Xuanhe Zhao

Before joining MIT in 2014 as an associate professor and Noyce Career Development Chair, Xuanhe Zhao obtained his PhD in mechanical engineering from Harvard University and founded the Soft Active Materials Laboratory at Duke University. His research has led to the design of bioactive hydrogels, hydrogel-based bioelectronics and biorobots that interface between the human body and machines. Dr. Zhao is a recipient of the National Science Foundation Career Award (2012), the Early Career Researcher Award by the AVS Biomaterial Interface Division (2012), the ONR Young Investigator Award (2014), the SES Young Investigator Medal (2017), and the Adhesion Society’s Young Scientist Award (2017).

“The properties of the human body and external machines are drastically different,” explains Zhao. “While the body is a soft, living organism, conventional machines are hard, dry, inanimate devices. As such, designing functional interfaces between the two is extremely challenging. My group is focused on developing seamless interfaces between these two systems.”

A systematic strategy using existing biocompatible polymers but making them into unconventional polymer network architectures

Zhao and his Soft Active Materials Laboratory recognized that to address the challenge of reconciling such disparate materials, it was essential to consider the composition of the human body, the major components of which are polymer networks infiltrated by approximately 70-90 percent water. Because hydrogels have similar mechanical and physiological properties to the human body, Zhao and his team set about designing new hydrogels to form compatible interfaces capable of working seamlessly in the body without interrupting its delicate nature. A further challenge involved instilling long-term robustness while maintaining adhesive properties for the placement of external engineering components. “To address these issues, we developed a systematic strategy using existing biocompatible polymers but making them into unconventional polymer network architectures,” explains Zhao. “These engineered hydrogels can be integrated with external devices such as sensors, actuators, even computer chips and drug delivery devices.”

Existing hydrogels are usually based on randomly cross linked polymer networks. “We rationally design the polymer networks within the hydrogels using biocompatible nanoparticles to enforce the networks or interpenetrate different networks to form composite structures. This is a multi-scale problem, so we’ve developed various design strategies across different length-scales to manufacture adhesive, active hydrogels. We use this technology as a core platform to interface between the human body and external machines.”

As a result of this novel approach, measuring temperatures, PH levels, ion concentrations, glucose levels and other physiological signals of the human body are entering a new era. Application areas with tremendous potential include sensing and diagnosing diseases as well as addressing and curing them. Zhao points to the possibility of long-term insulin pumps that can be embedded in the body of a diabetic patient and release insulin on demand.

He envisions these novel interfaces playing a key role in monitoring and curing diseases, while also having the potential to enhance the human body. “These new interfaces may be used to embed computer chips in the body to enhance memory, vision and auditory capabilities, among other things. There is a very broad spectrum of applications,” says Zhao, citing the possibility of electrical or mechanical stimulation to relieve chronic issues like fatigue.

Zhao and his team have also developed hydrogel-based “smart Band-Aids” that contain sensors and drug delivery channels. These devices not only monitor the temperature and inflammation of a wound but also send a signal to drug delivery devices. Other new applications include extremely active yet compliant hydrogel actuators. “We envision these devices will be used to handle delicate tissues within the human body, as they are capable of exerting pressure without causing damage.” These hydrogel-based actuators are optically transparent as well as being nearly transparent to ultrasound signals, which means they won’t block ultrasound diagnosis signals.

Neural probes are another potential application area that will benefit from Zhao’s work. Existing neural probes are based on silicon, steel and ceramics, and are characterized by their rigidity, making them far from ideal for use with the human brain, often causing damage after insertion. “In collaboration with the Anikeeva Bioelectronics Group at MIT, we are developing neural probes based on hydrogels with the same mechanical properties as the brain. In terms of stimulation, receiving signals and probing the brain, these hydrogel-based probes have the potential to give long-term, high-efficacy interfacing with the brain and help people with mental diseases around the world,” says Zhao.

Zhao believes that in the future, medicine and these new interfaces between machines and the human body will be highly customized for the individual patient. To achieve this level of customization, Zhao and his team are exploring the world of 3D printing. “We can print these hydrogel-based devices for the specific conditions of different people. Inside the customized devices, we can embed functional groups to achieve the specific function that is required for a specific patient.” This platform enables him to print biocompatible materials like hydrogels and biocomponents, including mammalian cells and bacteria, while integrating them with sensors, computer chips and actuators, all of which form a system capable of sensing, drug delivery, and stimulation.

With such a wide range of potential applications for his work, Zhao keeps the bigger picture firmly in his sights. “MIT emphasizes impact on society, ensuring the problems we address are truly impactful outside of academia. And the Industrial Liaison Program plays an integral role in that process,” says Zhao. “It has been extremely useful in terms of guiding my research to address grand societal challenges while introducing me to a broad spectrum of companies and industries.” Despite recent advancements, Zhao believes the interface between the areas of biology and external machines is still in its early stages. “I see a wonderful opportunity to leverage advancements in both areas at the same time,” he says. “Ideally, we’ll develop a bridge between them to enable impactful applications that will truly enhance the wellbeing of society.”