Jun 24, 2015 | By Alec

With all those fascinating 3D printable building projects for complicated robots and bionic prosthetics out there, it is hardly a secret that low-cost sensors are perfect additions to any maker’s toolkit and to any 3D printing project. But this was clearly not enough for a team of researchers from the University of Washington, who have succeeded in 3D printing sensors themselves.

Specifically, these are color-based mechanical force sensors, something that doesn’t really exist yet as they’re too complex and too time-consuming to build with standard manufacturing methods. So why not just 3D print them? As described in a recent research paper entitled ‘3D-Printed Mechanochromic Materials’, this team of researchers (led by assistant professor of Chemistry Andrew Boydston) has done exactly that. Key in that process are sensor-based polymers capable of changing shape and composition in response to external forces (light, temperature and force).

After printing (above) and after stretching (below).

As a test of these 3D printed polymers, the team 3D printed a bone-shaped plastic tab that changes color (to purple) when exposed to physical force; a very easy to way to register if objects are under pressure. As professor Boydston said, this is a fantastic achievement as it combines two often separated specialisms. ‘At the UW, this is a marriage that’s been waiting to happen — 3D printing from the engineering side, and functional materials from the chemistry side,’ he says on the university website.

Specifically, this test material is made using two 3D printerheads, as PhD students Gregory Peterson and Michael Larsen explain. One is filled with polycaprolactone (which can be compared to flexible filaments), while the other contains a regular plastic mixed with the occasional spiropyran molecule (a material that changes color when stretched). And remarkably, those qualities are transferred to the entire object when 3D printed. ‘We wanted to demonstrate that the functional chemistry could be incorporated readily into already printable materials,’ Boydston explains. ‘We found that designer chemistry can be incorporated into 3-D printing very rapidly.’

Remarkably, the white polymer object shows almost no aesthetic differences due to the molecules, and 3D prints very quickly (in about 15 minutes or so). The result is a mechanical sensor that is completely devoid of electronic parts and costs less than a dollar to manufacture. Low-cost instant customized sensors are thus easily to imagine through this approach, with sensors being incorporated into buildings to measure pressures. Boydston speculates that these can even be incorporated into football helmets to change color when exposed to too much force. Once similar materials capable of recording speed or impact are developed, the options seem endless. Theoretically, molecules that glow under UV light after being exposed to pressure are also possible. ‘Maybe the material isn’t currently under stress, but it had been several times prior to your observing it. And so these types of materials could record that load history,’ Boydston speculates.

What’s more, 3D printing makes these sensors very easy and diverse in use. Regardless of what you’re 3D printing, the color-changing stripes made with the separate printhead can be placed just about anywhere on the object in question – perfect for any custom 3D printing project.

While this project can thus create a wide range of 3D printable applications for many different fields, it is still largely a worp in progress. Boydston and his team are currently working on a wider range of molecules with different sensory abilities for a wide range of medical and engineering applications. In short, definitely something to keep an eye on.

 

 

Posted in 3D Printing Applications

 

 

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