Vital sign monitors are essential both in clinical settings and, increasingly, at home. But even state-of-the-art monitors can produce inaccurate readings, mistaking irrelevant, motion-related signals for critical patient data.
The underlying cause of these inaccuracies is often the significant mismatch in mechanical properties between the patient’s soft skin tissue and the stiff electronics of the monitor.
If only there were a way to bridge this gap.
Yanliang Zhang, Advanced Materials and Manufacturing Collegiate associate professor of aerospace and mechanical engineering at the University of Notre Dame, together with colleagues at the University of California, Los Angeles (UCLA) and Purdue University, has created a novel material that seamlessly transitions between soft tissues and stiff electronics—stretchy enough to move with the body’s dynamic changes yet stiff enough to maintain electrical connectivity. The team’s results have been published in Advanced Materials.
“Unlike bulky health monitors, our device is super thin and stretchable, and it sticks to human skin as if it were a temporary tattoo,” said Zhang.
Nature creates seamless transitions between soft and hard materials throughout the body—tendons transition into bones, skin turns into cartilage, and a tooth’s soft pulp turns into enamel. However, until recently, manufactured materials have been either soft or stiff—not both.
Zhang and his postdoctoral research associate Kaidong Song, the paper’s first author, used a unique, aerosol-based, multi-ingredient 3-D printing method to create a gradient interface, a material that gradually transitions between soft biological and stiff electronic components.
“We proved that when used for on-skin monitoring of blood oxygen saturation levels, pulse and body temperature, this super stretchable, strain-insensitive bioelectronic device has near perfect immunity to inaccuracies caused by strain and motion,” said Zhang.
In addition to wearable monitors, other application of the team’s gradient interface are implantable devices, such as those monitoring and treating complex conditions of the heart, brain and other important organs.
Future research, Song said, will aim to improve device durability across diverse environmental conditions and conduct human trials to validate performance and comfort in real-world scenarios.
Professors Anthony Hoffman, Ryan Roeder, and Thomas O’ Sullivan at the University of Notre Dame; professors Xiangfeng Duan and Lihua Jin from UCLA; and professor Babak Anasori from Purdue University contributed to this research.
— Karla Cruise, Notre Dame Engineering; Photos by Wes Evard, Notre Dame Engineering