Flame-retardant coatings are crucial for safety. However, flame-retardant materials are often hydrophilic, which causes them to dissolve easily in high-humidity environments, significantly limiting their durability. A team of scientists led by Wendong Liu from Dalian University of Technology in Dalian, China, recently drew inspiration from the bilayer architecture of human skin to develop a biomimetic coating that integrates superior water resistance with high-efficiency fire retardancy. This study was recently published in the journal Nano Research on April 15.
The biomimetic coating mimics the bilayer structure of the epidermis and dermis. Meanwhile, a superhydrophobic layer composed of silicone nanofilaments, PVDF-HFP, and PFDTS mimics the epidermal layer, protecting the flame-retardant materials from moisture and providing outstanding superhydrophobicity with a contact angle as high as 165°. The APP- and UPTMS-dominated intumescent flame-retardant layer mimics the dermal layer, providing heat insulation and flame retardancy. The synergistic effect of the flame-retardant and superhydrophobic layers led to excellent flame retardancy and self-extinguishing properties in the biomimetic coating.
"The core of our design lies in decoupling the distinctive requirements of waterproofing and flame-retardancy into two layers," explained corresponding author Professor Wendong Liu of Dalian University of Technology. "Just as skin uses a dense epidermis for waterproofing and a dermis composed of rich fibers and cells for thermal insulation, this biomimetic strategy is not only practical but also features a simple preparation process suitable for scale-up."
The performance of this coating is impressive. The superhydrophobic outer layer effectively repels various daily liquids, including coffee, tea, and cola, and remains stable across a wide pH range from 1 to 13. More crucially, it exhibits remarkable mechanical durability. Even after 1000 bending cycles between 90° and 180°, no significant change in the surface microstructure was observed, and the contact angle remained above 160° on both sides of the SFR-PET. demonstrating potential for use in flexible devices.
When exposed to flame, the coating's fire-retardant performance is equally exceptional. The inner flame-retardant materials expands and chars upon heating. The resulting char layer acted as a physical barrier to heat and oxygen, whereas the release of flame-retardant gases contributed to the self-extinguishing of the flame. Compared with the uncoated polymer substrate, the coating's limiting oxygen index (LOI) increased from 21.44% to 85.30%, while its peak heat release rate (PHRR) and fire growth index (FGI) decreased by 59.4% and 73.5%, respectively.
"The advantage of this coating lies in its multifunctionality, durability, and processability," added Professor Liu. "We have successfully applied it via spraying onto various flammable materials such as cardboard, fabrics, and foam, all of which received effective fire protection. This opens a promising new pathway for developing next-generation safe and durable flame-retardant materials."
The team believes this biomimetic, spray-applied intumescent flame-retardant and superhydrophobic coating is a promising strategy for fabricating robust, multifunctional flame-retardant materials. Its facile fabrication, combined with high thermal stability and mechanical robustness, offers substantial potential for scalable applications in safety-critical environments.
Other contributors include Mingxuan Zhang, Yuechang Lian, Haonan Liu, Siyuan Xiang, Yutao Wang, Bo Yang, Shengyang Tao, and Michael Kappl.
This work was supported by the National Natural Science Foundation of China (under Grant No. 22205031), the Natural Science Foundation of Liaoning Province (under Grant No. 2025-MSLH-149, 2022-MS-136), the Fundamental Research Funds for the Central Universities (under Grant No. DUT25Z2533), and the Open Project of State Key Laboratory of Supramolecular Structure and Materials (sklssm2023012).
DOI Link:
https://doi.org/10.26599/NR.2026.94908394
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
