Residual Monomers and Health Considerations in 3D Printing Resins
Photopolymer resins are reactive manufacturing materials. A “monomer-free” designation describes a formulation characteristic as supplied; it does not by itself establish universal safety or biocompatibility of a printed part. Hazard classification is defined by the applicable SDS, while final biological suitability depends on the specific Product/version, printing, cleaning, post-curing, specimen and intended use.
3Dresyns develops monomer-based and monomer-free (as supplied) material options for biomedical-development workflows. Any biological-evaluation, safety or regulatory claim must be tied to the specific Product/version, documented processing conditions, test endpoint and final intended use.
Why can materials described as “biocompatible” still show adverse biological results under some printing or post-processing conditions?
The publications below are examples of study-specific findings on commercial 3D-printed materials. Their results should be interpreted within the tested resin, printer, specimen preparation, post-processing, endpoint and study design; they should not be generalised to all resins or all workflows.
The cited Northwestern University study reported adverse biological findings for the tested Dental SG and LT Clear specimens under its documented experimental conditions. This is a study-specific result and should not be interpreted as a general statement about all uses, batches, printers or post-processing workflows for those products.
This publication "The Biological Effects of 3D Resins Used in Orthodontics: A Systematic Review" concluded that although these resins are considered biocompatible, they exhibit reproductive toxicity in mouse oocytes after direct and indirect exposure. The tested resins were Formlabs Dental SG resins (DSG) and Dental LT Clear (DLT), classified as biocompatible for medical use and currently used in dental surgical guides and oral retainers.
Conclusions: Within the scope of this review, it was noted that studies evaluating the biological effects of 3D resins in orthodontics are mostly conducted in vitro. Although mixed results are described, 3D printed aligners may present higher levels of cytotoxicity and genotoxicity when compared to thermoplastic resins, particularly those that have not been subjected to a final surface treatment. As such, clinical studies analyzing saliva, blood, or even urine samples must be carried out in the future to determine the levels of monomers released in humans upon the use of these devices.
In this publication: Evaluation of dimensional accuracy and degree of polymerization of stereolithography photopolymer resin under different postpolymerization conditions: An in vitro study the degree of polymerization of a Clear Formlabs 3D resin was evaluated following Formlabs printing and postprocessing protocol. Several specimens were cleaned with isopropanol in the Form Wash unit (Formlabs) for 15 minutes to remove excess resin and poscured with Formlabs light box Form Cure at 15 and 30 minutes and at 40, 60, and 80 ºC. The results are shown in the following table:
The reported degree of polymerisation in this study should not be converted directly into a residual-monomer percentage unless residual monomer was independently measured with an appropriate analytical method. Degree of conversion, residual monomer, extractables and leachables are related but distinct measurements and should be reported using the method actually used in the study.
Applicable residual-monomer or extractables requirements depend on the specific material, device, intended use, jurisdiction, standard and test method. FDA guidance, ISO 10993, ISO 13485 and dental-material standards should not be presented as establishing a single universal <0.1% residual-monomer limit for all 3D-printed medical devices.
Which is the risk of trapped residual monomers and other chemicals in printed devices for human health?
The answer depends on the type and concentration of physically trapped monomers and other leachables and extractables in the medical devices.
How can the risks for humans be figured out?
The SDS describes hazards and safe-handling information for the liquid material as supplied. Assessment of a cured medical device requires device- and workflow-specific evidence, including relevant analytical and biological-evaluation data where applicable; SDS ingredient hazards should not be treated as a direct measurement of final-device leachables.
- For more information read: Biocompatibility hints
- These findings reinforce the importance of validating the complete material–printer–cleaning–post-cure workflow and measuring relevant residuals or biological endpoints where required, rather than inferring final-part safety from a “monomer-free” or “biocompatible” label. Related material family: 3Dresyns monomer free 3D resins.
Similarly to the previously reported findings, the resin of Graphy for direct printing of aligners also may raise concerns on potential health hazards as reported in this paper published in the European Journal of Orthodontics: Leaching from a 3D-printed aligner:
"Although efficiently polymerized and BPA free, the great variability in the amount of UDMA monomer leached from the examined samples may raise concerns on potential health hazards after repeated intraoral exposure"
3Dresyns statement:
Adverse biological results can arise from formulation, insufficient conversion, cleaning/post-curing conditions, contamination, specimen geometry or other workflow variables. The cause must be established from the specific evidence rather than attributed to a material category in general.
Conclusion
Biological-response or safety failures can result from unsuitable material selection, insufficiently controlled printing/post-curing/post-processing, contamination or residual constituents. These factors should be evaluated for the specific Product, specimen, workflow and intended use.
Resin suppliers are responsible for the documentation and controls applicable to the materials they supply. Final medical-device manufacturers are responsible for validating their manufacturing process and demonstrating that the finished device meets the applicable safety, biological-evaluation and regulatory requirements for its intended use.
Photopolymer 3D resins are reactive raw materials used in manufacturing workflows; they are not, by virtue of being supplied as resin, certified finished medical devices.
For medical-device workflows, acceptance criteria for conversion, residuals, extractables/leachables, cleaning and post-curing should be defined and validated by the device manufacturer for the specific device and intended use.
Materials for biological-evaluation workflows
Discover 3Dresyns material options designed to support biological-evaluation requirements after appropriate printing and post-processing:
Customisation
3Dresyns provides custom formulation and process-development services for biomedical, food-contact and other regulated-development workflows. Final suitability, biological evaluation and regulatory compliance must be established for the specific Product, process and finished application.
You may contact us to discuss customisation services for synthetic, bio-based and biological-evaluation-oriented 3Dresyns and your specific performance goals at: info@3Dresyns.com
Learn more about Certification of biomedical devices and food packaging