Stem cell expansion and bioreactor development

Abstract

A major challenge to the clinical success of cell-based tissue engineering strategies is the ability to obtain sufficient numbers of cells within an acceptable time frame. The expansion of cells on microcarriers within spinner flask bioreactor has shown promise in meeting that challenge. Spinner flask microcarrier technology is space-saving and media utilisation efficient. However, further optimisation in terms of, for example, seeding efficiency, expansion rates and harvest efficiency is necessary to realise the clinical potential of this technology. The present work is designed to improve cell expansion rates. It involves investigation of microcarrier composition and surface structure and spinner flask shear stress on cell growth. BMSC growth on PHBV microcarriers was superior to PCL and PLGA microcarriers and comparable to Cytodex 1 microcarriers. Lower density PHBV microcarriers showed promise as a superior alternative to Cytodex 1. Two different impeller designs employed in the w/o/w method of microcarrier synthesis resulted in smoother and rougher PCL microcarriers with Ra = 1.77 ± 0.42 μm to 6.4 ± 1.48 μm respectively. Superior BMSC growth was observed on the rougher PCL microcarriers. Differentiation potential along the osteogenic and adipogenic lineages of BMSCs expanded on the microcarrier types was retained. Particle Image Velocimetry was used to quantify shear stress within a spinner flask bioreactor. It was found that 80% of the shear stress was localised within the impeller region which occupied 55% of the bioreactor working volume. Shear stress increased as Cytodex 1 microcarrier concentration and impeller rotational speed increased. Superior BMSC growth rates on microcarriers were observed for the lowest shear stress experimental group (3.4 x 10-3 N/m2 ≤ impeller region mean shear stress ≤ 4.6 x 10-3 N/m2) as compared to the three higher shear stress groups (5.5 x 10-3 N/m2 ≤ mean shear stress ≤ 1.3 x 10-2 N/m2). Expanded BMSCs on the cytodex 1 microcarriers retained multipotentiality for the range of shear stresses investigated.