New dropletronic devices could revolutionize biotechnology and medicine

Researchers at the University of Oxford have taken a significant step towards a form of “biological electricity” that could be used in a variety of biotechnology and biomedical applications, including communication with living human cells. The work has been published today (November 28) in the magazine Science.

Iontronic devices are one of the fastest growing and most exciting areas of biochemistry engineering. Instead of using electricity, they mimic the human brain by transmitting information through ions (charged particles), including sodium, potassium and calcium ions. Ultimately, iontronic devices could enable biocompatible, energy-efficient, and highly precise signaling systems, including drug delivery.

Until now, however, iontronic devices have typically been placed in fixed scaffolds, which prevents their integration into soft tissues. In this new study, researchers at the University of Oxford succeeded in developing miniaturized, multifunctional iontron devices built from biocompatible hydrogel droplets. Hydrogels act as ionic analogs of electronic semiconductors, which allows controlling the movement of ions in the same way as in electronics. The tiny micro-scale droplets are assembled by surfactants (soap-like molecules) and conducting ions after light has triggered them to connect to each other (a technique developed by the group).

The researchers have named their collection of devices dropletronics, a combination of droplet and iontronics. By creating microscale combinations of nanoliter hydrogel droplets, the team produced dropletronic diodes, transistors, logic gates, and memory devices. Dropletronic devices perform better than any soft iontronic device developed to date, including higher efficiency and faster response time. They are even comparable to solid iontron devices, with the added advantage of not being embedded in a hard matrix.

Ions have many advantages over electrons: for example, having different sizes and charges can be used to perform different functions in parallel. By incorporating large ionic polymers, we demonstrated a dropletronic device with long-term memory storage that has not been achieved by previous iontronic approaches and offers an unconventional path to neuromorphic applications.”

Dr. Yujia Zhang, lead researcher of the study, Department of Chemistry, University of Oxford

In addition to controlling ion movements, dropletronic devices can also communicate with cells and record biological signals from them, since devices and cells speak the same “ion language”. In this study, the research team used devices to record biocompatible sensors to record electrical signals from beating human heart cells.

“This is the first example of a biological sensor built in the laboratory that can detect and respond to changes in the activity of human heart cells in a dish,” said Dr. Christopher Toepfer, associate professor of cardiovascular science at Oxford University’s Radcliffe School of Medicine. “This discovery is an exciting step toward making more complex biological devices that detect various abnormalities in the body and respond by intelligently delivering drugs inside the body.”

Researchers plan to integrate droplettronics into living matter, which would provide a biocompatible approach to direct ion communication, including the ability to recognize several important ionic and molecular species, opening up new opportunities in various fields, especially in clinical medicine. Dropletronic circuits may also provide a route to build ionic logic systems that mimic neurons for neuromorphic data processing and computation.

Professor Hagan Bayley (Department of Chemistry, University of Oxford), leader of the study’s research team, said: “Dr Zhang has used a creative, highly interdisciplinary approach involving aspects of electrochemistry, polymer chemistry, surface physics and device design to produce the first microscale ‘droplettronic’ devices. The functional properties of these structures show that they can soon be developed into practical devices with applications in both basic science and medicine.