Theoretical and Practical Issues That Are Relevant When Scaling Up hMSC Microcarrier Production Processes

Area of Science:

• Biotechnology
• Stem Cell Biology
• Bioprocess Engineering

Background:

• Human mesenchymal stem cells (hMSCs) show promise for allogeneic cell therapies, necessitating efficient scale-up methods.
• Microcarrier-based stirred bioreactors are a promising approach for hMSC expansion.
• Formation of large microcarrier-cell-aggregates can limit mass transfer and lead to inhomogeneous cell distribution.

Purpose of the Study:

• To investigate the impact of impeller speed and shear stress on microcarrier-cell-aggregate formation in human adipose-derived stromal/stem cells (hASCs).
• To determine optimal conditions for scaling up hMSC expansion in microcarrier-based bioreactors.
• To evaluate the suitability of the suspension criterion N S1u for wave-mixed bioreactors.

Main Methods:

• Cultivation of hASCs on microcarriers in spinner flasks.
• Measurement of Sauter mean diameter (d 32) to assess aggregate formation.
• Analysis of cell density, expansion factor, and surface marker expression.
• Investigation of the N S1u suspension criterion in wave-mixed bioreactors.

Main Results:

• Cultivation at suspension criteria yielded d 32 values between 0.2 and 0.7 mm.
• Achieved highest cell densities (1.25 × 10^6 cells mL^-1 hASCs) and expansion factors (117.0 ± 4.7 on day 7).
• Maintained expression of specific surface markers under optimal conditions.

Conclusions:

• Optimizing impeller speed and shear stress prevents large microcarrier-cell-aggregate formation.
• Suspension criteria are effective for scalable hMSC expansion with high yields and marker expression.
• The N S1u criterion shows potential for scaling up microcarrier-based processes in wave-mixed bioreactors.