Mechanical resonator to measure magnetic susceptibility of structurally intact bone

Moore, Lee R.; Midura, Meredith; Royer, R.; Androjna, Charlie; Rozic, Richard; Waldorff, Erik I.; Zhang, Nianli; Ryaby, James T.; Midura, Ronald J.; Zborowski, Maciej

doi:10.1016/j.jmmm.2020.167488

Cited by 1 publication

(1 citation statement)

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“…The Lorentz force arising from interaction of the (induced) electric current in tissue and the combination of imposed oscillating and strong, and constant B-fields are capable of imparting mechanical force on tissue under carefully controlled laboratory conditions [21]- [23] and were also considered as a contributing factor in TMS biological effects [24]. We have previously reported on mechanical effect of slowly oscillating magnetic field (1 Hz) on bulk bone [25].…”

Section: Discussionmentioning

confidence: 99%

Cortical Bone Vibrations Induced by Electromagnetic Field Pulse

et al. 2022

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The purpose of our study was to test the hypothesis that the electromagnetic pulse (EMP) is capable of inducing mechanical vibrations in bone ex vivo. A thin segment of human femur diaphysis (from a tissue repository) suspended on a tensioned line (range T = 2.2-123 N) was exposed to EMP (mean B = 0.64 T, dB/dt = 5877 T/s, and the mean B-field gradient of 127 T/m) from a solenoid with axis orthogonal to tensioning line, forming a harmonic oscillator whose mechanical vibrations were measured using laser Doppler vibrometry (LDV, noise floor 1 µm/s). Calculated mean Maxwell stress and Lorentz forces acting on a weakly conducting, diamagnetic bone slice point away from the solenoid for maximum sensitivity of LDV measurement. The electromechanical origin of the LDV signal was confirmed by the order-of-magnitude agreement between calculated (range from 12 to 50 µm/s) and measured initial bone velocity amplitudes (e.g., 35.5 µm/s ± 7.5 µm/s at T = 22.2 N and 17.7 µm/s ± 2.5 µm/s at T = 58.2 N) and the increasing frequency (25-180 Hz) of decaying oscillations with the square root of T over the range of line tensions (r 2 = 0.978, p < 10 −4 , and n = 17). Theory and experiment show that magnetic field impulses are capable of exerting measurable mechanical forces on bone ex vivo. The results raise an interesting question if the electromechanical effect could be sufficiently large to contribute to bone remodeling, reportedly sensitive to vibration amplitudes as small as 1 nm, and considering long duration of orthopedic therapy using repetitive EMP (months).

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