The Safety of Micro-Implants for the Brain

Area of Science:

• Neuroscience
• Biomedical Engineering
• Materials Science

Background:

• Advancements in electronics and micromachining enable discrete wireless brain micro-implants.
• These leadless devices offer potential for brain stimulation/sensing without external leads, reducing infection and breakage risks.
• However, risks like implant migration and tissue reaction necessitate careful evaluation.

Purpose of the Study:

• To assess the post-implantation tissue reaction and migration of borosilicate glass-encapsulated micro-implants in the sheep brain cortex.
• To evaluate the biocompatibility and long-term stability of these novel neural implants.

Main Methods:

• Twenty borosilicate glass-encapsulated micro-implants were implanted in the cortex of 10 sheep for 6 months.
• Radiographs tracked implant position, and histological analysis (GFAP, IBA-1) assessed tissue reaction.
• Implant migration was referenced against skull-mounted screws.

Main Results:

• No significant difference in GFAP intensity and only a minor difference in IBA-1 were observed compared to controls.
• No glial scar formation was detected at the implant track site.
• Initial migration (up to 4.6 mm) occurred within the first 3 months, with no further movement observed in the subsequent 3 months. Histology showed no migration track or tissue damage.

Conclusions:

• Borosilicate glass-encapsulated micro-implants demonstrate minimal adverse tissue reactions in the brain.
• The observed initial migration did not lead to long-term displacement or tissue damage, suggesting a low risk profile.
• These findings support the potential clinical use of discrete, leadless brain implants.