Mechanoresponsive drug delivery: harnessing forces for controlled release
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Mechanically-activated delivery systems harness existing physiological and/or externally-applied forces to provide spatiotemporal control over the release of active agents. The presence and necessity of these forces in the human body and in the increasing use of mechanically-driven medical devices (e.g., stents, balloon catheters, gastric bands, tissue expanders) can serve as functional dynamic triggers. Therefore, this dissertation investigates the use of applied tensile strain and cyclic loading to control release of entrapped agents, and further translates the concept towards clinical applications by integrating the system with commercial medical devices that provide precise forces to trigger release. As an initial proof-of-concept, mechanoresponsive composites, consisting of highly-textured superhydrophobic barrier coatings over a hydrophilic substrate, are fabricated. The release of entrapped agents, controlled by the magnitude of applied strain, results in a graded response due to water infiltration through propagating patterned cracks in the coating. The strain-dependent delivery of anticancer agents with in vitro efficacy as well as the ex vivo delivery to esophageal tissue with an integrated stent system are demonstrated. Release is further modulated by barrier coating properties. Thicker coatings afford slower release rates with preserved in vitro activity for both a chemotherapeutic and an enzyme. Localizing coating crack patterns based on different geometric stress concentration factors further controls the selective sequential release of multiple agents. Finally, the development of a reversible mechanoresponsive system is investigated to provide cycle-mediated pulsatile release. Optimization of mechanical parameters results in delivery of multiple doses. To translate this concept towards the clinic, the system is integrated with commercial balloon catheters to provide multidose delivery of small molecules to ex vivo vessels. Using the inherent inflation and deflation of the catheter to trigger release, the system enhances existing capabilities to treat cardiovascular and peripheral artery diseases. In summary, the development of mechanoresponsive systems that respond to tensile strain and cycle number are described for the delivery of a wide-range of active agents (hydrophilic and hydrophobic small molecules as well as an enzyme), and their integration with existing medical devices. Furthermore, the comprehensive range of specific kinetic profiles, including triggered release, pulsatile delivery, and the sequential delivery of multiple agents, showcases the capabilities and versatility of these dynamic mechanoresponsive systems to modulate release for the treatment of various clinical diseases.