Dynamic Valve Bioreactor

Bioreactor for mechanical testing of aortic valves under cyclic strain

in collaboration with Dr. Jane grande-allen, Dr. varun krishnamurthy, dr. matthew sapp, dessy vekilov, saheba bhatnagar, nik liebster 

Problem Statement

Cardiovascular disease is the leading cause of mortality. The second most common cardiothoracic procedure performed in the US is the surgical intervention for aortic valve disease (AVD), where calcific AVD, the most common type, occurs in approximately 2% of the general population. Effective treatment, which requires improved understanding of the mechanical properties of aortic valves and the factors that affect them, is crucial for the prevention of disease onset and fatalities, including heart failure, severe infection, and even sudden death.

There is currently no cure for AVD, however, glycosaminoglycan (GAG) misexpression, specifically hyaluronan (HA) dysregulation, is a known factor that contributes to it. The goal is to observe the expression of proteins and markers involved in the dysregulation of HA homeostasis to further understand their relationships and interdependencies to understand the individual effect of each protein and the onset of metabolic abnormalities.

Current methods utilize static and dynamic cell and tissue cultures and static valve cultures. The data acquired from these methods may not tell the whole story as the aortic valve functions as a whole tissue in a dynamic state. 

Work Done and Proposed Solution 

To complement cell culture studies and further assess the effects of cyclical strain on HA dysregulation and extracellular matrix (ECM) remodeling, a custom designed mechanical bioreactor was assembled to reveal alterations in HA of whole aortic valve leaflets under realistic dynamic conditions. 

This system provides mechanical stimulation through a cyclic opening and closing action caused by a movable piston containing the securely mounted aortic valve tissue in culture medium under sterile conditions. Whole aortic roots along with their leaflets are isolated through dissection of fresh adult porcine hearts, and then maintained in PBS solution. The aortic valve tissue is locked in place within valve mounts (Figure 1) and tissue culture chambers (Figure 2) and filled with media. The cultured valve tissue is harvested and used for histology, to observe ECM remodeling, and tensile testing, to determine mechanical properties.

The cyclic motion of the bioreactor is powered by a Servo motor and a Gemini 6V6K controller acting as a movable piston and operated by custom written software on Motion Planner. The valve mounts and tissue culture chambers are 3D printed from custom designs on Fusion 360. Various iterations of both parts were studied in trial runs to ensure efficiency and effectiveness. The valve mounts are designed to fit various sizes of aortic valves and allow for suturing to maintain the valves in natural form. The tissue culture chambers are designed for watertightness and sterility and to maintain function as a check valve as media flows through. 

The bioreactor has undergone various trial runs and will continue to undergo testing. 

Outcome and Future Work

Further work is required in ensuring reproducible pressure gradients to mimic human conditions within the bioreactor and in sterilizing all parts via autoclave. The bioreactor will require more trial runs to ensure all variables are in optimal state before a study run is performed to gather data to assess the effects of cyclic strain on aortic valve tissue. 

The data collected from the bioreactor study and its further analysis will be invaluable in understanding HA dysregulation and ECM remodeling to advance our overall understanding of valve disease and the development of novel therapeutics.

Awards

American Heart Association Southwest Affiliate Undergraduate Student Research Fellowship (2016)

Sapp, M.C., Vekilov, D.P., Krishnamurthy, V.K., Zhang, Q., Grande-Allen, K.J. “Static and dynamic culture bioreactors for the study of hypoxia in valve disease”. In preparation. 2017. 

Krishnamurthy, V.K.*, Zhang, Q.*, Wong, F.F., Stout, A.J., Grande-Allen, K.J. “Update on the mechanistic roles of glycosaminoglycans and proteoglycans in valve diseases”. In preparation. 2017. *Co-first authors

Press

Rice’s new Summer Cardiovascular Research Internship Program focuses on heart disease by Kendall Schoemann (Rice University)

American Heart Association fellowships support student research by Shawn Hutchins (Rice University)