SWCNTs are formed from a single sheet of graphene rolled into a tube, with diameters usually between 0.4 and 2 nm. Their electrical properties are strongly influenced by their chirality whether the tube is in an armchair, zigzag, or chiral configuration, which determines whether they behave as metals or semiconductors. One of the most notable features of SWCNTs is their exceptionally high surface area, which can reach ∼1,300 m²/g. This large surface provides abundant sites for drug loading and bioconjugation. The complexes formed when used as drug carriers exhibit prolonged retention in systemic circulation compared with free drugs, enabling sustained cellular uptake via the enhanced permeability and retention (EPR) effect (Hughes et al., 2024).

Upon targeted delivery, functionalized SWCNTs gradually release their drug payload at the desired site. They are subsequently cleared from the body through the biliary system and excreted in feces. These findings highlight the potential of SWCNTs as efficient nanocarriers, making them promising platforms for drug delivery and wound-healing applications (Anzar et al., 2020).

MWCNTs are formed as coaxial cylinders, consisting of several concentric layers of graphene sheets wrapped into the shape of a tube-within-a-tube. They generally have outer diameters of 2–100 nm and inner diameters of 1–3 nm. The length of such nanotubes ranges from several nanometres to a few micrometres, depending on the fabrication technique. The multilayered structure of MWCNTs also makes them mechanically stronger and stiffer than SWCNTs (Rahamathulla et al., 2021). Therefore, they are suitable candidates for applications that require mechanical reinforcement, such as scaffolds in tissue engineering and wound healing. The hollow core with many sidewalls provides high load capacity for therapeutic molecules, making them well-suited as potential drug-delivery carriers. When loaded into biopolymeric scaffolds composed of chitosan, gelatin, alginate, and other biomaterials, MWCNTs instantly enhance cellular adhesion, viability, and proliferation while reducing cytotoxicity (Alhashmi Alamer and Almalki, 2022).

In addition to the classical SWCNTs and MWCNTs, several less conventional structural variants of CNTs have been reported, each offering unique physicochemical features. Graphenated CNTs (g-CNTs) consist of CNT backbones decorated with graphene layers, thereby significantly increasing their surface area and electron-transfer efficiency, making them attractive for electrochemical and biomedical applications (Eatemadi et al., 2014). Cup-stacked CNTs are another variant, composed of truncated-cone-like segments stacked. These structures have thousands of open edges and defect sites, providing a large number of chemical functionalization sites and, in turn, excellent reactivity (Kim et al., 2024). CNT torus (looped, ring) has been reported. This exotic shape endows unique magnetic and electronic properties, which can have broader applications in CNT-based high-end nanodevices and bioelectronics. In aggregate, these structural changes extend the utility of CNTs, enabling the engineering of desired properties for specific biomedical and technological applications (Thakur et al., 2022).

CNTs possess a high surface area and modifiable surface functionalization, which are beneficial for drug delivery, biosensing, antimicrobial agents, and wound healing. MWCNTs are rigid, multifunctional materials that are particularly appealing for biomedical applications (e.g., fields that require high strength and bioactivity) (Thakur et al., 2022). The chirality and conformations of CNTs strongly affect their electrical properties: armchair CNTs are metallic, while zigzag and chiral CNTs may be semiconductors. This electrical tunability renders CNTs highly attractive for future materials in electronics and biomedical applications (Costa et al., 2016).

In addition, CNTs are also well known for their outstanding mechanical strength (tensile strength up to 10–100 GPa and a Young’s modulus of nearly 1 TPa), enabling them to withstand high levels of strain without deformation failure (Nurazzi et al., 2021). They also have high thermal conductivity (2000–3000 W/mK), outstanding electrical conductivity (10⁶–10⁷ S/m). Another key feature is their extremely high surface area-to-volume ratio, which would further facilitate interaction with biomolecules and cells. Due to their high aspect ratio (>100), they can be used to create conductive percolation networks in polymer composites at very low loading levels (0.1%–1%), thereby substantially increasing the material’s electrical conductivity (Li et al., 2007). These characteristics make them suitable for use in efficient heat dissipation and electrical charge transfer applications. These distinct physicochemical attributes of CNTs set them apart from other nanomaterials and are responsible for their growing importance in biomedicine, energy technologies, sensing platforms, and catalytic systems (Gupta et al., 2019).

Despite CNTs’ inherent hydrophobicity and tendency to aggregate, biomolecule functionalization can significantly enhance dispersion, biocompatibility, and drug-loading capacity. In biomedical engineering, the exceptional properties of CNTs are considered particularly useful and have been used to fabricate composites with natural polymers such as alginate, collagen, gelatine, and chitosan, or synthetic polymers, to reinforce the mechanical strength of scaffolds, enhance electrical stimulation, and improve cell interactions (Murjani et al., 2022). Chemical or surface modifications have enabled CNTs to serve as multifunctional platforms in the biomedical field, providing a large surface area and tunable surface chemistry for drug loading (accessible adsorption sites) and structural support from their mechanical strength (Islam et al., 2022). Their excellent electrical properties have also been used to induce cellular responses, especially in electrically active tissues, including neural, cardiac, and muscular tissues, in which endogenous signals for cell-cell communication are essentially electrical (Nekounam et al., 2021).

These features render CNTs highly promising in biomedicine, including drug delivery, biosensing, tissue engineering, and wound healing. CNTs possess distinctive physicochemical properties and a broad range of biomedical applications. Their unique combination of mechanical strength, electrical conductivity, and controllable surface chemistry makes them among the most widely investigated nanomaterials in regenerative medicine, drug delivery, and wound healing. With advances in functionalization and toxicity reduction, CNTs are gradually moving towards translational biomedical applications (Gupta et al., 2019).

The initial step of wound management, especially in traumatology, is rapid hemostasis. Hemorrhage continues to be the leading cause of preventable mortality, and traditional dressings such as cotton gauze remain limited to acting as blood absorbents with negligible influence on coagulation. CNT-composites, however, shift this paradigm by introducing a nanoscale architecture that promotes platelet adhesion and fibrin netting formation to facilitate coagulation. Tan et al. reported that the addition of CNTs as fillers to carbonized cellulose aerogels could convert it into a highly efficient hemostatic material (Tan et al., 2025). Porous and ultralight structures enabled rapid blood absorption, and rough nanosurfaces promoted platelet adhesion/aggregation. In both animal liver and tail bleed in vivo models, compared to cellulose (control), the clotting time with CNT-aerogel was shortened by 3-fold, indicating that nanoscale reinforcement is not purely mechanical but also interacts actively with coagulation. Based on the concept of multifunctionality, Wu et al. reported a CNT-based sponge scaffold incorporating pyrrolidonecarboxylic acid zinc (PC₁Z₂) for the therapeutic treatment of diabetic wound healing, including inflammation and infection (Wu et al., 2025), as shown in Figure 4. The CNT network served as a pro-coagulant surface, while the zinc ions exerted antimicrobial and anti-inflammatory properties. This is especially beneficial for diabetic wounds, complicated by trauma-driven infection and inflammation. They showed that combining hemostatic and antimicrobial activities in a single dressing provides dual roles, simultaneously treating multiple early wound-healing challenges. Taken together, these studies demonstrate the transition of CNT-based dressings from passive absorbents into active, multimodal systems. Towards immediate enemy action: CNTs stop immediate bleeding and early infection risks by initiating blood clotting and inhibiting bacterial growth, suggesting significant potential for use in injured patients and even in chronic wound applications.

Once bleeding is stopped, wounds are at high risk of infection. Bacterial colonization delays healing and results in chronic inflammation, which may cause systemic complications. CNTs have been well established for their intrinsic antibacterial activities due to their hydrophobicity, membrane-puncturing potential, and ability to generate reactive oxygen species (ROS) (Maleki Dizaj et al., 2015). In a recent study, researchers fabricated a hydrogel-based composite system incorporating silver nanoparticles (AgNPs), MWCNTs, and Pluronic F127 to manage bacterial infection at the wound site, thereby imparting antioxidant and antimicrobial properties. The MWCNT-Ag/PF127 composites were demonstrated for enhanced antibacterial and anti-biofilm activities while maintaining a balance between bioactive properties and biocompatibility (Ryu et al., 2025). On the catalytic front, Wang et al. described hydrophobic Fe/Co-loaded CNTs (Chen et al., 2025). These composites disrupted bacterial membranes and generated ROS, resulting in effective bactericidal activity against both gram-positive and gram-negative strains. Their lipophilicity promoted close contact between bacterial membranes, thereby increasing permeabilization. Photothermal designs are another major direction for these studies. Chao et al. constructed CNT-lignin/PVA hydrogels that can induce local hyperthermia upon NIR irradiation at the wound site with the improved antibacterial activity against E. coli and S. aureus (Chao et al., 2023). In vivo studies demonstrated on-demand elimination of pathogen propagation at the wound site through a photothermal antibacterial effect, reduced inflammation, and rapid wound healing. Li et al. engineered CNT hydrogels exhibiting catalase and superoxide dismutase-mimicking “nanozyme” activity (Alhashmi Alamer and Almalki, 2022). These hydrogels simultaneously killed bacteria and scavenged ROS to re-establish redox homeostasis at the wound site. This dual-action system represents a significant innovation, as CNT composites can eradicate pathogens, modulate the inflammatory microenvironment, and facilitate angiogenesis. In another study, OuYang et al. introduced a carbon nanotube-based injectable nanoconductive hydrogel with a host-guest supramolecular macromolecule approach. The authors used single-walled carbon nanotubes to fabricate an endogenously electric-field-responsive hydrogel that promotes rapid migration of multiple cells at the wound site. In addition, the hydrogel was encapsulated with endothelial cell growth supplement for cell proliferation, and N-Formyl-Methionyl-Leucyl-phenylalanine to recruit neutrophils and induce Neutrophil Extracellular Traps. Altogether, the hydrogel modulates the inflammatory response, provides antimicrobial activity, and repairs wounds (Ou et al., 2025), as shown in Figure 5.

In another example of developing advanced systems for bioelectronic stimulation, Nie et al. developed mechano-electric CNT hydrogels that provided both antimicrobial action and electrical stimulation, thereby enhancing fibroblast migration and proliferation (Nie et al., 2025). Building on this, Xu et al. created a self-powered casein-CNT “E-dressing” capable of harvesting biomechanical energy from wound movement to deliver electrical cues, while also exhibiting photothermal antibacterial activity under NIR irradiation Xu et al., 2025. In the context of electronic skin (E-skin) devices, Song et al. fabricated thermoelectric CNT-polymer composites with dual antibacterial and thermoreceptor-like activity, pointing toward integrated sensory applications with self-healing properties (Song et al., 2025). Another study reported by Xu et al. demonstrated the development of CNT-GelMA-based electroactive macroporous nanocomposite hydrogels via pickering emulsions, combining antibacterial activity with structural porosity to facilitate cellular infiltration and enhance wound-healing performance. The mechanical performance, aside from pore dimensions and conductivity, can also be tailored by varying the CNT content (Xu et al., 2020). In a study aimed at developing treatments for anal fistula, Wang et al. developed quaternized CNT molecular brush grafted injectable microgel systems to effectively fill the fistula and facilitate the drainage of exudate with antibacterial and anti-inflammatory effects, as shown in Figure 6 (Wang et al., 2025a). Related investigations also highlighted multifunctional hydrogels with bacteriostatic, self-healing, conductive, and drug-delivery properties (Zarouki et al., 2025) (Lai et al., 2025). Overall, CNTs are not limited to antibacterial action through a single mechanism but instead contribute multiple strategies, including ROS generation, photothermal conversion, enzymatic mimicry, and electrical stimulation. This versatility enables tailored dressings for both acute trauma and chronic infection, providing a robust foundation for future multimodal infection-control systems.

Diabetic ulcers are one such clinical challenge, where the wound is usually impaired due to angiogenesis deficiency, mitochondrial dysfunction, and inflammation. CNT-based materials have been used to address these problems by combining bioactive delivery systems with conductive scaffolds. Zhang et al. synthesized an exosome/metformin self-healing conductive hydrogel using MWCNTs to promote chronic diabetic wound healing by interfering with mitochondrial fission (Zhang et al., 2023). The synthesized CNT-based injectable hydrogel sustained the release of exosomes and metformin, attenuated mitochondrial fission, normalized endothelial dysfunction, and induced angiogenesis, thereby interfering with the pathogenesis of diabetic ulcers at both the level of metabolic control and conductive signalling, as shown in Figure 7. In another study, Khalid et al. designed CNT-functionalized bacterial cellulose biomaterials to enhance fibroblast migration and angiogenic responses, thereby expediting the healing process in a diabetic wound model (Khalid et al., 2022). Tavakoli et al. employed a tri-layer CNT sponge scaffold incorporating insulin-like growth factor-1 for sustained delivery, to promote prolonged angiogenic signalling, durable vascular remodelling, and a faster rate of wound closure (Tavakoli et al., 2023). Recently, Naik et al. developed CNT-protein-cellulose-based conductive hydrogels for photothermal therapy and demonstrated in vivo photoacoustic imaging in a diabetic disease model (Naik et al., 2025). Here, the dual-purpose platform facilitated significantly faster, more effective wound closure while simultaneously monitoring vascular progression non-invasively, representing a significant breakthrough in diabetic wound care. These studies demonstrate the multifunctional potential of CNT composites, where conductivity, structural reinforcement, and therapeutic delivery converge. Such systems hold considerable promise for diabetic wound healing as they enhance angiogenesis, correct endothelial dysfunction, and stimulate fibroblast activity.

Apart from treatment for diabetic-related diseases, CNTs have been incorporated into regenerative scaffolds to enhance fibroblast activity, keratinocyte migration, stem cell therapies, and drug delivery. CNTs’ conductivity enables scaffolds to transmit bioelectric signals, while mechanical reinforcement improves structural stability. Liu et al. demonstrated that chitosan/gelatin/MWCNT scaffolds under electrical stimulation show enhanced fibroblast proliferation and elevated expression of type I and type III collagen compared with non-conductive counterparts (Liu et al., 2025). Forero-Doria et al. reported supramolecular CNT-cellulose hydrogels for sustained release of bioactive compounds with antimicrobial and in vivo wound-healing regenerative benefits (Forero-Doria et al., 2020). Wang et al. reported cellulose/polypyrrole/CNT-based electroactive hydrogels for enhanced cell proliferation under electrical stimulation in wound healing (Wang et al., 2020). Li et al. expanded the functionality of CNTs by fabricating self-healing hydrogels that retain conductivity and mechanical integrity under repeated deformation (Li et al., 2020). Recently, Chen et al.'s research group constructed an electroactive, oriented wound dressing using a CNT-aligned nanofibrous sheet, which provides directional cues for fibroblast and endothelial cell proliferation and migration, thereby accelerating the healing process (Chen et al., 2025). Figure 8 represents the fabrication of PCL/Gelatin/CNT scaffolds via electrospinning to provide electrostimulation (ES) and regulate the immune microenvironment. CNTs also provide conductivity, enabling the coupling of surrounding and applied electric fields to regulate macrophage phenotypes from M1 to M2 and promote the fibroblast and endothelial cell migration. In vivo studies showed that PCL/Gelatin/CNT scaffolds treated with electrical stimulation inhibited the early inflammation with increased angiogenesis and collagen deposition. Such dressing provides an efficient ES-assisted method for wound healing. In another report, Hashemi et al. and the research group seeded human Wharton’s jelly stem cells tagged with superparamagnetic iron oxide nanoparticles onto PVA/chitosan/CNT scaffolds to study their effect on burn wounds. The outcomes of their study include enhanced healing of burn wounds and MRI monitoring of transplanted cells, highlighting their clinical relevance (Hashemi et al., 2025). In the research reported by Cui et al., an electrospun PCL/CNT fibrous scaffold system was coated with polydopamine containing basic fibroblast growth factor (bFGF) to promote tissue regeneration (Cui et al., 2024). Encapsulation of CNTs modulates the immune microenvironment by promoting macrophage polarization from M1 to M2. As shown in Figure 9, the electroactive aligned fibres can promote fibroblast proliferation and guide cell assembly. In vitro and in vivo studies showed decreased inflammation, enhanced granulation tissue, increased collagen deposition, and re-epithelialization. Altogether, these studies portray CNT scaffolds as bioelectronic regenerative platforms that integrate cell guidance, drug delivery, and self-healing functions. They are versatile enough to support both routine wound closure and advanced strategies such as stem cell transplantation.

Recent advancements towards wound management include the development of innovative dressings that integrate therapeutic and sensing capabilities. CNTs’ conductivity, flexibility, and photothermal properties position them as prime candidates for bioelectronic skins and responsive hydrogel systems. Recently, Ji et al. synthesized CNT-based hydrogel bandage containing glucose and pH sensors for non-invasive monitoring of diabetic wounds (Ji et al., 2025). Liu et al. fabricated an electronic skin scaffold with therapeutic and diagnostic capabilities (Liu et al., 2023). Shen et al. reported a CNT-based nanocomposite conductive hydrogel for flexible monitoring of human motion in daily life and for detecting local temperature changes to monitor the wound-healing process (Shen et al., 2023). Song et al. developed a temperature-responsive electronic platform using a CNT-based thermoelectric polymer composite with self-healing and stretchable properties (Song et al., 2025). Shi et al. have fabricated a novel CNT-based hydrogel with heat-storage capacity, thermal-conductivity, and adhesive ability properties. Thus, CNTs are a potential candidate for burn therapy, laser treatment, and heat-protective clothing (Shi et al., 2022). Pantzke et al. reported that CNTs can modulate interactions between CNTs and fibers in the lungs of patients with pulmonary fibrosis, highlighting the importance of detailed long-term biosafety assessment as CNT-based dressings approach clinical use (Pantzke et al., 2023). Together, these intelligent systems exemplify the progression of CNTs applications: active dressings capable of sensing, stimulating, and healing in real time, accompanied by safety assessments to ensure clinical translation.

CNT-based wound healing materials have shown promise in preclinical models, with applications ranging from antimicrobial dressings to regenerative scaffolds. For instance, bacterial cellulose/MWCNT films achieved 99% wound closure in diabetic rat models within 21 days (Khalid et al., 2022), and CNT/GelMA demonstrated rapid hemostasis and sustained drug release in murine wounds (Li et al., 2022a) (Zhao et al., 2018). Early-phase clinical trials, primarily conducted in Asia and Europe, are largely centered on evaluating CNT-hydrogel composites for use in burn and surgical wounds, with a focus on safety and efficacy. Patents from 2023 to 2024 describe CNT-based dressings with integrated sensors for real-time wound monitoring, indicating industry interest in clinical applications (Hughes et al., 2024). However, no CNT-based wound healing product has yet received widespread regulatory approval (e.g., FDA or EMA), reflecting the nascent stage of translation.

Toxicity Concerns: A primary barrier is the potential cytotoxicity of CNTs, particularly pristine forms, which can induce inflammation, oxidative stress, or genotoxicity due to impurities (e.g., metal catalysts) or aggregation. Long-term bioaccumulation of non-biodegradable CNTs, especially MWCNTs, raises concerns about systemic toxicity, as they may persist in tissues or translocate to organs like the lungs or liver (Cheng et al., 2022). Functionalization with biocompatible groups (e.g., PEG, carboxyl) mitigates these risks; however, studies show variable biocompatibility depending on the CNT type, size, and dose. For example, high-dose SWCNTs (>1 mg/mL) caused fibroblast apoptosis in vitro, while low-dose functionalized CNTs (0.1–0.5 wt%) were well-tolerated (Fraser et al., 2020). Comprehensive toxicological profiling in complex models (e.g., porcine or humanized systems) is needed to establish safe exposure limits (Sayed and Shaikh, 2024).

Scalability and Cost: Producing high-purity CNTs at scale remains costly, with prices ranging from $50 to $ 500/g for biomedical-grade materials. Synthesis methods, such as chemical vapor deposition (CVD), require expensive catalysts and energy-intensive processes, while purification to remove impurities adds complexity. Scaling fabrication of CNTs composites, such as hydrogels or electrospun mats, is challenging due to difficulties in achieving uniform CNT dispersion and reproducibility. These factors limit cost-effectiveness, a critical consideration for widespread clinical adoption, especially in resource-limited settings (Madikere Raghunatha Reddy et al., 2025).

Regulatory Hurdles: Regulatory and translational challenges remain major hurdles for bringing CNT-based wound dressings into clinical use. Regulatory bodies require extensive, continuous data on biocompatibility, biodegradation, systemic distribution, and manufacturing consistency. However, CNT materials are intrinsically heterogeneous, varying in diameter, length, chirality, purity (metallic or semiconducting), surface chemistry, and degree of functionalization, which complicates the establishment of uniform toxicity tests and consistent batch-to-batch standards. This variability can lead to impurity-mediated cytotoxicity, endotoxin contamination, and unpredictable inflammatory responses.

Current nanomaterial standards, such as ISO/TS 80004, provide only high-level definitions and lack CNTs-specific protocols for assessing safety, degradation kinetics, sterility assurance, or long-term tissue retention. As a result, regulators must evaluate CNT-based devices individually, resulting in slowing the review process and hindering industrial translation. The clinical pipeline faces similar constraints, with a scarcity of long-term preclinical studies and an almost complete absence of randomized controlled clinical trials. Without robust human data in chronic wounds, burns, or diabetic ulcers, CNT-based dressings remain confined to laboratory and small-animal research.

Strategies to overcome challenges: Advances in purification techniques, such as acid washing and ultracentrifugation, reduce impurities, while biodegradable CNT derivatives (e.g., carboxylate CNTs) minimize bioaccumulation risks. Developing cost-effective synthesis methods, such as plasma-enhanced CVD, and scalable fabrication techniques (e.g., automated 3D printing) could lower costs. Collaborative efforts between academia, industry, and regulators are essential to establish standardized testing protocols and accelerate clinical trials. Emerging translational platforms, including injectable hydrogels, microneedle patches, and 3D-printed scaffolds, offer scalable, multifunctional strategies for clinical deployment. These approaches emphasize integrating nanomaterials with imaging-guided and precision-medicine paradigms.