Research led by Zhenan Bao – K.K. Lee Professor of Chemical Engineering and, by courtesy, Professor of Chemistry and Materials Science and Engineering – was published in Science in May 2023 for ground-breaking development of self-healing electronic skin. Bao’s research group’s e-skin uses soft, thin and flexible integrated circuits to convert pressure and temperature to send low voltage electric signals to the brain. Her e-skin was originally designed for use in prosthesis, and is now being applied to precision health as well as robotics and other consumer products and medical devices. The Bao Group’s electronic skin has evolved over the past 19 years from sensing hand grasping, blood pressure, neurochemicals, and brain waves, and is now also self-healing and biodegradable.
Bao told The Daily about her research, sources of inspiration and optimism about the next generation of engineers at Stanford and beyond.
This interview has been edited for length and clarity.
The Stanford Daily (TSD): What is E-skin and what are its applications?
Zhenan Bao (ZB): E-skin is basically a new generation of electronics. E-skin looks like skin, feels like skin, and has the capability of sensing and signal processing to allow us to interact with the external environment and generate signal patterns that our brain can understand. Also, e-skin has material properties similar to human skin, meaning it is stretchy, biodegradable, self-healable, and flexible.
There are many different applications for electronic skin ranging from medical applications, such as prosthesis for patients to regain their sense of touch, wearable and implantable electronics for precision health, detection and treatment of neurodegenerative diseases, consumer products including foldable displays and interactive 3D displays, and robotics.
TSD: What was the breakthrough that led to your research being published in Science Magazine recently?
ZB: After one of my talks at a conference, somebody in the audience asked, “Your electronic skin has more than one layer. How do you repair that?” And on my flight home, I was thinking to myself, “That is a really great question.” We then formulated hypotheses to address this question, and eventually discovered new phenomena that we did not anticipate before. Curiosity inspiring creativity is really the exciting aspect of doing research.
Our recent Science paper is about a new concept of self-healing, multilayer electronic skin. When your iPhone screen breaks, for example, it’s difficult to just repair the broken layers, you have to repair and replace the entire screen. There has been interest in the scientific community to develop materials which can self-repair damages where it happens. With electronic skin, there are many layers of conductors, semiconductors, dielectric layers, and encapsulation layers. Some of these layers are hundreds of times thinner than the diameter of a human hair. With such thin layers, it’s simply not possible to manually align them to ensure the layers heal with the correct counter parts.
Our Science paper describes our discovery of molecular design principles that permit multiple layers to self-recognize the correct ones to heal with, even though each layer is made with different materials.. Basically, we design intelligence into the material, without having to use any sensors and software.
TSD: How long do you think it will be before you have working e-skin prototypes for human use?
ZB: We already have e-skin prototypes for measuring, for example, the blood pressure, heart rate and breathing rate for humans, and some of those are being commercialized. For more advanced sensing, for example, sensing chemicals from sweat, we have a prototype that we are currently testing. For implantable e-skin, it will be a very, very long process due to the biocompatibility validation required to actually perform testing in humans. As a result, we are years away from commercializing implantable e-skin.
TSD: Why did your group choose to use biodegradable materials?
ZB: Well, biodegradability is one property of human skin, and since we design the plastic materials in e-skin from the molecular level, we wanted to design these materials to be biodegradable – and recyclable, depending on the chemistry employed during the design process – so that they have minimum environmental impact.
Also for implantable devices, there are cases of application when we perform the surgery to implant the electronics, and then after the usage, we may not want to perform another surgery to remove it. In that case, if the degraded products are also biocompatible, then it would be desirable to have the entire device to degrade away after the usage. However, that can be quite challenging, because not only does the material have to meet the requirements for high performance electronics, but the degraded products would also need to be biocompatible, which adds many constraints to the material.
TSD: How do you balance creativity with the extreme technical precision of your research?
ZB: For research, we need both focus and creativity. Focus is required to not deviate too far away from the bigger direction that we set to pursue, and it allows us to take initial concepts to a deeper level.
Day to day, when working on projects and thinking about new ideas, we need to be able to dream. In my lab, I want to give my students the freedom to explore ideas—sometimes even crazy ideas which may be risky and may not work. Such explorations may generate additional new ideas.
In both research and leadership, I believe collaboration among people from diverse backgrounds is critical for creativity. This diversity brings different perspectives that can allow people to think about problems from different angles and ask different kinds of questions, all of which promote creativity.
TSD: In the past few years, especially given your role serving as Chair of the Chemical Engineering Department during the pandemic, how has your leadership evolved?
ZB: Serving as Chair of the Chemical Engineering Department from 2018-2022, and having gone through the pandemic as a Chair, both really impacted me in terms of my way of thinking and approach to leadership in general. Serving in that role allowed me to have the opportunity to listen to voices from different parts of the department and university. In addition to interactions with my research group, I had the opportunity to interact closely with undergraduate students, graduate students, postdocs, staff, faculty and university leadership. They gave me broader perspectives on the challenges that people coming from different backgrounds and positions may face. It also made me appreciate the importance of communication. I found that potential solutions can be more effective if I can better understand the needs and particular challenges different people may face.
TSD: What advice do you have for the next generation of engineers?
ZB: For the next generation of engineers, regardless of what discipline you choose to major in, first have a solid foundation of the fundamentals that are involved in your discipline; then be open minded to learn to work with others from different backgrounds and different disciplines. Most importantly, learn how to learn new subjects quickly. It’s impossible for you to take courses on everything you need to know for whatever you will do in the future. Having solid fundamental knowledge and ability to learn quickly will allow you to easily get into a new field.
TSD: What do you think are the greatest opportunities and threats to research today and in the coming decade?
ZB: I think there are several grand challenges mankind is facing – climate change, the increasing population and the cost of healthcare, for example – and addressing those issues requires collaborative and interdisciplinary research. This is the direction research is going.
TSD: What are you most optimistic about?
ZB: I’m most optimistic about the future. There are so many exciting technology developments in a variety of different fields, so I think as we move towards the future when these various areas merge together, there will be new discoveries and breakthroughs that we are not able to predict currently. Exciting recent developments in multiple fields include AI, synthetic biology, sustainable plastics, catalysts for converting CO2 into fuel, battery materials and electronic skin. All these things may potentially converge and create new, exciting breakthroughs in the future.