Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150115

150115 - Resonant Characterization of Hysteretic Nonlinearity in Cranial Sutured Bones 

Cranial sutures are fibrous joints that connect the bones of the skull, allowing for growth and flexibility. Abnormal growth or premature fusion of these sutures, as seen in conditions like craniosynostosis, can lead to significant health issues affecting skull shape and brain development. While the static linearized characteristics of sutured bones have been extensively examined in the existing literature, the nonlinear elastic behavior of sutures remains uncharacterized. Investigating the nonlinear acoustic properties of cranial sutures could yield novel insights into their mechanical behavior and potentially pave the way for new diagnostic applications. In structural mechanics, it is well-established that micro-damage or close interfaces/contact within the micro-structure is the origin of hysteretic nonlinearity. Sutures, being interfaces or contact points between bone regions, are therefore likely to exhibit such nonlinear behavior. This study utilizes Nonlinear Resonant Acoustic Spectroscopy (NRAS) to investigate the acoustic properties of cranial sutures, aiming to characterize their nonlinear behavior and correlate it with their micro-structural features. The results present opportunities spanning from leveraging such suture nonlinearities for diagnostic purposes to understanding the nonlinearities coming from the skull in transcranial ultrasound. NRAS is a vibration-based method utilized to measure the non-classical or hysteretic nonlinearity parameter. This type of nonlinearity is characterized by a nonlinear stress-strain relationship that varies with the rate of loading. NRAS estimates the nonlinearity parameter by observing the shift in resonance frequency as the excitation amplitude increases. Sutured bones display notable hysteretic nonlinearity, while non-sutured bones do not exhibit this type of nonlinearity. This finding is consistent with the existing literature on the correlation between micro-structure and hysteretic nonlinearity, which establishes that closed cracks or contacts, which can open and close during high voltage amplitude excitations, contribute to hysteretic nonlinearity, whereas porosity does not. Among the various suture regions examined, the squamous and lambdoidal sutures exhibit nonlinearity when excited at both their first and second flexural modes. In contrast, the sagittal sutures only show nonlinearity when excited at their second flexural mode, and the coronal sutures do not exhibit any nonlinearity. Micro-CT imaging reveals that coronal sutures lack close contact between bone regions and appear porous, while the sagittal, squamous, and lambdoidal sutures display close contact geometry. These findings confirm that the hysteretic nonlinearity in cranial bones is solely due to the presence of sutures with close contact geometry, as non-sutured bones and coronal sutures, which are mainly porous, do not show close contact or interfaces in their structure. Although the sutured bones and non-sutured bones were not extracted from the same skull, they remain comparable. This is because the non-sutured bones were taken from an older skull, and literature reports that nonlinearity tends to increase with age. The nonlinearity parameter correlates well with micro-damages and suture contact conditions inferred from micro-CT images, indicating that the observed nonlinearity is related to the micro-structural characteristics of the sutures. Our results indicate that sutures are a source of nonlinearity in skull dynamics, which can have various implications spanning from the leveraging of that nonlinearity in diagnosis to understanding the sources of nonlinearity in medical ultrasound.

Presenting Author: Anna E Lisner Georgia Institute of Technology

Presenting Author Biography: Anna is a MS. student in mechanical engineering at Georgia Tech. Her research interests include biomedical applications of vibration and wave propagation.

Authors:

Anna E Lisner Georgia Institute of Technology
Nima Etemadi Georgia Institute of Technology
Prabhakaran Manogharan Georgia Institute of Technology
Alper Erturk Georgia Institute of Technology