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Investigating Viscoelastic Hyperthermia in Multiple Young and Aging Tendons

In-vivo studies of horse flexor tendons and human Achilles tendons have measured temperatures greater than 45° C and 41° C (respectively) during activity as a result of viscoelastic dissipation. Since these high temperatures could impact cell activity and potentially induce cell necrosis, it has been speculated that intra-tendinous viscoelastic hyperthermia could play a key role in tendon pathology. Nevertheless, while the viscoelastic properties of tendon are known to vary substantially with anatomical location and age, the regionally-varying temperatures generated in multiple tendons tested in different stages of life are unknown.

thermoUsing thermochromic dyes and internal thermocouples, temperature heat maps within the deformed tissue can be obtained as shown in this schematic.

To address this question, we are studying viscoelastic heating in a controlled, ex-vivotissue culture environment allowing for investigation of the effects of specific loading regimens (i.e., loading frequencies and number of loading cycles) on the internal temperature of live tendons. This system also enables us to measure how high temperatures induced by viscoelastic dissipation affect cell and tissue properties. We hypothesize that at a given set of conditions, tendons with load-bearing and/or ambulatory functions (e.g., Achilles and patellar tendons) are designed to dissipate less energy and generate lower temperatures than tendons that experience low stresses in vivo (e.g., FCU tendons). We further hypothesize that due to increased viscoelasticity, tendons in aging animals will generate higher temperatures than tendons from younger animals, resulting in an increased susceptibility to hyperthermic damage. Therefore, extreme thermo-viscoelastic heating may be an early indicator of tendon degeneration.

Researcher: Mark Raymond Buckley, Ph.D.
Viscoelasticity in soft biological tissues; soft tissue aging, disease and repair