Pre-Conditioning Heart Valves

Stewart, Faith; Nistler, Keely B.; Schilp, Jillian F.; Lowther, Amanda C.

Student Work

Pre-Conditioning Heart Valves

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Heart valve disease is a major health concern that affects millions of patients worldwide. Although valve replacement surgery is one of only two existing treatment options for this condition, many valve replacement options are not viable for long-term use and can cause significant adverse side effects. Emerging biomedical research has indicated that tissue engineered heart valves (TEHVs) could act as suitable replacements for diseased heart valve tissues due to their ability to grow and repair diseased tissue within the patient. However, TEHVs suffer from leaflet retraction when exposed to physiological forces in vivo. TEHVs can be mechanically preconditioned to alter their mechanical properties so that they more effectively withstand the environment in vivo. The purpose of this project was to develop a high-throughput stimulation system to automatically stretch and image model TEHV tissues to observe the effects of mechanical stimulation on tissue properties. This will enable researchers to study the interaction of preconditioning with other design parameters while providing quantitative outputs related to stress on the tissue, tissue stiffness, and tissue retraction. The system preconditions small tissue samples that are representative of specific regions within the TEHVs. Mechanical stimulation with a linear motor is used to stretch the tissue samples to 1-15% deformation at 0.1-2.0 Hz. Continuous stimulation lasts for a duration of up to one day while the TEHVs are cultured in cell culture media. After one day elapses, stimulation halts so that the cell culture media can be changed. The deformation of the tissue samples in response to stretching is observed optically with two cameras. One camera is dedicated to imaging the side of the tissue samples in order to capture the deformation of the PDMS post; the other camera is dedicated to imaging the bottom of the tissue samples to capture the thickness of the samples. The deformation of the PDMS post is used to calculate the force applied to the tissue, and the thickness of the samples is used to calculate the surface area of the tissue in order to calculate stress. These observations are used to understand the effects of mechanical conditioning on the valves. The Billiar Lab at Worcester Polytechnic Institute will utilize the device to condition tissue samples to conduct research with the ultimate goal of preventing leaflet retraction in vivo. We successfully designed a device that would stretch tissue samples at specified frequency and strain values, monitor tissue properties to calculate stress and strain, and illuminate the dark environment of the incubator utilizing three distinct subsystems. The device demonstrated the ability to maintain sterility for up to two weeks in an incubator. In the future, research personnel could improve on our design by selecting more durable materials to extend the longevity of the device, optimizing the automated imaging protocol, and improving the manufacturability of the device by designing improved jigs for standardized assembly.

This report represents the work of one or more WPI undergraduate students submitted to the faculty as evidence of completion of a degree requirement. WPI routinely publishes these reports on its website without editorial or peer review.

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