During the project, we often walked between engineering and biology labs to conduct experiments. On the way from engineering quad to medical school at Stanford campus, there are bricks and tiles engraved with the scientific stories and quotes. Towards the end of the project, one day, a quote caught my attention: “Children are not little adults- they need medicine sensitive to the changes in their biology as they grow.” I was thrilled. That’s what we were trying to achieve in the past two years. We want to develop implantable electronic medicine for pediatric population.

Implantable electronics, such as deep brain stimulators (DBS) or vagus nerve stimulators (VNS) have shown great promise in treating neurological and cardiovascular diseases. However, those implantable devices are not designed for children and adolescents to use. The rigid electronics materials cannot accommodate the body size increase and tissue growth during the developmental process. To understand more about the current clinical practice of using implantable electronics in the pediatric population, we went to Stanford hospital to interview pediatric neurosurgeons. We were not surprised to learn that the severe and even life-threatening complications are associated with implanting a rigid device on fragile and continuously growing nerves in young children. For VNS, chronic compression stress leads to nerve dysfunction and causes children unable to swallow and speak. In such cases, the implant needs to be removed by additional surgery. But such surgery is complicated to perform and often cause further damage to the nerve.

“What if we can make the implantable electronics ‘grow’ with the tissue,” we asked the question in a group meeting of Bao lab. Before this project, Bao lab has already developed many kinds of soft and elastic electronics devices. However, elastic materials constrain the tissue, although they are stretchable. The challenge was to create new electronics materials that exert minimal stress on the interfaced tissues, while accommodating the growing process.  

The initial inspiration came from my observation of pulling melted sugar by hand (viscoplastic behavior)  when I were buying hand-made wedding candies.  Can we develop implantable electronics that behave like melted sugar?  Together with my Ph.D. advisor Professor Zhenan Bao and Dr. Jinxing Li,  we came up with the idea of developing plastically deformable morphing electronics (MorphE). Viscoplastic conductor and insulator were developed by using viscous addictive and introducing a high percentage of hydrogen bonding, respectively. MorphE behaves like a ‘flowable liquid’ at strain rate comparable to tissue growth rate but behaved like a solid at higher strain rates during body movement.

To demonstrate the potential application of MorphE as a growth-adaptable neurostimulator, we collaborated with Professor Paul George at Stanford neurology department and postdoctoral fellow Shang Song and conducted the animal experiments. MorphE were implanted in rapidly growing rats for two months. During this period, the rats doubled their nerve diameter. The MorphE, consisting of a strain sensor and neuromodulation electrodes, maintains their function for the entire growing process and cause no negative impact on nerve function. In contrast, the conventional cuff electrodes failed after a 2-week time and caused permanent nerve damage.

We envision the viscoplastic electronic system will inspire the development of new tools to understand and interrogate morphogenesis (especially the nervous system) from the beginning of life to adulthood, without introducing a biomechanical disturbance. We hope that the MorphE will jump-start the development of pediatric electronic medicine and translate into clinical practice for the diagnosis and treatment of pediatric patients.

MorphE will not be possible without many biologists, chemical engineers, and bioengineers who worked together across labs to bring this research project together. Special thanks to my advisor Zhenan, my friend Jinxing and great collaborators Paul and Shang. 

Our paper is published on Nature Biotechnology. You can access the full article from the following link: Morphing electronics enable neuromodulation in growing tissue  

Dr. Yuxin Liu and Dr. Jinxing Li and Dr. Shang Song contributed equally to this work. Professor Zhenan Bao and Professor Paul George are the corresponding authors.