Determination of valid stress-strain relations for connective tissues like articular cartilage is a prerequisite for constructing models for joint lubrication. Often, due to high strain rates and/or large applied stresses, large strains occur in cartilage under physiological conditions as well as laboratory testing conditions. A finite deformation theory valid for describing cartilage as well as other soft hydrated connective tissues under large strain conditions has been developed. This theory is based on the choice of a specific Helmholtz free energy function whloh satisfies the QCN0 condition for the entire range of strain and the Baker-Erloksen Inequalities for compressive strains up to ~70% for tissue like cartilage. It also satisfies the requirement that large strains be maintained by large stresses. The straln-dependenoe of both porosity and permeability of the tissue are taken into account. Under uniaxial confined compression conditions, this finite strain theory describes accurately the large deformatlonal behaviors of cartilage observed in experiments. Three theoretical problems of oonflned compression, namely creep, stress-relaxation, and oycllo-excltation, under large loads and/or high strain rates were analyzed using this theory. It has also been used to determine the material properties of cartilage tested In incremental confined compression.

In the second part of this thesis, a study of the effeot of conformational ohanges on the flow properties of proteoglycan solutions is presented. The proteoglycans were biochemically prepared at Kennedy Institute Rheumatology, London, and Monteflore Hospital and Medical Center, New York. The samples were shipped to Rensselaer Polytechnlo Institute for rheologlcal measurements and analyses. All samples were tested in a oone-on-plate rheometer to determine their frequency-dependent complex moduli, shear-rate-dependent apparent vlsooslty, and shear-rate-dependent normal stress difference. These measured rheologlcal data were analyzed using the four-parameter rate-type Oldroyd model.