Researchers enhance longevity of neural implants with protective coating

Neural implants contain integrated circuits (ICs) — commonly called chips — built on silicon. These implants need to be small and flexible to mimic circumstances inside the human body. However, the environment within the body is corrosive, which raises concerns about the durability of implantable silicon ICs. A team of researchers from the Bioelectronics Section led by Dr. Vasiliki (Vasso) Giagka, address this challenge by studying the degradation mechanisms of silicon ICs in the body and by coating them with soft PDMS elastomers to form body-fluid barriers that offer long-term protection to implantable chips. These findings not only enhance the longevity of implantable ICs but also significantly broaden their applications in the biomedical field. The paper on this project is published in the prestigious journal Nature Communications.

Crucial research on brain diseases

Neural implants are crucial in order to study the brain and develop treatments for patients with diseases like Parkinson's or clinical depression. Neural implants electrically stimulate, block, or record signals from neurons or neural networks in the brain. For study and treatment, and specifically for chronic use, these neural implants must be durable.

Miniaturized neural implants have enormous potential to transform healthcare, but their long-term stability in the body is a major concern. Our research not only identifies key challenges but also provides practical guidelines to enhance the reliability of these devices, bringing us closer to safe and long-lasting clinical solutions."

Vasso Giagka, researcher at the Technical University Delft

The researchers evaluated the electrical and material performance of chips (from two different manufacturers, also known as foundries) over the course of one year through accelerated in vitro and in vivo studies. They used bare silicon IC structures and integrated them with soft PDMS elastomers to form body-fluid barriers that offer long-term protection to implantable chips. The chips used in the study were partially coated in PDMS (polydimethylsiloxane), which is a polymer containing silicon. This created two regions on the chips, a 'bare die' region and a 'PDMS-coated' region. During the accelerated in vitro study the chips were soaked in hot salt water and electrically biased (exposed to electrical direct currents). The chips were periodically monitored and results showed a stable electrical performance. This showed that the chips remained operational, even when directly exposed to bodily fluids.

Analysis of the materials of the chips revealed that there was degradation of the chips in the bare regions, but there was only limited degradation in the PDMS-coated regions.

This shows that PDMS is a highly suitable encapsulant for years-long implantation. These insights will inform and enable the design of state-of-the-art chip-scale active bioelectronic implants for minimally invasive brain-computer interfaces and chronic neuroscientific research. And based on the new insights, guidelines are proposed that may enhance the longevity of implantable chips, broadening their applications in the biomedical field.

Surprised scientists

"We were all surprised", shares PhD student Kambiz Nanbakhsh, who is the first author of this work. "I did not expect microchips to be so stable when soaked and electrically biased in hot salt water."

Vasso is also very excited by the results of the study. "Our findings demonstrate that bare-die silicon chips, when carefully designed, can operate reliably in the body for months. By addressing long-term reliability challenges, we are opening new doors for miniaturized neural implants and advancing the development of next-generation bioelectronic devices in clinical applications."

Vasso emphasizes the protective role of PDMS. "This work reveals the critical role of silicone encapsulation in shielding implantable integrated circuits from degradation. By extending the lifespan of neural implants, our study opens up pathways to more durable and effective technologies for brain-computer interfaces and medical therapies." Kambiz wholeheartedly agrees with Vasso: "This was a long investigation, but hopefully results will be useful for many."

The researchers are also thrilled to have their work published in the reputable journal Nature Communications.