Increased stiffness of the aorta is an important detrimental change that occurs with aging. Most previous research has implicated stiffening of the extracellular collagen matrix with age. The study reported in this thesis focused instead on the potential contribution from stiffening of the vascular smooth muscle cells (VSMCs) with age.

VSMCs previously obtained from young and old monkeys (macaca fascicularis) were seeded into a collagen gel to form a reconstituted tissue. The aim of this study was to quantitatively characterize the mechanical properties of this reconstituted tissue model via uniaxially stretching each ring to defined levels of strain. The total stiffness of the reconstituted tissue was divided into the sum of two components termed "Active" and "Passive" representing the mechanical contributions of the cell and matrix respectively. The passive component was obtained from measurements following biochemical treatment that abolished cellular, actin-dependant force. The active component was obtained by subtracting the passive component from the total stiffness. This approach indicates that there was no significant difference in VSMC active stiffness between young and old female monkeys as opposed to noticeable difference in VSMC stiffness seen with aging in male monkeys [in a separate study]. This gender difference may be related to observations in the literature indicating that female mammals are relatively cardiovascularly protected by estrogen hormone.