Microstructural mechanics of collagen gels and tissue equivalents

This aim of this study was to correlate the macro-scale mechanics of a collagen gel to the kinematics at the microstructural level, and formulate a mathematical model that addressed both.; Collagen gels, reconstituted in-vitro from type-1 collagen, are a useful model of tissue mechanics. The gel is comprised solely of collagen fibrils, a major mechanical component of soft tissues, and retains a large part of the in-vivo physiological character. Under the microscope, the gel appears a hydrated mesh of nearly straight fibrils. Confined compression experiments performed with simultaneous birefringence imaging suggested the fibrils to be interconnected. The bending of fibers (relative angle change) at interconnections and retardation by viscous drag was found responsible for the mechanics observed at the macro-scale. A network model of collagen gel mechanics was proposed.; Traditional models of fibrous tissue neglect load transfer between fibrils (as occurs in a network) and approximate the kinematics of the independently-deforming fiber to be affine with the matrix. A simulation study was performed on a microstructure based on the collagen gel, and it was concluded that the computationally-attractive affine assumption could not capture network behavior.; A multi-scale model of collagen-gel mechanics was proposed to the enable the study of macro-scale boundary value problems but with constitutive response determined at the micro-scale network level. The model was derived from ideas of Averaging theory and solved at the macro-scale using Finite Elements, and analyzed at the micro-scale using Representative Volume Elements. The mono-phasic model was able to predict key observations in a published study of tissue equivalents in uniaxial extension. A simplified wound mechanics problem was also simulated.; To simulate gel behavior in confined compression, a biphasic version of the network model was derived. A microstructural representation of an elastic network, with elastic bending resistance, and retarded by a Stokes-like viscous drag was able to reproduce the behavior observed in the experimental study.; This work contributes to the analysis of tissues where fibril-fibril load transfer is important. The insight into collagen gel micro-mechanics is a step towards deciphering the complex relation between microstructure and mechanical properties in real tissues.