Tiêu đề Clinical translation of ultrasoft Fleuron™ probes for stable, high-density and bidirectional brain interfaces.pdf ✅

Clinical translation of ultrasoft Fleuron probes for stable, high-density and bidirectional brain interfaces Axoft et al. 2025 (preprint) 4 of stimulation (1 mV cathodic pulse followed by an anodic pulse, each lasting 4 ms, with a 4 ms interpulse delay) with minimal variations in electrochemical impedance and voltage transient (Fig. 1I, 1J), highlighting the technology’s potential for reliable and long-term micro-stimulation applications. Minimally Invasive Implantation Process The headstage and the probe can be implanted and secured in a manner comparable to existing minimally invasive neurosurgical procedures, such as implantation of deep brain stimulation (DBS) leads and stereo-electroencephalography (sEEG) electrodes, ensuring its compatibility with established clinical workflows. Figures 2A and 2B depict the minimally invasive procedure in a porcine brain. After neuronavigation calibration, a small burr hole is made at the implantation site. After durotomy, the Fleuron probe is inserted to the planned depth using a custom 125 μm tungsten stylet, via either a frameless or frame-based approach. Once positioned, the stylet is disengaged and carefully withdrawn. The headstage is then secured to the skull, and the incision is closed. As shown in Figure 2C, implantation into a brain phantom demonstrates precise depth targeting with minimal retraction. The third panel shows the probe fully inserted to a depth of 45 mm with the stylet still in place, showcasing the ability to reach subcortical structures for brain- wide access. In panel four, positional shift during stylet retraction is limited to approximately 2%, highlighting the probe’s mechanical stability during deployment. Magnetic Resonance Imaging (MRI)-Visibility Depth placement of Fleuron probes can be confirmed after removal of the stylet using MRI. Figure 2D shows T2-weighted MRI scans at 3 Tesla from a porcine cadaver model, revealing the implanted probe as a distinct 1H signal void. This visibility arises from Fleuron’s low protium density and its sufficiently large geometrical dimensions, offering a clear contrast against surrounding brain tissue, unlike conventional hydrocarbon- based microelectrode arrays, like polyimide probes, that typically lack MRI contrast due to their atomic composition and narrow dimensions. The visibility of Fleuron probes in post-operative MRI enables confirmation of device placement, which is critical when targeting deep cortical and subcortical structures involved in many neurological disorders (13). Minimized Glial Encapsulation and Tissue Damage Around Larger Probes State-of-the-art laminar arrays fabricated from conventional rigid materials such as polyimide or silicon often induce significant tissue scarring over time, contributing to signal degradation and instability of neural recordings (7, 14). To minimize gliosis, the dimensions of rigid polyimide probes are typically constrained to widths below 70 μm and thicknesses under 2–5 μm (10). However, these size limitations restrict the integration of high-density sensing and stimulation sites, reduce tissue coverage, increase capacitive leakage, and elevate the risk of mechanical failure, ultimately limiting the scalability and performance of neural interfaces. In our previous work, we demonstrated that Fleuron probes with cross-sectional dimensions of up to 250 × 10 μm2 induced significantly less gliosis than rigid epoxy-based counterparts (SU-8) following up to 12 weeks of implantation (12). In the present study, we further increase the cross-sectional dimensions of both the Fleuron probes and a polyimide control to 700 × 10 μm2 and assess chronic local tissue responses using immunofluorescence imaging in a rat model. We use a 125 μm diameter tungsten stylet, a clinically relevant size that enables deep brain implantation while minimizing the risk of deflection during insertion. Horizontal brain slices (Fig. 3A) revealed a Figure 3 Chronic local tissue response to Fleuron probes versus Polyimide probes. (A) Representative immunofluorescence images of horizontal brain tissue sections obtained at 3 months and 6 months following implantation of a Fleuron probe (left) and a polyimide probe (right) in the same rat brain. Staining includes DAPI (blue) for cell nuclei, GFAP (pink) for astrocytes indicating glial scarring, and Iba1 (red) for activated microglia representing neuroinflammatory responses. Probes’ cross- sections are colored in orange. Both probes have identical geometries: 10 μm in thickness and 700 μm in width. Each probe is implanted in one hemisphere of the rodent brain. (B) Quantitative analysis of normalized GFAP fluorescence intensity as a function of distance from the probe- tissue interface for Fleuron (blue) and polyimide (pink) implants (N=5, 7 and 8 subjects per time point). Lines show the mean value and shaded regions show the standard error of the mean (SEM). (C) Normalized average cavity size in rodents at the electrode-tissue interface for both types of probes.