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Abstract
A micromechanical model of fibrous soft tissue has been developed. The model uses the theorems of least work and minimum potential energy to predict upper and lower bounds on material behavior based on the structure and properties of tissue components. The basic model consists of a composite of crimped fibers embedded in an elastic matrix. Upper and lower bound aggregation rules predict material behavior over a wide range of input parameters. As a necessary supplement required for obtaining the geometric data required by the micromechanical model, a method for determining local fiber orientation in soft tissue has been developed. The method involves edge detection and gradient analysis of digitized scanning electron micrograph images of collagen fibers in tissue samples. Predictions of the micromechanical model for two biological tissue samples are compared to experimental test data. For the highly organized structure of rat tail tendon, the upper bound rule predicts uniform strain behavior in the material. The model is fit to experimental data with a correlation factor of 0.98. Applied to cat knee joint capsule, the lower bound aggregation rule of the model predicts uniform stress within this more loosely organized tissue structure. These studies show that the nature of the interactions between the components in tissue differs depending upon its structure and that the biomechanical model is capable of analyzing such differences in structure.
