Micromechanical modeling of calcifying human costal cartilage using the generalized method of cells

Various tissues in the human body, including cartilage, are known to calcify with aging. There currently is no material model that accounts for the calcification in the costal cartilage, which could affect the overall structural response of the rib cage, and thus change the mechanisms and resistance to injury. The goal of this study is to investigate, through the development of a calcifying cartilage model, whether the calcification morphologies present in the costal cartilage change its effective material properties. A calcified cartilage material model was developed using the morphologies of calcifications obtained from microCT and the relaxed elastic modulus of the human costal cartilage obtained from indentation testing. The homogenized model of calcifying cartilage found that calcifications alter the effective material behavior of the cartilage, and this effect is highly dependent on the microstructural connectivity of the calcification. Calcifications which are not contiguous with the rib bone and constitute 0-18% of the cartilage volume increase the effective elastic modulus from its baseline value of 5MPa to up to 8MPa. Calcifications which are attached to the rib bone, which typically constitute 18-25% of the cartilage volume, result in effective moduli of 20-66MPa, depending on the microstructure, and introduce marked anisotropy into the material. The calcifying cartilage model developed in this study can be incorporated into biomechanical models of the aging thorax to better understand how calcifications in the aging thorax affect the structural response of the rib cage.