Functional, composite living materials with the potential for self-repair
Abstract
Biological materials form the natural environment we see around us and are typically capable of self- assembly, self-healing and multi-functionality, as the cells producing the components are found within the material itself. In contrast, man-made materials do not contain machinery for their own production, resulting in the inability to self-assemble and repair. In synthetic biology, at the cross-section between the living world and the synthetic, there are many opportunities to make biological material composites with new functions and the ability to self-repair when desired. This project will produce co-cultures that not only produce composites whose functions can be made to design, but with cells that will remain in the material which could facilitate new growth when repair is required. To engineer co-cultures of cells to ÔgrowÕ functional and composite materials we will use a mixed co- culture of engineered cells to grow a composite biomaterial layer containing cells that can survive weeks in dormant phase. We will co-culture a bacterium that produces large quantities of ultrapure cellulose fibres along with yeast that can programmably secrete protein components and perform sensing, logic and actuation functions. To make functional living material composites, we will first engineer our embedded yeast to secrete heterologous proteins into the extracellular space as the nanocellulose film is forming. Taking a modular approach we will genetically fuse proteins of interest to cellulose-binding domain proteins which strongly bind to cellulose microfibrils. This means that the yeast-made proteins in our system will then tightly interact with the nanocellulose network. To enable external control of the system, we plan to express these fusion proteins from inducible promoters. This means the added functionality of the composite can be tuned and positioned as desired within the material, for example by inducing only at certain times or at different locations during the growth of the material. To assess how these proteins alter the properties of the material, samples will be analysed using relevant testing equipment and visualised using electron microscopy. To assess and improve the self-repair of bioengineered living material layers we will cover a highly- interconnected layer of nanocellulose with a simple wax to create a flexible yet very tough ÔleatherÕ. Within this material, bacteria and yeast will become dormant due to lack of oxygen but should be activated when the wax is removed and water/nutrients are re-added. A lack of oxygen prevents cellulose biosynthesis. For self-repair, when material damage occurs the wax layer will break and cells at the air-medium interface will be exposed to oxygen, and thus capable of further growth and cellulose production. We will test this inherent self-repair by immersing or washing damaged material layers with water and cheap nutrients to determine how well cells grow and produce new material at the defect sites. We will investigate the self-healing ability in response to three types of damage: erosion, tearing, burning and will measure the rate of repair. To assess the self-healing effects we will qualitatively and quantitatively assess the layers by examining the thickness of cross- sections using light microscopy and also by looking at layers with electron microscopy. By demonstrating that co-culture can be used to produce functional, composite living materials, we will open the way towards modular design of composites where yeast cells can be quickly engineered to produce different proteins and mixed-in with the bacterial bulk material producer in different ratios and combinations in order to grow materials with different final compositions.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 01, 2019
- Source ID
- W911NF1810387
Entities
People
- Tom Ellis
Organizations
- Army Contracting Command
- Imperial College London
- United States Army