Thu, 01/18/2018 – 4:12pm
The challenges that today’s scientists and engineers face have evolved beyond answering a single question. Everything from improving materials performance to uncovering new drugs to designing new technologies must not only succeed technologically – it must also minimize its impact on the environment. Creating a sustainable world is both a noble and necessary goal, yet we do not need to reinvent the wheel to achieve it. It has already been done. Nature has created a vast toolbox of context-responsive, self-repairing, life-friendly and environmentally sustainable materials with an equally vast collection of uses. The field of biomimicry seeks to understand how these materials function, what they are composed of, and how they are manufactured to allow humans to emulate them in new use cases. However, many of these parts, structures, tissues and organs have been too complex, small or precise to be manufactured at the industrial scale, limiting their applicability and widespread use. This is changing; technological advances such as in silico materials modeling and simulation and additive manufacturing have placed many of these previously inaccessible areas of biomimicry research within reach.
Over the last 3.8 billion years, Nature has iteratively designed the wide array of compounds and structures which provide living things with their unique properties. These properties often perform as well as or better than the very best materials that humans have created; consider the strength to weight ratio of spider silk and steel. Additionally, these materials are self-assembled and self-repaired from a palette of widely available materials – primarily carbon, hydrogen, oxygen and nitrogen – all driven by solar power in water at relatively low temperatures and with high yields. Even the way these materials are manufactured has been thoroughly refined: from organelles to cells to tissues to organisms, the factories of life constantly tune themselves to ensure optimal performance. As our understanding of the chemical, systemic and structural characteristics of Nature-produced materials improves, so does our ability to emulate them. The goal of biomimicry, then, is rapidly adapting the billions of years of Nature’s iterative R&D for new use cases.
A Brief History of Institutionalized Plagiarism
The roots of biomimicry as it is currently defined can be traced back to the works of Leonardo da Vinci. His study of birds, exploring how anatomy provided a mechanism for heavier-than-air flight, led to some of the earliest designs of flying machines. This same methodology provided the Wright brothers with the inspiration for their own aircraft designs approximately 400 years later. Another less well-known (yet just as impactful) example is the invention of Velcro. In 1941, Swiss engineer George de Mestral noticed that burrs frequently clung to his clothes (and dog) when he went hiking. Upon further investigation, he discovered that these burrs were covered in tiny hooks, allowing them to reversibly stick to a variety of surfaces. After years of refinement, he patented his discovery in 1955, creating the now famous reversible, adhesive-less fastening system.
As technology advanced throughout the 20th century, so too did the scale of the structures explored by biomimicry, both large and small. In 1996, the Eastgate Centre opened in Harare, Zimbabwe. Its architect, Mick Pearce, modeled the building after termite mounds. 3D scans revealed that the mounds tend to take the shape of a chimney, interlaced with a variety of internal tunnels leading towards large vents. This allowed warm air to easily leave the structure and drew up cooler air from underground. By mimicking these structures within the Eastgate Centre, Pearce created a building which maintained a fairly constant temperature while using only 10 percent of the energy needed to maintain a traditional glass building of similar size. On the other end of the length scale, in 2015, scientists from the University of Santa Barbara published research demonstrating how adapting the chemistry of the foot proteins of mussels could create adhesives which work underwater. These foot proteins allow mussels to adhere to a variety of surfaces underwater – even other mussels – while withstanding strong waves and currents.
Successfully mimicking Nature, therefore, relies on developing an understanding of these materials across a variety of length scales. These materials are naturally “multiscale,” efficiently organized across nano-, micro-, meso-, and macro-scales. This hierarchical approach is also seen in how these materials are manufactured, continuously maintained by layers of specialized cells. The next generation of biomimicry research must adopt this multiscale thinking to not only copy Nature, but improve upon it.
Overcoming the Challenges of Biomimicry
The hierarchical nature of materials presents a unique problem for research: how to translate minute variations in the quantum state of one atom into the bulk properties of the whole part or machine they are designing. The solution requires building bridges between multiple fields of physics to account for the additive effects of small changes in material purity and structure as length and time scales change. Achieving this goal means moving beyond physical experimentation alone to utilize advances in materials modeling and simulation. For example, a lobster’s exoskeleton combines chitin and proteins into 20nm wide fibrils and arranges them into a multilayer mesh peppered with amorphous calcium carbonate nanoparticles. Multiple pores tunnel through this matrix to make it lighter while maintaining its mechanical strength. Finally, two of these layers covered by a waxy cuticle make up the shell we see. Exploring how changes in any one of these constituents could impact the entire structure at the lab bench alone could take years. Supplementing this research with in silico tools could speed up this research significantly. By running experiments in silico to more rapidly screen different combinations of materials and structures across different length and time scales, scientists can optimize the final product’s performance in a low risk, low resource environment. These in silico experiments can also help guide future research at the bench, helping teams answer the question “What should I test next?” faster, and providing the foundation for future predictive models. These multiscale methodologies can open doors for scientists and engineers to understand the fundamental mechanisms of action that underlie their materials’ properties, potentially unlocking new avenues to improve upon them.
The main challenge to adopting these sorts of materials, however, centers on developing scalable manufacturing processes for them. The goal for engineers, then, would be to recreate the microscopic manufacturing components of individual cells or tissues. For example, recreating the pigment-free colors seen on the wings of Morpho butterflies or other iridescent insects required refining advanced vapor deposition techniques to mimic the interference effects exhibited by the microstructures on their wings. While current technological limitations have placed some roadblocks in the way, new advances in the speed and precision of additive manufacturing techniques may provide a way forward. Additive manufacturing (building 3D parts by adding layer upon layer of material) provides clear benefits over the traditional reductive methods of “subtractive” manufacturing (cutting away material from a solid block to produce the shape of a new part), as it produces less waste and allows designers to incorporate internal structures into the design of the part. At its core, additive manufacturing mimics the layer-based deposition of materials seen in many natural processes, producing hierarchical structures with gradients of properties and materials. While older additive techniques relied on the sequential curing of photoreactive resins or the deposition of hot plastics to build a part, technological advances in additive manufacturing are unlocking new materials and methods that are catalyzing change, allowing us to consider materials as variables, not constraints. Constituent layers are becoming thinner, machine resolution and precision are improving and build speed is increasing. Machines can alternate the materials they print with, to the point where parts can be designed with gradient materials and properties in mind. All of these factors combine to provide scientists and engineers with the tools they need to take their first steps towards true multiscale thinking.
Biomimicry is an inherently noble pursuit: by taking advantage of the best that Nature has created, we can create materials, parts and products that perform better and are more sustainable. Natural selection has painstakingly crafted this toolbox of optimized materials and structures for researchers to use. By augmenting materials design with in silico modeling and simulation and additive manufacturing, scientists and engineers can test the ideal combination of materials and structures to create the ideal part. They can gain a deeper understanding of how their part works from the smallest to largest scales. It is important to note, however, that there will always be a need for work at the lab bench. Models are only as good as the data underlying them. As a result, in silico and real-world testing should not be used exclusively. Instead, a harmonization of these approaches provides the greatest value: experiments provide the data required to build a compelling model, while a model directs what should be tested next, providing the foundation to refine the original model or develop a new one. R&D teams, then, should leverage the work already done for them, both in the lab and by Nature herself. Achieving multiscale thinking is the key to biomimicry; it can make sustainability not just an ideal, but a standard.