Process developers have been working closely with equipment manufacturers to overcome the volume problem. In the manual paradigm,
cells adhere to the sides of flasks or roller bottles, which typically provide about 850 cm2 of surface area on which cells can grow. "What is a mammalian cell-culture flask," asks Tim Ward, director of product management
at The Automation Partnership (TAP) in Royston, UK. "It was not designed to make efficient use of its volume." And as an example,
he adds that to build an industrial-sized machine equivalent to a 20,000 L bioreactor that relies on roller bottles "would
require a facility the size of New York."
To address the problem, several companies are developing culture plates that increase the adhesive surface area within a given
volume. Corning Life Sciences (Lowell, MA), for example, has developed several cell culture vessels meant to be used in high-volume
cell production. Its "HYPERFlask," for example, provides a total of 1720 cm2 surface area on 10 growth layers within the footprint of one of the traditional T-flasks. According to Kim Titus, business
development manager and the commercial lead for HYPERFlask vessel at Corning, the cells sit on a gas-permeable film through
which all gas exchange takes place. Customers who have used the flask have verified that cells grow uniformly on each of the
layers, indicating that nutrients and gases are distributed evenly throughout the flask.
Those considering even larger-scale production often turn to Corning's "CellCube Culture System." Each growth layer in a CellCube
module provides 850 cm2 of surface area (the same area provided by one roller bottle) on as many as 100 growth layers for a total of 85,000 cm2 . The largest turnkey processes using the CellCube system right now uses four such 100-layer CellCube modules, but custom
processes have been developed by some users to allow the use of up to 10 × 100-plate Cubes simultaneously, creating 850,000
cm2 of surface area for cell culture. Andrew Lesniak, applications specialist for bioprocess for CellCube at Corning, notes
that the CellCube System, which was originally designed for bioprocessing those cells that could not go into suspension, can
easily be adapted to large-scale culture of adherent cells. Culture medium and gases are pumped around the whole system, he
notes, so that all of the cells in the cube have uniform access to them.
Providing adequate surface area on a reasonably-sized platform is just part of the challenge in considering large-scale cell
culture. Many issues loom large when process developers consider how to automate the process in order to make it economically
viable. When one considers all of the judgments that need be made in manual cell culture, it becomes clear that cell culture
is more art than science. But it's that assumption says TAP's Ward that may have stymied development of automated cell-culture
systems. By doing cell culture manually, "people find it difficult to get consistent results," he says. And that leads them
to believe that cells are too finicky to culture industrially by machines that can't recognize every nuance of cell behavior
and morphology. And that's where they make their mistake, says Ward. It's people's inconsistent handling of the cells that
leads to inconsistent outcomes, he says. "If you can automate the process and treat cells consistently, you get consistent
results. People's perception [of the challenge] is the reverse of reality."
The engineers at TAP, says Ward, "started out with some naiveté. Maybe if the team knew more about growing cells, we would
have never attempted to do it." What TAP engineers built into their machines was consistency. "Automation makes cell culture
more predictable. If you always treat cells in precisely the same way, you know exactly where they'll be in their life cycle
at any point during the process, and the outcomes will be consistent." Ward notes that among TAP's collaborations is one with
Manchester, UK-based Intercytex. According to an Intercytex press release, the two companies received a grant from the British
government to "develop a dedicated robotic system to support the commercial-scale production of dermal papilla cells, the
main cells involved in hair regeneration."
Even though the first generation of cell manufacturing is just starting to come on line, scientists like Rowley and Mason
are looking to the future, asking how the field can get to RegenMed 2.0. Interestingly, both envision a process in the future
where cell manufacture borrows even more from bioprocessing. The current paradigm, says Mason, mimics the manual procedures,
but in the future, he imagines the emergence of a new paradigm. In one possible scenario, he imagines adherent cells on the
surfaces of beads or wafers and then suspending the beads in bioreactors similar to the ones now being used for bioprocessing.
This would truly allow enormous scale-up to bioprocess-type volumes. "That approach has not yet worked for primary stem cells,"
says Rowley. "But it is certainly an interesting possibility and may be a medium-to long-term goal of the industry," he says.
Of course as the cell-culturing process becomes more and more standardized, process developers will be confronted with challenges
further down the manufacturing process. For example, cites Mason, stem cells are fragile and moving them into a container
can exert shear forces that will tear them if you move them too quickly. "But if you go too slowly," he cautions, "they stick
to the tube. There's a window of opportunity for moving them, and you have to hit it just right. There's a big investment
in producing plastics that cells won't stick to." Ultimately, says Mason, the goal after the process is all standardized is
"how to make it easier and cheaper to process cells."
1. C. Mason and M. Hoare, "Regenerative Medicine Bioprocessing: Building a Conceptual Framework Based on Early Studies,"
Tiss. Engin., 13 (2), 301–310 (2007).
2. L. Chue and D.K. Robinson, "Industrial Choices for Protein Production by Large-Scale Cell Culture," Current Opin. in Biotechnol., 12, 180–187 (2001).
3. C. Mason, "Regenerative Medicine: the Industry Comes of Age," Medic. Dev. Technol., 18 (2), 25–28 (2007).
4. The Automation Partnership, "Major Research Consortium Chooses CompacT SelecT for First European Study on Automating Cell
and Tissue Production," Company Press Release, Nov. 22, 2005.