GEHR Plastics MEDI FIL-A-GEHR PEEK MG Filament for 3D printing is an unfilled polyetheretherketone monofilament produced for fused filament fabrication applications that require a semi-crystalline high-temperature thermoplastic with repeated sterilization tolerance and lot-level medical documentation. The product is part of the FIL-A-GEHR series but differs from general-purpose PEEK monofilament not primarily through polymer chemistry, which remains polyetheretherketone, but through raw material selection, lot traceability, and packaging under conditions intended to preserve documentation integrity for medical device prototyping and production. The filament is available in nominal diameters of 1.75 mm and 2.85 mm, with a spool-to-spool diameter tolerance generally specified as ±0.05 mm; users must confirm the exact certificate of analysis because diameter variation greater than this can alter volumetric flow stability in high-temperature extrusion systems. Polyetheretherketone in this form exhibits a glass transition temperature near 143 °C and a melting transition near 343 °C, which places the feedstock in the same process class as medical PEEK filaments supplied for trauma device prototypes and surgical guide components. The monofilament is not a drop-in replacement for lower-temperature polymers such as polylactic acid or acrylonitrile-butadiene-styrene, because the entire melt path, build platform, and chamber must be rated for continuous operation above 400 °C and 150 °C, respectively. In addition, the material requires a drying protocol before extrusion when it has been exposed to ambient humidity above 35 % RH for more than 24 h. The combination of high melt viscosity and a narrow thermal processing band means that uncontrolled printing conditions produce interlayer delamination, nozzle blockages, and geometric distortion rather than usable parts.

What Processing Parameters Govern Successful Extrusion of MEDI FIL-A-GEHR PEEK MG?

Successful extrusion of MEDI FIL-A-GEHR PEEK MG depends on maintaining melt temperature, build surface temperature, and chamber air temperature within narrow bands. The nozzle setpoint is typically held between 400 °C and 430 °C; the lower limit is applied only when print speed does not exceed 30 mm/s, while the upper limit supports volumetric throughput at feed rates above 40 mm/s. At temperatures below 390 °C, the melt viscosity remains high enough to cause extruder motor stall and filament grinding, especially in Bowden configurations. A heated build plate held at 150 °C to 160 °C is required to prevent immediate debonding of the first layer. The build chamber should be maintained at 120 °C to 150 °C during the entire print, not only during the initial layers, because interruptions in chamber heating create anisotropic shrinkage gradients that propagate layer cracks. Direct-drive extruders with hardened steel gears are preferred over Bowden tubes because the high melt viscosity and rapid solidification of PEEK require short retraction paths; retraction distance should not exceed 1.5 mm for direct drive and 0.5 mm for Bowden systems, and retraction speed should not exceed 25 mm/s. A 0.40 mm hardened steel or high-temperature alloy nozzle operating at 0.15 mm layer height and 0.45 mm line width provides a stable thermal mass and sufficient extrusion pressure for interlayer diffusion without excessive shear heating. Nozzle pressures in small-diameter PEEK printing can exceed 10 MPa, which demands a stiff printer frame and a hot end thermistor verified for continuous operation at 400 °C. The use of a PTFE-lined hot end is incompatible with this filament because thermal decomposition of PTFE begins above 260 °C and releases toxic degradation products. Print speeds are usually confined to 20–50 mm/s; above 60 mm/s, the crystalline polymer cannot maintain sufficient interlayer strength, and the resulting parts fail under tensile loading perpendicular to the build plane when evaluated according to the ISO 527-2 specimen geometry. These parameters are starting values, not guarantees; lot-to-lot viscosity differences and printer-specific thermal gradients require calibration coupons tested to ISO 527-2 tensile criteria before final part production.

In production-scale fused filament fabrication of PEEK, the most common failure mode is not nozzle clogging but interlaminar splitting caused by a chamber air temperature that falls during tool path pauses. When the heated chamber is opened for powder or print removal, the surface temperature of a partially printed PEEK part can drop below 120 °C within minutes, locking in a tensile skin that delaminates when subsequent layers reheat the top surface. A second field failure mode is extruder feed grinding when retraction is set for flexible or lower-viscosity materials; PEEK filament is inherently stiff but the softened layer at the drive gear can be shaved if the idler tension is too high. Machines with long Bowden tubes and high retraction distances often show dimensional variation along the filament path because the high melt viscosity couples the nozzle pressure to the filament column elasticity. These observations support the narrow retraction and direct-drive preference for MEDI FIL-A-GEHR PEEK MG.

The melt flow behavior of unfilled PEEK is shear-thinning but remains high viscosity; at 400 °C and low shear, apparent melt viscosity is on the order of 10³ Pa·s, which is one to two orders of magnitude higher than typical ABS or PLA. This high melt strength resists stringing but limits maximum extrusion acceleration. Linear advance settings must be tuned with test towers because pressure propagation in a rigid filament column differs from that of softer feedstocks. A nozzle change from 0.40 mm to 0.25 mm increases extrusion pressure significantly and may require reducing print speed by 30 % to 50 %. The material should not be left idle at melt temperature for more than 15 min because prolonged exposure at 400 °C can initiate thermal-oxidative chain branching and discoloration. If printing pauses are unavoidable, the hot end should be lowered to 150 °C or purged with fresh material before resuming, and the interlayer bond at the pause plane should be inspected for delamination.

Before extrusion begins, moisture management defines the usable process window. PEEK monofilament absorbs ambient moisture slowly, but residual moisture in the polymer melt hydrolyzes at processing temperature, increasing melt flow index and reducing molecular weight locally. Drying at 150 °C for at least 3 h in a forced-air oven is necessary when a spool has been exposed to air above 35 % RH for more than 24 h. Storage in a sealed pouch with fresh desiccant or in a dry cabinet below 10 % RH permits the drying step to be omitted only for unopened spools. After exposure above 60 % RH, redrying is mandatory because PEEK is not hygroscopic in the same way as polyamide but still retains enough water at the surface and interphase to generate microvoids at melt temperatures above 400 °C. The effect of moisture is not a linear property reduction; in tensile testing to ISO 527-2, dry feedstock keeps ultimate tensile strength within the expected unfilled PEEK envelope, while wet feedstock can produce intermittent voids that reduce tensile strength by more than 20 % and increase scatter. A filament feed path purged with dry air or nitrogen is an operational boundary that prevents moisture regain during prints longer than 6 h.

Polyetheretherketone's processing behavior is governed by the relationship between glass transition, cold crystallization, and melting. In MEDI FIL-A-GEHR PEEK MG, the glass transition temperature near 143 °C defines the lower chamber bound; below this temperature, the printed layer vitrifies before sufficient molecular interdiffusion occurs. Cold crystallization begins during post-annealing at 200 °C and increases crystalline content from typical as-printed values of 20 % to 30 % to values closer to 35 % to 40 %. The increase in crystallinity improves chemical resistance and dimensional stability under steam, but it also raises modulus slightly and reduces ductility. Differential scanning calorimetry to ISO 11357-3 on printed coupons can be used to monitor this transformation; a broad melting endotherm between 340 °C and 350 °C is typical. This thermal history dependence means that two parts printed from the same filament spool can exhibit different sterilization shrinkage if they have different annealing histories or cooling rates. Lot-specific variation in melting peak and crystallinity onset should be recorded in the batch log as part of a medical quality system.

When Chamber Temperature Falls Below 120 °C, Warping Becomes Irreversible

PEEK forms a semi-crystalline structure during cooling, and the associated specific volume reduction is anisotropic when the part is not kept above the glass transition temperature long enough for stress relaxation. In chamber environments below 120 °C, the uppermost layers solidify and shrink against the already constrained lower layers, producing edge-lift and interlayer shear stresses that cannot be recovered by post-annealing. For parts with a build-plane dimension greater than 40 mm, this results in visible corner lifting even when the first layer adheres to a polyetherimide sheet or a high-temperature adhesive. The failure mode is not limited to aesthetics; dimensional deviations along the Z-axis can exceed 0.4 mm over a 100 mm tall print, and residual stress concentrations reduce the tensile strength measured parallel to the Z-axis under ISO 527-2. Therefore, the filament must be processed only on machines with a heated enclosure capable of maintaining at least 120 °C at the height of the printed component, not simply at the bed surface. Machines without active chamber heating, or with chamber temperatures below the glass transition temperature of the material, are incompatible with this product for any component requiring load-bearing function. If a printer cannot sustain 120 °C, the use of an external insulated enclosure may reduce drafts but does not replace a thermostatically controlled chamber. The produced part can subsequently be annealed at 200 °C for 2 h to increase crystalline fraction and stabilize dimensions before sterilization validation. Annealing reduces residual stress only partially; it does not correct delamination caused by cold-chamber processing.

The mechanical response of MEDI FIL-A-GEHR PEEK MG is characteristic of unfilled polyetheretherketone rather than of filled or blended compounds. The absence of carbon fiber or glass fiber means that the material can be processed without excessive abrasive wear on hardened steel nozzles, although brass is still not recommended at continuous temperatures above 400 °C. The following table compares the typical unfilled PEEK class with filled variants and a competing high-temperature amorphous polymer; values are literature-derived ranges, not lot-specific guarantees for the GEHR product.

Compared with general-purpose unfilled PEEK filament, MEDI FIL-A-GEHR PEEK MG occupies the same thermal and mechanical design envelope but differs in supplier-controlled raw material traceability and packaging intended for medical device documentation. The absence of random lots and recycled feedstock reduces batch-to-batch variation in melt flow behavior, which is relevant in a material where a small shift in melt viscosity can alter optimal extrusion temperature. General-purpose PEEK may have broader molecular weight distributions and non-declared additives; medical-grade feedstock is expected to align with change control required by ISO 13485. Compared with carbon-fiber-reinforced PEEK, the MG grade has lower tensile modulus and lower heat distortion capability, but it generates lower nozzle abrasion and avoids anisotropic mechanical properties associated with fiber alignment. Carbon-fiber-filled PEEK also increases melt viscosity and requires reinforced nozzles; unfilled MG can be processed with standard hardened steel nozzles and has lower electrical conductivity. Compared with polyetherimide, PEEK MG provides higher continuous-use temperature and superior resistance to chlorinated cleaning agents and superheated steam, but it places more stringent demands on extrusion hardware. Polyetherimide is printable in chamber temperatures near 90 °C and nozzle temperatures near 350 °C; the MG grade requires an additional 50 °C to 80 °C of nozzle capability and a hotter chamber. These distinctions are operational rather than merely cosmetic; a printer configured for polyetherimide will not necessarily reach stable PEEK MG processing conditions.

Regulatory Documentation and Lot Traceability

Medical-grade designation for a filament is not a single universal standard but a combination of supplier quality practice and available test documentation. For MEDI FIL-A-GEHR PEEK MG, the relevant framework includes ISO 13485:2016 for quality management of medical device suppliers, ISO 10993-1:2018 for biological evaluation planning, and EU MDR 2017/745 or FDA 21 CFR Part 820 depending on final device registration. The filament can support a biological evaluation file when used in a device that contacts intact skin or mucosal tissue, but the evaluation must be completed on the finished printed component, not on raw monofilament alone. Cytotoxicity testing to ISO 10993-5 on printed coupons is commonly used as a screening assay; sensitisation and irritation endpoints are selected according to the device contact duration and route. The manufacturer's lot documentation is intended to supply raw resin identity and consistent process parameters, but the user remains responsible for validating that the additive manufacturing process does not introduce contaminants from the hot end, build plate, or chamber. The table below lists the compliance frameworks typically referenced for medical PEEK supply chains.

Printed MEDI FIL-A-GEHR PEEK MG parts are often exposed to repeated steam sterilization in clinical maintenance cycles. Polyetheretherketone tolerates steam autoclave conditions at 134 °C for 4 min, but this tolerance refers to the polymer itself, not to as-printed stress states. Unannealed parts with high amorphous content can undergo secondary crystallization during the first autoclave cycle, producing shrinkage of 0.3 % to 0.8 % and dimensional distortion in thin-walled sections. Annealing at 200 °C for 2 h before sterilization reduces this shift by increasing crystallinity and relaxing print-induced thermal history. Hydrogen peroxide plasma and ethylene oxide sterilization may also be compatible, but compatibility with the specific cleaning agent and load configuration should be verified under ISO 17664, which governs processing information for re-sterilizable medical devices. Chemical resistance of PEEK to common hospital disinfectants and organic solvents is high; however, strong oxidizing acids and certain halogenated solvents at elevated temperature can cause stress cracking in printed parts with high residual stress. The operational boundary for most applications is therefore not steam temperature but the presence of residual stress from the printing process. Validation should include dimensional checks before and after sterilization on printed coupons with the same layer orientation and infill density as the final component.

Mechanical anisotropy in fused filament fabricated PEEK is dominated by interlayer fusion rather than material stiffness. Z-axis tensile strength in unfilled PEEK can remain as low as 40 % to 60 % of XY-axis strength when printed at low chamber temperatures; with the 120 °C to 150 °C chamber and 0.15 mm layer height, the Z-axis ratio improves but still remains below the isotropic value reported for injection-molded PEEK. Infill density should not be used as a simple strength adjustment because interlayer neck formation depends on local heat input, not on the number of raster lines. A solid infill with 0°/90° alternating orientation often provides better sterilizable load-bearing performance than sparse infill with high wall counts, because sparse infill introduces internal voids that can trap moisture and cleaning agents. For thin surgical guide components, a wall count of 4 to 6 perimeters and 90 % to 100 % rectilinear infill reduces permeability. This configuration also minimizes the surface area where residual moisture can absorb before sterilization.

The product is used in printed surgical guide bodies, dental transfer trays, sterilization trays, and functional prototypes for medical device housings. In each case, the part is a single-use or re-purposeable component that requires lot-level material documentation and dimensional stability after steam exposure. For implantable applications, this filament is not supplied with a master file granting implantable approval; final biocompatibility and clinical validation remain the legal responsibility of the device manufacturer. Use of MEDI FIL-A-GEHR PEEK MG as a temporary contact material may require additional testing under ISO 10993-10 for sensitization and ISO 10993-23 for irritation, depending on the contact duration and the printed surface condition. The rough surface produced by layer-by-layer deposition is less resistant to biofilm attachment than smooth injection-molded PEEK; therefore, post-printing machining or coating can be considered when the device is reused in a hospital environment.