Feature published in 2023 with a contribution from Liqcreate. Examples include established uses, training models and research directions; they do not share the same level of validation.
Photopolymer resins play an important role in several dental 3D printing applications. A wider choice of machines and materials has also encouraged other medical uses. A resin suitable for one application does not automatically become suitable for every patient-contact part.
Biocompatibility concerns a material or device performing its function with an appropriate biological response in a specific application. It does not mean the absolute absence of an immune response and is not simply a label attached to raw resin.
Selection therefore needs to consider intended use, available evidence, manufacturing and post-processing. This feature examines those questions beyond dentistry.
The review by Guttridge and colleagues found mainly dental resins among the products marketed as biocompatible that it surveyed. This does not mean most of all 3D printing resins are dental. Dental applications offer defined requirements and parts often compatible with machine build volumes. Each claimed use still needs support; a formulation does not receive universal authorization for every device.
CE marking follows conformity assessment. It is not approval from an agency called “CE”, or an automatic equivalent of an FDA decision.
Beyond dentistry, the applications discussed include orthoses and exoprostheses, surgical guides, hearing-device components, anatomical models and some specialized instruments. Contact lenses, intraocular lenses and implants have distinct requirements: their inclusion in a research overview does not establish that a commercial resin is suitable for these uses.
Some end-use parts can be made by vat photopolymerization. In a 3D Systems case report published in September 2020, ACS Custom reported a fourfold increase in capacity with Figure 4. The company used both directly printed parts and moulds for silicone components. This result concerns that workflow, not every hearing application or resin.
On another note, it’s crucial to keep in mind that the selection of a material for medical applications is directly linked to the selection of the 3D printer and the requirements to meet in a given application. It turns out that depending on their final purpose, medical applications may require flexible materials, rigid materials or multiple materials.
Which materials for which models and devices?
Rigid materials can reproduce bone structures as anatomical models, rather than fabricate living human bones. The review by Garcia and colleagues on medical education describes ABS models made by extrusion and examples using other processes. These extend beyond resin printing and serve training or procedural planning.
Flexible materials can reproduce aspects of tissue behaviour in heart, vessel and other organ models. Photopolymerization and material jetting offer different options. Mechanical fidelity needs assessment for the skill being taught; washing, finishing and post-curing depend on the system used.
Combining materials can create phantoms, or physical simulation models, with rigid and flexible regions. The challenge is to reproduce the properties relevant to the exercise, without confusing visual resemblance with biological behaviour.
A training model without patient contact and a device intended for implantation therefore have different requirements.
Biocompatibility, manufacturing and sterilization
For a skin-contact device, the nature and duration of contact inform biological risk assessment. The finished device, its constituents and possible residues also matter. A stated 24-hour duration alone is not certification.
Requirements depend on intended use. The material-process combination needs definition: machine, settings, washing and post-curing. Results from a specimen prepared under one protocol do not automatically transfer to another process. FDA technical considerations for AM devices emphasize control of manufacturing and post-printing operations.
Guttridge and colleagues found uneven information on intended uses, testing and post-processing among the surveyed resins. Marketing claims therefore need examination alongside documentation on use limits, test methods and preparation conditions.
Manufacturer instructions form part of the process to validate and control. Cleaning, post-curing and sterilization are separate operations. Where sterilization is required, the method must suit the device and its effect on properties must be assessed.
Implants, surgical guides and skin-contact parts have different risk profiles. Not every implant directly contacts blood; the tissues involved and exposure duration matter. Models used only for teaching have another context. Matching a mechanical property of PEEK or polyamide does not establish equivalent biological performance or suitability for long-term use.
In 2023, available options varied by application. An established titanium or thermoplastic solution does not automatically give a resin a shorter registration pathway. Development requires collaboration between formulators, device manufacturers and healthcare professionals around a defined use.
This article was first published in the March/April 2023 issue of 3D ADEPT Mag.
Authors and contributors
This article has been co-written with Liqcreate, a company that develops photopolymers for SLA and DLP technologies. Its photopolymers target several sectors including prototyping, industrial, entertainment, consumer goods, healthcare and automotive. In a previous article, 3D ADEPT Media worked with Liqcreate to shed light on the different forms of toxicity and solutions explored to reduce it in resin 3D Printing.
Other contributions include a study on “Biocompatible 3D printing resins for medical applications” and another one on “3D printing materials and their use in medical education.”
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