Strategies for Relating the Fracture Behavior of Hard Tissues to Cell Function Via Microstructure
Featuring B.N. Cox
Location: CS 174
*Refreshments will be served after seminar
Analyses of fracture data, especially load-deflection curves, suggest that engineering aspects of the fracture of human dentin and cortical bone can be described very well by cohesive fracture models. The cohesive zone in such a model corresponds to a band of nonlinear damage, which progresses to failure at a critical value of the local crack displacement. The constitutive behaviour of the zone, i.e., the cohesive law, can be deduced from fracture experiments and used to predict the outcome of experiments with different geometry or loading configuration, without reference to the mechanisms underlying the nonlinearity of the material. Nevertheless, there is obviously great merit in inquiring after the origins of the cohesive law, since they connect the fracture behaviour to the material morphology and thence, one hopes, to cell biology.
In cortical bone, dentin and enamel, microscopic evidence strongly suggests that the fracture process is controlled by morphological features that are direct consequences of the actions of individual cells.
Microcracks in cortical bone originate in the cement lines surrounding osteons and create bridging ligaments that give rise to most of the material’s toughness; a similar process occurs around tubules in dentin; and, in enamel, cracks almost never leave the interrod layers that exist between rods, even where the interlacing pattern of the rods frustrates continuous growth and creates discontinuities in the fracture surface.These specific features are the microstructural trails left behind by osteoblasts, odontoblasts, and ameloblasts. Thus a path is being discovered leading from the response functions of cells, which control the patterns in which cells move during material modelling, through the resulting morphology of the material, to the fracture resistance of the material. Illustrations of this expression of cell behaviour will be sought in models of human enamel.