Towards a Failure Criterion for Microtubules Based on Matching Strength Analysis in Finite Element Models to AFM Loads

In previous research studies, the geometric and elastic properties for a critical component of axon health, the microtubule (MT), have been determined using lateral indentation with the tip of an atomic force microscope (AFM). Although the response due to the indentations caused by the AFM was observed to be linear for most of the tests, forces greater than 300pN would result in a permanent irreversible collapse of the MT’s structure. While the intent of those researchers was not to evaluate microtubule strength properties, that load can be used as a starting point to evaluate internal stress failure criterion for such structures. To that end, the current research is investigating MT strength by replicating the loading and boundary conditions in a finite element model. This work is an extension of previous work aimed at using this 300 pN point load to develop failure criteria for MTs under more realistic loading conditions. In the present work, modeling has been used to correlate the AFM point load response with the more realistic distributed loading conditions that would result during a brain injury event. Furthermore, the impact of nearby MTs on the stresses that occur under similar loading conditions is also examined. These results are being used to analytically determine a stress threshold related to MT structural failure. Correspondingly, models that include dynamic wave propagation through the microtubule will be studied. The failure criterion determined in both cases would aid in evaluating brain injury studies that involve pressure wave propagation in whole-head finite element models, even when such models represent the white matter using homogeneous properties.