In this container, I am growing 100% pure cellulose with with the help of the bacteria Acetobacter xylinum. To compare wood consist of 50% cellulose. Chemically the cellulose is identical, but the bacteria creates smaller fibre that are closely woven together.
Instead of creating cellulose from photosynthesis like plants, the bacteria Acetobacer xylinium can procure glucose, sugar, glycerol, or other organic substrates and convert them into pure cellulose. In water containing nutrition, the bacteria will create tiny fibre that will be vowel together to a gelatinous mat at the surface of the water.
One of the unique features of the cellulose is its great water holding ability. The cellulose can hold hundreds of times its weight in water.
The cellulose membrane is very strong in the never dried state (Gif: http://2014.igem.org/Team:Imperial/Mechanical_Testing)
In dried state the material can be described as a cross between paper, leather and plastic depending on the treatment and thickness.
Here is how I prefer growing bacterial cellulose. The recipe is based on a cc-licensed recipe from biocouture, but I have done several modifications. The recipe can be scaled.
Use a container of class or plastic (no metal) The cellulose will take the shape of the container.
1 l water: I used tempered tap water, but depending on your water it may be wise boiling the water. Optimal growing temperature around 27-30° Celsius.
100g nutrition: The bacteria can eat Glucose, fructose og glycerol. This means you can add various types of fruit, vegetable, sugar or even grass. The choose of nutrition affect the speed of the growth, the material properties and look. Read more here
1dl vinegar/reuse of last brewing: My experience indicate that the cellulose grows best in a pretty acidic liquid (PH value around 3). Add some strong vinegar for your first brewing. The bacteria creates vinegar as a bi-product, so for your next brewing, you can simply reuse about 1/10 of the water.
*1 SCOBY starter culture: A SCOBY (symbiotic culture of bacteria and yeast) is the same culture used for brewing kombucha-tea, often called a "kombucha mother" or a "kombucha starting culure". Several kombucha-tea home-brewers give away these cultures for free as they would get an extra culture for each brewing. I recommend searching for local Kombucha brewing communities on Facebook. Cultures can also be be bought at sites like ebay or finn.no (norwegian) or kombu.de/suche2.htm. You will only need to buy/get a culture for your first brewing. Afterwards there will be sufficient of bacteria living in the water you reuse from previous brewing.
Keep the container in room temperature, away from directly sunlight. For quick growth optimal temperature should be around 28ºC. Do not shake the container after the growth has started. To avoid fruit flies, cover it with a textile. The culture needs oxygen to grow.
I started growing cellulose using this recipe from biocouture, but wanted to see if the culture was able to grow on other medium than sweetened tea.
Testing growth on vegetables
Cellulose grown on beetroot. The cellulose is colored by the vegetable. It seems like using more nutrition makes the cellulose grows faster, but with a “bubly” result.
The cellulose even grow on grass! This shows that unlike humans, the bacteria is able to use the nutrition in cellulose (that consist of glucose). The growth is a bit slow compared to sugar, fruit and vegetables.
Alternative use of nutrition like fruit and vegetables gave mostly an excellent growth, often with a better result than the use of sugar. I especially recommend sweet fruit and root-vegetables for a fast growth. I could harvest several layers form the same brewing, with a finer more transparent and less bubbly texture for each harvest.
Adding sugar to the liquid seems to give a thicker, more ductile culture in dry condition as the sugar get trapped inside the cellulose. It also seems to prevent mold. Too much sugar gives a ductile, super-sticky, fragile cellulose.
I also tested how robust I could be, using tap-water, unsterilized equipment and unwashed raw materials like potato peel. It worked surprisingly well, although having too dirty potatoes or vegetables floating on the surface gave me a couple of massive mold attacks.
Cultures stacked on top of each other makes efficient growth. The growth seems to be more even if the cultures fill the whole container.
To get a more even cellulose, skip the starting culture. With fast growing, the starting culture may create air bubbles, affecting the surface of the new culture. By reusing vinegar from last brewing there would be sufficient of bacteria and yeast to start the growing process.
Blended pieces of fruit will partly stick to the surface(because of sticky sugar) But will disturb the surface so that it is more fragile.
The cellulose does not blend with the sawdust.
I have been trying different methods to grow three-dimensional shapes by controlling the oxygen and nutrition. On this picture I try to grow around a shape with an aquarium pump and controlled lid at the surface. It seemed to work, but the fibre created did not stick together and was dissolved when harvesting.
When growing around fruit containing oxygen (apples) it creates a thin surface around the shape. It is very thin and fragile when dried, but shows that it is possible to grow under water.
Trying to use breathable, but waterproof material to make the culture grow along the edges, but the cellulose floats to the top. Please share with me if you have any suggestions of how to grow three-dimensional shapes in a simple way.
The cellulose has an remarkable capacity to hold water.
By drying the sheets on a piece of wood, the material will only shrink in the thickness. I have used a stove during the winter to speed up the drying process. Gently squeezing some water out of the material, will also make it dry faster.
The great water holding capacity makes the cellulose heavy. This is useful to create textures in the material, as it will lay closely to the surface you dry it on. You can see the structure of the wood it has been dried onto.
You can even dry it on plastic to get a polished surface. This will take some more time to dry as all the water need to evaporate.
Detail from plastic surface
Depending on the thickness and growing condition you can be able to stretch the surface over 3 dimensionally products.
When I started growing on vegetables instead of sugared tea I realized the dried cultures become thinner than the ones with sugar. This culture was 1cm thick, pressed and dried on plastic. This cellulose is non-transparent, stiff and brittle and does not swell in contact with water. To make cultures from vegetables or fruit thicker and more flexible, try soaking them in sugared water.
I have been looking at possible applications for bacterial cellulose. The cellulose has a range of interesting qualities that I discovered by doing simple testing. The picture is showing a less successful test with a bacterial cellulose teabag that is floating on the top of the water, not letting the tea escape.
Today bacterial cellulose is in commercial use within medicine (to treat burn damages and growing artificial vessels etc) and to create face masks. It is also used as a membrane in speakers and as the dessert Coco del Nata. There are examples of designers growing clothes and interior products. In my research I missed more examples of everyday products that used the beneficial properties of the material without needing synthetic engineering.
In the next posts you can see three examples that I think show some of the benefits, properties and interesting possibilities with the material:
In Kenya it is estimated that 870 000 girls are missing school every month due to a lack of sanitary pads and underwear. There is a huge need of affordable, disposable solutions as handling blood can be a danger to contamination of HIV and hepatitis B and C.
Depending of the way bacterial cellulose is dried, it can get completely opposite properties. When thinner layers are air dried, they become very absorbent. When a thicker layer is pressed and dried on plastic it become waterproof. With more investigation, I think it could be possible growing finished sanitary pads all in one process.
The sanitary pads can be grown at local resources, such as papaya, that are in surplus in some parts of Kenya. This papaya sanitary pad is grown in a small, standard plastic container.
Dried bacterial cellulose has the strength, flexibility and structure as leather, and it will get a worn patina when used. But this vegan material can be produced at home with no harmful chemicals.
Bacterial cellulose also has some distinguishing qualities that makes it interesting for products like cellphone covers; It is conductive, translucent and sound transducing.
The material is thin and strong and might get a leather-like surface when used over time.
Material grown with sugar and carrots. The material can easily be folded.
Material grown at red cabbage, then dyed in basic solution for change of color.
Material grown at carrots and sugar, later dipped in potato flour for a matte, soft surface.
Stiff and bubbly texture from material grown at beetroot.
I discovered how easy it was growing on various kinds of waste like peel or overripe goods from fruit or vegetables, and even the plant itself. Using waste from farming at the same place as the food is packaged can save transport, money and CO2 emissions. Bacterial cellulose could be a sustainable, biodegradable alternative to our increasingly precious natural resources. The pollution and non-degradable littering from plastic can not continue in the same scale as today.
To grow this his potato chip packaging I only needed a small amount of water, some potato peel and a start culture. The thin film is harvested, dried and put through a printer.
One of the promising qualities of this material is that it seems to work as a barrier for oxygen and aroma.
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