Glasgow University Develops 3D Printed PEEK Lattices with Tuned Auxetic Properties

Glasgow University researchers have made PEEK-based lattice parts with tunable auxetic properties. The team published their work in Materials Horizons, building on similar work from last year with PLA. In this case, the components were “finely tuned, self-monitoring materials with programmable properties such as strength, stretchability, and strain sensitivity.” The team did this by using Material Extrusion to make lattices from four different PEEK grades. Some of the materials had added carbon nanotubes, which gave them piezoresistivity. If they were subject to strain, the part’s electrical resistance would change. The researchers then made a family of geometries and measured the response to loads of these auxetic lattices. By being auxetic, they grow wider while being stretched and thinner when compressed; these properties make them ideal candidates for energy-absorbing structures. There has been a lot of work carried out in this area already, including a review paper, auxetic honeycombs, metamaterials, and energy harvesting.

The team also created a predictive model for how electrical resistance changes when subjected to mechanical stress in these geometries, which makes it a lot easier for them to create new shapes and properties going forward.

Professor Shanmugam Kumar said,

“By combining design, fabrication, and predictive modelling, we can now create materials that behave exactly as needed for a given application, whether that’s absorbing impact, sensing damage, or deforming in controlled ways. That means we can move towards a ‘design for failure’ philosophy where materials are not only strong and lightweight, but also intelligent, able to monitor their own integrity over time. We’ve shown that it’s possible to design PEEK lattices that are not only auxetic but also capable of sensing strain and damage without the need for embedded electronics, This could enable new applications in smart orthopaedic implants, aerospace skins, or even wearable technologies.”

With regards for the overall plan that they’re executing, Professor Kumar continued:

“We’re essentially giving designers a toolkit for building the next generation of multifunctional materials, ones that are as intelligent as they are strong. We believe this could be transformative for several sectors, from personalised medicine to aerospace safety and structural health monitoring.”

This is a compelling idea overall. If you look at strain sensors, for example, if they could be made much simpler, and easier to apply to all sorts of structures, and be an inexpensive way to measure the integrity of a building, bridge, or mechanical part. If you 3D printed the package, some kind of energy harvesting shape, and most of the sensor, it would absorb a lot of the cost. Beyond sensors, this kind of an approach could be used to make a whole host of embedded or ever-present electronics that would dispense with batteries and a lot of components, but instead rely more on additive.

The other obvious application is in body armor and things like helmets; here, such tuned materials could also make a lot of sense. PEEK is also widely available as an implant material. If you could make stents or other devices that behaved differently during surgery and when they were placed, and then differently again when they are removed, you may be able to make procedures less invasive. Hopefully, there could be a lot more internal geometric fiddling and a lot more variation in the shapes themselves. This could mean that the library they are building in Glasgow could grow significantly, which would make it much easier to dial in the right performance and create the right shape with the right characteristics. That, in turn, will let the team more quickly produce new final components with the right performance.

In body armor or protective padding, this could enable customers to develop end-use parts with this technology fairly quickly. I really like this approach, as it could lead to other researchers or companies commercializing things with this research much faster than if they just had a general idea or principle. It’s smart as well because if they expand the software tools and create an end-to-end workflow, from mechanical performance to slicing for example, they’ll have a technology stack that a lot of people will want to use. Rather than reading the paper and doing their own thing, people will then be tempted to use Dr. Kumar’s library of shapes and software. Programable auxetic structures have seen a lot of interest, but little in the way of commercialization, so this seems like a very solid step towards making it less of a science project and more of a usable technology. Given the advances possible with this and the new types of making that it could potentially unlock, this is very hopeful.

To learn more, you can read “Topology-Engineered Piezoresistive Lattices with Programmable Strain Sensing, Auxeticity, and Failure Modes” in Materials Horizons.