Nanomechanical and Topographic Properties of the Neonatal Rabbit Fibrocartilage of the Mandibular Condyle by Atomic Force Microscopy

The intrinsic properties of neonatal articular fibrocartilage, while important to the understanding of its growth and development, have not been studied. Objectives: We investigated whether different regions of neonatal fibrocartilage of the mandibular condyle have homogenous properties. Methods: The articular surface of the mandibular fibrocartilage from each of 18 condyles, harvested from 9, seven-day-old, New Zealand White rabbits, was divided into the anteromedial (AM), anterolateral (AL), posteromedial (PM) and posterolateral (PL) regions. Microdissection was applied to the entire articular surface of the condylar fibrocartilage to divide it into the above 4 regions, each of approximately 2 mm³ volume containing articular fibrocartilage and subchondral bone. After mounting the bony surface of the sample to an atomic force microscope (AFM), the cartilaginous surface was subjected to nanoindentation to obtain both topography and force spectroscopy in AFM's contact mode with oxide-sharpened Si₃N₄ tips. Results: Surface topography of each of the AM, AL, PM, and PL regions did not show significant differences by quantification of the root mean square of surface roughness. There was a narrow range of the average Young's moduli among the AM, AL, PM and PL regions from 0.95±0.15 to 1.04±0.15 MPa; these data were validated by comparing the elastic moduli between the left and right mandibular condyles (p > 0.05). The Poisson's ratios for the AM, AL, PM, and PL regions were very similar, ranging from 0.29±0.04 to 0.30±0.02. Conclusions: The intrinsic biomechanical properties of different regions of the articular fibrocartilage of the neonatal mandibular condyle are remarkably homogenous. These findings lead to at least two further questions: 1) whether homogeneity is general for other neonatal fibrocartilaginous tissues, and 2) whether neonatal homogeneity undergoes substantial changes during growth and maturation. Supported by Whitaker Biomedical Engineering Research Grant and USPHS Research Grants DE13088 and DE13964 from NIH/NIDCR.