The US Naval Research Agency and Johns Hopkins University have jointly developed a new coating additive for the maintenance and upkeep of military tactical vehicles. The new coating additive is called "fibroblast like cells", composed of polymer microspheres filled with oily liquid, which have strong corrosion resistance and can be added to existing coating primers for use. When the surface of the vehicle is damaged, the polymer microspheres in the surrounding coating of the damaged area will automatically rupture, releasing oily liquid and forming a wax like waterproof layer on the exposed metal material, effectively preventing the surface of the vehicle from rusting and maintaining a good appearance. With the evolution of modern warfare towards high-intensity and fast-paced forms, the "anti strike+self repair" capability of weapons and equipment may become one of the important factors affecting a certain battle. Currently, research teams from multiple countries are committed to developing new military self-healing coatings to enhance the survivability and combat effectiveness of weapons and equipment. The demand for protection is increasingly upgrading. Coatings, as functional materials for surface protection and corrosion prevention of metal substrates, have been widely used in human life and production. In the military field, coating is regarded as one of the important technical means to improve the performance and prolong the service life of weapons and equipment. According to statistics, over 60% of non combat losses of weapons and equipment can be attributed to material corrosion. For example, salt spray in marine environments can accelerate the electrochemical corrosion process of materials, high temperatures and sandstorms in desert areas can exacerbate material wear and oxidation, and polar low-temperature environments may cause materials to become brittle and reduce their impact resistance. These environmental factors pose serious challenges to the durability and reliability of weapons and equipment. At the same time, technological development and the evolution of warfare forms have raised higher requirements for military coatings, especially in dealing with high-speed flight aerodynamic impacts and complex biochemical threats. However, the limitations of traditional coatings are becoming increasingly prominent. Due to factors such as impact, wear, UV radiation, and corrosive media, the coating is prone to subtle damage that is difficult to detect. In practical applications, due to the limitations of detection methods and the constraints of repair costs, these minor damages are often difficult to detect and repair in a timely manner, which not only exacerbates the corrosion risk of surface materials of weapons and equipment, but also may cause serious structural problems internally. Therefore, developing new coatings with self-healing capabilities has become a focus of research and development in many countries. Compared with traditional military coatings, the new military self-healing coating incorporates a self-healing mechanism through innovative material science design. When the coating is damaged, the preset repair mechanism will automatically activate, achieving self-healing of the damaged area. How to achieve self-healing? According to different repair principles, military self-healing coatings are mainly divided into external self-healing coatings and intrinsic self-healing coatings. There are significant differences in the implementation path and technical characteristics between the two types of coatings. The core of external self-healing coatings is to achieve damage repair by introducing exogenous repair agents into the coating material. These types of coatings are typically embedded with microcapsules, nanocontainers, or functional fibers in the matrix. When the coating is subjected to mechanical damage or specific stimuli, the repair agent is released through physical rupture or chemical response, filling the damaged area and completing the self-healing process through physical curing or chemical reaction. The ceramic composite coating developed by the Siberian Branch of the Russian Academy of Sciences is a typical representative. The coating can maintain stable performance even at extreme high temperatures of 2700 degrees Celsius, and the glass like protective layer generated on its surface can effectively block oxygen and repair the damaged area within 10 minutes. At present, the coating has been applied in the thermal protection system testing of supersonic aircraft, and is expected to be further expanded to fields such as turbine engines and spacecraft power systems in the future. Intrinsic self-healing coatings are intelligent materials that do not rely on external repair agents. Their repair mechanism is based on reversible chemical reactions of resin molecules within the coating or dynamic reorganization of macromolecular microstructures. This type of coating can achieve self repair through chemical bond recombination or molecular chain rearrangement when damaged. Among them, indium gallium alloy liquid metal coating is a typical representative. This coating can achieve droplet deformation by adjusting surface tension. Researchers apply it to the inner surface of fighter jet circuit wires. When the circuit is damaged, the coating can quickly repair the circuit by changing its shape, reducing the failure rate of fighter jet circuits. Similar technology is also used in satellite antenna systems, which effectively repairs millimeter scale cracks by triggering the rearrangement of molecular chains in polysiloxane coatings through ultraviolet light. In fact, the core value of military self-healing coatings lies in enhancing the battlefield survival capability and sustained combat effectiveness of equipment through the self-healing ability of materials. Once traditional equipment is damaged, its combat effectiveness often drops sharply, while military self-healing coatings can enable equipment to achieve "hit and repair" after damage, extending combat time. It still takes time to move towards actual combat. Currently, military self-healing coatings mostly remain at the laboratory level, and there are still many challenges to move towards practical applications. Firstly, the current repair capability of military self-healing coatings is limited to micrometer level damage (such as scratches, small pits), and the repair effect on centimeter level penetrating damage caused by shell fragments is very limited. Research has shown that when the crack width on the coating surface exceeds 3 millimeters, the diffusion path of the repair agent is severely blocked, resulting in a significant decrease in the efficiency of molecular chain recombination. This means that existing self-healing coatings are more suitable as "daily protective layers" for equipment, rather than "battlefield protective layers" to cope with high-intensity impacts. Secondly, the inadequate adaptability of self-healing coatings in extreme environments has become another bottleneck in their practical applications. Under extreme temperature and humidity conditions, the repair efficiency of the new self-healing coating is generally significantly reduced, affecting the practicality and reliability of the coating. When the US F/A-18 Hornet fighter jet was tested in an environment of minus 40 degrees Celsius in the Arctic, the self-healing polymer coating froze due to restricted molecular chain movement and could not function properly. Engineers have to install micro heating elements on the coating to maintain its repair ability in low-temperature environments. Finally, cost and mass production challenges have become the main obstacles to the large-scale application of military self-healing coatings. Due to the complex preparation process, some high-performance self-healing coatings have high costs. Taking indium gallium alloy liquid metal coating as an example, if it is widely used on fighter jets, the total cost will be extremely high. In addition, the packaging process of this coating requires high requirements for the production line, and currently only small-scale trial production can be achieved. Analysts point out that developing low-cost and high-efficiency new coating preparation technologies has become an urgent task. In the future, with the advancement of materials science and the development of intelligent manufacturing technology, it may be possible to break through existing technological bottlenecks and achieve mass production and widespread application of military self-healing coatings. (New Society)