Biomaterials and Strategies for Nerve Regeneration

Biodegradable Electrospun Conduit with Aligned Fibers Based on Poly(lactic-co-glycolic Acid) (PLGA)/Carbon Nanotubes and Choline Bitartrate Ionic Liquid

Functionally active aligned fibers are a promising approach to enhance neuro adhesion and guide the extension of neurons for peripheral nerve regeneration. Therefore, the present study developed poly(lactic-co-glycolic acid) (PLGA)-aligned electrospun mats and investigated the synergic effect with carbon nanotubes (CNTs) and Choline Bitartrate ionic liquid (Bio-IL) on PLGA fibers. Morphology, thermal, and mechanical performances were determined as well as the hydrolytic degradation and the cytotoxicity. Results revealed that electrospun mats are composed of highly aligned fibers, and CNTs were aligned and homogeneously distributed into the fibers. Bio-IL changed thermal transition behavior, reduced glass transition temperature (Tg), and favored crystal phase formation. The mechanical properties increased in the presence of CNTs and slightly decreased in the presence of the Bio-IL. The results demonstrated a decrease in the degradation rate in the presence of CNTs, whereas the use of Bio-IL led to an increase in the degradation rate. Cytotoxicity results showed that all the electrospun mats display metabolic activity above 70%, which demonstrates that they are biocompatible. Moreover, superior biocompatibility was observed for the electrospun containing Bio-IL combined with higher amounts of CNTs, showing a high potential to be used in nerve tissue engineering.

Sciatic nerve injury regeneration in adult male rats using gelatin methacrylate (GelMA)/poly(2-ethy-2-oxazoline) (PEtOx) hydrogel containing 4-aminopyridine (4-AP)

One of the most important parts of the body is the peripheral nervous system, and any injuries in this system may result in potentially lethal consequences or severe side effects. The peripheral nervous system may not rehabilitate the harmed regions following disabling disorders, which reduce the quality of life of patients. Fortunately, in recent years, hydrogels have been proposed as exogenous alternatives to bridge damaged nerve stumps to create a useful microenvironment for advancing nerve recovery. However, hydrogel-based medicine in the therapy of peripheral nerve injury still needs a lot of improvement. In this study, GelMA/PEtOx hydrogel was used for the first time to deliver 4-Aminopyridine (4-AP) small molecules. 4-AP is a broad-spectrum potassium channel blocker, which has been demonstrated to increase neuromuscular function in patients with various demyelinating disorders. The prepared hydrogel showed a porosity of 92.2 ± 2.6% after 20 min, swelling ratio of 456.01 ± 2.0% after 180 min, weight loss of 81.7 ± 3.1% after 2 weeks, and good blood compatibility as well as sustainable drug release. MTT analysis was performed to assess the cell viability of the hydrogel and proved that the hydrogel is an appropriate substrate for the survival of cells. In vivo studies were performed for functional analysis and the sciatic functional index (SFI) as well as hot plate latency results showed that the use of GelMA/PEtOx+4-AP hydrogel enhances the regeneration compared to the GelMA/PEtOx hydrogel and the control group.

Bridging Gaps in Peripheral Nerves: From Current Strategies to Future Perspectives in Conduit Design

In peripheral nerve injuries (PNI) with substance loss, where tensionless end-to-end suture is not achievable, the positioning of a graft is required. Available options include autografts (e.g., sural nerve, medial and lateral antebrachial cutaneous nerves, superficial branch of the radial nerve), allografts (Avance^®; human origin), and hollow nerve conduits. There are eleven commercial hollow conduits approved for clinical, and they consist of devices made of a non-biodegradable synthetic polymer (polyvinyl alcohol), biodegradable synthetic polymers (poly(DL-lactide-ε-caprolactone); polyglycolic acid), and biodegradable natural polymers (collagen type I with/without glycosaminoglycan; chitosan; porcine small intestinal submucosa); different resorption times are available for resorbable guides, ranging from three months to four years. Unfortunately, anatomical/functional nerve regeneration requirements are not satisfied by any of the possible alternatives; to date, focusing on wall and/or inner lumen organization/functionalization seems to be the most promising strategy for next-generation device fabrication. Porous or grooved walls as well as multichannel lumens and luminal fillers are the most intriguing options, eventually also including the addition of cells (Schwann cells, bone marrow-derived, and adipose tissue derived stem cells) to support nerve regeneration. This review aims to describe common alternatives for severe PNI recovery with a highlight of future conduits.

Differentiating Lumbar Spinal Etiology from Peripheral Plexopathies

Clinicians have managed and treated lower back pain since the earliest days of practice. Historically, lower back pain and its accompanying symptoms of radiating leg pain and muscle weakness have been recognized to be due to any of the various lumbar spine pathologies that lead to the compression of the lumbar nerves at the root, the most common of which is the radiculopathy known as sciatica. More recently, however, with the increased rise in chronic diseases, the importance of differentially diagnosing a similarly presenting pathology, known as lumbosacral plexopathy, cannot be understated. Given the similar clinical presentation of lumbar spine pathologies and lumbosacral plexopathies, it can be difficult to differentiate these two diagnoses in the clinical setting. Resultingly, the inappropriate diagnosis of either pathology can result in ineffective clinical management. Thus, this review aims to aid in the clinical differentiation between lumbar spine pathology and lumbosacral plexopathy. Specifically, this paper delves into spine and plexus anatomy, delineates the clinical assessment of both pathologies, and highlights powerful diagnostic tools in the hopes of bolstering appropriate diagnosis and treatment. Lastly, this review will describe emerging treatment options for both pathologies in the preclinical and clinical realms, with a special emphasis on regenerative nerve therapies.

Evaluation of ethylene oxide, gamma radiation, dry heat and autoclave sterilization processes on extracellular matrix of biomaterial dental scaffolds

Scaffolds used to receive stem cells are a promising perspective of tissue regeneration research, and one of the most effective solutions to rebuild organs. In the near future will be possible to reconstruct a natural tooth using stems cells, but to avoid an immune-defensive response, sterilize the scaffold is not only desired, but also essential to be successful. A study confirmed stem cells extracted from rat's natural teeth, and implanted into the alveolar bone, could differentiate themselves in dental cells, but the scaffold's chemistry, geometry, density, morphology, adherence, biocompatibility and mechanical properties remained an issue. This study intended to produce a completely sterilized dental scaffold with preserved extracellular matrix. Fifty-one samples were collected, kept in formaldehyde, submitted to partial demineralization and decellularization processes and sterilized using four different methods: dry heating; autoclave; ethylene-oxide and gamma-radiation. They were characterized through optical images, micro-hardness, XRD, EDS, XRF, SEM, histology and sterility test. The results evidenced the four sterilization methods were fully effective with preservation of ECM molecular arrangements, variation on chemical composition (proportion of Ca/P) was compatible with Ca/P proportional variation between enamel and dentine regions. Gamma irradiation and ethylene oxide presents excellent results, but their viability are compromised by the costs and technology's accessibility (requires very expensive equipment and/or consumables). Excepted gamma irradiation, all the sterilization methods more than sterilizing also reduced the remaining pulp. Autoclave presents easy equipment accessibility, lower cost consumables, higher reduction of remaining pulp and complete sterilization, reason why was considered the most promising technique.

Application of Human Epineural Conduit Supported with Human Mesenchymal Stem Cells as a Novel Therapy for Enhancement of Nerve Gap Regeneration

Various therapeutic methods have been suggested to enhance nerve regeneration. In this study, we propose a novel approach for enhancement of nerve gap regeneration by applying human epineural conduit (hEC) supported with human mesenchymal stem cells (hMSC), as an alternative to autograft repair. Restoration of 20 mm sciatic nerve defect with hEC created from human sciatic nerve supported with hMSC was tested in 4 experimental groups (n = 6 each) in the athymic nude rat model (Crl:NIH-Foxn1^rnu): 1 - No repair control, 2 - Autograft control, 3 - Matched diameter hEC filled with 1 mL saline, 4 - Matched diameter hEC supported with 3 × 10⁶ hMSC. Assessments included: functional tests: toe-spread and pinprick, regeneration assessment by immunofluorescence staining: HLA-1, HLA-DR, NGF, GFAP, Laminin B, S-100, VEGF, vWF and PKH26 labeling; histomorphometric analysis of myelin thickness, axonal density, fiber diameter and myelinated nerve fibers percentage; Gastrocnemius Muscle Index (GMI) and muscle fiber area ratio. Best sensory and motor function recovery, as well as GMI and muscle fiber area ratio, were observed in the autograft group, and were comparable to the hEC with hMSC group (p = 0.038). Significant improvements of myelin thickness (p = 0.003), fiber diameter (p = 0.0296), and percentage of myelinated fibers (p < 0.0001) were detected in hEC group supported with hMSC compared to hEC with saline controls. At 12-weeks after nerve gap repair, hEC combined with hMSC revealed increased expression of neurotrophic and proangiogenic factors, which corresponded with improvement of function comparable with the autograft control. Application of our novel hEC supported with hMSC provides a potential alternative to the autograft nerve repair.

Mini review: Biomaterials in repair and regeneration of nerve in a volumetric muscle loss

Volumetric muscle loss (VML) following a severe trauma or injury is beyond the intrinsic regenerative capacity of muscle tissues, and hence interventional therapy is required. Extensive muscle loss concomitant with damage to neuromuscular components overwhelms the muscles' remarkable regenerative capacity. The loss of nervous and vascular tissue leads to further damage and atrophy, so a combined treatment for neuromuscular junction (NMJ) along with the volumetric muscle regeneration is important. There have been immense advances in the field of tissue engineering for skeletal muscle tissue and peripheral nerve regeneration, but very few address the interdependence of the tissues and the need for combined therapies to repair and regenerate fully functional muscle tissue. This review addresses the problem and presents an overview of the biomaterials that have been studied for tissue engineering of neuromuscular tissues associated with skeletal muscles.

Engineering Polysaccharides for Tissue Repair and Regeneration

The success of repair or regeneration depends greatly on the architecture of 3D scaffolds that finely mimic natural extracellular matrix to support cell growth and assembly. Polysaccharides have excellent biocompatibility with intrinsic biological cues and they have been extensively investigated as scaffolds for tissue engineering and regenerative medicine (TERM). The physical and biochemical structures of natural polysaccharides, however, can barely meet all the requirements of tissue-engineered scaffolds. To take advantage of their inherent properties, many innovative approaches including chemical, physical, or joint modifications have been employed to improve their properties. Recent advancement in molecular and material building technology facilitates the fabrication of advanced 3D structures with desirable properties. This review focuses on the latest progress of polysaccharide-based scaffolds for TERM, especially those that construct advanced architectures for tissue regeneration.

Enhanced proliferation and differentiation of neural stem cells by peptide-containing temperature-sensitive hydrogel scaffold

Hydrogel has attracted great attention in the past few years as a widely used material for repairing central nerve damage. However, conventional hydrogel bio-scaffold, such as chitosan, gelatin, and sodium alginate, lack sufficient biological activity and have limited nerve repair capabilities. Therefore, to explore biologically active and intelligent hydrogel materials is particularly important and necessary for central nerve repair. Herein, we developed a temperature-sensitive hydrogel grafted with a bioactive peptide IKVAV (Ile-Lys-Val-Ala-Val, IKVAV). The hydrogel was prepared by copolymerization of N-propan-2-ylprop-2-enamide (NIPAM) and AC-PEG-IKVAV copolymers via reversible addition-fracture chain transfer (RAFT) polymerization, using polyethylene glycol (PEGDA) and N, N'-Methylenebisacrylamide (BISAM) as cross-linking agents. The prepared hydrogel scaffold demonstrates a series of excellent properties such as rapid (de)swelling performance, good biocompatibility, regular three-dimensional porous structure, and in particular good biological activity, which can guide cell fate and mediate neuron's differentiation. Therefore, the developed peptide hydrogel scaffold provides a new strategy for designing biomaterials that are widely used in tissue engineering for central nervous system injury.

Combination of in-situ collagen injection and rehabilitative treatment in long-lasting facial nerve palsy: a pilot randomized controlled trial

BACKGROUND

Many rehabilitative attempts have been made to prevent or reduce residual deficits in patients with established and long-term facial palsy (FP). In many clinical settings in-situ injection of collagen-based medical devices have been demonstrated to provide nutritional support for tissues.

AIM

To test the effectiveness of a collagen-based treatment for patients complaining of long standing FP, who are following a proprioceptive neuromuscular facilitation protocol (Kabat method) (group A), compared to a FP group only undergoing the Kabat method (group B).

DESIGN

Randomised controlled trial.

SETTING

Tertiary referral outpatient center and University Hospital.

POPULATION

Forty-one patients with a medical diagnosis of long-term unilateral peripheral FP.

METHODS

Twenty-one Group A patients were compared, after randomization, to nineteen matched group B patients after 8 weeks of treatment. The outcomes were electromyographic findings, validated questionnaires (Facial Disability Index, FDI and General health-related quality of life assessment, QOL) and clinical grading (House-Brackmann, HB, and synkinesis grading scale). A correlation analysis was performed between pre-/post-treatment differences (Δ) in outcome and clinical-demographic measures.

RESULTS

A significant within-subjects improvement, both in electrophysiological and questionnaire scores, was found in both groups. When compared with group B, group A patients exhibited a significant reduction of post-treatment polyphasic potentials of voluntary activity of orbicularis oculi (P=0.017) and oris (P=0.015) and a significant increase in post-treatment duration of voluntary activity of orbicularis oris (P=0.018). Group A subjects demonstrated a significant improvement in questionnaire subscales regarding overall disease perception. Although positive correlations between the ∆FDI and ∆percentage of polyphasic potentials of voluntary activity were found in both groups, negative correlations in group A were found between disease duration and ∆duration of voluntary activity of orbicularis oculi and oris.

CONCLUSIONS

The combination of physical rehabilitative procedures with in-situ collagen injections, possibly acting in redirecting the phenomena of reinnervation/reorganization, demonstrated encouraging results in patients affected by long term FP.

CLNICAL REHABILITATION IMPACT

In-situ collagen injection could be a safe option enlarging the 'window of opportunity' to improve the voluntary muscle contraction pattern and general and specific disability referred by patients affected by long standing FP.

Peptide gels for controlled release of proteins

Treatment strategies in clinics have been shifting from small molecules to protein drugs due to the promising results of a highly specific mechanism of action and reduced toxicity. Despite their prominent roles in disease treatment, delivery of the protein therapeutics is challenging due to chemical instability, immunogenicity and biological barriers. Peptide hydrogels with spatiotemporally tunable properties have shown an outstanding potential to deliver complex protein therapeutics, maintain drug efficacy and stability over time, mimicking the extracellular matrix, and responding to external stimuli. In this review, we present recent advances in peptide hydrogel design strategies, protein release kinetics and mechanisms for protein drug delivery in cellular engineering, tissue engineering, immunotherapy and disease treatments.

Preprocessing of Medical Image Data for Three-Dimensional Bioprinted Customized-Neural-Scaffolds

IMPACT STATEMENT

Nerve damage, which can be devastating, triggers several biological cascades, which result in the insufficiencies of the human nervous system to provide complete nerve repair and regain of function. Since no therapeutic strategy exists to provide immediate attention and intervention to patients with newly acquired nerve damage, we propose a strategy in which accelerated medical image processing through graphical processing unit implementation and three-dimensional printing are combined to produce a time-efficient, patient-specific (custom-neural-scaffold) solution to nerve damage. This work aims to beneficially shorten the time required for medical decision-making so that improved patient outcomes are achieved.

Promoting Neurite Growth and Schwann Cell Migration by the Harnessing Decellularized Nerve Matrix onto Nanofibrous Guidance

Synergistic intercellular interactions have been widely acknowledged in tuning functional cell behaviors in vivo, and these interactions have inspired the development of a variety of scaffolds for regenerative medicine. In this paper, the promotion of Schwann cell (SC)-neurite interactions through the use of a nerve extracellular matrix-coated nanofiber composite in vitro was demonstrated using a cell culturing platform consisting of either random or aligned electrospun poly(l-lactic acid) nanofibers and decellularized peripheral nerve matrix gel (pDNM gel) from porcine peripheral nervous tissue. The pDNM-coated nanofiber platform served as a superior substrate for dorsal root ganglion culturing. Furthermore, SC migration was facilitated by pDNM gel coating on the nanofibers, accompanied with much faster axonal extension, in comparison with the effect of topographical guidance from the aligned electrospun fibers only. Finally, the decellularized nerve matrix promoted the ability of SCs to wrap around bundled neurites, triggering axonal remyelination toward nerve fiber functionalization.

PCL/gelatin nanofibrous scaffolds with human endometrial stem cells/Schwann cells facilitate axon regeneration in spinal cord injury

The significant consequences of spinal cord injury (SCI) include sensory and motor disability resulting from the death of neuronal cells and axon degeneration. In this respect, overcoming the consequences of SCI including the recovery of sensory and motor functions is considered to be a difficult tasks that requires attention to multiple aspects of treatment. The breakthrough in tissue engineering through the integration of biomaterial scaffolds and stem cells has brought a new hope for the treatment of SCI. In the present study, human endometrial stem cells (hEnSCs) were cultured with human Schwann cells (hSC) in transwells, their differentiation into nerve-like cells was confirmed by quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) and immunocytochemistry techniques. The differentiated cells (co-hEnSC) were then seeded on the poly ε-caprolactone (PCL)/gelatin scaffolds. The SEM images displayed the favorable seeding and survival of the cells on the scaffolds. The seeded scaffolds were then transplanted into hemisected SCI rats. The growth of neuronal cells was confirmed with immunohistochemical study using NF-H as a neuronal marker. Finally, the Basso, Beattie, and Bresnahan (BBB) test confirmed the recovery of sensory and motor functions. The results suggested that combination therapy using the differentiated hEnSC seeded on PCL/gelatin scaffolds has the potential to heal the injured spinal cord and to limit the secondary damage.

The combined effects of three-dimensional cell culture and natural tissue extract on neural differentiation of P19 embryonal carcinoma stem cells

Tissue engineering, as a novel transplantation therapy, aims to create biomaterial scaffolds resembling the extracellular matrix in order to regenerate the damaged tissues. Adding bioactive factors to the scaffold would improve cell-tissue interactions. In this study, the effect of chitosan polyvinyl alcohol nanofibres containing carbon nanotube scaffold with or without active bioglass (BG⁺ /BG^- ), in combination with neonatal rat brain extract on cell viability, proliferation, and neural differentiation of P19 embryonic carcinoma stem cells was investigated. To induce differentiation, the cells were cultured in α-MEM supplemented with neonatal rat brain extract on the scaffolds. The expression of undifferentiated stem cell markers as well as neuroepithelial and neural-specific markers was evaluated and confirmed by real-time Reverse transcription polymerase chain reaction (RT-PCR) and immunofluorescence procedures. Finally, the three-dimensional (3D) cultured cells were implanted into the damaged neural tubes of chick embryos, and their fates were followed in ovo. Based on the histological and immunofluorescence observations, the transplanted cells were able to survive, migrate, and penetrate into the host embryonic tissues. Gene network analysis suggested the possible involvement of neurotransmitters as a downstream target of synaptophysin and tyrosine hydroxylase. Overall, the results of this study indicated that combining the effects of 3D cell culture and natural brain tissue extract can accelerate the differentiation of P19 embryonic carcinoma cells into neuronal phenotype cells.

Brain and spinal cord injury repair by implantation of human neural progenitor cells seeded onto polymer scaffolds

Hypoxic-ischemic (HI) brain injury and spinal cord injury (SCI) lead to extensive tissue loss and axonal degeneration. The combined application of the polymer scaffold and neural progenitor cells (NPCs) has been reported to enhance neural repair, protection and regeneration through multiple modes of action following neural injury. This study investigated the reparative ability and therapeutic potentials of biological bridges composed of human fetal brain-derived NPCs seeded upon poly(glycolic acid)-based scaffold implanted into the infarction cavity of a neonatal HI brain injury or the hemisection cavity in an adult SCI. Implantation of human NPC (hNPC)–scaffold complex reduced the lesion volume, induced survival, engraftment, and differentiation of grafted cells, increased neovascularization, inhibited glial scar formation, altered the microglial/macrophage response, promoted neurite outgrowth and axonal extension within the lesion site, and facilitated the connection of damaged neural circuits. Tract tracing demonstrated that hNPC–scaffold grafts appear to reform the connections between neurons and their targets in both cerebral hemispheres in HI brain injury and protect some injured corticospinal fibers in SCI. Finally, the hNPC–scaffold complex grafts significantly improved motosensory function and attenuated neuropathic pain over that of the controls. These findings suggest that, with further investigation, this optimized multidisciplinary approach of combining hNPCs with biomaterial scaffolds provides a more versatile treatment for brain injury and SCI.

Biodegradable scaffolds seeded with human fetal brain cells can help repair neurological injuries in rodents. A team led by Kook In Park and Il-Shin Lee from the Yonsei University College of Medicine in Seoul, South Korea, created a mesh of plastic fibers that they bathed in neural progenitor cells. Over the course of several days, these cells differentiated into different types of brain cells, including neurons and glia. The researchers implanted these cell-scaffold complexes into the sites of injury in two rodent models: newborn mice with oxygen deprivation to the brain, and adult rats with severed spinal cords. In both cases, the treatment helped the injured tissues heal and improved the neurological or motor function of the animals. The authors suggest these tissue-engineered structures could also help people with brain or spine injuries.

Microstructure and Cytocompatibility of Electrospun Nanocomposites Based on Poly(ɛ-Caprolactone) and Carbon Nanostructures

Carbon nanostructures (CNSs) are attractive and promising nanomaterials for the next generation of tissue engineering scaffolds, especially in neural prosthesis. Optimizing scaffold vascularization may be an important strategy to promote the repair of damaged brain tissue. In this context, the idea was to evaluate the cell response of electrospun nanohybrid scaffolds loaded with CNSs. Fibrous composites based on poly(ɛ-caprolactone) (PCL) and CNSs were fabricated by means of electrospinning technique. High-purity carbon nanofibers (CNFs) and single-wall carbon nanotubes (SWNTs) were studied. A detailed microstructural characterization was performed to evaluate the most favorable experimental conditions for the realization of fibrous PCL/CNS fabrics. Electrospun mats comprised of rather uniform and homogeneous submicrometric fibers were obtained starting from 1:1 v/v mixture of tetrahydrofuran (THF) and N,N dimethylformamide (DMF). In vitro cytocompatibility tests were performed using rat cerebro-microvascular endothelial cells (CECs). Acquired results showed an increased cell viability for PCL/CNS nanocomposites, suggesting these materials as a suitable environment for endothelial cells. These results are indicative of the promising potential of CNS-based nanocomposites in biomedical devices for tissue engineering applications where endothelial functional properties are required.

Direct Laser Writing of Tubular Microtowers for 3D Culture of Human Pluripotent Stem Cell-Derived Neuronal Cells

As the complex structure of nervous tissue cannot be mimicked in two-dimensional (2D) cultures, the development of three-dimensional (3D) neuronal cell culture platforms is a topical issue in the field of neuroscience and neural tissue engineering. Computer-assisted laser-based fabrication techniques such as direct laser writing by two-photon polymerization (2PP-DLW) offer a versatile tool to fabricate 3D cell culture platforms with highly ordered geometries in the size scale of natural 3D cell environments. In this study, we present the design and 2PP-DLW fabrication process of a novel 3D neuronal cell culture platform based on tubular microtowers. The platform facilitates efficient long-term 3D culturing of human neuronal cells and supports neurite orientation and 3D network formation. Microtower designs both with or without intraluminal guidance cues and/or openings in the tower wall are designed and successfully fabricated from Ormocomp. Three of the microtower designs are chosen for the final culture platform: a design with openings in the wall and intralumial guidance cues (webs and pillars), a design with openings but without intraluminal structures, and a plain cylinder design. The proposed culture platform offers a promising concept for future 3D cultures in the field of neuroscience.

Bone marrow stromal cell sheets may promote axonal regeneration and functional recovery with suppression of glial scar formation after spinal cord transection injury in rats

OBJECTIVE

Transplantation of bone marrow stromal cells (BMSCs) is a theoretical potential as a therapeutic strategy in the treatment of spinal cord injury (SCI). Although a scaffold is sometimes used for retaining transplanted cells in damaged tissue, it is also known to induce redundant immunoreactions during the degradation processes. In this study, the authors prepared cell sheets made of BMSCs, which are transplantable without a scaffold, and investigated their effects on axonal regeneration, glial scar formation, and functional recovery in a completely transected SCI model in rats.

METHODS

BMSC sheets were prepared from the bone marrow of female Fischer 344 rats using ascorbic acid and were cryopreserved until the day of transplantation. A gelatin sponge (GS), as a control, or BMSC sheet was transplanted into a 2-mm-sized defect of the spinal cord at the T-8 level. Axonal regeneration and glial scar formation were assessed 2 and 8 weeks after transplantation by immunohistochemical analyses using anti-Tuj1 and glial fibrillary acidic protein (GFAP) antibodies, respectively. Locomotor function was evaluated using the Basso, Beattie, and Bresnahan scale.

RESULTS

The BMSC sheets promoted axonal regeneration at 2 weeks after transplantation, but there was no significant difference in the number of Tuj1-positive axons between the sheet- and GS-transplanted groups. At 8 weeks after transplantation, Tuj1-positive axons elongated across the sheet, and their numbers were significantly greater in the sheet group than in the GS group. The areas of GFAP-positive glial scars in the sheet group were significantly reduced compared with those of the GS group at both time points. Finally, hindlimb locomotor function was ameliorated in the sheet group at 4 and 8 weeks after transplantation.

CONCLUSIONS

The results of the present study indicate that an ascorbic acid–induced BMSC sheet is effective in the treatment of SCI and enables autologous transplantation without requiring a scaffold.

The Present and Future for Peripheral Nerve Regeneration

Peripheral nerve injury can have a potentially devastating impact on a patient's quality of life, resulting in severe disability with substantial social and personal cost. Refined microsurgical techniques, advances in peripheral nerve topography, and a better understanding of the pathophysiology and molecular basis of nerve injury have all led to a decisive leap forward in the field of translational neurophysiology. Nerve repair, nerve grafting, and nerve transfers have improved significantly with consistently better functional outcomes. Direct nerve repair with epineural microsutures is still the surgical treatment of choice when a tension-free coaptation in a well-vascularized bed can be achieved. In the presence of a significant gap (>2-3 cm) between the proximal and distal nerve stumps, primary end-to-end nerve repair often is not possible; in these cases, nerve grafting is the treatment of choice. Indications for nerve transfer include brachial plexus injuries, especially avulsion type, with long distance from target motor end plates, delayed presentation, segmental loss of nerve function, and broad zone of injury with dense scarring. Current experimental research in peripheral nerve regeneration aims to accelerate the process of regeneration using pharmacologic agents, bioengineering of sophisticated nerve conduits, pluripotent stem cells, and gene therapy. Several small molecules, peptides, hormones, neurotoxins, and growth factors have been studied to improve and accelerate nerve repair and regeneration by reducing neuronal death and promoting axonal outgrowth. Targeting specific steps in molecular pathways also allows for purposeful pharmacologic intervention, potentially leading to a better functional recovery after nerve injury. This article summarizes the principles of nerve repair and the current concepts of peripheral nerve regeneration research, as well as future perspectives. [Orthopedics. 2017; 40(1):e141-e156.].

Recurrent laryngeal nerve regeneration using an oriented collagen scaffold containing Schwann cells

OBJECTIVES/HYPOTHESIS

Regeneration of the recurrent laryngeal nerve (RLN), which innervates the intrinsic laryngeal muscles such that they can perform complex functions, is particularly difficult to achieve. Synkinesis after RLN neogenesis leads to uncoordinated movement of laryngeal muscles. Recently, some basic research studies have used cultured Schwann cells (SCs) to repair peripheral nerve injuries. This study aimed to regenerate the RLN using an oriented collagen scaffold containing cultured SCs.

STUDY DESIGN

Preliminary animal experiment.

METHODS

A 10-mm-long autologous canine cervical ansa was harvested. The nerve tissue was scattered and subcultured on oriented collagen sheets in reduced serum medium. After verifying that the smaller cultivated cells with high nucleus-cytoplasm ratios were SCs, collagen sheets with longitudinally oriented cells were rolled and inserted into a 20-mm collagen conduit. The fabricated scaffolds containing SCs were autotransplanted to a 20-mm deficient RLN, and vocal fold movements and histological characteristics were observed.

RESULTS

Scaffolds containing cultured SCs were successfully fabricated. Immunocytochemical examination revealed that these isolated and cultured cells, identified as SCs, expressed S-100 protein and GFAP but not vimentin. The orientation of SCs matched that of the oriented collagen sheet. Two months after successful transplantation, laryngeal endoscopy revealed coordinated movement of the bilateral vocal folds by external stimulation under light general anesthesia. Hematoxylin and eosin staining showed that the regenerated RLN lacked epineurium surrounding the nerve fibers and was interspersed with collagen fibers. Myelin protein zero was expressed around many axons.

CONCLUSIONS

Partial regeneration of RLN was achieved through the use of oriented collagen scaffolding.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:1622-1627, 2017.

Gelatin-methacrylamide gel loaded with microspheres to deliver GDNF in bilayer collagen conduit promoting sciatic nerve growth

In this study, we fabricated glial cell-line derived neurotrophic factor (GDNF)-loaded microspheres, then seeded the microspheres in gelatin-methacrylamide hydrogel, which was finally integrated with the commercial bilayer collagen membrane (Bio-Gide^®). The novel composite of nerve conduit was employed to bridge a 10 mm long sciatic nerve defect in a rat. GDNF-loaded gelatin microspheres had a smooth surface with an average diameter of 3.9±1.8 μm. Scanning electron microscopy showed that microspheres were uniformly distributed in both the GelMA gel and the layered structure. Using enzyme-linked immunosorbent assay, in vitro release studies (pH 7.4) of GDNF from microspheres exhibited an initial burst release during the first 3 days (18.0%±1.3%), and then, a prolonged-release profile extended to 32 days. However, in an acidic condition (pH 2.5), the initial release percentage of GDNF was up to 91.2%±0.9% within 4 hours and the cumulative release percentage of GDNF was 99.2%±0.2% at 48 hours. Then the composite conduct was implanted in a 10 mm critical defect gap of sciatic nerve in a rat. We found that the nerve was regenerated in both conduit and autograft (AG) groups. A combination of electrophysiological assessment and histomorphometry analysis of regenerated nerves showed that axonal regeneration and functional recovery in collagen tube filled with GDNF-loaded microspheres (GM + CT) group were similar to AG group (P>0.05). Most myelinated nerves were matured and arranged densely with a uniform structure of myelin in a neat pattern along the long axis in the AG and GM + CT groups, however, regenerated nerve was absent in the BLANK group, left the 10 mm gap empty after resection, and the nerve fiber exhibited a disordered arrangement in the collagen tube group. These results indicated that the hybrid system of bilayer collagen conduit and GDNF-loaded gelatin microspheres combined with gelatin-methacrylamide hydrogels could serve as a new biodegradable artificial nerve guide for nerve tissue engineering.

Biocompatibility and characterization of a peptide amphiphile hydrogel for applications in peripheral nerve regeneration

Peripheral nerve injury is a debilitating condition for which new bioengineering solutions are needed. Autografting, the gold standard in treatment, involves sacrifice of a healthy nerve and results in loss of sensation or function at the donor site. One alternative solution to autografting is to use a nerve guide conduit designed to physically guide the nerve as it regenerates across the injury gap. Such conduits are effective for short gap injuries, but fail to surpass autografting in long gap injuries. One strategy to enhance regeneration inside conduits in long gap injuries is to fill the guide conduits with a hydrogel to mimic the native extracellular matrix found in peripheral nerves. In this work, a peptide amphiphile (PA)-based hydrogel was optimized for peripheral nerve repair. Hydrogels consisting of the PA C₁₆GSH were compared with a commercially available collagen gel. Schwann cells, a cell type important in the peripheral nerve regenerative cascade, were able to spread, proliferate, and migrate better on C₁₆GSH gels in vitro when compared with cells seeded on collagen gels. Moreover, C₁₆GSH gels were implanted subcutaneously in a murine model and were found to be biocompatible, degrade over time, and support angiogenesis without causing inflammation or a foreign body immune response. Taken together, these results help optimize and instruct the development of a new synthetic hydrogel as a luminal filler for conduit-mediated peripheral nerve repair.

Characterization of Olfactory Ensheathing Glial Cells Cultured on Polyurethane/Polylactide Electrospun Nonwovens

The aim of this research was to evaluate novel biomaterials for neural regeneration. The investigated materials were composed of polyurethane (PU) and polylactide (PLDL) blended at three different w/w ratios, that is, 5/5, 6/4, and 8/2 of PU/PLDL. Ultrathin fibrous scaffolds were prepared using electrospinning. The scaffolds were investigated for their applicability for nerve regeneration by culturing rat olfactory ensheathing glial cells. Cells were cultured on the materials for seven days, during which cellular morphology, phenotype, and metabolic activity were analysed. SEM analysis of the fabricated fibrous scaffolds showed fibers of a diameter mainly lower than 600 μm with unimportant volume of protrusions situated along the fibers, with nonsignificant differences between all analysed materials. Cells cultured on the materials showed differences in their morphology and metabolic activity, depending on the blend composition. The most proper morphology, with numerous p75+and GFAP+cells present, was observed in the sample 6/4, whereas the highest metabolic activity was measured in the sample 5/5. However, none of the investigated samples showed cytotoxicity or negatively influenced cellular morphology. Therefore, the novel electrospun fibrous materials may be considered for regenerative medicine applications, and especially when contacting with highly sensitive nervous cells.

In vivo application of poly-3-hydroxyoctanoate as peripheral nerve graft

OBJECTIVE

This study aims to investigate the degree of biocompatibility and neuroregeneration of a polymer tube, poly-3-hydroxyoctanoate (PHO) in nerve gap repair.

METHODS

Forty Wistar Albino male rats were randomized into two groups: autologous nerve gap repair group and PHO tube repair group. In each group, a 10-mm right sciatic nerve defect was created and reconstructed accordingly. Neuroregeneration was studied by sciatic function index (SFI), electromyography, and immunohistochemical studies on Days 7, 21, 45 and 60 of implantation. Biocompatibility was analyzed by the capsule formation around the conduit. Biodegradation was analyzed by the molecular weight loss in vivo.

RESULTS

Electrophysiological and histomorphometric assessments demonstrated neuroregeneration in both groups over time. In the experimental group, a straight alignment of the Schwann cells parallel to the axons was detected. However, autologous nerve graft seems to have a superior neuroregeneration compared to PHO grafts. Minor biodegradation was observed in PHO conduit at the end of 60 d.

CONCLUSIONS

Although neuroregeneration is detected in PHO grafts with minor degradation in 60 d, autologous nerve graft is found to be superior in axonal regeneration compared to PHO nerve tube grafts. PHO conduits were found to create minor inflammatory reaction in vivo, resulting in good soft tissue response.

Repair of injured spinal cord using biomaterial scaffolds and stem cells

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

A review of bioactive release from nerve conduits as a neurotherapeutic strategy for neuronal growth in peripheral nerve injury

Peripheral nerve regeneration strategies employ the use of polymeric engineered nerve conduits encompassed with components of a delivery system. This allows for the controlled and sustained release of neurotrophic growth factors for the enhancement of the innate regenerative capacity of the injured nerves. This review article focuses on the delivery of neurotrophic factors (NTFs) and the importance of the parameters that control release kinetics in the delivery of optimal quantities of NTFs for improved therapeutic effect and prevention of dose dumping. Studies utilizing various controlled-release strategies, in attempt to obtain ideal release kinetics, have been reviewed in this paper. Release strategies discussed include affinity-based models, crosslinking techniques, and layer-by-layer technologies. Currently available synthetic hollow nerve conduits, an alternative to the nerve autografts, have proven to be successful in the bridging and regeneration of primarily the short transected nerve gaps in several patient cases. However, current research emphasizes on the development of more advanced nerve conduits able to simulate the effectiveness of the autograft which includes, in particular, the ability to deliver growth factors.

Challenges for nerve repair using chitosan-siloxane hybrid porous scaffolds

The treatment of peripheral nerve injuries remains one of the greatest challenges of neurosurgery, as functional recover is rarely satisfactory in these patients. Recently, biodegradable nerve guides have shown great potential for enhancing nerve regeneration. A major advantage of these nerve guides is that no foreign material remains after the device has fulfilled its task, which spares a second surgical intervention. Recently, we studied peripheral nerve regeneration using chitosan-γ-glycidoxypropyltrimethoxysilane (chitosan-GPTMS) porous hybrid membranes. In our studies, these porous membranes significantly improved nerve fiber regeneration and functional recovery in rat models of axonotmetic and neurotmetic sciatic nerve injuries. In particular, the number of regenerated myelinated nerve fibers and myelin thickness were significantly higher in rat treated with chitosan porous hybrid membranes, whether or not they were used in combination with mesenchymal stem cells isolated from the Wharton's jelly of the umbilical cord. In this review, we describe our findings on the use of chitosan-GPTMS hybrids for nerve regeneration.

3D nano/microfabrication techniques and nanobiomaterials for neural tissue regeneration

Injuries of the nervous system occur commonly among people of many different ages and backgrounds. Currently, there are no effective strategies to improve neural regeneration; however, tissue engineering provides a promising avenue for regeneration of many tissue types, including the neural context. Functional nerve conduits derived from tissue engineering techniques present bioengineered 3D artificial substitutes for implantation and rehabilitation of injured nerves. In particular, nanotechnology as a versatile vehicle to create biomimetic nanostructured tissue-engineered neural scaffolds provides great potential for the development of innovative and successful nerve grafts. Nanostructured conduits derived from traditional and novel tissue engineering techniques have been shown to be superior for successful neural function construction due to a high degree of biomimetic character. In this paper, we will focus on current progress in developing 3D nano/microstructured neural scaffolds via electrospinning, emerging 3D printing and self-assembly techniques, nanobiomaterials and bioactive cues for enhanced neural tissue regeneration.

Biomimetic polyurethanes in nano and regenerative medicine

Nature's inspiration is a promising tool to design new biomaterials especially for frontier technological areas such as tissue engineering and nanomedicine.

Micro-structural geometry of thin films intended for the inner lumen of nerve conduits affects nerve repair

Damage to peripheral nerves can cause significant motor or sensory injuries. In serious cases, a nerve is sacrificed from another part of the body to repair a damaged nerve (autograft). The development of biodegradable polymer conduits may offer an alternative to autografts. This study investigated the surface topography and mechanical properties of smooth, pitted and grooved structures of ultra-thin poly (ε-caprolactone)/poly lactic acid blended, solvent-cast films. We have investigated the effect of the groove shape on cell morphology and alignment. Photolithography and dry/wet etching was used to develop patterned silicon substrates with grooves with accurate geometries (V shaped, sloped walls and square shaped). Using a neural cell line (NG108-15), in vitro experiments confirmed good cell attachment and proliferation on all the polymer scaffolds. Imaging techniques demonstrated that there was different cellular responses and morphology according to the shape of the groove. Studies showed that the geometry, particularly the angle of the slope and the space between grooves, affected cellular responses. In addition, biomechanical studies showed that the patterned films had excellent mechanical properties and were stronger than the natural nerve. The conduit tubes were made by rolling the films around a mandrel and using a thermal welding technique to join the edges. The promising biomechanical and in vitro results demonstrate that nerve cell responses are affected by the shape of longitudinal grooves, and particularly by the angle of the slope of the groove walls.

Modified bacterial cellulose tubes for regeneration of damaged peripheral nerves

INTRODUCTION

The subject of the experiment was bacterial nanocellulose, a natural polymer produced by bacteria - Gluconacetobacter xylinus. Following a specific modification process a cartilage-like material for restoration of damaged tissues may be produced. The obtained implants with excellent biocompatibility, mouldability, biophysical and chemical properties perfectly fit the needs of reconstructive surgery. The goal of the experiment was to develop and analyze cellulosic guidance channels in vivo for the reconstruction of damaged peripheral nerves.

MATERIAL AND METHODS

The experiments were conducted on Wistar rats, femoral nerve. Cellulose was produced according to a self-patented method. In the experimental group tubulization was applied, whereas in the control traditional end-to-end connection was used. Observation time was 30, 60, 90, and 180 days. Results evaluation included histological analysis and postoperative observation of motor recovery.

RESULTS

The overgrowth of connective tissue and disorganisation of neural structures was evident in 86.67% of control specimens, while for cellulosic group it was only 35% (p = 0.0022). Tubulization prevented the excessive proliferation of connective tissue and isolated from penetration with scar tissue. Autocannibalism, being probably an evidence of neurotrophic factors amassment, was observed in cellulosic group but not in the control one. Motor recovery did not differ significantly (p > 0.05). Biocompatibility of implants was affirmed by very small level of tissue response and susceptibility to vascularisation.

CONCLUSIONS

Cellulosic neurotubes effectively prevent the formation of neuromas. They are of very good biocompatibility and allow the accumulation of neurotrophic factors inside, thus facilitating the process of nerve regeneration.