Aggregation of Culture Expanded Human Mesenchymal Stem Cells in Microcarrier-based Bioreactor.

Three-dimensional aggregation of human mesenchymal stem cells (hMSCs) has been used to enhance their therapeutic properties but current fabrication protocols depend on laboratory methods and are not scalable. In this study, we developed thermal responsive poly(N-isopropylacrylamide) grafted microcarriers (PNIPAM-MCs), which supported expansion and thermal detachment of hMSCs at reduced temperature (23.0 °C). hMSCs were cultured on the PNIPAM-MCs in both spinner flask (SF) and PBS Vertical-Wheel (PBS-VW) bioreactors for expansion. At room temperature, hMSCs were detached as small cell sheets, which subsequently self-assembled into 3D hMSC aggregates in PBS-VW bioreactor and remain as single cells in SF bioreactor owing to different hydrodynamic conditions. hMSC aggregates generated from the bioreactor maintained comparable immunomodulation and cytokine secretion properties compared to the ones made from the AggreWell®. The results of the current study demonstrate the feasibility of scale-up production of hMSC aggregates in the suspension bioreactor using thermal responsive microcarriers for integrated cell expansion and 3D aggregation in a close bioreactor system and highlight the critical role of hydrodynamics in self-assembly of detached hMSC in suspension.