Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Innovative Strategies in 3D Bioprinting for Spinal Cord Injury Repair

Spinal cord injury (SCI) is a catastrophic condition that disrupts neurons within the spinal cord, leading to severe motor and sensory deficits. While current treatments can alleviate pain, they do not promote neural regeneration or functional recovery. Three-dimensional (3D) bioprinting offers promising solutions for SCI repair by enabling the creation of complex neural tissue constructs. This review provides a comprehensive overview of 3D bioprinting techniques, bioinks, and stem cell applications in SCI repair. Additionally, it highlights recent advancements in 3D bioprinted scaffolds, including the integration of conductive materials, the incorporation of bioactive molecules like neurotrophic factors, drugs, and exosomes, and the design of innovative structures such as multi-channel and axial scaffolds. These innovative strategies in 3D bioprinting can offer a comprehensive approach to optimizing the spinal cord microenvironment, advancing SCI repair. This review highlights a comprehensive understanding of the current state of 3D bioprinting in SCI repair, offering insights into future directions in the field of regenerative medicine.

CD44-targeting hyaluronic acid-selenium nanoparticles boost functional recovery following spinal cord injury

BACKGROUND

Therapeutic strategies based on scavenging reactive oxygen species (ROS) and suppressing inflammatory cascades are effective in improving functional recovery after spinal cord injury (SCI). However, the lack of targeting nanoparticles (NPs) with powerful antioxidant and anti-inflammatory properties hampers the clinical translation of these strategies. Here, CD44-targeting hyaluronic acid-selenium (HA-Se) NPs were designed and prepared for scavenging ROS and suppressing inflammatory responses in the injured spinal cord, enhancing functional recovery.

RESULTS

The HA-Se NPs were easily prepared through direct reduction of seleninic acid in the presence of HA. The obtained HA-Se NPs exhibited a remarkable capacity to eliminate free radicals and CD44 receptor-facilitated internalization by astrocytes. Moreover, the HA-Se NPs effectively mitigated the secretion of proinflammatory cytokines (such as IL-1β, TNF-α, and IL-6) by microglia cells (BV2) upon lipopolysaccharide-induced inflammation. In vivo experiments confirmed that HA-Se NPs could effectively accumulate within the lesion site through CD44 targeting. As a result, HA-Se NPs demonstrated superior protection of axons and neurons within the injury site, leading to enhanced functional recovery in a rat model of SCI.

CONCLUSIONS

These results highlight the potential of CD44-targeting HA-Se NPs for SCI treatment.

Controlled extracellular vesicles release from aminoguanidine nanoparticle-loaded polylysine hydrogel for synergistic treatment of spinal cord injury

Pharmaceutical treatments are critical for the acute and subacute phases of spinal cord injury (SCI) and significantly impact patients' prognoses. However, there is a lack of a precise, multitemporal, integrated drug delivery system for medications administered in both phases. In this study, we prepare a hybrid polylysine-based hydrogel (PBHEVs@AGN) comprising short-term release of pH-responsive aminoguanidine nanoparticles (AGN) and sustained release of extracellular vesicles (EVs) for synergistic SCI treatment. When AGN is exposed to the acidic environment at the injury site, it quickly diffuses out of the hydrogel and releases the majority of the aminoguanidine within 24 h, reducing oxidative stress in lesion tissues. Enriched EVs are gradually released from the hydrogel and remain in the tissue for weeks, providing a long-term anti-inflammatory effect and further ensuring axonal regeneration. Fast-releasing aminoguanidine can cooperate with slow-release EVs to treat SCI more effectively by reducing the production of proinflammatory cytokines and blocking the TLR4/Myd88/NF-κB inflammatory pathway, creating a sustained anti-inflammatory microenvironment for SCI recovery. Our in vivo experiments demonstrate that PBHEVs@AGN reduces the occurrence of scar tissue, encourages remyelination, and speeds up axonal regeneration. Herein, this multi-drug delivery system, which combines the acute release of aminoguanidine and the sustained release of EVs is highly effective for synergistically managing the challenging pathological processes after SCI.

The Promising Role of a Zebrafish Model Employed in Neural Regeneration Following a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating event that results in a wide range of physical impairments and disabilities. Despite the advances in our understanding of the biological response to injured tissue, no effective treatments are available for SCIs at present. Some studies have addressed this issue by exploring the potential of cell transplantation therapy. However, because of the abnormal microenvironment in injured tissue, the survival rate of transplanted cells is often low, thus limiting the efficacy of such treatments. Many studies have attempted to overcome these obstacles using a variety of cell types and animal models. Recent studies have shown the utility of zebrafish as a model of neural regeneration following SCIs, including the proliferation and migration of various cell types and the involvement of various progenitor cells. In this review, we discuss some of the current challenges in SCI research, including the accurate identification of cell types involved in neural regeneration, the adverse microenvironment created by SCIs, attenuated immune responses that inhibit nerve regeneration, and glial scar formation that prevents axonal regeneration. More in-depth studies are needed to fully understand the neural regeneration mechanisms, proteins, and signaling pathways involved in the complex interactions between the SCI microenvironment and transplanted cells in non-mammals, particularly in the zebrafish model, which could, in turn, lead to new therapeutic approaches to treat SCIs in humans and other mammals.

Enzyme-Mediated Nerve Growth Factor Release from Nanofibers Using Gelatin Microspheres

Spinal cord injury is a complex environment, with many conflicting growth factors present at different times throughout the injury timeline. Delivery of multiple growth factors has received mixed results, highlighting a need to consider the timing of delivery for possibly antagonistic growth factors. Cell-mediated degradation of delivery vehicles for delayed release of growth factors offers an attractive way to exploit the highly active immune response in the spinal cord injury environment. In this study, growth factor-loaded gelatin microspheres (GMS) combined with methacrylated hyaluronic acid (MeHA) were electrospun to create GMS fibers (GMSF) for delayed release of growth factors (GFs). GMS were successfully combined with MeHA while electrospinning, with an average fiber diameter of 365 ± 10 nm and 44% ± 8% fiber alignment. GMSF with nerve growth factor (NGF) was tested on dissociated chick dorsal root ganglia cells. We further tested the effect of M1 macrophage-conditioned media (M1CM) to simulate macrophage invasion after spinal cord injury for cell-mediated degradation. We hypothesized that neurons grown on GMSF with loaded NGF would exhibit longer neurites in M1CM, showing a release of functional NGF, as compared with controls. GMSF in M1CM was significantly different from MeHA in serum-free media (SFM) and M0-conditioned media (M0CM), as well as GMSF in M0CM (p < 0.05). Moreover, GMSF + NGF in all media conditions were significantly different from MeHA in SFM and M0CM (p < 0.05). The goal of this study was to develop a biomaterial system where drug delivery is triggered by immune response, allowing for more control and longer exposure to encapsulated drugs. The spinal cord injury microenvironment is known to have a robust immune response, making this immune-medicated drug release system particularly significant for directed repair.

Nervous tract-bioinspired multi-nanoyarn model system regulating neural differentiation and its transcriptional architecture at single-cell resolution

Bioinspired by native nervous tracts, a spinal cord-mimicking model system that was composed of multiple nanofibrous yarns (NYs) ensheathed in a nanofibrous tube was constructed by an innovative electrospinning-based fabrication and integration strategy. The infilling NYs exhibited uniaxially aligned nanofibrous architecture that had a great resemblance to spatially-arranged native nervous tracts, while the outer nanofibrous tubes functioned as an artificial dura matter to provide a stable intraluminal microenvironment. The three-dimensional (3D) NYs were demonstrated to induce alignment, facilitate migration, promote neuronal differentiation, and even phenotypic maturation of seeded neural stem and progenitor cells (NSPCs), while inhibiting gliogenesis. Single-cell transcriptome analysis showed that the NSPC-loaded 3D NY model shared many similarities with native spinal cords, with a great increase in excitatory/inhibitory (EI) neuron ratio. Curcumin, as a model drug, was encapsulated into nanofibers of NYs to exert an antioxidant effect and enhanced axon regeneration. Overall, this study provides a new paradigm for the development of a next-generation in vitro neuronal model system via anatomically accurate nervous tract simulation and constructs a blueprint for the research on NSPC diversification in the biomimetic microenvironment.

Modulating neuroinflammation through molecular, cellular and biomaterial-based approaches to treat spinal cord injury

The neuroinflammatory response that is elicited after spinal cord injury contributes to both tissue damage and reparative processes. The complex and dynamic cellular and molecular changes within the spinal cord microenvironment result in a functional imbalance of immune cells and their modulatory factors. To facilitate wound healing and repair, it is necessary to manipulate the immunological pathways during neuroinflammation to achieve successful therapeutic interventions. In this review, recent advancements and fresh perspectives on the consequences of neuroinflammation after SCI and modulation of the inflammatory responses through the use of molecular-, cellular-, and biomaterial-based therapies to promote tissue regeneration and functional recovery will be discussed.

Multifunctional Integrated Nanozymes Facilitate Spinal Cord Regeneration by Remodeling the Extrinsic Neural Environment

High levels of reactive oxygen species (ROS) and inflammation create a complicated extrinsic neural environment that dominates the initial post-injury period after spinal cord injury (SCI). The compensatory pathways between ROS and inflammation limited the efficacy of modulating the above single treatment regimen after SCI. Here, novel "nanoflower" Mn3 O4 integrated with "pollen" IRF-5 SiRNA was designed as a combination antioxidant and anti-inflammatory treatment after SCI. The "nanoflower" and "pollen" structure was encapsulated with a neutrophil membrane for protective and targeted delivery. Furthermore, valence-engineered nanozyme Mn3 O4 imitated the cascade response of antioxidant enzymes with a higher substrate affinity compared to natural antioxidant enzymes. Nanozymes effectively catalyzed ROS to generate O2 , which is advantageous for reducing oxidative stress and promoting angiogenesis. The screened "pollen" IRF-5 SiRNA could reverse the inflammatory phenotype by reducing interferon regulatory factors-5 (IRF-5) expression (protein level: 73.08% and mRNA level: 63.10%). The decreased expression of pro-inflammatory factors reduced the infiltration of inflammatory cells, resulting in less neural scarring. In SCI rats, multifunctional nanozymes enhanced the proliferation of various neuronal subtypes (motor neurons, interneurons, and sensory neurons) and the recovery of locomotor function, demonstrating that the remodeling of the extrinsic neural environment is a promising strategy to facilitate nerve regeneration.

3D Gelatin Microsphere Scaffolds Promote Functional Recovery after Spinal Cord Hemisection in Rats

Spinal cord injury (SCI) damages signal connections and conductions, with the result that neuronal circuits are disrupted leading to neural dysfunctions. Such injuries represent a serious and relatively common central nervous system condition and current treatments have limited success in the reconstruction of nerve connections in injured areas, especially where sizeable gaps are present. Biomaterial scaffolds have become an effective alternative to nerve transplantation in filling these gaps and provide the foundation for simulating the 3D structure of solid organs. However, there remain some limitations with the application of 3D bioprinting for preparation of biomaterial scaffolds. Here, the approach in constructing and testing mini-tissue building blocks and self-assembly, solid 3D gelatin microsphere (GM) scaffolds with multiple voids as based on the convenient preparation of gelatin microspheres by microfluidic devices is described. These 3D GM scaffolds demonstrate suitable biocompatibility, biodegradation, porosity, low preparation costs, and relative ease of production. Moreover, 3D GM scaffolds can effectively bridge injury gaps, establish nerve connections and signal transductions, mitigate inflammatory microenvironments, and reduce glial scar formation. Accordingly, these 3D GM scaffolds can serve as a novel and effective bridging method to promote nerve regeneration and reconstruction and thus recovery of nerve function after SCI.

Construction of tissue-customized hydrogels from cross-linkable materials for effective tissue regeneration

Hydrogels are prevalent scaffolds for tissue regeneration because of their hierarchical architectures along with outstanding biocompatibility and unique rheological and mechanical properties. For decades, researchers have found that many materials (natural, synthetic, or hybrid) can form hydrogels using different cross-linking strategies. Traditional strategies for fabricating hydrogels include physical, chemical, and enzymatical cross-linking methods. However, due to the diverse characteristics of different tissues/organs to be regenerated, tissue-customized hydrogels need to be developed through precisely controlled processes, making the manufacture of hydrogels reliant on novel cross-linking strategies. Thus, hybrid cross-linkable materials are proposed to tackle this challenge through hybrid cross-linking strategies. Here, different cross-linkable materials and their associated cross-linking strategies are summarized. From the perspective of the major characteristics of the target tissues/organs, we critically analyze how different cross-linking strategies are tailored to fit the regeneration of such tissues and organs. To further advance this field, more appropriate cross-linkable materials and cross-linking strategies should be investigated. In addition, some innovative technologies, such as 3D bioprinting, the internet of medical things (IoMT), and artificial intelligence (AI), are also proposed to improve the development of hydrogels for more efficient tissue regeneration.

Designing electrospun fiber platforms for efficient delivery of genetic material and genome editing tools

Electrospun fibers are versatile biomaterial platforms with great potential to support regeneration. Electrospun fiber characteristics such as fiber diameter, degree of alignment, rate of degradation, and surface chemistry enable the creation of unique, tunable scaffolds for various drug or gene delivery applications. The delivery of genetic material and genome editing tools via viral and non-viral vectors are approaches to control cellular protein production. However, immunogenicity, off-target effects, and low delivery efficiencies slow the progression of gene delivery strategies to clinical settings. The delivery of genetic material from electrospun fibers overcomes such limitations by allowing for localized, tunable delivery of genetic material. However, the process of electrospinning is harsh, and care must be taken to retain genetic material bioactivity. This review presents an up-to-date summary of strategies to incorporate genetic material onto or within electrospun fiber platforms to improve delivery efficiency and enhance the regenerative potential of electrospun fibers for various tissue engineering applications.

[Experimental study on the construction of telmisartan/collagen/polycaprolactone nerve conduit and its repair effect on rat sciatic nerve defect]

OBJECTIVE

To construction the telmisartan/collagen/polycaprolactone (PCL) nerve conduit and assess its effect on repairing sciatic nerve defect in rats.

METHODS

The 60% collagen/hexafluoroisopropanol (HFIP) solution and 40% PCL/HFIP solution were prepared and mixed (collagen/PCL solution). Then the 0, 5, 10, and 20 mg of telmisartan were mixed with the 10 mL collagen/PCL solution, respectively. Telmisartan/collagen/PCL nerve conduits were fabricated via high voltage electrospinning technology. The structure of nerve conduit before and after crosslinking was observed by using scanning electron microscope (SEM). The drug release efficiency was detected by in vitro sustained release method. RAW264.7 cells were cultured with lipopolysaccharide to induce inflammation, and then co-cultured with nerve conduits loaded with different concentrations of telmisartan for 24 hours. The mRNA expressions of inducible nitric oxide synthase (iNOS) and Arginase 1 (Arg-1) were detected by using real-time fluorescence quantitative PCR. Forty adult Wistar rats were randomly divided into 4 groups ( n=10). After preparing 15-mm-long sciatic nerve defect, the defect was repaired by cross-linked nerve conduits loaded with 0, 5, 10, and 20 mg telmisartan in groups A, B, C, and D, respectively. After operation, the general condition of rats was observed after operation; the sciatic function index (SFI) was tested; the bridging between the nerve conduit and sciatic nerve, and the integrity of nerve conduit were observed; the tissue growth in nerve conduit and material degradation were observed by HE staining; the expressions of CD86 (M1 macrophage marker), CD206 (M2 macrophage marker), myelin basic protein (MBP), and myelin protein 0 (P0) in new tissues were also observed by immunohistochemical staining; the expressions of neurofilament 200 (NF-200) and S-100β in new tissues were assessed by immunofluorescence staining.

RESULTS

The general observation showed that the inner diameter of the nerve conduit was 1.8 mm and the outer diameter was 2.0 mm. After cross-linking by genipin, the nanofiber became thicker and denser. The drug release test showed that the telmisartan loaded nerve conduit could be released gradually. With the increase of telmisartan content in nerve conduit, the iNOS mRNA expression decreased and the Arg-1 mRNA expression increased; and the differences between 20 mg group and other groups were significant ( P<0.05). In vivo experiment showed that all animals in each group survived until the completion of the experiment. The SFI was significantly higher in groups C and D than in groups A and B at different time points ( P<0.05) and in group D than in group C at 6 months after operation ( P<0.05). HE staining showed that there were significantly more new tissues in the middle of the nerve conduit in group D after operation than in other groups. Immunohistochemical staining showed that CD86 and CD206 stainings were positive in each group at 1 month after operation, among which group D had the lowest positive rate of CD86 and the highest positive rate of CD206, and there were significant differences in the positive rate of CD206 between group D and groups A, B, and C ( P<0.05); the MBP and P0 stainings were positive in groups C and D at 6 months, and the positive rate in group D was significantly higher than that in group C ( P<0.05). Immunofluorescence staining showed that the NF-200 and S-100β expressions in group D were significantly higher than those in other groups.

CONCLUSION

Telmisartan/collagen/PLC nerve conduit can promote the sciatic nerve defect repair in rats through promoting the polarization of M1 macrophages to M2 macrophages, and the nerve conduit loaded with20 mg telmisartan has the most significant effect.

Biomaterial-based strategies for in vitro neural models

In vitro models have been used as a complementary tool to animal studies in understanding the nervous system's physiological mechanisms and pathological disorders, while also serving as platforms to evaluate the safety and efficiency of therapeutic candidates. Following recent advances in materials science, micro- and nanofabrication techniques and cell culture systems, in vitro technologies have been rapidly gaining the potential to bridge the gap between animal and clinical studies by providing more sophisticated models that recapitulate key aspects of the structure, biochemistry, biomechanics, and functions of human tissues. This was made possible, in large part, by the development of biomaterials that provide cells with physicochemical features that closely mimic the cellular microenvironment of native tissues. Due to the well-known material-driven cellular response and the importance of mimicking the environment of the target tissue, the selection of optimal biomaterials represents an important early step in the design of biomimetic systems to investigate brain structures and functions. This review provides a comprehensive compendium of commonly used biomaterials as well as the different fabrication techniques employed for the design of neural tissue models. Furthermore, the authors discuss the main parameters that need to be considered to develop functional platforms not only for the study of brain physiological functions and pathological processes but also for drug discovery/development and the optimization of biomaterials for neural tissue engineering.

Future Perspectives in Spinal Cord Repair: Brain as Saviour? TSCI with Concurrent TBI: Pathophysiological Interaction and Impact on MSC Treatment

Traumatic spinal cord injury (TSCI), commonly caused by high energy trauma in young active patients, is frequently accompanied by traumatic brain injury (TBI). Although combined trauma results in inferior clinical outcomes and a higher mortality rate, the understanding of the pathophysiological interaction of co-occurring TSCI and TBI remains limited. This review provides a detailed overview of the local and systemic alterations due to TSCI and TBI, which severely affect the autonomic and sensory nervous system, immune response, the blood-brain and spinal cord barrier, local perfusion, endocrine homeostasis, posttraumatic metabolism, and circadian rhythm. Because currently developed mesenchymal stem cell (MSC)-based therapeutic strategies for TSCI provide only mild benefit, this review raises awareness of the impact of TSCI-TBI interaction on TSCI pathophysiology and MSC treatment. Therefore, we propose that unravelling the underlying pathophysiology of TSCI with concomitant TBI will reveal promising pharmacological targets and therapeutic strategies for regenerative therapies, further improving MSC therapy.

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.

The design criteria and therapeutic strategy of functional scaffolds for spinal cord injury repair

Spinal cord injury (SCI) remains a therapeutic challenge in clinic. Current drug and cell therapeutics have obtained significant efficacy but are still in the early stages for complete neural and functional recovery. In the past few decades, functional scaffolds (FSs) have been rapidly developed to bridge the lesion and provide a framework for tissue regeneration in SCI repair. Moreover, a FS can act as an adjuvant for locally delivering drugs in the lesion with a designed drug release profile, and supplying a biomimetic environment for implanted cells. In this review, the design criteria of FSs for SCI treatment are summarized according to their biocompatibility, mechanical properties, morphology, architecture, and biodegradability. Subsequently, FSs designed for SCI repair in the scope of drug delivery, cell implantation and combination therapy are introduced, respectively. And how a FS promotes their therapeutic efficacy is analyzed. Finally, the challenges, perspectives, and potential of FSs for SCI treatment are discussed. Hopefully, this review may inspire the future development of potent FSs to facilitate SCI repair in clinic.

Delivery of pOXR1 through an injectable liposomal nanoparticle enhances spinal cord injury regeneration by alleviating oxidative stress

Oxidation resistance 1 (OXR1) is regarded as a critical regulator of cellular homeostasis in response to oxidative stress. However, the role of OXR1 in the neuronal response to spinal cord injury (SCI) remains undefined. On the other hand, gene therapy for SCI has shown limited success to date due in part to the poor utility of conventional gene vectors. In this study, we evaluated the function of OXR1 in SCI and developed an available carrier for delivering the OXR1 plasmid (pOXR1). We found that OXR1 expression is remarkably increased after SCI and that this regulation is protective after SCI. Meanwhile, we assembled cationic nanoparticles with vitamin E succinate-grafted ε-polylysine (VES-g-PLL) (Nps). The pOXR1 was precompressed with Nps and then encapsulated into cationic liposomes. The particle size of pOXR1 was compressed to 58 nm, which suggests that pOXR1 can be encapsulated inside liposomes with high encapsulation efficiency and stability to enhance the transfection efficiency. The agarose gel results indicated that Nps-pOXR1-Lip eliminated the degradation of DNA by DNase I and maintained its activity, and the cytotoxicity results indicated that pOXR1 was successfully transported into cells and exhibited lower cytotoxicity. Finally, Nps-pOXR1-Lip promoted functional recovery by alleviating neuronal apoptosis, attenuating oxidative stress and inhibiting inflammation. Therefore, our study provides considerable evidence that OXR1 is a beneficial factor in resistance to SCI and that Nps-Lip-pOXR1 exerts therapeutic effects in acute traumatic SCI.

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OXR1 is upregulated after SCI and may provide a protective effect in response to neural injury.

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OXR1 plasmid is condensed by VES-g-PLL micelles and then encapsulated into cationic liposomes.

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Liposome complexes significantly enhance the OXR1 protein expression in vivo and in vitro.

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Overexpressed OXR1 relieving oxidative stress after SCI through Nrf-2/HO-1 pathway.

A conductive dual-network hydrogel composed of oxidized dextran and hyaluronic-hydrazide as BDNF delivery systems for potential spinal cord injury repair

Spinal cord injury (SCI) often causes neuronal death and axonal degeneration. In this study, we report a new strategy for preparing injectable and conductive polysaccharides-based hydrogels that could sustainably deliver brain-derived neurotrophic factor (BDNF) for SCI repair. We used poly(lactic-co-glycolic acid) (PLGA) as a carrier to encapsulate BDNF. The resulting microspheres were then modified with tannic acid (TA). The polysaccharides-based hydrogel composed of oxidized dextran (Dex) and hyaluronic acid-hydrazide (HA) was mixed with TA-modified microspheres to form the ultimate BDNF@TA-PLGA/Dex-HA hydrogel. Our results showed that the hydrogel had properties similar to natural spinal cords. Specifically, the hydrogel had soft mechanical properties and high electrical conductivity. The cross-sectional morphology of the hydrogel exhibited a continuous and porous structure. The swelling and degradation behaviors of the Dex-HA hydrogel in vitro indicated the incorporation of TA into hydrogel matrix could improve the stability of the hydrogel matrix as well as extend the release time of BDNF from the matrix. Furthermore, results from immunostaining and real-time PCR demonstrated that BDNF@TA-PLGA/Dex-HA hydrogel could promote the differentiation of neural stem cells (NSCs) into neurons and inhibit astrocyte differentiation in vitro. These results show the great potential of this hydrogel as a biomimetic material in SCI regeneration.

Effective Modulation of CNS Inhibitory Microenvironment using Bioinspired Hybrid-Nanoscaffold-Based Therapeutic Interventions

Central nervous system (CNS) injuries are often debilitating, and most currently have no cure. This is due to the formation of a neuroinhibitory microenvironment at injury sites, which includes neuroinflammatory signaling and non-permissive extracellular matrix (ECM) components. To address this challenge, a viscous interfacial self-assembly approach, to generate a bioinspired hybrid 3D porous nanoscaffold platform for delivering anti-inflammatory molecules and establish a favorable 3D-ECM environment for the effective suppression of the neuroinhibitory microenvironment, is developed. By tailoring the structural and biochemical properties of the 3D porous nanoscaffold, enhanced axonal growth from the dual-targeting therapeutic strategy in a human induced pluripotent stem cell (hiPSC)-based in vitro model of neuroinflammation is demonstrated. Moreover, nanoscaffold-based approaches promote significant axonal growth and functional recovery in vivo in a spinal cord injury model through a unique mechanism of anti-inflammation-based fibrotic scar reduction. Given the critical role of neuroinflammation and ECM microenvironments in neuroinhibitory signaling, the developed nanobiomaterial-based therapeutic intervention may pave a new road for treating CNS injuries.

3D Printing and Bioprinting Nerve Conduits for Neural Tissue Engineering

Fabrication of nerve conduits for perfectly repairing or replacing damaged peripheral nerve is an urgent demand worldwide, but it is also a formidable clinical challenge. In the last decade, with the rapid development of manufacture technologies, 3D printing and bioprinting have been becoming remarkable stars in the field of neural engineering. In this review, we explore that the biomaterial inks (hydrogels, thermoplastic, and thermoset polyesters and composite) and bioinks have been selected for 3D printing and bioprinting of peripheral nerve conduits. This review covers 3D manufacturing technologies, including extrusion printing, inkjet printing, stereolithography, and bioprinting with inclusion of cells, bioactive molecules, and drugs. Finally, an outlook on the future directions of 3D printing and 4D printing in customizable nerve therapies is presented.

Strategies and prospects of effective neural circuits reconstruction after spinal cord injury

Due to the disconnection of surviving neural elements after spinal cord injury (SCI), such patients had to suffer irreversible loss of motor or sensory function, and thereafter enormous economic and emotional burdens were brought to society and family. Despite many strategies being dealing with SCI, there is still no effective regenerative therapy. To date, significant progress has been made in studies of SCI repair strategies, including gene regulation of neural regeneration, cell or cell-derived exosomes and growth factors transplantation, repair of biomaterials, and neural signal stimulation. The pathophysiology of SCI is complex and multifaceted, and its mechanisms and processes are incompletely understood. Thus, combinatorial therapies have been demonstrated to be more effective, and lead to better neural circuits reconstruction and functional recovery. Combinations of biomaterials, stem cells, growth factors, drugs, and exosomes have been widely developed. However, simply achieving axon regeneration will not spontaneously lead to meaningful functional recovery. Therefore, the formation and remodeling of functional neural circuits also depend on rehabilitation exercises, such as exercise training, electrical stimulation (ES) and Brain-Computer Interfaces (BCIs). In this review, we summarize the recent progress in biological and engineering strategies for reconstructing neural circuits and promoting functional recovery after SCI, and emphasize current challenges and future directions.

Phase-Change Materials for Controlled Release and Related Applications

Phase-change materials (PCMs) have emerged as a novel class of thermo-responsive materials for controlled release, where the payloads encapsulated in a solid matrix are released only upon melting the PCM to trigger a solid-to-liquid phase transition. Herein, the advances over the past 10 years in utilizing PCMs as a versatile platform for the encapsulation and release of various types of therapeutic agents and biological effectors are highlighted. A brief introduction to PCMs in the context of desired properties for controlled release and related applications is provided. Among the various types of PCMs, a specific focus is placed on fatty acids and fatty alcohols for their natural availability, low toxicity, biodegradability, diversity, high abundance, and low cost. Then, various methods capable of processing PCMs, and their mixtures with payloads, into stable suspensions of colloidal particles, and the different means for triggering the solid-to-liquid phase transition are discussed. Finally, a range of applications enabled by the controlled release system based on PCMs are presented together with some perspectives on future directions.

Electrospun fibers: an innovative delivery method for the treatment of bone diseases

INTRODUCTION

The treatment performances of current surgical therapeutic materials for injuries caused by high-energy trauma, such as prolonged bone defects, nerve-fiber disruptions, and repeated spasms or adhesions of vascular tendons after repair, are poor. Drug-loaded electrospun fibers have become a novel polymeric material for treating orthopedic diseases owing to their three-dimensional structures, thus providing excellent controlled drug-release responses and high affinity with local tissues. Herein, we reviewed the morphology of electrospun nanofibers, methods for loading drugs on the fibers, and modification methods to improve drug permeability and bioavailability. We highlight innovative applications of drug-loaded electrospun fibers in different treatments, including bone and cartilage defects, tendon and soft-tissue adhesion, vascular remodeling, skin grafting, and nervous-system injuries.

AREAS COVERED

With the rapid development of electrospinning technologies and advancement of tissue engineering, drug-loaded electrospun fibers are becoming increasingly important in controlled drug release, wound closure, and tissue regeneration and repair.

EXPERT OPINION

Drug-loaded electrospun fibers exhibit a broad range of application prospects and great potential in treating orthopedic diseases. Accordingly, a plethora of novel treatments utilizing the different morphological features of electrospun fibers, the distinctive pharmacokinetics, pharmacodynamics characteristics of different drugs, and the diverse onset characteristics of different diseases, is proposed.

An Effective Cationic Human Serum Albumin-Based Gene-Delivery Carrier Containing the Nuclear Localization Signal

Considerable effort has been devoted to the development of gene carriers over the years. However, toxicity, immunogenicity, and low transfection efficiency are still major barriers. How to overcome these obstacles has become a burning question in gene delivery. In the present study, a simple cationic human serum albumin (CHSA)-based gene-delivery system containing nuclear localization signals (NLSs) was constructed to conquer the limitations. CHSA/NLS/plasmid DNA (pDNA) complexes were prepared and characterized by Hoechst 33258 intercalation, gel retardation assay, morphological analysis, circular dichroism (CD) spectroscopy, particle size, and zeta potential measurements. Results showed that CHSA/NLS/pDNA complexes were able to condense and protect pDNA with high encapsulation efficiency. The complexes displayed a nutritional effect on cells at a low concentration and there was no significant cytotoxicity or immunogenicity. In addition, CHSA/NLS/pDNA complexes exhibited excellent cellular uptake rates and the mechanism was mainly the clathrin or macropinocytosis-dependent endocytosis pathway. Furthermore, CHSA/NLS/pDNA significantly enhanced gene expression efficiency in vitro. More importantly, CHSA/NLS/pDNA complexes showed a desired antitumor effect in vivo, exhibiting the highest inhibition rate (57.3%) and significant upregulation in p53 protein. All these results confirm that CHSA/NLS/pDNA complexes have a bright future as a safe and effective delivery system for gene therapy.