Cranial implant production using VESTAKEEP Care M40 3DF begins with drying and material-handling control because the grade is supplied as an unfilled polyether ether ketone filament on sealed spools for fused filament fabrication. Opened spools are dried at 150 °C in a dehumidified dry-air or vacuum dryer with a dew point no higher than -40 °C for a minimum of 4 h. Although bulk PEEK water uptake is commonly reported below 0.5% by weight at 23 °C after full immersion, even residual moisture at the filament surface can hydrolyse the melt during extrusion. The practical threshold for moisture-related void formation is frequently observed when processing is attempted without a dryer at relative humidity above 60%. Resulting microvoids appear as pinholes at layer interfaces and are typically detected by micro-computed tomography with voxel resolution of ≤15 µm. For implantable cranial applications, the final printed device is not considered compliant until biological evaluation is repeated on the finished part. The evaluation commonly follows ISO 10993-1:2018 for risk management, ISO 10993-5:2009 for cytotoxicity, ISO 10993-10:2010 for sensitisation, and ISO 10993-18:2020 for chemical characterisation. Device-level documentation is maintained under ISO 13485:2016 and, where applicable, under EU Medical Device Regulation 2017/745 or US 21 CFR Part 820 quality system requirements.

Extrusion for patient-matched cranial plates should be carried out with an all-metal hot end and a hardened steel nozzle. Brass and aluminium nozzles are unsuitable at these temperatures. The processing envelope for solid perimeters typically requires a nozzle setpoint between 400 °C and 430 °C. Below 395 °C, melt viscosity becomes high enough to produce under-extrusion and poor interlayer fusion at print speeds above 40 mm/s. Print speed is normally held between 20 mm/s and 40 mm/s for perimeters. The build plate is maintained at 160–180 °C on a polyimide film or high-temperature polymer adhesive. The chamber is the more critical variable. Small cross-sections of ≤10 mm can tolerate chamber temperatures near 120 °C, but sections above 20 mm require 160–200 °C to reduce warpage. Chamber uniformity should be held within ±2 °C, because inconsistent airflow can create asymmetric crystallisation and cause an edge lifting failure during the build.

Post-print annealing is required for cranial plates because the as-fused structure contains residual stress and incomplete crystallite development. A nitrogen-purged oven with oxygen below 1000 ppm is preferred. Annealing at 200 °C for 2 h, followed by a controlled cool and a second hold at 220 °C for 2 h, can raise crystallinity and reduce later dimensional movement. Differential scanning calorimetry per ISO 11357-3:2018 is used to verify the crystallinity change. Skipped annealing may produce shrinkage after the first steam sterilisation cycle. That shrinkage can be large enough to distort the bone-contacting surface of a large cranial plate. Dimensional verification is therefore performed after annealing, not immediately after printing. Bone-contacting surface error in patient-matched geometries is commonly specified with a root mean square deviation of ≤0.5 mm when compared with the clinical design file. Steam sterilisation at 134 °C for 18 min per ISO 17665-1:2006 should be run on a representative lot before final release because the crystallinity change during autoclaving is not uniform for printed parts.

How Does Residual Crystallinity Affect Spinal Cage Acceptance Tests?

Residual crystallinity is the central process variable for spinal cage builds because interlayer fracture occurs when the load axis crosses weakly fused roads. A cervical or lumbar interbody cage printed from VESTAKEEP Care M40 3DF is typically oriented with the endplate-bearing surfaces parallel to the XY plane. This orientation places the compressive load normal to the strongest printed plane. Rotating the same cage so that the load axis aligns with the build direction can depress compressive performance by a reported 30–50% relative to XY-oriented coupons. That difference is not governed only by bulk PEEK properties. It is driven by incomplete chain diffusion at the interface between consecutive layers, by trapped air at the weld lines, and by the rate of cooling from the melt in a heated chamber. For a spinal cage with strut widths below 0.5 mm, the build should use a 0.25 mm or 0.30 mm nozzle and a layer height of 0.1 mm. Larger layer heights leave thicker unfused regions and lower the measured stiffness under the acceptance test.

Annealing changes the crystallinity distribution inside the printed cage. The core regions cool more slowly than the surface and may develop higher relative crystallinity before annealing. The as-printed outer surface can remain low in crystallinity because the melt solidifies rapidly against the chamber gas. Annealing at 200 °C for 4 h under nitrogen raises the average crystallinity and improves chemical resistance. However, the process also releases frozen-in stress. If a cage is machined to shape before annealing, the dimensional movement can exceed the tolerances required for an implant-to-endplate interface. That interface tolerance is often held within ±0.1 mm on critical contact features. The practical sequence is to anneal first, then machine datum surfaces, then inspect. Final inspection should include coordinate measuring machine evaluation over the endplate contact area. A useful inspection protocol combines lateral radiograph verification of the implant position with mechanical testing of a representative lot.

Spinal devices manufactured from this filament also require cleaning of support features within lattice pores. Same-material PEEK supports are not removable by solvent. Support removal is performed by CNC machining or ultrasonic-assisted cutting with carbide tools. Burrs at internal strut junctions act as crack-initiation sites during pump-and-load testing. Final visual inspection should reject yellowed or brownish layers because oxidative discoloration indicates carbonyl formation. Oxygen above 1000 ppm in the annealing oven can produce that yellowing and is a tolerated limit only if the part is later machined below the discoloured surface. Repeated steam cycles at 134 °C can slightly change crystallinity further, so acceptance testing should be conducted after the same sterilisation history intended for the finished device. Interbody fusion devices evaluated under ASTM F2077-22 should therefore be conditioned with the packaged implant rather than with an annealed-only coupon.

Dental framework fabrication under ISO 13485:2016 quality control changes the trade-off between build speed and surface finish. A definitive or temporary PEEK framework printed from VESTAKEEP Care M40 3DF for composite veneering is usually built with a 0.25 mm nozzle at 0.1 mm layer height to reduce staircase defects on clasp assemblies. Clasp walls thinner than 1.2 mm are not recommended because bending during insertion creates interlayer stress at undercut regions. If a removable partial denture clasp is needed, the clasp area should be fabricated at full density with an additional perimeter and then adjusted by milling. The framework is annealed at 200 °C for 1 h after support removal, but annealing alone does not prepare the surface for adhesive bonding. PEEK has low surface energy, and veneering composite adhesion requires air-abrasion with 50 µm alumina at 2 bar, followed by etching with 98% sulfuric acid for 60 s. Etching times above 90 s can produce preferential pitting at printed layer boundaries. The surface is then rinsed with deionised water and dried; residual sulfate must be absent because it interferes with methacrylate cure. Bond strength to veneering composite is assessed by a micro-shear bond procedure based on ISO 29022:2013. For polymer-based crown and bridge frameworks, the material must also be evaluated under ISO 10477:2020 or the applicable national equivalent. Because the printed framework is patient-specific, each design file and each machine run becomes part of the device history record.

The process window for dental frameworks is narrower than for bulky implant blanks because thin clasp arms and occlusal rests respond to residual stress differently. The build chamber is held at 150–180 °C. A chamber at the lower end of that range improves surface detail retention but increases the chance of interlayer delamination when the framework is removed prematurely from the build plate. Cooling to below 100 °C before removal is mandatory to avoid thermal shock. After removal, the framework is stored dry. Reprocessing with 70% ethanol or peracetic acid should be validated under ISO 17664:2017. Steam sterilisation may be used depending on the dental practice protocol, but repeated autoclaving at 134 °C can cause dimensionally unstable thin sections to warp. If steam is required, multiple autoclave cycles should be included in the dimensional validation plan. The typical rejection point is a clasp gap change of more than 0.2 mm after reprocessing, because this degrades retention on the abutment tooth.

Trauma Plate Print Orientation and Its Effect on Wrought-Equivalent Property Gaps

Fracture fixation plates printed from unfilled PEEK create a property gap that is dominated by the Z-axis response. A solid XY coupon printed with a 0.4 mm nozzle and 0.15 mm layer height may approach the tensile modulus reported for machined VESTAKEEP PEEK when tested under ISO 527-2:2012. A specimen printed in the Z direction usually fails at lower strain because the limiting path runs along interlayer boundaries. This difference is widened by dust contamination, filament ovality outside the supplier tolerance, and insufficient drying. A filament wipe placed upstream of the feed mechanism and replaced every job can reduce inclusion-related early failure. The printer should be operated in a clean environment corresponding to ISO 14644-1 Class 7 or better when fixation plates are produced for clinical use. Traction from the feed gear also matters: titanium drive gears may gall at the elevated feed temperatures developed during long builds, so the extruder should use a hardened steel drive gear and a filament feed path with controlled idler pressure.

Mandibular reconstruction plates and maxillofacial fixation plates require careful selection of build orientation. If a plate thickness is below 2.5 mm, Z-oriented printing is not advisable for load-bearing mandibular applications. Instead, the plate is printed flat in XY and then finish-machined on the bone-facing side to improve fit. Screw holes are stress concentrators. In the printed geometry, the hole interrupts the perimeter path and forms a knit line at the edge. That knit line is not present in a machined PEEK plate. Annealing at 200–220 °C for 2–4 h recovers some interlayer strength but does not fully erase the knit line. Reaming the hole with a carbide end mill after annealing removes the damaged perimeter and improves fatigue behaviour. Nonmetallic bone plates are not universally covered by a single plate-testing standard, so manufacturers often use coupon-level flexural tests per ASTM D790-17 or ISO 178:2019 combined with device-specific four-point bending. Published data for printed PEEK trauma plates under full implant plate protocols is limited. Validation therefore requires a dedicated mechanical test plan that includes screw-hole bearing and bending across the intended anatomical load range.

The absence of fibre reinforcement in VESTAKEEP Care M40 3DF sets an upper bound on modulus and creep resistance. A high-load mandibular plate may require a thicker cross-section than a titanium counterpart. That design change is not a defect; it is a fundamental difference between unfilled PEEK and metallic fixation. Manufactures must not add fillers at the machine. Any blended or filled stock requires separate qualification because filler distribution and particle release may deviate from the implant-grade dossier. The printed plate should be checked for cavities by X-ray or micro-CT and for surface contamination by organic residue analysis. Gamma irradiation at 25–40 kGy per ISO 11137-1:2006 can be used after validating that interlayer embrittlement does not reduce the device below the specified bending strength. Steam sterilisation remains the default for many trauma plate workflows, but the sterilisation history must be identical for dimensionally critical lots before final fit testing on anatomical models.

When Osteotomy Guides Require Repeated Low-Temperature Sterilization

Patient-specific osteotomy guides printed from VESTAKEEP Care M40 3DF are not implanted, but they contact bone and blood and must be supplied sterile. The main process conflict is not simply reaching full density; it is balancing residual stress against re-sterilisation dimensional drift. The guide is designed with a minimum wall thickness of 2 mm and cutting slots between 1.0 mm and 1.5 mm. Same-material PEEK supports cannot be dissolved in a solvent bath. Breakaway supports are permitted only on non-critical outer surfaces. Inside cutting slots, supports are removed by a small-diameter end mill under magnification. A slot edge left with fractured support remnants creates stress concentration and can break during contact with oscillating saw blades.

Hydrogen peroxide gas plasma sterilisation at 45–55 °C is preferred over steam at 134 °C for these guides because the lower temperature reduces thermal stress release. The sterilisation process is validated under ISO 14937:2009. Bioburden and sterilant penetration are documented with biological indicators per ISO 11138-1:2017. If steam is the only available method, the guide is annealed at 200 °C for 4 h and measured after the first and second autoclave cycles. Steam exposure at 134 °C for 18 min can release enough residual stress to warp a long narrow guide beyond clinical acceptability. The rejection threshold for these guides is often a root mean square fit error above 0.5 mm against the patient-specific bone model. The same threshold applies after repeated low-temperature cycles. Dimensional checks are therefore performed after sterilisation, not before packaging.

Internal corner radius is a critical geometric control. Corners at the slot bases should be at least 0.5 mm in the model file. Sharper corners accumulate stress and crack after reprocessing. A common failure mode is a slot-side crack that initiates at an internal corner and propagates along a layer interface. If the cutting slot must be shorter or more angular, the part should be machined from an annealed printed blank rather than finished only by printing. The guide must also be reprocessed in accordance with the manufacturer-provided cleaning and disinfection instructions under ISO 17664:2017. Detergent and enzymatic cleaner compatibility should be validated because residual cleaning agents in the surface pits can react with hydrogen peroxide sterilant. Final packaging is performed in a cleanroom, and package sealing is validated by dye-penetration per ASTM F1929-15.

Short-run surgical instrument handles and aiming guides are printed from VESTAKEEP Care M40 3DF when metallic versions are too heavy or unsuitable for intraoperative magnetic resonance imaging environments. The unfilled PEEK structure is non-ferromagnetic and radiolucent, but a printed fused-filament part is not autoclavable indefinitely. Moisture entry along interlayer boundaries can cause surface microcracks after repeated steam exposure. Sterilisation cycle life is not a fixed property. It depends on chamber temperature, layer height, infill density, and post-annealing. A practical validation for printed instrument bodies uses visual inspection under ISO 17665-1:2006 after 20–50 steam cycles, although published data for this specific configuration is limited. Parts with delamination, surface blistering, or visible layer separation are rejected. Instrument bodies should be printed with a 0.3 mm nozzle and chamber temperature near 160 °C to maximise layer consolidation. Wall thickness is held at ≥4 mm in grip zones so that perimeter road width does not become a mechanical weak point. Thin ratchet features under 0.8 mm should be printed separately at reduced speed or finish-machined from an annealed blank.

Alkaline cleaning agents at pH above 10 can induce stress corrosion at layer boundaries if parts are not fully dried. Automated washer-disinfector cycles should be qualified under ISO 15883-1:2006 with the actual loading configuration. Chlorinated solvents are avoided because residual solvent in surface voids can violate leachable limits. Isopropyl alcohol may be used for intermediate wiping, but it must evaporate fully before steam sterilisation. The drive mechanism and build chamber should be dedicated to medical-grade PEEK to avoid contamination from previous filled polymers. If the same machine is used for carbon-fibre-filled PEEK, a purging sequence and a chamber cleaning protocol are required before implant-adjacent parts are produced. These housekeeping steps are part of the validation record and are typically audited under ISO 13485:2016.