Mosa Meat’s new patent application, Apparatus and process for production of tissue from cells, describes a novel culture vessel aimed at the scalable differentiation of muscle cells.
The patent application was filed in May of 2018, two months before Mosa Meat announced their Series A funding, suggesting that the patent application may have been a part of their funding pitch.
It is well known that scalability is one of the major challenges for cell-based meat. This can be further broken down into:
Scalable proliferation: Cells from livestock animals are generally much more difficult to culture than bacterial or fungal cells. In order to proliferate, animal cells tend to require specific nutrient compositions and growth factors, as well as an environment with certain pH levels, temperature, and oxygen content. Additionally, animal cells tend to require a surface to grow on, making it challenging to use the stirred-tank bioreactors traditionally used in other industries.
Scalable differentiation: Once there are enough cells, a further challenge is turning those cells into meat. A piece of meat involves many muscle fibers running in the same direction. These fibers are formed when multiple muscle precursor cells fuse together. One kind of solution to the scalable differentiation problem involves letting the fibers form on structure that emulates the role of bone or cartilage. However, this leads to the further challenges of seeding the cells homogeneously throughout the structure, and later harvesting the fibers which tend to want to stay on the structure.
While the technology in this patent application doesn’t attempt to solve the first problem, it does present a possible solution to scalable differentiation that mitigates the challenge of harvesting.
I found the mechanics behind this technology somewhat confusing, so I’ll start with an analogy. Imagine putting a small rubber band around the tip of your finger—the squeezing tension in the rubber band might cause it to roll from a thicker part of your finger to a thinner part of your finger. Given enough tension, it might roll off your finger completely.
The culture vessel utilizes a similar phenomenon–the rubber band is like the cells and your finger like the vessel itself.
During differentiation, muscle fibers link to form muscle tissue. These links create tension that pulls the muscle fibers together. The insight behind this new culture vessel design is that this tension can move the cell mass to a part of the culture vessel where it is easier to harvest the cells. The muscle fibers are formed at the base of a partial cone (the cone is referred to here as the inner wall, colored in green). Once the cells differentiate, the tension between the fibers moves the cells up the cone into a harvesting area (colored in purple), just like the rubber band moved to a thinner part of your finger.
The Culture Vessel
The main component of the culture vessel is a circular trough where the cells are initially deposited. The cells are enclosed by a straight outer wall, and a slanted inner wall, which prevents the initial liquid from spilling. As the cells differentiate, tension forms between the cells and fibers. Since the mass of cells is encircling the inner wall of the trough, the tension moves the cells up the inner wall to the harvesting area.
The harvesting area is detachable from the rest of the vessel to make it easier to harvest the cells. There is a groove running from top to bottom of the harvesting area where the circular fiber can be sliced. Since the rings of tissue are held in place only by their grip, cutting them causes them to fall off easily.
The system is scaled by increasing the number of culture vessels. Multiple culture vessels can be stacked around a single inner pole, and many of these stacks can be placed side-by-side.
It’s important to note that each vessel contains a very small number of cells . If the troughs were too big, media would not be able to reach the insides of the cell mass, causing those cells to die. Therefore, in any production system at scale, there would likely be an extremely large number of these culture vessel stacks.
To create meat using these vessels, Mosa Meat first deposits a cell mixture into the troughs. They can do this in a number of different ways. For example, they can slide tubes in between the stacks of culture vessels, and deposit the mixture over the outer walls. Alternatively, the inner pole itself can have holes through which they deposit the mixture. This has the added benefit of making it easier to provide media to the inner layer of cells later in the process.
The initial cell mixture is made up of proliferated cells, plus a hydrogel . Initially, the hydrogel is not crosslinked, which allows the mixture to be poured into the trough. After the mixture is in place, the hydrogel is crosslinked. Depending on which hydrogel is used, crosslinking can be achieved though heat, UV radiation, or some other method. The crosslinked chain then forms a scaffold in which cells can grow.
A hydrogel is used as the scaffolding for a number of reasons. Firstly, it makes it easier to pour the initial mixture into the troughs, since the scaffolding can be structured later in the process via crosslinking. Secondly, the scaffolding that the hydrogel forms is relatively soft, allowing the cells to move freely to restructure themselves. As the cells differentiate, they pull closer together, pushing out excess water. In a more rigid scaffolding structure, cells may be less able to migrate to the harvesting area.
After the hydrogel is crosslinked, Mosa Meat submerges the entire culture vessel in differentiation media, causing media to flow into each of the troughs. The differentiation media causes the cells to form fibers and begin their migration.
After the cells have migrated to the harvesting area, Mosa Meat removes the inner tube along with all of the differentiated cells. While the troughs are re-used for the next batch, Mosa Meat moves the inner tube to a further vessel where the muscle tissue can mature.
When the muscle tissue is ready, Mosa Meat finally harvests the tissue by slicing along the groove on the inner poles. This severs the fibers covering the groove and causes the muscle to fall off.
Mosa Meat doesn’t provide a model of how cost effective this system could be. However, if a sufficient number of cells can be harvested per vessel, it may be a feasible solution to the problem of scalable differentiation.
Thank to Alene Anello for feedback on drafts of this post, and Jonathan Breemhaar for providing additional information on the mechanics behind the patent application.
 The patent application doesn’t specify particular dimensions, but it gives some possible ranges. The length of the center pole can be between 20 and 1,000 millimeters, the diameter of the pole can be between 2 and 10 millimeters, the length of the inner harvesting area can be around 800 microns, the troughs can be vertically spaced 1 to 5 millimeters apart, and the troughs themselves can contain between 40 and 1,000 microliters of liquid.
Assuming the inner pole is 1,000 millimeters long and the troughs are 10 millimeters tall spaced 5 millimeters apart, up to 66 troughs could be contained on a single inner pole.
 A hydrogel is a substance somewhere in between a solid and a liquid. It involves a chain of hydrophilic molecules, linked together through some chemical bond (called “crosslinking”). Because these polymers are made up of hydrophilic molecules, they attract water (or in this case, media), and keep it in a semi-solid structure.