Apr 01, 2024 (Nanowerk Spotlight) Faced with mounting environmental challenges, scientists worldwide are seeking sustainable solutions. Engineering living materials—composites incorporating living organisms—offers great promise by reducing our reliance on fossil-fuel-derived materials and harnessing the unique properties of living systems.

Revolutionizing Material Science with Living Organisms

Living materials take inspiration from the natural world, where plants, animals and microbes routinely manufacture functional materials as part of their normal physiology. For instance, trees produce woody tissue composed of stiff cellulose fibers held together by lignin “glue”, while marine mussels secrete underwater adhesives, and some bacteria generate electricity. These living systems exhibit distinctive capabilities such as self-assembly, self-healing, responsiveness and biosynthesis that are difficult to achieve with synthetic materials. The field of synthetic biology offers tools to reprogram organisms at the genetic level, allowing scientists to engineer living materials with tailored properties. By introducing artificial gene circuits, microbes can be designed to sense signals from the environment and fabricate user-defined products accordingly. Materials scientists are also exploring how to integrate living components with non-living structures such as hydrogels and electronic devices. The resulting “hybrid living materials” aim to augment the functionality of organisms with the robustness and manufacturability of synthetic components. Several startups are now commercializing early living material technologies, but they remain beset by challenges such as high production costs and inferior mechanical strength compared to conventional materials. However, if these hurdles can be overcome, living materials may one day replace unsustainable conventional materials in applications ranging from packaging to infrastructure construction.

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Learning from Nature: Evolutionary Masterpieces in Material Design

Living organisms naturally produce an amazing array of functional materials using proteins, polysaccharides, and minerals. For instance, woody plants biosynthesize lignin, cellulose and hemicellulose to build sturdy tree trunks, while marine mussels secrete underwater adhesive proteins for attaching to surfaces. Most intriguingly, these living materials exhibit dynamic properties that synthetic counterparts lack, such as the ability to self-assemble, self-heal after injury, adapt to environmental stimuli and undergo continuous self-renewal. The field of bioinspired materials aims to mimic such natural structures, but replicating their living attributes remains challenging. Now, an emerging approach is to engineer the organisms themselves to serve as microbial “factories” for producing functional materials. As experts in biochemical synthesis after billions of years of evolution, living cells potentially offer a sustainable way to manufacture a huge diversity of tailored biopolymers. Researchers categorize living material systems based on their designs:

• Self-organizing living materials: Built solely from living components such as engineered bacteria, fungi or mammalian cells. They aim to recapitulate natural self-assembly and environmentally responsive behaviors.
• Hybrid living materials: Merge living components with abiotic scaffolds such as hydrogels and electronic devices. The non-living parts enhance manufacturability and augment the functionality of embedded organisms.

Adidas concept shoe, Stan Smith Mylo™, uses mushroom-derived materials. (Image: Adidas)

Programming living materials using synthetic biology

The young field of synthetic biology provides a toolkit to genetically reprogram organisms using principles of modularity, standardization and modeling. Using libraries of well-characterized DNA parts that encode basic genetic functions, synthetic biologists can introduce artificial gene circuits to give cells computer-like capabilities. For instance, engineered gene networks allow microbes to sense chemical signals, perform logic computations or synchronize their behaviors across populations. By leveraging synthetic biology, researchers are exploring various strategies to develop self-organizing living materials with programmed functionalities:

• Customizing material building blocks: Cell-secreted proteins or polysaccharides can be functionalized by fusing them with peptides or proteins using recombinant DNA technology. For example, E. coli biofilm matrix proteins have been modified to enable heavy metal absorption and underwater adhesion.
• Designing stimulus-responsive gene circuits: Introducing circuits that detect signals such as toxins, light or electric fields allows living materials to sense and respond to environments dynamically.
• Engineering cell-cell communication: Incorporating communication modules such as quorum sensing enables populations of engineered cells to collectively self-regulate material fabrication and performance.
• Constructing artificial microbial consortia: Divvying up tasks across different populations allows more complex material functions by distributing metabolic burden.

Beyond the examples mentioned, nature provides a treasure trove of inspiration. Spider silk boasts remarkable strength and flexibility, while bone demonstrates self-regenerating capabilities. Researchers are exploring how to mimic these properties in engineered materials. For instance, mycelium, the root-like structure of fungi, is being used to create sustainable packaging and building materials. Bacteria capable of producing calcium carbonate are being incorporated into self-healing concrete that can repair its own cracks. Scientists are even designing fabrics containing microbes that change color in response to pollution or temperature.

Bridging Worlds: The Synergy of Living-Nonliving Hybrid Materials

Although composed purely of life, the materials fabricated by engineered organisms currently suffer from limitations like weak mechanical strength. To address this, researchers are exploring hybrid systems that combine living cells with robust abiotic components while taking advantage of manufacturing techniques from materials science. For example, techniques such as 3D printing and microfluidics enable the controlled encapsulation of living cells within customizable polymer hydrogels. These gels provide a soft, aquatic environment to maintain cell viability while enhancing the physical characteristics of the overall hybrid material. In other cases, researchers have incorporated functional non-living components that synergize with microbial metabolism to enable new material capabilities. Examples include semiconducting nanoparticles that collect light energy for powering CO2-fixing bacteria and electronic sensors that interface with engineered genetic circuits.

Real-World Applications of Living Materials

The transformative power of living materials is not confined to laboratory benches or theoretical studies; it’s a reality unfolding in diverse sectors around the globe. These real-world applications demonstrate how the innovative integration of biology with engineering principles is making sustainable solutions tangible and accessible. From buildings that repair themselves to textiles that react to the human body, and packaging materials grown from fungal roots, the case studies below highlight actual products and technologies already making an impact. By bridging the gap between nature’s wisdom and human creativity, these examples not only underscore the practicality of living materials but also their potential to significantly alter industries, improve environmental outcomes, and enhance daily life. Living Architectural Structures The Hy-Fi installation, created by the architectural group The Living, exemplifies the potential of bioengineered materials in construction. Built from biodegradable bricks made of corn stalks and living mycelium, the structure demonstrates how living materials can be used to create sustainable, compostable architectural projects that don’t compromise on strength or design, hinting at the future of green building. Installation view of Hy-Fi. (Image: MoMA) Eco-Friendly Building Materials from Mycelium Mycelium, the root structure of fungi, is at the forefront of sustainable material innovation, with companies like MycoWorks and Ecovative Design leading the way. These firms harness mycelium’s natural growth processes to create materials that are not only strong and durable but also completely biodegradable. By feeding agricultural waste to mycelium, they shape it into products ranging from leather alternatives to packaging and insulation materials, offering a compelling example of circular economy principles in action. Self-Healing Concrete Basilisk Self-Healing Concrete represents a groundbreaking advancement in construction materials. This innovative concrete incorporates specific bacteria that, when exposed to water, activate to fill cracks with limestone, essentially healing the concrete. This process significantly extends the material’s lifespan, reduces maintenance costs, and offers an eco-friendly alternative by potentially lowering the concrete industry’s overall carbon footprint. Bioplastics Production Newlight Technologies’ AirCarbon tackles the dual challenges of plastic pollution and climate change by utilizing methane-eating bacteria to produce a biodegradable plastic alternative. This process captures methane—a potent greenhouse gas—from the air and converts it into a material that can be used for a wide range of products, from fashion items to food packaging, showcasing a novel approach to reducing carbon emissions and waste. Engineered Living Coatings Indigo Agriculture uses microbial seed coatings to enhance crop health and yield in a sustainable manner. These coatings contain beneficial bacteria that improve plant resilience against drought and pests, reducing the need for chemical fertilizers and pesticides. This innovative approach not only supports sustainable agriculture practices but also highlights the potential for living materials to contribute to global food security. Wearable Biosensors Morphing Matter Lab is pioneering bioLogic, the integration of living materials into the textile industry with its responsive fabric, which incorporates living cells of natto bacteria (Bacillus Subtilis) as a humidity-sensitive nanoactuator. The fabric’s flaps open and close in response to the wearer’s sweat, providing natural ventilation. This smart textile innovation opens up new possibilities for wearable technology, combining comfort, functionality, and sustainability.

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Realizing the sustainability potential of living materials

Advocates believe living materials could offer several sustainability benefits compared to conventional manufacturing, including:

• Using genetically modified microbes as cell factories to produce renewable bioplastics, leather substitutes and pigments. This reduces reliance on petrochemical feedstocks.
• Employing organisms for active bioremediation of pollutants and waste. Engineered microbes show promise for capturing carbon from the air or degrading plastic waste.
• Designing probiotic living coatings that prolong food shelf life, reducing spoilage and waste.
• Using nitrogen-fixing or mineral-depositing bacteria as microbe-based fertilizers for more sustainable agriculture, lowering requirements for synthetic fertilizers.

While living materials hold immense promise, several hurdles must be addressed before their widespread adoption. The production costs currently exceed many conventional materials. The use of genetically modified organisms raises biosafety concerns, requiring rigorous containment and environmental risk assessments. Public perception of synthetic biology varies, and clear communication about the benefits and potential risks will be crucial. Finally, engineering living materials demands a truly interdisciplinary approach, fostering collaborations between fields that might not traditionally interact. Nonetheless, living materials represent an exciting intersection between synthetic biology and materials science. With continued progress in engineering cells and managing microbial communities, living technologies may one day provide sustainable solutions for manufacturing chemicals, treating wastewater, sequestering carbon from the air and much more. But major advances in the field will be required to make this futuristic vision a reality. In conclusion, engineered living materials represent a groundbreaking approach to sustainable manufacturing, offering a compelling alternative to conventional synthetic materials. By harnessing the power of living organisms and integrating them with advanced engineering techniques, scientists and innovators are creating materials that exhibit remarkable properties such as self-assembly, self-healing, and adaptability. From eco-friendly building materials grown from mycelium to self-healing concrete and biodegradable plastics produced by bacteria, the real-world applications of living materials demonstrate their potential to revolutionize industries, reduce environmental impact, and enhance our daily lives. As the field continues to progress, with advancements in synthetic biology and interdisciplinary collaborations, living materials are poised to play a crucial role in shaping a more sustainable future. However, realizing this potential will require addressing challenges such as production costs, biosafety concerns, and public perception. Nonetheless, the promise of living materials is undeniable, and their development represents an exciting frontier in the quest for innovative solutions to global sustainability challenges.

Explore More: A Gateway to the Future of Living Materials

Living hydrogel fibers unveiling a new era of sustainable engineered materials Designed to adapt: Living materials are the future of sustainable building 3D-printed ‘living material’ could clean up contaminated water (w/video) Living structural materials could open new horizons for engineers and architects Engineering living hydrogels Researchers grow macroscale, modular materials from bacteria Using living bacteria to design self-growing engineering materials

By

Michael
Berger

– Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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