1735 Dynamic Micromechanical Characterization of Maturing Rabbit Mandibular Fibrocartilage by Atomic Force Microscopy
K. HU, P. RADHAKRISHNAN, R.V. PATEL, K. ROJAHN, and J.J. MAO, University of Illinois at Chicago, USA

The dynamic material properties of maturing rabbit mandibular fibrocartilage have rarely been investigated. Objective: Here we studied the dynamic micromechanical properties of the articular fibrocartilage of the mandibular condyle in maturing rabbits with atomic force microscopy (AFM). Methods: The articular surface of each of 18 condylar fibrocartilage samples, harvested from 9, eight-week-old, New Zealand White rabbits, was divided into the anteromedial, anterolateral, posteromedial and posterolateral regions, each of approximately 3 mm3 volume containing articular fibrocartilage and subchondral bone. After mounting the bony surface of the sample to the AFM, the cartilaginous surface was subjected to dynamic nanoindentation to obtain both topography and force spectroscopy in AFM's contact mode with oxide-sharpened Si3N4 tips. Results: Young's moduli differed significantly among the four regions in a descending range of 2.34 (0.26) to 0.95 (0.06) MPa: highest for the anteromedial region and lowest for the posterolateral region (p < 0.01). A third-order polynomial equation, Y=-354.98X3 + 480.95X2 - 201.69X + 27.84, provided the best fit for the distribution of Young's moduli of the four regions. The Poisson's ratios had the same trend of distribution as Young's moduli: highest for the anteromedial region (0.460.05) and lowest for the posterolateral region (0.310.05) (p < 0.01). The anterior regions showed more robust surface topography than the posterior regions. Conclusions: The articular fibrocartilage of the mandibular condyle in maturing rabbits is anisotropic with overall dynamic material properties that are capable of withstanding mechanical loads. Differential distribution of surface micromechanical properties likely results from regional variation of functional loads, leading to a new hypothesis that regional variation in micromechanical properties is general for other maturing fibrocartilaginous tissues such as the intervertebral disk. Supported by Whitaker Biomedical Engineering Research Grant and NIH grants DE13088 and DE13964.

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