Novel drug delivering conduit for peripheral nerve regeneration

Advances in biomaterial-based tissue engineering for peripheral nerve injury repair

Peripheral nerve injury is a common clinical disease. Effective post-injury nerve repair remains a challenge in neurosurgery, and clinical outcomes are often unsatisfactory, resulting in social and economic burden. Particularly, the repair of long-distance nerve defects remains a challenge. The existing nerve transplantation strategies show limitations, including donor site morbidity and immune rejection issues. The multiple studies have revealed the potential of tissue engineering strategies based on biomaterials in the repair of peripheral nerve injuries. We review the events of regeneration after peripheral nerve injury, evaluates the efficacy of existing nerve grafting strategies, and delves into the progress in the construction and application strategies of different nerve guidance conduits. A spotlight is cast on the materials, technologies, seed cells, and microenvironment within these conduits to facilitate optimal nerve regeneration. Further discussion was conducted on the approve of nerve guidance conduits and potential future research directions. This study anticipates and proposes potential avenues for future research, aiming to refine existing strategies and uncover innovative approaches in biomaterial-based nerve repair. This study endeavors to synthesize the collective insights from the fields of neuroscience, materials science, and regenerative medicine, offering a multifaceted perspective on the role of biomaterials in advancing the frontiers of peripheral nerve injury treatment.

A tacrolimus-eluting nerve guidance conduit enhances regeneration in a critical-sized peripheral nerve injury rat model

Critical-sized peripheral nerve injuries pose a significant clinical challenge and lead to functional loss and disability. Current regeneration strategies, including autografts, synthetic nerve conduits, and biologic treatments, encounter challenges such as limited availability, donor site morbidity, suboptimal recovery, potential immune responses, and sustained stability and bioactivity. An obstacle in peripheral nerve regeneration is the immune response that can lead to inflammation and scarring that impede the regenerative process. Addressing both the immunological and regenerative needs is crucial for successful nerve recovery. Here, we introduce a novel biodegradable tacrolimus-eluting nerve guidance conduit engineered from a blend of poly (L-lactide-co-caprolactone) to facilitate peripheral nerve regeneration and report the testing of this conduit in 15-mm critical-sized gaps in the sciatic nerve of rats. The conduit's diffusion holes enable the local release of tacrolimus, a potent immunosuppressant with neuro-regenerative properties, directly into the injury site. A series of in vitro experiments were conducted to assess the ability of the conduit to maintain a controlled tacrolimus release profile that could promote neurite outgrowth. Subsequent in vivo assessments in rat models of sciatic nerve injury revealed significant enhancements in nerve regeneration, as evidenced by improved axonal growth and functional recovery compared to controls using placebo conduits. These findings indicate the synergistic effects of combining a biodegradable conduit with localized, sustained delivery of tacrolimus, suggesting a promising approach for treating peripheral nerve injuries. Further optimization of the design and long-term efficacy studies and clinical trials are needed before the potential for clinical translation in humans can be considered.

Efficacy of using adipose-derived stem cells and PRP on regeneration of 40 -mm long sciatic nerve defect bridged by polyglycolic-polypropylene mesh in canine model

BACKGROUND

Sciatic nerve repair becomes a focus of research in neurological aspect to restore the normal physical ability of the animal to stand and walk. Tissue engineered nerve grafts (TENGs) provide a promising alternative therapy for regeneration of large gap defects. The present study investigates the regenerative capacity of PRP, ADSCs, and PRP mixed ADSCs on a long sciatic nerve defect (40-mm) bridged by a polyglycolic polypropylene (PGA-PRL) mesh which acts as a neural scaffold.

MATERIALS AND METHODS

The study was conducted on 12 adult male mongrel dogs that were randomly divided into 4 groups: Group I (scaffold group); where the sciatic defect was bridged by a (PGA-PRL) mesh only while the mesh was injected with ADSCs in Group II (ADSCs group), PRP in Group III (PRP group). Mixture of PRP and ADSCs was allocated in Group IV (PRP + ADSCs group). Monthly, all animals were monitored for improvement in their gait and a numerical lameness score was recorded for all groups. 6 months-post surgery, the structural and functional recovery of sciatic nerve was evaluated electrophysiologically, and on the level of gene expression, and both sciatic nerve and the gastrocnemius muscle were evaluated morphometrically, histopathologically.

RESULTS

Numerical lameness score showed improvement in the motor activities of both Group II and Group III followed by Group IV and the scaffold group showed mild improvement even after 6 months. Histopathologically, all treated groups showed axonal sprouting and numerous regenerated fascicles with obvious angiogenesis in proximal cut, and distal portion where Group IV exhibited a significant remyelination with the MCOOL technique. The regenerative ratio of gastrocnemius muscle was 23.81%, 56.68%, 52.06% and 40.69% for Group I, II, III and IV; respectively. The expression of NGF showed significant up regulation in the proximal portion for both Group III and Group IV (P ≤ 0.0001) while Group II showed no significant difference. PDGF-A, and VEGF expressions were up-regulated in Group II, III, and IV whereas Group I showed significant down-regulation for NGF, PDGF-A, and VEGF (P ≤ 0.0001).

CONCLUSION

ADSCs have a great role in restoring the damaged nerve fibers by secreting several types of growth factors like NGF that have a proliferative effect on Schwann cells and their migration. In addition, PRP therapy potentiates the effect of ADSCs by synthesis another growth factors such as PDGF-A, VEGF, NGF for better healing of large sciatic gap defects.

Pleiotropic effects of nitric oxide sustained-release system for peripheral nerve repair

The regenerative microenvironment after peripheral nerve injury is imbalanced and difficult to rebalance, which is mainly affected by inflammation, oxidative stress, and inadequate blood supply. The difficulty in remodeling the nerve regeneration microenvironment is the main reason for slow nerve regeneration. Traditional drug treatments have certain limitations, such as difficulty in penetrating the blood-nerve barrier and lack of pleiotropic effects. Therefore, there is an urgent need to build multifunctional nerve grafts that can effectively regulate the regenerative microenvironment and promote nerve regeneration. Nitric oxide (NO), a highly effective gas transmitter with diatomic radicals, is an important regulator of axonal growth and migration, synaptic plasticity, proliferation of neural precursor cells, and neuronal survival. Moreover, NO provides potential anti-inflammation, anti-oxidation, and blood vessel promotion applications. However, excess NO may cause cell death and neuroinflammatory cell damage. The prerequisite for NO treatment of peripheral nerve injury is that it is gradually released over time. In this study, we constructed an injectable NO slow-release system with two main components, including macromolecular NO donor nanoparticles (mPEG-P(MSNO-EG) nanoparticles, NO-NPs) and a carrier for the nanoparticles, mPEG-PA-PP injectable temperature-sensitive hydrogel. Due to the multiple physiological regulation of NO and better physiological barrier penetration, the conduit effectively regulates the inflammatory response and oxidative stress of damaged peripheral nerves, promotes nerve vascularization, and nerve regeneration and docking, accelerating the nerve regeneration process. STATEMENT OF SIGNIFICANCE: The slow regeneration speed of peripheral nerves is mainly due to the destruction of the regeneration microenvironment. Neural conduits with drug delivery capabilities have the potential to improve the microenvironment of nerve regeneration. However, traditional drugs are hindered by the blood nerve barrier and cannot effectively target the injured area. NO, an endogenous gas signaling molecule, can freely cross the blood nerve barrier and act on target cells. However, excessive NO can lead to cell apoptosis. In this study, a NO sustained-release system was constructed to regulate the microenvironment of nerve regeneration through various pathways and promote nerve regeneration.

An extracellular matrix mimicking alginate hydrogel scaffold manipulates an inflammatory microenvironment and improves peripheral nerve regeneration by controlled melatonin release

Low efficiency of nerve growth and unstable release of loaded drugs have become a major problem in repairing peripheral nerve injury. Many intervention strategies were focused on simple drug loading, but have still been less effective. The key challenge is to establish a controlled release microenvironment to enable adequate nerve regeneration. In this study, we fabricate a multilayered compound nerve scaffold by electrospinning: with an anti-adhesive outer layer of polycaprolactone and an ECM-like inner layer consisting of a melatonin-loaded alginate hydrogel. We characterized the scaffold, and the loaded melatonin can be found to undergo controlled release. We applied them to a 15 mm rat model of sciatic nerve injury. After 16 weeks, the animals in each group were evaluated and compared for recovery of motor function, electrophysiology, target organ atrophy status, regenerative nerve morphology and relative protein expression levels of neural markers, inflammatory oxidative stress, and angiogenesis. We identify that the scaffold can improve functional ability evidenced by an increased sciatic functional index and nerve electrical conduction level. The antioxidant melatonin loaded in the scaffold reduces inflammation and oxidative stress in the reinnervated nerves, confirmed by increased HO-1 and decreased TNF-α levels in regenerating nerves. The relative expression of fast-type myosin was elevated in the target gastrocnemius muscle. An improvement in angiogenesis facilitates neurite extension and axonal sprouting. This scaffold can effectively restore the ECM-like microenvironment and improve the quality of nerve regeneration by controlled melatonin release, thus enlightening the design criteria on nerve scaffolds for peripheral nerve injury in the future.

Regenerative Strategies in Treatment of Peripheral Nerve Injuries in Different Animal Models

BACKGROUND

Peripheral nerve damage mainly resulted from traumatic or infectious causes; the main signs of a damaged nerve are the loss of sensory and/or motor functions. The injured nerve has limited regenerative capacity and is recovered by the body itself, the recovery process depends on the severity of damage to the nerve, nowadays the use of stem cells is one of the new and advanced methods for treatment of these problems.

METHOD

Following our review, data are collected from different databases "Google scholar, Springer, Elsevier, Egyptian Knowledge Bank, and PubMed" using different keywords such as Peripheral nerve damage, Radial Nerve, Sciatic Nerve, Animals, Nerve regeneration, and Stem cell to investigate the different methods taken in consideration for regeneration of PNI.

RESULT

This review contains tables illustrating all forms and types of regenerative medicine used in treatment of peripheral nerve injuries (PNI) including different types of stem cells " adipose-derived stem cells, bone marrow stem cells, Human umbilical cord stem cells, embryonic stem cells" and their effect on re-constitution and functional recovery of the damaged nerve which evaluated by physical, histological, Immuno-histochemical, biochemical evaluation, and the review illuminated the best regenerative strategies help in rapid peripheral nerve regeneration in different animal models included horse, dog, cat, sheep, monkey, pig, mice and rat.

CONCLUSION

Old surgical attempts such as neurorrhaphy, autogenic nerve transplantation, and Schwann cell implantation have a limited power of recovery in cases of large nerve defects. Stem cell therapy including mesenchymal stromal cells has a high potential differentiation capacity to renew and form a new nerve and also restore its function.

The Role of Metals in the Neuroregenerative Action of BDNF, GDNF, NGF and Other Neurotrophic Factors

Mature neurotrophic factors and their propeptides play key roles ranging from the regulation of neuronal growth and differentiation to prominent participation in neuronal survival and recovery after injury. Their signaling pathways sculpture neuronal circuits during brain development and regulate adaptive neuroplasticity. In addition, neurotrophic factors provide trophic support for damaged neurons, giving them a greater capacity to survive and maintain their potential to regenerate their axons. Therefore, the modulation of these factors can be a valuable target for treating or preventing neurologic disorders and age-dependent cognitive decline. Neuroregenerative medicine can take great advantage by the deepening of our knowledge on the molecular mechanisms underlying the properties of neurotrophic factors. It is indeed an intriguing topic that a significant interplay between neurotrophic factors and various metals can modulate the outcome of neuronal recovery. This review is particularly focused on the roles of GDNF, BDNF and NGF in motoneuron survival and recovery from injuries and evaluates the therapeutic potential of various neurotrophic factors in neuronal regeneration. The key role of metal homeostasis/dyshomeostasis and metal interaction with neurotrophic factors on neuronal pathophysiology is also highlighted as a novel mechanism and potential target for neuronal recovery. The progress in mechanistic studies in the field of neurotrophic factor-mediated neuroprotection and neural regeneration, aiming at a complete understanding of integrated pathways, offers possibilities for the development of novel neuroregenerative therapeutic approaches.

Polymeric Fibers as Scaffolds for Spinal Cord Injury: A Systematic Review

Spinal cord injury (SCI) is a complex neurological condition caused by trauma, inflammation, and other diseases, which often leads to permanent changes in strength and sensory function below the injured site. Changes in the microenvironment and secondary injuries continue to pose challenges for nerve repair and recovery after SCI. Recently, there has been progress in the treatment of SCI with the use of scaffolds for neural tissue engineering. Polymeric fibers fabricated by electrospinning have been increasingly used in SCI therapy owing to their biocompatibility, complex porous structure, high porosity, and large specific surface area. Polymer fibers simulate natural extracellular matrix of the nerve fiber and guide axon growth. Moreover, multiple channels of polymer fiber simulate the bundle of nerves. Polymer fibers with porous structure can be used as carriers loaded with drugs, nerve growth factors and cells. As conductive fibers, polymer fibers have electrical stimulation of nerve function. This paper reviews the fabrication, characterization, and application in SCI therapy of polymeric fibers, as well as potential challenges and future perspectives regarding their application.

Fabrication Techniques of Nerve Guidance Conduits for Nerve Regeneration

Neuronal loss and axonal degeneration after spinal cord injury or peripheral injury result in the loss of sensory and motor functions. Nerve regeneration is a complicated and medical challenge that requires suitable guides to bridge nerve injury gaps and restore nerve function. Due to the hostility of the microenvironment in the lesion, multiple conditions should be fulfilled to achieve improved functional recovery. Many nerve conduits have been fabricated using various natural and synthetic polymers. The design and material of the nerve guide conduits were carefully reviewed. A detailed review was conducted on the fabrication method of the nerve guide conduit for nerve regeneration. The typical fabrication methods used to fabricate nerve conduits are dip coating, solvent casting, micropatterning, electrospinning, and additive manufacturing. The advantages and disadvantages of the fabrication methods were reported, and research to overcome these limitations was reviewed. Extensive reviews have focused on the biological functions and in vivo performance of polymeric nerve conduits. In this paper, we emphasize the fabrication method of nerve conduits by polymers and their properties. By learning from the existing candidates, we can advance the strategies for designing novel polymeric systems with better properties for nerve regeneration.

Reconstruction of the Rat Sciatic Nerve by Using Biodegradable and Non-Biodegradable Conduits

The aim of the study was to compare two types of conduits made of either non-resorbable Reperen or resorbable Tissucol for their effects on the regeneration of the rat sciatic nerve under conditions of stump diastasis.

Development of a conduit of PLGA-gelatin aligned nanofibers produced by electrospinning for peripheral nerve regeneration

A promising alternative to conventional nerve grafting is the use of artificial grafts made from biodegradable and biocompatible materials and support cells. The aim of this study has been to produce a biodegradable nerve conduit and investigate the cytocompatibility with stem cells and its regeneration promoting properties in a rat animal model. A poly (lactic-co-glycolic acid) (PLGA) conduit of aligned nanofibers was produced by the electrospinning method, functionalized with gelatin and seeded either with mouse embryonic stem cells (mESCs) or with human mesenchymal stem cells (SHED). The cell proliferation and viability were analyzed in vitro. The conduits were implanted in a rat model of sciatic nerve lesion by transection. The functional recovery was monitored for 8 weeks using the Sciatic Functional Index (SFI) and histological analyses were used to assess the nerve regeneration. Scaffolds of aligned PLGA fibers with an average diameter of 0.90 ± 0.36 μm and an alignment coefficient of 0.817 ± 0.07 were produced. The treatment with gelatin increased the fiber diameter to 1.05 ± 0.32 μm, reduced the alignment coefficient to 0.655 ± 0.045 and made the scaffold very hydrophilic. The cell viability and Live/dead assay showed that the stem cells remained viable and proliferated after 7 days in culture. Confocal images of phalloidin/DAPI staining showed that the cells adhered and proliferated widely, in fully adaptation with the biomaterial. The SFI values of the group that received the conduit were similar to the values of the control lesioned group. In conclusion, conduits composed of PLGA-gelatin nanofibers were produced and promoted a very good interaction with the stem cells. Although in vitro studies have shown this biomaterial to be a promising biomaterial for the regeneration of nerve tissue, in vivo studies of this graft have not shown significant improvements in nerve regeneration.

Three-Dimensional Engineered Peripheral Nerve: Toward a New Era of Patient-Specific Nerve Repair Solutions

Reconstruction of peripheral nerve injuries (PNIs) with substance loss remains challenging because of limited treatment solutions and unsatisfactory patient outcomes. Currently, nerve autografting is the first-line management choice for bridging critical-sized nerve defects. The procedure, however, is often complicated by donor site morbidity and paucity of nerve tissue, raising a quest for better alternatives. The application of other treatment surrogates, such as nerve guides, remains questionable, and it is inefficient in irreducible nerve gaps. More importantly, these strategies lack customization for personalized patient therapy, which is a significant drawback of these nerve repair options. This negatively impacts the fascicle-to-fascicle regeneration process, critical to restoring the physiological axonal pathway of the disrupted nerve. Recently, the use of additive manufacturing (AM) technologies has offered major advancements to the bioengineering solutions for PNI therapy. These techniques aim at reinstating the native nerve fascicle pathway using biomimetic approaches, thereby augmenting end-organ innervation. AM-based approaches, such as three-dimensional (3D) bioprinting, are capable of biofabricating 3D-engineered nerve graft scaffolds in a patient-specific manner with high precision. Moreover, realistic in vitro models of peripheral nerve tissues that represent the physiologically and functionally relevant environment of human organs could also be developed. However, the technology is still nascent and faces major translational hurdles. In this review, we spotlighted the clinical burden of PNIs and most up-to-date treatment to address nerve gaps. Next, a summarized illustration of the nerve ultrastructure that guides research solutions is discussed. This is followed by a contrast of the existing bioengineering strategies used to repair peripheral nerve discontinuities. In addition, we elaborated on the most recent advances in 3D printing and biofabrication applications in peripheral nerve modeling and engineering. Finally, the major challenges that limit the evolution of the field along with their possible solutions are also critically analyzed.

Fundamentals and Current Strategies for Peripheral Nerve Repair and Regeneration

A body of evidence indicates that peripheral nerves have an extraordinary yet limited capacity to regenerate after an injury. Peripheral nerve injuries have confounded professionals in this field, from neuroscientists to neurologists, plastic surgeons, and the scientific community. Despite all the efforts, full functional recovery is still seldom. The inadequate results attained with the "gold standard" autograft procedure still encourage a dynamic and energetic research around the world for establishing good performing tissue-engineered alternative grafts. Resourcing to nerve guidance conduits, a variety of methods have been experimentally used to bridge peripheral nerve gaps of limited size, up to 30-40 mm in length, in humans. Herein, we aim to summarize the fundamentals related to peripheral nerve anatomy and overview the challenges and scientific evidences related to peripheral nerve injury and repair mechanisms. The most relevant reports dealing with the use of both synthetic and natural-based biomaterials used in tissue engineering strategies when treatment of nerve injuries is envisioned are also discussed in depth, along with the state-of-the-art approaches in this field.

Zero-valent iron nanoparticles containing nanofiber scaffolds for nerve tissue engineering

Regeneration of nerve tissue is a challenging issue in regenerative medicine. Especially, the peripheral nerve defects related to the accidents are one of the leading health problems. For large degeneration of peripheral nerve, nerve grafts are used in order to obtain a connection. These grafts should be biodegradable to prevent second surgical intervention. In order to make more effective nerve tissue engineering materials, nanotechnological improvements were used. Especially, the addition of electrically conductive and biocompatible metallic particles and carbon structures has essential roles in the stimulation of nerves. However, the metabolizing of these structures remains to wonder because of their nondegradable nature. In this study, biodegradable and conductive nerve tissue engineering materials containing zero-valent iron (Fe) nanoparticles were developed and investigated under in vitro conditions. By using electrospinning technique, fibrous mats composed of electrospun poly(ε-caprolactone) (PCL) nanofibers and Fe nanoparticles were obtained. Both electrical conductivity and mechanical properties increased compared with control group that does not contain nanoparticles. Conductivity of PCL/Fe5 and PCL/Fe10 increased to 0.0041 and 0.0152 from 0.0013 Scm^-1 , respectively. Cytotoxicity results indicated toxicity for composite mat containing 20% Fe nanoparticles (PCL/Fe20). SH-SY5Y cells were grown on PCL/Fe10 best, which contains 10% Fe nanoparticles. Beta III tubulin staining of dorsal root ganglion neurons seeded on mats revealed higher cell number on PCL/Fe10. This study demonstrated the impact of zero-valent Fe nanoparticles on nerve regeneration. The results showed the efficacy of the conductive nanoparticles, and the amount in the composition has essential roles in the promotion of the neurites.

Modeling diffusion-based drug release inside a nerve conduit in vitro and in vivo validation study

The objective of this work was to develop a model and understand the diffusion of a drug into and throughout a drug delivering nerve conduit from a surrounding reservoir through a hole in the wall separating the lumen of the conduit and the reservoir. A mathematical model based on Fick's law of diffusion was developed using the finite difference method to understand the drug diffusion and the effect of varying device parameters on the concentration of drug delivered from a hole-based drug delivery device. The mathematical model was verified using a physical microfluidic (μFD) model and an in vitro/in vivo release test using prototype devices. The results of the mathematical model evaluation and microfluidic device testing offered positive insight into the reliability and function of the reservoir and hole-based drug delivering nerve conduit. The mathematical model demonstrated how changing device parameters would change the drug concentration inside the device. It was observed that the drug release in the conduit could be tuned by both concentration scaling and changing the hole size or number of holes. Based on the results obtained from the microfluidic device, the error in the mathematical drug release model was shown to be less than 10% when comparing the data obtained from mathematical model and μFD model. The data highlights the flexibility of having a hole-based drug delivery system, since the drug release can be scaled predictably by changing the device parameters or the concentration of the drug in the reservoir. Graphical abstract .

The advances in nerve tissue engineering: From fabrication of nerve conduit to in vivo nerve regeneration assays

Peripheral nerve damage is a common clinical complication of traumatic injury occurring after accident, tumorous outgrowth, or surgical side effects. Although the new methods and biomaterials have been improved recently, regeneration of peripheral nerve gaps is still a challenge. These injuries affect the quality of life of the patients negatively. In the recent years, many efforts have been made to develop innovative nerve tissue engineering approaches aiming to improve peripheral nerve treatment following nerve injuries. Herein, we will not only outline what we know about the peripheral nerve regeneration but also offer our insight regarding the types of nerve conduits, their fabrication process, and factors associated with conduits as well as types of animal and nerve models for evaluating conduit function. Finally, nerve regeneration in a rat sciatic nerve injury model by nerve conduits has been considered, and the main aspects that may affect the preclinical outcome have been discussed.

Development of Oxidized Polyvinyl Alcohol-Based Nerve Conduits Coupled with the Ciliary Neurotrophic Factor

Functionalized synthetic conduits represent a promising strategy to enhance peripheral nerve regeneration by guiding axon growth while delivering therapeutic neurotrophic factors. In this work, hollow nerve conduits made of polyvinyl alcohol partially oxidized with bromine (OxPVA_Br2) and potassium permanganate (OxPVA_KMnO4) were investigated for their structural/biological properties and ability to absorb/release the ciliary neurotrophic factor (CNTF). Chemical oxidation enhanced water uptake capacity of the polymer, with maximum swelling index of 60.5% ± 2.5%, 71.3% ± 3.6% and 19.5% ± 4.0% for OxPVA_Br2, OxPVA_KMnO4 and PVA, respectively. Accordingly, hydrogel porosity increased from 15.27% ± 1.16% (PVA) to 62.71% ± 8.63% (OxPVA_Br2) or 77.50% ± 3.39% (OxPVA_KMnO4) after oxidation. Besides proving that oxidized PVA conduits exhibited mechanical resistance and a suture holding ability, they did not exert a cytotoxic effect on SH-SY5Y and Schwann cells and biodegraded over time when subjected to enzymatic digestion, functionalization with CNTF was performed. Interestingly, higher amounts of neurotrophic factor were detected in the lumen of OxPVA_Br2 (0.22 ± 0.029 µg) and OxPVA_KMnO4 (0.29 ± 0.033 µg) guides rather than PVA (0.11 ± 0.021 µg) tubular scaffolds. In conclusion, we defined a promising technology to obtain drug delivery conduits based on functionalizable oxidized PVA hydrogels.

Tissue-engineered nerve grafts using a scaffold-independent and injectable drug delivery system: a novel design with translational advantages

OBJECTIVE

Currently commercially available nerve conduits have demonstrated suboptimal clinical efficacy in repairing peripheral nerve defects. Although tissue-engineered nerve grafts (TENGs) with sustained release of neurotrophic factors (NTFs) are experimentally proved to be more effective than these blank conduits, there remains a lack of clinical translation. NTFs are typically immobilized onto scaffold materials of the conduit via adsorption, specific binding or other incorporation techniques. These scaffold-based delivery strategies increase complexity and cost of conduit fabrication and lack flexibility in choosing different drugs. Therefore, to facilitate clinical translation and commercialization, we construct a TENG using a scaffold-independent drug delivery system (DDS).

APPROACH

This study adopted a scaffold-independent DDS based on methoxy-poly (ethylene glycol)-b-poly(γ-ethyl-L-glutamate) (mPEG-PELG) thermosensitive hydrogels that undergo sol-to-gel transition at body temperature. In addition, TENG, a chitosan scaffold filled with nerve growth factor (NGF)-loaded mPEG-PELG that gel in the lumen upon injection during surgery and function as a drug-releasing conduit-filler, was designed. Subsequently, the efficacy of DDS and therapeutic effects of TENG were assessed.

MAIN RESULTS

The results demonstrated that NGF-loaded mPEG-PELG controllably and sustainably released bioactive NGF for 28 d. When bridging a 10 mm rat sciatic nerve gap, the morphological, electrophysiological, and functional analyses revealed that NGF-releasing TENG (Scaffold  +  NGF/mPEG-PELG) achieved superior regenerative outcomes compared to plain scaffolds and those combined with systemic delivery of NGF (daily intramuscular injection (IM)), and its effects were relatively similar to autografts.

SIGNIFICANCE

This study has proposed a TENG using thermosensitive hydrogels as an injectable implant to controllably release NGF, which has promising therapeutic potential and translatability. Such TENGs obviate the need for conduit modification, complex preloading or binding mediators, therefore they allow the ease of drug switching in clinical practice and greatly simplify the manufacturing process due to the independent preparation of drug delivery system.

3D melatonin nerve scaffold reduces oxidative stress and inflammation and increases autophagy in peripheral nerve regeneration

Peripheral nerve defect is a common and severe kind of injury in traumatic accidents. Melatonin can improve peripheral nerve recovery by inhibiting oxidative stress and inflammation after traumatic insults. In addition, it triggers autophagy pathways to increase regenerated nerve proliferation and to reduce apoptosis. In this study, we fabricated a melatonin-controlled-release scaffold to cure long-range nerve defects for the first time. 3D manufacture of melatonin/polycaprolactone nerve guide conduit increased Schwann cell proliferation and neural expression in vitro and promoted functional, electrophysiological and morphological nerve regeneration in vivo. Melatonin nerve guide conduit ameliorated immune milieu by reducing oxidative stress, inflammation and mitochondrial dysfunction. In addition, it activated autophagy to restore ideal microenvironment, to provide energy for nerves and to reduce nerve cell apoptosis, thus facilitating nerve debris clearance and neural proliferation. This innovative scaffold will have huge significance in the nerve engineering.

Controlled release of FK506 from micropatterned PLGA films: potential for application in peripheral nerve repair

After decades of research, peripheral nerve injury and repair still frequently results in paralysis, chronic pain and neuropathies leading to severe disability in patients. Current clinically available nerve conduits only provide crude guidance of regenerating axons across nerve gap without additional functionality. FK506 (Tacrolimus), an FDA approved immunosuppressant, has been shown to enhance peripheral nerve regeneration but carries harsh side-effects when delivered systemically. The objective of this study was to develop and evaluate a bioresorbable drug delivery system capable of local extended delivery of FK506 that also provides topological guidance cues to guide axon growth via microgrooves. Photolithography was used to create micropatterned poly(lactide-co-glycolic acid) (PLGA) films embedded with FK506. Non-patterned, 10/10 μm (ridge/groove width), and 30/30 μm patterned films loaded with 0, 1, and 3 μg/cm² FK506 were manufactured and characterized. In vitro FK506 rate of release testing indicated that the films are capable of an extended (at least 56 days), controlled, and scalable release of FK506. Neurite extension bioactivity assay indicated that FK506 released from the films (concentration of samples tested ranged between 8.46–19.7 ng/mL) maintained its neural bioactivity and promoted neurite extension similar to control FK506 dosages (10 ng/mL FK506). The multi-functional FK506 embedded, micropatterned poly(lactide-co-glycolic acid) films developed in this study have potential to be used in the construction of peripheral nerve repair devices.