The Third Thumb: Body extension at the forefront of haptic design

Jun.24, 2024

By YouFab 2017 Executive Committee

Among the many projects in competition for the Haptic Design Award, one in particular stuck out like—well, a sore thumb.
That project was The Third Thumb, a 3D-printed extension of the hand designed by UK-based New Zealand native Dani Clode. Not only does The Third Thumb serve as a fascinating investigation on the relationship between the human body and prosthetics, it sparks surprise, fascination and even joy in the people who try it out.

Clode sat down with the organizer of Haptic Design project Kouta Minamizawa at FabCafe Tokyo for a chat about the project, the present and future of prosthetics, and why the thumb is her favorite part of the body.

Text / Matt Schley, Photos/ Hajime Kato

Three Thumbs Up

Minamizawa: I was really impressed by your project—not only in terms of the technology, but the design. It’s a really interesting take. How did you come up with the idea of augmenting the body?

Clode: So, I wrote my Master’s dissertation on human extension, and extension in general—looking into animals that extend their senses, for example, and into prosthetics as well. Then I came across the Latin origin of the word “prosthesis,” and I found that it meant “in addition to—to add onto.” That just completely shifted my whole perspective on how we understand what a prosthetic is. I realized that it’s not something that replaces, but something that extends ability.

For me, prosthetics are such unique objects. They cross these different boundaries between a product and the body and experience in a way no other product seems to do. I wanted to experience it for myself, and explore the idea of extension.

Also, I just love the thumb! The thumb is amazing to me.

Minamizawa: Why?

Clode: Thumbs are just so human. They’re one of our most human qualities. One of the most unique movements that we do, unlike any other mammal. It’s also one of the biggest challenges in a prosthetic hand, so I thought I’d tackle it.

Minamizawa: Could you talk a little about the design process?

Clode: I was really inspired by what’s called living hinge design. That’s when the design of the material put under force creates the movement, so there’s no interlocking mechanisms. That was important, because I decided I didn’t want any interlocking hinges—we don’t have them in our hands.

I started prototyping a lot with laser-cutting gaps out of material, so when put under force, it would give in those areas. Lots of 3D-printed processes, lot of materials. Then I found NinjaFlex, which is a flexible filament for 3D printers. That completely opened up my options for prototyping, and enabled me to put in internal channels for all my wires—and it flexed in a way I just loved. Then I worked with a Formlabs resin for the hand, because it’s a really soft, high-res resin that also allowed for those internal channels.

I prototyped a lot how it was attached to the hand also. I really looked at the hand in terms of where the movement is. I needed a rigid part to attach to, which was daunting, because the hand has so much movement. I found that the small area underneath the pinky finger has almost no movement… it’s just kind of squishy, so that was a really good place to put it. I also had to work on how to get it to fit the most hands. The current model is made for my hand, but I’ve made it in a way that it can fit the most hands possible. I’ve only met three hands it couldn’t fit (laughs). After I developed all that, I worked on the control.

Minamizawa: The Third Thumb uses sensors on the toes for control. When we extend the body, one of the most important things is how we control those extensions. How did you hit on the idea of foot control?

Clode: I did a few prototypes that relied on the hand, but they weren’t very functional, so I decided to go wider and explore the entire body. A lot of prosthetics are controlled by electromyography sensors, but that’s built off muscle memory of the vestigial limb. Obviously, there’s no muscle memory for The Third Thumb, so I decided that it could be anything, really. I looked at the flex of our skin, and joints—elbows, knees. But then I realized the feet are so… we have a lot of control over our toes, but we don’t utilize it that much. I also realized the thumb and the big toe are kind of connected—if you look through evolution, there’s a connection between our hands and our feet.

Minamizawa: How long does it take users to get used to the controls?

Clode: Getting a response from it is quite quick, but it does take a while to get more subtle movements out of it. I’ve found that the more I’ve used it, the more I’ve grown attached to it. That’s something that’s very interesting about the project: the feeling of attachment that’s being created.

Minamizawa: In your video introducing the thumb, all the users look like they’re having fun, and are surprised. What kind of reactions have you seen?

Clode: Right! With the video, I made sure everything you see was their first reaction—that was really important for me. I set up all the cameras beforehand, so those are their real initial reactions. It is really a unique and weird experience. It’s been very positive. It starts off as kind of a shock—one girl actually got kind of scared from it. Then you go from shock to intrigue, then start to explore with it.

Minamizawa: Were there any findings you didn’t expect?

Clode: I think the most unexpected finding is the attachment I’ve started to feel with it. At one point, I was wearing it on and off every day for about two weeks, and after taking it off, I felt like there was something missing on my hand. I think because of the subtle movements, you grow quite attached to it. That’s definitely something I wasn’t expecting.

The Future of Body Extension

Minamizawa: What do you think will happen when people start to extend their bodies like this?

Clode: Good question! We’re still really in the early stages. One thing that has to change is that the parts need to get smaller. I’m still struggling with the fact that servos and things are still big blocks. But as that changes, I think it’s going to open up a lot more opportunity to design ourselves.

I think expanding our senses is going to be something interesting. In terms of wayfinding and becoming more aware of our environment. Maybe not physically altering ourselves, but extending our senses, is definitely something that will be very interesting.

Minamizawa: I think this is exactly why we chose your project for award. Haptic refers to our sense of touch. But if we only think about it in terms of our own receptors, our own sense of touch, we can’t change. Your project points a way forward for how our bodies can change—and if our bodies change, our behavior changes, and our view of the environment might change as well.

Clode: Thank you.

Minamizawa: Tokyo is going to host the Olympics and Paralympics in 2020. How do you think events like the Paralympics affect prosthetics as a whole?

Clode: I do think you see a lot of interesting innovation with the Paralympics, just because of all the money and support that goes into that development. The US BMW wheelchair design for the 2016 Paralympics, for example. Innovative design elements built for that level of competition can be translated back into everyday wheelchairs, which is so amazing. My most favorite is the cheetah leg, the running prosthetic. That innovation came from looking at the end solution, rather than trying to recreate the human body. It’s just an incredible innovation. It’s even exceeding the ability of a human leg, which brings up all kinds of interesting questions about our bodies.

Minamizawa: What knowledge or technology do you think is still required in this field?

Clode: I think we need more development on attaching to the body. That, and designing for our bodies, and how different each of us are. We’re not just small, medium, large. We’re all so unique, and so mass customization is a big challenge. I think we’re getting there with footwear and certain kinds of sports clothing, which is at the high end of being adapted to our bodies.

A lot of ethical questions come up when we look at where this is going in the future too: there are interesting questions about both adding to and replacing parts of our bodies, and we need to start talking about that more as our technologies get better than our bodies.

Minamizawa:Yes, the ethical issues in terms of changing or editing our bodies are really interesting—we also need to have discussions about acceptance. In Asian religions, we have a lot of deities with multiple arms, faces, and things like that, so I feel like we’re kind of primed for acceptance, in a way. How far along do you find social acceptance of prosthetics in the west?

Clode: I’ve definitely had a lot of mixed reactions to The Third Thumb. A lot of people say, “whoa, that’s just too weird.” Especially on the hands—I think there’s something quite visceral about our hands. It’s our contact point—it’s our interaction point with the world. To edit your hands is a bit too weird for some people.

But I think things like the Paralympics will help with it—help people accept that our bodies are so different, and that there are people extending their ability through technology.

Future Plans

Minamizawa: What body part would you like to try next?

Clode: I’m not sure—I’ve been so focused on the thumb. It would be cool to try the whole arm. I design prosthetic arms as well, so it would be cool to combine them. But I think the biggest challenge would be how it’s controlled. You would need a unique way to control it.

Minamizawa: From a scientific point of view, you need two things: agency and ownership. Agency meaning freely controlling it as you wish, and ownership meaning feeling some sort of stimulus or feedback. Your foot control definitely gives your users agency, but are you working on anything in terms of ownership?

Clode: Yeah, ownership would take The Third Thumb to the next level. Feedback is hard. There’s a lot out there in terms of vibration, or sound feedback, for example, that’s really interesting. I’ve seen something interesting called skin stretch. It becomes more of an attachment to the hand, and you feel the feedback in terms of stretch on your skin. That could be a route I might go down.

Minamizawa: Feedback like that is important, because it helps the brain start to change its body map. I think your approach could also be used for people with disabilities, people who don’t have hands or fingers, for example. Do you have any ideas in terms of fabricating things for them?

Clode: I’ve been contacted by so many people from the prosthetics community, and it’s been so validating for me to be approached by them. I get the feeling they see the potential in my project. One of the reasons I did a project like this in the first place, as a designer, was to understand prosthetics better, to have first-hand knowledge of what it’s like to add something to your body. Absolutely, I’d love to take it down that route.

Minamizawa: We’re seeing more of this in Japan now too. A whole community of people using 3D printing to design their own prosthetic hands.

Clode: I think 3D printing for prosthetics is so interesting, because it is that kind of mass customization that you need. So many people need it, but all of them need it to be so unique.

Minamizawa: What are you working on now?

Clode: I’m currently working with the Alternative Limb Project, making prosthetic arms. I’m also working on developing The Third Thumb further with a team of neuroscientists from The Plasticity Lab at University College London. What their research is finding is that some amputees are choosing not to use their prosthetics, and instead using their biological arm, twice as much. They came across my work, and they’re interested in if we add another digit to the biological arm of amputees, how that could potentially help them instead of, or as well as, a prosthetic.