Leading Thoughts: Designing Next-Gen Devices

Interim Dean Van Citters discusses Professor Zhang's research. (Photo by Rob Strong '04)

Since he came to Dartmouth 12 years ago, Zhang has been building on the school's long tradition of translating biomedical engineering advances into clinical use. Here, he speaks with Interim Dean Doug Van
Citters '99 Th'03 Th'05 about research in biosensors for continuous monitoring and self-powered devices.

You’ve been working on small, flexible, wearable energy harvesters and sensors. What advances have you seen in your laboratory and in the field? 

ZHANG: Dartmouth has this long tradition of exciting research in biomedical engineering, starting from biomaterials and biomechanics for orthopedics to medical imaging—some of which are in clinical use right now. I hope my research adds a new dimension to this exciting portfolio. My recent work is about making devices that can do continuous monitoring of biomarkers and medical implants with a self-sustainable power supply for long-term operation. Along those lines, we have two different projects. One of them is looking at the next-generation "battery-less" cardiac pacemakers. In this country alone, 10 percent of the population have medical implants, and among these, 10 percent have pacemakers. One big issue is you have to replace a battery every few years to make the device function. To address that issue, my lab has been working on a flexible material and devices that can harvest mechanical motion from the human body, especially heart motion, to supply power to the pacemaker. Another direction is to continuously monitor physiological signals using lab-on-chips technologies. In addition to orthopedic sensors in collaboration with colleagues at Thayer, I work with Dartmouth Health anesthesiology to develop a wearable sensor that can monitor blood pressure 24/7. 

With the self-powered devices, we are working closely with a group of clinicians across the country and a major industrial partner. The goal is to reduce the overall size of the current leadless pacemaker. Currently, about 60 percent of its volume is just the battery. What if we can reduce that by having a much smaller device supply the power while opening the other space for sensing? With continuous power supply, we also open up opportunities to detect all the other parameters in the chamber. This close academic and industrial collaboration is to accelerate the development of next-generation, intelligent, self-sustainable medical implants. 

That's incredible. Can you describe the breadth of your team? 

ZHANG: It's a really multidisciplinary team that covers sensor materials development, device design and modeling, micro and nanofabrication, and preclinical trials. As an example, I started this energy harvesting project almost 18 years ago in collaboration with a cardiologist, Dr. Marc Feldman, a long-term collaborator at UT San Antonio. The spectrum of the work is broad, from coming up with a new type of porous, soft piezo material to tuning piezo constant efficiency and conformable device design to fit in a pacemaker prototype for animal studies. We have been trying pig model studies to demonstrate the prototype's power is over the desirable power threshold that industry is passionate about. 

Precise engineering is a key enabler of our work. That's the beauty of the enhanced micro-engineering lab we will have here. WeFab [the West End Fabrication facility] is opening this spring, which I'm very excited about. 

What's the next big thing that you want to tackle? 

ZHANG: Moving forward, computation will play an increasingly important role in our "hardware" research, including device designs, understanding of operations under various physiological conditions, and data integration and analytics. In the coming decades, artificial intelligence will be part of a massive network of sensors, at low cost and massively deployable, that will enhance our life quality. Autonomous medical devices will make us very powerful. 

The questions are how to seamlessly integrate more functions without the limitation by power and how to make the data not only abundant but meaningful. In that regard, my recent projects sponsored by the National Science Foundation and National Institutes of Health all involve computational experts on design modeling, algorithms, and machine learning to turn sensor data into meaningful analytics to benefit decision-makers. 

The course you teach in sensors is taking advantage of this cutting-edge technology. It sounds as though your research plays right into the needs of the course. 

ZHANG: Engineering education is an integrated part of our research. This is beyond just having undergraduate and graduate researchers in the lab. It's having the research outcome incorporated into the curriculum and energizing students in the classroom. When I started the course on molecular sensors and nanodevices 10 years ago, it was a lecture-based class that discussed various sensor technologies. What I quickly learned from students is they really want to see the ongoing impact of technology development on healthcare. 

So I added a sequence of lab modules directly from our research—starting with making micro-fluidic chips on polymers and then synthesizing nanosensors to benchmark biomarkers on a chip—so students can understand better the real-world context of what they learn. Our students are top-notch intellectually, but they're also very hands-on. I think this course serves that well.