Above: Dr. Jin in her Mechanics of Soft Materials Lab at UCLA.
Soft materials are capable of large deformation, and have mechanical properties comparable to those of biological tissues. Recent developments in soft materials are enabling the rise of soft robotics, stretchable electronics, and biomechatronics. These new fields are profoundly altering the interactions between human beings and machines. Through the integration of analytical modeling, computational simulation and experiment, UCLA MAE Assistant Professor Lihua Jin and her lab group aim to investigate the fundamental physics and mechanics of soft materials, such as their constitutive relation, nonlinear deformation, instability, and fracture. Her lab also strives to develop new materials, structures, and functions for soft robotics and stretchable electronics.
How would you explain the concept of soft robotics to someone who has never heard that term before?
The Disney movie “Big Hero 6” is a good statement for soft robotics, as that movie features a soft robot called Baymax. Hard robots are usually a bit dangerous, and working closely with them may get you hurt. But in “Big Hero 6” kids make friends with Baymax, and they even hug each other.
The advantage of soft robots is that they are soft. They have mechanical properties close to soft tissue of the human body. They can safely interact with human beings. For industry that advantage would mean that soft robots can handle very fragile objects, or even they can be implanted into the body so they would not hurt tissue in the body.
You work on hydrogels? What are they?
Hydrogels are elastomers dispersed in a solvent. They are often used for drug delivery. You can also potentially control when and where you want the drug to be released.
How would hydrogels be a form of soft robotics?
Hydrogels are a potential for soft robotics in the future. For soft actuators, you need some mechanism to actuate them. If you develop a hydrogel that can change its shape or volume in response to a magnetic field, it can be squeezed to release drugs when the magnetic field is turned on. So far people are using a device to deliver drugs, but there is the potential to make a hydrogel into a robot. You can make use of the magnetic field to control how it migrates within your body and then goes to the side you want. It can potentially do more than passively release the drug.
What are your current major thrusts of research?
We are working on stimuli-responsive materials. We develop material in the lab, and we do a lot of modeling and simulations, so that we can quantitatively tell the spatio-temporal response of these materials. These materials respond to external stimuli, which means you can use them in a non-mechanical way. You can use light, heat, magnetic, and electrical fields to trigger their deformation.
Another field that we work on a lot is the mechanics of soft materials. In classical solid mechanics, people study metal and ceramics, the deformation of which is usually on the order of 1%. For our soft materials you can easily deform them to 100%. Then we see a lot of new phenomena in subjects such as instability and fracture. We’re combining theory, computation, and experiments to study the new mechanical behavior in soft materials.
On the application side, we are making soft robots based on either stimuli-responsive materials or pneumatic actuation. We model and design those soft robotics to achieve new functionalities. Particularly, we are making use of some so-called mechanical metamaterials. For stimuli-responsive materials or other soft materials, their properties are largely determined by their chemistry. It’s a bit hard to change and get new properties. The idea of mechanical metamaterials is that by tuning some geometry in a small scale, you can change the macroscopic properties of the materials. We are also developing 3D printing techniques to fabricate those metamaterials. By integrating the mechanical metamaterials into soft robotics, we hope to achieve unique mechanical properties and functions.
If these materials are continuously deforming, how do you prevent cracks or other defects, and is that part of your research?
Understanding fracture of those materials and designing a better material is also an important part of our research. Our daily life examples of hydrogels include Jello that we eat, and contact lenses we wear – those are hydrogels. For Jello, you can use a spoon to easily break it. Those materials are not that useful in soft robotics. People are making a lot of efforts to improve their fracture properties by understanding fracture mechanics, and introducing energy dissipation mechanisms into those materials. We and other researchers are working on that. Right now tough hydrogels can be stretched for many times of their own length without breaking, in strong contrast to Jello, which you can easily break using a spoon.
Where are soft materials used in everyday life where people are not even aware of it?
There are definitely important applications of soft materials. For example, you need sealing in your thermal cups. Another big example is tires made of rubber. For bridges, you need dampers to isolate vibration. These are some classical applications of soft materials.
It’s better to think of soft robotics as a subset of robotics?
Yes, definitely. People realize that soft robotics is not going to replace hard robots, but it becomes more and more important in some fields, such as biomedical engineering and food packing. People have already been using robotic hands to handle a lot of things. But in packing food like strawberries, so far people are still using human hands. Soft robotics can play a big role in these areas.
Maybe in the near future you’ll be able to use soft robotics to do that packing, and humanity won’t have to spend all that time and labor on it?
Yes. Soft robotics is a relatively new field and of course there is a lot of research going on. Actually, even 20 years ago people started to study the fundamentals, but only in the last 10 years the field started to explode, and people realized its importance. I believe it’s partially because now people care more about human health and invest more in biomedical engineering. The field of soft robotics will continue rising.
When you were in China you wanted to come to the United States and do research here. When did you first become aware of UCLA? When did you think “Hey that might be a pretty good place to work and do research?”
When I was in China, I applied to Ph.D programs in 2008. UCLA was ranked pretty high in mechanical engineering, so I had a very good impression of UCLA.
When did you visit Los Angeles for the first time?
The first time was my interview at UCLA. My impression of UCLA MAE was that the Nano/MEMS area was very strong, and its smart materials program was also strong.
When you came out for your interview, what did you think about the campus?
The campus was definitely very beautiful. The buildings are very uniform and well designed. I took a lot of photos on campus during the interview trip since I didn’t know whether I would come back or not.
Do you still have research contacts in China?
Yes, I’m still collaborating with some people in China. China now also supports visiting students and scholars studying abroad, and I have some in my group.
Is soft materials an international field of research?
Yes, soft materials, together with a few other key words, such as soft active materials, mechanical metamaterials, advanced manufacturing and 3D printing are all universally popular.
By 2050 what will be the impact on the world of all this soft materials research and its subsets?
A few days ago I was listening to a podcast of a scientific journal. It was envisioning soft robots going into the human body and removing cancer tissues. Right now, researchers are doing fundamental work, but I can already see some of the work starting to be transferred into industry and some start-up companies have been established based on those technologies. I can imagine there will be more surgical robots making use of soft robotics probably in even less than 30 years.
Another big field is stretchable electronics. We’ve already started to see curving cell phone from Samsung. In China there is a start-up company which has already developed a phone that can be folded up when you need to. You can open it up so that you have a full screen. These companies have already started to develop flexible and stretchable electronics. I think in probably less than ten years if you want to make your phone screen larger, you’ll just stretch it.
And will this be commonplace?
I believe so. I think it will start with flexible electronics. Flexible meaning you can bend it. As long as you make the materials thin enough, you can easily bend it like a thin piece of paper. That’s flexible, but the next step would be stretchable. If you want to stretch your phone screen then you really need the material to be stretchable. In electronics, you have various materials like semiconductors, dielectrics and conductors, and you need all the materials to be stretchable. Semiconducting material is a particular challenge. There has already been work, which I am a co-author of, showing stretchable semiconductors that can be stretched to 100%, without sacrificing its electrical performance.
What would you say to high school students who are interested in going into the study of soft materials, and all the subsets such as soft robotics?
Soft material is a new and interdisciplinary field. This field needs chemists to synthesize new materials, needs material scientists to characterize their properties, and needs mechanical engineers, like us, to quantify and understand their mechanical behavior. There are lots of new mechanics in soft materials. Mechanics of stiff materials, like metal and ceramics, is relatively established, but in soft materials, due to their nonlinear behavior and large deformation, people are still observing lots of new phenomena which don’t and can’t occur in stiff materials. On the application side, the fields, such as soft robots, biomedical devices, and stretchable electronics, are wide open.