Team:StanfordBrownSpelman/Cellulose Acetate

Biomaterials

The body of the UAV is designed to consist a styrofoam-like filler consisting of fungal mycelia, coated with a cellulose acetate covering. The skin will be biologically waterproofed. Material Waterproofing, Biosensors can be linked to the cellulose acetate skin (see Amberless Hell Cell), through a biological cross-linker (see Cellulose Cross Linker.)

Cellulose acetate is a biodegradable thermoplastic polymer used for a variety of industrial applications.[1] The monomer of cellulose acetate is glucose with one or more of its available hydroxyl groups replaced with acetyl groups. Cellulose acetate is industrially produced by treating cellulose, typically from wood or cotton, with acetic anhydride and sulfuric acid at high temperatures.[1] Our aim is to engineer bacterial cells to produce industrial-grade cellulose acetate biologically, allowing this plastic to be produced anywhere that bacterial colonies can be grown (i. e. in space). This material could then be used as a basis or coating for a biodegradable UAV. Many species of bacteria produce cellulose fibers; however, Gluconacetobacter hansenii has been identified as species producing the highest yield of cellulose. [2] Another strain of bacteria, the SBW25 isolate of the species Pseudomonas fluorescens, produces a biofilm containing cellulose fibers with a small degree of acetylation (.14 acetyl groups per glucose monomer).[3] Industrial-grade cellulose acetate must have at least 1.71 acetyl groups per glucose monomer. [4] In order to engineer a bacterium to efficiently produce cellulose acetate, our strategy is to transform G. hansenii with the four genes, wssF, wssG, wssH, and wssI, that have been identified [3] as being involved in cellulose acetylation in P. fluorescens, and to use directed evolution to further increase percent acetylation of the polymer.

In addition, we seek to create a streptavidin/cellulose-binding-domain fusion protein which will have the capacity to both cross-link bacterial cellulose acetate polymers (improving material properties) and allow the modular addition of cells (e.g. biosensors). This will be accomplished through the expression on the cells of a biotinylated membrane protein. This will allow biological sensors to be added directly to our cellulose acetate fibers, allowing bacterial sensors to be attached directly to the body of our UAV.

Click here to download our project journal, which details our design and engineering process and included descriptions of the protocols we developed and used.

Results

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Methods & Safety

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Click here to download our project journal, which details our design and engineering process and included descriptions of the protocols we developed and used.

Building a Biological UAV

Our team modeled, prototyped, and collaborated with Ecovative Design to grow a mycelium-based chassis for our biological drone. Below you'll find process photos, part designs, and links to open source model files for downloading and additively manufacturing your own biological or bio-inspired unmanned aerial vehicle. Finally, you can see images of the biological, biodegradable UAV that we built and flew! Check our more about the material, design, and construction aspects of our biomaterial project here.

References

1. Fischer, et al. Properties and Applications of Cellulose Acetate. Macromol. Symp., 262, 89-96. 2008.

2. Ross, P., Mayer, R., & Benziman, M. Cellulose Biosynthesis and Function in Bacteria. Microbiological Reviews, 55, 35-58. 1991.


3. Spiers, A. J., Bohannon, J., Gehrig, S. M., & Rainey, P. B. Biofilm formation at the air–liquid interface by the Pseudomonas fluorescens SBW25 wrinkly spreader requires an acetylated form of cellulose. 2003. Molecular Microbiology, 50, 15-27.

4. The United States Pharmacopeial Convention. Cellulose Acetate. USP-NF. 2013.


5. Hall, P. E., Anderson, S. M., Johnston, D. M., Cannon, R. E. Transformation of Acetobacter xylinum with Plasmid DNA by Electroporation. Plasmid, 28, 194-200. 1992.


6. Close, T. J., Zaitlin, D., & Kado, C. I. Design and Development of Amplifiable Broad-Host-Range Cloning Vectors: Analysis of the wir Region of Agrobacterium tumefaciens Plasmid pTiC58. Plasmid, 12, 111-118. 1984.

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