Keratin 3D bioprinting
by Eliot Roth
originally posted at: https://medium.com/@elliotroth
I want us to rethink the way we interact with our waste products.
A notable, long-lasting component of human waste is keratin, which is found in shedded skin, fingernails and hair. It is also used as a structural bio-polymer by many different organisms. The current manner of disposing of cut hair for instance is to throw it away, thus wasting an incredibly valuable polymer, that could be used for many different applications.
The human body produces keratin at a constant rate, although under periods of high-stress or radiation exposure, it may shed it at a higher rate. Keratin does not easily decay in normal environments and may cause problems for communities existing in isolated environments. Astronauts have had difficulty ensuring that it does not clog air filters or get into sensitive equipment. The current method of dealing with keratin is to package and throw it away; this is true even for terrestrial situations. That process is wasting an energy-intensive natural filament that can be re-purposed to construct necessary built items for low-resource communities.
Keratin is a bio-polymer composed of repeated dimers of alpha helices. These dimers can grow up to lengths of 310 repeated subunits and are grouped together in bundles to form hair filaments. These filaments are held together by cysteine residues which form cross links of disulfide bonds. ER oxidoreductin (Ero1), is an enzyme that catalyzes the formation of disulfide bonds in the presence of oxygen. Therefore, when interspersed in a solution of water, an electrolytic beam of light can catalyze disulfide bond formation with the reaction from the cross-linking of the two thiol groups resolving to water.
This is very similar in nature, to the way stereolithographic 3D printers are currently used. A good example of one of these printers can be found here. UV light would be focused on the photopolymer (in this case broken keratin with Ero1 suspended in a homogeneous solution of water). This would promote the electrolysis of water which would produce oxygen, which combined with Ero1 would catalyze the reformation of the disulfide bond, thus forming a cohesive shape out of a natural polymer.
In order to make this process work, two separate chambers or devices will be used. The first will be necessary to break apart the disulfide bonds and recycle the hair into a liquid form. One of the methods most commonly used to do that, is the application of perms. Perms use chemical, thermal or physical methods to reshape hair. They do this through a very low-strength chemical solution, washed through the hair briefly. By immersing keratin in a high-strength chemical solvent like thioglycolic acid, the keratin would break apart into dimers with thiol groups capping both ends. After the precipitate is treated, it is then extracted and can be suspended in water in a non-oxygenated environment. Ero1 is then added in order to prep the solution for 3D stereolithography. When an energetic probe is passed through the solution, it electrolyzes the water at the contact point, thus catalyzing the reaction with Ero1 to reform the sulfide bonds. This means that an item can be printed while being suspended in solution.
I will be investigating different ways to build this printer and testing different solvents for keratin in the near future. Be on the lookout for updates.