Jan. 26, 2023, by Chris Lefteri
How Auxetics, Thermo Bimetals & Hybrid Living Materials Are Used in 3D Design
Material design expert Chris Lefteri works with the Substance team to create cutting-edge materials in 3D.
Working with reactive materials in 3D
The behavior of reactive materials is very difficult to showcase and animate. Working with such materials in 3D allows designers to explore the possibilities available when working with materials that are currently difficult to create and work with, due to practical constraints.
Moreover, concepting and designing in a digital medium allows designers to go much further than a simple recreation of what is possible with an analog, ‘real-life’ approach. Working in 3D provides greater flexibility, as well as quicker iteration of ideas. It also lowers the costs associated with prototyping.
For this project, we opted to create five reactive materials. Materials like these, that change shape, or that have some element of movement attached to them, are some of the most exciting, advanced technology material groups we have, and my team member Daniel Liden and I felt that they were a perfect fit to demonstrate the possibilities available in the Substance apps. The Substance apps made it possible to do things that, due to practical constraints, it would have been very difficult to realize at the same level in a physical way. For instance, the auxetic effect would have been complex to realize in a real material, because we wanted to explore putting together different layers of fabric, playing with combinations of color and light and making sure that the adhesion between those layers is correct, and that you cut the fabric the right way… It would have taken a long time.
The Substance apps gave us a much more immediate creative way to explore the technology. And the project was very much a collaboration with the Substance 3D design team throughout; the Substance team understood very early on what each material possibility we presented was about, and their insights in terms of what would be most suitable to the Substance apps allowed us to filter down our initial possibilities to the final materials we designed, and to overcome any obstacles along the way.
Significantly, this project began just after just after lockdown, and travel between the teams involved was not easy. Consequently, all our communication was carried out through screens. I can’t see that this caused any real problems – but if we were to do a project like this again, I’d choose to do things in a more face to face way, if only to more easily share samples and have a hands-on play session.
The materials we designed for this project were:
(Above) A 3D auxetic material.
A physical sample that provided inspiration for this material.
While most stretchy materials, like rubber, foam, and textiles grow thinner when you stretch them, auxetic materials behave in the opposite way, and expand when stretched. This may seem counterintuitive and a little difficult to get your head around, but when you think about it should be clear how auxetic materials are extremely useful in a wide range of applications, such as clothing that will open up in response to the movement of your body to allow for better ventilation, and then close up again to preserve heat when you are not moving around. There is also an emerging field of so-called compliant mechanisms that are cut or molded from a single material using auxetic principles, making them capable of different types of movement without the need for complex assemblies of different parts and materials.
In its simplest form, creating an auxetic material can be as easy as cutting specific patterns into paper and other sheet materials. A wide range of auxetic cutting patterns that behave in different ways are available, and the same principles can be adapted to textiles, netting and other woven and knitted textile structures, or by controlling how cell structures form at the molecular level in foams and other synthetic materials.
The best examples of products that use this technology harness the hidden and unexpected quality of auxetic materials to offer real benefits in everything from medical implants that can be moved into position and the stretched to expand once they are in place, or athletic shoes that provide adaptable support depending on how the sole is stretched while moving.
Thermo-bimetals/shape memory alloys
In their simplest form, thermo-bimetals and metal shape memory alloys consist of two metals that expand and contract at different rates in response to temperature changes. This means that these materials are capable of translating temperature changes into kinetic movement, such as sheets and strips that bend, or coils and wire springs that expand and contract in response to heat, paving the way for all kinds of self-regulating mechanisms.
Chris and his team carrying out experiments with thermo-bimetals.
Broadly speaking, thermo-bimetals are materials that change shape when heated up and then return to their original state when they are cooling down. Shape memory alloys work in a slightly different way – you can bend and reshape them repeatedly and then simply heat them up to make them return to their initial shape, which is really what ‘shape memory’ is referring to.
Digital design concepting — context-aware product morphing.
Reproducing this behavior in the Substance apps provides designers with the opportunity to venture beyond many conventional design principles. The animation above illustrates one such use case, for instance – by incorporating thermal bimetals covered by a fabric, we can envisage buttons or controllers that rise, and become accessible, only when necessary. When such buttons are not needed, they become flat, and invisible, once more. Such design might be incorporated into the doors or dashboard of a car, for example.
Both material types are extremely useful, efficient and reliable. The history of thermo-bimetals goes all the way back to the mid-1700s where they were first used in clocks to make them run more evenly by compensating for temperature changes. Since then, thermo-bimetals have been used in everything from thermostats to ventilation systems. More recently, the work of the LA-based architect Doris Sung explores a wide range of uses for thermo-bimetals in architecture, potentially replacing complex systems that rely on sensors, motors and electricity to control the temperature, lighting, and potentially even the shape of buildings. Other applications include ‘breathing’ cars with panels that open up or close to regulate the flow of air through the interior depending on the temperature, as well as shape-shifting knitted textiles made with thermo-bimetal wire.
While most of us have an instinctive feel for how magnetic materials work and behave, it’s more difficult to visualize what magnetic fields actually look like, which is why ferrofluid is such an interesting material. Essentially small particles of magnetic material suspended in an oily liquid, ferrfofluids transform and change shape in response to magnetic fields – right in front of our eyes the material takes on the character of something more akin to an alien life form. Ferrofluid can be used on its own, or poured into another medium like water, becoming suspended droplets that converge and disperse in 3D space in reaction to magnetic fields.
A physical experiment with ferrofluid.
So far, ferrofluids have mostly been used in technical applications inside electrical devices such as hard drives, but also for decorative purposes, including for visualising sound waves in the Van der Waals speaker, and the watch arms in the Ink-Magnetic watch by the Chinese designer Han Ye. Other potential applications might include dynamic architectural screens with patterns that emerge, change shape and disappear again in response to the environment.
Designing a Substance graph that morphs, step 1 (left) and step 2 (right).
Ferrofluid is one of those materials whose properties are so unusual that it’s a little difficult to understand its full potential. If the carrier liquid in a ferrofluid material were to be replaced with a liquid resin, it could potentially be used as a vehicle for magnetic forming of plastics by configuring magnets to achieve the desired shape and then letting the resin cure into a solid state. The Dutch designer Jólan van der Wiel designed shoes, bags and other accessories in this way for Iris van Herpen’s SS15 collection, taking this otherworldly material in a new direction.
Digitally designing magnetic field-driven structured patterns.
Materials and design have many things in common with food and cooking – just as different ways of preparing food will change the taste and consistency of ingredients, materials are also sensitive and will react to different processes. This is clear in conventional mass-production processes, such as injection molding, where a sudden change in processing temperature, pressure or other manufacturing parameters almost certainly leads to defect parts. But new processes like additive manufacturing offer a much higher degree of control of these parameters, which can open up new and unexplored material opportunities.
Velocity painting is a great example – by carefully controlling the temperature and extrusion speed of fused filament fabrication (FFF) 3D printers, it is possible to achieve fine and highly accurate color and transparency changes in the material, meaning that surfaces can be decorated directly on the 3D printing machine rather than using a secondary finishing process.
This extends the potential for customization and fine tuning that is inherent in additive manufacturing beyond the actual shape that is being printed to also include surface decoration. The translucency of clear materials can also be controlled in this way, making it possible to print parts that go from opaque or translucent to clear without using two different materials or additives like color pigments to make clear materials opaque.
Potential uses include illumination for applications such as interiors and transport, or just as decoration in product design, fashion and sports equipment. Experimentation with clear materials is particularly interesting, as velocity painting makes it possible to control the light transmission through the entire thickness of the material, as opposed to a surface texture applied to the surface of the material.
Hybrid living materials
Unlike conventional manufacturing processes, where control and repeatability are central, hybrid living materials introduce a degree of unpredictability. A 3D printing system developed by the Mediated Matter group at MIT, hybrid living materials allow for the inclusion of bacteria embedded directly into the material itself. Depending on the type of bacteria, various processes that are usually invisible to the naked eye are visualised when enzymes and proteins react and change color. This is not so different to how many traditional materials react to the environment in different ways – metals oxidise, fungal infections can create beautiful patterns in wood, and so on. Hybrid living materials make it possible to bring these processes into the world of high-tech manufacturing as a kind of updated take on patina for the digital age.
3D printing with hybrid living materials is based around using two materials – a biocompatible and biodegradable plastic capable of sustaining bacterial growth, and a conventional rigid plastic material to provide structure. Combined with other, non-reactive materials, multi-material 3D-printed parts can be developed for a wide range of applications including surfaces that change color in response to specific bacteria that are transmitted by touch, from food or any other source. This is useful in packaging or interiors that are sensitive to contamination, such as hospitals and clean rooms. Or these materials could be used simply for decoration in surfaces that age and develop over time in contact with the environment.
Substance 3D Assets now includes 9 materials designed by Chris Lefteri and his team: Multilayer Composite Auxetic Pattern, Auxetic Curtain Wall, Random Ferrofluid Pattern, Velocity Painted Plastic, Hybrid Living Plastic, Thermo Bimetal, Thermo Bimetal Curtain Wall, Thermo Bimetal Stripes, and Thermo Bimetal Composite Fabric.