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J Biomech Eng. 2017 Nov 1;139(11). doi: 10.1115/1.4037937.

Wireless Implantable Sensor for Noninvasive, Longitudinal Quantification of Axial Strain Across Rodent Long Bone Defects.

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George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332.
Parker H. Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, GA 30332.
Department of Biomedical Engineering, Michigan Technological University, Houghton, MI 49931.
School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332.
School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332.
Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, PA 19104.
Department of Orthopaedics, Emory University, Atlanta, GA 30303.
Atlanta Veteran's Affairs Medical Center, Department of Orthopaedics, Decatur, GA 30033.
Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA 30332.


Bone development, maintenance, and regeneration are remarkably sensitive to mechanical cues. Consequently, mechanical stimulation has long been sought as a putative target to promote endogenous healing after fracture. Given the transient nature of bone repair, tissue-level mechanical cues evolve rapidly over time after injury and are challenging to measure noninvasively. The objective of this work was to develop and characterize an implantable strain sensor for noninvasive monitoring of axial strain across a rodent femoral defect during functional activity. Herein, we present the design, characterization, and in vivo demonstration of the device's capabilities for quantitatively interrogating physiological dynamic strains during bone regeneration. Ex vivo experimental characterization of the device showed that it possessed promising sensitivity, signal resolution, and electromechanical stability for in vivo applications. The digital telemetry minimized power consumption, enabling extended intermittent data collection. Devices were implanted in a rat 6 mm femoral segmental defect model, and after three days, data were acquired wirelessly during ambulation and synchronized to corresponding radiographic videos, validating the ability of the sensor to noninvasively measure strain in real-time. Together, these data indicate the sensor is a promising technology to quantify tissue mechanics in a specimen specific manner, facilitating more detailed investigations into the role of the mechanical environment in dynamic bone healing and remodeling processes.

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