Coatings for Bioreactor Scale-up vs Other Stem Cell Production Systems

Many stem cell companies use small-scale cultures, such as 6-well plates or flasks, to quickly develop initial processes for stem cell production and meet early milestones. When it comes time to produce stem cells on a larger scale, new factors come into play. Choosing the right extracellular matrix (ECM) coating and process is critical to scale-up success.

Here's a closer look at bioreactor scale-up, other options for scaling up stem cell production, and some coating considerations for large-scale production.

The Challenge of Scaling Up Stem Cell Production

Stem cell companies and laboratories may eventually need to produce much larger volumes of cells than those used in research and development. For example, a cell-based therapy company may need to go from 200,000 cells to inject into a mouse to 200 million cells to inject into a human patient.

The cells in the final product need to be high-quality and consistent, and they need to retain the safety and therapeutic characteristics that were demonstrated at smaller scales. It's important not to underestimate the complexity of this feat. In particular, increasing scale brings in considerations such as cost, cell health, and cell fate, and the choice of coating influences each of these.

As explained by Robert Padilla, a field application scientist at Corning, the way scale-up is implemented can have a huge impact on stem cells' destiny. "It's not just about cell attachment and health," he said. "There are also many signaling aspects that affect what the cells will become. The cardiomyocytes you're trying to grow could be pushed into a neural lineage. So, you need to make sure scale-up doesn't change the product."

Scale-up vs. Scale-out

Options for massively increasing the volume of adherent stem cells include stacked vessels, bioreactors, and microcarriers.

Stacked vessels, like Corning® CellSTACK® and HYPERStack® vessels, consist of stacked flasks or plates that are connected for easier filling and maintenance. Corning Field Application Scientist Whitney Wilson explained that stacked vessels are more accurately called "scale-out" solutions because they replicate the same conditions cells experienced in small-scale culture but multiplied many times. This makes the transition to large-scale culture more straightforward.

Guide to Seeding, Expanding, and Harvesting Stem Cells

Stem Cell Therapy Production Infographic

With scale-up solutions, by contrast, the growth vessel changes, and so do the conditions cells experience. Bioreactors (large vessels for cell growth) and microcarriers (tiny spheres that can be coated with ECM and placed in a container of media so cells can grow on the exterior surface) are scale-up solutions. They require careful optimization to ensure cells maintain their quality and multipotency or pluripotency. However, compared to stacked vessels, microcarrier and bioreactor scale-up systems often require less operator time to set up and maintain.

If scaling up doesn't produce the results you need, try scaling out with stacked vessels, Wilson said. This is often necessary for neuronal cultures, for example.

Vessel Choices and Coating Processes

The initial coating process for stacked vessels can be more labor-intensive compared to bioreactor or microcarrier systems, since each vessel must be coated by hand. Companies need to consider the employee time (and, therefore, cost) required to coat stacked vessels versus other systems with ECMs. Another consideration is that, with a greater number of vessels, there is a greater chance of variability between operators.

Bioreactor scale-up enables large-volume growth with a less labor-intensive coating process, but coatings for adherent cells must be optimized to prevent clogging or flow problems in the vessel. For example, care must be taken to ensure tubes don't clog and bioreactor layers are not too close together to accommodate the necessary ECM layers.

Microcarrier cell culture offers a hybrid space between suspended and adherent cultures. The tiny sphere-shaped carriers are first coated with ECM, then placed in a vessel seeded with cells. This eliminates worries about blocking bioreactor tubes while minimizing the labor required for coating. Corning offers pre-coated microcarriers with several coating options. However, microcarriers don't work for every cell type. As Wilson explained, some cell types are better able to grow on the curved surface of the tiny spheres than others. Other cells may alter their gene expression and therapeutic function when grown on a curved surface.

Maintaining Chromosomal Integrity During Large-Scale Production

In addition to keeping stem cells from differentiating, investigators and manufacturers need to ensure the cells maintain genomic stability.

In the human body, cancer cells sometimes arise when genetic changes make them more stem cell-like. This connection between stem cells and cancer cells means that manufacturers need to monitor for chromosome abnormalities in stem cell cultures while taking measures to lessen the risk of oncogenicity, including choosing a coating that supports genomic stability.

According to Wilson, "Matrigel® is still the most consistent substrate for maintaining chromosome integrity" in stem cells. However, as always, the choice of substrate for scale-up depends on weighing different considerations.

Padilla pointed out that cells that "proliferate at a fast rate are more likely to have chromosome aberrations. Sometimes, there is a need to intentionally slow the growth down, using specific media components."

Optimizing Coatings Can Drive Down Costs

For therapeutic products, companies must look ahead to a time when product will be offered to patients. Controlling the cost of the final therapeutic product increases the chances that insurance will reimburse for the product and that patients will have access.

Many steps in stem cell production involve cost considerations or trade-offs, but there are opportunities to drive down the cost of the final product even from the early stages of development. Wilson recommended that companies plan ahead and consider scale-up in early stem cell testing. "I hear it at least once a week — these coatings get really expensive. Cost is a huge consideration."

Padilla suggested experimenting with lower ECM protein concentrations in vessel coatings. "I recommend to our customers: How low can you go? Try some dilutions. If you used 10 mg/ml to coat a 6-well plate, that may be way more protein than you need. There's a really important step where process development tests dilutions."

Companies should also consider overall expense when choosing between animal-derived, xeno-free, or synthetic coating options.

Corning's Stem Cell Experience

For decades, Corning has been supporting stem cell researchers and manufacturers with innovative products. Visit our resource pages to learn about Corning's stem cell expansion offerings and cell culture surfaces, or get in touch today.