PEEK (polyetheretherketone) is a semi-crystalline, high-performance thermoplastic specified for spinal cages, trauma plates, surgical instrument handles, dental abutments, and endoscopic components where repeated steam autoclaving or gamma sterilization is required. Three medical-grade families dominate 2026 procurement: unfilled (VICTREX PEEK 450G or equivalent), carbon-fiber-reinforced (CFR-PEEK, typically 30 wt% short carbon fiber), and glass-fiber-reinforced (GFR-PEEK, typically 30 wt% short glass fiber), each with distinct mechanical, radiolucent, and processing profiles [S7].
Titanium, stainless steel, and cobalt-chrome remain the materials of choice for load-bearing fracture-fixation hardware and joint replacements, because PEEK's modulus (roughly 3-4 GPa unfilled) is an order of magnitude below Ti-6Al-4V (about 110 GPa) and is not a drop-in substitute where structural stiffness drives the design [S7]. Selection should start from the sterilization regime, the regulatory classification under FDA Class I/II/III or EU MDR Class I/II/III, and the biocompatibility evidence file.
Regulatory baseline: ISO 10993, ASTM F2026, and FDA classification
ASTM F2026 is the standard specification for PEEK polymers for surgical implant applications, governing composition, biocompatibility testing per ISO 10993-1, and characterization of the finished-form material, and it is the document most implant OEMs cite on technical files [S2]. ISO 10993-1 sets the biocompatibility evaluation framework, while ISO 13485 governs the quality management system that any PEEK medical-device manufacturer must hold for FDA, Health Canada, and EU MDR market access [S2][S4].
FDA classifies most PEEK spinal interbody cages and trauma plates as Class II 510(k) devices, while permanent load-bearing implants and many long-duration contact devices fall under Class III and require Premarket Approval (PMA) under 21 CFR Part 814, with Investigational Device Exemption (IDE) studies run under 21 CFR Part 812 [S4]. Health Canada mirrors this with four device classes and a Medical Device License (MDL) for Class II-IV, plus MDSAP audit certification as a hard prerequisite for the Canadian market [S1].
Mechanical and thermal property windows for the three medical grades
Unfilled medical-grade PEEK offers a tensile strength around 100 MPa, a tensile modulus near 3.5 GPa, a glass transition near 143 deg C, a melting point around 343 deg C, and continuous use temperatures up to about 260 deg C, making it the default for instrument handles, sterilizable trays, and short-term implant trials [S7]. Carbon-fiber-reinforced PEEK raises the modulus to roughly 20-25 GPa and the tensile strength to 220-260 MPa, which is why CFR-PEEK is specified for spinal cages and load-bearing trauma plates where bone-implant modulus mismatch matters.
Glass-fiber-reinforced PEEK sits between the two: tensile strength around 180 MPa and modulus near 10-12 GPa, with better dimensional stability than unfilled, but it shows up less in implant cores because the GFR-PEEK fibers complicate radiolucency assessment on CT and MRI. All three grades are radiolucent on X-ray and CT (artefact-free imaging), a property the FDA and EU notified bodies repeatedly cite when approving PEEK over titanium for spinal-cage windows where post-op fusion monitoring matters [S7].
For reference data on related high-purity polymer use in energy equipment, polycarbonate spec windows for 2026 follow a similar ISO-grade and sterilization-compatibility logic, though the temperature ceiling is far lower than PEEK.
Sterilization compatibility: gamma, EtO, steam autoclave
PEEK tolerates all three mainstream sterilization routes, which is the single biggest reason it displaced polysulfone and early PPSU in reusable instrument handles. Gamma irradiation at the standard 25-40 kGy medical dose causes minor chain scission and a measurable drop in elongation at break, capped roughly at 10-15% after 50 kGy cumulative dose, while tensile strength and modulus are essentially preserved [S7].
Ethylene oxide (EtO) per ISO 11135 is the gentlest route for PEEK and is preferred for combination products with drug coatings or sensitive surface chemistries, since the thermal and radiation exposure is minimal [S2]. Steam autoclave at 134 deg C / 18 minutes per ISO 17665 is the most demanding test: unfilled PEEK survives 500+ cycles with no significant change in tensile properties, while CFR-PEEK and GFR-PEEK show some interfacial degradation at the fiber-matrix boundary after 200-300 cycles, a known limit worth tracking in the validation report.
Comparison table: unfilled vs CFR-PEEK vs GFR-PEEK vs titanium
The decision matrix below lines the four most common options for Class II/III medical-device cores against four criteria: tensile modulus, radiolucency on CT/MRI, steam-autoclave cycle life, and biocompatibility file maturity. Use it as a first-pass filter before locking the resin grade and the manufacturing route. [S2]
Unfilled PEEK: modulus about 3.5 GPa, fully radiolucent, 500+ autoclave cycles, ISO 10993-1 and ASTM F2026 data widely available. CFR-PEEK (30 wt% short carbon fiber): modulus about 20-25 GPa, near-radiolucent with minor beam-hardening artefact, 200-300 autoclave cycles before interfacial degradation, ISO 10993-1 and ASTM F2026 data available from major suppliers. GFR-PEEK (30 wt% short glass fiber): modulus about 10-12 GPa, partial radiopacity that complicates imaging, 200-300 autoclave cycles, ISO 10993-1 and ASTM F2026 data available. Ti-6Al-4V titanium: modulus about 110 GPa, fully radiopaque (significant CT/MRI artefact), effectively unlimited autoclave cycle life, decades of FDA Class III data and an unmatched mechanical file [S7].
For applications that need polymer-like imaging clarity with metal-like stiffness, a hybrid PEEK-titanium composite or a CFR-PEEK cage with titanium markers is common, not pure PEEK as a metal replacement. For context on adjacent spec-driven polymer selection, PEEK grade work for aerospace cabins in 2026 uses the same CFR / GFR / unfilled split but with FAR 25.853 flammability and outgassing limits instead of ISO 10993.
Manufacturing route: injection molding vs machining vs 3D printing
Injection molding of PEEK requires barrel temperatures of 360-400 deg C, mold temperatures of 170-250 deg C to reach the crystallinity window (typically 30-35%), and is the only viable route for high-volume disposables like single-use catheter components and laparoscopic jaw inserts. Machining of PEEK is preferred for short-run implant trials and patient-specific spinal cages made from extruded or compression-molded stock, since unfilled PEEK chips cleanly and CFR-PEEK tolerates CNC milling with diamond-coated tooling [S7].
3D printing of PEEK via fused filament fabrication (FFF) or selective laser sintering (SLS) is now permitted under ASTM F3335 for patient-specific anatomical models and is moving into FFF-printed spinal-cage trials, but printed PEEK shows about 70-80% of the tensile strength of compression-molded stock along the build direction, so the design must derate accordingly. For related process-route thinking in adjacent hospital infrastructure, steel strand selection for hospital structural frames follows a comparable lot-traceability logic to PEEK implant-grade resin.
Limitations, failure modes, and what PEEK is NOT for
PEEK is not a metal substitute in any application where a sudden load above roughly 100 MPa (unfilled) or 250 MPa (CFR-PEEK) drives a fracture-mode failure, and the published stress-strain curves show a much lower yield point than Ti-6Al-4V's roughly 880 MPa tensile strength. Creep under sustained load above 60 deg C is a second hard limit: PEEK creep modulus at 100 MPa and 100 deg C drops below 1 GPa over 1000 hours, so design teams derate by a factor of 3-5x for static-loaded implants that cross 60 deg C in service [S7].
Oxidative aging in hot air above 250 deg C is irreversible and shows up as a yellowing and a drop in ductility; PEEK in service should never see sustained exposure above its continuous-use temperature of about 260 deg C, even though the melt point is 343 deg C. UV sterilization is not a standard medical route for PEEK, since the polymer is UV-sensitive and the ISO 10993-1 file does not cover UV-induced surface changes.
What to track next: EU MDR data files and MDR shortfall
Two signals are worth watching over the next 1-2 quarters. First, the European Commission continues to push EU MDR 2017/745 implementation, and the 2026 study of data-driven medical devices flags that synthetic-data validation and adaptive-AI provisions are still gapped, which directly affects any PEEK device with embedded sensors or machine-learning-enabled imaging markers [S5]. Second, the refurbished medical-device market, sized at USD 20.89 billion in 2026 and growing at 9.87% CAGR to 2031, creates a parallel PEEK-instrument resale and resterilization validation workload that is not yet addressed in the current ISO 17665 autoclave cycle-life literature [S3].
For the relevant spec sheets and selection criteria, see peek, pressure transmitter, and flow meter.