FINE (Flat Interface Nerve Electrode)

One-line verdict: A non-penetrating cuff that deliberately reshapes a nerve into a flatter cross-section to improve fascicle access and functional selectivity, trading simplicity (and some compression risk margin) for better selectivity than round cuffs.

Quick tags: Stimulation (primary) · Recording (possible, limited) · Species: Human (research deployments) · First demonstrated: early 2000s

Overview

What it is: The Flat Interface Nerve Electrode (FINE) is an extraneural cuff electrode designed to reshape a nerve from a roughly round cross-section into a flatter/oblong geometry so that more fascicles lie closer to the cuff contacts. The goal is improved selective stimulation (and, in some configurations, improved access for recording) without penetrating the nerve.

Why it matters: FINE is one of the most important “selectivity boosts without penetration” ideas in peripheral nerve interfaces. It sits between conventional round/spiral cuffs (safest, least selective) and intraneural arrays (most selective, higher biological risk).

Most comparable devices: spiral/helical cuffs (lower selectivity), split-cylinder cuffs, C‑FINE (composite/structured variants of the flat-interface concept).

Spec Card Grid

Identity

• Device name: FINE (Flat Interface Nerve Electrode)
• Canonical ID: BTSD-PNI-0005
• Inventor / key authors: D. J. Tyler; D. M. Durand (foundational work)
• Org / manufacturer: academic/research builds (not a single commercial SKU)
• First demonstrated (year): 2002 (selective stimulation demonstration)
• First implanted (year): chronic research implants reported in later neuroprosthesis literature (study-specific)
• Species: human (research) and animal models (foundational/chronic response)
• Regulatory / trial status: research implants / feasibility studies (varies by program)
• Primary use: stimulation (primary); recording possible but not the dominant deployment
• Primary target: mixed peripheral nerves (application-dependent)

Geometry & Architecture

• Interface type: flat-interface cuff (extraneural)
• Penetrating?: no
• Form factor: cuff that reshapes the nerve to a flatter cross-section
• Array layout: multi-contact cuff (contact count varies by build and nerve)
• Footprint (mm): application-dependent; not a single universal dimension across studies
• Insertion method: surgical exposure; cuff placed around nerve; closure/fit depends on design variant
• Anchoring method: mechanical conformity + lead strain relief; fibrosis over time provides additional stabilization
• Packaging location: lead routed to IPG or to percutaneous/external connectors in research systems

Electrode & Channel Physics

• Channel count: variable (multi-contact)
• Active sites used (vs total): study-dependent
• Electrode material: varies by fabrication (metal contacts in polymer/silicone cuffs; variants exist)
• Recording modality: CAP/LFP possible; generally low SNR compared with stimulation utility
• Stimulation capability: yes (core function)
• Charge injection / safe stim range: not a single canonical number (depends on contact material/area and waveform)

Tissue Interface & Bioresponse

• Target tissue: peripheral nerve trunk (extraneural)
• Vascular disruption risk: low–moderate (surgical handling + compression risk if over-flattened or poorly fit)
• Micromotion sensitivity: low relative to intraneural interfaces; lead management still matters
• Encapsulation: fibrotic encapsulation expected (typical cuff behavior); can alter thresholds/selectivity over time
• Typical failure mode: threshold drift/reduced selectivity from encapsulation + mechanical/lead failures; for percutaneous systems, infection dominates risk

System Architecture

• Onboard electronics: none in cuff; stimulation/recording electronics in IPG or external controller
• Data path: lead to IPG or external stim/record platform
• Power: IPG battery or external supply (study-dependent)
• Surgical complexity: moderate peripheral nerve exposure; careful fit is crucial because the device purposefully reshapes tissue

Performance Envelope

• Core performance claim: improved functional selectivity vs round cuffs due to nerve reshaping and closer fascicle–contact proximity
• Stability over time: demonstrated in chronic research contexts (program-dependent)
• Notable demos / tasks: selective stimulation demonstrations; nerve-cuff selectivity work relevant to standing/gait and upper-limb neuroprostheses

Clinical / Preclinical Evidence

• Evidence base: foundational selectivity paper + chronic tissue response work + later fabrication/high-density cuff methods papers
• Key limitation: “FINE” is a design concept, not a single manufactured device — contact counts, materials, and packaging differ across implementations; performance should be tied to a specific build/study

Engineering Verdict

Strengths:

• non-penetrating interface with a real selectivity advantage over round cuffs
• compatible with both therapy-style packaging (IPG) and research externalization

Limitations / failure modes:

• requires controlled reshaping: too much flattening can increase chronic compression risk; too little reduces selectivity benefit
• heterogeneous implementations make a single spec sheet misleading

Scaling constraints:

• more contacts can improve selectivity but increases lead/packaging burden

What newer designs try to fix:

• composite/segmented-stiffness approaches (e.g., C‑FINE) aiming for reshaping with better compliance and packaging practicality

References

• Tyler DJ, Durand DM. Functionally selective peripheral nerve stimulation with a flat interface nerve electrode. IEEE Trans Neural Syst Rehabil Eng. 2002;10(4):294–303. doi: 10.1109/TNSRE.2002.806840. PubMed: https://pubmed.ncbi.nlm.nih.gov/12611367/
• Tyler DJ, Durand DM. Chronic response of the rat sciatic nerve to the flat interface nerve electrode. Ann Biomed Eng. 2003;31(6):633–642. doi: 10.1114/1.1569263. PubMed: https://pubmed.ncbi.nlm.nih.gov/12797612/
• Dweiri YM, Stone MA, Tyler DJ, McCallum GA, Durand DM. Fabrication of High Contact-Density, Flat-Interface Nerve Electrodes for Recording and Stimulation Applications. J Vis Exp. 2016;(116):54388. doi: 10.3791/54388. PubMed: https://pubmed.ncbi.nlm.nih.gov/27768048/