Combination therapy of stem cell derived neural progenitors and drug delivery of anti-inhibitory molecules for spinal cord injury

Chondroitinase as a therapeutic enzyme: Prospects and challenges

The chondroitinases (Chase) are bacterial lyases that specifically digest chondroitin sulfate and/or dermatan sulfate glycosaminoglycans via a β-elimination reaction and generate unsaturated disaccharides. In recent decades, these enzymes have attracted the attention of many researchers due to their potential applications in various aspects of medicine from the treatment of spinal cord injury to use as an analytical tool. In spite of this diverse spectrum, the application of Chase is faced with several limitations and challenges such as thermal instability and lack of a suitable delivery system. In the current review, we address potential therapeutic applications of Chase with emphasis on the challenges ahead. Then, we summarize the latest achievements to overcome the problems by considering the studies carried out in the field of enzyme engineering, drug delivery, and combination-based therapy.

Application and progress of three-dimensional bioprinting in spinal cord injury

Spinal cord injury (SCI) is a central nervous system disorder that can lead to sensory and motor dysfunction, which can seriously increase pressure and economic burden on families and societies. The current SCI treatment is mainly to stabilize the spine, prevent secondary damage, and control inflammation. Drug treatment is limited to early, large-scale use of steroids to reduce the effects of edema after SCI. In short, there is no direct treatment for SCI. Recent 3D bioprinting development provides a new solution for SCI treatment: a series of spinal cord bionic scaffolds are being developed to improve spinal cord function after injury. This paper reviews the pathophysiological characteristics of SCI, current treatment methods, and the progress of 3D bioprinting in SCI. Finally, its challenges and prospects in SCI treatment are summarized.

Engineering of hybrid anticancer drug-loaded polymeric nanoparticles delivery system for the treatment and care of lung cancer therapy

Chemotherapy with combination drugs has become one of the most commonly used cancer prevention treatments, with positive clinical results. The goal of this study was to develop compostable polymeric nanomaterials (NMs) for the delivery of puerarin (PRN) and 5-fluorouracil (5FU), as well as to investigate the anticancer activity of the drug delivery system (PRN-5FU NMs) against in vitro and in vivo lung cancer cells. Since double antitumor drugs PRN and 5FU are insufficiently compressed in polymer-based bio-degradable nanoparticles, encapsulation of PRN and 5FU antitumor drugs were co-encapsulated with polyethylene glycol and polylactidecoglycolide nanoparticles (NMs) is efficient. The arrangement of PRN NMs, 5FU NMs, and PRN-5FU NMs, as well as the nanoparticles shape and scale, were studied using transmission electron microscopy (TEM). 5FU-PRN NMs triggered apoptosis in lung carcinoma cell lines such as HEL-299 and A549 in vitro. Acridine orange/ethidium bromide (AO/EB) and nuclear damaging staining techniques were used to observe morphologies and cell death. The mechanistic analysis of apoptosis was also confirmed by flow cytometry analysis using dual staining. When compared to free anticancer products, the hemolysis analysis findings of the 5FU-PRN NMs showed excellent biocompatibility. Taken together the advantages, this combination drug conveyance strategy exposed that 5FU-PRN NMs could have a significant promising to improve the effectiveness of lung cancer cells.

Geniposide exerts protective effects on spinal cord injury in rats by inhibiting the IKKs/NF-κB signaling pathway

BACKGROUND

Spinal cord injury (SCI) is a traumatic condition of the central nervous system , which can cause nerve injury and affect nerve regeneration, thus leading to severe dysfunction of motor and sensory pathways, and unfortunately these effects are irreversible. Inflammatory response constitutes one of the important mechanisms of spinal cord secondary injury. Geniposide (Gen) is reported to possess anti-inflammation and neuronal repair capacities.

OBJECTIVES

To investigate the effect and mechanism of Gen on motor function and inflammatory response in SCI rats.

METHODS

Sprague-Dawley (SD) rats were randomly grouped, and the SCI model was established by Allen's method. The motor function of rats was evaluated by the Basso, Beattie, and Bresnahan (BBB) scale. The protective effect of Gen on the injured spinal cord tissues was evaluated by measuring the water content, myeloperoxidase (MPO) activity, and levels of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6. Moreover, the protein level of the inflammation-related pathway was detected by spectrometry and Western blot assays.

RESULTS

Gen significantly promoted the recovery of SCI rats, decreased the edema of spinal cord tissues, reduced the area of cavity, increased the number of NF-200-positive neurons, as well as increased the number of horseradish peroxidase (HRP) retrograde tracing-positive neurons and regenerated axons with myelin sheath. Additionally, compared with the control group, the neutrophil infiltration, contents of TNF-α, IL-1β, and IL-6, the activity of inhibitor of nuclear factor κB kinase subunit β (IKKβ) kinase, and protein levels of (nuclear factor κB) NF-κB p65 and phosphorylated inhibitor of NF-κB (p-I-κB) in the Gen experimental group were significantly decreased.

CONCLUSION

Gen effectively alleviated inflammatory response after SCI by inhibiting the IKKs/NF-κB signaling pathway and promoted the recovery of motor function and axon regeneration in rats.

SIGNIFICANCE

This study can provide novel insights for the early and effective intervention of SCI and confer basic data for the treatment of spinal cord secondary injury.

Optimizing Olfactory Ensheathing Cell Transplantation for Spinal Cord Injury Repair

Cell transplantation constitutes an important avenue for development of new treatments for spinal cord injury (SCI). These therapies are aimed at supporting neural repair and/or replacing lost cells at the injury site. To date, various cell types have been trialed, with most studies focusing on different types of stem cells or glial cells. Here, we review commonly used cell transplantation approaches for spinal cord injury (SCI) repair, with focus on transplantation of olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system. OECs are promising candidates for promotion of neural repair given that they support continuous regeneration of the olfactory nerve that occurs throughout life. Further, OECs can be accessed from the nasal mucosa (olfactory neuroepithelium) at the roof of the nasal cavity and can be autologously transplanted. OEC transplantation has been trialed in many animal models of SCI, as well as in human clinical trials. While several studies have been promising, outcomes are variable and the method needs improvement to enhance aspects such as cell survival, integration, and migration. As a case study, we include the approaches used by our team (the Clem Jones Centre for Neurobiology and Stem Cell Research, Griffith University, Nathan, QLD, Australia) to address the current problems with OEC transplantation and discuss how the therapeutic potential of OEC transplantation can be improved. Our approach includes discovery research to improve our knowledge of OEC biology, identifying natural and synthetic compounds to stimulate the neural repair properties of OECs, and designing three-dimensional cell constructs to create stable and transplantable cell structures.

Combining cell therapy with human autologous Schwann cell and bone marrow-derived mesenchymal stem cell in patients with subacute complete spinal cord injury: safety considerations and possible outcomes

Background

Cellular transplantations have promising effects on treating spinal cord injury (SCI) patients. Mesenchymal stem cells (MSCs) and Schwann cells (SCs), which have safety alongside their complementary characteristics, are suggested to be the two of the best candidates in SCI treatment. In this study, we assessed the safety and possible outcomes of intrathecal co-transplantation of autologous bone marrow MSC and SC in patients with subacute traumatic complete SCI.

Methods

Eleven patients with complete SCI (American Spinal Injury Association Impairment Scale (AIS); grade A) were enrolled in this study during the subacute period of injury. The patients received an intrathecal autologous combination of MSC and SC and were followed up for 12 months. We assessed the neurological changes by the American Spinal Injury Association’s (ASIA) sensory-motor scale, functional recovery by spinal cord independence measure (SCIM-III), and subjective changes along with adverse events (AE) with our checklist. Furthermore, electromyography (EMG), nerve conduction velocity (NCV), magnetic resonance imaging (MRI), and urodynamic study (UDS) were conducted for all the patients at the baseline, 6 months, and 1 year after the intervention.

Results

Light touch AIS score alterations were approximately the same as the pinprick changes (11.6 ± 13.1 and 12 ± 13, respectively) in 50% of the cervical and 63% of the lumbar-thoracic patients, and both were more than the motor score alterations (9.5 ± 3.3 in 75% of the cervical and 14% of the lumbar-thoracic patients). SCIM III total scores (21.2 ± 13.3) and all its sub-scores (“respiration and sphincter management” (15 ± 9.9), “mobility” (9.5 ± 13.3), and “self-care” (6 ± 1.4)) had statistically significant changes after cell injection. Our findings support that the most remarkable positive, subjective improvements were in trunk movement, equilibrium in standing/sitting position, the sensation of the bladder and rectal filling, and the ability of voluntary voiding. Our safety evaluation revealed no systemic complications, and radiological images showed no neoplastic overgrowth, syringomyelia, or pseudo-meningocele.

Conclusion

The present study showed that autologous SC and bone marrow-derived MSC transplantation at the subacute stage of SCI could reveal statistically significant improvement in sensory and neurological functions among the patients. It appears that using this combination of cells is safe and effective for clinical application to spinal cord regeneration during the subacute period.

3D biomaterial models of human brain disease

Inherent limitations of the traditional approaches to study brain function and disease, such as rodent models and 2D cell culture platforms, have led to the development of 3D in vitro cell culture systems. These systems, products of multidisciplinary efforts encompassing stem cell biology, materials engineering, and biofabrication, have quickly shown great potential to mimic biochemical composition, structural properties, and cellular morphology and diversity found in the native brain tissue. Crucial to these developments have been the advancements in stem cell technology and cell reprogramming protocols that allow reproducible generation of human subtype-specific neurons and glia in laboratory conditions. At the same time, biomaterials have been designed to provide cells in 3D with a microenvironment that mimics functional and structural aspects of the native extracellular matrix with increasing fidelity. In this article, we review the use of biomaterials in 3D in vitro models of neurological disorders with focus on hydrogel technology and with biochemical composition and physical properties of the in vivo environment as reference.

Dual-enzymatically cross-linked gelatin hydrogel enhances neural differentiation of human umbilical cord mesenchymal stem cells and functional recovery in experimental murine spinal cord injury

Recently, an advanced stem cell and tissue engineering approach has been recognized as an emerging and fascinating strategy to promote neural repair in spinal cord injury (SCI). Hydrogels can be properly engineered to encapsulate cells, enhance cell viability and neural differentiation, and provide the advantage of flexible adaptation to irregular defects. In this study, a dual-enzymatically cross-linked gelatin hydrogel with hydrogen horseradish peroxidase (HRP) and galactose oxidase (GalOx) was proposed to combine human umbilical cord mesenchymal stem cells (hUC-MSCs) for facilitating nerve regeneration post-SCI. In vitro, hUC-MSCs in this 3D gelatin hydrogel displayed good viability, proliferation, and neuronal differentiation. To further evaluate the neural regeneration effect of hUC-MSCs loaded into gelatin hydrogels in vivo, a clinically-relevant and force-controlled contusion model of mouse spinal cords was established. We found that implantation of a hydrogel loaded with hUC-MSCs significantly promoted the motor function recovery evaluated by Basso Mouse Scale (BMS) and footprint tests. Further histological analysis showed that the hydrogel and hUC-MSC combined transplantation dramatically decreased inflammation, inhibited apoptosis and promoted neurogenesis. Overall, implantation of this dual-enzymatically cross-linked and MSC-laden 3D gelatin hydrogel is a promising therapeutic strategy for SCI treatment.

Combined treatment with enteric neural stem cells and chondroitinase ABC reduces spinal cord lesion pathology

BACKGROUND

Spinal cord injury (SCI) presents a significant challenge for the field of neurotherapeutics. Stem cells have shown promise in replenishing the cells lost to the injury process, but the release of axon growth-inhibitory molecules such as chondroitin sulfate proteoglycans (CSPGs) by activated cells within the injury site hinders the integration of transplanted cells. We hypothesised that simultaneous application of enteric neural stem cells (ENSCs) isolated from the gastrointestinal tract, with a lentivirus (LV) containing the enzyme chondroitinase ABC (ChABC), would enhance the regenerative potential of ENSCs after transplantation into the injured spinal cord.

METHODS

ENSCs were harvested from the GI tract of p7 rats, expanded in vitro and characterised. Adult rats bearing a contusion injury were randomly assigned to one of four groups: no treatment, LV-ChABC injection only, ENSC transplantation only or ENSC transplantation+LV-ChABC injection. After 16 weeks, rats were sacrificed and the harvested spinal cords examined for evidence of repair.

RESULTS

ENSC cultures contained a variety of neuronal subtypes suitable for replenishing cells lost through SCI. Following injury, transplanted ENSC-derived cells survived and ChABC successfully degraded CSPGs. We observed significant reductions in the injured tissue and cavity area, with the greatest improvements seen in the combined treatment group. ENSC-derived cells extended projections across the injury site into both the rostral and caudal host spinal cord, and ENSC transplantation significantly increased the number of cells extending axons across the injury site. Furthermore, the combined treatment resulted in a modest, but significant functional improvement by week 16, and we found no evidence of the spread of transplanted cells to ectopic locations or formation of tumours.

CONCLUSIONS

Regenerative effects of a combined treatment with ENSCs and ChABC surpassed either treatment alone, highlighting the importance of further research into combinatorial therapies for SCI. Our work provides evidence that stem cells taken from the adult gastrointestinal tract, an easily accessible source for autologous transplantation, could be strongly considered for the repair of central nervous system disorders.

Application of fibrin-based hydrogels for nerve protection and regeneration after spinal cord injury

Traffic accidents, falls, and many other events may cause traumatic spinal cord injuries (SCIs), resulting in nerve cells and extracellular matrix loss in the spinal cord, along with blood loss, inflammation, oxidative stress (OS), and others. The continuous development of neural tissue engineering has attracted increasing attention on the application of fibrin hydrogels in repairing SCIs. Except for excellent biocompatibility, flexibility, and plasticity, fibrin, a component of extracellular matrix (ECM), can be equipped with cells, ECM protein, and various growth factors to promote damage repair. This review will focus on the advantages and disadvantages of fibrin hydrogels from different sources, as well as the various modifications for internal topographical guidance during the polymerization. From the perspective of further improvement of cell function before and after the delivery of stem cell, cytokine, and drug, this review will also evaluate the application of fibrin hydrogels as a carrier to the therapy of nerve repair and regeneration, to mirror the recent development tendency and challenge.

Multimodal treatment for spinal cord injury: a sword of neuroregeneration upon neuromodulation

Spinal cord injury is linked to the interruption of neural pathways, which results in irreversible neural dysfunction. Neural repair and neuroregeneration are critical goals and issues for rehabilitation in spinal cord injury, which require neural stem cell repair and multimodal neuromodulation techniques involving personalized rehabilitation strategies. Besides the involvement of endogenous stem cells in neurogenesis and neural repair, exogenous neural stem cell transplantation is an emerging effective method for repairing and replacing damaged tissues in central nervous system diseases. However, to ensure that endogenous or exogenous neural stem cells truly participate in neural repair following spinal cord injury, appropriate interventional measures (e.g., neuromodulation) should be adopted. Neuromodulation techniques, such as noninvasive magnetic stimulation and electrical stimulation, have been safely applied in many neuropsychiatric diseases. There is increasing evidence to suggest that neuromagnetic/electrical modulation promotes neuroregeneration and neural repair by affecting signaling in the nervous system; namely, by exciting, inhibiting, or regulating neuronal and neural network activities to improve motor function and motor learning following spinal cord injury. Several studies have indicated that fine motor skill rehabilitation training makes use of residual nerve fibers for collateral growth, encourages the formation of new synaptic connections to promote neural plasticity, and improves motor function recovery in patients with spinal cord injury. With the development of biomaterial technology and biomechanical engineering, several emerging treatments have been developed, such as robots, brain-computer interfaces, and nanomaterials. These treatments have the potential to help millions of patients suffering from motor dysfunction caused by spinal cord injury. However, large-scale clinical trials need to be conducted to validate their efficacy. This review evaluated the efficacy of neural stem cells and magnetic or electrical stimulation combined with rehabilitation training and intelligent therapies for spinal cord injury according to existing evidence, to build up a multimodal treatment strategy of spinal cord injury to enhance nerve repair and regeneration.

Formulation of thrombin-inhibiting hydrogels via self-assembly of ionic peptides with peptide-modified polymers

Cell therapy for spinal cord injuries offers the possibility of replacing lost cells after trauma to the central nervous system (CNS). In preclinical studies, synthetic hydrogels are often co-delivered to the injury site to support survival and integration of the transplanted cells. These hydrogels ideally mimic the mechanical and biochemical features of a healthy CNS extracellular matrix while also providing the possibility of localized drug delivery to promote healing. In this work, we synthesize peptide-functionalized polymers that contain both a peptide sequence for incorporation into self-assembled peptide hydrogels along with bioactive peptides that inhibit scar formation. We demonstrate that peptide hydrogels formulated with the peptide-functionalized polymers possess similar mechanical properties (soft and shear-thinning) as peptide-only hydrogels. Small angle neutron scattering analysis reveals that polymer-containing hydrogels possess larger inhomogeneous domains but small-scale features such as mesh size remain the same as peptide-only hydrogels. We further confirm that the integrated hydrogels containing bioactive peptides exhibit thrombin inhibition activity, which has previously shown to reduce scar formation in vivo. Finally, while the survival of encapsulated cells was poor, cells cultured on the hydrogels exhibited good viability. Overall, the described composite hydrogels formed from self-assembling peptides and peptide-modified polymers are promising, user-friendly materials for CNS applications in regeneration.

Coating Materials for Neural Stem/Progenitor Cell Culture and Differentiation

Neural stem/progenitor cells (NSPCs) have a potential to treat various neurological diseases, such as Parkinson's Disease, Alzheimer's Disease, and Spinal Cord Injury. However, the limitation of NSPC sources and the difficulty to maintain their stemness or to differentiate them into specific therapeutic cells are the main hurdles for clinical research and application. Thus, for obtaining a therapeutically relevant number of NSPCs in vitro, it is important to understand factors regulating their behaviors and to establish a protocol for stable NSPC proliferation and differentiation. Coating materials for cell culture, such as Matrigel, laminin, collagen, and other coating materials, can significantly affect NSPC characteristics. This article provides a review of coating materials for NSPC culturing in both two dimensions and three dimensions, and their functions in NSPC proliferation and differentiation, and presents a useful guide to select coating materials for researchers.

Repair strategies for traumatic spinal cord injury, with special emphasis on novel biomaterial-based approaches

As a part of the central nervous system (CNS), the adult mammalian spinal cord displays only very poor ability for self-repair in response to traumatic lesions, which mostly lead to more or less severe, life-long disability. While even adult CNS neurons have a certain plastic potential, their intrinsic regenerative capacity highly varies among different neuronal populations and in the end, regeneration is almost completely inhibited due to extrinsic factors such as glial scar and cystic cavity formation, excessive and persistent inflammation, presence of various inhibitory molecules, and absence of trophic support and of a growth-supportive extracellular matrix structure. In recent years, a number of experimental animal models have been developed to overcome these obstacles. Since all those studies based on a single approach have yielded only relatively modest functional recovery, it is now consensus that different therapeutic approaches will have to be combined to synergistically overcome the multiple barriers to CNS regeneration, especially in humans. In this review, we particularly emphasize the hope raised by the development of novel, implantable biomaterials that should favor the reconstruction of the damaged nervous tissue, and ultimately allow for functional recovery of sensorimotor functions. Since human spinal cord injury pathology depends on the vertebral level and the severity of the traumatic impact, and since the timing of application of the different therapeutic approaches appears very important, we argue that every case will necessitate individual evaluation, and specific adaptation of therapeutic strategies.

A prevascularized nerve conduit based on a stem cell sheet effectively promotes the repair of transected spinal cord injury

Spinal cord injury (SCI) can result in severe loss of motor and sensory function caused by ischemia and hypoxia, which are the key limiting factors of SCI rehabilitation. Vascularization is considered an effective way to resolve the issues of ischemia and hypoxia. In this regard, we first fabricated prevascularized nerve conduits (PNC) based on the prevascularized stem cell sheet and evaluated their repair effects by implanting them into transected SCI rats. A better healing effect was presented in the PNC group than in the control group and the nonprevascularized nerve conduit (NPNC) group as shown in H&E staining and the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale assessment. In addition, the expression of β-III tubulin (Tuj-1) in the PNC group was higher than that in the control group and the NPNC group because of the introduction of MSCs. Conversely, the expression of the glial fibrillary acidic protein (GFAP) in both experimental groups was lower than that in the control group because of the inhibitory effect of MSCs on glial scar formation. Taken together, the introduction of prevascularization into the neuron conduit was an effective solution for improving the condition of ischemia and hypoxia, inhibiting glial scar formation, and promoting the healing of SCI, which implied that the PNC may be a potential alternative material to biomaterials for SCI rehabilitation. STATEMENT OF SIGNIFICANCE: 1. Prevascularized stem cell sheet was first used to repair spinal cord injury (SCI). 2. Prevascularized stem cell sheet use can effectively resolve the challenges faced during SCI, including ischemia and hypoxia and the limited regenerative ability of the remained neurons. 3. Prevascularized stem cell sheet was found to accelerate the healing of SCI as compared to those in the control group and the pure stem cell sheet group. 4. The introduction of stem cells can effectively inhibit the formation of a glial scar.

Recent advances in the therapeutic uses of chondroitinase ABC

Many studies, using pre-clinical models of SCI, have demonstrated the efficacy of chondroitinase ABC as a treatment for spinal cord injury and this has been confirmed in laboratories worldwide and in several animal models. The aim of this review is report the current state of research in the field and to compare the relative efficacies of these new interventions to improve outcomes in both acute and chronic models of SCI. We also report new methods of chondroitinase delivery and the outcomes of two clinical trials using the enzyme to treat spinal cord injury in dogs and disc herniation in human patients. Recent studies have assessed the outcomes of combining chondroitinase with other strategies known to promote recovery following spinal cord injury and new approaches. Evidence is emerging that one of the most powerful combinations is that of chondroitinase with cell transplants. The particular benefits of each of the different cell types used for these transplant experiments are discussed. Combining chondroitinase with rehabilitation also improves outcomes. Gene therapy is an efficient method of enzyme delivery to the injured spinal cord and circumvents the issue of the enzyme's thermo-instability. Other methods of delivery, such as via nanoparticles or synthetic scaffolds, have shown promise; however, the outcomes from these experiments suggest that these methods of delivery require further optimization to achieve similar levels of efficacy to that obtained by a gene therapy approach. Pre-clinical models have also shown chondroitinase is efficacious in the treatment of other conditions, such as peripheral nerve injury, stroke, coronary reperfusion, Parkinson's disease and certain types of cancer. The wide range of conditions where the benefits of chondroitinase treatment have been demonstrated reflects the complex roles that chondroitin sulphate proteoglycans (its substrate) play in health and disease and warrants the enzyme's further development as a therapy.

Regenerative Therapies for Spinal Cord Injury

Spinal cord injury (SCI) is a serious problem that primarily affects younger and middle-aged adults at its onset. To date, no effective regenerative treatment has been developed. Over the last decade, researchers have made significant advances in stem cell technology, biomaterials, nanotechnology, and immune engineering, which may be applied as regenerative therapies for the spinal cord. Although the results of clinical trials using specific cell-based therapies have proven safe, their efficacy has not yet been demonstrated. The pathophysiology of SCI is multifaceted, complex and yet to be fully understood. Thus, combinatorial therapies that simultaneously leverage multiple approaches will likely be required to achieve satisfactory outcomes. Although combinations of biomaterials with pharmacologic agents or cells have been explored, few studies have combined these modalities in a systematic way. For most strategies, clinical translation will be facilitated by the use of minimally invasive therapies, which are the focus of this review. In addition, this review discusses previously explored therapies designed to promote neuroregeneration and neuroprotection after SCI, while highlighting present challenges and future directions. Impact Statement To date there are no effective treatments that can regenerate the spinal cord after injury. Although there have been significant preclinical advances in bioengineering and regenerative medicine over the last decade, these have not translated into effective clinical therapies for spinal cord injury. This review focuses on minimally invasive therapies, providing extensive background as well as updates on recent technological developments and current clinical trials. This review is a comprehensive resource for researchers working towards regenerative therapies for spinal cord injury that will help guide future innovation.

Neuronanotechnology for brain regeneration

Identifying and harnessing regenerative pathways while suppressing the growth-inhibiting processes of the biological response to injury is the central goal of stimulating neurogenesis after central nervous system (CNS) injury. However, due to the complexity of the mature CNS involving a plethora of cellular pathways and extracellular cues, as well as difficulties in accessibility without highly invasive procedures, clinical successes of regenerative medicine for CNS injuries have been extremely limited. Current interventions primarily focus on stabilization and mitigation of further neuronal death rather than direct stimulation of neurogenesis. In the past few decades, nanotechnology has offered substantial innovations to the field of regenerative medicine. Their nanoscale features allow for the fine tuning of biological interactions for enhancing drug delivery and stimulating cellular processes. This review gives an overview of nanotechnology applications in CNS regeneration organized according to cellular and extracellular targets and discuss future directions for the field.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Regulation of autophagy in mesenchymal stem cells modulates therapeutic effects on spinal cord injury

Transplantation with mesenchymal stem cells (MSCs) has shown beneficial effects in treating spinal cord injury. Autophagy is an evolutionarily conserved process of degradation and recycling of cellular components that plays an important role in tissue homeostasis and cellular survival. Whether regulating autophagy in MSCs may affect their therapeutic potential in spinal cord injury repair has not yet been determined. In this study, autophagy was inhibited in MSCs with lentiviruses expressing short hairpin RNA (shRNA) to knock down Becn-1 expression, and autophagy was upregulated in MSCs under nutrient starvation. These MSCs were then labelled with Hoechst and applied to spinal cord-injured rats to evaluate their therapeutic effects. After transplanting MSCs into rats with spinal cord injuries, functional recovery, immunohistochemistry, and remyelination analyses were performed. After inducing autophagy, the MSCs exhibited an accumulation of LC3-positive autophagosomes in the cytoplasm. The expression levels of neurotrophic factors, including vascular endothelial growth factor and brain derived neurotrophic factor, were significantly higher in autophagic MSCs than normal MSCs. The in vivo study showed that more labelled MSCs migrated to the lesion site after induction of autophagy. Inducing autophagy in MSCs promoted functional recovery after spinal cord injury, whereas functional recovery was weak after inhibiting autophagy in MSCs. In contrast to the autophagy inhibition group, transplanting autophagic MSCs exhibited a greater positive impact on axon regeneration, growth of serotonergic fibers, blood vessel regeneration, and myelination, indicating a multifactorial contribution to spinal cord injury repair. These results suggest that autophagy plays important roles in MSCs during spinal cord injury repair. Regulation of autophagy in MSCs before in vivo transplantation may be a potential therapeutic interventional strategy for spinal cord injury.

Trehalose attenuates spinal cord injury through the regulation of oxidative stress, inflammation and GFAP expression in rats

OBJECTIVE

Inflammation and oxidative stress are implicated in pathogenesis of spinal cord injury (SCI). Trehalose, a nonreducing disaccharide, exhibits anti-inflammatory and antioxidant effects. The present study investigated the therapeutic efficacy of trehalose in the SCI model.

DESIGN AND SETTING

An experimental study was designed using 120 male Wistar rats which were randomly divided into three groups including SCI, SCI + phosphate buffer saline (vehicle) and SCI + trehalose. All rats were subjected to SCI. Immediately after SCI, vehicle and trehalose groups received intrathecal injection of buffer and trehalose, respectively.

OUTCOME MEASURES

The level of tissue TNFα, IL-1β, nitric oxide, malondialdehyde, myeloperoxidase, glial fibrillary acidic protein (GFAP) as well as hindlimb function were assessed at 4 hours, 1, 3 and 7 days post-SCI.

RESULTS

Data indicated an early significant decrease in inflammatory and oxidative responses following SCI in trehalose treated group. Moreover, trehalose reduced GFAP expression as soon as 1-day post-trauma. Furthermore, trehalose treatment increased the score of hindlimb function.

CONCLUSION

Our results indicated that treatment with trehalose reduces the development of secondary injury associated with SCI. This effect likely underlies improved neurological function.

Neuroprotective Effects of Combined Treatment with Minocycline and Olfactory Ensheathing Cells Transplantation against Inflammation and Oxidative Stress after Spinal Cord Injury

Objective

Traumatic spinal cord injury (SCI) is considered one of the most devastating injuries leading to neuronal disruption. Olfactory ensheathing cells (OECs) and minocycline have been shown to promote locomotor function after spinal cord injury. In this study, we have tested the efficacy of combined treatment with minocycline and OECs after contusive spinal cord injury.

Materials and Methods

In this experimental study, adult female Wistar rats were randomly divided into five groups. Rats received an intraperitoneal injection of minocycline immediately after SCI, and then 24 hours after the injury. Transplantations were performed 7 days after the injury. Functional recovery was evaluated using the Basso, Beattie and Bresnahan scale (BBB). After that, the animals were sacrificed, and T11 segment of the spinal cord was removed after 5 weeks, and then used for histopathological, immunohistochemical, and biochemical assessments. Western blot analysis was applied to determine the protein expression of tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL1β) and caspase3.

Results

The results of this study showed that the combination of OECs graft and minocycline reduced the functional deficits and diminished cavitation and astrogliosis in spinal tissue. The analysis of protein expression by western blotting revealed that minocycline treatment along with OECs transplantation further decreased the level of IL-1β, TNF-α, caspase-3, and the oxidative stress as compared with when minocycline or OECs transplantation was used alone.

Conclusion

The combinatory treatment with OECs graft and minocycline induced a more effective response to the repair of spinal cord injury, and it is considered a therapeutic potential for the treatment of SCI.

Biomaterials and Gene Manipulation in Stem Cell-Based Therapies for Spinal Cord Injury

Spinal cord injury (SCI), a prominent health issue, represents a substantial portion of the global health care burden. Stem cell-based therapies provide novel solutions for SCI treatment, yet obstacles remain in the form of low survival rate, uncontrolled differentiation, and functional recovery. The application of engineered biomaterials in stem cell therapy provides a physicochemical microenvironment that mimics the stem cell niche, facilitating self-renewal, stem cell differentiation, and tissue reorganization. Nonetheless, external microenvironment support is inadequate, and some obstacles persist, for example, limited sources, gradual aging, and immunogenicity of stem cells. Targeted stem cell gene manipulation could eliminate many of these drawbacks, allowing safer, more effective use under regulation of intrinsic mechanisms. Additionally, through genetic labeling of stem cells, their role in tissue engineering may be elucidated. Therefore, combining stem cell therapy, materials science, and genetic modification technologies may shed light on SCI treatment. Herein, recent advances and advantages of biomaterials and gene manipulation, especially with respect to stem cell-based therapies, are highlighted, and their joint performance in SCI is evaluated. Current technological limitations and perspectives on future directions are then discussed. Although this combination is still in the early stages of development, it is highly likely to substantially contribute to stem cell-based therapies in the foreseeable future.

Transplanting Cells for Spinal Cord Repair: Who, What, When, Where and Why?

Cellular transplantation for repair of the injured spinal cord has a rich history with strategies focused on neuroprotection, immunomodulation, and neural reconstruction. The goal of the present review is to provide a concise overview and discussion of five key themes that have become important considerations for rebuilding functional neural networks. The questions raised include: (i) who are the donor cells selected for transplantation, (ii) what is the intended target for repair, (iii) when is the optimal time for transplantation, (iv) where should the cells be delivered, and lastly (v) why does cell transplantation remain an attractive candidate for promoting neural repair after injury? Recent developments in neurobiology and engineering now enable us to start addressing these questions with multidisciplinary expertise and methods.

Nanomaterial-involved neural stem cell research: Disease treatment, cell labeling, and growth regulation

Neural stem cells (NSCs) have been widely investigated for their potential in the treatment of various diseases and transplantation therapy. However, NSC growth regulation, labeling, and its application to disease diagnosis and treatment are outstanding challenges. Recently, nanomaterials have shown promise for various applications including genetic modification, imaging, and controlled drug release. Here we summarize the recent progress in the use of nanomaterials in combination with NSCs for disease treatment and diagnosis, cell labeling, and NSC growth regulation. The toxicity of nanomaterials to NSCs is also discussed.

Novel multi-drug delivery hydrogel using scar-homing liposomes improves spinal cord injury repair

Proper selection and effective delivery of combination drugs targeting multiple pathophysiological pathways key to spinal cord injury (SCI) hold promise to address the thus far scarce clinical therapeutics for improving recovery after SCI. In this study, we aim to develop a clinically feasible way for targeted delivery of multiple drugs with different physiochemical properties to the SCI site, detail the underlying mechanism of neural recovery, and detect any synergistic effect related to combination therapy.

Methods: Liposomes (LIP) modified with a scar-targeted tetrapeptide (cysteine-alanine-glutamine-lysine, CAQK) were first constructed to simultaneously encapsulate docetaxel (DTX) and brain-derived neurotrophic factor (BDNF) and then were further added into a thermosensitive heparin-modified poloxamer hydrogel (HP) with affinity-bound acidic fibroblast growth factor (aFGF-HP) for local administration into the SCI site (CAQK-LIP-GFs/DTX@HP) in a rat model. In vivo fluorescence imaging was used to examine the specificity of CAQK-LIP-GFs/DTX binding to the injured site. Multiple comprehensive evaluations including biotin dextran amine anterograde tracing and magnetic resonance imaging were used to detect any synergistic effects and the underlying mechanisms of CAQK-LIP-GFs/DTX@HP both in vivo (rat SCI model) and in vitro (primary neuron).

Results: The multiple drugs were effectively delivered to the injured site. The combined application of GFs and DTX supported neuro-regeneration by improving neuronal survival and plasticity, rendering a more permissive extracellular matrix environment with improved regeneration potential. In addition, our combination therapy promoted axonal regeneration via moderation of microtubule function and mitochondrial transport along the regenerating axon.

Conclusion: This novel multifunctional therapeutic strategy with a scar-homing delivery system may offer promising translational prospects for the clinical treatment of SCI.

Bench to bedside: Current advances in regenerative medicine

Regenerative medicine is a diverse and rapidly evolving field, employing core expertise from biologists, engineers, and clinicians. Recently the field has made significant progress towards regenerating or replacing tissues lost to age, disease or injury. Current strategies include transplantation of adult or pluripotent stem cells to replace tissue or support tissue healing. Promising approaches for the future of regenerative medicine include stimulating endogenous stem cells for in situ repair, transplantation of organoids to repair minor tissue injury, and the use of interspecies chimerism to produce functional metabolic organs for transplantation. In our review we focus on these emerging strategies, paying particular attention to their current and prospective translational impacts and challenges.

CRISPR-Cas9 genome engineering: Treating inherited retinal degeneration

Gene correction is a valuable strategy for treating inherited retinal degenerative diseases, a major cause of irreversible blindness worldwide. Single gene defects cause the majority of these retinal dystrophies. Gene augmentation holds great promise if delivered early in the course of the disease, however, many patients carry mutations in genes too large to be packaged into adeno-associated viral vectors and some, when overexpressed via heterologous promoters, induce retinal toxicity. In addition to the aforementioned challenges, some patients have sustained significant photoreceptor cell loss at the time of diagnosis, rendering gene replacement therapy insufficient to treat the disease. These patients will require cell replacement to restore useful vision. Fortunately, the advent of induced pluripotent stem cell and CRISPR-Cas9 gene editing technologies affords researchers and clinicians a powerful means by which to develop strategies to treat patients with inherited retinal dystrophies. In this review we will discuss the current developments in CRISPR-Cas9 gene editing in vivo in animal models and in vitro in patient-derived cells to study and treat inherited retinal degenerative diseases.

Biofunctionalized aligned microgels provide 3D cell guidance to mimic complex tissue matrices

Natural healing is based on highly orchestrated processes, in which the extracellular matrix plays a key role. To resemble the native cell environment, we introduce an artificial extracellular matrix (aECM) with the capability to template hierarchical and anisotropic structures in situ, allowing a minimally-invasive application via injection. Synthetic, magnetically responsive, rod-shaped microgels are locally aligned and fixed by a biocompatible surrounding hydrogel, creating a hybrid anisotropic hydrogel (Anisogel), of which the physical, mechanical, and chemical properties can be tailored. The microgels are rendered cell-adhesive with GRGDS and incorporated either inside a cell-adhesive fibrin or bioinert poly(ethylene glycol) hydrogel to strongly interact with fibroblasts. GRGDS-modified microgels inside a fibrin-based Anisogel enhance fibroblast alignment and lead to a reduction in fibronectin production, indicating successful replacement of structural proteins. In addition, YAP-translocation to the nucleus increases with the concentration of microgels, indicating cellular sensing of the overall anisotropic mechanical properties of the Anisogel. For bioinert surrounding PEG hydrogels, GRGDS-microgels are required to support cell proliferation and fibronectin production. In contrast to fibroblasts, primary nerve growth is not significantly affected by the biomodification of the microgels. In conclusion, this approach opens new opportunities towards advanced and complex aECMs for tissue regeneration.

Biomaterial strategies for limiting the impact of secondary events following spinal cord injury

The nature of traumatic spinal cord injury (SCI) often involves limited recovery and long-term quality of life complications. The initial injury sets off a variety of secondary cascades, which result in an expanded lesion area. Ultimately, the native tissue fails to regenerate. As treatments are developed in the laboratory, the management of this secondary cascade is an important first step in achieving recovery of normal function. Current literature identifies four broad targets for intervention: inflammation, oxidative stress, disruption of the blood-spinal cord barrier, and formation of an inhibitory glial scar. Because of the complex and interconnected nature of these events, strategies that combine multiple therapies together show much promise. Specifically, approaches that rely on biomaterials to perform a variety of functions are generating intense research interest. In this review, we examine each target and discuss how biomaterials are currently used to address them. Overall, we show that there are an impressive amount of biomaterials and combinatorial treatments which show good promise for slowing secondary events and improving outcomes. If more emphasis is placed on growing our understanding of how materials can manage secondary events, treatments for SCI can be designed in an increasingly rational manner, ultimately improving their potential for translation to the clinic.

3-D Bioprinting of Neural Tissue for Applications in Cell Therapy and Drug Screening

Neurodegenerative diseases affect millions of individuals in North America and cost the health-care industry billions of dollars for treatment. Current treatment options for degenerative diseases focus on physical rehabilitation or drug therapies, which temporarily mask the effects of cell damage, but quickly lose their efficacy. Cell therapies for the central nervous system remain an untapped market due to the complexity involved in growing neural tissues, controlling their differentiation, and protecting them from the hostile environment they meet upon implantation. Designing tissue constructs for the discovery of better drug treatments are also limited due to the resolution needed for an accurate cellular representation of the brain, in addition to being expensive and difficult to translate to biocompatible materials. 3-D printing offers a streamlined solution for engineering brain tissue for drug discovery or, in the future, for implantation. New microfluidic and bioplotting devices offer increased resolution, little impact on cell viability and have been tested with several bioink materials including fibrin, collagen, hyaluronic acid, poly(caprolactone), and poly(ethylene glycol). This review details current efforts at bioprinting neural tissue and highlights promising avenues for future work.

Combinatorial Therapies After Spinal Cord Injury: How Can Biomaterials Help?

Traumatic spinal cord injury (SCI) results in an immediate loss of motor and sensory function below the injury site and is associated with a poor prognosis. The inhibitory environment that develops in response to the injury is mainly due to local expression of inhibitory factors, scarring and the formation of cystic cavitations, all of which limit the regenerative capacity of endogenous or transplanted cells. Strategies that demonstrate promising results induce a change in the microenvironment at- and around the lesion site to promote endogenous cell repair, including axonal regeneration or the integration of transplanted cells. To date, many of these strategies target only a single aspect of SCI; however, the multifaceted nature of SCI suggests that combinatorial strategies will likely be more effective. Biomaterials are a key component of combinatorial strategies, as they have the potential to deliver drugs locally over a prolonged period of time and aid in cell survival, integration and differentiation. Here we summarize the advantages and limitations of widely used strategies to promote recovery after injury and highlight recent research where biomaterials aided combinatorial strategies to overcome some of the barriers of spinal cord regeneration.

Creation of an intramedullary cavity by hemorrhagic necrosis removal 24 h after spinal cord contusion in rats for eventual intralesional implantation of restorative materials

Intramedullary hemorrhagic necrosis occurs early after spinal cord injury at the site of injury and adjacent segments. It is considered harmful because of its potential to aggravate secondary injury, and to interfere with axonal regeneration; it might also lead to an unfavorable environment for intralesional implants. Removal of hemorrhagic necrosis has been attempted before with variable results. The invasive nature of these procedures carries the risk of exacerbating damage to the injured cord. The overall objective for this study was to test several strategies for non-damaging removal of hemorrhagic necrosis and characterize the resulting cavity looking for a space for future intralesional therapeutic implants in rats with acute cord injury. Rats were subjected to graded cord contusion, and hemorrhagic necrosis was removed after 24h. Three grades of myelotomy (extensive, medium sized, and small) were tested. Using the small surgical approach to debridement, early and late effects of the intervention were determined by histology and by analytical and behavioral analysis. Appearance and capacity of the resulting cavity were characterized. Satisfactory removal of hemorrhagic necrosis was achieved with all three surgical approaches to debridement. However, bleeding in spared cord tissue was excessive after medium sized and extensive myelotomies but similar to control injured rats after small cord surgery. Small surgical approach to debridement produced no swelling nor acute inflammation changes, nor did it affect long-term spontaneous locomotor recovery, but resulted in modest improvement of myelination in rats subjected to both moderate and severe injuries. Cavity created after intervention was filled with 10 to 15 μL of hydrogel. In conclusion, by small surgical approach to debridement, removal of hemorrhagic necrosis was achieved after acute cord contusion thereby creating intramedullary spaces without further damaging the injured spinal cord. Resulting cavities appear suitable for future intralesional placement of pro-reparative cells or other regenerative biomaterials in a clinically relevant model of spinal cord injury.

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.

Valproic acid preserves motoneurons following contusion in organotypic spinal cord slice culture

OBJECTIVE

Spinal cord injury (SCI) is a devastating condition causing neuronal loss. A key challenge in treatment of SCI is how to retain neurons after injury. Valproic acid (VPA) is a drug recently has been appreciated for its neuroprotective and neurotrophic properties in various SCI models. In this study the role of VPA was assessed in organotypic spinal cord slice culture following the contusion.

DESIGN

The lumbar enlargement of adult rat was cut transversely and slices were cultured. Seven days after culturing, injury was induced by dropping a 0.5 gram weight from 3 cm height on the slice surface. One hour after injury, the VPA was administered at 1, 5 and 10 µM concentrations. Afterward, at day 1 and 3 post injury (DPI: 1 and 3) propidium iodide (PI) and immunohistochemistry staining were performed to evaluate the cell death, NeuN and β-Tubulin expression, respectively.

RESULTS

The PI staining of slices at DPI: 1 and 3 following treatment with VPA revealed significant decreases in the cell death in all three concentrations comparing to the non-treated group. Also immunostaining showed VPA only at 5 µM concentration considerably rescued ventral horn' MNs from death and protected the neuronal integrity.

CONCLUSION

The results of this study indicate applying VPA one hour after injury can prevent the death of a majority of cells, importantly MNs and preserve the neuronal integrity. Since the first 24 hours after SCI is a critical period for employing any treatment, VPA can be considered as an option for further evaluation.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

Biomaterial Strategies for Delivering Stem Cells as a Treatment for Spinal Cord Injury

Ongoing clinical trials are evaluating the use of stem cells as a way to treat traumatic spinal cord injury (SCI). However, the inhibitory environment present in the injured spinal cord makes it challenging to achieve the survival of these cells along with desired differentiation into the appropriate phenotypes necessary to regain function. Transplanting stem cells along with an instructive biomaterial scaffold can increase cell survival and improve differentiation efficiency. This study reviews the literature discussing different types of instructive biomaterial scaffolds developed for transplanting stem cells into the injured spinal cord. We have chosen to focus specifically on biomaterial scaffolds that direct the differentiation of neural stem cells and pluripotent stem cells since they offer the most promise for producing the cell phenotypes that could restore function after SCI. In terms of biomaterial scaffolds, this article reviews the literature associated with using hydrogels made from natural biomaterials and electrospun scaffolds for differentiating stem cells into neural phenotypes. It then presents new data showing how these different types of scaffolds can be combined for neural tissue engineering applications and provides directions for future studies.

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.

Combination therapies for neurobehavioral and cognitive recovery after experimental traumatic brain injury: Is more better?

Traumatic brain injury (TBI) is a significant health care crisis that affects two million individuals in the United Sates alone and over ten million worldwide each year. While numerous monotherapies have been evaluated and shown to be beneficial at the bench, similar results have not translated to the clinic. One reason for the lack of successful translation may be due to the fact that TBI is a heterogeneous disease that affects multiple mechanisms, thus requiring a therapeutic approach that can act on complementary, rather than single, targets. Hence, the use of combination therapies (i.e., polytherapy) has emerged as a viable approach. Stringent criteria, such as verification of each individual treatment plus the combination, a focus on behavioral outcome, and post-injury vs. pre-injury treatments, were employed to determine which studies were appropriate for review. The selection process resulted in 37 papers that fit the specifications. The review, which is the first to comprehensively assess the effects of combination therapies on behavioral outcomes after TBI, encompasses five broad categories (inflammation, oxidative stress, neurotransmitter dysregulation, neurotrophins, and stem cells, with and without rehabilitative therapies). Overall, the findings suggest that combination therapies can be more beneficial than monotherapies as indicated by 46% of the studies exhibiting an additive or synergistic positive effect versus on 19% reporting a negative interaction. These encouraging findings serve as an impetus for continued combination studies after TBI and ultimately for the development of successful clinically relevant therapies.

In vitro selection technologies to enhance biomaterial functionality

Cells make decisions and fate choices based in part on cues they receive from their external environment. Factors that affect the interpretation of these cues include the soluble proteins that are present at any given time, the cell surface receptors that are available to bind these proteins, and the relative affinities of the soluble proteins for their cognate receptors. Researchers have identified many of the biological motifs responsible for the high-affinity interactions between proteins and their receptors, and subsequently incorporated these motifs into biomaterials to elicit control over cell behavior. Common modes of control include localized sequestration of proteins to improve bioavailability and direct inhibition or activation of a receptor by an immobilized peptide or protein. However, naturally occurring biological motifs often possess promiscuous affinity for multiple proteins and receptors or lack programmable actuation in response to dynamic stimuli, thereby limiting the amount of control they can exert over cellular decisions. These natural motifs only represent a small fraction of the biological diversity that can be assayed by in vitro selection strategies, and the discovery of "artificial" motifs with varying affinity, specificity, and functionality could greatly expand the repertoire of engineered biomaterial properties. This minireview provides a brief summary of classical and emerging techniques in peptide phage display and nucleic acid aptamer selections and discusses prospective applications in the areas of cell adhesion, angiogenesis, neural regeneration, and immune modulation.

Insight on stem cell preconditioning and instructive biomaterials to enhance cell adhesion, retention, and engraftment for tissue repair

Stem cells are a promising solution for the treatment of a variety of diseases. However, the limited survival and engraftment of transplanted cells due to a hostile ischemic environment is a bottleneck for effective utilization and commercialization. Within this environment, the majority of transplanted cells undergo apoptosis prior to participating in lineage differentiation and cellular integration. Therefore, in order to maximize the clinical utility of stem/progenitor cells, strategies must be employed to increase their adhesion, retention, and engraftment in vivo. Here, we reviewed key strategies that are being adopted to enhance the survival, retention, and engraftment of transplanted stem cells through the manipulation of both the stem cells and the surrounding environment. We describe how preconditioning of cells or cell manipulations strategies can enhance stem cell survival and engraftment after transplantation. We also discuss how biomaterials can enhance the function of stem cells for effective tissue regeneration. Biomaterials can incorporate or mimic extracellular function (ECM) function and enhance survival or differentiation of transplanted cells in vivo. Biomaterials can also promote angiogenesis, enhance engraftment and differentiation, and accelerate electromechanical integration of transplanted stem cells. Insight gained from this review may direct the development of future investigations and clinical trials.