(107g) Monitoring Dissolved Oxygen Concentrations in Tissue Engineered Substitutes | AIChE

(107g) Monitoring Dissolved Oxygen Concentrations in Tissue Engineered Substitutes


Gross, J. D. - Presenter, Georgia Tech and Emory University
Long, Jr., R. - Presenter, Emory University
Constantinidis, I. - Presenter, University of Florida
Sambanis, A. - Presenter, Georgia Institute of Technology

Dissolved oxygen (DO) concentrations available to cells within tissue engineered constructs impacts distribution, viability and function of cells. In addition, DO concentrations vary widely depending on the site of implantation ? e.g. well vascularized sites offer higher DO concentration ? and the geometry of the construct ? e.g. the greater the distance of diffusion into a construct the lower the DO concentration. It has been previously shown that even at a fixed implantation site, DO can fluctuate greatly over time. Given the importance of the DO concentration for proper function of cells, establishing methods to non-invasively monitor DO concentrations within tissue substitutes is essential for improving treatments based on tissue implants and determining when and why a substitute fails. Nuclear magnetic resonance (NMR) has been shown by our group to be a potent tool in monitoring cell functionality, cell viability, and bioenergetic status within a construct non-invasively. Previous studies utilizing proton NMR imaging and spectroscopy demonstrated the ability to assess structural features and the number of viable cells within a tissue engineered pancreatic substitute in vitro and post-implantation in vivo. The research presented here uses perfluorocarbons (PFCs) and 19F NMR spectroscopy to monitor dissolved oxygen concentrations within a construct in vitro and in vivo. Due to constraints especially in vivo, 19F measurements represent an average of the oxygen concentration over the entire construct volume and do not reflect local differences due to concentration gradients, which also change as the construct remodels. Therefore, a mathematical model was developed to account for such regional differences within a spherical geometry. Utilizing the model, the weighted average pO2 measurements?as would be acquired by 19F NMR?were mapped to both cellular and pO2 profiles within the construct for a variety of initial cell densities and external oxygen concentrations. Experiments were performed with an NMR compatible perfusion system containing alginate-encapsulated mouse insulinoma cells. The perfusion system was designed for use in a 500 MHz vertical bore magnet, and it implemented continuous monitoring and control of temperature and DO concentration in the perfusion medium. A calibration curve using the PFC T1 relaxations was developed, utilizing the perfusion system's ability to maintain oxygen concentrations at desired levels. The response of the encapsulated cell system to prescribed changes in the medium DO concentration was evaluated, and the usefulness of the model in assessing the intrabead cellular and oxygen distributions at different time points during the experiments was established. Extending these studies to the in vivo monitoring of oxygen in implanted constructs, and using these measurements to elucidate the mechanism of implant failure, will be discussed.