Ultra-flexible, thin-film electrode arrays for chronic neural recording and stimulation of brain cavity wall

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https://lirias.kuleuven.be/handle/123456789/362998
Introduction: Brain injuries are a major source of difficult-to-treat deficits and human disability. Brain lesion cavities are seen in stroke, brain trauma, congenital brain disorders and after successful resection of brain tumors and abscesses. Brain computer interfaces offer an exciting new approach to address deficits resulting from brain lesions. The idea is to implant mechanically flexible implants that adopt the shape of the lesion cavity wall and that are covered with electrode contacts for recording neuronal signals and electrical stimulation. This should enable us to interact with the residual intact brain tissue and partially restore functionality by interacting with pathological circuits.
Aim: The aim of this research is to design and develop a highly-flexible, biocompatible electrode array that can be used for long-term recording of neuronal signals.
Methods: Using soft lithography, thin-film (7 micron), net-shaped 4 x 4 electrode arrays were produced. Platinum electrode contacts were separately embedded in 0.4 mm wide square islands that were connected by 0.2 mm long spring-like structures. This design guarantees flexibility and optimal adhesion to curved surfaces (cortical gyri and sulci) and lesion cavities. Platinum contacts were 92 micron in diameter and were placed at a pitch of 675 micron. These electrode arrays were implanted on the sensorimotor cortex of healthy rats for histological assessment of biocompatibility (n=3, ) and for recording evoked potentials (EP, n=4, repeated measurements up to 4 months after implantation). EP recording was performed with peripheral stimulation of fore- and hindlimbs, both ipsi- and contralateral to the electrode array implant.
Results: The electrode arrays adopted the surface of the sensorimotor cortex in rat and chronic implantation induced no overt discomfort. Tissue damage due to the implantation procedure was seen around 300 micron deep, but was comparable to sham implantation procedures. Preliminary data demonstrate that electrophysiological EP responses could be recorded over the 4 month follow-up period.
Conclusion: The design of this electrode array allowed implantation on curved surfaces and can be used for chronic electrophysiological measurements. One of the possible applications is interaction with the lesion cavity wall, in order to restore function.