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Abstract

Biological materials display great adaptability to their environment, as is the case of bones, muscles, and skin which can adapt in response to mechanical stimuli by changing their composition and structure through a process called mechanotransduction. These systems efficiently convert mechanical stimuli into chemical signals that can drive reactions leading to structural changes, deposition, and removal of material. These adaptive properties give them great advantage in terms of efficiency and durability. Currently, synthetic polymeric materials mostly lack similar adaptability, resulting in mismatches in their physical properties, and the need to replace them repeatedly. Self-strengthening polymeric materials would be useful for reinforcement in fiber composites, improving the lifetime of deployed structural materials, and creating polymers that tailor and fit themselves to individual users, such as prosthetics and robotics. Significant effort has been devoted in designing stimuli-responsive chemistries which impart synthetic polymers with self-reporting and self-healing properties. Several reports have shown the use of heat, light, electricity, pH, and pressure changes to mediate the identification of a failure in polymeric material, deposition of new material, or the formation of new chemical bonds. However, much more work remains to be done to develop mechanoresponsive systems that target adaptation of the material. Conversion of mechanical stimuli into chemical reactivity is an attractive target since mechanical stress is the most common form of energy experienced by materials. Recently, we and others have started investigating methods to use mechanical energy, in the form of ultrasound, mechanical vibrations, and cyclic loading, to conduct controlled polymerization and crosslinking reactions. Piezoelectricity offers a unique approach to convert mechanical stimuli into chemical energy by creating redox micro-environments within a polymer matrix through the piezoelectrochemical effect. Previously, our group demonstrated that ultrasonic agitation of piezoelectric BaTiO3 nanoparticles could promote atom transfer radical polymerization (ATRP) of acrylate monomers by reducing a Cu(II) complex to Cu(I) polymerization promoters. Subsequently, others showed that ATRP is compatible with other monomers and other ceramic piezoelectric nanoparticles. This thesis describes (1) the current advances in the application of piezoelectric nanoparticles to initiate or promote polymerization and crosslinking reactions via mechanical activation (i.e., piezo-polymerization), (2) the use of piezo-polymerization as a method to fabricate and reinforce composite polymeric gels, and (3) a current study about mechanically-promoted mineralization of polymeric composites.

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