The FDA clearly describes "what is a medical device?":

A medical device is "an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent, or other similar or related article, including a component part, or accessory which is:
  • recognized in the official National Formulary, or the United States Pharmacopoeia, or any supplement to them,
  • intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease, in man or other animals, or
  • intended to affect the structure or any function of the body of man or other animals, and which does not achieve any of its primary intended purposes through chemical action within or on the body of man or other animals and which is not dependent upon being metabolized for the achievement of any of its primary intended purposes." by the FDA What is a medical device?

    A 3D resin is a starting raw material used for making medical devices, but not a medical device as supplied, as it is clearly described in this statement published by the FDA:

    "the starting material may undergo significant physical and/or chemical changes. As such, the starting material can have a significant effect on the success of the build cycle, as well as on the properties of the final finished device."  by the FDA Technical Considerations for Additive Manufactured Medical Devices (page 15).

      In the same document it is mentioned the importance of controlling the post processing of medical devices for ensuring their safety:

      "Final device performance and material properties can be affected by post-processing steps of AM (i.e., manufacturing steps occurring after the printing process). These steps could include removing manufacturing residues from the device, heat treatments of the device to relieve residual stress, and final machining. All post-processing steps should be documented and include a discussion of the effects of post-processing on the materials used and the final device. As stated previously, manufacturers must establish and maintain procedures for monitoring and control of process parameters for validated processes to ensure that the specified requirements continue to be met." (page 17).

        The "Material Chemistry" section of the same document indicates:

        "Since the AM process creates the final material or alters the starting material during the process, all materials involved in the manufacturing of the device should be identified. As noted in Section V.C Material Controls, this information should include the source and purity of each material used. Certificates of Analysis and/or Materials Safety Data Sheets (MSDS) can facilitate the review of each material." (page 24).

          The "Material Physical Properties" and the need for measuring the degree of cure are also discussed in the document:

          "If your device is additively manufactured using polymers, we recommend that you ensure the AM process is consistently creating a device or component that has properties that meet your specifications. For example, in situ crosslinked devices may have crosslink density gradients across the build. For AM processes that use polymer crosslinking, the percent crosslinking and degree of curing should be evaluated to ensure that the AM process results in a material that is fully cured and within specifications." (page 25).

            Section "Removing Manufacturing Material Residues and Sterilization" highlights: 

            "validation of the reduction of the manufacturing material residue to levels that do not adversely affect the device’s quality and sterilization process validation should account for the complex geometry of your device under worst-case conditions" (page 26).

              European Commission perspective

              The Directive 93/42/EEC applies for the trading of medical devices,which need to be CE marked for confirmation that meets the basic requirements according to Annex 3 and has undergone the conformity assessment procedures. This Directive applies to medical devices, not to their constituents or raw materials, in our case 3D resins, which cannot be considered medical devices since need to be polymerised, printed and postprocessed with ISO certified procedures and protocols by the medical device manufacturer.Conformity assessment procedures for 3D printing and 3D printed products.

              This Conformity assessment procedures for 3D printing and 3D printed products to be used in a medical context for COVID-19 published by the European Commission applies to medical devices and accesories, not to their constituents, or raw materials, or 3D resins used for producing them: 

              "3D printed products in themselves may be used to produce medical devices which fall within the scope of specific EU product legislation, such as the Medical Devices Directive 93/42/EEC . Therefore, manufacturers of such medical devices must ensure that 3D printed products meet the requirements of the applicable EU legislation, carry out the necessary conformity assessment procedures, compose a technical file, draft the EU declaration of conformity and affix the CE marking, before placing them on the EU market."

                With effect from 26 May 2021, Regulation (EU) 2017/745 of the European Parliament and of the Council of 5 April 2017 on medical devices regulations MDR replaced Council Directive 90/385/EEC on active implantable medical devices and Council Directive 93/42/EEC on medical devices. The basic principles of the old and new Regulation with regards the definition and requirements for medical devices are maintained but are expanded in the new EU Medical Device Regulation MDR.  

                Conclusions

                3D resins cannot be considered medical devices, but "photo reactive" constituents or starting raw materials, which undergo significant physical changes (from liquid to solid), and chemical reactions (photopolymerisation reactions). As such, as "photo reactive" starting materials, the way they are printed (synthesised, photopolymerised, or cured), and processed has a significant effect on the final quality and safety (mechanical and biocompatibility properties) of medical devices. The overall workflow specifications of all associated variables, including but not limited to the design and implementation of appropriate printing and postprocessing equipment, processes, protocols and quality controls are crucial for manufacturing safe medical devices with the required warranties for ensuring maximum safety and biocompatibility.