Nanobiotechnology-Based Strategies for Targeting Neuroinflammation and Neural Tissue Engineering

Abstract

Neuroinflammation is a central hallmark of numerous neurological disorders, including Alzheimer’s disease, Parkinson’s disease, traumatic brain injury, and spinal cord damage. Its persistent and dysregulated nature not only accelerates neuronal loss but also impedes endogenous repair, posing a major challenge for effective therapeutic intervention. Recent advances in nanobiotechnology have opened transformative opportunities to modulate neuroinflammation with unprecedented precision while simultaneously supporting neural regeneration. This review highlights emerging nanomaterial-based strategies including lipid-based, polymeric, inorganic nanoparticles designed to traverse the blood–brain barrier (BBB), deliver anti-inflammatory agents, modulate immune cell behavior, and attenuate glial activation. Extending beyond nanoparticle-based delivery systems, recent advances also emphasize the integration of nanomaterials into biomimetic architectures to provide structural and functional cues for neural repair. We further summarize how these functional nanostructured scaffolds, such as extracellular matrix (ECM) mimetic, nanofibrous and conductive hydrogels, are being leveraged in neural tissue engineering to direct stem cell fate, promote axonal outgrowth, and rebuild damaged neuroarchitectures. Moreover, pharmacokinetics, biodistribution, safety, clinical trials, regulatory considerations and limitations of nanotherapeutics in neurodegenerative diseases are discussed. By outlining the current progress, mechanistic insights, and translational challenges, this review underscores the potential of nanobiotechnology-enabled therapeutics to revolutionize the treatment of neuroinflammatory conditions and advance next-generation neural repair technologies.

1. Introduction

Inflammation is a fundamental biological defense mechanism activated in response to injury, infection, or tissue stress [1]. It involves a coordinated cascade of molecular and cellular events aimed at restoring homeostasis and eliminating harmful stimuli [2]. Inflammation is essential for host protection, but its dysregulation can lead to chronic tissue damage and impaired repair. It is characterized by redness, edema, heat, pain, activation of immune cells and a loss of tissue function [3]. In recent years, significant interest has emerged in understanding how inflammatory processes operate within the central nervous system (CNS), where the structural and immunological environment is distinct from peripheral tissues [4].

Inflammatory reactions that arise specifically within the brain and spinal cord are collectively termed neuroinflammation [5]. Neuroinflammation refers to a localized immune response in CNS tissues, mainly driven by the activation of microglia and astrocytes. These cells release inflammatory mediators such as cytokines (e.g., interleukin (IL)-1b, IL-6, and tumor necrosis factor (TNF)α), chemokines (e.g., CCL2, CCL5, CXCL1), reactive oxygen species (ROS), and other secondary messengers (nitric oxide (NO) and prostaglandins) that trigger neuroinflammation [6,7] (Figure 1). These signaling molecules are also produced by endothelial cells and infiltrating peripheral immune cells that gain access during pathological states. Among all, microglia are considered as key regulators of neuroinflammation due to their primary immune surveillance and macrophage-like activities in the CNS [8].

The consequences of neuroinflammatory activity extend beyond classical immune responses. Depending on the nature, severity, and persistence of the initiating insult, neuroinflammation can trigger a wide spectrum of physiological, biochemical, and behavioral outcomes [9]. Under controlled, transient conditions, it can support neuroprotection and tissue repair. However, prolonged or excessive neuroinflammation disrupts neuronal function, alters synaptic signaling, compromises the BBB, and accelerates neurodegeneration, leading to a wide range of neurodegenerative diseases, psychiatric conditions, and cerebral injuries [10] (Figure 1).

Clinically, the significance of neuroinflammation is profound. Aberrant inflammatory activation is now recognized as a key contributor to the onset and progression of numerous neurological disorders. It is reported that there are around 600 known brain diseases, and all of them are correlated to neuroinflammation affecting key functions of humans—thought, speech, emotion, and movement [11]. Around 15% of the world’s population is affected by neurological disorders, which mainly include Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, traumatic brain injury (TBI), encephalitis, stroke, and spinal cord injury (SCI) [12,13]. The context and duration of the inflammatory stimulus determine whether the response is adaptive or pathological, shaping disease severity and influencing therapeutic outcomes. Consequently, a deeper understanding of CNS-specific inflammatory dynamics has become critical for developing targeted interventions that modulate neuroinflammation without disrupting essential neural functions. Several strategies have been reported for treating neuroinflammation. The conventional therapeutic strategies have shown clinical utility, yet their effectiveness remains limited by poor BBB penetration, off-target effects, an insufficient modulation of complex immune cascades due to low therapeutic concentrations, and a short half-life and stability [14]. In this context, nanotechnology has emerged as a promising platform to enhance the targeted delivery of anti-inflammatory drugs and immunomodulatory agents within the CNS [15]. Beyond attenuating inflammatory damage, nanomaterial-based systems such as biomimetic hydrogel scaffolds also provide structural and biochemical cues that support tissue repair and regeneration [16].

This review focuses on neuroinflammation as a central and unifying driver of neurological disorders, highlighting its dual role in both repair and disease progression. It critically discusses conventional therapeutic strategies, their limitations, and the emerging challenges that hinder durable clinical outcomes. The review provides a comprehensive overview of nanomaterial-based interventions for targeting neuroinflammation, spanning lipid-based, polymeric and inorganic nanocarriers, alongside nanobiotechnology-enabled approaches for neural tissue engineering and regeneration. Special emphasis is placed on advanced immunomodulatory and conductive scaffolds, as well as exosome- and stem cell-integrated nanoplatforms that enhance neurogenesis and functional recovery. Furthermore, pharmacokinetics, biodistribution, and the physicochemical properties of nanocarriers are discussed, while addressing regulatory considerations and translational bottlenecks. By integrating therapeutic design, biological response, and clinical feasibility, this review offers a forward-looking framework to guide the development of next-generation neurotherapeutics and accelerate their path toward reproducible and impactful clinical translation.

2. Dual Nature of Neuroinflammation

Though active microglia and the production of cytokines/chemokines are considered as markers of neuroinflammation, which is often linked to pathological conditions, the effects of neuroinflammation depend on intensity and duration, which decide the degree of neuroinflammation. Thus, it is known for its dual nature, promoting neuroprotection or neurodegeneration [17,18]. Acute inflammatory responses are observed to positively influence molecular cascades in the CNS, helping in immune conditioning, brain development and plasticity and the promotion of tissue repair [5]. Such responses are tightly regulated, and are considered beneficial and adaptative to the host by critically regulating neuroimmune communication, signal propagation, and behavioral output. For instance, active microglia provide support, synaptic pruning and immunological activities within the CNS [19]. IL-1 signaling is important in the repopulation of depleted microglia from a local progenitor source [20]. Furthermore, enhanced neuroinflammatory signaling between T-cells and resident CNS cells is implicated in normal memory and learning [21]. In some cases, transient neuroinflammation is triggered as a part of the coordinated CNS interpretation of peripheral infection. Such conditions are not associated with a significant infiltration of adaptive immune cells into the brain, BBB breakdown, or cell death, and are beneficial for the host [5,22].

On other hand, in chronic neuroinflammation due to severe CNS infection, trauma, stoke or neurodegenerative diseases are observed, with the activation of CNS glia, significant cytokine and chemokine production, the infiltration of peripheral immune cells, edema, increased BBB permeability, and breakdown. This causes primary and secondary damage and can also have long-term neuroinflammatory components that may never resolve. For instance, in autoimmune diseases such as multiple sclerosis, the demyelination of axons occurs, which turns chronic over time, leading to the loss of axons [23,24]. Alzheimer’s disease is another neuropathological condition which shows chronic, progressive, and increasing neuronal damage and death over time [25]. Parkinson’s disease also has shown inflammatory processes that worsen dopaminergic neuronal loss in the substantia nigra, with enhanced cytokine levels and oxidative stress [26].

3. Current Therapeutic Strategies and Challenges

Therapeutic strategies that target neuroinflammation have become a critical focus in addressing diverse neurological disorders such as Alzheimer’s disease, Parkinson’s disease, epilepsy and multiple sclerosis [27,28]. Conventional drug therapies and surgical interventions primarily aim to alleviate symptoms and provide palliative relief, rather than restoring or reversing the underlying disease [29]. Current treatment strategies are centered on reducing inflammatory signaling, protecting neural cells, and re-establishing immune homeostasis within the CNS. These approaches encompass a broad range of categories, including conventional non-steroidal anti-inflammatory drugs (NSAIDs), monoclonal antibodies (mAbs), antioxidant-based treatments, and emerging cell-based therapies designed to regulate immune activity and support neural recovery (Figure 2) [18,30,31,32].

NSAIDs are well known for lowering excessive immune activation mainly by cyclooxygenase (COX) enzyme-dependent (inhibition of prostaglandins) and COX-independent (by NF-κB activation and nuclear translocation) mechanisms. These drugs aim to reduce the release of pro-inflammatory cytokines, inhibit COX pathways, and stabilize activated microglia and astrocytes [33]. However, long-term NSAID use is constrained by significant safety concerns, including gastrointestinal complications from COX-1 inhibition, renal dysfunction due to disrupted prostaglandin signaling, and elevated cardiovascular risks, especially with COX-2-selective agents [34,35]. Corticosteroids such as dexamethasone and methylprednisolone also have been used for treating neuroinflammation and act by activating glucocorticoid receptors, which then translocate into the nucleus and regulate gene expression to suppress pro-inflammatory cytokines (e.g., IL-1β, TNF-α, and IL-6) and enhance the expression of anti-inflammatory genes (e.g., IL-10). These actions reduce cytokine production, limit immune-cell recruitment to inflamed tissues, stabilize the BBB, and promote the apoptosis of overactivated immune cells. However, their clinical use is limited by significant side effects including immunosuppression, metabolic alterations, neuropsychiatric issues and osteoporosis when used long term [18].

Beyond conventional anti-inflammatory drugs, monoclonal antibodies (mAb) such as natalizumab, infliximab, and adalimumab have garnered great attention in the treatment of neuroinflammation due to their high specificity in molecular targeting [18]. Natalizumab is an anti-α4 integrin mAb which prevents the adhesion and subsequent transmigration of leukocytes across the BBB, inhibiting the infiltration of immune cells in the CNS, which triggers demyelination and neurodegeneration, as observed in multiple sclerosis [36]. Infliximab and adalimumab are anti-TNF-α antibodies which neutralize both soluble and membrane-bound TNF-α, preventing the activation of TNF receptors, thereby inhibiting the induction of inflammatory responses, oxidative stress, and neuronal damage. Similarly, mAbs-targeting cytokines such as IL-1β (Canakinumab), receptors such as IL-6R (Tocilizumab), Aβ plaques in Alzheimer’s disease (aducanumab), and complement protein C5 (Eculizumab) have shown promising results for mitigating neuroinflammatory responses and are under clinical trials. However, their delivery across the BBB and immunosuppression, which may render the patient susceptible to infection, are some of the challenges [18].

Emerging microglial modulators offer new therapeutic avenues by aiming to correct dysfunctional microglial activity and reducing the damage caused by chronic activation. The colony-stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 is one such modulator which can deplete or reprogram microglia by blocking survival and proliferation signals, shifting them toward a more quiescent or neuroprotective phenotype [37]. This modulation lowers pro-inflammatory cytokine and ROS production, thereby helping to curb sustained microglia-driven neuroinflammation [38]. Additionally, antioxidant-based therapies, such as quercetin, curcumin derivative, epigallocatechin gallate (EGCG), astaxanthin, or resveratrol, have been reported to mitigate oxidative stress in neuroinflammatory conditions [39].

However, though these strategies provide symptomatic relief or delayed disease progression in certain CNS disorders, their overall efficacy often remains limited due to the complex, dynamic nature of the brain microenvironment and neuroinflammatory signaling. One of the major challenges is the selective permeability of the BBB, which prevents most small molecules, peptides, and biologics from reaching therapeutic concentrations within the CNS [40]. It is reported that around 95% of evaluated pharmaceuticals fail to penetrate the BBB, and the drugs that successfully penetrate it often exhibit short half-lives, leading to transient effects and necessitating repeated dosing [32]. Many systemic anti-inflammatory agents lack the specificity required to modulate CNS-resident immune cells without affecting peripheral immunity, resulting in adverse off-target effects or immune suppression. Furthermore, most current therapeutics are unable to provide sustained or context-dependent immunomodulation, an essential requirement given that neuroinflammation fluctuates across acute, chronic, and degenerative stages of disease. The heterogeneity of neuroinflammatory mechanisms across different pathological conditions also poses a major barrier. Furthermore, in the case of chronic conditions, prolonged systemic treatment increases the risk of toxicity, metabolic burden, and patient non-compliance. Due to these issues, many neurological disorders do not have a single approved drug for treatment (Figure 3).

Collectively, these challenges highlight the need for next-generation therapeutic platforms capable of crossing the BBB, achieving precise targeting, and delivering a long-lasting, multimodal regulation of neuroinflammatory responses. This emphasizes the need for advanced nanobiotechnology-based interventions, which have emerged as a transformative platform capable of addressing many of the shortcomings associated with traditional therapeutics, advancing the fields of drug delivery, tissue engineering and regenerative medicines, bioimaging and biosensing. In the next sections, we will be focusing on nanobiotechnology-based approaches for targeting neuroinflammation and neural regeneration.

4. Nanobiotechnology-Based Therapeutics for Targeting Neuroinflammation

Nanobiotechnology has emerged as a powerful approach for addressing neuroinflammation by enhancing drug delivery, improving BBB penetration, and providing intrinsic antioxidant or immunomodulatory effects. Nanomaterials such as nanoparticles (NPs) can overcome the major limitations of conventional therapeutics, such as poor solubility, instability, rapid degradation, and off-target toxicity, thereby improving treatment efficacy for chronic neuroinflammatory conditions. Although NPs are traditionally defined as 1–100 nm in size, many composite or drug-loaded systems exceed this range while still retaining nanoscale behavior and functionality [41]. NPs designed for drug delivery are mainly transported through active or passive mode. Structurally, these NPs are composed of two functional components (core and shell) mainly delivered via passive transport: One component enables drug encapsulation, protects the payload from enzymatic degradation, facilitates brain targeting and BBB penetration, and allows pH-responsive release, while the second component forms the nanoengineered core structure [42]. Nanomaterials are categorized as organic and inorganic, and their physicochemical properties, particularly their size, strongly influence biodistribution, cellular uptake, degradation, and therapeutic release kinetics. Smaller particles tend to aggregate more readily and exhibit faster drug release due to their large surface-to-volume ratio, whereas larger particles often degrade more slowly and support a prolonged release profile [42,43]. Understanding these design parameters is essential for engineering effective nanocarriers capable of navigating the complex CNS environment. Given the importance of CNS access for therapeutic success, Figure 4 summarizes key targeting strategies and delivery routes designed to facilitate NP entry into the brain, which mainly include passive transport, cell-mediated transport and receptor-mediated transport [14]. A wide range of nanocarriers, including lipid-based, polymeric, and metallic/metal oxide nanoparticles, have been explored for mitigating neuroinflammation due to their biocompatibility, stability, and controlled drug release profiles, with emerging targeted strategies and immunomodulatory platform designs offering additional routes to enhance treatment efficiency, as discussed in the following sections.

4.1. Lipid-Based Nanoparticles

Lipid nanocarriers, including liposomes, solid lipid nanoparticles (SLNs), nanostructured lipid carriers (NLCs) and exosomes, have demonstrated significant promise for CNS drug delivery. However, their performance varies substantially depending on composition, surface chemistry, and disease [44]. Liposomes consist of lipid bilayers surrounding an aqueous core and can encapsulate both hydrophilic and hydrophobic agents. Their tunable size (25 nm to several micrometers) and membrane-mimicking structure enhance biocompatibility, drug entrapment efficiency, and stability. Formulation modifications, such as incorporating stearic acid into the bilayer, further improve particle stability and sustain drug release [45]. Nevertheless, liposomes often suffer from rapid clearance, limited brain specificity, and batch-to-batch variability, which continue to constrain their translational robustness [46].

Several studies report successful BBB traversal and therapeutically relevant CNS drug concentrations at target sites using liposomes, yet these outcomes are frequently model-dependent and not always reproducible across various diseases. Liposomes are promising carriers for CNS drug delivery due to their ability to traverse the BBB and deliver therapeutically relevant drug concentrations to target sites. For instance, a novel liposome-based formulation was developed for the delivery of levodopa, which contains natural antioxidants such as L-ascorbic acid and quercetin, preventing the drug from oxidation and enhancing its stability [47]. Moreover, the surface modification of liposomes with molecules such as poly(ethylene glycol) (PEG) has been shown to prolong circulation during BBB transit. In addition, transferrin-based targeting enhances BBB crossing, while the incorporation of glucose–vitamin C complexes improve liposomal accumulation at the intended site [48]. Liposome-based systems have been clinically used in CNS therapies for a long time and include formulations such as DepoCyt^® for lymphomatous meningitis, Doxil^® (Caelyx^®) for glioblastoma multiforme and DaunoXome^® for pediatric brain tumor treatment [49]. However, most liposomal anticancer formulations primarily exploit disrupted BBB regions rather than achieving uniform parenchymal delivery, highlighting a persistent limitation for diffuse neurodegenerative disorders [50].

SLNs, composed of a solid lipid core stabilized by surfactants, offer a high stability and reduced drug leakage [51]. They provide advantages such as controlled drug release, high biocompatibility, and protection of the drug from degradation. For enhancing their specificity, SLNs can be functionalized by targeting ligands [52]. Due to these properties, SLNs are reported for several CNS disorders such as Parkinson’s disease, Huntington’s disease, Alzheimer’s disease, multiple sclerosis, ischemic stroke, epilepsy, brain tumors and cancer [53]. However, drug expulsion during lipid crystallization and the limited loading of hydrophilic molecules remain key drawbacks. For example, quercetin-loaded SLNs improved memory retention in Alzheimer’s disease rat models compared to free quercetin, yet long-term safety and efficacy data remain scarce [54]. NLCs, which incorporate a small proportion of liquid lipids into the solid matrix, provide an even greater drug-loading capacity and long-term physicochemical stability compared with SLNs [51,55]. Despite these advantages, some synthetic lipid NPs may trigger immune activation or oxidative stress in neural tissue [56]. This has increased interest in biomimetic lipid vesicles, such as exosomes, which naturally facilitate intercellular communication and possess outstanding biocompatibility, low immunogenicity, and an inherent ability to cross the BBB [57].

Exosomes (50–150 nm) are secreted by many cell types and play dual roles in neurodegeneration: they can propagate inflammatory signals and pathological protein aggregates, but they also serve as promising therapeutic vectors [58]. Stem cell-derived exosomes, particularly those conditioned by inflammatory or hypoxic stimuli, have shown enhanced regenerative and anti-inflammatory effects in preclinical models of Alzheimer’s disease and other neurodegenerative disorders [59,60]. The combined delivery of berberine and palmatine using transferrin-depleted extracellular vesicles has been shown to efficiently eliminate Aβ aggregates, modulate neuroinflammation, and markedly enhance learning and memory in Alzheimer’s disease mouse models [61]. Likewise, silibinin-loaded macrophage-derived exosomes demonstrated improved brain targeting, reduced Aβ deposition, and inhibited astrocyte activation, collectively leading to improved cognitive performance in Alzheimer’s disease [62].

4.2. Polymeric Nanocarriers

Polymeric nanocarriers include nanocapsules, nanospheres, nanogels, micelles and dendrimers. These are typically fabricated from natural polymers (e.g., peptides, polysaccharides) or synthetic materials such as poly(lactic-co-glycolic acid) (PLGA), PEG and poly(amidoamine) (PAMAM) [63]. Their properties depend on their polymer chemistry and formulations, and they offer a high drug-loading capacity, excellent stability, controlled release, and biodegradability. Their surfaces can be readily functionalized to enhance targeting specificity, cellular uptake, and BBB penetration [64,65]. For instance, PEGylation prolongs systemic circulation and reduces immune clearance, while polymers like chitosan provide mucoadhesive properties suitable for intranasal CNS delivery; however, the targeting efficiency and BBB penetration remain model-dependent [66]. In another study, Rabies Virus Glycoprotein (RVG29)-conjugated polymeric NPs were developed to deliver miR-124 for targeting neuroinflammation in Parkinson’s disease, demonstrating a low toxicity and effective brain targeting. miR-124 delivery suppressed pro-inflammatory signaling (MEKK3/NF-κB), reduced apoptosis, and enhanced neuroprotective responses in cellular and animal models, but their long-term safety and translational scalability remain to be established [67]. Responsive polymeric NPs offer a versatile strategy for neuroinflammation therapy by enabling targeted, stimuli-controlled drug release in response to pH, redox state, or external triggers such as light. These systems can cross the BBB and modulate key inflammatory pathways, reducing oxidative stress and pro-inflammatory cytokine signaling while enhancing neuroprotection. For example, near-infrared photothermal responsive conjugated polymer NPs were engineered to cross the BBB and mitigate amyloid-β (Aβ) protein-induced neuroinflammation. By reducing Aβ aggregation, suppressing ROS generation, and inhibiting TRPM2-mediated Ca²⁺ influx, the system effectively lowered oxidative stress and pro-inflammatory cytokine levels, with potential concerns regarding tissue heating and penetration depth [68]. These biomimetic systems combine biocompatibility with advanced targeting capabilities, offering a next generation platform for regulating neuroinflammation and promoting neural repair. Despite their advantages, polymeric NPs face certain challenges such as potential toxicity from degradation by-products, uncontrolled or incomplete drug release in vivo, batch-to-batch variability, and limited scalability. The repeated administration of these NPs may also trigger anti-polymer antibodies, such as those against PEG, causing accelerated blood clearance and reduced circulation time affecting therapeutic efficiency [69].

4.3. Metallic and Metal Oxide NPs

Metallic and metal oxide NPs possess distinct physicochemical properties, such as a high surface area, tunable reactivity, and optical responsiveness, which allow them to function both as drug carriers and as intrinsic therapeutic agents [70]. These materials are capable of delivering small molecules, nucleic acids, and proteins, while also modulating oxidative stress and inflammatory signaling [71].

Gold, silver, iron, silicon oxide, cerium oxide, and zinc oxide NPs are among the most widely studied inorganic systems [72,73]. Gold NPs provide a chemically adaptable platform for delivering therapeutic molecules while exerting antioxidative and anti-inflammatory effects by modulating various pathways. They can bind to amyloid-βand inhibit fibrillization, reducing peptide toxicity [74]. They act through pathways such as Nrf2 for antioxidant and NF-kB/MAPK for anti-inflammatory effects, which enhance neuroprotection [75]. In animal models, gold NPs have been shown to protect mitochondrial ATP production, lower oxidative stress, reduce neuroinflammation, and improve cognitive performance [76]. Despite these advantages, concerns regarding the long-term accumulation of gold NPs in the brain highlight the need for careful safety assessment.

Cerium oxide NPs exhibit regenerative redox cycling between Ce³⁺ and Ce⁴⁺ states, allowing the continuous scavenging of ROS. This antioxidant capability protects neurons from amyloid-induced injury and may slow neurodegenerative progression [77,78]. Zinc oxide NPs have also shown therapeutic promise by reducing plaque burden and inflammatory responses in mouse models of Alzheimer’s disease [79]. Biosynthesized zinc oxide NPs have been reported to inhibit enzymes associated with aging and amyloid pathology [80]. However, zinc oxide systems can induce cytotoxicity and off-target effects depending on their particle size, composition, and exposure duration [81]. These inorganic NPs demonstrate a significant potential for reducing oxidative stress, modulating inflammation, and promoting neuronal survival [81]. Yet their long-term biodistribution, degradation profiles, and potential neurotoxicity remain critical considerations for future development and clinical translation.

4.4. Targeted Delivery Strategies

Targeted delivery approaches are essential for improving NPs transport across the BBB and enhancing accumulation within inflamed neural regions. One widely used method involves ligand functionalization, where NPs are decorated with molecules such as transferrin, lactoferrin, apolipoprotein E, or antibodies that recognize receptors upregulated on brain endothelial cells during neuroinflammation. Endothelial activation leads to an increased expression of adhesion molecules such as ICAM-1 and VCAM-1, which can be exploited for selective targeting [82]. Liposomes conjugated with anti-ICAM-1 or anti-VCAM-1 antibodies demonstrate significantly improved cerebral uptake compared with traditional transferrin-based systems, although the extent of uptake and off-target deposition remain highly dependent on the inflammatory state and endothelial activation profile. Beyond endothelial targeting, cell-mediated delivery offers an alternative means of directing therapeutics to inflamed CNS sites. Circulating immune cells, including neutrophils, monocytes, and macrophages, can internalize drug-loaded NPs and deliver them to regions of active inflammation [83,84]. Neutrophil-carried NPs have been shown to penetrate injured brain tissue during acute inflammation, while monocyte-based carriers provide longer therapeutic windows, but with an increased variability in biodistribution [85].

In addition to molecular targeting, several non-invasive delivery routes have been developed to bypass or transiently modulate the BBB. Intranasal administration is a particularly promising approach, as drugs deposited onto the respiratory and olfactory epithelium can travel to the brain via either systemic absorption or direct nose-to-brain pathways [86,87]. This strategy is further enhanced when NPs are incorporated into composite hydrogels or lipid-based matrices that improve mucosal adhesion and promote transport along the olfactory route [88,89]. Hydrogels fabricated from natural and synthetic polymers can also serve as carriers for embedded NPs, improving retention and enabling controlled release during nasal administration [88,89]. Magnetic targeting allows external magnetic fields to guide magnetically responsive NPs to areas of injury or inflammation. The magnetic labeling of immune cells, using superparamagnetic iron oxide NPs, further enables guided delivery to specific CNS regions under external magnetic fields [90].

Ultrasound-assisted delivery, especially when combined with microbubbles, can temporarily increase BBB permeability in a spatially controlled manner, facilitating local NPs entry while minimizing widespread barrier disruption [91]. These strategies collectively improve the precision and efficiency of NP-based therapeutics for neuroinflammation.

Table 1. Recent nanoparticle platforms for targeted CNS delivery and modulation of neuroinflammation.

Sr. No.	Nanoparticle Type/Composition	Disease Model/System	Target Cell/Tissue	Mechanism/Key Findings	Therapeutic Outcome	Advantages	Limitations	Ref.
1	Anti-ICAM1/Anti-VCAM1 liposomes LNPs	Acute brain inflammation (mouse)	Activated endothelial cells	Ligand-mediated selective endothelial targeting	Reduced edema, BBB stabilization	Extremely high specificity	Vascular only targeting	[92]
2	Magnetic mPEG-PCL micelles	Healthy rat	Remote brain region	Magnetic field-guided delivery	Increased brain penetration	Noninvasive, Biocompatible polymer, tunable size	External magnet required	[93]
3	NSC-coated PLGA NPs	Stroke/TBI (mouse)	SDF-1 expressing cells	Stem cell-mediated homing	Neuroprotection	Biomimetic, no external trigger	Complex fabrication	[94]
4	Magnetite NPs	Epilepsy (mouse)	Inflamed hippocampus	Magnetic guidance to epileptogenic region	Higher brain accumulation	Very high selectivity	Altered liver and spleen accumulation	[95]
5	MWCNTs	Human iPSC-derived organoids	Neural cells	NF-κB pathway modulation	Neuroprotective	Human-relevant model	No targeting or therapy	[96]
6	ZnO NPs	PC12 cells, mouse	Neurons	Oxidative stress pathways	Dual effects; dose dependent	Demonstrated CNS access route	Strong neurotoxicity	[97]
7	Silica NPs	Microglia, neurons	Glial cells	ROS damage, pyroptosis	Toxicity study	Cell-type specificity	Not a delivery platform	[98]
8	Mn3O4 NPs	PC12 cells	Neurons	ROS modulation	Dose-dependent apoptosis	Mechanistic insight	Strong neurotoxicity	[99]
9	CeO2 NPs	Zebrafish/mice	Neurons/glia	Redox cycling antioxidant	Reduced inflammation	Highlights antioxidant–toxic duality	Non-mammalian model	[100]
10	Neutrophil-based microrobots (Ag NP)	Glioma	Tumor microenvironment	Magnetic navigation	Targeted tumor delivery	Particle size-effect	Reduced neuronal viability and function	[101]

summarizes key nanoparticle platforms that demonstrate advanced targeting capabilities for CNS delivery, including ligand-mediated strategies, immune cell-assisted transport, magnetic guidance, and biomimetic coating approaches.

Collectively, ligand-mediated targeting, immune cell-assisted transport, intranasal pathways, and magnetically or ultrasonically guided systems represent complementary strategies that significantly improve NP delivery efficiency and therapeutic precision for neuroinflammation.

4.5. Immunomodulatory Nanoplatforms

The modulation of immune response is a central objective in treating neuroinflammatory disorders, and nanotechnology offers innovative tools to regulate immune signaling within the CNS. Microglia, the primary immune cells of the brain, can adopt a pro-inflammatory M1 phenotype or a pro-regenerative M2 phenotype [102]. Several NP platforms have been engineered to influence this polarization process and shift microglia toward a neuroprotective state by delivering anti-inflammatory agents, small interfering RNA, cytokines, or pathway-specific modulators that suppress M1-associated signaling and promote M2-associated gene expression [103]

In addition to immune modulation controlled by NPs, novel approaches focus on immunomodulatory scaffolds that blend an active regulation of the neuroinflammatory microenvironment with structural support [104]. After CNS damage, glial scar formation and the deposition of inhibitory ECM components are promoted by the activation of microglia and astrocytes, which generally restricts axonal regeneration [105]. In particular, the biophysical features of the scaffold, specifically its stiffness, impact the immune cells’ behavior. Biomaterials tailored to match the brain stiffness (~0.1–1 kPa) can minimize reactive gliosis, M1 microglial polarization and pro-inflammatory signaling via mechanotransduction pathways [106]. For instance, a study reported that a stiffness-varied alginate anisotropic capillary hydrogel scaffold implanted into the spinal cord of an adult rat demonstrated yes-associated protein (YAP) nuclear translocation [106]. Therefore, mechanically tuned nanoscaffolds can bridge the gap between tissue repair and immunoregulation by fostering a pro-regenerative environment.

An emerging dimension of this field lies in the integration of nanotechnology with neurobiology to support both immune regulation and structural repair. Recent studies highlight the synergistic working of bioscaffolds and bioactive small molecules to address the complex pathology of neurotrauma [107,108]. These studies illustrate two foundational strategies guiding the next generation of neurotherapies, which are biomaterial scaffolds that remodel the injury site and promote regeneration and small molecule agents that attenuate neuroinflammation. The role of nanotechnology in neural tissue engineering and regeneration is explained in detail in next section.

5. Nanobiotechnology for Neural Tissue Engineering and Regeneration

Neural tissue damage resulting from acute injury, neurodegenerative disorders, ischemia, or inflammation often leads to irreversible functional losses due to the inherently limited regenerative capacity of the CNS [109]. In contrast to peripheral tissues, neurons demonstrate a limited intrinsic proliferative capacity, and the post-injury microenvironment becomes exceedingly restrictive, marked by an altered ECM structure, the release of inflammatory cytokines, oxidative stress, and diminished bioelectrical connectivity [109,110]. These barriers inhibit axonal sprouting, synaptic reconnection, and neuronal survival, particularly after CNS injury, rendering traditional therapeutic techniques ineffective [111]. The major challenge in treating these conditions is the absence of a structural support that permits the repopulation of cells and repairs the damage [112,113].

Nanobiotechnology has emerged as a novel method for neural tissue engineering, combining different nanomaterials to create biomimetic scaffolds that mimic the native ECM microenvironment of tissues [114]. Neural tissue engineering focuses on approaches that minimize neural inflammation and fibrotic responses following the implantation of biomaterial scaffolds that support cellular growth and proliferation. Ideally, these scaffolds should closely replicate the native extracellular matrix to create a biomimetic milieu for neural development, while maintaining sufficient structural integrity and stability during surgical implantation [115,116]. Nanostructured scaffolds provide nanoscale architecture, biomimetic functionalities and biochemical cues mimicking in vivo-like features for supporting cell adhesion, proliferation, and guided neurite migration and extension [117,118]. The selection of material for scaffold development is a critical step, and the selected material should have desirable properties that support cellular growth, proliferation, and migration with minimal inflammatory responses. Generally, these scaffolds are composed of natural polymers (e.g., silk fibroin, collagen and chitosan), synthetic polymers (e.g., PCL, PLGA and PLLA) and hybrid composites that facilitate cellular adhesion, neurite extension and axonal regeneration [119]. In addition, conductive nanomaterials also introduce an electrical signal which potentially directs stem cells into functional neuronal networks [120]. Advanced fabrication techniques such as electrospinning, 3D bioprinting and self-assembly are then employed to develop nanofibrous and hydrogel-based scaffolds for neural tissue engineering and regeneration [121]. In this section, we discuss the role of ECM and different types of ECM-mimicking nanostructured scaffolds explored for regulating neural regeneration.

5.1. Role of ECM in Neural Cell Behavior

ECM is an acellular, three-dimensional scaffold which accounts for about 20% of the brain and spinal cord. It is composed of two main types of biomolecules: proteoglycans (hyaluronic acid, heparan sulfate, chondroitin sulfate and keratan sulfate) and proteins (collagens, laminin, elastin, and fibronectin). One of the main components of the ECM is collagen, which is found in the ECM as fibrillar proteins that offer resident cells structural support. From cell adhesion and survival to cell differentiation and the production of paracrine signals, it controls several cell-signaling systems [122]. Laminin and fibronectin are multifunctional adhesion ligands which play a key role in the guidance, regulation and mediation of cell functions [123]. In comparison to the other connective tissues, the brain ECM contains less fibrous proteins like collagen or fibronectin and a larger amount of glycosaminoglycans (GAGs) like hyaluronan, which are present either coupled to protein or in free form [124]. Overall, in the neural system, neuronal behavior is predominantly regulated by the ECM, which aids in contact guidance and also plays an important role in neural development and regeneration processes such as neocortex folding, peripheral nerve regeneration, cell migration, axonal growth and many more [125]. The following sections therefore focus on ECM-mimicking nanoscaffolds for promoting neural repair and regeneration.

5.2. ECM-Mimicking Nanostructured Scaffolds

ECM-mimicking nanoscaffolds play a role in neural tissue engineering as they replicate the native architecture, biochemical signals, mechanical softness, and conductive properties of the neural ECM. This allows cell adhesion, neurite extension, synaptic connectivity, and functional neural regeneration where the native ECM is damaged [126]. The ECM-mimicking properties of engineered nanostructured scaffolds can be broadly classified into four major functional categories: first, the structural features, including pore size, porosity and interconnectivity for guiding cell infiltration, nutrient exchange, and neurite extension [127]; second, the biophysical, biomechanical, and electroconductive properties, such as stiffness, viscoelasticity, topographical cues, and electrical conductivity, which are designed to mimic the native neural tissue [128]; third, these scaffolds incorporate mechanisms for the controlled release of biochemical signals such as adhesive ligands and growth factors that regulate cell adhesion, migration, differentiation, and survival [129]; finally, advanced ECM-mimicking nanostructured scaffolds integrate sensing and actuating capabilities, enabling dynamic feedback, stimulus responsiveness, and the real-time modulation of the cellular microenvironment to support neural regeneration [130]. In this section, we explore the different nanofibrous and hydrogel-based scaffolds replicating neural ECM for cell adhesion and neurite extension.

5.2.1. Hydrogel-Based Nanoscaffolds

Biomimetic hydrogels are three-dimensional (3D) network, mimicking structures of the ECM with entangled fibers on a comparable scale, offering neuronal cell development and physical supports [131]. These interconnected networks are made of polymer chains which possess mechanical properties, exhibit high cytocompatibility, mimic tissue water content, and promote cell migration and tissue integration through their porous structure. Additionally, their adaptability to temperature or pH variations increases their versatility [132,133]. 3D hydrogels can be classified as natural, synthetic and hybrid. Natural polymers include cellulose and its derivatives, sodium alginate, agarose, collagen, gelatin, chitosan and hyaluronic acid, while poly(methyl methacrylate) (PMMA)-, PEG- and poly(2-hydroxyethyl methacrylate) (poly(HEMA))-based polymers belong to synthetic polymers [134].

Though these polymers are biocompatible, their poor electrical conductivity restricts their use in applications that rely on electrical stimulation, such as neural tissue engineering. However, blending hydrogels with conducting materials such as polyaniline and polypyrrole improves their electrical conductivity, suitable for neural cell growth and regeneration [135].

5.2.2. Nanofibrous Scaffolds

Nanofibrous scaffolds are engineered fibrous structures fabricated using several techniques including electrospinning, phase separation, self-assembly, and template synthesis to duplicate the nanoscale fibrillar architecture of the native neural ECM [136]. As one of the most widely used techniques, electrospinning has garnered a lot of interest due to its advantages over alternative procedures [137]. In particular, template synthesis technology is a time-consuming method that lacks the production of continuous nanofibers, but it can effectively control the fiber diameter [138]. Phase separation technology is easy to use, affordable, and allows for the mass manufacturing of consecutive nanofibers. However, this technique is not suitable for all polymers due to several significant drawbacks, as it is time-consuming, structurally unstable, and has difficulty maintaining a uniform porosity [139].

On the other hand, electrospinning has several advantages, such as being simple to use, having a controllable scaffold structure and fiber diameter, and working with a variety of materials. Electrospun nanofibers embedded in scaffolds have a high surface area-to-volume ratio for cell adhesion, a porous structure for cell infiltration, and flexible mechanical properties to guide the mechanoresponses of the residing cells [128]. Electrospinning uses a wide range of polymers, classified into three types: natural, synthetic, and composite [140]. Natural polymers such as collagen, silk fibrin, chitosan and fibrinogen exhibit a strong biocompatibility and biodegradability. Synthetic polymers including polycaprolactone, PLA, PGLA, polypyrrole (PPy), and PLLA have a greater mechanical strength than natural materials, and their properties are tuneable for repeatable outcomes. In order to improve natural cell affinity and enhance guidance for nerve regeneration, synthetic and naturally derived materials are frequently combined to form composites [141,142]. Although such nanofibrous scaffolds provide an excellent biomimetic framework for neural tissue engineering, integrating conductive components can significantly improve their ability to support neural signaling and regeneration.

A comparative summary of natural and synthetic hydrogel scaffolds and nanofibrous scaffolds, including their polymer composition, structural functions, and neural regenerative applications, is presented in

Table 2. Comparative summary of ECM-mimetic polymer scaffolds for neural applications.

Sr. No.	Polymer	Scaffold	Neural Application	Advantage	Limitations	Relative Performance	Reference
1	Chitosan	Hydrogel	Cortical neurons, DRGs, and NSCs in neural tissue engineering	Biocompatible; supports 3D neural growth; injectable	Limited mechanical strength; rapid degradation without modification	Comparable neurite support to HA-based gels but inferior mechanical stability	[143]
2	Chitosan–alginate	Hydrogel	Olfactory ensheathing cells and NSC proliferation	Injectable; enhanced cell adhesion vs pure chitosan	Weaker axonal guidance cues; limited long-term stability	Improved cell adhesion over pure chitosan; lower guidance efficiency compared to aligned nanofibers	[144]
3	Chitosan	Hydrogel	PC12 neuronal-like cell growth for CNS lesions	Minimally invasive delivery; fills irregular CNS lesions	Lacks directional guidance; modest neurite extension	Suitable for detect filling but falls short of nanofibrous scaffolds for oriented regeneration	[145]
4	Fibrin	Hydrogel	SCI repair in canine model	Excellent biocompatibility; supports axonal guidance	Rapid degradation; weak mechanical durability	Superior to polysaccharide gels for axonal guidance but inferior long-term stability	[146]
5	Hyaluronic acid	Hydrogel	Post-traumatic brain tissue reconstruction	High cytocompatibility	Poor mechanical strength	Outperforms synthetic polymers in neural compatibility but structurally weaker	[147]
6	Alginate–gelatin	Hydrogel	Hematopoietic stem cell neurogenesis	Bioactive signaling; immunomodulatory	Limited alignment control; less suitable for long axonal repair	Better biochemical signaling than inert hydrogels but weaker guidance than nanofibers	[146]
7	Elastin-Like Polypeptide (ELP)	Hydrogel	CNS and PNS injury repair as injectable scaffolds and drug depots	Injectable; customizable bioactivity; drug depot capability	Costly synthesis; limited clinical translation	Superior tunability compared to natural polymers but less established in vivo	[148]
8	Poly-L-lactide (PLLA)	Nanofibers	Peripheral nerve regeneration; enhances Schwann cell proliferation and PC12 neurite outgrowth along fiber direction vs bare PLLA nanofibers	Strong directional guidance; sustained biochemical cues	Hydrophobicity without surface modification	Outperforms hydrogels in neurite alignment and guidance efficiency	[149]
9	PLLA/PCL blends	Nanofibers	Peripheral nerve injury and SCI; promote neurite extension, NSC proliferation, and improved functional recovery in sciatic nerve defect models	Balanced stiffness and degradation; immunomodulation	Complex fabrication	Superior functional recovery compared to single-polymer nanofibers	[150]
10	PCL	Nanofibers	Human neural progenitors and NSCs in vitro; aligned PCL nanofibers increase fraction of TUJ1+ neurons and direct neurite orientation along fiber axis	Strong mechanical strength; excellent topographical cues	Slow degradation; hydrophobic	Better neuronal alignment than hydrogels but inferior bioactivity without modification	[151]
11	Gelatin	Nanofibers	Peripheral nerve regeneration in rodent models; conduit promotes axon regeneration and functional recovery better than unmodified amniotic membrane in surgical nerve gap repair	Bioactive; improved mechanics vs native membrane	Rapid degradation if not crosslinked	Improved regeneration over native ECM but less durable than synthetic fibers	[152]
12	Hyaluronan–gelatin	Nanofibers	Peripheral nerve repair; supports Schwann cell viability and promotes neurite outgrowth; proposed as nerve guidance material for injured peripheral nerves	ECM-like chemistry with nanofiber guidance	Moderate mechanical strength	Combines biochemical advantages of hydrogels with partial fiber alignment benefits	[153]

.

5.2.3. Conductive Scaffolds

Conductive scaffolds act as nerve guidance conduits that promote neuronal growth, migration, differentiation and axonal regeneration through electrical stimulation, which results in neural repair, as shown in the schematic in Figure 5A. The US Food and Drug Administration (FDA) has approved electrical stimulation-based treatments for Parkinson’s disease, obsessive–compulsive disorder, stroke and depression [113,154]. Its main design approach is to encourage regeneration by mimicking the electrophysiological milieu of nerve tissue and working in tandem with bioelectrical signal regulation and physical guiding [155]. Conductive scaffolds bridge the gap between nanoscale topography, softness, and anisotropy with electrical functionality. Some of the conductive materials include polymers such as polyaniline (PANI), polypyrrole, and nanomaterials such as graphene-based structures, carbon nanotubes (CNTs), and metal-based nanostructures such as gold, silver and iron NPs, which are widely explored owing to their good electrical conductivity, chemical stability and easy functionalization [156]. As shown in Figure 5B, PC12 cells and bone marrow-derived mesenchymal stem cells (BMSCs) seeded on the surface of PCL/PLLA/SWNT nanofibrous scaffolds exhibited cell adhesion, and their morphology changed from circular to elongated spindle-shaped [157]. However, several studies have reported the potential toxicity of these nanomaterials, linking their exposure to adverse effects such as cell cycle interference, inflammation, fibrotic responses, oxidative stress and DNA damage [158,159]. Some of the types of conductive scaffolds are discussed below in detail.

i.

Conductive polymer-based scaffolds

Conductive polymers such as polythiophene poly(3,4-ethylenedioxythiophene) (PEDOT), PPy, and PANI are widely employed in neural repair scaffolds owing to their favorable electrical properties and compatibility with biological systems [160]. These polymers contain π-conjugated systems that enable charge transport through delocalized electrons, creating continuous electrical pathways. As a result, they can efficiently deliver electrical, electrochemical, and electromechanical cues directly to cells [161]. However, their relatively poor mechanical properties limit their usability and medical translation, which emphasizes the need for blending natural and synthetic polymers [162]. Electroconductive scaffolds composed of PANI/polyacrylonitrile (PANI/PAN) and functionalized with carboxymethyl chitosan (CMC) have been developed for nerve tissue regeneration. These scaffolds supported hADMSC adhesion and proliferation, with enhanced MAP2 expression at both mRNA and protein levels and indicated a synergistic neurogenic effect arising from CMC functionalization and electrical cues [163]. In another study, cellulose hydrogels with micro/nanostructured PANI were synthesized through the interfacial polymerization method and showed enhanced biocompatibility and mechanical properties and superior sciatic nerve regeneration for adult SD rats without any extra treatment [164].

ii.

Graphene-based scaffolds

Graphene-based nanomaterials are composed of sp²-hybridized carbon atoms organized in a two-dimensional honeycomb lattice. Graphene oxide (GO), an oxidized derivative of graphene, consists of functional groups such as epoxide, hydroxyl, and carboxylic acid on its single layer plane [165]. These groups actively adsorb peptides, proteins, and DNA through chemical bonding or physical adsorption. Owing to their high surface area, robust mechanical strength, and superior electron transport properties, they are widely used in nerve regeneration [166]. Several studies have reported that GO-based scaffolds support synapse formation, stimulate neurite outgrowth, and promote the formation of large neural networks [167]. For instance, a GO-modified nanofiber scaffold significantly promoted Schwann cell (SC) migration, proliferation and myelination and promoted PC12 cell differentiation. It also repaired a 10 mm sciatic nerve defect, exhibiting a healing capacity to autograft [168]. Similarly, a graphene-based conductive fibrous scaffold exhibited an electrical conductivity of 3.12 S/m, which upregulated the secretion of neurotrophic factors and accelerated the recovery of an injured peripheral nerve [169]. Another study reported that 3D conductive scaffolds printed from PLCL microfibers and coated with rGO layers achieved a high conductivity of 0.95 S/cm and promoted neuronal network formation under 100–150 mV/cm electrical simulation for nerve regeneration [170]. However, concerns remain regarding the biocompatibility ofgraphene-based materials, as an excessive exposure to these materials has been associated with oxidative stress, DNA damage, physical destruction, necrosis and organ damage [171].

iii.

Carbon nanotube-based scaffolds

CNTs are hollow, cylindrical nanostructures made of rolled graphene sheets, with unique properties including good mechanical properties, strong electrical conductivity, and customizable nanotopography [172]. Using CNTs in conjunction with suitable materials and electrical stimulation could be a potential way to promote axon growth and neural regeneration [172]. For example, a CNT/sericin conduit combined with 1h electrical stimulation (3 V, 0.1 ms, 20 Hz) promoted the structural repair and recovery of a 10 mm rat sciatic nerve defect [173]. In another study, a single-walled carbon nanotube (SWCNT) combined with silk fibroin and an electrospun fibronectin nanofiber (SF/SWCNT/FN) conduit supported U373 cell adhesion and growth in vitro. Both SF/SWCNT and SF/SWCNT/FN NGCs stimulated myelinated axon development and enhanced nerve conduction velocities when inserted into 10 mm sciatic nerve gaps in a rat model, exhibiting functional nerve regeneration after five weeks [174]. Similarly, multi-walled carbon nanotube (MWCNT)-reinforced PCL–collagen-based neural scaffolds exposed to electrical stimulation (100 mV/cm for 20 min, 2 times/day) increased the expression of the neuronal differentiation markers MAP2 and β-tubulin in cells [175].

iv.

Wireless stimulation

In addition to traditional wired electrical simulation, wireless stimulation technologies are rapidly being integrated into conductive scaffold designs to provide non-invasive, controlled electrical cues that aid in neuronal healing, including axonal growth and improved nerve recovery [176]. These technologies use magnetoelectric or piezoelectric effects, which allow localized electrical currents to be induced within the scaffold without the need for power supplies or implanted wires by external magnetic fields, ultrasound, or other triggers [177]. For instance, capacitive coupling-responsive conductive hydrogel under external wireless in situ electrical simulations promoted functional repair by enhancing remyelination, accelerated axonal regeneration, aided the differentiation of endogenous NSCs, and activated calcium downstream signaling pathways [178]. Similarly, a hybrid neural ECM-mimicking hyaluronan/collagen hydrogel loaded with core/shell-structured Fe₃O₄@BaTiO₃ NPs was developed to recapitulate magnetoelectricity that remotely controlled and enhanced the expression of PC12 cells and elongated axons for SCI repair [179]. In another study, a novel theoretical approach was reported that used wireless-charging sustained oxygen release from conductive microgels (SOCO) to promote the angiogenic (Il1a, Lgals3) and GABAergic pathways by modulating GAD65/67 activity for brain recovery in TBI [180]. Such wireless stimulation technologies reduce the risks associated with conventional wired systems such as infections and surgical complexity. For clinical translation, major challenges remain in maximizing field penetration, limiting heat effects and ensuring long-term biocompatibility.

5.2.4. Other Metal-Based Nanostructures

Several metal-based conductive nanomaterials are being explored for neural regeneration. It is reported that metals such as platinum, silver, copper, gold and magnesium provide guided axonal growth or mechanically induced electrical cues for tailored neural repair [156,181]. For instance, micro/nano-channeled PCL/PLGA film scaffolds decorated by gold NPs significantly promoted PC12 differentiation and elongation on the films [182]. Glial cell line-derived neurotrophic factor (GDNF)–gelatin methacryloyl (Gel)/hydroxylapatite (HA)–Mg (GDNF-Gel/HA-Mg) enhanced SC maturity and dedifferentiation and regulated the PPAR-γ/RhoA/ROCK pathway in peripheral nerve repair [183]. Furthermore, electrospun PHA graphene-decorated (RGO/Au) hybrids were fabricated, which had an enhanced electrical conductivity and nanoscale fiber architecture conducive to neural interface formation. In vitro studies revealed that this electroactive scaffold dramatically increased Schwann cell proliferation and directional migration, emphasizing its applicability for peripheral nerve regeneration applications [184]. However, the literature has reported that metal ions such as Ag and Cu can be neurotoxic at high concentrations; however, when used at controlled low doses, they remain cytocompatible with effective antibacterial activity [185,186].

Table 3. Conductive scaffolds used in neural regeneration and tissue engineering.

Sr. No.	Polymer	Conducting Material	Major Findings	Advantages	Limitations	Relative Performance	Reference
1	Chitosan/gelatin	PANI/graphene (PAG) nanocomposite	Porous scaffold with 2.5% PAG showed higher adhesion and proliferation of Schwann cells	Enhanced conductivity and mechanical strength; improved Schwann cell adhesion	Reduced porosity, swelling and biodegradability at higher PAG	Good for PNS repair	[187]
2	ECM components (collagen, hyaluronic acid, and laminin)	PEDOT:PSS	The scaffold showed enhanced cell survival, proliferation and promoted neuronal differentiation in situ in SHSY5Y cells	Biomimetic; promotes neuronal survival and differentiation	Mechanical tuning needed; long-term stability and potential leaching of PEDOT:PSS	Excellent bioactivity	[188]
3	Alginate	MWCNTs and graphene flakes	Enhanced growth, proliferation, and differentiation of MSCs and NPCs were observed; viscolelastic scaffolds produced dense neurite network	Formation of dense neurite network; viscoelastic CNS-like mechanics	Need modification to improve cell adhesion; CNT dispersion and toxicity issues	Suitable for neurite network formation	[189]
4	Chitosan	Graphene oxide	Schwann cells showed spindle-like morphology with increased expression of nerve repair-associated markers (Krox20, Zeb2, and TGF-β) and repair of sciatic nerve defects in vivo	Promotes SC repair; positive in vivo nerve repair	Limits 3D guidance; GO dose-dependent cytotoxicity	Suitable for PMS regeneration	[190]
5	GelMA	MWCNTs/Co	Stem cells from apical papilla (SCAP) showed enhanced growth and neuronal differentiation on electrical stimulation	Supports electrical simulation-mediated neuronal differentiation	Optimization required; possible metal/CNT toxicity	Effective with electrical simulation	[191]
6	Polycaprolactone	CNTs	Fibrous scaffold promoted proliferation, and the expressions of myelination related genes in vitro and in vivo, suitable for peripheral nerve regeneration	Enhances myelination gene expression; aligned fibers guide axon	Slow degradation of PCL	Excellent for aligned PNS repair	[192]
7	PCL/gelatin	1393-B3-based borate bioactive glasses with Zn, Ag, Ce	Scaffold showed cytocompatibility and alignment of NG108-15 neural cells	Good alignment; antibacterial effect	Risk of ion cytotoxicity	Moderate conductivity	[193]
8	PCL/cellulose acetate	Gold nanorods	Hybrid scaffold supported proliferation and differentiation of PC12 cells, with enhanced expression markers of β-tubulin, MAP2 and nestin	Increased conductivity; supports neuronal marker expression	High costs; clearance and safety issues	Limits in translational	[194]

enlists different conductive scaffolds for neural tissue engineering.

5.3. Exosome and Stem Cell Nanoplatforms for Enhanced Neurogenesis

Exosomes are spherical, lipid-bilayered, single-membrane, nanoscale (40–100 nm) extracellular vesicles that contain a variety of bioactive materials, including proteins, lipids, enzymes, DNA, miRNAs, and cell metabolites [195]. They were first believed to be the “garbage bags” that assisted cells in eliminating undesirable materials, but recent findings reveal that their contents play a crucial role in cell-to-cell communication [196].

Neural stem cell (NSC)-derived exosomes can facilitate SCI repair by reducing spinal cord cavities, promoting motor function recovery, and encouraging angiogenesis of the spinal microvascular endothelium [197]. NSC-derived exosomes (FTY720-NSCs-Exos) were used to deliver FTY720, an S1P1 antagonist with systemic side effects. This strategy decreased inflammation and neuronal death, enhanced hind-limb motor performance, and decreased disease in SCI models. Additionally, FTY720-NSCs-Exos shielded the spinal microvascular endothelium barrier from hypoxia in vitro [198]. Likewise, Schwann cell-derived exosomes can promote functional recovery in mice following SCI by increasing the expression of toll-like receptors (TLR2) in astrocytes and decreasing the deposition of CSPGs via NF-κB/PI3K signaling [199]. Subsequently, mesenchymal stem cell-derived exosomes (MSC-Exos) play an important role in promoting cellular metabolic reprogramming and controlling cell migration [196].

Combinations of exosomes with biomimetic scaffolds have shown great therapeutic promise in angiogenesis and tissue regeneration. Together, exosomes with biomaterial scaffolds improve the stability and retention at the injury site due to the limited effectiveness of stem cell-derived exosomes [200]. In contrast to therapy with exosomes alone, a composite hydrogel system incorporating exosomes (GelMA-Exos) was developed to encourage axonal development [201]. Studies have demonstrated that an injectable adhesive anti-inflammatory F127-polycitrate-polyethyleneimine hydrogel (FE) with a sustained and long-term release of exosomes encapsulated on the damaged spinal cord inhibits inflammation and glia scar formation while promoting axonal regeneration [202].

Hydrogel-encapsulated exosomes can also be employed to transfer proteins, mRNAs, and microRNAs (miRNAs) to aid in functional recovery. Electroconductive hydrogels containing BMSC-derived exosomes stimulated tissue repair and functional recovery after SCI by activating the PTEN/PI3K/AKT/mTOR pathway, boosting axonal regeneration, neurogenesis, and decreasing inflammation. Combining BMSC-exosomes with GMP hydrogels pushed microglia toward the M2 phenotype, decreasing phosphorylated IKKα/β, IκBα, and P65, reducing neuroinflammation [203]. Another study reported that a collagen scaffold functionalized with a dual biospecific peptide that improves neural stem cell motility and paclitaxel administration was fabricated using human umbilical cord MSC-derived exosomes (MExos) as drug carriers. Strong cell adhesion and development were supported by the ECM-like characteristics of collagen, and its linear alignment (LOCS) made it possible to form a multifunctional scaffold (LOCS-BSP-MExos-PTX, LBMP). In fully transected SCI rats, this platform enhanced functional recovery, decreased scar formation, and encouraged nerve regeneration [204].

There is currently no completely effective treatment due to the intricate neural microenvironment. Despite the potential of exosome–scaffold techniques, there is currently a lack of clear recommendations for scaffold safety, exosome purification, and ideal graft time. To further evaluate treatment risks and increase the clinical relevance of preclinical models, future research should employ larger, longer-lived animals and incorporate for neural regeneration.

6. Pharmacokinetics and Biodistribution of Nanomaterials

Pharmacokinetics refers to the quantitative study of how NPs are taken up across all major tissues over a period of time from administration to the elimination phase [205]. The continuous monitoring of NPs is essential to characterize their pharmacokinetic behavior, distribution, metabolism and clearance profiles [205,206]. Similarly, biodistribution describes physiological distribution or the accumulation of NPs across organs and tissues at specific time points [206]. These NPs show targeted therapy and an improved bioavailability; therefore, their pharmacokinetics and biodistribution profiles must be thoroughly evaluated to ensure therapeutic safety and efficacy. These profiles are also influenced by physicochemical characteristics such as particle size, morphology, surface charge, concentration, biological interactions and chemical composition [205,207].

6.1. NPs Absorption, Circulation, and Clearance Mechanisms for Neuronal System

When a drug delivery system is administered, a drug carrier should have two targeting functionalities, i.e., to cross the BBB and to reach the targeting region. The NPs which are using the simple diffusion method can face significant obstacles such as viscous drag caused by ECM molecules, channel walls and other different types of potential cellular obstructions [208]. Moreover, when a drug is delivered intravenously (IV), it generally follows two paths, comprising (i) passive blood circulation and extravasation and (ii) active targeting [209]. In the case of passive blood circulation and extravasation, the major challenge is posed by the BBB due to its enzymatic, physical, transport and immunological defenses, which make the passive accumulation of a drug almost impossible unless there is any enhanced permeability and retention (EPR) effect which may occur in some diseases, such as tumors [210]. Additionally, it has been shown that diseases involving neuroinflammation lack an additional nutrient and oxygen supply and create an acidic microenvironment due to glycolysis; therefore, NPs can be synthesized in such a way where they remain stable in neutral pH, but can release their cargo in an acidic environment [211]. But recent studies showed that the EPR model cannot be always effective due to a number of factors such as high tumor interstitial fluid pressure (IFP), poor blood flow and angiogenesis (highly populated and disordered blood vessels) [212]. Therefore, in order to reduce EPR-dependent failures, therapeutic nanomedicine should be studied on a more clinically relevant tumor model, and EPR should be accounted for on a case-by-case basis [213].

6.1.1. Active Targeting

There are different methods for active targeting, including employing magnetic targeting; stimulus-responsive release triggered by pH, temperature, or hypoxic conditions; and functionalization with ligands [214]. Magnetic NPs (MNPs) hold the potential to deliver drugs to the brain by crossing the BBB, and they can be guided to the diseased region after being subjected to an external magnetic field. Moreover, many studies have shown an improved drug accumulation and retention at the target site. These MNPs generally exhibit low toxicity and high biocompatibility with CNS tissues. Interestingly, MNPs also showed around a ~12-times increase in concentration within rat brain tumor tissues compared to non-magnetic NPs [215,216].

In most tumor and neurodegenerative disorders, pH plays a major role, which led to the development of pH-responsive NPs. For example, dual pH-responsive polymer NPs were reported to deliver doxorubicin into breast cancer stem cells. After endocytosis, the targeted release of doxorubicin further improves cytotoxicity towards tumor cells. This technology is currently only limited to breast cancer cells but could be translated to the CNS, where a similar pH change is observed in the extracellular or intracellular environment [217,218]. For instance, acidity-triggered rational membrane (ATRAM)-functionalized bovine serum albumin (BSA)-PLGA (drug-loaded PGLA) NPs showed efficient and targeted drug delivery [219]. A similar approach was reported for neurotherapeutics using pullulan acetate nanocarriers that facilitated pH-responsive release and enhanced the intranasal transport of silibinin (an antioxidant) to the brain [220]. Another example is pH-responsive redox NPs, which provide selective neuroprotection by maintaining mitochondrial integrity under acidic pathological conditions [221]. Additionally, temperature can also be used for targeted drug delivery, where NPs linked to nucleic acids, lipids, polymers, or carbohydrates undergo denaturation at elevated temperatures, leading to the controlled release of drug molecules. In a study of glioma-possessing rats, pH- and temperature-sensitive magnetic nanogels were conjugated with dye-labeled lactoferrin and inserted via direct brain injection. It has been observed that they were able to respond with a high sensitivity to changed pH and temperature [222]. Furthermore, redox-triggered delivery systems showed site-specific delivery, for example, in the case of ferrocene-loaded doxorubicin, where ferrocene served to trigger redox reactions causing drug release within the system of HeLa cervical cancer cells [223]. However, the studies related to CNS drug release are still in their infancy stage and require some optimization and proof-of-concepts.

Targeting ligands would help in the active release of drugs by crossing the BBB and providing the ability to actively penetrate into a diseased region. This can be achieved by dual-targeting which includes signal-targeting ligands crossing the BBB and releasing the drug at targets. For signal-targeting ligands, pH-sensitive PAMAM dendrimers and PEGylated PLA NPs with two targeting ligands, TGN (a 12-amino acid sequence ligand) and QSH (a d-enantiomeric peptide), were reported [224,225,226]. However, although targeting ligands have the potential for use as a drug delivery method, they need thorough regulation to be employed for clinical treatment in neuroinflammatory or neuro diseases. Therefore, the circulation of NPs in the neural system is not an easy task, but it can be tackled with the right approaches to drug delivery.

6.1.2. Clearance of Nanomaterials

As nanomaterials are administered into the CNS, they can be rapidly cleared from the brain parenchyma [227]. There are basically four mechanisms for clearance from the brain: (1) extracellular degradation by metabolizing enzymes; (2) internalization and degradation by the neurovascular unit; (3) entrance into the cerebrospinal fluid bulk flow and reabsorption into the bloodstream or cervical lymphatics; and (4) brain-to-blood efflux via abluminal transporters [228]. Moreover, there are several families of enzymes such as CYP450s, hyaluronidases, epoxide hydrolases and monoamine oxidases, etc., which are mostly involved in the breakdown of many foreign particles in the brain parenchyma [208]. Therefore, there is a need for a thorough understanding of the clearance mechanisms of nanomaterials in the neural system.

NPs generally utilize glymphatic and cervical lymphatic systems for clearance. The glymphatic–lymphatic system comprises primarily meningeal lymphatic vessels (MLVs) and perivascular spaces (PVs), which play a crucial role in maintaining the dynamic homeostasis of the brain environment by clearing danger/damage-associated molecular patterns (DAMPs) in a non-selective manner. It is a physiologically modulated CNS-wide fluid transport system, which allows the flow of cerebrospinal fluid (CSF) from the periarterial spaces of penetrating arteries to deep inside of the brain region through the brain parenchyma to clear metabolic waste [229]. In the same manner, the glymphatic system clears NPs during sleep/arousal states, enhanced by hypertonic saline or aquaporin-4 channels on astrocytic end feet. Experimental studies have demonstrated that small NPs such as gold nanoparticles (AuNPs) having a size from 10 to 50 nm can achieve a brain-wide distribution following intrathecal or intraparenchymal administration, with reported half-lives ranging from ~a few hours to ~24 h [229]. However, in the case of neuroinflammation (cases related to TBI and Alzheimer’s disease), glymphatic dysfunction significantly impairs the clearing mechanism, which leads to prolonged NP retention and altered distribution dynamics. Therefore, engineered “nano-plumbers”, i.e., engineered NPs, have been proposed as therapeutic modulators, reversing the injured microenvironment wherein NPs suppress microglial/astrocytic activation and improving therapeutic outcomes. Importantly, such improvements are observed under repeated dosing regimens like three dosages over multiple days [230,231,232]. For NPs with a short CNS residence time, dosing intervals of 12–24 h maybe required to sustain therapeutic levels, avoiding accumulation. Intrathecal routes further exploit glymphatic transport for rapid clearance, as evidenced by human imaging studies using gadolinium-labeled nanoparticle tracers, which report a clearance slope of approximately 0.03–0.05 min⁻¹ [229,230].

The cervical lymphatic system serves as a crucial clearance pathway for CSF, meningeal antigens and NPs, facilitating clearance from cisterna magna toward deep cervical lymph nodes and, in certain cases, allowing retrograde movement toward the meninges or brain parenchyma while partially bypassing veins. The pathway was validated by the detection of superparamagnetic iron oxide nanoparticles (SPIONs), exosomes loaded with SPIONs, gold nanorods and tracer materials such as Chinese ink within brain tissue following cervical lymphatic injection. Recent pharmacokinetic studies further indicate that particle size, hydrophilicity, and surface charge influence lymphatic uptake and residence time, with smaller and neutrally charged NPs exhibiting more efficient lymphatic drainage. Notably, clearance kinetics through cervical lymphatics appear comparable to glymphatic transport [233,234].

Under inflammatory and neurodegenerative conditions, cervical lymphatics play a key role in modulating neuroimmune surveillance by regulating immune cell trafficking and antigen presentation. NPs targeting cervical nodes can exploit this mechanism to modulate immune response either by inhibiting metastasis or by delivering anti-inflammatory agents to lymphoid tissues. From a translational perspective, pharmacokinetic modeling suggests that a dosing interval of ~24–48 h is optimal for lymphatic targeting NP systems. Such dosing strategies are mainly relevant for chronic CNS disorders, including Parkinson’s disease and multiple sclerosis, where sustained immunomodulation is required, rather than continuous NP accumulation [233,234].

6.1.3. Effect of Physicochemical Properties of Nanocarriers on BBB Transport and Accumulation

Physicochemical properties such as the size, surface charge, shape, and composition of nanocarriers are important parameters which decide safety and therapeutic performance. Therefore, understanding these parameters is required for investigating pharmacokinetics and functionality.

i.

Size

The optimal NP size range for brain drug delivery is still widely debated, as it depends on different biological factors [235]. Smaller-sized molecules more easily pass through BBB gaps; moreover, they have a high surface area-to-volume ratio, which can enhance interaction and uptake by endothelial cells [236,237]. For instance, in the case of carbamazepine-loaded methoxy poly(lactide-co-glycolide)-b-poly(ethylene glycol) methyl ether (mPEG-PLGA) NPs with sizes 120 nm, 90 nm, and 60 nm developed for epilepsy treatment, the smallest nanocarriers proved to be the most effective at crossing the BBB [238]. Similarly, insulin-coated AuNPs crossed the BBB at a size of 20 nm compared with NPs having sizes of 50 nm and 70 nm. However, smaller nanocarriers can enhance BBB penetration, but their reduced size can also affect their biocompatibility and increase the toxicity risks. NPs < 100 nm have a longer systemic circulation due to their innate ability to avoid clearance through the reticuloendothelial system (RES), but this extended time can also cause a neurotoxic response [236].

ii.

Shape

Among the various shapes (cubical, rod-like, spherical, cylindrical, etc.), a spherical shape can exhibit a higher reproducibility and surface functionalization in NPs. These characteristics influence their uptake, distribution and interaction with cellular membranes and subsequent intracellular fate [239]. However, spherical nanocarriers have fewer binding sites due to their curved shape, leading to a relatively lower internalization [240]. Moreover, several studies have reported that spherical NPs exhibit a higher uptake in the human brain compared to anisotropic shapes such as stars, rods and quasi-ellipsoids [241]. NPs with a higher aspect ratio, such as nanorods, show superior uptake due to their large surface area and initiate endocytosis [237,240]. However, non-spherical morphologies also demonstrated highly effective endocytosis, and intracellular internalization showed conflicting observations [241,242]. This suggests that uptake efficiency is not only governed by shape but also depends on other physicochemical properties or even particle orientation [243]. The fillomiceles (made from degradable di-block copolymers having PEG-polycaprolactone) showed a longer systemic circulation than the spherical nanostructures. This extended retention showed a selective accumulation within tumors tissues, governed by an enhanced permeability and retention effect, while showing a comparatively lower uptake in other non-tumor organs [244,245]. Although fillomiceles are advantageous for tumor shrinkage, emerging studies showed that they may cause cumulative neurotoxicity, particularly in neurodegenerative disorders. This is consistent with the previous studies, which displayed that non-spherical shapes were more toxic compared to spherical ones. This emphasizes the need for more comparative studies to elucidate how particle shape influences BBB transport and shape-dependent neurotoxicity and to derive a generalized conclusion [237,246].

iii.

Surface Charge

The surface charge is also an important factor that influences BBB permeability and the overall effect of NPs. Compared with negatively charged transferosomes of smaller size, positively charged nanovesicles exhibited a higher brain targeting and retention efficiency along with an enhanced bioavailability [236,247]. These cationic NPs have a higher internalization efficiency due to their interactions with negatively charged proteoglycans in BBB endothelial cells, but they can cause acute neurotoxicity and a disruption in BBB integrity [248,249]. However, cationic NPs can be easily cleared by the body due to high opsonization and high interactions with negative-charged proteins such as albumin and immunoglobulins (Ig) [250]. The negatively or neutral-charged nanocarriers generally showed a lower uptake, higher retention time due to lower opsonization, better biocompatibility and reduced toxicity, while positively charged NPs may induce ROS generation, cell damage, necrosis or apoptosis [236,251]. However, due to the low permeability of anionic NPs, cationic NPs can serve as a promising targeted delivery system for negatively charged genetic material [252].

iv.

Concentration

Neurotoxicity is concentration-dependent, rising with a higher concentration of NPs irrespective of chemical composition. For instance, neuroblastoma cells exposed to TiO₂ NPs (0.75–75 mg/L) and CeO₂ NPs (0.075–10 μg/L), as well as differentiated rat PC-12 neuronal-like cell lines treated with SWCNTs (1–100 μg/mL), cadmium selenide (CdSe) quantum dots (1–10 μg/mL), fullerenes (C60) (1–100 μg/mL), carbon black (CB) NPs (1–100 μg/mL), and silica nanospheres (10 μg/mL), demonstrated maximum neurotoxic effects, leading to a reduction in cell viability [250,253,254].

While physicochemical parameters such as size, surface charge, shape and concentration govern nanoparticle distribution and safety, their therapeutic impact mainly relies on defined biological mechanisms. Specifically, nanoparticles exert anti-neuroinflammatory effects through BBB modulation, the regulation of inflammatory signaling cascades, and targeted interactions with immune cells.

6.2. Mechanism of Action for Therapeutic NPs

One of most discussed mechanisms involves enhanced BBB penetration when functionalized with ligands such as angiopep-2, transferrin or peptides that facilitate receptor-mediated endocytosis, preferentially accumulating in microglia-rich inflammatory regions of the brain. Importantly, microglial-specific uptake allows localized immunomodulation, allowing the direct regulation of inflammatory agents [14]. For instance, peptide-functionalized polymeric nanocarriers capable of BBB penetration and microglial targeting allow the systemic delivery of IRAK4 inhibitors to treat hypothalamic inflammation [230].

Beyond BBB transport, many NPs exert therapeutic effect through the direct modulation of microglia activation states. Targeted NPs functionalized via surface ligands (e.g., for TREM2 or CD44) to deliver antisense oligonucleotides (ASO), siRNA, or small molecules that downregulate pro-inflammatory genes restore phagocytic function and enhance debris clearance. Mechanistically, they reprogram microglia from the pro-inflammatory M1 to the anti-inflammatory M2 phenotype by inhibiting signaling pathways like NF-κB, JAK/STAT, p38 MAPK, and ERK, thereby reducing cytokines (TNF-α, IL-1β, IL-6) and promoting neuronal survival [255,256]. Examples include TREM2-lowering ASO-loaded NPs that enhance amyloid-β clearance in Alzheimer’s models, or resveratrol-loaded NPs that boost phagocytic capacity [256].

NPs also serve as a platform for the sustained and localized delivery of antioxidants (resveratrol, polyphenols), NSAIDs and enzyme mimetics loaded into liposomes, PLGA, or polymeric NPs for sustained release and reduced systemic toxicity [230]. Gold NPs and iron oxide NPs exert intrinsic anti-inflammatory effects by scavenging ROS and attenuating microglial activation without additional drugs. These mechanisms show efficacy in models of Alzheimer, Parkinson’s disease, cancer-associated neuroinflammation, and lipopolysaccharide-induced CNS inflammation [256,257]. NPs sometimes target the gut–brain axis to deliver prebiotics, probiotics, or anti-inflammatory drugs to modulate microbiota and suppress peripheral cytokine production, which contributes to CNS inflammation. This indirect approach complements direct brain targeting (BBB targeting) approaches, restoring homeostasis in chronic neurodegenerative diseases [258].

7. Safety, Biocompatibility, and Toxicity

Nanomaterials are increasingly employed for different applications and have shown biocompatibility at therapeutic doses; however, concerns arise due to neurotoxicity, immune activation and long-term accumulation in neural tissues [259]. Consequently, a comprehensive evaluation of their biological safety and toxicological profiles is essential before these nanomaterials can be adopted into clinical or diagnostic applications [259]. Many studies have shown that nanomaterials can induce cytotoxicity, oxidative stress and immune responses in various cell types, with mechanisms such as ROS, inflammatory responses and lysosome disruption [260]. For instance, the in vitro toxicity of engineered nanomaterials was evaluated using TiO₂, ZnO, SiO₂, CeO₂, Ag NPs, and MWCNTs, and showed cytotoxicity, ROS production and pro-inflammatory response [260]. Moreover, when innate immunity directly interacts with nanomaterials, it can induce toxicity at the tissue and organ levels [250,261]. The toxicity of nanomaterials greatly depends on their size, shape, surface charge, chemical composition, and surface modification [261]. Several in vitro and in vivo studies have demonstrated that an exposure to TiO₂ NPs induced apoptosis, inhibited cell proliferation, elevated ROS levels, and initiated cytokine production, which caused neuroinflammation, membrane damage and a decrease in cell proliferation [262]. Moreover, it also increased the levels of caspase-3 and 9, Bax, and cytochrome c and decreased the levels of Bcl-2 in the hippocampus of mice [263]. Additionally, the exposure of neural precursor cells to Ag-NPs increases the level of cell proliferation and apoptosis inactivation. They are mostly internalized by astrocytes, which cause morphological modification and damage to several synaptic structures in rats [264,265]. Similarly, Cu-NPs exposure in mice showed a decreased number in the cortex and altered serotonin, nor-epinephrine and dopamine levels across different regions of the CNS [266,267].

Au-NP exposure has also been shown to alter microglial activity induced by Au-NPs, where it increases the expression levels of toll-like receptor 2 (TLR-2), interleukin-1a (IL-1a) and granulocyte macrophage colony-stimulating factor (GM-CSF) [268]. Additionally, the hippocampal CA1 neurons of mice displayed a reduced action-potential threshold, increased frequency of shorter-duration action potentials and intensified seizure activity. Overall, these findings showed that NPs with varying physicochemical characteristics are able to elicit neurotoxic effects and neuroinflammatory responses in different CNS regions [269,270].

A short-term exposure to these NPs may not be lethal for therapeutic outcomes; however, chronic exposure may be responsible for immunosuppression through the sustained suppression of microglia and astrocytes or the modulation of the peripheral immunity. Such prolonged immunosuppression may increase susceptibility to infections, impaired CNS surveillance, fibrosis, cumulative neurotoxicity and long-term inflammatory consequences [14,271,272]. Prolonged NP exposure can shift microglial polarization to excessive M2 (anti-inflammatory) polarization, thereby impairing their surveillance and phagocytic roles and allowing pathogen persistence or the accumulation of cellular debris in the brain. This chronic suppression may mimic corticosteroid-like side effects, including increasing the susceptibility to infections, pneumonia and gastric bleeding, exacerbated when NPs carriers undergo lysosomal degradation or induce long-term alterations in immune cell phenotypes. Dose-dependent effects further complicate safety profiles, as low doses may be responsible for neuroprotection, whereas sustained high-dose exposure causes ROS imbalance, neuronal apoptosis, and long-term cognitive deficits [14,273,274]. The systemic immunosuppression caused by NPs induces a persistent release of immunoregulatory cytokines such as IL-10 and TGF-β, leading to the inhibition of T-cells, macrophages, and complement activity, and increases susceptibility to infections, tumor progression and infections caused by viruses and bacteria. For instance, iron oxide NPs suppress interferon signaling and reduce IL-6 and TNF-α production, while liposomal and titanium-based nanomaterials have been associated with an elevated cancer risk via macrophage inhibition. Moreover, the protein corona on NPs can trigger fibrinogen unfolding and sequential pro-inflammatory responses followed by suppressive cascades, ultimately promoting macrophage-mediated clearance, which reduces therapeutic efficacy while promoting fibrosis tissue response [273,274].

Chronic accumulation and off-target toxicity is prominent particularly in metal-based NPs such as Ag, Cu, and Fe oxides. These materials cause BBB disruption, astrocyte swelling, and damage to the mitochondria, endoplasmic reticulum (ER) and DNA, thereby linking immunosuppression with neurodegeneration. Chronic accumulation evades glymphatic clearance in inflamed brains, leading to iron dysregulation, synaptic disruption, and irreversible tissue injury. Although strategies such as rapamycin-loaded NP formulations can mitigate some toxicities, they remain associated with hyperlipidemia, kidney damage, and bone marrow suppression [14,272].

Overall, the incomplete clearance and long-term tissue accumulation of non-biodegradable NPs represent a critical factor for neurodegeneration. In injured brains, impaired lymphatic drainage systems allow NPs to remain within the perivascular or parenchymal compartment, leading to iron dysregulation, axonal damage and the infiltration of peripheral immune cells. Therefore, there is a need for biodegradable and dose-controlled NPs for safe and long-term application in neuroinflammatory disorders [275,276].

7.1. Regulatory Considerations for Nano-Pharmacological Therapeutics

Since the late 20th century, discussions regarding the regulation of nanomaterials have been continuously evolving. Although several NPs such as TiO₂ and ZnO are already commercially available, a comprehensive regulatory framework addressing human toxicity has yet to be fully established [277,278]. However, initiatives have been started by the FDA and the economic commission and organization for economic co-operation and development (OECD) in order to standardize the safety evaluation process for therapeutics containing nanomaterials [278]. For example, under the NANoREG project, many researchers have proposed the need for thorough guidance on the available tools, such as decision tress and standardized test methods, for evaluating the safety of drugs containing NPs [279]. The FDA has also issued a document emphasizing the importance of assessing the biological fate of nanocarriers and its potential safety implication, highlighting that safety evaluation should not be restricted to the active pharmaceutical ingredient (API) but also to the NP carrier system. In addition, the clinical development of drug formulations loaded with NPs is supported by several non-binding recommendations, including the requirement for the comprehensive pharmacokinetic evaluation of NP-based formulations. These recommendations highlight the importance of the absorption, distribution, metabolism, excretion and toxicity (ADMET) properties of nanocarriers [280,281]. But these recommendations are not specifically adapted to evaluate the toxic effects on the brain whether they are meant to target the brain or not, although valuable insights can still be drawn from existing regulatory documents [278]. The evidence showed that conventional combined approaches for both quantitative and qualitative assessment can help in risk evaluation of nanoformulations. Therefore, for drugs containing NPs developed from a reference formulation, single- and multiple-dose pharmacokinetic and pharmacodynamic studies, generally for medium- and high-risk categories, can offer stronger evidence of systemic behavior. Nevertheless, the absence of standardized protocols designed specifically for nanoscale materials limits the sensitivity to detect subtle toxicological effects. Currently, the safety assessment of NPs depends primarily on two analytical methods, i.e., in vivo and in vitro toxicological assays [250]. In July 2020, the FDA published a report highlighting development strategies for the safety evaluation of nanomaterials, yet the document lacks guidance on addressing specificity-related challenges. Therefore, there is an urgent need for an appropriate regulatory framework which is able to respond to the safety challenges of NPs, especially those that are applied for therapeutic applications. The efforts undertaken by the FDA, the European Union, and the OECD should aim to standardize safety validation processes, thereby reducing the dependency on a case-by-case approach [282].

7.2. Recent Studies and Ongoing Clinical Trials Targeting Neuroinflammation Using Nanocarriers

Recently, there are many NPs which have been developed for the treatment of neuroinflammation and other brain-related disorders. For instance, chitosan glutamate nanoparticles (CGNPs) have been used to enclose rasagiline (RAS), a clinically prescribed drug for treating the symptoms of Parkinson’s diseases. Moreover, it belongs to the class of drug called monoamine oxidase B (MAO-B) inhibitors and is a dopamine receptor agonist. As an oral formulation, RAS exhibited a short duration of action and limited absorption, which could result in gastrointestinal side effects such as vomiting and nausea. When nanoparticle-enclosed RAS was used, it increased the drug’s rate of dissolution and brain targeting when administered intranasally compared to IV delivery [48]. SLNPs and nanostructured lipid carriers are also considered a safe and clinically advanced system for IV delivery due to their advantages of biocompatibility, scalability, higher stability and ability for surface modifications [283]. For example, valproic acid-loaded NLCs delivered a higher drug concentration to the brain and more efficiently inhibited tonic–clonic partial seizures compared to a conventional drug solution in a seizure model [284]. Moreover, PLA/PLGA NPs have demonstrated a significant potential for brain-targeted drug delivery. For example, olanzapine-loaded PLGA NPs resulted in a 10-times higher brain drug uptake as compared to a free drug. Similarly, in vivo studies have shown that optimized PEG-PLGA-NPs conjugated with odorranalectin (attaches to l-fucose expressed on the olfactory epithelium) exhibited a prolonged residence time of NPs in the nasal cavity and enhanced brain distribution following IV administration [285,286]. Chitosan-based NPs have also been explored for neuroprotective applications. It has been observed that glial cell-derived neurotrophic factor (GDNF) enhances the survival rates of dopaminergic neurons. In one study, GDNF-loaded NPs were developed using a chitosan-coated nanostructured lipid system with a surface modified with the cell-penetrating peptide transactivator of transcription (TAT). Chitosan and TAT peptides helped to enhance the drug residence time in the nasal cavity, protect GDNF from degradation, and promote brain penetration. Notably, only the intact formulation showed therapeutic efficacy in a mouse model of Parkinson’s disease. Interestingly, the administration of intact formulation decreased the loss of dopaminergic neurons in the striatum and substantia nigra, decreased reactive microglial activation, and improved motor behavior [287].

7.3. Limitations in Translation and Reproducibility

The wide applicability of nanomedicines in healthcare is transforming current diagnostic and therapeutic strategies; however, only a limited number of products ultimately reach the market. Successful translation requires a comprehensive preclinical safety assessment which includes pharmacology, efficacy, physicochemical characterization and toxicology evaluation. Major challenges in physicochemical characterization come from the lack of sensitive and appropriate analytical methods. Similarly, determining efficacy is complicated by the selection of appropriate experimental models, ensuring efficient drug encapsulation and controlled release, maintaining formulation stability, and evaluating biological activity. Moreover, pharmacology and toxicology evaluations face additional problems, including NPs biodistribution, the limited availability of relevant animal models, the difficulty in explaining the toxicity mechanism and a poor correlation between in vitro and in vivo toxicity assays. Therefore, nanomedicine translation requires a better understanding of crucial physicochemical characteristics, in vivo behavior and in vitro characterization to demonstrate safety and efficacy [246,268,288,289].

The development of nanomedicines requires a product quality that should meet the expectations of the industry, manufacturing processes, patients and regulatory authorities. The identification of product control quality attributes (CQAs) helps in determining whether a production batch satisfies the standard requirements. Thus, defining the key process parameters that ensure these attributes is fundamental for achieving consistent product performance. The quality-by-design (QbD) approach is recommended for the development of a high-quality product because the QbD approach can contribute in gaining thorough product and process knowledge and enabling cost-effective manufacturing, which also meets the CQAs necessary for clinical performance. Thus, in order to support the effective implementation of QbD, structured training programs are needed to enhance the understanding of scientists regarding CQAs, design space, and relevant analytical and computational tools [289,290,291,292].

The selection of raw materials is a crucial step in nanomedicine manufacturing, requiring the implementation of process analytical technology (PAT) to monitor the product quality. Moreover, the FDA has also approved the use of PAT to obtain real-time data acquisition and to strengthen quality assurance in the manufacturing process. PAT techniques can provide valuable understanding and insights for process optimization and help to reduce product variability and improve regulations. Therefore, integrating PAT with QbD principles is expected to accomplish the successful clinical translation of nanomedicines [293,294].

Moreover, reproducibility is also a great concern; therefore, in order to get NP batches with identical properties, there is a need for high-throughput methods capable of systematically evaluating nano–bio interactions [246]. Technologies such as microfluidics have the potential to accelerate the discovery and clinical translation of nanomedicines. Another step is the integration of nanomedicine development into a single system through the incorporation of robotics, automation and microfluidics technologies. Therefore, there is a need for interdisciplinary collaboration among experts in materials science, microfluidics, pharmaceutical formulation, and biomedical engineering. Additionally, while stimuli-responsive nanomedicines present promising opportunities, their translation can be affected by inter-individual variability in physiological triggers such as pH and enzymatic activity, which can lead to inconsistent therapeutic responses [268,295,296].

Beyond the synthesis, characterization, and safety evaluation of nanotechnology-based strategies for neuroinflammatory diseases, successful clinical translation also relies on additional considerations. Factors such as species-specific immune differences, patient-to-patient heterogeneity and stringent regulatory requirements present significant challenges in advancing nanoparticle-based therapeutics from preclinical studies to clinical application. The rodent models often used in preclinical studies do not fully replicate the complexity of immune responses in the human nervous system, particularly in terms of microglial heterogeneity, BBB architecture, and innate immunity. For instance, human microglia resist repolarization more than rodent microglia, affecting the NP-induced M1-to-M2 polarization shift observed in preclinical studies. While non-human primates more closely mimic human-complement activation and NLRP3 inflammasome responses, their high cost and ethical concerns restrict widespread translation usage. Species-dependent differences in protein corona (e.g., dysopsonins in human plasma compared with rodents) further alter NP clearance kinetics and immunogenicity, highlighting the need for humanized immune models or organoids [14,297].

Since the population suffering from neuroinflammation varies by age, genetics (e.g., TREM2 mutations in Alzheimer’s), comorbidities (obesity amplifies cytokines), and disease stage, patient immunological heterogeneity further complicates the clinical translation [297]. Additional factors, including biological sex, microbiome, and HLA genotype, further influence NP immunogenicity and protein corona formation, highlighting the biomarker dosing strategy, complicating dosing in heterogeneous cohorts [297].

In the context of neural tissue engineering, strategies to promote neural repair and regeneration have predominantly been emphasized in the recent past [298,299]. However, despite their promising results in in vitro and pre-clinical studies, these scaffolds and implants face significant limitations in addressing critical immune responses, foreign body reactions (FBR), and long-term neuroimmune interactions, often leading to chronic inflammation and implant failure [300,301,302]. These challenges highlight the need for greater immunological integration through immunoregulatory biomaterials that modulate macrophage polarization and enhance biocompatibility to promote sustained neuroimmune homeostasis [302].

Regulatory challenges add another layer of complexity as agencies such as the US FDA and European Medicines Agency (EMA) evaluate nanomedicine on a case-by-case basis in the absence of unified, nano-specific regulatory guidelines. Moreover, approval pathways require extensive physicochemical characterization (size, surface charge, corona composition), biodistribution, immunotoxicity, and long-term safety assessments [255,303]. Manufacturing scalability, reproducibility, batch-to-batch variability, and nanotoxicity assessments delay the process, contributing to the slow progression rate of nanomedicines. For the CNS, the lack of standardized assays for BBB penetration, glymphatic clearance, and microglial biomarkers remains a major limitation, with EMA/FDA agencies increasingly emphasizing human-related data over rodent efficacy [255,297,303].

8. Conclusions and Future Directions

Neuroinflammation is a complex biological process associated with various neurological disorders, exerting both protective and pathogenic effects depending on its intensity, duration, and microenvironmental context. This review highlighted the limitations of conventional treatment strategies, which mainly reduce the symptoms but fail to modulate this dynamic inflammatory landscape or support neural repair. On the other hand, nanobiotechnology-based strategies offer a paradigm shift by enabling a precise control over inflammation while simultaneously fostering neural regeneration. Through tailored NPs, bio-responsive delivery systems, and immunomodulatory scaffolds, it is now possible to cross the BBB, regulate key inflammatory pathways, and recreate biomimetic environments that support neuronal survival, connectivity, and functional recovery.

The applications of nanomaterials in neural tissue engineering have further expanded therapeutic possibilities, allowing scaffolds to act not only as structural supports but also as active regulators of immune response and neurogenesis. However, successful clinical translation remains contingent on a deeper understanding of pharmacokinetics, biodistribution, long-term safety, and reproducibility, alongside a compliance with evolving regulatory frameworks. Current clinical trials underscore both the promise and the challenges of nanotherapeutics, emphasizing the need for standardized evaluation and scalable manufacturing.

Looking ahead, the integration of artificial intelligence and machine learning holds substantial potential to accelerate this field by optimizing nanomaterial design, predicting biological interactions, and personalizing therapeutic strategies. By combining data-driven approaches with rational nanobiotechnology, future research can move beyond proof-of-concept toward robust, clinically viable solutions. In conclusion, these reports emphasize nanobiotechnology as a transformative force in managing neuroinflammation and engineering neural repair, paving the way for more effective, reliable and durable treatments for neurological diseases.