Microencapsulated Hematopoietic Stem Cell Model Proliferation in a Small Scale Stirred Tank Bioreactor: Influence ofMixing Rate

Background and Aim: Stem cells are known for their self- renewalproperties. Due to the importance of stem cells in the treatment ofdiseases, their use for medical applications is very important. Staticsystems are not responsive and it is necessary for the development ofdynamic systems (bioreactor). Among the bioreactors, stirred bioreactorsare simply used for design and construction for dynamic growth.Methods: In this study, a bioreactor with optimal hydrodynamic conditions(a height of 6 cm, diameter of 6.5 cm and impeller diameter of 3.25cm) was designed and built. Hydrodynamic parameters (integrated shearfactor (ISF), the maximum shear rate (τmax) and etc) were calculated. Theworking volume of bioreactor was 100 mL and the initial cell density was1×105 cells/mL, respectively. The proliferation of hematopoietic stem cellmodel (U937) in suspension and microencapsulated in Alginate- Gelatinmicrocapsules (1%- 1.25%) was compared at different impeller speeds(50 and 100 rpm) with static T- flask. Microcapsules with an averagediameter of 500 μm (±50 μm) were produced through electrostaticmethods. The amount of substrate consumed and produced metaboliteswere also measured during the process.Results: The results showed that at 50 rpm, compared to the staticculture, the final number of suspended cells increased by 10%, and thefinal number of cells in the bioreactor after 7 days reached 274 millioncells, while the cells at 100 rpm in the bioreactor showed statisticallydecrease in proliferation as compared to the static cultures. This can bedue to the high shear stress at 100 rpm as ISF was calculated 5.46 1/s and10.46 1/s at 50 rpm and 100 rpm, respectively. To reduce shear stressexerted on the cells at 100 rpm, the cells were microencapsulated inalginate-gelatin microcapsules. The number of microencapsulated cellsreached 11 million after the end of the 7 day period at 100 rpm. The sizeof the microcapsules containing the cell was larger than eddies createdat 100 rpm. Therefore, the collision of eddies and microcapsules reducedgrowth and proliferation of microencapsulated cells.Conclusion: Given the need for at least 2×106 cells per kilogram fortreatment of stem cell-based blood diseases, the use of this bioreactorcan have a good potential for the growth and proliferation of suspensionand microencapsulated stem cells in the treatment of blood patients. However, the size of microcapsules and mixing rate in the bioreactor areimportant issues that should be considered.

کلیدواژه ها:

Hematopoietic stem cell ، proliferation ، Microcapsule ، Smallscale stirred tank bioreactor