A promising strategy to overcome the limited survival of dental restorations lies is the addition of healing microcapsules in the organic matrix of the restorative materials. These capsules, when reached by the crack, are broken and release the healing agent, inhibiting its propagation. However, there are several critical gaps and crucial improvements to make this approach suitable and commercially viable. Our long-term goals are to introduce optimized healing agents, minimize the side effects of addition of the capsules, via shell wall functionalization, and validate advanced method for encapsulation. Previous studies revealed that low viscosity amides are capable of modulating the polymerization reaction, and more tough and degradationresistant than methacrylates, so these compounds are going to be used as alternative healing agents. In addition, thiourethane surface functionalization has been shown to be an efficient method to increase fracture toughness and reduce polymerization stress, so we propose to functionalize the capsule surface with this compound -the methods for functionalization were developed in my post-doctoral mentor's laboratory, which increases the chance of success. Finally, we aim at overcoming the main issues involved in the doubleemulsion method, such as poor size control of the capsules and high sensitivity of the method, by utilizing the green chemistry coaxial electrohydrodynamic atomization (CEHDA) technique for the encapsulation process. In summary, the following Specific Aims are proposed to: (1) Introduce amides as healing agents, (2) Functionalize the microcapsule's surface with thiourethane oligomers, and (3) Improve encapsulation process with advanced technology. The K99 mentored phase has been focused on tailoring and optimizing the microcapsules synthesis in order to encapsulate properly compounds with different hydrophilicities and minimize the healing agent leakage. The second main goal of this phase was to enhance the double torsion fracture toughness technique to assess the healing efficiency and the kinetics of the crack propagation under a more clinically relevant scenario. Collected data has highlighted that the incorporation of the microcapsules into the thermosetting polymeric networks changes dramatically the kinetics of the crack formation and propagation. Therefore, in the independent phase of this proposal, the crack growth kinetics and the polymer healing will be closely monitored by the incorporation of fluorescent dyes into the encapsulated healing agents, the investigation of the magnitude of the effects promoted by the addition of the microcapsules in systems containing the unreacted compound triethylene glycol dibutanoate, and the use of digital image correlation (DIC) technology. The central hypothesis is that the tough healing agent, shell wall functionalization, and introduction of CEHDA method to produce capsules will significantly increase the potential and viability of self-healing dental materials. This proposal will broadly impact the field by modifying and improving essential self-healing components and developing an alternative method for encapsulation process, making this approach a tangible resource for resin composites survival.

Self-healing dental materials have the capability of autonomically repairing damage that may occur when the restoration is subjected to, for example, excessive masticatory forces. This study proposes the synthesis of tougher healing agents, which will be able to bring this technology closer to translation to real-life uses. These modifications will prevent resin composite weakening by the addition of surface-functionalized microcapsules and turn self-healing dental materials into a feasible strategy by the introduction of coaxial electrohydrodynamic atomization, as advanced method for capsules synthesis.