3.12

## University of Wollongong

Skip to 0 minutes and 8 secondsThe quest to create a 3D-printed ear in order to treat patients with microtia presents us with some new challenges in 3D bioprinting. We need to create the shape that replicates the ear, we need to distribute mechanical properties throughout that structure, and we also need to be able to grow cartilage, living cartilage within that that 3D-printed structure. So we're going to explore each of those three aspects in this new 3D printing challenge. First of all, let's talk about how we might distribute mechanical properties throughout a printed structure using a single material, but using appropriately internally designed arrangements in order to distribute that mechanical properties, or to distribute those mechanical properties.

Skip to 0 minutes and 53 secondsSo Farzad, can you explain to us how we could change structure, internal structure, to influence mechanical properties. So to be able to get different mechanical properties in the same structure, we needed to design a structure with different internal properties, or strand sizes. So in this project, I designed a structure with two-- for example, for this one, with two different strand sizes. And when we change the strand sizes, we change the mechanical properties of the structure. So we have an internal network of struts in three dimensions, and by changing the actual diameter of those struts, as well as the arrangement in three dimensions, you can vary the mechanical properties using a single material. Is that correct? That's correct.

Skip to 1 minute and 45 secondsSo understanding how we distribute mechanical properties in three dimensions using simple 3D printing routines, now we move on to the challenge of doing that in a very complex shape, in the shape of an ear. Can you explain how we can do that in such a complex shape? Because we wanted to 3D model an ear with different mechanical properties, we divided our model into six different sections, and each section, we gave it different strand sizes. And then we 3D printed this ear model. And after that, we did some mechanical tests on that, and we proved that we could print a sample, an ear model, with different mechanical properties in different sections.

Skip to 2 minutes and 30 secondsSo you use finite element analysis in order to build a predictive model, a model that can help you predict the distribution of mechanical properties in a 3D-printed structure? Yeah, we use finite element analysis to be able to predict the behaviour of ear model, as I said before, under different types of loading, and see what the reaction of the model is going to be in different situations. So this is going to help us to be able to predict the mechanical properties of the ear under different loading situations. Having built that model, how do you verify the accuracy of it?

Skip to 3 minutes and 11 secondsSo because the parameters was taken from a mechanical test to be able to model this finite element analysis, we use the same situations and conditions in our 3D modelling in finite element analysis. And after that, we compare the results that we get from our finite element analysis to actual mechanical properties, and from there, we can prove that our model and our results are accurate. And so you were able to verify the model by measuring the tensile strength and the compressive modulus of those different areas within the ear, where we know we have to have different mechanical properties? Yes, that's true. We usually measure strain and stresses in the structure. So you're measuring tensile strength and compressive modulus?

Skip to 4 minutes and 1 secondYes, compressive and tensile stress and strains. So what Farzad has been able to do is to create a 3D-printed ear structure using a single material. And with that compromising the shape of the ear, he's able to distribute mechanical properties throughout that ear so that we can start to replicate, in a physical sense and in a mechanical sense, the real, living ear, to replicate that ear for the patient with microtia.

# The design

Researchers are now working with clinicians to print two types of materials simultaneously - Stem Cells into a Cartilage Gel structure. This would provide critical support for new biological structures such as a 3D printed ear.

The design process is really a quest to create and recreate the integral qualities of a structure. It is very important to consider the shape, mechanical properties and the distributive properties needed to accurately produce a structure that will be able to function as intended. In the case of the ear, each component is identified and the necessities of that component are also identified and catered for in the design process.

In the previous step you were asked to discuss a clinical challenge that you have identified from your own personal experiences. Considering the same clinical challenge, we encourage you to use the discussion space to consider how you would hypothetically approach the design phase. Please use the following questions to guide your contribution:

• What existing technologies would you utilise?
• What limitations would impact upon the design stage?
• How would you consider and incorporate shape, mechanical property and distributive property into the design to achieve functionality?
• Are there any specific structures or unique qualities you’d built into the design of your structure?

Please note: we encourage learners to share their ideas irrespective of educational background and scientific expertise. We also encourage you share your enthusiasm on learners’ case selection and your own knowledge if you believe it can assist somebody else’s case. Please be mindful to always do this in a considerate manner