Once we had an idea of how we could create small shapes using cells we wanted a quick overview how larger objects could be made. This discusses the different possibilities of the creation of 3D structures and shapes in a general sense, using different forms of bio-printng.
An idea we considered was using polymer excreting cells to 3D print structures. 3D bio-printers exist but are used to create living tissue and organs. What we thought of creating was ordinary plastic objects. The main advantage of this being that the resulting plastic could be bio-degradable, self-sustaining and carbon neutral. Currently there are 8 million tonnes of plastic dumped into oceans each year, which is set to double in the next 10 years and will be tenfold by 2020.
We thought of printing cells into the desired shape using fused deposition modelling (adding layers of cells to create a structure). Once it has been printed the cells would then secrete a plastic which would form the shape. This would have the advantage over normal FDM printers which produce anisotropic materials with an underlying weakness in the z-axis, between the layers of plastic which is the biggest limitation of the technology. This weakness is caused by a lack of adhesion between already partially solidified plastic layers, this stops structurally strong items being made. Our proposed method would eliminate the directionality of strength and would create a structure of uniform strength and flexibility.
However the size of an E.coli cell is larger than the diameter of the smallest plastic filament possible, so the resulting structure may be less detailed, however if we developed a cell with a small enough radius this problem will be subverted.
The image to the left shows how FDM works in regards to plastic.
Another method of 3D printing is stereo-lithography, which works by creating a vat of plastic, in this case cells which then has two lasers, above and below which move and cause the plastic to harden (or cells to react and secrete plastic). The benefit of this is that you can create far more complex and detailed shapes. Shapes could possibly be made with precision at a cellular level, this sort of accuracy would be of paramount importance for the creation of heart valves and even a bone structure with the correct fibre arrangement.
However it would require larger amount of E.coli cells to be held together without dying, a very large challenge to overcome. For this we would use E.coli which would secrete plastic once it is subjected to a certain wavelength of light which would be provided by the two lasers.
We also though of using a process similar to selective laser sintering, where a film of E.coli cells are spread onto a surface then a laser ‘draws’ the first layer. A second layer of cells is spread on top and the process is repeated. This process takes longer but could be used to make much larger structures.
