From Mush to Meat: Scaffolding to Structure Cultured Meat Products
The year is 2079, and you’re getting ready for a nice steak dinner. You pop a bag of beef cells in your family’s mini bioreactor (which sits between the toaster and coffee maker), pour some culture medium on top and press “grow”.
A couple hours later you expect to be able to slide some complete steaks onto a plate for your family to enjoy. However, when you open the door all you see is a big wad of congealed mush.
What happened — this isn’t what the bag promised?!
First, a quick review. Cells are (generally) cultured in three main steps.
- Stem Cells (cells which have the potential to become any type of specialized cell) are extracted from the animal.
- They are immersed in a culture medium — basically a large power smoothie — which gives the cells all the essential nutrients, carbohydrates, proteins and fats they need to grow and multiply.
- They are put in a bioreactor which exercises and introduces the cells to growth factors and encourages them to differentiate into many different kinds of specialized cells.
So this is great and all — from a handful of unspecialized cells, we can produce the juicy steak we have been dreaming of.
But then, why didn’t you — the anxious family dinner assembler — actually get that steak?
Right now, while you have all the kinds of cells that you would want in your meat, you don’t have the shape and structure. Right now, your cells are more akin to a pile of mush than something discernable, and why wouldn’t they be — all you’ve done is stick them in a bioreactor and let them float around randomly.
So, how can you get that well structured steak out of our meat cells? After all, as your meat loving family knows, it’s not just the taste of the meat that matters, but how it looks as well.
Enter the scaffold — the solution to all your problems.
The scaffold is basically a mold of the object you want your cells to turn into. It is put inside the bioreactor for the cells to grow on so they can get organized while they get specialized. In recent years, many different materials have been studied for the purposes of creating scaffolds, each having its own potential applications and weaknesses. The purpose of this article is to highlight the most popular ones.
Decellularized Plant Tissue
Decellularized plant tissue (also known as cellulose) is the most abundant polymer in nature, and is renewable making it ideal for cellular agriculture. It’s created by
- Obtaining a sample of plant tissue
- Coating it in surfactant: this create pores in the tissue and “decellularizes” it
- Cross Linking: treating the cells with a reagent which modifies the cell membrane and introduces new mechanical properties.
- Vascularization: adding more blood vessels so that nutrients can more effectively travel through it to the animal cells and overcome diffusion limits
- Coating it in protein: cellulose does not naturally exhibit many of the biochemical cues which we need to grow mammalian cells. Depending on the cells that are being grown, the tissue may be coated in a certain type of protein to make up for these cues.
This protein coating can also improve seeding efficiency — how quickly the cells can attach to the scaffold.
Cellulose has a variety of topography, which allows for cells to align in different configurations. It does, however, lack the customizable “bottom” up approach, making it hard to change on a basic level for a specific cell lines.
Chitin is found in the exoskeletons of insects, the shells of many sea invertebrates and fish as well as in fungi. Through a process called alkaline deacetylation, chitin is converted into chitosan. The extremity of this process determines many of the biochemical cues the chitosan will have.
Chitosan can be blended with other polymers which enables it to be further fine tuned for each type of cells, and it does have antibacterial properties which means that less antibiotics can be used in the cell culture.
Chitosan degrades when exposed to lysozymes which are naturally excreted by animals when they digest carbohydrates. If leveraged correctly, this could be a helpful property because it would allow the scaffold to eventually be digested and leave a pure cut of meat.
Recombinant collagen is collagen after it’s put through the recombinant process — basically generating collagen building blocks which can be assembled to create more complicated structures.
One characteristic that decellularized plant tissue and chitosan both lack is “functionalization”. Recombinant collagen on the other hand has this quality and could coat decellularized plant tissue and chitosan to fix this.
Alright, so the electrospun 3-dimensional silk fibroin nanofibrous scaffold — a bit of a mouthful.
Here’s how it is made
- Silkworm cocoons are boiled to make pure silk fibroin (SF)
- The solution is “lyophilized” which gives it a spongy texture
- It is put on a spinneret and spun under a DC current
- It is immersed in a methyl bath to be sterilized
- It is frozen and cut into small 2x2x2 cubes which are then sterilized even more
The 3T3 mouse cell line was cultured using this scaffold at 37 degrees Celsius, 5% carbon dioxide and 10% FBS (typical culture conditions), it exhibited good cell adhesion and cell migration.
Overall, decellularized plant tissue is favourable because of it’s “one size fits all” quality and abundance. Chitosan is useful because it can be fine tuned on at many stages. Recombinant collagen is a good option because of its ability to functionalize. Silk fibroin was effective because of its ability to simulare biochemical cues.
The production of each of these four scaffolds is relatively elaborate, and even more so when it comes to customization. While this quality can be overcome on a small scale, it does pose some challenges when scaled up to a commercial level.
So, why not skip the scaffold entirely?
Well, we can with 3D printing.
Using 3D printing allows production to not rely on scaffolding at all. It’s based around additive manufacturing — extruding the cells layer by layer until it forms a particular shape.
This process is highly favoured because it is fast, cheap, highly controllable and does not use other materials which have the potential to interrupt or transmit incorrect biochemical cues.
In a collaboration between 3D Bioprinting Solutions, Meal Source Technology, Aleph Farms and Finless Foods, this technology was actually used to successfully produce meat (in space). Making use of a magnetic field so that the shape was maintained, the Organ.Aut printer was used to print 3D printed cartilage and a thyroid gland from a cow. Although it was done in space (the ISS to be specific), the technology will be used to help scale production on earth.
So there you go 2079 you, four things you can use to get your family some solid steaks.