Biocompatibility Analysis of Thin-Film Titanium and Gold Coatings on Parylene-Insulated Glass Wires for MRI-Compatible Implantable Leads.

Implantable stimulators, such as those connected to intracranial electrodes for deep brain stimulation (DBS), are not fully MRI-compatible due to the presence of extension leads containing metal microwires, which pose significant safety risks. To address this challenge, we developed and tested a Resistive Tapered Stripline (RTS) design for DBS lead microwires. This design features a sharp impedance transition between two segments of thin metal layers deposited on a non-conductive substrate wire. The interface between segments reflects undesired radiofrequency currents induced in the wire back toward the pulse generator, thereby significantly reducing heating at both ends while maintaining the necessary electrical conductivity. Thin films of titanium and gold were deposited onto the substrate wire using physical vapor deposition, with the design optimized for both electrical performance and biological safety through numerical simulationsTo ensure biocompatibility, the selected materials were evaluated in accordance with ISO 10993-6 guidelines in a rodent study. Brain tissues from rats implanted with RTS wires and a commercially available control lead were processed for microscopic assessment after a 35-day implantation period. Biomarkers and stains were used to evaluate microgliosis, astrocytosis, neurodegeneration, demyelination, and cellular components. No differences were observed between the test and control leads across endpoints, indicating the biocompatibility of RTS wires.Clinical Relevance- The RTS technology represents a transformative advancement in the design of implantable stimulators, enabling safe MRI while maintaining long-term functionality and meeting stringent biocompatibility standards. The versatile materials and manufacturing approach proposed extend beyond DBS applications, offering the potential to enhance the safety and performance of other chronically implantable devices, such as spinal cord stimulators and cardiac pacemakers.