Continuous MXene fibers with near-gigapascal tensile strength via radial confinement and axial stretching

Domain: chemistry
Published: 2026-01-07
Editorial outcome: major_revision

Abstract
Assembling titanium carbide MXene nanosheets into macroscopic high-performance fibers is very challenging because of the voids caused by transverse wrinkles, hindering their practical applications in wearable smart textiles. Here we continuously fabricate ultrastrong MXene fibers by coaxial-wet-spinning-assisted radial confining integrated with roll-to-roll-assisted axial stretching under near room temperature. Wet-spun MXene fibers are bridged with calcium ions and radially confined to reduce the voids resulting from transverse wrinkles by an in-situ bridged sodium alginate encapsulation layer, followed by stretching to axially align nanosheets. The resultant MXene fibers provide record tensile strength (958 MPa) and electrical conductivity (13,692 S cm-1). Large-area textiles made from the MXene fibers present extraordinary electromagnetic interference shielding capacity (6,509 dB cm-1). The proposed strategy opens an avenue for scalable assembling other two-dimensional nanosheets into high-performance fibers.

Introduction
Lightweight, strong, deformable, and multifunctional fibers are of great interest for use in smart textiles1–4, flexible electronics5,6, aerospace7–9, and energy storage devices10–12, among many others. Titanium carbide (Ti3C2Tx) MXene13,14, as an emerging two-dimensional (2D) transition metal carbide, integrates exceptional mechanical15–18 and electrical19–23 properties, which is an ideal building block for constructing such fibers1,4,24–29. Thus, it is of utmost importance to assemble MXene nanosheets into macroscopic high-performance fibers. Wet-spinning24,28,30,31, coating32, electrospinning33, biscrolling34, and thermal drawing35 methods have been developed to fabricate macroscopic MXene fibers. For example, Eom et al.28. fabricated MXene fibers by wet-spinning, where MXene solution was extruded into a coagulant composed of ammonium chloride and ammonium hydroxide, achieving a tensile strength of 63.9 MPa and an electrical conductivity of 7713 S cm−1. However, the weak interlayer interactions, misalignment, and voids degrade the mechanical and electrical properties and ambient stability of the obtained macroscopic fibers18,25,28,35, greatly hindering their practical applications.

Considerable efforts have been focused on improving the properties of MXene fibers by reinforcing interlayer interactions36–40 and increasing nanosheet alignment25,35,41,42 during wet-spinning. The connectivity between adjacent MXene nanosheets can be strengthened by hydrogen36, ionic37,43,44, and covalent38 bonding. For example, strong MXene-silk fibroin fibers having a tensile strength of 70 MPa were constructed by hydrogen bonding36. MXene-metal ion fibers were reinforced by ionic bonding, providing a Young’s modulus of 6.86 GPa37. Adjacent MXene nanosheets were covalently bridged to enhance the tensile strength and toughness of MXene fibers to 401 MPa and 2.49 MJ m−3, respectively38. Ionic and covalent bonding were also combined to promote the tensile strength of MXene fibers to 502 MPa39. Unfortunately, the insertion of bonding agents usually disrupts the electron transport between adjacent MXene nanosheets, decreasing the electrical conductivity of MXene fibers36,39. For example, the electrical conductivity of MXene-silk fibroin fibers36 is sharply decreased from 7500 S cm−1 for pristine MXene fibers to 134 S cm−1. By contrast, aligning MXene nanosheets by axial stretching35 can simultaneously improve the mechanical and electrical properties of MXene fibers that provide a tensile strength of 707 MPa and an electrical conductivity of 12,000 S cm−1. However, the realized properties of macroscopic fibers are still substantially lower than for monolayer MXene nanosheets15,16,19,20. This huge property gap is mainly because of the neglected loose assembly of MXene nanosheets in the transverse direction, resulting from the nanosheet wrinkling induced by the capillary contraction during drying17,45,46. Thus, the fabrication of high-performance MXene fibers remains a great challenge because of the transverse wrinkles and resulting voids.

Here, we report the continuous fabrication of high-performance MXene fibers by combining a coaxial-wet-spinning-assisted radial confining process with a roll-to-roll-assisted axial stretching process under near room temperature. Wet-spun MXene fibers were bridged with calcium ions (Ca2+) and radially confined to densely assemble MXene nanosheets by an in-situ bridged sodium alginate (SA) layer, followed by stretching to axially align MXene nanosheets, resulting in the highly aligned and compact MXene fibers with strong interlayer interactions. The obtained confined and stretched MXene (CSM) fibers integrate high mechanical and electrical properties, as well as excellent resistance to oxidation, cyclic mechanical deformation, and sonication damage. Moreover, the CSM fibers can be woven into large-area textiles, which present exceptional electromagnetic interference (EMI) shielding capacity, Joule heating, service stability, and biocompatibility.

Results
Fabrication of CSM fibers
The absence of the 104 peak in the X-ray diffraction curve (Supplementary Fig. 1) of Ti3C2Tx MXene powder verifies the successful exfoliation of MXene nanosheets from Ti3AlC2 MAX phase18. Additionally, the interplanar spacing of Ti3C2Tx MXene (1.23 nm) is larger than for Ti3AlC2 MAX (0.93 nm) because of the introduction of intercalated water and surface functional groups47. The exfoliated MXene nanosheets have an average lateral size of 11.0 μm (Supplementary Fig. 2) and a thickness of approximately 1.25 nm (Supplementary Fig. 3), which is larger than the theoretical thickness of monolayer MXene because of the presence of water on the MXene surface15. SA is a biomaterial with good biocompatibility and has abundant hydroxyl and carboxyl groups available for coordinating with Ca2+ and hydrogen bonding with MXene nanosheets47,48.

Figure 1a, Supplementary Fig. 4 show the fabrication process of CSM fibers under near room temperature. MXene and SA sols exhibiting rheological shear-thinning behavior (Supplementary Fig. 5) were extruded into calcium chloride (CaCl2) solution by coaxial wet-spinning, during which Ca2+ was infiltrated into the whole fiber and bridged with SA and MXene nanosheets. Subsequently, the fiber was continuously stretched and washed with deionized water (DIW) by a roll-to-roll process. Finally, a roll of CSM fiber was collected after drying (Fig. 1b, Supplementary Movie 1).

For comparison, using a collection speed (V1) equal to the extrusion speed (V0), three types of confined MXene (CM) fibers (CM-I to CM-III) with increasing SA concentration were fabricated. MXene sol was assembled into MXene fibers using the same wet-spinning, washing, and drying process. The strongest version of CM fibers, corresponding to CM-III with an SA concentration of 40 mg mL−1, was used to fabricate CSM fibers. Three types of CSM fibers (CSM-I to CSM-III) with increasing stretching ratio (defined as SR = V1/V0) were fabricated. Additionally, stretched MXene (SM) fibers were fabricated by treating MXene fibers using the same roll-to-roll-assisted stretching process. Note that CM fibers will become wrinkled using excess SA concentration, while CSM fibers will become discontinuous using excess SR (Supplementary Fig. 6). The real content of Ca2+ and SA in MXene, SM, CM, and CSM fibers, characterized by energy-dispersive X-ray spectroscopy (EDS) and thermogravimetric analysis (Supplementary Fig. 7), is tabulated in Supplementary Table 1. Unless otherwise stated, the strongest versions of CM and CSM fibers were selected to compare their microstructures and properties.

Structural characterization of CSM fibers
X-ray photoelectron spectroscopy (Supplementary Fig. 8) spectra show that compared with MXene and SA powder, CSM fibers have a new Ca2+ peak, indicating the modification of Ca2+. Additionally, the cross-sectional EDS results (Supplementary Fig. 9) of MXene and CSM fibers confirm the uniform distribution of Ca2+. Moreover, Ti 2p3/2 (I, II, IV) and Ti 3p3/2 (I, II, IV) peaks are downshifted from 455.8 eV and 456.9 eV for MXene powder to 455.5 eV and 456.6 eV for CSM fibers, respectively, verifying that Ca2+ was bonded onto MXene nanosheets47. The O–C=O peak of CSM fibers is slightly downshifted from 288.2 eV for SA powder to 287.9 eV, demonstrating the coordination between Ca2+ and –COO– groups of SA molecules47.

Fourier transform infrared spectra (Supplementary Fig. 10) show that the –OH peak of MXene fibers is redshifted from 3,433 cm−1 for MXene powder to 3,424 cm−1, further confirming the formation of H–O→Ca2+ coordination47,49. Compared with MXene fibers, the –OH peak of CM and CSM fibers is redshifted to 3,417 cm−1, suggesting the hydrogen bonding between MXene nanosheets and SA molecules47,49. Additionally, the –COO– peak is redshifted from 1,603 cm−1 for SA powder to 1,587 cm−1 for CM and CSM fibers, further verifying the coordination between Ca2+ and –COO– groups47. Thus, the inner MXene layer in CSM fibers is strongly crosslinked with the outer bridged SA layer by hydrogen and ionic bonding.

The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images (Fig. 2a, Supplementary Fig. 11a) of the cross-section for MXene fibers, having a high porosity of 15.3 ± 0.4% (Fig. 2c, Supplementary Table 2), show numerous large voids between wrinkled MXene nanosheets. Compared with MXene fibers, the porosities of SM and CM fibers are reduced to 12.1 ± 0.3% and 11.9 ± 0.3%, respectively, demonstrating the structural densification induced by axial stretching and radial confining. Additionally, the radial confinement effect on reducing the voids of CM fibers is increased with increasing thickness of the bridged SA layer (Supplementary Table 2). Moreover, CSM fibers show the densest structure (Fig. 2b, Supplementary Figs. 11b, 12), having a low porosity of 7.47 ± 0.30% because of the synergistic densification of radial confining and axial stretching. Small-angle X-ray scattering patterns (Supplementary Fig. 13) and density measurements (Supplementary Fig. 14) further demonstrate that the magnitude of the porosity for fibers decreases as follows: MXene > SM > CM > CSM.

MXene nanosheet alignment was described by Herman’s orientation factor derived from wide-angle X-ray scattering patterns (Supplementary Figs. 15–17). The alignment of dry MXene fibers (0.717 ± 0.003; Fig. 2d, Supplementary Fig. 18a and Supplementary Table 3) is much lower than for wet MXene fibers (0.795 ± 0.004) because of the MXene nanosheet wrinkling (Fig. 2a) caused by the capillary contraction during drying17,45,46. Compared with wet MXene fibers, wet SM (0.841 ± 0.002) and CM (0.820 ± 0.003) fibers have higher alignment, indicating that the axial loading induced by stretching and the radial confinement induced by the shrinkage of the SA layer during bridging48 improve the stacking order of wet MXene nanosheets. Additionally, the retention percentages of alignment for SM and CM fibers after drying are higher than for MXene fibers (Supplementary Fig. 18b). This implies that the axial loading induced by stretching and the radial confinement induced by the shrinkage of the bridged SA layer during drying can inhibit the capillary contraction of MXene nanosheets, thereby freezing their aligned structure. Moreover, the radial confinement effect on improving the stacking order of dry MXene nanosheets is increased with increasing thickness of the bridged SA layer (Supplementary Fig. 16).

As a result of the synergistic effect of axial stretching and radial confining on inhibiting capillary contraction, dry CSM fibers show a highly aligned structure (Fig. 2b) having the highest alignment (0.903 ± 0.003). Additionally, CSM fibers (1.20 ± 0.01 nm; Fig. 2e, Supplementary Fig. 19) have a smaller interplanar spacing than MXene fibers (1.32 ± 0.01 nm), further demonstrating the compact structure of CSM fibers. Note that axial stretching can improve the crystallinity (Supplementary Fig. 20) of SA molecules and induce the shrinkage of the bridged SA layer (Supplementary Fig. 21), further promoting the radial confinement35. Radial confinement of the bridged SA layer can also improve the structural integrity of fibers during axial stretching, explaining why the maximum SR used for fabricating CSM fibers (1.8) is higher than for SM fibers (1.1). Furthermore, axial stretching using a larger SR can induce a better synergistic effect with radial confining on improving the alignment and compactness of dry CSM fibers (Supplementary Fig. 17, Supplementary Table 2). Moreover, coarse-grained molecular dynamics simulation results (Fig. 2a, b, Supplementary Figs. 22–24 and Supplementary Movies 2–4) show that the magnitude of the compactness and alignment for dry fibers decreases as follows: CSM > CM > SM > MXene, which is consistent with the experimental results.

Properties of CSM fibers
Figure 3a, Supplementary Fig. 25 display the typical tensile stress-strain curves of MXene, SM, CM, and CSM fibers. Benefiting from the highly aligned and compact structure with strong interlayer interactions, CSM fibers provide the highest tensile strength of 958 ± 29 MPa, as well as a Young’s modulus of 26.7 ± 1.5 GPa, a toughness of 66.3 ± 3.7 MJ m−3, and a strain of 10.7 ± 0.3%, which are 9.96, 3.07, 76.1, and 6.99 times higher than for MXene fibers (Fig. 3b, Supplementary Table 4), respectively. Additionally, the tensile strength and Young’s modulus of CSM fibers are 2.31 and 2.28 times higher than for CM fibers, while the tensile strength, toughness, and strain of CSM fibers are 5.10, 93.6, and 15.8 times higher than for SM fibers, respectively. Furthermore, the tensile strength and toughness of CSM fibers surpass those reported for previous wet-spun MXene fibers (Fig. 1d, Supplementary Table 5). A folded CSM fiber can easily lift the weight of 400 g (Supplementary Fig. 26), demonstrating its excellent mechanical properties. Moreover, MXene fibers show flat fracture edges, while CSM fibers show curled fracture edges (Supplementary Fig. 27), verifying the strengthened interlayer interactions in CSM fibers.

Because an aligned and compact structure can decrease the electron transport path and promote the MXene interlayer electron transport50, CSM fibers provide the highest electrical conductivity of 13,692 ± 116 S cm−1 (Fig. 3b, Supplementary Table 6), which is 1.19, 1.27, and 1.47 times higher than for SM, CM, and MXene fibers, respectively. The electrical conductivity of CM fibers is higher than that of MXene fibers, demonstrating that the bridged SA encapsulation promotes the electron transport along the fiber. This is because the radial confinement induced by bridged SA encapsulation effectively improves the alignment of MXene nanosheets and removes the voids resulting from transverse wrinkles. Additionally, the electrical conductivity of CSM fibers exceeds that reported for previous MXene fibers (Fig. 1d, Supplementary Table 5). Moreover, CSM fibers have higher oxidative stability than MXene fibers (Fig. 3c) because the bridged SA protection layer and compact structure impede the penetration of oxygen and water molecules into the MXene interlayer18. More specifically, CSM fibers can retain 94.6% of their initial electrical conductance after storing in humid air for 14 days.

The existing voids, acting as initial cracks17, greatly decrease the fatigue resistance of MXene fibers to cyclic stretching and bending. For example, MXene fibers can be cyclically stretched for only 1847 times under a stress ranging from 10 to 60 MPa (Fig. 3d) and bent for only one time at an angle ranging from 0° to 180° (Supplementary Fig. 28). Because the synergistic densification induced by radial confining and axial stretching effectively eliminate the initial cracks, CSM fibers provide higher fatigue resistance than MXene fibers. More specifically, CSM fibers can be cyclically stretched for 26,793 times under a stress ranging from 650 to 700 MPa and retain 97.5% of their initial electrical conductance after cyclic bending for 6000 times. Additionally, compared with MXene fibers, CSM fibers show higher resistance to the structural damage produced by sonication (Supplementary Fig. 29). More specifically, after sonicating for 60 min, the retention percentage of the electrical conductivity for CSM fibers is 98.1 ± 0.4% (Supplementary Fig. 30). The internal structure of CSM fibers after sonicating is similar to that before sonicating (Supplementary Fig. 31), demonstrating their excellent durability.

Reflecting excellent electrical conductivity, CSM fibers show exceptional Joule heating performance and can be quickly heated to about 103 °C when applying a voltage of 4 V, which is much higher than for MXene fibers (34 °C; Supplementary Fig. 32a). The surface temperature of CSM fibers increases monotonically with increasing voltage (Supplementary Fig. 32b). Additionally, CSM fibers can be heated and cooled to fixed values repeatedly during 5000 voltage’s on-off cycles (Fig. 3e, Supplementary Fig. 33), indicating good long-term Joule heating stability. Moreover, whether bending at an angle ranging from 0° to 180° or knotting with a diameter ranging from 3.4 mm to 0.5 mm, CSM fibers show a similar surface temperature, demonstrating high deformable stability (Supplementary Fig. 34).

When using as electrical wires, MXene fibers bent at an angle of 90° show obvious cracks (Fig. 3f, Supplementary Fig. 35a) and are even broken, being failed to light up a light-emitting diode (LED, Supplementary Movie 5), while knotted CSM fibers show good structural integrity (Fig. 3f) and can normally light up the LED (Supplementary Fig. 35b). Additionally, the brightness of LED is stable when cyclic bending CSM fibers (Supplementary Movie 6), further confirming their high fatigue resistance to bending. CSM fibers also remain highly conductive during stretching (Supplementary Fig. 36), and their inner MXene and bridged SA encapsulation layers are broken almost simultaneously at the mechanical failure point (Supplementary Movie 7), partly because of the strong interfacial interactions. Moreover, the density of CSM fibers (2.07 ± 0.03 g cm−3) is much lower than for copper wires (9.7 g cm−3), while their tensile strength and toughness are much higher than for copper wires (256 MPa and 51.8 MJ m−3)42, suggesting promising application in flexible electrical wires.

Properties of CSM textiles
Flexible and strong CSM fibers can be woven into large-area textiles using a hand loom (Fig. 1c, Supplementary Fig. 37), while brittle MXene fibers are easily broken during manual weaving. Reflecting excellent electrical conductivity, 108-μm-thick CSM textiles provide a high average EMI shielding effectiveness (SE) of 70.3 dB between 8.2 GHz and 12.4 GHz (Fig. 4a). The thickness-averaged SE (SE/t) of CSM textiles is 6509 dB cm−1, which surpasses that reported for previous textiles woven using polymer, metal, carbon, and MXene composite fibers (Fig. 1e, Supplementary Table 7). The SE of absorption (SEA), reflection (SER), and total (SEtotal) for CSM textiles is plotted in Fig. 4b. The main shielding mechanism of CSM textiles is absorption in part because of the highly aligned structure, which is similar to layered MXene films23. Additionally, compared with 108-μm-thick textiles, 216-μm-thick CSM textiles have a much higher SEA and comparable SER. The proposed shielding mechanism is shown in Fig. 4c. When the incident electromagnetic (EM) waves encounter conductive CSM textiles, some EM waves are immediately reflected back because of the numerous free electrons of highly conductive CSM fibers. The residual EM waves pass through the lattice structure of CSM textiles, where the interaction with the high electron density of CSM fibers and multiple internal reflections dissipates the EM waves41.

Benefiting from the high fatigue resistance of CSM fibers, the EMI shielding capacity of CSM textiles is highly stable during cyclic bending (Fig. 4d, Supplementary Fig. 38a). More specifically, CSM textiles cyclically bent for 1 × 105 times retain 96.3% of their initial EMI SE. Additionally, CSM textiles show good structural integrity (Supplementary Fig. 39) and provide a high EMI SE retention percentage of 92.0% after cyclic washing for 1 × 103 times (Supplementary Fig. 38b). The structure of CSM textiles is also highly stable during long-term sonication (Supplementary Fig. 40). Furthermore, the Joule heating performance of various deformed CSM textiles is almost the same as that of flat ones (Fig. 4e, Supplementary Fig. 41). Moreover, the fibroblasts cultured on CSM textiles are alive, suggesting their good biocompatibility (Supplementary Fig. 42). These results demonstrate the enormous potential of CSM fibers for constructing wearable smart textiles that can be used to provide personal protection in EMI shielding and electrothermal management.

Methods
Materials
Lithium fluoride (LiF, ≥99.99%) and anhydrous CaCl2 (96.0%) were provided by Aladdin. SA (90%, 300 mPa∙s) was received from Macklin. Hydrochloric acid (HCl, 36%~38%) was purchased from Sinopharm Chemical Reagents Co., Ltd. These reagents were used as received without further purification. DIW (resistivity > 18 MΩ cm) was collected from a Milli-Q Biocel water purification system.

Preparation of Ti3AlC2
Ti3AlC2 powder was fabricated by mixing commercial TiC powder (2 μm) and gas-atomized TiAl powder (74 μm) in a molar ratio of 2:1, followed by ball-milling in ethanol for 24 h. The resultant mixture was then dried, pressed into a graphite die, and sintered for 2 h at 30 MPa and 1500 °C under an Ar atmosphere. Finally, the resultant Ti3AlC2 block was ground and sieved to obtain Ti3AlC2 powder (<38 μm).

Preparation of Ti3C2Tx nanosheets
Ti3C2Tx MXene nanosheets were exfoliated from Ti3AlC2 based on a modified minimally intensive layer delamination method under an Ar atmosphere51. Typically, LiF (3.2 g) was mixed with HCl (40 mL, 9 M) by stirring for 5 min at room temperature. Subsequently, Ti3AlC2 powder (2.0 g) was slowly added, followed by stirring for 30 h at 50 °C. The reaction mixture was then cooled to room temperature and repeatedly washed with DIW by centrifuging at 1330 g for 5 min until the pH of the supernatant was about 6. After discarding the supernatant, the swelled sediment was diluted with DIW and mildly vibrated, followed by centrifuging at 244 g for 30 min to remove non-exfoliated particles. Finally, the supernatant was centrifuged at 977 g for 20 min, obtaining MXene nanosheets in the sediment.

Preparation of CSM fibers
MXene (46 mg mL−1) and SA sols were extruded into CaCl2 solution (5 wt%) at a velocity of V0 by coaxial wet-spinning using a spinneret consisting of an inner 28-gauge needle and an outer 21-gauge needle. The resultant gel fiber was then continuously stretched and washed with DIW by a roll-to-roll process. Finally, a roll of CSM fiber was collected at a velocity of V1 after drying. Based on the SR, the following three types of CSM fibers were fabricated using an SA sol having a concentration of 40 mg mL−1: CSM-I (1.4), CSM-II (1.6), and CSM-III (1.8). Additionally, based on the concentration of SA, the following three types of CM fibers were fabricated using the same coaxial wet-spinning, stretching, washing, and drying process with an SR of 1: CM-I (10 mg mL−1), CM-II (20 mg mL−1), and CM-III (40 mg mL−1). MXene and SA sols were assembled into MXene and SA fibers, respectively, using the same wet-spinning, stretching, washing, and drying process with an SR of 1. SM and stretched SA (SSA) fibers were fabricated from MXene and SA sols using the same wet-spinning, stretching, washing, and drying process with an SR of 1.1 and 1.8, respectively.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This manuscript by Prof. Cheng and co-authors presents a continuous strategy for preparing MXene fibers through coaxial-wet-spinning-assisted radial confining integrated with roll-to-roll-assisted axial stretching. The wet-spun MXene fibers were firstly bridged with calcium ions and then radially confined to reduce the voids through transverse wrinkles by an in-situ bridged sodium alginate encapsulation layer through stretching. The resultant MXene fibers having strong interlayer interactions are highly aligned and densified. The record tensile strength of 958 MPa and electrical conductivity of 13,692 S cm-1 are achieved.\nThis manuscript is well-written, and the experimental data is well organized and robustly supports the conclusions. The general readers of Nature Communications will be interested in this new fabrication strategy and the outstanding properties of MXene fibers. Thus, this manuscript is strongly recommended for publication in Nature Communication after the following minor revision:\n1. Much more details should be added in the figure captions for easily understanding the figures.\n2. Much more discussions on fabrication and performance of reported MXene fibers should be added in the introduction, which is important for readers to understand the development of MXene fibers.\n3. The format of references should be consistent with requirements of Nature Communications, please carefully double check main text.", "reviewer_2": "This work mainly reported a continuous fabrication strategy of high-performance MXene fibers by coaxial-wet-spinning-assisted radial confining integrated with roll-to-roll-assisted axial stretching. The reported data are solid, experimental methods is detailed, and the manuscript was well written and structured logically. I recommend this work for publication in Nature Communications. Some minor suggestions are listed below.\n1. It is appreciated that the continuous fabrication process of CSM fibers has been recorded in the Supplementary Video 1. The manuscript can further improve its clarity by describing the diameter of spinneret channel, the extrusion speed (V0), and the collection speed (V1) in the caption of Supplementary Video 1.\n2. It would be beneficial to specify the frequency range in the Supplementary Table 7 when comparing the EMI shielding performance of CSM textiles with that of the previous textiles woven using polymer, metal, carbon, and MXene composite fibers.\n3. What is the density of CSM fibers? The CSM fibers are largely likely lighter than traditional metal wires, such as copper. Thus, comparing the mechanical properties and density of CSM fibers with those of copper wires is helpful to highlight the superiority of CSM fibers used as electrical wires.\n4. The CSM fibers seems to be fabricated under near room temperature, which should be highlighted considering that many high-performance fibers, such as graphene fibers, are usually fabricated under high temperature (>2000 ºC).\n5. What is the molecular weight or viscosity of SA powder? It should be described in the Methods section.\n6. SR should be defined using full name upon first appearance in the Supplementary Information.", "reviewer_3": "This study provides a strategy for fabricating highly aligned and densely packed MXene-based fibers by combining coaxial wet spinning with sodium alginate bridging, followed by axial stretching. The reported mechanical strength, electrical conductivity, and EMI shielding performance of the MXene fibers are certainly impressive. However, there are several issues including discussion, experimental method, and format that must be solved before publication. After careful review, I suggest major revision subjected to the corrections for the publication in Nature communications.\n1. The manuscript suggests that the MXene-infused fiber maintains electrical conductivity even under tensile deformation, implying a strong mechanical-electrical coupling. However, the reviewer is concerned that an embedded MXene network inside a CSA fiber could be disrupted under strain, potentially cracking the internal structure and breaking conductive pathways. Did the authors perform simultaneous tensile testing (e.g. on a UTM) with in situ resistance measurements to verify that conductivity is preserved during stretching? If not, on what basis do they claim that the fiber remains conductive under load? Demonstrating real-time electrical continuity during elongation is essential to validate the claimed electromechanical coupling.\n2. The authors combine radial confinement with axial stretching to produce MXene fibers, describing this as a new synergistic strategy. Yet inserting a 2D nanomaterial into a tubular polymer structure and stretching it for alignment has been explored in prior studies[R1,R2]. Given that coaxial wet-spinning and post-drawing are established techniques for producing aligned composite fibers, what specifically is novel here? How does the proposed method fundamentally differ from or improve upon earlier MXene fiber fabrication approaches (e.g. core-sheath fibers or stretched composites)? The reviewer requests a clearer delineation of the unique innovations and advantages of this work, to convincingly establish its novelty beyond the existing literature.\n3. Supplementary Fig S7, the TGA of the MXene shows virtually no weight loss, which is surprising. Even pristine Ti3C2Tx MXene typically exhibits a mass loss due to absorbed water and decomposition of surface terminations upon heating. How do the authors explain the absence of any weight change in their MXene sample? Was the material pre-dried or treated in a way that eliminates adsorbed species, or might there be an issue with the TGA measurement (e.g. calibration or baseline drift)? This unexpected result raises concerns about sample preparation or instrument accuracy.\n4. The introduction notes that introducing binders or crosslinkers can strengthen MXene fibers at the cost of electrical conductivity (since added agents disrupt inter-sheet contact). In this work, the MXene fibers are encapsulated with a calcium-crosslinked alginate shell intended to densify and reinforce the structure. How do the authors ensure that this encapsulation (and the presence of Ca2+ ions) does not impede electron transport along the fiber? The reported conductivity (13692 S cm-1) is exceptionally high for a composite fiber, suggesting minimal electrical compromise. Did the authors compare conductivity between fibers with and without the alginate sheath, or measure whether the alginate layer adds any contact resistance at the MXene interface? A discussion of how the fiber maintains such high conductivity despite the polymer encapsulation would be valuable.\n5. A central claim of the manuscript is that radial confinement through alginate/Ca2+ encapsulation densifies the MXene structure by eliminating transverse wrinkles and voids. While SAXS and TEM images are presented to support this, the evidence remains largely qualitative. Have the authors measured the bulk density (mass per unit volume) of the fibers with and without radial confinement? Quantitative density analysis is essential to validate the claimed densification. Without such data, it is difficult to objectively assess how much structural compaction was achieved.\n6. The manuscript reports a tensile strength of 958 MPa, which is among the highest values for MXene-based fibers. However, from the shape of the S-S curve, it is unclear where and how the internal MXene network fails during elongation. To ensure practical applicability, it is important to determine whether the electrical pathways persist up to or beyond the mechanical failure point. Could the authors clarify at what strain level the electrical conductivity is lost, and whether the fracture originates from disruption of the MXene stack or from the surrounding matrix?\n7. Although the manuscript provides cycling and sonication experiments in the SI, the reviewer finds the validation incomplete. Specifically, after sonication, the study does not clearly show whether the electrical conductivity is retained or how the internal structure is affected (e.g., cracks, delamination, or collapse). Can the authors provide comparative post-sonication conductivity data, or high-resolution structural images to assess damage? Given that sonication imposes significant mechanical agitation, the fiber’s performance post-treatment is critical to prove its durability.\n[R1] Zhou, Tianzhu, et al. \"Ultra-compact MXene fibers by continuous and controllable synergy of interfacial interactions and thermal drawing-induced stresses.\" Nature Communications 13.1 (2022): 4564.\n[R2] Zhou, Tianzhu, et al. \"Interlocking‐governed ultra‐strong and highly conductive MXene fibers through fluidics‐assisted thermal drawing.\" Advanced Materials 35.51 (2023): 2305807."}, "author_response": "We would like to express our appreciation to the three reviewers for their very helpful comments and constructive suggestions. We realize that all of you spent a considerable amount of time carefully reading the manuscript and formulating a strategy of action for us to make this paper better. We are very grateful for this.\nWe have attempted to address all the issues raised in the review and to revise the paper exactly along the lines suggested. Below we provide the reviewers’ comments in black and our responses in blue.\nReviewer 1:\nThis manuscript by Prof. Cheng and co-authors presents a continuous strategy for preparing MXene fibers through coaxial-wet-spinning-assisted radial confining integrated with roll-to-roll assisted axial stretching. The wet-spun MXene fibers were firstly bridged with calcium ions and then radially confined to reduce the voids through transverse wrinkles by an in-situ bridged sodium alginate encapsulation layer through stretching. The resultant MXene fibers having strong interlayer interactions are highly aligned and densified. The record tensile strength of 958 MPa and electrical conductivity of 13,692 S cm-1 are achieved.\nThis manuscript is well-written, and the experimental data is well organized and robustly supports the conclusions. The general readers of Nature Communications will be interested in this new fabrication strategy and the outstanding properties of MXene fibers. Thus, this manuscript is strongly recommended for publication in Nature Communication after the following minor revision:\nReply: We appreciate the reviewer’s positive comments. We have tried to revise the manuscript exactly along the following suggestions.\n1. Much more details should be added in the figure captions for easily understanding the figures.\nReply: We appreciate the reviewer’s insightful suggestions. The details have been added in the captions of Figures 1~4 of the revised manuscript with highlighted in yellow.\n2. Much more discussions on fabrication and performance of reported MXene fibers should be added in the introduction, which is important for readers to understand the development of MXene fibers.\nReply: We appreciate the reviewer’s insightful suggestions. The discussions on the fabrication and performance of reported MXene fibers have been added in the introduction section of the revised manuscript with highlighted in yellow.\n3. The format of references should be consistent with requirements of Nature Communications, please carefully double check main text.\nReply: We appreciate the reviewer’s kind reminding. The format of references has been checked and corrected in the revised manuscript according to the requirements of Nature Communications.\nReviewer 2:\nThis work mainly reported a continuous fabrication strategy of high-performance MXene fibers by coaxial-wet-spinning-assisted radial confining integrated with roll-to-roll-assisted axial stretching. The reported data are solid, experimental methods is detailed, and the manuscript was well written and structured logically. I recommend this work for publication in Nature Communications. Some minor suggestions are listed below.\nReply: We appreciate your encouraging comments. We have tried to revise the manuscript exactly along the following suggestions.\n1. It is appreciated that the continuous fabrication process of CSM fibers has been recorded in the Supplementary Video 1. The manuscript can further improve its clarity by describing the diameter of spinneret channel, the extrusion speed (V ), and the collection speed (V ) in the caption of Supplementary Video 1.\n0 1\n2. It would be beneficial to specify the frequency range in the Supplementary Table 7 when comparing the EMI shielding performance of CSM textiles with that of the previous textiles woven using polymer, metal, carbon, and MXene composite fibers.\nReply: We appreciate the reviewer’s insightful suggestions. The frequency range has been specified in the Supplementary Table 7 of the revised manuscript with highlighted in yellow.\n3. What is the density of CSM fibers? The CSM fibers are largely likely lighter than traditional metal wires, such as copper. Thus, comparing the mechanical properties and density of CSM fibers with those of copper wires is helpful to highlight the superiority of CSM fibers used as electrical wires.\nReply: We appreciate the reviewer’s insightful questions and suggestions. The density of CSM fibers is 2.07 ± 0.03 g cm-3, which is lower than for copper wires (9.7 g cm-3, Nano-Micro Lett. 2022, 14, 111). Additionally, the tensile strength and toughness of CSM fibers (958 ± 29 MPa and 66.3 ± 3.7 MJ m-3, Nano-Micro Lett. 2022, 14, 111) are much higher than for copper wires (256 MPa and 51.8 MJ m-3), respectively. The following comparison has been made in the revised manuscript with highlighted in yellow: Moreover, the density of CSM fibers (2.07 ± 0.03 g cm-3) is much lower than for copper wires (9.7 g cm-3), while their tensile strength and toughness are much higher than for copper wires (256 MPa and 51.8 MJ m-3)42, suggesting promising application in flexible electrical wires.\n4. The CSM fibers seems to be fabricated under near room temperature, which should be highlighted considering that many high-performance fibers, such as graphene fibers, are usually fabricated under high temperature (>2000 ºC).\nReply: We appreciate the reviewer’s insightful suggestions. The “near-room-temperature fabrication process” has been emphasized in the sections of Abstract, Introduction, Fabrication of CSM fibers, and Discussion of the revised manuscript with highlighted in yellow.\n5. What is the molecular weight or viscosity of SA powder? It should be described in the Methods section.\nReply: We appreciate the reviewer’s kind reminding. The viscosity of SA powder is 300 mPa∙s, which has been added in the Methods section of the revised manuscript with highlighted in yellow.\n6. SR should be defined using full name upon first appearance in the Supplementary Information.\nReply: We appreciate the reviewer’s kind reminding. Stretching ratio has been defined as SR upon first appearance in Supplementary Figure 6 of the revised Supplementary Information with highlighted in yellow.\nReviewer 3:\nThis study provides a strategy for fabricating highly aligned and densely packed MXene-based fibers by combining coaxial wet spinning with sodium alginate bridging, followed by axial stretching. The reported mechanical strength, electrical conductivity, and EMI shielding performance of the MXene fibers are certainly impressive. However, there are several issues including discussion, experimental method, and format that must be solved before publication. After careful review, I suggest major revision subjected to the corrections for the publication in Nature communications.\nReply: We appreciate the reviewer’s comments. We have performed additional experiments and tried to clarify the following questions.\n1. The manuscript suggests that the MXene-infused fiber maintains electrical conductivity even under tensile deformation, implying a strong mechanical-electrical coupling. However, the reviewer is concerned that an embedded MXene network inside a CSA fiber could be disrupted under strain, potentially cracking the internal structure and breaking conductive pathways. Did the authors perform simultaneous tensile testing (e.g. on a UTM) with in situ resistance measurements to verify that conductivity is preserved during stretching? If not, on what basis do they claim that the fiber remains conductive under load? Demonstrating real-time electrical continuity during elongation is essential to validate the claimed electromechanical coupling.\nReply: We appreciate the reviewer’s insightful comments and suggestions. The real-time electrical conductance of CSM fibers was measured during tensile testing, as shown in Figure R1. Upon tensile loading, the electrical conductance of CSM fibers is slightly decreased because of the slippage of MXene nanosheets and can maintain more than 90.4% of its initial value. At the moment of fracture of CSM fibers, their electrical conductance retention is sharply decreased from 90.4% to 0.00012%, indicating that the inner MXene layer does not break prematurely during stretching. Thus, CSM fibers remain highly conductive during stretching. The above result and discussion have been added in the revised manuscript with highlighted in yellow. Figure R1 is Supplementary Figure 36 in the revised manuscript. Additionally, CSM fibers remain highly conductive during cyclic bending (Supplementary Figure 28) or knotting (Supplementary Figures 34 and 35b).\nFigure R1. Tensile stress-strain curve of CSM fibers and their electrical conductance retention percentage during tensile testing.\n2. The authors combine radial confinement with axial stretching to produce MXene fibers, describing this as a new synergistic strategy. Yet inserting a 2D nanomaterial into a tubular polymer structure and stretching it for alignment has been explored in prior studies [R1,R2]. Given that coaxial wet-spinning and post-drawing are established techniques for producing aligned composite fibers, what specifically is novel here? How does the proposed method fundamentally differ from or improve upon earlier MXene fiber fabrication approaches (e.g. core-sheath fibers or stretched composites)? The reviewer requests a clearer delineation of the unique innovations and advantages of this work, to convincingly establish its novelty beyond the existing literature.\nReply: We appreciate the reviewer’s insightful comments. The mentioned previous studies (R1: Nat. Commun. 2022, 13, 4564; R2: Adv. Mater. 2023, 35, 2305807) mainly fabricated core-sheath and aligned MXene fibers by thermal drawing a molten polymer tube under a temperature typically higher than 200 ºC. Very recently, the coaxial wet-spinning and post-drawing have also been developed to fabricate core-sheath and aligned MXene fibers under near room temperature (Nano-Micro Lett. 2022, 14, 111; Adv. Funct. Mater. 2025, 25, 2419923; Small 2025, 21, 2411735; Adv. Mater. 2025, 35, 2501485). Improving the properties of MXene fibers by designing the core-sheath and stretch-induced aligned structure seems like the similarity between these previous studies and our current work. However, the interfacial interactions between core and shell layers are usually weak and even neglected in the previous studies, largely decreasing the properties of MXene fibers. Additionally, the thermal drawing process is complex and energy-consuming. What differentiates the current work from these previous studies mainly includes the following aspects:\n(1) The fabrication process of CSM fibers in our current work is under near room temperature, which is lower energy-consuming compared with thermal drawing process.\n(2) The inner MXene layer is strongly crosslinked with the outer bridged SA layer by hydrogen and ionic bonding (please see the Structural characterization of CSM fibers section of the revised manuscript) in our current work, which is largely differ from the weak core-shell interfacial interactions of the MXene fibers fabricated by thermal drawing or coaxial wet-spinning and post-drawing in the previous studies. The strong core-shell interfacial interactions is responsible for the excellent mechanical properties of CSM fibers and their good structural integrity and high electrical conductivity retention during deformation (please see the detailed response to your comments 1 and 6).\n(3) Wet-spun MXene fibers usually show loose assembly of MXene nanosheets in transverse direction because of the nanosheet wrinkling induced by the capillary contraction during drying. We found in the current work that axial stretching (can induce the shrinkage of bridged SA layer) and radial confining can synergistically inhibit the capillary contraction of MXene nanosheets and reduce the voids resulting from transverse wrinkles (please see the Structural characterization of CSM fibers section of the revised manuscript), which has not yet been reported in the previous studies.\nWe strongly believe that the above novelties and advantages can fully differentiate our current work from the mentioned previous studies (R1 and R2) and other reported works. The following description has been added in the revised manuscript with highlighted in yellow: (1) under near room temperature; (2) Thus, the inner MXene layer in CSM fibers is strongly crosslinked with the outer bridged SA layer by hydrogen and ionic bonding; (3) synergistically reducing the voids resulting from transverse wrinkles.\n3. Supplementary Fig S7, the TGA of the MXene shows virtually no weight loss, which is surprising. Even pristine Ti C T MXene typically exhibits a mass loss due to absorbed water and decomposition of surface terminations upon heating. How do the authors explain the absence of any weight change in their MXene sample? Was the material pre-dried or treated in a way that eliminates adsorbed species, or might there be an issue with the TGA measurement (e.g. calibration or baseline drift)? This unexpected result raises concerns about sample preparation or instrument accuracy.\nReply: We appreciate the reviewer’s kind reminding. We have re-tested the TGA curve of MXene powder under a nitrogen atmosphere with a temperature rising from room temperature to 550 ºC at a rate of 10 ºC min-1 (Figure R2). The mass loss of MXene powder is about 3.16% because of the removal of absorbed water and decomposition of surface terminations upon heating from room temperature to 550 ºC. Figure R2 is Supplementary Figure 7 in the revised manuscript.\nFigure R2. TGA curves of MXene powder, CM-I to CM-III fibers, CSM fibers, and SA powder.\n4. The introduction notes that introducing binders or crosslinkers can strengthen MXene fibers at the cost of electrical conductivity (since added agents disrupt inter-sheet contact). In this work, the MXene fibers are encapsulated with a calcium-crosslinked alginate shell intended to densify and reinforce the structure. How do the authors ensure that this encapsulation (and the presence of Ca2+ ions) does not impede electron transport along the fiber? The reported conductivity (13692 S cm-1) is exceptionally high for a composite fiber, suggesting minimal electrical compromise. Did the authors compare conductivity between fibers with and without the alginate sheath, or measure whether the alginate layer adds any contact resistance at the MXene interface? A discussion of how the fiber maintains such high conductivity despite the polymer encapsulation would be valuable.\nReply: We appreciate the reviewer’s insightful comments and suggestions. Compared with MXene fibers (9,325 ± 107 S cm-1) without SA sheath, CM fibers (10,818 ± 112 S cm-1) with SA sheath have higher electrical conductivity (Supplementary Table 6), demonstrating that the SA encapsulation promotes the electron transport along the fiber. This is because the radial confining induced by SA encapsulation effectively improves the alignment of MXene nanosheets (Supplementary Table 3) and removes the voids resulting from transverse wrinkles (Supplementary Table 2). Note that both MXene and CM fibers fabricated using calcium chloride as coagulant contain Ca2+ ions. The following discussion has been added in the revised manuscript with highlighted in yellow: The electrical conductivity of CM fibers is higher than for MXene fibers, demonstrating that the bridged SA encapsulation promotes the electron transport along the fiber. This is because the radial confining induced by bridged SA encapsulation effectively improves the alignment of MXene nanosheets and removes the voids resulting from transverse wrinkles.\n5. A central claim of the manuscript is that radial confinement through alginate/Ca2+ encapsulation densifies the MXene structure by eliminating transverse wrinkles and voids. While SAXS and TEM images are presented to support this, the evidence remains largely qualitative. Have the authors measured the bulk density (mass per unit volume) of the fibers with and without radial confinement? Quantitative density analysis is essential to validate the claimed densification. Without such data, it is difficult to objectively assess how much structural compaction was achieved.\nReply: We appreciate the reviewer’s insightful comments and suggestions. The bulk density of the MXene layer in MXene, SM, CM, and CSM fibers has been measured, as shown in Figure R3. The magnitude of the density for MXene layer in fibers increases as follows: MXene < SM < CM < CSM, which is consistent with SAXS and TEM characterizations. This result further demonstrates the densification induced by radial confining and axial stretching. The density analysis has been added in the revised manuscript with highlighted in yellow. Figure R3 is Supplementary Figure 14 in the revised manuscript.\nFigure R3. Density of the MXene layer in MXene, SM, CM, and CSM fibers.\n6. The manuscript reports a tensile strength of 958 MPa, which is among the highest values for MXene-based fibers. However, from the shape of the S-S curve, it is unclear where and how the internal MXene network fails during elongation. To ensure practical applicability, it is important to determine whether the electrical pathways persist up to or beyond the mechanical failure point. Could the authors clarify at what strain level the electrical conductivity is lost, and whether the fracture originates from disruption of the MXene stack or from the surrounding matrix?\nReply: We appreciate the reviewer’s insightful questions. The real-time conductance measurements during tensile testing show that the inner MXene layer does not break prematurely during elongation and the electrical conductivity is lost at the mechanical failure point (please see the detailed response to your comment 1). Additionally, the stretching process of CSM fibers was observed by in-situ SEM (Supplementary Movie 7), demonstrating that the bridged SA encapsulation layer does not break prematurely during elongation. The fracture surface also shows that the inner MXene layer is closely boned with the outer SA encapsulation layer (Supplementary Figure 12h). Thus, the inner MXene and bridged SA encapsulation layers are broken almost simultaneously at the mechanical failure point of CSM fibers, partly because of the strong core-shell interfacial interactions. The following discussion has been added in the revised manuscript with highlighted in yellow: CSM fibers also remain highly conductive during stretching (Supplementary Figure 36) and their inner MXene and bridged SA encapsulation layers are broken almost simultaneously at the mechanical failure point (Supplementary Movie 7), partly because of the strong interfacial interactions.\n7. Although the manuscript provides cycling and sonication experiments in the SI, the reviewer finds the validation incomplete. Specifically, after sonication, the study does not clearly show whether the electrical conductivity is retained or how the internal structure is affected (e.g., cracks, delamination, or collapse). Can the authors provide comparative post-sonication conductivity data, or high-resolution structural images to assess damage? Given that sonication imposes significant mechanical agitation, the fiber’s performance post-treatment is critical to prove its durability.\nReply: We appreciate the reviewer’s insightful suggestions. The electrical conductivity of CSM fibers after sonicating was measured (Figure R4) and their cross-sectional structure was also characterized (Figure R5). After sonicating for 60 minutes, the retention percentage of the electrical conductivity for CSM fibers is 98.1 ± 0.4%. Additionally, the internal structure of CSM fibers after sonicating is similar to that before sonicating (Supplementary Figure 11b), demonstrating their excellent durability. The above results and discussion have been added in the revised manuscript with highlighted in yellow. Figures R4 and R5 are Supplementary Figures 30 and 31 in the revised manuscript, respectively.\nFigure R4. Electrical conductivity retention percentage of CSM fibers after sonicating for 1, 30, and 60 minutes.\nFigure R5. SEM images of the cross-section cut by focused ion beam for CSM fibers after sonicating for 60 minutes. Scale bars, 10 μm in low-resolution image and 1 μm in high-resolution image.\n[R1] Zhou, Tianzhu, et al. \"Ultra-compact MXene fibers by continuous and controllable synergy of interfacial interactions and thermal drawing-induced stresses.\" Nature Communications 13.1(2022): 4564.\n[R2] Zhou, Tianzhu, et al. \"Interlocking‐governed ultra‐strong and highly conductive MXene fibers through fluidics‐assisted thermal drawing.\" Advanced Materials 35.51 (2023): 2305807."}, {"round": 2, "reviewer_comments": {"reviewer_1": "This version is fine to be accepted.", "reviewer_2": "As my comments were considered during their revision process, the revised version can be accepted,", "reviewer_4": "I am reviewing the manuscript “Continuous ultrastrong MXene fibers via the synergy of radial confining and axial stretching” in response to the editor’s request. The authors have meticulously and clearly addressed all the concerns raised by the Reviewer 3 in the previous round of peer review. The authors have measured the real-time electrical conductance during tensile testing, TGA curve, bulk densities, the in-situ SEM of stretching process, and the electrical conductivity and cross-sectional SEM after sonicating. Additionally, the revised manuscript has provided a convincing discussion on high conductivity and a clear description of its unique innovations and advantages, which are very impressive on me. The supplemented data are solid and further verify the conclusions, as follows:\n1. The real-time electrical conductance results clearly demonstrate that CSM fibers preserve high conductivity and the inner MXene layer does not break prematurely during stretching.\n2. The low energy-consuming fabrication process under near room temperature, strong core-shell interfacial interactions, and synergistic densification effect induced by axial stretching and radial confining are presented as the novelties and advantages of this work that can fully differentiate from the prior studies.\n3. The re-tested TGA curve is fine and consistent with the previous reports.\n4. The authors have compared the conductivity of MXene fibers without SA sheath and CM fibers with SA sheath, firmly verifying that the SA encapsulation promotes the electron transport along the fiber. A reasonable explanation strongly supported by structural characterization has also been provided that the radial confining induced by bridged SA encapsulation effectively improves the alignment of MXene nanosheets and removes the voids resulting from transverse wrinkles.\n5. The bulk density of the MXene layer in MXene, SM, CM, and CSM fibers has been measured. The result is consistent with SAXS and TEM characterizations, further demonstrating the densification induced by radial confining and axial stretching.\n6. The stretching process of CSM fibers has been observed by in-situ SEM, clearly demonstrating that the bridged SA encapsulation layer does not break prematurely during elongation. Together with real-time electrical conductance results, it is convincing to claim that the inner MXene and bridged SA encapsulation layers are broken almost simultaneously at the mechanical failure point of CSM fibers, partly because of the strong core-shell interfacial interactions.\n7. After sonicating, CSM fibers are still compact and have a high conductivity retention, well demonstrating their excellent durability.\nIn short, the revised manuscript has good enough data for verifying the conclusions, and this work will be an good advance in the field of MXene, 2D materials and fibers. I recommend that this work can be published in Nature Communications."}, "author_response": "We would like to express our appreciation to the three reviewers for their very helpful comments and constructive suggestions. We realize that all of you spent a considerable amount of time carefully reading the manuscript and formulating a strategy of action for us to make this paper better. We are very grateful for this. Below we provide the reviewers’ comments in black and our responses in blue.\nReviewer 1:\nThis version is fine to be accepted.\nReply: We appreciate the reviewer’s positive comments.\nReviewer 2:\nAs my comments were considered during their revision process, the revised version can be accepted.\nReply: We appreciate the reviewer’s positive comments.\nReviewer 4:\nI am reviewing the manuscript “Continuous ultrastrong MXene fibers via the synergy of radial confining and axial stretching” in response to the editor’s request. The authors have meticulously and clearly addressed all the concerns raised by the Reviewer 3 in the previous round of peer review. The authors have measured the real-time electrical conductance during tensile testing, TGA curve, bulk densities, the in-situ SEM of stretching process, and the electrical conductivity and cross-sectional SEM after sonicating. Additionally, the revised manuscript has provided a convincing discussion on high conductivity and a clear description of its unique innovations and advantages, which are very impressive on me. The supplemented data are solid and further verify the conclusions, as follows:\n1. The real-time electrical conductance results clearly demonstrate that CSM fibers preserve high conductivity and the inner MXene layer does not break prematurely during stretching.\n2. The low energy-consuming fabrication process under near room temperature, strong core-shell interfacial interactions, and synergistic densification effect induced by axial stretching and radial confining are presented as the novelties and advantages of this work that can fully differentiate from the prior studies.\n3. The re-tested TGA curve is fine and consistent with the previous reports.\n4. The authors have compared the conductivity of MXene fibers without SA sheath and CM fibers with SA sheath, firmly verifying that the SA encapsulation promotes the electron transport along the fiber. A reasonable explanation strongly supported by structural characterization has also been provided that the radial confining induced by bridged SA encapsulation effectively improves the alignment of MXene nanosheets and removes the voids resulting from transverse wrinkles.\n5. The bulk density of the MXene layer in MXene, SM, CM, and CSM fibers has been measured. The result is consistent with SAXS and TEM characterizations, further demonstrating the densification induced by radial confining and axial stretching.\n6. The stretching process of CSM fibers has been observed by in-situ SEM, clearly demonstrating that the bridged SA encapsulation layer does not break prematurely during elongation. Together with real-time electrical conductance results, it is convincing to claim that the inner MXene and bridged SA encapsulation layers are broken almost simultaneously at the mechanical failure point of CSM fibers, partly because of the strong core-shell interfacial interactions.\n7. After sonicating, CSM fibers are still compact and have a high conductivity retention, well demonstrating their excellent durability.\nIn short, the revised manuscript has good enough data for verifying the conclusions, and this work will be an good advance in the field of MXene, 2D materials and fibers. I recommend that this work can be published in Nature Communications.\nReply: We appreciate the reviewer’s encouraging comments."}]

Decision letter