Introduction

Lightweight, strong, deformable, and multifunctional fibers are of great interest for use in smart textiles1,2,3,4, flexible electronics5,6, aerospace7,8,9, and energy storage devices10,11,12, among many others. Titanium carbide (Ti3C2Tx) MXene13,14, as an emerging two-dimensional (2D) transition metal carbide, integrates exceptional mechanical15,16,17,18 and electrical19,20,21,22,23 properties, which is an ideal building block for constructing such fibers1,4,24,25,26,27,28,29. 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 interactions36,37,38,39,40 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).

Fig. 1: Preparation process, structural model, and performances of confined and stretched MXene (CSM) fibers.
Fig. 1: Preparation process, structural model, and performances of confined and stretched MXene (CSM) fibers.
Full size image

a Schematic of the preparation process and structural model for CSM fibers. MXene and sodium alginate (SA) sols were extruded into calcium chloride (CaCl2) solution with a concentration of 5 wt% by coaxial wet-spinning, followed by continuous stretching, washing with DIW, and drying to obtain CSM fibers. b, c Photographs of a roll of CSM fiber (b) and a CSM textile having a lateral size of 8 × 9 cm2 (c). Scale bars, 2 cm. d Tensile strength, toughness, and electrical conductivity of CSM fibers (red star) exceed those of previously reported wet-spun pure MXene fibers (green triangles) and MXene composite fibers (purple squares). The names of the materials, detailed data and references corresponding to the sample numbers in the scatter plot are listed in Supplementary Table 6. e SE/t of CSM textiles (red) surpasses that of previously reported textiles woven using polymer (black), metal (green), carbon (pink), and MXene (blue) composite fibers. The names of the materials, detailed data and references corresponding to the sample numbers are listed in Supplementary Table 7. Source data are provided as a Source Data file.

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 Ca 2p 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, Ti2+ (I, II, IV) 2p3/2 and Ti3+ (I, II, IV) 2p3/2 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.

Fig. 2: Structural characterization of MXene and CSM fibers.
Fig. 2: Structural characterization of MXene and CSM fibers.
Full size image

a, b SEM and bright field TEM images (repeated independently with similar structures three times) of the cross-section and axial-section cut by focused ion beam and the corresponding model snapshots from theoretical simulations for MXene (a) and CSM (b) fibers. The first and fourth columns are SEM images, while the second and fifth columns are TEM images. The different MXene nanosheets in the model snapshots are post-rendered using different colors. Scale bars, 10 μm, 50 nm, 20 μm, and 10 nm from left to right. c Volume percent porosity of MXene fibers (blue) and the inner MXene layer in CSM fibers (red). d Herman’s orientation factor of wet (red) and dry (blue) MXene and CSM fibers. e Interplanar spacing of MXene (blue) and CSM (red) fibers. Data are presented as mean ± standard deviation from three independent experiments, where applicable. Source data are provided as a Source Data file.

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.

Fig. 3: Properties of MXene and CSM fibers.
Fig. 3: Properties of MXene and CSM fibers.
Full size image

a Typical tensile stress-strain curves of MXene and CSM fibers. b A radial plot comparing the tensile strength, Young’s modulus, toughness, strain, and electrical conductivity of MXene (blue) and CSM (red) fibers. c Electrical conductance retention percentages as a function of time for MXene and CSM fibers stored in humid air with 100% relative humidity. d Dependence of the number of cycles to failure on the maximum stress level at a stress amplitude of 50 MPa and a loading frequency of 1 Hz for MXene and CSM fibers. e Temperature as a function of time for CSM fibers during cyclic on-off Joule heating at a voltage of 4 V. f SEM images of a bent MXene fiber and a knotted CSM fiber (repeated independently with similar structures for three times). Scale bars, 20 μm in the left and 50 μm in the right. Source data are provided as a Source Data file.

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 handloom (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.

Fig. 4: EMI shielding and Joule heating performances of CSM textiles.
Fig. 4: EMI shielding and Joule heating performances of CSM textiles.
Full size image

a EMI SE as a function of frequency for 108-μm-thick and 216-μm-thick CSM textiles. The inset shows an SEM image of a 108-μm-thick CSM textile (repeated independently with similar structures three times). Scale bar, 1 mm. b SEA (blue), SER (pink), and SEtotal (red) at a frequency of 8.2 GHz for 108-μm-thick and 216-μm-thick CSM textiles. The main contribution to the shielding of CSM textiles is from absorption. c Schematic illustrating the EMI shielding mechanisms for CSM textiles, including reflection and absorption. d EMI SE retention percentages as a function of cycle number for CSM textiles that are cyclically bent from 0° to 180°. e Joule heating retention percentages for flat, bent, and twisted CSM textiles. The insets show the optical and infrared images of these textiles heated using a voltage of 8 V. Scale bar, 2 cm. Source data are provided as a Source Data file.

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.

Discussion

We demonstrate a continuous strategy to synergistically eliminate the voids resulting from transverse wrinkles and improve axial alignment by coaxial-wet-spinning-assisted radial confining in combination with roll-to-roll-assisted axial stretching under near room temperature, obtaining highly aligned and compact MXene fibers with strong interlayer interactions. The resultant MXene fibers show high tensile strength, toughness, electrical conductivity, and resistance to oxidation, cyclic mechanical deformation, and sonication damage. Additionally, large-area textiles woven from the MXene fibers integrate extraordinary EMI shielding capacity, Joule heating, service stability, and biocompatibility. The presented strategy not only paves a feasible way for realizing the practical applications of MXene in wearable smart textiles for EMI shielding and electrothermal management but also provides an avenue for the scalable assembly of other 2D nanosheets into high-performance fibers.

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.

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.