In their quest to develop materials that can greatly enhance human health and longevity, researchers at Sungkyunkwan University (SKKU) in South Korea are seeking inspiration from some surprising sources. “To come up with new ideas for biologically inspired biomaterials, our researchers often visit museums, talk to zoologists and watch nature documentaries,” says Nae-Eung Lee, the dean of Engineering at SKKU. The results include technology based on octopus suction cups, beetle hairs and spider organs.
One key has been interdisciplinary initiatives such as the Biomedical Institute for Convergence at SKKU (BICS), which bring together researchers working on diverse topics such as integrated theragnostic approaches, nanomaterials, drug-delivery systems, nerve sensors and bioimaging systems.
Inspiration from nature
Taking inspiration from biopolymers, such as cellulose, collagen and exosomes — small packages of biomolecules that are released by cells — SKKU researchers are developing a technology that can directly sense parameters such as pH and temperature in the body. And it can deliver therapy based on the measurement results. “Nanomedicine promises to provide better treatment options for diseases such as cancer, rheumatoid arthritis and diabetes,” Lee says.
Larger scale internal medical technology includes integrated bioelectronics that can attach to organs, tissue engineering for effective drug delivery, and neuroprosthetics that can connect machines directly into the brain. Integrating technology with humans is a revolution that Sang-Woo Kim believes could push human longevity above 100.
Using static electricity to charge devices
Kim’s group is trying to harness triboelectricity to charge biomedical devices. A phenomenon known to the ancient Greeks, triboelectricity is the static electricity generated by friction between dissimilar materials; it is behind the crackles and sparks that occur when removing synthetic clothing. Kim plans to use this static electricity to charge batteries in implanted devices. Tiny devices with layers of different materials that move back and forth with body movements, breathing or pulse can harvest energy, thereby eliminating the need for surgery to replace batteries.
Kim initially hoped to use natural body movements, but they don’t provide enough energy. So to supplement this charging, his team is using ultrasound, which passes through tissue harmlessly and stimulates the triboelectric components to move back and forth. His group has painstakingly explored the best materials to use, including both existing materials such as Teflon and perovskites whose triboelectric properties had never been tested and new, more efficient materials. They have also improved the efficiency of the devices by using nanostructuring and porous structures to increase the surface area, to maximize the charge, and to funnel it into batteries before it discharges.
Adding a topping to a pizza
The variability of triboelectric pulses is not ideal for the slow, constant charging that batteries require, and so SKKU researchers began exploring supercapacitors for incorporating into triboelectric nanogenerators. They found that a better option was to build capacitance into the electrodes of the batteries. One example is black phosphorus, which is already used in batteries, despite its sluggish kinetics. The team improved its performance with an approach inspired by pizza. Instead of topping their black phosphorus with pepperoni, they added oxide molecules to the surface, which can quickly store charge like a capacitor. “Pristine black phosphorus is like mediocre plain pizza,” says Kim. “By adding toppings of oxygen atoms, we have developed a pseudo-capacitive device with a fast, reversible charge-storage mechanism.”
Dissolving implanted devices safely
Thanks to SKKU researchers’ impressive control of material properties, they are employing ultrasound to solve another problem: how to dispose of implanted devices that are no longer needed. Kim’s group is developing devices that can be dissolved at will using focused ultrasound. “The fact that we can choose the time to be absorbed would provide high practicality of transient implanted medical devices and eliminate inflammation or side effects from material residue,” Kim says.
Making perovskites more competitive
SKKU researchers are also addressing planetary health, by developing high-efficiency solar cells based on perovskites. Perovskites are organic–inorganic lead or tin halide-based crystalline materials that are challenging silicon-based cells in the efficiency stakes. “Because perovskites have high efficiency and are low cost they will play an important role,” says Nam-Gyu Park.
Park says perovskites’ early problems with instability caused by humidity can be overcome by encasing the cells in watertight layers. However, other challenges still need to be addressed, he says, citing Nobel Laureate Herbert Kroemer’s quote “the interface is the device.” Perovskites are currently used with silicon cells in tandem cells, which increases the number of interfaces. But Park and his group believe they can improve the efficiency of perovskite cells beyond 30% and make them viable stand-alone cells. Already, by creating a wrinkly surface they have improved the electrical properties, and now they are exploring the effect of defects in the crystals.
Cracking that problem will need a fundamental shift in understanding, Park says. “Perovskites are mysterious materials that behave differently to conventional semiconductors. It’s an interesting journey to understand this intrinsic material.”