Plant Cell Wall-Inspired Interfacial Bridging Enables Ultrastrong and Tough Carbon Nanotube Fibers

Achieving simultaneous enhancement of strength and toughness in carbon nanotube fibers (CNTFs) remains a persistent challenge due to inefficient interfacial load transfer, low nanotube alignment, and high porosity. Herein, inspired by the hierarchical architecture and borate-mediated cross-linking of plant cell walls, we report a bioinspired interfacial bridging strategy to fabricate ultrastrong and tough CNTFs. This approach involves the sequential infusion of poly(pyridobisimidazole) (PIPD) nanofibers and chains into CNTF networks, followed by borate-induced covalent cross-linking and mechanical densification. The PIPD molecular backbone consists of alternating pyridobisimidazole and dihydroxyphenyl rings, which enable the formation of hydrogen bonding and borate-mediated covalent cross-linking network with CNTs. The resulting fibers exhibit strong intertube interactions, improved alignment, and reduced porosity. Consequently, CNTFs achieve an ultrahigh tensile strength of 8.45 ± 0.28 GPa and a high toughness of 238.42 ± 14.78 MJ·m^-3, surpassing the performance of commercial high-performance fibers. Additionally, the fibers exhibit high impact resistance with a specific penetration energy of 1.26 MJ·kg^-1, outperforming many state-of-the-art protective materials. Experimental characterizations combined with first-principles calculations reveal that the synergistic interplay between the highly ordered assembly and strengthened interfacial interactions enables cooperative deformation and efficient energy dissipation. This work establishes a scalable and biomimetic pathway for fabricating CNTFs with a combination of ultrahigh strength and toughness, making them promising candidates for advanced structural and protective applications.