Controlling the Release of Neurotrophin-3 and Chondroitinase ABC Enhances the Efficacy of Nerve Guidance Conduits

Electrospun drug-loaded scaffolds for nervous system repair

Nervous system injuries, encompassing peripheral nerve injury (PNI), spinal cord injury (SCI), and traumatic brain injury (TBI), present significant challenges to patients' wellbeing. Traditional treatment approaches have limitations in addressing the complexity of neural tissue regeneration and require innovative solutions. Among emerging strategies, implantable materials, particularly electrospun drug-loaded scaffolds, have gained attention for their potential to simultaneously provide structural support and controlled release of therapeutic agents. This review provides a thorough exploration of recent developments in the design and application of electrospun drug-loaded scaffolds for nervous system repair. The electrospinning process offers precise control over scaffold characteristics, including mechanical properties, biocompatibility, and topography, crucial for creating a conducive environment for neural tissue regeneration. The large surface area of the resulting fibrous networks enhances biomolecule attachment, influencing cellular behaviors such as adhesion, proliferation, and migration. Polymeric electrospun materials demonstrate versatility in accommodating a spectrum of therapeutics, from small molecules to proteins. This enables tailored interventions to accelerate neuroregeneration and mitigate inflammation at the injury site. A critical aspect of this review is the examination of the interplay between structural properties and pharmacological effects, emphasizing the importance of optimizing both aspects for enhanced therapeutic outcomes. Drawing upon the latest advancements in the field, we discuss the promising outcomes of preclinical studies using electrospun drug-loaded scaffolds for nervous system repair, as well as future perspectives and considerations for their design and implementation. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Implantable Materials and Surgical Technologies > Nanotechnology in Tissue Repair and Replacement Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

A responsive cascade drug delivery scaffold adapted to the therapeutic time window for peripheral nerve injury repair

Peripheral nerve injury (PNI) is a common clinical challenge, requiring timely and orderly initiation of synergistic anti-inflammatory and reparative therapy. Although the existing cascade drug delivery system can realize sequential drug release through regulation of the chemical structure of drug carriers, it is difficult to adjust the release kinetics of each drug based on the patient's condition. Therefore, there is an urgent need to develop a cascade drug delivery system that can dynamically adjust drug release and realize personalized treatment. Herein, we developed a responsive cascade drug delivery scaffold (RCDDS) which can adapt to the therapeutic time window, in which Vitamin B12 is used in early controllable release to suppress inflammation and nerve growth factor promotes regeneration by cascade loading. The RCDDS exhibited the ability to modulate the drug release kinetics by hierarchically opening polymer chains triggered by ultrasound, enabling real-time adjustment of the anti-inflammatory and neuroregenerative therapeutic time window depending on the patient's status. In the rat sciatic nerve injury model, the RCDDS group was able to achieve neural repair effects comparable to the autograft group in terms of tissue structure and motor function recovery. The development of the RCDDS provides a useful route toward an intelligent cascade drug delivery system for personalized therapy.

Advances in Large Gap Peripheral Nerve Injury Repair and Regeneration with Bridging Nerve Guidance Conduits

Peripheral nerve injury is a common complication of accidents and diseases. The traditional autologous nerve graft approach remains the gold standard for the treatment of nerve injuries. While sources of autologous nerve grafts are very limited and difficult to obtain. Nerve guidance conduits are widely used in the treatment of peripheral nerve injuries as an alternative to nerve autografts and allografts. However, the development of nerve conduits does not meet the needs of large gap peripheral nerve injury. Functional nerve conduits can provide a good microenvironment for axon elongation and myelin regeneration. Herein, the manufacturing methods and different design types of functional bridging nerve conduits for nerve conduits combined with electrical or magnetic stimulation and loaded with Schwann cells, etc., are summarized. It summarizes the literature and finds that the technical solutions of functional nerve conduits with electrical stimulation, magnetic stimulation and nerve conduits combined with Schwann cells can be used as effective strategies for bridging large gap nerve injury and provide an effective way for the study of large gap nerve injury repair. In addition, functional nerve conduits provide a new way to construct delivery systems for drugs and growth factors in vivo.

Targeting Chondroitin Sulphate Synthase 1 (Chsy1) Promotes Axon Growth Following Neurorrhaphy by Suppressing Versican Accumulation

Versican is a chondroitin sulfate proteoglycan (CSPG), which deposits in perineurium as a physical barrier and prevents the growth of axons out of the fascial boundary. Several studies have indicated that the chondroitin sulfate (CS) chains on versican have several possible functions beyond the physical barrier, including the ability to stabilize versican core protein in the extracellular matrix. As chondroitin sulfate synthase 1 (Chsy1) is a crucial enzyme for CS elongation, we hypothesized that in vivo knockdown of Chsy1 at peripheral nerve lesion site may decrease CS and versican accumulation, and result in accelerating neurite regeneration. In the present study, end-to-side neurorrhaphy (ESN) in Wistar rats was used as an in vivo model of peripheral nerve injury to evaluate nerve regeneration after surgical intervention. The distribution and expression of versican and Chsy1 in regenerating axons after ESN was studied using confocal microscopy and western blotting. Chsy1 was silenced at the nerve lesion (surgical) site using in vivo siRNA transfection. The results indicated that Chsy1 was successfully silenced in nerve tissue, and its downregulation was associated with functional recovery of compound muscle action potential. Silencing of Chsy1 also decreased the accumulation of versican core protein, suggesting that transient treating of Chsy1-siRNA may be an alternative and an effective strategy to promote injured peripheral nerve regeneration.

A biomimetic and bioactive scaffold with intelligently pulsatile teriparatide delivery for local and systemic osteoporosis regeneration

Osteoporosis is one of the most disabling consequences of aging, osteoporotic fractures and higher risk of the subsequent fractures leading to substantial disability and deaths, indicating both local fractures healing and the early anti-osteoporosis therapy are of great significance. Teriparatide is strong bone formation promoter effective in treating osteoporosis, while side effects limit clinical applications. Traditional drug delivery is lack of sensitive and short-term release, finding a new non-invasive and easily controllable drug delivery to not only repair the local fractures but also improve total bone mass has remained a great challenge. Thus, bioinspired by the natural bone components, we develop appropriate interactions between inorganic biological scaffolds and organic drug molecules, achieving both loaded with the teriparatide in the scaffold and capable of releasing on demand. Herein, biomimetic bone microstructure of mesoporous bioglass, a near-infrared ray triggered switch, thermosensitive liposomes based on a valve, and polydopamine coated as a heater is developed rationally for osteoporotic bone regeneration. Teriparatide is pulsatile released from intelligent delivery, not only rejuvenating osteoporotic bone defect, but also presenting strong systemic anti-osteoporosis therapy. This biomimetic bone carrying novel drug delivery platform is well worth expecting to be a new promising strategy and clinically commercialized to help patients survive from the osteoporotic fracture.

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A novel NIR-triggered three-in-one smart platform was proposed.

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Highly NIR-sensitive in vivo controlled release and self-regulating pulsatile release can be achieved.

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Local precise pulsatile release accelerates osteoporotic bone healing.

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This study focused on the osteoporotic bone regeneration of both skull and femur at the same time.

Neural tissue engineering: From bioactive scaffolds and in situ monitoring to regeneration

Peripheral nerve injury is a large-scale problem that annually affects more than several millions of people all over the world. It remains a great challenge to effectively repair nerve defects. Tissue engineered nerve guidance conduits (NGCs) provide a promising platform for peripheral nerve repair through the integration of bioactive scaffolds, biological effectors, and cellular components. Herein, we firstly describe the pathogenesis of peripheral nerve injuries at different orders of severity to clarify their microenvironments and discuss the clinical treatment methods and challenges. Then, we discuss the recent progress on the design and construction of NGCs in combination with biological effectors and cellular components for nerve repair. Afterward, we give perspectives on imaging the nerve and/or the conduit to allow for the in situ monitoring of the nerve regeneration process. We also cover the applications of different postoperative intervention treatments, such as electric field, magnetic field, light, and ultrasound, to the well-designed conduit and/or the nerve for improving the repair efficacy. Finally, we explore the prospects of multifunctional platforms to promote the repair of peripheral nerve injury.

Implantable Biomaterials for Peripheral Nerve Regeneration–Technology Trends and Translational Tribulations

The use of autografted nerve in surgical repair of peripheral nerve injuries (PNI) is severely limited due to donor site morbidity and restricted tissue availability. As an alternative, synthetic nerve guidance channels (NGCs) are available on the market for surgical nerve repair, but they fail to promote nerve regeneration across larger critical gap nerve injuries. Therefore, such injuries remain unaddressed, result in poor healing outcomes and are a limiting factor in limb reconstruction and transplantation. On the other hand, a myriad of advanced biomaterial strategies to address critical nerve injuries are proposed in preclinical literature but only few of those have found their way into clinical practice. The design of synthetic nerve grafts should follow rational criteria and make use of a combination of bioinstructive cues to actively promote nerve regeneration. To identify the most promising NGC designs for translation into applicable products, thorough mode of action studies, standardized readouts and validation in large animals are needed. We identify design criteria for NGC fabrication according to the current state of research, give a broad overview of bioactive and functionalized biomaterials and highlight emerging composite implant strategies using therapeutic cells, soluble factors, structural features and intrinsically conductive substrates. Finally, we discuss translational progress in bioartificial conduits for nerve repair from the surgeon’s perspective and give an outlook toward future challenges in the field.

Anisotropic Silk-Inspired Nerve Conduit with Peptides Improved the Microenvironment for Long-Distance Peripheral Nerve Regeneration

A lack of effective bioactivity to create a desirable microenvironment for peripheral nerve regeneration has been challenging in successful treatment of long-distance injuries using nerve guidance conduits (NGCs) clinically. Herein, we developed a silk-inspired phototriggered gelation system combining dual therapeutic cues of anisotropic topography and adhesive ligands for improving peripheral nerve regeneration. Importantly, enhanced cell recruitment and myelination of Schwann cells were successfully achieved by the Arg-Gly-Asp (RGD)-peptide-immobilized hydrogel scaffolds to promote axon growth. Moreover, as the orientated growth of Schwann cells and rapid axon growth were facilitated by aligned grooved micropatterns, this multifunctional bioactive system provides remarkable nerve regeneration with function recovery for long-distance nerve injury. Therefore, this bioengineered silk-inspired nerve guidance conduit delivers a platform for desirable peripheral nerve repair.

In Situ Fabrication of Nerve Growth Factor Encapsulated Chitosan Nanoparticles in Oxidized Bacterial Nanocellulose for Rat Sciatic Nerve Regeneration

Autograft is currently the gold standard in the clinical treatment of peripheral nerve injury (PNI), which, however, is limited by the availability of a donor nerve and secondary injuries. Nerve guidance conduits (NGC) provide a suitable microenvironment to promote the regeneration of injured nerves, which could be the substitutes for autografts. In this study, nerve growth factor (NGF) encapsulated chitosan nanoparticles (CSNPs) were first constructed in situ in an oxidized bacterial cellulose (OBC) conduit using the ion gel method after the introduction of a CS/NGF solution under pressure to enable a sustainable release of NGF. A novel NGF@CSNPs/OBC nanocomposite with antibacterial activity, biodegradability, and porous microstructure was successfully developed. In vitro experiments showed that the nanocomposite promoted the adhesion and proliferation of Schwann cells. When the nanocomposite was applied as NGC to repair the sciatic nerve defect of rats, a successful repair of the 10 mm nerve defect was observed after 4 weeks. At week 9, the diameter, morphology, histology, and functional recovery of the regenerated nerve was comparable to the autografts, indicating that the NGC effectively promoted the regeneration and function recovery of the nerve. In summary, the NGF@CSNPs/OBC as a novel NGC provides great potential in the treatment of PNI.

Gastrodin modified polyurethane conduit promotes nerve repair via optimizing Schwann cells function

Peripheral nerve regeneration and functional recovery remain a major clinical challenge. Nerve guidance conduit (NGC) that can regulate biological behavior of Schwann cells (SCs) and facilitate axonal regeneration through microenvironmental remodeling is beneficial for nerve regeneration and functional recovery. Gastrodin, a main constituent of a Chinese traditional herbal medicine, has been known to display several biological and pharmacological properties, especially antioxidative, anti‐inflammatory and nerve regeneration. Herein, polyurethane (PU) NGCs modified by different weight ratio of Gastrodin (0, 1 and 5 wt%) were designed for sequential and sustainable drug release, that created a favorable microenvironment for nerve regeneration. The scaffold showed suitable pore structure and biocompatibility in vitro, and evidently promoted morphological and functional recovery of regenerated sciatic nerves in vivo. Compared to the PU and 1%Gastrodin/PU scaffolds, the 5%Gastrodin/PU significantly enhanced the proliferation, migration and myelination of SCs and up-regulated expression of neurotrophic factors, as well as induction of the differentiation of PC12 cells. Interestingly, the obvious anti-inflammatory response was observed in 5%Gastrodin/PU by reduced expression of TNF-α and iNOS, which also evidenced by the few fibrous capsule formation in the subcutaneous implantation. Such a construct presented a similarity to autograft in vivo repairing a 10 mm sciatic nerve defects. It was able to not only boost the regenerated area of nerve and microvascular network, but also facilitate functional axons growth and remyelination, leading to highly improved functional restoration. These findings demonstrate that the 5%Gastrodin/PU NGC efficiently promotes nerve regeneration, indicating their potential for use in peripheral nerve regeneration applications.

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NGC with a sustained release of Gastrodin creates a favorable microenvironment. .

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Gastrodin/PU has superior anti-inflammatory effects.

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SCs-mediated tissue engineering strategies effectively drive myelination.

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5Gastrodin/PU boosts nerve regeneration and functional restoration in vivo.

An adherent drug depot for retinal ganglion cell protection and regeneration in rat traumatic optic neuropathy models

Traumatic optic neuropathy (TON) describes an injury to the optic nerve following either blunt or penetrating trauma, and remains an important cause of vision loss. No generalized treatment of TON has been established so far to restore the injured optic nerve. We developed an adherent drug-encapsulated bi-layered depot (DBP) as a dual drug vehicle for local treatment to protect the residual retinal ganglion cells (RGCs) and regenerate axons following optic nerve damage. The inner layer of the depot was prepared by co-electrospinning poly(d,l-lactide-co-glycolide acid) (PLGA: 75 : 25) and collagen (COL) with the hydrophobic corticosteroid triamcinolone acetonide (TA) loaded. The outer layer was made of PLGA and the hydrophilic neuroprotective agent Fasudil (FA). The DBP showed suitable morphology, hydrophilicity and mechanical properties, and slowly released TA and FA in vitro by undergoing time-dependent degradation and swelling. All depots showed good biocompatibility with L929 mouse fibroblasts, and DBP was helpful in maintaining the morphology of RGCs in vitro. In addition, direct implantation of DBP at the injured optic nerve in a rat model mitigated inflammation and the death of RGCs, and increased the expression of nerve growth-related protein GAP-43. Therefore, DBP maybe a promising local therapy against TON in future.