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Skip to 0 minutes and 11 seconds So with the 3D printed ear, we need to create a structure that replicates shape with some very fine features, and we need to be able to distribute mechanical properties throughout a 3D structure. So Steve, from the materials inventory that we have available, what types of materials or what particular materials could we use? So in the case of this sort of project, we need a material that’s got a robust extrusion principal capability, and ideally, will retain form as we extrude it or at multiple different lengths. Polycaprolactone is one such material– a low melt temperature that’ll be easily extrudable and we can modify.

Skip to 0 minutes and 46 seconds And in terms of distributing those mechanical properties throughout the structure, I mean one of the great things about 3D printing of course is it doesn’t have to be uniform. That we can have gradients of mechanical properties. We can actually map mechanical properties throughout a complex 3D structure, like the ear. I mean, how would you do that in using this type of printing? Now we can look at the different types of printing that are available to us. Extrusion-based printing, so FDM type printing technologies, allow us to have a control over the filament of material as it’s being extruded out.

Skip to 1 minute and 18 seconds Unlike inkjet printing, where we’d have to have a uniform coating of material within a printed layer, with FDM or extrusion type printing, we can then distribute the spacing of those filaments as they’re being deposited down onto the substrate. So really, extrusion printing is the only approach, the only 3D printing approach where you could take the predictive models and you could actually start to create these 3D structures to distribute those mechanical properties. So combining FDM or extrusion printing and the particular material of choice, yes, it’s the only candidate.

Skip to 1 minute and 51 seconds And I’d imagine that you’d need a fair bit of flexibility in the actual printing system that you’re going to use in order to create those complex 3D structures– especially those really fine features that we have in the ear– and yet, that ability at the same time to distribute the mechanical properties. That is, of course, true. And what we’re really describing there is a very bespoke piece of software that allows us to finely control the spacing of the filaments. Now your common 3D printer, you’re using proprietary software that will take an STL file and apply its printing conditions to that file, when in this type of application we need to be able to define each layer as it’s being put down.

Skip to 2 minutes and 28 seconds So we need to write software code that allows us to control each one of the printing patterns And this particular printer that we’re using in order to distribute those properties and to measure them, could that actually be used to replicate what we need eventually in the ear, which will be multiple materials in that structure? The basic 3D printer that we have here, the FDM printer, is limited in that it’ll only do a single material at any one time. We can vary the extrusion parameter. So we can vary the filament profile or the distribution of those films, but we can’t account for support materials or additional materials that we’d want to include in a structure.

Skip to 3 minutes and 7 seconds So it’s ideal for that initial task in developing the ear where we’d want to use a single material, we want high resolution, and we need continuity in the filaments, and the ability to distribute structure, and also diameter and size throughout that in a single print. That’s right. It allows us to first of all prove the material before we move on to a more advanced printing technology.

The materials

Finding functional materials is essential

Selecting the materials

The material selection phase is crucial to the successful construction of a functional component. Not only does the shape of the final product need to be considered but so too does the qualities of each selected material.

During week 1, we learned that when selecting the materials for a prosthetic we needed to consider structural support, weight, robustness and durability. We heard that ABS was low cost but could produce high resolution/high detailed components (via FDM). Alternatively we could use PLA or materials that will provide dimensional accuracy and long life stability.

The case of the titanium heel, during week two, demonstrated to us that metal 3D printing is a possibility. Though metal 3D printing technology isn’t as mature as the polymer technology we encountered in week one, it definitely suits particular applications and some implants. Some of the surrounding considerations included developing the materials to remove the heat from the weld zone.

During the glaucoma case, we considered that the materials needed to be compatible with the environment of the eye including chemical and biological properties. We learned that the materials available tended to be connected to the printing technology. In this particular case we needed high detailed parts with good quality surface finish so required an inkjet based technology such as PolyJet technology involving UV-curable resin such as MED610. This material allows for short term implantation and achieved high layer resolution (16 microns), so to achieve small internal features. The resolution required in the final structure really needed to be considered when selecting the materials.

Your turn

We’d like you to take the knowledge you currently have, and consider your chosen clinical need from the last couple of steps.

  • What materials would you choose to use in your own case?

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This video is from the free online course:

Bioprinting: 3D Printing Body Parts

University of Wollongong