About the importance of tuning 3D resins in accordance with appropriate printing and postprocessing units/protocols for maximum biocompatibility

Following 3Dresyns Instructions for Use "IFU" for printing our 3D resins is required for achieving good printing results. For more info read: 

• About the importance of following 3Dresyns Instructions for Use "IFU"

The manufacturing of biomedical devices not only requires the selection of biocompatible 3D resins, but also their tuning in "appropriate" printers and light boxes.

Unfortunately, most commercial printers and light boxes are variable black box systems, which performance, in particular, their light power naturally decays upon time. This intrinsic limitation can be overcome with 3Dresyns support.

The selection of the right resin for the specifications of each biomedical device type, and its tuning to the right printer and light box system are mandatory to design safe biocompatible medical devices. For more info read: 

• About Certification of biomedical devices and food packaging
• Responsibilities of manufacturers of 3D resins for medical uses

Implementing professional printing and postprocessing setups requires properly designed printers, lightbox units, and quality control instrumentation and workflows. The whole setup needs to be properly designed and configured, with clearly integrated protocols and workflows, which should include the appropriate design, tuning and optimisation of the resin with appropriate biocompatible printing and postprocessing units and protocols for ensuring maximum biocompatibility and safety of biomedical devices to final users.

There are few "certified" 3D resins which failed biocompatiblity testing despite being printed and postprocessed following the manufacturers´s instructions,  such as the mentioned ones in these articles: 

• Assessing and Reducing the Toxicity of 3D-Printed Parts
• Dental resins used in 3D printing technologies release ovo-toxic leachates
• Biocompatibility of Photopolymers in 3D Printing
• Assessment of biocompatibility of 3D printed photopolymers using zebrafish embryo toxicity assays

Cleaning parts with alcohol cannot provide any warranty that extractables and leachables are fully removed before use.

Failing to implement properly designed biocompatible protocols may end up in negative biocompatibility results. As example, let us analyse the results obtained in this publication: 3D Printing of Biocompatible Scaffolds for Eye Tissue Engineering:

"Surprisingly, 3Dresyn CT MF Clear and Tough Monomer Free #3, #4, and #5 resins did not pass the test already at 24h: these formulations are not suitable for our purposes. Dental LT resin gave better results: indeed, resin-treated cells survived also at longer timepoints,even though slowed down in their growth rate. Also, Elastic 50A and 3Dresyn CT Clear and Tough #6 resins gave satisfactory results: both did not impair cell viability and only had a little, usually not significant, impact on cell growth rate.
For these reasons, we can conclude that 3Dresyn CT Clear and Tough #6 resin is the best for our purposes among the ones tested: it could be used in cell culture without concerns of cell death induction. However, since some detrimental effects on cell growth persist, we are still looking for better solutions.
Another feature to be considered when using resin samples in cell culture is their transparency. The as-built resin samples did not allow cell visualization because of the interference of the printing layers; post-processing with 2000 grit sandpaper, wetted with water, highly increased cell visibility. However, we still need a more standardized method to make 3D printed resin specimens more transparent, even if at the moment we consider our achievements acceptable for our purposes."

Fortunately, our 3Dresyn CT Clear and Tough version #6 gave the best biocompatibility results, partially due to the optimisation and tuning of the resin to the chosen printer by the authors of the paper, which used a low power LCD printer, which is not ideal for printing biocompatible biomedical devices. Surprisingly, versions #3, #4, and #5 resins did not pass the biocompatibility tests, but version #6 luckily outstanded among the different tested commercial 3D resins.

Unfortunately, the paper does not mention in detail the protocols used for postcuring and cleansing the 3D printed parts, if any, rather than the prints were "sterilised by autoclave". For your information: autoclaving does not eliminate extractables from 3D prints. Consequently, passing or failing the different biocompatibility testing was a matter of “luck”. Biocompatible biomedical devices need to include appropriate postcuring and cleansing protocols, to say, postprocessing protocols, to ensure that unreacted free monomers, reaction by products, impurities, all being in practice leachable and extractable contaminants during usage.  

What are the main reasons for some versions failing whilst other pass the cytotoxicity testing?

There are several potential reasons which affect in more or less degree to the biocompatibility results:

1. the resin composition used, since some are purer than others, and more or less prone to release residuals, uncured monomers, by products, etc...
2. the printer technology used since despite LCD printers are an excellent choice for printing functional engineering materials due to their low relative cost, are not ideal for printing biocompatible biomedical devices. Biomedical devices require the use of higher power printers with constant "non variable" light power output to permit the design of reliable 3D printed biocompatible materials with lower levels of byproducts, leachables, and extractables
3. the tuning of the resin since different types and dosages of Fine Tuners affect in more or less degree to the biocompatibility and cytotoxicity
4. the light postcuring unit specifications and implemented protocol since the conversion from monomer to polymer depends on its performance 
5. the cleaning process since the level of impurities, byproducts, leachables and extractables trapped in the prints depends on the cleansing process used: solvents used, specific cleansing process used, etc.
6. the design of biocompatible quality control protocols and workflows to ensure that quality and safety are ensured and constant upon time

 The authors of the paper also concluded that the resins were not clear but translucent. Instead of sanding the prints, they might have followed our Instructions for Use for getting 100% water white clear finishes: IFU for ultra gloss and transparency

In this second paper Eye model for floaters’ studies: production of 3D printed scaffolds the authors concluded that:

Conclusions

3Dresyns has designed detailed scientific printing and postprocessing protocols to help its customers to get optimum biocompatibility results. It is very important to follow our IFU exactly as written, without cutting corners, without reinventing the wheel, to ensure maximum printing quality and biocompatibility.

Biomedical device manufacturers are responsible for the quality and safety of their products. They cannot pass the hot potato to their raw materials suppliers  since 3D resins as supplied are liquid photoreactive raw materials, not biomedical devices.

Depending on how 3D resins are printed, and postprocessed, which are beyond the control and responsibility of the any 3D resin supplier, biocompatibility can be enhanced or diminished, affecting the overall quality and biocompatibility of the biomedical device or biocompatible system.

Unfortunately, the majority of printers and light boxes suffer from a natural light power decay upon usage and lack having any control units to prevent their natural decay, affecting negatively on the reliability, reproducibility, quality and safety of 3D printed biomedical and bioprinting systems.

If you want to produce 3D printed biomedical devices take it seriously and get consulted. 3Dresyns can help you to design the right 3D resin and printer setup for your needs at the lowest possible cost, without sacrificing quality nor safety.

Note: before publishing any results related to 3Dresyns follow our IFU and comply with our legal terms, permission to publish and non defamation & non disparagement policies.