Novel Coating Extends Lifespan of Neural Implants

By HospiMedica International staff writers
Posted on 09 Jan 2025

Image: Silicon-IC test structures prepared for long-term accelerated in vitro and in vivo aging (Photo courtesy of Nature Communications, DOI:10.1038/s41467-024-55298-4)

Neural implants play a vital role in studying the brain and developing treatments for conditions such as Parkinson's disease and clinical depression. These implants electrically stimulate, block, or record signals from neurons or neural networks within the brain. Neural implants include integrated circuits (ICs), commonly referred to as chips, which are built on silicon. To function properly within the human body, these implants need to be both small and flexible. For long-term use, especially in chronic treatment and research, the durability of these implants is essential. However, the body's internal environment is corrosive, raising concerns about the longevity of silicon ICs. Researchers have now addressed this issue by studying the degradation mechanisms of silicon ICs in the body and applying a soft coating of PDMS (polydimethylsiloxane) elastomers, which create body-fluid barriers to protect the implants over time. This innovation not only extends the life of implantable ICs but also significantly expands their potential applications in the biomedical field.

A research team from Delft University of Technology (Delft, The Netherlands) assessed the electrical and material performance of chips from two different manufacturers over one year using accelerated in vitro and in vivo studies. They used bare silicon IC structures, which were coated with soft PDMS elastomers to create protective barriers that shield the chips from body fluids. The chips in the study were partially coated with PDMS, resulting in two distinct regions: a "bare die" region and a "PDMS-coated" region. During the in vitro study, the chips were exposed to hot salt water and subjected to electrical biasing (direct current exposure). The chips were periodically monitored, and the results, published in Nature Communications, demonstrated stable electrical performance, indicating that the chips remained functional even when directly exposed to bodily fluids.

When the chips were analyzed for material degradation, it was found that the bare regions experienced significant degradation, while the PDMS-coated areas showed minimal degradation. This result demonstrates that PDMS is a highly effective encapsulant for implants intended for long-term use. These findings are expected to guide the design of advanced chip-scale active bioelectronic implants, which can be used in minimally invasive brain-computer interfaces and long-term neuroscientific research. Based on these new insights, the researchers propose guidelines that could enhance the longevity of implantable chips, further broadening their applications in the biomedical sector.

"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," said Dr. Vasiliki (Vasso) Giagka, who led 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.”