Figure 3: (a) Autonomic healing concept incorporating encapsulated healing agent and embedded catalyst particles in a polymer matrix; (i) damage event causes crack formation in the matrix; (ii) crack ruptures the microcapsules, releasing liquid healing agent into crack plane; (iii) healing agent polymerizes upon contact with embedded catalyst, bonding crack closed; (iv) typical SEM image of the urea-formaldehyde microcapsules containing dicyclopentadiene prepared by emulsion in situ microencapsulation, adapted from [35]. (b) (i) Schematic diagram of smart repair concepts considered for hollow glass fiber polymer matrix composites. Use single-part, two-part resin and hardener, or resin with a catalyst/hardener. (ii) Typical scanning electron microscopy (SEM) image of the hollow glass fiber, adapted from [20]. (c) Biomimetic microvascular self-healing. (i) Schematic diagram of a capillary network in the dermis layer of skin with a cut in the epidermis layer (ii) Schematic diagram of the self-healing structure composed of a microvascular substrate and a brittle epoxy coating containing embedded catalyst, adapted from [23]. (iii) Optical image of the 3D microvascular network embedded in an epoxy matrix (Credit Photo D. Therriault).