Custom Medical Electrode Design Guide: From Geometry to Validation

JASPER certifications: ISO 9001, ISO 13485, IATF 16949, and ISO 14001.

1. Start with the electrode's job, not its outline

The first decision is the physical job at the body interface. A recording electrode receives a low-level biopotential. A stimulation electrode delivers a controlled waveform. A bioimpedance electrode may source current, sense voltage, or do both through separate terminals. An electrochemical sensor uses working, reference, and counter-electrode functions. Those roles change geometry, conductor choice, interface chemistry, host electronics, and the tests that matter.

FDA's 2020 criteria for cutaneous electrodes for recording purposes have a deliberately narrow scope: single-use recording electrodes on normal, healthy, intact skin. They should not be stretched into a universal design rule for stimulation, invasive contact, damaged skin, or electrochemical sensing. IEC 60601-2-25, IEC 60601-2-27, and IEC 60601-2-47 likewise address diagnostic, monitoring, and ambulatory ECG equipment respectively; they are not standalone approvals for every electrode connected to that equipment.

A team reviewing printed medical electrode component options should therefore open the specification with intended use, patient-contact category and duration, reuse status, host device, user environment, and regulatory role. These inputs decide whether a screen-printed flexible construction is even a sensible candidate.

2. Incomplete inputs produce coupled failures

Electrode failures rarely stay within one layer. A larger conductive print may change the dielectric aperture. The new aperture may increase gel contact area. That may alter adhesive land width, edge lift, pouch dimensions, and the biological-evaluation matrix. ISO 14971:2019 frames risk management across the medical-device life cycle; for an electrode project, this is why geometry, material, process, and package changes need a documented impact review rather than an artwork-only approval.

The cost of a poor input set is not just another drawing revision. It can invalidate material screening, fixtures, sample comparisons, aging work, and the risk-control evidence tied to a prior configuration. A sound development record keeps four baselines synchronized: geometry, bill of materials, process route, and verification method.

3. Ten inputs in a custom medical electrode design guide

The ten inputs below form a linked system. Resolve them in order, but review the whole set after any material or geometry change. Each subsection gives a useful project signal and a disqualifying shortcut.

3.1 Intended use, contact, and regulatory role

Write the functional statement before drawing the electrode. It should name whether the part records, stimulates, measures impedance, or supports an electrochemical reaction; where it contacts the body; whether contact is intact skin, compromised surface, or another tissue; the duration and reuse model; the host device; and the legal manufacturer. FDA's ISO 10993-1 guidance makes biological evaluation dependent on contact, duration, materials, manufacturing, and use—not on a supplier's generic “medical” label.

The regulatory role also affects quality-system obligations. FDA's Quality Management System Regulation became effective on February 2, 2026 and incorporates ISO 13485:2016 by reference. Its applicability turns on the actual regulatory role, including whether an article is only a component or is itself a finished device or accessory. The commercial purchase description does not decide that question.

Good signal: A one-page intended-use input names modality, anatomical site, contact category and duration, reuse, host electronics, user environment, legal manufacturer, and target markets.

Red flag: The brief says only “medical electrode,” “wearable patch,” or “FDA material.”

3.2 Custom electrode geometry and anatomical placement

Custom electrode geometry is more than the external die line. A drawing may need separate contours for the backing, adhesive, hydrogel, printed electrode, dielectric opening, liner, pull tab, and terminal. The coordinate system should reference an anatomical or device-placement datum, not a floating graphic center. Multi-electrode arrays also need channel IDs, center coordinates, orientation marks, spacing tolerances, and left/right or size-variant rules.

Curves and edge radii are functional. Acute corners can concentrate mechanical strain or make converting less stable. A narrow adhesive land around a larger gel aperture can invite squeeze-out or edge lift. A stimulation electrode may need field-distribution analysis that a recording electrode does not. Those decisions belong to the finished-device design owner; the converter should confirm whether the geometry can be printed, registered, laminated, and cut within the agreed tolerances.

Good signal: A dimensioned drawing separates every functional footprint and establishes datums, tolerances, channel identity, orientation, placement, and keep-out zones.

Red flag: The supplier receives a PDF outline with no layer-specific geometry or anatomical placement reference.

3.3 Active area, aperture, and edge conditions

The electrically active area is the interface exposed through the dielectric and coupled through gel, adhesive, fluid, or another medium. It is not automatically equal to the printed conductor area or external patch size. Define the overlap between conductor, dielectric aperture, and conductive interface so registration variation cannot expose an unintended edge or reduce the minimum contact area.

The active-area calculation must match the modality. Recording teams may focus on coupling stability and motion artifact. Stimulation teams may need to evaluate current distribution, local temperature, edge effects, and waveform limits. Electrochemical sensors may control working-electrode area and area ratios to reference/counter functions. No universal area rule spans those cases.

Good signal: The drawing labels nominal and minimum active area, conductor overlap, aperture tolerance, edge radius, gel boundary, and the analysis or test that confirms the configuration.

Red flag: “Electrode diameter” appears once without saying whether it means print, dielectric window, gel, or finished patch.

3.4 Printed electrode circuit design

Printed electrode circuit design should be released as electrical artwork, not decorative line work. Identify every net, exposed contact, trace, crossover, insulating region, terminal pad, and fiducial. State trace width and spacing rules, the allowed route around apertures, print registration, and where a dielectric covers the conductor. The terminal transition needs its own strain zone because a stiff snap, crimp, wire, or connector can move bending into the printed trace.

Test criteria must name a method. “Check resistance” is incomplete without the test points, fixture, meter mode or stimulus, conditioning, sample state, and acceptance limit. The same applies to impedance: frequency, amplitude, electrode pair, gel/contact condition, pressure, temperature, and elapsed time can change the result.

Good signal: Native vector artwork and a controlled net table show test points, conductors, dielectric openings, registration marks, terminal pads, bend keep-outs, and a defined electrical acceptance method.

Red flag: A raster image is the master, traces change width to fit the artwork, or a single ohmic limit is applied to every electrode modality.

3.5 Substrate and backing mechanics

Select the substrate after defining strain and converting—not simply because PET is common in printed electronics. The material callout should include polymer or textile type, grade, thickness, surface treatment where relevant, dimensional behavior through cure, flex or stretch requirement, operating/storage conditions, and compatibility with adhesive, hydrogel, ink, die cutting, and packaging.

PET can be a practical platform for dimensionally controlled flexible circuits, but a conventional PET circuit may be the wrong architecture for high stretch, repeated washing, sharp folding, or long-term conformity over a moving joint. TPU, textile, elastomeric films, or hybrid islands-and-interconnect structures may handle some of those cases better, though each brings its own print, bond, registration, and validation burden.

Good signal: The material specification connects the exact substrate and thickness to strain, bend, cure, lamination, cutting, storage, and body-conformability requirements.

Red flag: “Flexible film” is specified with no grade, thickness, strain map, cure ceiling, or qualification evidence.

3.6 Conductor and electrode-interface system

Silver, Ag/AgCl, carbon, and specialty materials serve different functions. Silver may form a low-resistance trace. Ag/AgCl can provide an electrochemical interface in specific recording, stimulation, or reference-electrode constructions. Carbon is common in electrochemical working electrodes and may be selected for other project-specific interface reasons. None is a drop-in substitute for another without reviewing chemistry, polarization behavior, conductivity, print thickness, substrate adhesion, flex, cure, gel compatibility, and aging.

DuPont's Micromax 5881 sheet, for example, describes a solvent-based Ag/AgCl composition for screen printing on polyester film and lists ECG/EKG, EMG, EEG, TENS/EMS, glucose-monitoring, and electrochemical reference/counter applications. That is a supplier-specific material example, not proof that the ink suits a given device or that JASPER uses it. The selected grade, process window, and qualification evidence must appear in the controlled bill of materials.

Good signal: The material grade and print/cure process are tied to substrate, interface medium, waveform or measurement method, trace role, aging plan, and change-control requirements.

Red flag: The bill of materials says only “silver ink” or “Ag/AgCl” with no grade, ratio/formulation identifier, process window, or approved substitute rule.

3.7 Skin adhesive, hydrogel, and release liner

Separate mechanical attachment from electrical coupling. Some designs use a conductive hydrogel over the active area plus a nonconductive perimeter adhesive. Others rely on different conductive-interface and fixation architectures. Specify each material by grade, thickness, coated area, aperture, liner, application side, intended contact duration, wear environment, removal condition, storage, and package interaction.

FDA's 2023 biocompatibility guidance does not make a typical adhesive electrode automatically eligible for the Attachment G approach for certain intact-skin-contacting devices merely because it contacts intact skin. Hydrogels and adhesives used to attach electrode pads directly to skin require product-specific biological evaluation or a justified alternative within the finished-device risk assessment. “Medical-grade” does not settle irritation, sensitization, cytotoxicity, residue, removal, or wear performance.

One material sheet illustrates why values need context. Axelgaard's AG625 datasheet publishes a nominal 0.6 mm thickness, maximum volume resistivity of 600 Ω·cm, and minimum skin-side peel of 240 g/in. These figures are a initial supplier benchmark only. They are not a universal target, a JASPER result, or evidence for a finished device. Replace or remove them after the actual hydrogel and test methods are selected.

Good signal: Exact interface and fixation grades are linked to a risk-based biological evaluation, defined wear/removal tests, aging conditions, liner, and moisture-barrier package.

Red flag: “Conductive gel plus medical adhesive” is the complete material specification.

3.8 Lead, snap, tail, and connector integration

A connector callout needs the mating half and mechanical load case. For a lead wire, define conductor, insulation, length datum, termination, polarity or channel ID, pull direction, flexing, strain relief, and any overmold or bond. For a snap, identify the mating geometry, orientation, material stack, attachment method, and force path. For a printed tail, control contact pitch, exposed pad length, stiffener, insertion direction, bend zone, and mating connector.

The shortest electrical route is not always the safest mechanical route. A lead exit near the active area can transfer tugging into the skin interface. A rigid terminal at an unsupported edge can focus strain where printed ink meets a plated or crimped feature. Fixture-based pull, bend, and handling tests should reproduce the assembled device and expected user load direction.

Good signal: Interface control drawings identify both mating parts, pinout, tolerances, material transitions, support, strain relief, bend keep-outs, pull direction, and test fixture.

Red flag: “Add snap” or a connector series name appears without the mating drawing, assembly process, or mechanical-load requirement.

3.9 Converting, registration, and packaging

The converting drawing should state lamination order, layer datums, registration tolerances, kiss-cut versus through-cut features, liner splits, pull tabs, waste-removal rules, inspection zones, and whether parts ship as pieces, sheets, reels, or subassemblies. Tolerance must be allocated across print, lamination, and cutting rather than assigned as if all features are created in one operation.

Package design belongs in development because hydrogel, adhesive, liner release, printed chemistry, and cleanliness can change with moisture and time. Define pouch or tray materials, seal geometry, barrier requirement, packing orientation, labels, lot identification, storage, distribution conditioning, and shelf-life protocol. If sterilization is required, name the method early and verify that every material, bond, print, package, and performance requirement survives the validated process. This guide makes no claim that a JASPER electrode construction is sterile or sterilization-compatible.

Good signal: The prototype plan includes production-intent converted parts and package materials, with registration and package acceptance criteria linked to aging and distribution work.

Red flag: Loose hand-cut samples are approved, while liner design, pouch barrier, seal, cleanliness, and shelf life remain “to be decided.”

3.10 Verification, validation, and controlled transfer

Agree on critical-to-quality characteristics before the pilot build. The component maker may inspect dimensions, registration, printed continuity, resistance by a defined method, dielectric coverage, laminate adhesion, terminal workmanship, and package seal features if those activities are in the quote. The legal manufacturer must decide which component records feed the finished-device design history and which tests remain at device level.

A functional stack—not a universal recipe

The following diagram is a design-review map. Layer order and presence vary by use category.

BODY / SAMPLE INTERFACE
        │
        ├─ Conductive interface: hydrogel, dry interface, or fluid/reagent system
        ├─ Skin-fixation adhesive or perimeter fixation (when used)
        ├─ Dielectric aperture defining exposed active area
        ├─ Printed electrode + conductive trace system
        ├─ Printed dielectric / encapsulation over non-active conductors
        ├─ Flexible substrate or structural backing
        ├─ Terminal transition: snap, lead, crimp, printed tail, or connector
        ├─ Release liner / handling feature (skin-applied designs)
        └─ Package + label + moisture / cleanliness controls
DEVICE / INSTRUMENT INTERFACE

4. Medical electrode development: six controlled steps

Medical electrode development works best as a sequence of evidence decisions. Each step closes inputs needed by the next; none converts a component supplier into the legal manufacturer by default.

Step 1 — Write the intended-use and responsibility brief

Document the modality, users, anatomical site, contact category and duration, host instrument, use environment, reuse model, target jurisdictions, and legal manufacturer. Add a responsibility map for component design, finished-device design, risk management, biological evaluation, software/algorithm work, packaging, shelf life, sterilization, and regulatory submission. This prevents a phrase such as “complete electrode” from hiding ten different deliverables.

Step 2 — Release architecture and risk-linked drawings

Create layer-specific geometry and electrical artwork. Mark active apertures, conductor overlaps, traces, dielectric, adhesive and gel footprints, liners, terminals, datums, tolerances, and inspection points. Link risk controls to measurable characteristics: a minimum overlap, a protected bend zone, a controlled edge radius, or an approved material grade. The drawing should distinguish a design target from a supplier process allowance.

Step 3 — Screen material and interface combinations

Use documented candidate grades, not generic material families. Evaluate print/cure compatibility, dimensional change, conductor adhesion, flex or strain, interface chemistry, adhesive/gel behavior, liner release, and planned package. Supplier data can narrow candidates, but production-intent coupons and assembled prototypes must use the actual process route. JASPER's prototyping capabilities can be discussed for the quoted build scope; the project team should confirm materials, fixtures, and tests rather than infer them from the link.

Step 4 — Build engineering samples with controlled differences

A useful prototype round changes one planned variable at a time or uses a documented design of experiments. Identify each sample by artwork revision, bill-of-material revision, process route, date or lot, and package state. Hand-built concept samples can answer early fit questions, but approval samples should represent production-intent printing, lamination, conversion, terminal attachment, liner, and package closely enough to expose process interactions.

Step 5 — Run component verification and finished-device validation

Compare samples using pre-agreed methods. Component verification may include dimensional registration, conductor inspection, continuity/resistance, dielectric coverage, terminal workmanship, laminate adhesion, and package features. Finished-device work may include signal quality or delivered-energy performance, motion and wear conditions, skin-contact biological evaluation, usability, cleaning or reuse, transport, package integrity, aging, shelf life, and sterilization where applicable. Record conditioning, fixtures, sample size, failures, and disposition; “passed bench test” is not a reproducible result.

Step 6 — Freeze transfer records and change controls

Release controlled artwork, bill of materials, process flow, inspection plan, test methods, fixtures, sampling, golden or limit samples where appropriate, packaging specification, and approved deviations. Agree which changes require notification and re-evaluation: ink grade, gel or adhesive, substrate, print geometry, cure, terminal, cutting tool, package, and manufacturing site are common candidates. The quality testing discussion should be tied to the exact quoted scope and the customer's finished-device plan.

5. When a printed PET-and-hydrogel construction is not the best choice

A screen-printed conductor on PET with a hydrogel interface can suit many flexible disposable electrodes, but it is not a universal recommendation. Choose a different architecture when the use condition conflicts with the material system or when the evidence burden exceeds what the proposed stack can support.

“Not the best choice” does not mean the alternative is automatically valid. It means the design team should reopen architecture selection and generate new verification evidence rather than forcing a familiar process into the wrong load, interface, or regulatory context.

6. Drawing and project-scope checklist

Send one controlled package, not separate email assumptions. The following checklist supports a drawing review and an RFQ without turning the article into a purchase page.

For recording applications, a related ECG electrode patch circuit page can help organize application-specific questions. It does not replace the intended-use and host-system requirements for the actual project.

7. Sample approval and finished-device validation are different gates

A component sample can conform to its drawing and still be unsuitable in the finished device. Keep the gates separate, but connect them through configuration control. FDA's ECG-electrode guidance and ISO 10993-1:2025 both reinforce the need to evaluate the intended final configuration rather than infer device performance from a material name.

ASTM D3330/D3330M-04(2025) can define 180° or 90° peel tests for pressure-sensitive tape or a specified laminate coupon. ASTM also cautions that such quality-assurance results do not necessarily predict functional performance. A D3330 value therefore cannot, by itself, establish skin-wear duration, safe removal, irritation risk, or clinical suitability.

Before approval, verify the sample against the actual housing or host device, intended cable routing, application method, body location or representative fixture, package, and conditioned state. Record failures as evidence. A failed edge, intermittent trace, painful removal observation, or package-open change should trigger root-cause work—not an undocumented sample tweak.

8. Frequently asked questions

What information is required for a custom medical electrode drawing?

A useful drawing defines intended use, finished outline, active electrode and dielectric-window geometry, gel/contact and adhesive footprints, printed nets and traces, materials, terminal, layer order, datums, tolerances, converting features, package, and acceptance methods. The project scope should also identify the legal manufacturer and assign finished-device validation responsibilities.

How is custom electrode geometry different from the patch outline?

Custom electrode geometry includes the electrically active print, exposed aperture, conductive interface, spacing, orientation, and edge conditions. The patch outline is only the external converted shape. Adhesive, hydrogel, dielectric, conductor, liner, and backing may all use different contours and tolerances.

Which ink should a printed medical electrode use?

There is no universal ink. Silver, Ag/AgCl, carbon, and specialty systems serve different trace and interface functions. Selection must account for modality, substrate, cure, print process, gel or sample chemistry, flex/strain, electrical method, aging, and supplier qualification. Name an exact approved grade in the bill of materials.

Is Ag/AgCl always better than carbon for medical electrodes?

No. Ag/AgCl is common in certain biopotential, stimulation, and reference-electrode interfaces; carbon is common in many electrochemical working electrodes and other project-specific designs. ‘Better’ depends on interface chemistry, measurement or waveform, geometry, substrate, process, and validation evidence.

Can hydrogel values from a supplier datasheet become the device specification?

Only after the selected material, test method, and finished construction are justified. A supplier sheet can screen candidates, but its peel, resistivity, thickness, or biological-test statements are product-specific. They do not become JASPER results or finished-device performance claims by citation.

What belongs in a printed electrode circuit design file?

The controlled file should include native vector conductor and dielectric layers, net names, exposed areas, trace widths and spacing, crossovers, terminal pads, fiducials, registration tolerances, bend keep-outs, test points, and revision data. Any resistance or impedance limit also needs a fixture, stimulus, conditioning, and sample-state definition.

Which tests can a component manufacturer perform?

That depends on the quote and verified capability. Common project requirements may include dimensions, registration, visual inspection, continuity, resistance by an agreed method, dielectric coverage, laminate adhesion, terminal workmanship, and package features. The legal manufacturer still owns the finished-device validation and regulatory rationale unless a contract assigns a documented task differently.

Does a printed medical electrode component need ISO 10993 testing?

The finished-device biological evaluation should follow contact type, duration, materials, manufacturing, and intended use under the applicable regulatory framework. FDA's 2023 guidance and ISO 10993-1:2025 do not support a blanket answer based on one component name. Adhesive and hydrogel electrode constructions require project-specific assessment; supplier data may contribute but does not replace that assessment.

9. Send the electrode drawing and project scope

A useful review package contains the intended-use brief, layer-specific geometry, printed circuit, material candidates, connection drawing, converting plan, package concept, and responsibility/test matrix. Send that package with the expected prototype and production context through JASPER's electrode pads route. Ask the team to state exactly which printed, converted, assembled, test, and packaging operations are included before relying on them.

Technical References

• Source: FDA Use of ISO 10993-1 Biological Evaluation Guidance. Accessed 2026.
• Source: ISO 10993-1:2025 Biological Evaluation of Medical Devices. Accessed 2026.
• Source: ISO 14971:2019 Medical Device Risk Management. Accessed 2026.
• Source: FDA Design Control Guidance for Medical Device Manufacturers. Accessed 2026.
• Source: cutaneous electrodes for recording purposes. Accessed 2026.
• Source: ISO 10993-1 guidance. Accessed 2026.
• Source: Quality Management System Regulation. Accessed 2026.
• Source: Cutaneous Electrodes for Recording Purposes. Accessed 2026.
• Source: Use of International Standard ISO 10993-1. Accessed 2026.
• Source: Electrocardiograph Electrodes: Class II Special Controls Guidance. Accessed 2026.
• Source: ISO 10993-1:2025. Accessed 2026.
• Source: ISO 14971:2019. Accessed 2026.
• Source: ASTM D3330/D3330M-04(2025). Accessed 2026.
• Source: IEC 60601-2-25:2011. Accessed 2026.
• Source: IEC 60601-2-27:2011. Accessed 2026.
• Source: IEC 60601-2-47:2012. Accessed 2026.
• Source: AG625 technical data sheet. Accessed 2026.