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Christopher Paetsch
Civil & Environmental Engineering

Bio
An Oregon native, Chris received an M.S. from Tufts and B.S. from Santa Clara University, both in mechanical engineering. Chris was part of the Structural Engineering and Mechanics program and was a member of the Mechanics of Soft Materials Lab. His research focused on constitutive modeling and non-linear finite element analysis of highly deformable structures and material.

IGERT Research
As an IGERT fellow working with Prof. Luis Dorfmann (Civil and Environmental Engineering) and Prof. Barry Trimmer (Biology), Chris was interested in the modeling of muscle tissue and its use in biohybrid materials and devices. Other research efforts included the application of numerical simulation to assist in the design and control of highly deformable robots and actuators. Chris was a member of our first SMR IGERT cohort and is our first SMR IGERT alumnus, having been awarded his Ph.D. in Civil and Environmental Engineering in May 2014.

PhD Dissertation: Nonlinear modeling of active biological material
Abstract: The use of tissue engineered muscle constructs as bioactuators in demonstration devices has become increasingly common in recent years. Both the ability to scale in size and use in vivo energy supplies make bioactuation an attractive option over conventional means. This thesis aims to address key issues related to the nonlinear modeling of such active biological tissues. Experimental active and passive stress-stretch data of muscle tissue explanted from Manduca sexta, commonly known as the tobacco hornworm, is presented and an energy function is proposed. The model incorporates muscle contraction through an active strain approach and a pseudo-energy function is given to account for hysteric loading-unloading behavior. Next, the incompressible model is adapted for use in a finite element code, where a slightly compressible form is considered. The explicit expression of the stress rate, required for the particular numerical implementation, is given along with the associated derivatives of the non-standard kinematic quantities. A simulation of a biohybrid gripper is then qualitatively compared to experimental results found in the literature. Lastly, restrictions on the constitutive relation for active biological tissue are investigated, similar to those found for purely elastic materials. To this end, the concept of material stability is adapted, based on a generalization of the strong ellipticity condition. The active acoustic tensor is derived and stability of a prototype model is discussed.

What Chris is up to now
Chris is now in the research division at Bose Corporation, working on nonlinear modeling of materials and systems. His work email is christopher_paetsch@bose.com.


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