Date of Award

7-2010

Degree Name

MS in Engineering - Biomedical Engineering

Department

Biomedical and General Engineering

Advisor

Dr. Kristen Cardinal

Abstract

ABSTRACT

Implementation of Physiologic Pressure Conditions in a Blood Vessel Mimic Bioreactor System

Kevin Mark Okarski

Tissue engineering has traditionally been pursued as a therapeutic science intended for restoring or replacing diseased or damaged biologic tissues or organs. Cal Poly’s Blood Vessel Mimic Laboratory is developing a novel application of tissue engineering as a tool for the preclinical evaluation of intravascular devices. The blood vessel mimic (BVM) system has been previously used to assess the tissue response to deployed stents, but under non-physiologic conditions. Since then, efforts have been made to improve the vessel and bioreactor’s ability to emulate in vivo conditions. The ability to tissue engineer constructs similar to their native tissue counterparts is heavily reliant upon controlling the environment and mechanical stimuli the construct is exposed to. Mimicking physiologic conditions influences cellular growth, proliferation, and differentiation. Two important mechanical stimuli are cyclic strain and wall shear stress. Previous work sought to improve these factors within the BVM bioreactor and resulted in the implementation of pulsatile perfusion and increased fluid viscosity. These previous bioreactor design modifications generated pulsatile pressures of approximately 80 mmHg and a wall shear stress of 6.4 dynes/cm2. However, physiologic pressure waveforms were not achieved.

Studies in this thesis were carried out to implement an effective means of establishing a more physiologic pressure wave within the bioreactor that is accurate, consistent, and easily adjustable. As a result of conducting the present studies, modifications to the bioreactor system were made that uphold the overall goals of efficacy and efficiency. The desired pressure wave was created by setting the degree of pump tubing occlusion on the 3-roller peristaltic pump head and using a water column to backpressure the bioreactor chamber. Maintaining a desired backpressure within the system necessitated the development of a new bioreactor chamber with increased extraluminal leak pressure resistance. The opportunity was also used to further improve upon the bioreactor chamber design to allow for 360° rotation to reduce cell sedimentation. Modifications to the bioreactor system required quantitative evaluation to assess their impact upon local flow dynamics to the tissue construct. A system model was created and evaluated using computational modeling.

Through the work performed in this thesis, pulsatile pressure waves of approximately 120/80 mmHg were successfully established within the bioreactor. The ability to accurately model physiologic pressures will ultimately help yield tissue constructs more similar to native tissues – both healthy and pathological. The newly designed bioreactor chamber and computational model for the system will be helpful tools for implementing or evaluating future bioreactor developments or improvements. While the main objective of the thesis has been completed by creating a system capable of emulating physiologic pressure fluctuations, there still remains room for further improvements in back-pressuring and scaling the system, refining the rotational bioreactor chamber design, and building upon the complexity and accuracy of the computational model.

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