Functional mechanical loading has been known to play an important role in healing of fractured bones. Studies on low magnitude, high frequency (LMHF) loading (tens of micro-strains and ~30 Hz) also show improved bone regeneration. Additionally, the use of low intensity pulsed ultrasound (LIPUS) at fractured bone sites shows mechanical vibrations at ultrasound frequency can also significantly improve fractured and nonunion bone healing outcomes. While these mechanical loading regimes, with vast differences in loading magnitudes and frequencies, have been extensively investigated and their working mechanisms explored on an individual basis, a comprehensive understanding of the cumulative effects of these loading regimes is still lacking due to the limitations imposed by current load application techniques. For example, ultrasound is not capable of providing a static or low frequency load on the healing site, while direct functional loading methods typically involve only static loading. The goal of this project is to develop a bone fixation plate that utilizes an integrated actuator and sensor based on magnetoelastic (ME) materials which change in physical dimension from tens of nanometers to a few microns depending on the strength of an externally applied magnetic field. The force produced by the ME actuator is transferred to the bone fixation plate which acts directly on the bone-implant interface, resulting in extremely focused and localized loading. The externally controlled mechanical loading and real-time sensor feedback will create a valuable interface for investigating the effect of various types of mechanical stimulus on bone healing. Specifically, this project will focus on osteogenesis and vascularization in large segmental bone defects in rats. The focus of this project is to (1) develop a device that can generate variable mechanical loads on large bone defects in rats and (2) to conduct an in vivo study assessing the effects of different types of mechanical loading on vascularization and osteogenesis.
Among the 7.9 million bone fractures that occur in the US annually, 5-10% develop into delayed or nonunion fractures that often require multiple surgical interventions, thus better understanding of bone fracture healing mechanisms and new effective treatment methods are important for reducing the number of surgical interventions and resolving fractures that could otherwise burden patients for a lifetime. Mechanical stimulus has been shown to play an important role in accelerating bone healing and improving successful healing rates in delayed and nonunion fractures; however, the absence of comprehensive studies showing the effect of a wide range of mechanical stimuli on bone healing is a limitation in designing appropriate therapies based on mechanical loading. To address this issue, this project will improve the understanding of mechanical loading effects of various types on bone healing and will develop a new research and therapeutic tool for treating delayed and nonunion fractures.
