Medical implants (implantable medical devices)

01

Plan the biocompatibility evaluation of the finished device

FDA's guidance on ISO 10993-1 states that the agency clears or approves a device in its final finished form, not the individual materials, so the risk assessment should cover the materials, their processing, the manufacturing methods including sterilisation, and residues from manufacturing aids, together with the anatomical location, duration of exposure and patient population. Contact is grouped as limited (up to 24 hours), prolonged (over 24 hours to 30 days) and long term (over 30 days). The endpoints considered include cytotoxicity, sensitisation, irritation, acute systemic toxicity, material-mediated pyrogenicity, subacute and subchronic toxicity, genotoxicity, implantation, haemocompatibility, chronic toxicity, carcinogenicity, reproductive and developmental toxicity and, for materials intended to degrade, degradation. [1]

The guidance notes that CDRH and CBER request genotoxicity information for devices with prolonged or long-term contact with blood, bone, mucosa or other tissue, and for materials not previously used in legally marketed devices. It gives examples of manufacturing changes that can alter biocompatibility: a different surface passivation method that removes less pyrogenic material, risking fever after implantation, and a new resin supplier that leaves processing solvents such as formaldehyde in the device. [1]

Under 21 CFR 860.3, a device counts as an implant only if it is intended to remain implanted continuously for 30 days or more, unless FDA determines otherwise; Class III covers devices needing premarket approval, including life-supporting or life-sustaining devices and those presenting a potential unreasonable risk of illness or injury where general and special controls are not enough. [3]

Give the supplier the device type, anatomical location, contact duration and patient population, the target market and regulatory class, the material and grade, and every process step (machining fluids, surface treatment, cleaning, passivation, coating, sterilisation, packaging); ask how each change will be assessed for biocompatibility.

02

Plan MR safety testing and labelling

FDA's guidance on safety in the magnetic resonance environment recommends labelling each device with one of three terms: MR Safe, MR Unsafe or MR Conditional. It names ASTM F2052 for magnetically induced displacement force, ASTM F2213 for magnetically induced torque, ASTM F2182 for radiofrequency-induced heating near passive implants, ASTM F2119 for image artefacts, ASTM F2503 for marking, and ISO/TS 10974 for active implantable medical devices. Safety and conditions of use should be assessed, or a scientific rationale given, for each field strength (for example 0.25, 1.2, 1.5, 3.0 and 7.0 T) and RF coil type. [2]

The guidance distinguishes passive implants, which serve their function without electrical power, from active implantable medical devices that rely on a power source. A passive implant smaller than 2 cm in every direction and at least 3 cm from another passive implant does not need RF heating testing at 3.0 T or less, as it is expected to warm by less than 2 °C in Normal Operating Mode over 1 hour; the exclusion has stated exceptions. [2]

Ask for the MR labelling term and conditions (field strength, spatial field gradient, SAR or B1+rms limits, scan time), the test reports for displacement, torque, heating and artefact, and, for active implants, the ISO/TS 10974 assessment.

03

Name the implant-grade material specification in the order

FDA's guidance asks for the material and its processing to be assessed in the finished device, so the purchase order needs to name the material grade exactly. ASTM publishes material specifications for metallic implants (F136 is under Committee F04), and each one below fixes chemical, mechanical and metallurgical requirements for a named alloy and product form. [1] [4]

ASTM F136 covers wrought annealed titanium-6aluminum-4vanadium ELI (extra low interstitial) alloy, UNS R56401, for the manufacture of surgical implants, in strip, sheet, plate, bar, forging bar and wire; the heat analysis must meet the specified composition, and tension and bend tests must be performed. F136 states its values in inch-pound units, with SI values for information only. [4]

ASTM F67-24 covers four grades of unalloyed titanium (UNS R50250, R50400, R50550 and R50700) in strip, sheet, plate, bar, billet, forging and wire, and states that any agreement between purchaser and supplier must meet its minimum requirements. ASTM F138-19 covers wrought 18 chromium–14 nickel–2.5 molybdenum stainless steel bar and wire, UNS S31673. ASTM F1537-20 covers three wrought cobalt–28 chromium–6 molybdenum alloys, UNS R31537, R31538 and R31539, in bar, rod and wire. [5] [6] [7]

Editorial note: these specifications cover the raw material only. A device made from a compliant bar still needs the finished-device biocompatibility evaluation and, for metallic implants, the MR displacement, torque and heating assessment described above; ask the supplier for the mill certificate against the named specification and edition, and for the process records that link each heat to finished parts. [1] [2]

04

Recognise the implant categories that change the evidence

Categories that change the evaluation in the reviewed FDA documents.

05

Trace what the evaluation must cover

Elements named in the FDA biocompatibility guidance.

06

Fill the specification fields with values for your implant

The table explains each field, gives values where a reviewed source states them, and says what to obtain from the supplier. Limits for a given implant come from its device standards and design file.

07

Send the device, use and evidence needs together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Device: [type; drawings; material and grade]
Use: [anatomical location; contact duration; population]
Market: [country; regulatory class]
Process: [machining; surface; cleaning; sterilisation; packaging]
Evidence: [ISO 10993-1 evaluation; MR testing; mechanical tests]
Change control: [notification; re-evaluation]
Supply: [quantity; lot traceability; documentation]

See manufacturer records Send an enquiry through CNFX