Small-Scale Bioreactors for the Culture of Embryonic Stem Cells

Abstract

Stem cells have great potential for use as a regenerative therapy for degenerative diseases, such as diabetes or Parkinson’s. However, to create a large-scale and reproducible protocol, large homogeneous cell populations are required. For example, it is estimated that to treat one patient with stem cell-derived functional beta-cell equivalents for diabetes would require approximately 1 billion homogeneous beta-cell equivalents (Docherty et al. 2007). To reproducibly expand ESCs to this order remains a major research hurdle. Suspension bioreactors offer major advantages over traditional, static culture methods, including the ability to monitor and control important bioprocess parameters such as dissolved oxygen, pH, and temperature. In addition, for clinical implementation of a stem cell therapy, automation associated with bioreactors will aid in compliance with regulatory protocols (Martin et al. 2009). Other advantages of suspension bioreactors over traditional (static) cell culture methods, include scalability, enhanced oxygen and nutrient transfer, homogeneity, and increased reproducibility. However, the use of larger-scale bioreactors (for example, greater than 100 mL working volume) incurs significant expenses as considerable amounts of media, cells, and other supplies are required. In addition, extensive time and handling is necessary to generate enough cells for inoculation. Small-scale bioreactors (less than 100 mL working volume) require fewer cells, are more economical, and require less labour than larger bioreactors. The use of small-scale bioreactors potentially permits high-throughput experimentation to test operating and growth conditions (media components, agitation rate, cell density) and the resulting interactions. In a suspension bioreactor, cells are suspended in liquid medium which consists of a mixture of water, glucose, amino acids and dissolved oxygen, among other factors. As the suspension bioreactor is agitated, the environment within the bioreactor is more homogeneous than traditional culture environments, such as a T-flask, where gradients occur in the static media. The hydrodynamic environment created by agitation of the suspension bioreactor is known to influence cell survival. Excessive amounts of shear stress can lead to damage to cell membranes (Betts and Baganz 2006) whereas insufficient amounts of shear stress can cause excessive agglomeration (Li et al. 2009). In addition, manipulating