# Advanced Micro/Nanocapsules for Self-Healing Coatings
## 5 Types of Self-Healing Capsules  
The development of self-healing coatings has led to the development of multiple self-healing capsule types, each tailored to meet specific requirements and overcome obstacles in different applications. These capsules are designed to encapsulate healing agents and release them when damaged, thereby enabling the self-healing process. The common types of self-healing capsules are inorganic capsules, polymer microcapsules, hollow glass microcapsules, core-shell nanocapsules, vesicles/liposomes, and nanocontainers with controlled release (Figure 4) [70]. One of the main types of self-healing capsules is based on microencapsulation technology. Microencapsulation involves encapsulating the core drug in a protective shell distributed throughout the material. If the material is damaged, the capsules rupture and release the healing agent to repair the crack or break. This process not only prevents further damage but also extends the life cycle of the material. Microencapsulation technology has found widespread use in self-healing materials, from concrete to polymers, and offers a promising solution for improving the durability of various structures. Chemical self-healing capsules play a crucial role in the development of advanced micro/nanocapsules for self-healing coatings [71]. These capsules are designed to encapsulate various active agents capable of repairing damage within coatings, offering a sustainable solution for enhancing material longevity and performance. The introduction of chemical self-healing capsules marks a significant advancement in the field of material science, particularly in the realm of protective coatings for various applications. By understanding the mechanism of action of these capsules, researchers and engineers can harness their potential for creating innovative self-healing materials. The mechanism of action of chemical self-healing capsules involves the controlled release of healing agents in response to damage or external stimuli. When a coating containing these capsules experiences a scratch, crack, or other forms of damage, the capsules rupture, releasing the encapsulated healing agents. These agents then react with the surrounding environment to initiate the healing process, effectively repairing the damage and restoring the coating's integrity [39]. This self-healing mechanism offers a dynamic and autonomous approach to maintaining the functionality and aesthetics of coatings over time, reducing the need for frequent repairs or replacements. Chemical self-healing capsules include urea-formaldehyde (UF) capsules, which have been prepared using an in-situ encapsulation method. These capsules demonstrate a significant size reduction, enhancing their efficiency in delivering healing agents within coatings [72]. Additionally, organic shell nano/microcapsules such as poly(urea-formaldehyde), polystyrene, and polyurethane have been synthesized for self-healing applications, showcasing the versatility and adaptability of chemical self-healing capsules [73]. The development of microcapsule-type self-healing coating systems highlights the potential for these capsules to self-heal cracks and maintain the structural integrity of coatings over extended periods [74]. Through continued research and innovation, the utilization of chemical self-healing capsules is poised to revolutionize the field of protective coatings, offering sustainable and cost-effective solutions for enhanced material performance and longevity. Biological self-healing capsules are a fascinating innovation in the realm of self-healing coatings, offering a unique approach to repairing damage inspired by natural biological processes. These capsules are designed to encapsulate self-healing agents and release them when needed to repair defects in coatings, such as those used in anti-corrosion applications.