Polycarbonate (PC) is an amorphous thermoplastic produced by interfacial polymerisation of bisphenol A and phosgene or by melt transesterification with diphenyl carbonate. Medical-grade PC resins are typically characterised by a melt volume-flow rate of 6–12 cm³/10 min at 300 °C under a 1.2 kg load per ISO 1133-1:2022, a glass transition temperature near 147 °C, and a Vicat B50 softening temperature near 145–150 °C. Unplasticised PC commonly exhibits a tensile stress at yield of 60–68 MPa at 23 °C and 50 % RH when tested according to ASTM D638-14. Because the repeat unit contains a carbonate linkage, PC is classified as a condensation polymer with sensitivity to hydrolytic chain scission in aqueous environments above 100 °C. A review of a medical PC part does not focus on these properties in isolation; it is structured around chemical identity, biological risk, sterilisation compatibility, mechanical ageing, and supply-chain control under ISO 10993-1:2018 and EU MDR 2017/745.

What a Notified Body Asks About a Medical Polycarbonate Part

The initial technical queries concern intended clinical use and contact duration categories defined in ISO 10993-1:2018, Clause 5.3. For a surface-contacting PC housing used for less than 24 h, the Notified Body may accept a reduced endpoint matrix. For a long-term implantable PC component contacting mucosal tissue or circulating blood beyond 30 days, the request expands to chemical characterisation, toxicological risk assessment, systemic toxicity, genotoxicity, and implantation data. The Notified Body commonly requires a justification file linking resin grade, colourants, mould-release agents, heat stabilisers, and regrind level to the tested final device. A material certificate alone is insufficient; the review seeks traceability from granulate to moulded part and an assessment of whether heat history, shear, sterilisation, and ageing alter molecular weight distribution relative to the virgin resin.

Because PC is a bisphenol A-based polycarbonate, the toxicological profile of the final device is driven by the unreacted monomer, cyclic oligomers, and additive package. The dossier must identify all additives above 0.1 % w/w because EU MDR 2017/745, Annex I, Chapter II, clause 10.4.1 requires disclosure of substances present in the device or in contact with the patient. Polycarbonate medical parts frequently contain heat stabilisers such as tris(2,4-di-tert-butylphenyl) phosphite, mould-release agents such as pentaerythritol tetrastearate, and blue or violet toners to offset initial yellowness. Each additive has a migration potential that the Notified Body expects to be considered in an extractables study. Where a processing aid has a number-average molecular weight below 1,000 g/mol, the reviewer may request a quantitative structure-activity relationship assessment or an in silico toxicology screen because low-molecular-mass species are more likely to migrate. The Notified Body also requests the regrind policy; regrind levels above 20 % are generally expected to be challenged with mechanical and biological data unless a validated closed-loop recycling process is documented.

Why gamma-induced chain scission shifts the molecular weight distribution and yellowness index

PC is not intrinsically gamma-stable. At sterilisation doses of 25 kGy and 50 kGy, ionising radiation produces phenoxy and phenyl radicals that participate in three competing pathways: chain scission at carbonate linkages, chain branching by radical recombination, and oxidative formation of quinoid chromophores. The practical consequence at 25 kGy is a measurable increase in yellowness index from approximately 0.8 to 7–12 for unstabilised grades and a reduction in molecular weight of 5–15 % as measured by gel permeation chromatography. If the part is exposed to a second dose because of terminal sterilisation plus packaging rework, the shift in number-average molecular weight may reduce notched Izod impact resistance below the design threshold of 10 kJ/m² at 23 °C per ASTM D256-10. Medical PC manufacturers therefore specify radiation-stable grades with additives that promote radical recombination. The Notified Body will ask for the dose map, the minimum and maximum dose across the pallet, and the test report after worst-case maximum dose. Where dose exceeds 40 kGy, the review may request additional chemical characterisation for radiolysis products.

Steam sterilisation of PC is limited by hydrolysis of the carbonate linkage. At 121 °C, the equilibrium water absorption of PC at room-temperature saturation is approximately 0.35 %; at 134 °C with pressurised steam, hydrolytic chain scission is sufficiently rapid that unstabilised PC parts may show a drop in tensile elongation from 110 % to 35 % after 10–20 autoclave cycles. The Notified Body asks for the total number of sterilisation cycles in the device lifecycle, including reprocessing if the device is reusable. Because PC is sensitive to alkaline detergents used in hospital washer-disinfectors, the review also examines compatibility with cleaning agents at pH > 9; exposure at 60–80 °C can induce stress cracking in moulded parts with residual stress above 10 MPa. Validation therefore requires ISO 17665-1:2006 documentation and tensile and impact testing after worst-case cleaning and steam exposure, with chemical resistance screened according to ASTM D543-14.

Chemical characterisation data under ISO 10993-18 cannot be replaced by toxicity screening alone

Notified Body reviews under ISO 10993-1:2018, Clause 5.3 identify chemical characterisation as a first step. For a medical PC part, the analytical evaluation should include exhaustive extraction with polar and non-polar solvents, headspace gas chromatography for volatile organic compounds, liquid chromatography with high-resolution mass spectrometry for non-volatile organic compounds, and inductively coupled plasma mass spectrometry for trace elements from colourants or processing aids. The extraction vehicle is selected according to the intended contact environment: water at 37 °C for 72 h, 0.9 % NaCl for simulated blood, and a lipophilic solvent such as hexane or sesame oil for lipid contact. The Notified Body will ask whether the analytical evaluation threshold is derived from clinical exposure; a threshold calculation is required rather than a fixed generic value. PC grades also contain cyclic oligomers formed during interfacial polymerisation, predominantly linear and cyclic dimer to pentamer species. These oligomers are extractable in organic solvents and are routinely detected in extractables screening. A Notified Body will ask whether cyclic carbonate oligomers are included in the analytical scope, because generic LC-MS methods with C18 columns may miss them if the mass range is cut off below 300 Da. The extractables report should include size-exclusion chromatography or a specific LC method for oligomers up to 2,000 Da.

After the biological endpoint matrix is agreed, the review shifts to whether sterilisation and ageing degrade the PC part below its intended physical specification. The Notified Body requests tensile strength, elongation at yield, tensile modulus, notched Izod impact, and heat deflection temperature after real-time and accelerated ageing per ASTM F1980-21. Type I tensile specimens are tested according to ASTM D638-14, notched Izod specimens according to ASTM D256-10, and heat deflection temperature at 1.82 MPa according to ASTM D648-18. For flexion-critical components, a three-point flexural modulus test may be added under ISO 178:2019. The comparison is made to an unaged control stored at 23 °C and 50 % RH, and the acceptance criterion is usually defined as no loss greater than 20 % in tensile strength or 50 % in elongation after worst-case ageing.

When residual bisphenol A limits are reviewed under EU MDR 2017/745

When a PC part is used in a neonatal or paediatric device, the Notified Body may apply a lower tolerable exposure for residual bisphenol A than the tolerable daily intake used for food-contact polycarbonate. No harmonised numeric migration limit for bisphenol A exists specifically for medical devices; the manufacturer must derive a tolerable intake from the toxicological profile and justify the analytical detection limit. The review may request residual phenol data as well because phenol is a hydrolytic degradation product of PC and has its own toxicological threshold. For devices with a long-term implantable classification, published data for specific configurations is limited, and the Notified Body will expect an extractables study that demonstrates whether residual bisphenol A remains below the limit of quantification under simulated clinical conditions. High-purity medical PC grades typically require a documented residual bisphenol A limit below 10 µg/g resin, with the final device tested by LC-MS/MS after solvent extraction. The toxicological risk assessment under ISO 10993-17:2002 must address each detected compound, not only residual bisphenol A.

Because EO diffusion in amorphous PC is slower than in semi-crystalline polyolefins, ethylene oxide sterilisation requires aeration to reduce residuals below the limits in ISO 10993-7:2008. PC sorbs EO into the polymer matrix, and desorption follows Fickian diffusion with a time constant dependent on part thickness, temperature, and airflow. Aeration at 50–55 °C for 8–24 h is common, but the Notified Body will request EO residual data for both the device and its sterile barrier packaging under worst-case loading. For steam and gamma, packaging integrity after sterilisation is evaluated according to ISO 11607-1:2019 and ISO 11607-2:2019. PC trays inside Tyvek pouches may undergo dimensional distortion if moulded-in stress is not relieved. Annealing at 100–110 °C for 1–2 h can reduce moulded-in stress but may increase initial yellowness. The Notified Body may request differential scanning calorimetry or annealed-part dimensional data to confirm that the final device remains within print tolerances.

Supply-chain control and grade substitution risk

In a second-source qualification, the Notified Body compares the master grade and alternate grade for melt stabiliser chemistry, mould-release additives, molecular weight distribution, and colourant package. Substitution of a general-purpose PC with a medical-grade PC may alter the stabiliser package, mould-release chemistry, and extractable profile; under EU MDR 2017/745 and ISO 13485:2016, the change must be evaluated under change control with biological risk review per ISO 14971:2019. A validated injection moulding process for medical PC parts typically operates with melt temperature 280–320 °C, mould temperature 80–120 °C, back pressure 0.5–2.0 MPa, and hold pressure 60–100 MPa. Drying before moulding must reduce moisture below 0.02 % by weight; residual moisture above 0.05 % is associated with splay and hydrolytic reduction in molecular weight. Batch records should confirm drying at 120 °C for 4 h in a desiccant dryer with a −40 °C dew point. A clamp force of 4–7 kN/cm² of projected area is typical, and weld lines formed around pins or louvers may reduce notched Izod impact to 30–50 % of the base resin value. The Notified Body may audit process validation records, cavity-to-cavity consistency, regrind ratios, and the dimensional stability of parts after exposure to hospital cleaning and sterilisation cycles.