Date of Award



Biomedical and General Engineering


Scott Hazelwood


Space exploration and microgravity have substantial negative effects on the human body. Symptoms of space explorers include cardiovascular deconditioning, bone loss, muscular atrophy, and impairment of neurovestibular and sensory function. The great loss of bone due long-duration spaceflight increases fracture risk, jeopardizing the success of the mission and postflight recovery. Bisphosphonates may be able to counteract this bone loss by altering the remodeling process. These drugs increase bone mass, thus reducing fracture risk, but also lead to increased levels of fatigue microdamage. Fracture risk can be lowered by increasing both bone mass (quantity) and bone quality.

The purpose of this study was to create a computer model to simulate bisphosphonate treatment on astronauts while traveling in space in order to examine the ability of bisphosphonates to maintain bone mass in a microgravity environment and reduce fracture risk of bone upon return to Earth. Various bisphosphonate treatment potencies and bone balance ratios given at different time points (either at or before spaceflight) were examined. Flight duration was also varied to examine short-term (10 days) to long-term (1 year) effects of microgravity on bone mineral density (BMD), a measure commonly used to estimate bone strength, and damage accumulation. The model predicted bisphosphonate treatments with low to intermediate suppression of remodeling activation and that create higher bone balance ratios cause reductions in fracture risk. The simulation also predicted significant changes to BMD and damage upon return to Earth as the remodeling response readjusted to higher stress conditions. For treatments highly suppressing remodeling activation, these predicted postflight changes included decreased BMD and increased damage accumulation. Low levels of remodeling suppression led the model to predict substantial increases in BMD and small increases in damage postflight. Postflight changes were minimal for treatments with intermediate suppression.