Biomaterial design strategies for the treatment of spinal cord injuries

Bundle Gel Fibers with a Tunable Microenvironment for in Vitro Neuron Cell Guiding

As scaffolds for neuron cell guiding in vitro, gel fibers with a bundle structure, comprising multiple microfibrils, were fabricated using a microfluidic device system by casting a phase-separating polymer blend solution comprising hydroxypropyl cellulose (HPC) and sodium alginate (Na-Alg). The topology and stiffness of the obtained bundle gel fibers depended on their microstructure derived by the polymer blend ratio of HPC and Na-Alg. High concentrations of Na-Alg led to the formation of small microfibrils in a one-bundle gel fiber and stiff characteristics. These bundle gel fibers permitted for the elongation of the neuron cells along their axon orientation with the long axis of fibers. In addition, human-induced pluripotent-stem-cell-derived dopaminergic neuron progenitor cells were differentiated into neuronal cells on the bundle gels. The bundle gel fibers demonstrated an enormous potential as cell culture scaffold materials with an optimal microenvironment for guiding neuron cells.

Transplantation of Schwann Cells Inside PVDF-TrFE Conduits to Bridge Transected Rat Spinal Cord Stumps to Promote Axon Regeneration Across the Gap

Among various models for spinal cord injury in rats, the contusion model is the most often used because it is the most common type of human spinal cord injury. The complete transection model, although not as clinically relevant as the contusion model, is the most rigorous method to evaluate axon regeneration. In the contusion model, it is difficult to distinguish regenerated from sprouted or spared axons due to the presence of remaining tissue post injury. In the complete transection model, a bridging method is necessary to fill the gap and create continuity from the rostral to the caudal stumps in order to evaluate the effectiveness of the treatments. A reliable bridging surgery is essential to test outcome measures by reducing the variability due to the surgical method. The protocols described here are used to prepare Schwann cells (SCs) and conduits prior to transplantation, complete transection of the spinal cord at thoracic level 8 (T8), insert the conduit, and transplant SCs into the conduit. This approach also uses in situ gelling of an injectable basement membrane matrix with SC transplantation that allows improved axon growth across the rostral and caudal interfaces with the host tissue.

An injectable hydrogel enhances tissue repair after spinal cord injury by promoting extracellular matrix remodeling

The cystic cavity that develops following injuries to brain or spinal cord is a major obstacle for tissue repair in central nervous system (CNS). Here we report that injection of imidazole-poly(organophosphazenes) (I-5), a hydrogel with thermosensitive sol–gel transition behavior, almost completely eliminates cystic cavities in a clinically relevant rat spinal cord injury model. Cystic cavities are bridged by fibronectin-rich extracellular matrix. The fibrotic extracellular matrix remodeling is mediated by matrix metalloproteinase-9 expressed in macrophages within the fibrotic extracellular matrix. A poly(organophosphazenes) hydrogel lacking the imidazole moiety, which physically interacts with macrophages via histamine receptors, exhibits substantially diminished bridging effects. I-5 injection improves coordinated locomotion, and this functional recovery is accompanied by preservation of myelinated white matter and motor neurons and an increase in axonal reinnervation of the lumbar motor neurons. Our study demonstrates that dynamic interactions between inflammatory cells and injectable biomaterials can induce beneficial extracellular matrix remodeling to stimulate tissue repair following CNS injuries.

The cystic cavity that develops following injuries to brain or spinal cord is a major obstacle. Here the authors show an injection of imidazole poly(organophosphazenes), a hydrogel with thermosensitive sol–gel transition behavior, almost completely eliminates cystic cavities in a clinically relevant rat spinal cord injury model.

Human placenta-derived mesenchymal stem cells loaded on linear ordered collagen scaffold improves functional recovery after completely transected spinal cord injury in canine

Traumatic spinal cord injury (SCI) is a major challenge in the clinic. In this study, we sought to examine the synergistic effects of linear ordered collagen scaffold (LOCS) and human placenta-derived mesenchymal stem cells (hPMSCs) when transplanted into completely transected beagle dogs. After 36 weeks observation, we found that LOCS+hPMSCs implants promoted better hindlimb locomotor recovery than was observed in the non-treatment (control) group and LOCS group. Histological analysis showed that the regenerated tissue after treatment was well integrated with the host tissue, and dramatically reduced the volume of cystic and chondroitin sulfate proteoglycans (CSPGs) expression. Furthermore, the LOCS+hPMSCs group also showed more neuron-specific βIII-tubulin (Tuj-1)- and NeuN-positive neurons in the lesion area, as well as axonal regeneration, remyelination and synapse formation in the lesion site. Additionally, dogs in the LOCS+hPMSCs group experienced enhanced sprouting of both ascending (CGRP-positive) sensory fibers and descending (5-HT- and TH-positive) motor fibers at the lesion area. All these data together suggested that the combined treatment had beneficial effects on neuronal regeneration and functional improvement in a canine complete transection model. Therefore, LOCS+hPMSCs implantation holds a great promise for bridging the nerve defect and may be clinically useful in the near future.

Biomaterials for Local, Controlled Drug Delivery to the Injured Spinal Cord

Affecting approximately 17,000 new people each year, spinal cord injury (SCI) is a devastating injury that leads to permanent paraplegia or tetraplegia. Current pharmacological approaches are limited in their ability to ameliorate this injury pathophysiology, as many are not delivered locally, for a sustained duration, or at the correct injury time point. With this review, we aim to communicate the importance of combinatorial biomaterial and pharmacological approaches that target certain aspects of the dynamically changing pathophysiology of SCI. After reviewing the pathophysiology timeline, we present experimental biomaterial approaches to provide local sustained doses of drug. In this review, we present studies using a variety of biomaterials, including hydrogels, particles, and fibers/conduits for drug delivery. Subsequently, we discuss how each may be manipulated to optimize drug release during a specific time frame following SCI. Developing polymer biomaterials that can effectively release drug to target specific aspects of SCI pathophysiology will result in more efficacious approaches leading to better regeneration and recovery following SCI.

Thermogelling chitosan lactate hydrogel improves functional recovery after a C2 spinal cord hemisection in rat

The present study was designed to provide an appropriate micro-environment for regenerating axotomized neurons and proliferating/migrating cells. Because of its intrinsic permissive properties, biocompatibility and biodegradability, we chose to evaluate the therapeutic effectiveness of a chitosan-based biopolymer. The biomaterial toxicity was measured through in vitro test based on fibroblast cell survival on thermogelling chitosan lactate hydrogel substrate and then polymer was implanted into a C2 hemisection of the rat spinal cord. Animals were randomized into three experimental groups (Control, Lesion and Lesion + Hydrogel) and functional tests (ladder walking and forelimb grip strength tests, respiratory assessment by whole-body plethysmography measurements) were used, once a week during 10 weeks, to evaluate post-traumatic recoveries. Then, electrophysiological examinations (reflexivity of the sub-lesional region, ventilatory adjustments to muscle fatigue known to elicit the muscle metaboreflex and phrenic nerve recordings during normoxia and temporary hypoxia) were performed. In vitro results indicated that the chitosan matrix is a non-toxic biomaterial that allowed fibroblast survival. Furthermore, implanted animals showed improvements of their ladder walking scores from the 4th week post-implantation. Finally, electrophysiological recordings indicated that animals receiving the chitosan matrix exhibited recovery of the H-reflex rate sensitive depression, the ventilatory response to repetitive muscle stimulation and an increase of the phrenic nerve activity to asphyxia compared to lesioned and nonimplanted animals. This study indicates that hydrogel based on chitosan constitute a promising therapeutic approach to repair damaged spinal cord or may be used as an adjuvant with other treatments to enhance functional recovery after a central nervous system damage. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2004-2019, 2017.

Cation Tuning of Supramolecular Gel Properties: A New Paradigm for Sustained Drug Delivery

Hydrogels formed by the self-assembly of low-molecular-weight gelators (LMWGs) are promising scaffolds for drug-delivery applications. A new biocompatible hydrogel, resulting from the self-assembly of nucleotide-lipid salts can be safely injected in vivo. The resulting hydrogel provides sustained-release of protein for more than a week.

Biomaterials and cells for neural tissue engineering: Current choices

The treatment of nerve injuries has taken a new dimension with the development of tissue engineering techniques. Prior to tissue engineering, suturing and surgery were the only options for effective treatment. With the advent of tissue engineering, it is now possible to design a scaffold that matches the exact biological and mechanical properties of the tissue. This has led to substantial reduction in the complications posed by surgeries and suturing to the patients. New synthetic and natural polymers are being applied to test their efficiency in generating an ideal scaffold. Along with these, cells and growth factors are also being incorporated to increase the efficiency of a scaffold. Efforts are being made to devise a scaffold that is biodegradable, biocompatible, conducting and immunologically inert. The ultimate goal is to exactly mimic the extracellular matrix in our body, and to elicit a combination of biochemical, topographical and electrical cues via various polymers, cells and growth factors, using which nerve regeneration can efficiently occur.

Collagen/heparin sulfate scaffolds fabricated by a 3D bioprinter improved mechanical properties and neurological function after spinal cord injury in rats

Effective treatments promoting axonal regeneration and functional recovery for spinal cord injury (SCI) are still in the early stages of development. Most approaches have been focused on providing supportive substrates for guiding neurons and overcoming the physical and chemical barriers to healing that arise after SCI. Although collagen has become a promising natural substrate with good compatibility, its low mechanical properties restrict its potential applications. The mechanical properties mainly rely on the composition and pore structure of scaffolds. For the composition of a scaffold, we used heparin sulfate to react with collagen by crosslinking. For the structure, we adopted a three-dimensional (3D) printing technology to fabricate a scaffold with a uniform pore distributions. We observed that the internal structure of the scaffold printed with a 3D bioprinter was regular and porous. We also found that both the compression modulus and strengths of the scaffold were significantly enhanced by the collagen/heparin sulfate composition compared to a collagen scaffold. Meanwhile, the collagen/heparin sulfate scaffold presented good biocompatibility when it was co-cultured with neural stem cells in vitro. We also demonstrated that heparin sulfate modification significantly improved bFGF immobilization and absorption to the collagen by examining the release kinetics of bFGF from scaffolds. Two months after implantating the scaffold into transection lesions in T10 of the spinal cord in rats, the collagen/heparin sulfate group demonstrated significant recovery of locomotor function and according to electrophysiological examinations. Parallel to functional recovery, collagen/heparin sulfate treatment further ameliorated the pathological process and markedly increased the number of neurofilament (NF) positive cells compared to collagen treatment alone. These data suggested that a collagen/heparin sulfate scaffold fabricated by a 3D bioprinter could enhance the mechanical properties of collagen and provide continuous guidance channels for axons, which would improve the neurological function after SCI. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1324-1332, 2017.

A bridging SF/Alg composite scaffold loaded NGF for spinal cord injury repair

Neurons loss and axons degeneration after spinal cord injury (SCI) gradually give rise to result in functional motor and sensory impairment. A bridging biomaterial scaffold that allows the axons to grow through has been investigated for the repair of injured spinal cord. In this study, we introduced a silk fibroin (SF)-based neurobridge as scaffold enriched with/without nerve growth factor (NGF) that can be utilized as a therapeutic approach for spinal cord repair. NGF released from alginate (Alg) microspheres on SF scaffold (SF/Alg composites scaffolds) to the central lesion site of SCI significantly enhanced the sparing of spinal cord tissue and increased the number of surviving neurons. This optimal multi-disciplinary approach of combining biomaterials, controlled-release microspheres and neurotrophic factors offers a promising treatment for the injured spinal cord.

Three-dimensional aligned nanofibers-hydrogel scaffold for controlled non-viral drug/gene delivery to direct axon regeneration in spinal cord injury treatment

Spinal cord injuries (SCI) often lead to persistent neurological dysfunction due to failure in axon regeneration. Unfortunately, currently established treatments, such as direct drug administration, do not effectively treat SCI due to rapid drug clearance from our bodies. Here, we introduce a three-dimensional aligned nanofibers-hydrogel scaffold as a bio-functionalized platform to provide sustained non-viral delivery of proteins and nucleic acid therapeutics (small non-coding RNAs), along with synergistic contact guidance for nerve injury treatment. A hemi-incision model at cervical level 5 in the rat spinal cord was chosen to evaluate the efficacy of this scaffold design. Specifically, aligned axon regeneration was observed as early as one week post-injury. In addition, no excessive inflammatory response and scar tissue formation was triggered. Taken together, our results demonstrate the potential of our scaffold for neural tissue engineering applications.

Stem cells for spinal cord injury: Strategies to inform differentiation and transplantation

The complex pathology of spinal cord injury (SCI), involving a cascade of secondary events and the formation of inhibitory barriers, hampers regeneration across the lesion site and often results in irreversible loss of motor function. The limited regenerative capacity of endogenous cells after SCI has led to a focus on the development of cell therapies that can confer both neuroprotective and neuroregenerative benefits. Stem cells have emerged as a candidate cell source because of their ability to self-renew and differentiate into a multitude of specialized cell types. While ethical and safety concerns impeded the use of stem cells in the past, advances in isolation and differentiation methods have largely mitigated these issues. A confluence of work in stem cell biology, genetics, and developmental neurobiology has informed the directed differentiation of specific spinal cell types. After transplantation, these stem cell-derived populations can replace lost cells, provide trophic support, remyelinate surviving axons, and form relay circuits that contribute to functional recovery. Further refinement of stem cell differentiation and transplantation methods, including combinatorial strategies that involve biomaterial scaffolds and drug delivery, is critical as stem cell-based treatments enter clinical trials. Biotechnol. Bioeng. 2017;114: 245-259. © 2016 Wiley Periodicals, Inc.

NFAT5 protects astrocytes against oxygen-glucose-serum deprivation/restoration damage via the SIRT1/Nrf2 pathway

Nuclear factor of activated T cells (NFAT) is a multifunctional cytokine family. NFAT5 was recently reported to be involved in many neuronal functions, but its specific function remains unclear. In this study, our aim is to investigate whether NFAT5 overexpression can protect astrocytes against oxygen-glucose-serum deprivation/restoration (OGSD/R) damage. In vivo, rats were subjected to ischemia-reperfusion injury, resulting in increased water content, infarct volume, and expression of NFAT5 protein in rat spinal cord. After primary culture for spinal cord astrocytes, the in vitro OGSD/R model was established. The results of the CCK8 assay and flow cytometry showed that, in the OGSD/R group, astrocyte cell viability was downregulated, but astrocyte apoptosis increased. Caspase 3 activity increased as well. Levels of NFAT5, as detected by real-time quantitative PCR and western blot, decreased under OGSD/R, as did SIRT1. Commercial kits for activity assays were used to show that OGSD/R inhibited SIRT1 activation but accelerated SOD activation after OGSD/R. Next, pcDNA-NFAT5 or NFAT5 siRNA was transfected into astrocytes. Overexpression of NFAT5 not only promoted the survival of the astrocytes and SIRT1 activation under OGSD/R but also inhibited cell apoptosis and SOD activation. Moreover, overexpression of NFAT5 apparently diminished histone acetylation and promoted the nuclear transport of Nrf2. Our results show that NFAT5 protects spinal astrocytes in a manner that depends on activation of the SIRT1/Nrf2 pathway. These findings present a novel potential molecular mechanism for NFAT5 therapy in the context of spinal cord injury.

Electrospun Fibers for Drug Delivery after Spinal Cord Injury and the Effects of Drug Incorporation on Fiber Properties

There is currently no cure for individuals with spinal cord injury (SCI). While many promising approaches are being tested in clinical trials, the complexity of SCI limits several of these approaches from aiding complete functional recovery. Several different categories of biomaterials are investigated for their ability to guide axonal regeneration, to deliver proteins or small molecules locally, or to improve the viability of transplanted stem cells. The purpose of this study is to provide a brief overview of SCI, present the different categories of biomaterial scaffolds that direct and guide axonal regeneration, and then focus specifically on electrospun fiber guidance scaffolds. Much like other polymer guidance approaches, electrospun fibers can retain and deliver therapeutic drugs. The experimental section presents new data showing the incorporation of two therapeutic drugs into electrospun poly-L-lactic acid fibers. Two different concentrations of either riluzole or neurotrophin-3 were loaded into the electrospun fibers to examine the effect of drug concentration on the physical characteristics of the fibers (fiber alignment and fiber diameter). Overall, the drugs were successfully incorporated into the fibers and the release was related to the loading concentration. The fiber diameter decreased with the inclusion of the drug, and the decreased diameter was correlated with a decrease in fiber alignment. Subsequently, the study includes considerations for successful incorporation of a therapeutic drug without changing the physical properties of the fibers.

Tissue Engineering Approaches to Modulate the Inflammatory Milieu following Spinal Cord Injury

Tissue engineering strategies have shown promise in promoting healing and regeneration after spinal cord injury (SCI); however, these strategies are limited by inflammation and the immune response. Infiltration of cells of the innate and adaptive immune responses and the inflammation that follows cause secondary damage adjacent to the injury, increased scarring, and a potently inhibitory environment for the regeneration of damaged neurons. While the inflammation that ensues is typically associated with limited regeneration, the immune response is a crucial element in the closing of the blood-brain barrier, minimizing the spread of injury, and initiating healing. This review summarizes the strategies that have been developed to modulate the immune response towards an anti-inflammatory environment that is permissive to the regeneration of neurons, glia, and parenchyma. We focus on the use of biomaterials, biologically active molecules, gene therapy, nanoparticles, and stem cells to modulate the immune response, and illustrate concepts for future therapies. Current clinical treatments for SCI are limited to systemic hypothermia or methylprednisolone, which both act by systemically mitigating the effects of immune response but have marginal efficacy. Herein, we discuss emerging research strategies to further enhance these clinical treatments by directly targeting specific aspects of the immune response.

Combination scaffolds of salmon fibrin, hyaluronic acid, and laminin for human neural stem cell and vascular tissue engineering

Human neural stem/progenitor cells (hNSPCs) are good candidates for treating central nervous system (CNS) trauma since they secrete beneficial trophic factors and differentiate into mature CNS cells; however, many cells die after transplantation. This cell death can be ameliorated by inclusion of a biomaterial scaffold, making identification of optimal scaffolds for hNSPCs a critical research focus. We investigated the properties of fibrin-based scaffolds and their effects on hNSPCs and found that fibrin generated from salmon fibrinogen and thrombin stimulates greater hNSPC proliferation than mammalian fibrin. Fibrin scaffolds degrade over the course of a few days in vivo, so we sought to develop a novel scaffold that would retain the beneficial properties of fibrin but degrade more slowly to provide longer support for hNSPCs. We found combination scaffolds of salmon fibrin with interpenetrating networks (IPNs) of hyaluronic acid (HA) with and without laminin polymerize more effectively than fibrin alone and generate compliant hydrogels matching the physical properties of brain tissue. Furthermore, combination scaffolds support hNSPC proliferation and differentiation while significantly attenuating the cell-mediated degradation seen with fibrin alone. HNSPCs express two fibrinogen-binding integrins, αVβ1 and α5β1, and several laminin binding integrins (α7β1, α6β1, α3β1) that can mediate interaction with the scaffold. Lastly, to test the ability of scaffolds to support vascularization, we analyzed human cord blood-derived endothelial cells alone and in co-culture with hNSPCs and found enhanced vessel formation and complexity in co-cultures within combination scaffolds. Overall, combination scaffolds of fibrin, HA, and laminin are excellent biomaterials for hNSPCs.

STATEMENT OF SIGNIFICANCE

Interest has increased recently in the development of biomaterials as neural stem cell transplantation scaffolds to treat central nervous system (CNS) injury since scaffolds improve survival and integration of transplanted cells. We report here on a novel combination scaffold composed of fibrin, hyaluronic acid, and laminin to support human neural stem/progenitor cell (hNSPC) function. This combined biomaterial scaffold has appropriate physical properties for hNSPCs and the CNS, supports hNSPC proliferation and differentiation, and attenuates rapid cell-mediated scaffold degradation. The hNSPCs and scaffold components synergistically encourage new vessel formation from human endothelial cells. This work marks the first report of a combination scaffold supporting human neural and vascular cells to encourage vasculogenesis, and sets a benchmark for biomaterials to treat CNS injury.

Enhanced noradrenergic axon regeneration into schwann cell-filled PVDF-TrFE conduits after complete spinal cord transection

Schwann cell (SC) transplantation has been utilized for spinal cord repair and demonstrated to be a promising therapeutic strategy. In this study, we investigated the feasibility of combining SC transplantation with novel conduits to bridge the completely transected adult rat spinal cord. This is the first and initial study to evaluate the potential of using a fibrous piezoelectric polyvinylidene fluoride trifluoroethylene (PVDF-TrFE) conduit with SCs for spinal cord repair. PVDF-TrFE has been shown to enhance neurite growth in vitro and peripheral nerve repair in vivo. In this study, SCs adhered and proliferated when seeded onto PVDF-TrFE scaffolds in vitro. SCs and PVDF-TrFE conduits, consisting of random or aligned fibrous inner walls, were transplanted into transected rat spinal cords for 3 weeks to examine early repair. Glial fibrillary acidic protein (GFAP)⁺ astrocyte processes and GFP (green fluorescent protein)-SCs were interdigitated at both rostral and caudal spinal cord/SC transplant interfaces in both types of conduits, indicative of permissivity to axon growth. More noradrenergic/DβH⁺ (dopamine-beta-hydroxylase) brainstem axons regenerated across the transplant when greater numbers of GFAP⁺ astrocyte processes were present. Aligned conduits promoted extension of DβH⁺ axons and GFAP⁺ processes farther into the transplant than random conduits. Sensory CGRP⁺ (calcitonin gene-related peptide) axons were present at the caudal interface. Blood vessels formed throughout the transplant in both conduits. This study demonstrates that PVDF-TrFE conduits harboring SCs are promising for spinal cord repair and deserve further investigation. Biotechnol. Bioeng. 2017;114: 444-456. © 2016 Wiley Periodicals, Inc.

Reducing neuroinflammation by delivery of IL-10 encoding lentivirus from multiple-channel bridges

The spinal cord is unable to regenerate after injury largely due to growth‐inhibition by an inflammatory response to the injury that fails to resolve, resulting in secondary damage and cell death. An approach that prevents inhibition by attenuating the inflammatory response and promoting its resolution through the transition of macrophages to anti‐inflammatory phenotypes is essential for the creation of a growth permissive microenvironment. Viral gene delivery to induce the expression of anti‐inflammatory factors provides the potential to provide localized delivery to alter the host inflammatory response. Initially, we investigated the effect of the biomaterial and viral components of the delivery system to influence the extent of cell infiltration and the phenotype of these cells. Bridge implantation reduces antigen‐presenting cell infiltration at day 7, and lentivirus addition to the bridge induces a transient increase in neutrophils in the spinal cord at day 7 and macrophages at day 14. Delivery of a lentivirus encoding IL‐10, an anti‐inflammatory factor that inhibits immune cell activation and polarizes the macrophage population towards anti‐inflammatory phenotypes, reduced neutrophil infiltration at both day 7 and day 28. Though IL‐10 lentivirus did not affect macrophages number, it skewed the macrophage population toward an anti‐inflammatory M2 phenotype and altered macrophage morphology. Additionally, IL‐10 delivery resulted in improved motor function, suggesting reduced secondary damage and increased sparing. Taken together, these results indicate that localized expression of anti‐inflammatory factors, such as IL‐10, can modulate the inflammatory response following spinal cord injury, and may be a key component of a combinatorial approach that targets the multiple barriers to regeneration and functional recovery.

Self-assembled nanofiber hydrogels for mechanoresponsive therapeutic anti-TNFα antibody delivery

Low molecular weight hydrogels, prepared from glycosyl-nucleoside-lipid amphiphiles, exhibit shear-thinning behaviour and reversible thermally- and mechanically-triggered sol-gel transitions. Using mechanical shear stimulation, the release of entrapped anti-TNFα increases and the released anti-TNFα demonstrates efficacy in in vitro neutralization bioassays. Delivery of anti-TNFα is of general interest and broad medicinal utility for treating autoimmune diseases such as rheumatoid arthritis.

Using primate neural stem cells cultured in self-assembling peptide nanofiber scaffolds to repair injured spinal cords in rats

STUDY DESIGN

Transplanted primates' neural stem cells (NSCs) tissue engineering complex into spinal cord injury (SCI) model rats, analyze and evaluate the long-term effects of repairing.

OBJECTIVES

Primate NSCs were cultured in self-assembling peptide nanofiber scaffolds to repair SCI.

SETTING

Sun Yat-sen Memorial Hospital, Guangzhou, China.

METHODS

Primate NSCs were isolated and cultured in self-assembling peptide nanofiber scaffolds. T10 SCI model was established; the rats were randomly divided into four groups: NSC plus self-assembling peptide scaffold group; NSC group; self-assembling peptide scaffold group; and control group. Immunohistochemical staining and electronic microscope were used to investigate the growth and differentiation of transplanted NSCs. The motor function of the hind limbs of rats was evaluated (P<0.05 was considered as statistically significant).

RESULTS

NSCs and NSCs cultured in self-assembling peptide nanofiber scaffolds could be induced to differentiation into neurons, glial cells and oligodendrocytes in vitro. The primate NSC culture was established in self-assembling peptide scaffolds. No significant difference was seen in the differentiation rate between primate NSCs cultured in self-assembling peptide nanofiber scaffolds and primate NSCs cultured in regular medium. The motor function of the hind limbs in the NSC plus self-assembling peptide scaffold group was significantly better than that of the other three groups. In addition, the NSCs of the NSC group mainly differentiated into astrocytes.

CONCLUSION

Transplantation of primate NSCs cultured in self-assembling peptide scaffolds is efficient for repairing the injured spinal cord and for improving the motor function of spinal cord in rats.

SPONSORSHIP

The National Natural Science Foundation of China; Science and Technology Office of Guangdong Province.

Inhibitor of PI3K/Akt Signaling Pathway Small Molecule Promotes Motor Neuron Differentiation of Human Endometrial Stem Cells Cultured on Electrospun Biocomposite Polycaprolactone/Collagen Scaffolds

Small molecules as useful chemical tools can affect cell differentiation and even change cell fate. It is demonstrated that LY294002, a small molecule inhibitor of phosphatidylinositol 3-kinase (PI3K)/Akt signal pathway, can inhibit proliferation and promote neuronal differentiation of mesenchymal stem cells (MSCs). The purpose of this study was to investigate the differentiation effect of Ly294002 small molecule on the human endometrial stem cells (hEnSCs) into motor neuron-like cells on polycaprolactone (PCL)/collagen scaffolds. hEnSCs were cultured in a neurogenic inductive medium containing 1 μM LY294002 on the surface of PCL/collagen electrospun fibrous scaffolds. Cell attachment and viability of cells on scaffolds were characterized by scanning electron microscope (SEM) and 3-(4,5-dimethylthiazoyl-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay. The expression of neuron-specific markers was assayed by real-time PCR and immunocytochemistry analysis after 15 days post induction. Results showed that attachment and differentiation of hEnSCs into motor neuron-like cells on the scaffolds with Ly294002 small molecule were higher than that of the cells on tissue culture plates as control group. In conclusion, PCL/collagen electrospun scaffolds with Ly294002 have potential for being used in neural tissue engineering because of its bioactive and three-dimensional structure which enhances viability and differentiation of hEnSCs into neurons through inhibition of the PI3K/Akt pathway. Thus, manipulation of this pathway by small molecules can enhance neural differentiation.

Differentiation of Human Endometrial Stem Cells into Schwann Cells in Fibrin Hydrogel as 3D Culture

Human endometrial stem cells (hEnSCs) are a new source of adult multipotent stem cells with the ability of differentiation into many cell lineages. Many stem cell sources are desirable for differentiation into Schwann cells. Schwann-like cells derived from hEnSCs may be one of the ideal alternative cell sources for Schwann cell generation. In this study, for differentiation of hEnSCs into Schwann cells, hEnSCs were induced with RA/FSK/PDGF-AA/HRG as an induction medium for 14 days. The cells were cultured in a tissue culture plate (TCP) and fibrin gel matrix. The viability of cultured cells in the fibrin gel and TCP was analyzed with 3-[4,5-dimethyl-2-thia-zolyl]-2, 5-diphenyl-2H-tetrazolium bromide (MTT) assay for 7 days. The attachment of cells was analyzed with SEM and DAPI staining. The expression of S100 and P75 as Schwann cell markers was evaluated by immunocytochemistry and quantitative real-time PCR (RT-PCR). The evaluation of the MTT assay and gene expression showed that the survival rate and differentiation of hEnSCs into Schwann cells in the fibrin gel were better than those in the TCP group. These results suggest that human EnSCs can be differentiated into Schwann cells in the fibrin gel better than in the TCP, and the fibrin gel might provide a suitable three-dimensional (3D) scaffold for clinical applications for cell therapy of the nervous system.

Biochemical Monitoring of Spinal Cord Injury by FT-IR Spectroscopy--Effects of Therapeutic Alginate Implant in Rat Models

Spinal cord injury (SCI) induces complex biochemical changes, which result in inhibition of nervous tissue regeneration abilities. In this study, Fourier-transform infrared (FT-IR) spectroscopy was applied to assess the outcomes of implants made of a novel type of non-functionalized soft calcium alginate hydrogel in a rat model of spinal cord hemisection (n = 28). Using FT-IR spectroscopic imaging, we evaluated the stability of the implants and the effects on morphology and biochemistry of the injured tissue one and six months after injury. A semi-quantitative evaluation of the distribution of lipids and collagen showed that alginate significantly reduced injury-induced demyelination of the contralateral white matter and fibrotic scarring in the chronic state after SCI. The spectral information enabled to detect and localize the alginate hydrogel at the lesion site and proved its long-term persistence in vivo. These findings demonstrate a positive impact of alginate hydrogel on recovery after SCI and prove FT-IR spectroscopic imaging as alternative method to evaluate and optimize future SCI repair strategies.

Synthesis and characterization of a chitosan based nanocomposite injectable hydrogel

The aim of the current study was to enhance the mechanical property of chitosan/β-glycerophosphate disodium salt (CS/GP) injectable hydrogels. A novel nanocomposite injectable hydrogel was prepared by introducing attapulgite (ATP) nano particles into the CS/GP hydrogels. The mechanical properties of the composite hydrogels with two different water contents were characterized by tensile test, the results shown that the tensile strength and elongation at break of composite hydrogels both increased obviously with increasing of ATP content. And, in our testing range, the maximum values of tensile strength and elongation at break were both more than 5 times larger than that of neat CS/GP hydrogel. We discussed this enhancement effect in detail by Scanning electron microscope observations (SEM) and Fourier transform infrared spectroscopy testing (FT-IR). The SEM images of composite hydrogels shown quite different from the neat CS/GP hydrogel, where the pores were more tightly and with some uniform and smaller holes dispersed on the wall. FT-IR test results revealed that the introduction of ATP increased the cross-link density because of the hydrogen bonds formation between ATP nanoparticles and CS molecules. Also, we studied the impact of ATP introduction on gelation speed through tracking the dynamic process of the sol-gel transition by means of rheological measurement, and the results shown that the reaction rate increased significantly with the increase of ATP concentration.

Biomaterial Approaches to Enhancing Neurorestoration after Spinal Cord Injury: Strategies for Overcoming Inherent Biological Obstacles

While advances in technology and medicine have improved both longevity and quality of life in patients living with a spinal cord injury, restoration of full motor function is not often achieved. This is due to the failure of repair and regeneration of neuronal connections in the spinal cord after injury. In this review, the complicated nature of spinal cord injury is described, noting the numerous cellular and molecular events that occur in the central nervous system following a traumatic lesion. In short, postinjury tissue changes create a complex and dynamic environment that is highly inhibitory to the process of neural regeneration. Strategies for repair are outlined with a particular focus on the important role of biomaterials in designing a therapeutic treatment that can overcome this inhibitory environment. The importance of considering the inherent biological response of the central nervous system to both injury and subsequent therapeutic interventions is highlighted as a key consideration for all attempts at improving functional recovery.

Neural stem/progenitor cell-laden microfibers promote transplant survival in a mouse transected spinal cord injury model

Previous studies have demonstrated that transplantation of neural stem/progenitor cells (NS/PCs) into the lesioned spinal cord can promote functional recovery following incomplete spinal cord injury (SCI) in animal models. However, this strategy is insufficient following complete SCI because of the gap at the lesion epicenter. To obtain functional recovery in a mouse model of complete SCI, this study uses a novel collagen-based microfiber as a scaffold for engrafted NS/PCs. We hypothesized that the NS/PC-microfiber combination would facilitate lesion closure as well as transplant survival in the transected spinal cord. NS/PCs were seeded inside the novel microfibers, where they maintained their capacity to differentiate and proliferate. After transplantation, the stumps of the transected spinal cord were successfully bridged by the NS/PC-laden microfibers. Moreover, the transplanted cells migrated into the host spinal cord and differentiated into three neural lineages (astrocytes, neurons, and oligodendrocytes). However, the NS/PC-laden scaffold could not achieve a neural connection between the rostral end of the injury and the intact caudal area of the spinal cord, nor could it achieve recovery of motor function. To obtain optimal functional recovery, a microfiber design with a modified composition may be useful. Furthermore, combinatorial therapy with rehabilitation and/or medications should also be considered for practical success of biomaterial/cell transplantation-based approaches to regenerative medicine.

Neuronal Differentiation of Human Mesenchymal Stem Cells Using Exosomes Derived from Differentiating Neuronal Cells

Exosomes deliver functional proteins and genetic materials to neighboring cells, and have potential applications for tissue regeneration. One possible mechanism of exosome-promoted tissue regeneration is through the delivery of microRNA (miRNA). In this study, we hypothesized that exosomes derived from neuronal progenitor cells contain miRNAs that promote neuronal differentiation. We treated mesenchymal stem cells (MSCs) daily with exosomes derived from PC12 cells, a neuronal cell line, for 1 week. After the treatment with PC12-derived exosomes, MSCs developed neuron-like morphology, and gene and protein expressions of neuronal markers were upregulated. Microarray analysis showed that the expression of miR-125b, which is known to play a role in neuronal differentiation of stem cells, was much higher in PC12-derived exosomes than in exosomes from B16-F10 melanoma cells. These results suggest that the delivery of miRNAs contained in PC12-derived exosomes is a possible mechanism explaining the neuronal differentiation of MSC.

Functional recovery in spinal cord injured rats using polypyrrole/iodine implants and treadmill training

Currently, there is no universally accepted treatment for traumatic spinal cord injury (TSCI), a pathology that can cause paraplegia or quadriplegia. Due to the complexity of TSCI, more than one therapeutic strategy may be necessary to regain lost functions. Therefore, the present study proposes the use of implants of mesoparticles (MPs) of polypyrrole/iodine (PPy/I) synthesized by plasma for neuroprotection promotion and functional recovery in combination with treadmill training (TT) for neuroplasticity promotion and maintenance of muscle tone. PPy/I films were synthesized by plasma and pulverized to obtain MPs. Rats with a TSCI produced by the NYU impactor were divided into four groups: Vehicle (saline solution); MPs (PPy/I implant); Vehicle-TT (saline solution + TT); and MPs-TT (PPy/I implant + TT). The vehicle or MPs (30 μL) were injected into the lesion site 48 h after a TSCI. Four days later, TT was carried out 5 days a week for 2 months. Functional recovery was evaluated weekly using the BBB motor scale for 9 weeks and tissue protection using histological and morphometric analysis thereafter. Although the MPs of PPy/I increased nerve tissue preservation (P = 0.03) and promoted functional recovery (P = 0.015), combination with TT did not produce better neuroprotection, but significantly improved functional results (P = 0.000) when comparing with the vehicle group. So, use these therapeutic strategies by separately could stimulate specific mechanisms of neuroprotection and neuroregeneration, but when using together they could mainly potentiate different mechanisms of neuronal plasticity in the preserved spinal cord tissue after a TSCI and produce a significant functional recovery. The implant of mesoparticles of polypyrrole/iodine into the injured spinal cord displayed good integration into the nervous tissue without a response of rejection, as well as an increased in the amount of preserved tissue and a better functional recovery than the group without transplant after a traumatic spinal cord injury by contusion in rats. The relevance of the present results is that polypyrrole/iodine implants were synthesized by plasma instead by conventional chemical or electrochemical methods. Synthesis by plasma modifies physicochemical properties of polypyrrole/iodine implants, which can be responsible of the histological response and functional results. Furthermore, no additional molecules or trophic factors or cells were added to the implant for obtain such results. Even more, when the implant was used together with physical rehabilitation, better functional recovery was obtained than that observed when these strategies were used by separately.

Bone Marrow Stromal Cells Combined with a Honeycomb Collagen Sponge Facilitate Neurite Elongation in Vitro and Neural Restoration in the Hemisected Rat Spinal Cord

In the last decade, researchers and clinicians have reported that transplantation of bone marrow stromal cells (BMSCs) promotes functional recovery after brain or spinal cord injury (SCI). However, an appropriate scaffold designed for the injured spinal cord is needed to enhance the survival of transplanted BMSCs and to promote nerve regeneration. We previously tested a honeycomb collagen sponge (HC), which when applied to the transected spinal cord allowed bridging of the gap with nerve fibers. In this study, we examined whether the HC implant combined with rat BMSCs increases nerve regeneration in vitro and enhances functional recovery in vivo. We first evaluated the neurite outgrowth of rat dorsal root ganglion (DRG) explants cultured on HC with or without BMSCs in vitro. Regeneration of neurites from the DRGs was increased by BMSCs combined with HC scaffolds. In the in vivo study, 3-mm-long HC scaffolds with or without BMSCs were implanted into the hemisected rat thoracic spinal cord. Four weeks after the procedure, rats implanted with HC scaffolds containing BMSCs displayed better motor and sensory recovery than those implanted with HC scaffolds only. Histologically, more CGRP-positive sensory fibers at the implanted site and 5-HT-positive serotonergic fibers contralateral to the implanted site were observed in spinal cords receiving BMSCs. Furthermore, more rubrospinal neurons projected distally to the HC implant containing BMSCs. Our study indicates that the application of BMSCs in a HC scaffold in the injured spinal cord directly promoted sensory nerve and rubrospinal tract regeneration, thus resulting in functional recovery.

Hydrogels and Cell Based Therapies in Spinal Cord Injury Regeneration

Spinal cord injury (SCI) is a central nervous system- (CNS-) related disorder for which there is yet no successful treatment. Within the past several years, cell-based therapies have been explored for SCI repair, including the use of pluripotent human stem cells, and a number of adult-derived stem and mature cells such as mesenchymal stem cells, olfactory ensheathing cells, and Schwann cells. Although promising, cell transplantation is often overturned by the poor cell survival in the treatment of spinal cord injuries. Alternatively, the therapeutic role of different cells has been used in tissue engineering approaches by engrafting cells with biomaterials. The latter have the advantages of physically mimicking the CNS tissue, while promoting a more permissive environment for cell survival, growth, and differentiation. The roles of both cell- and biomaterial-based therapies as single therapeutic approaches for SCI repair will be discussed in this review. Moreover, as the multifactorial inhibitory environment of a SCI suggests that combinatorial approaches would be more effective, the importance of using biomaterials as cell carriers will be herein highlighted, as well as the recent advances and achievements of these promising tools for neural tissue regeneration.

Does what we measure matter? Quality-of-life defined by adolescents with brain injury

OBJECTIVES

To determine if domains included in popular measurement systems (e.g. the Peds QL™) reflect the adolescent survivor of a brain injury's sense of QoL and explore this relationship in reference to an emerging model of wellbeing in the adolescent with TBI.

METHODS

Mixed methods; adolescent QoL assessed using the PedsQL™ self-report and a semi-structured interview created by the lead author. Adolescent self-report was compared to adolescent narratives.

RESULTS

Ten adolescents participated. Adolescent PedsQL™ total was within normal limits. Adolescents reported that changes identified by the PedsQL were not important and did not impact on their sense of QoL. The importance on social components of QoL-as opposed to cognitive-provide additional support of the emerging model of wellbeing in adolescents with TBI.

CONCLUSIONS

The PedsQL can identify changes post-TBI, but fails to consider whether these changes are relevant to the adolescent. Alternate methods of exploring QoL-which emphasize the interaction of social networks and friendships, should be considered to avoid an oblique view of QoL outcomes after TBI.

Directional migration and differentiation of neural stem cells within three-dimensional microenvironments

Harnessing neural stem cells to repair neuronal damage is a promising potential treatment for neuronal diseases. To enable future therapeutic efficacy, the survival, proliferation, migration and differentiation of neural stem/progenitor cells (NPCs) should be accurately studied and optimized in in vitro platforms before transplanting these cells into the body for treatment purposes. Such studies can determine the appropriate quantities of the biochemical and biomechanical factors needed to control and optimize NPC behavior in vivo. In this study, NPCs were cultured within a microfluidic device while being encapsulated within the collagen matrix. The migration and differentiation of NPCs were studied in response to varying concentrations of nerve growth factor (NGF) and within varying densities of collagen matrices. It was shown that the migration and differentiation of NPCs can be significantly improved by providing the appropriate range of NGF concentrations while encapsulating the cells within the collagen matrix of optimal density. In particular, it was observed that within collagen matrices of intermediate density (0.9 mg ml(-1)), NPCs have a higher ability to migrate farther and in a collective manner while their differentiation into neurons is significantly higher and the cells can form protrusions and connections with their neighboring cells. Within collagen matrices with higher densities (1.8 mg ml(-1)), the cells did not migrate significantly as compared to the ones within lower matrix densities; within the matrices with lower collagen densities (0.45 mg ml(-1)) most of the cells migrated in an individual manner. However, no significant differentiation into neurons was observed for these two cases. It was also found that depending on the collagen matrix density, a minimum concentration of NGF caused a collective migration of NPCs, and a minimum concentration gradient of this factor stimulated the directional navigation of the cells. The results of this study can be implemented in designing platforms appropriate for regeneration of damaged neuronal systems.

X-ray phase-contrast computed tomography visualizes the microstructure and degradation profile of implanted biodegradable scaffolds after spinal cord injury

Tissue engineering strategies for spinal cord repair are a primary focus of translational medicine after spinal cord injury (SCI). Many tissue engineering strategies employ three-dimensional scaffolds, which are made of biodegradable materials and have microstructure incorporated with viable cells and bioactive molecules to promote new tissue generation and functional recovery after SCI. It is therefore important to develop an imaging system that visualizes both the microstructure of three-dimensional scaffolds and their degradation process after SCI. Here, X-ray phase-contrast computed tomography imaging based on the Talbot grating interferometer is described and it is shown how it can visualize the polyglycolic acid scaffold, including its microfibres, after implantation into the injured spinal cord. Furthermore, X-ray phase-contrast computed tomography images revealed that degradation occurred from the end to the centre of the braided scaffold in the 28 days after implantation into the injured spinal cord. The present report provides the first demonstration of an imaging technique that visualizes both the microstructure and degradation of biodegradable scaffolds in SCI research. X-ray phase-contrast imaging based on the Talbot grating interferometer is a versatile technique that can be used for a broad range of preclinical applications in tissue engineering strategies.

Right care, right time, right place: improving outcomes for people with spinal cord injury through early access to intervention and improved access to specialised care: study protocol

Background

Traumatic spinal cord injury is a devastating condition impacting adversely on the health and wellbeing, functioning and independence, social participation and quality of life of the injured person. In Australia, there are approximately 15 new cases per million population per year; economic burden estimates suggest 2 billion dollars annually. For optimal patient outcomes expert consensus recommends expeditious transfer (“<24 hours of injury”) to a specialist Spinal Cord Injury Unit, where there is an interdisciplinary team equipped to provide comprehensive care for the many and complex issues associated with traumatic spinal cord injury. No study of this patient population has been undertaken, that assessed the extent to which care received reflected clinical guidelines, or examined the patient journey and outcomes in relation to this. The aims of this study are to describe the nature and timing of events occurring before commencement of specialist care, and to quantify the association between these events and patient outcomes.

Methods and design

The proposed observational study will recruit a prospective cohort over two years, identified at participating sites across two Australian states; Victoria and New South Wales. Included participants will be aged 16 years and older and diagnosed with a traumatic spinal cord injury. Detailed data will be collected from the point of injury through acute care and subacute rehabilitation, discharge from hospital and community reintegration. Items will include date, time, location and external cause of injury; ambulance response, assessments and management; all episodes of hospital care including assessments, vital signs, diagnoses and treatment, inter-hospital transfers, surgical interventions and their timing, lengths of stay and complications. Telephone follow-up of survivors will be conducted at 6, 12 and 24 months.

Discussion

There is limited population level data on the effect of delayed commencement of specialist care (>24 hours) in a Spinal Cord Injury Unit. Examining current health service and clinical intervention pathways in this Australian population-based sample, in relation to their outcomes, will provide an understanding of factors associated with patient flow, resource utilisation and cost, and patient and family quality of life. Barriers to streamlined effective early-care pathways and facilitators of optimal treatment for these patients will be identified.

The linear-ordered collagen scaffold-BDNF complex significantly promotes functional recovery after completely transected spinal cord injury in canine

Spinal cord injury (SCI) is still a worldwide clinical challenge for which there is no viable therapeutic method. We focused on developing combinatorial methods targeting the complex pathological process of SCI. In this study, we implanted linear-ordered collagen scaffold (LOCS) fibers with collagen binding brain-derived neurotrophic factor (BDNF) by tagging a collagen-binding domain (CBD) (LOCS + CBD-BDNF) in completely transected canine SCI with multisystem rehabilitation to validate its potential therapeutic effect through a long-term (38 weeks) observation. We found that LOCS + CBD-BDNF implants strikingly promoted locomotion and functional sensory recovery, with some dogs standing unassisted and transiently moving. Further histological analysis showed that administration of LOCS + CBD-BDNF reduced lesion volume, decreased collagen deposits, promoted axon regeneration and improved myelination, leading to functional recovery. Collectively, LOCS + CBD-BDNF showed striking therapeutic effect on completely transected canine SCI model and it is the first time to report such breakthrough in the war with SCI. Undoubtedly, it is a potentially promising therapeutic method for SCI paralysis or other movement disorders caused by neurological diseases in the future.

Material stiffness effects on neurite alignment to photopolymerized micropatterns

The ability to direct neurite growth into a close proximity of stimulating elements of a neural prosthesis, such as a retinal or cochlear implant (CI), may enhance device performance and overcome current spatial signal resolution barriers. In this work, spiral ganglion neurons (SGNs), which are the target neurons to be stimulated by CIs, were cultured on photopolymerized micropatterns with varied matrix stiffnesses to determine the effect of rigidity on neurite alignment to physical cues. Micropatterns were generated on methacrylate thin film surfaces in a simple, rapid photopolymerization step by photomasking the prepolymer formulation with parallel line-space gratings. Two methacrylate series, a nonpolar HMA-co-HDDMA series and a polar PEGDMA-co-EGDMA series, with significantly different surface wetting properties were evaluated. Equivalent pattern periodicity was maintained across each methacrylate series based on photomask band spacing, and the feature amplitude was tuned to a depth of 2 μm amplitude for all compositions using the temporal control afforded by the UV curing methodology. The surface morphology was characterized by scanning electron microscopy and white light interferometry. All micropatterned films adsorb similar amounts of laminin from solution, and no significant difference in SGN survival was observed when the substrate compositions were compared. SGN neurite alignment significantly increases with increasing material modulus for both methacrylate series. Interestingly, SGN neurites respond to material stiffness cues that are orders of magnitude higher (GPa) than what is typically ascribed to neural environments (kPa). The ability to understand neurite response to engineered physical cues and mechanical properties such as matrix stiffness will allow the development of advanced biomaterials that direct de novo neurite growth to address the spatial signal resolution limitations of current neural prosthetics.

Purine-crosslinked injectable chitosan sponges promote oligodendrocyte progenitor cells' attachment and differentiation

Oligodendrocyte Progenitor Cells (OPCs) reside in the central nervous system (CNS) and are responsible for remyelinating axons after a spinal cord injury (SCI). However, the remyelination process is incomplete and abnormal due to the inability of OPCs to fully differentiate at the site of injury. In this study a newly developed injectable chitosan sponge crosslinked using guanosine 5'-diphosphate (GDP) was used to enhance OPC survival, attachment and differentiation. This purine-based biomaterial is the first of its kind and its inception was based on the growing body of literature concerning the role of purinergic signalling in the CNS. GDP-crosslinked chitosan sponges are rapidly-gelling and can be easily administered in situ using an injection system based on a double-lumen design. The chitosan sponges prompted OPC differentiation even in the presence of mitogens. Moreover, neurotrophin-3 (NT-3) was successfully entrapped in the sponges and a sustained release for up to 30 days was achieved. OPCs were shown to differentiate into mature oligodendrocytes that express myelin basic protein (MBP) when cultured on sponges containing NT-3. These findings, along with the suitable physicochemical and biological properties, make these sponges conducive to use as viable therapeutic agents for enhancing remyelination post-SCI.

The effects of controlled release of neurotrophin-3 from PCLA scaffolds on the survival and neuronal differentiation of transplanted neural stem cells in a rat spinal cord injury model

Neural stem cells (NSCs) have emerged as a potential source for cell replacement therapy following spinal cord injury (SCI). However, poor survival and low neuronal differentiation remain major obstacles to the use of NSCs. Biomaterials with neurotrophic factors are promising strategies for promoting the proliferation and differentiation of NSCs. Silk fibroin (SF) matrices were demonstrated to successfully deliver growth factors and preserve their potency. In this study, by incorporating NT-3 into a SF coating, we successfully developed NT-3-immobilized scaffolds (membranes and conduits). Sustained release of bioactive NT-3 from the conduits for up to 8 weeks was achieved. Cell viability was confirmed using live/dead staining after 14 days in culture. The efficacy of the immobilized NT-3 was confirmed by assessing NSC neuronal differentiation in vitro. NSC neuronal differentiation was 55.2 ± 4.1% on the NT-3-immobilized membranes, which was significantly higher than that on the NT-3 free membrane. Furthermore, 8 weeks after the NSCs were seeded into conduits and implanted in rats with a transected SCI, the conduit+NT-3+NSCs group achieved higher NSC survival (75.8 ± 15.1%) and neuronal differentiation (21.5 ± 5.2%) compared with the conduit+NSCs group. The animals that received the conduit+NT-3+NSCs treatment also showed improved functional outcomes, as well as increased axonal regeneration. These results indicate the feasibility of fabricating NT-3-immobilized scaffolds using the adsorption of NT-3/SF coating method, as well as the potential of these scaffolds to induce SCI repair by promoting survival and neuronal differentiation of transplanted NSCs.

Implantation of cauda equina nerve roots through a biodegradable scaffold at the conus medullaris in rat

BACKGROUND CONTEXT

Traumatic injuries occurring at the conus medullaris of the spinal cord cause permanent damage both to the central nervous system and to the cauda equina nerve roots.

PURPOSE

This proof-of-concept study was to determine whether implanting the nerve roots into a biodegradable scaffold would improve regeneration after injury.

METHODS

All experimental works involving rats were performed according to the approved guidelines by the Mayo Clinic Institutional Animal Care and Use Committee. Surgical procedures were performed on 32 Sprague-Dawley rats. Four ventral cauda equina nerve roots were reimplanted either directly into the ventral cord stump or through a poly(lactic-co-glycolic acid) (PLGA) scaffold. These experimental groups were compared with a control group in which the nerves were inserted into a muscle fascia barrier that was placed between the spinal cord and the nerve roots. Animals were sacrificed at 4 weeks.

RESULTS

There was no difference in motor neuron counts in the spinal cord rostral to the injury in all treatment groups, implying equal potential for the regeneration into implanted nerve roots. One-way analysis of variance testing, with Tukey post hoc test, showed a statistically significant improvement in axon regeneration through the injury in the PLGA scaffold treatment group compared with the control (p<.05, scaffold n=11, control n=11).

CONCLUSIONS

This pilot study demonstrated that a PLGA scaffold improved regeneration of axons into peripheral nerve roots. However, the number of regenerating axons observed was limited and did not lead to functional recovery. Future experiments will employ a different scaffold material and possible growth factors or enzymes to increase axon populations.

Repair of injured spinal cord using biomaterial scaffolds and stem cells

The loss of neurons and degeneration of axons after spinal cord injury result in the loss of sensory and motor functions. A bridging biomaterial construct that allows the axons to grow through has been investigated for the repair of injured spinal cord. Due to the hostility of the microenvironment in the lesion, multiple conditions need to be fulfilled to achieve improved functional recovery. A scaffold has been applied to bridge the gap of the lesion as contact guidance for axonal growth and to act as a vehicle to deliver stem cells in order to modify the microenvironment. Stem cells may improve functional recovery of the injured spinal cord by providing trophic support or directly replacing neurons and their support cells. Neural stem cells and mesenchymal stem cells have been seeded into biomaterial scaffolds and investigated for spinal cord regeneration. Both natural and synthetic biomaterials have increased stem cell survival in vivo by providing the cells with a controlled microenvironment in which cell growth and differentiation are facilitated. This optimal multi‒disciplinary approach of combining biomaterials, stem cells, and biomolecules offers a promising treatment for the injured spinal cord.

Neural pathfinding on uni- and multidirectional photopolymerized micropatterns

Overcoming signal resolution barriers of neural prostheses, such as the commercially available cochlear impant (CI) or the developing retinal implant, will likely require spatial control of regenerative neural elements. To rationally design materials that direct nerve growth, it is first necessary to determine pathfinding behavior of de novo neurite growth from prosthesis-relevant cells such as spiral ganglion neurons (SGNs) in the inner ear. Accordingly, in this work, repeating 90° turns were fabricated as multidirectional micropatterns to determine SGN neurite turning capability and pathfinding. Unidirectional micropatterns and unpatterned substrates are used as comparisons. Spiral ganglion Schwann cell alignment (SGSC) is also examined on each surface type. Micropatterns are fabricated using the spatial reaction control inherent to photopolymerization with photomasks that have either parallel line spacing gratings for unidirectional patterns or repeating 90° angle steps for multidirectional patterns. Feature depth is controlled by modulating UV exposure time by shuttering the light source at given time increments. Substrate topography is characterized by white light interferometry and scanning electron microscopy (SEM). Both pattern types exhibit features that are 25 μm in width and 7.4 ± 0.7 μm in depth. SGN neurites orient randomly on unpatterned photopolymer controls, align and consistently track unidirectional patterns, and are substantially influenced by, but do not consistently track, multidirectional turning cues. Neurite lengths are 20% shorter on multidirectional substrates compared to unidirectional patterns while neurite branching and microfeature crossing events are significantly higher. For both pattern types, the majority of the neurite length is located in depressed surface features. Developing methods to understand neural pathfinding and to guide de novo neurite growth to specific stimulatory elements will enable design of innovative biomaterials that improve functional outcomes of devices that interface with the nervous system.