Date of Award

5-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Committee Member

Dr. Richard Figliola, Committee Chair

Committee Member

Dr. Donald Beasley

Committee Member

Dr. Ethan Kung

Abstract

Chronic venous insufficiency (CVI) is a medical disease caused as a result of incompetent vein valves in the lower extremities by the failure to reduce venous pressure during calf exercise. This condition affects 2.5 million individuals in the United States; some estimates are over 6 million due to undiagnosed cases. Healthy venous flow is characterized by the calf muscle producing a lower venous pressure with competent vein valves maintaining this reduced pressure by preventing blood from flowing back into the lower legs; instead of returning to the heart. Conversely, an individual suffering from CVI has partially or fully incompetent vein valves which allow retrograde blood flow. The symptoms from the disease can range from a minor case in which blood pools in the feet, causing swelling and discomfort, to more severe cases including venous ulcers; potentially leading to disability for patients. Treatment options for patients with less severe cases include compression sleeves for the affected areas, exercise, medication, and some minimally invasive, outpatient procedures. Unfortunately, the only medical alternatives if these treatments prove to be ineffective include more aggressive interventions to attempt to repair, replace, or transplant new valves to the affected area; however, these procedures can be technically difficult to perform and are not always effective. Another option for treatment of CVI that has seen improvement over recent years is the manufacturing of prosthetic vein valves for implantation into individuals; one of which is using 3-D printing technology to produce bio-compatible valves composed of a PEGDA pre-polymer solution. In order to test the concept of this approach and to improve the effective design of these valves, an experimental flow loop derived from a lumped parameter model of the leg venous system was used. The resting pressure of the system was set to one-half that of the adult pressures due to the presently available gel material used for the printing of the valves is inadequate. The system was tuned to match the physiological ankle pressure response during exercise by the adjustment of specific system parameters to match the ambulatory venous pressure and recovery time criteria. An ideal venous valve was first tested as a controlled baseline, and the 3-D printed valves were then tested for utility. Valves were then tested for the appropriate ambulatory venous pressure response to verify if the tested valves met the desired physiological criteria. Additionally, a sample of valves was statistically analyzed to offer information on the capability of the valves, to assess the consistency in valve printing, and to determine the life cycle of the valves during continuous use. A Weibull distribution analysis was performed to draw conclusions on the life cycle test results. In conclusion, the tests showed that the 3-D printed valves are able to satisfy the desired pressure-related parameters of time to ambulatory venous pressure, mean ambulatory venous pressure, and recovery time at the reduced system pressure that was one-half of that measured in an adult patient. The gels require material improvements to handle the normal hydrostatic leg pressures and longevity. Of the two valve geometries tested, the ‘sinus’ geometry produce more desirable results in all of the parameters mentioned above, and in the fatigue test.

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