Researchers from Hochschule für Technik und Wirtschaft Dresden, a German university of applied sciences with a focus on engineering and materials research, and the Leibniz Institute of Polymer Research Dresden have demonstrated a method to manufacture monodisperse, count-accurate microplastic reference materials using additive manufacturing. The work, published in Nature, shows that microextrusion via modified, commercially available 3D printers can reliably produce microplastic particles with defined size, shape, and exact particle numbers, addressing a long-standing limitation in microplastic analysis.
Microplastic reference materials are required to standardize analytical methods used to quantify plastic pollution in environmental samples. Microplastics are defined as synthetic polymer particles smaller than 5 mm and have been detected in water, soil, sediments, and biological systems worldwide. Regulatory demand has increased following the EU Drinking Water Directive (EU) 2020/2184, which obliges EU member states to implement methods for measuring microplastic content in drinking water, and amendments to the EU Urban Waste Water Directive introduced in 2024 that establish limits for microplastic emissions and promote avoidance strategies.
Current analytical approaches fall into two broad categories. Mass-based techniques include pyrolysis-GC/MS, thermal extraction desorption GC/MS, and differential scanning calorimetry, while particle-counting methods rely on optical identification combined with FTIR or Raman microscopy. Data produced by these approaches are not directly comparable, even when applied to samples from identical locations. Several studies have highlighted that this incompatibility complicates environmental monitoring and regulatory assessment. One central reason is the lack of reference materials that combine a narrow particle size distribution with an exact and known particle count.
Established production routes for microplastic reference materials present substantial limitations. Cryogenic grinding followed by sieve fractionation produces broad size distributions, consumes large amounts of energy and material, and cannot generate defined particle counts. Yield within the desired size fraction is often low, with reported values below 20 percent for certain polymers and size ranges. Synthetic polymerization methods can yield monodisperse particles but are largely restricted to a limited set of polymers, primarily polystyrene and polymethyl methacrylate, and do not intrinsically provide count accuracy. Other experimental approaches, including CNC-based micromachining or laser printing of polymer-toner mixtures, generate significant waste, require extensive post-processing, or remain limited in polymer scope.
To address these constraints, the Dresden-based teams explored microextrusion-based additive manufacturing. Modified Elegoo Neptune 4 Pro fused-layer modeling printers were used as the production platform. Hardware and software modifications enabled CNC-controlled operation, allowing precise specification of nozzle temperature, filament feed distance, retraction length, particle spacing, and target particle count via G-code. Polymer filaments were extruded through brass nozzles with opening diameters of 80, 100, 200, and 400 micrometers. Individual molten droplets were deposited onto a steel printing plate in a regular grid pattern and cooled to form solid particles.
The method was evaluated using thermoplastics commonly detected in environmental samples, including low-density polyethylene, polyamide, polylactic acid, polycaprolactone, and polymethyl methacrylate. Depending on nozzle diameter and polymer type, particle diameters between 224 and 1,349 micrometers were achieved. Production rates exceeded 1,000 particles per hour, with a maximum of approximately 5,000 particles per batch, constrained primarily by print-plate area and particle spacing. Count accuracy was verified visually, as missing or over-extruded particles could be directly identified within the printed grid.
Particle characterization was performed using optical microscopy and automated image analysis. Size variability remained low across most fractions. Relative standard deviations were typically below 10 percent for particles produced with 400 micrometer nozzles and below 15 percent for most other combinations of polymer and nozzle diameter. According to VDI guideline 3491, these distributions qualify as monodisperse. Higher deviations were observed for certain polymer–nozzle combinations, particularly polyamide at smaller nozzle diameters, which the authors attribute to polymer-specific rheological behavior and filament dimensional accuracy.
Particle shape was described as hemispherical or droplet-like, with round base areas. Aspect ratio and roundness values were quantified using ImageJ analysis. Chemical integrity of the polymers was verified by FTIR spectroscopy, which showed no evidence of degradation or compositional change induced by the extrusion process. For selected particle fractions, mass measurements were performed using precision balances, enabling direct correlation between total mass and particle count.
Several procedural measures supported count accuracy. Wetting particles with ethanol or water prior to removal from the printing plate reduced losses caused by electrostatic charging or air movement. Side walls around the plate holder and a drainage system allowed complete transfer of particle suspensions to storage containers. Sampling and characterization followed ISO 33405:2024, with at least 10 percent or a minimum of 10 particles analyzed per fraction to ensure representativeness.
Compared with cryogenic grinding and direct synthesis, microextrusion-based additive manufacturing generated minimal waste. Typically, only the first 100 particles of each batch were discarded due to process stabilization. All remaining particles were produced at the intended size and count. Commercial filaments are available for a wide range of thermoplastic polymers, and custom filaments can be produced using standard extrusion equipment, as demonstrated for low-density polyethylene in the study.
Particle sizes produced in this work remain larger than many microplastics observed in environmental samples, particularly those below 100 micrometers. Further size reduction may require smaller nozzle diameters, alternative extrusion conditions, or different printer architectures. Particle shape may also influence transport, sedimentation, and biological interaction, indicating directions for future investigation.
The research was carried out by Maurice Hauffe, Robert Möhn, and Thomas Himmer from the Faculty of Mechanical Engineering at Hochschule für Technik und Wirtschaft Dresden, together with Lucas Kurzweg, Tilmann Priebe, Arne Cierjacks, and Kathrin Harre from the university’s Faculty of Agriculture, Environment, and Chemistry. Polymer characterization and physical chemistry analysis were conducted with contributions from Leibniz Institute of Polymer Research Dresden, where Lucas Kurzweg is also affiliated.
Help shape the 2025 3D Printing Industry Awards. Sign up for the 3DPI Expert Committee today.
Are you building the next big thing in 3D printing? Join the 3D Printing Industry Start-up of the Year competition and expand your reach.
Subscribe to the 3D Printing Industry newsletter to stay updated with the latest news and insights.
Featured image shows Boxplot of particle sizes for PLA particles manufactured with different nozzle opening diameters. Image via Nature.
