| Collagenous networks form the structural basis of many connective tissues including skin, cartilage, blood vessels, and tendons. It is widely accepted that anomalies in the collagen network cause many diseases including many forms of arthritis, Ehlers-Danlos syndrome, and brittle-bone disease. However, there has not been a direct correlation between these network-level (microscopic) anomalies and the resulting tissue-level (macroscopic) dysfunctions.;Attempts to describe the macroscopic properties of tissues based on microscopic properties of the network have been limited by the size of the problem, and therefore constitutive descriptions have been used to approximately describe network behavior. These descriptions are limited by the complexity of the network. We provide a new microscopic-macroscopic method to model network behavior, which combines the tractability of a macroscopic approach and the flexibility of a microscopic approach.;In the solid-phase, two-dimensional, microscopic-macroscopic model, the macroscopic domain is divided into a set of finite elements. Instead of a constitutive equation, a microscopic scale network is introduced in each finite element. The macroscopic stress-strain problem is distributed to each of the finite elements and the microscopic scale problem is solved. The stresses obtained from the microscopic problem are converted to macroscopic stresses and the weak form of Cauchy's stress-continuity equation is solved over the domain. The time for solution by the model scaled by a power of 1.1 as the total degrees of freedom was increased. Tensile tests conducted on synthesized tissue equivalents (TEs) revealed an order of magnitude difference in model predictions.;The biphasic nature of connective tissues determines their long-term viscoelastic behavior. To capture the transient behavior of tissues, the microscopic-macroscopic model was incorporated in a non-linear, biphasic system of equations. Articular cartilage (AC) was chosen as the system of interest and the transient properties of AC in confined and unconfined compression were predicted. The predicted values agreed qualitatively with reported values in literature but were different by an order of magnitude. An examination of the influence of varying microstructure within AC on its load-bearing properties, permeability, and deformation provided an interesting picture of fiber-level mechanics during in vitro AC loading. |
