A 3D printer lays down used coffee grounds to make a flower planter. (Image: Michael Rivera)

Assistant professor Michael Rivera and his colleagues have developed a method for 3D printing a wide range of objects using a paste made entirely out of old coffee grounds, water, and a few other sustainable ingredients.

The team has already experimented with using coffee grounds to craft jewelry, pots for plants, and even, fittingly, espresso cups. The technique is also simple enough that it will work, with some modifications, on most low-cost, consumer-grade 3D printers.

“You can make a lot of things with coffee grounds,” Rivera said. “And when you don’t want it anymore, you can throw it back into a coffee grinder and use the grounds to print again.”

“Our vision is that you could just pick up a few things at a supermarket and online and get going,” Rivera added.

The vision to 3D print coffee grounds began — where else — in a coffee shop.

When Rivera was a graduate student at Carnegie Mellon University, he often worked out of a café in Pittsburgh called Arriviste Coffee Roasters. The coffee shop contracted with a local group to pick up its used coffee grounds for composting, but during the COVID-19 pandemic, that wasn’t possible. The waste began to pile up.

“The owner told me, ‘I don’t know what to do with it. So I just throw it away,’” said Rivera. “I looked at the grounds and said, ‘Maybe I can do something with them.’”

Rivera explained that most consumer 3D printers on the market today print with thermoplastics of some kind. The most common is polylactic acid (PLA). This material is, theoretically, compostable, but only a fraction of composting facilities will accept it.

“If you throw it in a landfill, which is where the majority of PLA ends up, it will take up to 1,000 years to decompose,” Rivera said.

He realized he could solve several problems at the same time: Reduce plastic waste, find something to do with all those used grounds, and enjoy some warm cups of coffee in the process.

“To make the material, you take dry spent coffee grounds, mix in the right proportion with cellulose gum and xanthan gum,” Rivera said in an exclusive Tech Briefs interview, the entirety of which can be read below. “Then you add that combination into some water until the mixture has the consistency of peanut butter.

“To print the material, you load it into a syringe and use a syringe pump with an off-the-shelf 3D printer. In our setup, we used an open-source syringe pump  attached to an Ender 3V2 , which is a commonly used low-cost consumer 3D printer.”

“We’ve made objects with a ton of usage,” Rivera said. “We’ve dropped them, and they haven’t broken yet.”

He sees a lot of potential for turning coffee grounds into tangible objects. Rivera, for example, has made small planters out of coffee grounds, which can be used to grow seedlings for acid-loving plants like tomatoes. Once the plants get tall enough, you can plant them, pot and all, in the soil. The team can also add activated charcoal to its grounds to make parts that can conduct electricity, such as buttons for sustainable electronics.

Rivera noted that printing with coffee grounds may never become a widespread practice. Instead, he sees the project as a step toward discovering other kinds of sustainable 3D printing materials that could, one day, replace plastics.

Here is the Tech Briefs interview — edited for length and clarity — with Rivera.

Tech Briefs: I’m sure there were too many to count, but what was the biggest technical challenge you faced while developing this 3D-printing method?

Rivera: Probably the most difficult challenge we faced was figuring out the right combination of bio-based materials to combine with the coffee grounds. We wanted to produce a paste that would support itself stacking during 3D printing and be strong when dried. Material development on its own is challenging.

When you emphasize sustainability considerations like only using compostable materials and avoiding the use of heat — a big driver of the environmental impacts of 3D printing — the process becomes much more difficult. We went through a lot of material exploration and testing, combining different binders in various proportions, before we were able to get a solid mixture.

Tech Briefs: Can you explain in simple terms how it works?

Rivera: Part of what makes this material and the process so unique is that it is truly simple. You can make the material at home using tools that most people already have in their kitchen. All you need are some spent coffee grounds, cellulose gum, and xanthan gum. The cellulose gum and xanthan gum are food additives used to thicken and bind together things like pastries, ice cream, and even toothpaste. You can easily find them in a grocery store or online.

We describe this information in more detail in our freely available research paper which can be downloaded from our lab’s website .

Tech Briefs: 1) What’s the next step? Do you have any plans for further research? 2) Do you have any other kinds of plastic-replacing sustainable 3D printing materials in mind?

Rivera: The spent coffee grounds material is rigid and works for prototyping, but it isn’t at the same level of strength as commonly used thermoplastics like PLA and ABS. Part of our current work is looking at other material formulations that could offer increased strength without sacrificing sustainability considerations.

Along similar lines, there are many thermoplastic materials used in 3D printing for different functional and aesthetic reasons — there are ones that are flexible like TPU; others that are conductive; and you can even get materials in a variety of colors. My lab is also currently exploring using other bio-based materials like agar-agar as more sustainable alternatives to these types of thermoplastics. More broadly, we hope our efforts inspire others to see opportunities to reuse other commonly wasted bio-based materials (like orange peels and eggshells) and to emphasize sustainability, whether that be for 3D printing or something else.

Tech Briefs: Could we one day see this used in a concrete mixture?

Rivera: Interestingly enough, I saw an article a few weeks ago  that discussed how researchers were able to add spent coffee grounds into a concrete mix and make the concrete almost 30 percent stronger. So, it looks like that day has already come!

Tech Briefs: Do you have any advice for engineers/researchers aiming to bring their ideas to fruition?

Rivera: When you see an interesting idea realized or a cool product, it’s easy to forget that a lot of effort and experimentation goes behind bringing that idea to fruition. As you are working on your own ideas, remember that challenges are part of the process, and they are obstacles that are meant to be overcome.

Tech Briefs: Anything else you’d like to add?

Rivera: If people are interested in learning more about my lab’s work, they can check out our website: utilityresearchlab.org .