The mechanical behavior of soft tissues such as blood vessels is complex and not completely understood. A detailed study of this behavior is important to understand the function of organs such as the heart and blood vessels, which undergo repeated changes in pressure during each heart beat. Many diseases result in changes in both mechanical behavior and microscopic structure of tissues. Thus, understanding how tissue structure, geometry, mechanical properties, and function are related may lead to advances in health care. This project focuses on measuring the structure and mechanical behavior of blood vessels, together with simpler model systems such as collagen tubes. The measured properties will be used to build mathematical models that can predict changes in tissue function resulting from disease. An important part of this work is measuring mechanical properties on the microscopic scale, since the local mechanical environment controls how tissues behave during development and after injury.