medium (10% FBS) have been reported in the range of 0.14–0.65 Â 10
6 cells/mL for
cultivations in stirred bioreactors up to benchtop scale. Schirmaier et al. [62] and
Lawson et al. [63] reported maximum cell densities of up to 0.3 Â 10
6 cells/mL for
cultivations in stirred bioreactors at pilot scale with a cell culture medium
supplemented with 10% hPL or 5% FBS. Jossen et al. [11] even reported maximum
peak cell densities of up to 1.25 Â 10
6 cells/mL for hMSCs from the adipose tissue in
spinner flask cultures with 5% FBS. A proven alternative to FBS is human platelet
lysate (5–15%). However, there is still a controversial discussion about whether the
cells retain their immunomodulatory properties and their full differentiation capabilities [64–66]. Moreover, there is still a risk of human pathogens and their
components being poorly characterized. Therefore, there is a high level of interest
in serum- and xeno-free, chemically defined cell culture media. Various formulations are now available on the market (e.g., Mesencult-XF, MSCGM-CD,
StemMACS MSC XF, etc.). The careful selection and supplementation of the XF
basal medium with suitable growth factors and hormones are important, especially
when working with MCs in stirred bioreactors. Special attention has to be paid to cell
attachment efficiency and shear stress sensitivity. It is an established fact that the
maximum cell densities (0.04–0.40 Â 10
6 cells/mL) and expansion factors that have
been achieved in stirred bioreactors with xeno- and serum-free cell culture media are
still lower than those achieved in serum-containing medium (see Table 4). Heathman
et al. [67] reported a maximum cell density of 0.31 Â 10
6 cells/mL and an expansion
factor of 10 within 6 days of using PRIME-XV SF medium in a 100 mL BellCo
spinner flask. Carmelo et al. [68] even achieved a maximum cell density of up to
0.36 Â 10
6 cells/mL but a slightly lower maximum expansion factor of 8 with the
StemPro MSC medium. Maximum cell densities of between 0.04 and
0.40 Â 10
6 cells/mL were reported for the ATCC and MSCGM-CD medium in
the BioBLU 0.3c and BioBLU 5c bioreactor systems.
3 Computational Fluid Dynamics as a Modern Tool
for Bioreactor Characterization
Numerical methods, such as CFD, are widely used in the biotech industry to
investigate local properties (e.g., flow velocities, shear stresses) in bioreactors and
offer an alternative to experimental measurements (e.g., Particle Image Velocimetry
(PIV), Laser Doppler Anemometry (LDA)), which are often time-consuming and
expensive. Thus, it is unsurprising that CFD is also a valuable tool for the characterization of bioreactor systems used for the production of cell therapeutics. In the
following section, a short overview of the basic principle of CFD and various
investigations described in the literature are presented. In addition, a case study
will be discussed that demonstrates the use of CFD for the characterization of two
spinner flask types used for the MC-based hMSC expansion.
200
V. Jossen et al.
6 cells/mL for
cultivations in stirred bioreactors up to benchtop scale. Schirmaier et al. [62] and
Lawson et al. [63] reported maximum cell densities of up to 0.3 Â 10
6 cells/mL for
cultivations in stirred bioreactors at pilot scale with a cell culture medium
supplemented with 10% hPL or 5% FBS. Jossen et al. [11] even reported maximum
peak cell densities of up to 1.25 Â 10
6 cells/mL for hMSCs from the adipose tissue in
spinner flask cultures with 5% FBS. A proven alternative to FBS is human platelet
lysate (5–15%). However, there is still a controversial discussion about whether the
cells retain their immunomodulatory properties and their full differentiation capabilities [64–66]. Moreover, there is still a risk of human pathogens and their
components being poorly characterized. Therefore, there is a high level of interest
in serum- and xeno-free, chemically defined cell culture media. Various formulations are now available on the market (e.g., Mesencult-XF, MSCGM-CD,
StemMACS MSC XF, etc.). The careful selection and supplementation of the XF
basal medium with suitable growth factors and hormones are important, especially
when working with MCs in stirred bioreactors. Special attention has to be paid to cell
attachment efficiency and shear stress sensitivity. It is an established fact that the
maximum cell densities (0.04–0.40 Â 10
6 cells/mL) and expansion factors that have
been achieved in stirred bioreactors with xeno- and serum-free cell culture media are
still lower than those achieved in serum-containing medium (see Table 4). Heathman
et al. [67] reported a maximum cell density of 0.31 Â 10
6 cells/mL and an expansion
factor of 10 within 6 days of using PRIME-XV SF medium in a 100 mL BellCo
spinner flask. Carmelo et al. [68] even achieved a maximum cell density of up to
0.36 Â 10
6 cells/mL but a slightly lower maximum expansion factor of 8 with the
StemPro MSC medium. Maximum cell densities of between 0.04 and
0.40 Â 10
6 cells/mL were reported for the ATCC and MSCGM-CD medium in
the BioBLU 0.3c and BioBLU 5c bioreactor systems.
3 Computational Fluid Dynamics as a Modern Tool
for Bioreactor Characterization
Numerical methods, such as CFD, are widely used in the biotech industry to
investigate local properties (e.g., flow velocities, shear stresses) in bioreactors and
offer an alternative to experimental measurements (e.g., Particle Image Velocimetry
(PIV), Laser Doppler Anemometry (LDA)), which are often time-consuming and
expensive. Thus, it is unsurprising that CFD is also a valuable tool for the characterization of bioreactor systems used for the production of cell therapeutics. In the
following section, a short overview of the basic principle of CFD and various
investigations described in the literature are presented. In addition, a case study
will be discussed that demonstrates the use of CFD for the characterization of two
spinner flask types used for the MC-based hMSC expansion.
200
V. Jossen et al.