Alteration of Bone’s Nonlinear Elastic and Viscoelastic Nanomechanical Properties Is Triggered by Low Intensity Pulsed Ultrasound

Abstract

Dynamic mechanotransduction, particularly under high frequency, low amplitude signals, has been proven effective in mediating bone loss and improving mechanical strength for tissues affected by estrogen deficient osteopenia. Ultrasound, which behaves as an alternating pressure wave in bone, may offer an effective, non-invasive technology for delivery of anabolic signals. In vitro, dynamic mechanical signals delivered using ultrasound have been shown to increase osteoblast proliferation [1], and in vivo studies have established ultrasound as an effective treatment for delayed and non-union fractures [2]. Previously, we showed that ultrasound signals similar to those currently used in a clinical setting for fracture healing were effective in mediating decreases in bone volume and mechanical strength at the millimeter length-scale in response to estrogen deficient osteopenia [3]. Due to bone’s inherent viscoelasticity and the dynamic nature of the applied ultrasound signals, it is particularly important to consider both elastic and viscous components of bone’s adaptive response to applied loads. In light of these findings, the goal of this study was to determine the role of therapeutic ultrasound signal intensity in modulating changes in bone’s nanoscale elastic and viscoelastic material properties associated with estrogen deficient osteopenia. We hypothesize that bone is sensitive to dynamic mechanical signals delivered via ultrasound and that bone’s tissue level nano-scale material properties, particularly nonlinear viscoelastic properties, are sensitive to ultrasound signal intensity.