Linear Ordered Collagen Scaffolds Loaded with Collagen-Binding Brain-Derived Neurotrophic Factor Improve the Recovery of Spinal Cord Injury in Rats

Functionalized collagen scaffold implantation and cAMP administration collectively facilitate spinal cord regeneration

Previous studies have demonstrated that several mechanisms, including numerous inhibitory molecules, weak neurotrophic stimulation and deficient intrinsic regenerative responses, collectively contribute to the failure of mature spinal cord axon regeneration. Thus, combinatorial therapies targeting multiple mechanisms have attracted much attention. In the present study, a porous collagen scaffold was used to support neuronal attachment and bridge axonal regeneration. The scaffold was specifically functionalized using neutralizing proteins (CBD-EphA4LBD, CBD-PlexinB1LBD and NEP1-40) and collagen-binding neurotrophic factors (CBD-BDNF and CBD-NT3) to simultaneously antagonize myelin inhibitory molecules (ephrinB3, Sema4D and Nogo) and exert neurotrophic protection and stimulation. Cerebellar granular neurons cultured on the functionalized collagen scaffold promoted neurite outgrowth in the presence of myelin. Furthermore, a full combinatorial treatment comprising functionalized scaffold implantation and cAMP administration was developed to evaluate the synergistic repair ability in a rat T10 complete removal spinal cord injury model. The results showed that full combinatorial therapy exhibited the greatest advantage in reducing the volume of cavitation, facilitating axonal regeneration, and promoting neuronal generation. The newborn neurons generated in the lesion area could form the neuronal relay and enhance the locomotion recovery after severe spinal cord injury.

STATEMENT OF SIGNIFICANCE

A porous collagen scaffold was specifically functionalized with neutralizing proteins and neurotrophic factors to antagonize the myelin inhibitory molecules and exert neurotrophic protection and stimulation for spinal cord regeneration. Cerebellar granular neurons seeded on the functionalized collagen scaffold showed enhanced neurite outgrowth ability in vitro. The functionalized scaffold implantation combined with cAMP administration exhibited synergistic repair ability for rat T10 complete spinal cord transection injury.

Human induced pluripotent stem cell-derived cardiac tissue on a thin collagen membrane with natural microstructures

We present a new strategy to produce a thin collagen membrane from porcine tendons and engineered cardiac tissues using hiPSC-derived cardiomyocytes.

Functionalized Collagen Scaffold Neutralizing the Myelin-Inhibitory Molecules Promoted Neurites Outgrowth in Vitro and Facilitated Spinal Cord Regeneration in Vivo

Research has demonstrated that many myelin-associated inhibitory molecules jointly contribute to the failure of adult spinal cord regeneration. Therapies comprehensively targeting the multiple inhibitory nature of the injured spinal cord are being concerned. Here, two collagen-binding proteins, CBD-EphA4LBD and CBD-PlexinB1LBD, were constructed, respectively, to neutralize the axon guidance molecules ephrinB3 and sema4D that inhibit the regeneration of nerve fibers. The two neutralizing proteins have proven their ability to specifically bind collagen and to continuously release from collagen scaffolds. They could also promote neurites outgrowth of cerebellar granular neurons and dorsal root ganglion neurons in vitro. Subsequently, the functionalized collagen scaffolds by physically absorbing NEP1-40 and immobilizing CBD-EphA4LBD and CBD-PlexinB1LBD were transplanted into a rat T10 complete spinal cord transection model. Our results showed that rats that received the treatment of transplanting the functionalized collagen scaffold exhibited great advantage on axonal regeneration and locomotion recovery after spinal cord injury.

Advances in regenerative therapies for spinal cord injury: a biomaterials approach

Spinal cord injury results in the permanent loss of function, causing enormous personal, social and economic problems. Even though neural regeneration has been proven to be a natural mechanism, central nervous system repair mechanisms are ineffective due to the imbalance of the inhibitory and excitatory factors implicated in neuroregeneration. Therefore, there is growing research interest on discovering a novel therapeutic strategy for effective spinal cord injury repair. To this direction, cell-based delivery strategies, biomolecule delivery strategies as well as scaffold-based therapeutic strategies have been developed with a tendency to seek for the answer to a combinatorial approach of all the above. Here we review the recent advances on regenerative/neural engineering therapies for spinal cord injury, aiming at providing an insight to the most promising repair strategies, in order to facilitate future research conduction.

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.

Regeneration of uterine horns in rats using collagen scaffolds loaded with human embryonic stem cell-derived endometrium-like cells

A variety of diseases may lead to hysterectomies or uterine injuries, which may form a scar and lead to infertility. Due to the limitation of native materials, there are a few effective methods to treat such damages. Tissue engineering combines cell and molecular biology with materials and mechanical engineering to replace or repair damaged organs and tissues. The use of human embryonic stem cells (hESCs) as a donor cell source for the replacement therapy will require the development of simple and reliable cell differentiation protocols. This study aimed at efficiently generating endometrium-like cells from the hESCs and at using these cells with collagen scaffold to repair uterine damage. The hESCs were induced by co-culturing with endometrial stromal cells, and simultaneously added cytokines: epidermal growth factor (EGF), platelet-derived growth factor-b (PDGF-b), and E2. Expression of cell specific markers was analyzed by immunofluorescence and reverse trascription-polymerase chain reaction to monitor the progression toward an endometrium-like cell fate. After differentiation, the majority of cells (>80%) were positive for cytokeratin-7, and the expression of key transcription factors related to endometrial development, such as Wnt4, Wnt7a, Wnt5a, Hoxa11, and factors associated with endometrial epithelial cell function: Hoxa10, Intergrinβ3, LIF, ER, and PR were also detected. Then, we established the uterine full-thickness-injury rat models to test cell function in vivo. hESC-derived cells were dropped onto collagen scaffolds and transplanted into the animal model. Twelve weeks after transplantation, we discovered that the hESC-derived cells could survive and recover the structure and function of uterine horns in a rat model of severe uterine damage. The experimental system presented here provides a reliable protocol to produce endometrium-like cells from hESCs. Our results encourage the use of hESCs in cell-replacement therapy for severe uterine damage in future.

Nerve regeneration and functional recovery by collagen-binding brain-derived neurotrophic factor in an intracerebral hemorrhage model

Brain-derived neurotrophic factor (BDNF) exerts therapeutic effects following intracerebral hemorrhage (ICH). However, it is difficult to maintain sufficient concentrations in the hemorrhage hemisphere. We demonstrated previously that BDNF fused to a collagen-binding domain (CBD) could bind to collagen in the ventricular ependyma and stimulate cell proliferation in the subventricular zone (SVZ). In this study, we verified the therapeutic effects of CBD-BDNF in the rat ICH model induced by bacterial collagenase by injecting CBD-BDNF into the lateral ventricle of ICH rats. The results demonstrated that CBD-BDNF was retained at high levels in the hemorrhage hemisphere, where it promoted neural regeneration and angiogenesis, reduced tissue loss, and improved functional recovery.

Linear ordered collagen scaffolds loaded with collagen-binding basic fibroblast growth factor facilitate recovery of sciatic nerve injury in rats

Natural biological functional scaffolds, consisting of biological materials filled with promoting elements, provide a promising strategy for the regeneration of peripheral nerve defects. Collagen conduits have been used widely due to their excellent biological properties. Linear ordered collagen scaffold (LOCS) fibers are good lumen fillers that can guide nerve regeneration in an ordered direction. In addition, basic fibroblast growth factor (bFGF) is important in the recovery of nerve injury. However, the traditional method for delivering bFGF to the lesion site has no long-term effect because of its short half-life and rapid diffusion. Therefore, we fused a specific collagen-binding domain (CBD) peptide to the N-terminal of native basic fibroblast growth factor (NAT-bFGF) to retain bFGF on the collagen scaffolds. In this study, a natural biological functional scaffold was constructed using collagen tubes filled with collagen-binding bFGF (CBD-bFGF)-loaded LOCS to promote regeneration in a 5-mm rat sciatic nerve transection model. Functional evaluation, histological investigation, and morphometric analysis indicated that the natural biological functional scaffold retained more bFGF at the injury site, guided axon growth, and promoted nerve regeneration as well as functional restoration.

Neurotrophin strategies for neuroprotection: are they sufficient?

As people are living longer, the prevalance of neurodegenerative diseases continues to rise resulting in huge socio-economic consequences. Despite major advancements in studying the pathophysiology of these diseases and a large number of clinical trials currently there is no effective treatment for these illnesses. All neuroprotective strategies have either failed or have shown only a minimal effect. There has been a major shift in recent years exploring the potential of neuroregenerative approaches. While the concept of using neurotropins for therapeutic purposes has been in existence for many years, new modes of delivery and expression of this family of molecules makes this approach now feasilble. Further neurotropin mimetics and receptor agonists are also being developed. The use of small molecules to induce the expression of neurotropins including repurposing of FDA approved drugs for this approach is another strategy being pursued. In the review we examine these new developments and discuss the potential for such approaches in the context of the pathophysiology of neurodegenerative diseases.

Protocol and cell responses in three-dimensional conductive collagen gel scaffolds with conductive polymer nanofibres for tissue regeneration

It has been established that nerves and skeletal muscles respond and communicate via electrical signals. In regenerative medicine, there is current emphasis on using conductive nanomaterials to enhance electrical conduction through tissue-engineered scaffolds to increase cell differentiation and tissue regeneration. We investigated the role of chemically synthesized polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT) conductive polymer nanofibres for conductive gels. To mimic a naturally derived extracellular matrix for cell growth, type I collagen gels were reconstituted with conductive polymer nanofibres and cells. Cell viability and proliferation of PC-12 cells and human skeletal muscle cells on these three-dimensional conductive collagen gels were evaluated in vitro. PANI and PEDOT nanofibres were found to be cytocompatible with both cell types and the best results (i.e. cell growth and gel electrical conductivity) were obtained with a low concentration (0.5 wt%) of PANI. After 7 days of culture in the conductive gels, the densities of both cell types were similar and comparable to collagen positive controls. Moreover, PC-12 cells were found to differentiate in the conductive hydrogels without the addition of nerve growth factor or electrical stimulation better than collagen control. Importantly, electrical conductivity of the three-dimensional gel scaffolds increased by more than 400% compared with control. The increased conductivity and injectability of the cell-laden collagen gels to injury sites in order to create an electrically conductive extracellular matrix makes these biomaterials very conducive for the regeneration of tissues.

Neural ECM mimetics

The consequence of numerous neurological disorders is the significant loss of neural cells, which further results in multilevel dysfunction or severe functional deficits. The extracellular matrix (ECM) is of tremendous importance for neural regeneration mediating ambivalent functions: ECM serves as a growth-promoting substrate for neurons but, on the other hand, is a major constituent of the inhibitory scar, which results from traumatic injuries of the central nervous system. Therefore, cell and tissue replacement strategies on the basis of ECM mimetics are very promising therapeutic interventions. Numerous synthetic and natural materials have proven effective both in vitro and in vivo. The closer a material's physicochemical and molecular properties are to the original extracellular matrix, the more promising its effectiveness may be. Relevant factors that need to be taken into account when designing such materials for neural repair relate to receptor-mediated cell-matrix interactions, which are dependent on chemical and mechanical sensing. This chapter outlines important characteristics of natural and synthetic ECM materials (scaffolds) and provides an overview of recent advances in design and application of ECM materials for neural regeneration, both in therapeutic applications and in basic biological research.

Scaffolds to promote spinal cord regeneration

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

Single-molecule level binding force between collagen and collagen binding domain-growth factor conjugates

Biological studies have shown that collagen/collagen binding domain (CBD)-growth factor composites are effective biomaterials systems for tissue engineering and regeneration. Here we present atomic force spectroscopy (AFM)-based investigations at the single molecule level to address fundamental biophysical questions such as CBD binding sites distribution and the mechanism for controlled release of growth factors from the collagen scaffold. Non-uniformly distributed CBD binding sites on collagen membrane are directly visualized with a quantum dot-based bimodal imaging method. AFM force spectroscopy unbinding experiments reveal that modest unbinding force and dissociation constant of the CBD/collagen interaction could be the key for its successful application in controlled release systems.

Biomaterial-based interventions for neuronal regeneration and functional recovery in rodent model of spinal cord injury: a systematic review

CONTEXT

There is considerable interest in translating laboratory advances in neuronal regeneration following spinal cord injury (SCI). A multimodality approach has been advocated for successful functional neuronal regeneration. With this goal in mind several biomaterials have been employed as neuronal bridges either to support cellular transplants, to release neurotrophic factors, or to do both. A systematic review of this literature is lacking. Such a review may provide insight to strategies with a high potential for further investigation and potential clinical application.

OBJECTIVE

To systematically review the design strategies and outcomes after biomaterial-based multimodal interventions for neuronal regeneration in rodent SCI model. To analyse functional outcomes after implantation of biomaterial-based multimodal interventions and to identify predictors of functional outcomes.

METHODS

A broad PubMed, CINHAL, and a manual search of relevant literature databases yielded data from 24 publications; 14 of these articles included functional outcome information. Studies reporting behavioral data in rat model of SCI and employing biodegradable polymer-based multimodal intervention were included. For behavioral recovery, studies using severe injury models (transection or severe clip compression (>16.9 g) or contusion (50 g/cm)) were categorized separately from those investigating partial injury models (hemisection or moderate-to-severe clip compression or contusion).

RESULTS

The cumulative mean improvements in Basso, Beattie, and Bresnahan scores after biomaterial-based interventions are 5.93 (95% CI = 2.41 - 9.45) and 4.44 (95% CI = 2.65 - 6.24) for transection and hemisection models, respectively. Factors associated with improved outcomes include the type of polymer used and a follow-up period greater than 6 weeks.

CONCLUSION

The functional improvement after implantation of biopolymer-based multimodal implants is modest. The relationship with neuronal regeneration and functional outcome, the effects of inflammation at the site of injury, the prolonged survival of supporting cells, the differentiation of stem cells, the effective delivery of neurotrophic factors, and longer follow-up periods are all topics for future elucidation. Future investigations should strive to further define specific factors associated with improved functional outcomes in clinically relevant models.

Collagen--emerging collagen based therapies hit the patient

The choice of biomaterials available for regenerative medicine continues to grow rapidly, with new materials often claiming advantages over the short-comings of those already in existence. Going back to nature, collagen is one of the most abundant proteins in mammals and its role is essential to our way of life. It can therefore be obtained from many sources including porcine, bovine, equine or human and offer a great promise as a biomimetic scaffold for regenerative medicine. Using naturally derived collagen, extracellular matrices (ECMs), as surgical materials have become established practice for a number of years. For clinical use the goal has been to preserve as much of the composition and structure of the ECM as possible without adverse effects to the recipient. This review will therefore cover in-depth both naturally and synthetically produced collagen matrices. Furthermore the production of more sophisticated three dimensional collagen scaffolds that provide cues at nano-, micro- and meso-scale for molecules, cells, proteins and bulk fluids by inducing fibrils alignments, embossing and layered configuration through the application of plastic compression technology will be discussed in details. This review will also shed light on both naturally and synthetically derived collagen products that have been available in the market for several purposes including neural repair, as cosmetic for the treatment of dermatologic defects, haemostatic agents, mucosal wound dressing and guided bone regeneration membrane. There are other several potential applications of collagen still under investigations and they are also covered in this review.

GDNF mediates glioblastoma-induced microglia attraction but not astrogliosis

High-grade gliomas are the most common primary brain tumors. Their malignancy is promoted by the complex crosstalk between different cell types in the central nervous system. Microglia/brain macrophages infiltrate high-grade gliomas and contribute to their progression. To identify factors that mediate the attraction of microglia/macrophages to malignant brain tumors, we established a glioma cell encapsulation model that was applied in vivo. Mouse GL261 glioma cell line and human high-grade glioma cells were seeded into hollow fibers (HF) that allow the passage of soluble molecules but not cells. The glioma cell containing HF were implanted into one brain hemisphere and simultaneously HF with non-transformed fibroblasts (controls) were introduced into the contralateral hemisphere. Implanted mouse and human glioma- but not fibroblast-containing HF attracted microglia and up-regulated immunoreactivity for GFAP, which is a marker of astrogliosis. In this study, we identified GDNF as an important factor for microglial attraction: (1) GL261 and human glioma cells secret GDNF, (2) reduced GDNF production by siRNA in GL261 in mouse glioma cells diminished attraction of microglia, (3) over-expression of GDNF in fibroblasts promoted microglia attraction in our HF assay. In vitro migration assays also showed that GDNF is a strong chemoattractant for microglia. While GDNF release from human or mouse glioma had a profound effect on microglial attraction, the glioma-induced astrogliosis was not affected. Finally, we could show that injection of GL261 mouse glioma cells with GDNF knockdown by shRNA into mouse brains resulted in reduced tumor expansion and improved survival as compared to injection of control cells.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Induction of rat facial nerve regeneration by functional collagen scaffolds

Nerve conduit provides a promising strategy for nerve regeneration, and the proper microenvironment in the lumen could improve the regeneration. Our previous work had demonstrated that linear ordered collagen scaffold (LOCS) could effectively guide the oriented growth of axons. Laminin is known as an important nerve growth promoting factor and can facilitate the growth cone formation. In addition, ciliary neurotrophic factor (CNTF) and brain-derived neurotrophic factor (BDNF) can effectively improve the nerve regeneration after nerve injuries. However, in practice, diffusion caused by the body fluids is the major obstacle in their applications. To retain CNTF or BDNF on the scaffolds, we produced collagen binding CNTF (CBD-CNTF), collagen binding BDNF (CBD-BDNF) and laminin binding CNTF (LBD-CNTF), laminin binding BDNF (LBD-BDNF) respectively. In this work, we developed laminin modified LOCS fibers (L × LOCS) by chemical cross-linking LOCS fibers with laminin. Collagen binding or laminin binding neurotrophic factors were combined with LOCS or L × LOCS, and then filled them into the collagen nerve conduit. They were found to guide the ordered growth of axons, and improve the nerve functional recovery in the rat facial nerve transection model. The combination of CNTF and BDNF greatly enhanced the facial nerve regeneration and functional recovery.

The potential for cellular therapy combined with growth factors in spinal cord injury

Any traumatic spinal cord injury (SCI) may cause symptoms ranging from pain to complete loss of motor and sensory functions below the level of the injury. Currently, there are over 2 million SCI patients worldwide. The cost of their necessary continuing care creates a burden for the patient, their families, and society. Presently, few SCI treatments are available and none have facilitated neural regeneration and/or significant functional improvement. Research is being conducted in the following areas: pathophysiology, cellular therapies (Schwann cells, embryonic stem cells, induced pluripotent stem cells, mesenchymal stem cells, olfactory ensheathing cells), growth factors (BDNF), inhibitory molecules (NG2, myelin protein), and combination therapies (cell grafts and neurotrophins, cotransplantation). Results are often limited because of the inhibitory environment created following the injury and the limited regenerative potential of the central nervous system. Therapies that show promise in small animal models may not transfer to nonhuman primates and humans. None of the research has resulted in remarkable improvement, but many areas show promise. Studies have suggested that a combination of therapies may enhance results and may be more effective than a single therapy. This paper reviews and discusses the most promising new SCI research including combination therapies.

Delivery of growth factors for tissue regeneration and wound healing

Growth factors are soluble secreted proteins capable of affecting a variety of cellular processes important for tissue regeneration. Consequently, the self-healing capacity of patients can be augmented by artificially enhancing one or more processes important for healing through the application of growth factors. However, their application in clinics remains limited due to lack of robust delivery systems and biomaterial carriers. Interestingly, all clinically approved therapies involving growth factors utilize some sort of a biomaterial carrier for growth factor delivery. This suggests that biomaterial delivery systems are extremely important for successful usage of growth factors in regenerative medicine. This review outlines the role of growth factors in tissue regeneration, and their application in both pre-clinical animal models of regeneration and clinical trials is discussed. Additionally, current status of biomaterial substrates and sophisticated delivery systems such as nanoparticles for delivery of exogenous growth factors and peptides in humans are reviewed. Finally, issues and possible future research directions for growth factor therapy in regenerative medicine are discussed.

Biomimetic hydrogels for controlled biomolecule delivery to augment bone regeneration

The regeneration of large bone defects caused by trauma or disease remains a significant clinical problem. Although osteoinductive growth factors such as bone morphogenetic proteins have entered clinics, transplantation of autologous bone remains the gold standard to treat bone defects. The effective treatment of bone defects by protein therapeutics in humans requires quantities that exceed the physiological doses by several orders of magnitude. This not only results in very high treatment costs but also bears considerable risks for adverse side effects. These issues have motivated the development of biomaterials technologies allowing to better control biomolecule delivery from the solid phase. Here we review recent approaches to immobilize biomolecules by affinity binding or by covalent grafting to biomaterial matrices. We focus on biomaterials concepts that are inspired by extracellular matrix (ECM) biology and in particular the dynamic interaction of growth factors with the ECM. We highlight the value of synthetic, ECM-mimicking matrices for future technologies to study bone biology and develop the next generation of 'smart' implants.

Design and synthesis of binding growth factors

Growth factors play important roles in tissue regeneration. However, because of their instability and diffusible nature, improvements in their performance would be desirable for therapeutic applications. Conferring binding affinities would be one way to improve their applicability. Here we review techniques for conjugating growth factors to polypeptides with particular affinities. Conjugation has been designed at the level of gene fusion and of polypeptide ligation. We summarize and discuss the designs and applications of binding growth factors prepared by such conjugation approaches.

Biofunctionalisation of polymeric scaffolds for neural tissue engineering

Patients who experience injury to the central or peripheral nervous systems invariably suffer from a range of dysfunctions due to the limited ability for repair and reconstruction of damaged neural tissue. Whilst some treatment strategies can provide symptomatic improvement of motor and cognitive function, they fail to repair the injured circuits and rarely offer long-term disease modification. To this end, the biological molecules, used in combination with neural tissue engineering scaffolds, may provide feasible means to repair damaged neural pathways. This review will focus on three promising classes of neural tissue engineering scaffolds, namely hydrogels, electrospun nanofibres and self-assembling peptides. Additionally, the importance and methods for presenting biologically relevant molecules such as, neurotrophins, extracellular matrix proteins and protein-derived sequences that promote neuronal survival, proliferation and neurite outgrowth into the lesion will be discussed.

Combination therapies in the CNS: engineering the environment

The inhibitory extracellular environment that develops in response to traumatic brain injury and spinal cord injury hinders axon growth thereby limiting restoration of function. Several strategies have been developed to engineer a more permissive central nervous system (CNS) environment to promote regeneration and functional recovery. The multi-faced inhibitory nature of the CNS lesion suggests that therapies used in combination may be more effective. In this mini-review we summarize the most recent attempts to engineer the CNS extracellular environment after injury using combinatorial strategies. The advantages and limits of various combination therapies utilizing neurotrophin delivery, cell transplantation, and biomaterial scaffolds are discussed. Treatments that reduce the inhibition by chondroitin sulfate proteoglycans, myelin-associated inhibitors, and other barriers to axon regeneration are also reviewed. Based on the current state of the field, future directions are suggested for research on combination therapies in the CNS.

Roles of BDNF in spinal neuroplasticity in cats subjected to partial dorsal ganglionectomy

This study investigated the role of brain-derived neurotrophic factor (BDNF) in neuroplasticity in cats subjected to the removal of dorsal root ganglia (DRG). Following partial ganglionectomy, the number of BDNF-positive varicosities from spared L6 DRG decreased significantly. This reduction was observed at 3 days post operation (dpo) in spinal lamina II of L3 and L5. Whereas the percentages of positive neurons for BDNF and its mRNA in spared L6 DRG at 10 dpo were significantly increased, and accumulated BDNF was seen on the DRG side of the ligated axons. Importantly, BDNF antibody neutralization in vivo results in a significant reduction in the number of varicosities in spinal lamina II, evidenced by BDNF and calcitonin gene-related peptide immunohistochemical staining. These findings suggested that peripheral-derived BDNF could play a critical role in spinal neuroplasticity in cats subjected to partial ganglionectomy. This may underlie the basis of molecular therapy depending on gene drug-like BDNF release.

A myocardial patch made of collagen membranes loaded with collagen-binding human vascular endothelial growth factor accelerates healing of the injured rabbit heart

Tissue-engineered myocardial patches could be useful in the repair of myocardial injuries. The aim of the present study was to evaluate a collagen targeting delivery system for myocardial repair. A specific peptide collagen-binding domain (CBD) was fused to human vascular endothelial growth factor (VEGF) to enhance the binding of VEGF to collagen. In this study, collagen membranes loaded with CBD-VEGF, natural VEGF, or phosphate-buffered saline are used as cardiac patches to repair the infarcted myocardium in a rabbit model. CBD-VEGF/collagen group could effectively induce more cells to penetrate into the collagen membrane after 4 weeks and promote more vascularization in infarcted myocardium after 12 weeks compared with the other two control groups. Echocardiography and hemodynamic studies both show cardiac function improvement in the CBD-VEGF/collagen group. These results reveal that implantation of CBD-VEGF collagen membrane patch into the infarcted myocardium could effectively improve left ventricle cardiac function and increase the vascular density.

Supplement moderate zinc as an effective treatment for spinal cord injury

Spinal cord repair is a challenging task that has puzzled clinical specialists and scientists for a long time. Zinc plays an important role in regulating the expression of brain-derived neurotrophic factor (BDNF) in nervous system, which can improve the pathological state of neurons and promote regeneration of injured neurons, reduce neuronal apoptosis. Our previous studies demonstrated that the serum zinc levels in SCI model group were significantly decreased and zinc concentrations in spinal cord were gradually increased in 24 h after SCI, which induces the up-regulation of zinc transporter 1 (ZnT-1). The mRNA levels of ZnT1 and BDNF were both increased after SCI, and there is a positive correlation between them. Excess zinc exposure has been proved to be a risk factor for neuron death in brain and spinal cord injuries, but supplement of the right amount of zinc may be useful in promoting the recovery of spinal cord function.

Signaling cue presentation and cell delivery to promote nerve regeneration

Limitations in current nerve regeneration techniques have stimulated the development of various approaches to mimic the extrinsic cues available in the natural nerve regeneration environment. Biomaterials approaches modulate the microenvironment of a regenerating nerve through tailored presentation of signaling molecules, creating physical and biochemical guidance cues to direct axonal regrowth across nerve lesion sites. Cell-based approaches center on increasing the neurotrophic support, adhesion guidance and myelination capacity of Schwann cells and other alternative cell types to enhance nerve regrowth and functional recovery. Recent advances in presenting directional guidance cues in nerve guidance conduits and improving the regenerative outcomes of cell delivery provide inspirations to engineering the next generation of nerve repair solutions.

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

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

Suspension matrices for improved Schwann-cell survival after implantation into the injured rat spinal cord

Trauma to the spinal cord produces endogenously irreversible tissue and functional loss, requiring the application of therapeutic approaches to achieve meaningful restoration. Cellular strategies, in particular Schwann-cell implantation, have shown promise in overcoming many of the obstacles facing successful repair of the injured spinal cord. Here, we show that the implantation of Schwann cells as cell suspensions with in-situ gelling laminin:collagen matrices after spinal-cord contusion significantly enhances long-term cell survival but not proliferation, as well as improves graft vascularization and the degree of axonal in-growth over the standard implantation vehicle, minimal media. The use of a matrix to suspend cells prior to implantation should be an important consideration for achieving improved survival and effectiveness of cellular therapies for future clinical application.

Clinical and experimental advances in regeneration of spinal cord injury

Spinal cord injury (SCI) is one of the major disabilities dealt with in clinical rehabilitation settings and is multifactorial in that the patients suffer from motor and sensory impairments as well as many other complications throughout their lifetimes. Many clinical trials have been documented during the last two decades to restore damaged spinal cords. However, only a few pharmacological therapies used in clinical settings which still have only limited effects on the regeneration, recovery speed, or retraining of the spinal cord. In this paper, we will introduce recent clinical trials, which performed pharmacological treatments and cell transplantations for patients with SCI, and evaluate recent in vivo studies for the regeneration of injured spinal cord, including stem-cell transplantation, application of neurotrophic factors and suppressor of inhibiting factors, development of biomaterial scaffolds and delivery systems, rehabilitation, and the combinations of these therapies to evaluate what can be appropriately applied in the future to the patients with SCI.

Bladder regeneration by collagen scaffolds with collagen binding human basic fibroblast growth factor

PURPOSE

Studies show that basic fibroblast growth factor can promote bladder regeneration. However, the lack of targeting delivery approaches limits its clinical application. We investigated a collagen based targeting system for bladder regeneration. A collagen binding domain was added to the native basic fibroblast growth factor N-terminal to allow it to bind to collagen.

MATERIALS AND METHODS

Sprague-Dawley rats underwent partial cystectomy. Collagen scaffolds loaded with collagen binding domain basic fibroblast growth factor, native basic fibroblast growth factor or phosphate buffered saline were grafted to the remaining host bladders, respectively. At days 30 and 90 reconstructed bladders were evaluated by histological analysis and urodynamics.

RESULTS

This targeting basic fibroblast growth factor delivery system induced satisfying bladder histological structures. It promoted more vascularization and smooth muscle cell ingrowth. Urodynamics revealed well accommodated bladder tissue with volume capacity and compliance.

CONCLUSIONS

Results show that the targeting delivery system consisting of collagen binding domain basic fibroblast growth factor and collagen membranes induced better bladder regeneration at the injury site. Thus, this targeting delivery system may be an effective strategy for bladder regeneration with potential clinical applications.

Current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury using polymer scaffolds

This review highlights current tissue engineering and novel therapeutic approaches to axonal regeneration following spinal cord injury. The concept of developing 3-dimensional polymer scaffolds for placement into a spinal cord transection model has recently been more extensively explored as a solution for restoring neurologic function after injury. Given the patient morbidity associated with respiratory compromise, the discrete tracts in the spinal cord conveying innervation for breathing represent an important and achievable therapeutic target. The aim is to derive new neuronal tissue from the surrounding, healthy cord that will be guided by the polymer implant through the injured area to make functional reconnections. A variety of naturally derived and synthetic biomaterial polymers have been developed for placement in the injured spinal cord. Axonal growth is supported by inherent properties of the selected polymer, the architecture of the scaffold, permissive microstructures such as pores, grooves or polymer fibres, and surface modifications to provide improved adherence and growth directionality. Structural support of axonal regeneration is combined with integrated polymeric and cellular delivery systems for therapeutic drugs and for neurotrophic molecules to regionalize growth of specific nerve populations.