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Thesis Defense – Katie Hollar

Controlling Strain Energy Density in 3D Cellular Collagen Constructs During Complex Loads

August 23rd, 2019 at 10:30am in MEC 114


Mechanical stimulation applied to damaged soft tissues, such as ligament, can promote tissue remodeling to accelerate healing. To help identify treatments that encourage ligament healing, bioreactors have been designed to subject 3D cellularized constructs to various loading conditions, such as tension, compression, and shear, to determine the mechanical mechanisms that trigger cell-mediated repair. An innovative approach is to use a bioreactor to apply controlled states of biaxial stress to study the effects of strain energy density and distortion energy on cell activity. Tissue distortion has been linked to changes in the structure and function of the ligament, yet the specific impact of distortion energy on cell response has not been quantified. This is due to challenges in establishing a method to apply targeted levels of strain energy density to cellularized constructs. The goal of this study was to develop a novel methodology of subjecting 3D cellularized collagen constructs to differing magnitudes of distortion energy while maintaining a targeted strain energy density. To vary the levels of distortion energy, the 3D cellular constructs were subjected to simple and complex loading conditions using a biaxial bioreactor. The bioreactor was able to accurately apply a targeted strain energy density of 300 J/m3 to the constructs during the various loading conditions with an average error of 12.7%. The complex loading conditions generated over 2-fold greater distortion energy than the simple loading conditions and was 22% greater when fibroblast cells were present. For the first time, this study has developed an experimental methodology to control the total strain energy density in a localized region of 3D cellular constructs as well as quantify the distortion energy in these constructs.

About the presenter

Katie Hollar

Katie graduated with a B.S. degree in mechanical engineering and a minor in biomedical engineering in 2017. For the past four years, she has conducted biomedical engineering research in the Northwest Tissue Mechanics Laboratory, where her undergraduate work focused on developing a novel imaging technique to quantify surface wear in acetabular liners used in joint replacement devices. Because of her potential to advance the fields of science and engineering, she received a 2018 National Science Foundation Graduate Research Fellowship. 

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