Hydrogel-perfluorocarbon composite scaffold promotes oxygen transport to immobilized cells.

Cell encapsulation provides cells a three-dimensional structure to mimic physiological conditions and improve cell signaling, proliferation, and tissue organization as compared to monolayer culture. Encapsulation devices often encounter poor mass transport, especially for oxygen, where critical dissolved levels must be met to ensure both cell survival and functionality. To enhance oxygen transport, we utilized perfluorocarbon (PFC) oxygen vectors, specifically perfluorooctyl bromide (PFOB) immobilized in an alginate matrix. Metabolic activity of HepG2 liver cells encapsulated in 1% alginate/10% PFOB composite system was 47-104% higher than alginate systems lacking PFOB. A cubic model was developed to understand the oxygen transport mechanism in the alginate/PFOB composite system. The theoretical flux enhancement in alginate systems containing 10% PFOB was 18% higher than in alginate-only systems. Oxygen uptake rates (OURs) of HepG2 cells were enhanced with 10% PFOB addition under both 20% and 5% O2 boundary conditions, by 8% and 15%, respectively. Model predictions were qualitatively and quantitatively verified with direct experimental OUR measurements using both a perfusion reactor and oxygen sensing plate, demonstrating a greater OUR enhancement under physiological O2 boundary conditions (i.e., 5% O2). Inclusion of PFCs in an encapsulation matrix is a useful strategy for overcoming oxygen limitations and ensuring cell viability and functionality both for large devices (>1 mm) and over extended time periods. Although our results specifically indicate positive enhancements in metabolic activity using the model HepG2 liver system encapsulated in alginate, PFCs could be useful for improving/stabilizing oxygen supply in a wide range of cell types and hydrogels.

Enhancing oxygen tension and cellular function in alginate cell encapsulation devices through the use of perfluorocarbons.

Encapsulation devices are often hindered by the inability to achieve sufficient oxygen levels for sustaining long-term cell survival both in vivo and in vitro. We have investigated the use of synthetic oxygen carriers in alginate gels to improve metabolic activity and viability of HepG2 cells over time. Perfluorocarbons (PFCs), specifically perfluorotributylamine (PFTBA) and perfluorooctylbromide (PFOB), were emulsified with alginate and used to encapsulate HepG2 cells in a spherical geometry. Cellular state was assessed using the MTT assay and Live/Dead stain as well as through analysis of both lactate and lactate dehydrogenase (LDH) levels which are indirect indicators of oxygen availability. Addition of 1% surfactant resulted in stable emulsions with evenly dispersed PFC droplets of the order of 1-2 microm in diameter, with no influence on cell viability. Both PFCs evaluated were effective in increasing cellular metabolic activity over alginate-only gels. The presence of 10% PFOB significantly increased cellular growth rate by 10% and reduced both intracellular LDH and extracellular lactate levels by 20-40%, improving glucose utilization efficiency. The characteristic drop in cellular metabolic activity upon encapsulation was eliminated with addition of 10% PFC and viability was better maintained throughout the bead, with a significant decrease in necrotic core size. Results were consistent under a physiologically relevant 5% oxygen environment. The incorporation of PFC synthetic oxygen carriers into encapsulation matrices has been successfully applied to improve cell function and viability with implication for a variety of tissue engineering applications.