockade of N-methyl-D-aspartate receptors on the neurochemical sequelae of experimental brain injury. J Neurochem. 1990, 55 (4): 1170-1179.

  69. 69.

    Keirstead HS, Ben-Hur T, Rogister B, O'Leary MT, Dubois-Dalcq M, Blakemore WF: Polysialylated neural cell adhesion molecule-positive CNS precursors generate both oligodendrocytes and Schwann cells to remyelinate the CNS after transplantation. J Neurosci. 1999, 19 (17): 7529-7536.

  70. 70.

    Buzsaki G, Smith A, Berger S, Fisher LJ, Gage FH: Petit mal epilepsy and parkinsonian tremor: hypothesis of a common pacemaker. Neuroscience. 1990, 36 (1): 1-14.

  71. 71.

    Philips MF, Mattiasson G, Wieloch T, Bjorklund A, Johansson BB, Tomasevic G, Martinez-Serrano A, Lenzlinger PM, Sinson G, Grady MS, McIntosh TK:Neuroprotective and behavioral efficacy of nerve growth factor-transfected hippocampal progenitor cell transplants after experimental traumatic brain injury. J Neurosurg. 2001, 94 (5): 765-774.

  72. 72.

    Wong AM, Hodges H, Horsburgh K: Neural stem cell grafts reduce the extent of neuronal damage in a mouse model of global ischaemia. Brain Res. 2005, 1063 (2): 140-150.

  73. 73.

    Perri BR, Smith DH, Murai H, Sinson G, Saatman KE, Raghupathi R, Bartus RT, McIntosh TK: Metabolic quantification of lesion volume following experimental traumatic brain injury in the rat. J Neurotrauma. 1997, 14 (1): 15-22.

  74. 74.

    Modo M, Rezaie P, Heuschling P, Patel S, Male DK, Hodges H: Transplantation of neural stem cells in a rat model of stroke: assessment of short-term graft survival and acute host immunological response. Brain Res. 2002, 958 (1): 70-82.

  75. 75.

    McIntosh TK, Smith DH, Voddi M, Perri BR, Stutzmann JM: Riluzole, a novel neuroprotective agent, attenuates both neurologic motor and cognitive dysfunction following experimental brain injury in the rat. J Neurotrauma. 1996, 13 (12): 767-780.

  76. 76.

    Riess P, Zhang C, Saatman KE, Laurer HL, Longhi LG, Raghupathi R, Lenzlinger PM, Lifshitz J, Boockvar J, Neugebauer E, Snyder EY, McIntosh TK: Transplanted neural stem cells survive, differentiate, and improve neurological motor function after experimental traumatic brain injury. Neurosurgery. 2002, 51 (4): 1043-1052. discussion 1052–4

  77. 77.

    Riess P, Molcanyi M, Bentz K, Maegele M, Simanski C, Carlitscheck C, Schneider A, Hescheler J, Bouillon B, Schafer U, Neugebauer E: Embryonic stem cell transplantation after experimental traumatic brain injury dramatically improves neurological outcome, but may cause tumors. J Neurotrauma. 2007, 24 (1): 216-225.

  78. 78.

    Hoane MR, Becerra GD, Shank JE, Tatko L, Pak ES, Smith M, Murashov AK: Transplantation of neuronal and glial precursors dramatically improves sensorimotor function but not cognitive function in the traumatically injured brain. J Neurotrauma. 2004, 21 (2): 163-174.

  79. 79.

    Gao J, Prough DS, McAdoo DJ, Grady JJ, Parsley MO, Ma L, Tarensenko YI, Wu P: Transplantation of primed human fetal neural stem cells improves cognitive function in rats after traumatic brain injury. Exp Neurol. 2006, 201 (2): 281-292.

  80. 80.

    Alvarez-Dolado M, Calcagnotto ME, Karkar KM, Southwell DG, Jones-Davis DM, Estrada RC, Rubenstein JL, Alvarez-Buylla A, Baraban SC: Cortical inhibition modified by embryonic neural precursors grafted into the postnatal brain. J Neurosci. 2006, 26 (28): 7380-7389.

  81. 81.

    Richardson RM, Singh A, Sun D, Fillmore HL, Dietrich DW, Bullock MR: Stem cell biology in traumatic brain injury: effects of injury and strategies for repair. J Neurosurg. 2010, 112 (5): 1125-1138.

  82. 82.

    Sanberg PR, Eve DJ, Cruz LE, Borlongan CV: Neurological disorders and the potential role for stem cells as a therapy. Br Med Bull. 2012, 101: 163-181.

  83. 83.

    Shindo T, Matsumoto Y, Wang Q, Kawai N, Tamiya T, Nagao S: Differences in the neuronal stem cells survival, neuronal differentiation and neurological improvement after transplantation of neural stem cells between mild and severe experimental traumatic brain injury. J Med Invest. 2006, 53 (1–2): 42-51.

  84. 84.

    Wallenquist U, Brannvall K, Clausen F, Lewen A, Hillered L, Forsberg-Nilsson K: Grafted neural progenitors migrate and form neurons after experimental traumatic brain injury. Restor Neurol Neurosci. 2009, 27 (4): 323-334.

  85. 85.

    Harting MT, Sloan LE, Jimenez F, Baumgartner J, Cox CS: Subacute neural stem cell therapy for traumatic brain injury. J Surg Res. 2009, 153 (2): 188-194.

  86. 86.

    Ma H, Yu B, Kong L, Zhang Y, Shi Y: Transplantation of neural stem cells enhances expression of synaptic protein and promotes functional recovery in a rat model of traumatic brain injury. Mol Med Rep. 2011, 4 (5): 849-856.

  87. 87.

    Shear DA, Tate MC, Archer DR, Hoffman SW, Hulce VD, Laplaca MC, Stein DG: Neural progenitor cell transplants promote long-term functional recovery after traumatic brain injury. Brain Res. 2004, 1026 (1): 11-22.

  88. 88.

    Sun D, Gugliotta M, Rolfe A, Reid W, McQuiston AR, Hu W, Young H: Sustained survival and maturation of adult neural stem/progenitor cells after transplantation into the injured brain. J Neurotrauma. 2011, 28 (6): 961-972.

  89. 89.

    Skop NB: A Multifunctional Microsphere Scaffold to Deliver Neural Precursors for Traumatic Brain Injury Repair. 2013, U.S.A: p. Ph.D. Thesis. Rutgers The State University of NJ

  90. 90.

    Mo L, Yang Z, Zhang A, Li X: The repair of the injured adult rat hippocampus with NT-3-chitosan carriers. Biomaterials. 2010, 31 (8): 2184-2192.

  91. 91.

    Meredith JE, Fazeli B, Schwartz MA: The extracellular matrix as a cell survival factor. Mol Biol Cell. 1993, 4 (9): 953-961.

  92. 92.

    Ingber DE: Extracellular matrix as a solid-state regulator in angiogenesis: identification of new targets for anti-cancer therapy. Semin Cancer Biol. 1992, 3 (2): 57-63.

  93. 93.

    Aplin AE, Howe AK, Juliano RL: Cell adhesion molecules, signal transduction and cell growth. Curr Opin Cell Biol. 1999, 11 (6): 737-744.

  94. 94.

    Aplin AE, Juliano RL: Integrin and cytoskeletal regulation of growth factor signaling to the MAP kinase pathway. J Cell Sci. 1999, 112 (Pt 5): 695-706.

  95. 95.

    Stichel CC, Muller HW: The CNS lesion scar: new vistas on an old regeneration barrier. Cell Tissue Res. 1998, 294 (1): 1-9.

  96. 96.

    Brazel CY, Alaythan AA, Felling RJ, Calderon F, Levison SW: Molecular Features of Neural Stem Cells Enable their Enrichment Using Pharmacological Inhibitors of Survival-Promoting Kinases. J Neurochem. 2013, 128 (3): 376-390.

  97. 97.

    Nisbet DR, Crompton KE, Horne MK, Finkelstein DI, Forsythe JS: Neural tissue engineering of the CNS using hydrogels. J Biomed Mater Res B Appl Biomater. 2008, 87 (1): 251-263.

  98. 98.

    Ta HT, Dass CR, Dunstan DE: Injectable chitosan hydrogels for localised cancer therapy. J Control Release. 2008, 126 (3): 205-216.

  99. 99.

    Peng HT, Shek PN: Development of in situ-forming hydrogels for hemorrhage control. J Mater Sci Mater Med. 2009, 20 (8): 1753-1762.

  100. 100.

    Banerjee A, Arha M, Choudhary S, Ashton RS, Bhatia SR, Schaffer DV, Kane RS: The influence of hydrogel modulus on the proliferation and differentiation of encapsulated neural stem cells. Biomaterials. 2009, 30 (27): 4695-4699.

  101. 101.

    Brannvall K, Bergman K, Wallenquist U, Svahn S, Bowden T, Hilborn J, Forsberg-Nilsson K: Enhanced neuronal differentiation in a three-dimensional collagen-hyaluronan matrix. J Neurosci Res. 2007, 85 (10): 2138-2146.

  102. 102.

    Engler AJ, Sen S, Sweeney HL, Discher DE: Matrix elasticity directs stem cell lineage specification. Cell. 2006, 126 (4): 677-689.

  103. 103.

    Flanagan LA, Ju YE, Marg B, Osterfield M, Janmey PA: Neurite branching on deformable substrates. Neuroreport. 2002, 13 (18): 2411-2415.

  104. 104.

    Georges PC, Miller WJ, Meaney DF, Sawyer ES, Janmey PA: Matrices with compliance comparable to that of brain tissue select neuronal over glial growth in mixed cortical cultures. Biophys J. 2006, 90 (8): 3012-3018.

  105. 105.

    Hynes SR, Rauch MF, Bertram JP, Lavik EB: A library of tunable poly(ethylene glycol)/poly(L-lysine) hydrogels to investigate the material cues that influence neural stem cell differentiation. J Biomed Mater Res A. 2009, 89 (2): 499-509.

  106. 106.

    Saha K, Keung AJ, Irwin EF, Li Y, Little L, Schaffer DV, Healy KE: Substrate modulus directs neural stem cell behavior. Biophys J. 2008, 95 (9): 4426-4438.

  107. 107.

    Seidlits SK, Khaing ZZ, Petersen RR, Nickels JD, Vanscoy JE, Shear JB, Schmidt CE: The effects of hyaluronic acid hydrogels with tunable mechanical properties on neural progenitor cell differentiation. Biomaterials. 2010, 31 (14): 3930-3940.

  108. 108.

    Lo CM, Wang HB, Dembo M, Wang YL: Cell movement is guided by the rigidity of the substrate. Biophys J. 2000, 79 (1): 144-152.

  109. 109.

    Wang S, Roy NS, Benraiss A, Goldman SA: Promoter-based isolation and fluorescence-activated sorting of mitotic neuronal progenitor cells from the adult mammalian ependymal/subependymal zone. Dev Neurosci. 2000, 22 (1–2): 167-176.

  110. 110.

    Balgude AP, Yu X, Szymanski A, Bellamkonda RV: Agarose gel stiffness determines rate of DRG neurite extension in 3D cultures. Biomaterials. 2001, 22 (10): 1077-1084.

  111. 111.

    Willits RK, Skornia SL: Effect of collagen gel stiffness on neurite extension. J Biomater Sci Polym Ed. 2004, 15 (12): 1521-1531.

  112. 112.

    Lamoreux P, R.E.B.a.S.R.H: Direct evidence that growth cones pull. Nature. 1989, 340 (6229): 159-162.

  113. 113.

    Kai D, Prabhakaran MP, Stahl B, Eblenkamp M, Wintermantel E, Ramakrishna S: Mechanical properties and in vitro behavior of nanofiber-hydrogel composites for tissue engineering applications. Nanotechnology. 2012, 23 (9): 095705-

  114. 114.

    Barbucci R: Hydrogels: Biological Properties and Applications, Volume XII. 2009, 200-

  115. 115.

    Sinha VR, Singla AK, Wadhawan S, Kaushik R, Kumria R, Bansal K, Dhawan S: Chitosan microspheres as a potential carrier for drugs. Int J Pharm. 2004, 274 (1–2): 1-33.

  116. 116.

    Leipzig ND, Shoichet MS: The effect of substrate stiffness on adult neural stem cell behavior. Biomaterials. 2009, 30 (36): 6867-6878.

  117. 117.

    Nicholas AP, McInnis C, Gupta KB, Snow WW, Love DF, Mason DW, Ferrell TM, Staas JK, Tice TR: The fate of biodegradable microspheres injected into rat brain. Neurosci Lett. 2002, 323 (2): 85-88.

  118. 118.

    Emerich DF, Tracy MA, Ward KL, Figueiredo M, Qian R, Henschel C, Bartus RT: Biocompatibility of poly (DL-lactide-co-glycolide) microspheres implanted into the brain. Cell Transplant. 1999, 8 (1): 47-58.

  119. 119.

    Kou JH, Emmett C, Shen P, Aswani S, Iwamoto T, Vaghefi F, Sanders L, Cain G: Bioerosion and biocompatibility of poly(d,llactic-co-glycolic acid) implants in brain. J Control Release. 1997, 43: 123-130.

  120. 120.

    Wong DY, Hollister SJ, Krebsbach PH, Nosrat C: Poly(epsilon-caprolactone) and poly (L-lactic-co-glycolic acid) degradable polymer sponges attenuate astrocyte response and lesion growth in acute traumatic brain injury. Tissue Eng. 2007, 13 (10): 2515-2523.

  121. 121.

    Nisbet DR, Crompton KE, Nisbet DR, Horne MK, Finkelstein DI, Forsythe JS: Review: Neural Tissue Engineering of the CNS Using Hydrogels. J Biomed Mater Res B. 2007, 87 (1): 251-263.

  122. 122.

    Zuidema JM, Pap MM, Jaroch DB, Morrison FA, Gilbert RJ: Fabrication and characterization of tunable polysaccharide hydrogel blends for neural repair. Acta Biomater. 2011, 7 (4): 1634-1643.

  123. 123.

    Elias PZ, Spector M: Implantation of a collagen scaffold seeded with adult rat hippocampal progenitors in a rat model of penetrating brain injury. J Neurosci Methods. 2012, 209 (1): 199-211.

  124. 124.

    Jin K, Mao X, Xie L, Galvan V, Lai B, Wang Y, Gorostiza O, Wang X, Greenberg DA: Transplantation of human neural precursor cells in Matrigel scaffolding improves outcome from focal cerebral ischemia after delayed postischemic treatment in rats. J Cereb Blood Flow Metab. 2010, 30 (3): 534-544.

  125. 125.

    Liang Y, Walczak P, Bulte JW: The survival of engrafted neural stem cells within hyaluronic acid hydrogels. Biomaterials. 2013, 34 (22): 5521-5529.

  126. 126.

    Wang JY, Liou AK, Ren ZH, Zhang L, Brown BN, Cui XT, Badylak SF, Cai YN, Guan YQ, Leak RK, Chen J, Ji X, Chen L: Neurorestorative effect of urinary bladder matrix-mediated neural stem cell transplantation following traumatic brain injury in rats. CNS Neurol Disord Drug Targets. 2013, 12 (3): 413-425.

  127. 127.

    Park KI, Teng YD, Snyder EY: The injured brain interacts reciprocally with neural stem cells supported by scaffolds to reconstitute lost tissue. Nat Biotechnol. 2002, 20 (11): 1111-1117.

  128. 128.

    Bible E, Chau DY, Alexander MR, Price J, Shakesheff KM, Modo M: The support of neural stem cells transplanted into stroke-induced brain cavities by PLGA particles. Biomaterials. 2009, 30 (16): 2985-2994.

  129. 129.

    Cheng TY, Chen MH, Chang WH, Huang MY, Wang TW: Neural stem cells encapsulated in a functionalized self-assembling peptide hydrogel for brain tissue engineering. Biomaterials. 2013, 34 (8): 2005-2016.

  130. 130.

    Aliabadi HM, Lavasanifar A: Polymeric micelles for drug delivery. Expert Opin Drug Deliv. 2006, 3 (1): 139-162.

  131. 131.

    de Boer R, Knight AM, Spinner RJ, Malessy MJ, Yaszemski MJ, Windebank AJ: In vitro and in vivo release of nerve growth factor from biodegradable poly-lactic-co-glycolic-acid microspheres. J Biomed Mater Res A. 2010, 95 (4): 1067-1073.

  132. 132.

    Kerkhoff H, Jennekens FG: Peripheral nerve lesions: the neuropharmacological outlook. Clin Neurol Neurosurg. 1993, 95 (Suppl): S103-S108.

  133. 133.

    Maxwell DJ, Hicks BC, Parsons S, Sakiyama-Elbert SE: Development of rationally designed affinity-based drug delivery systems. Acta Biomater. 2005, 1 (1): 101-113.

  134. 134.

    Pean JM, Venier-Julienne MC, Boury F, Menei P, Denizot B, Benoit JP: NGF release from poly(D,L-lactide-co-glycolide) microspheres. Effect of some formulation parameters on encapsulated NGF stability. J Control Release. 1998, 56 (1–3): 175-187.

  135. 135.

    Taylor SJ, McDonald JW, Sakiyama-Elbert SE: Controlled release of neurotrophin-3 from fibrin gels for spinal cord injury. J Control Release. 2004, 98 (2): 281-294.

  136. 136.

    Yoshimura N, Bennett NE, Hayashi Y, Ogawa T, Nishizawa O, Chancellor MB, de Groat WC, Seki S: Bladder overactivity and hyperexcitability of bladder afferent neurons after intrathecal delivery of nerve growth factor in rats. J Neurosci. 2006, 26 (42): 10847-10855.

  137. 137.

    Andrieu-Soler C, Aubert-Pouessel A, Doat M, Picaud S, Halhal M, Simonutti M, Venier-Julienne MC, Benoit JP, Behar-Cohen F: Intravitreous injection of PLGA microspheres encapsulating GDNF promotes the survival of photoreceptors in the rd1/rd1 mouse. Mol Vis. 2005, 11: 1002-1011.

  138. 138.

    Fu AS, Thatiparti TR, Saidel GM, von Recum HA: Experimental studies and modeling of drug release from a tunable affinity-based drug delivery platform. Ann Biomed Eng. 2011, 39 (9): 2466-2475.

  139. 139.

    Grondin R, Gash DM: Glial cell line-derived neurotrophic factor (GDNF): a drug candidate for the treatment of Parkinson's disease. J Neurol. 1998, 245 (11 Suppl 3): P35-P42.

  140. 140.

    Moore AM, Wood MD, Chenard K, Hunter DA, Mackinnon SE, Sakiyama-Elbert SE, Borschel GH: Controlled delivery of glial cell line-derived neurotrophic factor enhances motor nerve regeneration. J Hand Surg [Am]. 2010, 35 (12): 2008-2017.

  141. 141.

    Willerth SM, Sakiyama-Elbert SE: Approaches to neural tissue engineering using scaffolds for drug delivery. Adv Drug Deliv Rev. 2007, 59 (4–5): 325-338.

  142. 142.

    Wood MD, Moore AM, Hunter DA, Tuffaha S, Borschel GH, Mackinnon SE, Sakiyama-Elbert SE: Affinity-based release of glial-derived neurotrophic factor from fibrin matrices enhances sciatic nerve regeneration. Acta Biomater. 2009, 5 (4): 959-968.

  143. 143.

    Agterberg MJ, Versnel H, van Dijk LM, de Groot JC, Klis SF: Enhanced survival of spiral ganglion cells after cessation of treatment with brain-derived neurotrophic factor in deafened guinea pigs. J Assoc Res Otolaryngol. 2009, 10 (3): 355-367.

  144. 144.

    Hou S, Tian W, Xu Q, Cui F, Zhang J, Lu Q, Zhao C: 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. Neuroscience. 2006, 137 (2): 519-529.

  145. 145.

    Mehrotra S, Lynam D, Maloney R, Pawelec KM, Tuszynski MH, Lee I, Chan C, Sakamoto J: Time Controlled Protein Release from Layer-by-Layer Assembled Multilayer Functionalized Agarose Hydrogels. Adv Funct Mater. 2010, 20 (2): 247-258.

  146. 146.

    Johnson PJ, Parker SR, Sakiyama-Elbert SE: Controlled release of neurotrophin-3 from fibrin-based tissue engineering scaffolds enhances neural fiber sprouting following subacute spinal cord injury. Biotechnol Bioeng. 2009, 104 (6): 1207-1214.

  147. 147.

    Johnson PJ, Tatara A, Shiu A, Sakiyama-Elbert SE: Controlled release of neurotrophin-3 and platelet-derived growth factor from fibrin scaffolds containing neural progenitor cells enhances survival and differentiation into neurons in a subacute model of SCI. Cell Transplant. 2010, 19 (1): 89-101.

  148. 148.

    Willerth SM, Rader A, Sakiyama-Elbert SE: The effect of controlled growth factor delivery on embryonic stem cell differentiation inside fibrin scaffolds. Stem Cell Res. 2008, 1 (3): 205-218.

  149. 149.

    Asmani MN, Ai J, Amoabediny G, Noroozi A, Azami M, Ebrahimi-Barough S, Navaei-Nigjeh M, Ai A, Jafarabadi M: Three-dimensional culture of differentiated endometrial stromal cells to oligodendrocyte progenitor cells (OPCs) in fibrin hydrogel. Cell Biol Int. 2013, 37 (12): 1340-1349.

  150. 150.

    Delgado-Rivera R, Harris SL, Ahmed I, Babu AN, Patel RP, Ayres V, Flowers D, Meiners S: Increased FGF-2 secretion and ability to support neurite outgrowth by astrocytes cultured on polyamide nanofibrillar matrices. Matrix Biol. 2009, 28 (3): 137-147.

  151. 151.

    Galderisi U, Peluso G, Di Bernardo G, Calarco A, D'Apolito M, Petillo O, Cipollaro M, Fusco FR, Melone MA: Efficient cultivation of neural stem cells with controlled delivery of FGF-2. Stem Cell Res. 2013, 10 (1): 85-94.

  152. 152.

    Keenan TM, Grinager JR, Procak AA, Svendsen CN: In vitro localization of human neural stem cell neurogenesis by engineered FGF-2 gradients. Integr Biol (Camb). 2012, 4 (12): 1522-1531.

  153. 153.

    Lam HJ, Patel S, Wang A, Chu J, Li S: In vitro regulation of neural differentiation and axon growth by growth factors and bioactive nanofibers. Tissue Eng Part A. 2010, 16 (8): 2641-2648.

  154. 154.

    Lee YB, Polio S, Lee W, Dai G, Menon L, Carroll RS, Yoo SS: Bio-printing of collagen and VEGF-releasing fibrin gel scaffolds for neural stem cell culture. Exp Neurol. 2010, 223 (2): 645-652.

  155. 155.

    Nakajima M, Ishimuro T, Kato K, Ko IK, Hirata I, Arima Y, Iwata H: Combinatorial protein display for the cell-based screening of biomaterials that direct neural stem cell differentiation. Biomaterials. 2007, 28 (6): 1048-1060.

  156. 156.

    Yamashita T, Deguchi K, Nagotani S, Abe K: Vascular protection and restorative therapy in ischemic stroke. Cell Transplant. 2011, 20 (1): 95-97.

  157. 157.

    Gelain F, Panseri S, Antonini S, Cunha C, Donega M, Lowery J, Taraballi F, Cerri G, Montagna M, Baldissera F, Vescovi A: Transplantation of nanostructured composite scaffolds results in the regeneration of chronically injured spinal cords. ACS Nano. 2011, 5 (1): 227-236.

  158. 158.

    Shoichet MS, Tator CH, Poon P, Kang C, Baumann MD: Intrathecal drug delivery strategy is safe and efficacious for localized delivery to the spinal cord. Prog Brain Res. 2007, 161: 385-392.

  159. 159.

    Bible E, Qutachi O, Chau DY, Alexander MR, Shakesheff KM, Modo M: Neo-vascularization of the stroke cavity by implantation of human neural stem cells on VEGF-releasing PLGA microparticles. Biomaterials. 2012, 33 (30): 7435-7446.

  160. 160.

    Aktas Y, Andrieux K, Alonso MJ, Calvo P, Gursoy RN, Couvreur P, Capan Y: Preparation and in vitro evaluation of chitosan nanoparticles containing a caspase inhibitor. Int J Pharm. 2005, 298 (2): 378-383.

  161. 161.

    Bodmeier R, Chen HG, Paeratakul O: A novel approach to the oral delivery of micro- or nanoparticles. Pharm Res. 1989, 6 (5): 413-417.

  162. 162.

    Pan Y, Li YJ, Zhao HY, Zheng JM, Xu H, Wei G, Hao JS, Cui FD: Bioadhesive polysaccharide in protein delivery system: chitosan nanoparticles improve the intestinal absorption of insulin in vivo. Int J Pharm. 2002, 249 (1–2): 139-147.

  163. 163.

    Sun D, Bullock MR, McGinn MJ, Zhou Z, Altememi N, Hagood S, Hamm R, Colello RJ: Basic fibroblast growth factor-enhanced neurogenesis contributes to cognitive recovery in rats following traumatic brain injury. Exp Neurol. 2009, 216 (1): 56-65.

  164. 164.

    Yoshimura S, Teramoto T, Whalen MJ, Irizarry MC, Takagi Y, Qiu J, Harada J, Waeber C, Breakefield XO, Moskowitz MA: FGF-2 regulates neurogenesis and degeneration in the dentate gyrus after traumatic brain injury in mice. J Clin Invest. 2003, 112 (8): 1202-1210.

  165. 165.

    Rifkin DB, Moscatelli D: Recent developments in the cell biology of basic fibroblast growth factor. J Cell Biol. 1989, 106: 87-95.

  166. 166.

    Shiba T, Nishimura D, Kawazoe Y, Onodera Y, Tsutsumi K, Nakamura R, Ohshiro M: Modulation of mitogenic activity of fibroblast growth factors by inorganic polyphosphate. J Biol Chem. 2003, 278 (29): 26788-26792.

  167. 167.

    Sommer A, Rifkin DB: Interaction of heparin with human basic fibroblast growth factor: protection of the angiogenic protein from proteolytic degradation by a glycosaminoglycan. J Cell Physiol. 1989, 138 (1): 215-220.

  168. 168.

    Skop NB, Calderon F, Levison SW, Gandhi CD, Cho CH: Heparin crosslinked chitosan microspheres for the delivery of neural stem cells and growth factors for central nervous system repair. Acta Biomater. 2013, 9 (6): 6834-6843.

  169. 169.

    Skop NB, Calderon F, Cho CH, Gandhi CD, Levison SW: Optimizing a multifunctional microsphere scaffold to improve neural precursor cell transplantation for traumatic brain injury repair. J Tissue Eng Regen Med. 2013

  170. 170.

    Blits B, Kitay BM, Farahvar A, Caperton CV, Dietrich WD, Bunge MB: Lentiviral vector-mediated transduction of neural progenitor cells before implantation into injured spinal cord and brain to detect their migration, deliver neurotrophic factors and repair tissue. Restor Neurol Neurosci. 2005, 23 (5–6): 313-324.

  171. 171.

    Sakata H, Narasimhan P, Niizuma K, Maier CM, Wakai T, Chan PH: Interleukin 6-preconditioned neural stem cells reduce ischaemic injury in stroke mice. Brain. 2012, 135 (Pt 11): 3298-3310.

  172. 172.

    Mahor S, Collin E, Dash BC, Pandit A: Controlled release of plasmid DNA from hyaluronan nanoparticles. Curr Drug Deliv. 2011, 8 (4): 354-362.

  173. 173.

    Miao PH, He CX, Hu YL, Tabata Y, Gao JQ, Hu ZJ: Impregnation of plasmid DNA into three-dimensional PLGA scaffold enhances DNA expression of mesenchymal stem cells in vitro. Pharmazie. 2012, 67 (3): 229-232.

  174. 174.

    Oh SH, Kim TH, Jang SH, Im GI, Lee JH: Hydrophilized 3D porous scaffold for effective plasmid DNA delivery. J Biomed Mater Res A. 2011, 97 (4): 441-450.

  175. 175.

    Xiao B, Wang X, Qiu Z, Ma J, Zhou L, Wan Y, Zhang S: A dual-functionally modified chitosan derivative for efficient liver-targeted gene delivery. J Biomed Mater Res A. 2013, 101 (7): 1888-1897.

  176. 176.

    Kim JH, Park JS, Yang HN, Woo DG, Jeon SY, Do HJ, Lim HY, Kim JM, Park KH: The use of biodegradable PLGA nanoparticles to mediate SOX9 gene delivery in human mesenchymal stem cells (hMSCs) and induce chondrogenesis. Biomaterials. 2011, 32 (1): 268-278.

  177. 177.

    Capito RM, Spector M: Collagen scaffolds for nonviral IGF-1 gene delivery in articular cartilage tissue engineering. Gene Ther. 2007, 14 (9): 721-732.

  178. 178.

    Myon L, Ferri J, Chai F, Blanchemain N, Raoul G: [Oro-maxillofacial bone tissue engineering combining biomaterials, stem cells, and gene therapy]. Rev Stomatol Chir Maxillofac. 2011, 112 (4): 201-211.

  179. 179.

    Nie H, Wang CH: Fabrication and characterization of PLGA/HAp composite scaffolds for delivery of BMP-2 plasmid DNA. J Control Release. 2007, 120 (1–2): 111-121.

  180. 180.

    Mehta M, Schmidt-Bleek K, Duda GN, Mooney DJ: Biomaterial delivery of morphogens to mimic the natural healing cascade in bone. Adv Drug Deliv Rev. 2012, 64 (12): 1257-1276.

  181. 181.

    Kizjakina K, Bryson JM, Grandinetti G, Reineke TM: Cationic glycopolymers for the delivery of pDNA to human dermal fibroblasts and rat mesenchymal stem cells. Biomaterials. 2012, 33 (6): 1851-1862.

  182. 182.

    McGinn AN, Nam HY, Ou M, Hu N, Straub CM, Yockman JW, Bull DA, Kim SW: Bioreducible polymer-transfected skeletal myoblasts for VEGF delivery to acutely ischemic myocardium. Biomaterials. 2011, 32 (3): 942-949.

  183. 183.

    Thiersch M, Rimann M, Panagiotopoulou V, Ozturk E, Biedermann T, Textor M, Luhmann TC, Hall H: The angiogenic response to PLL-g-PEG-mediated HIF-1alpha plasmid DNA delivery in healthy and diabetic rats. Biomaterials. 2013, 34 (16): 4173-4182.

  184. 184.

    Chen F, Wan H, Xia T, Guo X, Wang H, Liu Y, Li X: Promoted regeneration of mature blood vessels by electrospun fibers with loaded multiple pDNA-calcium phosphate nanoparticles. Eur J Pharm Biopharm. 2013, 85 (3 Pt A): 699-710.

  185. 185.

    Cholas RH, Hsu HP, Spector M: The reparative response to cross-linked collagen-based scaffolds in a rat spinal cord gap model. Biomaterials. 2012, 33 (7): 2050-2059.

  186. 186.

    McConnell SK: Constructing the cerebral cortex: neurogenesis and fate determination. Neuron. 1995, 15 (4): 761-768.

  187. 187.

    Zou B, Liu Y, Luo X, Chen F, Guo X, Li X: Electrospun fibrous scaffolds with continuous gradations in mineral contents and biological cues for manipulating cellular behaviors. Acta Biomater. 2012, 8 (4): 1576-1585.

Download references


This study was partially supported by the New Jersey Commission on Brain Injury Research grant number 08.001.BIR2 awarded to C.D.G. and S.W.L. and fellowship grant number CBIR12FEL025 awarded to N.B.S.

Author information

Correspondence to Steven W Levison.

Additional information

Competing interests

The authors have no competing interests to report.

Authors’ contributions

NBS and SWL drafted the review. All of the authors read, edited and provided their approval of the final manuscript.

Authors’ original submitted files for images

Below are the links to the authors’ original submitted files for images.

Authors’ original file for figure 1

Authors’ original file for figure 2

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark


  • Tissue engineering
  • Neural stem cells
  • Scaffold
  • Biomaterials
  • CNS
  • Brain injury
  • TBI
  • Stroke
  • Transplantation
  • Review