Resin composite restoration failure is strongly associated to internal microcracks caused by the masticatory forces. A promising strategy to overcome this shortcoming lies is the addition of healing microcapsules in the organic matrix. 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 degradation-resistant 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 our laboratory, which increases the chance of success. Finally, we will aim at overcoming the main issues involved in the double-emulsion method, such as poor size control of the capsules and high sensitivity of the method, by utilizing coaxial electrohydrodynamic atomization (CEHDA) technique for the encapsulation process. In summary, the following Specific Aims are proposed: (1) To introduce amides as healing agents, (2) To functionalize the microcapsule?s surface with thiourethane oligomers, and (3) To improve encapsulation process with advanced technology. Capsules will be characterized by SEM, HPLC, and Mid-IR spectroscopy. Self-healing composites will be tested for: kinetics, DMA, and mechanical properties under simulate oral conditions, and finally, the healing process analyzed by Serial Block-Face SEM. 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. The skills and new techniques necessary to accomplish the research plan will be acquired from the mentoring team (Drs. Carmem Pfeifer, Jack Ferracane, Luiz Bertassoni, Mary Anne Melo, Sung Yi and Travis Walker), who have pioneering expertise in using the proposed methods and strategies. Complementary background will be gained from seminars, structured tutorials and courseworks. The combination of the new skills learned during the K99 mentored phase with my prior expertise in dental materials characterization, and the advanced clinical training in Prosthodontics will lay the foundation of my independent career, focused on smart dental materials. Additionally, 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.
