Korean researchers have developed an artificial synapse that consumes less energy than human brain synapses, made from crab shells, soybeans, and plant stem extracts. The device is expected to help address the electronic waste problem as it completely decomposes in soil after use.
A research team led by Professor Ko Hyunhyub at the Ulsan National Institute of Science and Technology (UNIST) announced Thursday that they created a high-performance artificial synapse using only eco-friendly biodegradable materials.
A synapse is the point where signals are transmitted between brain neurons, with neurotransmitters released from one neuron binding to receptors on the next neuron to continue electrical signals.
The artificial synapse developed by the team has a sandwich-like structure, with an ion-binding layer positioned between ion-active layers. When electrical stimulation is applied to the ion-active layers, sodium ions acting as neurotransmitters are released and bind to the ion-binding layer serving as a receptor. Some ions remain in place even after the electrical stimulation ends, regulating the output intensity of subsequent signals. This principle closely resembles how neurotransmitters in human synapses bind to receptors and partially remain to strengthen memory.
The artificial synapse uses only 0.85 femtojoules (10⁻¹⁵ joules) of energy for signal transmission, less than human synapses. Even energy-efficient human synapses consume approximately 1 to 10 femtojoules (2.4 × 10⁻¹⁵ to 2.4 × 10⁻¹⁴ calories).
The device also recorded a long-term memory retention time of 5,994 seconds (approximately 100 minutes), the longest among biodegradable artificial synapses reported to date. Long-term memory retention increases as ions remain longer between the ion-binding and ion-active layers.
Both the ion-active and ion-binding layers are eco-friendly biodegradable materials that decompose completely in soil within 16 days. The ion-binding layer is made of cellulose acetate processed from cellulose derived from plant stems, while the ion-active layer consists of chitosan extracted from crab shells and a guar gum complex polymer extracted from soybeans.
The research team also created a "bionic reflex robot hand" that learns and remembers heat stimuli to respond to dangerous situations. When temperature rises, ion movement within the synapse becomes more active, increasing signal transmission efficiency, and this change remains stored in the artificial synapse. When dangerous levels of heat are detected again, the amplified signal goes directly to the motor moving the hand, reproducing the reflex of immediately releasing a hot object.
Researchers Jang Yu-jin, Dr. Na Sang-yoon, and Dr. Noh Yun-gu from the Department of Energy and Chemical Engineering participated as first authors. The team explained, "Biodegradable materials generally have poor moisture and heat resistance, but we solved this by designing materials capable of strong hydrogen bonding. The synapse structure is also simple, making it easy to manufacture."
Professor Ko Hyunhyub emphasized, "This research is significant in simultaneously solving the long-standing challenges in artificial synapse technology: ultra-low power consumption, long-term memory, mechanical stability, and complete biodegradability. This will serve as an important turning point in establishing the foundation for sustainable next-generation neuromorphic device development."
The research was conducted with support from the National Research Foundation of Korea's Individual Basic Research Program (Mid-career Research) and was published on November 27 in Nature Communications, a sister journal of the prestigious journal Nature.
