Skip to 0 minutes and 19 seconds Because metal 3D printing isn’t as mature technology as the polymer counterparts, a lot of the work that we do goes into actually setting up the structure– how we want to orientate the structure and generate the support material to most effectively remove heat from the weld zone. This allows us to have a highly reproducible, high-quality component that will have the least amount of deformation during the building process. In the cases of 3D-printed heel, the base data is coming from CT or MRI scans. We can take those scans and bring them into a piece of proprietary software, and segment out the actual area of interest. So you’ve seen how we were able to segment out the heel.
Skip to 1 minute and 1 second We can then take that heel, perform some cleaning operations on it so we get nice, smooth surfaces. We can then bring it into another piece of propriety software and manipulate that geometry so that we can remove material, reduce the weight of the component, and have strength in the areas of most important. We can then prepare the file so that it’s ready for 3D printing. We take that three dimensional model, we bring it into a piece of software which then slices it into the thin layers that we want to produce. We then add the hatching and the raster structures to that model, and prepare it with a support structure, and send it to the 3D printer.
Skip to 1 minute and 46 seconds Once we perform the 3D printing, we then have to remove the part from the build tray, removing its sacrificial support structure, and then clean up that surface. This is a manual operation where we generally glass bead blast components to remove any of the lightly bound structures. Areas can then be manually buffed and polished to give a high-quality surface finish. The part will then be taken away, and further cleaning done to remove any loosely bound particles. This will give us our final, finished object. This is the part that comes straight off the 3D printer. And as you can see, it hasn’t been post-processed into an implant yet. So it’s quite coarse in its texture.
Skip to 2 minutes and 32 seconds However, a part, once it’s completed post-processing in the lab, ends up suitable for implantation. So you can see there, with the articulating surface, nicely high shined. You’ve got suture tabs for the Achilles tendon and the foot pad there. Another one. And then more recently, we optimised the weight of the implant to actually reduce the weight to around about 20% of the original weight by opening up the porosity of the implant.
Skip to 3 minutes and 12 seconds After you implant this device, as with any device, there is a period of healing. During this period, perhaps six weeks to three months, patient is wrapped in cotton wool, as it were, taking things quietly on crutches. But soon after that, we allow him to start moving his ankle up and down, sideways, and in a very protected way, increase the weight bearing through his foot. He’s now at a time where we’re about to do the one year review. I know that at eight months, he did go away on a long holiday to Canada, where he was able to tour. Of course, using a walking aid as he did so, but able to enjoy that on his own two feet.
The heel: Material selection
The use of metals
Metals have been extensively used in medical implants for a hundred years, commonly as surgical pins and bone-splints. Early on it was found that iron and steel corroded too quickly for making stable, long-term implants.
When stainless steel was developed it enabled highly stable, yet cost effective implants. Key applications include stents and artificial knee implants.
Titanium, with its low density and high strength, is perfect for load bearing implants such as the artificial hip. Its surface can also be tailored to encourage ‘osteoconduction’, where the bone literally grows around and into the metal, naturally fixing the implant in position.
To encourage this ingrowth, metals are sometimes coated with a ceramic called hydroxyapatite (naturally found within human teeth and bones).
© University of Wollongong, 2020