Engineered Living Materials (ELM)

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The Engineered Living Materials (ELM) program will develop design tools and methods that enable the engineering of structural features into cellular systems that function as living materials, thereby opening up a newdesign space for construction technology. These methods will be validated through the production of living materials that display hallmarks of biological systems, such as the ability to actively sense and respond to the environment, or to heal after damage. Successful completion of ELM program objectives will require innovations in the ability to functionally unite living components with inert structural materials, to program structural features into living systems, and to extend the scale of synthetic biology building blocks from the molecular to the cellular. The deliverables from this program will comprise a suite of technologies that enable the production of living structural materials tailored to design specifications, such as those provided by architects and builders.

The structural materials that are used to construct our homes, buildings, and infrastructure are expensive to produce and transport, are subject to damage due to environmental insults and aging, and have limited ability to respond to changes in the immediate surroundings. As a result, the energy and financial costs of building and infrastructure construction and repair, to both the DoD and the nation, are enormous. Living biological materials may have advantages over inert materials, in that they might be grown on-site from simple feed stocks under ambient conditions, self-repair when damaged, or respond to changes in their surroundings. The inclusion of living components in our built environments has obvious benefits; however, today we are unable to control the structural aspects (shapes and sizes) of living materials so that they can be useful for construction. The ELM program seeks to deliver technologies that will enable the addition of living structural materials into our built environments. Such novel materials would reduce the energy and financial burden associated with the manufacture and transport of materials to construction sites, since they will be able to grow on-site from natural feedstocks. Furthermore, as they will contain elements that are alive, the resulting structures will be endowed with the ability to self-repair and respond appropriately to changes in the environment.

A major inspiration for the ELM program is the recent development of biologically-sourced structural materials that are grown to specified size and shape from inexpensive feedstocks. For example, mycelia can be grown on agricultural byproducts to produce materials that are drop-in replacements for polystyrene. Similarly, bacteria can be used to bind sand to produce drop-in replacements for bricks. That factory-scale production of grown materials can be economically competitive with materials as common as polystyrene and brick, demonstrates the feasibility of using biological approaches to reduce the energy and waste associated with the manufacture of structural materials. However, as the final products are rendered inert during the manufacturing process, these early examples of grown materials retain few of the benefits of the biological components they contain; for example, the ability to respond to environmental cues or to selfrepair.

DARPA is seeking technologies that enable the engineering of hybrid materials composed of structural scaffolds that support the rapid growth and long-term viability of living cells that endow the final products with biological functions. These materials should exhibit aspects of both the inert grown materials that are being produced today at the factory scale, such as structural integrity, as well as those of living systems, such as self-repair. The platform technologies developed in the ELM program are intended to be scalable and generalizable, so as to be transitioned from the lab to industry in the near-term.

In addition, DARPA seeks the ability to engineer structural properties directly into the genomes of biological systems, so that living materials can be grown from progenitor cells (e.g., seeds), without the need of non-living scaffolds or external developmental cues. To address this goal, it will be necessary to program developmental pathways that result in multicellular systems with defined patterns and 3D shapes. The ability of multicellular organisms to develop and maintain defined body plans is evidence of the inherent potential of genetically-programmed biological structures. However, it is not yet possible to engineer these properties de novo. To enable genetic programming of multicellular morphology, synthetic biology will need to advance toward the engineering of multicellular systems derived from a single genotype. It is expected that successful proposers will not only create new advances in synthetic biology, but also leverage the state-ofthe- art in experimental and/or theoretical developmental biology.

Through ELM, DARPA seeks to cultivate foundational principles, as well as novel approaches and methods that will ultimately enable living structural materials with advanced capabilities to be rationally designed, and implemented through genetic engineering. DARPA has identified five fundamental capabilities that can conceivably be used in combination to enable the invention of a wide range of living materials of arbitrary form and function. The demonstration of these fundamental capabilities will form the major deliverables of the program, and are:
(1) on-site growth, maintenance, and reproduction of a living structural material on inexpensive feedstock;
(2) the precise coordination of cells and inert particles to form tunable multi-scale patterns;
(3) the ability to self-repair in response to damage;
(4) genetically programmed multicellular patterns; and
(5) genetically programmed multicellular 3D shapes.