Localized small molecule delivery to improve tendon-to-bone integration following anterior cruciate ligament reconstruction - Bone fractures are common injuries that impact millions of people each year, and poorly healed fractures cause impaired mobility, long-term nursing care, or even premature death. It is known that controlled mechanical loading can improve the quality and speed of fracture repair, but our understanding of mechano- therapeutics is still underdeveloped. Recent research has indicated that zinc may play a fundamental role in the evolution of fracture repair. Zinc is known to stimulate new bone formation, preserve bone mass, and regulate apoptosis. Importantly, intracellular zinc homeostasis must be carefully coordinated to regulate uptake, excretion, and intracellular storage/trafficking. It is believed that zinc may be mechanosensitive; however, the relationships between mechanical loading, zinc homeostasis, and fracture healing remain unclear. This project will generate preliminary data regarding the relationships between mechanotransduction in regenerative cells and establish links between mechanical load transfer and intracellular Zinc homeostasis in bone fractures. Our global hypothesis is that the combination of zinc with mechanical loading will lead to synergistic bone healing responses. In Aim 1, we will extend our existing K25 study with an in vivo rat femoral osteotomy model and determine changes in bone healing caused by zinc delivery and load transfer. Sprague Dawley rats will undergo femoral osteotomy and reconstruction. Mechanical loads across the callus will be controlled with either rigid locking plates (0-3% strain, low load across fracture) or more compliant locking plates (10-15% strain, high load across fracture). Zinc levels in animals will be manipulated locally by implantation of a non-loadbearing intramedullary nail. We hypothesize that the combinatory application of mechanical loads and localized zinc delivery will lead to synergistic improvements in bone healing that are demonstrated by faster and more robust development of callus. Changes in bone healing will be quantified with micro-CT imaging, biomechanical testing, histology, and qPCR. In Aim 2, we will define the causal relationships between zinc delivery, load transfer, zinc storage/trafficking, and osteoblast formation in an in vitro cell culture model. Here, we will use cell culture techniques to examine the fate of human mesenchymal stem cells. We hypothesize that zinc-rich cells plated on stiff, smooth surfaces will elicit improved osteoblastic proliferation and superior calcium matrix formation. These experiments will yield fundamental new understanding into the mechanisms by which cells receive and respond to mechanical stimuli and provide foundational data for long-term development of Zinc-augmented mechano-therapeutics. Characterizing these relationships may have immense implications for cellular mechanobiology and development of mechano- therapeutic approaches for bone regeneration and repair.
