Ian Y. Wong, Ph.D., is Assistant Professor of Engineering, Molecular Pharmacology, Physiology and Biotechnology at Brown University in Providence, RI. He and colleagues have developed a new type of hydrogel blocks that can be assembled like LEGO®s.
Tech Briefs: What is your project?
Professor Ian Y. Wong: I’d like to start with a basic introduction. Hydrogels are water-swollen polymer networks — they’re materials that are over 90% water. People use them to deliver drugs, or as actuators and are also getting interested in using them for robots. The problem is that normally if you make a slab of hydrogel; it just sits there and doesn’t do anything interesting. Since it’s mostly water, it’s pretty fragile and breaks easily. Finally, hydrogels aren’t very sticky and tend to slide apart. We were interested in making hydrogels where we could control the shape —that’s where 3D printing comes in.
We wanted to make them a little bit stronger and also have them be able to stick to each other in a reversible way. We were inspired by Legos because you can attach Legos together in defined configurations based on where the connectors are, without needing any specialized training. So, we wanted to do the same things with these hydrogels — we wanted to be able to give somebody some DIY toolkits with a bunch of Lego-like hydrogels and give them salt water, so and they can just build devices on their own without any complex equipment.
Tech Briefs: What does the salt water do?
Prof. Wong: Hydrogels are usually based on polymers that are attached to each other by covalent bonds. Our key innovation is that we’re using ionic polymers that have a negative charge. When you add a positive ion, it functions as a reversible linker that spans between the negative charge groups on the polymer.
Tech Briefs: Have you thought about the toolkits, how you would provide them, who you would provide them to?
Prof. Wong: We are a biomedical engineering lab — biologists perform labor-intensive experiments that involve things like living cells, so they don’t want to mess around with making new materials and 3D printing. But if we gave them a bunch of Lego blocks that are already made, maybe they could put cells in there, or use them to manipulate liquid solutions with different biomolecules. So, it’s targeted toward more biological applications, but you can imagine giving people a box of Lego parts to put together and make whatever they want.
Tech Briefs: You make channels for the microfluidics in each block?
Prof. Wong: Right, so as we’re making a Lego block, we can also make a pattern inside, so, if you have half of a channel on the top and the other half of an open channel on the bottom, once you attach the Lego blocks you have one sealed channel. You could imagine having different Lego blocks with different channel geometries. You can use them to make more complicated devices.
People are very interested in, for instance, trying to mix two fluids together. This doesn’t work very well in small channels because the liquids are very viscous. So that’s something we were playing around with. It’s very difficult to make channels that mix two fluids together because of very complicated geometry, but now we can print them and stack them together very easily.
Tech Briefs: Would you tailor the blocks to an individual user, or would they be able to create their own channels?
Prof. Wong: One idea I had is that Lego gives you a standardized system for interfacing between different blocks, so you can imagine maybe we’d have some mass produced set of blocks that we give the user, but they could also custom print their own if they have a special channel geometry in mind. Since everything is based on this Lego system of connectors, they could attach them together.
Tech Briefs: How do you create the channels?
Prof. Wong: Since these are 3D printed blocks, we encode it into our computed aided design (CAD) file.
Tech Briefs: So, do you envision this going to other labs or to biotech firms?
Prof. Wong: Yes, I could see this going to other labs. I’m also hoping it could even be something that high school students could use. There’s a lot of interest in DIY maker projects that are easily accessible for beginners. I think it can work well, LEGOs are intuitive to everyone and they’re relatively inexpensive.
Tech Briefs: Then, there are robots. It’s hard for me to imagine a soft robot. You described how one lifted a one-gram object.
Prof. Wong: It doesn’t do very well compared to a metal robot, but I could make an argument for why you might want a softer robot. One idea is there are certain jobs that are very laborious, but couldn’t be easily implemented by hard robots, like picking fruits or vegetables. It’s very hard for a robot to recognize fruit or grab onto it without crushing it. If you make it out of a softer material, however, it might be able to form around the fruit and more gently pull it out. Beyond fruit, if you want a robot that could care for human patients, they would need be gentler than they if they are making cars. The general idea is that using a softer material that’s a little bit more conformable, could be useful for certain applications in, say, biology or food processing that might benefit.
Tech Briefs: How would you activate the robots to make certain motions? How would you give them commands?
Prof. Wong: So, we’ve shown the different concepts, but we haven’t implemented them together yet. Imagine that if we incorporate these channels within the actuator, then we could start to flow in different salt concentrations and start to actuate the hydrogel. It may be more relevant to make a hydrogel that changes shape, rather than one that actually grips. For instance, if you need a pump or something like that, you would just need to pulse it regularly. As a proof of concept, it should work — there are also other mechanisms to actuate soft materials.
Tech Briefs: How would you implement more complex motions rather than simple expansion and contraction?
Prof. Wong: If you lay down more than one channel, you could flow ions to the different channels and then you might be able to actuate in a more complicated way.
Tech Briefs: Do you plan to continue your work on this?
Prof. Wong: We demonstrated it using 3D printing, which was labor intensive, but we had to do that because we weren’t quite sure what would work. So, we’re interested in ways to make it a little bit easier, and we’re interested in other hydrogels as well, to use for maybe a diagnostic. We think this would work with a lot of different types of polymer chemistries — we’re just getting going on seeing what will work.
Tech Briefs: How are these devices used for diagnostics?
Prof. Wong: One advantage of making very small channels is that there’s a lot of surface area relative to the volume of fluid you’re flowing in. So, it’s really good at collecting, for instance molecules, in a sample of interest. So, before doing this work, I was very interested in cancer, where you’re trying to take a tube of blood and isolate cancer cells from it. Historically, they had specialized technicians who used a centrifuge and carefully pipetted out a certain layer from the tube, which required some specialized training and resulted in some human error.
Tech Briefs: What excites you about this project?
Prof. Wong: I think I’m still a kid at heart so I really do like this idea of having Lego blocks that you can put together. But even beyond the Lego blocks; with 3D printing, you can really fabricate anything you imagine – now with interesting responsive and self-adhering properties. This is really something that people can relate to – having an idea and then producing it on demand for the real world.
An edited version of this interview appeared in the June Issue of Tech Briefs.