January 15, 2018 (Vol. 38, No. 2)
System Enables Improved Scale Up
Microcarriers are 100- to 300-micron-sized beads that support the attachment and growth of adherent cells in stirred culture. They enable more cost-effective cell production by reducing the fixed costs (e.g., footprint and labor) and variable costs (e.g., media consumption) in large-scale manufacturing.
A critical parameter that needs to be considered when selecting the optimal microcarrier is the intended use of the product. For cell therapy applications, a viable, functional cell is the desired product. Unfortunately, most commercially available microcarriers have significant disadvantages that hinder their use for cell therapy applications. Most microcarriers are composed of a solid matrix, which requires that the microcarrier be separated from the dissociated cells during downstream processing. This separation step is not trivial; it adds complexity and expense to the overall production process.
Another limitation observed with microcarriers is the inability to efficiently dissociate cells following cell expansion due to the strength of cell attachment. For these microcarriers, overall cell yield is significantly reduced and, more importantly, the functionality of the harvested cells may be impacted by the harsh cell dissociation methods that are required.
An Innovative Solution
Corning dissolvable microcarriers provide an ideal solution for large-scale cell expansion. The dissolvable microcarriers are composed of cross-linked polysaccharide polymers that can be efficiently dissolved during the cell harvest step (Figure 1). The ability to completely dissolve the microcarrier results in simpler downstream purification processes and eliminates the need to physically separate the cells and microcarriers.
The microcarriers are quickly dissolved through the addition of a harvest solution containing EDTA, pectinase, and a standard cell culture protease. When calcium ions are chelated by EDTA, the microcarrier polymer destabilizes, and subsequent polymer degradation is achieved by pectinase. An additional cell culture protease (e.g., trypsin, Thermo Fisher Scientific’s Gibco TrypLE, or Innovative Cell Technologies’ Accutase) breaks down cell-cell interactions and extracellular matrices, resulting in a single-cell suspension in a solution of small sugar oligomers.
Corning dissolvable microcarriers are optically transparent, consisting of ~250-μm-size beads with a density of 1.01–1.03 g/cm3 and a surface area of 5,000 cm2/g. Their narrow distribution in size and surface area, compared with other commercially available microcarriers, supports a more uniform cell seeding and growth to confluence, resulting in a homogeneous cell suspension. Further, the narrow microcarrier size range and density support better alignment of agitation speed with complete microcarrier suspension within a bioreactor.
Figure 1. Ionically cross-linked pectic acid microcarriers are dissolved during cell harvest with a solution of EDTA and pectinase.
Backed by Data
Several studies have demonstrated equivalent or better cell expansion and recovery using dissolvable microcarriers instead of traditional microcarriers. Scientists have demonstrated:
- Successful multipassage human mesenchymal stem cell (hMSC) expansion on dissolvable microcarriers in serum-free media (CLS-BP-PST-020 and CLS-AN-480).
- Better or equivalent hMSC growth in less time with higher cell recoveries on dissolvable microcarriers compared with polystyrene microcarriers; experiments were confirmed for both adipose- and bone marrow–derived hMSCs from different cell donors (www.corning.com/worldwide/en/products/life-sciences/resources/webinars.html).
- Dissolvable microcarriers support the expansion and recovery hMSCs in 5-L bioreactors. Cells were recovered from dissolvable microcarriers in 20 minutes and retained standard elongated morphology, normal karyotype, and multipotency (CLS-AN-470).
- Increased human induced pluripotent stem cell (hiPSC) productivity per day on dissolvable microcarriers compared with Matrigel-coated polystyrene microcarriers. Dissolvable microcarriers supported an easier and less aggressive cell recovery process compared with that required for hiPSC recovery from polystyrene microcarriers (Internal Corning data shared on conference poster and presentation).
- Efficient MRC5 and Vero cell growth and recovery on dissolvable microcarriers in spinner flasks and bioreactors. (CLS-PST-BP05 and CLS-BP-PST-020).
Dissolvable microcarriers support efficient cell production and recovery for several cell types including: hMSC, hiPSC, Vero, and MRC5. This new generation of dissolvable microcarrier supports the effective and efficient recovery of high cell yields without the need for microcarrier separation, resulting in a more cost-effective and less laborious harvest process that supports cell health maintenance and functionality.
